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Soil Science Society of America Journal Abstract -

Kinetics and Mechanisms of Aluminum Adsorption on Kaolinite Using a Two-site Nonequilibrium Transport Model1


This article in SSSAJ

  1. Vol. 49 No. 4, p. 867-873
    Received: Sept 10, 1984
    Accepted: Feb 1, 1985

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  1. P. M. Jardine,
  2. J. C. Parker and
  3. L. W. Zelazny2



Kinetics of Al adsorption on Ca-kaolinite at selected concentrations, pH, and column lengths were studied using a miscible displacement technique. Observed breakthrough curves (BTC) for continuous injection of pH 4.3, 0.75 to 7.75 µg mL−1 Al solution were well-described by a two-site nonequilibrium transport model which assumes that sorption sites can be divided into two fractions: (1) instantaneous equilibrium sites and (2) sites following first-order reversible kinetics. Independent verification of the fitted parameter β, related to the fraction of type-1 equilibrium sites, was possible by assuming negative surface charge sites of kaolinite were in local equilibrium with the solution phase. Confirmation of the fitted parameter R, which is a measure of the total Al adsorbed, was not possible due to the nonsingular nature of the equilibrium adsorption isotherm. First-order rate coefficients (α) for Al adsorption on kaolinite were unaffected by column length. Effects of influent Al concentration on α were small but suggested that kinetic reaction of Al with kaolinite was not strictly first-order. Decreasing the pH of influent solution from 4.3 to 4.0, eliminated type-2 kinetic sites. These effects indicate that kinetic reactions involve Al polymerization on kaolinite while equilibrium reactions reflect Ca-Al exchange. This scenario is supported by Ca desorption data of the effluent and by potentiometric titrations of effluent solutions.

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