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Process mineralogy in the mining industry Jacques Eksteen Consulting MetallurgiMarch 2011. Factors to investigate during process development. The mineralogical microstructure of the ore body - PowerPoint PPT Presentation
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Lonmin Plc
Process mineralogy in the mining industryJacques EksteenConsulting MetallurgiMarch 2011
Factors to investigate during process development• The mineralogical microstructure of the ore body• Not only the minerals / metals of interest, but specifically
the minerals associated with the mineral / metal of interest.• The degree of dispersion of the valuable mineral within the
matrix of less valuable minerals.• The morphology (size, shape, crystallinity and texture) of
the minerals• One ore high in a valuable mineral / metal grade may still
not necessarily be economical to extract compared to one of a lower grade, due to a difference in associated minerals or the level of dispersion and intergrowth patterns.
Techniques to characterize ore mineralogy• X-Ray Fluorescence (XRF): Technique which can be used to determine the quantities
of elements present…usually reported as their oxides. It is a quantitative method.• X-Ray Diffraction (XRD): Identifies minerals based on the effect their different
crystallographies have on the diffraction of X-rays. Used in conjunction with Rietveld refinement it becomes semiquantitative. Amorphous solid phases and glasses are not easily quantifiable.
• Inductively coupled plasma (ICP): A quantitative method to determine the quantities of elements present after a samples has been dissolved. • It is normally couples to MS or OES depending on the concentrations of the species to be measured.
• Laser ablation ICP – MS: Solid state ICP-MS• Scanning electron microscopy with energy dispersive system (SEM-EDS): Used to
identify intergrown minerals, relative quantities, mineral chemistries i.t.o. their elements.
• Optical Microscopy: Mineral identification using transmitted or reflected light• Liberation analysis and diagnostic leaching: Grinding and wet chemical analysis to
analyze mineral associations.
Common binary intergrowth patterns
Effect of particle morphology on processes
Mineral Shape & Porosity
• Shape can be isometric, plate-like, irregular, fibrous, etc.• Shape influence behaviour in process• Shape deviations (from the spherical particle form) may cause
difficulties when screening, floating, or transporting mineral slurries• Porous ores are easier to leach or roast than dense ones, as the
lixiviant or roasting gas can enter via the pores in the ore to gain access to the mineral to be transformed.
Mineral associations may vary as one mines deeper into an ore body
• As a mineral reef are characterized by a certain assemblage of valuable and associated gangue minerals, mining into a different reef would result in a different combination of valuable and gangue minerals.• Example: Merensky reef, Plat reef and UG2 reef found in the Bushveld
Igneous Complex• Example: Reef outcrops tend to show weathering (oxidation and effect of
carboxylated water and humic acids) which change their mill & float behaviour, leaching behaviour and smelting behaviour.
• Different reefs within the same mine might require an adaptation of existing technologies, e.g. platinum mines used to mine the more accessible and easier-to-process Merensky Reef, but due to the reef becoming scarcer, they have to adapt their processes to handle the chrome-rich UG2 layer, which is more difficult to obtain a low chromite flotation concentrate and causes significant problems when conventional smelting and converting operations are used.
Typical composition of Merensky and UG2 reefs
Mineral Name Mineral Composition Volume % Volume %
Merensky Reef UG2 Reef
Enstatite (Mg, Fe)SiO3 55-60 15-20
Feldspar (Ca, Na)(Al, Si)2O3 35-40 3-5
Chlorite (Mg, Fe, Al)6(Al, Si)4O10(OH)8 ≈1 <1
Talc Mg3Si4O10(OH)2 2-3 1-2
Tremolite Ca2Mg5Si8O22(OH)2 1 ----
Serpentine (Mg, Fe, Ni)3Si2O5(OH)4 <1 <1
Chromite (Fe, Mg)(Cr ,Al, Fe)2O4 1 70 – 75
Pyrrhotite Fe1-xS (x ≤ 0.2)
Pentlandite (Ni,Fe)9S8 ≈1 <0.1
Chalcopyrite CuFeS2
Pyrite FeS2
Sulphides
Platinum Group Metal (PGM) MineralizationClass Minerals Vol% in Merensky Vol% in UG2
PGM Alloys Ferroplatinum: Pt3Fe 29.1 21.2
Palladium Alloy: (Pd, Cu)
Electrum (Au, Ag)
Arsenides Sperrylite : PtAs2 17.2
PGM sulphides Braggite (Pt, Pd) NiS 25.4 45.5
Cooperite PtS
Laurite (Ru, Os, Ir)S2 9.8 29.8
Tellurides Moncheite: PtTe2 16.8
Merenskyite: PdTe2
Others 0.1 3.5
Occurrence with
Sulphides 67 53
Silicates 32 20
Chromite <1 3
Liberated PGM 24
Typical PGM Content of the UG2 and Merensky Reefs
Merensky UG2
Metal Grade g.ton-1
% total PGM
Value R.ton-1
Grade g.ton-1
% total PGM
Value R.ton-1
Pt 3.24 59.2 482 2.46 41.0 366
Pd 1.37 25.0 127 2.04 34.0 190
Ru 0.44 8.0 8 0.72 12.0 13
Rh 0.16 2.9 37 0.54 9.0 125
Ir 0.06 1.1 5 0.11 1.8 9
Os 0.04 0.7 0.10 1.7
Au 0.17 3.1 16 0.03 0.5 3
Total PGM
5.43 675 6.00 706
Ni 1800 250
Cu 1300 100
General remarks
• UG2 often has an inherently higher PGM value than Merensky, however:
• UG2 reef has much PGMs associated with silicates and chromites (or on
their grain boundaries), and requires energy intensive ultrafine grinding to
liberate.
• Complete rejection of the chromite is nearly impossible as flotation
separation between gangue and valuable particles become more difficult
as the particles becomes finer (especially below 20 micron).
General remarks (continued)
• UG2 concentrates are high in altered silicates such as talc, which can
relaase significant water during heating in a furnace. Halogen (F, Cl) ions
in the crystal latice, together with water released during smelting cause
severe corrosion.
• the fineness of grind to liberate the PGMs from the host minerals, leads to
significant dusts losses in the furnace.
• The fine particle size contribute significantly to the loss of concentate bed
porosity in a furnace leading to overheating of the liquid bae meta
sulphide (matte).
13
BMS Liberation Graph – Merensky Concentrate
+45µm+38µm
+25µm+10µm
+2µmCombined
Lock
Mid
Lib0
10
20
30
40
50
60
70
80
90
100
% o
f T
ota
l BM
S
14
BMS Binary Locking Graph – Merensky Concentrate
+45µm+38µm
+25µm+10µm
+2µmCombined
PGM
Chromite
Other Silicates
Altered Silicates
Pyroxene
Others
0
2
4
6
8
10
12
BM
S (
% o
f to
tal
Min
eral
)
BMS locked in Binary particles with...
15
Ternary Locking Graph – Merensky Concentrate
+45µm+38µm
+25µm+10µm
+2µmCombined
PGM
Chromite
Other Silicates
Others
Altered Silicates
Pyroxene
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
BM
S (
% o
f to
tal
Min
eral
)
BMS locked in Ternary particles with...
16
Relative PGM abundance (Area %)Mineral ANM PSL MConc* EHG ELG RHG RLG
Electrum 0.0 0.0 1.7 0.0 0.0 0.3 0.0
Ferroplatinum 7.5 7.7 1.5 0.4 0.0 10.2 4.1
Atokite 0.1 0.2 0.3 0.6 0.1 0.2 0.6
Plumbopalladinite 5.3 5.3 0.2 1.1 0.3 1.3 2.8
Sudburyite 1.7 0.0 0.0 1.0 0.2 0.0 0.2
Stumpflite 0.0 0.0 0.3 0.0 0.0 0.0 0.0
PGE Alloys 6.1 25.8 0.1 0.1 0.0 0.5 0.7
Cooperite 16.1 17.9 22.7 15.3 15.1 23.9 16.6
PtRhCuS 3.2 6.5 0.1 19.7 23.6 5.7 7.5
Kharaelakhite 2.0 3.7 0.3 6.8 4.6 3.3 5.8
Braggite 4.0 4.5 20.6 37.4 20.3 32.5 11.7
Vysoskite 2.7 2.9 0.0 1.4 2.8 1.4 0.0
Laurite 0.6 0.0 0.8 3.6 18.3 4.4 32.5
Sperrylite 19.6 17.1 9.4 1.2 2.1 4.1 1.4
Atheneite 0.0 0.0 0.0 0.5 0.0 0.6 0.2
Arsenopallandinite 0.8 0.1 0.5 3.6 0.4 0.6 0.1
Stillwaterite 1.6 0.0 0.0 1.1 0.4 0.3 0.0
PtPdAs 1.8 1.6 1.5 2.1 2.5 1.9 2.9
Platarsite 0.7 0.7 1.3 0.8 1.8 1.7 0.2
PtPd Sulpharsenide 3.6 4.4 0.6 1.4 4.2 3.1 3.6
Hollingworthite 0.5 0.0 0.0 0.1 0.1 0.0 0.0
Irarsite 3.0 0.3 0.0 0.7 1.2 1.6 0.7
Ruarsite 0.0 0.0 0.0 0.0 0.1 0.0 0.0
Temagamite 0.8 0.0 0.8 0.6 0.7 0.4 1.8
Maslovite 9.6 0.4 29.5 0.2 0.9 1.1 6.2
Moncheite 0.4 0.0 2.8 0.2 0.0 0.0 0.0
Kotulskite 8.3 0.8 4.7 0.1 0.3 0.9 0.3
Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0
17
Relative PGM abundance by PGM mineral Group
0%
20%
40%
60%
80%
100%
ANM PSL MConc EHG ELG RHG RLG
Min
eral
Are
a %
PGE Alloys PGE Sulphides PGE Arsenides PGE Sulpharsenide PGE Tellurides
18
PGM deportment in Merensky Concentrate
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
<10 >10<20 >20<40 >40<80 >80<160 >160<320
Particle size categories (µm)
We
igh
t % Locked
Middlings
Liberated
No. of Particles = 227PGM d50 = 15 µm
N = 108 N = 61 N = 33 N = 14 N = 9 N = 2
19
PGMs in Merensky Concentrate
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