Cyanide process

Cyanide process, also known as the cyanidation process or the MacArthur-Forrest process, is a hydrometallurgical technique for extracting gold from low-grade ore by converting the gold to a water-soluble coordination complex. It is the most commonly used leaching process for gold extraction. The process was invented in 1887 by John Stewart MacArthur, Robert Forrest, and William Forrest.

Process Overview

The cyanide process involves several steps: the preparation of a gold-bearing ore, the dissolution of gold from the ore in a dilute cyanide solution, the separation of the gold-cyanide complex from the ore slurry, and the recovery of gold from the gold-cyanide complex. The process can be broken down into four main stages:

1. Ore Preparation: The gold-bearing ore is crushed and ground to expose the gold particles.
2. Leaching: The ground ore is treated with a dilute solution of sodium cyanide (or sometimes potassium cyanide), which dissolves the gold, forming a gold-cyanide complex.
3. Separation: The gold-cyanide complex is separated from the ore slurry, typically by adsorption onto activated carbon.
4. Gold Recovery: The gold is recovered from the gold-cyanide complex through processes such as electrowinning or the Merrill-Crowe process, which involve precipitating the gold from the solution.

Environmental and Safety Concerns

The use of cyanide in gold extraction has been a subject of intense debate due to its toxic nature. Cyanide is highly toxic to humans and wildlife, and its use in the mining industry has led to concerns over environmental pollution and the health and safety of mine workers and surrounding communities. As a result, the cyanide process is subject to strict environmental regulations in many countries.

Alternatives

Due to the environmental and safety concerns associated with the cyanide process, research into alternative gold extraction methods is ongoing. These alternatives include the use of thiosulfate, chlorine, and gravity concentration techniques. However, none of these methods have yet been proven as effective and economical as the cyanide process for large-scale gold extraction.

Conclusion

The cyanide process remains the primary method for gold extraction from ores. While it is effective and efficient, its use raises environmental and safety concerns. The mining industry continues to seek and evaluate alternative methods that minimize environmental impact while maintaining economic viability.