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Fine Grinding - IsaMill

Fine Grinding

12

• There are several commercially available fine grinding technologies including:

• It is not mandated to use IsaMill equipment for the Albion Process, although thistechnology would be considered the most advanced (>80 mills installed in 16countries with >130 MW installed power)

• Key requirements of fine grinding is efficient grinding of product to P80 of 10 µmto12 µm having a tight particle size distribution

Metso- Detritor

Metso- Vertimill

Xstrata Technology- IsaMIll

Fine Grinding

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• Typical refractory gold IsaMill fine grind window 25-90 kWh/t to millpyrite concentrates to P80 10-12 µm

10

30

50

70

90

110

1 10 100

Spec

ific

Ener

gy(k

Wh/

t)

Size (um)

High - 90 kWh/tonne

Low - 25 kWh/tonne

Mean - 60 kWh/tonne

Fine Grinding

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• Commercial IsaMill Installations

Operation: KCGMOwner: Newmont Mining CorpLocation: Western AustraliaTreatment Rate: 12 tph pyrite concentrateGrind Size: 10-12 µm (ahead of CIL)Equipment: 1 x M3000 IsaMill

Fine Grinding

15

• Commercial IsaMill Installations

Operation: KumtorOwner: CenterraLocation: KyrgyzstanTreatment Rate: 30-35 tph pyrite concentrateGrind Size: 10-12 µm (ahead of CIL)Equipment: 1 x M10000 IsaMill

Fine Grinding

16

• Commercial IsaMill Installations

Operation: MacraesOwner: Oceana Gold LimitedLocation: New ZealandTreatment Rate: 12 tph concentrateGrind Size: 15µm (ahead of POX)Equipment: 1 x M1000 IsaMill

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Sulphide Oxidation – Albion Process

Sulphide Oxidation

18

• Within the Albion Process there are two process chemistries that can beemployed: Acid Albion Leaching (AAL) Neutral Albion Leaching (NAL)

• Acid Albion Leach process: sulphide oxidation occurs predominatelyvia the action of ferric ion intermediates:

• This presentation will focus on Neutral Albion Leaching for treatmentof pyrite bound refractory gold

Albion Process leach conditions can be controlled to vary the extent of these reactions such that the leaching stepcan usually be operated without the addition of acid from external sources

Step 1 – MS + Fe2(SO4)3 = MSO4 + 2FeSO4 + So

Step 2 – So + 3Fe2(SO4)3 = 4H2SO4 + 6FeSO4

Sulphide Oxidation

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• Neutral Albion Leach process: oxidative leaching of pyrite destroys thesulphide matrix to liberate ferric ions and sulphuric acid.

FeS2 + 15/4O2 + 1/2H2O = 1/2Fe2(SO4)3 + 1/2H2SO4

• Ferric ions and acid are neutralized insitu to form goethite and gypsumby continual addition of limestone slurry. The overall reaction becomes:

FeS2 + 15/4O2 + 9/2H2O + 2CaCO3 = FeO.OH + 2CaSO4.2H2O + CO2

• Typical operating conditions: pH 5.5 and 95-98oC (depends on siteelevation and sulphide oxidation rate)

Sulphide Oxidation

20

• Advantages & Features of Neutral Albion Leach:

1. No elemental sulphur formationa. No passivationb. Reduced cyanide consumptionc. Reduced thiocyanate production (CN destruction)

2. Goethite major iron precipitatea. Minimizing silver losses to jarositeb. No ferri/ferro cyanide formation (CN consumption minimized)

3. Low back ground salt levels in solutiona. Minimizes scale formation due low degree of super saturation (simply operation and

maintenance)b. Enhances oxygen solubility and oxygen mass transfer

4. Eliminates the need for CCD and external dedicated neutralization circuits (reduced capital)