Mixed Shredded Aluminium (source: ntxscrap.com)

We have has recently completed work studying the potential of digitalisation to change recycling of the four bulk materials which produce ⅔ of industrial GHGs – steel, plastics, aluminium and cement. The first three commonly exist in different alloys and grades, each specifically made to produce specific properties tailored to a specific use. The specific properties give the materials their value. After use, mixed waste collections of different alloys of steel and aluminium, and different types and formulations of plastics, will destroy most value unless they are separated before recycling. Digital sorting potentially enables this with high accuracy, and our research investigated the likelihood of new recycling processes making significant reductions in virgin material use before 2050.

The results are mixed. For steel, a large developing world market exists for unsorted, contaminated, mixed steel scrap to make into concrete reinforcing bars, and the economic incentive to sort steel for high-quality recycling is low. Unfortunately, this is likely to lead to global surpluses of contaminated scrap by 2040, unusable under current technologies.

For plastics, 40% are used for single-use applications – these are scrapped almost immediately. Packaging could be marked for digital sorting using existing technologies if the supply chain could agree on a solution, but cross-supply chain cooperation is low.

Cement changes chemically as it sets, making reuse impossible. There are initiatives to recover unreacted portions from used concrete, and other trials to reduce the cement content of concrete to save GHGs, but these are small. So the volume of GHGs from cement is unlikely to reduce near term.

Lastly, there is good news about aluminium. Laser Induced Breakdown Spectroscopy machines that sort scrap aluminium in volume are being launched this month (June 2023). A laser pulse fired at the material vaporises a tiny amount and this plasma is digitally analysed to identify it. Potentially this transforms aluminium recycling, allowing the grades to be separated and avoiding large scale alloy mixing and loss of value currently occurring, in turn reducing the amount of virgin aluminium mined at refined at a huge GHG cost.

By Martin Burgess, Environmental Change Institute – Oxford