2. Hydrometallurgy

In almost all cases, gold hydrometallurgy is based on solution leaching with cyanide (the metal is then contained in the etching liquor). Two techniques are used: dynamic leaching in mechanically stirred reactors at the plant, and static leaching in open-air heaps or pits. In both cases, the ore has first undergone more or less complex pre-treatment operations.

• In conventional mill processing, mined ore is crushed and ground before being leached. When gold particles are easily releasable and fairly coarse (> 75 µm), gravimetric concentration can reject a definitive barren and produce a pre-concentrate. Very high concentration coefficients (from 100 to 1,000) can thus be achieved. When gold is closely associated with metallic sulfides, concentration by flotation produces a sulfide preconcentrate. If the proportion of free gold is high,...