Catalytic behavior of Mn during molten salt oxidation of cationic exchange resins in Li2CO3–Na2CO3–K2CO3 melt

Abstract

Cationic exchange resins are used in nuclear power circuits to remove the nuclide ions to maintain the safe and efficient operation of nuclear power plants. Meanwhile, the production of spent resins is expanding significantly due to the rapid technological advancements in the nuclear industry, causing the study of resin treatment to be of great significance. This study reveals the catalytic behavior of Mn from cation exchange resins during molten salt oxidation. Mn has many isotopic ions and a catalytic effect on the treatment process. Kinetic analysis reveals that the introduction of Mn decreases the activation energy of the styrene–divinylbenzene skeleton from 48.164 kJ mol⁻¹ to 41.696 kJ mol⁻¹ and decreases the degradation temperature of the resin by 78 °C. Compared to the original resin, the destruction and removal efficiency of Mn-doped cation exchange resin increased from 75.07% to 85.28% during molten salt oxidation at 650 °C. According to the scanning electron microscope analysis and characterization studies, Mn promotes a 55.71% reduction in the average particle diameter of resin structural fragments. Fourier-transform infrared spectroscopy analysis of the resin residues demonstrates that Mn doping influences the catalytic decomposition of –SO₂– and S–O within sulfonic acid groups. This catalytic effect induces destabilization and subsequent ring-opening of the benzene ring. These results imply that Mn doping can facilitate molten carbonate oxidation destruction of cation exchange resins. The X-ray diffraction analysis of waste salt reveals that with increasing oxidation time, the transformation of Mn proceeds as (Mn₂O₆)⁶⁻ → (MnO₃)²⁻ → (MnO₂)⁻ at 750 °C.