Submitted to: Book Chapter
Publication Type: Review Article
Publication Acceptance Date: 9/29/2007
Publication Date: 1/10/2008
Citation: Goldberg, S.R., Criscenti, L.J. 2007. Modeling adsorption of heavy metals and metalloids by soil components. inL A. Violante, P.M. Huang and G. Stotzsky (editors) Biophysico-Chemical Processes of Heavy Metals and Metalloids in Soil Environments. J. Wiley & Sons, New York, NY. Chapter 6 pp: 215-264. Interpretive Summary:
Technical Abstract: Various empirical and chemical models of metal adsorption are presented and discussed. Empirical model parameters are only valid for the experimental conditions under which they were determined. Surface complexation models are chemical models that provide a molecular description of metal and metalloid adsorption reactions using an equilibrium approach. Four such models, the constant capacitance model, the diffuse layer model, the triple layer model, and the CD-MUSIC model will be described. Characteristics common to all the models are equilibrium constant expressions, mass and charge balances and surface activity coefficient electrostatic potential terms. Various conventions for defining the standard state activity coefficients for the surface species will be described. Methods for determining parameter values for surface site density, capacitances, protonation-dissociation constants, and metal surface complexation constants will be presented. Experimental methods of establishing metal surface configuration include: vibrational spectroscopy, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, x-ray absorption spectroscopy, and x-ray reflectivity. Metal surface speciation can also be inferred indirectly from point of zero charge shift and ionic strength dependence experiments and ab initio molecular modeling calculations. Applications of the surface complexation models to heterogeneous systems using the component additivity and the generalized composite approaches will be described. Continuing research is needed to develop consistent and realistic protocols for describing metal adsorption reactions. The availability of standardized model parameter databases is critical.