Hydrometallurgical processing of complex rare earth ores: trade-offs between REE recovery and radionuclide mobility

Review article, 2026

Rare earth elements (REEs) are critical to low-carbon and advanced technologies, yet their extraction remains challenging due to complex mineralogy and the frequent presence of naturally occurring radioactive materials (NORM), particularly thorium (Th) and uranium (U). This review provides an integrated analysis of hydrometallurgical processing routes for REE-bearing ores, with a specific focus on the mechanisms governing Th and U mobility during mineral dissolution. Unlike conventional reviews that treat mineralogy, leaching chemistry, and radionuclide behavior separately, this work links these factors through a speciation-driven framework to explain and predict radionuclide partitioning across process streams. A systematic evaluation of literature published between 2000 and 2026 is presented, examining the performance of major lixiviants and the influence of mineralogical and geochemical variables on REE recovery and radionuclide behavior. The analysis shows that Th and U mobility is controlled by competing hydrolysis, complexation, polymerization, and redox reactions, which are highly sensitive to process conditions such as pH, temperature, and acid-to-ore ratio. Across processing routes, a consistent trade-off is identified: conditions that maximize REE recovery, particularly low-temperature sulfuric acid baking at high acid dosages, tend to promote significant co-dissolution of Th and U, whereas high-temperature roasting and alkaline treatment routes suppress radionuclide mobility but may reduce extraction efficiency or shift radiological burdens to solid residues. These relationships define a continuum of process performance and reveal the existence of ore-specific operational windows in which REE recovery can be balanced with controlled radionuclide partitioning and manageable impurity levels. The position of these windows is strongly governed by mineralogical characteristics, including REE host phases and gangue composition. This review therefore reframes REE hydrometallurgy as a speciation-controlled, mineralogy-constrained system, where process optimization must consider not only extraction efficiency but also radionuclide behavior and downstream separability. The proposed framework provides a basis for developing more selective, predictable, and environmentally compliant REE processing strategies.