Fine Grinding - IsaMill

11 Fine Grinding

• There are several commercially available fine grinding technologies including:

Xstrata Technology- IsaMIll Metso- Detritor

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

• Key requirements of fine grinding is efficient grinding of product to P80 of 10 µm to12 µm having a tight particle size distribution

12 Fine Grinding

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

110

90 High - 90 kWh/tonne ) t / h W

k 70 ( y g r e n

E Mean - 60 kWh/tonne c i f i

c 50 e p S

30 Low - 25 kWh/tonne

10 Size (um) 1 10 100

13 Fine Grinding

• Commercial IsaMill Installations

Operation: KCGM Owner: Newmont Corp Location: Western Australia Treatment Rate: 12 tph pyrite concentrate Grind Size: 10-12 µm (ahead of CIL) Equipment: 1 x M3000 IsaMill

14 Fine Grinding

• Commercial IsaMill Installations

Operation: Kumtor Owner: Centerra Location: Kyrgyzstan Treatment Rate: 30-35 tph pyrite concentrate Grind Size: 10-12 µm (ahead of CIL) Equipment: 1 x M10000 IsaMill

15 Fine Grinding

• Commercial IsaMill Installations

Operation: Macraes Owner: Oceana Gold Limited Location: New Zealand Treatment Rate: 12 tph concentrate Grind Size: 15µm (ahead of POX) Equipment: 1 x M1000 IsaMill

16 Sulphide Oxidation – Albion Process

17 Sulphide Oxidation

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

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

o Step 1 – MS + Fe2(SO4)3 = MSO4 + 2FeSO4 +S o Step 2 – S +3Fe2(SO4)3 = 4H2SO4 + 6FeSO4

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

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

18 Sulphide Oxidation

• Neutral Albion Leach process: oxidative leaching of pyrite destroys the sulphide 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 gypsum by 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 site elevation and sulphide oxidation rate)

19 Sulphide Oxidation • Advantages & Features of Neutral Albion Leach:

1. No elemental sulphur formation a. No passivation b. Reduced cyanide consumption c. Reduced thiocyanate production (CN destruction)

2. Goethite major iron precipitate a. Minimizing silver losses to jarosite b. No ferri/ferro cyanide formation (CN consumption minimized)

3. Low back ground salt levels in solution a. 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)

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