Answer. Roasting: It is a process of heating the concentrated ore to a high temperature in excess of air. For example; copper pyrite (CuFeS2) is strongly heated in excess of air to convert it into a mixture of cuprous sulphide and ferrous sulphide (Cu2S + FeS). While impurities sulphur, phosphorus arsenic etc. react with oxygen to form volatile oxides. Such as
2 CuFeS2(s) + O2(g) ———> Cu2S(s)+ 2FeS(s)+ SO2(g)