Heterovalent, Ternary Cation Exchange Equilibria: NH4+‐Ba2+‐La3+ Exchange on Montmorillonite

Abstract

AbstractData were obtained at 25°C on the composition of the aqueous solution and exchanger phases in NH4‐Ba‐La, La‐Ba, La‐NH4, and Ba‐NH4 aqueous systems comprising the chloride salts of the three cations and a montmorillonite clay from Nevada. The data for the three binary cation exchange systems were incorporated into a thermodynamic model which was used to predict the composition of the aqueous solution phase of the ternary NH4‐Ba‐La system as a function of exchanger phase composition. The model employed, known as the subregular model, involved a MacLaurin expansion of the exchanger phase rational activity coefficients to third order in the mole fractions of the exchanger components. The constant coefficients in the MacLaurin expansion could be determined solely with experimental data on the infinite‐dilution, rational activity coefficients of exchanger components in binary exchange systems. Thus no data on ternary exchange systems were required to apply the model. The model calculations were in reasonably good agreement with experiment, suggesting that further efforts to predict ternary exchange behavior from binary exchange data are warranted.