Brine Pretreatment Improves Ion-Exchange Resin Regeneration with Associated Physicochemical Changes

Regeneration efficiency governs the long-term performance and sustainability of ion-exchange processes, yet resin fouling and limited accessibility of exchange sites can restrict regeneration effectiveness and ion transport. This study investigates controlled brine pretreatment as a regeneration-enhancement strategy before conventional acid–base regeneration. Under optimized conditions (5% NaCl, 1:1 resin-to-brine ratio, and 55 °C), pretreated resins achieved approximately 306% higher Ca2+ removal and 222% higher Mg2+ removal than untreated regenerated resins. In individual column runs, breakthrough analysis showed a longer resin utilization period for the pretreated resin, with the exhaustion time increasing from 49 to 69 min. The times to reach C/C0 values of 0.90 and 0.95 also increased from 43 to 62.8 min and from 45.1 to 65.0 min, respectively. SEM showed no obvious surface-associated deposits on the pretreated resin, while FTIR analysis indicated minor spectral changes with characteristic resin functional groups largely retained. Particle-size analysis showed a shift toward smaller particle sizes after brine pretreatment. These physicochemical changes may influence exchange-site accessibility and ion transport. ICP–MS analysis further showed that approximately 65.6% of Ca2+ and 66.4% of Mg2+ were displaced during the brine pretreatment stage before subsequent acid–base regeneration. The findings provide indirect physicochemical evidence linking controlled brine pretreatment to observed changes in resin characteristics and regeneration behavior.