Abstract
Waste electrical and electronic equipment or e-waste generation has been skyrocketing over the last decades. This poses waste management and value recovery challenges, especially in developing countries. Printed circuit boards (PCBs) are mainly employed in value recovery operations. Despite the high energy costs of generating crushed and milled particles of the order of several microns, those are employed in conventional hydrometallurgical techniques. Coarse PCB pieces (of order a few centimetres) based value recovery operations are not reported at the industrial scale as the complexities of the internal structure of PCBs limit efficient metal and non-metal separation. Since coarse PCB particles’ pre-treatment is of paramount importance to enhance metal and non-metal separations, thermal, mechanical, chemical and electrical pre-treatment techniques were extensively studied. It is quite evident that a single pre-treatment technique does not result in complete metal liberation and therefore several pre-treatment flowsheets were formulated for coarse PCB particles. Thermal, mechanical and chemical pre-treatments integrated flowsheets were derived and such flowsheets are seldom reported in the e-waste literature. The potential flowsheets need to be assessed considering socio-techno-economic considerations to yield the best available technologies (BAT). In the wider context, the results of this work could be useful for achieving the United Nations sustainable development goals.
Highlights
With the expeditious innovations in technology and the expanding businesses of electrical and electronic equipment (EEE) production, waste electrical and electronic equipment (WEEE) is regarded as one of the fastest growing municipal solid waste streams on the globe [1,2,3]
When coarse printed circuit boards (PCBs) particles are prepared by comminution, a complete metal liberation would not be expected since the resultant PCBs are formed by different components/materials [82]
Moyo et al [21] discerned that effective metal liberation can be achieved by applying different combinations of pre-treatment methods, which do not rely on heavily mechanised equipment
Summary
With the expeditious innovations in technology and the expanding businesses of electrical and electronic equipment (EEE) production, waste electrical and electronic equipment (WEEE) is regarded as one of the fastest growing municipal solid waste streams on the globe [1,2,3]. The high concentration of flame retardants detected in the samples of soil, air, water and sediments obtained from informal e-waste processing sites elucidate the seriousness of the environmental pollution [10] This implies the urgent requirement for organised and sustainable e-waste management (i.e., employ extended producer responsibility or EPR schemes to collect e-waste) and value recovery operations, especially in developing countries [11]. The production of coarse PCB particles (e.g., 1–3 cm), while eliminating the conventional milling step, is considered as a potential pre-treatment method pertaining to hydrometallurgy based e-waste value recovery. This niche area in e-waste recycling is not extensively studied. Since this burgeoning area of research is not yet well studied, the objective of this work is to analyse suitable coarse PCB particles’ pre-treatment mechanisms to produce metal fractions prior to hydrometallurgy based metal extraction and recovery operations
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