Decomposition mechanisms of nuclear-grade cationic exchange resin by advanced oxidation processes: Statistical molecular fragmentation model and DFT calculations

The treatment and disposal of radioactive waste are presently facing great challenges. Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks. In this paper, a simplified model of cationic exchange resin is proposed, and the degradation processes of cationic resin monomer initiated by hydroxyl radicals (·OH) are clarified by combining statistical molecular fragmentation (SMF) model and density functional theory (DFT) calculations. The prediction of active sites indicates that the S-O bonds and the C-S bond of the sulfonic group are more likely to react during the degradation. The meta-position of the sulfonic group on the benzene ring is the most active site, and the benzene ring without the sulfonic group has a certain reactivity. The C11-C14 and C17-C20 bonds, on the carbon skeleton, are the most easily broken. It is also found that dihydroxy addition and elimination reactions play a major role in the process of desulfonation, carbon skeleton cleavage and benzene ring separation. The decomposition mechanisms found through the combination of physical models and chemical calculations, provide theoretical guidance for the treatment of complex polycyclic aromatic hydrocarbons.