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).

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BMS Liberation Graph – Merensky Concentrate

+45µm+38µm

+25µm+10µm

+2µmCombined

Lock

Mid

Lib0

10

20

30

40

50

60

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80

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100

% o

f T

ota

l BM

S

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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...

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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

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tal

Min

eral

)

BMS locked in Ternary particles with...

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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

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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

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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

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PGMs in Merensky Concentrate