Question 60
Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.

Sulphide ore of low reactivity: Metal sulphide like $\text{HgS}$ reacts with ${\text{O}}_2$ to form mercuric oxide and sulphur dioxde. Mercuric oxide being unstable changes to Hg(l) which can be refined by distillation. The reactions involved are:

$2{\text{HgS}}_4+3{\text{O}}_2⟶2\text{HgO}+2{\text{SO}}_2\text{HgS}+2\text{HgO}⟶3\text{Hg}+{\text{SO}}_2$

Sulphide ore of medium reactivity: Sulphide ore like Zn, on roasting gives metal oxide which on reduction with metal sulphide (ZnS) or suitable reducing agent gives metal which is refined by electrolyte refining. The reactions involved are:

$2\text{ZnS}+3{\text{O}}_2⟶2\text{ZnO}+2{\text{SO}}_{2}2\text{ZnO}+\text{ZnS}⟶3\text{Zn}+{\text{SO}}_2$

Alternative method of reduction:
$\text{ZnO}+\text{C}⟶\text{Zn}+\text{CO}$
Pure zinc is obtained by electrolytic refining.