Aluminium LCA: the twentyfold gap between primary and secondary

Aluminium is an instructive material for LCA: almost all of its impact concentrates in one process and one input. Hall-Héroult electrolysis consumes between 13 and 15 MWh of electricity per tonne of primary aluminium, tying the footprint almost one-to-one to the electricity source.

Same product, fourfold difference

Aluminium from a hydro-powered smelter sits near 4 t CO₂e per tonne, while the same product from a plant on a coal-heavy grid can reach 16 to 20 t CO₂e. Same chemistry, same product; the only difference is where the electricity came from.

For any manufacturer using aluminium that is a direct sourcing decision. Two aluminium supplies at the same price and alloy but different origin produce very different footprints in your product. Origin documentation is a calculation parameter, not a marketing detail.

The lines beyond electrolysis

Bauxite mining and alumina production via the Bayer process come before electrolysis and carry their own energy burden; alumina refineries typically use fossil fuel for steam. During electrolysis the carbon anode is consumed, producing process CO₂ directly. Anode effect events form perfluorocarbons.

PFCs are tiny by mass but their global warming potentials run into the thousands — around 6,600 for CF₄ and 11,000 for C₂F₆. Modern cell control systems have greatly reduced anode effect frequency, and that is a measurable abatement line.

Secondary aluminium: a twentieth of the energy

Producing aluminium from scrap takes roughly five per cent of the energy of primary production. Electrolysis is skipped entirely; only melting and refining remain. It is one of the largest recycling advantages in the materials world and the basis of aluminium's circular economy story.

• Scrap quality decides the outcome — mixed-alloy scrap downgrades to low-value casting alloys
• Sorted single-alloy scrap can return to the same product (closed loop)
• Melt losses (dross) vary with scrap quality and furnace type
• Coated or painted scrap requires pre-treatment and emission control
• Recycled content is declared in the EPD and must be verifiable

Reporting recycled content in an EPD

Under EN 15804+A2, recycled content is modelled with the cut-off approach: secondary input carries only collection and reprocessing burden. The potential benefit of material recoverable at end-of-life is reported separately in Module D and cannot be netted off the A1-A3 total.

That distinction matters especially in aluminium, because the Module D value is large and negative. Adding the two into a single 'net' figure breaches EN 15804 reporting rules and is rejected in verification.