Metal Recovery from E-wastes
Résumé
Waste electrical and electronic equipment (WEEE) is an important secondary resource of metals and critical raw materials. Printed circuit boards (PCBs), which account for the major fraction of valuable metals in e-waste, are mainly recycled using pyrometallurgy, though there is currently no suitable option for low-grade PCBs and more generally a lack of PCB processing capacity. Between 2001 and 2021, over 60 publications described the technical viability of bioleaching PCBs using acidophilic microorganisms to recover base metals. While most of these have been simple laboratory-scale tests, together with more comprehensive, larger-scale work carried out the state of the art by the end of 2021 was that: (1) indirect bioleaching is applicable at commercial scale; (2) adaptation of the microbial consortia to PCB leachate and raffinate should be possible; (3) microbial colonisation of PCB leaching reactors is not only possible, but advantageous. Furthermore, iron in the PCBs can be recycled and oxidised biologically, providing sufficient oxidant for the process to be continuous. However, some issues, such as acid consumption, are still pending. A few studies are now scaling up the process and aim to optimise the operating conditions as well as to gather techno-economic and environmental data to evaluate the commercial feasibility of PCB bioleaching. The integration of the process in the whole recycling chain, with consideration of PCB pre-treatment and metal recovery from the leachate and residue, is now required.