Selenate and Selenite Sorption on Iron Oxides An Infrared and Electrophoretic Study

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Abstract
We studied selenate and selenite sorption by amorphous Fe oxide [am‐Fe(OH)3] and goethite (α‐FeOOH) as a function of time (25 min–96 h), pH (3–12), ionic strength (0.01–1.0 M NaCl), and total Se concentration (0.0001–1.0 M). We examined sorbed selenate and selenite by in situ attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and electrophoresis to deduce sorption mechanisms. Sorption of both selenate and selenite reached equilibrium in 3 The structure of selenite complexes in am‐Fe(OH)3 –solution interface was uncertain due to insensitivity of the in situ ATR–FTIR technique. The DRIFT spectra of selenite on am‐Fe(OH)3 showed ν3 splitting as evidence of complexation. The DRIFT spectra of selenite on goethite showed bridging bidentate complex of selenite. We conclude that the influence of ionic strength on Se sorption cannot be used as a criterion for distinguishing outer‐ vs. inner‐sphere complex formation.