Ion exchange in concentrated media. Correlations for variation of selectivity coefficients with medium

Abstract

An attempt to relate the different values of the ion-exchange selectivity coefficient in different media is made by considering the two phases as ionic solutions where the activity coefficients of species can be evaluated by means of Mikulin's equation. The selectivity coefficients of the NH 4 +/H +, Na +/H +, and Li +/H + exchanges in a sulfonated cation exchanger and of the NO 3 −/Cl − exchange in a quaternary ammonium anion exchanger have been measured under different conditions characterized by the degree of crosslinking of the ion exchanger, the water activity of the solution, the concentration ratio of two counterions, and the concentration ratio of a third possible counterion. The water activity of the solution is an essential parameter to be controlled, particularly in dilute or moderately concentrated solutions. A representation of the experimental results on the ion-exchange selectivity coefficient is given in terms of two parameters allowing the selectivity coefficient to be predicted even in very concentrated ionic media.