Sorption of iodine on Mg-Al-layered double hydroxide

From leaching experiments with metallic uranium-aluminium material test reactor fuel elements in repository-relevant MgCl2-rich salt brines, a Mg-Al-layered double hydroxide with chloride as interlayer anion was identified as a crystalline secondary phase component. In the present study, this Mg-Al-Cl-layered double hydroxide (Mg-Al-Cl-LDH) was synthesized and its ability to adsorb iodine was evaluated. The adsorption of I- was rapid, and equilibrium for an initial concentration of 4.25 x 10(-5) mole/l was obtained within 48 It. Further results indicated that the adsorption isotherm for I- retention could be fitted to Freundlich and Dubinin-Radushkevich equations. The values obtained indicate that iodine is adsorbed on Mg-Al-Cl-LDH by an anion-exchange process. The adsorption of I- was also studied as a function of pH. In the pH range between 3.5 and 8.5, the adsorption was independent of the pH. The effects of competiting anions were investigated using an MgCl2-solution instead of water, and indicate that chloride anions have a greater affinity towards the Mg-Al-Cl-layered double hydroxide than iodine.