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

In the electrometallurgy of aluminium, a fused mixture of purified alumina ($A{l}_{2}{O}_{3}$), cryolite ($N{a}_{3}AI{F}_{6}$) and fluorspar ($Ca{F}_{2}$) is electrolysed. In this electrolysis, graphite is used as the anode and graphite-lined iron is used as the cathode. During the electrolysis, Al is liberated at the cathode, while CO and $C{O}_{2}$ are liberated at the anode, according to the following equation.

If a metal is used instead of graphite as the anode, then ${O}_{2}$ will be liberated. This will not only oxidise the metal of the electrode, but also convert some of the Al liberated at the cathode back into $A{l}_{2}{O}_{3}$ . Hence, graphite is used for preventing the formation of ${O}_{2}$ at the anode. Moreover, graphite is cheaper than other metals.