Degradation of Spent Radioactive Ion Exchange Resins and Its Mechanisms by Fenton Process

Abstract

Spent IERs are released during the operation and decommissioning of nuclear facilities. The safe and efficient treatment of spent IERs is an emergent problem in nuclear industry. IRN77 is a typical ion exchange resin widely used in many nuclear power plants. Fenton process can degrade organic resins and reduce the radioactive residues volume and the disposal cost significantly. In this work, the IRN77 resin was selected as a model ion exchange resin and its treatment via Fenton process was investigated. The influencing factors for resin degradation, including catalyst dosage, reaction time, initial pH, temperature and oxidant dosage were investigated and optimized via the single-factor experimental method. Under the reaction temperature of 100°C and reaction time of 120 min at initial pH of 2, more than 97% COD was removed with 1.66 g H2O2 and 32 mg FeSO4·7H2O added to per gram of wet resin. The catalyst dosage and H2O2 dosage can decrease 78% and 50% respectively compared to previous results. SEM, FT-IR and ion chromatograph were employed to characterize the resin beads, soluble organics and intermediates during the degradation reaction. Based on the characterization results, the resin degradation pathway was discussed in detail and it is proposed to three stages including beads dissociation, styrene and divinylbenzene decomposition and carboxylic acids mineralization. During the IERs degradation, formic acid, acetic acid, propionic acid and oxalic acid were quantitatively monitored as main intermediates, and oxalic acid accounted for over 90% of COD in the final residue solution. Fenton process is suggested as a promising resin degradation method.