Design a variety of cation exchange hydrogel resins using gamma irradiation to remove hard/scale metal cations from saline water under different circumstances.

This study aims to develop a series of cation exchange hydrogel resins via gamma irradiation technique through copolymerizing styrene sodium sulfonate with three acrylamide derivatives (designated as poly(X-co-styrene sodium sulfonate), where X refers to acrylamide (PAASS), methacrylamide (PMASS), and isopropyl acrylamide (PIASS)). The prepared hydrogel resins were characterized and tested for the adsorption removal of hard/scale metal cations (e.g., Ca²⁺, Mg²⁺, Ba²⁺, and Sr²⁺) from saline water under varying conditions. Results demonstrated that PMASS and PIASS displayed closed porous networks with a significant pH-responsive swelling behavior, increasing from 1.41 to 5.62 g/g in acidic conditions and approximately 41.49 to 45.83 g/g under neutral conditions swelling ratios, while PAASS exhibited an open porous network structure with the stable swelling ratio of around 35 g/g within mild and neutral pH ranges. All hydrogel resins also showed rapid initial adsorption of Ca²⁺ > Mg²⁺ > Ba²⁺ > Sr²⁺, depending on ionic metal size, with adsorption equilibrium within 3-6 h. Maximum removal was achieved at neutral-basic pH when sulfonate groups were fully deprotonated with a total capacity of about ~ 147-175 mg/g overall mixed metal ions. When exposed to lower concentration solutions, about 87% of metal ions were effectively removed.