Comparative Leaching Behavior and Radiological Assessment of Igneous and Sedimentary Ore-Derived Phosphogypsum from Five Major European Deposits

Phosphogypsum (PG), a major by-product of phosphate fertilizer production, is an underutilized secondary source of rare-earth elements (REEs) and naturally occurring radioactive materials. This study presents a comparative assessment of REE leaching behavior and radionuclide partitioning in PG from major European deposits in Poland, Spain, Croatia, and Ukraine. Comprehensive chemical, mineralogical, and radiochemical characterization was combined with controlled leaching experiments under varying conditions. The results revealed strong deposit-dependent differences in REE content, extractability, and radiological properties, influenced by phosphate rock origin and processing history. Mineral acids (HCl, HNO 3 , and H 2 SO 4 ) achieved the highest REE recoveries, with optimal conditions at pH 1–2, 30–40°C, and 3–4 h. Kinetic analysis using the shrinking-core model indicated diffusion-controlled leaching, enhanced by increasing acid strength. Radiochemical evaluation showed partial mobilization of uranium-series radionuclides into leachates, while thorium remained in solid residues, and radium was largely retained due to sulfate precipitation. Activity concentration indices and hazard parameters remained within recommended safety limits, indicating minimal radiological risk. These findings demonstrate that PG can be selectively valorized as a secondary REE resource while maintaining radiological safety.