Adsorption of Iodine from Aqueous Solution on Modified Silica Gel with Cyclodextrin Derivatives

The presence of excessive amount of iodine, especially radioactive iodine is dangerous in the environment. The aim of this research is to prepare functionalized silica with cyclodextrin with different hydrophobic cavity sizes to investigate their performance in iodine adsorption. Cyclodextrin (CD) derivatives (αCD, βCD, γCD and hp-βCD) were successfully immobilized on silica gel surface via epichlorohydrin as a cross linker. The ratio of silica (Si) to CD was optimized in preliminary experiments based on the highest uptake of iodine. Selected adsorbents with varied ratios of silica to CD derivatives are investigated, including Si-αCD (3:2), Si-βCD (4:1), Si-γCD (4:1) and Si-hp-βCD (4:1). The adsorption of iodine (I₂ /KI) solution was investigated in terms of initial pH, contact time, iodine concentration and temperature. No significant variations was noticed for iodine adsorption at different pH values, thus, initial pH 6 was selected for further studies. Equilibrium adsorption was reached faster on Si-hp-bCD than other adsorbents with kinetic adsorption data fitting well pseudo second order model. Activation energy (E_a) was found to be in the range of 12.7-23.4 kJ/mol. Equilibrium adsorption data were found to fit well the Langmuir adsorption model with lower uptake as temperature rises. Iodine uptake follows the order: Si-hp-βCD (714 mg/g) >Si-αCD (625 mg/g) >Si-βCD (555.6 mg/g)> Si-γCD (435 mg/g). Thermodynamic study showed that iodine adsorption is exothermic and spontaneous. Adsorbents’ reuse exhibited excellent performance for iodine adsorption with a decrease in iodine uptake of ~2-4% in the third adsorption cycle. The study shows that the functionalized silica with hp-bCD shows best performance in terms of kinetics and equilibrium.