What is the name of the gold extraction process using sodium cyanide?

Cyanidation is the gold-extraction process that uses sodium cyanide. Also called gold cyanidation, the cyanide process, or the MacArthur–Forrest process, it leaches gold from crushed ore by forming a water-soluble gold–cyanide complex.

In the process, finely ground ore is contacted with a cyanide solution in the presence of oxygen and water. Gold oxidizes and dissolves as dicyanoaurate, which can then be recovered from the solution by activated carbon, electrowinning, or the Merrill–Crowe zinc-precipitation process. The method is especially useful for low-grade ores, where physical separation alone would recover too little metal.

The industrial process was developed in 1887 by John Stewart MacArthur with Robert and William Forrest. It was first used on South African goldfields around 1890 and helped make large, previously difficult deposits economically workable. The answer is “cyanidation,” not the Merrill–Crowe process: Merrill–Crowe is a downstream recovery method, not the leaching process itself.

Cyanide’s toxicity makes handling and environmental control essential. Industrial operations commonly keep the solution strongly alkaline, above about pH 10.5, to reduce the risk of forming volatile hydrogen cyanide. Alternatives such as thiosulfate exist, but cyanidation remains the standard industrial technique.