| An investigation of the effect of electrolyte composition and specific adsorption on cation exchange was performed through a systematic experimental and modeling study of multi-component ion exchange on the strong acid cation exchange resin Amberlite 200. A comprehensive data set for single, binary, and ternary cation adsorption involving Na, Mg, and Zn in the single and binary anion systems of Cl;Thermodynamic and mass action models exhibited moderate accuracy in predicting binary and ternary cation exchanges in different anion background at various ionic strengths. The ternary cation exchange data exhibited characteristics not entirely captured by fitting the related binary cation exchanges. Among the mass action models, the Gaines-Thomas model was best able to predict ternary cation exchange. While mass action models are easy to implement and are used widely, their accuracy in predicting multi-component exchange is limited. Also, they provide little insight into the physico-chemical processes that influence cation exchange.;The surface complexation/Gouy-Chapman model yielded the reasonably good predictions for binary and ternary cation exchanges in the different anion backgrounds and ionic strengths. Overall, the predictions of the SCGCM were comparable to or more accurate than those obtained with the conventional thermodynamic and mass action models for ion exchange. In addition, the SCGCM yielded useful insights into the mechanisms governing ion exchange. Modeling of the data with the SCGCM indicated that specific adsorption played a dominant role in the cation exchange on the resin. The success in predicting binary and ternary exchange with the SCGCM suggests that it may be useful in modeling multi-component ion exchange in more complex systems. Data requirements would be substantial for application of the SCGCM to such systems, as the model requires detailed knowledge of the surface characteristics and the surface complexation constants for the discrete charged sites.;The experimental results indicated that the amount of adsorbed cations became larger than the cation exchange capacity of the resin at higher ionic strengths, and that cation selectivity in binary cation exchange was dependent on the types of background anions. Exceedance of cation exchange capacity could be explained by adsorption of cation-anion complexes. The effects of anion type on cation selectivity could be explained by solution complexation and by anion adsorption. The ternary exchange data indicated that the selectivity of divalent cations over Na was influenced by the presence of the third cation in a consistent manner with respect to anion nature and ionic strength. |
