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SELECTIVE FLOCCULATION OF COPPER MINERALS
A thesis submitted for the degree
of Doctor of Philosophy in the
University of London
by
YOSPY ABDELHADY ISMAIL ATTIA
Imperial College of Science and Technology,
London, S.W.7. July, 1974.
1
ABSTRACT
This thesis can be considered to consist of three
parts. The first refers to the surface chemistry of
copper minerals; the solubility, surface energy, oxidation
and surface electrical properties of copper minerals in
water under atmospheric conditions have been studied and
the inter-relation between these phenomena has been
illustrated. Thus the solubility is affected by the surface
energy and oxidation (or reduction), and the electrical
charge is influenced by the solubility. The correspondence
of the zero point of charge (z.p.c.) to the pH of minimum
solubility of the mineral has also been discussed.
The zeta-potential of malachite at different pH
values has been measured by the micro-electrophoresis
method; the z.p.c. is between pH 9-9.5. The effects of
copper sulphate, sodium carbonate, polyphosphate and poly-
acrylate on the zeta-potential of malachite have been
determined at various pH values.
The second part is concerned with the chemistry of
polymeric flocculants and the origins of their selectivity.
A series of flocculants containing thiol (-SH) and other
metal-complexing groups has been developed and tested. The
anticipated selectivity for copper minerals has been
confirmed by flocculation tests on separate minerals and
synthetic mixtures.
The various aspects of the preparation, purification,
analysis, physical and chemical properties of the polymeric
flocculants have been established, and a number of techniques
for characterization of these polymers have been attempted.
2
The third part is concerned with the technical
application of the previous two parts to the processing of
a real copper ore. For this purpose, conditions have been
worked out for beneficiating a particular dolomitic copper
ore (from Zaire) containing a variety of finely disseminated
copper minerals. In the development of this process,
attention has been given to finding a suitable dispersion
medium which would give full liberation and enhance the
differential response of the various minerals to floccula-
tion. Finally, substantially selective flocculation of
copper minerals from the ore, at high solid suspensions
(up to 31% by weight) in laboratory tap-water has been
achieved, with up-grading from 4.5% to 18.2% copper.
The process appears to be economical.
3
ACKNOWLEDGEMENTS
I wish to express my sincere gratitude to
Dr. J.A. Kitchener for his guidance and encouragement.
I am also grateful .to B.T.I. Chemical Limited,
Bradford, for their support and interest in this project,
especially Dr. P.F. Wilde and Dr. R.W. Dexter who prepared
polyacrylamide-dithiocarbamate for me.
My thanks are due to Dr. R. Gochin who has kindly
supplied me with information and invaluable assistance in
appraising the economics of the selective flocculation
process.
It is a pleasure to recognize the assistance received
from the technical staff, in particular Mr. C. Emmitt
the glass blower and Mr. J.D. Sullivan of the workshop.
I am also indebted to the Higher Institute of Petroleum
and Mining Engineering, Suez, Egypt and the Egyptian
Ministry of Higher Education for the scholarship and leave
of absence which enabled me to carry out this research.
° CONTENTS
Page
ABSTRACT
ACKNOWLEDGEMENTS
1
3
Chapter 1. GENERAL INTRODUCTION 11
1.1. The application of selective flocculation
to mineral processing
11
1.2. The concept of flocculation 12
Adsorption of polymers on solid surfaces :
factors controlling adsorption
1.3. Selective flocculation
previous work : selective adsorption of
flocculants
17
1.4. Aims of this work 20
Chapter 2. SURFACE CHEMISTRY OF COPPER. MINERALS 23
2.1. Introduction; types of mineral 23
2.2. Hydrolysis of cupric ions in distilled
water in equilibrium with atmospheric
carbon dioxide
25
2.3. Solubility of copper minerals 26
2.3.1. effect of pH on solubility of:
cupric hydroxide, tenorite,
cuprite, malachite, azurite,
covellite and chalcocite.
27
2.3.2. effect of particle size 44
2.3.3. effect of "inert" electrolytes 46
2.4. Solubility of chrysocolla 47
2.4.1. effect of pH, experimental 148
2.4.2. effect of sodium chloride,
experimental
50_
2.5. Surface oxidation of copper minerals : 51
redox equilibria-
2.5.1. control of oxidation potential of 51
aqueous suspensions by atmos-
pheric oxygen : oxidation of Cu+
to Cu2+.
2.5.2. surface oxidation of chalcocite
2.5.3. surface oxidation of covellite
2.5.4. surface oxidation of cuprite and
other copper minerals
2.6. Surface electrical properties of copper
minerals
2.6.1. introduction; origins of surface
charge; preferential adsorption
of hydrolyzed metal ions
2.6.2. Zeta-potential of malachite 58
experimental procedure
2.6.3. pH of zero point of charge and pH 61
of minimum solubility
2.6.4. pH of copper minerals 62 zpc
Chapter 3. THE CHEMICAL ORIGIN OF SELECTIVITY OF POLYMERIC 64
FLOCCULANTS
3.1. Formation and stability of complex com- 65
pounds; the stability constants
3.2. Classification of ligands; the chelate 67
effect
3.3. Classification of metal cations 70
3.4. Factors affecting the formation and 71
stability of complexes
3.5. Selectivity and specificity of complex 75 formation
52
53
54
55
56
3.6. Synthesis of selective polymeric floceulants 80
6
Chapter 4. CELLULOSE XANTHATE 84
4.1. Introduction; formation, structure and 84 selectivity of cellulose xanthate
4.2. Preparation of cellulose xanthate 88
4.2.1. laboratory preparation; standard 92
method, preparation of cellulose
xanthate from different cellulose
sources
4.2.2. preparation of NaCX of high 93 molecular weight
4.2.3. preparation of NaCX of different 94 degrees of xanthation; effect of
CS2 ratio; effect of temperature
4.2.4. preparation of uniformly distributed 96
xanthate groups
4.2.5. preparation of dry NaCX powder of 98 uniform reactivity; emulsion
xanthation
4.2.6. xanthation of various derivatives cawc/se
preparation of: methyl/xanthate,
sodium carboxy methyl cellulose
xanthate, hydroxypropyl methyl
cellulose xanthate
99
4.3. Purification of cellulose xanthate 100
4.3.1. precipitation with alcohol 100
4.3.2. dialysis of cellulose xanthate 102
4.3.3. ion-exchange method 103
4.4. Analysis of cellulose xanthate 107
4.4.1. detection and measurement of 107
xanthate groups
4.4.2. detection and measurement of 111
cellulose in dilute solutions
7
4.5. Physical and chemical properties of 113 cellulose xanthate:physical character-
istics, chemical reactions with heavy
metal ions; decomposition of xanthate
groups, oxidative degradation, of
cellulose chain
4.6. Flocculation properties of cellulose 121 xanthate:selective flocculation of
sulphides, flocculation of chrysocolla,
flocculation of sulphidized chrysocolla,
selective flocculation of chrysocolla
from quartz
4.7. Conclusions 129
Chapter 5. OTHER SELECTIVE FLOCCULANTS CONTAINING SULPHER 131
5.1. Polyvinyl alcohol xanthate
5.1.1. introduction, formation 131
5.1.2. preparation of polyvinyl alcohol 133
xanthate (PVAX),purification
5.1.3. flocculation properties of PVAX 134
5.2. Polyacrylamide-Dithiocarbamate (PAD)
138
5.2.1. composition and properties 138
5.2.2. flocculation effects on mineral 139
suspensions, selectivity of PAD
5.2.3. selective flocculation of copper 141
minerals from mixed suspensions
5.2.4. inhibition of flocculation of 143
galena in mixtures with copper
minerals, effect of Na2S and
NaF, effect of K2Cr207
5.2.5. Discussion and conclusions 145
8
Chapter 6. POLYACRYLAMIDE-GLYOXAL-BIS-(2-HYDROXYANIL)
147
6.1 Introduction: choice of GBHA: formation 147
of PAMG polymers
6.2 Preparation of PAMG polymers- experimental 154
6.2.1. preparation of PAMG 2.1, PAMG 2.2 155
6.2.2. preparation of PAMG 6 157
6.2.3. preparation of PAMG 7 157
6.3. Purification of PAMG 2 polymers 158
6.3.1. the alcohol precipitation method 158
6.3.2. Gel chromatography method 161
6.4. Preparation of dry powder of pure PAMG 2.3 166
polymer: preparation; purification and
drying; grinding; 'grinding dry solids;
solubility in water
6.5. Characterization of PANG polymers 168
6.5.1. The alcohol precipitation technique 168
6.5.2. The dialysis technique 169
6.5.3. Membrane filtration technique: 169
size distribution of PAMG 2.1
polymer segments
6.5.4. ultra-violet and infra-red spectra 179
6.5.5. degree of substitution 189
6.6. Selective flocculation properties of 192
PAMG 2.1
6.6.1. flocculation effects on mineral 193
suspensions
6.6.2. selective flocculation of copper 194
minerals from mixed suspensions:
chryscocolla from calcite;
chrysocolla and malachite from
mixtures with feldspar, calcite and
quartz; chalcocite, malachite and
chrysocolla from mixtures with feld-
spar, calcite and quartz; malachite
from dolomite.
9
Chapter 7.
6.6.3. the comparative selectivity of
PAMG 2.1
6.6.4. the role of unattached GBHA groups on the flocculation
behavior of methylolated PAM
195
197
6.7. Conclusions 198
PROCESSING OF COPPER ORES BY SELECTIVE 200
FLOCCULATION
7.1. Introduction, criteria of selectivity,
materials and equipment
200
7.2. Preliminary investigations 207
7.3. Design of flow-sheets for selective flocculation process
212
7.3.1. flow-sheet 1 213
7.3.2. bulk flocculation procedure:
flow-sheet 2
217
7.3.3. multi-stage flocculation: flow- sheet 3
220
7.3.4. "starvation" addition of flocculant:
flow-sheet 4 223
7.3.5. multi-stage addition of flocculant: semi-cyclic flow-sheet 5, effect of
225
"ageing" on selective flocculation
7.3.6. the standard flow-sheet; flow-sheet 7 229
7.4. Studies to improve grade and recovery 232
7.4.1. experiment with PAMG 7 232
7.4.2. dispersion of the ore suspensions:
effect of ultrasonic vibrations,
effect of reducing the interfacial
energy
238
7.5. Effect of solids content on selective 246
flocculation
7.6. ECfect of tap water on selective flocculation 249
10
7.7. Use of tap water and high solids content 251
7.8. Discussion 253
7.9. Economic assessment of selective flocculation 256
process
7.10.Conclusions 260
Chapter 8. CONCLUSIONS 261
REFERENCES 26.6
APPENDIX 1: Calorimetric determination of copper with 276
bis-cyclohexane oxalyldihydrazone
APPENDIX 2: Determination of copper content by atomic 278
absorption spectrometry
APPENDIX 3: Adsorption of polyacrylamide on hydrophobic 279
surfaces
11
CHAPTER 1 GENERAL INTRODUCTION
1.1 The a
lication of selective flocculation to mineral ..
processing
Several authors(1'2,3,4,5)
have emphasized the need
to develop a new technology to cope with the extraction
of fine grained minerals. At present, the fine size
particles ( <101.1m), known as "slimes" in the mineral
technology field, are often discarded after crushing of
the rock and before applying separation process
such as froth flotation to the ores, thus resulting in
losses of up to 30% of the total ore values in some plants.
Also, there exist some large ore bodies in which the
valuable minerals are already too finely disseminated in
the original ore to be extracted satisfactorily by con-
ventional methods. Typical examples are some copper ore
deposits in Mount Isa (Australia)( 6)
, and some cassiterite
ores in Cornwall (England)( 7). The authors quoted consider
that the most promising method proposed to deal with these
problems is "selective flocculation". The various aspects
of the slimes problems and the possible ways of .recovering
fine grained valuable minerals, including selective flocculation,
have been well reviewed in the literature by Collins and
Read( 8)
It is well known that chrysocolla (a copper silicate)
presents great difficulties to extraction on a commerical
scale by any process at present available, except acid
leaching. In the ores where chrysocolla is associated with
other acid-soluble minerals (e.g. calcite, dolomite) the
12
acid leaching process becomes economically unattractive.
Ammoniacal leaching or extraction with EDTA(9,10,11)
is feasible, but costly. This problem might be solved by
selective flocculation, as will be shown in later Chapters.
Although malachite and azurite can be extracted by
froth flotation after sulphidization, their extraction is
often not very efficient and it becomes even less efficient
when the particles size is very small. The recovery of
copper sulphide minerals by froth flotation is well developed;
however, when the particle size becomes very small (<5 pm),
the process becomes less efficient, apparently because of
hydrodynamic problems.
It is for these reasons it appeared that the develop-
ment of a process of selective flocculation would be timely
so, as a contribution to the better use of the worlds
limited resources in non-ferrous metals. The case of the
copper minerals was chosen for detailed study firstly
because of the high (and rising) value of copper (which
would justify expenditure on chemical reagents) and
secondly, because copper should be particularly amenable
to selection by "complexing" flocculants, as explained
later.
1.2 212222.222 aatl_on
Flocculation by polymers is a process of aggregation
brought about by means of a bonding agent (flocculant)
that ties the particles together (12,13)
.In order to
achieve this result, the flocculant must first be adsorbed
on the particles and be capable of briding the gap between
13
adjoining particles(12'14 Thus the effective flocculant
must have an extended and flexible (or elastic) configuration
in the solution; the first is to achieve bridging and the
latter is to produce strong flocs capable of withstanding
moderate shear forces without rupturing(1205) It is there-
fore understandable that the most effective flocculants
known are water soluble compounds of high molecular weight
6, ( .?-10 ). The earliest flocculants were natural products
such as proteins and gums; but linear polymers are more
efficient because of their greater lengths. The development
of the "bridging mechanism" concept has been recently
reviewed in the literature(14,16)
Adsorption of polymers on solid surfaces
A polymer cannot flocculate unless it is adsorbed on
the particles. Therefore the surface chemistry of the
minerals is a basic question. The chief factors involved
in the surface reactions of minerals (in aqueous suspensions)
are (i) dissolution, (ii) hydration (e.g. of oxides) and
(iii) surface ionization with formation of an electrical
double layer.
It is known(17) that the surfaces of natural minerals
(in water) are to some extent heterogeneous with regard
to electrical charge. Thus there may be some areas of
higher or lower local zeta-potential or even with a zeta-
potential opposite in sign to the overall zeta-potential
of the surface (as with kaolinite). However, the surfaces
may be made more uniform by treatment with electrolytes(17)
The anchoring of the polymer on the surface is thought
to be by the multiple-point attachment(12). This attachment
14
arises from the interaction of particular functional groups
on the polymer with sites on the solid with the formation
of "bonds". This bonding may be due to either chemical
type forces (which operate over very short distances), or
to electrical type forces (which extend over longer distances)
(18/ 19) or a combination of both types. The electrical
forces can briefly be summarized as follows:
1. ElectrostaticlEoulombial_forces result in the
adsorption of polyelectrolytes on to any surface of opposite •
charge, irrespective of their chemical nature. Typical
examples(17) are: (a) the adsorption of ,anionic polyacrylamide
on positively charged fluorite, barite, calcite and synthetic
corundum; (b) the flocculation of clays by cationic derivatives
of polyacrylamide. The interaction energy of this bonding
may be much greater than 10 kcal mole-1 (39) and, therefore,
practically irreversible.
2. Di ole attraction forces were suggested(12,20)
to
explain the flocculation of ionic-type crystal (e.g.
fluorite) by non-ionic polyacrylamide. This type of bonding
has a weak interaction energy (<2kcal mole -1)(39)
3. London-van der Waals attraction forces: Although
these forces are fundamentally electromagnetic in character
they are considered electric forces(39), because their
origin can be explained in terms of temporary dipole
interactions. The neutral molecules or atoms cor4tute
systems of oscillating charges producing synchronized
dipoles that attract each other(39). The energy of inter-
action resulting from these forces ranges between 2 - 10 kcal
-1 mole . It is established that London forces are approx-
15
±mately additive, and this explains the mutual attraction
of all disperse particles(12)
4. Hydrophobic association The tendency of non-polar
molecular groups (or substances) to escape from an aqueous
environment leads to the well known property of (physical)
"Surface-activity": for example, alcohols are adsorbed at
an air/water or an oil/water interface, irrespective of
the chemistry of the phases. It is believed that association
between non-polar ("hydrophobic") molecular groups occurs
within protein molecules (as in micelles of soaps) and
also explains the adsorption of proteins and amphipathic
polymers (such as incompletely hydrolyzed polyvinyl
acetate) at oil/water interfaces and on to hydrophobic
solids such as graphite.
The important chemical forces which result in a covalent
type bondscan be classified to:
5. Chemical bonding: Reactions of the polymer groups with
ionic sites on the solid surface with the formation of
insoluble compounds. For example, adsorption of polyacrylic
acid on calcium-containing minerals (e.g. limestone, calcite,
sheelite), with the formation of insoluble deposits of calcium
acrylate on the solid surfaces(17) The interaction energy of
the chemical bonding is generally greater than 10 kcal mole-1 (39)
6. "Coordination" bonding: (i.e., chelation and complex
formation): Examples of this type of bonding are:
(1) flocculation of copper carbonate by polyethylene
imine(12), (2) flocculation of the various copper minerals
by the special chelating polymers PAMG to be described in
Chapters 6 and 7 in this thesis. The principles of specific
16
chelating (and complexing) bonding are discussed in
Chapter 3.
7. Hydrogen bonding: In the organic compounds where the
hydrogen atom is combined with a strongly electronegative
atom (0,S,N), the hydrogen atom is able to accept electrons
from atoms on the solid surface(17)
, mainly from the -OH
groups of the hydrated surface of an oxide mineral(111° , with
the formation of the hydrogen bond. The proton resonates
between two electronegative atoms. The interaction energy
for this bonding ranges between 2 - 10 kcal mole-1 (39)
An example is the adsorption of polyacrylamide onto the
hydroxyl groups of oxide surfacesWO
The adsorption of polymers on solid surfaces by chemical
forces against electrostatic repulsion can only happen when
the polymer approaches the surface closely by means of
other mechanisms. These may be either due to London-van
der Waals forces or to strong collisions between the
polymer molecules and the solid surfaces. The contribution
of the London-van der Waals forces to specific adsorption
by chemical forces is illustrated in the case where a
n- polystyrene sulphonate [CH2-CH-CH-SO] n
adsorbed readily on to a negatively charged silica surface(39)
Adsorption of anionic polymers on negative surfaces is
common. In this work, another example is provided by the
anionic cellulose xanthate polymer which readily adsorbs
on the negatively charged chryscolla (in Chapter 4).
is
17
1.3 Selective flocculation
Previous work: It has been found empirically by several
authors0,2,3,22-32)
that under certain conditions, various
polymeric flocculants can exhibit,some degree of selectivity
when applied to mixed dispersions. A number of successful
separations by selective flocculation on binary and ternary
systems have been reported in the literature. For example,
selective flocculation of calcite and galena from mixtures
with quartz by strongly hydrolysed polyacrylamides (A 130,
A150 13.T.I.) and that of galena from mixtures with calcite
by a weakly hydrolysed polyacrylamide (A100) were performed
(2) (1) by Yarar and Kitchener . Usoni and co-workers
reported selective flocculation of pyrite, sphalerite and
smithonite; each from mixtures with quartz. Similarly,
Read(3) achieved selective flocculation of hematite from
a mixture with silicate and silicate from mixtures with
hematite by strongly and weakly hydrolysed (anionic)
polyacrylamide, respectively. Similar results were achieved 2)
earlier on similar systems by Frommer and Iwasaki and
co-workers 2: , using various natural starches. Selective
flocculation of a phosphate ore from clays was patented
by Haseman(24)
and selective flocculation of manganese
dioxide (Mn02) slimes during the flotation of quartz or
prior to its flotation with carboxy methyl cellulose and
polyacrylamide type flocculants was achieved by Yousef et al
and Gogitidze et al and Temchenko et al(25,26,27)
Selective flocculation of coal slimes from clays, as quoted
by Schulz(28) have been performed in some east European
countries(29)
. The use of selective flocculation in the
18
flotation of sylvinite ores has been described by Aleksand-
(30) rovich et al and Brogoitti et al(31).
A review on
various selective flocculation systems has been presented
by Mosina(32). Except for the American work with iron
ores, all these are laboratory scale experiments. It is
believed that Frommeros iron ore process is being put on a
pilot scale.
However, these examples did not illustrate the basic
principles governing selectivity of the flocculants. In
fact, most of these examples were discovered after considerable
work of trial and error(4). What is needed for the proper
design of the selective flocculation processing is a better
understanding of the factors controlling adsorption of
polymeric substances by minerals.
Selective adsor tion of flocculants
Selective flocculation can only be operated if the
flocculant is selectively adsorbed on certain components
in the mixed suspension. Adsorption due to electrical
attraction and hydrogen bonding are generally unselective
(though the II-bonding is more specific than electrical
forces), although, the electrostatic forces could be used
to improve selectivity by employing adjustments in the
surface potentials of the various minerals(4'5). The
chemical and "coordination" bonding, therefore seem to
offer most promise for obtaining selective adsorption of
flocculants by certain minerals.
It has been suggested(14) that more selective flocculants
than those at present available could be prepared by
incorporating in the polymer chains chemical groupings
19
having a strong affinity for ions in the mineral to be
flocculated (i.e., complexing or chelating groups). This
possibility stemmed from the well-known selectivity of
the various types of flotation "collectors". A familiar
example is the use of various thiol ("sulphydryl")
compounds such as xanthates, dithiocarbamates and dithio-
phosphates, as flotation reagents for the "heavy metal"
minerals. Such reagents selectively form insoluble compounds
with heavy metals (e.g., Pb and Cu) and not with earth
alkalineLmetals. If such groups were grafted onto water-
soluble polymers, they would be expected to act as
selective flocculants, ideally giving a case of adsorption
or no adsorption. Examples of this type of flocculants
are given in Chapter 4 and 5. Gutzeit(33) pointed out that
a great many organic reagents which form insoluble (often
coloured) chelates with metal ions can act as flotation
collectors. Whether these chelating collectors react
directly with the metallic atoms of the crystal lattice or
with identical ions adsorbed by the mineral surface from
the solution has not been proven, though, according to
Gutzeit, certain experimental facts seem to favour the
latter theory. Gutzeit also pointed out that the same
principle could be used to find selective depressants
for preventing flotation of particular minerals by having
chelating groups attached to other hydrophilic groups.
Since the adsorption of polymeric molecules is the result
of multiple linkings of some of the individual molecular
groups in the surface, it is clear that adsorption could
be enhanced by having many chelating units in the chain.
20
Selectivity of the flocculant could also arise from
its differential adsorption strength on the various minerals.
For example, the polymer may strongly adsorb onto copper
minerals but be weakly held on calcite or feldspar and in
both cases it would cause flocculation. But by introducing
another ligand (i.e. depressant), strong enough to "compete"
with the polymer for the calcite or feldspar, the flocculant
would then be free to adsorb predominantly on the copper
minerals. Examples of this type of selective flocculants
are given in Chapers 5 and 6.
Whatever the chemical type, all copper minerals release
minute traces of Cu2+ ions into aqueous media, as shown in
Chapter 2. Even if other complexing agents - such as OH,
CO23
, etc., are present and anionic Cu- species may be the
dominant ones at high pH - nevertheless there are still low
concentrations of Cu2+ ions in equilibrium, capable of
being complexed by strong enough complexing agents. Fo-r,
example, malachite is virtually "insoluble" in weakly
\2- alkaline media only traces of. Cu(OH)3, Cu(OH)4 , etc., go
into solution, but malachite can be dissolved by ammonia
or EDTA(9,10)
The choice of complexing groups and the factors
controlling their selectivity are discussed in detail in
Chapter 3.
1.4 The aims of this work were to illustrate the chemical
origin of selectivity; to explore the possibilities of
developing new, more selective flocculants and to establish
the fundamental principles for the proper design of the
21
selective flocculant process, as a method of separation
for a copper ore. The findings of this research should
also apply to other types of ore.
However, to arrive to these aims, basic studies must
first be made on individual minerals and on artificial
mixtures of minerals. As in froth flotation, selective
flocculation exploits the differences of the surface-chemical
properties of the minerals. In order to select a region
for selectivity, three aspects have to be carefullyconsidered.
a) The flocculant - the type of the functional groups,
physical and electro-chemical properties.
b) The mineral(s) - the electro-chemical state of the
surface and other physical properties.
c) The aqueous medium of flocculation - types and con-
centrations of the various electrolytes present, influence
of pH and the hydrodynamic factors.
The aqueous medium affects the electro-chemical and
physical properties of the polymer. Coiling up and uncoiling
(or even decomposition) of the polymer are certainly affected
by the types and content of the electrolytes, as well as
pH of the medium. The electro-chemical state of the mineral
surface is controlled by the medium, Thus adsorption of
the polymer on the mineral surface can be strengthened or
prevented by proper control of the medium. Selective
flocculation, although it depends primarily on the functional
groups of the polymer and the surface chemical groups on
the minerals, is the result of the differential effects of
the aqueous medium on the different minerals.
22
This thesis can conveniently be divided into three
parts. The first part deals with the "aquatic" chemistry
of copper minerals (Chapter 2). The second part (Chapters
3 - 6) deals with the chemical origin of selectivity and
the development of new selective flocculants. The third
part is concerned with the processing of one particular
copper ore by selective flocculation (Chapter 7).
23
Chapter 2 SURFACE CHEMISTRY OF COPPER MINERALS
2.1 Introduction; minerals:
In an ore, copper minerals are generally found in
small proportions and in various forms of different
composition and structure, in association with other
minerals. The practical methods of extracting the copper
minerals from (or "upgrading") the ore depend on their
composition and structure; for instance, copper sulphides
are easily separable by froth flotation and not by acid
leaching, while extraction of copper carbonates and
silicates is easier by acid leaching than by froth flotation.
The types of copper minerals most commonly treated are
often divided into "sulphides" and "oxides"; the term oxide
often implies all non-sulphide minerals. It is relevant to
consider both classes as potential subjects for selective
flocculation, as they often occur together. The types of
the main groups of minerals, both copper-containing and
commonly associated non-copper minerals, are summarized in
Table 2.1 below following the literature(34)
In this thesis, selective flocculation experiments
were made on the various types of copper minerals except
the halide and the sulphate minerals, as they are less
commonly found in copper ores. The surface chemical
properties (namely; solubility, surface oxidation reduction
(redox), electrical properties and surface energy) of some
common copper minerals are investigated in this Chapter.
24
Table 2.1: Types of copper and associated gangue minerals
Chemical class Copper minerals Associated non-copper minerals
name formula name formula
Sulphides
covellite
chalcocite
bornite
chalcopyrite
neodigenite
CuS
Cu2S
Cu5FeS4
CuFeS2
Cu9S5
pyrite
galena
sphalerite
FeS2 PbS
ZnS
Oxides,
hydroxides,
and
multiple
oxides
tenorite
cuprite
CuO
Cu20
quartz
hematite
cassiterite
goethite
ilmenite
SiO2 Fe203 Sn0
2 Fe0(OH)
FeTiO3
Halides atacamite u ci(oH)
3 fluorite
sylvite
CaF2 KC1
Carbonates
malachite
azurite
(OH)2CO3
3(OH)2(CO3
dolomite
calcite
rhodochriocite
CaMg(CO3)2
CaCO3
MnC03
Sulphates
chalcanthite
brochantite
cu504'5H20
u4SO4(OH)6
barite
gypsum
anglesite
BaS04 CaS
°4.2H2°
PbSO4
Silicates
crypto-
crystalline
framework
sheet-
structure
chrysocolla CuSiO3.2H20
(approx.) microcline
(triclinic feldspars)
Kaolinite
talc
muscovite
KA1Si308
Al2Si205(OH)4
Mg3S14010(OH)2
KA12 [AlSi
3o10)(co)2
25
2.2 Hydrolysis of cupric ions in distilled water in
equilibrium with atmosRlheric carbon dioxide
Traces of Cu can be detected in the supernatant when
finely-divided copper minerals are dispersed in water, but
simple Cu2+ ions are not the only form present. From the
solubility equilibria, the theoretical concentrations of
soluble species such as Cu00, Cu2(OH)2+ , CuCO3, Cu(OH)3, N2- N2 Cu(011) , Cu(CO3)2' , HCO
3 , 0 and OH- in equilibrium
with Cu2+ and CO2(g) in the atmosphere can be calculated.
If the concentration of Cu2+ is equal to or larger than
that needed to precipitate cupric hydroxide, then more
soluble species will be controlled by the solubility
product of Cu(OH)2 (see section 2.3.1). At this stage,
it is assumed that the concentration of Cu2+ is less than
is needed for precipitating Cu(OH)2. The following
equations hold for 25°C and ionic strength I = 0(35,36,37,61)
1. Cu2+ + H2O Cu OH + H ; pK = 8
. . log [Cu0H+] = pH -8 + log [Cu2+] (1)
2. 2Gu2+ + 2H20 = Cu2(OH)22+ + Pe; pK = 10.6
. . log [Gu2 (OH)21] = 2pH - 10.6 + 2 log [0u2-1 ] (2)
3. Cu2+ + 30H = Cu(OH)3 pK = -15.3 ,
. • . log [Cu(OH)3 ]= 3 pH - 26.8 + log [Cu2+] (3)
4. Cu(OH)3 + H2O = Cu(OH)2- + 111- ; pK 13.1
. . [cu(oH) ] = 4 pH - 39.9 + log [2+] (4) 4
26
If the solutions are allowed to come to equilibrium with
air, the CO2-H20 equilibria must be taken into account.
5. CO2 (g) H2O = HCO3 + 11+; pK =
for pure air, log PCO = -3.52
7.9
2
log [HCO3] = pH - 11.42 (5)
6. HOC3 = CO2- + H+; pK = 10.3
. . log [CO3 -] = 2 pH -21.72 (6)
7. cu2+ + CO3- = CaCO3 (aq.) ; pK = -6.77
. . log [CuCO3] = 2pH - 14.95 log [Cu21 (7)
8. Cu2+ + 2CO23--- Cu(CO3 2 )2 ; pK = -10
. . log [Cu(CO3 )2- ] = 4 pH -33.44 log [Cu2+]
(8)
From these equations, the concentration of any cupric
species can be calculated at any pH provided that the
concentration of Cu2+ is known. In solving the solubility
equilibria of copper minerals these equations will be used
whenever applicable. The source of Cu2+ ions will be from
the dissolution of the mineral in water.
2.3 Solubility of copper minerals
In considering the theoretical ("thermodynamic")
properties of minerals in water it is important to realise
that dissolution (and oxidation) processes are often slow,
so that during a practical period of "conditioning", full
equilibrium will rarely be reached. The thermochemical
data therefore indicate the direction of change and the
limits that would be reached if sufficient time were available.
27
2.3.1. Effect of pH
In calculating the theoretical solubilities, it is
assumed that copper minerals are in equilibrium with the
ionic species in solutions and the atmospheric carbon
dioxide. The solubility of a given copper mineral is
defined as the sum of the stoichlometric concentrations
of all dissolved species containing copper(38,39,40). In
order to study the effect of pH on solubility, hydrolysis
reactions of the mineral involving hydrogen ions or hydroxyl
ions must be considered.
The solubility of a given mineral obtained by the
thermodynamic calculations is only approximate, since the
value for the solubility constant (e.g., solubility
product) given by different authors often differsmarkedly.
Yet it is possible in many cases to calculate the pH of
minimum solubility. The importance of this pH will be
discussed later in this Chapter, since it was found in
some cases to correspond to the zero point of charge
(z.p.c.) of the mineral. In this work the pH of minimum
solubility was obtained from the solubility diagram of
the mineral. The solubility diagram is constructed by
considering all the known possible reactions for the
solid phase including the formation of polynuclear
complexes as a function of pH. The sum of all the soluble
copper species gives the line that surrounds the shaded
area, i.e., the solubility at any pH. The data for
solubility constants and the hydrolysis reactions were
obtained from the literature(35- . The solubility
diagrams for a few copper minerals were constructed in
the following manner.
28
SolubilitxEfauurichydroxide (Cu(OH)21
Although cupric hydroxide is not commonly found as a
mineral, its solubility was calculated because of its
importance as a metastable phase in the equilibriUm system
Cu2+-H2O-0O2 . The solubility of Cu(OH)2 in equilibrium
with various ionic species and the atmospheric CO2 gas was
calculated from the following equations (at 25°C and I = 0).
9. Cu(OH)2(0= Cu.24- 20e ; pK = 18.8 r u.24-1j . . log LC = log K -2 log [0H]
From the solubility product of water, log OH- ] = pH - 14.
r 1 . 2+ . log LCu j = 9.2 - 2 pH
10. Cu(OH)....e (aq.) = liCuO2 + HA- ; pK = 10
. . log [HC13.02] = pH -10
11. Cu(OH)2 (s) 20H = Cu(OH)24 ; pK = 2.7
. . log [cu(OH)4 J. 2pH - 30.7
(((111234):
12. Cu(OH)2 (s) + OH- = Cu(OH)3 ; pK = 3.7
. . log [Cu(OH)3 ] = pH -17.7
13. Cu(OH)2 (s) + 3C0 - = Cu(CO3)3- + 20H ; pK = 7.2
from equation 6 and the solubility product of water
... log [Cu(CO3) ] = 4 pH - 44.36
2- 14. HC-a072 = Cu02 + H-1-; pK = 13.1
2- , . .log [Cu02 j = 2pH - 23.1
Comparison of the data in the classical works (e.g., refs.
36,42,43)
35, with that in the modern ones (e.g., refs:
39,4o,41) 'revealed that the Cu(OH) (aa ) in eqn.10, is
equivalent to the "cupric acid" (H2CuO2) in the old texts.
Consequently, the following two species known as "bicuprate"
(Heu02) and "cuprate" (CuO22- ) are equivalent in the modern
x2- texts to Cu(OH)3 and Cu(OH)4 • respectively. (This is due
(9)
(io)
29
to the water molecules in the hydration shells of cupric ions
being considered in the modern interpretations of these
reactions). The stability constant for the aqueous cupric
hydroxide in equilibrium with the solid cupric hydroxide
has not yet been determined experimentally. Nonetheless,
it is believed that the activity of the aqueous hydroxide
is negligible and eqns. 10 and 14 will not therefore,be
considered in the construction of the solubility diagram
for the solid cupric hydroxide.
In the metastable equilibrium of Cu(OH)2' eqns. 11
‘2- and 4 should produce the same result for Cu(OH)4 and
eqns. 12 and 3 should also produce the same results for
Cu(OH)3* (Minor differences, however, occurred due to
the differences in the values of the constants chosen.)
The cupric ions from eqn.(9) can be used in eqns.
1 - 4, 7 and 8 to give the concentrations of the various
cupric complexes in solution at a given pH. Table 2.1
summarizes the calculated concentrations of these species
in equilibrium with cupric hydroxide in pH range 2 - 12.
From Table 2.1 the solubility diagram of cupric
hydroxide was constructed (Fig. 2.1). The pH of minimum
solubility is seen to be between 8-9.
The solubility of Cu(OH)2 in the alkaline range was
43) observed to diminish with time (42,43 and the solid phase
is simultaneously slowly converted to probably tenorite or
aqueous oxide. According to the same authors (42,43)
the oxide solubility does not change with time and the
solubility equilibrium of Cu(OH)2 is therefore a metastable one.
pH -
f-.
2
3
4
5
(1
7
8
9
10 _.
11
1 r) t: •
...
[ J 2+ Table 2.2 - log Cu soluble species in equilibrium with Cu(OH)2 solid
and the atmospheric CO2 •
+ ( )2+ CUCO~ CU(C03)~- Cu2+ CU(OH)~- CU(OH); CU(COJ)~- Approx. total CuOH CU 2 OB 2 --
0.8 I -3.8 5.75 20.24 -5.2 26.7 15.7 36.36 -5.22
1 .8 -1.8 5.75 18.24 -3.2 24.7 14.7 32.36 -3.22
2.8 0.2 5.75 16.24 -1.2 22.7 13.7 28.36 -1.22
3.8 2.2 5.75 14.24 0.8 20.7 12.7 24.36 0.8
4.8 4.2 5.75 12.24 2.8 18.7 11 .7 20.36 2.75
5.8 6.2 5.75 10.24 4.8 16.7 10.7 16.36 4.76
6.8 8.2 5.75 8.24 6.8 14.7 9.7 12.36 5.68
7.8 10 .. 2 5.75 6.24 8.8 12.7 8.7 8.36 5 .. 63
8 .. 8 12.2 5.75 4.24 10.8 10.7 7.7 4.36 3.99
9.8 14.2 5.75 2.24 12.8 8 .. 7 6.7 0.36 0.36
10.8 16.2 5.75 0.24 14.8 6.7 5.7 -3.64 -3.64 W· o
31
pH
Fig.2.1 Solubility diagram of Cupric hydroxide
Solubility of tenorite CuO
The following equations at 25°C and I = 0 were
used:
15. CuO (s) H2O = Gu2+ + 20H-; pK = 20.5
. . log [0u21 = 7.5 - 2pH
- 16. Ou0(s) + H2O + 20H- = 0u(OH)4 • pK = 4.4
. . log [Cu(OH)4
= 2 pH - 32.4
17. Ou0(s) + OH- = H0u02 K = 1.03 x 10-5
. . log [H0u07.1 = pH - 18.99 2-
18. CuO(s) + 20H = Cu022- + H20; K = 8.1 x 10 5
r 1 . . log Lu02 2- j = 2 pH - 32.1
As explained earlier with Cu(OH)2, HCuO2 and Cu022
x 2- in eqns. 17 and 18 correspond to Cu(OH)3 and Cu(OH)
calculated by eqns. 3 and 4 respectively with the aid
of eqn. 15. The Cu2+ released in equation 15 may undergo
the hydrolysis reactions 1-4, 7 and 8. The concentrations
of all the soluble cupric species in equilibrium with
tenorite are summarized in Table 2.3 overleaf.
From this table the solubility diagram for tenorite
was constructed in Fig. 2.2. The pH of minimum solubility
is about 8.5. It is seen that CuO is much less soluble
than Cu(OH)2, (which, as mentioned previously, is a
metastable phase).
32
(15)
(16)
(17)
(18)
Table 2.3: - log[ ]Cu soluble species in equilibrium with tenorite and
CO2 (g) in the atmosphere
pH Cu2+ / .2 Cu(OH)4 CuOH+ / .2+ kOH)2 Cu CO3 .2- Cu/ CO3)2 Cu(OH)3 Total
2 -3.5 28.4 2.5 -0.4 7.45 21.94 17.3 -3.5
3 -1.5 26.4 3.5 1.6 7.45 19.94 16.3 -1.5
4 0.5 24.4 4.5 3.6 7.45 17.94 15.3 0.5
5 2.5 22.4 5.5 5.6 7.45 15.94 14.3 2.5
6 4.5 20.4 6.5 7.6 7.45 13.94 13.3 4.5
7 6.5 18.4 7.5 9.6 7.45 11.94 12.3 6.42
8 8.5 16.4 8.5 11.6 9.94 11.3 7.38
9 10.5 14.4 9.5 13.6 7.94 10.3 7.32
10 12.5 12.4 10.5 15.6 7.45 5.94 9.3 5.93
11 14.5 10.4 11.5 17.6 7.45 3.94 8.3 3.94
12 1 16.5 8.4 12.5 19.6 7.45 1.94 7.3 1.94 ____J
12 4
TENORITE
4,o Cu CO3
0 E n
10- 0
15-
20
Fig.2.2 Solubility diagram of Tenorite
2
3't
35
• Solubilit of cuLite_LC12.21
At 25 C and I = 0, this reaction holds:
19. 2 cu20 (s) .1. ,.11120 = Cu+ + 0H-; pK = 14.7
from this reaction . . log [Cu+] = pH - 0.7
In the pH range 2 - 11.85, the Cu+ ions will be
oxidized quickly to Cu2+ and the cuprite surface will be
slowly changing to tenorite due to the atmospheric oxygen.
These oxidations are discussed in more detail in 2.5.1.
The Cu2+ ions thus obtained may undergo hydrolysis to the
various complexes as in eqns. 1 - 4 and 7 - 14. For the
surface chemical purposes, in the presence of dissolved
oxygen. (02) in the solution, the cuprite surface may be
considered as that of tenorite. Hence the solubility of
cuprite would be expected to be controlled by that of
tenorite. The equilibrium in eqn. 19 therefore, cannot
be satisfied under atmospheric conditions. No actual
data was available on the kinetics of the oxidation of
cuprite to tenorite at room temperature, although it is
known to be slow
SolUIDilitofn 2(OH)2 003,1
At 25°C and I = 0, the following equation holds:
20. CU2(OH)2 003 (s) + = Ca2+ 002 (g) + H20; pK = -
For air, log p00 = -3.52 2
. . log [Cu2+] .8.25- 2 pH
The cupric ions thus released from malachite, may
undergo hydrolysis according to eqns. 1 - 4, 7 and 8.
The concentrations of the hydroxy and carbonato complexes
In equilibrium with malachite under atmospheric conditions
(19)
49
(20)
36
(i.e., constantPC0 ) were calculated using eqn. 20.
Accordingly the solubility diagram for malachite was
constructed in Fig. 2.3. The pH of minimum solubility
is between 8 - 9. In nature, malachite is the commonest
"oxidized" copper mineral.
Solubility of azurite (21.3(OH)21223121
The following equation holds at 25°C and I = O.
Cu3 (OH)2 (003)2 (s) + Cu2+ +liCO2 (g) +i H20; (21)
(under atmospheric conditions, log p = -3.52) pK = -6.47 CO2 r 1 . . log LCu2+ j = 8.82 - 2 pH.
From this equation the concentrations of the hydroxy
and carbonato complexes in equilibrium with azurite were
calculated from eqns. 1 - 4, 7 and 8. Accordingly the
solubility diagram for azurite in equilibrium with the
atmospheric CO2 was constructed in Fig. 2.4. The pH of
minimum solubility is between 8 - 9.
Solubility of covellite (CuS)
The following equation holds for 25°C and I = 0:
22. CuS (s) + 2H+ = Cu2+ + H2S (g); PK =14.2 (22)
The solubility of covellite in equilibrium with H2S
gas was calculated for three hypothetical cases:
Case 1: The mineral suspension is closed to the
atmosphere and the partial pressure of H2S gas = 1 atm.
From eqn. 22; log [Cu2+] -14.2 - 2 pH (23)
The cupric ions released may only form hydroxy
complexes. The theoretical concentrations of the soluble
species in equilibrium with covellite are calculated in
Table 2.4, from which the solubility diagram was constructed
in Fig. 2.5. According to the diagram, the pH of minimum
solubility is around pH 9.5, but in practical termsIthe
37
I I I I I 2
8 10 12
pH
Fig.2-3 Solubility diagram of Malachite in equilibrium with atmospheric CO2
4 2 1 -111111
6 8 10 12
0
pH
Fig. 24 Solubility diagram of Azurite in equilibrium with atmospheric CO2
38
0) ~ ~J
--Q)
0 E . n u 0")
0
I
39
18K-=~ ---===_. ===--~
20 ~-=~=_-=~~~~~-~~ '---COVELLITE-- '---
251 ~ ~-------------------
~-------------;
q .... 0 ~x
~---------
,------"'-,--
30
35
2 4 6 8 10 12
pH
Fifj.2 a 5 Solubility diagram of CovelHte at pH.,s=1 atfn., in a ciosed sysh~rn
t;,.
40
•
mineral is virtually completely "insoluble" to all
ordinary analytical techniques.
Table 2.4: - log[ ]soluble species in equilibrium
with covellite
pH Cu2+ CuOH+ Cu(OH); Cu(OH) - total
2 18.2 24.2 39 50.1 18.2
3 20.2 25.2 38 48.1 20.2
4 22.2 26.2 37 46.1 22.2
5 24.2 27.2 36 44.1 24.2
6 26.2 28.2 35 42.1 26.196
7 28.2 29.2 34 40.1 28.159
8 30.2 30.2 33 38.1 29.9
9 32.2 31.2 32 36.1 31.159
10 34.2 32.2 31 34.1 31.0
11 36.2 33.2 30 32.1 30.0
12 38.2 34.2 29 30.1 29.0
The equilibria of the system H2S (g) - H2O are
characterized by the following equations.
24. H2S (g) = H2S (aq.); log K = -0.99
at pH 2s = 1
. . log [F[2S] = -0.99
25. H + HS- = H2S (aq.); log K = 6.99
. . log [HS-] = pH -7.98
26. H+ + 82- = HS ; log K = 12.9
r 1 . . log LS 2-j = 2 pH - 20.88
(24)
(25)
(26)
41
Since no complexation reactions between Cu2+
and
HS or S2 were reported in the literature, these equations
will not affect the solubility diagram of covellite.
Case 2: The system (covellite suspension) is open
to atmosphere and pH2S is 10-4 atm. (p = 10=3.52and CO2
p0 = 0.21). But no oxidation is supposed to occur. 2
equilibrium with covellite under these conditions can be
obtained from equation 27, . • . log [Cu21= -10.2 - 2 pH (27)
The Cu2+ ions released may undergo hydrolysis according to
eqns. 1 - 4, 7 and 8. The theoretical concentrations of
these complexes were calculated and the solubility diagram
was constructed in Fig. 2.6 accordingly. The pH of
minimum solubility is between 8 - 9. Because of the lower
postulated partial pressure of H2S' the solubility is
greatly increased; but it is still analytically insignificant.
Case 3: The system is open to the atmosphere and
= 10-10
pH2S = 10
-3.52' p0 = 0.21). atm' (p00 2
But no oxidation is supposed to occur.
Under these conditions, equation 27 can be rewritten
r as follows: log [Cu2+] = -4.2 - 2 pH
The solubility diagram for covellite under these
conditions was constructed in Fig. 2.7, in a similar way
as in case 2 above. According to the diagram, the pH of
minimum solubility is between 8 - 9. It is interesting
to note that the pH of minimum solubility for the two open
systems is the same regardless of the partial pressure of
From reaction 22, the concentration of Cu2+ in
(28)
T. 4J
a) 0 E
U C4 0
L12
pH
Fig.2•6 Solubility diagram of CoveHite at pH2s=10-4 atm., with access of atmospheric CO2
_lo
g C
,m
ole
/ litre
Fig. 2.7 Solubility diagram of Cove Hite at pH2s =10-1° atm., with access of atmospheric CO2
411
H2S in the atmosphere. The solubility, however, is higher
at the lower ID -H It is clear from eqns. 23, 27 and 28,
2
that Cu(OH)2 will not be precipitated at any pH range,
since the concentration of Cu2+ released from covellite
in the three cases is always less than that required to
form the hydroxide in eqn. 9. Dissolution of sulphide
minerals is, however, greatly increased by oxidation,
which is discussed later. Whatever the mechanism, this
is thermodynamically equivalent to.maintainence of a very
low vo -H2S• Solubilit of chalcocite Cu2SJ
The following reaction holds at 25°C and I = 0;
29. 2 Gu2S (s) H+ = cu+ (g) ; pK = 13.5
However, in the pH range 2 - 11.85, both the Cu+
ions and the chalcite surface will presumably be oxidized
rapidly to Cu 2+ and covellite, due to the atmospheric
oxygen as shown later in section 2.5. Hence the equilibrium
in eqn. 29 cannot be satisfied in this pH range. For
surface chemical purposes, in the presence of dissolved
air in the solution, the chalcocite surface can be considered
as that of covellite, though the solubility of chalcOcite
may be higher than that of covellite due to the initial
stages of oxidation as shown later by eqn. 39 in section
2,5.
2.3.2. Effect of article size on solubility
It has been established(39,) that very finely
divided solids have a greater solubility than large
crystals. In general, for particles smaller than 1 far;, or
of specific surface area greater than a few square metres
per gram, surface energy may become sufficiently large to
from 31 and 32 S - v = M« (33) d Pd
45
influence surface properties. The change in the free
energy AG involved in grinding a coarse solid suspended
in water ( S = 0 d =co ) into a finely powdered one
of molar surface S and particle size d is given by
401 eqn. 30 (39,AG fiS. where 7■3 is the mean free
surface energy (interfacial tension) of the solid-
liquid interface.
The molar surface S = NS
where N is the number of particles per mole,
S = surface area of a single particle = Kd2
The volume of a single particle, v = ld3
(31 )
and the molar volume V = = Nv (32)
where m = 1 = the shape factor, and M =
formula weight of solid.
From the relation, AG = RT in [ K so (fines)/k so(coarse)]
(40 ) and equations 31 and 33, Shindler obtained the
following equations
9-!25.1.21j log so
(s) = log Kso (s=o) + RT or or
na2 d-1 :211L log K50 (d) = log K50 (d = 00) + 2 RT
Although values of for for solid/solution interfaces
are not reliably known, the effect of the particle size(or
molar surface) on the solubilities of CuO, Cu(OH)2 and
(40,41) ZnO has been confirmed by Shindler and coworkers
In their studies, it was assumed that V remains independ-
ent of the surface area. The increase in solubility of
a given copper mineral due to the fine particle size is
(34)
(35)
Li 6
not likely to change the pH of minimum solubility signi-
ficantly, since the concentrations of almost all the
complexes of cupric or cuprous ions are dependent on the
concentration of Cu2+.
2.3.3. Effect of "inert" electrolytes on solubility
The effect of adding "inert electrolytes" (i.e., those
of different chemical composition that do not have common
ions with the solid crystal) on the solubility of a solid
can be explained in terms of the activities of the ionic
species. In dilute solutions the charged ions exert long-
range electrostatic forces upon one another which generally
result in reducing the activity coefficients('g ) (38). On
further dilution, the effects of these electrostatic forces
diminish and the activity coefficients increase. As the
solution approaches infinite dilution, the interaction
between cations and anions vanishes and the activity
coefficients are taken as unity, by definition. The
electrostatic effects depend primarily on the ionic strength
of the solution, I, the charge and diameter of the hydrated
ionic species according to the Debye-Huckel theory. The
ionic strength is defined as I =M1 Zi' 2
where Mi is the
molality and Z. is the charge of the ith ion in the solution.
The activity coefficient 0) was shown(38) to decrease
as the ionic strength is increased up to I = 1. At values
of I >1, the activity coefficient may increase again. The
relationship between 1.) and I given by the Debye-Huckel
theory is
I— A Zit NI I -log/ ai BIT. where A and B are constants
47
characteristic of the solvent at known temperature and
pressure. The quantity a. has a value dependent on
the "effective diameter" of the hydrated ion.
The solubility of a given copper mineral (Mt),is the
sum of all dissolved species containing copper Ms:
Mt = s. The activity of the ionic species a= Ms V s.
• • • M
as as and M
t =
V s Vs
The last equation means that the mineral solubility
is inversely proportional to the activity coefficient of
the solute species. Thus it can be concluded that in
dilute solutions (1 <1), the solubility of the mineral is
generally enhanced in the presence of inert electrolytes.
In more concentrated solutions (I >1), the activity
coefficients may become greater than unity and the solubility
of the mineral may become smaller again.
The increase in solubility will not, however, change
the pH of minimum solubility significantly so long as no
new species are formed as a result.
Activity coefficient effects are generally negligible
in the dilute solutions encountered in mineral processing
operations.
2.4 Solubilit of chr socolla
Chrysocolla is a copper silicate, commonly present in
oxidized zones of ores. Because of a complete absence of
published data on the solubility constants of chrysocolia,
its solubility was investigated experimentally. The lack
of data may be due to the widely varying composition and
structure of the mineral. Chrysocolla is a heterogeneous
/48
mineral and the copper content varies over a distance of
a few {441 According to sdme author (4) the
structure of the mineral was found to be a mixture of a
crystalline copper silicate phase dispersed in an amorphous
silica hydrogel with a composition that can be expressed
in terms of CuO, Si02 and H20. The structure of the
crystallites was proposed(45) to be a distorted chain
silicate structure of the general formula (Si4010)2 Cu8(OH)12.
8H20 0 or (Si, 010)2 Cu8(OH)12, in which there may be minor
Cu substitution by di- and trivalent ions. This proposition
is largly in agreement with an earlier work(46) where the
structure was stated to be of a porous aggregate of approxi-
mately 100 R diameter crystallites. The copper is present
in the cupric state and both hydration water and bound OH-
are present in the structure.
Therefore the varying copper content in different
mineral samples depends on the variations in the abundance
of this crystalline copper silicate phase within each
grain of chrysocolla. The surface of chrysocolla should
consist of alternating crystalline copper silicate phase
and amorphous silica hydrogel(47)
2.4.1. Effect of H on solubility of chrysocolla
Experimental: In a series of experiments, 0.5 g
samples of finely ground chrysocolla (obtained from
Arizona, U.S.A.) were shaken in 50 ml double-distilled
water of pre-adjusted pH (2, 4, 5.9, 8 and 10) for 5, 15
and 30 minutes. When the suspensions were filtered on
filter paper, colloidal suspensions were obtained. 10 ml
of the colloidal filtrate were mixed with 10 ml of 2.55%
49
NaCI to effect immediate coagulation and precipitatioll of
the colloidal particles leaving clear supernatants which
were filtered easily. The clear filtrates were analysed
f C 2+ . or U lons by the colorimetric method using b~s-cyclo-
hexane oxalyl-dihydrazone. This method is described in
Appendix I. The resul ts are shown in Table 2.5 below'.
Table 2.5: Concentrations of Cu2 + in p.p.m.
released from chrysocolla at
different pH.values.
T~ (min. ) 2' 4 5.9 9 10
5 130 2.3 2.0 0.8 0.7
15 330 1 .0 2.0 1 .7 1 .0
30 430 1 • 1 1.2 2. 1 1 .0
From Table 2.5 it appears that [Cu2 +] sharply
increased b~low pH 4 and the [Cu2 +] 4 in the pH range -10
was more or less constant. It is clear from this table
that raising the leaching time from 15 to 30 min. did
not increase the ~u2+] significantly in this range.
There may be some exaggeration in the amount of Cu2
+
released due to the use of NaCl in the coagulation stage
because of cation exchange from colloidal chrysocolla
particles. Thus no particular significance can be attached
to the low values in the pH range 4 - 10, except to note
that they never reached the theoretical solubility
expected for CU(OH)2 (Fig. 2.1), and only below pH 4 solubility
became large .. One important consequence of these results
50
is that in practice chrysocolla is found to be sufficiently
soluble at pH 2 to produce precipitation of Cu(OH)2 if the
pH is subsequently raised into the region 6 - 8.
2.4.2. Effect of sodium chloride on solubility of
of chrysocolla
Experimental: In a series of experiments, 0.5 g
samples of finely ground chryscolla were shaken in 50 ml
distilled water containing preadjusted amounts of NaCl.
The pH of the distilled water was 5.9. The shaking was
performed for 15 min. and 30 min. at each level of NaC1
(except at 2.55 % NaC1). The suspensions were filtered
and 10 ml of the filtrates were taken for the determination
of [Cul by the calorimetric method described in Appendix 1.
Some experiments were duplicated. The results are shown
in Table 2.6 below.
Table 2.6: Concentrations of Cu in p.p.m. released
from chrysocolla at different NaC1 %
in solution.
NaC1 % Time (min.)
0.0255 0.255 1.835 2.55
15
30
0.62
1.2
0.8
*1.5
2.7
*2.8
_ ___
6.0
(* these values are the average of two measurements
(duplicates) ).
The results show that [Cul released increases with [Cul
increasing NaC1 content. The mechanism was probably ion-
exchange.
51
2.5. Surface oxidation of copperjniz2=122 iLadox equilibria
2.5.1. Control of oxidation .otential of aqueous
suspensions br atmospheric oxygen
All sulphide minerals are subject to atmospheric
oxidation to greater or lessuextent. Oxidation reactions
of substances by molecular 02 at room temperature are often
much slower than the reactions of other oxidizing agents
having theoretically less favourable potentials(53). This
sluggishness of oxygen (02) is due in part to the initial
difficulty in breaking the bond between the two oxygen
atoms. (According to Sato(5‘i, the faster reactions of
02 are those in which the bond remains unbroken). It is
established(36) that hydrogen peroxide (H202) or its basic
equivalent peroxyl ion (H02 ) is an intermediate product
of 02 reduction in the presence of H+. Thus the oxidation
potential of an aqueous system in contact with free 02 is
controlled primarily by the potential of H202-02 couple.
The oxidation potential of the aqueous system, therefore,
should be at or above the potential of the H202-02 couple
so long as a detectable amount of free oxygen is present
in the system. If the oxidation potential of the aqueous
system is less than the potential (Eh) of H202-02, then
02 will immediately be consumed in the oxidation of sub-
stances in the system, being itself reduced to H202 and
further to H2O.
When the oxidation potential of the solution exceeds
that of H202-02 couple, the peroxide is catalytically
decomposed by the heavy metal species, and oxygen becomes
52
no longer available for further oxidation. At this state,
a metastable equilibrium is reached between 02 and H202
and the Eh value of the system is determined as follows(53)
p0 36. H201. 0
2 + 2H++.2e Ph = 0.682 - 0.0591 pH + 0.0295 log B--(57 -
2
where the round bracket represents the activity. The ratio
PO was chosen by Sato(53) to be equal to 106, at I.
(11202)
PO2 = 0.21 atm, which appeared to agree with his results.
Thus the oxidation potential, Fh, of the aqueous solution
at equilibrium will be: Eh = 0.859 - 0.0591 pH. (37)
This equation will be used in this. work to calculate the
oxidation potential of the aqueous systems at the various
pH values.
•
Oxidation of Cu+ to Cu2+• Cuprous ions are oxidized
to cupric in aqueous solutions according to the equation (39):
38. CV2+
+ e = Cut; log K = 2.7, Eh° (standard potential) = 0.16. 2
i.e. Eh = 0.16 + 0.0591 log
According to equations 37 and 38, substantial oxidation
Cu2+ of cuprous ions into cupric ions, i.e., when = 1.0,
should proceed up to pH 11.85, where the standard potential
of Cu2+ - Cu+ system is equal to the oxidation potential of
H202-02 couple.
2.5.2. Surface oxidation of chalcocite
According to Sato (S5), chalcociteis fairly rapidly
oxidized to covellite, which in turn is slowly oxidized
to cupric ions and sulphur.
39. Cu2S = CuS + Cu2+
+ 2e
40. CuS = Ou24- + S + 2e
The electrode potential of copper sulphides should be
dependent only. on the activity of rsuprits ions since fale
(38)
53
other oxidation products are solids. For reaction 39;
= 0.530 + 0.0295 log (Cu2+ ). (39). This reaction will
be taken in this work as the oxidation determining step
for chalcocite, due to its rapidity. Comparison of
equations 39 and 37, reveals that this oxidation is
possible in the pH range considered here (2 - 11.5).
The Eh for chalcocite was stated(55) to be independent
of the sulphate ion SOT or sulphur activities. Thus it
can be concluded that the surface of chalcocite is generally
coated with the covellite mineral as an oxidation product.
The electrode potential of chalcocite- in alkaline
solutions was measured by Lekki and Laskowski(5) . They
concluded that the chalcocite electrode in alkaline
solutions can be treated as an oxide electrode, for which
the potential is determined by the 11+ and OH ions. In
arriving to this conclusion they assumed that solid
cupric hydroxide forms under these conditions. The same
assumption was made by Sato(55). However, precipitation
1 of Cu(OH)
2 can only be possible when the [ Cu
2+jreleased
from the mineral is equal to or greater than that is
required for forming Cu(OH)2 in equation 9. It may be
possible that the surface oxidation of chalcocite to
covellite, proceeds with formation of digenite (Cu9S5)
as an intermediate(55)
2.5.3. Surface oxidation of covellite
The oxidation reaction for covellite is (55)
CuS = Cu2+ + S + 2e., Eh = 0.591 + 0.0295 log (eu
2+ )
(40)
54
The activity of cupric ions will be taken as approximately
equal to the calculated concentration of Cu2+ in section
2.3. Comparison of equations 40 and 37 reveals that the
oxidation of covellite is possible in the pH range 2 - 12,
even at a partial pressure of H2S gas 10_10.
However,
this reaction is said(55) to be slower than reaction 39.
In the presence of free 02, sulphur thus produced
should eventually be oxidized to sulphate ions (S00
through various stages of oxidation. The Eh of
covellite oxidation, however, was found to be independent
of the SO activity(55) showing that the oxidation chain
of reactions was not in thermodynamic equilibrium.
2.5.4. Surface Oxidation of cuprite and other
copper minerals
According to Garrels and Christ(38), the oxidation
of cuprite surfaces may be represented by the following
equations:
1 41. cup(s) 02 (g) = 2 CuO(s) ; K = PoZ
42. 3 cup(s) + 4 002 (g) + 2 02 (g) + 21120 = 2 Cu3 (0102(CO3 )2 (s) ;
1 K = p4 p/2
02 2
43 . 01120(s) + 2 02 (g) 002 (g) + H2O = Cu2(011)2 CO3 (s). 1 _
P 02 PCO2
Reaction 41 explains the darkening of red-colour
cuprite powder on long storage. However, at ordinary
temperatures these reactions are slow because of the
sluggishness of reactions with molecular oxygen, as
55
explained earlier. 'Therefore for the purpose of investigating
the effect of surface oxidation on selective flocculation
or flotation processes during the experimental periods
usually encountered, these reactions can possibly be
ignored.
Similarly, the effects of the surface alteration of
tenorite to malachite and other solid state reactions:
2 CuO CO2 (g) H2O = Cu2 (OH)2 CO3; and of azurite to
malachite; 3 Cu2 (OH)2 CO3 002 (g) = 2 Cu3(OH)2(CO3)2 H20;
or vice versa could only be considered relevant if their
reaction rates were fast enough. Apparently nothing is
known on the kinetics of these reactions at room temperature.
2.6. Surface electrical propeELLtsofamatnzinerals
2.6.1. Introduction:
Knowledge of the electrical charge of the solid
surface is often necessary to interpret and predict
behaviour of the mineral suspensions e.g., the stability
and state of dispersion, rheology of suspensions, adsorption
properties, flotation, flocculation and coagulation (47,49,
52,58, 5,21). Since the potential difference between
the charged mineral surface (or its "plane of closest
approach) and the bulk of the solution ( yo or yo cannot be measured directly(39) zeta-potential ( ), althoughLis
smaller in magnitude than yo or y8(59,60) offers useful
information. The zeta-potential or the charge at the plane
of shear'' is usually computed from electrophoretic
mobility or other electrokinetic measurements. These
measurements concern only the diffuse part of the electrical
double layer.
56
Origins of surface charge: These were briefly
summarized as follows:(39)
1. Chemical reactions on the surface: which can be classified
into:
a. Acid-base ionization of the surface functional
zamaas: The charge of the surface is dependent on the
degree of ionization and consequently on the pH of the
medium, e.g., silica surface (ionization of silanol
groups).
b. Coordination of solutes to the solid surface°
s,ecific adsorption.: The alteration in surface
charge results from chemical reactions.
Examples: /c -/s) + S2-
/ S2-
/ / 3
Cu(s) + 2H2S = ICu(SH)2 11 + 2 1-. 2
Fe0OH(s) + HP02 Fe0HP04 + OH
4 •
2. Lattice imperfections and isomorphous substitutions:
For example, in clays replacement of silicon ions by Al
ions in the SiO2 structure results in a negatively charged
frame-work.
3. 22-La.a.192- aa: Preferential adsorption of one type
of ion on the surface can arise from London-van der Waais
interactions and from hydrogen bonding. Examples are
(a) adsorption of surfactants on clays or humic acid on
silica surface,(b) adsorption of multinuclear hydroxy-
(°9 complexes and polymers on a calcite surface
and /
57
Preferential adsorption of hydrolyzed metal ions: It
(39,48,49,51,52,57) has been observed that the hydrolysis
products of multivalent ions, cationic as well as anionic
(even polysilicates and polyphosphates) are adsorbed more
readily at the particle-water interfaces, than non-
hydrolyzed metal ions. This tendency to be adsorbed even
against electrostatic repulsion is especially pronounced
for polynuclear polyhydroxy species. This may be because(39):
(1) the hydrolyzed species are larger and less hydrated
than non-hydrolyzed species; (2) or the presence of a
coordinated hydroxyl group, (the anchoring of the metal
hydroxy complexes may be due to the formation of a covalent
bond between the central metal atom in the hydroxy species
and specific sites on the solid surface); (3) more than one
hydroxyl group per "molecule" can become attached at the
interface. Likewise polymers have a strong tendency to
accumulate at interfaces because of multiple-link attach-
ment.
From the foregoing discussion it may be supposed that
the metal hydroxy complexes can be considered as potential-
(48,49,52,57,51,47,39) determining ions for metallic minerals,
all of which are controlled by the pH of the medium.
Accordingly, the potential-determining ions of copper
N minerals, may be considered to be: Cu2(OH)22+ , Cu(OH)-F ,
CuCO3, Cu2+ , Cu(CO )2- , Cu(CO )4- , Cu(OH)2- 3, 3 2 3 V
-.. Cu(OH)3 , OH and H+ , all of which are, of course
controlled by the pH of the medium.
i.e., y (my) = 12.9 velocit potential gradient
58
2.6.2. Zeta-•Ote tial of malachite
Experimental: The mobility of malachite particles
was measured at various pH values with Rank Bros.Particle
Electrophoresis Apparatus (Mark II) (Cambridge, England),
using a quartz flat cell (1 x 10 mm). The interelectrode
distance (or the effective length of the cell "L") and
the microscope eye piece graticule (X = 97.5 vu) were
calibrated. The first was determined by measuring the
resistance (R) of the cell containing electrolyte solution
(0.1 M KC1) of known specific conductance (K = 1.289 x 10-2
-1 cm
-1 at 25°C) by a conductance bridge (Portland
conductivity meter). The effective cell length (L) was
calculated from the equation: R = KA , where A is the
. cross-sectional area of the cell (0.1 x 1 cm2). The
stationary levels were taken at 19.4% and 80.6% of the
observed thickness of the cell (approximately 0.75 mm in
water). The applied voltage across the cell was 100 volts
and the time required for the particles to move one square
in the graticule in seconds (t) was measured at the station-
ary levels at a constant temperature of 25°C. The zeta-
potential (C) was calculated from the Smoluchowski
equation at 25°C. 4 = 12.9 u, where u is the mobility,
- 12.9 vx/t/L
Procedure: A sample of malachite was finely ground in
an agate mill to minus 325 mesh. The powder was dispersed
in distilled water (at the natural pH 5.9) in an open beaker
at high shear with a magnetic stirrer for a few minutes.
The dilute suspension was allowed to stand for a few minutes
and the settled particles were discarded, only the suspension
59
being used. Small samples of this suspension were taken
for measurements. The pH of each sample was adjusted,
while stirring, by HCl or NaOH solutions. The average
time of adjusting the pH was about 25 minutes, or until
the change in the particular pH reading was very slow or had
apparently stopped. The times taken for the particles to
travel one square in the graticule were measured at both
the stationary levels in the electrophoretic cell at the
pH values 6 - 11. The zeta-potential of malachite was
calculated for the various pH values from the above
equation.
t The effects of cupric sulphate 00-4 M CuSO4), sodium
f 4 carbonate 00 M Na2CO3),Dispex N 40 (50 p.p.m.) and Calgon
(400 p.p.m.) on the zeta-potential of malachite at
various pH values were measured in the same way as before.
The results are shown on Table 2.7 and Fig. 2.8.
Table 2.7: Zeta-potential (in mV) of malachite at 25°C.
PH 7 8 9 10 11
Solution medium
dist. water +26,1 +24.7 +21.5 + 9.2 -12.3 -24.4
CuS04' 104m +20.4 +22.8 +17.1 +10.2 -11.6 -22.0
Na2CO3 10-4 M - - - -19.5 -21.9 -26.7
Dispex, 50 p.p.m. - - - -43.8 -44.7 -45.9
Calgon,400 p.p.m. - - - -49.9 -53.2 -53.5
From Fig. 2.,8 the pH of zero point of charge of malachite
in distilled water is seen to be between 9 and 9.5 and is _4
probably at pH 9.3. The addition of 10 M Cu 2+ ions did
not change the z.p.c., while the carbonate changed the
Zet
a-po
tent
ial,(
mV
)
10
15
20
25
30
35
40
45
50
9
10
(",o
47
0 Rs
46
C
0
N
4:3 42.)
0T; IT; co 041 th
6 in distilled water (+HCI or NaOH) o M Cu SO4 solution
in 10-4M Nat CO3 solution o in 50 p.p.m. Dispex solution A in 400 p.p.m.Calgon solution
55 7 pH 9 10 11
61
z.p.c. to a lower value. The non-effect of CuSO4 on z.p.c.
can be explained by the fact that the 104m CuSO4 would be
precipitated as Cu(OH)2 in the pH range 7 - 10. The figure
also shows the sharp increase in negative zeta-potential on
addition of Calgon and Dispex, indicating their adsorption.
These are clear examples of "specific" adsorption because
the already negative surface is rendered more strongly
negative. It seems certain that the binding of these
polymers must arise from close interaction of some of the anionic
groups with Cu2+ ions from the solid, the net strength of
adsorption being enhanced by multiplicity of linkages.
2.6.3. kliatzallaP2Int of c12221aLa2112Ellalmiaimam
solubility
It is interesting to note that the pH of malachite zpc
in distilled water nearly corresponds to its pH of minimum
solubility ( "/ pH 9) obtained from the solubility diagram
in Fig. 2.3. Similar observations were made in the case
of calcite by Somasundaran and Agar(49) who found that the
PH of Calcite (8 71/9.5) in equilibrium with carbon zpc
dioxide in the air closely corresponds to pH of minimum
solubility (8 - 10). Earlier, Parks and DeBruyn(51) showed
that the pHzpc
or i.e.p. of cc-hematite corresponds to
its pH of minimum solubility.
The concept that pH of minimum solubility for a solid
phase in equilibrium with the solution was shown by Beck(48)
to correspond to the solids isoelectric point (i.e.p.).
This may be true only in the absence of complications such
as those caused by structural or adsorbed impurities and
the equilibrium conditions specified°9). Bearing this in
62
mind, the z.p.c. of the solid should correspond to the pH
of charge balance (electroneutrality) of the potential-
determining ions(39,/43) which corresponds under the conditions
specified to the pH of minimum solubility. The concept
that pH corresponds to the pH of minimum solubility zpc
should help to predict at least qualitatively the effects
of certain variables on the z.p.c.. Measurements of z.p.c.
by electrokinetic methods could lead to varying results,
depending on the time allowed for the mineral to equilibrate
with the solution at each pH. The correspondence of pH zpc
to the pH of minimum solubility, thus depends in part on
the kinetics of attaining equilibrium between the mineral
and its hydrolysis products in the solution at each pH
value. The theoretical identification of these two points
implies that the acid-base character of groups exposed on
the surface of the solid is exactly the same as for isolated
units in solution. This assumption may be a useful
approximation, but is not expected to be exactly correct.
2.6.4. pH zpc of copper miae
The pHzpc of CuO (tenorite) has been given as 9.5(39)
which corresponds to its pH of minimum solubility (pH ms)
before reaching an equilibrium with (or in the absence of)
CO2 in the atmosphere in Fig. 2.2. If the mineral is
x allowed to equilibrate with CO, in the air (P = 10-3.52), CO2 the pHms should lie between pH 8 - 9.
Assuming this concept holds, the pH of cupric zpc
hydroxide, azurite, covellite, chalcocite and cuprite in
equilibrium with their solutions under atmospheric conditions
should correspond to pH 8-9, If the zop,ce of these minerals
63
are measured before reaching equilibrium with the atmospheric
CO2' their values will tend to be higher than the corresponding
pHms. The pHzpc of Cu(OH)2 was given as 7.7 by Yoon and
Salman(56) • Chrysocolla did not exhibit a zero point of charge at
any pH value(50,47) and was always negative. Partially
leached chrysocolla on the other hand had two zero points
of charge at pH 6.4 and 9.4(47). This behaviour was the
result of initially conditioning the chrysocolla at pH 4
before determining the mobility of the particles as the pH
was raised. The lower pH value of z.p.c- (6.4) was attrib-
uted to the precipitation of Cu(OH)2 on the surface of the
particles. The behaviour of the mineral at higher pH
was similar to that of CuO (tenorite) with a z.p.c. at
pH 9.5. It is interesting to note that in these measure-
ments(47s50) the mineral suspensions were not allowed to
reach equilibrium with CO2 in the atmosphere. The
negative charge below this was attributed to the silicate
part of the structure(50)
64
CHAPTER 3 THE CHEMICAL ORIGIN OF SELECTIVITY OF
POLYMERIC FLOCCULANTS
It has been established(12,14,15)that an effective
polymeric flocculant consists of a water-soluble macro-
molecular substance which could be adsorbed through its
functional groups by mineral particles in a suspension,
and acts as a molecular bridge between them. A fully
selective flocculant would adsorb only on to certain
minerals in a mixed mineral suspension. The selectivity
of adsorption could be due to the affinity of the functional
groups of the polymer towards certain metal ions, supplied
by the mineral, and indifference to other types of metal
ions; e.g., xanthates and dithiocarbamates tend to form
strong complexes with heavy metals, but are largely
indifferent to cations such as Ca2+, Al3+ and Mg2+. On the
other hand, the functional groups may complex with many
metal ions, but with varying degrees of strength; the
stability of some (or one) metal complexes being much higher
than the rest. In this case, the presence of another
ligand in the system may help to suppress complex formation
of the ions, leaving only those of strongest affinity to
the functional groups of the polymer, thus resulting in
selective adsorption.
Although many commercial flocculants at present
available are found to exhibit some degree of selectivity,
their use in selective flocculation processes is rather
limited. It has (14)
as been suggested that selectivity of
flocculants could be enhanced by incorporating in the
65
polymer chemical groupings which have strong affinity for
ions in the mineral to be flocculated. The choice of these
chemical groupings, however, requires better understanding
of the chemical origin of their selectivity, which is the
main concern of this chapter. An attempt is made in this
chapter to summarize current ideas on the fundamental
aspects of selective reactions and the possible methods
of synthe5izing selective flocculants.
3.1 Formation and stabilit of complex compounds;
the stabilit constants
It is well established that metallic ions occur as
hydrated complexes in aqueous solutions; consequently,
formation of complex compounds usually involves replacement
of water molecules in the hydration shell by other ligands.
Generally, complex formation is therefore accompanied by
reduction of hydration. The complex may become oil-soluble.
The complex may form a precipitate if the ligand links two
or several metallic ions together (bridging ligands
e.g.,CO3=, OH ). For most complexes, reactions between:Jigands
and cations proceed stepwise; that is if the concentration
of a ligand "L" in a solution with a metal ion "M" is
successively increased, a whole series of complexes, ML1,
with value of i from zero to maximum of n, is formed one
after the other. The processes generally come almost
immediately to equilibrium. According to Schwarzenbach(62)
there are almost a1ways more than two complexes present
simultaneously in solution. The equilibrium constants,
K. and B. therefore provide suitable criteria for
assessing quantitatively the coordinative behaviour of
66
various cations and their general reactivity. The values
of K and J3 which are the formation constants of individual
complexes and for the over-all process respectively, are
obtained from the equations: K.
[M.]
[M.] [111 [L.]
[1,1 However, not all complexes form new chemical bonds,
many are formed simply as an ion association because of
the electrostatic forces between the cations and anions
or a polar ligand. In such reactions, the change in enthalpy,
AH, is numerically small and may even be positive
(endothermic); nevertheless the formation constants of
the complexes can still be large. This is because of the
large and positive entropy change, AS, accompanying the
reaction, owing to the liberation of many water molecules
from the hydration shell following the partial neutralization
of charges. It is because of this fact, together with the
lack of information on AH for many complexing reactions,
that the change in the free energy, AG, is used as a
measure for the overall tendency of formation and stability
of complexes, the quantitative relationship being
AG i ° = -RT ln K (where AG is the standard free energy
for the reaction). In this chapter, the stability constant
K/ , was used as an indicator for the change in the free
energy of formation of the first complex.
The formation of precipitates can also be taken into
consideration in judging the tendency to coordination.
Mononuclear species are almost always present in the
solution in equilibrium with the precipitate; therefore,
their formation constants, K1 , when available, could be
fi -
67
used for the comparison with other soluble complexes.
If ne such values for K1 are available, the solubility
products, K so, of the slightly soluble precipitates may
be compared with one another. The smaller the solubility
products, of course, the more stable are the "bonds"
between metal cations and ligand anions. To illustrate
this point, the following example was given(63,64,65)in a
solution in which AgCl is being precipitated by an chrok
alkali/, the complex species AgC1, Agel2 and Ag+ are
present in equilibrium with the precipitate. The total
concentration of all species in solution could be measured
at different alkali chloride concentration and the values
of K1 , K2 for the formation of the simple chloro-complexes
of silver could thus be obtained.
3.2 Classification of ligands
The ligandsjor the complexing groups, can be classified
according to the type of the "donor" atom, the number of
donor atoms in a ligand and the structure of the complex
formed. The ligand behaviour is largely determined by the
nature of the donor atom which is responsible for binding
the ligand to the metal ion. Some "common" ligand atoms
are briefly considered here:
1. Halogens donors; F , Cl , Br and I coordinate as
simple anions, producing mononuclear complexes or sparingly
soluble halides.
2. Oxygen donors; e.g., OH , NO2 , NO3 , C0,1 , P0143—,
-- -- polyphosphates, SO , 5 `- SO /4 and various organic complexing
agents such as ethers, R-O-R, alcohols phenols and
68
carboxyl groups, form mono- and polynuclear species or
precipitates with many metal ions.
3. §2.221-arciaaam; such as HS , S , SO3 S203 ,
SCN, thioethers R-S-R, mercaptans and their anions
(R,SH, R.S-), thiocarboxylates, dithiocarbamates and
dithiocarbonates (xanthates); these show selective
tendency to coordinate with group B and transition
metal cations and not with A-cations (see below).
4. NitroP-en donors; like NO2 , SCN often add on to
metal ions through nitrogen. Organic ligands are
exemplified in primary, secondary and tertiary amines
(RNH2' R2NH R3 N)* Schiff's bases and carboxylic amides
R.CO. NH2.
5. Carbon donors; the only known ligand that has been
studies in aqueous solution is CN.
Ligands can also be classified according to the
number of donor atoms they contain, as unidentate and
multidentate (e.g., ammonia NH3 and EDTA respectively)
depending whether the ligand contains one or more donor atoms,
suitably situated to bond simultaneously to the one
acceptor atom. In general the multidentate ligands tend
to form much more stable complexes than unidentate ligands.
Another classification of ligands is according to the
structure of the complexes they form.
(a) Those which form mononuclear complexes and
essentially unidentate are considered "simple" ligands
e.g., F-, Cl, NH3,1
(b) Those which form polynuclear complexes and
precipitates by linking two or several metallic ions
together are called "br:Idging" ligands e.g,, OH-, CO, __ 3 _ 11
( 0-c-0- ) .
69
(c)
And those which form closed rings of atoms by
coordination links are termed "chelates", e.g., ethylene-
diamine (CH2 NH2)2, EDTA [(CH2.N(CH7„CO2)2)2 1, anions
of iminodiacetic acid NH(CH2-COO)2 , tartarates and citrates. --
The chelate complexes are usually much more stable
(66) than complexes with simple ligands. It has been shown
that five-membered chelate rings are more stable than six-
membered rings and the increase in stability in forming
chelates with seven-and eight-membered rings is insignificant
(67,68) On the other hand, ring strain arises for rings
with less than five-members; four..-membered rings as a result
do not increase the stability much over simple complexes,
and the formation of three-membered rings is still less
likely(62). Apparently some ring strain can also occur
with five-and six-membered rings, depending on the coor-
dination positions of the metal ion, as for Ag+ and Hg
4.4.((;48,69)
where the coordination positions are diametrically opposite •
and therefore, they form linear arrangements rather than
chelate rings.
The chelate effect. The reason for the higher
stability of chelate complexes in comparison with those of
simple ligands can be explained as follows: It is well
known that metal cations occur as hydrated complexes in
aqueous solutions; thus when a ligand combines with a
metal cation, it replaces water molecule from the hydration
shell, and the water-molecule as a result becomes free.
With simple ligands, the number of liberated water
molecules will be the same as the number of ligands which
disappear from the solution during complex formation,
appreciable stability. There is no
donors such as dithiocarbamates and
reaction with sulphur
xanthat e s (61. in
70
whereas a multidentate ligand (e.g.,chelate) replaces
several water molecules from the hydration shell. There-
fore, the association of a chelate ligand leads to a greater
entropy increase than the association of simple ligands,
although the change in enthalpy, AH, may be practically the
same, because the nature of the bonds which are broken and
newly formed is identical in both cases. The large entropy
rise for the chelate formation results in a greater decrease
in the free energy, AG, or a larger equilibrium constant,
K1 than for the association of simple ligands. Thus, chelate
complexes have greater probability of formation than the
corresponding complexes of unidentate ligands.
3.3 Classification of metal cations
The metal cations are classified according to the number
of electrons in their outer shell to A-cations and B-cations,
with the transition metal cations ranges between them.
(a)
Class A-cations have the electron configuration
of inert gases (d°-cations) and are of low polarizability(62,39,94,95)
i.e., their electron sheaths are not readily deformed under
the influence of an electric field. Such cations include
Mg2+, Ca2+, Be2+, Ba
2+, Al3+, Ti4+ and Zr4+. These cations
have a tendency to form complexes only with F- and oxygen
as donor atoms in aqueous solutions. They do not coordinate
with sulphur and nitrogen atoms to form complexes of
addition, no sulphides (precipitates or complexes) are
formed. Addition of ammonia, alkali sulphides or alkali
cyanides produces solid hydroxides, because the ligandstake
protons from the solvent and leave OH to react with the
71
metal ions. A-cations tend to form difficultly - soluble
precipitates with OH , CO3
and PO43-
(b) Class B-cations. These have an outer shell of
/ \ eighteen electrons, kd
10 - d
12), and high pblarizability;
such cations include Au+, Ag+, Cu+$ Zn2+$ Cd
2+, Hg
2+, and
Sn.4+. In general they form more stable complexes with N,S,
Cl and I donors than with oxygen and fluoride. B-cations
react with sulphur donors to produce both insoluble and
soluble compounds.
(c) Transition metal cations are intermediate between
class A- and B-cations; that is, they have between zero and
(d0 \
ten d-electrons kd0 - d10). The divalentcations in this
) class follow the well-known Irving-Williams order (70,71
in which the stability of complexes increase in the series
Mn21-<Fe24- CO21- < N.24- < Cu > Zn2+. This rule is
recognized to be valid for almost every ligand except for
certain compounds such as some polydentate chelate ligands
whose structure do not fit sterically into the quasi-square
coordination of Cu2+ (in which case, the octahedral N.
forms more stable complexes than Cu2+ (62)).
Cations of this
class, like B-cations, tend to form stronger complexes than
class A-cations.
3.4 Factors affectin the formation and stabilit of
complexes
In the complexes of A-cations, electrostatic forces
are mainly responsible for binding the cations with the
ligands (72)
; this type of interaction is referred to as
"electrovalent". Therefore, the formation and stability of
these complexes depend on the strength of these forces.
2-
72
These binding forces are known to depend on the following
factors : (a) The electric charge on both the metal ions
and the ligands, so that, the stability increases markedly
with increase in charge. (b) The cation-radius; .thus
for a series of cations of the same valency, those with the
smallest radius form the most stable complexes, except when
the chelating species possesses more than three to four ligand
atoms; e.g., EDTA. (c) The ligand basIallz; i.e., affinity
for protons; for a series of anionic ligands, the stability
of the complex increases sharply with the basicity of the
ligand oxygen, so that the following stability sequence
01I > phenolate > carboxylate > F is valid. It must be
remembered that the complex stability also increases with
the number of donor atoms in the ligand; this is generally
true for all three classes of cation.
On the other hand, in the complexes of B and transition
metal cations, non-electrovalent forces (i.e., all other
types of forces apart from electrostatic, including the
possibility of crystal field stabilization (73) ), in
addition to electrovalent forces are operative. The bond
formed between the central atom and the ligand is essentially
covalent. The tendency toward formation and stability of
complexes depends on the following factors: (a) The
ionization .otential of the metal, which determines the
capability of the cation to take up electrons;
(b) The electronegativity of the-li and donor atom; i.e.,
the affinity for electrons, which controls the tendency of
the ligand atom to donate electrons into a covalent bond.
The stability of the complex is found to increase with the
73
ionization potential of the metal and with decreasing
electronegativity of the ligand atom. In the electro-
negativity series F>a›N>C1>Br>it,iCrvS, the complex
stability increase from left to right. Electrovalent
interaction, however, increases with increasing charge and
decreasing radius of the cation. There are other factors
such as geometry of the ligand structure and entropy effects.
Thus the stability sequence with B-cations are often irregular.
The stability sequency of Irving-Williams can be explained
in terms of the difference between electrovalent and non-
electrovalent interaction. The radii of transition metal
cations decrease from Mn2+ to Cu
2+ but increase again for
- Zn2+, while the ionization potential of the metal increases
from Mn to Cu and falls again with Zn2+. However, since the
large changes in ionization potentials are much more effective
than the smaller changes in ionic radii, non-electrovalent
interaction is considered responsible for the marked changes
in complex stability.
The above factors were arranged in Table 3.1 so that
electronegativity of the ligand atoms is in decreasing
order from left to right, whereas the charge,basicity and
number of donor atoms are in an approximately increasing
order from left to right. The metal cations are arranged
according to their respective classes; within each class,
the cations are arranged according to their charge (or
valency), in increasing order from top to bottom. Further-
more, within the same valency group, radii of cations decrease
from top to bottom. The equilibrium constant for mononuclear
complexes, K1 , was used as a quantitative index for the
tendency of formation or stability of complexes. Values of
F OXYGEN NITROGEN Cl SULPHUR donor atoms Class
of Cations F- OH CO= 3 SO= 4 P0 4 P4 04- 2 Phenol Cit Tart EDTA PAA NO- 2 SCI- NH3 tren Penten Cl Et X- Et2 Cb- 8= SO= S2 0= 3 Ligand Ca tio n
0..I.5 -5.98
0.64 -8.3 - * 9.96 4.99 2.59 2.5 8 <0 < 0 -0.13
No complex formation
2.2 Ea++ 1.35
9
n P el- 1-, 0 M
mb ---1
1.04 -10.6*
1.5 -5.26
5.2 1'0.35
2.28 -5.0*
2.7 -26.0*
5.4 3.55 2.8 10.6 2.0 -0.1 <0 < 0 '26.5 1.98 Ca++ 0 0.99A
1.82 2.58 10.9*
3.4 -5.0*
2.21 2.5 5.17 3.96 1.3 8.7 1.8 -0.1 1.8 Mg++ 0.65 X
7.0 33.5* -18.2* 16.5
Slightly solu
ble
hydroxides
Al(OH 3 PP
formation
Al3+ 0.5 X
9.3 14.3 54.0*
3.7 29.5 2.0 0.3 Zr4+ 0.8 X
12.5 6.5 Ti 4+ fl, 4.68
1.25 6.47 -15.2*
6.77 9.6*
2 .32 -36.9* 3.18 5.9 3.2 18.8 4.8 1.23 2.5 4.0 18.8 22.4 0.4 14.9 Org
1'35.4 6.1 d9 oil++
0.96X
Transition m etals
cations (do - d10)
0.66 4.7 -15.2*
10.9 -6.87*
8
2.4
2.4
-30.3*
-34.7*
4.95 5.4
5.0
18.6
16.5 2.6
1.76
1.51
2.8
1.99
14.8
12.8
19.3
15.8
0.23
0.69
'112.0
- * 13.0
- * 20.7
* -22.5
2.06
2.05
88 ++ Ni
87++ CO ,-,.4 -r--, -14.8*
3.9 10.3 -15.1* r10.7*
2.3 4.4 14.2 1.31 1.4 8.8 11.2 0.3 - * 8.0
* -17.3 2.0 d6
Fe
4.5 -12.8*
10.9 -10.7*
2.3 2.6 5.74 2.7 14.5 3.36 1.23 0.8 5.8 9.4 0.0 * + 2.0
* -12.6 1.95 85++ mn
0.91 X
1.26 4.36 -15.7*
10.3 -10.7*
2.3 -32.0* 4.98 2.68 16.2 3.32 1.19 2.59 14.7 16.2 -0.19 * - 9.0 - * 23.8 2.29 810 ++ Zn
0.74 * -30.0 Au+
1.37 % I:1 n M 1-, 0 m
ill n
M. .... A.)
V
0.56 2.3 -7.8*
-11.4* 1.3 -4.5*
- * 19.9 0.34 * -12.2 7.3 1.15
-3.2* 4.75
-12.0* 3.31 10.3 3.23
_9.5* 8.3 Org
* -51.2 5.6 8.8 A-g+ o
1.26 A
L14.7* 2.34 5.93 : 6.7 :20.0 * -48.0 10.35 cu+ 0
0.96 A
11.5 25.5*
-16.0* 10.9 21.7 6.77 8.8 25.8 29.6 6.7 - * 51.8 12.0 14.7 Hg++ o 1.10 A
0.46 5.5 -14.2*
-12.o* 2.29 :32.6 3.75 16.9 1.7 2.51 2.57 12.3 16.8 2.0 -14.0 14.9 Org
- * 27.9 2.1 3.9 Cd++ 0.97 A
1
1.19 14.7 2.29 Zn++ 0.74 A
0 U
o P I c+ vi 0 Ci a
2
0 `0
° g o
a a
0 oa
* Logarithm of the solubility product, Org = in organic medium, [Mil K1 [Ml[Ll
75
K1 were taken from "The Stability Constants" b5).
3.5 Selectivit and s ecificitv of com lex formation
The selectivity of complex formation and even specificity
(i.e., capability of a ligand to attach to only one metal ion)
are influenced mainly by two important factors amongst others
mentioned earlier:
I) The nature of the ligand atoms
As shown in the previous sections and on Table 3.1
F and 0 donors form complexes with practically all polyvalent
metal cations, while N, S and C donors do not form complexes
of appreciable stability with A-cations and therefore are
more selectiVe. The selecttivity is noted to increase with
decreasing electronegativity of the donor atom. Nitrogen
donors, notably, polyamines (e.g. "tren." and "penten." on
Figures 3.1 and 3.2 respectively) are much stronger
and selective complex formers for B-cations and transition
metals than polycarboxylates, e.g. citrates and EDTA, Figures
343 and 3.4 . Sulphur donors show even more marked
selectivity where insoluble compounds are formed only with
B- and transition cations; such sulphur ligands are dithio-
carbonates (xanthate or R-X-) in Figure 3.5 and dithio-
carbamate (P.2 - Cb) in Figure 3.6
II) Geometr of the 11 and structure
Increased selectivity could be produced when the metal
ion and the chelate ligand are geometrically as compatible
as possible. The configuration of the chelate donor atoms
should have a steric arrangement to fit especially well to
the coordination sphere of one of another meta]. cation.
Thus the enclave of the diaminocyclohexanetetra-acetate,
CH2.CH2.NH2
N CH2-CH2.NH2
CH2-CH2.N H2
Fig.3.1 iren:c6 H18 N4: Triaminotriethylarnine
,--CH2.CH2.NH2 _---N
CH2 -------CH2CH2.N H2 1 CH2 CH 2'CH2'N H2 ----N
CHTCH2'N H2
Fig.:3.2 Penten:cio H28 N6; Tetra-(2-aminoethyl )- ethylenediamine
CH2-000-
HOC COO-
CH2.000-
.3.3 Cit:c6t1507,citrate
_--N CH2 --"*"--C1.42.000"
CH2 _--CH2.000- -----N
Fig.3-4 ED1A:c10 H16 08 N2
'S c2H5—o—c
Ns- Fig.3.5 Et-X: Ethyl xanthate
C2H5 S N—C
C----2H5 NS-
Fig.3- 6 Et 2rb: Diethyldithiocarbarnate
CH2 _--N
CH2 CH -----CH2-000-
CH2 CH CH2C00-
CH2
Fig.3.7Diaminocyciohexanetetraacetate
77
Fig. 3."7k fits especially well for the dimensions of
the calcium ion but is too small for the barium ion and
a little too large for the magnesium ion, and, as a resit,
it forms a calcium complex of higher stability than those
of magnesium and barium (66) . Specificity for a metal
ion would best be attained if the steric arrangement of
the ligand were rigid. Many examples of the effect of
the structural geometry on selective formation of
complexes can be found in the literature 94, 95, 96)
Although perfect specificity for a single metallic
element has not yet been achieved with synthetic chelating
agents, there are certain living organisms which are
capable of achieving this result. Bielig and Bayer
(74, 75, 76 ) have found that the concentration of
vanadium in the blood cells of the tunicate "Phallusia
mamillata" is a million times greater than that in sea-
water, and the concentration of copper in the blood of
the cuttlefish "Octopus vulgaris" is about a hundred
thousand times. The phenomena of enrichment of metals
in the marine organisms have been treated by Goldberg(77),
who found a qualitative correspondence between the enrich-
ments and the Irving-Williams order. Another example
of "specific" complexing agents in nature is a group of
compounds known as "ferrichromes", which strongly bind
Fe3+ ions (39). Ferrichromes appear to be widely
distributed in micro-organisms, and fungi have been
used for routine preparation of ferrichromes in the
laboratory(78)
78
Although ideal specificity of this order cannot yet
be attained with synthetic chelates, any attempt to
prepare chelating groups with high affinity even to few
metals would represent a step forward toward specificity.
With this aim in mind, Bayer and co-worders (79 synthesized
chelating resins possessing high selectivity for rare
metal ions in the hope of extracting these metals from
sea-water. The work of these authors will be discussed
in more detail in chapter 6.
A synthetic chelating resin was prepared from poly-
methacroylacetone by Teyssie and co-worker(80) who
used the resin as a selective ion-exchanger in the separation
of several cation-systems e.g., Cu/Ni; Cu/Co; Cu/Zn;
Be/Mg, Ca; and Zn/Mg.. Fanta and co-w (81) orkers have
grafted mixture of acrylamide and the nitrate of
dimethylaminoethyl methacrylate onto unmodified wheat
starch, with ferrous ammonium sulphate hydrogen peroxide
initiation. The polymer produced was difficultly soluble
in water. After many trials, they finally dissolved it
by a steam-jet cooker, which unfortunately reduced the
molecular 1,7ight, and, when the polymer was tested for
flocculation on a 3% suspension of diatomaceous silica
(celite), it was found inefficient as a flocculant.
( Packham s2) has prepared cross-linked co-polymers of
4-acetoxystyrene and divinylbenzene which on hydrolysis
yielded insoluble poly-4-hydroxystyrene with different
degrees of cross-linking, and according to Packham, most
of these polymers exhibited ion-exchange and chelating
79
properties in aqueous solution. Audsley and co-workers(83)
prepared anion-exchange resins by the reaction of poly-
vinyl chloride beads with concentrated aqueous solution
of aliphatic di- and polyamines; the resin was suitable
for the recovery of uranium from siliceous liquors as
the amine-groups were more selective to uranium than to
silica. Shepherd and Kitchener(84)
prepared transparent
colourless rods of anion-exchange resin based on poly-
ethyleneimine (cross-linked by reaction with ethylene
dibromide); the resin had a high affinity for copper and
to a smaller extent cobalt and nickel by ammine formation.
The possibility of using the chelating resin Dowex A-1
for the separation of metals was ruled out by Van Willigen
and his colleagues (85) because the differences between
stability constants of metal-resin complexes were too
small to promote efficient separation. Stamberg et al(86)
investigated an ion-exchange resin selective for nickel,
which contained dioxime and oxime groups. Green and La-w(87)
investigated a commercial ion-exchange resin with high
selectivity for gold. The resin was found to collect only
gold from acid solutions, while the "common" metals were
not collected nor did they interfer. The authors did not
reveal the nature of their resin. Parrish (88)
prepared
a number of ion-exchange resins based on polystyrene.
which showed selective behaviour, e.g. polythiolmethylstyrene
took up mercury but not magnesium, and polystyrene -
(4-azo-5)-8- hydroxyquinoline strongly adsorbed copper,
nickel, and cobalt in the pH range 2-3, whereas zinc,
mapganese, aluminium, magnesium and calcium were either
80
weakly adsorbed or not taken up at all, depending on pH
and ionic strength of solutions. Gregor and co-workers( 89)
claimed that the m-phenylene diglycine-formaldhyde resin,
which they synthesized, had a high degree of specificity
at certain -pH levels. In a review, Hale(90 cited
numerous examples of attempts to produce selective ion-
exchange resins for the separation of various metal cations.
From the above examples, it can be safely concluded
that selectivity of one resin or another was primarily
due to the presence of either nitrogen or sulphur as
donor atoms in the corresponding chelating groups.
Consequently, water-soluble polymers of the same chemical
. 44 types (i.e. not cross-linrd) could confidently be expected
to bind the metal ions in the same way.
3.6 Synthesis of selective of meric flocculants
There are four general methods by which polymers could
be prepared. These methods are briefly defined in this
section, but more detailed descriptions are to be found
in the literature (91,92,93)
3.6.1 Polymer modification
In this method, an existing polymer is subjected to
certain chemical reactions so that a distinctly different
polymer is obtained. For example, cellulose may be
modified through reaction of some of its hydroxyl groups
to give polymers like cellulose xanthate (Chapter 4),
cellulose acetate, methyl cellulose, etc. Polyvinyl
acetate when treated with methanol (alcoholysis), changes
to polyvinyl alcohol, which can be further modified to
polyvinyl alcohol xanthate (Chapter 5), or treated with
aldehyde to give polyvinyl acetal. Similarly, polyacrylamido
may be modified to produce many new polymers some of which
81
are already known in industry (e.g. anionic and cationic
flocculants). Two new modifications are described in
Chapters 5 and 6, where polyacrylamide is linked with
copper-selective groups namely; dithiocarbamates and
glyoxal-bis-hydroxyanil. The number of possibilities
is obviously very great, though the ease of preparation.:
of derivatives can vary enormously.
3.6.2 Polrmerization throu h functional groups
In this method, polymers are prepared from relatively
simple starting materials (monomers), where interaction
proceeds through their functional groups. The polymers
produced may contain new groups which are not found in the
monomers, e.g. polyamides (nylon 11, nylon 6,6, and
nylon 6.10), polycarbonate, polysulphide, etc. These
polymerizations almost always proceed in a stepwise manner
and the polymer chain is built up by a sequence of discreet
interactions between pairs of functional groups.
3.6.3 Polm=iaallanthrg pouhmultile bonds
This method is regarded as the joining together of
unsaturated molecules through the opening of multiple
bonds and linking as a chain. The polymer composition
and structural units are otherwise essentially unchanged.
This type of polymerization may be divided into 3-main
categories:
1. Linylolymerization, where the vinyl compounds,
i.e., those containing the CH2=c11- group, polymerizes to R
produce long-chair polymers with -C-C-C- backbone.
For example, ethylene, propylene, styrene, vinylchloride
and methyl methacrylate, can be reacted to give the
82
corresponding polymers. The process of vinyl polymerization
consists of 3 parts; namely; initiation, in which an active
species capable of starting polymerization is formed,
21222L2112a, in which the molecular weight of the polymer
is determined and finally, termination, in which the
polymerization process is deactivated and the final stable
polymer is produced. Vinyl polymerization is further,
divided into 3-different methods, according to the type
of the active species, namely; free, radical, anionic and
cationic polymerizations.
2. 211912211.2117219.11aLtion, where the unsaturated
diene compounds (i.e., organic compounds containing
two carbon to carbon double bonds) undergo polymerization
through their multiple bonds, e.g. butadiene
[CH2 = CH - CH = CH2]; chloroprene [CH2 = y - CH = CH2], Cl
and isoprene [CH2 = 9- CH = CH2] . As in vinyl
CH
by the three methods namely; free radicals, anionic and
cationic processes.
3. .ITknIIA T1.2E1Raila=iapli2a, unlike
vinyl and diene processes, where the carbon-carbon double
bond is the active cite, this method untilizes other
elements besides carbon to form polymers of hetero-
atomic chains. An example is found in formaldhyde
polymerization:/1 H_2C= 0 [- CH2 - O -1n •
3.6.11 Polymerization through ring-opening
In this method, polymer formation results from
polymerization of cyclic compounds undergoing ring-opening
reactions, e.g., the formation of polyether (polyethylene
3 polymerization, diene polymerization could be accomplished
83
oxide) from ethylene oxide. Polymers prepared in this
way usually have the same chemical composition as the
monomers.
The polymerization reactions are generally classified
into two types; namely, condensation polymerization and
addition polymerization. The condensation method leads to
a polymer having a structural unit containing fewer atoms
than the monomers, whereas the addition polymerization
results in a polymer having a structural unit with the
same molecular formula as the monomer. Polymerization
reactions are also classified as stepwise and chain
polymerization. The main difference between the two types
is the rate of polymerization; thus in a stepwise
process the polymer is built up relatively slowly by a
sequence of discrete reactions; while in the chain polymer-
ization the polymer molecule grows extremely rapidly once
the initiation has occurred.
Of all these methods, polymer modification probably
offers the most convenient technique for the synthesis of
selective flocculants. It is important to obtain a very
inng molecule in the final product, but many polymerization
reactions are difficult to control, and so it is simpler
to start with a pre-formed polymer of high molecular
weight and modify it. By incorporating certain chemical
groupings having strong affinity to particular metal
ions the polymer could be made to selectively complex
with such ions and since the complexes are less water
soluble, it seems likely that the polymer would selectively
adsorb on the corresponding minerals. Examples of
modified polymers are given in chapters 4, 5 and 6 where
attempts to produce selective flocculants are described
111
84
CHAPTER 4 CELLULOSE XANTHATE
4.1 INTRODUCTION
4.1.1 Formation o cellulose xanthate
Cellulose xanthate in the sodium form is an inter-
mediate in the manufacture of rayon, the concentrated
viscous solution in aqueous sodium hydroxide solutions
being technically called "viscose". It is formed by
reacting alkali cellulose with carbon disulphide, CS2,
according to the equationM: Cell-ONa + CS2 = Cell-OC(S)SNa,
where "Cell" means the cellulose molecule (C6H7(OH)3)n,
"n" ranges between 50-5000.
In this reaction some of the many OH-groups are
substituted by xanthate groups. The degree of substitution
.T”, "the number of xanthate groups per 100 glucose units",
usually ranges between 50-70 on average. Higher degrees of
substitution can, however, be obtained. Apparently, the
substitution of xanthate groups is not the same for all the
OH-groups of the glucose ring(98) It has been established
that substitution onto position 6- (fig.4.1), "1?6", may
amount to 60-75/0 of .4,ttal in freshly prepared xanthate
and to about 75-100% of nytotal" in newly prepared viscose())
The distribution of xanthate groups along the polymer chain
in fresh viscose has been found to be random, depending
however, on the conditions of xanthation. This distribution
may be modified in the subsequent stages of "ripening" of
6 0O ) viscose due to the de-xanthation and re-xanthation processes
85
4.1.2 Structure of cellulose xanthate
The basic unit of organization of native cellulose,
whether fibre, membrane or unorganized products, is a
0 fibril about 100A in diameter and of varied length
These fibrils bundle together to form the fibre with a
0 diameter of about 100,000A, while the fibrils themselves
consist of many cellulose molecules with a diameter of
0 .less than 10A. Figure 4.1 shows a diagram of the
structure of cellulose.
The structure of sodium cellulose xanthate, NaCX,
has been investigated by infra-red spectrophotometry0o1)
It was found that the C=S group is perpendicular to the
plane of the pyranose ring, while the C-S group is parallel
to it. Figure 4.2 shows the possible structure of
sodium cellulose xanthate accordingly.
4.1.3 Choice of cellulose xanthate as
flocculant
The choice of cellulose xanthate in selective floccul-
ation stemmed from the fact that xanthates of low moleulcar
weights are used as selective flotation collectors of
sulphides and some sulphidized oxides and carbonates. This
selectivity, as shown in Chapter 3, is due to the fact that
some ligands containing sulphur as the donor atom do not
react with minerals of cations with rare gas configuration,
like Ca2+
, Mg2+, Ba2+, Al3+, nor with silica. It is also
known that xanthates react with transition metal cations
such as Cu2+ . ,
2+ Zn2+ , Co
2+ and Fe2+ to form water-
insoluble compounds 043).
Therefore, when xanthates are
attached to a long-chain polymer such as cellulose, they
are expected to act as selective flocculants.
a selective
OH H 2C
i 3C H
I OH
Fig.4.1 Structure of Cellulose
ICI GH
OH H 0
C( )C4 1C )C C( 0 H H OH
1-1 C
CH2OH
n-2 n=50-5000
6CH2OH 5 I
Fig.4.2 Structure of Cellulose Xanthate
9H2o-c-s-
c
H 0 \ /C C ( \ 0
H
\ \ OH H
i 1 C
C
HI 1
0—c---s- g
87
4.1.4 Evidence of selectivity_
Sodium cellulose xanthate ("NaCX") in its unpurified
form, "viscose", was prepared and tested for flocculation
on some minerals at pH 10. It is believed that most
minerals acquire a negative charge at this pH; therefore
any flocculation effect due to charge neutralization
would be eliminated as the polymer acquires negative,
charge too. It was found that it has some flocculation
effects on minerals like galena, pyrite, chalcopyrite
and later chrysocolla. The "NaCX" was added at a dose
of 1 p.p.m. Flocculation of sphalerite was noticed at
pH 6.8, as the sphalerite suspension could not be
brought to pH 10 without coagulation. Furthermore, the
flocculation became more rapid, when the concentrations
of "NaCX" in suspensions were increased to 5 p.p.m.
On the other hand, it has no flocculation effects
on minerals such as quartz, calcite, feldspar and clays
even at a dose of 100 p.p.m. in the case of clays (6)
The clay minerals tested were bentonite, kaolinite and
illite.
4.1.5 The aim of the present work was to explore
the flocculation properties further and the possibility
of recovering the wasted chrysocolla fines from the
various copper processing plants. In order to achieve
that aim, various preparation methods had to be examined
or developed, so that the desirable properties of
the flocculant such as molecular weight, degree and uniformity
of xanthation could be obtained. The study of the physical
88
and chemical properties should help to utilize the polymer
properly and to establish a method for obtaining a dry,
pure polymer which could be kept for long periods and
withstand long transportation.
4.2 PREPARATION OF CELLULOSE XANTHATE
The standard procedure of preparation in the textile
industry can be summarized in 5 steps (A - E) as follows:-
A. Treatment of the cellulose raw, material with 18%
sodium hydroxide, this process being known as
mercerization or steeping). The objectives of this
step are to induce swelling of the cellulose fibres
and distortion of the crystalline cellulose so that
the penetration of CS2 into the fibrils becomes easier,
also absorption of NaOH,with uniform and complete
formation of "alkali cellulose- I". This reaction is
exothermic, and a rise in temperature of 2-3°C
usually occurs(". At the same time, hemicellulose
and other low molecular weight impurities are removed
from the cellulose.
The success of this step depends on temperature,
concentration of NaOH and time. It is also
influenced by the nature of cellulose starting
material. Apparently swelling is not enhanced at
high temperatures and high NaOH concentrations. This
step is a relatively rapid reaction. The time of
steeping is determined largely by the time necessary
to solubilize and remove hemicellulose and other
89
impurities from the pulp. The minimum time is 15
minutes depending on the nature of cellulose.
Wetting agents are sometimes used to improve the
penetration of NaOH and shredding, thus giving more
uniform xanthation.
B. Removal of the excess NaOH by pressing and filtering
the cellulose pulp to a press ratio of 3-4 of the
cellulose weight. Excess of NaOH will react waste-
fully with CS2 and increase the by-products; on the
other hand, too much pressing will lower the NaOH
content, which affects the ageing process and the
uniformity of CS2 uptake.
C. Shredding the "alkali cellulose I" by mechanical
disintegration to increase the surface area of the
alkali cellulose and hence the reactivity and
uniformity of CS2 uptake. This process is sensitive
to oxygen and temperature.
D. Ageing the shredded "alkali cellulose I" by storing
in a closed container for 65 hours at 25-30°C, during
which time oxidative degradation of the cellulose
chains by oxygen takes place(102)and results in a
lower molecular weight. This process is controlled
to give a suitable molecular weight for the purpose
of the textile industry.
E. Xanthation i.e. treatment of the aged "alkali
cellulose I" with CS2 at a temperature between
o 20-35C for 1-3 hours, forming sodium cellulose
90
xanthate and other by-products of yellow-red colour.
The reacted crumbs are then dissolved in water and
NaOH (18%), producing the viscose solution. The
viscose is left to ripen, during which period re-
xanthation and de-xanthation occur as well as
oxidative degradation of the polymer chain to a
lower molecular weight.
The xanthation of alkali cellulose causes an additional
swelling of the micelles but the native fibre morphology
of cellulose is largely retained, as observed by optical
microscopy(103} Subsequently, the xanthated fibre is
dispersed in dilute NaOH as a soluble polyelectrolyte.
Figure 4.3 shows the swelling of partially reacted
micelles.
The formation of cellulose xanthate is always
accompanied by formation of low molecular weight poly-
sulphides which may interfere in the flocculation process
of minerals. Oprits and RassolovOW+)
have derived mathe-
matical equations to give optimum operating conditions
which Five the shortest reaction time and the lowest
yields of sodium polysulphide by-products. Sintola(105)
has patented a quick method with no side reactions.
Von Horstig(10 prepared cellulose xanthate at a temperature
of 50-60oC from CS24! -H,0 vapour mixtures and the alkali
cellulose, but this process, besides being unsafe, also
increased the production of polysulphides. Andreason
et al(107)have studied the formation of cellulose xanthate
in homogeneous medium; they concluded that xanthate
• • • • • 0 0 0 0
e • • • 0 • •
• • • • • • •
• • • • • •
• • •
•
•
• •
0 0
• 0 •
•
•
• • 0 0
• • • 0 •
• 0 • 0 • • • • •
• • • • • • • • • O • • • • • • • • •
0 •
• 0 •
•
•
0
•
•
• • •
•
•
•
0
•
0
• •
•
• •
• •
•
• •
0 • •
0 0 0 • 0 0 0 • • • • • • • • • O 0 • • • • 0 • • • 0
0 • • • • • • • • • • •
• 0 0 0
0 0 0
• • • 0
• 0 • 0
• 0 • •
Fig.4-3 Reactivity of Cellulose
91
ORIGINAL MICELLE
PARTIALLY REACTED MICELLE
0 Glucose ring • OH-group s- Xanthate - group
92
formation is a second order reaction determined by the
concentrations of CS2 and alcoholate. CZajlik and
Treiber0100 measured the total heat of reaction of
xanthation as 12 kcal/mole CS2. The heat of the real
xanthation reaction is estimated to be less than 10 kcal/mole
CS2.
4.2.1 Laboratory preparation of sodium cellulose
xanthate:
Standard Method:
The source of cellulose used in the preparation of
sodium cellulose xanthate in a highly viscous form was
ordinary filter paper. Approximately 10g of shredded
filter paper were soaked in 18% sodium hydroxide in a
sealed container at 21°C for 1 hour, thus forming the
"alkali cellulose I". The excess sodium hydroxide was
removed by filtration and the "alkali cellulose I" was
stored in the sealed container for 65 hr. The aged
alkali cellulose was shaken with 4g CS2 in the sealed
container at 21°C for 3 hours; after which it was
diluted with 17 ml of 18% sodium hydroxide and 76 ml
distilled water. The shaking was continued for another
2 hours with a laboratory mechanical shaker.
The "viscose" thus produced normally contains about
6% cellulose and 7% sodium hydroxide, and the CS2 content
is 40%, based on the cellulose weight. The colour of
"viscose" is orange to deep carrot red.
Preparation of cellulose xanthate from different
cellulose sources. The "viscose" prepared from filter
paper contained some undissolved crumbs; therefore it
was thought that less fibrous cellulose sources would
93
yield more homogeneous solutions. Therefore three
samples of 10 g each from 3 different cellulose sources
namely; "cellophane", cellulose powder and filter paper,
were treated with 18% sodium hydroxide to form the "alkali
cellulose I", as described in the standard method. The
alkali celluloseswere stored in sealed containers for
17 hours and thereafter shaken with 4 g CS2 at 21°C for
3 hours. The three samples were diluted with 17 ml NaOH
and 76 ml distilled water and shaking was continued for
a further.2 hours.
The cellulose powder and cellophane gave the most
uniform solutions, but on the other hand less viscous
products than the filter paper.
The three products were tested for flocculation on
galena, chalcopyrite, pyrite and sphalerite. They all
showed flocculation effects; the filter paper product,
however, was more effective (i.e. gave better flocculation)
than the cellophane and the cellulose powder products,
which induced weak flocculation at a concentration of
1 p.p.m. and 5 p.p.m. in the mineral suspensions.
When the three products were tested for flocculation
on quartz, calcite and feldspar, no flocculation effects
were noticed even at a dose of 10 p.p.m. or more.
4.2.2 Preparation of cellulose xanthateallhiah
molecular weight
For the purpose of using cellulose xanthate in
flocculating mineral particles, it is necessary to obtain
a high molecular weight polymer. Therefore, it seemed
logical that ageing and ripening time must be reduced or
eliminated. This was supported by the findings of Das
and Choudhury(135), that by reducing the ageing time,
higher molecular weight polymers were obtained. According
to the literature, products of molecular weight up to 106
can be obtained. This is the order of magnitude used in
modern synthetic flocculants.
Therefore, the cellulose xanthate was next prepared
from filter paper as in the standard method, in three
experiments of varying ageing times namely; 3 days, 65
hours and 17 hours respectively. A difference of viscosity
of the three products was detected visually, and was found
to increase with decreasing the ageing time. On the other
hand, the longer ageing times yielded more uniform solutions.
In another experiment, two batches of cellulose
xanthate with CS2 content of 400%, were prepared according
to the standard method but the ageing times were 3 days
and zero (i.e. no ageing), respectively. Uniform products
were obtained but the non-aged product was more viscous
than the aged product.
4.2.3 Pre aration of cellulose xanthate of different
degrees of xanthation
Sufficiently high degree of xanthation must be attained
to produce solubility and in order to increase the effective-
ness of the polymer in flocculation. The highest degree of
xanthation is when the three hydroxide groups of each
cellulose molecule are substituted with xanthate groups.
However, this can only be achieved when the cellulose raw
material is in the molecular state and not in the fibrous
state.
95
Effect of CS2 ratio. To investigate the effect of ------
CS2 ratio, three samples, of cellophane of 10 g each were
shredded and treated with 18% sodium hydroxide as described
in the standard procedure. The alkali cellulose were
stored in sealed containers for 17 hours and thereafter'
shaken with different amounts of CS2 namely; 2g, 4g and
8g at 21°C for 3 hours. The three samples were diluted
as before and the shaking was continued for a further 2
hours.
It was found that the solutions became more uniform
at higher CS2 contents.- The xanthate content was markedly
higher for the 80% CS2 than for the 20% or 40%, as measured
by ultra-violet spectroscopy at wave lengths X= 300 - 303 mp.
In another experiment, two batches of filter paper
of lOg each were treated as before, but the CS2 ratios
were 40% and 400%, and the ageing time was 3 days. The
xanthate content of the 400% product was higher than the
40% products; it was also more uniform.
Effect oflEmerature. With the objective of reducing
degradation of cellulose, an experiment was carried out on
10g filter paper in the same manner as the standard
procedure except that the alkali cellulose was stored in
the refrigerator at about 5 - 6°C for 12 hours. It was
found that the crumbs did not react with CS2 to any
significant extent and consequently did not di4olve in
the dilute sodium hydroxide solution.
96
4.2.4 a-‘earationz Ia distributed
xanthate groups
The problem of uniformity of xanthation has taken the
attention of several authors(97-138). They all agree that
the reaction of carbon disulphide with alkali cellulose
is non-uniform. This is mainly because of the incomplete
exposure of the hydroxyl groups of the cellulose melecules
for reaction with CS2. As the CS2 reagent transfers to the
fibrils by diffusion, and the diffusion rate depends on the
degree of swelling, the incomplete exposure of the hydroxyl
groups is due to incomplete swelling of the cellulose
fibres.
Even in the swollen alkali cellulose, the reactivities
of the three OH-groups of the cellulose unit are not equal.
It has been stated (97)that the reactivity of the primary
hydroxyl group is tenfold greater than any of the two
secondary hydroxyls. If the nature of substitution is
determined by the rates of reactions of the three hydroxyls,
the proportion of substitution will be as the ratio 1:1:10.
This ratio, however, may be modified according to the
medium surrounding the individual hydroxyl groups.
The incomplete exposure of the hydroxyl groups to
CS2 can also be attributed to the incomplete coverage of
the swollen alkali cellulose because of the small volume
of carbon disulphide. Therefore, the ways to solve the
problem of uniformity should be along the following lines:
a) improving the swelling properties of cellulose fibres,
b) introducing CS2 in large volume, or diluted in an
organic solvent,
97
c) using water-soluble cellulose derivatives or non-
crystalline cellulose sources.
The study of the problem of uniformity in this work
was pursued because of its importance to improve the
flocculation characteristics of the polymer.
In an attempt to improve uniformity of xanthation
by adding CS2 in large volume, an experiment was carried
out on a 5g sample of cotton wool. The sample was shredded
and treated with 18% NaOH while shaking at 30°C for 1 hour.
The alkali cellulose was recovered, after filtering the
excess NaOH, and 4g of carbon disulphide was introduced
as a 1.0% solution in diethyl ether. The shaking was
continued at 30°C for 2 hours, but the colour of the crumbs
was only pale yellow. The shaking was then continued at
30°C for 12 hours, but the orange colour did not form and
the crumbs were still pale yellow and did not dissolve to
a great extent in 4% NaOH aqueous solution. When the
solution was analyzed by ultraviolet spectroscopy, the
xanthate content was very low.
Improving the swelling properties of cellulose fibres
with the aid of a wetting agent was attempted(108? which
improved the rate of xanthation through reducing the surface
tension of the liquids, thus-promoting the penetration
of NaOH into the cellulose fibres. "Emulsion xanthation"
was found satisfactory. This process is described in
section 4.2.5
The use of water-soluble cellulose derivatives to
produce uniform cellulose xanthate polymer is described
in section 4.2.5.
98
4.2. 512r owd22:of2-21form reactivity.
A sample of 5g of cotton wool was shredded and steeped in
18% NaOH while shaking at 30°C for 60 minutes. The excess
sodium hydroxide was filtered and the alkali cellulose was
shaken with Itg carbon disulphide at 30°C for 2 hours. In
this process, the alkali cellulose had taken up all the
added CS2. The solids were then shaken with dry diethyl
ether (dried by sodium) at 0°C for about 10 minutes. The
diethyl ether was filtered off and the solids were dried
under vacuum desiccator over phosphorous pentoxide. The
dry solids were shredded to fine size particles by a
mechanical shredder.
Tests for solubility in 4% sodium hydroxide aqueous
solutions indicated that about 85% of the solids were
dissolved in 60 minutes of moderate stirring. The
undissolved white portion, when dried in the oven at 120°C,
developed a yellow-orange colour. This indicates that these
solids may require a longer period to dissolve.
Emulsion xanthation. In this procedure(109), 2.5g of
cellulose raw material (cotton wool) is shaken mechanically
for six hours with 15 .ml of CS2 and 30m1 of 18% aqueous
NaOH at 23°C. At the end of xanthation, the product is
vigorously stirred with an equal volume of water until
homogeneity is attained. In the experiment, the cellulose
raw material used was cotton wool (medical type), which
was disintegrated before treatment. It was observed that
the by-products of carrot-red colour were formed after 1
hour, and the cotton was yellow. At the end of xanthation,
homogeneity of the viscose solution was attained after
99
about 60 minutes of vigorous shaking. It was not,
however, completely uniform, but it was definitely
more uniform than that obtained by the standard
procedure.
4.2.6 Xanthation of various cellulose derivatives
prepalationofri se,canthate. The methyl
cellulose used is technically known as "TYLOSE" H4000p,
from Kalle Aktiengesllschaft, Wiesbaden-Biebrick, West
Germany. A sample of "TYLOSE", 2.5g was shaken in 30 ml
18% sodium hydroxide and 15 ml carbon disulphide at 30-
35°C in a water-bath for 2.5 hours. At the end of
xanthation, 50 ml distilled water was added and the product
was shaken at room temperature for 1.5 hours. The product
was homogeneous and free from solids. The presence of the
xanthate groups was confirmed by the u.v. spectroscopy.
The sodium methyl cellulose xanthate was later purified
and tested for flocculation, as described in section 4.6.
Preparation of sodium carboxy methyl cellulose
xanthate. A sample of sodium carboxy methyl cellulose
from W. & R. Balston Ltd., England, commercially coded
CM70, was used in this experiment. Thus 2.5g of CM7O was
treated in the same manner as methyl cellulose. Uniformity
of the product was attained after about 60 minutes of
mechanical shaking with distilled water. The colour of
the product was orange-carrot like. The xanthate groups
were detected by the u.v. spectroscopy in both the
unpurified and the purified forms. It was purified by
ion exchange.
The purified sodium carboxymethyl cellulose xanthate
(NaCMCX) of 1.0% aqueous solution was noticed to decompose
to orange-colour products after 12 days storage at 5-6°C
100
The dilute solution, 0.1%, decomposed after 6 - 7 days
storage. During this time, the purified methyl cellulose
xanthate and the ordinary cellulose xanthate 1.0% solutions,
did not decompose. The flocculation properties are
described in section 4.6.
Preparation of hydroxylpropyl methyl cellulose
xanthate. Approximately 2.5g of hydroxypropyl methyl
cellulose xanthate supplied by British Celanese Ltd.,
Spondon, Derby, England, was emulsion xanthated in the
same way as methyl cellulose and carboxy methyl cellulose
in the previous sections. The hydroxypropyl methyl
cellulose xanthate dissolved to a uniform solution when
shaken with distilled water for less than 60 minutes. The
solution was more viscous than any other cellulose xanthate
prepared by the emulsion xanthation method. The presence
of the xanthate groups was also detected by the u.v.
spectroscopy.
4.3. PURIFICATION OF CELLULOSE XANTHATE
4.3.1. Precipitation with alcohol
In this method, the high molecular weight cellulose
xanthate is precipitated with methyl or ethyl alcohol,
while the low molecular weight polysulphides remain in
solution. Thus on filtering, the low molecular weight
polysulphides are removed. This process is known in the
texts(97, 109) as "coagulation" of cellulose xanthate with
alcohol.
The "viscose" solution is poured into a 4 litre
beaker and 3 litres of ice-cold methanol is added while
stirring continuously. The stirring is continued at 0oC
for 1.5 hours or until enough gel is formed. The solution
101
is then filtered and the precipitate is washed with 1i00 ml
of cold methanol. The solids are transferred to a beaker
and kept in 1 litre of 5% acetic acid in methanol for 20
minutes at 0°C with occasional stirring. The solution is
again filtered and the solids are washed several times with
cold methanol until the filtrate fails to turn moist
litmus paper red. The solids are then shaken with dry
ether for sometime, after which, the ether is filtered
off and the solids are dried in a vacuum desiccator over
phosphorus pent oxide.
This method was slightly modified and performed on
various cellulose xanthates prepared by emulsion xanthation.
Thus, the viscose of emulsion xanthated cotton wool was
dropped in small portions into a tall beaker containing
methanol at 0°C, in order to obtain fairly uniform particles.
Instead, it formed a pale-yellow bulky precipitate. At
the end of the process, the vacuum dried cellulose xanthate
was too tough to be ground in the agate mortar, or shredded
by a mechanical shredder.
When dissolved in water, the product did not give a
uniform solution. Some of the undissolved solids were in
the colloidal state, which gave rise to difficulties in
filtration.
The emulsion xanthated sodium carboxy methyl cellulose
solution was dropped into ethylalcohol contained in a 1
litre beaker which was surrounded by 2 litre beaker with
ice particles in between. The solution was stirred by a
magnetic stirrer and a glass rod. The precipitates were
noticed to stick on the bottom of the beaker, the magnetic
stirrer and the glass rod. Attempts to separate the
102
polymer precipitates were not very successful. The method
was therefore modified. The 1 litre beaker was replaced
by a 1-litre measuring cylinder and the solution was
stirred intensely by the magnetic stirrer. The "viscose"
was injected from a 20 ml syringe to produce fine drops,
which precipitated to small, uniform size particles. Then
the process was continued as before.
The colour of the vacuum-dried particles was pale
yellow. The solids were dissolved in water to a uniform
solution. But the 1% solution decomposed to an orange-
coloured solution and white sediment, after about 12 days
storage at 5-600.
It was concluded that this method of purification
was not convenient and an ion-exchange column was used
instead.
4.3.2. Dialysis of cellulose xanthate
The dialysis method was established in industry to
( remove mainly sodium hydroxide from the viscose 111). The
method can be summarized as follows: About 600m1 of the
viscose solution of about 4% cellulose is kept in a
regenerated cellulose bag at 15°C for 1 hour, or until
dialysis is complete. The solution is diluted to 2%
cellulose and the pH is adjusted to pH 11. The dilute
viscose solution is then fed to a spray dryer, where
heated air at 130°C is introduced at high velocity.
According to the author (111) ,this method will give a
powder of 12.5% xanthate sulphur. This powder has the
trade name "Sup-R-S".
In the laboratory, a small sample of viscose was
103
put in a dialysis bag and kept in a beaker, where a current
of water was flowing continuously. After many hours, the low
molecular weight sulphides were still colouring the flowing
water. This method was not pursued because it was very slow.
4.2.3. Ion-exchange column
Removal of low molecular weight polysulphides by an
ion-exchange column was established by Samuelson and
Gartner(112) In this method, the alkaline-saturated ion-
exchange resin retains the polysulphides and not the cellulose
xanthate because of its large molecular size. Dux and
Phifer(113) have modified the ion-exchange column to purify
the cellulose xanthate in a shorter time; they introduced
air pressure to a steel column to force the viscose through.
In the present work, the ion exchange multi-column
apparatus was designed to work at 0°C, in order to avoid
decomposition of xanthate. The reason for the multi-
columns was that the cellulose xanthate was not completely
separated in only one column. The three consecutive
columns provided long contact time between the viscose
and the resin, thus enhancing the fractionation process.
Vacuum was applied to the system to accelerate the flow.
The ion-exchange operation of the viscose solution takes
about 3-5 minutes, depending on the concentration and the
viscosity of the solution. The strong basic resin
"Deacidite FF-IP" was used.
Design of the vacuum multi-column ion-exchange
Apparatus
The apparatus, Fig. 4.4, consists of glass tubes each
5cm in diameter and 37-40cm long, surrounded by larger
U
O
Sin
tere
d gl
ass
bed
supp
ort
co
a
C co
co 0 X
Lk]
0 C E
0
747a -5
000 00000 00 a 0
C
E cn
Purif
ied
Ce l
lulo
se X
anth
ate
04
105
ones to provide enough space for the ice granules. The
connecting tubes were made as short as possible to avoid
unnecessary complications. The tubing was mainly of soft
polyvinyl chloride, so that dismantling of any part of the
system was easy. The end tube was connected to three
vacuum flasks for receiving the purified cellulose xanthate,
sampling during ion-exchange operation, and washing the
resins. The viscose solution was fed from a beaker contained
in a larger one, with ice granules between them. The resin
bed supports were sintered glass and metal sieves of
200 mesh. The various components of the apparatus were
mounted on metal stands.
In the design of the apparatus, attention was given to
simplicity and flexibility. Any part of the apparatus could
be easily dismantled for cleaning, repairs, changing the
resin, etc. The design consists of the minimum number
of pieces required.
Preparation of the resin. The anion exchange resin
used was "Deacidite FF-IP" SRA 61, manufactured by The
Permutit Company Ltd., (supplied by BDH Chemicals Ltd.,).
The functional groups are quarternary ammonium type I. The
resin was supplied in the chloride form and bead size
range 14-52 mesh. It has an exchange capacity of 1.2 meq./m1
The beads were elutriated many times to discard the
fine particles, to avoid clogging of the bed support. In
packing the beds, the columns were half filled with distilled
water and the resin beads were allowed to settle freely
down the columns. This process was continued until the
height of the beds were about 30cm, The resin was allowed
to swell for about 30 minutes, then vacuum as applied
106
for a short time to Make the beds more firm. The resin
beds were washed with distilled water for sometime. The
resin beds represented low and uniform resistance to the
eluant flow and were free from air bubbles. It was difficult
to calculate the equivalent amount of resin needed (in
terms of equivalents) to ion-exchange with the polysulphides
because the concentration of polysulphides was not known,
and it was considered unnecessary if excess of resin were
provided.
Conversion of the resin to the hydroxide form. The
resin beds were treated with an excess of 4% sodium
hydroxide, the flow-rate being kept very low for 30 minutes
until the colour of the beds became darker. The beds were
then washed with 2-3 litres of distilled water until the pH
of the effluent became neutral. By this treatment, the
resin was transformed to the hydroxide form.
Regeneration of anion exchanged resin. The resin was
transferred to a beaker and covered with excess hydrochloric
acid of moderate strength. This process had to be carried
out in the fume cupboard because of the unpleasant effects
of the sulphur compounds generated from the reaction. The
reaction was left to proceed until no more hydrogen sulphide
could be detected. The excess hydrochloric acid was then
removed and the resin washed with distilled water. This
process should produce the resin in the chloride form, which
can be re-used.
Operating _the ion-exchangeapparatus. For optimum
results, the operating procedure must be carried out as
follows: The resin beds are first washed with excess
107
distilled water, the effluent is received in the washing
flask. The viscose solution is then run through. The
flow of viscose should be watched carefully through the
columns. When it reaches the end tube, the washing flask
is switched off and the solution is diverted to the xanthate
flask until the whole viscose solution is run through.
Washing of the beds with distilled water is then resumed
and the effluent is diverted again to the washing flask.
By this procedure unnecessary dilution was avoided.
The concentration of xanthate in the purified form should
be more or less equal to its concentration in the viscose
form. When sampling is needed, the xanthate solution can
be diverted either wholly or partly to the sampling flask.
Some viscose solutions prepared earlier were run
through the ion-exchange columns as 1.0% solutions under
moderate vacuum. The xanthate groups were detected in
both the viscose and the purified form by u.v. spectra-
scopy. Careful operation was needed in order to minimize
the difference in xanthate concentration of the viscose
and the purified form.
4.4 ANALYSIS OF CELLULOSE XANTHATE
4.4.1. Detection and measurement of xanthate
Following many investigators (113,114,115,116,117)
the concentration of xanthate groups in dilute solutions
of purified sodium cellulose xanthate was measured by
u.v. spectrophotometry. The xanthate group has two
absorption bands, a primary peak at 300-3 mi and secondary
peak at 226 ma.. The molar extinction coefficient (e) )
108
reported by Dux and Phifer(113) was 15,900 (mole-1 cm-1,
measured on cellulose xanthate which was purified by ion
exchange.
In the present work, measurements were made on the
purified "NaCX" solutions, In an experiment, 5g of cellulose
powder was emulsion xanthated to form 5% viscose solution.
A sample of viscose was diluted to 0.5% in distilled water -
based on the cellulose content - and ion-exchanged. The
cellulose xanthate was further purified by the alcohol
precipitation method and dried under vacuum. The pure
sodium cellulose xanthate powder was dissolved in distilled
water to make up 0.1% and 0.01% solutions. The absorbances
of the xanthate groups were measured by a double-beam u.v.
spectrophotometer in 1cm quartz cells. The absorption
spectra are shown in Fig. 4.5.
There are alternative methods of determining the
xanthate content directly from the viscose i.e. without
purification of "NaCX" solutionS113,114,116). In one
method, the absorption wave bands and the molar extinction
coefficients of the various components of viscose were
predetermined in separate experiments. The absorbances
of the viscose sample at the various wave bands were
measured and a series of simultaneous equations were
formulated according to Beer-Lambert law of light absorption.
Solutions of these equations were done with the aid of
computer and the concentrations of the various components
of the viscose, including xanthate, were established.
Table 4.1 shows the viscose components together with
their absorption wave bands and their molar extinction
1.8 0-117,NaCX
0.01X, NaCX
Fig .4.5 Absorpilon Spectrum of Cellulose Xanthat,,
2.0
—1.9
1.7
1.6
1.5
1.4
1.3
I 1 I I F I I- 1 I 00 180 200 220 240 260 280 300 320 340 360 380 400
Wavelength mu
109
Table 4.1 : Molar Extinction Coefficients of Viscose Compounds
----------,,..___zavelength
Compounds —,__________ 336 my 303 IN 272 my 250 IN 226 TN 206 TN
Sod, cellulose xanthate 17508.2 10928.3
Sod.cellulose dixanthogen 6861.64 12396.2
Sod. dithiocarbonate 600. 10500. 3250.
1-- Sod. trithiocarbonate 18200. 3440. 12230.
Sod. sulphide 1690. 7730.
Carbon disulphide I 60,000-70,000
0
coefficients according to the literature(114)
This method of computation was not used in this
work because the purification of the viscose was made
possible by the vacuum ion-exchange apparatus.
4.4.2. Detection and measurement of cellulose in
dilute solutions
For the purpose of estimating the degree of sub-
stitution, the cellulose content must be known. The
importance of the degree of substitution is in the study
of the chemical stability of the sodium cellulose xanthate
solutions. Because of the decomposition of cellulose
xanthate in 'dilute solutions and some inevitable dilution
during the ion-exchange process, the cellulose con-
centration is expected to change.
Unfortunately, there was no quick method for deter-
mining the cellulose content in dilute solutions of
"NaCX". Elmgren(117) determined the cellulose content
by a dichromate titration but this method is not
suitable- for quick determinations.
A simple method was attempted in the laboratory.
It was based on the fact that cellulose itself is not
soluble in water; therefore decomposition of xanthate
groups by dilute acid will result in precipitating the
cellulose. The acid, however, should not be concentrated
in order to avoid the degradation of cellulose to small
segments and the excess should be titrated by sodium
hydroxide.
In this method, a known volume of cellulose xanthate
solution of certain strength (i.e. percent NaCX) is
1 1 1 •
112
treated with an aqueous solution containing 10% sulphuric
acid and 2% magnesium sulphate. When precipitation of
cellulose has taken place, the excess acid is titrated
with 10% sodium hydroxide, using phenolphaleiln as an
indicator. The end-point is noted when the colour
changes to pink. The precipitate is filtered on a filter
paper of known weight and washed several times with,
distilled water and dilute acetic acid (5%). The solids
are then dried at 100°C and weighed. The amount of dry
cellulose obtained should be equal to that in the starting
solution.
An experiment was carried out to check this method.
In this experiment, 0.5g of dry sodium cellulose xanthate
powder was dissolved in 50m1 distilled water for 30
minutes. The solution was filtered off on a filter paper
of known weight. The undissolved portion when dried; it
weighed 0.234g, hence the dissolved cellulose xanthate
was 0.266g, i.e. 0.532% of the solution. The solution
was treated as described above. It was noticed that
precipitation of cellulose took a long time; it was
left to settle for 12 hours. The dried cellulose, when
weighed, was only 0.018g, therefore about 0.249g were
not precipitated in this method.
A modification of this method was attempted. The
dilute solution of "NaCX" was evaporated by an infra-red
lamp in a known weightevaporating dish. The dry solids
were treated with 100m1 of the 10% sulphuric acid, 2%
magnesium sulphate solution. The settling of the precipi-
tate was accelerated by decantation, and the decanted
1 1 3
solution was treated twice with excess of the acid solution
as before in order to recover more cellulose. The cellulose
precipitate was mixed with 50m1 of 0.2% sodium sulphide
warm solution (about 60-65 C) for a few minutes. The
mixture was centrifuged and the cellulose solids were
separated, washed with distilled water and dried by
infra-red lamp. It was noticed that the cellulose
material was burned in the drying process. That was
perhaps due to some acid left with the cellulose precipitate
which became too concentrated upon evaporation.
Although the idea of this method:seems sound, the
method itself failed to give accurate results. It was
not pursued further in this work, but future consideration
of this method would be desirable.
4.5 PHYSICAL AND CHEMICAL PROPERTIES OF CELLULOSE
XANTHATE
Physical characteristics
Sodium cellulose xanthate is a polyelectrolyte, the
functional groups being negatively charged xanthates
(-0C(S)S-) . According to the literature(791 134,136,138)
electrolytes in aqueous medium affect the polymer
configuration (or "coiling up") through a screening
effect on the functional groups, i.e. reducing the
repulsion between charged xanthate groups. Sodium
hydroxide, however, has most effect in reducing the
viscosity, perhaps due to interaction with hydroxyl
groups on the cellulose chain. Thus in 0.2% NaOH
solutions, the polymer uncoils and assumes a fairly
rod-like configuration, while it coils up to a considerable
114
extent in 6% NaOH solution. This was confirmed from the
viscosity measurements(134) on cellulose xanthate samples
of different degrees of polymerization (D.P.), i.e. of
different numbers of cellulose monomers in the chain
segments. The extended length of cellulose xanthate
chain of D.P. of 790 in 0.2% NaOH was 22808, and in 6% NaOH
was 14408; the total length was 4040.. The total length
was computed by multiplying D.P. by the length of the
monomer unit (5.150. At a D.P. of 264, the extended
length in 0.2% NaOH was 870R and in 6% NaOH was 670, the
total length of the polymer chain was 13508. These results
demonstrate that the molecules were not completely extended
in 0.2% NaOH, indicating that further uncoiling of the
cellulose xanthate molecules could occur in very dilute
solutions.
The molecular weight of NaCX in dilute NaOH solutions
has been estimated from viscosity, light scattering and
sedimentation velocity measurements. Das and co-workers
(135,137)measured the viscosity of 12 samples of purified
cellulose xanthate in 1N sodium hydroxide solutions. The
average molecular weights of these samples were found to
range between 5 x 104 and 1 x 106. Their studies also
showed that the CX chain is substantially stiffer than
synthetic polymers but comparable to other cellulose
derivatives and that the viscosity of cellulose xanthate
in dilute NaOH solutions increases with increasing degree
of substitution.
Chemical reactions with heavy metal ions
Literature on the reactions of heavy metal cations
115
with cellulose xanthate is rather meagre. In industry,
zinc cellulose xanthate is an intermediate in the pre-
paration of cellulose thiourethan(141) In this method,
viscose is reacted with a Zinc salt to produce a pale
yellow precipitate of zinc cellulose xanthate. Cellulose
xanthate is reacted with copper salt in the manufacture
of copper xanthate fibre(142)
. It has been reported that
insoluble metal xanthates were converted into "cellulose
IV" on decomposition by dilute sulphuric acid in hot water
(6°c) (140), while sodium cellulose xanthate was converted
into "cellulose II".
Xanthates of lower molecular weight, e.g. ethyl
xanthate, butyl xanthate, etc., are known to form water-
insoluble compounds with heavy metal cations(143) such
as: Au+, Ag+, Cu{ Pb
++, Ni++ Zn++, Fe
++, etc. Cupric
sulphate reacts with potas'sium xanthate to form a dark S S
brown cupric xanthate: 2R0-C-SK + Cu++ + + Cu[-S-C-OR] 2'
but cupric xanthate, being unstable, rapidly decomposes
into cuprous xanthate of intense yellow colour and
dixanthogen: S S S S
2 Cu [ -s-C-oR1 2 —0
Cu2 [-S-C-OR]2 + ROCSSCOR .
In the laboratory, 20m1 of 1% CuSO4 solution was
added to 15m1 cellulose xanthate 1% solution; the mixture
was shaken for 1 minute, and a large pale yellow precipitate
was obtained, the pH being 4.8. This experiment was
repeated at much lower concentrations of CuSO4 (10 p.p.m.
0.1%) and NaCx (1-10 p.p.m,), with the aid of centrifugation.
The pale yellow precipitates were obtained in each case.
These precipitates are believed to be cuprous cellulose
116
xanthate.
Cellulose xanthate is susceptible to oxidation,
producing cellulose dixanthogen,(143) Oxidation of
cellulose xanthate for 24 hours results in a 50-60%
conversion to dixanthogen. Cellulose dixanthogen has
also been prepared by treating an aqueous solution of
sodium cellulose xanthate with diethyl dixanthogen. In
technical viscose, however, oxidation is not of great
significance because the other sulphur compounds present
are more susceptible to oxidation, and therefore, consume
a large proportion of oxygen and hinder oxidation of
cellulose xanthate.
Decomposition of xanthate groups in NaCX solutions
In order to understand the decomposition of Cell-
xanthate, it was necessary to study the reactions during
xanthation and ripening of viscose. The following
reactions are believed to occur(79,1231
many of them are
reversible. Rcell denotes the cellulose macromolecule
A - During xanthation
1 - Rcell = NaOH = TRcellONa (sod. cellulose)
2 - RcellONa+C5
2 = Rcell-O-C(=S)-SNa (cellulose xanthate)
3 - 3CS2 + 6NaOH = 2Na2CS3(sod. trithiocarbonate)+Na2CO3 +3H20
4 - Rcell-0-C(=S)-SNa + 2NaOH = Nja2CO2S (sod.monothiocarbonate)
+ Na2CS3 Rcell
5 - NaOH = Na2CO2S = Na2CO3 NaSH
B - During ripening of viscose (deomposition)
6 - Rcell -0-C(=S)-SNa + H2O = Rcell -0-C(=S)-SH + NaOH
7 - Rcell-0-C(=S)-SH H2O = HOCSSH Rcell [r CS2 H2O
117
8 - Rcell-0-C(=S)-SNa + 2H20 = NaOH + CS2 + H2O + Rcell
9 - 5CS2 + 12NaOH = Na2S + 2Na2CO3 + 2NaCS3 + 6H20
10- CS2 + Na2S = Na2CS3
11- C$2 + H2O = H2S + COS
12- CS2
+ 2NaHS = Na2CS3 + H2S
13- 3NaOH + Na2CS3 = 3NaHS + Na2CO3
14- NaCS3
+ 3H20 = Na2CO3 + 3H2S
15- NaCS3
+ 2H20 = H2CS3 + 2NaOH
H2S + CS2
From these equations the following comments can be
made:
a) Reaction (5), by consuming Na2CO2S (which is a product
of reaction (4) ) increases the tendency forreaction
(4) to proceed to the right i.e., decomposition of
NaCX by NaOH, while reaction (3) decreases the tendency
of both reaction (4) and (5) to proceed to the right.
Therefore it helps to limit the decomposition of NaCX
during xanthation.
b) The main causes of decomposition of cellulose xanthate
are hydrolysis and rise of temperature. From (8),
NaCX decomposes to CS2, NaOH, H2O and solid cellulose.
This suggests increasing [NaOH] and [CS2] in order to
restrict the decomposition of NaCX. However, it is
more logical to remove the H2O altogether when storing
NaCX for long periods, i.e., by storing dry NaCX
powder. Yamada et al(118) stored NaCX dry powder
treated with CaO for six months without losing its
solubility in water.
1 1 8
c) The idea of increasing [C52] and [NaOH] in order to
decrease the tendency of decomposition (reaction 8)
must take into consideration the results of reaction
(9), for increasing these reactants will help to
increase the amounts of sodium sulphides and thio-
carbonates.
The effect of temperature should also be taken into
account. Elmgren(117) studied the dexanthation rate of
ripened viscose at 25, 18, 0 and -14°C and found a relation
between the gross dexanthation rate constant k' (in units
1N hr ) and the absolute temperature T as follows: log k' = 14.6-
5000/T. At -14°C, 0.05% of the xanthate groups decomposed
per day or 25% decomposed over a one year period. He found
no decomposition of viscose at -65°C. Lyselius and Samuelson
(11 ) 9- investigated the actual rate of decomposition by
ripening the viscose in the presence of anion exchange
resin which eliminates the rexanthation. They concluded
that the decomposition rate is the sum of two first-order
reactions occurring simultaneously, a fast one which is
ascribed to the decomposition of 2,3-xanthate, and a slower
one which is ascribed to the decomposition of 6-xanthate.
They also studied the influence of NaOH concentration
upon the rate of decomposition and concluded that the net
rate of ripening is only slightly affected by the NaOH
, concentration (see also
(122) ). Theycalculated the
activation energies for the actual dexanthation rates of
6- and 2,3-xanthates as 19 kcal/mole and 20 kcal/mole
respectively. Their work has been confirmed by Dunbrant
and Samuelson(120). The rate of dexanthation of viscose
119
increases in dilute solutions(121),
probably because of
a lower rate of rexanthation; at very low cellulose con-
centration, the rexanthation can be eliminated completely.
The rate of dexanthation was found to be independent of
the cellulose concentration. The role of pH has also
been studied(124,125,126,127,128,130,131)
• As the de-
composition of cellulose xanthate passes through the
r 1 formation of xanthic acid (reactions 6 8c7 ), [H+ ]becomes
important. In general, the decomposition rate increases
r , with increasing pi+j. Lissfelt (129)suggested a formula
for the de-composition rate of xanthate in aqueous buffer
solutions, namely:- -d[X]idt = k[X] [H+] + k2 [X] [1120].
He claims that in the pH range 2-6 the first term dominates,
while above pH 7 the second term dominates and the
reaction is substantially independent of pH. He
calculated the activation energies for the decomposition
of cellulose xanthate at pH 4 and 30°C as 19 kcal per
mole, which is in agreement with previous work(119,132)
He also believes that cellulose xanthate does not decompose
via molecular xanthic acid. The decomposition and
oxidation of xanthate was found to be enhanced in the
presence of ions of those metals that form insoluble
complexes with xanthates(133).
Therefore the rate of
dexanthation in a xanthate solution containing a suspension
of solid metal xanthate is much greater than its normal
rate of reaction in a homogeneous solution.
Conclusions. From the above studies, it can be
concluded that storing purified or unpurified NaCX
solutions is possible under conditions of low temperature,
120
and high [NaOH] - about 6N. Air must be excluded as well
as heavy metallic ions. Dilute solutions will decompose
fairly quickly: therefore it is best to prepare them
freshly when needed from a stock of concentrated NaCX
solution stored at low temperatures. Storing dry NaCX
powder is more convenient still.
Oxidative degradation of the cellulose chain
Chain degradation which accompanies some types of
cellulose oxidation is not the result of direct scission
of the molecular chain(79), but is the result of the
formation of chemically labile groups in the molecule,
which are sensitive to alkaline cleavage. Periodic acid
oxidizes the glycol groups in the 2,3-position to the
corresponding aldehydes with a carbon-carbon bond cleavage.
In this case the hydrogen on the« -carbon is removed by
the base; this is followed by an electron shift to form a
double bond between cc - and p- carbon atoms with simultaneous
carbon-oxygen scission. The cleavage which occurs results
in a chain break in the molecule and a corresponding increase
in fluidity of the solution.
Oxidation of alkali cellulose by oxygen is initiated
according to the following reactions:
Rcell CHO + 02 ---* Rcell CO. + H00.
CO.+ Rcell CO(00.) Rcell 02
CO(00) + Rcell H —40 Rcell CO(00H) +.Rcell Rcell
The net results of these oxidations are the degradation
of chains to shorter segments. This has been confirmed by
electron microscopy and viscosity studies. In the present
work, the fall in viscosity of dilute solutions of purified
121
NaCX was observed. Furthermore, such aged solutions formed
very weak flocs or none at all.
4.6 FLOCCULATION PROPERTIES OF CELLULOSE XANTHATE
Selective flocculation of sulphide minerals
The flocculation properties of cellulose xanthate were
investigated on two classes of mineral; the "common"
valuable minerals e.g., galena, chalcopyrite, sphalerite
and pyrite, and the "common" gangue minerals like quartz,
calcite and feldspar. The minerals were dry4-ground
separately in an agate mill to particle size below 400 mesh
(B.S). They were stored in sealed polythene bags during
the period of investigations. No purification processes
were attempted on these minerals.
The cellulose xanthate flocculants tested included
sodium cellulose xanthate (NaCX), sodium carboxy methyl
cellulose xanthate (NaCMCX), and sodium methyl cellulose
xanthate (NaMCX). They were prepared by the emulsion
xanthation method as dry powders. Fresh solutions of 1%
of these polymers were ion-exchanged at 0°C to remove low
molecular weight polysulphides. Solutions of 0.1% of these
polymers were used in the flocculation experiments. The
purified polymer solutions were stored at low temperature
to avoid decomposition of xanthate.
The procedure of the flocculation experiments was as
follows: A 250m1 suspension of the mineral was made as
1.0% solids at pH 10. The suspension was transferred to
a 250m1 measuring cylinder and kept standing for 6 minutes.
The suspension was decanted into a beaker and the coarse
settled particles were discarded. The pH was readjusted
122
and the flocculant was added while stirring by a magnetic
stirrer at high rate for 30 seconds. The shear rate was
dropped to low intensity and continued for 1.5 minutes.
The suspension was transferred again to the 250m1 measuring
cylinder and the flocs were helped to grow by slow rotation
of the cylinder on an angle for a few minutes. Distilled
water was used throughout the experiments.
The qualitative results of these experiments are
shown on Table 4.2 • The following notations were
used to discribe the flocculation effects:
= good flocculation, leaving clear supernatant
= partial flocculation, leaving turbid supernatant
= slight flocculation
no flocculation
Description of the flocculation process and the
size of the flocs were expressed as follows:
f = fast flocculation process in which the flocs
were formed and settled rapidly, i.e., within
1 minute of adding the flocculant.
sl = slow flocculation where the flocs were formed
and settled in a relatively longer period.
1 = large floc size
small floc size.
Discussion of the results
The experiments were carried out at pH 10 ± 0.1 in
order to avoid the effect of the electrostatic forces
on flocculation (particles and polymer all being
negatively charged). The cellulose xanthate flocculant
is known to alquire negative charge in the alkaline region
123
Table 4.2
Minerals Dose
Flocculants 1 p.p.m. 5 p.p.m. 10 p.p.m.
galena NaCX NaMCX NaCMCX
- - -
+ s - -
± f.s
chalcopyrite NaCX NaMCX NaCMCX
7 s + s
± f.s. + s
2' f.l. ± + f.s.
pyrite NaCX NaMCX NaCMCX
+ f + f
7 s
+ - f.l. + - f 7 s
+ f.l. - f.l. -1- — s
sphalerite NaCX
NaMCX NaCMCX
- -
+ s + s
± f.s. -F s
quartz NaCX NaMCX NaCMCX
- - -
- - -
- - -
calcite NaCX NaMCX NaCMCX
- - -
- - -
- - -
feldspar NaCX NaMCX NaCMCX
- - -
- - -
- - -
1214
of pH. As most of•the minerals also acquire electrical
charge at pH 10, any flocculation effect due to electro-
static attraction between the negative polymer and the
positive mineral surface is eliminated. The flocculation
effects at pH 10 should therefore be due only to chemical
bonding between the polymer and the mineral surface;
however, the flocculation of the sphalerite suspension
was carried out at pH 6.7 because of the instability of
this suspension at pH 9-10, where coagulation of the
particles took place. This instability phenomenon was
noticed only on suspensions freshly prepared from the
sphalerite powder and not on the 'aged' suspensions. The
phenomenon was dependent on pH and reversible.
The results on Table 4.2 indicate definitely that
cellulose xanthate polymers produce selective flocculation
effects on the sulphides minerals, while no flocculation
was detected. on the common gangue minerals. The results
also suggest that plain sodium cellulose xanthate (NaCX)
was more effective than sodium carboxymethyl cellulose
xanthate (NaCMCX) and sodium methyl cellulose xanthate
(NaMCX). Its superiority was probably due to higher
molecular weight, rather than different chemical composition.
Floceulation of chrysocolla with cellulose xanthate
221ining the pH of flocculation. When the pH
of a chrysocolla suspension was raised from 4 to 9 or 10,
an immediate coagulation of the particles took place.
The coagulation disappeared when the pH was lowered to
pH4, but reappeared on raising the pH to 9 again. This
coagulation was reversible and believed to be due to the
125
formation of cupric hydroxide. It has been shown earlier
that chrysocolla releases curpric ions in acidic solutions
in amounts depending on the concentration of electrolytes.
These ions form cupric hydroxide at high pH. The zero
point of charge (z.p.c.) of cupric hydroxide, as mentioned
in Chapter 2 , lies in the pH range 7.7- 10, depending on
the concentration of electrolytes in solution.
It has also been stated that chrysocolla particles
acquire a negative charge over the pH range 4-12 in
distilled water. Therefore, to separate the actions of
coagulation and possible effects of charge neutralization
from the real effects of cellulose xanthate, the pH of
the suspension must not be more than 7 (or alternatively
must be above 10). The pH chosen for the flocculation
experiments was pH 7.
Flocculation experiments and results
Because of the high negative charge on both the
mineral surface and the sodium cellulose xanthate, sodium
chloride was used to lower the repulsion forces so that
the polymer can reach the particles surfaces. This was
found necessary.
About lg of chrysocolla particles of size below 30im
was dispersed in 250m1 distilled water containing 1%
sodium chloride in a 400m1 beaker at pH7. The suspension
was transferred to a 250m1 measuring cylinder and kept
standing for 5 minutes. The suspension was decanted back
into the beaker and the settled particles were rejected.
The pH of the suspension was readjusted carefully to pH 7,
and the flocculant was added while stiring at high shear
126
rate by a magnetic stirrer for 30 seconds. The flocculation
process was continued at low shear rate for another 1.5
minutes; thereafter the suspension was transferred to
the 250m1 cylinder and slowly rotated at an angle for
3-4 minutes.
Small flocs of chrysocolla particles were noticed
when the concentration of cellulose xanthate in the suspension
was raised from 1 p.p.m. to 5 p.p.m. More flocculation
and bigger flocs were obtained at 10 p.p.m. CX; much of
the suspension was flocculated in about 12 minutes. At
a concentration of 20 p.p.m. CX, most of the suspension
was flocculated with big flocs in about 10 minutes, and
the supernatant was practically clear.
The above experiment was repeated on chrysocolla
suspension of particles size below 18im, and the cellulose
xanthate was added at a dose of 20 p.p.m. in one addition.
Flocculation of the suspension took place and the super-
natant was clear after 14 minutes. The difference between
this experiment and that on coarser size above was that
the formation of the flocs was initially slow.
Effect of sodium chloride concentration on flocculation.
In this experiment, the concentration of (NaC1) was raised
from 1% to 2.6% (; 1%N .1. ) in the aqueous medium. The
flocculation experiment was repeated on the minus 18im
particles and the CX flocculant was run in, with incremental
additions. Flocculation was detected at 5 p.p.m. CX
dose and was found to increase with the CX concentration.
At 20 p.p.m. CX almost all the particles were flocculated
and the supernatant was nearly clear after 14 minutes.
127
When the CX concentration was raised to 30 p.p.m. the
rate of flocculation was increased and flocculation was
complete after 14 minutes.
The results of this experiment were not significantly
different from the previous experiments where the NaC1
content was 1%. This experiment suggests that the high
content of NaC1 did not enhance flocculation.
Experiments without sodium chloride were performed
at different pH values, namely, 4, 7, 9 and 10 on fresh
suspensions of chrysocolla. Different cellulose xanthates
were used in the purified and the unpurified states at
varying concentrations from 1-10 p.p.m. No flocculation
was produced in any of these experiments, probably because
of repulsion between the negatively charged surfaces of
the particles and the polymer. Therefore the presence
of sodium chloride (or similar electrolyte) was essential
for flocculation.
When attempted on a different sample of chrysocolla
of poor quality, these flocculation experiments -could hot
be easily reproduced.
Flocculation of sul hidized chr socolla
A 250m1 dilute suspension of fine particles of
chrysocolla containing 1% NaC1 at pH7 was prepared. The
suspension was transferred to a measuring cylinder and
left for 10 minutes. The settled coarse particles were
rejected after decanting off the suspension into a 400m1
beaker. Sodium sulphide (Na2S) was added to the suspension
at a concentration of 80 p.p.m. while stirring at high
128
shear-rate for 5 minutes. Purified cellulose xanthate
was mixed with the suspension at concentrations of 5, 10
and 20 p.p.m. The pH was kept at 7 throughout the
experiment.
Strong flocculation took place. The floc size increased
with the concentration of CX. At 20 p.p.m., the flocculation
was complete, leaving a clear supernatant. This experiment
was repeated four times, and the results were confirmed.
Again presence of NaC1 was found to be essential;
without it flocculation was not obtained. Thus the
adsorption of negatively charged CX molecules was enhanced,
resulting in strong flocs.
The effects of Na2S NaC1 and NaCX on flocculation of
chrysocolla were investigated qualitatively at different
doses of Na2S (40-200 p.p.m.), NaC1 (0.3 - 1.0%), and
NaCX (5-20 p.p.m.) In general, some flocculation was
obtained at low doses, but more complete and rapid
flocculation at higher doses.
Selective flocculation of chr socolla from uartz.
When dilute quartz suspensions were treated with
80 p.p.m. Na9S, and 1% NaC1 at pH 7, no flocculation was
detected with CX even at 25 p.p.m. These were the conditions
where chrysocolla was strongly flocculated.
A 250 ml dilute suspension (,\/ 2% solids) of a
mixture of quartz and chrysocolla containing 1% NaC1
was treated with 80 p.p.m., and the flocculation procedure
was continued as before.
Only chrysocolla flocculated, while the quartz
remained suspended. The experiment was reproduced
several times.
129
At high concentration of NaC1 t >1%) some quartz
particles were noted with the sediment, but this was probably
due to partial coagulation of some quartz particles. Therefore,
NaC1 should be used at concentrations lower than or equal to
1%.
4.7. CONCLUSIONS
Sodium cellulose xanthate has proved to be a selective
flocculant. It has flocculation effects on heavy metal
sulphides such as galena, sphalerite, chalcopyrite and pyrite.
Flocculation of these minerals can be improved by finding
the optimum conditions e.g., pH, electrolyte concentrations
and adequate mixing and dispersion.
Cellulose xanthate does not flocculate quartz, clays,
calcite and feldspar. Therefore, selective flocculation of
heavy metal sulphides from these common gangue minerals is
possible in principle.
When chrysocolla was flocculated by cellulose xanthate,
sodium. chloride was found necessary to reduce the repulsion
between the negatively charged xanthate and chrysocolla
particles. Flocculation of sulphidized chrysocolla by
cellulose xanthate was also achieved.
Selective flocculation of sulphidized chrysocolla from
quartz was shown possible.
Although cellulose xanthate has shown selective
flocculation properties and is simple to prepare cheaply,
it has two disadvantages: a) the molecular weight is
normally lower than that desirable for formation of strong
flocs, b) there are difficulties in preparing a stable
130
form which could survive long storage and transportation.
The lowering of the molecular weight of cellulose
xanthate was shown to result from degradation of the
cellulose chain by oxidation. Therefore, air should be
excluded from the polymer during preparation and storage.
To minimize decomposition of xanthate, the polymer is best
kept in dry form at low temperature; fresh solutions
could be prepared when needed.
Xanthation of methyl cellulose, carboxymethyl
cellulose and hydroxy propyl methyl cellulose was established
and uniform solutions were achieved. The flocculation
properties were similar to ordinary sodium cellulose
xanthate, though the molecular weights of methyl cellulose
xanthate and sodium carboxy methyl cellulose xanthates were
rather low, which resulted in weak flocculation.
131
CHAPTER 5 OTHER SELECTIVE FLOCCULANTS CONTAINING SULPHUR
5.1 POLYVINYL ALCOHOL XANTHATE
5.1.1 Introduction
Polyvinyl alcohol xanthate (PVAX) may be formed by
reacting polyvinyl alcohol (PVA) with sodium hydroxide and
carbon disulphide according to the equation:
-'CH -CH-CH -CH" + NaOH + CS ----p---4 e■CH -CH-CH -CH,-.." . 2 1 2 1 2 t 2 1 OH OH 0 OH
C-SNa+ H S
In this reaction some or most of the secondary hydroxyl
groups in the polyvinyl alcohol are replaced by xanthate
groups. The reaction is allowed to proceed in the
emulsion xanthation process as described in detail in
section 5.1.2. It is expected that PVAX thus produced
would be stronger and more selective flocculant for heavy
metal minerals than the unxanthated PVA. The xanthate
group,as shown in chapter 3 and 4, tends to selectively
form strong compounds with heavy metals as against earth
alkaline metals, whereas the alcoholic OH-groups of PVA
are only weakly acidic and not particularly selective.
Although PVA was found to adsorb strongly on clay minerals,
(namely, montmorillonite, illite and kaolinite,) the bond
between the polymer and solid surfaces is not a strong
one. In addition to clay minerals, Greenland( 144)examined
the adsorption of polyvinyl alcohol on a range of alumin-
ium oxides and hydroxides as well as silica. He found
that apart from clay minerals, none of the other minerals
1:32
adsorbed any measurable amount of PVA. Ignited silica
(heated at 80000 for 4hrs.) however, adsorbed the polymer
strongly whereas hydrated silica did not. This adsorption
phenomenon was explained in.terms of hydrophobic associa-
tion and hydrogen bonding. Thus the adsorption of PVA
on clays and ignited silica results in a large positive
entropy change owing to the displacement of a large
number of water-molecules by each polymer molecule
adsorbed (similar to the chelate effect described in
chapter 3). The failure of PVA to adsorb at the silanol
(Si-OH) and aluminol (Al-OH) surfaces was probably due
to the fact that water is strongly hydrogen bonded to
these surfaces, while it is weakly held at the siloxane
surfaces (Si-0) of the ignited silica and clay minerals.
Polyvinyl alcohol has been found to have flocculation
properties(145) and examples of its use as a flocculant
were reported by several authors(17,145-150). For instance
Fleer (14'6 )achieved an efficient flocculation. of silver
iodide with PVA in the presence of a salt, but the flocs
were small in size. Kuzkin and Nebera(17) tested the
action of PVA, amongst other polymers, for flocculation;
they tacitly concluded that although flocculation was not
strong in some cases, PVA could serve as a good flocculant
in neutral and alkaline media. The small size of these
flocs could be explained in terms of the molecular weight
of the polymer. For most commercial polyvinylalcohols,
the average molecular weight varies between 25,000 and
300,000, depending on the initial polyvinylacetate(91)
from which the PVA is prepared.
133
Polyvinylalcohol is a non-ionic, water-soluble
polymer. It is prepared commercially from polyvinyl-
acetate (PVAc) because vinylalcohol monomer transforms
into acetaldehyde(151). Thus polyvinylacetate is
hydrolyzed by treating an alcoholic solution with aqueous
acid or alkali. The polyvinylalcohol thus obtained
usually contains some acetate groups if prepared by
alkaline hydrolysis, or traces of acid which are difficult
to remove and may lead to instability of the polymer, if
prepared by acid hydrolysis. A more efficient method for
preparing PVA is by the alcoholysis of polyvinylacetate.
In this method, PVAc is treated with methanol in the
presence of sodium methoxide as catalyst. Detailed
description of preparation, properties, and applications
of polyvinylalcohol are to be found in the literature(91,151-154)
Because of the reactivity of the secondary hydroxyl
groups of PVA, many derivatives have been prepared(91)
Among other commercial derivatives are the polyvinylacetals
which form by treating PVA with aldehydes or ketones, the
acid sulphates (suggested as ion-exchange resins), the
hydroxylethyl ethers and the thiols, which find use in the
isolation of metals such as silver, mercury and platinum
by the formation of insoluble mercaptides.
5.1.2 Preparation of221/zial lathatt
LA2frimental: Polyvinylalcohol used in this work
was supplied by BDH Chemicals Ltd., (Poole, England) and
was stated by them to have an average molecular weight
of 125,000. Polyvinylalcohol xanthate (PVAX) was
prepared in the laboratory by the emulsion xanthation
134
method. In this procedure, 2g of PVA was dissolved in
40 ml of 18% aqueous NaOH. The solution was treated with
10 ml of CS2 and the mixture was shaken for 6 hrs. at
27°C. At the end of xanthation, the product was diluted
with 50 ml distilled water, and shaking was continued
until homogeneity was attained. Excess CS2 was removed
by applying a vacuum. The colour of the product was
orange to deep carrot-red.
Purification of PVAX: During the xanthation process,
low molecular weight polysulphides were produced as by-
products (indicated by the carrot-red colour). These
by-products were removed from the PVAX solution by the
ion-exchange method, using the vacuum ion-exchange multi-
column apparatus described in Chapter 4. Thus the 2%
xanthation product was run through the apparatus, following
the same procedure in section 4.3.3, to avoid unnecessary
dilution. The ion-exchanged PVAX solution was clear, and
slightly pale yellow in colour. Some frothing was noticed
inside the tubes of the apparatus, indicating the partially
hydrophobic character of the polymer. The presence of
xanthate groups in the ion-exchanged solution was detected
by ultra-violet spectroscopy at wave length band
= 300 - 303 my.
5.1.3 Flocculation ro erties of PVAX
The xanthate groups were shown earlier not to react
with metals like Ca2+, Mg2+, Al3+ and silica; therefore
the PVAX is not expected to adsorb onto (and subsequently
flocculate) minerals such as calcite, dolomite, feldspar,
135
clays, quartz and aluminium oxides. It has been already
shown by Greenland(14-4)t
hat PVA does not adsorb to any
appreciable extent onto hydrated silica and various
aluminium oxides and hydroxides; therefore PVAX is not
likely to adsorb on these minerals either. Galena,
chalcopyrite and other heavy metal sulphides, on the
other hand, are expected to react with xanthate leading
to the adsorption of the polymer and the subsequent
flocculation. Thus PVAX should act as a selective
flocculant for heavy metal bearing minerals and act in a
similar way to cellulose xanthate (described in Chapter
Li). Another factor affecting flocculation is the con-
figuration of the polymer. It has been reported(17)
that X-ray investigation of PVA confirmed its crystalline
structure and plane zig-zag configuration of carbon
chain. Because of the negative charge of xanthate groups,
their presence in the polymer structure should extend its
linear configuration, thus improving bridging and
flocculation effectiveness of the polymer.
Flocculation_procedure: A250 ml suspension of fine
galena particles was made using a magnetic stirrer. It
was transferred and kept standing in a 250 ml measuring
cylinder for 5 min., then the suspension was decanted
back into a beaker and the settled particles were
rejected. The suspension was treated with the polymer
while stirring at a moderate shear-rate for about 1 min.,
and at low shear-rate for another 1 min. The suspension
was then transferred to the 250 ml cylinder, where
gentle rotation of the inclined cyclinder was applied for
136
a few minutes. The pH was maintained throughout the
experiment at 7.
Results: Flocculation of galena particles was noted
visually at 5 p.p.m., increasing at higher doses of the
polymer. The flocs were small in size and some particles
were noted to adhere to the water surface; this was
probably due to the residual acetate groups in the PVAX
polymer which makes it (like the PVA) weakly surface-
active.
In a similar experiment, the effect of polyvinyl-
alcohol (PVA) on galena was studied, following the same
procedure and conditions as above. When the concentration
of PVA in the galena suspension was 1 p.p.m., no
flocculation occurred at all. Then the dosage of PVA was
progressively increased by increments of 1 p.p.m. up to
5 p.p.m., thereafter it was adjusted to 10, 15 and 20
p.p.m., consecutively. The polymer was added to the cylinder,
where dispersion was carried out by shaking and turning
the cylinder end over end and after each addition followed
by rotation for a few minutes.
Results: There was no flocculation up to 5 p.p.m.;
however, only slight flocculation occurred at 10 p.p.m.,
which was marginally increased at 15 and 20 p.p.m. On
the other hand, the rate of settling of the fine particles
was roughly inversely proportional to PVA concentration,
so that the particles remained suspended for a much.. longer
period at 20 p.p.m., than that at p.p.m.,or 1 p.p.m.
This experiment clearly indicated that PVA had
adsorbed on galena particles, yet it did not effect
1 37
strong flocculation, whilst PVAX flocculated galena at
5 p.p.m. Thus the introduction of xanthate groups to
PVA, has markedly improved its flocculation effectiveness,
which might be due to the stronger bonding between xanthate
and galena and the extended configuration of PVAX as a
result of the negative charge of xanthates.
Conclusions: In spite of the encouraging features
of PVAX, no more flocculation experiments were carried
out on other minerals to study its. selectivity. It was
foreseen that this polymer, like cellulose xanthate, would
suffer from two main disadvantages: (a) Decomposition of
xanthate groups, (b) The relatively low molecular weight
of the polymer. Most efficient, modern flocculants have
an average molecular weight of 106. However, if
polyvinylalcohol of high molecular weight could be
obtained, and the PVAX could be stored dry without
losing the xanthate groups, polyvinylalcohol xanthate
would prove a potentially selective flocculant.
Polyvinylalcohol has an advantage over cellulose raw
materials in producing readily uniform xanthation, and
having a -C-C-C- chain, which is much less susceptible to
hydrolytic scission than is the carbohydrate chain of
cellulose.
138
5.2 POLYACRYLAMIDE-DITHIOCARBAMATE
5.2.1 Comp 1tiLLITLLLLTEMEIEILU. By polyacrylamide-dithiocarbamate (PAD) is meant
ordinary polyacrylamide with some dithiocarbamate groups
introduced into it. The dithiocarbamate group, as
mentioned in Chapter 3, is a sulphur donor ligand which
does not react with class A-cations i.e., mainly earth
alkaline cations. On the other hand, dithiocarbamate
tends to form strong compounds with heavy metal ions, and
especially with copper ions. (Sodium diethyldithio-
carbamate is a well known colorimetric reagent for copper).
Thus by incorporating these groups into the polyacrylamide
chain, a markedly improved selectivity should be attained.
PAD was kindly prepared and supplied by B.T.I. Chemicals
Co. Ltd., (Bradford, England).
PAD was anticipated to be an anionic flocculant,
because of dithiocarbamate groups. The polymer was, of
course, water-soluble and of high molecular weight,
having been prepared from ordinary PAM flocculant. It
was slightly yellow in colour. Its dilute aqueous solutions
(e.g., 0.1%) decomposed more slowly than cellulose xanthate;
some of the solutions decomposed extensively only after
5-6 weeks. No measurements were made on the decomposition
products nor the decomposition rate. The decomposition
was indicated by formation of precipitates.
No purification was attempted on this polymer, and
it was used in flocculation as supplied.
139
5.2.2 Flocculation effects on mineral sus ensions
Exploratory experiments: The unpurified PAD polymer
was tested on suspensions of approximately 0.4% solids of
the following minerals: malachite, chrysocolla, chalcopyrite,
galena, calcite, feldspar and quartz. The experiments were
run in the same way as those described earlier in section
5.1.3, where the pH was kept constant at 7 and the polymer
concentration in the suspensions was 1 p.p.m. All but
quartz were found to be flocculated by this polymer.
In order to ascertain the difference between PAD
and unmodified polyacrylamide, two partially hydrolysed
polyacrylamides, namely, A130 and A80 manufactured by
B.T.I. Co., were used. These polymers, like PAD, are
characterized by their anionic functional groups. Thus,
flocculants A130 and A80 were tested on suspensions of
the following minerals: chrysocolla, chalcopyrite, galena,
calcite, feldspar and quartz. The experiments were run
in the same manner as before at pH 7 and a polymer dose
of 1 p.p.m. Except for quartz, flocculation was noted in
all suspensions. In comparison with PAD flocculent, the
only noticeable difference was that PAD gave stronger
flocs (larger size) than A130 and A80.
Selectivity of PAD: Selectivity of the flocculent
could arise from its differential adsorption strength on
the various minerals. For example, the polymer may
strongly adsorb on to copper minerals but be weakly held
on calcite or feldspar and in both cases it would cause
flocculation. But by introducing another ligand strong
enough to compete with the polymer for calcite and feldspar,
1240
the flocculant would then be free to adsorb on copper
minerals only. Thus, the inhibition effect of this
ligand on gangue minerals together with the strong
affinity of the polymer groups to bind with copper
minerals, could result in selective flocculation of
the latter. In this work both 'Calgon' (sodium hexa-
metaphosphate) and "Dispex N40", a sodium salt of a
synthetic polycarboxylic acid supplied by Allied
Colloids Co. Ltd., were used as flocculation inhibitors
for gangue minerals.
The main advantage of PAD over A130 and A80 was
found to be its capability of forming strong linkages with
copper minerals in the presence of Dispex N40 and Calgon.
Thus in a series of experiments, A130 failed to flocculate
chrysocolla at pH 7 in the presence of 0.2% and 1.0%
Dispex in suspension, while PAD caused flocculation at
1 p.p.m. Similarly malachite was flocculated by PAD in
the presence of 0.5% Dispex, while A130 had no effect;
and a mixture of galena, calcite, feldspar and quartz
could be inhibited by 1 % Dispex from flocculation with
A130 but not with PAD.
Another set of experiments was carried out to explore
the selective action of PAD on dilute suspensions, following
the same procedure as before at pH 7 using Calgon and
Dispex as inhibitors for gangue minerals. Thus calcite
was inhibited from flocculation with PAD by addition of
50 p.p.m. Calgon and feldspar was not flocculated in the
presence of 100 p.p.m. Calgon and 1% Dispex. Galena was
also depressed by 100 p.p.m. Calgon, while chrysocolla
and malachite were flocculated in the presence of 100
p.p.m. Calgon and 1% Dispex. The qualitative results
of these experiments are summarized in Table 5.1.
5.2.3 Selective flocculation of copper minerals
.......:EftTIampts2.211raa
The selectivity of PAD to copper minerals (i.e.
chrysocolla and malachite) was further investigated at
pH 10.5. It was assumed that at this pH both the minerals
and the polymer groups acquire a negative charge.
Adsorption of PAD would then be due to chemical bonding
with Cu-sites on the mineral surfaces.
In one experiment, a mixed suspension of calcite,
feldspar and quartz was treated with 100 p.p.m. Calgon
at pH 10.5. The suspension was stirred by a magnetic
stirrer for 5 min. and Dispex solution was added at a
dose of 1% while stirring was continued for further 5
min. The treated suspension was transferred into a 250 ml
cylinder and was kept for about 5 min. in order to reject
coarse particles. Thereafter, the suspension was
decanted back into a beaker where 2 p.p.m., PAD polymer
was added during stirring at high shear-rate for 1 min.,
followed by low shearing for 1 min. and gentle rotation
in a cylinder fora fewminutes. No flocculation occuried
even after 60 minutes.
In another experiment, a mixed suspension of chryso-
colla malachite, calcite, feldspar and quartz was treated
in the same way as in the preceding experiment, that is in
the presence of 100 p.p.m. Calgon and 1% Dispex at pH 10.5.
The green flocs of chrysocolia and malachite were noticed
142
Table 5.1 : Flocculation effects of PAD compared with A130
at H7 on mineral sus ions of > 0.4° solids
Exp. Reagents A130 PAD
No. Minerals 1 p.p.m. 1 p.p.m.
1 chrysocolla +
- «
+
+a; - + b,c
2 malachite +
- b
+
- + b,c
3' chalcopyrite + +
4 quartz - -
5 feldspar +
- c *
+
- c,p
6 calcite +
- c *
+
- «
7 galena +
- c *
+
- p
8 mixture ,of
galena, quartz,
calcite and
feldspar
+
- c
+
+ - c
Notations: + good flocculation
no flocculation
partial flocculation
deduced from exp. No. 8
Dispex NLIO a = 0.2%, b = 0.5%, c = 1%
Calgon « = 50 p,p.m., p = 100 p.p.m.
143
at the bottom of the cylinder, at a PAD dose of 1 p.p.m.,
and complete flocculation was formed at higher doses. No
white flocs were noticed even at 15 p.p.m. PAD and the
white suspension remained stable. Thus copper minerals
were selectively flocculated, while calcite, feldspar and
quartz particles remained suspended. The experiment was
reproducible.
Selective flocculation of malachite and chrysocolla
from mixed suspensions containing galena was carried out.
The aim of this attempt was to see whether PAD is especially
selective to copper minerals. Thus, a mixture of galena,
feldspar, calcite and quartz was inhibited from flocculation
with PAD in the presence of 100 p.p.m.,•Calgon and 1%
Dispex at pH 10.5, following the same procedure as above.
When another suspension containing chrysocolla and
malachite, in addition to galena, feldspar, calcite and
quartz, was treated with 2 p.p.m. PAD under the same
conditions of the preceding experiment, galena was noticed
to flocculate with the copper minerals. It was decided to
investigate the possibility of depressing flocculation of
galena from mixtures with copper minerals.
5.2.4 Inhibition of flocculation of galena in
mixtures with copper minerals
Effect of Na2S and NaF: These two compounds were
used so that the sulphide ion would precipitate any mobile
Cu2+ or Pb2+
released by copper minerals and galena, and
the fluoride ion would complex Ca2+ , Al'q+ and K from
feldspar and calcite, thereby avoiding random activation.
Thus a mixed suspension containing galena, chrysocolla
144
malachite, calcitelfeldspar and quartz was treated with
100 p.p.m. Na2S at pH 10.5 and stirred at high shearing
for 5 min. An addition of 100 p.p.m. NaF was made and
stirring was continued for 5 min. The suspension was
transferred to a cylinder and was kept for 10 min. in
order to get rid of coarse particles. 1 p.p.m. of PAD
solution was then added to the decanted suspension, while
stirring at high shear rate for 1 min. follwed by 1 min.
low shearing and a few minutes gentle rotation in a
cylinder. The experiment was also repeated, using 200
p.p.m. of each Na2S and NaF. In both experiments galena
was noticed to flocculate with chrysocolla and malachite.
Thus Na2S and NaF failed to inhibit flocculation of
galena.
Effect of potassium dichromate: A series of
experiments were made on galena suspensions, using
potassium dichromate at doses of 10, 20, 50, 100 and
200 p.p.m. Thus 50 ml suspensions were shaken by hand
(including turning the tubes end over end) for a few
minutes before and after the addition of K2Cr207 at
pH 10.5. The suspensions were then treated with 1 p.p.m.
PAD flocculant and shaking was continued for 1 min.
followed by rotation of tubes at an angle for a few
minutes. Flocculation took place at all doses.
In another experiment, a suspension containing
galena, chrysocolla, and malachite was treated with
200 p.p.m. K2Cr207 at pH 10.5, while stirring for 3 min.
by magnetic stirrer. The coarse particles were rejected
after keeping the suspension in a cylinder for about 3
145
min. PAD solution was added to the suspension at a dose
of 1 p.p.m. while stirring at high shear rate for 1 min.
and at low shearing for 1 min. further. Flocculation of
the mixture took place but was apparently unselective.
Thus K2Cr2O7 also failed to depress galena from floccula-
tion. This matter was not pursued any further.
5.2.5 Discussion and conclusions
According to the literature mentioned in Chapter 3
dithiocarbamate groups do not add on earth alkaline
metals. Therefore PAD should adsorb strongly on minerals
containing transition and B-cations, especially copper
minerals, because Cu2+ ions form very strong compounds
with dithiocarbamate groups, but also lead minerals.
Flocculation of calcite and feldspar was somewhat
unexpected with PAD, but this might have been due to
some sites on the polymer which were not converted to
dithiocarbamate. Since not much information was
available about the analysis and structure of the
polymer this explanation remains speculative.
In spite of the flocculation effects of PAD on
calcite and feldspar, selective flocculation of
copper minerals, namely malachite and chrysocolla,
from mixed suspensions was achieved. PAD could there-
fore be considered a selective flocculant. The experimental
procedure adopted in this work was mostly arbitrary and
results were qualitative since the main concern was the
study of the basic principles of the chemistry of the
flocculation process.
1116
Little knowledge is available about the decomposition
behaviour of the polymer groups. The polymer was noted to
decompose and lose its strong flocculation effect after a
period of 6 weeks. This problem could be overcome if the
polymer could be stored dry and fresh solutions may then
be made. PAD flocculant may prove useful in the future
and therefore deserves further detailed studies on the
various aspects of preparation, purification, analysis,
physical and chemical properties, so that it can be used
to best advantage.
147
CHAPTER 6 EalET2111121EzEIELLL.JIL27.:1271111222g2EEL/
6.1 Introduction
The selectivity of glyoxal-bis-(2-hydroxyanil) (or
GBHA) to copper ions was first discovered by Bayer (155,156)
who found that GBHA groups were particularly suitable for
sequestering copper and uranyl ions. Only copper, uranyl
and nickel ions were strongly bound to GBHA in weakly
acidic media; there was no complex formation with either
alkaline earth ions or with other heavy metals below pH7(157)
This selective behaviour towards a few metals is said to
be mainly due to the special steric structure and the iso-
merism of GBHA(79) In alkaline media, the ring form of
GBHA Fig. 6,1a, re-arranges to form the open-chain
structure Fig. 6.1b, which is the true complexing agent
and as a result, less stable complexes are formed with
Co2+ Zn2+ Cd2+ and even with alkaline earth ions.
The stability of the metal-GBHA chelates has been
shown to depend essentially on the covalent bonding between
the metal atom and the two nitrogen atoms. The phenolic
oxygens cannot approach the metal atom sufficiently closely
to form either a covalent oxygen-metal bond or a firm
electrostatic bond. Therefore, the five-membered chelate
rings, N-M-N-C-C, are obtained(79). The stability order
of the coordinative complexes of heavy metal ions is:
Cu>IJO2>Ni > Co >Mn> Zn >Cd, whereas vanadium and iron
form weak complexes in alkaline media.
056050 Bayer was able to prepare water insoluble
resins containing GBHA groups by condensing di- and
tri-aminophenols with excess of glyoxal. This resin was
used (79,159) successfully to selectively extract copper
and uranium from sea-water. GBHA groupings were also used
in the micro-determination and selective separation of
uranium, with the aid of,light absorption spectroscopy (160)
Bayer's findings are in agreement with the principles
mentioned in Chapter 3, where the nitrogen donor ligands
have no strong tendency to form stable coordinative com-
pounds with class A-cations. Accordingly the selectivity
of GBHA could be utilized in the separation of metallic
ions by one of the following alternatives:
A - In acidic media (pH 2-7), where GBHA reacts only
with copper, nickel and uranyl ions but not with alkaline
earth and other heavy metal ions, or
B In alkaline media (pH 7-11), where GBHA forms
complexes with many cations but with different degrees
of strength, in which case, by introducing another
competing ligand in the medium to suppress those com-
plexes of lower strength, selectivity to those cations
forming strong complexes with GBHA, especially copper,
could be achieved.
It was anticipated that if GBHA groups were introduced
into a long-chain water-soluble polymer such as poly-
acrylamide, a selective flocculant for copper minerals
could thus be obtained.
Polyacrylamide-glyoxal-bis-(2-hydroxyanil) polymer
was the reaction product of a non-ionic polyacrylamide
(PAM) with formaidhyde and glyoxal -bis-(2-hydroxyanil)
groups (GBHA). These chelating groups were also known as
1148
149
di-(2-hydroxy phenyl-imino)-ethane, [C6H4(OH).N:CH] 2.
For simplicity, this polymer will be referred to as PAMG.
The techniques of introducing GBHA into polyacrylamide
through the reaction with formaldhyde, probably involved
the following reactions:
A. -CH -CH- 2 1 C=0
NH2 (PAM)
+HCHO
(formaldhyde)
-CH -CH- 2 / C=0
NH
CH2OH
B. -CH2 1 -H- +GBHA ----* -CH2 1 -CH- +H2O. C --
C=0 C=0 I I NH NH I I CH2OH CH 1 2
GBHA
C. GBHA + HCHO GBHA - CH2OH •
D. GBHA - CH2OH + -CH -CH- -CH -CH - +H20 •
2 1 2 1 C=0 C=0 I I NH2 NH
CH 2 GBHA
The structure of GBHA, according to Bayer(? 9) in
acidic and the alkaline pH is shown in Fig. 6.1 (a,b),
and the possible structure of PAM-GBHA polymer is
illustrated in Fig. 6.2. The average molecular weight
of this chelating polymer was expected to be about one
million, since it was prepared from a polyacrylamide
150
o"0 H C — CH I I H H /
(a) In acidic media HC—CH
(b) In alkaline media
Fig.6-1 Structure of GBHA
CH2 CH — CH— C H—CH — CH— CH—CH—CH —CH— CH—CH- i i
1 C=--- 0 c =0 C=----0 C=0 C=0 C=0 I I I I I I NH NH NH2 NH NH NH I I I I CH2 CH2 CH2 CH2 O .0 HC —CH 0 / P1 N'i \N Ck‘ "A*4 0, ,-G'-:,‘,‘ H H ■
N\ \A' - \A \*4 \A Vt‘
Fig.6.2 Possible structure of PAMG polymers
151
sample of that average molecular weight.
It has been established (91,161,162,163)that polyacrylamide
reacts with formaldhyde under alkaline conditions to
produce methylolated polyacrylamide, owing to the reactivity
of the amide groups. The reaction proceeds to equilibrium
(equation A) and as a result some free formaldhyde remain
in solution (161). Schiller and Suen(163)prepared anionic
derivatives of polyacrylamide through sulphomethylation de
with formalhyde and sodium bisulphite, and cationic
derivatives via the aminomethylation (Mannich reaction)
with formaldhyde and amines. In the sulphomethylation de
method, they found that the rate of formalhyde uptake on
PAM depended on the pH and temperature. The reaction did
not proceed to any significant extent below pH 10 even
at 70-75°C in 2 hours. However, the rate of uptake increased
sharply upon raising the pH to 10.5; about 60% of the
formaldpyde had already been combined with PAM before the
temperature reached 50°C. When the reaction was carried
out at 70°C, the initial rate of uptake was greater than
that at 50°, yet the same extent of reaction was reached
at both temperatures over a period of 4 hours. Schrieber
and Reinwald(164) modified polyacrylamide by the reaction
with paraformaldhyde and piperidine at room temperature
in acidic pH (Mannich reactior065Vhey used the product
for flocculation of enzymes formed in Bacillus subtilis
cultures. The modified form gave a clear supernatant as
against turbid supernatant with unmodified polyacrylamide.
Polyacrylamide can also react with glyoxal through
the amide groups under alkaline conditions to produce a
152
water-insoluble polymer, provided the molecular weight is
high (161)
.The amide groups of PAM undergo hydrolysis
under alkaline conditions, which results in the formation
of carboxylate groups on the polymer. Apparently, the
amide groups of PAM could be converted to yet more active
sites for covalent coupling of biomolecules( 160_ for
example, the conversions of "Bio-Gel p" (polyacrylamide
gel) to the aminoethyl and hydrazide forms(166). The first
was formed by reacting PAM with ethylene diamine:
-CH2 -CH- + H2NCH2CH2NH2
90 C o, -CH2 -CH- + NH3.
C=0 C-0 I I NH2 NH
CH -CH 2 2
NH2
and the hydi!zide form was prepared by reacting PAM with
hydrazine (N2H4):
-CH -CH- + H2NNH2 -CH2-CH- + NH3 . 2 1 C=0 C=0
NH2 NH
NH2
The hydrazide derivative could be used directly to couple
protein amino groups. Detailed properties and reactions
of polyacrylamide were reviewed in the literature(167)
The reactions between GBHA and formaldhyde can be
best explained in terms of the condensation of phenol
and formaldhyde, since GBHA consists of two substituted e
phenols. Phenol and formaldhyde normally condense to
form polymers consisting of aromatic rings linked together
mainly by methylene bridges (91,92,168,169) The bridging is
primarily in the ortho or para positions to the phenolic
groups (51,9); CH2OH CH2OH, CH2OH, CH2OH CHZOH,
carried out in the presence of catalysts, with the aid
of heating; the catalysts can be either bases or acids.
The reactions of phenol and formaldhyde in alkaline
conditions result in the formation of 0-, p-methylol OH OH OH
153
hydroxyls. In these condensations, phenol is a tri-
functional molecule and formaldhyde a difunctional one.
The ortho or para substituted phenols, however, can only
yield linear. polymers (9 . The reactions are usually
0-120H which are more reactive towards formaldhyde than the
original phenol. If the reactions were allowed to proceed
to a higher degree of condensation, these phenol alcohols
would undergo self-condensation with the formation of
ethylene- and ether-bridges(170).The products of these
base-catalysed condensations, known as tresoll resins,
tend to folat water-insoluble net-work polymers upon
prolonged heating, due to the branching effects of the
reactive phenoxide ions.
The reactions between phenol and formaldhyde under
acidic conditions (usually below pH 3.6), i.e. acid-
catalysed condensations, proceed through the protonation
of formaldhyde to give carbonium ions: CH2=0f-Ns
+ H+ CH?-OH,
which react with phenol to form 0-$ p-methylol groups (91)
Acidic catalysts seem to favour the formation of p, p'
linkages, although 0, p' and 0, 0' linkages may also form0(6)
In the presence of more acid, the methylol groups react
with free phenol to form dihydroxydiphenyl methanes(91).
Unlike the base-catalysed condensations, in the acid-
154
catalysed reactions, the first substitution in the phenolic
nucleus substantially deactivates the ring against further
substitution(91) and as a result, the polymer has a linear
structure. The polymer would remain water-soluble so
long as the ratio of phenol to formaldhyde was less than
equimolar(92). As the condensation products are unable to
polymerize to a great extent (the average molecular weight
of a typical commercial novolak is about 600 which
corresponds to about 6 phenolic nuclei per chain(91)), there
is no danger of gelation during production (171'172)
6.2 Preparation of PAMG polymers
In this work, three main techniques were attempted;
in two techniques the condensation of GBHA on PAM was
carried out by direct reactions with formaldhyde. In
the third technique, formation and reaction of GBHA with
PAM was conducted through the condensation of a diamino-
phenol (in the hydrochloride form) with glyoxal and
formaldhyde. The reactions of GBHA with PAM and formaldhyde
were conducted at pH 10.5, where PAM has been shown (161,163)
to react with formaldhyde at an appreciable rate. The
intention of the dissolution of GBHA in either aqueous or
alcoholic media containing formaldhyde at pH 2.5 in the
methods described in 6.2.1 and 6.2.3 was to avoid the
possibilities of cross-linking of GBHA groups, which
might have resulted in forming water insoluble resins.
It was believed that formaldhyde would form methylol
groups on GBHA, catalysed by the acidic medium, without
much polymerization of GBHA, thus leaving them ready to
155
condense on PAM in alkaline media. However, condensation
of formaldhyde on GBHA would also be expected in the alkaline
medium, where the phenolic rings of GBHA, by analogy with
other phenols (91,91
, would have more active sites for
reaction.
The chemicals used in these preparations were from
BDH chemicals Ltd., Poole, England, and the polyacrylamide
was NlOOS from B.T.I.Chemicals Ltd., Bradford, England.
According to information supplied by B.T.I.Ltd., the poly-
acrylamide N100S was of high grade i.e. of low content
of carboxylate groups (iv .5%) and was of an average
molecular weight of 106. EXPERIMENTAL
6.2.1 Preparation of PAMG2 polymers
In this method, an ethanol solution of GBHA was used
in the reaction because of its limited solubility in cold
water. Three PAMG2 polymers namely; PAMG 2.1, PAMG 2.2
and PAMG 2.3, were prepared. PAMG 2.1 and PAMG 2.2 are
described in this section and PAMG 2.3 is described in
6.4.
Preparation of PAMG 2.1: 0.2 g GBHA powder was
dissolved in 25 ml cold ethyl alcohol. At the end of
dissolution, 25 ml double distilled water was added
together with 0.02 g formaldhyde (0.05 ml formalin) and
the pH was adjusted to 2.5. The solution became turbid
on addition of water. It was kept in a water-bath at
75-80°C under reflux for 30 min. The colour of solution
was yellow. After cooling, the product solution was
mixed with 50 ml of 0.2% aqueous solution of PAM (i.e.
0.1 g) and the final pH was adjusted to 10.5. The
156
mixture was kept at• 75-80oC in a water-bath under reflux
for 30 min. The product was dark brown in colour and
contained some solids. The concentration of this solution
was taken as 0.1%, based on the weight of PAM. The product
had flocculation effects on suspensions of chrysocolla,
feldspar and calcite at pH 5, and no effect on quartz.
The effect of excessively high temperature on the
polymer structure was demonstrated in an experiment where
the amounts of reactants and conditions were the same as
those of PAMG 2.1, except that the mixture (i.e., after
adding PAM solution) was allowed to boil for a few seconds
on a hot-plate, without refluxing. The product contained
much of a dark brown, insoluble gel precipitate. Never-
theless it produced good flocculation on suspensions of
chrysocolla, feldspar and calcite at pH 5 and had no
effect on quartz suspension. The product was named PANG 3.
Preparation of PAMG 2.2: 0.1 g GBHA was dissolved in
25 ml ethyl alcohol (with the aid of warming and shaking)
to give bright-yellow colour solution. 25 ml double
distilled water and 0.02 g formaldhyde were added and the
pH was adjusted to 2.5 (with 3 drops of conc. H01). The
solution was maintained at an average temperature of 73
(68-76°) in a water-bath under reflux for 30 min. The
colour of the solution changed to red-wine colour but
there was no solids. After cooling, the solution was
mixed with 50 ml of 0.1% aq. solution PAM (i.e. 0.05 g)
and the pH was adjusted to 10.5, usinp. NaOH aq. solution.
The mixture solution was kept at 75°C for 30 min. under
reflux. The product was dark brown in colour and did not
157
contain solids. The polymer solution (0.05% PAM), produced
good flocculation on chrysocolla suspension. It was used
in the alcohol precipitation purification processes described
in sections 6.3.1 and 6.5.1.
6.2.2 22:222Ea-Li2ILaiLyA_,,
In this technique, the polymer was formed by the
condensation of a diaminophenol with glyoxal and formaldhyde
on polyacrylamide. Thus 3.15 g of 2,4- diaminophenol
hydrochloride(amidol) [ (NH2)2 C6H3.0H.3HCL], 0.5 g
glyoxal [(CH0)21 , 0.25 g formaldhyde (CH20) and 1.0 g
polyacrylamide PAM ( N100S), were dissolved in one litre
of double distilled water. The pH of the mixture was
raised to 10.5. The solution was then refluxed at an
. average temperature of 55°C (50-60o) for 2 hours, in a
2 litre, flat bottom flask, while stirring in a nitrogen
atmosphere. The product was very dark brown in colour and
contained insoluble gel particles. It had good flocculation
effects at pH 6 on suspensions of chrysocolla and feldspar
but not on a quartz suspension; it was used in the
flocculation experiments in Chapter 7.
6.2.3 Preparation of PAMG 7 polymer
In this method, an aqueous solution of GBHA was used
instead of the ethanol solutions used for PAMG 2 polymers.
Thus 0.3 g GBHA powder was dispersed in 100 ml distilled
water at pH 10.7. The dispersion was kept at 70°C in a
water-bath under reflux for 3-days. On filtration,
however, it appeared that only 0.1 g GBHA had dissolved.
11 ml of 1.0% aq. solution of PAM and 0.163 g formaldhyde
(0.41 ml formalin) were added and the pH was adjusted to
158
10.7. The mixture was heated at 5000 for 1.5 hour. The
product solution (0.1% based on PAM) was yellow to pale-
brown in colour with only a little solids suspended.
The theoretical molar ratios of reactants used in
the preparations of PAMG polymers namely; PAMG 2.1,
PAMG 2.2, PAMG 2.3 (Section 6.4), PAMG 6 and PAMG 7,
are shown on Table 6.1.
Table 6.1 The molar ratios of reactaILUUIIRE221=Ina
PAMG polymers
reactants PAM (A.M=71
GBHA (240)
formaldhyde (30)
glyoxal (58)
diaminophenol hydrochloride
(197) polymers ---,
PAMG 2.1 1 0.589 0.475 - -
PAMG 2.2 1 0.589 0.95 - -
PAMG 2.3 1 0.298 0.473 - -
PAMG 6 1 - 0.59 0.61 1.13
PAMG 7 1 0.298 3.8 - -
6.3 Purification o£
6.3.1 Thea22212. .method
Excess ethyl alcohol was found to precipitate these
polymers from their aqueous solutions to give dark brown
precipitates. Similarly, ethyl and methyl alcohols also
precipitated (unreacted) polyacrylamide from its aqueous
solutions to give white amorphous precipitate (ppt.).
The alcohol content must, however, be equal to or more
than 50% of the total volume of the solution. PAM
159
granules were found experimentally to dissolve in 30%
ethanol or methanol solutions, whereas in 50% ethanol
solutions there was no dissolution or even swelling of
PAM.
On the other hand, GBHA powder was, of course,
soluble in ethyl and methyl alcohols. Thus by treating
the PAMG 2 polymer solutions with equal volumes or excess
of ethyl alcohol, the polymer would precipitate in a
solid form while any free GBHA and other by-products of
lower molecular weight would remain in solution.
Separation of the two phases by filtration or decantation
and washing with alcohol several times should therefore
yield a purified polymer. The rapidity and completeness
of precipitation would, of course, .depend on the concentration
of the polymer in solution.
Experimental: This method was applied to PAMG 2.2,
prepared as in 6.2.1. 100 ml of polymer solution was mixed
with 200 ml of absolute ethyl alcohol and left for 30
minutes at room temperature. In order to aid settling of
the precipitate, part of the polymer suspension was
centrifuged and the ppt. was washed several times with
ethyl alcohol and was recovered. The other part was left
overnight in a covered beaker, where the polymer precipitated
in a large volume at the bottom of the beaker. It was
filtered on an ordinary filter-paper and washed 4 times
with ethyl alcohol until there was no more colour released
into the solution above the precipitate. The colour of the
ppt. was brown; when the ppt. was dissolved in distilled
water, it gave a yellow solution. When 100 ml of this
160
yellow solution was mixed with 20 ml ethyl alcohol, the
brown ppt. formed immediately leaving no colour in the
alcohol solution.
An experiment was carried out to study whether any by-
products of the formation reactions of PAMG 2.2 had also
precipitated in alcohol. Thus 0.1 g GBHA was dissolved in
25 ml of warm ethylalcohol (warming at 50-60° and shaking
for few minutes); the colour of the solution was bright
yellow. Then 75 ml of cold distilled water was added and
the pH was adjusted to 10.5; the colour changed to pink.
On addition of water some precipitation of GBHA took place,
the dispersion was kept at an average temperature of 73°C
in a water-bath, under reflux for 40 min. When the
dispersion was allowed to cool, the colour was a brownish-
green. After cooling, the precipitate was filtered and
dried and weighed; about 40% of GBHA remained in solution.
To the clear GBHA solution, 0.05 ml formalin (0.02 g
formaldhyde) was added at pH 10.5 and the mixture was kept
at 75°C for 30 min. The colour became dark brown and there
was no solids formed. 20 ml of this solution "Product I"
was mixed with 30 ml ethyl alcohol and was left for 20
minutes. There was no precipitation of solids at all,
even after many hours.
Another experiment was carried out with PAM. Thus
0.1 g PAM was dissolved in 100 ml dist. water containing
25% ethyl alcohol, the pH was raised to 10.5 and 0.05 ml
formalin (0.02 g formaldhyde) was added. The mixture was
kept at 75 i C in a water-bath under reflux for 30 min.
When it was allowed to cool, there was no formation of
161
solids or gel i.e. no cross-linking of PAM. 20 ml of this
solution "Product II" (methyolated PAM) was mixed with
30 ml ethyl alcohol. A white precipitate was formed
immediately, which re-dissolved readily in 20 ml distilled
water. A mixture of 10 ml of product II was mixed with
5 ml of product I and 30 ml ethyl alcohol, but no
precipitation took place immediately, probably due to
dilution of the polymer solution;
Instead, 10 ml of 1.0% PAM (ordinary) aq. solution
was mixed with 6 ml of product I plus 30 ml ethyl alcohol.
Only a white precipitate was formed, leaving the yellow
solution alone. The ppt. was separated and washed with
alcohol several times but the alcohol solution remained
uncoloured. This experiment was repeated several times
with different amounts of product I and even with GBHA
ethanol solution, and the same results were obtained.
These tests proved that there was no entrapment
of colouring substances in the precipitate of PAM, nor
was there precipitation of any reaction by-products in to
alcohol. Therefore, the brown colour of PAMG 2.2 product
precipitated by alcohol was due to a truly new polymer.
6.3.2 Gel chromatography method
This technique was tried in this work in an attempt
to isolate the PAMG polymers from other lower-molecular
weight substances. This method works on the principle
that different size molecules will be eluted at different
speeds from a column of swollen gel particles. Molecules
larger in size than the largest pores of the swollen gel
beads i.e. above "the exclusion limit", cannot penetrate
162
the gel particles; instead they move outside the particles
through the bed and thus are eluted first. On the other
hand, smaller molecules penetrate the gel particles to a
varying extent depending on their size and shape.
Molecules are therefore eluted from the gel bed in order
of decreasing molecular size or molecular weight.
Dasii ....I192221211E: The glass column used was 40 cm
x 1.7 cm with a bed support of 400 mesh nylon cloth;
the gel bed height was 30 cm. The tubing was mainly
glass and soft polyvinylchloride of diameter 2.0 mm.
The length of the tubing segments was kept as short as
possible to minimize the dead space volume. The dead
space volume beneath the bed support was also minimal,
to avoid unnecessary dilution of effluent fractions and
to enhance the chromatographic resolution since large
dead-space volume could act as an effluent mixing chamber(173)
The eluant was de-aerated double-distilled water and the
hydrostatic pressure was regulated simply by calibrating
a measuring tape so that zero pressure corresponded to
the bottom of the air vent in the eluant container. The
design was simple and the column was easy to dismantle
for cleaning, repacking and repairs.
The gel medium used was "Bio-Gel P-300" (BIORAD
Laboratories) U.S.A. According to the manufacturers(17
substances of molecular size larger than the exclusion
limit would be eluted from the bed at a volume equal to
the void volume (i.e. the volume of the space outside
the gel beads), which they estimated as 38-42% of the total
bed volume. The maximum separation between the different
1'63
molecular weight substances could be estimated in advance'
provided that the ratio of elution volume to void volume
lEv ‘Evo) for a particular molecular weight was known.
According to the manufacturers (174) theEv/Evo for sub-
stances of molecular weight 106 on Bio-Gel P-300 was
approximately equal to 1.225. The separation (in terms
of elution volume) between different molecular size,
fractions could be estimated as follows:
Total gel bed = 11* x (1.7)2 x 30 = 68.06 ml (or 68 ml) 7-- •
The void volume = 68 x 38% = 25.8 ml
or = 68 x 42% = 28.6 mi.
Hence, the"peak heigheof 106 polymer
= 25.8 x 1.225 = 31.6 ml
or = 28.6 x 1.225 = 33.2 ml
This should be the difference in elution volume between
the 106 substances and other substances. Similarly the
"peak height"of 105 polymer would be = 25.8 x 2.0 = 51.6 ml
or 28.6 x 2.0 = 57.2 ml, where Ev/Evo = 2.0. This
volume should be the difference in elution volume between
105 fraction and the 104 fraction which was the minimum
separable on this gel P-300. Therefore it was expected
that the 106 molecular weight fraction would be
completely eluted in an effluent volume of 30-33 ml and
the 105 fraction within 50-57 ml and the rest of the
substances within perhaps 70 ml.
LIEtrialLEILl: The gel used was of bead size range
100-200 mesh. About 10 g of the dry gel beads were hydrated
in 500 ml double-distilled water for 8 days. The gel
164
slurry was elutriafed to get rid of the fines and was
de-aerated before packing into the column. The gel-bed
was carefully packed, avoiding entrapped air bubbles in
the system. Thus the column and the side tube were filled
with the de-aerated eluant by vacuum the column was
immersed in the eluant ) so that no air bubbles were
present. The hydrated gel beads were poured through a
funnel into the column and allowed to settle for a few
centimeters, a mild pressure of 10 cm -15 cm was gradually
applied to pack the bed more tightly. The bed was covered
with filter-paper on top to retain solid matter. After
washing the bed with the eluant for at least 3 days, the
samples (10 ml of 0.01% PAMG 2.1, PAMG 6, PAMG 7 at pH 8.3)
were applied gently over the bed and were allowed to drain
down to the bed level before addition of the eluant and
connecting to the eluant reservoir.
In practice the effluent flow-rate was slow, about
1.7 ml/hr. at a hydrostatic pressure of 15 cm (which was
the maximum recommended). When the gel bed was repacked
carefully, an initial flow-rate of 4.0 ml/hr could be
obtained but it eventually became 1.7 ml/hr. at 15 cm
pressure.
In an experiment, 10 ml of 0.01% PAMG 2.1 flocculant
was run through and samples were taken every 4 hours
(i.e. 6.8 ml), a total of 10 samples being taken. The PAMG
2.1 polymer was detected in the effluent solution by
u.v. absorption spectroscopy at 558 my.. The results are
shown in Figure 6.3. It appeared that a fraction of the
polymer was eluted within 17-20 ml, presumably the 106
O 0 <ID
Abs
orba
nce
( 558
mit)
0.00
0.04—
0.20
Sample 1
1 O
.
0
4
. • •
• • • • •
5
I I I 1 a a (-) nr to
Effluent volume tml)
0.16—
0.12—
0.08 —
. • • • . • • •
2
3
•
6 7
Fig.6.3 Fractionation PA M G 2.1 by gel chromatography
166
fraction,and another fraction was separated at the peak
height 44-50 ml; the separation in elution volume, was
therefore between 27-30 ml which was roughly in agreement
with predicted estimation.
Conclusions: Unfortunately the flow-rate became
very slow due to partial blockage of the bed. When
examined, the gel bed was found to contain bacterial growth.
Attempts to sterilize the bed were not successful and
repacking the bed did not improve the flow-rate. Also,
this process resulted in dilution of the polymer solution
to an only roughly known extent; therefore the doses of
the polymer to be used subsequently in the flocculation
experiments would be very inaccurate.. This process was
not therefore considered suitable for a routine purification
process, but might be useful as an analytical aid.
Possibly a column of porous glass beads would be more
convenient than "Bio-Gel p".
6.4 Preparation of dry powder of purePAMG 2.3 polymer,
Experimental: 3 g of GBHA powder was dissolved in
250 ml absolute alcohol in a 2-litre flask, with the aid
of warming at 50°C for 2.5-3 hours under reflux. 250 ml
dist. water was added together with 1.5 ml formalin
(0.6 g forrnaldhyde) and the pH was adjusted to 2.5. The
mixture was kept at an average temperature of 65°C
(60-70°) for 35 min. The solution was brown to wine in
colour and contained solids. 3 g of PAM 1005, dissolved
in 500 ml double distilled water, was added to the GBHA
suspension and the final pH was adjusted to 10.5. The
167
mixture was kept at 73°C for 35 min. and at 75°C for a
further 35 min. The product was a brown, viscous solution,
and contained colloidal solids. It was kept in two
1-litre beakers in a refrigerator over-night.
Purification aal slExiaa af PAMG 2.2: The contents
of both beakers were added to a total of 2.5-3 litres
ethyl alcohol in small portions and stirred with glass
rods. The precipitated PAMG 2.3 polymer was collected on
these glass rods. Washing the polymer was carried out
by stirring the glass rods in consecutive beakers of
ethyl alcohol, until no colour was noticed in the last
beaker. The precipitated polymer was skimmed off the
glass rods into a weighed evaporating dish, and washed
with alcohol again. The solid product was dried in a
vacuum desiccator, under vacuum over P205 for about 2
days. An attempt to filter some of the product (before
mixing with alcohol) on a 1.0 v. membrane, under 2 kg/cm2
of nitrogen was not successful and some of the product
was lost during handling. The product solution was very
viscous, and the idea of filtration was rejected. Another
attempt to produce granules of PANG 2.3 by dropping the
solution into a long cylinder (2-litre) containing about
1-litre of alcohol, while stirring by a magnetic stirrer,
was also not successful. The droplets became relatively
large in size under the impact on the alcohol surface.
However, this technique could be improved by reducing
both the volume of the droplet (e.g. by using a fine
needle) and the travelling distance to the surface of
alcohol.
168
Grinding of the dry solids was done with a mortar
and pestle by hand. The colour of the powder was light
brown and it was light in weight (i.e., larger volume
0 per unit weight) compFed with PAM granules. About 2.7 g
of the PAMG 2.3 powder was recovered.
Solubility in water: At least, 0.05 g PAMG 2.3 was
dissolved in cold water out of 0.1 g powder, in 2 days
stirring (i.e., 50 %) by a magnetic stirrer at a moderate
shear-rate. It was easier to disperse 0.05 g PAMG 2.3 in 100 ml dist. water (or 0.1 g in 200 ml), but some solids
remained undissolved and could be removed by filtration.
The 0.05% solution of PAMG 2.3 was tested for flocculation on suspensions of dolomite and malachite,
both separately and in mixture. For each of the 3 different
suspensions, 2 different depressant conditions were used;
50 p.p.m. Dispex N40 and 350 p.p.m. Calgon, both at pH 10.5.
Selective flocculation of malachite was achieved, though
the flocculation rate was rather slow at 4 p.p.m. PAMG 2.3.
6.5 Characterization of PAMG polymers
6 - 5.1 - Ilt2122222121722i211211sIIfuluELlaa In section 6.3.1, it was shown that PAMG 2 polymers
could be precipitated from their aqueous solutions by
alcohol. This method was also used here to establish
whether any modification of PAM took place as a result
of the reaction with GBHA. In this technique, the criterion
was the colour of the precipitate. It has already been
shown that any low-molecular weight by-products and free
169
GBHA remained in solution in alcohol; therefore the ppt.
would only be the PAMG 2 polymer. PAM precipitated by
ethyl alcohol is white, while PAMG 2 was brown. This
difference in colour indicated that modification of PAM
and formation of a new polymer PAMG 2 took place. This
technique was performed on many samples of PAMG 2 solutions
and the brown ppt. was produced in every case, and remained
after repeated dissolution and reprecipitation.
6.5.2 The dialysis technique
Experimental: 10 ml of 0.1% solution of unpurified
PAMG 2.1 was placed in a regenerated cellulose dialysis
bag. The bag was immersed in 800 ml double distilled
water and stirred gently by a magnetic stirrer. After 24
hours the solution outside the dialysis bag became yellow;
it was replaced by another 800 ml of double distilled
water. The replacements of the effluent solution was
continued until no more coloured substances diffused into
the solution i.e. colourless effluent. The process was
then stopped after approximately a week and the polymer
inside was recovered. It was brown to dark brown in
colour. This finding was a further confirmation of the
result of the alcohol precipitation technique and was
another indication for the definite change of polyacrylamide
due to the reaction with GBHA.
6.5.3 Membrane filtratiortechre
In this technique, a membrane filter would retain
the polymer segments of molecular size larger than the
membrane pores and let through the smaller size fractions.
If the optical absorption density was measured before and
170
after filtration, then the difference-of absorbance would
be due to the polymer retained on the membrane. If there
were no absorbing groups on the polymer (i.e. no reaction)
there should be no significant difference in the absorption
density at 400 mkt, since PAM does not absorb at this
wavelength (see fig. 6.5). Therefore the difference in
the absorbance would indicate that PAM had reacted with
GBHA to produce a new polymer. The ratio of the absorb-
ance(difference before and after filtration, in relation
to the 'absorbance of solution before filtration, that
is, the absorbance would be due to the GBHA groups on
the polymer plus the other by-products and including
free GBHA) could indicate the extent of reaction of PAM
with GBHA. Thus the greater this ratio, the greater the
number of GBHA groups reacted with PAM. However, this
simple ratio did not include the proportion of the
undissolved polymer (probably due to cross-linking),
nor the proportion of reacted polymer of sizes smaller
than the pores of the finest membrane used (0.01 kim)
(which might be due to the configuration of the polymer
segments). Nevertheless, this ratio could be an indication
of the extent of reaction of the soluble polymer in the
large size fraction, where the effective flocculation
properties were to be expected.
LaaLanalLp.nd materials:
1. Pressure filter: The filter used was from "Sartorius
Membrane filteeGMBH D-34 Gottingen, Germany.
171
2. Filter membranes: The 1.0 ym and 0.01 ym membrane
filters were also from Sartorius-Membran filter;
the 0.3, 0.5, 0.22 ym membranes were from Millipore
Filter Corp. Bedford, U.S.A. These membranes are
made of cellulose derivatives.
3. Light absorptionsuestr2m2Ier_ : The Perkin-Elmer
double beam spectrometer was used. The tungsten
lamp was used for the visible range and the
deuterium lamp from 380-180 my.. When the deuterium
lamp was used for determining the spectra of PAMG 2.1
solution in the range 600-360 my, an absorption peak
appeared at about 560 my which was sensitive to
the change in concentration of the polymer. This
peak also appeared with GBHA ethanol solutionsbut
not with ethanol alone nor with water. However,
when the tungsten lamp was used in the range 600-
370 my this peak disappeared from GBHA and PAMG 2.1
solutions. After several measurements on GBHA and
PAMG 2.1 solutions of different concentrations using
the tungsten lamp from 600-380 my and the deuterium
lamp from 380-180 my, it appeared that the range
440-400 my was very sensitive to change in con-
centration. In this section, measurements at 400 my
were considered best.
Experimental rocedure: 20 ml of 0.01% solutions
of PAM 2.1, PAMG 6 and PAMG 7 were filtered on 1.0 dam
membranes under nitrogen pressure of about 15 p.s.i..
Some frothing was noted during the filtration of PAMG 2.1
172
and PAMG 6. The membranes were placed in 20 ml dist. water
to disperse the retained portions of the polymers. 5 ml
of these dispersions were tested for flocculation. The
minus 1.0 im filtrates were also tested for flocculation
on 50 ml chrysocolla suspensions at natural pH using 2 ml
of the filtrates,and their absorption spectra were recorded
from 500-200 my. Filtration of the minus 1.0 iim solutions
on 0.01 im membranes was carried out under nitrogen pressure
of about 25 p.s.i. and the absorption spectra of the filtrates
were recorded. The filtrations were repeated in order
to check that the absorption spectra were constant. The
minus 0.01 tm solutions were also tested for flocculation
on suspensions of chrysocolla at natural pH, using 5 ml
of filtrate solutions. The 0.01 ym membranes were kept in
18 ml dist. water to recover the retained polymers.
5 ml of these plus 0.01 ym solutions were tested for
flocculation. The results are summarized in Table 6.2,
and the u.v. spectra of the polymers fractions PAMG 2.1,
PAMG 6 and PAMG 7 are shown in Fig. 6.4 (a, b and c).
This procedure was repeated twice on different solutions
of these polymers and the above results were confirmed.
NOTE: Because the pressure filter was made of
stainless steel (i.e. it might contain nickel), polymer
solutions were run through the filter several times to
cover the the contact surfaces of the filter with a polymer
coating before commencing the actual testing procedure
described above. This should eliminate possible errors
due to specific absorption of the polymers on the filter
contact surfaces.
Table 6.2
No. Properties PAMG 2.1 PAMG 6 PAMG 7
flocculation effect of minus 1.0 pm filtrate good weak good
2 flocculation effect of minus 0.01 pm filtrate no flocn. no flocn. weak
3 flocculation effect of plus 0.01 pm dispersion good weak good
4 flocculation effect of plus 1.0 pm dispersion good good weak
5 absorbance of minus 1.0 pm filtrate at 400 mu 0.48 0.27 0.127
6 absorbance of minus 0.01 pm filtrate 0.25 0.21 0.097
7 absorbance difference of minus 10 pm plus 0.01 pm 0.23 0.06 0.03
8 ratio of the absorbance difference to minus 47.9% 22.2% 23.6%
1.0 pm filtrate absorbance
__J.ILILIJIII1111
—1.2
Abso
rban
ce
—0.6 0.01 filterate
i-Ou filterate
(a) PAMG 2.1 I I I 1 1TIII11111
200 300 400
Wavelength
0.0 500
Fig.6.4.1Nspectra of (a) PAMG 2.1 (b)PAMG 6 (c)PAMG 7 solutions fractioned by the membrane filteration technique
Abs
orba
nce
500 200 300 400
I l I 11_11111 _I
1:2
0.6
0-01u filterate
1.0 filterate
I r5
00
Wavelength mi
L I
176
—1-2
Abs
orba
nce
0.01v filterate
10 filterate
•• ...................... (c) PAMG 7
I I I I 300
•••••• .......
I I I I I 1 I I 5 400 500 200
0.0
Wavelength mil
177
Size distribution of PAMG 2.1 polymer segments:
Experimental: A dilute solution of PAMG 2.1 was
filtered on 1.0, 0.3, 0,2, 0.05 and 0.01 lm membranes
and the absorptions of the filtrates were measured at
Ltoo mn. The filtrates were also tested for flocculation
on 50 ml suspensions of chrysocolla at natural pH. All
fractions except the minus 0.01 tm effected good floccula-
tion, though to varying degrees. The percent absorbance differ-
ences were taken as a measure of the size distribution
of the polymer molecules. The results are shown in
Table 6.3. It must be remembered that the minus 0.01 -vm
fraction contained also other by-products of the reaction.
The effective flocculation range (E.F.R.) was found in
the plus 0.01 kxm fractions. Therefore the size distri-
bution of polymer molecules in the effective flocculation
range could be calculated on the basis of the absorbance
differences, excluding the absorbance of the minus 0.01 km
fraction, as shown in Table 6.3.
Conclusions: The results on Fig. 6.4 (a, b and c)
and table 6.2, had clearly indicated that PAM had reacted
with GBMA and formed new polymers. Table 6.2 also shows
that PAMG 2.1 had the highest extent of reaction while
table 6.3 indicated that PAMG 2.1 consisted of molecules
of wide size-range. The larger size fractions were
usually more effective flocculants than the smaller
fractions. From the u.v spectra, a new absorption
peak or "hump" had appeared between 280-265 mu, which
did not appear in GBHA nor PAM nor methylolated PAM in
Fig. 6.5. It is interesting to note that the dispersion
Membrane
size, v.m
absorbance Size fraction
im
absorbance
difference
absorbance
difference %
size distribution
of E.F.R.
1.0 0.47 - 1.0 + 0.3 0.05 10.6 20.4
0.3 0.42 - 0.3 + 0.2 0.045 9.6 18.4
0.2 0.375 - 0.2 + 0.05 0.03 6.4 12.3
0.05 0.345 - 0.05 + 0.01 0.12 25.5 48.0
0.01 0.225 - 0.01 0.225 47.9 --
Total 0.47 100.0 100.0
Table 6.3 Size distribution of PAMG 2.1 molecules in solutions, in terms of the
absorbance difference percent at 400 mkt.
179
of the solids residue of PAMG 2.1, PAMG 6 and PAMG 7 on
1.0 tam membranes also had effective flocculation properties,
which was probably due to some soluble polymer molecules,
glued to the solid particles.
6.5.4 Ultraviolet and infra-red s ectra
A. Ultra violet spectroscopy
The u.v. spectra of the dilute solutions of GBHA,
PAM, methylated PAM and pure PAMG 2.3 are recorded in
Fig. 6.5 (a-d), measured on the Perkin-Elmer double-
beam spectrometer. The tungsten lamp was used from
500-380 mkt and the deuterium lamp for 380-180 mkt. 10 mm
quartz cells were used. The GBHA spectrum in Fig. 6.5 a
has the characteristic absorption peaks at wave-length
442-420, 417.5, 290 and 240 mkt, which are in agreement
with published work (157).
The concentration of GBHA used
for this spectrum was 0.01% in methylalcohol; the solution
was heated to 70°C for 30 min. under reflux at pH 10.9,
using NaOH aq. solution,before recording the u.v. spectrum.
The 0.01% methanol solution was made from 0.1% methanol
solution of GBHA, previously heated at 70°C for 60 minutes
at pH 10.7. This treatment was carried out in order to
simulate the GBHA reacted in the PAMG 2.3 polymer. Since
it was noticed experimentally that the absorption of
GBHA increased at high pH and temperature especially in
the region 500-320 mkt, the effect of temperature was more
pronounced than that of pH. In Fig. 6.5 b, the u.v.
spectrum of PAM (0.01 % aq- solution), there is an
absorption peak at ni 195 mkt.; however, there is also
some absorption gradually increasing from 320-220 mki. The
180
2•
2-0 GBHA, pH 10.9 heated 30 min. at 70°C (0-01% soln. in methanol
U 1.5 c 0 L. 0
< 1.0
0.5
0 200 250 300 350 400
Wavelength (mpl 450 500
Fig 6.5a: Ultra violet spectrum of glyoxal-bis --- (2-hydroxyanill
U C 0 1 0 (4 0.5
1.0'
0 r
1 8 1
200 250 300 350 400 450 500 Wavelength (mp)
FIG 6.5b: Ultra violet spectrum of polyacrylamide.
1 82
1-5
PAM-1-1CHO Produc (0.01% solni co 1-0
<0•5
200 250 300 350 466i5.) Wavelength (m),J)
500
,FIG 6-5c: Ultra violet spectrum of methyloltated polyacrylamide.
urified PAM 2.3 (--0.05%)
1.5
1.0
0.5
op
183 A
bsor
banc
e
200 250 300 350 400 450 500 Wavelength (mp)
FIG 6.5 d: Ultra -violet spectrum of polyacrylamide -glyoxal -( 2 -hydroxyanil .)
184
spectrum of the methylolated PAM 0.01% aq. soln.) in
Fig. 6.5 c is rather similar to that of PAM except for
one extra absorption hump between 290-280 my. On the
other hand the spectrum of PAMG 2.3 ( 0.05% aq. soln.)
in Fig. 6.5 d, shows an absorption hump between 442-420 my,
280-260 mi and a peak at 204 my. By comparing these
spectra, the absorption at 442-420 my is the same as in
the GBHA spectrum; however, the 417.5 my in GBHA has
disappeard in the PAMG 2.3 spectrum. Also, the absorption
at 290 my in GBHA has disappeared in the PAMG 2.3 spectrum;
instead a new absorption between 280-260 my has appeared,
which is characteristic to the new polymers. For example,
in Fig. 6.4, the absorption at 280-270 mi for PAMG 2.1,
PAMG 6 and PAMG 7 appears to varying extents. This is an
indication of the reaction between PAM and GBHA with
formaldhyde.
B. Infra-red spectroscopy
The infra-red spectra of pure PAMG 2.3, PAM and GBHA
were recorded in Fig. 6.6 (a-c).. Samples of the dry
powder of these compounds were dispersed in potassium
bromide discs. The samples discs were prepared as follows:
5 mg of each of the dry powder samples was mixed and ground
with 400 mg KBr (infra-red grade) in a small vibratory
mill (lined with tungsten carbide) for 1 min. Then 202.5 mg
samples of each of the ground mixtures (containing 2.5 mg
sample and 200 mg KBr) were placed in a die, where 6.8 ton/sq.
inch pressure was applied for 1-2 minutes, in a manual
hydraulic press. The discs were then carefullyextracted
from the die and evacuated in a vacuum desiccator over
185
P205 for 2-3 days before recording their infra-red
spectra against a 200 mg KBr disc as a reference. The
discs were stored in a desiccator over silica gel for
re-investigation purposes. Details of preparing sample
discs with alkali halide are described in the literature075)
The infra-red spectrometer used was the double beam
spectromaster made by Grubb, Parsons and Co. Ltd.,
Newcastle upon Tyne, (G.B.).
Results and discussion, Inspection of Fig. 6.6 c
shows that the spectrum of GBHA against KBr is in good
agreement with published work (157) and that the sample
used in this work was probably a mixture of GBHA and its
sodium salt. According to Bayer (157) the absorption
band at 2.94 kam (3400/cm) is due to the N-Hbond, whereas
the absorption band at 6.1 km is characteristic'for the
C = N double bond. However, it seemed from the literature
076,177,178) that the N-Hstretching bond invariably
absorbs in the region 2.86-3.24 dam and the absorption
region of 5.95-6.1 was assigned by some authors(177) to
C = 0 stretching bond in the amide structure. The
absorption at 6.2-6.3 was suggested to be due to N-H
deformation. The C - N stretching bond absorbs in the
regions 6.45-6.7 -km and 7.15-7.8 tam. These absorption
regions were noticed in PAM spectrum (Fig. 6.6 b). In
the spectrum of pure PAMG 2.3 polymer, a new absorption
peak appears between 9.65-9.85 vm, namely at 9.7 um which
also appears in the GBHA spectrum. The spectrum of PAMG 2.3
against PAM was also recorded (Fig. 6.6 d). It was
expected that the difference spectrum would be due to
WAVE LENGTH ( pm)
3-3.15 rn :4 -4
— (3)
W
• FIG 6.6a: Infra-red spectrum of PAMG 2:3 using KBr as a reference.
'
i i co ti
0 40 z
0
100
0 8 03
60 -0
0 40 z
2
0
2. 5-3.17 ,J — Crl
Ob lJ
u.' r N.) cr)
FIG spectrum
6.61D:infra-red of PAM
KBr as a reference using
I 1 ti (4)
100
X 60
100
» 80 CD (J1 o :;u 60 -0 -1
040 L
~ 20
o
I
I I I
/ ! !
~} J
100
J> 80 (0 tn o ::0 60 U -I
040 Z
f-------
I I
I
7
/"
I I
I
~
I
'" I i
""fJ~ 1\ ~ ~ N.r-.. OlN
r\
v V\ ~
--- 'v
WAY
w ~
Ih -::::J "---.
'" "--
I I I
-~f
;-l ~) l~
m ~\ w I~ . 0'1 Ul
I ..... ~
11 0"1
--" 1/ W W -:-: ~ Y
~ i--. to Ul
~ CP
I I "¥.) ,I \
i~ Ii ~ V V v~ ~ ~\ II <:p' ~
FIG 6·6c: Infra-red spectrum Ul
of GBHA using KBr as a .r-.. U1
I reference.
Ir~ \ ...... ...... ...... (Q I\) t\) <0 ...... ...... tv ......
E LENGTH ( }Jm
I
FIG 6·6d : tnfra~red spectrum of PAMG_2·3 using P~.M as a
to
refer'ence. .- .--
()) co --0'1 0
~
f\ i 1\ ~ ""I'.... /
~ " u '-~!I VI
I .r-..
~ f\ I ...... ...... I\) t\) 1.1 - ......, <0 ...... ...... -...
<0 -...
tGO
» no OJ0 Ui o :rJ 60 U --(
040 Z
~20
a
.--I
I
( ! I
-...
100
» 80 CD (j')
I /i\ ~I -t-r \A I I
I I I ~ I ~
"'-I--- J ~ I I
I
~60 -0
..... --(I ~ -i I
-40 o Z
'CR. 20
IV W
I \~ w ~ (
j I "1\ ( -
m "'-J
f~ CPW, lD ~ ... ::: n )ill/i:~ --~ . w Ul "'I~:'>"'~ 11'111 Ul
f I L\ /'\ t\ I \ ~ I, W ·W ~
IIj ;V"-..1
~;\j ~r '-' ~ ' -....J L.n
v:':" CP V ~I
----v~
Ul . Ul
Ul . Ul'-J
f\
..... .....
vVAVE LENGTH (}Jm)
en .. : U1
":'1
rJ ~ U1
v
I~ 1\
w ~
0:> 0:> 0 c» W 0:> W --
::;l? Ul
'-JlD
- ~ IlD ~ ~ iLJ
~ vVU
U
..... .....
lD U1
. FIG 6·70 :Infra-red spectrum of a 2:1 mixture of PAM and G B HA using KBr
.-
as a reference. .
: I ..... "
Ww u,~
~N
FIG 6'7b: Infra -red spectrum of a 2:1 mixture
"- \ of PAM &GBHA usingPAM as a reference. I
~ lD
~ W
Ul ~ .,IV'- --.~ .....
"
189
the new groups in PAMG 2.3. It was not possible, however,
to determine the exact structure of the PANG 2.3 by
examination of the 1.r. spectrum.
In order to check that PAMG 2.3 was not just a mixture
of PAM and free GBHA, a mixture of GBHA and PAM dry powder
of the ratio 1:2 was dispersed in KBr and made into a disc
following the same method mentioned earlier. The spectra
of the mixture against KBr and PAM as references were
recorded in Fig. 6.7 (a,b). Comparison of these spectra
with those of Fig. 6.6 (a-d) reveals at once that PAMG 2.3
was a reaction product between PAM and GBHA and not a
mixture. It should be remembered that the initial molar
ratio of GBHA/AM (PAM) used in preparing PANG 2.3 was
about 0.3:1, whereas the initial molar ratio used in
preparing PAMG 2.1 was about 0.6 : 1. PAMG 2.1 was used
throughout the flocculation experiments on the copper ore
reported in Chapter 7.
6.5.5 Degree of substitution
In principle, the number of GBHA groups per 100
acrylamide monomers i.e. the degree of substitution in
the PAMG polymers, could be estimated from the change in
the atomic ratio of nitrogen to carbon WO. In the
unmodified polyacrylamide, the acrylamide monomer theore-
tically contains 3 carbon atoms (total atomic weight 36)
and one nitrogen atom (at. wt. 1!t); hence the ratio N/C is
1 4 6- equal to -5- i.e. 0.389. If the molar ratio of GBHA/AN
in the PANG polymers was 1/1, that is one GBHA group per
one AM monomer, the PANG monomer would contain 18 carbon
(at. wt. 216) and 3 nitrogen atoms (42); therefore the N/C
190
ratio would be = 2 0.194. Thus for 100% substitution,
the change of N/C ratio would be = 0.38888 - 0.19444 =
0.194, and for 10% substitution, the change of N/C ratio
would be 0.0194, and for 1.0% substitution the change in
N/C ratio would be equal to 0.00194 and so on. On the
other hand if the molar ratio of GBHA/AM was 1/2, that is
one GBHA was attached to two amide groups of two acrylamide
monomers, the PANG monomer would contain 11 carbon atoms
(at wt. 132) and 2 nitrogen atoms (at wt. 28); hence the
N/C ratio would be 28/132 = 0.212. Thus for a 100%
substitution, the change of N/C would be 0.3888 - 0.21212
= 0.17676, and for 10% substitution, the change of N/C
would be 0.017676, and for 1.0% substitution, N/C change
would be 0.00177, and so on.
Thus depending on the structure of PAMG polymers, that
is on whether each GBHA group had reacted with one or two
amide groups, the N/C ratio could be used to estimate the
degree of substitution.
Experimental: Three samples of PAMG 2.3, PAM and
alkali-treated PAM were analysed for the carbon and nitrogen
contents by the Microanalytical Laboratory at Imperial
College, London. The purpose of analyzing the alkali-
treated PAM was to establish whether there was any change
in N/C ratio prior to the reaction with GBHA during the
preparation of PAMG 2.3 polymer. Thus 50 ml of 1.0% PAM
aqueous solution was kept at pH 10.5 for 1 hour at an
average temperature of 65°C under reflux. After cooling
to room temperature, the polymer was precipitated in 100 ml
ethyl alcohol and the precipitate was dried at 80°C overnight.
191
The dry solid was ground to powder in an agate mortar and
pestle.
Results: The analysis of the three samples for carbon
and nitrogen contents were shown in Table 6.4. The
accuracy was stated to be on each element ± 0.3%. The
change of N/C ratio of PAMG 2.3 from PAM was = 0.0131.
Therefore the degree of substitution of PAMG 2.3 •
calculated on these figures would probably be 6.6% or
7.4% depending on whether the imolai ratio of GBHA/AM
was 1/1 or 1/2.
Table 6.4 Microanalysis of PAM, PAMG 2.3 and alkali-treated
PAM.
Polymer PAM PAMG 2.3 Alkali-treated PAM
carbon% 42.41 44.01 46.03
nitrogen% 16.69 16.80 17.26
N/C 0.3948 0.3817 0.3753
N/C, change
in relation to - 0.0131 0.0195
PAM.
However, when the limits of error of the analysis are taken
into account, the result must be treated with caution, as
the change of N/C is within the experimental error and the
analysis was made only once.
192
6.6. Selective flocculation pro e ties of PAMG 2.1
The selective flocculation properties of PANG 2.1
were tested in suspension media containing competing
ligands at pH 10.5, following the principles laid down
in Chapter 5. The competing ligands used were "Calgon"
a sodium hexametaphosphate, an oxygen donor ligand and
"Dispex N40", believed to be a polyacrylamide and sodium
acrylate copolymer of average molecular weight between
2000 and 4000; (Allied Colloid Chemicals Ltd).
The experimental procedure followed throughout the
tests can be summarized as follows. About 1% suspension
of fine particles of the minerals or mixtures of minerals
were made in distilled water. The required amounts of
Calgon or Dispex N40 (or both) were added in dilute
solutions and the suspensions were dispersed with a
magnetic stirrer at high shear rate at pH 10 for approx-
imately 10 min. The suspensions were transferred to a
cylinder where they were kept still for 5 minutes; then
the suspensions were decanted back into the beaker and
settled particles were rejected. The pH of the
suspensions was checked before adding the flocculant
PANG 2.1, while stirring at high shear rate for lmdnute
in order to disperse the flocculant,and at low shear-
rate for a further 1 min; then the flocculation sus-
pensions were transferred again into the cylinder, where
slow rotations were performed for a few minutes and
flocculation was observed visually in the cylinder.
193
Results:.
6.6.1 Flocculation effects on minerals sus ensions
at pH 10.
1. Calcite was not flocculated by 6 p.p.m. PAMG 2.1 in
the presence of 300 or 200 p.p.m. Calgon; however, in
the presence of only 50 p.p.m. Calgon, calcite was
flocculated.
2. Quartz was not flocculated by PANG 2.1 and even in
the absence of Calgon at pH 5.
3. Feldspar was inhibited from flocculation with 5. p.p.m.
PAMG 2.1 by 300 p.p.m. Calgon but not with 200 or 100
p.p.m.
4. Dolomite was inhibited from flocculation with 5
p.p.m. PANG 2.1 by 350 p.p.m. Calgon at pH 10.5;
also 20 and 50 p.p.m. Dispex N40 inhibited its
flocculation with 10 p.p.m. PANG 2.1.
5. Chrysocolla and malachite were flocculated in the
presence of 350 p.p.m. Calgon at pH 10 and 10.5 by
2-3 p.p.m. PANG 2.1.
6. Chalcocite was flocculated with 1 p.p.m. PANG 2.1
In the presence of 350 p.p.m. Calgon.
7. Chalcopyrite was flocculated with 1-2 p.p.m. PANG 2.1,
in the presence of 350 p.p.m. Calgon, leaving slightly
turbid supernatant which did not flocculate even at
high doses of PANG 2.1 and PAM. The flocculated portion,
1914
however formed strong and large flocs. The turbidity
was probably due to impurity minerals.
8. Cuprite was partly flocculated with 1-2 p.p.m.
PAMG 2.1 in the presence of 350 p.p.m. Calgon.
The flocculated portion formed strong flocs, while
the turbid supernatant remained stable even at
6 p.p.m. PANG 2.1.
Thus in the presence of a competing ligand, namely
Calgon, the selectivity of PAMG 2.1 to copper minerals
against common gangue minerals in the form of feldspar,
calcite, quartz and dolomite was proved.
6.6.2 Selective flocculation of copper minerals
from mixed suspensions at pH 10.
1. Chrysocolla from calcite: A mixture of chrysocolla
and calcite of ratio 1:1 by weight was treated with 300
p.p.m. Calgon. Chrysocolla was strongly flocculated with
2.5 p.p.m. PANG 2.1, while calcite remained suspended.
The green flocs of chrysocolla re-formed readily after
re-dispersing the suspension while no white flocs were
noticed to form. The same results were achieved in the
presence of 200 and 1000 p.p.m. Calgon.
2. Mixed suspension of calcite, feldsp_a tz was
inhibited from flocculation with 7 p.p.m. PANG 2.1 by
350 p.p.m. Calgon.
3. Selective flocculation of chrysocolla and malachite
from mixtures with feldspar, calcite and quartz was
achieved with 2-3 p.p.m. PAMG 2.1 and 350 p.p.m. Calgon.
195
The green flocs re-formed readily after redispersing the
suspension, but they became smaller in size after 2 days.
4. Selective flocculation of chalcocitet. malachite and
chrysocolla from mixtures with feldspar, calcite and quartz
was repeatedly achieved with 2-3 p.p.m. PANG 2.1 in the
presence of 35❑ p.p.m. Calgon or 50 p.p.m. Dispex N40
or both. The flocculation was more rapid at higher doses
of PANG 2.1 ( ?„. 5 p.p.m.) and the floes re-formed again
after re-dispersing the suspension even after a period of
few weeks.
5. Selective flocculation of malachite from mixtures with
dolomite was achieved with 3-4 p.p.m. PANG 2.1 (and
PANG 2.3) in the presence of 50 p.p.m. Dispex at pH 10.5.
The settling rate of some malachite floccules was rather
slow, but was improved by increasing PAMG 2 dose up to
6 p.p.m.; meanwhile the dolomite particles remained
suspended.
From these examples the PAMG 2.1 polymer was con-
sidered a selective flocculant for copper minerals and
was later used to separate copper minerals from a dolomitic
ore; the details and results of the process are described
in Chapter 7. Flocculants PAMG 6 and PAMG 7 were also
used in the separation of copper minerals from the dolomitic
ore by selective flocculation.
6.6.3 The comparative selectivity of PAMG 2.1
A series of experiments was run following the same
procedure as_in 6.6.1, at pH 10 in the presence of 350
p.p.m. Calgon to study (1) the selectivity of PAM to
196
copper minerals, and (2) the improvement in selectivity
due to reaction with GBHA, by comparing the flocculation
effects of PAM.with those of PAMG 2.1.
Results: PAM flocculated a mixture of chrysocolla
and malachite with 2 p.p.m., but partly flocculated
suspensions of feldspar, calcite and quartz with 1-2
p.p.m.; with PAMG 2.1, however, there was no flocculation
of suspensions of feldspar, calcite and quartz even at
7-10 p.p.m.
In a mixed suspension with feldspar, calcite and
quartz, PAM flocculated chrysocolla and malachite (forming
green flocs) but with also some (separate) white flocs at
1-2 p.p.m., whereas with PAMG 2.1 there were no white
flocs. From these experiments, it can be concluded that
PAM had shown some selectivity to copper minerals, but
the modified PAM, namely PAMG 2.1, was more selective.
PAM, presumably being a strong hydrogen bonding agent
(as shown in appendix 3 ), is more capable of binding to
minerals like calcite, feldspar and dolomite than PAMG 2.1.
Possible improvement of PAM selectivity would therefore
need the expense of using vast quantities of depressants.
This was confirmed when PAM and PAMG 2.1 were later
tested under identical conditions on two separate samples
of the dolomitic copper ore (cf. Chapter 7). In those
experiments, PAM flocculated 48% of the total weight of
the ore sample and upgraded the copper content from
5.8% to 9.1%. In contrast, PAMG 2.1 flocculated only
18% of the total sample weight and upgraded the copper
197
content from 5.18% to 16.0%. The "enrichment ratio"
(CuGo in concentrate \ C140 in feed ) obtained with PAM was about 1.56, and
with PAMG 2.1 was 3.1. The "selectivity ratio"
(Cu°0 in concentrate \ 9.1 011°0 in tailings ) was 1.45 - 6.28 for PAM, compared
with 16"08 = 8.9 for PAMG 2.1.
6.6.4 The role of unattached GBHA groups on the
flocculation behaviour of meth lolated PAM
A series of experiments was carried out in order to
establish. whether the selectivity shown by PAMG 2.1 might
have been due to the methylolated PAM, perhaps also
activated by unattached GBHA groups or their by-products.
Thus samples of the reaction product of GBHA and formald-
hyde "Product I" in 6.3.1, and methylolated PAM "Product
II" (also in 6.3.1), were tested for flocculation on
suspensions of malachite, chrysocolla, calcite and feldspar.
The flocculation procedure was essentially the same as
described in 6.6.1; i.e. using 350 p.p.m. Calgon at pH 10.
The doses of GBHA "Product I" used were twice that of
methylolated PAM "Product II" to correspond to the proportion
used in the preparation of PAM 2.1.
Results: Malachite and chrysocolla mixed suspension
was flocculated with a mixture of 2 p.p.m. "Product II"
and 4 p.p.m. GBHA "Product I", leaving slightly turbid
supernatant compared with clear supernatants obtained
with PAM in section 6.7.3. Feldspar and calcite suspensions
were noticed to start flocculation when the mixture con-
centration was 2 p.p.m. PAM "Product II" and 4 p.p.m.
GBHA ."Product I". Flocculation was increased gradually
as the doses of the two products were increased gradually
198
up to 6 p.p.m. PAM "product II" and 12 p.p.m. GBHA
"Productl", where partial flocculation of the suspensions
occurred.
6.7. Conclusions:
PANG is a less powerful flocculant for feldspar and
calcite than a simple mixture of methylated PAM and GBHA-
formaldhyde product. Increasing the dosage of PAMG 2.1
up to 10 p.p.m. still did not flocculate feldspar and
calcite.
The reaction conditions in the preparation of
PAMG polymers were not optimized and higher degrees of
substitution could possibly be obtained for PAMG polymers.
However, very high degrees of substitution may not be
essential for obtaining the desired properties; for
example, most of the commercially produced cellulose
xanthates have a:degree of substitution of 50, which
corresponds to about 16.7% of the number of reactive
OH-groups, yet it is sufficient to change the cellulose
polymer properties completely.
It should be possible to graft GBHA onto water-
soluble polymers such as polyvinylalcohol (PVA), starches
(e.g. amylose) and polyvinyl pyrrolidone (PVP), since they
too react with formaldhyde(161)
If GBHA groups are attached to lower molecular weight
polymers, selective dispersants and depressants for copper
minerals (or ions) could be obtained.
Similarly, there are many chelating groups selective
to copper ions which could be grafted onto various long-
chain polymers to obtain a large number of selective
199
flocculants. These principles can also be applied to
many other cations and their corresponding minerals.
200
CHAPTER 7 PROCESSING OF COPPER ORES BY SELECTIVE FLOCCULATION
7.1 Introduction
In treating a poly-disperse suspension by selective
flocculation, all minerals should have similar electrical
charge (either negative or positive) to avoid the
possibility of hetero-coagulation. For example, in a mixture
of calcite (z.p.c. pH 9-10)(17 , malachite (z.p.c. pH
9-9.5) and quartz (z.p.c. pH 2-3), hetero-coagulation
would be expected in the pH region 2-9 or 10. In order to
avoid this happening, the pH must be 10 or E 2. It is
obviously impracticable to maintain the mixture at the low
pH (problem of dissolution); therefore the appropriate pH
should be 10.
One of the essential requirements for the selective
flocculation process is that the suspension must be well
dispersed and comparatively stable. However, the stability
period of the suspension need not be longer than that needed
for selective flocculation to be carried out. To induce
stability, the zeta--potentialof the minerals must be
strongly negative and the ionic strength low. Since the
zeta-potential acquired by the minerals, even at high pH,
is not usually high enough to keep the suspension stable,
the use of low molecular weight dispersants is necessary.
In Chapters 1 and 2, it has been shown that natural
minerals, suspended in water, usually release some ionic
species common to their lattice structure and these ions
behave differently at different pH values, forming various
201
hydroxy complexes. These ionic species may adsorb
specifically or randomly onto other minerals in the
suspension. These effects could become more complicated
in the presence of contaminating species, originally
adsorbed on the minerals and the possible interaction of
the various ionic species. To prevent the interference
of these ionic species with the selective adsorption of
the flocculant, the use of masking agents would be
necessary.
In the flocculation experiments, "Calgon" and "Dispex
N40" were used as multi-function reagents. As well as
masking the various soluble cationic species, they can
also adsorb on the solids surfaces at high pH values,
thus increasing the zeta-potential. This effect was
recorded on malachite suspension in Chapter 2. The
adsorption of these reagents can also result in
inhibition of flocculation by competing with the flocculant
groups for the surface sites on the minerals.
Criteria of selectiva. Assessment of the performance
of the flocculation processes on a plant can be described
by the "grade" and "recovery" of copper in concentrates.
In developing the present experiments, the absolute values
of grade and recovery were not adequate description of the
various facets of the performance. Therefore, two more
terms were found useful, besides the copper grade in the
tailing, to assess the selectivity of the process. These
terms are:
a) "Selectivit ratio": which is the ratio of the
copper grade in the concentrate to that of the tailings;
202
b) "Enrichment ratio": which is the ratio of the
copper grade in the concentrate to that of the untreated
ore (feed).
Thus in judging the performance of the selective
flocculation process, the following criteria were employed:
the weight of each of the flocculated concentrates and
tailings, copper grade and recovery in both the concentrates
and tailings, enrichment and selectivity ratios.
Materials and equipment:
1. The eepperare: A sample of a dolomitic copper ore
from the Congo, kindly supplied by Charter Consolidated Co.,
was investigated. The ore was stated by the company to
consist of malachite, chalcocite, chalcopyrite, neodigenite,
covellite and chrysocolla as copper minerals, with dolomite,
quartz, calcite, pyrite and rhodocryiocite as gangue minerals
as well as heterogenite080
and traces of some unidentified
cobalt minerals. A preliminary mineralogical examination
supplied by the company is given in Table 7.1. According
to a report from the company, the copper sulphides are
not associated with gangue minerals to a significant
extent and their liberation is good, although chalcocite
and neodigenite are often intergrown in composite grains.
Malachite, on the other hand is associated with the
carbonates and mainly with dolomite. The liberation
size of malachite and the size distribution of the various
copper minerals were not reported. The determination of
the size distributions and the liberation size for copper
minerals was not performed in this work either, since
the main concern at that stage was to establish the funda-
203
Table 7.1 Approximate mineralogical of the
Edolc2jLLLcsa2ptrIEt
Mineral 12r....9.221..i
Malachite 3
chalcocite 3
neodigenite 3
chalcopyrite < 1
covellite < 1
pyrite < 1
rhodocriocite <1
dolomite 20
calcite 1
quartz 70
204
mental aspects of the selective flocculation process.
However, it is firmly believed that knowledge of the
liberation size will certainly help to improve the
results. The typical particle size of a dry ground sample
of the ore, shown in Fig. 7.1, was generally below 10
microns and mainly in the 1-2vm range. There was an
appreciable number of particles in the sub-micron range.
The copper content in the ore sample was about 5.0%.
2. The flocculants: PAMG 2.1, PAMG 6 and PAMG 7 were
used "as prepared" in Chapter 6,1.e., they were not purified.
The concentration of the polymers in solutions was 0.1%
based on the original weights of PAM used in their
preparation.
3. The flocculation apparatus: This apparatus consisted
of a glass cylinder either 5 cm or 10 cm in diameter and
42 cm total length, including a conical discharge outlet,
as shown in Fig. 7.2. In designing this cylinder, it is
arranged that the angle of joining the conical part with
the cylindrical part was high so that the flocs could
slide along smoothly without hinderance. The rotating
system consisted of two steel rollers about 3 cm x 9 cm
each (total length 14 cm), connected with a variable
speed motor. The distance between the rollers was about
3 cm. The whole system was mounted on a pivoted metal
support about 11.5 x 32.5 cm so that the inclination
angle could be adjusted. The total length of base was
40.5 cm. Separation of suspensions from the flocs was
•
G. S
•
4 0
0 5
4 •
• '7) •
a
•
10 tim
FIG. 7.1: PHOTOMICROGRAPH OF ZAIRE OXIDIZED COPPER ORE, AFTER FINE GRINDING (AS USED IN SELECTIVE FLOCCULATION TESTS).
FIG. 7.2: LABORATORY CONDITIONING APPARATUS FOR IMPROVING SELECTIVE FLOCCULATION SEPARATIONS.
206
'done by either vacuum suction or introducing water jets,
as shown in Fig. 7.2. However, to avoid dilution in the
flocculation experiments, the vacuum suction was preferred
The purpose of this apparatus was to favour the
growth of the floes and to aid their separation as well
as releasing some of the entrapped particles. At the
start of flocculation, the inclination angle of the
cylinder should be small to minimize the travel of the
flocs. By increasing the angle at a later stage, the
flocs could be made to move to the discharge outlet,
leaving the suspension above.
The role of the slow rotation of the inclined
cylinder in increasing the floc growth and the release
of entrapped particles was first observed and described
by Yarar and Kitchener( 2' 179).
4. Micronizin mill: A laboratory vibratory mill
from McCrone Research Associates Ltd., London) was used
for the wet grinding of the ore samples up to 10 g in
40 ml of water. The grinding elements in this mill are
stated by the supplier to be of fine-grained non-porous
sintered corundum (alumina) and are contained in a
125 ml polythene jar. Some abrasion of the polythene jar
due to grinding was noticed. The abraded particles
appeared floating on the suspension surface and were
skimmed before commencing the flocculation experiments.
5. Agate mortar and porcelain mill: The agate mortar
was used in the dry grinding of small samples, and
the porcelain mill in the wet grinding of larger samples
(up to 41 g). The grinding medium was porcelain balls,
207
cleaned with conc. HC1 and washed with distilled water
several times before use.
6. 2ihprapR22 An ultrasonic probet ma.gxietic stirrer, light
absorption spectrometer, glass beakers and cylinders were
also used. An atomic absorption spectrometer was used
for the determination of copper content in solutions
prepared from the minerals. Dissolution of minerals for
use with atomic absorption is described in Appendix 2.
7.2 Preliminary investigations
A small sample of the ore was dry ground in an agate
mortar and made into approximately 1% suspension with dist.
water containing 350 p.p.m. Calgon at pH 10.5. When this
suspension was treated in the same manner as that in
Chapter 6.6 - much of the ore sample was flocculated
unselectively by 1 p.p.m. PAMG 2.1 - contrary to
expectations based on the previous tests with separate
minerals or synthetic mineral mixtures.
This observation led to a study of the difference
between an ore and a synthetic mixture. In an attempt
to understand the difference, the possible differences
were rationalized as overleaf:
208
Ore Synthetic mineral mixture
1 The minerals have been exposed
to the same geological con-
ditions i.e., weathering etc.,
which may result in altering
the minerals to different phases
The minerals are usually from
different origins, and were not
exposed to the same geological
conditions as the ore; the
degrees and kinds of alter-
ations may be very different.
2 The minerals may contain
traces of different ionic
species and possibly colloids
as contamination,
The minerals may also be con-
taminated but it may be
entirely different kinds and
degrees of contamination.
3 The minerals are ground to- gether; problem of slimes
coating and smearing of
minerals are familiar in
mineral processing.
The minerals are essentially .
ground separately.
4 The proportion of copper minerals may be low.
The proportion may be higher.
209
The following steps were taken, to investigate
factors 1, 2 and 4 by simulating the ore and checking
selective flocculation. Thus a mixture of
(a) uartz dolomite calciLl_aaallpariLa of the.same
proportions to those in the ore (i.e. approximately
7 : 2 : 0.1 : 0.1) was made into a 1% suspension with
distilled water containing 350 p.p.m. Calgon at pH 10.5.
When the suspension was treated with the flocculant in
the same manner as before, no flocculation was noticed
even at 7 p.p.m. PAMG 2.1.
A mixture (b) of chalcocite, malachite, chrysocolla
2.0. 22.2129- 1pyriteof the proportions 6 : 3 : 2 : 1 was made
into a 1% suspension and treated as before. Flocculation
was noticed to start at 1 p.p.m. PAMG 2.1 and increased
at 2-3 p.p.m.
Then a mixture (c) of all minerals of mixtures (al
ana_021, also of a similar proportion to those in the ore, was treated as in mixtures (a) and (b). However,
the flocs did not form immediately as in the previous
synthetic mixtures in Chapter 6, where copper minerals
were in higher proportions. Instead, they formed in
appreciable amount only after about 10 minutes of slow
rotation; no white or black flocs were seen to form, and
only grey-to-green flocs of the copper minerals were
formed. This indicated that selective flocculation of
copper minerals from the ore was feasible.
The slowness of the rate of flocculation might be
explained in terms of the rate of collision of the copper
minerals particles, which depend on. the probability of
210
collision between these particles. The probability of
collision is a function of the following factors:
(a) the rate and time of shearing (i.e. intensity),
(b) the hydrodynamic pattern of mixing, (c) solids content
in suspension, (d) proportion of copper minerals particles
in the suspension, and (e) the particle size distribution.
With an ordinary magnetic stirrer at a constant moderate
shear-rate, there can be a situation of non-collision
between two copper mineral particles moving at a distance
with the rotating mass of suspension. The higher solids
content and particles size distribution (i.e. amount of
fine particles) would increase the viscosity of the
suspension which might present physical hindrance to
collision. It can be concluded that with high solids
content suspension containing fine particles and a small
proportion of copper minerals, good mixing techniques
and high shear intensity would be necessary to obtain a
high rate of collisions and hence a high rate of
flocculation.
To investigate the significance of factor (3), that
is the effect of co-grinding, again a model of the ore
was simulated by a synthetic mixture of the major
minerals in the same proportions as the ore. A small
sample of this mixture was dry ground in an agate mortar
for 1 hour, then tested for flocculation in a similar
fashion to that of mixture (c) earlier. Much of it was
Immediately flocculated unselectively by 1 p.p.m. PAMG 2.1.
In another experiment, the co-ground mixture suspension
was dispersed with an ultrasonic probe at high energy for
211
3 min., and with magentic stirring at high shear-rate
for 2 min. before adding the flocculant. Again much
of it was flocculated unselectively by 1 p.p.m. PAMG 2.1.
From these experiments the important problems were
seen to be (1) the effects of dry-grinding, (2) the effect
of the proportion of copper minerals in the ore, and
(3) the effect of contaminations naturally found with an
ore. These problems were overcome as follows:
(1) wet grinding in the presence of dispersants at high
pH, (2) improving the collision rate by increasing the
shear-rate during flocculation, and (3) use of greater
amounts of Calgon and Dispex N40.
Experimental:
In three experiments, 3 samples of 5 g each were
ground in the McCrone mill with 40 ml dist. water at
pH 10.5 containing (1) 50 p.p.m. Dispex, for 35 min.,
(2) 350 p.p.m. Calgon for 30 min, and (3) 350 p.p.m.
Calgon and 50 p.p.m. Dispex for 30 min. Small parts of
these suspensions were diluted to 50 ml to make the
following solids content: 1.4%, 2.0% and 1.3% respectively.
The reagents were adjusted accordingly by the same ratio.
1 p.p.m. of PAMG 2.1 was added to each suspension, while
stirring at high shear-rate for 1 min. and at low shear-
rate for a further 1 min. The suspensions were then
transferred to 250 ml cylinders where they were diluted
to 200 ml and rotated slowly for about 5 min. The
flocculated portions ('boncentratd) were separated from
the suspensions ("tails") by decantation, then dried,
weighed and assayed for copper.
212
From the results shown in Table 7.2, experiment (3)
(using both Calgon and Dispex) gave the highest copper
grade in the flocculated fractions. It was decided,
therefore, to use both Calgon and Dispex in the grinding
and flocculation circuits at pH 10.5-11.
Table 7.2 Results of experiments 1-3
Products Wt. % Cu % Cu-distribution % gip' o.
1 conc. 22.5 8.5 43.5
tails 77.5 3.2 56.5
calc. heads 100.0 (4.39) 100.0
2 conc. 17.0 8.5 32.2
tails 83.0 3.5 66.8
talc. heads 100.0 (4.35) 100.0
3 conc. 5.1 15.0 14.4
tails 94.9 4.8 85.6
talc. heads 100.0 (5.32 100.0
In all the following experiments, grinding was carried
out in the McCrone mill except in experiment 25. Also,
400 ml beakers were used for suspensions volumes between
200-300 ml, and 250 ml glass beakers for volumes between
50-150 ml.
7.3 Design of flow-sheets for selective flocculation
arocess
The flow-sheets attempted in this work were somewhat
analogous to those of froth flotation, in that they
213
included rougher (R), cleaner (C1), recleaner (Reel) and
scavenger (Sc) stages. Each stage was preceeded by a
dispersion (D) process. Several flow-sheets were attempted,
with the combined variations in the levels of "conditioning"
reagents, flocculent dose, mode of addition of reagents
and the shear-rate.
7.3.1. Flow-sheet
This flow-sheet, shown in Fig. 7.3, consisted of 3
stages of flocculation namely; rougher, cleaner and
scavenger, each preceeded by a dispersion process. This
flow-sheet was attempted in two experiments, 4 and 5.
Experiment 4: 5 g of the ore sample was ground in
40 ml dist. water containing 350 p.p.m. Calgon and 50
p.p.m. Dispex at pH 10.5 for 1 hr. The suspension was
diluted to 250 ml (i.e., 2% solids) and the concentrations
of reagents were readjusted accordingly. The suspension
was stirred at high shear-rate by a magnetic stirrer for
5 min. and was left still in the beaker for further 5 min.
The purpose of this step was to estimate the amount of
coarse particles present in the suspension which might
interfere with the flocculation process. The coarse
particles were separated from the suspension by decantation;
when dried, this fraction was about 8% of the total sample
weight. This fraction was not used in the experiment.
The suspension was treated with 1 p.p.m. PAMG 2.1 while
stirring at high shear rate for 1,5 min. then at low
shear-rate for 2 min., followed by 7 min. of slow rotation
in a 250 ml cylinder. The flocculated portion was recovered
by decantation and washed with 50 ml dist. water while
214
stirring for 5 min. The flocculated fraction (Cl.conc.)
was recovered, dried and weighed. The concentrations of
Calgon and Dixpex were readjusted to 350 p.p.m. and 50 p.p.m.
respectively at pH 10.5 in the suspension (300 ml). 0.5 p.p.m.
PAMG 2.1 was added during stirring at high shear for 2 min.
and at low shear for further 2 min. followed by slow
rotation in a cylinder (by hand) for 7 min. The flocculated
portion (Sc. conc.) was separated from the stable suspension
(Tails). The products were dried, weighed and assayed for
copper. The results are shown in Table 7.3. The total
consumption of PAMG 2.1, Dispex and Calgon in kg tonne
ore treated was: 0.087, 3.0 and 21.0 respectively.
Table 7.3: results of experiment 4
Products Wt. % Cu % Cu-distribution %
Cl. conc. 6.9 18.0 25.3
Sc. conc. 26.1 8.4 44.7
Tails 67.0 2.2 30.0
calc. heads 100.0 (4.9) 100.0
selectivity ratio = 8.2
enrichment ratio = 3.67
The results indicated that selective flocculation had
occurred but the recovery of copper in the concentrate
was rather low. Therefore an attempt to increase the
recovery, as described in experiment 5.
215
Experiment 5: A 5 g sample of the ore was ground in
40 ml dist. water containing 350 p.p.m. Calgon and 50 p.p.m.
Dixpex at p11 10.5 for 2 hrs. Part of the suspension was
diluted for 250 ml (to make roughly 3.6% solids) and the
doses of both Calgon and Dixpex were readjusted accordingly
(i.e. to 350 p.p.m. Calgon and 50 p.p.m. Dispex) at pH 10.5.
After stirring at high shear for 5 min., the suspension was
mixed with 1.5 p.p.m. PAMG 2.1, while stirring was continued
for 1.5 min. at high shear. The suspension was left still
in the beaker for 2 minutes, then the flocculated fraction
was recovered and washed with 50 ml dist. water during
stirring for 5 min., at high shear. The flocculated
concentrate (Cl.conc.) was recovered, dried and weighed.
The concentrations of Calgon and Dispex in the suspension
(300 ml) were adjusted to 350 p.p.m. and 50 p.p.m.
respectively at pH 10.5. 3 p.p.m. PAMG 2.1 was then
administered while stirring for 2 min. at high shear. The
suspension was left still in a cylinder for 2 min. followed
by slow rotation by hand for 10 min. The flocs (Sc. cone.)
were separated from suspension by decantation and were
dried and weighed. The total consumption in kg/tonne of
PAMG 2.1, Dixpex and Calgon was: 0.354, 4.16 and 29.1
respectively.
The results are shown in Table 7.4.
216
Ore suspension
Tails
Cl.conc.
Fig.7.3 Flow-sheet 1
Ore suspension
Flocculant
R Tails
Cl
Sc Sc.tail
Cl.conc. Sc.conc.
Fig.7-4 Flow-sheet 2:Bulk flocculation
217
Table 7.4: Results of experiment 5
Products wt. Cu % Cu-distribution %
Cl. conc. 63.4 7.4 92.0
Sc. conc. 0.8 0.75 0.1
Tails 35.8 1.10 7.9
calc. heads 100.0 (4.99) 100.0
selectivity ratio = 6.6
enrichment ratio = 1.48
The results showed an increased recovery of copper
in the Cl. conc. but the grade was rather low. Much of
the ore was flocculated (63.4%), and the selectivity
ratio (6.6) and the enrichment ratio (1.48) were not
high. An attempt to improve the performance of the
process was made in flow-sheet II.
7.3.2. Bulk flocculation rocedure• flow-sheet II
Experiments 6 and 7 were carried out following flow-
sheet II, illustrated in Fig. 7.4, which consists of a
rougher, a cleaner and a scavenger stage.
Experimental;
A 5 g sample was ground in 40 ml dist. water containing
400 p.p.m. Calgon and 100 p.p.m. Dispex at pH 10.5 for 2 hrs.
The suspension was divided into 2 parts, each of which was
diluted to 100 ml suspension and the concentrations of
Calgon and Dispex were adjusted accordingly at 400 p.p.m.
and 100 p.p.m. respectively, at pH 10.5. It appeared
218
later that the suspension used in experiment 6 contained
2.2% solids and that in experiment 7 contained 2.8% solids.
Experiment 6: After stirring for 5 min. at high
shear, the 100 ml (2.2% solids) suspension was treated
with 3 p.p.m. PAMG 2.1 and stirring was continued for
1 min. at high shear rate, then at low shear for 2 min.
followed by 10 min. of slow rotation in a cylinder.
The flocculated concentrate was separated by decantation
and redispersed in 100 ml dist. water containing 400 p.p.m.
Calgon and 100 p.p.m. Dispex at pH 10.5 by stirring for 5 min.
at high shear rate, followed by slow rotation in a cylinder
for 10 min. The flocculated fraction (Cl. cone.) was recovered,
while the decanted suspension- was allowed to flocculate
for further 10 min. under slow rotation in the cylinder.
The flocs,(Sc. conc.) were separated from the suspension
(Sc. tail). All samples were dried, weighed and assayed
for copper. The results are shown in Table 7.5. The
total consumption of PAMG 2.1, Dispex and Calgon in kg/tonne
was: 0.136, 9.1 and 36.4 respectively.
Table 7.5: results of experiment 6
Products ELt_i, Cu % La=c1LtLELlaIlaa%.
Cl. conc. 17.8 16.0 55.0
Sc.conc.
Sc. tail
3.8 7.8 5.7
28.2 4.0 21.8
fail 50.2 1.8 17.5
calc. heads 100.0 5.18) 100.0
selectivity ratio = 8.9
'enrichment ratio 3.1
219
The results indicated an overall improvement in the
performance. The grade in the concentrate was higher than
in experiment 5. Also, the enrichment ratio and selectivity
ratio were higher in experiment 6 than those of experiment 5.
Experiment 7.: In this experiment, ordinary poly-
acrylamide (PAM) was tested, in order to establish the
improvement in performance due to its modification to
PAMG 2.1. Thus the 100 ml suspension (2.8% solids) was
treated with 3 p.p.m. PAM, following the same procedure
and conditions in experiment 6. The results are shown
in Table 7.6. The total consumption of PAM, Dispex and
Calgon in kg/tonne was: 0.107, 7.15 and 28.5 respectively.
Table 7.6: results of experiment 7
Products Wt. Cu- distribution O
1. cone.
:c. cone.
1. tail
ail
calc. heads
48.1
6.3
34.0
11.6
100.0
9.1
9.1
2.2
1.45
(5.86)
74.5
9.8
12.8
2.9
100.0
selectivity ratio = 6.28
nrichment ratio = 1.56
irrlir'at,=,d that a large proportion of the
ore sample was flocculated compared with experiment 6. The
enrichment ratio (1.56) and selectivity ratio (6.28) were
low compared to 3.1 and 8.9 with PAMG 2.1 in experiment 6.
220
Although the reagents consumption in experiment 7 was
slightly less than in experiment 6, it is not likely
that the performance of PAM would be better or even
similar to that of PAMG 2.1 at the same or even higher
reagents consumption, as these flocculation experiments
were proved later to be not very sensitive to small
changes in reagents concentrations. Therefore it can be
concluded that PAMG 2.1 was more selective flocculant
than PAM.
7.3.3. Multi-stage flocculation; flow-sheet
This flow-sheet, as shown in Fig. 7.5, consisted of
one rougher and two cleaning stages, followed by two
scavenging stages of the two cleaners tailings.
Experimental:
An ore sample of 5 g was ground in 40 ml dist. water
containing 400 p.p.m. Calgon and 100 p.p.m. Dispex at pH 10.5
for 2 hrs. The ground ore suspension was diluted to 200 ml
and divided into two 100 ml volumes and the levels of
Calgon and Dispex were readjusted accordingly. One volume
was used in experiment 8 and the other was used in
experiment 9 in 7.3.4.
Experiment 8: The 100 ml suspension (2.2% solids)
containing 400 p.p.m. Calgon and 100 p.p.m. Dispex at pH 10.5,
was dispersed by stirring at high shear for 5 min. The
flocculant PAMG 2.1 was added while stirring was continued
for 1 min. at high shearing, and for 2 min. at low shearing,
followed by slow rotation in a cylinder by hand for 10 min.
This dispersion procedure was adopted in all the dispersion
stages in this experiment. Then 6 p.p.m. PAMG 2.1
221
(•v0.273 kg/tonne) was added and the flocculated fraction
was recovered from the suspension (Tail) by decantation.
The flocs were redispersed twice in 100 ml dist. water
containing 400 p.p.m. Calgon and 100 p.p.m. Dispex at
pH 10.5 to produce recleaned concentrate(Recl.conc.).
The tailings of each cleaning stage were treated with
1 p.p.m. PAMG 2.1 to produce the corresponding scavenging
concentrates (Sc. conc. 1 and Sc. conc. 2). The total
consumption of PAMG 2.1, Dispex and Calgon in kg/tonne ore
was : 0.364, 13.6 and 54.5 respectively. The results are
shown in table 7.7. below.
Table 7.7: results of experiment 8
Products Wt. Cu % -_-/ Cu-distribution %
reel. conc. 20.3 20.0 68.8
c. conc. 1 4.5 4.6 3.5
.c. conc. 2 3.6 10.0 6.1
all 40.5 1.88 12.9
1. tail 1 22.1 1.56 5.85
'1. tail 2 9.0 1.89 2.88
alc. heads 100.0 (5.9) 100.03
-electivity ratio = 10.65
-nrichment ratio = 3.39
The results indicated improvements in the grade and
recovery in the flocculated concentrate (Reel. conc.) over
those of experiment 6. Also, both the selectivity ratio
and the entrichment ratio are higher than those in
Recl
Sc.conc.2 Recl conc.
— Flocculant
Tails
Cl. tail 1
Hoc culant Sc. conc.1
Cl.tail 2
Cl.conc.1 CI. tail 1 Cl. tail 2
Cl.conc.2 Cl. Sc. conc.
Flocculant
Tails
Flocculant
Cl. tail 3
027 Ore suspension
Fig.7.5 Flow-sheet 3:Multi-stage flocculation
Ore suspension
Fig.7.6 Flow-sheet 4: Starvation flocculation
223
experiments 6 and 7. The copper content in the feed (5.9%)
was higher than the stated average content, perhaps due to
inadequate sample selection. However, when experiment 9
is also considered, as both experiments were from one ore
sample, the average copper content in that sample was
about 5.55% which was not far off the bulk value. In this
work, no special attention was given to sampling and each
ore sample in each experiment was taken independently.
An attempt to increase the copper grade in the concentrate
and thence the selectivity and enrichment ratios was made
in experiment 9.
7.3.4 "Starvation" addition of flocculant;
flow-sheet IV
This flow-sheet, as shown in Fig. 7.6, consisted of
6 flocculation stages.
Experiment 9: The 100 ml suspension of 2.8% solids,
containing 400 p.p.m. Calgon and 100 p.p.m. Dispex at
pH 10.5 was stirred for 3 min. at high shear. The
suspension was treated with 0.5 p.p.m. PAMG 2.1 while
stirring was continued for 2 min. at high shear (to disperse
the flocculant), followed by 2 min. at low-shear and 10
min. of slow rotation in a cylinder (250 ml). This dispersion
procedure was used wherever there was an addition of the
flocculant; otherwise, it was only stirred for 5 min. at
high shear-rate. The flocculated portion was recovered
and then washed (i.e. redispersed) in 100 ml dist. water
containing 400 p.p.m. Calgon and 100 p.p.m. Dispex at
pH 10.5. The products of this cleaning stage (C1- conc. 1
and Cl, tail 1) were recovered. The tailings of the
224
first flocculation stage (Rougher 1) were treated with
another 0.5 p.p.m. PAMG 2.1, (Rougher 2) and the flocculated
fraction was similarly cleaned in 100 ml dist. water
containing 400 p.p.m. Calgon and 100 p.p.m. Dispex at pH 10.5
to produce a second concentrate (Cl. conc. 2), and tailing
(Cl. tail 2). The tailings of the Rougher 2 were treated
with 6 p.p.m. PAMG 2.1 to recover more copper (scavenging)
as shown in Fig. 7.6, the product of which was similarly
redispersed in 100 ml dist. water containing 400 p.p.m.
Calgon and 100 p.p.m. Dispex at pH 10.5 to produce
scavenger conc. (Cl. sc. conc.) and tailings (final tail
and Cl. tail 3). The results are shown in Table 7.8. The
total consumption of PAMG 2.1, Dispex and Calgon in kg/tonne
ore treated was 0.267, 14.3 and 57.2 respectively.
Table 7.8: results of experiment 9
Products Wt. Cu % Cu-distribution °o
Cl. conc. 1 1.13 28.0 6.03
Cl. tail 1 6.59 8.5 10.64
Cl. conc. 2 10.82 16.5 33.92
Cl. tail 2 7.82 1.07 1.59
Cl. sc. conc. 30.76 6.45 37.70
CL. tail 3 19.31 1.45 5.32
final tail 23.57 1.07 4.80
calc. heads 100.00 (5.26) 100.00
selectivity ratios = 28/1.07 = 26.2 & 16.5/1.07 = 15.2
enrichment ratios = 28/5.26 = 5.32 & 16.5/5;26 = 3.14
225
The results shdwed a sharp rise in the 'copper grade
in the concentrate (Cl. conc. 1) due to the starvation
additions of the flocculant, indicating a high selectivity
But unfortunately the recovery in that concentrate was
very low. (However, a combined concentrate of Cl. conc. 1
and Cl. conc. 2, could make a mixture of average 17.5%
copper and 40% recovery). The selectivity ratio (26.2)
and the enrichment ratio (5.32) in the first concentrate
were the highest achieved so far. The reagents consumption
was rather high; but because the economic factor was not
the main concern at this stage, no attempt to reduce the
consumption was made. The economic factor was considered
in later experiments (21-25).
7.3.5. Multi-sta e addition of flocculent•
semi-c clic flow-sheet V.
In this more complicated arrangement in Fig. 7.7, the
flocculant was added in small increments, followed by short
periods of dispersion, following the results of experiment 9.
Experiment 10: In this experiment, the dispersion
procedure was as follows. The suspension was stirred at
high shear for 5 min. before adding the polymer and for
1 min. after each addition, then at low shear for further
1 min. The suspension was transferred to the flocculation
apparatus in Fig. 7.2, and was kept rotating slowly
(between about 20-40 r.p.m.) for 10 min., except that in
the rougher stage it was kept for 50 min.
Thus a 100 ml suspension of /%., 2.8% solids containing
400 p.p.m. Calgon and 100 p.p.m. Dispex at pH 10.5 was
treated with 1 p.p.m. PANG 2.1 according to the flow-sheet.
CI
Tail 3 Sc 3
Sc. conc.
226
Ore suspension Fig:7-7 Flow-sheet 5
(Semi-cyclic)
Tail 1
Sc 2 —Tail 2
Red. conc.
Reel
Ore suspension
Fig.7.8 Flow-sheet 6
Cl
R
Red
Tail 1
Tail 2
Red. conc. Sc. conc.
227
The polymer was added in 5 increments of 0.2 p.p.m. each.
The suspensions from the rougher and cleaning stages were
treated with 1 p.p.m. PAMG 2.1 in the scavenger. The
flocculated concentrates of the rougher and scavenger
were cleaned twice in dist. water containing 400 p.p.m.
Calgon and 100 p.p.m. Dispex using 0.2 p.p.m. PAMG 2.1
in each stage, to produce recleaned concentrate (Reel.
conc.), scavenger concentrate (Sc. conc.) and three
tailings. The results are shown in Table 7.9. The total
consumption of PAMG 2.1, Dispex and Calgon in kg/tonne ore
was: 0.171, 17.85 and 71.5 respectively.
Table 7.9: Results of experiment 10.
Products 21.L2Z Cu % Cu-distribution 2
Reel. conc. 11.6 22.0 50.4
Sc. conc. 16.7 7.5 24.7
Tail 1 51.5 1.75 17.8
Tail 2 11.4 1.4 3.2
Tail 3 8.8 2.25 3.9
calc. heads 100.0 (5.06) 100.0
selectivity ratio = between 22.0/1.4 = 15.75 & 22/2.25 = 9.8
enrichment ratio = 22.0/5.06 = 4.35
The results show an increase in copper grade in
concentrate (Recl. conc.) over experiment 8, but the
recovery was lower. There is also an increase in the
selectivity ratio and the enrichment ratio. However,
228
it can be concluded that the effect of addition of the
polymer in many small increments did not increase the
performance significantly. It seems that the total
concentration of the polymer in each flocculation stage
is the important factor and not the mode of addition.
Effect 2ffsatil on selective flocculation was
investigated in the following experiment, following flow-
sheet VI in Fig. 7.8.
Eu2rimentili A 100 ml suspension of 2.7% solids
containing 450 p.p.m. Calgon and 200 p.p.m. Dispex at
pH 10.5 was stored for 7 days at room temperature. The
suspension was dispersed following the same procedure of
experiment 10, but the flocculation time in the apparatus
was increased to 20 min, and for the rougher stage to 30
min. 1.5 p.p.m. PAMG 2.1 was added in small increments of
0.25 p.p.m. in the rougher, and the flocculated fraction
was washed twice in 100 ml dist. water containing 450 p.p.m.
Calgon and 200 p.p.m. Dispex at pH 10.5. Only 0.1 p.p.m.
flocculant was added to each cleaning stage. The two
suspensions from the rougher and the first cleaner were
treated in the scavenger with 1.5 p.p.m. PAMG 2.1, added
in small increments of 0.25 p.p.m. The flocculated
fraction was cleaned in the 100 ml suspension (Tail) of
the second cleaner as shown in Fig. 7.8 and treated with
0.1 p.p.m. flocculant to produce scavenger concentrate
(Sc. conc.) and Tail 2, The results are shown in Table 7.10.
The total consumption of PAMG 2.1, Dispex and Calgon in
kg/tonne ore was 0.178, 22.2 and 50.0 respectively.
229
Table 7.10; Rdsults of experiment 11.
Products 12/2 Cu % Cu-distribution
Reel. conc. 22.0 14.0 64.3 •
Sc. cone. 2.5 6.0 3.1
Tail 1 65.9 2.15 29.5
'Mal 2 9.6 1.55 3.1
calc. heads 100.0 (4.8) 100.0
selectivity ratio = between 14. ----- = 9.0 & 14/2.15 = 6.5 1 .55
enrichment ratio = 2.92
The results clearly indicate a sharp drop in the copper
grade in the concentrate (Reel. conc.) compared with
experiment 10. Also, the enrichment and the selectivity
ratios were lower than in experiment 10. Therefore, it
can be concluded that ageing of suspension can have a
deleterious effect on selective flocculation. The com-
parison with experiment10 is valid despite the difference
in reagents levels which might make it less accurate.
This conclusions is in agreement with published literature 2
7.3.6. The standard flow-sheet; flow-sheet VII
In this design, there were four flocculation stages,
as shown in Fig. 7.9; one of each of the rougher and the
scavenger, and two for cleaning the concentrate. This
flow-sheet was adopted in all of the flocculation experiments
in the following sections in this Chapter (unless other-
wise stated).
CI Cl.tail
230
Ore suspension
R --Tail
Sc. conc.
L Red Recl.tail
Rect. conc.
Fig.7-9 Flow-sheet 7: Standard flow-sheet
Products EIILZ2-m Wt. % Cu % units Cu-distribution
ecl. conc.
Sc. conc.
Reel tail
Cl. tail
Final tail
calc. heads
0.804 15.9 22.5 357.8
0.605 12.0 7.25 87.0
0.288 5.7 0.725 4.13
0.541 10.7 1.4 14.98
2.812 55.7 1.01 56.26
5.05 100.0 (5.202)520.17
68.8
16.7
0.8
2.9
10.8
100.0
selectivity ratio 22.5/1.01 = 22.3
rnrichment ratio 22.5/5.2 4.32
231
Experiment 12: A 5 g sample was ground in 40 ml dist.
water containing 300 p.p.m. Dispex and 200 p.p.m. Calgon
at pH 11 for 2.5 hrs. The suspension was diluted to 200 ml
( i.e. 2.5% solids) and the levels of reagents were adjusted
accordingly. After stirring at high shear for 5 min, 3
p.p.m. PAMG 6 was added in two portions of 1.5 p.p.m. each
while stirring was continued for a further 5 min. after
each addition. The flocculating suspension was slowly
rotated in the flocculation apparatus for about 15 min.,
except that in the rougher it was 36 min- The flocculated
concentrate was cleaned twice in 100 ml dist. water con-
taining 300 p.p.m. Dispex and 200 p.p.m. Calgon at pH 11.
It was treated with 1.5 p.p.m. PAMG 6 in the first cleaner,
and with 0.5 p.p.m. in the second cleaner. The tailings
of the rougher were treated with 1.5 p.p.m. flocculant in
the scavenger, to produce scavenger concentrate as a
middling and a final tail. The results are shown in Table
7.11. The total consumption of PANG 6, Dispex and Calgon
in kg/tonne ore was: 0.22, 24.0 and 16.0 respectively.
Table 7.11: Results of experiment 12
232
The results indicate good overall performance of the
process. The selectivity ratio and the enrichment ratio
were high and 'the copper grade and recovery in the con-
centrate were higher than in most of the previous experiments.
The results were encouraging but more development work was
needed to improve them further. This is described in the
following sections.
7.4 Studies to improve grade and recovery
In the previous experiments, copper concentrates of
copper grade over 20% (up to 28%) had been achieved, while
the recovery in most cases was about 60-70%. To improve
the recovery, it was first thought that the effectiveness
of the polymer should be enhanced further. Thus PAMG 7
was developed with this aim in mind. Preparation of
PAMG 7 was described in Chapter 6.
7.4.1. aeE)Jatments aT.
Experiment 13: A 5 g sample was ground in 40 ml
dist. water containing 410 p.p.m. Dispex and 140 p.p.m.
Calgon at pH 11 for 2,5 hrs. It was diluted to 200 ml
(1.e. 2.5% solids) and the Calgon and Dispex concentrations
were readjusted accordingly at pH 11. The suspension was
treated with 4 p.p.m. polymer, added in two portions of
3 and 1 p.p.m., following the standard flow-sheet in
Fig. 7.9. The dispersion procedure was as follows:
stirring at high shear for 1 min. after the polymer addition
and at low shear for 2 min. after the last addition of the
polymer, followed by 20 min. of slow rotation in the
flocculation apparatus. The initial dispersion of suspensions
233
was at high shear rate for 5 min. The flocs were washed
twice in 200 ml and 100 ml dist. water containing 410
p.p.m. Dispex and 140 p.p.m. Calgon each, at pH 11. The
polymer additions were 2, 0.7 and 1.5 p.p.m. in the
cleaner, recleaner and the scavenger respectively. The
suspensions were separated from the flocculated con-
centrate by vacuum suction. The results are shown in
Table 7.12. The total consumption of PAMG 7, Dispex and
Calgon in kg/tonne ore was : 0.314, 41.0 and 14.0
respectively.
Table 7.12: Results of experiment 13
Products Wt. dram Wt. Cu al-dis... ._7_9...22.2a.t1
Reel. conc. 2.22 43.9 14.0 97.4
Recl. tail 0.485 9.6 0.335 0.5
Cl. tail 0.805 15.9 0.20 0.5
O'inal tail 1.544 30.6 0.335 1.6
$c. conc. 0.00 0.0
calc. heads 5.054 100.0 (6.312) 100.0
selectivity ratio = 14/0.335 = 41.7 and 14/0.2 = 70.0
enrichment ratio = 14.0/6.3 = 2.22
The results show very high recovery of copper in the
concentrate. Also, the selectivity ratio was very high
and the copper loss in tailings was minimal but the
enrichment ratio was only 2.22 and the grade was rather low.
There was no flocculation in the scavenging stage (i.e.,
weight of Sc. conc. = 0). The weight of flocculated
concentrate was more than in experiment 12 which accounts
for the high recovery in experiment 13.
Experiment 14: A 2.5 % solids suspension was treated
in the same way as experiment 13, except that the polymer
addition was 1 p.p.m. more in the two cleaning stages
(i.e., 2 p.p.m. instead of 1 p.p.m.). A third cleaning
stage was attempted in this experiment, where 1 p.p.m. of
the polymer was added. The total reagents consumption of
PAMG 7, Dispex and Calgon in kg/tonne ore was : 0.334,
49.3 and 16.8 respectively.
Table 7.13: Results of experiment 14
Products Wt. % -Cu % Cu-distribution
Reel. conc. 31.98 12.2 85.8
Sc. conc. 0.35 3.364 0.25
Recl. tail 2 4.86 1.75 1.85
Reel. tail 1 8.79 1.30 2.5
Cl. tail 15.96 0.826 2.9
Final tail 38.06 0.80 6.7
cab. heads 100.00 (4.55) 100.0
selectivity ratio = 15.2
enrichment ratio = 2.68 ----
2311-
235
From these results it was concluded that the extra
stage did not improve the copper grade, although the
selectivity ratio was 15.2.
Experiment 15: A 5 g sample was ground in 40 ml
dist. water containing 410 p.p.m. Dispex and 140 p.p.m.
Calgon at pH 11 for 3 hrs. The suspension was diluted to
200 ml (i.e. 2.5% solids) and the concentrations of Calgon
and Dispex were readjusted accordingly at pH 11. The
dispersion procedure was the same as in experiment 13.
2 p.p.m. of the polymer was added in small portions of 0.5
p.p.m. each, in the rougher stage and 1 p.p.m. of two
increments of 0.5 p.p.m. in each of the two cleaning stages.
1.5 p.p.m. polymer was used in the scavenger stage in one
addition. Each of the two cleaning stages was carried
out in 100 ml dist. water containing 410 p.p.m. Dispex
and 140 p.p.m. Calgon at pH 11. The total consumption of
PAMG 7, Dispex and Calgon in kg/tonne ore was: 0.32, 32.8
and 11.2 respectively. The results are shown in Table 7.14
below:
Table 7.14: Results of experiment 15
Products Wt. gram W . °,4 Cu °/0 units - -distribution V
tecl. conc. 1.805 35.9 3.5 484.65 94.6
Recl. tail 0.445 8.85 0.595 5.27 1.0
Cl. tail 0.896 17.8 0.315 5.61 1.1
Sc. conc. 0.048 0.95 1.40 1.33 0.3
inal tail 1.832 36.5 0.425 15.51 3.0
calc. heads 5.026 100.0 5.124) 512.37 100.0 ..0m......
electivity ratio = 31.8
enrichment ratio = 2.65
236
The results show high recovery and selectivity ratio
but the grade and the enrichment ratio were rather low.
It seems that PAMG 7 is a strong flocculant, but the
copper grade was always low in experiments 13-15. An
experiment was made with PAMG 6 in order to check whether
the lower grade in these experiments was due to the effect
of the concentration of Dispex and Calgon. The experiment
is described below.
Experiment 16: A sample of 5 g was ground 40 ml dist.
water containing 410 p.p.m. Dispex and 140 p.p.m. Calgon
at pH 11 for 2.5 hrs. It was diluted to 200 ml (i.e. 2.5%
solids) and the levels of reagents were readjusted accordingly
at the same pH. The suspension was stirred for 5 min. at
high shear rate, then 3 p.p.m. PAMG 6 was added followed
by 2 min. stirring at high shear. This was followed by
another addition of 1 p.p.m. PAMG 6 and the dispersion
was continued for 5 min. at high shear, then at low shear
for 2 min. followed by 30 min. slow rotation in the floccu-
lation apparatus. The flocculated concentrate was cleaned
(re-dispersed) twice each in 100 ml dist. water containing
410 p.p.m. Dispex and 140 p.p.m. Calgon at pH 11. The
dispersion was carried out at high shear for 5 min. The
polymer additions in the cleaner, precleaner and scavenger
stages were 1, 0.5 and 1.5 p.p.m. respectively. The
polymer additions were followed by 2 minutes of high shear,
2 min. of low shear and 20 min. of slow rotation in the
flocculation apparatus. The total consumption of PAMG 6,
Dispex and Calgon in kg/tonne ore was: 0.25, 32.8 and
11.2 respectively. The results are shown in Table 7.15
237
below.
Table 7.15: Results of experiment 16
Products W-tti° 922Z Cu-distribution °°
Reel. conc. 15.0 17.82 55.3
Reel. tail 4.3 0.955 0.85
Cl. tail 6.6 0.85 1.15
Sc. conc. 176 6.55 23.8
Final tail 56.5 1.62 18.9
calc. heads 100.0 (4.84) 100.0
selectivity ratio = 11.0
enrichment ratio = 3.7
By comparison with experiment 12, the performance of
the process was rather inferior. But the copper grade in
the concentrate was higher than that of experiments 13-15.
Thus the change of reagents levels and modes of addition
was partly responsible for the lower grade in experiments
13-15. The levels of reagents in these experiments 13-16
were determined from a computer programming of the previous
experiments.
The results of the flocculation experiments recorded
in this Chapter so far, showed in one extreme that when the
copper grade was high (28%), the recovery was very low
(6%), and on the other extreme, when the copper recovery
in the concentrate was high (97.4 %), the grade WU5 rather
low (14%). Aruiattempts to improve the grade were invariably
238
accompanied by losses in the recovery and vica versa. This
is the familiar dilemma in mineral processing of grade
versus recovery.
In an attempt to understand the "grade versus recovery"
dilemma, the following viewpoint was put forward. If the copper
minerals are surrounded by gangue minerals, either by
"slimes coating" or embedding in a matrix, then the copper
particles will behave as gangue minerals, which results
in low recovery. On the other hand, if the copper minerals
are surrounding the gangue minerals, the ore particles will
behave as copper minerals, thus resulting in low-grade
concentrate. The phenomenon of slimes coating can be
overcome by good dispersion whereas embedding in matrix
requires further grinding to liberation sizes.
7.4.2 Dis ersion of the ore suspensions
Good dispersion can be effected by (1) mechanical
"de-aggregation" of slimes (e.g. use of high-shear mixers,
ultra-sonic vibrations or even grinding) and (2) chemical
modulation of interfaces. The latter can be implemented
by (a) regulating the electrical potential to induce
repulsion between interfaces, or (b) reducing the inter-
facial energy of the particles by addition of a surface
active agent.
In all the previous experiments, factor (2-a) was
fulfilled by the use of Calgon and Dispex. Since both
reagents were found to increase the zeta- potential of
malachite as described in Chapter 2. It can be supposed
that electrostatic repulsion alone was not sufficient to
produce good dispersion (i.e. dispersion of the individual
239
particles) in concentrated suspensions, seven though the
suspensions were apparently sufficiently stable. Therefore
extra aids of mechanical and chemical means were possibly
needed. A comprehensive account on the various aspects
of dispersion is given in the literature(21)
Effect of ultrasonic vibrations on dispersion of the
ore suspensions
pExerimemt17: A 5 g sample of the ore was ground in
40 ml dist. water containing 400 p.p.m. and 150 p.p.m.
Calgon at pH 11 for 2.5 hrs. The suspension was divided
into approximately two equal volumes, and each was diluted
to 100 ml (i.e. about 2.5% solids). The levels of Calgon
and Dispex were readjusted accordingly at pH 11. One
volume was subjected to the maximum shear-rate by a
magnetic stirrer and the other to irradiation of an ultra-
sonic probe at intermediate energy, for 3 minutes each.
To test the effect, two one-stage flocculation experiments
were performed using 3 p.p.m. of PAMG 7 in each experiment.
The additions of the polymer were followed by 1 min.
dispersion at the same level in each system, followed by
20 min. of slow rotation in the flocculation apparatus.
The results arc shown 4n Table 7.16 below.
Table 7.16: Results of experiment 17
dispersion Products Ett 222E2 C Cu-distribution 'c techRiana
ultrasonic probe
conc.
tail
calc. heads
19.8
80.2
100.0
14.0
2.6
(/4.86)
57.1
42.9
100.0
magnetic stirrer
conc.
tail
calc. heads
51.1
48.9
100.0
6.95
1.25
(4.16)
85.3
14,7
100.0
24o
It is evident that ultrasonic dispersion had a
superior effect in dispersing the ore particles, which
subsequently raised the copper grade in the concentrate
to about twice that provided by the magnetic stirrer.
The effect of ultrasonic dispersion on the stability
of the ore suspension was studied in the following
experiment.
appriment 18: Two suspensions of 50 ml each (2.5%
solids) of the ground ore sample (for 2.5 hrs.), containing
400 p.p.m. Dispex and 150 p.p.m. Calgon at pH 11 were
tested. One suspension was dispersed by a magnetic stirrer
at high shear-rate (its maximum r.p.m.) and the other with
the ultrasonic probe at an intermediate energy level (i.e.,
at 0.6 of its maximum) each for 3 min. The suspensions
were transferred into 50 ml cylinders and were left standing
for a few days while small samples were taken from the top
of the suspensions for measuring the percent ransmission
at the wavelength 602 my in a spectrophotometer. The
results are shown in Fig. 7.10.
The results indicate that the ultrasonic dispersion
improved the stability of the suspension, even though the
suspension obtained by stirring only by magnetic stirrer
was sufficiently stable for selective flocculation purposes.
The stability was probably due mainly to the effects of
Calgon and Dispex in both cases. The effect of ultrasonic
dispersion was believed to be in liberating the finest
particles of copper minerals from the gangue slimes. To
confirm these conclusions the following experiment was
carried out.
25
1 I I t 15
30 45 60 75 Time( hours)
Fig.7.10 Stability of ore suspensions dispersed by; magnetic stirrer® , ultrasonic vibrations®
18.7
8.5
13.7
12.9
46.2
100.0
selectivity ratio = 21.5
3.44 9.24
0,895 8.6
(4.8) 100.0
19.3 1.56
1.50
75.12
2.76
4.28
enrichment ratio
242
Eperiment 1 . A 100 ml suspension of 2.8% solids of
the ground ore sample (for 2.5 hrs.), containing 400 p.p.m.
Dispex and 150 p.p.m. Calgon at pH 11 was used. The
suspension was dispersed by a magnetic stirrer at high
shear-rate (max. r.p.m.) for 3 min. followed by ultra-
sonic dispersion at high energy (0.6 max.) for further 3
min. The suspension was stirred at high shear by the
magnetic stirrer for 1 min. before and after adding 2
p.p.m. PANG 7, followed by 1 min. of low shear and 20 min.
of slow rotation in the flocculation apparatus. The
flocculated fraction was re-dispersed twice each in 100 ml
dist. water containing 400 p.p.m. Dispex and 150 p.p.m.
Calgon at pH 11, following the same dispersion procedure
above, except that the slow rotation in the apparatus was
only 15 min. 1 p.p.m. PANG 7 was added to each of the
cleaning stages. The rougher tailing was dispersed by a
magnetic stirrer for 3 min. at high shear, then 1.5 p.p.m.
of the polymer was added while stirring was continued for
1 min. followed by 1 min. of low shear and 15 min. of slow
rotation. The result are shown in Table 7.17. The total
consumption of PANG 7, Dispex and Calgon in kg/tonne ore
was 0.196, 42.8 and 16.1 respectively.
Table 7.17: Results of experiment 19
243
These results show a marked improvement in the
performance of the process with PAMG 7 compared with
experiments 13-15, especially in the enrichment ratio,
the weight of concentrate and the copper grade. The
higher copper grade and the relatively small weight of
concentrate, in particular, appeared to be the direct
results of the effect of the improved dispersion
techniques.
Effect of reducing the interfacial energy on dispersion
The effect of adsorption of surface-active substances
by a solid on its structural strength has been investigated
by Rehbinder and others(182-187),In theory, if the inter-
facial energy (surface tension) could be decreased to very
low values, the solid would become very weak and eventually
breakdown spontaneously even in the absence of external
forces (if the discrete particles were small enough units).
In practice, however, spontaneous peptization is very rare,
and virtually unknown for dried solids, though swelling
clays almost achieve this phenomenon. To weaken the strength
of solids by reducing the interfacial energy, three basic
requirements have to be fulfilled: (1) Tht surface-active
agent must bring the interfacial energy of solids in
to low values; (2) It must, therefore, be absorbed on the
solids; (3) For the purpose of dispersion of slimes, the
surface-active agent must have a lbw molecular weight
(small size) in order to penetrate between the fine particles.
The effect of three surface-active agents, namely;
n butanol , sodium lignosulphonate and "Dispersol T"
(which is believed to be a naphthalene-sulphonic acid /
formaldehyde condensate) was tested. It is known that the
244
interfacial tension of n-butanolfwater at 250 is 1.6
dyne/cm,(-U) It is also known that the other two reagents
help dispersion by reducing the interfacial energy of
solids (1$9). The testing procedure is described in
experiment 20.
Experiment 20: One-stage flocculation experiments
were carried out on 100 ml suspensions of 2.5% solids
(of the finely ground ore samples) to test the effect of
these surface-active agents in the presence of Dispex at
pH 11. The level of reagents used in each experiment were
400 p.p.m. surface-active agent and 100 p.p.m. Dispex.
Each suspension was subjected to the ultrasonic probe at
high energy (0.6 max.) for 3 min., followed by 1 min. of
high shear by magnetic stirrer before and after adding
3 p.p.m. PAMG 2.1 flocculant. The suspension was then
stirred at low shear-rate for 1 min. and slowly rotated
in the flocculation apparatus for about 20-25 min. The
results are shown in Table 7.18 below.
Table 7.18: Results of experiment 20
,_._.. Dispersant Products Wt. % Cu °o Cu-distribution %
------ ---r--- - - 1B-conc.
"n-Butanol" B-tail
53.85 46.15
8.1 1.8
84.0 16.0
calc. heads 100.00 (5.19) 100.0
S-conc. 37.32 9.6 65.6 Sodium ligno- S-tail sulphonate calc. heads
62.68 100.00
3,0 (5.46
34.4 100.0
D-conc. 47.63 9.4 84.2
"Dispersol T" D-tail 52.37 1.6 15.8
calc. heads 100.00 (5.32) 100.0
245
The results of these experiments were not encouraging.
Presumably, this was because the surface-active agents did
not satisfy the three basic requirements stated earlier.
The butanol, although possessing very low surface tension
against water and being of low molecular weight; does not
have special affinity to adsorb on the various ore particles.
The other two reagents are known to adsorb on various
minerals, but their high molecular weight may hinder their
migration in between the slimes aggregates. They may also
interfer in the subsequent conditioning. The investigations
were not pursued any further, though the possibility of
utilizing the Rehbinder effect for dispersing heterogeneous
ores deserves more study. The late Academician Rehbinder
remarked privately to Dr. Kitchener that water is already
a powerful reducer of surface energy for hydrophilic
minerals: therefore, to get any substantial further
improvement would require some rather special surfactant).
There are possibilities of developing new dispersants
to help to improve the dispersion process. Two new reagents
were designed and prepared in the laboratory and proved to
be good dispersants as well as flocculation inhibitors.
They were named "Acrisol I" and "Acrisol II". It is believed
that they consist of ordinary Dispex with some phenolic
groups attached to it. It was found that Acrisol I
depresses the common gangue minerals from flocculation at
very low levels of additions. If it is used at high
levels, it depresses the copper minerals also from
flocculation and keeps them dispersed for long periods. It
has been used in some of the flocculation experiments.
246
7.5 Effects of solids content on selective , flocculation
Two experiments were carried out on suspensions of
5% and 10 % solids content. The flow-sheets used were
the same as shown in Fig. 7.9, (i.e., the standard flow-
sheet).
Experiment 21: A 10 g sample of the ore was ground
in 40 ml dist. water containing 100 p.p.m. Acrisol I and
400 p.p.m. Calgon at pH 11 for 3 hrs. in the McCrone mill.
It was diluted to 100 ml (1.e.,10 % solids) and the levels
of reagents were readjusted accordingly at pH 11. The
dispersion processes were carried out with a magnetic
stirrer at high shear for 2 min., then by ultrasonic probe
for 3 min. at high energy, followed by 1 min. high shear
by magnetic stirrer during which the polymer PAMG 2.1 was
added. Dispersion of the flocculant was continued at high
shear for 1 min. and at low shear for further 1 min, both
stages by magnetic stirrer. This was followed by 20 min.
of slow rotation in the flocculation apparatus. The
flocculated concentrate was redispersed twice each in
100 ml dist. water containing 50 p.p.m. Acrisol I and
200 p.p.m Calgon at pH 10.8. The flocculant additions
were 6, 4, 3 and 2 p.p.m. in the following stages:
rougher, cleaner, recleaner and scavenger. The total.
consumption of PAMG 2.1, Acrisol I and Calgon in kg/tonne
ore was : 0.17, 2.0 and 8.0 respectively. The results are
shown in Table 7.19 overleaf.
247
Table 7.19: Results of experiment 21
Products Wt.gram Wt. % units Cu-distribution 00
Reel. cone. 1.673 17.1 28.2 482.22 68.2
Reel. tail 0.702 7.2 3.18 22.896 3.2
Cl. tail 1.35 13.8 3.05 42.09 6.0
Sc. cone. 1.217 12.4 3.95 48.98 6.9
Final tail 4.858 49.5 2.25 111.375 15.7
calc. heads 9.8 100.0 (7.076) 707.561 100.0
selectivity ratio .n.,, 12.5
enrichment ratio /..v 4.0
The results indicate that there was no fundamental
change in the performance of the process. The enrichment
and the selectivity ratios are comparable with those of
the previous experiments at lower solids content. The
estimated copper grade in the feed was rather high in
relation to the previous experiments, but that might be
due to segregation of copper minerals in that ore sample.
(No special attention was given to statistical sampling,
since the main concern was to establish the fundamental
aspects of the process).
Experiment 22: A sample of 10 g was ground in 40 ml
dist. water containing 200 p.p.m. Dispex and 400 p.p.m.
Calgon at pH 11 for 3 hrs. It was diluted to 200 ml
(i.e., 5 % solids) and the levels of reagents were readjusted
accordingly. The dispersion procedure was the same as in
experiment 21. The suspension was treated with 3 p.p.m.
248
PAMG 2.1 flocculant and the flocculated fraction was
redispersed (cleaned) twice: first (i.e., cleaner) in 100 ml
dist. water containing 100 p.p.m. Dispex and 200 p.p.m.
Calgon, and in the second (i.e. recleaner) in 100 ml
dist. water containing 100 p.p.m. Dispex and 100 p.p.m.
Calgon; both at pH 10.8. The levels of additions of
PAMG 2.1 in each of the cleaner, recleaner and the
scavenger were about 4 p.p.m. The total consumption of
PAMG 2.1, Dispex and Calgon in kg/tonne ore was: 0.24,
6.0 and 11.0 respectively. The results are shown in
Table 7.20 below.
Table 7.20: Results of experiment 22.
Products E-12 Cu % 2.12112.1.11.1-1,211-an_L.
Reel. conc. 15.7 23.5 64.4
Reel. tail 3.5 2.23 1.4
Cl tail 6.4 2.1 2.3
Sc. conc. 34.2 3.8 22.7
Final tail 40.3 1.3 9.2
calc. heads 100.1 (5.72) 100.0
selectivity ratio = 18.1
enrichment ratio = 4.13
The results confirm the previous conclusions, that
there were no fundamental changes in the performance of
the process due to increasing the solids content. The
overall performance of this experiment was quite good,
but the recovery needs to be improved.
249
7.6 Effect of t -water on selective flocculation
Experiment 23: A 10 g sample of ore was ground in
40 ml of London tap-water containing 100 p.p.m. Acrisol I
and 400 p.p.m. Calgon at pH 11.5 for 4 hrs. in the McCrone
mill. It was diluted to 100 ml with tap water (i.e., 10 %
solids) and the levels of reagents were adjusted accordingly.
The dispersion procedure was the same as in experiment 22.
The suspension was treated with 6 p.p.m. PAMG 2.1 in the
rougher stage at pH 10.8. The flocculated concentrate was
redispersed (cleaned) twice; (i.e., in the cleaner and
recleaner stages) in 100 ml tap-water containing 50 p.p.m.
Acrisol I and 100 p.p.m. Calgon at pH 10.5-10.8.
respectively. The polymer was added to the cleaner,
recleaner and the scavenger in the respective amounts;
4, 3 and 2 p.p.m. The suspension was diluted in the
scavenger to 200 ml, in order to facilitate recovering
more copper in the scavenger middling (Sc. conc.) The
total consumption of PAMG 2.1, Acrisol I and Calgon in
kg/tonne ore was: 0.17, 2.0 and 6.0 respectively. The
results are shown in Table 7.21 below.
Table 7.21: Results of experiment 23
Products wt. % Ea26 Cu-distribution %
Reel. conc. 17.2 19.6 62.4
Reel. tail 6.7 1.85 2.3
Cl. tail 6.9 1.4 1.8
Sc. conc. 12.2 5.3 12.0
Final tail 57.0 2.05 21.5
calc. heads 100.0 (5.41) 100.0
selectivity ratio = 9.55
enrichment ratio 3.63
Products Wt. 1
22.23 16.7
17,3 3.9
15.2 1.65
13.4 1.7
31.87 1.25 loo.00 .26)
selectivity ratio = 13,4 enrichment rate 1-7
0 I
Recl. conc.
Reel. tail
Cl. tail
Sc. conc.
Final tail
calc, heads
250
The result suggest a drop in both the copper grade
and recovery in the concentrate compared with experiment
22, though these differences are not of great significance.
The tap-water, thus, had a deleterious effect on the
performance of the process, which could be minimized by
raising the level of reagents. The reagents consumption
was still economical.
Experiment2L1 A 10 g sample was ground in tap-water
containing 150 p.p.m. Acrisol I and 500 p.p.m. Calgon at
pH 11 for 4 hrs. It was diluted to 140 ml (i.e., 7 % solids)
and the level reagents were regulated accordingly. The
dispersion procedure was the same as in experiment 23. The
suspension was mixed with 8 p.p.m. PAMG 2.1 in the rougher
at pH 10.8. The flocculated concentrate was redispersed
twice; in 100 ml tap-water containing 150 p,p.m. Acrisol I
and 200 p.p.m. Calgon in the cleaner, and 50 p.p.m.
Acrisol I and 150 p.p.m. Calgon in the recleaner, both at
pH 10.8. The concentration of PAMG 2.1 used in the
cleaner, recleaner and scavenger were: 5,6 and 2 p.p.m.
respectively. The total consumption of PAMG 2.1,
Acrisol I and Calgon in kg/tonne ore was: 0.252, 4.1 and
10.5 respectively.
The results are shown in table 7.22 below:
Table 7.22: Results of experiment 24
251
The results suggest another decreaSe in enrichment
ratio and the copper grade in concentrate compared with
experiment 23. On the other hand the selectivity ratio
and the recovery were higher. It was noticed, however,
that some white coarse particles of quartz were settling
with the flocs, which implied insufficient grinding.
(The McCrone mill becomes inefficient when used to grind
quantities of about 10g).Thus the drop in grade was mainly
due to the settling of the coarse particles rather than
the effect of tap-water.
7.7 Use of tap-water and high solids content
Experiment 25: About 40 g sample was ground in 100 ml
tap-water containing 150 p.p.m. Dispex and 500 p.p.m.
Calgon at pH 11 for 2 hrs. in a porcelain mill. After
washing the grinding media with tap-water, the volume of
suspension became 650 ml; it was centrifuged and the
clear aqueous medium was rejected. The solids were
redispersed in 130 ml (i.e., 30.8 % solids) tap-water
containing 150 p.p.m. Dispex and 500 p.p.m. Calgon at
pH 11. The dispersion procedure was the same as
experiment 24. The suspension was treated with 8 p.p.m.
PAMG 2.1 at pH 10.8 and the flocculated concentrate was
redispersed (cleaned) twice; in 130 ml tap-water containing
75 p.p.m. Dispex and 200 p.p.m. Calgon in the cleaner, and
in 100 ml tap-water containing 50 p.p.m. Dispex, 200 p.p.m.
Calgon in the recleaner, both at pH 10.8. The amounts of
PAMG 2.1 used in the cleaner, recleaner and scavenger
stages were: 4, 4 and 3 p.p.m. respectively. The total
252
consumption of PAMG.2.1, Dispex and Calgon in kg/tonne
ore was: 0.06, 0.855 and 2.77 respectively. . If, however,
the amounts of. Calgon and Dispex lost due to centrifugation
were taken into account, then the total consumption of
PAMG 2.1, Dispex and Calgon would be : 0.06, 1.23 and
4.025 kg/tonne. The results are shown in Table 7.23
below.
Table 7.23: Results of experiment 25
Products III4 Elam Wt. % cyt. units Cu-distribution
Reel. cone 6.19 15.4 18.2 280.28 62.3
Reel, tail 2.99 7.5 3.15 23.625 5.3
Cl. tail 5.117 12.7 2.0 25.4 5.6
Sc. conc. 1.269 3.2 3.0 9.6 2.1
Final tail 24.558 61.2 1.82 111.384 24.7
calc. heads 40.124 100.0 (4.503) 450.289 100.0
selectivity ratio = 10.0
enrichment ratio = 4.05
The results show that selective flocculation was
successfully achieved and the combined effects of the high
solids and tap-water on the selectivity criteria were not
of fundamental importance. Both the enrichment and the
selectivity ratios are comparable with those in earlier
experiments. During flocculation, however, some coarse
white particles of quartz were seen to settle with the
flocs. This was confirmed by microscopic examination of
253
of the concentrate. These coarse particles were, of
course, due to insufficient grinding. (In treating an
ore containing soft copper minerals and some hard gangue
grains such as quartz, it would obviously be advantageous
to reject the latter in a hydrocyclone after selective
grinding). The reagents consumption in this experiment
was considered to be very economical, considering the
rising price of copper in the world market.
7.8 Discussion
In developing the selective flocculation process in
this Chapter, the parameters investigated can be grouped,
for simplicity, as follows:
A - Dispersion of the ore suspension: To study the
mechanical factors of the dispersion process, the effects
of the following parameters were investigated. The
shear-rate, shear time, both together with the volume of
suspension and size of the container for defining the
hydrodynamic pattern. Solids content and technique of
dispersion were also investigated. The effects of the
chemical parameters such as: zeta-potential, surface energy
and ageing time as well as the quality of water, on
dispersion and stability of suspensions were studied.
B - Dispersion of the flocculant: The effects of the
following parameters were established: shear-rate, shear-
time and multi-stage additions of the polymer.
C Conditionin of flocculation after addition of the
polymer: The effects of the shear-rate, flocculation time
and slow rotation in the flocculation apparatus were illustrated.
254
D - Flocculation reagents: Types, amounts, and mode of
additions of the flocculants, depressors and dispersants.
E - Grinding time and technique, F - pH of flocculation, and G Flow-sheet arran events: multi-stage flocculation,
including redispersion processes to help release the
entraped particles.
The effects of these variables on the processing of
this ore by selective flocculation have been established
from the experiments in this Chapter and also in Chapter 6.
For further development work, these variables can be
reduced to only three, namely, the flocculant dose, the
concentrations of the modifying reagents (e.g. Calgon and
Dispex or Acrisol I) and grinding to liberation size. The
use of ultrasonic dispersion could probably be replaced by
the use of a good mixer capable of producing high shear-
rate mixing.
The roles of modifying agents, solids content,
dispersion of the flocculant and conditioning of flocculation
at low shear in the selective flocculation process have
also been previously studied by Yarar and Kitchener ( 2).
The stable state of dispersion was found necessary and
redispersion was suggested as a means for releasing
entrapted particles. The rheological properties of
flocculated suspensions treated with polymeric flocculants
as against coagulation were investigated by Friend and
Kitchener(5). The authors studied the possibilities of
employing zeta-potential as a means of controlling
selective flocculation. The effectof low molecular
weight polyacrylates on the dispersion and depression of
255
of dolomite gangue during the sulphidization flotation of
malachite was investigated by Van Lierde(181
) who found
that lower molecular weight polymers (5,000 - 10, 000)
were more efficient than those of higher molecular weight.
More recently, Schulz (28) studied the effects of
solids content, agitation time, agitation rate, sedimentation
time and multi-stage flocculation with inserted redispersion
on selective flocculation. The author deduced the theore-
tically and practically obtainable parameters, proceeding •
from the statement of Smoluchowski for quick coagulation.
For operating selective flocculation on a large scale,
Read and Whitehead(191) suggested the use of large elutriation
columns, while the possibility of using classifier cyclones
in the separation of flocs in the clarification of industrial
effluents has been studied by Visman and Hamza(191
Another possible technique for separating the flocs from
suspensions was described by Friend, Iskra and Kitchener092)
Thus, the engineering of selective flocculation does not
seem to present insuP'erable problems.
256
7.9. Economic assessment of the selective flocculation
process applied to an oxilizedsozpeLrore
To be practical a new separation process must be not
only technically feasible but also economical in comparison
with alternative procedures for obtaining the same result.
In the case of the fine-grained oxidized copper ore investi-
gated in this Chapter selective flocculation appears to be
a feasible method of up-grading the ore from 5.0 % Cu to
about 23.0 % Cu. Several routes might subsequently be
taken to extract copper metal from the concentrate. The
simplest might involve leaching with acid, followed by
solvent extraction with a chelating agent dissolved in
kerosene). Therefore, in this case, the question is whether
selective flocculation would be cheaper than direct leaching
of the ore. Unfortunately, however, a break-down of the
costs of this route are not yet published, as the solvent
extraction process for copper metallurgy is too recent.
As a second best, one can estimate the saving in sulphuric
acid and size of the leaching plant, though this is not the
whole advantage, since the leach liquor from the concentrate
will be very superior to that obtained from the raw ore.
Alternatively, the cost of traditional smelting of a copper
ore can be crudely compared with the cost of the selective
flocculation step. It is recognized, of course, that with-
out pilot scale tests only a very approximate estimate of
the cost can be obtained.
Experiment 25 described in 7.7 was chosen for the
economic evaluation of the selective flocculation process,
although this was not fully. optimized. In this experiment
257
the process employs hard water and about 31% solids content.
The results in Table 7.23 show three "middlings" products
namely; "Recleaned tail" "Cleaned tail" and "Scavenger
concentrate", besides the main two products, the "Recleaned
concentrate" and "Final tailings". In a continuous process,
however, these middlings would eventually split up to the
main two products (i.e., Recl.conc. and Final tail).
Assuming the middling units (wt.% x Cu%) would split
into Z (wt.%) of 18.2% Cu as concentrate, and 23.4 - Z(wt.%)
of 1.82% Cu as the tailing (where 23.4 is the total wt.% of
the three middlings). Thus from Table 7.23 . . 68.63 .
Z x 18.2% + (23.4 - z) x 1.82% . . Z = 1.55 % (
This increase in weight of concentrate would increase the
recovery to 67.3%.
Therefore, in order to produce one tonne of dry con-
centrate containing 18.2% Cu and with 67.3% recovery from an
ore containing 4.5% Cu (in experiment 25), approximately
(184.5 .2 x 67
100 3) o . tonnes of ore would have to be treated. .
1. Cost of chemical rea•ents in selective flocculation
a. Cost of sodium hydroxide: In order to raise the
pH of one litre of water from pH 7 to pH 10.8 (i.e., p0H 3.2),
approximately 25.2 mg of sodium hydroxide will be needed.
Therefore, in experiment 25, where a total of 360 ml
suspensions were used, the consumption of NaOH can be
taken as 0.23 kg/tonne ore. However, it was found in an
experiment that 4 ml of 0.1 N sodium hydroxide was needed
to bring the pH of a 100 ml ore suspension (3% solids)
from the natural pH 7.8 (in tap water) to pH 10.8. That
is, the consumption of NaOH is about 5.3 kg/tonne ore.
258
Although the presence of Calgon and Dispex in the suspension
medium will reduce the consumption of NaOH, this rate
(5.3 kg/tonne) was used in this calculation. The price of
NaOH (U.K. price) is about £4.56 /100 kg (98% solid)(193).
. . cost of NaOH per tonne ore = 5.3 x 0.046 = £0.24.
b. Cost of Calgon: The price of Calgon was taken
as approximately the same as that of a tripolyphosphate"3),
namely, £11.5 /100 kg (U.K. price). The consumption of
Calgon in this process is 2.77 kg /tonne.
. . Cost of Calgon per tonne ore = £0.33.
c. Cost of Dispex: The price of Dispex delivered
in Congo (Zaire) would probably be between £1000- 1200/dry
tonne (1910. In this calculation, the price of 1 kg is taken
as £1.2. The consumption of Dispex is 0.855 kg/tonne.
. . Cost of Dispex per tonne ore = £1.03.
d. Cost of PAMG 2.1. flocculant: The price of this
polymer may be estimated as roughly twice of that of
polyacrylamide, (which is between £1100-1400 /tonne,
\ delivered in Zaire(194)). In this calculation the price
of PAMG 2.1 is estimated at £2.5/kg.
. Cost of flocculant per tonne ore = £0.15.
Total cost of reagents per tonne of ore treated
= 0.15 + 1.03 + 0.33 + 0.24 = £1.75.
. . Total cost of reagents per 6 tonnes of ore treated by
selective flocculation = £10.5 cv$25).
1. Other costs: Values for costs of the following processes
are based on practical experience in processing copper
(195) ores with flotation
259
2. Mining cost: at an average of $5/tonne'ore mined.
. . cost of mining 6 tonnes of ore = $30.
3. Other treatments: (Such as crushing, grinding,
thickening and drying) cost on average $4/tonne ore.
. . Cost of 6 tonnes of ore = $24.
The total processing costs to produce one dry tonne
concentrate of 18.2% Cu = 24 + 30 + 25 = $79, say $80.
4. Smelting costs: The price of copper metal was taken
as announed by the London Metal Exchange at an average
value of £1000/tonne (i.e., £1/kg or $2.4/kg).
Smelting costs may include the following items:
a. The total cost of freight (plus assay, etc.) =
$10/tonne dry concentrate.
b. Smelter deduction of 1% of concentrate weight
(in copper metal) that is the value of 10 kg Cu for
each tonne concentrate.
. . Smelter deduction = 10 x 2.4 = $24
. . The total copper metal in one tonne of concentrate
after smelter deduction = 182 - 10 = 172 kg.
c. Smelter charges = $30 /tonne concentrate
d. Pefinin charges = $0.10 /kg copper metal
. cost of refining = 172 x 0.1 = $17.2.
e. Provision for smelter participation in high copper
prices (about 5%) = 5% x M000 = ( $120).
Total smelting cost = 10 + 24 + 30 + 17.2 + 120 = $201.2
. . The total value of copper from one tonne of
concentrate = 172 x 2.4 = $412.8
• Revenue from the smelter = 412.8 - 201.2 = $211.6,
(smelter return)
TV 212
The net'profit after treatments costs (items 1-3) = $132
260
Profit ratio net profit x 100 . . - total treatments cost (items 1-3) - 132 - 80 x 100 = 162%
Even if another $20 was allowed for machinery,
labour and development work in the selective flocculation
process, the profit ratio would be 112%. The relative
cost of selective flocculation reagents is about 8.9%
of the overall cost of producing copper metal. It is
anticipated that the capital cost of a selective flocculation
plant will be low.
7.10 Conclusions
The flocculation experiments reported in this Chapter
are considered sufficient evidence for the selectivity of
the new flocculant when used on a real copper ore, and
the feasibility of selective flocculation as a unit
process. Further improvements with a given ore could
certainly be achieved by further attention to details of
liberation, dispersion, optimization of reagent consumptions
and processing routes, but such development work for
commercial purposes is considered outside the scope of the
present investigation. The reagents consumption was low
(especially in experiments 21-25) which makes the selective
flocculation process very economical. The reagents
consumption could be reduced further by removing most of
the clays (by scrubbing and desliming) and quartz (by
employing "stepwise" grinding and desliming) in the early
stages of the processing.
261
CHAPTER 8: CONCLUSIONS
The main conclusions reached as a result of the
present research can be briefly summarized as follows:
1. The zero point of charge (z.p.c.) of malachite in
distilled water is between pH 9-9.5 (about pH 9.3) and
closely corresponds to its calculated pH of minimum
solubility (pH 8-9). The zeta-potential of malachite
becomes more negative and consequently the z.p.c. shifts
in to the acidic range) in the presence of "Dispex N40",
"Calgon" and sodium carbonate, but no significant effect
was detected on the z.p.c. in the presence of cupric
-4 sulphate (10 M). This is probably due to the precipi-
tation of CuSO4
as cupric hydroxide in the range pH 7-10.
2. Chrysocolla releases some copper ions on shaking
with distilled water, but leaching of Cu by acid sets in
only below pH 4. In the presence of sodium chloride, the
concentration of copper ions released from chrysocolla
increases with increasing NaC1 content. The mechanism is
probably ion-exchange.
Although the concentrations of Cu2+ ions released
from other copper minerals (oxide, carbonate and sulphide)
are very much lower than that from chrysocolla, all such
minerals release some copper ions, which could react with
compounds that strongly bind Cu2+. In the case of the
copper sulphide minerals, surface oxidation plays an
important part.
It would be valuable to study the release of Cu2+
ions from copper minerals with the aid of an ion-selective
262
electrode (though this was not available in the present
work).
3. The selectivity of the chemical bonding between the
polymer's "functional" groups and the mineral surface is
the principal factor controlling the selectivity of
adsorption of flocculants. This may be enhanced or hindered
by the electrical forces.
4. Sodium cellulose xanthate (NaCX) has shown selective
flocculation properties on heavy metal minerals and
especially copper minerals, but has no flocculation effects
on minerals like quartz, clays, calcite and feldspar.
Selective flocculation of chrysocolla from mixtures with
quartz can be achieved with or without sulphidization of
chrysocolla. Although the polymer is simple to prepare
cheaply, it has two disadvantages; (a) the molecular
weight is normally lower than that desirable for formation
of strong flocs, (b) there are difficulties in preparing
a stable form which could survive long storage and trans-
portation. However, decomposition of xanthate can be
minimized if the polymer is stored in the dry form at low
temperature and fresh solutions could then be made up when
needed. To avoid degradation of the cellulose chain,
oxygen should be excluded from the polymer during prepara-
tion and storage.
5. Xanthation of methyl cellulose, carboxymethyl cellulose
and hydroxypropylmethyl cellulose was proved possible and
uniform solutions can be achieved. Their selective flocc-
ulation properties were similar to ordinary cellulose
263 but
xanthate,Ithe molecular weights of methyl and carboxymethyl
cellulose xanthate were rather low which resulted in weak flocculation.
6. The introduction of xanthate groups to polyvinyl-
alcohol (PVA) produced a marked improvement on its floccu-
lation effectiveness on galena. This might be due to the
stronger bonding between the polymer's xanthate groups and
galena surface, and the extended configuration of polyvinyl-
alcohol xanthate (PVAX) as a result of the negative
charge of xanthate. The PVAX polymer could prove a more
potentially selective flocculant if prepared from a
polyvinylalcohol of higher molecular weight (i.e., of the
\ order of 106 . The problem of decomposition of xanthate
can be overcome by storing dry.
7. Selective flocculation of malachite and chrysocolla
from mixtures with calcite, feldspar and quartz can be
achieved with polyacrylamide-dithiocarbamate (PAD)
flocculant. The polymer was noted to slowly decompose
but this can be avoided by storing the polymer dry and
fresh solutions may then be made up. Little knowledge
is available at present about PAD, and therefore, it
deserves further detailed study on the various aspects
of preparation, purification, analysis, physical and
chemical properties so that it could be used to best
advantage.
8. The chelating polymers, PAMG, have proved to be
selective flocculants for copper minerals from gangue
minerals (e.g., calcite, dolomite, feldspar and quartz)
in both artificial mixtures and natural ores. Their
264
improved selectivity over ordinary polyacrylamide is due
to presence of the copper chelating groups (GBHA), Glyoxal-
bis-(2-hydroxyanil), in the polymer structure. Further
improvements in PAMG polymer's selectivity could certainly
be achieved by an extended investigation of the organic
chemical reactions which might be employed to "graft" the
GBHA complexing group on to polyacrylamides.
9. Selective flocculation of copper minerals from a
dolomitic ore has proved both technically and economically
feasible as a unit process, even under conditions of high
solids content ( ^i 31%) and of hard water (London tap-
water). Further improvements with a given ore could
certainly be achieved by further study of the liberation
size, dispersion, optimization of reagents consumption and
processing routes; but such development work for commercial
purposes is considered outside the scope of the present
thesis.
10. Following the same principles of preparation of PAMG
polymers, it should be possible to graft GBHA groups onto
other water soluble polymers such as polyvinyl- alcohol
(PVA), starches (e.g., amylose) and polyvinyl pyrrolidone
(PVP), since they, too, react with formallhyde. Similarly,
a selective cdepressant for copper minerals could be obtained
by grafting GBHA groups onto lower molecular weight
polymers ( <
11. Similarly, there are many other chelating groups with
a high affinity for copper ions, which could be grafted onto
various long-chain polymers to obtain a large number of
265
selective flocculant•s, or onto short-chain polymers to
obtain selective depressants.
12. These principles should also be applicable to many
other cations and their corresponding minerals. Thus an
almost unlimited series of chelating polymers can be
envisaged and could no doubt be prepared, based on the
principles illustrated by the present research.
266
REFERENCES
1. Usoni, L. et al; Proceed. 8th Intern. Min. Proc. Conan, D-13 (1968}•
2. Yarar, B. & Kitchener, J.A.; Trans. Instn. Min. Met. 79,(1970) C23.
3. Read, A.D.; Trans Instn. Min. Met., 80, (1971) C24-31.
4. Friend, J.P. & Kitchener, J.A.; Filtn. and Sepn., 2, (1972) 25-28.
5. Friend, J.P. & Kitchener, J.A.; 28, (1973) 1071-1080.
6. Attia, Y.A.: M.Sc. Dissertation, Univ. of London (1971), (R.S.M.).
7. Osborne, D.; Liplaa_nat, 128 (4), (1973).
8. Collins, D.N. & Read, A.D.; Minerals Sc12 Enanaa,, 2, (1971) 19-30.
9. Wilmhurst, R.F.; Proceed. 10th Intern. Min. Proc. Congr., Paper 26 1973 .
10. Bauer, D.J. &Lindston, R.E.; J.Metals, 29 (5), (May 1971) 31-33.
11. Paynter, J.C.; J.S.A. Instn. Min. Met., VI, (1973) 158.
12. Kitchener, J.A.; Filtn. and Sepn., 6, (1969) 553-560.
13. LaMer, V.K.; J. Colloid Sci. 19, (1964) 291
14. Kitchener, J.A.; Br. Polym. J., 4, (1972) 217-229.
15. Slater, R.W., Clark, J.P. & Kitchener, J.A.; Proceed. 8th Intern. Min. Proc. Congr., C-5 (1968).
16. Crees, 0.L.; Proceed. Ro . Austral. Chem. Inst. (Nov. 1972) 333-339.
17. Kuz'kin, S.K. & Nebera, V.P.; Synthetic Flocculants in De-watering Processes, Boston Spa, NLL (1966).
18. Fowkes, F.M.;Attractive Forces at Interfaces, in Chemistry and Physics at Interfaces, Am. Chem. Soc, Washington D.C. (1965).
19. Fowkes, F.M.; J. Colloid Interface Sci., 28, (1968) 493.
20. Slater, R.W. & Kitchener, J.A.; Disc. Faraday Soc., 42, (1966) 267.
267
21. Parfitt, G.D.; Dispersion of Powders in Liquids, 2nd edn., Applied Science, London (1973).
22. Frommer, D.W.; Blast Furnace and Steel Plant, (May 1969) 380.
23. Iwasaki, I. & Lipp, R.J.; Prog. Rep. No. 23 (1971), Univ. of Minnosota.
24. Haseman, I.F.; U.S. Patent 2,660, 303 (1953).
25. Yousef, A.A., Arafa, M.A. & Boulos, T.R.; Trans Tnstn. Min. Met., 80, (1971), C223.
26. Gogitidze, T.A. et al; Soobshch. Akad. Nauk. Gruz. SSR, 65(2), (1972) 401-403.
27. Temchenko, O.I. et al; Obogashch. Polez. Iskop., (12), (1973) 35-39.
28. Schulz, G.; f1:211222rs...chanatlttt9) A212, (1973) 95-115.
29. KorCagin, L.V. et al; as quoted in ref. 28.
30. Aleksandrovich, K.M. et al; Dokl. Akad. Nauk. Beloruss. SSR., )6(7), (1972) 635-638.
31. Brogoitti, W.B. & Howald, P.P.; German Patent 23,095,82, U.S. Patent 070472.
32. Mosina, N.V.; Issled. Tekhnol. Protsessov Dob ehi Pererab. Rud., 1971 123-130.
33. Gutzeit, G.; Trans. Amer. Inst. Min. Met. Engrs. (AIME), 1612 TiTiT) 272-286.
34. Roble, R.A. & Waldbaum, D.R.; Geol. Survey Bull., (1259), (1968) (U.S. Dept. of Interior, Washington D.C.).
35. "Stability Constants", (Ed. Special publication No. 17 Special publication No. 25 London.
36. Latimer, W.M.; Oxidation Potentials, The oxidation states of elements, Prentic-Hall, New York (1952).
37. Perrin, D.D.; Dissociation Constants of inorganic acids and bases in aqueous solution, Pure and Applied Cbem., 20(2), (1969),
38. Garrets, R.M. & Christ, C.L.; Solutions, Minerals and Equilibria, Harpur and Row, London (1965).
39. Stumm, W. & Morgan, J.; Aquatic Chemistry, Wiley-Interscience, New York, London (1970).
L.G. S1114'n & A.E. Martell)
p1964) and Supplement No. 1: 971), The Chemical Soc.,
268
40. Shindler, P.; in Equilibrium Concepts in natural water systems, Advances in Chem. Series, No. 67, Am. Chem. Soc. (1967).
41. Shindler, P. et al; Hely. Chim. Acta, 48, (1965) 1204.
42. Miller, E.; Z. Physik. Chem., 105, (1923) 73.
43. McDowell, L.A. & Johnston, H.L.; J. Am. Soc. 5.11, (1936) 2009-2014.
44. Newberg, D.W.; Econ. Geol., 62 (932), (1967).
45. Van Oosterwyck Gastuche, M.C.; C.R. Acad. Sci., Serie D; 271 (21), (1970) 1837-1840.
46. Prossor, Wright, A.J. and Stephens, J.D.; Trans. Instn. Min. Met., 74, (1965).
47. Scott, J.W. & Poling, G.W.; Trans. Can. Met. Quart. 12(1), (1973).
48. Beck, M.T.; Acta Chim. Acad. Sci. Hung., 4, (1954) 227.
49. Somasundaran, P. & Agar, G.E.; J. Colloid and Interface Sci., 24 (1967) 433-440.
50. Bowdish, F.W. & Plouf, T.M.; Trans. Soc. Min. Engineers_, AIME, 254, (1973) 66-67.
51. Parks, G.A. & Debruyn, P.L.; J. Phys. Chem., 66, (1962) 967.
52. Parks, G.A.; in Equilibrium concepts in natural water systems, Advances in Chemistry Series, Am. Chem. Soc., 67, (1967) 121-160.
Geol. 53. Sato, M.; Econ 22, (1960) 928-961.
54. Lekki, J. & Laskowski, J.; Abstr. Int. Soc. Electrochem 22nd meeting (DITBR0vNiK),(i971).
55. Sato. M.; Econ. Geol., 55, (1960) 1202.
56. Yoon, R.H. & Salman, T.; Can. Met. Quart. - 10, (1971) 171.
57. Predali, J.J. & Cases, J.M.; J. Colloid and Interface Sci., 45(3), (1973) 449-457.
58. Pugh, R. & Kitc ener, J. A,; J Colloid and Interface Sol., 35(4), (1971) 656-664.
59. Black, A.P.; J. Am. Water Works Assoc., 52, (1960) 1192.
269
60. Bier, M. & Cooper, F.C.; in Principles and applications of water chemistry, Editors: Faust, S.D. & Hunter, J.V., Wiley, New York, (1967)
61. Schindler, P. et al; Hely. Chim. Acta (1968) 1845.
62. Schwarzenbach, G.; in Advances in Inorganic Chemistry and Radiochemistry, Academic Press, (Ed., Emeleus, H.J. and Sharpe, A.G.), 2, (1961) 257-285.
63. Jonte, J.H. & Martin, B.S.; J. Am. Chem. Soc., 714, (1952) 2052.
64. Lenden, I.: Svensk. Tidskr. 64, (1952) 249.
65. Lenden, I.; ibid. 65, (1953) 88.
66. Schwarzenbach, G.; in Chemical Specificity in Biological. Interactions, Ed., Gurd F.R.N., Academic Press, New York (1954) 164-192.
67. Schwarzenbach, G.; z.2121111a.gapm., 282, (1955) 286.
68. Schwarzenbach, G., Senn, H. & Andergg, G.; Hely. Chim. Acta 40, (1957) 1886.
69. Schwarzenbach, G.; Hely. Chim. Acta, 35, (1952) 2333-2337
70. Irving, H. & Williams, R.J.P.; Nature, 162, (1948) 746
71. Irving, H. & Williams, R.J.P.; . Chem. Soc. (1953) 3192.
72. Gurney, R.W.; Ionic Processes in Solution, McGraw-Hill, New York, (1953).
73. Basolo, F. & Pearson, R.G.; Mechanisms of Inorganic Reactions, Wiley, New York (1958).
74. Bielig, H.J. & Bayer, E.; LiebigsAnnell., 580, (1953) 135.
75. Bielig, H.J. et al; Pubbl. Staz. Zool. Na oli, E2, (1954) 26.
76. Bayer, E.; Experi=LL 12, (1956) 365.
77. Goldberg, E.D.; in Chemical Oceanography, (Ed.: Riley, J.P. & Skirrow, G.) Academic Press, New York(1965) 163.
78. Neilands, J.B.; in Essays in Coordination Chemistry, Ed.: Schneider, W., Gut, R. & Anderegg, Birkhauser, Basel (1964) 222.
79. Bayer, E.; ..../kagait gtern. (Intern. Editn.), 3, (1964) 325-392.
80. Tcyssi6, M.T. & Teyssie, P.; ItfRlymer Sci., L, (1961) 253-264.
270
81. Fanta, G.F. et'al;J. Applied rrxjt Ssi., 16, (1972) 2835-2845.
82. Packham, D.I.; J. Chem. Soc., (1964) 2617-2624
83. Audsley, A. et al; Trans. Instn. Min. Met., 12, (1966) C13-25.
84. Shepherd, E.J. & Kitchener, J.A.; J. Chem. Soc., 12, (1957) 86-92.
85. Van Willigan, J.H. & Schonebaum, R.C.; Recveil Des Travaux Chimiques des Pays-Bas, T.85 (1),(1966) 35-40.
86. Stamberg, J. et al; J. Polymer Sci., a, (1958) 15-24.
87. Green, T.E. & Law, S.A..; U.S. Dept. of Interior, Bureau of Mines, R17358 (1970).
88. Parrish, J.R.; Chem. and Ind., (1956) 137
89. Gregor, H.P. et al; Ind. and Eng. Chem., 44, (1952) 2834-2839.
90. Hale, D.K.; The Analyst, J. of the Society for Analytical Chemistry, 83 (982), (1958) 3-9.
91. Saunders, K.J.; Organic Polymer Chemistry, Chapman and Hall, London, (1973)
92. Ravve, A.; Organic Chemistry of Macromolecules, Edward Arnold Ltd., London, (1967).
93. Flory, P.; Principles of Polymer Chemistry, Cornell Univ. Press, New York (1953).
94. Burger, K.; Coordination Chemistry: Experimental Methods, (English Edn. by: Millar,I.T. & Allen, D.W.) Butterworths, London, (1973).
95. Burger, K.; Organic reagents in metal analysis, Pergamon Press Oxford (1973).
96. Muzzarelli, R.A.A.; Natural Chelating Polymers: Alginic acid, chitin and chitosan, Pergamon Press, Oxford (1973).
97. Ott, E. & Spurlin, H.; Cellulose and cellulose derivatives, (high polymers vol. 5) Part I and PartIl, 2nd edn. (1963), Part III 2nd edn. (1955) Interscience Pub. Inc., New York London.
98. Miller, I.K. & Geerdes, J.D.; 131st Meeting of Amer. Chem. Soc., Miami, (1957)
99. Cichowski, Z.; Wiad. Chem., 21(9), (1969) 585-599.
100. Phillipp, B. & Liu, T.; Faserforsch. Textiltechn., 109 (1959) 555.
271
101. Sobue, H. et al; Seikel Daigaku Kogaku Hokoku, 2, (1957) 381-382.
102. reinby, B.G. et al; spakexstid.Svensl , 59, (1956) 117 and 205.
103. Hess, K.; Techn. Ind. Papet. Bull., 5, (1964) 164.
104. Oprits, 0.V. & Rassolov, O.; Khim. Volokna, 2, (1968) 27-29.
105. Sihtola, H.; Patent 1,924, 804 (C1. C08b), 1969 (German).
106. Von Horstig, W.; Eala.s.fs:29., 1L1(7), (1969) 397-405.
107.'Andersson, L., Samuelson, O. & Tornell, B.; Makromol. Chem. 112, (1968) 133-139.
108. Claus, W. & Schmiedeknecht, H.; Faserforsch Textiitechn. 11(12), (1966), 571-576.
109. Whistler, R.; Methods in Carbohydrate Chemistry, Part III, Academic Press, London, New York (1963) 238-251.
110. Czajlik, I. and Treiber, E.; HolzfLorschna, 2.2 (4), (1969) 133-135.
111. Tennant, H.R.; Textile Ind., 131(7), (1967) 143-145.
112. Samuelson, O. & Ggrtner, F.; Acta Chem. Scand., 5,(1951) 596.
113. Dux, J.P. & Phifer, L.H.; Anal tic. Chem., 29, (1957) 1842-1845.
114. Tune, D. & Bampton, R.F. & Muller, T.E.; Tappi, 52(10),(1969), 1882-1885.
115. RRnby, B.G.; Makromol. Chem., 42, (1960) 68.
116. Crow, u. & Dux, J.P. & Phifer, L.H.; Tappi, 43, (1960)620
117. Elmgren, H.; Arkiv, Kern, 24(13), (1965) 237-282.
118. Yamada, H. and Saegi, T. & Shindo, Yoji; Japanese pat. 6915675 (cl. 26F2), (1969).
119. Lyselius, A. & Samuelson, 0.;,Svensk paperstidin., 64, (1961) 815.
120. Dunbrant, S. & Samuelson, 0,4 Tazoni, 46, (1963) 520.
121. Dolby, I. & Dunbrant, S. & Samuelson, O.; LI2121222perstidn., 67, (1964) 110,
122. Dolby,I & Samuelson, O.; SveaLlspausrstidn., 68, (1965) 136.
272
123. Dolby, I & Samuelson, 0.; Las1122211-alticiaL, 69, (1966) 305-310.
124. Wellisch, E. & Rivlin, J.B.;Holzforschun, 22(5), (1968) 157-163.
125. Rivlin, J.B. & Wellisch, E.; TE121, 52(6), (1969) 1149-1153.
126. Philipp, B. & Fichte, C.; Faserforsch. Textiltechn., 11, (1960) 118 and 172.
127. Philipp, B. et al.; Faserforsch. Textiltechn., 20(12), (1969) 573-577.
128. Philipp, B. et al.; Faserforsch. Textiltechn., 20(4),
129.
130.
(1969) 179-184.
Lissfelt, J.; 131st meetin of Amer. Chem. Soc. (1957).
Tornell, B.; 12(9) , (1968) 2142-2152.
131. Sinev, 0.P; Khim. Volokna, 2, (1969) 42-44.
132. Dux, J.P. et al.; (1957).
131st meeting_of Amer. Chem. Soc.,
133. Allison, S.; Nat. Inst. Met., (1971) rep. No. 1125.
134. Tait, C.W. et al.; 2:t polnerSciL,, 7, (1951) 261-276.
135. Das, B. & Choudhury, P.K.; J. Polymer Sci., 5(A-1), (1967) 769-777.
136. Elmgren, H.; J. Chim. Phys. Physiochim, Biol., 65(1), (1968) 206-210.
137. Das, B. et al.; J. Phys. Chem., 73(10), (1969) 3413-3416.
138. Ghosh, K. & Choudhury, P.K.; Svensk papperstidn., 68, (1965) 72-75.
139. Kurata, M. & Stockmayer, W.H.; Cl, (1963) 137.
140. Takahashi, T.; Sen-i-Gakkaishi, 22(7), (1969) 319-324.
141. Allewelt, A.L. & Watt, W.R.; 11211..._Eng2Chem., 49,(1957) 68-78.
142. Nepochatykh, V.I. et al.; Khim. Volokna, (2), (1966) 49-51.
143, Rao, S.R.; Xanthates and related compounds, Marcel Dekker, New York (1971).
273
144. Greenland, D.J.f Meded Foc.Landbouwweteusch. univ. Gent., 2/, 1972 915-922.
145. Livshits A.K. & Gabrielova, L.I.; Gornyi Zhurnal, 2, (1960).
146. Fleer, G.J.; Thesis, (1971) Agricultral Univ. Wageningen; Meded. Landbouwhogesch. Wageningen 72-20 (1971).
147. Staudinger, H. & Warth, H.; J. Prakt. Chem., 155, (1940) 261.
148. Nakajima, A. & Furutate, K.; Kobunshi Kagaku (Chem. High polymers, Tokyo), 6, (1949) 460.
149. Flory, P.J. & Leutner, F.S.; 3, (1948) 880.
150. Dieu, H.A.; J. Polym. Sc!., 12, (1954) 497.
151. Hackel, E.; in Properties and applications of polyvinyl alcohol, S.C.I. Monograph No. 30, Soc. Chem. Ind., London (1968).
152. Finch, C.A.; ibid.
153. Pritchard, J.G.; PVA, Basic Properties and Uses, Macdonald & Co. (Pub.) London (1970).
154. Kurata, M. & Stockmayer, W.H.; Fortschr. HochEalm. Forsch., 3, (1963) 196.
155. Bayer, E.; Chem. Ber., 22, (1952) 2325.
156. Bayer, E.; Chem. Ber., 90, (1957) 2785.
157. Bayer, E. & Schenk, G.; Chem. Ber., 93, (1960) 1184.
158. Bayer, E.; German Patent 1102, 397 (Sep. 1961).
159. Bayer, E. & Fiedler, H.; Anew. Chem., 72, (1960) 921.
160. Bayer, E. & Mgllinger, H.; Angew. Chem,, 71, (1959)426.
161. Montgomery, W.H.; in Water-soluble Resins, (Ed.; Davidson, R.L. and Sittig, M.) Reinhold (1962).
162. American Cyanamide, Co., Market development Dept., "Cyanamer P2 Acrylamide copolymer - cyanamar P250 polyacrylamiae", (1959).
163. Schiller, A.M. & Suen, T.J.; ILLD2L,22.ta,, 48, (1956) 2132-2137.
164. Shreiber, W. &. Reinwald, E.; German Patent 2159028 Cl. Cl2f).
274
165. Norman, R.O..C.; Principles of Organic Synthesis, Methuen, London (1968) and Science paperback (1970).
166. Bio-Rad Laboratories, Catalogue Y (Aug. 1973) 47.
167. American Cyanamide Co., "Cyanomer polyacrylamides", Product information booklet, Process Chemicals Dept., Wayne NJ07470
168. Martin, R.W.; The Chemistry of Phenolic Resins, Wiley (Interscience) New York (1956).
169. Megson, N.J.L.; Phenolic Resin Chemistry, Butterworths, London (1954
170. Lilley, H.S.; J. Soc. Chem. Ind., 67, (1948) 196.
171. Vanscheidt, A.; Izv. Akad. Nauk. SSR Otd. Khim. Nauk otd. Fiz. Mat. Nauk., 1, 1943 20.
172. Megson, N.J.L.; Trans. Faraday Soc., 23, (1930 336.
173. Bio-Rad Laboratories; Gel chromatography (a Lab. manual for use with Bio-Gel polyacrylamide) California (U.S.A.) (1971).
174. Bio-Rad Laboratories; Price list catalogue (s) (Feb. 1967).
175. Miller, R.G.J.; Laboratory Methods in Infra-red Spectroscopy, Hyden & Son, London (1965).
176. Little, L.H.; Infra-red Spectra of Adsorbed Species, Academic Press, London (1966).
177. Elliott, A.; Infra-red Spectra and Structure of organic long chain Polymers, Edward Arnold, London (1969).
178. Tahoun, S.A. & Mortland, M.M.; Soil Sci., 102(5), (1966) 314.
179. Yarar, B.; Ph.D. Thesis, Univ. London (1969).
180. Vernon, P.N.; (Charter Consolidated Co.), Private communications (1973).
181. Van Lierde, A.; Trans Instn. Min. Met. 81, (1972) C204.
182. Rehbinder, P.A.; Colloid J. USSR, 20, (1958) 493.
183. Bartenev, G.M. et al; ibid, (1958) 611.
184. Khodakov, G.S. & Rehbinder, P.A.; ibid, 22, (1960) 375•
185. Rehbinder, P.A. & Taubman, A.B.; ibid, (1961) 301.
275
186. Shchukin, E.D. & Rehbinder, P.A.; ibid, 20, (1958) 601.
187. Rehbinder, P.A. & Shbhukin, E.D.; Progress in Surface Science, Vol. 3 Part 2, Pergamon Press, Oxford (1972) 97.
188. Jaycock, M.J.; in Dispersion of Powders in Liquids, 2nd edn. (Ed. Parfitt, G.D.) Applied Science, London (1973) 50.
189. Black, W.; ibid, 146.
190. Visman, J. & Hamza, H.A.; Can. Min. Met. (CIM), (Feb. 1973) 78.
191. Read, A.D. & Whitehead, A.; Proceed. 10th Intern. Min. Process. Con r.,London 7773).
192. Friend, J.P., Iskra, J. & Kitchener, J.A.; Trans. Instn. Min. Met., 82, (1973) 0235.
193. European Chem. News, (Feb. 1974).
194. Allied Colloid Co. (Bradford); Private communications to Dr. J.A. Kitchener.
195. Dr. R. Cochin; Private communctions.
196. Somers, E. & Garraway, J.L.; Chem. and Industry, (March 1957) 395.
197. Griot, O. & Kitchener, J.A.; Trans. Farada Soc., 61 (509) Pt.5, (1965), (Part 11 1026-1031, Part 2) 1032-1038.
276
APPENDIX 1. Colorimetric determination Of copper with
o h
This method is said to be very sensitive; the complex
obeys Beer-Lambert's law from 0-1 p.p.m. Cu(196) (i.e.,
it gives a linear plot of optical density against copper
concentration). According to the same authors(196) 7 it
is not affected by the presence of 100 kig of the following
ions: Fe3+ , Ni2+ , Co2+, Mn2+, Mg2+
, Ca2+, Zn2+, A13+,
2- 3 Cr4 and PO4- .
Reagents
1. EiszcyclohexanemLLELILLIae: 0.5% solution in
equal volumes of ethyl alcohol and distilled water; it
dissolves by heating.
2. Ammonium citrate; 10% solution
3. Borate buffer: 400 ml of 0.5 M boric acid + 60 ml of
0.5 M (2%)NaOH to give pH 8.1.
4. Saliarnide: 3N (i.e., 12%) solution.
5. Neutral red; 0.05% solution.
Construction of the calibration curve:
Procedure:
1. Transfer 10 ml of copper solution of different
concentrations (5, 2.5, 1, 0.5, 0.3, 0.1, 0.05 and 0.0 p.p.m.)
in eight flasks of 50 ml capacity each.
2. To each flask, add 5 ml of ammonium citrate (10% soln.)
followed by one drop of neutral red (0.05% soln.).
3. Neutralize the solutions with about 6 drops NaCl
(12% and 2% soln.) until the colour becomes yellow, then
add 5 ml of the borate buffer (pH 8.1).
277
4. 0.5 ml of bis-cyclohexane oxalyldihydraZone (0.5%
soin.) is then added to each flask and their volumes
are made to 50 ml with dist. water. The final conc-
centrations would be: 1, 0.5, 0.2, 0.1, 0.06, 0.02, 0.01
and 0.00 p.p.m. Cu respectively.
5. The optical density of the solutions are then
measured by a spectrophotometer at wave length,
X= 595 mit, in a 5 cm cylindrical cell. A linear plot
should be obtained of the optical density/copper
concentration.
The calibration curve thus obtained, was used to
determine the copper content in solutions in contact with
chrysocolla in Chapter 2, following the same procedure.
The blue copper complex develops within 10 minutes
and it is said to be stable for 3 hours(i96),
thereafter
it fades away. However, it was found in the construction
of the calibration curve, that measurements after 2.5 h
gave abnormal readings and the measurements made after
30 minutes did not give a straight line plot. But
measurements made within only 20 minutes after adding
the complexing agent (bis-cyclohexane oxalyldihydrazone)
gave a straight line graph.
All glass ware used in these determinations were
cleaned by a mixture of nitric acid and sulphudric acid,
then by washing 3-times with distilled water.
278
APPENDIX 2: Determination of copper content-by atomic
absorption spectrometry
The copper content of the various samples solutions
was determined by measuring the atomic absorption density.
Before each determination, a calibration curve was
established by measuring the atomic absorption density of
known concentration (1-10 p,p.m.) copper solutions (cupric
chloride at pH 0.5 - 1.0). The solid samples were
dissolved as follows:
1. To 0.1 g (or less) solid sample, 20 ml of cold
concentrated nitric acid was added. The suspension was
gradually heated on a hot-plate until its volume became
small (or just before dryness).
2. After cooling 20 ml of cold concentrated hydrochloric
acid was added and heating was resumed until the suspension
was reduced to small volume. The suspension was allowed
to cool before adding distilled water and then filtered.
The copper chloride solutions thus obtained were made
up to 100m1 volumes and the atomic absorption densities
were measured on a Atom-Spek (Hilger and Watts) apparatus.
279
APPENDIX 3. The action 012111Elmata=paugImjall_
on the flocculation of talc by polyacrylamide
A series of flocculation experiments were made in
order to establish the mechanism of attachment of poly-
acrylamide (PAM) on the naturally hydrophobic surface of
talc. If adsorption is due to hydrogen bonding between
PAM and the talc surface, then this should be inhibited
by the presence of "competing H-bonding agents. Griot
and Kitchener(197) reported that flocculation of pyrogenic
silica ("Aerosil") was prevented by addition of various
simple compounds such as ethers, phenols etc, which are
thought to be powerful hydrogen-bonding substances. The
failure of these H-bonding agents to inhibit flocculation
of talc with PAM would suggest that other mechanism was
operating. This mechanism was suggested by Dr. J.A. Kitchener
to be due to the h,c32":2213.0.s...22211-11212. of the hydrophobic
part of PAM and the hydrophobic surface of talc.
Procedure: 1.0% suspensions of finely ground talc
were prepared by stirring the powders in distilled water
containing different amounts of the various H-bonding
agents at pH 5 for 5 min. at high shear rate. The
suspensions were then treated with 1 p.p.m. non-ionic
polyacrylamide (N100S, D.T.I.), and flocculation was
observed visually. The results are shown in the following
Table. The following notations were used:
▪ = strong flocculation; = no flocculation;
- • = partial flocculation.
280
no.
, content
reagent type ---"--"---------,
.
10% 20%
1 urea (carbamide) + +
2 bis [2-(2-methyoxyethoxy)ethyllether + +
3 methoxy polyethylene glycol laurate + - _* -*
4 phenol +
5 aniline +
6 polyethyleneglycol 400 +
7 formdimethylamide +
8 diethyl digol +
even at 8 p.p.m. PAM
From these results, it seems that adsorption of PAM.
or talc is not likely to be due to H-bonding; but more
probably with the hydrophobic association. However,
further tests should be made to confirm these results.
