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Title: Application of surface complexation models to anion adsorption by natural materials

item Goldberg, Sabine

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2014
Publication Date: 8/7/2014
Citation: Goldberg, S.R. 2014. Application of surface complexation models to anion adsorption by natural materials. Environmental Toxicology and Chemistry. 33(10):2172-2180.

Interpretive Summary:

Technical Abstract: Various chemical models of ion adsorption will be presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model will be described. Characteristics common to all the surface complexation models are equilibrium constant expressions, mass and charge balances and surface activity coefficient electrostatic potential terms. Methods for determining parameter values for surface site density, capacitances, and surface complexation constants will be discussed. Spectroscopic experimental methods of establishing ion adsorption mechanisms include: vibrational spectroscopy, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, x-ray absorption spectroscopy, and x-ray reflectivity. Experimental determinations of point of zero charge shifts and ionic strength dependence of adsorption results and molecular modeling calculations can also be used to deduce adsorption mechanisms. Applications of the surface complexation models to heterogeneous natural materials such as soils using the component additivity and the generalized composite approaches will be described. Emphasis will be on the generalized composite approach for predicting anion adsorption by soils. Continuing research is needed to develop consistent and realistic protocols for describing ion adsorption reactions on soil minerals and soils. The availability of standardized model parameter databases for use in chemical speciation-transport models is critical.