The Tucano Gold Mine employs a comprehensive gold processing circuit designed to handle a blend of predominantly (90%) hard sulphide ore at a design capacity of 3.4 Mt/a, with expansions enabling treatment of 3.6 Mtpa. The process integrates crushing, grinding, leaching, adsorption, elution, and tailings detoxification, with notable innovations in oxygen injection and hybrid CIL configuration.
Processing and Recovery Methods
1. Crushing and Stockpiling:
– Primary crushing: METSO C-150 jaw crusher (1400 mm × 1200 mm, CSS 125 mm) with a vibrating grizzly to bypass sticky oxide ore.
– Ore blending: Oxide and sulphide ores are stockpiled separately and blended via front-end loader feed to meet grade targets.
– Emergency handling: Surge bin (30 min residence) and spent ore feeder for direct SAG mill bypass.
2. Milling and Classification:
– SAG mill: Outotec 7.32 m diameter × 7.95 m EGL, 7 MW drive, open circuit.
– Ball mill: Outotec 6 MW motor, closed circuit with 10 hydrocyclones (80% <75 µm P80).
– Cyclone feed: Two Weir 490 HP pumps; cyclones feature 210 mm apex and 5″ vortex.
– Pre-leach thickening: 28 m diameter Outotec thickener recycles water to grinding; underflow pumped to pre-leach tank (24 hr residence at 450 t/hr).
3. Hybrid CIL Circuit:
– Tank configuration: One 2,650 m³ pre-leach tank + six 2,650 m³ CIL tanks in series.
– Oxygen injection: >15 ppm dissolved oxygen (DO) in pre-leach tank (Tank 1) via dedicated pulp recycle; supplemental oxygen in Tanks 2–4; air in Tanks 5–7.
– Carbon management:
– Counter-current carbon flow (Tank 6 to Tank 1) using recessed-impeller transfer pumps.
– Mechanically swept wedge-wire inter-tank screens (12 m² each) for carbon retention.
– “Pump screen” design eliminates stepped tank arrangement, simplifying civil works.
– Reagents: Sodium cyanide (Leach Tank 1), lime slurry (pH control), lead nitrate (gold dissolution aid).
4. Elution and Carbon Regeneration:
– Zadra pressure elution: 135°C, 0.1% NaCN + 1% NaOH solution, 720 kW heater.
– Capacity: 4.8 t/d carbon (operating at 14.4–19.2 t/d to reduce gold inventory).
– Carbon regeneration: 700°C kiln; quenched and screened to remove fines before returning to CIL.
5. Electrowinning and Smelting:
– Electrowinning: Four cells with stainless-steel wool cathodes; 12–15 hr cycle.
– Gold recovery: Sludge dried, fluxed, and smelted in gas-fired furnaces to produce doré bars.
6. Tailings and Cyanide Detoxification:
– Tailings disposal: Pumped 6.5 km to East Pond TSF; water reclaimed for reuse.
– Cyanide destruction: Two-tank air/SO₂ circuit (60 min residence) using SMBS, lime, and CuSO₄, reducing cyanide to ~10 ppm in return water.
Key Technical Specifications and Parameters
– Throughput: 3.4–3.6 Mtpa (450 t/hr design).
– Grinding product size: 80% <75 µm.
– Leach residence time: 24 hours.
– Energy demand: 17 MW (fresh ore), 15.5 MW (30% oxide blend).
Innovations and Challenges
– Hybrid CIL design: Pre-leach tank enhances gold adsorption kinetics by ensuring gold dissolution before carbon contact.
– Oxygen optimization: Dual oxygen plants (2018–2019) boost DO levels for sulphide ore treatment.
– Carbon inventory management: Elution circuit operates above design capacity to minimize gold lock-up.
Recovery Efficiencies
– Adsorption kinetics: Improved by pre-leach tank DO control (>15 ppm).
– Cyanide destruction: Tailings detoxified to environmentally compliant levels (36% solids discharge).
The circuit demonstrates robust integration of crushing, grinding, and leaching technologies, with tailored solutions for sulphide dominance and scalable throughput. Operational challenges include carbon inventory optimization and maintaining DO levels in leaching.
