Nanopowders from waste printed circuit boards: Review and evaluation from an alternatives assessment perspective

Recovery of valuable resources from waste printed circuit boards (WPCBs) is affected by the low recycling rate of discarded WPCBs and their highly heterogeneous material composition. Conventional electronic waste management processes, including incineration and disposal in landfills, generate toxic pollution. Alternatively, the valuable metals contained in WPCBs make "urban mining" of this resource increasingly attractive. Instead of conventional recovery processes that convert valuable metals in WPCBs into pure substances, recent strategies focus on alternative material recovery processes that can directly convert WPCBs into functional value-added materials, such as nanopowders. In this study, recently-developed experimental processes for producing copper-based nano-/superfine powders from WPCBs were reviewed. Six alternative material recovery processes were selected for assessment, including three chemical processes: selective leaching, slurry electrolysis, and microemulsion; two thermal processes: low- and high- temperature thermal processing; and one physical process: mechanical alloying. An alternatives assessments (AA) approach was applied to evaluate functional performance, scale-up potential, and sustainability of each of these material recovery processes. The results from the evaluation of fourteen attributes showed that chemical processes performed better in functional performance but were material intensive. In contrast, thermal and physical processes showed better scale-up potential but were energy intensive. Thus, this study provides a robust assessment to guide future process design before these processes advance into commercial production. Moreover, by incorporating multiple divergent attributes for evaluation, the comprehensive and scientifically rigorous AA framework informs strategies to improve the circular economy of WPCBs by systematically comparing the benefits and potential drawbacks of early-stage alternative material recovery processes.