Selenium(IV) Sorption Onto γ‑Al2O3: A Consistent Description of the Surface Speciation by Spectroscopy and Thermodynamic Modeling

Abstract

The sorption processes of Se(IV) onto γ-Al2O3

were studied by in situ Infrared spectroscopy, batch sorption studies, zeta potential measurements and surface complexation

modeling (SCM) in the pH range from 5 to 10. In situ attenuated total reflection fourier-transform infrared (ATR FT-IR)

spectroscopy revealed the predominant formation of a single inner-sphere surface species at the alumina surface, supporting

previously reported EXAFS results, irrespective of the presence

or absence of atmospherically derived carbonate. The adsorption

of Se(IV) decreased with increasing pH, and no impact of

the ionic strength was observed in the range from 0.01 to

0.1 mol L−1 NaCl. Inner-sphere surface complexation was also

suggested from the shift of the isoelectric point of γ-Al2O3

observed during zeta potential measurements when Se(IV) concentration was 10−4 mol L−1. Based on these qualitative findings,

the acid−base surface properties of γ-Al2O3 and the Se(IV) adsorption edges were successfully described using a 1-pK

CD-MUSIC model, considering one bidentate surface complex based on previous EXAFS results. The results of competitive

sorption experiments suggested that the surface affinity of Se(IV) toward γ-Al2O3 is higher than that of dissolved inorganic

carbon (DIC). Nevertheless, from the in situ experiments, we suggest that the presence of DIC might transiently impact the

migration of Se(IV) by reducing the number of available sorption sites on mineral surfaces. Consequently, this should be taken

into account in predicting the environmental fate of Se(IV).