The diffusion of selenite (labeled with Se-75) in compacted Beishan granite (BsG) was investigated using the in-diffusion capillary method at pH values from similar to 2.0 to similar to 11.0 under oxic and anoxic conditions. The results indicate that the apparent diffusion coefficient (D-a) values of selenite in BsG always reached the minimum at approximately pH 5. Unexpectedly, the D-a values under oxic conditions are nearly one order of magnitude lower than those under the anoxic conditions. Further characterization reveals the existence of redox-sensitive Fe(II)-containing components, which can be responsible for the great difference in D-a values. Fe(2p) X-ray photoelectron spectroscopy (XPS) results show that more Fe(III)oxyhydroxide coating is formed on the granite's surface under aerobic conditions than is formed under anaerobic conditions. Correspondingly, Se(3d) spectra indicate that more selenium is sorbed under oxic conditions, and the sorbed amount always reached the maximum at pH values from similar to 4 to similar to 5. A linear combination fit of X-ray absorption near edge structure (XANES) spectroscopy data revealed that Se(0) was formed under anoxic condition and that selenite preferred to form inner-sphere complexes with Fe(III)-oxyhydroxide. Overall, this study indicates that natural Fe-bearing minerals can greatly attenuate selenite diffusion and the retardation would be enhanced under aerobic conditions. (C) 2016 Elsevier B.V. All rights reserved.