Question

Extraction of gold and silver involes leaching with $CN^-$ ion. Silver is later recovered by :-

• A. distillation
• B. zone refining
• C. displacement with Zn
• D. liquation

Answer 1

Answer: (C)

displacement with Zn

Answer 2

Zn is more reactive than Ag and Au, therefore Zn will displace them.

From Native ore,

$4 Ag +8 NaCN +2 H _{2} O + O _{2} \stackrel{\text { Leaching }}{\longrightarrow} \underset{\text{Soluble Sodium dicyanoargentate(I)}}{4Na [Ag(CN)_2]} + 4 Na OH$
$2 Na \left[ Ag ( CN )_{2}\right]+ Zn \stackrel{\text { Displacement }}{\longrightarrow} Na _{2}\left[ Zn ( CN )_{4}\right]+2 Ag \downarrow$