Extraction of gold and silver involves leaching the metal with CN- ion. The metal is recovered by ......

1.  Displacement of metal by some other metal from the complex ion.

2.  Roasting of metal complex.

3.  Calcination followed byroasting.

4.  Thermal decomposition of metal complex.

Extraction of gold and silver involves leaching the metal withCN-ion. The metal is recovered by displacement of metal by some other metal from the complexion. This is an oxidation reaction.
4Aus+8CN-aq+2H2Oaq+O2g4 Au CN2-aq+ 4OH-aq
4 Au CN2 aq+Zn s2 Au s + Zn CN42- aq
 
Here, Zn acts as a reducing agent