Submitted to: Journal of Colloid and Interface Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2005
Publication Date: 1/18/2005
Citation: Goldberg, S.R. 2005. Inconsistency in the triple layer model description of ionic strength dependent boron adsorption. Journal of Colloid and Interface Science. 285:509-517. Interpretive Summary: Boron is a specifically adsorbing anion that can be detrimental to plants at elevated levels. Detrimental levels can occur because of high levels of boron in the soil solution or from additions of boron via the irrigation water. Adsorption of boron by soils and soil minerals was evaluated as a function of solution pH and solution ionic strength. A chemical model was evaluated for its ability to describe the B adsorption data. Our results will benefit scientists who are developing models of boron movement in arid zone soils. The results can be used to improve descriptions of boron behavior in soils and thus aid action and regulatory agencies in the management of soils and waters which contain elevated concentrations of boron.
Technical Abstract: Understanding anion adsorption mechanisms is necessary to allow prediction of anion adsorption behavior. This study was conducted to evaluate the ability of the triple layer model, a chemical surface complexation model. to describe the effect of changes in solution ionic strength (0.01-1.0 M NaCl) and solution pH (3-11) on B adsorption by the iron oxide, goethite, the aluminum oxide, gibbsite, the clay minerals, kaolinite and montmorillonite, and two arid zone soils. Ionic strength dependence of adsorption suggest an inner-sphere adsorption mechanism for goethite, kaolinite, montmorillonite, and the two soils and an outer-sphere adsorption mechanism for gibbsite. The triple model, containing an inner-sphere adsorption mechanism, was able to describe B adsorption on goethite, kaolinite, montmorillonite, and the two soils. The model was able to describe B adsorption on gibbsite using an outer-sphere adsorption mechanism. A problematic inconsistency exists in the triple layer model description of ionic strength dependent B adsorption between the type of B surface complex defined in the model and the ionic strength dependence of the model result. That is, postulating an inner-sphere adsorption mechanism in the triple layer model resulted in an ionic strength dependence appropriate for the formation of outer-sphere surface complexes and vice versa. Additional tests of the ability of the triple layer model to describe ionic strength dependent adsorption of additional ions are needed to establish whether the inconsistencies are limited to the B system or are of concern in other triple layer model applications.