The carbon footprint of primary aluminum is mostly dependent on the source of the electricity used due to the energy-intensive Hall Heroult electrolysis process use to make the product.
In a position paper published by aluminum maker Norsk Hydro, the company looks at ways to reduce aluminum’s carbon footprint by tweaking this process and using more recycled aluminum.
According to the report, the carbon footprint of primary aluminum varies between less than four tons CO2-equivalents per ton aluminum in hydropower-based regions to more than 20 tons CO2-equivalents per ton aluminum in coal power-based regions. However, the aluminum recycling process requires lesser energy and emits less CO2 – approximately 0.5 tons of CO2-equivalents per ton aluminum.
What is the carbon footprint of recycled aluminum?
Regarding recycled aluminum, postconsumer scrap is defined as aluminum scrap that comes from products that have fulfilled the purpose for which they were produced.
This scrap might range from aluminum cans with a lifetime of about 60 days to buildings with a lifetime of more than 50 years. When this scrap is recycled, it starts its second life as a recycled product, with no carbon footprint history attached to it. As a result, post-consumer scrap has a carbon footprint of about 0.5 tons CO2 per ton of aluminum resulting from scrap collection, transport, sorting, and remelting.
The situation is quite different for process scrap, which is a by-product of processing aluminum products, such as extruded profiles or rolled foil. During aluminum processing, around 20-30pc ends up as process scrap, which is of high value, and the recycling rate of this scrap is close to 100pc. However, process scrap has never fulfilled its purpose as a product, and thus carries the carbon footprint of the original primary aluminum from which it is produced.
Thus the carbon footprint of recycled process scrap is not 0.5 tons CO2 per ton aluminum, but the carbon footprint of the original primary aluminum PLUS 0.5 tons CO2 per ton aluminum. Some companies claim that the carbon footprint of process scrap is equal to the carbon footprint of post-consumer scrap. Such an approach would equalize the carbon emissions to hydropower-based aluminum
and coal-based aluminum as soon as the metal is processed. This approach would lead to “greenwashing”, would favor industrial inefficiencies, and is not supported by Hydro.
Hydro’s method
Hydro calculates the carbon footprint of aluminum by modeling physical realities as closely as possible by following acknowledged LCA methodologies, as outlined in ISO 14040-44. The company does not equalize process scrap and post-consumer scrap in its calculations but regards process scrap as primary aluminum that has to be remelted once more. As a result, the carbon footprint of recycled process scrap is equal to or even higher than that of primary aluminum. Post-consumer scrap, on the other hand, has fulfilled its purpose in its first life cycle, is starting its second life cycle and has thus no historical carbon footprint attached to it.
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