Studies on the sorption of I? (iodide) and IO3 ? (iodate) onto Andosols

Abstract

In order to understand the sorption phenomena of I on Andosols, one of the most typical soils in Japan, radiotracer experiments were carried out using I− (iodide), IO3 − (iodate), and for comparison, Cl−(chloride) by the batch method, with special emphasis on the influence of solution pH and concentration of the respective ions. Kanuma soil composed of allophane, one of the main consistent minerals in most Andosols, was also examined regarding sorption. The sorption of I− and Cl− on Kanuma soil increased with decreasing pH and the sorptions were expressed by Henry isotherms. This indicated that these anions were electrostatically adsorbed on the positive charges which appeared on the surface of Kanuma soil. Sorption of Cl− onto Andosol could also be explained by electrostatic adsorption. Both I− and IO3 − were readily sorbed on Andosol from water even under weakly alkaline conditions. The adsorption isotherm of IO3 − on Andosol almost overlapped with that on Kanuma soil, suggesting that the high IO3 − sorption on Andosol was caused by the high adsorbability of IO3 −on allophane and/or sesquioxides of Fe and Al. However, the high I− sorption on Andosol could not be explained analogously.