The Essakane Gold Mine employs a comprehensive gold recovery process combining crushing, grinding, gravity concentration, and carbon-in-leach (CIL) cyanidation. The processing circuit has undergone expansions and optimizations since its initial 2008 feasibility study, increasing throughput capacity from 7.5 Mt/a to >11.7 Mt/a.
Processing and Recovery Methods
1. Crushing Circuit:
– Primary Crushing: Gyratory crusher processes ore at 1,912 t/h.
– Secondary Crushing: Upgraded from MP1000 to MP1250 cone crusher (750 kW) to enhance capacity.
– Screening: Double-deck vibrating screen separates oversize for secondary crushing.
2. Grinding Circuit (SABC Configuration):
– SAG Mills: Two lines (A & B), each with a 9.1 m diameter × 4.3 m EGL mill (7 MW motor).
– Ball Mills: One 6.1 m diameter × 10.2 m EGL ball mill per line (7 MW motor).
– Pebble Crushers: One per line, operating in closed circuit with SAG mills.
– Cyclones: Classify ground slurry to a target P80 of 125 µm.
3. Gravity Concentration:
– Centrifugal Concentrators: Two per line recover coarse gold, achieving ~45% recovery (theoretical potential: 75%).
– Intensive Cyanidation: Gravity concentrate undergoes inline leaching, with gold recovered via electrowinning and smelting.
4. Leach-CIL Circuit:
– Pre-Leach Thickening: Cyclone overflow thickened to 50% solids in a 50 m diameter thickener.
– CIL Trains:
– Line A: Ten tanks (16.56 m diameter × 19.56 m tall), first tank for pre-aeration.
– Line B: Eight tanks (same dimensions).
– Cyanidation: Oxygen (15 t/day plant) and cyanide are added; activated carbon adsorbs gold.
– Elution & Electrowinning: Loaded carbon is acid-washed, eluted, and regenerated in a kiln. Gold sludge is smelted into doré.
5. Tailings Management:
– Thickened tailings are stored in a pond, with water reclaimed for reuse.
Technical Specifications & Operational Parameters
– Throughput: 11.7 Mt/a (blended ore) or 10.8 Mt/a (100% fresh rock).
– Power Consumption:
– Grinding: 6.0 kWh/t (saprolite), 10.0 kWh/t (transition), 17.5 kWh/t (hard rock).
– Total plant demand: ~35 MW (out of 40 MW total site usage).
– Reagents: Sodium cyanide, lime, activated carbon, flocculants, and grinding media (50–120 mm balls).
Innovations & Challenges
– Expansions:
– Line B (2014): Doubled fresh rock capacity via secondary crusher, additional SAG/ball mills, and CIL tanks.
– 2019 Upgrades: MP1250 crusher, high-capacity screens, and pebble crusher bypass mode improved efficiency.
– Energy Optimization: Solar plant (14.92 MWp DC) reduces CO2 emissions by 18,000 t/year.
Recovery Efficiencies
– Gravity circuit recovers ~45% of gold; overall recovery via CIL is not explicitly stated but optimized for ore blends.
Key Challenges
– Ore Variability: Hard rock increases energy demands (17.5 kWh/t vs. 6.0 kWh/t for saprolite).
– Water Management: Reliance on seasonal Gourouol River, mitigated by recycling from tailings.
The Essakane circuit exemplifies a robust, scalable design with continuous debottlenecking to adapt to ore hardness and throughput demands.
