Question

The process of concentrating Au and Ag ores is based upon their solubility in :

• A. $N{H}_3$
• B. $HN{O}_3$
• C. $HCl$
• D. $KCN$

Answer 1

Answer: (D)

$KCN$

Cyanide process (Mac Arthur Forrest Process):

This is very good process for the removal of gold from tailings of amalgamation process or from even poorer ores. It is based on the fact that gold dissolves in dilute solution of sodium/potassium cyanide in presence of atmospheric oxygen with the formation of complex cyanide.

Reaction of process:

$A{g}_{2}S+4KCN\to 2K\left[Ag\right(CN{)}_2]+K_{2}S$

Silver is obtained by reaction with Zn:

$2K\left[Ag\right(CN{)}_2]+Zn\to K_2[Zn\left(CN{)}_4\right]+2Ag$