Adsorption of selenium(VI) onto nano transition alumina

The adsorption of selenium(VI) onto nano transition alumina (γ/δ-Al2O3) was investigated at both macroscopic and molecular levels. The uptake of selenium(VI) was found to decrease upon increasing pH (5-10) and ionic strength (0.01-0.1 mol∙L−1). At the molecular level, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy established the predominant formation of a bidentate outer-sphere surface complex throughout the investigated pH range. The acid-base surface properties of transition alumina (surface charge) together with the Se(VI) adsorption edges were successfully described using a 1-pK with charge distribution surface complexation model and one outer-sphere surface species, namely {(≡AlOH2+0.5)2SeO42−}, according to the IR studies. These new spectroscopic results can be implemented in reactive transport models to enable a more consistent and trustworthy prognostic modeling of the environmental fate of selenium(VI).