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

• Published in: Environmental science & technology 2018-01, Vol.52 (2), p.581-588
• Main Authors: Mayordomo, Natalia, Foerstendorf, Harald, Lützenkirchen, Johannes, Heim, Karsten, Weiss, Stephan, Alonso, Ursula, Missana, Tiziana, Schmeide, Katja, Jordan, Norbert
• Format: Article
• Language: English
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.7b04546

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).