Efficient adsorption of radioactive iodine using silver-incorporated bentonite–chitosan hydrogel: Batch and column studies

The discharge of radioactive iodine, particularly through nuclear wastewater, poses a persistent environmental threat, which demands effective remediation strategies. In this study, we investigated a novel chitosan-bentonite-silver (CBA) hydrogel designed to efficiently remove radioactive iodine. The bentonite-silver (Ben-Ag) composite was synthesized using a straightforward ion-exchange method and subsequently embedded in a chitosan matrix to form the hydrogel structure. The synthesized CBA hydrogels were systematically characterized using multiple analytical techniques and evaluated for iodide removal performance through batch and continuous column studies. The optimized hydrogel, CBA50, exhibited a notable maximum adsorption capacity of 21.6 mg/g, corresponding best to the Langmuir isotherm model, and kinetic analysis revealed that the data aligned closely with the PSO kinetic model, which suggests a chemisorption-driven adsorption process. Moreover, the hydrogels showed robust adsorption performance across a broad pH spectrum (pH 4–11) and in various anions and cations coexisting environments. Regeneration experiments exhibited considerable removal efficiency over five successive cycles, which highlights the potential reuse of hydrogels. Several removal mechanisms involving precipitation, electrostatic interactions, ion exchange, pore filling, and hydrogen bonding were proposed. These findings suggest that the CBA hydrogels are both efficient and environmentally friendly adsorbents for the removal of radioactive iodine in wastewater.