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Title: Macroscopic experimental and modeling evaluation of selenite and selenate adsorption mechanisms on gibbsite

Author
item Goldberg, Sabine

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2014
Publication Date: 2/21/2014
Citation: Goldberg, S.R. 2014. Macroscopic experimental and modeling evaluation of selenite and selenate adsorption mechanisms on gibbsite. Soil Science Society of America Journal. 78(2):473-479.

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

Technical Abstract: Selenite Se(IV) and selenate Se(VI) selenium adsorption behavior was investigated on gibbsite as a function of solution pH and solution ionic strength. Adsorption of both Se redox states decreased with increasing solution pH. Electrophoretic mobility measurements showed downward shifts in point of zero charge indicative of the formation of inner-sphere Se(IV) and Se(VI) surface complexes. However, the downward shift was less than for strongly adsorbing anions such as phosphate and arsenate, suggesting that outer-sphere surface complexes are also present. The triple layer model, a chemical surface complexation model, was well able to describe Se(IV) and Se(VI) adsorption as a function of solution pH and solution ionic strength by simultaneously optimizing both inner-sphere and outer-sphere surface complexation constants. Direct spectroscopic investigations of selenite surface configuration are needed to corroborate the species suggested by the macroscopic experiments and obtained from the triple layer model optimizations.