Cyanide is probably one of the most universally recognized poisons. Cyanide contains a carbon atom connected to a nitrogen atom, hence the chemical formula CN. However, the term cyanide is used to refer to a wide array of chemicals containing cyanide. Cyanides can be manufactured (from ammonia and natural gas, or as a by-product of acrylic fibres and plastics production) but they also occur in nature.
Due to its toxic nature, cyanide has been used as a fumigant and poison since early time, however, its most familiar use in the Yukon is in the mining industry. Over 90% of the gold mined in Canada is extracted using a cyanidation process. Cyanide forms a very stable complex with several metals and has been used since 1887 to extract gold, silver, copper, zinc and molybdenum from ores.
Waste cyanide in tailings ponds and abandoned heap leach pads can be dealt with in several ways: natural degradation or attenuation, chemical degradation, hydrogen peroxide process, alkaline chlorination, sulphur dioxide-air oxidation, or microbial processes.
Long term adverse effects associated with mining sites are related primarily to metals rather than cyanide. Cyanide can naturally degrade rapidly in the environment by volatilizing to hydrogen cyanide gas (HCN). This gas is dangerous in a closed system but much less so when gradually released in an out-of-doors environment.
The toxicity of cyanide is very dependent on its form. Mine effluents, tailings and leach pond water can contain cyanide in many forms ranging from the cyanide ion to strong metal cyanide complexes. The toxicity of cyanide compounds depends on the compound's ability to release the cyanide.
Each mine in the Yukon must abide by a Water Licence issued by the Yukon Territory Water Board. The licence ha standards of cyanide concentration that must be met in the effluent before it is discharged to the receiving environment.
