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Comparison of Selenate and Sulfate Adsorption on Goethite
René P. J. J. Rietra1, Tjisse Hiemstra, Willem H. van Riemsdijk
1Department of Environmental Sciences, Sub-department of Soil Quality, Wageningen Agricultural University, Wageningen, 6700 EC, The Netherlands
Abstract:
The adsorption behavior of selenate (SeO(4)) on goethite has been studied under a wide range of conditions. SeO(4) adsorption has been compared with the binding of SO(4). The experimental results are interpreted in view of very recent spectroscopic work on the speciation and coordination of adsorbed selenate and sulfate on goethite. The spectroscopic results suggest that at pH values above 6 outersphere complexes are dominant while in the main adsorption range at lower pH values monodentate innersphere complexes are dominant. The qualitative results from spectroscopy agree very well with the CD-MUSIC modeling of the large set of SeO(4) adsorption data. The charge distributions obtained for the innersphere complexes are in line with the spectroscopically determined coordinations of the adsorbed anions. The formation of outersphere complexes cannot be established from the macroscopic adsorption data without the spectroscopic knowledge. However, description of the adsorption data including and differentiating between both species can be done very satisfactorily with the CD-MUSIC approach. Copyright 2001 Academic Press.