Modeling Multicomponent Ion Exchange:  Application of the Single-Parameter Binary System Model

Abstract

The single-parameter model for binary ion exchange equilibria is applied to the prediction of ternary and quaternary equilibria. This model is based on a statistical thermodynamic approach to exchanger-phase behavior, coupled with the Pitzer model for activity coefficients in aqueous solution and an explicit description of ion association phenomena. Exchange between alkali metal and alkaline earth cations on commercially available strong acid resins is investigated in the presence of a variety of nonexchanging anions. All systems can be predicted acceptably using parameters fitted to binary chloride-based systems. Model predictions from these parameters are highly accurate in many cases, while those systems that are not predicted as accurately from binary data are able to be described by recalculating one parameter using the ternary or quaternary data. This model fits all criteria required to be met by any description of ion exchange equilibria, and provides a simple yet highly effective approach to the description of equilibria in “real-world” ion exchange systems.

High‐Resolution X‐ray Diffraction and Fluorescence Microscopy Characterization of Alkali‐Activated Slag‐Metakaolin Binders

“…In a multicomponent system involving relatively simple anionic ion‐exchange sites (and probably in the C–S–H type gels here, although not always in zeolites), calcium will usually be sorbed onto the solid in preference to sodium according to the thermodynamic equilibrium relationships between sorbed and dissolved species . In the alkali‐activated slag/metakaolin binders containing more MK, it is likely that a significant proportion of the Na + is consumed in the activation of MK to form a sodium aluminosilicate‐type gel, reducing the availability of Na + species in the pore solution, and therefore reducing the alkalinity from the high levels which would favor zeolite growth, even with the higher alkali dosage added to these samples (Table ).…”