Calcination : It is the process of converting an ore into its oxide byheating it strongly below its melting point either in absence or limitedsupply of air. $\mathrm{Fe}_2\mathrm{O}_3\cdot x\mathrm{H}_2\mathrm{O}\xrightarrow{\Delta}\mathrm{Fe}_2\mathrm{O}_3+x\mathrm{H}_2\mathrm{O}$ $\mathrm{ZnCO}_{3(s)}\xrightarrow{\Delta}\mathrm{ZnO}_{(s)}+\mathrm{CO}_{2(g)}$ Roasting : In roasting, the ore is heated in a regular supply of air in afurnace at a temperature below the melting point of the metal.$2\mathrm{ZnS}+3\mathrm{O}_2\rightarrow 2\mathrm{ZnO}+2\mathrm{SO}_2$$2\mathrm{PbS}+3\mathrm{O}_2\rightarrow 2\mathrm{PbO}+2\mathrm{SO}_2$