Roasting is a process of heating the concentrated ore to a high temperature in presence of air. Generally, sulphide ores are roasted.
Example
2ZnS + 3O2 ⟶ 2ZnO + 2SO2
Calcination is a process of heating ore in the absence of air to a high temperature, but insufficient to melt the ore. Generally, carbonates and hydrated ores are calcined.
Example:
(i) ZnCO3 ⟶ ZnO + CO2
(ii) Anhydrous alumina is left behind when bauxite is calcined and water is removed.
Al2O3.2H2O ⟶ Al2O3 + 2H2O
