Extraction of gold and silver involves leaching the metal with `CN^(-)` ion. The metal is recovered by :

Options

A. Displacement of metal by some other metal from the complex ion
B. Roasting of metal complex
C. Calcination followed by roasting
D. Thermal decomposition of metal complex

Answer

A

Explanation

Extraction of gold and silver involves leaching the metal with `CN^-` ion. The metal is recovered by displacement of metal by some other metal from the complex ion. This is an oxidation reaction
`4Au(S) + 8CN^(-)(aq) + 2H_2O(aq) + O_(2)(g) rarr 4[Au(CN)_2]^(-) (aq) + 4OH^(-)`
`4[Au(CN)_2](aq) + Zn(s) rarr 2Au(s) + [Zn(CN)_4]^(2-)(aq)`
Here, Zn acts as a reducing agent.