The Role of Dissolved Mineral

species in

Calcite-Apatite Flotation

K. P. Anan thapadmanabhan

and

P. Somasundaran

Henry Krumb School of Mines

Columbia University

New York, N.Y~ 10027

l.

-4-

solution. The pH of the supernatant prepared in this manner was

adjusted to the desired value.

Preliminary tests, indicated development of turbidityTurbidity.

in certain collector solutions after contacting them with calcite

Turbidity of these solutions were therefore monitored by measuring

the' of light transmitted using a spectronic20 spectrophotometer.

RESULTS

Calcite flotation

The results obtained for the pH dependence of flotation of

-4 3calcite using 10 kmol/m potassium oleate at two levels of

pH. Interestingly, flotation at the minimum is found to increase

from about 25% to 85% with increase in KNO3 from 0 to 3 x 10-2

kmo1/m3. Flotation again increases to about 100% around pH 13.

The effect of apatite supernatant on oleate flotation of

calcite at both levels of KNO3 is to depress the flotation marked-

ly in the pH region of 6 to 12.5 (see Figure 2). Most interesting-

the effect of calcite supernatant on its own flotation is

also to depress it significantly in this pH range (see Figure 3)

Thus, while both the supernatants of calcite and apatite depress

calcite flotation under s~ilar pH conditions, their effect is

the depressing effect of apatiteminimal above pH 13. Also,

supernatant is more severe than that of the calcite supernatant.

implications of these observations to the use of recycled water

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K2CO3 and K3PO 4 to depress the flotation Inarkedly and Ca (NO3) 2

not to have a measurable influence. Evidently, the effects

of supernatants of calcite and apatite on apatite flotation are

due to carbonate and phosphate species respectively.

DISCUSSION

Flotation being the result of adsorption of collector on

the mineral surface during conditioning, any process that iner-

teres or minimizes such adsorption can lead to a decrease in

flotation. Such processes are alteration of the mineral surface

or the adsorbed film on it and the alteration or depletion of the

collector and other flotation agents. Specifically they include

change in the interfacial potential of the particle

change in the chemical or mineralogical composition

of the surface due to dissolution and other surface

chemical reactions or precipitation on the surface

coating of the mineral particle by prec:1.pitate

particles OJ: slimes

adsorption of depressants

depletion of the active collector species by precipitation,

hydrolysis or decomposition

observed depression of apatite and calcite flotation

under various conditions is examined here in the light of minera~~

solution equilibria involving various dissolved mineral species,

chemical additives and the collector

Calcite Flotation

The effects of apatite and calcite supernatants on calcite

flotation is to depress the flotation markedly in the neutral

to alkaline pH (pH < 13) range. A comparison of the effects

of added inorganics with those of the supernatants suggests that

the depressing effect of apatite supernatant is the combined

effect of,calcium and phosphate species in solution. The effect

of calcite supernatant is mostly that of calcium and possibly

some of carbonate. A comparison of the shape of the flotation

curve, the extent of depression, the pH range of depression and

the pH dependence of turbidity in different cases suggests the

"Ca effect" to be the dominant effect responsible for depression

by the supernatants. The individual effects of a Ca as well as

carbonate and phosphate can be somewhat altered.. in the presence

of one another.

Carbonate and phosphate species can be expected to chemisorb- --

on the calcite surface and thus can compete with oleate for the

surface Casites resulting in flotation depression. Ca on the~ - - -

other hand 9an be expected to interact with oleate leading to- ~ ...

Ca-oleate precipitation. If the latter occurs preferentially-

the precipitate can impart hydrophobicityon the mineral surface,

to the mineral. Bulk precipitation may however only deplete~the available oleate and thus result in a depression in f1otation.

- --'-

The correlation of the flotation to the changes in turbidity of

the supernatant of calcite and apatite and CA(NO3)2 solutions

-9-

~Su9gests bulk precipitation of Ca~leate to be a major factor re-

sponsible for the observed depression

The above hypothesis involving oleate depletion by precipitation

can be tested by determining the thermodynamic conditions under

which bulk precipitation of Ca oleate is expected. The pre-

cipitation of Ca-o13ate can occur in the system, when

activities of calcium and oleate satisfy the condition,

a . .2Ca++ 01- sp (1)--

~~-- K =15.6 (1)sp- --

The source of calcium in a single mineral-water/KNO3 system

will be the mineral itself and hence the precipitation of Ca-

~ J(

-where

oleate can be expected to depend upon the rate of dissolution of

the mineral. Further more, if oleate can undergo other reactions

such as adsorption on the mineral surface and pH dependent pre-

cipitation in the form of oleic acid, some of which may not be

totally reversible, then the relative kinetics of various re-

actions including that of the mineral dissolution will determine

the state of the system.

In tests using supernatant where the dissolved calcium is

,

instantaneous bulk precipitation of Ca-oleate can be expected

under certain pH conditions. The amount of dissolved calcium~

in turn is governed by the complex chemical equilibrium that pre-

For example~ the equilibria that controlsvails in the system.

the dissolution of apatite are given below (9-12):

-10-

4+ 10 ca2+ + 2(F,OH K

PO3-+ H+4 1012.3...+

+ H PO-2 4 107.2+ H ...+

...+ 102.2H3PO4

+CaOH + H

(5)

ca2+ +. +10-12.9820 +

ca2+ 10-22.8+ 280-+2

+ H+ 103.1F HF..,..

102.7+... CaHPO 4 (aq

104.3CaHPO4(aq) CaHPO4(S)+:.. ().O)

ca2+ 101-.1+ H2PO4 :

ca2+ + 2F' 1010.4(5)caF2...+

2+ .Ca + F :+ 101.0CaF+

...

Using the above chemical equilibria and the two stoichiometric

restrictions, activities of various species were computed for

different pH values: ca2+ activity obtained in this manner is

given in Figure 14. The experimentally obtained value of

(5.8)at the end of 10 minutes of conditioning in water is in agreement

with the value obtained from the above thermodynamic calculations

13-12-

owing to Ca-oleate precipitation.

The role of Ca-oleate precipitation in causing the depression

by calcite supernatant and Ca(NO3) 2 is next examined using the cor-

responding thermodynamic data for calcite. Calcite supernatant pre-

(pH-9.8) was analyzed to containpared under natural pH conditions

l.75xlO-4kmol/m3 calcium. The calcium in equilibrium with calcite

that can be expected from thermodynamic considerations can be

computed from the following equilibria-+- 2+ 2-caCO3(s) ... Ca + CO3

13, 14)(10,

10-8.4 (14)

(15)1010.3

106.3

J;O~l.S

100.8

103.3

10-12.9

(16)

(17)

(18)

(19)

CO~- + H+ :: HCO;- +-+HC03 + B ... B2C03

C02(g)+H20:: B2C03.2+ - -+- +Ca +HC03 ... CaBC032+ 2 -+Ca +CO 3 ... Cac03(aq)2 -+ + +Ca + H2O ... CaOH + H

Ca2+ +282° :::: Ca (OH) 2 +28." ~ _: (21)

It is to be noted that solubility of calcite in water exposed

(20).. 10-22.8

to the atmosphere is significantly different from that of calcite

in a closed system (see Figure 14). In the present study, the super-

natants were prepared in a closed system under natural pH conditions

and the experimentally obtained calcium concentration

is in agreement with the calculated value indicating that the min-

eral solution dissolution has attained equilibrium in this case

It is evident from Figure 1 that at thisalso within ten minutes.

level of calcium, precipitation of Ca-oleate can be expected above a

suchpH of 6.7. Again, as in the case of apatite supernatant,

:'1

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in the presence of supernatants to coincide with that of

calcium-oleate precipitation. Calcium-oleate precipitation

is minimized in the high alkaline pH region due to reduction

in ca2+activity owing to hydrolysis and ionic strength

effects.

The observed flotation-depression by apatite supernatant6.was restored upon adding excess oleate further indicating

that the depletion of oleate due to precipitation is indeed

responsible for the decrease in flotation.

7. Flotation of apatite also was depressed by the supernatants

of both calcite and apatite.

The effects of supernatants of calcite and apatite on ap-8.atite flotation is attributed to that of carbonate and

phosphate species respectively.

Competition between oleate and phosphate/carbonate for the9.surface calcium sites is suggested to be responsible

for the effects of phosphate/carbonate species on apatite

flotation. Calcium oleate precipitation does not occur

to a significant extent in this case due to the lower

level of oleate used for the flotation of apatite

10. The observation that the flotation of calcite and apatite

is markedly affected by their ~. supernatants reveals

the importance of realtive kinetics of interactions, min-

eral dissolution and bulk precipitation versus that of

adsorption or surface precipitation of oleate.

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11. The results obtained for the effects of supernatants

clearly show that the use of recyceled water in plants

can deleteriously affect flotation.

ACKNOWLEDGEMENTS

Support of the Minerals and Primary Materials Program of

the National Science Foundation is greatly acknowledged.

REFERENCES

1. Fuerstenau, M.C. and Palmer, B.R., "Anionic flotation ofOxides and Silicates," Flotation, M.C. Fuerstenau, Ed., Pub.AIME, New York, 1976.

2. Sun,.S.C., Snow, R.E. and Purcell, W.I.., "Flotation Character-istics of Flotida leached Zone Phosphate Ore with Fatty

Acids," Trans. AIME, Jan. 1957, p. 70

3. Smani, M.S. et-a1., "Bene£iciation of Sedimentary MoroccanPhosphate Ores," Trans. AIME, ~, 1975, p.168-182.

4. Hanna, H.S. and Gruner, H., "the Influence of Electrolytes onthe flotation of Fluorite and Barite with Oleic Acid,"Freiberger Forschungth, AS1a, 1972, p.61 (Ger. Text)

5. Orphy, M.K. Saleeb, F.Z. and Hanna, H.S., "Studies on theSelective Flotation of Phosphate Minerals," Bull, Faculty Eng.,Cairo Univ., 1967-68, P. 505.

6. Bilsing, U. and Gruner, H.,"The Effect of Dissolved Ions onFlotation of Spar Minerals," Freiberger Forschungth, AS13 1973,PP 29-43. (Ger. Text)

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8. Fuerstenau, D.W., Metzger, P.H., Seele, G.D., "How to Use thisModified Hallimnd Tube for Better Flotation Testing,"~, ~ (3), 1957, P. 93.

9. Somasundaran, P. "Zeta Potential of Apatite in Aqueous Solutionsand Its Change During Equilibration," J.Co11. and Interface Sci.,27 (4), 1968, P. 659.

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Stumm, W. and Morgan, J.J., Aquatic Chemistry, Wiley Inter-science, New York, 1981.

11. Avnimelech, Y. Moreno, E.C. and Brown, W.E., "Solubility andSurface Properties of Finely Divided Hydroxyapatite," J. Resof,NBS, 77, A1, Jan-Feb., 1973, p. 149.

12. Chander, S. and Fuerstenau, D.W. "On the Dissolution andInterfacial properites ofiHydi:ox".lapat~--"~J.ioids and. Surfaces.4 (2),1982, p. 101. ,_.,-

13. Somasunadaran, P. and Agar, G.E., "Zero Point of Charge ofCalcite,. J. Coll, and Interface Sci, ~, 1967, p. 433.

Garrels, R.M. and Christ, C.C., ~oluti~~~_Minerals and Equilibria,Freeman, Cooper & Co., San Franc~sco, 1965.

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