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Soil Science Society of America Journal Abstract -

Standard Free Energies of Exchange for Alkali Metal Cations on Wyoming Bentonite1


This article in SSSAJ

  1. Vol. 33 No. 1, p. 37-41
    Received: Mar 8, 1968
    Accepted: Aug 12, 1968

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  1. R. G. Gast2



Standard free energies of exchange, Δ Go, were determined for the exchange of Na with Li, K, Rb, and Cs and Li with K between 0.001N chloride solutions and 5% Wyoming bentonite gels at 25C. Values were also determined for Na → Rb, Na → Cs, and Rb → Cs exchanges between 0.0075N chloride solutions and 0.75% Wyoming bentonite suspensions. Application of the additivity rule indicates that the values are accurate to within ±50 to 100 cal mole-1. Values for the 5% gels range from +48 cal mole-1 for Na → Li exchange to −1,081 cal mole-1 for Na → Cs exchange. There is a small but consistent increase in the ΔGo values for the 0.75% suspensions compared to those for the 5% gels. With the possible exception of Li, a linear relationship was found between ΔGo values and Debye-Huckle parameters for the respective cations indicating that the adsorption of monovalent cations from strong electrolyte solutions is governed by their hydrated radii.

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