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

ABSTRACT

Standard free energies of exchange, G^o, 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 G^o 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 G^o 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.

¹ This manuscript is published with the permission of the Director of the University of Tennessee Agr. Exp. Sta., Knoxville.

² Agricultural Research Laboratory of the University of Tennessee, Oak Ridge; operated by the Tennessee Agr. Exp. Sta. for the US Atomic Energy Commission under Contract no. AT-40-1-GEN-242.

Received for publication March 8, 1968. Accepted for publication August 12, 1968.

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