i) If the metal is found in the form of sulphides, They are roasted (roasting is the process of heating[less than the melting point of metal] metals sulphides (metal sulphides) to remove sulphur gas from the metal,. and the metal is converted to metal oxide as a step of purification ), and reduced to oxide form,.
Eg: copper is found as copper sulphide so, they are roasted to form copper oxide.
Cu2S+3O2(g)Heat−−−→2Cu2O(s)+2SO2(g)
ii) If the metal is found in the form of carbonates. They are calcinated (calcination is the process of heating metal carbonates just below the melting point, in limited supply (or no supply) of oxygen to get metal oxide as a step of purification).
Eg: Zinc is found as Zinc carbonate.It is calcinated to form Zinc carbonate,
ZnCO3(S)Heat−−−→ZnO(S)+CO2(g)