Recovery process of rare earths, Al, U, and Th from ionic rare earth purification residue using sequential alkaline leaching, acid leaching solvent extraction and stripping

Ionic rare earth purification residue (PR) originates from refining of ionic rare earth ores and is predominantly composed of rare earth elements (REEs), aluminum (Al), and silicon (Si). This is a recyclable secondary resource. It provides substantial challenges due to its classification as low-level radioactive waste (LLW). Recognizing the distinctive properties of PR, this paper describes a highly efficient process for the recovery and enrichment of Al, REEs, uranium (U), and thorium (Th) through a multistep process encompassing alkali digestion, hydrochloric acid leaching, sole extractant enrichment and separation. At a controlled temperature of 70 °C, the Al digestion efficiency reached 88.9 %. The alkali digestion residue underwent hydrochloric acid leaching, yielding leaching efficiencies of 99.9 %, 99.4 %, and 99.0 % for REEs, U(VI), and Th(IV), respectively. Notably, the amount of insoluble residue was reduced by 90 %, and it was transformed from LLW into general solid waste residue. Additionally, the utilization of 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) as the sole extractant provided 100 % extraction efficiencies for U(VI) and Th(IV). After stepwise stripping processes, the purities of both U(VI) and Th(IV) exceeded 90 %. The REEs were precipitated as RE₂(C₂O₄)₃ and subsequently calcined to produce rare earth oxides with a recovery of 90.1 % and a purity of 97.4 %. This comprehensive scheme addressed the persistent challenges associated with long-term storage and radiological environmental risk.