Oxalic acid crosslinked chitosan as an adsorbent for the removal of Ce(III) ion from acidic solutions

Cerium (Ce), one of the most abundant and commonly used rare earth elements (REEs), poses increasing risks of water pollution due to rising demand. In this study, oxalic acid crosslinked chitosan (CHOA) was synthesized and characterized through quantitative and spectroscopic analysis to remove Ce(III) ions from aqueous solutions, while the adsorption efficiencies were investigated through batch adsorption studies. Spectroscopic and qualitative analyses confirmed successful crosslinking, improved surface area, and enhanced stability of the adsorbent material. ATR-FTIR, SEM-EDX, BET, and XRD analyses validated the structural and physicochemical changes in CHOA. Under the optimum conditions (pH of 4, CHOA amount of 0.01 g, 200 rpm stirring speed), CHOA exhibits a high adsorption capacity of 408.71 mg.g-1 for a 30 min equilibrium time at 300 K. The kinetic data fit the pseudo-second-order (PSO) model, while the isotherm data follow the Freundlich model. The thermodynamic parameters, such as ∆G°, ∆H°, and ∆S°, confirmed that the adsorption process was spontaneous, endothermic, and increased randomness at the solid-liquid interface, respectively. However, the desorption efficiency and regeneration of CHOA were low, with an approximate 40% desorption efficiency achieved after only two regeneration cycles using a strong acid. Therefore, ion exchange, chelation, and precipitation were identified as the primary mechanisms underlying the adsorption process. Due to its high adsorption capacity and rapid kinetics, CHOA exhibits strong potential for Ce(III) removal; however, further improvement is required for enhanced recovery and reusability.