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

Abstract

AbstractStandard 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.