Heap Leaching Fundamentals
Heap leaching is a mineral processing technique where crushed ore is stacked in a heap and irrigated with chemical solutions that dissolve valuable metals. It is particularly suitable for low-grade ores that would be uneconomical to process by conventional milling.
Gold Heap Leaching
Process Overview:
- Crushed ore stacked on lined pad (typically -1.5mm or 10mm)
- Cyanide solution sprayed over heap
- Gold dissolves in cyanide solution (Elsner's equation)
- Solution collected and gold recovered
Key Parameters:
- Crush size: Finer crushing improves recovery but costs more
- Irrigation rate: 5-15 L/m²/hr typical
- Leach time: 30-90 days depending on ore
- Cyanide concentration: 100-500 ppm
Copper Heap Leaching
Oxide Copper Minerals:
- Chrysocolla, malachite, azurite respond well
- Sulfuric acid leaching (pH 1-2)
- Lower cost than cyanide
- Established technology
Sulfide Copper Minerals:
- Requires bacteria-assisted leaching (bioleaching)
- Longer leach times
- Lower recovery rates
Heap Leaching Technology
Heap Construction
Pad Liner System:
- Clay or synthetic liner prevents solution loss
- Leak detection system recommended
- Drainage gravel and piping for solution collection
Heap Geometry:
- Typical lift height: 4-10 meters
- Multiple lifts build the final heap
- Solution distribution through drip or spray emitters
Solution Management
- Pregnant Leach Solution (PLS): Carries dissolved gold/copper
- Barren solution: After metal recovery, recirculated
- Make-up solution: Replenishes losses
- Recovery process: Activated carbon (gold), solvent extraction (copper)
WSHT provides heap leaching equipment including irrigation systems, solution management and process design support.
