Project Overview
The Johannesburg Crushing & Mineral Processing Complex is a brownfield expansion project converting a former gold mine into a modern CIL processing facility. WSHT Mining Group designed and supplied the complete comminution and leach circuit for processing 3,000 TPD of underground gold ore from the Witwatersrand Basin.
Ore Characteristics
The Witwatersrand gold ore is quartzite-hosted with fine-grained gold particles (average 4.5 g/t Au) disseminated through pyritic reef units. The ore is competent (UCS 180-220 MPa) and requires aggressive grinding to liberate the fine gold from the siliceous gangue. Bond Ball Mill Work Index: 16.2 kWh/t.
Process Flow
Crushing: Underground ore is tip-loaded to a 200-tonne receiving bin. A vibrating grizzly feeder scalps fines to bypass the C160 jaw crusher (primary, 400-800 t/h). Secondary and tertiary crushing is performed by two HP800 Symons cone crushers in series, producing a P80 = 10 mm product at 150 t/h.
Grinding: A Φ6.2×2.5 m SAG mill (4,500 kW, gearless drive) operates in closed circuit with a vibrating screen, reducing product to P80 = 2 mm. Two Φ4.0×6.0 m ball mills (each 2,200 kW) grind to 80% passing 75 microns in closed circuit with hydrocyclone clusters. Combined grinding power: 8,900 kW.
CIL Circuit: Ground slurry is thickened to 50% solids and pumped through 8 CIL tanks (6.0 m diameter × 6.5 m height, 185 m³ each). Cyanide concentration is maintained at 200-300 ppm NaCN at pH 10.5 (lime dosing). Total leach residence time: 36 hours. Activated carbon (24×48 mesh coconut shell) is loaded at 15 g/L and advanced counter-current to the slurry flow.
Gold Recovery: Loaded carbon is stripped in a Zadra elution circuit at 110°C and 1% NaCN/NaOH solution. Gold is recovered by electrowinning on stainless steel cathodes and smelted to doré bars (98.5% Au, 1.2% Ag). Strip efficiency: 99.5% in 6 stages.
Key Equipment
| Equipment | Specification | Capacity |
|---|---|---|
| C160 Jaw Crusher | 1600×1200 mm feed opening | 400-800 t/h |
| 2× HP800 Cone Crushers | Secondary + tertiary | 200-400 t/h each |
| Φ6.2×2.5 m SAG Mill | 4,500 kW, gearless drive | 150 t/h |
| 2× Φ4.0×6.0 m Ball Mills | 2,200 kW each | 120 t/h each |
| 8× CIL Tanks | 6.0 m dia × 6.5 m, 185 m³ | 36 h residence |
| Zadra Elution Circuit | 3-stage, 110°C | 20 t carbon |
| Electrowinning Cell Bank | 48 cathodes, stainless steel | 150 kg Au/day |
| Induction Furnace | 500 kg capacity | Doré production |
Project Highlights
- Capacity: 3,000 TPD (900,000 TPA) gold ore
- Gold Recovery: 94-96% CIL recovery
- Concentrate: Doré bars 98.5% Au purity
- Power: 12 MW installed, 8.5 MW average
- Water: 70% recycling, 1.8 m³/t ore
- Staffing: 120 operational personnel
- Timeline: 24 months EPC delivery
- Location: Johannesburg, Gauteng, South Africa
