Metals recycling maps and allocation procedures in life cycle assessment

The aim of this work is to present guidance on the application of ISO 14044 to allocation procedures for metal recycling. As such, graphical patterns of metal recycling and generic “rules” for metal recycling maps are presented. The results are intended to be useful in assessing and validating the suitability of allocation procedures for metal recycling in the context of life cycle assessment (LCA) and assist in the understanding of metals flow patterns in product systems. LCA uses a product-focus; therefore, the perspective here is on recycling metals in post-consumer products. The discussions, analysis, and illustrations in this paper emphasize old (post-consumer) scrap and do not detail flows of new (post-manufacturing, pre-consumer) or prompt (internal) scrap. The work included participation and review from International Council on Mining and Metals, the Nickel Institute, the International Copper Association, the International Zinc Association, worldsteel (formerly International Iron and Steel Institute), and the International Aluminium Institute.

A survey of generic metal flows was conducted for three major non-ferrous metals—nickel, copper, and zinc. Based on the results of this survey, four metal recycling map models were developed. Implications of these recycling maps for LCA were then considered, and parameters necessary to model metal recycling were presented. Relationships of inherent properties and recycling loops are provided and connected to the allocation procedures in the context of LCA.

Four metals recycling map models were generated based on a survey and analysis of current metals flow analysis. The utility of the recycling maps is to serve the basis of a structured approach to recycling allocation in life cycle assessment and leveraging the efforts of harmonized recycling metrics.

A consensus on mapping metals is important in order to achieve an accurate understanding and measurement of metals recycling. To this end, consensus mapping presentation of a general allocation approach and identification of harmonized metrics were achieved among representatives of ferrous and non-ferrous metals groups.

For the future, allocation factors based on sound empirical data needs to be developed. Those metrics will empower the various stakeholders—industry, policy makers, non-governmental organizations, and academics to make appropriate decisions based on agreed scientific bases.