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Assessing the environmental footprint of the production of rare earth metals and alloys via molten salt electrolysis

Vahidi, Ehsan, Zhao, Fu
Resources, conservation, and recycling 2018 v.139 pp. 178-187
alloys, cathodes, chemical treatment, clean energy, databases, ecological footprint, ecotoxicology, electric energy consumption, electrolysis, energy balance, eutrophication, fluorides, life cycle inventory, mining, molybdenum, neodymium, refining, solvents, stoichiometry, China
Much attention has been given in recent years to the rare earth elements, considering their significance in a number of high-tech and clean energy applications. Despite the environmental destructive operations to produce rare earth elements, limited life cycle assessment investigations have yet been carried out. This is specifically true regarding the reduction of rare earth compounds to produce rare earth metals and alloys. In combination with mass/energy balance and stoichiometry, life cycle inventories of molten slat electrolysis process were developed in this study using industrial datasets gathered from different facilities in China and the Ecoinvent v3 database. The results showed that although mining, chemical treatment, and solvent extraction stages are the dominant contributors to the whole neodymium metal production process for most impact categories, molten salt electrolysis significantly impacts ecotoxicity, carcinogenics, non-carcinogenics, and eutrophication categories. Moreover, neodymium fluoride production, electricity consumption, and molybdenum use in cathodes are the dominant contributors in the molten salt electrolysis process. In addition, the neodymium metal production at facilities which produce larger amounts of heavy rare earth metals/alloys demonstrates relatively lower impacts on all impact categories compared to the production of neodymium metal at refining facilities which produce light rare earth metals/alloys.