Extraction of gold and silver involves leaching with $$C{N^ - }$$   $$ion.$$  Silver is later recovered by

Solution :
Extraction of gold and silver involves leaching with $$C{N^ - }$$   $$ion.$$  Silver is later recovered by distillation of $$Zn.$$
In the metallurgy of silver or gold, the respective metal is leached with a dilute solution of $$NaCN$$  or $$KCN$$  in the presence of air to obtain the metal in solution as complex. From the complex, metal is obtained later by replacement.
In general,
$$4M\left( s \right) + 8C{N^ - }\left( {aq} \right) + $$     $$2{H_2}O\left( {aq} \right) + {O_2}\left( g \right) \to $$     $$4{\left[ {M{{\left( {CN} \right)}_2}} \right]^ - }\left( {aq} \right) + 4O{H^ - }\left( {aq} \right)$$
$$2{\left[ {M{{\left( {CN} \right)}_2}} \right]^ - }\left( {aq} \right) + Zn\left( s \right)$$     $$ \to {\left[ {Zn{{\left( {CN} \right)}_4}} \right]^{2 - }}\left( {aq} \right) + 2M\left( s \right)$$
$$M = Ag\,\,{\text{or}}\,Au$$
This method is known as Mac-Arthur Forest cyanide process.