MacArthur Forrest Process

Developed in 1887 by two Glasgow doctors, Robert and William Forrest, and a chemist, John S. MacArthur, this cyanide process became the basis of most gold extraction, especially in South Africa whose gold mining industry might not have expanded so soon without it.

In the MacArthur Forrest Process the ore is crushed to a fine powder and circulated through tanks containing a weak solution of cyanide, which has an affinity for gold. The solution dissolves the gold and the remaining rock pulp is filtered off. Zinc dust added to the cyanide solution to replace the gold causes the fine specks of gold to be precipitated out and the precipitate is then refined.