Question

Give the reaction involve during extraction of zinc from its ore by-
a) roasting of zinc ore.
b) calcination of zinc ore.

Answer 1

The different steps involved in the extraction of zinc from zinc blende (ZnS) are given below:

(i) Concentration of ore First, the gangue from zinc blende is removed by the froth floatation method.
(ii) Conversion to oxide (Roasting) Sulphide ore is converted into oxide by the process of roasting. In this process, ZnS is heated in a regular supply of air in a furnace at a temperature, which is below the melting point of Zn.

2ZnS + 3O2  →  2ZnO  +  2SO2

(iii) Extraction of zinc from zinc oxide (Reduction) Zinc is extracted from zinc oxide by the process of reduction. The reduction of zinc oxide is carried out by mixing it with powdered coke and then, heating it at 673 K.

ZnO + C  →  Zn + CO

(iv) Electrolytic Refining Zinc can be refined by the process of electrolytic refining. In this process, impure zinc is made the anode while a pure copper strip is made the cathode. The electrolyte used is an acidified solution of zinc sulphate (ZnSO4). Electrolysis results in the transfer of zinc in pure from the anode to the cathode.

Anode:   Zn  →  Zn2+  + 2e- 

Cathode : Zn2+  + 2e-   →  Zn

Answer 2

2ZnS + 3O₂ →2ZnO + 2SO₂

and

ZnCo₃→ZnO+CO

respectively