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A nonelectrostatic surface complexation model for lead sorption on soils and mineral surfaces

Van Benschoten, J.E., Young, W.H., Matsumoto, M.R., Reed, B.E.
Journal of environmental quality 1998 v.27 no.1 pp. 24-30
adsorption, aluminum oxide, data collection, engineering, ferric oxide, goethite, guidelines, lead, ligands, mineral soils, models, silica, soil pollution, soil remediation, solutes, stoichiometry, trace elements
A nonelectrostatic surface complexation model is applied to three data set of increasing complexity: synthetic data for Pb adsorption to hydrous ferric oxide (HFO); data from the literature involving Pb adsorption to three mineral surfaces (goethite, alumina, and silica); and data for Pb adsorption on a field soil. The model is intended for engineering applications (e.g., soil remediation) rather than to provide a comprehensive description of sorption phenomena. The model is simple enough that it can be implemented on a standard spreadsheet and in its simplest form requires only two fitting parameters. Proton stoichiometry for the surface reactions is determined using Kurbatov plots; total site density (ST) and surface-binding constant (Kpb) are fit to experimental sorption data. Complexation reactions between Pb and major ligands are included in the model. Although similar models have been presented previously by other researchers, dissolved solute speciation often was ignored and applications focused on trace metal adsorption and not on soil contamination and remediation. Model applications to Pb sorption data for mineral surfaces have shown excellent correlation with experimental data (r2 values from 0.95 to 0.99, SE of 3-7%). For an environmental soil, r2 values from 0.82 to 0.96 and std errors from 4 to 8% were observed. The model simulates effects of solution chemistry on sorption nearly as well as traditional surface complexation models, but with fewer fitting parameters. Interpretation of fitted parameters and guidelines for model use are discussed.