Why Leach Gold
For fine or finely disseminated gold, leaching is the workhorse. Instead of physically separating gold from rock, leaching dissolves the gold into a solution, which is then recovered onto activated carbon or by another means. On suitable ores, recovery can reach 99%.
Cyanidation: The Standard Route
Cyanidation dissolves gold using a dilute cyanide solution. It is the most widely used gold leaching method and comes in two circuit arrangements:
- Carbon-in-Pulp (CIP) — leaching happens in dedicated tanks first, then the gold-bearing solution moves to a separate train of carbon tanks.
- Carbon-in-Leach (CIL) — leaching and carbon adsorption happen together in the same tanks, which suits slow-leaching ores.
Both routes use dual-impeller agitation tanks up to 20 m × 20 m, followed by elution, electrowinning and smelting to recover doré gold.
Heap Leaching
Heap leaching is a lower-cost route for low-grade, large-tonnage deposits. Crushed ore is stacked on a lined pad and irrigated with a leaching solution, which percolates through and dissolves the gold. The pregnant solution is collected and the gold recovered.
Heap leaching trades lower recovery for much lower capital and operating cost, which makes it viable on ores that would not justify a milling and agitation plant.
Alternatives to Cyanide
Where cyanide is restricted or unsuitable, alternatives exist, including thiosulphate and other lixiviants. These are less common and are selected only when testwork shows the ore and the local conditions demand them.
Choosing a Leaching Route
The right leaching route depends on ore grade, particle size, leaching kinetics and site conditions — all measured in the laboratory before design. A route selected on test data protects both recovery and operating cost.