Question

Compare roasting and calcination.

Distinguish between:

Roasting - Calcination

Answer 1

	Roasting	Calcination
1.	This method is generally used for sulphide ores	This method is generally used for carbonate ores.
2.	In this method, ores are heated in excess of air.	In this method, ores are heated in a limited supply of air.
3.	In roasting, generally sulphur dioxide gas is evolved.	In calcination, generally carbon dioxide gas is evolved.
4.	In this method, sulphide ores are oxidized to form metal oxides. E.g. \[\ce{2ZnS + 3O2 -> 2ZnO + 2SO2 \uparrow}\]	In this method, carbonate ores decompose to form metal oxide. E.g. \[\ce{ZnCO3 -> ZnO + CO2 \uparrow}\]