5. Cyanidation Wastes of Gold-Silver Ores

Cyanide is a general term which refers to a group of chemicals whereby carbon and nitrogen combine to form compounds (CN^–). Cyanide leaching is currently the dominant process used by the minerals industry to extract gold (and silver) from geological ores. Gold extraction is accomplished through the selective dissolution of the gold by cyanide solutions, that is, the so-called process of cyanidation. This hydrometallurgical technique is so efficient that the mining of low-grade precious metal ores has become profitable, and modern gold mining operations extract a few grams of gold from a tonne of rock. As a result, exceptionally large quantities of cyanide-bearing wastes are produced for a very small quantity of gold. The wastes of the cyanidation process are referred to as cyanidation wastes. At modern gold mining operations, cyanidation wastes occur in the form of heap leach residues, tailings, and spent process waters. While the bulk of the cyanide used in the mining industry is applied to gold ores, cyanide is also added as a modifier in the flotation of base metal sulfide ore s in order to separate base metal sulfides from pyrite. Therefore, some process circuits of base metal ores may generate cyanide-bearing tailings and spent process waters.