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

Author
item Goldberg, Sabine

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2014
Publication Date: 4/23/2015
Citation: Goldberg, S.R. 2015. Modeling selenate adsorption behavior on oxides, clay minerals, and soils using the triple layer model. Soil Science. 179(12):568-576.

Interpretive Summary: Selenate is an 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 selenate by aluminum and iron oxide, clay minerals, and 18 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 selenate movement in arid zone soils. The results can be used to improve descriptions of selenate behavior in soils and thus aid action and regulatory agencies in the management of soils and waters which contain elevated concentrations of selenate.

Technical Abstract: Selenate adsorption behavior was investigated on amorphous aluminum oxide, amorphous iron oxide, goethite, clay minerals: kaolinites, montmorillonites, illite, and 18 soil samples from Hawaii, and the Southwestern and the Midwestern regions of the US as a function of solution pH. Selenate adsorption decreased with increasing solution pH. The triple layer model, a chemical surface complexation model, was able to describe Se(VI) adsorption as a function of solution pH by simultaneously optimizing either two outer-sphere Se(VI) surface complexation constants or one inner-sphere and one outer-sphere Se(VI) surface complexation constant. The fit of the triple layer model to Se(VI) adsorption by oxides, clay minerals, and soils was excellent. The predominantly outer-sphere Se(VI) surface speciation predicted using the triple layer model was in agreement with the weak adsorption behavior previously observed using electrophoretic mobility measurements and ionic strength dependence of adsorption. Direct spectroscopic investigations of Se(VI) surface configurations are needed to corroborate the species predicted by the triple layer modeling approach.