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Title: Modeling selenite adsorption envelopes on oxides, clay minerals, and soils using the triple layer model

item Goldberg, Sabine

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2012
Publication Date: 1/16/2013
Citation: Goldberg, S.R. 2013. Modeling selenite adsorption envelopes on oxides, clay minerals, and soils using the triple layer model. Soil Science Society of America Journal. 77(1):64-71.

Interpretive Summary: Selenite is a specifically adsorbing anion that is toxic to animals at elevated concentrations. Toxic concentrations can occur in agricultural soils and irrigation waters. A better understanding of the adsorption behavior of this ion is necessary. Adsorption behavior of selenite by aluminum and iron oxide, clay minerals, and 45 soil samples under changing conditions of solution pH was described using a chemical surface complexation model. Our results will benefit scientists who are developing models of selenite movement in arid zone soils. The results can be used to improve descriptions of selenite behavior in soils and thus aid action and regulatory agencies in the management of soils and waters which contain elevated concentrations of selenite.

Technical Abstract: Selenite adsorption behavior was investigated on amorphous aluminum and iron oxides, clay minerals: kaolinite, montmorillonite, and illite, and 45 surface and subsurface soil samples from the Southwestern and Midwestern regions of the USA as a function of solution pH. Selenite adsorption decreased with increasing solution pH. The triple layer model, a chemical surface complexation model, was able to describe selenite adsorption as a function of solution pH by simultaneously optimizing both inner-sphere and outer-sphere selenite surface complexation constants. The fit of the triple layer model to selenite adsorption by soils was much improved over that obtained previously by optimizing solely an inner-sphere selenite surface complexation constant and the protonation constant in the constant capacitance model. In this previous application the deprotonation constant had been neglected; therefore, preventing the reactive surface hydroxyl group from deprotonating, a chemically unrealistic situation. The selenite surface speciation predicted using the triple layer model was in agreement with that obtained for other strongly adsorbing anions such as molybdate. Direct spectroscopic investigations of selenite surface configuration are needed corroborate the species predicted by the modeling approach.