Give reason why roasting is carried out on sulphide ores and not on carbonate ores

It is easier to obtain metals from their oxides (by reduction) than from carbonates or sulphides.

 

So before reduction can be done, the ore is converted into metal oxide.

 

The concentrated ores can be converted into metal oxide by calcination or roasting.

 

Calcination: It is the process in which a carbonate ore is heated strongly in the absence of air toconvert it into a metal oxide.

Example:When zinc carbonate is heated strongly in the absence of air, it decomposes to form zinc oxideand carbon dioxide

 

Roasting: It is the process in which a sulphide ore is strongly heated in the presence of air to convert it into a metal oxide.

This is done in case of sulphide ores so as to remove sulphur in the form of SO₂  and to obtained corresponding metal oxide.