Question

Differentiate between roasting and calcination.

Answer 1

Roasting

Calcination

Roasting is the process of heating ore in the presence of excess oxygen. (O2). It is a displacement reaction. Mainly done for sulfide ores. Ore is converted to the oxide by heating below its melting point. Moisture present in the ore is not removed. A large amount of toxic, acidic, and metallic compounds are released. Example for roasting: $\underset{\mathrm{Lead}\mathrm{sulfide}}{2\mathrm{PbS}\left(\mathrm{s}\right)}+\underset{\mathrm{oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\stackrel{∆}{\to }\underset{\mathrm{Lead}\mathrm{oxide}}{2\mathrm{PbO}\left(\mathrm{s}\right)}+\underset{\mathrm{Sulfur}\mathrm{dioxide}}{2{\mathrm{SO}}_2\left(\mathrm{g}\right)}$

Calcination is the process of heating ore in the absence or limited supply of oxygen. (O2). It is a decomposition reaction. Mainly done for carbonate ores. Ore is converted to the oxide by heating above its melting point. Moisture content is removed during the process. Carbon dioxide is given out during calcination. Example for calcination: $\underset{\mathrm{Zinc}\mathrm{carbonate}}{{\mathrm{ZnCO}}_3\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\mathrm{Zinc}\mathrm{oxide}}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$