In this process, a fused mixture of alumina, cryolite and fluorspar(CaF2) is electrolysed using graphite as anode and steel as cathode.During electrolysis, Al is liberated at the cathode whereas CO and CO2are liberated at the anode.
Cathode: Al3+(melt) ––––▶Al( l)
Anode : C(s)+O2−( ‌melt) ––––▶CO( g)+2e−
C(s)+2O2−(melt) ––––▶ CO2( g)+4e−
If some other metal is used as the anode other than graphite, then O2liberated will not only oxidise the metal of the electrode but would alsoconvert some of the Al liberated at the cathode back to Al2O3. Since graphiteis much cheaper than any metal, graphite is used as the anode. So, the roleof graphite in electrometallurgy of Al is to prevent the liberation of O2 atthe anode which may otherwise oxidise some of the liberated Al back toAl2O3.