Outline the principels of refining of metals by the following methods :
(i) Distillation
(ii) Zone refining
(iii) Electrolysis.

Explanation

Distillation : It is used to remove the non- volatile impurities from volatile metal like zinc, cadmium and mercury. The impure metal is heated in a retory when the pure metal vaporises and condenses separately leaving behind the non-volatile impurities.
Reactions in different zones in blast furnace during extraction of iron.
(i) Zone of combustion `C(S) +O_2to CO_2`
(ii) Zone of heat aborption. `CO_2+C(S)to 2CO(g)`
(iii) Zone of slag formation : `CaCo_3(s) overset(1123K)to CaO(s)Co_2(g)`
`CaO(s)+SiO_2(s) overset(1123K)to underset("Slag")(CaSiO_3(s) `
(iv) Zone of reduction
`underset((s))(3Fe_2O_3)+underset((g))(CO)overset (573-673K)to 2Fe_3O_3(s) +CO_2(g)`
`Fe_3O_4(s)+CO(g)overset(773-873K)to 3FeO(s) +CO_2(g)`
`Fe_2O_3(s) +CO(g) overset(773-873K)2FeO(s)+CO_2(g)`
`FeO(s) +CO9(g) overset(1123K)to Fe(s)+CO_2(g)`