Processing and Recovery Methods
The Haile Gold Mine (HGM) employs a conventional flotation and cyanide leaching flowsheet for gold recovery. The plant commenced commercial operation in 2017 with an initial capacity of 2.3 Mtpa and has since been upgraded to 3.8 Mtpa through debottlenecking.
1. Crushing & Grinding:
– Primary crushing: ROM ore is reduced to <100 mm via a jaw crusher.
– SABC circuit (SAG-Ball Mill-Pebble Crusher):
– SAG mill operates in closed circuit with a pebble crusher (Sandvik CH-440) and vibrating screen.
– Ball mill operates with hydrocyclones to achieve a P80 of 75 µm.
– Energy efficiency: Haile ore requires 30% less energy than initially predicted, validated by power modeling and SMC testing.
2. Flotation Circuit:
– Flash flotation: A portion of the ball mill circulating load is treated in a flash flotation cell.
– Bulk rougher flotation: Recovers sulfide mineralization; combined concentrate is reground in a two-stage circuit:
– Nippon Eirich ETM-1500 tower mill (1.2 MW) to P80 <40 µm.
– M10000 Isamill (3 MW) to a target P80 of 13 µm.
– Recovery rates:
– Sulfur recovery: Improved from 60% to 80% post-regrind circuit upgrades (2019).
– Challenges: Blending oxidized ore reduced flotation efficiency; resolved via feed segregation.
3. Leaching & Adsorption:
– Pre-aeration thickener: 14 m diameter high-rate unit for dewatering reground concentrate.
– Carbon-in-Leach (CIL):
– Gold dissolution and adsorption onto activated carbon.
– Gold recovery: Initially below feasibility targets due to coarse regrind product; optimized to meet +2.5% adjusted model (2020).
– Key upgrades: Additional interstage screens, carbon safety screens, and cyanide destruction tanks.
4. Elution & Electrowinning:
– Loaded carbon is acid-washed, stripped with hot caustic-cyanide, and electrowon to produce gold-silver doré bars.
– Thermal regeneration: Reactivates carbon for reuse in CIL.
5. Tailings & Water Management:
– Tailings Storage Facility (TSF):
– Zero-discharge design; capacity expanded to 63 Mt (from 36 Mt).
– Tailings are detoxified via cyanide recovery and oxidation before storage.
– Water Treatment Plant (WTP):
– Two-stage pH adjustment (target pH 9.4) for metal precipitation, followed by microfiltration.
– Capacity expansion from 1,100 gpm to 2,640 gpm planned.
Key Technical Specifications & Equipment
– SAG mill: Throughput 389–492 t/h (2020–21), utilization 85–90%.
– Regrind mills: Tower mill (ETM-1500) and Isamill (M10000).
– Thickeners: Upgraded with Outotec Vane Feedwell systems.
– Reagents: Sodium isobutyl xanthate (SIBX), frother, NaCN, lime, flocculants.
Throughput & Recovery Performance
– Mill throughput: Exceeded predictions; 3.5–3.8 Mtpa achievable depending on ore blend.
– Gold recovery:
– Fresh sulfide ore: ~92% (feeds >1.7 g/t Au).
– Oxide/transitional ore: ~68%.
– Constraints: Ore competency, high moisture events, and regrind fineness impact recovery.
Innovations & Optimizations
– Expert control systems (Andritz): Implemented for SAG mill, CIL, and cyanide destruction.
– Froth cameras: Installed on rougher cells for better mass pull control.
– Diagnostic leaching: Monthly MLA and lab tests to identify gold losses.
Challenges & Solutions
– Regrind circuit bottleneck: Original SMD mills failed to achieve target fineness; replaced with tower mill/Isamill.
– Carbon activity issues: Addressed via kiln upgrades and regeneration optimization.
– Tailings pumping: Upgraded pumps and booster stations to support higher throughput.
Capacity & Costs
– Operating cost: US$11.57/t milled (LoM average).
– Unit consumables:
– Grinding media: 0.35 kg/t (ball mill), 0.32 kg/t (SAG).
– NaCN: 0.6 kg/t ore.
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This summary provides a comprehensive technical overview of the Haile Gold Mine’s processing circuit, emphasizing operational parameters, recovery efficiencies, and key upgrades. Let me know if you need further elaboration on any section.
