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This article in SSSAJ

  1. Vol. 30 No. 1, p. 17-22
    Received: Mar 23, 1965
    Accepted: Oct 7, 1965

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Contribution of Adsorbed Cations to Diffusion in Clay-Water Systems1

  1. J. C. van Schaik,
  2. W. D. Kemper and
  3. S. R. Olsen2



Self-diffusion of sodium and calcium ions was measured in bentonites containing various amounts of water and the respective chlorides. The contribution of mobile exchangeable cations to diffusion was calculated from the data by subtracting measured rates of free electrolyte diffusion from the total rate of self-diffusion measured in these systems. Mobile exchangeable cations accounted for from 3 to over 500 times as much diffusive movement as was accounted for by free electrolyte cations in these systems. The fractions of the exchangeable cations that were in the diffuse layer were estimated from the contribution of exchangeable ions to diffusion, the fluidity of water near clay particles and the calculated concentration distributions of the adsorbed cations. Approximately 70% of exchangeable sodium ions were mobile. Approximately 25% of exchangeable calcium ions were mobile.

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