Dissolution and degradation of nuclear grade cationic exchange resin by Fenton oxidation combining experimental results and DFT calculations

Abstract

The Fenton oxidation of nuclear grade cationic exchange resin was investigated in view of the effects of initial temperature, H2O2 dosage, catalyst type and concentration as well as initial pH. Initial temperature and H2O2 dosage exhibited a significant positive effect on the decomposition of cationic resins, whereas the initial pH showed a negative effect. Ferrous ions had higher catalytic ability than copper ions to the H2O2 activation for resin decomposition, and the best Fe2+ concentration was 0.3 M. Under the conditions of initial temperature of 75 °C, H2O2 dosage of 200 mL, Fe2+ concentration of 0.3 M and initial pH of 0.01, a weight reduction of 73% was achieved. The experimental results on Co-substituted mock samples indicated that the radionuclides loaded in the resins were concentrated in liquid residue. The decomposition of cationic resins followed the two-stage first-order kinetics that composed of a dissolution period of resin beads (first-stage) and a followed degradation stage of resin solution (second-stage). Combined with the UV–visible and infrared spectra and their corresponding density functional theory (DFT) calculations, the dissolution of resin beads was due to the desulfonation of the sulfonated aromatic rings and the oxidative fragmentation of the polymer backbone by hydroxyl radicals (OH) formed in Fenton reactions. After the dissolution of resin beads, the oxidative degradation and mineralization process proceeded by the attack of OH mainly in aqueous medium.