196. Discuss briefly the role of coordination compounds in extraction/metallurgy of metals.

Extraction/metallurgy of Metals:

(i) Extraction of metals like silver and gold is carried out by forming their soluble cyanide complex, e.g.,

$4\mathrm{Au}+16{\mathrm{CN}}^{-}+6{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2 \to \underset{\mathrm{Dicyano} \mathrm{gold} \left(\mathrm{I}\right) \left(\mathrm{soluble}\right)}{ 4 {\left[\mathrm{Au}(\mathrm{CN}{)}_2\right]}^{-}}+ 12{\mathrm{OH}}^{-}$

The solution containing cyanide complex is then treated with zinc, when gold is precipitated.

2[Au(CN)₂]^– + Zn → [Zn(CN)₄]^2– + 2Au

(ii) Coordination compounds of silver and gold are used as the constituents of electroplating baths for the controlled delivery of Ag⁺ and Au ions, during electro-refining of these metals.