Study on the transformation of organic sulfur in cationic exchange resins in a ternary Li2CO3–Na2CO3–K2CO3 molten salt system

Abstract

Cationic exchange resins (CERs) are generally used for the purification and clarification processes of nuclear industry wastewater. The molten-salt oxidation method (MSO) can be effectively applied to the treatment of spent resins and the absorption of acid gas (such as SO₂). In this study, the transformation of organic sulfur in resins in ternary molten carbonates was investigated. The FT-IR spectra proved that the existence of molten carbonates could promote the decomposition of the benzene ring, S–O and C–S bonds in the resin structure. The XRD pattern analysis revealed that organic sulfur in the sulfonic acid functional group of resins was fixed in spent salt in the form of sulfate. The XPS results showed the transformation of sulfur species into residues in the carbonate melt. The increase in temperature promoted the conversion of thiophene sulfur to sulfoxide sulfur and further to sulfones sulfur at over 550 °C in the carbonate melt. The retention rate of organic sulfur in spent salt was 82.55% at 800 °C. This study provides more theoretical guidance for the industrial treatment of spent resins and some technical support for the sustainable development of the nuclear industry.