The process of purifying the crude metals is called refining.

Distillation: -

This is very useful forlow boiling metalslike zinc and mercury. The impure metals are evaporated to obtain the pure metals as distillate.

Liquation: -

In this method alow melting metallike tin can be made to flow on a sloping surface, in this way it is separated from higher melting impurities.

Electrolytic refining: -In this method the impure metal is made to act asanode a strip of some metal in pure form is used ascathode. They are put in a suitable electrolytic bath containing soluble salt of the some metals the more basic metal remains in the solution and the less basic ones go to the anode mud.

Anode :M→Mn+ + ne-

Cathode :Mn+ + ne−→M

Zone refining: -

It is based on the principle that impurities are more soluble in the melt than in thesolidstate of the metal.

The impure metal is heated with the help of circular heaters atone endof the rod of impure metal. The molten zone moves forward along with the heater with impurities and reaches the other end and is discarded.

Pure metal crystallizes out of the melt. The process is repeated several times and heater is moved in thesamedirection.

It is used for purifying semiconductors like B, Ge, Si, Ga

Vapour phase refining:-

The crude metals are free fromimpurities by first converting it into a suitablevolatile compoundby heating it with specific reagent at a lower temperature and then decomposing the volatile compound at somehigher temperature to give the pure metal.