A deficiency in environmental iodine can cause a number of health problems. Understanding how iodine is sequestered by materials is helpful for evaluating and developing methods for minimizing human health effects related to iodine. In addition, 1291 is considered to be strategically important for safety assessment Of underground radioactive waste disposal. To assess the long-term stability of disposed radioactive waste, an understanding of 1291 adsorption on geologic materials is essential. Therefore, the adsorption of I- on naturally occurring oxides is of environmental concern. The surface charges of hydrous ferric oxide (HFO) in Nal electrolyte solutions were measured by potentiometric acid-base titration. The surface charge data were analyzed by means of an extended triple-layer model (ETLM) for surface complexation modeling to obtain the I- adsorption reaction and its equilibrium constant. The adsorption of I- was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent X-ray absorption near-edge structure (XANES) observation of I- adsorbed oil HFO The. adsorption equilibrium constants for I- on beta-TiO2 and gamma-Al2O3 were also evaluated by analyzing the surface charge data of these oxides in Nal solution as reported in the literature. Comparison of these adsorption equilibrium constants for HFC, beta-TiO2, and gamma-Al2O3 based on site-occupancy standard states permitted prediction of I- adsorption equilibrium constants for all oxides by means of the Born solvation theory. The batch adsorption data for I- on HFO and amorphous aluminum oxide were reasonably reproduced by ETLM with the predicted equilibrium constants, confirming the validity of the present approach. Using the predicted adsorption equilibrium constants, we calculated distribution coefficient (K-d) values for I- adsorption on common soil minerals as a function of pH and ionic strength. (c) 2008 Elsevier Inc. All rights reserved.