Separation of Trace Radium from Thorium-Rich Systems via BaSO4 Co-Precipitation

212Pb is an important medical radionuclide for targeted alpha therapy, and its reliable supply depends on the efficient production of parent nuclides such as 228Ra, 228Th, and 224Ra. Natural thorium resources are abundant and represent a potential source of these radionuclides. However, the separation and enrichment of trace radium from thorium-rich high-salinity systems remain challenging due to extremely low radium concentrations and Th/Ra mass ratios on the order of 109. In this work, a radium separation strategy based on BaSO4 co-precipitation was developed. The precipitation behavior of BaSO4, precipitation kinetics, radium co-precipitation efficiency, and thorium recovery in concentrated thorium nitrate solutions were systematically investigated. The results show that elevated ionic strength and competitive interactions between Th4+ and SO42− reduce the effective sulfate activity under high-thorium conditions, making excess sulfate necessary to achieve efficient BaSO4 precipitation. Under optimized conditions, the radium co-precipitation recovery exceeded 80% at a Ba2+ concentration of 3 mM. Meanwhile, thorium exhibited negligible incorporation into the BaSO4 phase and could be almost completely recovered via subsequent hydroxide precipitation. The proposed method features operational simplicity, use of common reagents, low cost, and compatibility with high-salinity matrices. It provides a feasible technical pathway for the subsequent production of high-purity 228Th or 224Ra and the preparation of 228Th/212Pb or 224Ra/212Pb generator systems.