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This article in SSSAJ

  1. Vol. 46 No. 6, p. 1147-1152
    Received: Jan 7, 1982
    Accepted: July 20, 1982

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On the Use of the Langmuir Equation in the Interpretation of “Adsorption” Phenomena: II. The “Two-Surface” Langmuir Equation1

  1. Garrison Sposito2



A rigorous, mathematical representation of a sorption isotherm as a Stieltjes transform is employed to prove a theorem about the “two-surface” Langmuir equation. This theorem states that, if the distribution coefficient for an ion sorbed by a soil is a finite, decreasing function of the amount sorbed, q, and extrapolates to zero at some finite value of q, then the sorption isotherm can always be represented mathematically by a two-surface Langmuir equation. Since the proof of this theorem does not depend on the chemical mechanism of ion sorption, it follows that the adjustable parameters in the two-surface Langmuir equation cannot be interpreted in terms of surface reactions without additional, independent evidence that only adsorption on two kinds of surface site actually is involved in the ion sorption reaction.

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