Answer. In the electro-refining, of copper, anode is made of impure copper metal. It consists of impurities like gold and silver. When oxidation takes place at anode, there metallic ions dissolve in the solution. Cu2+ ions reduce and deposit at cathode while gold and silver impurities settle down as anode mud.
Test Yourself.16.2 (MANUFACTURE OF SOOIUM CARBONATE BY SOLVAY'S PROCESS)