Materials Handling and Mineral Processing
Handling
Materials handling links stopes to the mill: LHDs and trucks in stopes, ore passes, conveyors and hoists. Truck productivity is driven by cycle time (load, haul, dump, return, queue) and payload - measure tonnes per operating hour, not kilometres travelled. Conveyors are limited by belt speed and material cross-section; hoisting by skip capacity and cycle time.
Comminution and separation
Liberation by size reduction comes first. Bond's equation, W = 10 Wi (1/√P80 − 1/√F80), gives specific energy in kWh/t when sizes are in micrometres; it is the standard estimating tool and a favourite calculation. Crushing precedes SAG and ball milling; hydrocyclones close the circuit and circulating loads of 200–350% are normal. Separation methods include flotation (collector, frother, activator, depressant, pH, residence time), gravity (jigs, spirals, tables), magnetic and electrostatic separation, and leaching (CIP/CIL for gold, heap and dump leach). Dewatering uses thickeners and filters; tailings report to a storage facility.
Metallurgical accounting
Recovery = metal in concentrate ÷ metal in feed; grade is the concentration in the product. The grade–recovery curve trades one against the other, and the economic optimum is rarely maximum recovery.
Traps
- Feeding Bond's equation millimetres or centimetres instead of micrometres.
- Confusing recovery with grade, or concentrate mass with feed mass.
- Assuming conveyor capacity is fixed regardless of incline and idler configuration.
- Ignoring dilution added by ore passes and rehandling.
Worked example
Wi = 13 kWh/t, F80 = 10,000 µm, P80 = 100 µm. W = 10 × 13 × (1/10 − 1/100) = 130 × 0.09 = 11.7 kWh/t.