Cyanide 5
Cyanide 5 : Also called cyanidation. A process for extracting gold from crushed rock by contacting it with aqueous sodium or potassium cyanide in the presence of air. The gold is converted to an aurocyanide: 4Au + 8KCN + 2H2O + O2 + 4KAu(CN)2 + 4KOH. The solution is then reduced with metallic zinc: 2KAu(CN)2 + Zn + K2Zn(CN)4 + 2Au. (Check source for accuracy of chemical formula)