2.Route 1: primary (electrolytic) smelting

Alumina is reduced by electrolysis. Oxygen from the alumina reacts with the carbon anode to form CO2, so anodes are consumed continuously. Cells use either pre-baked anodes (replaced regularly) or a Søderberg anode (baked in place, topped up with paste). Molten metal is then alloyed and cast into ingots, slabs or billets.

Inside the boundary:

• CO2 from anode (electrode) consumption;
• CO2 from fuels (drying, pre-heating, casting);
• CO2 from flue gas treatment, soda ash or limestone;
• PFCs from anode effects (see A5).

Outside or zero:

• Alumina, anodes, paste and additives are raw materials with zero embedded emissions.
• Making anodes (even on site) and making alumina are outside.
• No precursors. Electricity is not counted.

KEY Anode consumption is in; anode production is out. Consumption = anodes put in minus anode stumps returned for recycling.

Sources: MA Annex I 3.17.2.1 p.25; G5e §2.2.3.1 p.13-14, §3.1.1 p.19, §4 p.25.