Gold
It is now the most important and widely used process for extracting gold from ores.
The ore is first finely ground and concentrated by flotation.
To remove certain impurities, it may be roasted.
It is then mixed with a dilute solution of sodium cyanide (or potassium or calcium cyanide) while air is bubbled through it.
Soluble aurocyanide complex ion, Au(CN)-2^-1 is formed .
Silver, usually present as an impurity, also forms a similar soluble ion.
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