Question

Describe various processes used for the refining of a crude metal.

Answer 1

The processes used for refining a crude metal are:

1. Distillation: Used for low boiling metals like zinc and mercury by heating and collecting pure metal vapor.
2. Liquation: For metals with low melting points like tin, lead; molten metal flows leaving impurities.
3. Poling: Removes oxides by stirring molten metal with green wood logs releasing gases that reduce oxides.
4. Cupellation: Impurities are oxidized and removed by passing air over molten metal in a special crucible.
5. Electrolytic Refining: Impure metal is anode, pure metal cathode; metal ions move and deposit pure metal at cathode.
6. Zone Refining: A heater moves along a metal rod; impurities concentrate at one end which is cut off.
7. Vapour Phase Refining: Metal is converted to a volatile compound and then decomposed to obtain pure metal.