Fine Grinding - IsaMill 11 Fine Grinding There are several - - PowerPoint PPT Presentation

11

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 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

Metso- Detritor Metso- Vertimill Xstrata Technology- IsaMIll

Fine Grinding

13

• Typical refractory gold IsaMill fine grind window 25-90 kWh/t to mill

pyrite concentrates to P80 10-12 µm

10 30 50 70 90 110 1 10 100 Specific Energy (kWh/t) Size (um) High - 90 kWh/tonne Low - 25 kWh/tonne Mean - 60 kWh/tonne

Fine Grinding

14

• Commercial IsaMill Installations

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

Fine Grinding

15

• 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

Fine Grinding

16

• 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

17

Sulphide Oxidation – Albion Process

Sulphide Oxidation

18

• 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:

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

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

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

Sulphide Oxidation

19

• 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)

Sulphide Oxidation

20

• 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)