Enhanced separation of palladium from simulative high-level liquid waste using a silica-supported polymer functionalized with aminopyridine

Spent fuel reprocessing typically produces high-level liquid waste (HLLW), where lots of palladium and other radioactive nuclides exist. Palladium recovery from HLLW contributes to not only increasing the palladium supply but also addressing the issue of furnace clogging during the vitrification of HLLW. To achieve this, several aminopyridine-functionalized silica-based resins (SiPAc-NH-Pys) were prepared in this study through in-situ polymerization and post-synthetic modification, and the adsorption behaviors and mechanisms toward palladium were systematically studied by batch experiment and spectroscopy. The results showed that aminopyridine-functionalized SiPAc-NH-Pys with porous structure and uniform shapes were successfully prepared. These SiPAc-NH-Pys exhibited high selectivity for palladium in simulative HLLW, with almost no affinity for lanthanides or alkaline metal ions. In addition, SiPAc-NH-Pys exhibited fast adsorption and desorption kinetics, with equilibrium reached within 10 min. The adsorption kinetics were fitted well by the pseudo-second-order kinetic model, and the adsorption isotherm was well described by the Langmuir model. Spectroscopy experiments suggested that the nitrogen atom in the pyridine ring was the main active site for palladium adsorption and that nitrate anions were involved in palladium coordination; thus, they were co-adsorbed. The direct and selective recovery of palladium from simulative HLLW was finally realized in column mode, with the recovery rate close to 100 %. Overall, this work provides excellent functional material candidates for the separation of rare metal palladium from HLLW, showing significant potential.