- Distillation
- Liquation
- Electrolytic refining
- Zone refining
- Vapour phase method
- Mond process of refining nickel
- Van Arkel method for refining Zr / Ti
DISTILLATION
- Employed in case of low boiling volatile metals
- E.g. zinc (BP. 1180 K), Hg (630 K)
- Impure metal is heated to evaporate.
- The vapours are condensed to obtain pure metal.
LIQUATION
- Employed to remove impurities with high melting points from metals having low mpt such as tin, lead, mercury, bismuth etc.
- Crude metal is heated to form fusible liquid.
- It is allowed to flow on an inclined surface (sloping hearth of a reverberatory furnace).
- Heating occurs in absence of air.
- The molten metal is collected and solidified.
ELECTROLYTIC REFINING
- The crude metal is refined by electrolysis.
- The less electropositive impurities in the anode settle down at the bottom. It is called anode mud.
Electrolytic refining of silver
- Electrolyte : Acidified aqueous solution of silver nitrate.
- Cathode : Pure silver
- Anode: Impure silver rods
- Current is passed through the electrolytic set up.
- At anode oxidaton occurs
- At cathode reduction occurs
Zone Refining
- Principle: fractional crystallisation