The Hall–Héroult process (electrolysis of alumina to make aluminium) uses a sacrificial carbon anode - every 2 atoms of Al you produce results in 3 CO2 molecule

The Hall–Héroult process (electrolysis of alumina to make aluminium) uses a sacrificial carbon anode - every 2 atoms of Al you produce results in 3 CO2 molecules - so for every kg of Al you make ~2.4 kg of CO2