Recovery of rare earth elements and thorium from acid leaching residue of ionic rare earth concentrates

The acid leaching residue (ALR) of ionic rare earth (IRE) concentrates containing radioactive elements such as thorium (Th) is classified as low-level radioactive waste. ALR holds valuable strategic resources such as rare earth and Th, while improper long-term heaping storage of ALR poses a substantial environmental risk. This paper proposes a comprehensive process involving low-temperature roasting, hydrochloric acid leaching, single extractant enrichment, and stepwise stripping to recover rare earth elements and thorium from ALR. The achieved leaching efficiencies are 80.11% of LnY, 99.43% of Sc(III), and 98.67% of Th(IV) after the carbonization of the organic phase in the ALR through low-temperature roasting. Despite large amounts of acid and impurities present in the leachate, 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) still exhibits nearly 100% extraction efficiency for Sc(III) and Th(IV). The effective separation of LnY, Th(IV), and Sc(III) was achieved by implementing fractional extraction enrichment of Th(IV) and Sc(III), followed by Th(IV) removal through HSO and Sc(III) removal via NaOH from the loaded organic phase. This scheme successfully achieves a recovery of RE and Th and offers a viable solution for the safe disposal of ALR.