Enhanced Ni(II) Removal from Water Using a Magnetite-Based Hybrid Ion-Exchange Material: Adsorption Performance and Process Optimization

Nickel contamination in aquatic systems is an important environmental concern, creating a need for efficient and easily recoverable materials for Ni(II) removal from water. This study investigated a commercial macroporous cation-exchange resin (Purolite® S-930E, IX-P) and its magnetically modified derivative (IX-P-MNp), focusing on the effects of in situ magnetic modification on adsorption performance and process optimization. IX-P-MNp was synthesized by in situ co-precipitation of magnetite within the porous resin structure and characterized using complementary analytical techniques. Batch experiments were conducted to evaluate adsorption kinetics and equilibrium behavior, while the effects of pH, contact time, resin dosage, initial Ni(II), Ca2+, and Mg2+ concentrations were assessed using a Definitive Screening Design. Magnetic modification reduced the equilibrium time from 6 to 4 h and increased the maximum adsorption capacity by approximately 95%, from 4.44 to 8.65 mg/g according to the Sips model, with comparable values obtained using the Langmuir model (4.49 and 8.87 mg/g, respectively). Contact time was the most influential factor for both materials, while resin dosage and initial Ni(II) concentration also significantly affected Ni(II) removal. For IX-P-MNp, Mg2+ concentration and the interaction between pH and initial Ni(II) concentration were additionally significant. Experimental validation showed good agreement between predicted and experimental values for IX-P, whereas greater deviation was observed for IX-P-MNp. Overall, in situ magnetic modification enhanced the adsorption performance of IX-P and provided the additional advantage of magnetic separation, demonstrating the potential of IX-P-MNp for Ni(II) removal from water.