Calcination:
(i) it involves heating of the ore in the absence of air
(ii) it is generally used for carbonate ores
Calcination:
ZnCO3 → ZnO(s) + CO2
Roasting:
(i) it involves the heating of the ore in the presence of air
(ii) it is generally used for sulphide ores
Roasting:
2ZnS + 3O2→2ZnO + 2SO2