Life cycle assessment of resource recovery from waste electrical and electronic equipment: A case study of tantalum recovery by chain-using drum-typed impact mill

The recovery of metal resources from urban mines such as waste electrical and electronic equipment (WEEE) has become an emerging issue. The establishment of technology and social systems for recycling rare metals is of especially high priority due to their worldwide shortage. This study tackles the recycling of rare metals, especially tantalum, by applying a chain-using drum-type impact mill (CDIM) for pulverization of WEEE in the intermediate treatment for physical separation of components contained in plastic routers. A life-cycle assessment (LCA) was conducted based on actual process inventories of the CDIM, segregation and concentration of electronic parts. Climate change and resource depletion were adopted as the impact category indicated by life-cycle greenhouse gas emission (LC-GHG) and characterized resource consumption in this LCA. Although the tantalum contained in WEEE is input into the copper smelting and cannot be separated from other metals in conventional recycling systems, it was demonstrated that the CDIM intermediate treatment could selectively concentrate the tantalum capacitors. The tantalum capacitors can be converted into sintered tantalum, substitutes for Ta₂O₅, which can reduce resource consumption potentials at the expense of additional energy consumption. Most of the LC-GHG was derived from energy, especially public electricity. Decarbonization in the power grid can reduce the LC-GHG attributable to the recycling system. Rare metals other than tantalum should also be recoverable from WEEE. Physical and chemical treatment processes for metal recovery should be developed, demonstrated, and implemented in line with the recycling systems for various products.