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<p>The growing demand for high-purity rare earth elements (REEs), coupled with a cerium oversupply, necessitates more efficient separation strategies. Cerium is typically separated by solvent extraction, a costly process that can require hundreds to over a thousand stages for full REE separation. This study evaluates calcium hypochlorite as a practical oxidant for early-stage cerium removal from mixed REE chloride solutions, aiming to reduce solvent extraction demands. Thermodynamic Eh–pH analysis showed that Ca(OCl)<sub>2</sub>, via HClO, can generate oxidation potentials high enough to oxidize Ce<sup>3+</sup> to insoluble Ce(IV) above pH ~ 4, while most trivalent REEs remain soluble in the same window, design of experiments, and post-precipitation aging were used to optimize conditions for selective Ce precipitation while minimizing co-removal of other REEs. Approximately 90% Ce removal was achieved at pH 4.2–4.5, 65–70&#xa0;°C, and 2.6 times the stoichiometric oxidant dosage. Aging at 60&#xa0;°C and pH 3–4 redissolved up to 90% of co-precipitated REEs while retaining most Ce in precipitate form. These results render calcium hypochlorite a scalable and selective oxidative separation agent, offering a practical alternative to other oxidizers and traditional solvent extraction for cerium removal, thereby enhancing the sustainability of rare earth hydrometallurgy.</p> Graphical Abstract <p></p>

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Selective Cerium Separation from Rare Earth Chloride Solutions Using Calcium Hypochlorite: Thermodynamics and Process Optimization

  • 期刊论文

  • 发表日期：

    2026年1月7日

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  • Maziar E. Sauber,
  • Antonio Di Feo

摘要

The growing demand for high-purity rare earth elements (REEs), coupled with a cerium oversupply, necessitates more efficient separation strategies. Cerium is typically separated by solvent extraction, a costly process that can require hundreds to over a thousand stages for full REE separation. This study evaluates calcium hypochlorite as a practical oxidant for early-stage cerium removal from mixed REE chloride solutions, aiming to reduce solvent extraction demands. Thermodynamic Eh–pH analysis showed that Ca(OCl)2, via HClO, can generate oxidation potentials high enough to oxidize Ce3+ to insoluble Ce(IV) above pH ~ 4, while most trivalent REEs remain soluble in the same window, design of experiments, and post-precipitation aging were used to optimize conditions for selective Ce precipitation while minimizing co-removal of other REEs. Approximately 90% Ce removal was achieved at pH 4.2–4.5, 65–70 °C, and 2.6 times the stoichiometric oxidant dosage. Aging at 60 °C and pH 3–4 redissolved up to 90% of co-precipitated REEs while retaining most Ce in precipitate form. These results render calcium hypochlorite a scalable and selective oxidative separation agent, offering a practical alternative to other oxidizers and traditional solvent extraction for cerium removal, thereby enhancing the sustainability of rare earth hydrometallurgy.

Graphical Abstract