Anion exchange on hydrous zirconium oxide materials: application for selective iodate removal

Abstract

The radioactive ¹²⁹I is a top-priority radionuclide due to its the long half-life (1.57 × 10⁷ years) and high mobility. Because of the planned and accidental releases to the environment, specific separation technologies are required to limit the potential radiation dose to human beings. Zirconium oxides are known for their adsorption capability and selectivity to oxyanions and here the applicability to selective IO₃⁻ removal has been investigated regarding the uptake mechanism, regeneration and competition caused by other anions, like environmentally relevant SO₄²⁻. Granular aggregates of hydrous zirconium oxides with and without Sb doping showed high potential for the selective IO₃⁻ removal in the presence of competing anions, like the forementioned SO₄²⁻ (apparent capacity between 0.1–0.4 meq g⁻¹ depending on SO₄²⁻ concentration). The main uptake mechanism was found to be outer-sphere complexation (ion-exchange) to the protonated hydroxyl groups of hydrous zirconium oxides, but also minor mechanisms were identified including inner-sphere complexation and reduction to I⁻. The materials were observed to be easily and successively regenerated using dilute acid. Hydrous zirconium oxides showed high potential for IO₃⁻ removal from waste solutions regarding technical (high selectivity and apparent capacity) and ecological/economic (feasible regeneration) aspects.