Outline the principle of refining of metals by
(i) Zone refining.
(ii) Electrolytic refining.

Explanation

(ii) Electrolytic refining. This method is based upon the phenomenon of electroysis. The crude metal is made anode whereas the thin sheet of pure metal is made cathode. Electrolyte is the solution of some salt of the metal to be refused. On passing electricity, the pure metal from the anode goes into solution as ions due to oxidation while pure metal gets deposited at the cathode due to reduction of metal ions. The less electropositive impurities settle down below the anode as anode mud.
At anode : `M(s) hArr M^(n+)(aq) + n e`
At cathode: `M^(n+) (aq) + n e^(-) to M(s)`

(iii) Vapour phase refining. Vapour phase refining is explained in brief review.