Extraction of gold involves leaching the metal with CN- giving metal complex.
4Au + 8CN- (aq) + 2H2O + O2(g) 4[Au(CN)2] - (aq) + 4OH- (aq)
The metal is later recovered by displacement method with zinc acting as reducing agent.
2[ Au(CN)2]- (aq) + Zn(s) 2Au(s) + [Zn(CN)4] - (aq)
