Comparison of selenate and sulfate adsorption on goethite

The adsorption behavior of selenate (SeO4) on goethite has been studied und er a wide range of conditions. SeO4 adsorption has been compared with the b inding of SO4. The experimental results are interpreted in view of very rec ent spectroscopic work on the speciation and coordination of adsorbed selen ate and sulfate on goethite. The spectroscopic results suggest that at pH v alues above 6 outersphere complexes are dominant while in the main adsorpti on range at lower pH values monodentate innersphere complexes are dominant. The qualitative results from spectroscopy agree very well with the CD-MUSI C modeling of the large set of SeO4 adsorption data. The charge distributio ns obtained for the innersphere complexes are in line with the spectroscopi cally determined coordinations of the adsorbed anions. The formation. of ou tersphere complexes cannot be established from the macroscopic adsorption d ata without the spectroscopic knowledge. However, description of the adsorp tion data including and differentiating between both species can be done ve ry satisfactorily with the CD-MUSIC approach. (C) 2001 Academic Press.