The following reactions happen during the metallurgy of aluminium at anode where oxidation takes place.

C(s) + O₂^– (melt) → CO(g) + 2e^–

C(s) + 2O₂^– (melt) → CO₂ (g) + 4e^–

At cathode

Al³⁺ (melt)+3e^-→Al(s)

Overall Reaction:

2Al₂O₃ +3C→ 4Al +3CO₂

Solid carbon(graphite) gets oxidised to carbon monoxide and carbon dioxide.