When you think of gold mining, you probably think of an old prospector searching for nuggets in the hillside. Or, if you are more industrial minded, you imagine a network of sluices capturing a bounty of alluvial gold. While such mining forms are not extinct, they are a bit antiquated. Gold is extremely valuable, so miners want to get every molecule they can. Using modern mining techniques, they literally can get every molecule of gold out of a chunk of ore. Chemical mining is one of the most efficient ways to mine gold and one of the most popular. It’s also one of the most dangerous, as it uses cyanide.
Gold cyanidation technically started back in 1783 when Carl Wilhelm Scheele discovered that one could dissolve gold in an aqueous cyanide solution. In 1887, this knowledge was applied to gold mining with the development of the MacArthur-Forrest Process. The basic premise of this process is simple: gold ore is crushed and ground as fine as possible, then combined with a solution of cyanide which leaches the gold out of the ore. Later iterations of the MacArthur-Forrest Process oxygenated the cyanide mixture to increase the rate at which cyanide leached gold from the solution. Once the gold is successfully leached from the ore, miners have a number of options to recover the gold from the cyanide solution, including the carbon-in-pulp method, the Merrill-Crowe process, electrowinning, and the Resin-in-pulp method.
Despite it effectiveness, gold cyanidation has come under fire from time to time because of the danger of using so much cyanide in major mining operations. Spills or leaks in the system can – and have – caused major environmental damage. Fortunately, cyanide solutions break down rapidly in natural conditions. So, if a disaster occurs, it tends to be short lived. As long as safe practices are enforced, gold cyanidation is an efficient method for mining gold.
