Avoiding downcycling
The recyclate use rate in new products is at a very low level and has hardly changed noticeably from 11.6% to 12.2% since 2015 (the start of recording) until today. Why is this? When metals are recovered from end-of-life products, significant quality losses occur due to the mixing of different scrap and alloy types in the recycling process. This phenomenon, known as "downcycling," is due on the one hand to contamination of the recycled metals with undesirable impurities, and on the other hand to inseparable alloying elements that are not needed in the target alloy. To keep the loss of quality as low as possible, considerable quantities of primary raw materials are added as "diluents" during metallurgical processing.
Recycling processes as part of the waste hierarchy and as causes of downcycling.picture: HZDR
Metal raw materials from end-of-life products are therefore not currently fed into a closed (economic) cycle and are subject to downcycling with corresponding material and quality losses. In a proposal for a harmonized and more specific terminology, the term "downcycling" was clearly defined for the first time in the work of Helbig et al. (2022) as the phenomenon of quality reduction of the recycled target alloy compared to its original quality. The reduced quality can be expressed thermodynamically, functionally as well as economically and thus covers all perspectives of downcycling, such as dilution, contamination or reduced demand for secondary raw materials. For the quantification of downcycling, the thermodynamic downcycling degree plays a special role and is determined via a thermodynamic process simulation in Raatz et al. (2022).
In order to ensure high-quality recycling in the future, alloy-specific material flows must be separated from each other with the highest possible sorting depth with regard to the accompanying elements. The "OptiMet" project (Raatz et al. 2022) therefore investigated which combinations of innovative camera/sensor systems, coupled with automation and AI, guarantee a high degree of separation accuracy in order to ensure a high quality of recyclates. It is recommended that binary single sorting processes be replaced by multi-channel, multi-stage sorting across the board.
By introducing these novel sorting technologies in scrap processing, for example, up to 290,000 tons of primary material and up to 90 percent CO2 can be saved in aluminum recycling. This makes it possible to keep raw materials in the cycle for longer, to use metals more frequently and in higher quality, and thus to significantly increase the recyclate use rate and drastically reduce the raw material-related environmental impact. This makes it possible to achieve a sustainable circular economy and also support the security of supply of metal raw materials.
References:
Helbig, C., Huether, J., Joachimsthaler, C., Lehmann, C., Raatz, S., Thorenz, A., Faulstich, M., & Tuma, A. (2022). A terminology for downcycling. Journal of Industrial Ecology, 1–11. doi.org/10.1111/jiec.13289
Raatz, S., Seidel, P., Tuma, A., Thorenz, A., Helbig, C., Reller, A., Faulstich, M., Joachimstaler, C., Steger, S., Hagedorn, W., Bickel, M., Liedtke, C. (2022). OptiMet: Ressourceneffizienzsteigerung in der Metallindustrie - Substitution von Primärrohstoffen durch optimiertes legierungsspezifisches Recycling. Umweltbundesamt (UBA) Texte 81/2022, ISSN 1862-4804