Mutual solubility between the metal which is produced with the sulphide makes extraction of product very difficult. Therefore, the production of metal from sulphides cannot be done by directly reducing sulphide into metal; so the only route is that for sulphide to be converted to oxide. Thus, in all pyrometallurgical extraction of metal from sulphide ore, one of the important unit is the roasting. Another important manifestation of roasting is byproducts SO2 and SO3 of roasting. These sulphurious gases can be used to manufacture H2SO4.
For example:
2Cu2S + 3O2 → 2Cu2O + 2SO2
2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4
