Electrolysis of fused alumina

Electrolysis of fused alumina OR

            Describe the process of preparation of aluminium by the electrolysis of alumina. OR

            Explain the electrolytic reduction of alumina.

Ans.

1. The electrolytic cell consists of a rectangular steel tank lined from inside with graphite.
2. The carbon lining i.e. graphite acts as a cathode. The anode consists of graphite rods suspended in the molten electrolyte.
3. Alumina has very high melting point of greater than 2000⁰C. The electrolysis of alumina is carried out at a low temperature by dissolving it in molten Cryolite.
4. The solution of alumina in Cryolite with added small amount of fluorspar is electrolysed at about 1000⁰C.
5. When we passing an electric current, alumina is electrolysed. Molten aluminium is collected at the cathode, while oxygen gas is evolved at the anode.
6. The molten aluminium is heavier than the electrolyte. Hence, it sinks to the bottom of the electrolyte and is removed from time to time.
7. The aluminium is obtained by this process is about 99% pure.
8. The reactions taken place at electrodes are shown below.