Mechanisms of Selenate Adsorption on Iron Oxides and Hydroxides

• Published in: Environmental science & technology Vol. 36; no. 7; pp. 1460 - 1466
• Main Authors: Peak, D, Sparks, D. L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.04.2002
• Subjects: Absorptiometry, Photon; Adsorption; analysis; Applied sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; chemistry; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Ferric Compounds; Ferric Compounds - chemistry; Hydrogen-Ion Concentration; Iron; Pollution; Pollution, environment geology; Selenic Acid; selenium; Selenium Compounds; Selenium Compounds - chemistry; Soil and sediments pollution; soil chemistry; Soil Pollutants; Soil Pollutants - analysis; Soils; Spectroscopy, Fourier Transform Infrared; Hematite; Fourier transform spectroscopy; Pollutant behavior; Selenium VI; Geochemistry; Soil pollution; EXAFS spectrometry; Sorption; Infrared spectrometry; Local structure; Adsorption; Total attenuated reflection; Medium effect; Binding mode; Reaction mechanism; Selenates; Iron III Hydroxides; Soil interaction; Iron III Oxides; Goethite
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/es0156643

Selenate (SeO4 2-) is an oxyanion of environmental importance because of its toxicity to animals and its mobility in the soil environment. It is known that iron(III) oxides and hydroxides are important sorbents for SeO4 2- in soils and sediments, but the mechanism of selenate adsorption on iron oxides has been the subject of intense debate. Our research employed Extended X-ray absorption fine structure and attenuated total reflectance−Fourier transform infrared spectroscopies to determine SeO4 2- bonding mechanisms on hematite, goethite, and hydrous ferric oxide (HFO). It was learned that selenate forms only inner-sphere surface complexes on hematite but forms a mixture of outer- and inner-sphere surface complexes on goethite and HFO. This continuum of adsorption mechanisms is strongly affected by both pH and ionic strength. These results suggest that adsorption experiments should be conducted on several different iron oxides and over a wide range of reaction conditions to accurately assess the reactivity of oxyanions on iron oxides.