Modeling and optimization of nickel (II) ion removal from aqueous solutions using sodium carboxymethyl cellulose hydrogel crosslinked with ferric chloride

Background: Recent years have witnessed a growing interest in utilizing biocompatible and renewable polymers as efficient adsorbents for removing heavy metals from aqueous solutionsz. This study investigates the efficacy of carboxymethyl cellulose (CMC) hydrogel crosslinked with ferric chloride as a low-cost and effective adsorbent for nickel (Ni) removal from aqueous solutions. Materials and Methods: In this research, CMC hydrogel was synthesized through a chemical crosslinking process with ferric chloride. The structural properties of the hydrogel were evaluated using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Optimal conditions for Ni removal were determined using Response Surface Methodology (Box-Behnken design) by examining the influence of key variables, including initial Ni concentration, pH, adsorbent dosage, and contact time. Results: FTIR and SEM analyses revealed that the carboxyl and hydroxyl functional groups present in the hydrogel structure, along with its unique morphology, facilitate Ni adsorption from aqueous solutions through potential mechanisms such as chelation, electrostatic interactions, and the formation of coordination bonds. The highest Ni removal efficiency (87.88%) was achieved under conditions with an initial concentration of 80 ppm, pH of 7.5, adsorbent dosage of 1.5 g/L, and contact time of 30 minutes. The study of variable effects demonstrated that increasing pH enhances Ni removal, while adsorbent dosage and contact time exhibit a lesser impact on removal efficiency. Additionally, results indicated that the reduced second-order statistical model (Box-Behnken) effectively describes the experimental data, and the predicted values align well with observed values. Conclusion: The findings of this study highlight the high efficiency of CMC hydrogel as an effective polymeric adsorbent for removing Ni ions from moderately polluted aqueous solutions. Furthermore, the results clearly indicate that Ni removal by this adsorbent is significantly influenced by the initial Ni concentration and solution pH. However, the effects of contact time and adsorbent dosage were not significant in the subsequent stages of the process. For future studies, it is recommended to modify the CMC structure through advanced crosslinking methods and combine it with minerals to increase specific surface area, surface charge, and ultimately enhance performance and adsorption capacity.