What is the role of graphite in the electrometallurgy of aluminium ?

Explanation

Hall-Heroult Process : In this process a fused mixture of alumina `(Al_(2)O_(3))` cryolite `(Na_(3).AlF_(6))` or. flourspar `(CaF_(2))` is electrolysed using graphite as anode and graphite lined iron as cathode. Cryolite or fluourspar not only reduces the melting point of alumina, but also increase the electrical conductivity of the molten bath. During electrolysis, Al is liberated at the cathode while CO and `CO_(2)` are liberated at the anode.

At cathode : `Al^(3+)("melt")+3e^(-) to Al(l)`
At anode : `C(s)+O^(2-) ("melt") to CO(g)+2e^(-)`
`C(s)+2O^(2-) ("melt") to CO_(2)(g)+4e^(-)`
The graphite anode is useful here for the reduction of`Al_(2)O_(3)` to Al. For every kg of Al produced, about 0.5 kg of carbon anode is burnt away. This reduces the consumption of electricity and hence the cost of production of aluminium.