Factors Involved in Cation Exchange Equilibria^1,2

Abstract

Studies of the NH< +-H + and Ag +-H + exchanges on Dowex 50 at 25°in solutions of unit ionic strength have shown that the equilibrium composition of solid and liquid phases is determined by (a) the extent of simple equivalent ion exchange, which may be regarded as a chemical reaction, (b) the absorption or desorption of water by the resin, (c) the adsorption of electrolyte by the resin, and (d) the apparent molal volume change of the solute. Water absorption is a linear function of resin composition, but electrolyte adsorption depends in a more involved fashion on both resin and solution composition. New data for the Na+-H + exchange on Dowex 50 in solutions of ionic strength 1.0 and 0.3 M have been combined with solution activity coefficient ratios from the literature to obtain, by a method of graphical integration, the activity coefficients of the resin components and the true exchange equilibrium constant. The activity coefficients, less than unity, agree well for the two ionic strengths. The value of the equilibrium constant at 25°is 1.70 ± 0.03.

The Adsorption of Water and Carbon Monoxide by Zinc Oxide

“…dry H-resin as determined by blotting the wet resin with filter paper, placing in a bottle and weighing, then drying and reweighing. 1 (a) The Ion-exchange Equilibrium.-Measured weights of H-resin were stirred with known volumes of a solution of mercuric perchlorate containing perchloric acid to prevent hydrolysis. Samples of solution were withdrawn at intervals and analyzed.…”

Ion and solvent selectivity of zeolite A in mixed media. An extension of the Gibbs-Donnan model

“…(In this alcohol-water composition range where the mole fraction of ethanol in the zeolite in less than 0.05 the partial molar volume of water is unaffected21 to provide the basis for this estimate.) With the mole fraction, xw, of water in the solvent mixture sorbed by the zeolite phase available, on this basis fiw = *w0w0 (6) where 6W°= 0.16, the value assigned earlier to the activity of water in the zeolite equilibrated in aqueous media. The value of ow was available for every solvent distribution case examined19 and 0.018 L is a credible Vv value for use in eq 2b.…”

“…Aqueous Selectivity Data Zeolite prepared without Fe extraction cycle 6. Zeolite prepared with Fe extraction cycle.…”

Ion Exchange Reactions of Clays

“…On the basis of these considerations, estimates may be made of the apparent activity in the exchanger phase, after suitable exchange data are available to permit evaluation of the parameters C in equations. Recently, however, it has been pointed out that the constancy of K in equation (2) is a thermodynamic necessity (Argersinger, et al, 1950;Bonner, et al, 1952;Ekedahl, et al, 1950;Hogfeldt, et al, 1950Hogfeldt, et al, , 1950a arising from the definition of activities and independent of the mechanism of the reaction. Accordingly, the expression for the equilibrium constant is combined with the Gibbs-Duhem equation to determine from the experimental data, when the activities of the ions in the mixed electrolyte solutions are known, both the true equilibrium constant and the activity coefficients for the ions in the solid phase.…”

“…Such processes as molecular adsorption, formation of complex solution ions, formation of difficultly soluble salts, or formatiou of complexes with the exchanger phase may be superimposed on the ion exchange reaction itself in a given system. (Bonner, Argersinger, and Davidson, 1952). In the present discussion of the ion exchange reaction, attention will be directed toward those systems in which the distribution of ions arises primarily from the ion exchange reaction itself.…”