Calcination and Roasting of Ore

The concentrated ore is converted into metal oxide by calcination or roasting.

Calcination

Calcination involves heating of the concentrated ore in a limited supply of air so that it loses moisture, water of hydration and gaseous volatile substances. The ore is heated to a temperature so that it does not melt.

Removal of water of hydration

Al₂O₃.2H₂O → Al₂O₃ + 2H₂O

Expulsion of CO₂ from carbonate

ZnCO₃ → ZnO + 2CO₂

Roasting

Roasting is a process in which the concentrated ore is heated in a free supply of air at a temperature insufficient to melt it.

Calcination and roasting are generally carried out in a reverberatory furnace or in a multiple hearth furnace.