Boonen, Katrien; Vercalsteren, An; Buyle, Matthias; Christis, Maarten; Nys, Charlotte; Oorts, Koen

Chromium (Cr) has a high economic importance to the EU. However, Europe is highly dependent on its import, while industrial waste flows containing a substantial amount of Cr are available. Extracting Cr and other residual metals from these waste flows has the additional benefit that the remaining matrix can be applied more widely in the construction sector due to reduced Cr content. The aim of the H2020 funded CHROMIC project was to develop new processes to recover Cr and other metals from industrial waste. Various chemical and physical processes were developed, tested and validated. To assess the sustainability of the newly developed recovery routes, an integrated assessment was performed from an environmental (LCA), economical (LCC) and health and safety risk assessment (RA) perspective. The LCA and LCC followed an iterative approach which allowed providing feedback in an early stage and steering the development from lab to pilot scale where necessary. In the final iteration, the recovery routes developed on pilot scale were assessed and compared to the current standard approaches for slag treatment. Three flowsheets were developed in the pilot-scale upscaling step: traditional roasting and leaching for carbon steel (CS) slag, microwave roasting and leaching for stainless steel (SS) slag and heap leaching for SS slag. The LCA/LCC showed that, for all treatment routes, the recovery of Cr and the use of the residual matrix after recovery of the valuable metals results in avoided environmental impacts and costs. However, these benefits are generally not large enough to compensate for the impacts and costs of the treatment process. Valorisation of the residual matrix as bricks often has larger benefits than the recovered Cr itself. When comparing all CHROMIC technologies studied, the heap leaching route applied to SS slag showed to be the most favourable, mainly due to lower energy requirements than the routes that include roasting.