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Soil Science Society of America Journal Abstract -

Kinetics of the Formation and Breakdown of Ca-Montmorillonite Tactoids1


This article in SSSAJ

  1. Vol. 33 No. 4, p. 547-551
    Received: Dec 27, 1968
    Accepted: Feb 11, 1969

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  1. I. Shainberg and
  2. A. Kaiserman2



The kinetics of Ca-montmorillonite tactoid formation and breakdown was followed by recording the changes in light transmission as a function of time when Ca-montmorillonite suspensions of 0.05% (w/v) concentration were added to Na-montmorillonite suspensions of the same concentration in a titrating vessel placed in the light path of a spectrophotometer. Tactoid formation was found to be instantaneous whereas the breakdown of Ca tactoids took about 10 min. It was suggested that the initial step upon mixing sodium and calcium montmorillonite was the redistribution of adsorbed ions. For tactoids to break, ions have to interdiffuse into the tactoids. Since the mobility of ions adsorbed on the internal surfaces is low, tactoid breakdown is slow. Ion diffusion on the single platelets of Na clay and the external surfaces of the tactoids is high; thus the formation of tactoids is instantaneous.

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