In both calcination and roasting, an ore is converted into its oxide, albeit through different chemical pathway. Calcination is the process in which the ore is heated below its melting point, either in the absence or in a limited supply of air, in an aim to drive off volatile expunges, moisture, water of hydrates and organic matter from the ore. Carbonate, bicarbonate and hydroxide ores are generally subjected to calcination which produce the metal oxide after expelling CO2 or H2O in the process.
ZnCO3 → ZnO + CO2
CaCO3 → CaO + CO2
2Al(OH)3 → Al2O3 + 3H2O
In the process of roasting concentrated ore is heated strongly, below its melting point, in presence of air with or without some other additives, in order to bring about some desired changes. Generally sulphide ores are subjected to roasting whereupon oxides are formed and SO2 is expelled.
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
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