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

Explanation

In the electrometallurgy of aluminium, electrolysis of a fused mixture of alumina, cryolite and fluorspar is carried out using graphite rods as the anode and gas carbon lined iron tank as the cathode. During electrolysis of this mixture, aluminium is liberated at the cathode while carbon monoxide `(CO)` and carbon dioxide `(CO_(2))` are liberated at the anode.
`"At cathode: "Al^(3+) ("melt")+3erarrAl(l)`
`"At anode : "C(s)+O^(2-)("melt")rarr CO(g)+2e`
`C(s) +2O^(2-)("melt")rarr CO_(2)(g)+4e`
Is some other metal is used as anode, instead of grahite then the liberated `O_(2)` would oxidise the metal of the electrode along with aluminium liberated at the cathode, to `Al_(2)O_(3)`. Thus, graphite is used as the anode since it is much cheaper. The role of graphite in the electrometallurgy of aluminium is to prevent the liberation of `O_(2)` at the anode, which may otherwise oxidise some of the liberated Al back to `Al_(2)O_(3)`.