Extraction of Aluminium:-

Alumina (Al₂O₃) has very high melting Pt (2323k) and fused Alumina (Al₂O₃) is a bad conduction of electricity. Therefore cryolite (Na₃AlF₆) and fluorspar (CaF₂) are added which not only make alumina a good conductor but also reduces its M, Pt. to 1140k. This process is called the Hall and Herault Process. The temperature of the bath is maintained at 1173k. Following reactions take place during electrolysis:

Thus the electrode C is eaten away during electrolysis and is periodically replaced. The metal obtained is 99.5% pure. The use of C electrode is that it takes away oxygen and does not allow the oxygen to combine back with Al.