Describe the Hall-Heroult's process for the extraction of aluminium from alumina. Draw a labelled diagram for the process.

Explanation

Aluminium obtained by, Hall Héroult process is nearly 99% pure and contains small quantities of iron, silicon, aiumina and carbon as impurities. The metal can further the refined to get 99.99% pure metal by Hoope.s electrolytic refining. In this process an iron only (Fe) lined with carbon contains three layers of fused masses having different specific gravities. The impure aluminium is made heaver by alloying with copper to form the bottom layer which acts as anode. A mixture of cryolite, aluminium flouride, bårium, flouride and alumina in the fused state forms the middle-layer. The upper layer consists of pure refined aluminium and serves as cathode: Electric.current is passed when aluminiumn-from middle layer is transferred into the upper layer and more aluminium from the bottom layer is transferred into the middle layer. As the electrolysis proceeds, there is a continuous gradual transference of aluminium from the bottom to the top layer, from where it is drawn off from time to time.