Enhanced molten salt oxidation effect of nuclear grade cation exchange resin in lithium containing catalytic salt system

[Display omitted] •The catalytic enhancement effect of Li+ is reflected by reducing the residue mass and increasing the peak gas concentration of CO2 and SO2.•Li+ can reduce the fracture temperature of CERs skeleton by 50℃.•The Li2O formed by the decomposition of Li2CO3 is an oxygen ion donor in addition to oxygen in the air.•The Na2CO3 and K2CO3 are more likely to absorb SO2 than Li2CO3 according to the results of thermodynamic calculation. The Cation ion-exchange resins (CERs) can be effectively oxidized in molten Li2CO3-Na2CO3-K2CO3, but the high price of Li2CO3 requires further clarification of its necessity in the molten salt oxidation (MSO) process of CERs. In this paper, Li+ ions are introduced into CERs by ion exchange, and the direct oxidation of pure CERs and Li+ doped CERs and the MSO process of Li+ doped CERs in Na2CO3-K2CO3 (Li+ in CERs), pure CERs in Li2CO3-Na2CO3-K2CO3 (Li+ in molten salt) and pure CERs in Na2CO3-K2CO3 (without Li+) were compared. Thermo-gravimetric analyzer (TGA) and gas mass spectrometry data illustrate that the introduction of Li+ can increase the peak content of CO2 and SO2 and reduce the mass of residue. Fourier transform infrared spectroscopy (FT-IR) results reflect that the presence of Li+ can advance the temperature of resin skeleton destruction. Scanning electron microscope (SEM) displays the fracture degree of CERs is more severe in Li2CO3-Na2CO3-K2CO3 than other two systems. X-ray diffraction spectrum (XRD) and the content of carbonate and sulfate are used to analyze the composition of waste salt after MSO. Compared with other two systems, the content of sulfate produced by adsorption of SO2 and residual carbonate are the highest in Li2CO3-Na2CO3-K2CO3. Thermodynamic calculation using HSC chemistry 6.0 evidences that in Li2CO3-Na2CO3-K2CO3, Li2O produced by decomposition of Li2CO3 can provide oxygen ions, while Na2CO3 and K2CO3 can absorb SO2. Changing the oxidation temperature and oxidation time in different systems, the destruction and removal efficiency (DRE) of CERs are comprised. The DRE of Li+ in molten salt can achieve 99.99 % of CERs at a lower oxidation temperature and less oxidation time than other salt systems. In summary, the superiority of Li2CO3 in ternary salts is difficult to replace at present.