Cyanidation
Dissolving gold out of crushed rock with a dilute cyanide solution — the method that made low-grade ore worth mining, and the reason gold mining is an environmental argument.
Gold is unreactive, which is why it is found as metal, and that same unreactivity makes it hard to separate chemically. Cyanide is one of the few reagents that will dissolve it under mild conditions, forming a soluble complex that can be washed out of crushed rock and the metal recovered from the solution.
The consequence is economic. Cyanidation works on ore containing gold at a few grams per tonne — concentrations invisible to the eye and far below anything panning or amalgamation could recover — which turned enormous volumes of otherwise worthless rock into ore.
Environmental impact
The method's advantages and its hazards are the same fact. Cyanide is acutely toxic, it is used in large volume in open ponds, and the tailings retain it after the gold has gone.
Failures of tailings dams have released cyanide-bearing water into river systems, and those events, more than the mining itself, are what shape how gold extraction is regulated. Some jurisdictions prohibit the technique outright; most require destruction of the cyanide before discharge.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
produces
takes as input
- Water — compound · as the leach solution: the cyanide is a few hundred parts per million and the rest is water
Sources
- Material WorldOur own writing