Goethite surface reactivity: III. Unifying arsenate adsorption behavior through a variable crystal face - Site density model |
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Authors: | Carlos Salazar-Camacho |
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Institution: | Grupo de Bio-Geoquímica Ambiental, Facultad de Química, Universidad Nacional Autónoma de México (UNAM), Coyoacán, Ciudad Universitaria, México 04510, D.F, Mexico |
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Abstract: | We developed a model that describes quantitatively the arsenate adsorption behavior for any goethite preparation as a function of pH and ionic strength, by using one basic surface arsenate stoichiometry, with two affinity constants. The model combines a face distribution-crystallographic site density model for goethite with tenets of the Triple Layer and CD-MUSIC surface complexation models, and is self-consistent with its adsorption behavior towards protons, electrolytes, and other ions investigated previously. Five different systems of published arsenate adsorption data were used to calibrate the model spanning a wide range of chemical conditions, which included adsorption isotherms at different pH values, and adsorption pH-edges at different As(V) loadings, both at different ionic strengths and background electrolytes. Four additional goethite-arsenate systems reported with limited characterization and adsorption data were accurately described by the model developed. The adsorption reaction proposed is: |
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