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Clays and Clay Minerals

, Volume 14, Issue 1, pp 117–132 | Cite as

Electrostatic forces Between Clay and Cations as Calculated and Inferred from Electrical Conductivity

  • I. Shainberg
  • W. D. Kemper
Symposium on Surface Reactivity

Abstract

Equivalent conductivities of adsorbed cations were determined in clays saturated with Na+, Cs+, Ca++ and with mixtures of these cations. Measurements were also made on Ca++ clays which had been forced by previous drying into bundles of platelets or tac-toids. The average mobility of adsorbed Ca++ and Cs+ is much lower than that of adsorbed Na+.

It was concluded that the average mobility of adsorbed Ca++ is low because most of this Ca++ is on the internal surfaces of tactoids. Ca++ adsorbed between these internal surfaces appears to have a mobility much lower than Ca++ on the external surfaces which has a mobility of the same order of magnitude as Na+. Polarization of adsorbed Cs+ accounts at least partially for its low mobility in these clays.

Demixing of adsorbed cations (segregation with Na+ dominant between some platelets and Ca++ between others) is suggested as an initial step leading to breakup of a Na+-Ca++ clay mass into tactoids. The tactoid model, with Ca++ and Na+ preferentially on the internal and external surfaces respectively, furnishes an explanation of the instability of clay and soil aggregates with 15% exchangeable sodium.

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Copyright information

© Clay Minerals Society 1966

Authors and Affiliations

  • I. Shainberg
    • 1
  • W. D. Kemper
    • 1
  1. 1.U.S. Department of Agriculture and Colorado State UniversityFort CollinsUSA

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