Molecular insights into the migration of organic contaminants during purification of epoxy resin waste salt: A comparative study of interfacial wetting and ethanol/water extraction processes

Organic contaminants are a major factor restricting the efficient purification and resource utilization of industrial waste salts. Interfacial wetting (IW) and extraction/water extraction (E/W E) are the primary pretreatment processes for the removal of organic contaminants from waste salts. However, the molecular-level understanding of the removal and migration behaviors of organics during purification remains limited. In this study, molecular-level characterization based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with bulk characterization techniques, was employed to compare the removal characteristics of organic contaminants from epoxy resin waste salt by the IW and E/W E processes. The results showed that the removal efficiency of total organic carbon and the reduction in fluorescence intensity followed the order E/W E > IW. Molecular-scale analysis revealed differences in the structure selectivity of the two processes for organic contaminants in waste salt. Specifically, E/W E exhibited more pronounced structure selectivity at the molecular scale, particularly toward polyphenolic and highly unsaturated phenolic structures. In contrast, IW showed no significant selectivity, and left a significant amount of aromatic and unsaturated components from the treated salt. This could be attributed to differences in solvent polarity and molecular interaction mechanisms within the water-ethanol system. Therefore, E/W E is more suitable as a pretreatment process for industrial waste salts dominated by phenolic or lignin-like contaminants. By revealing the molecular-level migration pathways and structural selectivity of organic contaminants during different pretreatment processes, this study provides new insights into the purification of industrial waste salts, thereby facilitating the development of more efficient purification strategies for their resource utilization.