Aluminum complexes selenates

Evaporation of solutions of alumina in sulfuric acid yields crystals of A12(S04)3T6H20. If a group I sulfate is also present, the products are alums MA1(S04)2T2H20, in which aluminum exists as [Al(OH2)fi]3+. Analogous selenates but not tellurates have been prepared. Basic salts, e.g. Al2(OH)2(SO4)210H2O, and solids obtained from aluminum sulfate solutions above 100 °C also contain complex ions in which the coordination sphere of Al3+ is occupied by OH groups and/or water molecules rather than sulfate ions. Thermal decomposition of the hydrate A12(S04)3-16H20 yields practically anhydrous A12(S04)3 at 450 °C further decomposition to... 

Suarez et al. (36) use a combination of FTIR spectroscopy, electrophoretic mobility and pH titration data to deduce the specific nature of anionic surface species sorbed to aluminum and silicon oxide minerals. Phosphate, carbonate, borate, selenate, selenite and molybdate data are reviewed and new data on arsenate and arsenite sorption are presented. In all cases the surface species formed are inner-sphere complexes, both monodentate and bidentate. Two step kinetics is typical with monodentate species forming during the initial, rapid sorption step. Subsequent slow sorption is presumed due to the formation of a bidentate surface complex, or in some cases to diffusion controlled sorption to internal sites on poorly crystalline solids. 

Identification of the specific species of the adsorbed oxyanion as well as mode of bonding to the oxide surface is often possible using a combination of Fourier Transform Infrared (FTIR) spectroscopy, electrophoretic mobility (EM) and sorption-proton balance data. This information is required for selection of realistic surface species when using surface complexation models and prediction of oxyanion transport. Earlier, limited IR research on surface speciation was conducted under dry conditions, thus results may not correspond to those for natural systems where surface species may be hydrated. In this study we review adsorbed phosphate, carbonate, borate, selenate, selenite, and molybdate species on aluminum and iron oxides using FTIR spectroscopy in both Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) modes. We present new FTIR, EM, and titration information on adsorbed arsenate and arsenite. Using these techniques we... 

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