Efficient fixation of Co2+ and organic sulfur from cation exchange resins into CaO enhanced molten Li2CO3-Na2CO3-K2CO3 system

Abstract

The radioactive spent resins produced by the nuclear power plant contain a certain amount of 60Co. These spent resins are easy to generate volatile substances during the heat treatment process, resulting in the leakage of radionuclide. The molten salt oxidation (MSO) can effectively prevent the volatilization of Co, and can facilitate the removal of sulfur exists in the resins. In this work, ternary carbonate (Li2CO3-Na2CO3-K2CO3) was used as molten salt system, and CaO was used as a sulfur pollutant capture agent. The non-radioactive CoCl2 served as simulate radioisotopes, and the Co2+ doped cation exchange resins (Co-CERs) were obtained by the ion exchange method. The introduction of Co2+ promoted the further oxidation of the thermally stable structure SC, and the harmful gases SO2 and H2S generated during the MSO process were effectively absorbed by carbonate with the participation of CaO. The retention rate of S could reach 87.79 % with the addition of CaO at 800 °C, which was 1.81 % higher than that without CaO. The test results of X-ray diffraction (XRD), scanning electron microscope (SEM) and inductively coupled plasma mass spectrometry (ICP-MS) confirmed that the addition of CaO promoted the formation of sulfide and thermally stable CoSO4. The retention rate of Co2+ in waste salt reached 97.36 % at 800 °C. The CaO enhanced molten carbonate system can realize the efficient treatment of Co-CERs and possess potential applications on organic contaminant treatment.