In this process, a fused mixture of alumina, cryolite and fluorspar$(\mathrm{CaF}_2)$ is electrolysed using graphite as anode and steel as cathode.During electrolysis, Al is liberated at the cathode whereas CO and $\mathrm{CO}_2$are liberated at the anode. Cathode: $\mathrm{Al}^{3+}(\text{melt}) \xrightarrow{} \mathrm{Al}_{(\text{l})}$ Anode $: \mathrm{C}_{(s)} + \mathrm{O}^{2-}(\text{melt}) \xrightarrow{} \mathrm{CO}_{(\text{g})} + 2e^{-}$ $\mathrm{C}_{(s)} + 2\mathrm{O}^{2-}(\text{melt}) \xrightarrow{} \mathrm{CO}_{2(\text{g})} + 4e^{-}$If some other metal is used as the anode other than graphite, then $\mathrm{O}_2$liberated will not only oxidise the metal of the electrode but would alsoconvert some of the Al liberated at the cathode back to $\mathrm{Al}_2\mathrm{O}_3$. 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 $\mathrm{O}_2$ atthe anode which may otherwise oxidise some of the liberated Al back to$\mathrm{Al}_2\mathrm{O}_3$.