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

Explanation

In the electrometallurgy of aluminum, a fused mixture of alumina, cryolite and flourspar (`Ca F_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^( 3 + ) ("melt" ) to Al(l) `
At anode : ` C (s) + O ^( 2 - ) (" melt" ) to CO (g) + 2 e ^( - ) `
` C (s) + 2 O ^( 2 - ) ("melt ") to CO_ 2 (g) + 4 e ^( - ) `
If instead of graphite, some metal is used as the anode, then ` O _ 2 ` liberated will not only oxidise the metal of the electrode but would also convert some of the Al liberted at the cathode 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 oxidise some of the liberated Al back to ` Al _2 O _ 3`.