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

Abstract

The extraction of rare earth elements (REEs) from rare earth fluoride molten-salt electrolytic slag has recently attracted attention because of the potential environmental hazards of this material and its rich content of valuable REEs. In this study, we used a selective nitration method to completely transform powdered samples into a nitrate mixture. We conducted a suitable selective roast-water leaching treatment, which resulted in >98% extraction efficiency for the REEs and Li; oxides of Fe and Al were left behind in the residue, which was attributed to the lower decomposition temperature of Fe(NO3)3 and Al(NO3)3. Furthermore, F volatilized in the exhaust as HF and was absorbed by an alkaline solution. HSC modeling and TG-DTA were conducted to simulate the nitration process to obtain the optimum conditions for electrolytic slag nitration. Fe, Al, and F impurities were separated from the lixivium to a great extent, thereby enabling the production of REE oxalates with >99% purity. Such a solution could be directly processed to extract metals without the need for pretreatments to remove impurities. The defluorination method and subsequent extraction of REEs and Li from fluoride molten-salt electrolytic slag address the exponential increase in REE production.