Question

why is the impure metal always kept at anode during electrorefining?

Answer 1

1. In the simple process of electrolysis,anode is the centre for oxidation.
2. The impure metal is placed at anode,as impurities will remain on anode,and the metal will oxidise and gets released in the solution by the following reaction :

M $\to$Mⁿ⁺ + ne^​-
3. When this has happened,the pure metal ions reach cathode and then get reduced to pure metal.

Mⁿ⁺ + ne^- $\to$M