Metallurgical recycling processes: Sustainability ratios and environmental performance assessment

• An evaluation model combining emergy evaluation and exergetic life cycle assessment.
• Metallurgical recycling processes taking into account material and quality losses.
• The average transformity of recycled materials on all previous recycling.
• Sustainability ratios: resource efficiency ratio, performance ratio and eco-design ratio.

Recycling is considered as core element of the sustainable development. In reality, however, due to the physical and chemical limits of current recycling technologies, material and quality losses occur that affect the efficiency of recycling. This paper aims to assess the environmental performance of metallurgical recycling, from both a donor and user-side perspective, by using the emergy evaluation combined with exergetic life cycle assessment (ELCA). The developed evaluation model is based on Ulgiati's proposition to erase the memory of the recovered material and to account only for the current recycling cycle. The use of an average transformity is proposed to measure the environmental performance of recycled materials. Contrary to classical transformities, it evaluates the material based on all previous processes that generated the material while avoiding the “double counting”. Finally, three sustainability ratios have been defined to further assess the benefits and limits of consecutive metallurgical recycling processes: the resource efficiency ratio α, the performance ratio β and the eco-design ratio χ. Their functions have been described and clarified with provided examples.