In the commercial extraction of iron, roasting is adopted because

Roasting: The process of conversion of the ore into its oxide by heating it below its melting point in the presence of oxygen. So It does not prevent slag formation by Fe2​O3​.During roasting S, As, and Sb will be oxidized into their volatile oxides SO2​.As2​O3​ and Sb2​O3​, respectively. It does not remove impurities of S, As, and Sb in the form of their elemental vapor.