Question

Leaching of gold is done by which compound?

• A. $KCN$
• B. $Zn{CN}_2$
• C. $NaCN$
• D. By both $\left(a\right)$ and $\left(b\right)$

Answer 1

Answer: (A), (C)

The correct options are
A $NaCN$
C $KCN$

Cyanide process:
It is the most common used process for gold extraction. This process involves the dissolution of gold ( and of any silver present in soluble form) from the ground ore in a dilute cyanide solution (usually NaCN otr KCN) in the presence of lime and oxygen according to the reactions:
$2Au+4KCN+O_2+2H_{2}O=2KAu(CN{)}_2+2KOH+H_2{O}_2$
$2Au+4KCN+H_2{O}_2=2KAu(CN{)}_2+2KOH$
$4Au+8C{N}^{-}+O_2+2H_{2}O⟶4Au(CN{)}_2^{-}+4O{H}^{-}$
With optimum cyanide concentration, clean gold particles dissolve at a rate of 3.25mg per sq. cm per hour while for silver the rate is about one-half that of gold. Therefore , coarse gold particles are usually removed by gravity concentration methods before cyanidation. In general, cyanidation process consists of percolation or agitation leaching of gold and silver ores with dilute cyanide solution, generally less than 0.3 percent sodium cyanide.
conclusion: hence option (A) and (C) is corrcet.