Determination of Ion Exchange Parameters for Binary Systems and Application to Ternary Systems

Abstract

<p>Ion exchange equilibrium data can be used to predict the viability of a proposed process. Ion exchange equilibria have been studied considerably since the 1950's but the complexity of the basic research has tended to reduce its direct usefulness to the practising engineer. This research has been undertaken to determine if a moderately simple method of experimentation and analysis could be applied to predict ion exchange equilibria to within limits of accuracy acceptable to engineers.</p> <p> The first step in the research was to develop a simple mathematical model for a binary system to calculate the selectivity coefficient and resin capacity from batch experiments. The model was successfully applied for the exchange of Na+ with five heavy metal ions: Ni²⁺; Cu²⁺; Cd²⁺; Pb²⁺ and Zn²⁺ on a typical commercial resin (Dowex HCR-W2). The binary parameters were then used to predict the equilibrium values for several ternary systems. From these ternary experiments, it was determined that binary data can be used to predict ternary systems if the selectivity coefficients of the two ions involved are either almost equal or differed by at least a factor of five. A kinetic effect was proposed to explain the discrepancies observed between the predicted and experimental values for the intermediate ratios of selectivity coefficients of the involved ions, although further work is required to confirm this hypothesis.</p> <p> Several packed bed experiments were performed to check some of the results from the binary and ternary system experiments and as exploratory work for future research. These experiments confirmed the capacity data calculated from the binary system experiments and were consistent with the trends observed in the ternary system experiments.</p>