The Pueblo Viejo processing plant is designed to treat refractory ore at a rate of 24,000 tonnes per day (tpd). The plant employs a pressure oxidation (POX) circuit as the primary method for sulfide sulfur oxidation, followed by carbon-in-leach (CIL) cyanidation for gold and silver recovery.
Processing and Recovery Methods
1. Crushing & Grinding
– Primary Crushing: ROM ore is crushed to P80 of 130 mm using a gyratory crusher, then conveyed to a coarse ore stockpile.
– Grinding: A SAG mill (closed circuit with pebble crusher) and ball mill (closed circuit with hydrocyclones) reduce the ore to P80 of 80 µm.
– Expansion: A new single-stage SAG (SS-SAG) mill is being added to increase throughput.
2. Pressure Oxidation (POX) Circuit
– Autoclave Conditions: Operates at 225°C and 3,100 kPag (500 PSIG) with a 60-minute retention time.
– Oxygen Supply: The oxygen plant is a bottleneck, designed to oxidize 80 tph of sulfide sulfur (requiring 2.2 tonnes O₂ per tonne sulfide sulfur).
– Hot Cure: Oxidized slurry is held at >90°C for 12 hours to dissolve ferric sulfate, reducing neutralization costs.
3. Counter Current Decantation (CCD) Wash Circuit
– A three-stage CCD circuit removes dissolved metal sulfates and sulfuric acid.
– CCD overflow (containing >99% dissolved metals) is used for autoclave quench cooling, reducing emissions.
4. Lime Boil & Neutralization
– Lime Boil: Slurry is reheated to 95°C to break down jarosites and liberate silver.
– Neutralization: Uses limestone and lime in a high-density-sludge (HDS) circuit to precipitate metal sulfates.
5. Carbon-in-Leach (CIL) Cyanidation
– Gold/Silver Extraction: Cyanide and activated carbon recover gold/silver from cooled slurry (50°C).
– Carbon Regeneration: Loaded carbon is acid-washed, stripped via Zadra elution, and reactivated in kilns.
– Electrowinning (EW): Gold/silver are recovered from pregnant solution, then smelted into doré bars.
6. Tailings & Effluent Treatment
– Cyanide Destruction: Uses the INCO process (SO₂ + air + Cu catalyst) to detoxify tailings.
– Acid Rock Drainage (ARD) Treatment: Neutralized sludge is thickened and sent to the tailings facility.
Expansion Project (14 Mtpa Capacity)
– Flotation Circuit: Added to upgrade low-grade ore, with rougher-scavenger cells and a Float Tails CIL (FTCIL) circuit.
– Autoclave Optimization: A flash recycle thickening circuit increases residence time without new autoclaves.
– New Equipment:
– Second gyratory crusher (TSU 1100×1800, 1,645 tph).
– SS-SAG mill (23,000 kW).
– Flotation cells (2 trains of 5 cells).
– Expanded oxygen plant (additional 3,000 tpd capacity).
Key Technical Challenges & Solutions
– Oxygen Bottleneck: Expansion increases O₂ demand; new plant capacity addresses this.
– Sulfide Sulfur Handling: Controlled feed blending ensures stable autoclave performance.
– Mercury Management: Carbon kilns include mercury absorbers to capture off-gases.
Throughput & Recovery Metrics
– Current: 24,000 tpd (8.6 Mtpa).
– Expanded: 14 Mtpa (38,356 tpd).
– Recovery Rates: Not explicitly stated, but optimized via CCD, CIL, and flotation.
Innovations
– Flash recycle thickening enhances autoclave efficiency.
– Integrated HDS neutralization reduces acid consumption.
– On-site lime/limestone production minimizes costs.
The plant’s flowsheet integrates POX, CIL, and flotation to maximize recovery from refractory ore, with expansion focusing on lower-grade ore treatment and tailings capacity.
