Explain the applications of coordination compounds in metallurgy.

(N/A) Coordination compounds play a crucial role in the extraction and purification of metals.
$1$. Extraction of Gold and Silver: Gold and silver are extracted by leaching them with a dilute solution of $NaCN$ or $KCN$ in the presence of air (for $O_2$),which forms a soluble coordination complex: $4Au(s) + 8CN^-(aq) + 2H_2O(aq) + O_2(g) \rightarrow 4[Au(CN)_2]^-(aq) + 4OH^-(aq)$. The metal is then recovered from this complex by displacement with a more electropositive metal like zinc.
$2$. Purification of Nickel: The Mond process is used for the purification of nickel. Nickel reacts with carbon monoxide to form a volatile coordination complex,tetracarbonylnickel$(0)$,which is then decomposed at higher temperatures to yield pure nickel: $Ni(s) + 4CO(g)$ $\rightarrow [Ni(CO)_4](g)$ $\rightarrow Ni(s) + 4CO(g)$.