Thermodynamics of Aqueous Electrolyte Solutions - Application to Ion Exchange Systems

The thesis addresses the thermodynamics involved in describing the properties of aqueous solutions of electrolytes and of mixtures with ion exchanging materials. The work uses both existing and new approaches for the description of these properties and also presents new data for ion exchange isotherms and adsorption/swelling of several different ion exchange resins in aqueous electrolyte solutions. Chapter 1 is a short introduction to the thesis and describes some of the motivation for why the work has been carried out. Chapter 2 gives a short introduction to the area of aqueous electrolyte thermodynamics including the most important definitions for the understanding of the following chapters. The basic thermodynamic models based on the theory of Debye and Hückel are shortly introduced and examples of more comprehensive models are given. Chapter 3 deals with the volumetric properties of aqueous electrolyte solutions. Different theoretical approaches for description of these properties are discussed. A modification of the Masson equation combined with Young’s rule based on ion specific parameters is applied to volumetric data for different mixtures of salts. The model is easily applied to multicomponent mixtures, and it is shown that the relative errors of the predicted results in both ternary and
quaternary systems are well within the experimental accuracy of the data. In chapter 4 the phase behavior of aqueous electrolyte solutions is dealt with. The Extended UNIQUAC model is used for describing the vapor - liquid equilibria, solid - liquid equilibria and thermal properties of aqueous solutions of electrolytes in the presence of phosphoric and nitric acid. The model parameters are regressed on the basis of a large amount of experimental data and there is a good agreement between calculated and experimental data points. Chapter 5 introduces the basic principles of ion exchange equilibria. The different phenomena connected with the equilibria between an ion exchanging material and aqueous solutions of electrolytes are presented. The different theoretical approaches to describing these types of equilibria are discussed. Chapter 6 deals with modeling of ion exchange isotherms using a model treating the ion exchanger and counter-ions as a solid solution. The approach is very simple and gives only information about the selectivity of the ion exchanging material. New ion exchange isotherm data is presented for the H⁺ - K⁺ and H⁺ - Ca⁺⁺ systems. The approach is applied to both new data and data found in literature, and the results are reasonable accurate. Chapter 7 presents new experimental data for the distribution of solvent and ions between an aqueous solution and several different ion exchange resins. The data is modeled using the Extended UNIQUAC model for describing the thermodynamic properties of the two aqueous phases combined with an elastic term taking the elastic properties of the resin structure into account. The model is able to produce good predictions, and the deviations between model results and experimental data are all within the experimental error. Chapter 8 gives a general conclusion of the work completed in this thesis.