Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.
Theextraction of gold and silver involves leaching the metal with CN–. This is also an oxidation reaction (Ag → Ag+ or Au → Au+). The metal is later recovered by displacement method.MacArthur-Forrest process of gold cyanidation takes place as follows
4Au(s) + 8CN– (aq) + 2H2O(aq) + O2(g) → 4[Au(CN)2] – (aq) + 4OH– (aq)
2[Au(CN)2] – (aq) + Zn(s) → 2Au(s) + [Zn(CN)4] 2– (aq)
Zinc places the role of a reducing agent. It reduces Au+ to pure Au.