Mechanisms of selenate adsorption on iron oxides and hydroxides.
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.
Peak
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Department of Plant and Soil Sciences, University of Delaware, Newark 19717-1303, USA. dpeak@udel.edu
Sparks
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DL
D015502:Absorptiometry, Photon; D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D064586:Selenic Acid; D018036:Selenium Compounds / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D017550:Spectroscopy, Fourier Transform Infrared
D005290:Ferric Compounds; D018036:Selenium Compounds; D012989:Soil Pollutants; C000499:ferric oxide; C021024:ferric hydroxide; D064586:Selenic Acid