Question

Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.

Answer 1

(i) $4Au\left(s\right)+8C{N}^{-}\left(aq\right)+2H_{2}O\left(aq\right)+O_2\left(g\right)⟶4\left[Au\right(CN{)}_2{]}^{-}\left(aq\right)+4O{H}^{-}\left(aq\right)$
(ii) $2\left[Au\right(CN{)}_2{]}^{-}\left(aq\right)+Zn\left(s\right)⟶2Au\left(s\right)+\left[Zn\right(CN{)}_4{]}^{2-}\left(aq\right)$
Zinc acts as a reducing agent in this reaction.