Comparative Ion Exchange Performance of Iminodiacetate and Aminophosphonate Resins for Efficient Cadmium Removal From Aqueous Solutions

The removal of cadmium ions (Cd2+) from aqueous media was systematically investigated using two commercial chelating ion-exchange resins: Puromet MTS9300, functionalized with iminodiacetic acid groups, and Puromet MTS9500, containing aminophosphonic acid groups. The effects of resin dosage, solution pH, temperature, and contact time on Cd2+ removal were evaluated through batch experiments. The results revealed that both resins exhibited high Cd2+ removal efficiencies, achieving complete removal under optimized conditions. Ion exchange performance was strongly influenced by solution pH, as both resins possess weakly acidic functional groups that undergo protonation in acidic media, thereby reducing Cd2+ uptake. Kinetic data fitted well to the pseudo-second-order model. The equilibrium data correlated closely with the Langmuir model, with maximum exchange capacities of 201.33 mg/g for MTS9300 and 191.44 mg/g for MTS9500 at 30 °C. Thermodynamic analysis confirmed the spontaneous nature of Cd2+ removal for both resins, with ΔG° values ranging from –26.37 to –30.09 kJ/mol. MTS9500 exhibited an endothermic exchange process, while MTS9300 displayed exothermic behaviour. Regeneration experiments demonstrated excellent reusability with both HCl and H2SO4 solutions, maintaining nearly 100% regeneration efficiency. These findings highlight the high potential of MTS9300 and MTS9500 resins as efficient, regenerable materials for the removal of cadmium ions from contaminated water.