Comparison of roasting and calcinations:
| Roasting |
Calcination |
(i) The ore is heated in the excess of air.
(ii) Generally, sulphide ores are roasted, so SO2 is given off.
2ZnS + 3O2 + 800°c - 900°c→ 2ZnO + 2SO2
(iii) Volatile impurities are removed as oxides and the ore becomes porous and more reactive.
|
(i) The ore is heated in the absence of air.
(ii) Carbonate and hydrated ores are calcined and so,CO2 and water vapours are given off.
(iii) Moisture and organic impurities are removed and the ore becomes porous and more reactive
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