An initial life cycle assessment of rare earth oxides production from ion-adsorption clays

Abstract

Rare earth elements (REEs) have found applications in the aerospace, automotive, consumer electronics and lighting industries, among others. A special class of REEs known as heavy rare earths (HREEs) is of particular importance to energy applications. With the growing clean energy technologies incorporating HREEs, it is valuable to examine their environmental emissions and energy requirements. Currently, extraction of HREEs is mainly carried out in China, where they are extracted mainly via open pit mining of bastnasite and/or monazite and leaching of ion-adsorption clays. Leach mining varies significantly from open pit mining technique in that the ores have much lower REE content but REEs stay as cations thus there is no need for physical and chemical beneficiation. To date limited life cycle assessment (LCA) studies have been done on REEs production and all of them are for the bastnasite/monazite route. This paper presents the first LCA of in-situ leach mining of REEs from ion adsorption clays in southern China. The function unit was defined as production of 1kg of mixed rare earth oxides (REOs) of purity 92%. Ecoinvent 3.0 database was adopted for inventory analysis with material and energy flow information gathered from Chinese literature. To facilitate the use of results in U.S. and EU, TRACI and ILCD in SimaPro 8 were used for environmental impact assessment and cumulative energy demand was also considered as one additional category. The results showed that the environmental impacts for REOs derived from ion adsorption clays are similar in categories such as global warming and cumulative energy demand, but differs significantly in categories of eutrophication and acidification. Since the content of high value HREEs is much higher in ion adsorption clays, when economic value based allocation is used individual REO from in situ leaching has lower environmental impacts across all categories considered. With estimates of HREEs derived from ion-adsorption clays accounting for approximately 35% of the Chinese output, this LCA is a step towards getting a full understanding of the true environmental impact of technologies incorporating HREEs.