Being elements, metals can in theory be recycled infinite times without losing original properties. In reality, however, this ideal situation is hampered by unintentional mixing of different metals in recycling processes. This can result in function losses and dissipation of species with distinctive functions, and contamination by unintentional presence of incongruous metals, besides material losses that result from losses in recovery, refining, and manufacturing. Dynamic MFA studies of metals concerned with the latter type of losses abound. To our knowledge, however, those concerned with the former type of losses are almost nonexistent, though the importance of addressing qualitative aspects of recycling is frequently acknowledged (Ohno et al. 2014, Haupt et al. 2016).
To fill this gap, we developed a new dynamic model of MFA, MaTrace-alloy to exactly address the issue of secondary metal contamination and non-functional losses. Starting from the MaTrace model (Nakamura et al. 2014), a dynamic MFA model capable of tracing the fate of a material over time across products, we extended it to the general case where products consist of alloys that in turn consist of substances. MaTrace-alloy is capable of tracing the fate of substances that initially occurred in a cohort of products over repeated cycles of recycling, under explicit consideration of losses of both function and material occurring in end-of-life products recovery, transformation into scrap including disassembling, separation, and sorting, re-melting and refining into new alloys, and manufacturing into new products.
The model was implemented using a large-scale IO data for Japan extended for flows of iron, chromium and nickel involving 27 steel alloys and 115 final products with intensive steel use (Ohno et al. 2014). Scenario analysis involving alternative sorting schemes revealed quantitative implications of the efficiency of scrap sorting and re-melting technologies on the magnitudes of both function and material losses.
References
Haupt, M.; Vadenbo, C.; Zeltner, C.; Hellweg, S. (2016) Influence of input-scrap quality on the environmental impact of secondary steel production. J. Ind. Ecol., doi:10.1111/jiec.12439
Nakamura, S.; Kondo, Y.; Kagawa, S.; Matsubae, K.; Nakajima, K.; Nagaska, T. (2014) MaTrace: Tracing the fate of materials over time and across products in open-loop recycling. Environ. Sci. Technol. 48, 7207–7214
Ohno, H.; Matsubae, K.; Nakajima, K.; Nakamura, S.; Nagasaka, T. (2014) Unintentional flow of alloying elements in steel during recycling of end-of-life vehicles. J. Ind. Ecol. 18, 242–253
