Explain the leaching and oxidation-reduction process in the metallurgy of gold.

(N/A) The leaching of gold and silver is carried out using $CN^-$. This is an oxidation process $(Au \rightarrow Au^+)$.
The metal is subsequently recovered by the displacement method.
$4Au_{(s)} + 8CN^-_{(aq)} + 2H_2O_{(aq)} + O_{2(g)} \rightarrow 4[Au(CN)_2]^-_{(aq)} + 4OH^-_{(aq)}$
$2[Au(CN)_2]^-_{(aq)} + Zn_{(s)} \rightarrow 2Au_{(s)} + [Zn(CN)_4]^{2-}_{(aq)}$
In this reaction,$Zn$ acts as a reducing agent.