Abstract:

This work presents a comprehensive study on the separation of tetravalent elements hafnium (Hf), zirconium (Zr), uranium (U), and thorium (Th) from a rare earth element (REE) bearing leachate generated through sulfuric-acid heap leaching of the Round Top deposit. EDicient removal of tetravalent species is essential to prevent downstream poisoning of phosphoric acid based extractants such as DEHPA and Ionquest 801, which are used in subsequent solvent-extraction (SX) circuits for REE separation. A primary-amine extractant, Primene JM-T was evaluated for its ability to selectively extract tetravalent elements from the leachate. Bench-scale shakeout tests were performed to investigate the eDects of organic to aqueous (O:A) volumetric ratios in both extraction and stripping stages, strip agent composition concentration. Across these tests, Primene JM-T demonstrated extremely high separation factors between tetravalent species and REEs. As a result, incorporation of a scrub stage was deemed unnecessary, simplifying the overall flowsheet. Based on bench-scale results, operating conditions were determined for a continuous pilot scale SX circuit. The pilot was run using three diDerent strip chemistries nitric acid, sodium nitrate, and ammonium nitrate, to evaluate stripping eDiciency, loading behavior, and the ability to concentrate tetravalent ions into a strip product( preg) solution. Process parameters were optimized during the continuous campaign, with emphasis on maximizing tetravalent concentrations in the strip product while maintaining complete rejection of these ions to the raDinate, which feeds downstream REE purification circuits. The pilot results validated the robustness of the Primene JM-T extraction system and provided key design data for scale up, including equilibrium loading behavior, potential crud formation and strip agent selection. The same extractant system was further investigated for selective hafnium recovery from the tetravalent-rich preg stream. Conventional Hf/Zr separation agents such as tributyl phosphate (TBP) and methyl isobutyl ketone (MIBK) typically operate eDectively only in clean nitrate media, and their extraction behavior deteriorates significantly in sulfatecontaining solutions. As the Round Top leachate and subsequent preg streams contain substantial sulfate concentrations, traditional approaches are not suitable without complex sulfate removal steps. In contrast, Primene JM-T maintains selective extraction behavior in sulfate media, provided nitrate levels are adequately moderated. Using bench- scale experiments, a commercial-grade hafnium product was successfully produced, and the process will be validated on a continuous basis as part of the ongoing studies.

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Ms. Sophie Berg