Cyanidation
Gold exhibits highly stable chemical properties; however, it can dissolve in an aqueous solution containing cyanide and oxygen, forming soluble gold–cyanide complexes. Gold cyanidation is a hydrometallurgical process in which cyanide is used as the lixiviant to dissolve gold from gold-bearing ores. Cyanidation remains one of the principal modern methods for extracting gold from suitable ores.
Gold cyanide leaching processes can generally be classified into percolation leaching and agitated leaching. Percolation leaching includes several configurations, such as in-situ leaching, heap leaching and Tank leaching.
Agitated cyanide leaching is commonly implemented through two major carbon-based processes: CIP (Carbon-in-Pulp) and CIL (Carbon-in-Leach). CIL is an important process within modern gold cyanidation. In the CIL process, activated carbon is added directly to the leaching tanks, allowing gold dissolution and adsorption onto activated carbon to occur simultaneously. In the CIP process, cyanide leaching and activated-carbon adsorption are performed as separate sequential stages; first leaching and subsequently carbon adsorption.
The principal differences between CIP and CIL include:
- In the CIP process, silver-bearing minerals generally have a relatively limited effect on gold leaching performance.
- CIP circuits may require additional slurry handling, washing, and filtration arrangements, resulting in greater process complexity and potentially higher capital investment, particularly when processing ores containing high levels of clay or shale. The CIL configuration can reduce some of these operational challenges by integrating leaching and adsorption in the same circuit.