Chemical recovery of waste electrical and electronic equipment by microwave-assisted pyrolysis: A review

Over the past few decades, electrical and electronic equipment has become more accessible to people of different social status. Currently, however, only a small fraction of the resulting waste is treated properly, even though it has the potential to become a major source of raw materials. Waste electrical and electronic equipment (WEEE), or e-waste, is mainly composed of plastics and metals that can be recovered with a lower environmental impact and more efficiently in comparison with conventional processes, even when similar technologies are used. Pyrolysis is a thermochemical processing technique that is able to exploit the polymers in WEEE as well as concentrate the metals into a solid residue. Furthermore, this process can be adapted or combined with other technologies to minimize the content of organic halides that stem from the hazardous brominated flameretardants (BFRs), which are common additives used in these products. Microwave-assisted pyrolysis (MAP) uses a heating mechanism that differs significantly but has advantages over conventional pyrolysis, such as a rapid volumetric heating or a higher energy efficiency. Despite the increasing interest in the application of MAP over the last years, research to date in this field remains scarce. As such, this article reviews current studies into the treatment of WEEE by MAP, thereby shedding light on the different variables that have an impact on its effectiveness and efficiency, to provide a comprehensive understanding of this technology. In addition, this review offers an overview of the characteristics of pyrolysis products and possible routes for their subsequent refining.