Selective extraction of rare earths and lithium from rare earth fluoride molten-salt electrolytic slag by sulfation

Abstract

Rare earth fluoride molten-salt electrolytic slag has recently attracted significant attention because it is a potential environmental hazard that is rich in rare earth elements (REEs). Sulfation is commonly applied to the extraction of mineral commodities or scraps, such as REEs, Li, Ni, and Ti, as preparation for recycling. In this study, a selective sulfation method was performed by completely transforming powdered samples into a sulfate mixture. A suitable selective roast-water leaching treatment resulted in >95% extraction efficiencies for REEs and Li, while Fe and Al remained in the resultant residue as oxides. F was volatilized in the exhaust and then absorbed as LiF by a 1.0-M LiOH alkaline solution. Fe, Al, and F impurities were also separated from the lixivium, enabling the production of REE oxalates with >99% purity. Such a solution could be directly treated with subsequent precipitation processes without impurity removal pretreatments. The method of defluorination and extraction of REEs and Li from the rare earth fluoride molten-salt electrolytic slag is viable to address the exponential increase in REE production.