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This article in SSSAJ

  1. Vol. 50 No. 1, p. 52-57
    Received: July 30, 1984
    Accepted: Aug 15, 1985

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Specific and Nonspecific Cation Adsorption to Clays: Solution Concentrations and Surface Potentials1

  1. Shlomo Nir2



A model for cation adsorption to negatively charged surfaces is developed by taking into account specific cation binding to the surface sites and adsorption in the double layer region. Equations are given for any combination of mono and divalent cations in solution and for one type of binding site. Variations in solution concentrations of cations due to adsorption are explicitly included in the model in the framework of an iterative procedure. The results indicate that a Langmuir type of adsorption isotherm may represent the data over a certain range of cation concentrations. When a certain cation is present in such small concentrations that it does not affect the surface potential, then an increase in its concentration results in a proportional increase in its adsorbed amount. For a wide range of concentrations the amount of cation adsorbed appears to be independent of its concentration in solution. However, the adsorbed amounts are very sensitive to cation competition. An increase in the concentration of surface sites results in as reduction in the fractional binding per sits. A source of difference between sorption and desorption of cations is explained.

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