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Soil Science Society of America Journal Abstract -

Applications and Misapplications of the Langmuir Equation to Soil Adsorption Phenomena1


This article in SSSAJ

  1. Vol. 41 No. 6, p. 1077-1080
    Received: Feb 18, 1977
    Accepted: June 24, 1977

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  1. Robert D. Harter and
  2. Dale E. Baker2



When the development of the Langmuir adsorption equation is critically examined, it is evident that the equation soil scientists have been using [C/x/m = C/k + I/kb, where C is concentration of adsorbate, x/m is the amount adsorbed per unit weight adsorbent, k is the adsorption maximum, and b is a constant] is in the wrong form. This error is of no great importance when the equation is merely used to obtain a calculated adsorption maximum for comparison to other adsorbent properties. However, it does become important when attempts are made to understand adsorption dynamics and bonding strengths. The commonly reported curvilinear nature of the C/x/m vs. C plots is simply the result of not considering the effect of desorbed ions in the equilibrium solution, rather than being due to multiple adsorption mechanisms. When the equation is corrected by considering desorbed ions, the isotherm becomes linear. In addition, the constant, b, of the Langmuir equation is not simply related to the bonding energy of the adsorbed ion, but to the ratio of adsorbed and desorbed ion bonding energies.

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