Leaching of gold with dilute aqueous solution of NaCN in presence...

Extraction of gold is carried out by leaching process.

Sodium cyanide $( NaCN )$ has been used as leaching reagent for gold.

Metal is converted into the soluble cyanide complex on reaction with sodium cyanide.

$4Au + 8 {CN}^{-} + 2{H}_{2}O + {O}_{2} \to 4\mathop{[ Au ( CN{)}_{2}{]}^{-}}_{X} + 4{OH}^{-}$

Silver is later recovered by displacement with $Zn$.

$2{\left[Au{\left(CN\right)}_{2}\right]}^{-} + Zn\overset{\text{Displacement}}{\to}\mathop{{\left[Zn{\left(CN\right)}_{4}\right]}^{2 -}}_{Y} + 2Au$

$X\text{and}Y$ are $[ Au ( CN{)}_{2}{]}^{-}$ and $[ Zn ( CN{)}_{4}{]}^{2-}$, respectively.