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This article in SSSAJ

  1. Vol. 36 No. 1, p. 14-19
     
    Received: Jan 7, 1971
    Published: Jan, 1972


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doi:10.2136/sssaj1972.03615995003600010003x

Alkali Metal Cation Exchange on Chambers Montmorillonite1

  1. R. G. Gast2

Abstract

Abstract

Standard free energies of exchange, ΔG°, were determined for the exchange of Na with Li, K, Rb, and Cs on a 0.1–0.5 micron fraction of Chambers montmorillonite having an exchange capacity of 123 ± 2 meq/100 g. The ΔG° values ranged from +80 cal mole-1 for Na→Li exchange to -1886 cal mole-1 for Na→Cs exchange and were approximately twice as large as those found previously for similar exchange reactions on Wyoming bentonite having an exchange capacity of 92 ± 2 meq/100 g. The ΔG° values reflect cation selectivity differences of a factor of two to three between the two clays. In contrast, the standard heats of exchange, determined calorimetrically, were approximately the same for both clays and ranged from + 125 cal mole-1 for Na→Li exchange to -2575 cal mole-1 for Na→Cs exchange. These results indicate that the differences in free energies of exchange between the two clays are due to entropy effects.

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