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Soil Science Society of America Journal Abstract -

Adsorption of Aluminum by a Smectite: II. An Al3+-Ca2+ Exchange Model1


This article in SSSAJ

  1. Vol. 41 No. 6, p. 1073-1077
    Received: Dec 3, 1976
    Accepted: July 15, 1977

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  1. M. B. McBride and
  2. P. R. Bloom2



The adsorption of Al by Ca2+-montmorillonite has been found to be described by a Langmuir-type equation in which the activity of Al3+ in solution is a function of the coverage of the mineral surfaces by Al. The classical mass-action equations were inadequate in describing the exchange reaction where the Ca2+ activity was allowed to vary, weighting the effect of the Ca2+ ion activity on the equilibrium too heavily. The model suggests the relative solutionlike nature of adsorbed Ca2+ compared to the much more strongly adsorbed Al3+. Hydrolysis and precipitation reactions of Al3+ at higher pH complicated the exchange model by introducing significant quantities of adsorbed hydroxyl-Al into the system.

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