Extraction of gold and silver involves leaching the metal with CN– ion. The metal is recovered by ________________.
4M(s) + 8CN– (aq)+ 2H2O(aq) + O2(g) → 4[M(CN)2] – (aq) + 4OH– (aq) (M= Ag or Au)
2[M(CN)2]-(aq) +Zn(s) →[Zn(CN)4]2-(aq) + 2M(s)
Here the metal M(M=Ag or Au) is displaced from the complex by the action of zinc as a reducing agent.