Blister copper contains Fe, Zn, Pb, Ag, Au as impurities which reduce the conductivity of copper, so blister copper is refined by the electrolytic process.
In this process blocks of impure copper (blister copper are used as anodes and very thin sheets of pure copper act as cathodes. The anodes and cathodes are suspended in copper sulphate solution (CuS04), acidified with a little amount of dilute sulphuric acid (H2S04)
The electrolysis is carried out at 50°C by passing an electric current of 1.3 volts, which helps to deposit pure copper metal at cathode by dissolving impure (blister) copper anodes forming Cu2• ions. The impurities of less active metals like Zn, Ag, Au etc are left over un-dissolved and fall at the bottom of the cell as anode mud.