Preparation and characterization of a mesoporous silica-based copolymer loaded with bis(2-ethylhexyl) phosphate for the efficient separation of trace radium from natural thorium

Targeted α-nuclide therapy (TAT) has attracted significant attention in recent years due to its unique advantages in cancer treatment. As one of the most important TAT nuclides, 212Pb is quite rare and strongly depends on the supply of its parent nuclides with an appropriate half-life, such as 228Ra or 224Ra. Therefore, establishing a stable and effective method to obtain these nuclides is critical. To address this issue, a silica-supported copolymer loaded with bis (2-ethylhexyl) phosphate (HDEHP) was prepared, characterized, and investigated for the separation of 228Ra and 224Ra from natural 232Th in the nitric acid media. The experimental results showed that the adsorbent was prepared successfully with 19.5 wt% HDEHP loading, and possessed a small particle size and a porous structure. Compared with traditional cation exchange resin, the adsorbent exhibited ultrahigh selectivity and ultrafast adsorption kinetics towards thorium, with the equilibrium time less than 3 min. The adsorption isotherm was well described by the Langmuir model, and the maximum adsorption amount towards thorium could reach 72.0 mg/g. Thermodynamic investigations suggested that the thorium adsorption was endothermic and spontaneous. On basis of batch experiments, the separation behaviors were further investigated in column modes, and the separation of 228Ra and 224Ra from thorium was finally demonstrated using 226Ra as the tracer nuclide. The chemical recovery rate to 226Ra reached 96.7%, and the decontamination factor to thorium exceeded 105. The spectroscopic assessment suggested that the adsorbed species was mainly the positive Th4+ cation and almost no barium and nitrate ions were involved. The adsorption mechanism was dominated by compounding with oxygen in P-O-H and P=O groups. This work exhibited an excellent material and an efficient method for separating 228Ra and 224Ra from natural thorium, rendering it particularly significant in the future preparation and application of 212Pb.