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

Explanation

In the electrometallurgy of aluminium a fused mixture of alumina, cryolite and flourspar `(CaF_2)` is electrolysed using graphite as anode and graphite lined iron as cathode. During electrolysis , Al is liberated at the cathode while CO and `CO_2` are liberated at the anode.
At cathode: `Al_(mel t)toAl(1)`
AT anode: `C_(s)+O^(2-)toCO_(g)+2r^(ɵ)`
`C_(s)+2O^(2-)toCO_2+4e^(ɵ)`
If instead of graphite, some metal is used as the anode then `O_2` liberated will not only oxidese the metal of the electrode but would also convert some of the Al liberated at the cathod back to `Al_2O_3`. Since graphite is much cheaper than any metal, therefore graphite is used as the anode, thus the role of graphite in electrometallurgy of Al is to prevent the liberation of `O_2` at the anode which may otherwise oxidese some of the liberated Al back to `Al_2O_3`.