4 Au(s) + 8 CN-(aq)+ 2H2O (aq)+ O2(g) → 4[Au(CN)2]-(aq) + 4OH-
2[Au(CN)2]- (aq)+ Zn (s) → [Zn(CN)4]2- (aq)+ 2Au (s)
Gold is leached with a dilute solution of NaCN in the presence of air (For O2) from which the metal is obtained later by replacement. in the extraction of gold and silver, the metal is leached with NaCN or KCN, which is an oxidation reaction, during this process Ag is formed by the replacement of Zinc.
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