In this work, a temperature-dependent thermodynamic model based on heat capacity was proposed to predict the osmotic and mean ion activity coefficients of metal chloride aqueous solutions. The CaCl 2 −H 2 O system was used to verify the model and the results show the predicted values can well agree with the reported data, indicating that the proposed thermodynamic model is reliable. Meanwhile, the heat capacities at constant pressure of both CuCl 2 −H 2 O and NiCl 2 −H 2 O systems in the range from 298.15 to 363.15 K were calculated from the enthalpy changes determined by the calorimetric experiments. Therefore, the osmotic and mean ion activity coefficients of the two systems within 4 mol•kg −1 were predicted in a wide temperature range with the established model. The calculated results were well consistent with the data in the literature and further indicate the thermodynamic model was reliable and convenient.
In this work, the osmotic coefficients and water activities of NiCl 2 −NH 4 Cl−H 2 O ternary system and its two subsystems were obtained by isopiestic measurements at 308.15 K. The mean ion activity coefficients of NiCl 2 −H 2 O and NH 4 Cl−H 2 O systems with different molalities at 308.15 K were calculated by the Pitzer ion interaction model. Meanwhile, the self-consistency of experimental data was validated by Gibbs−Duhem equation, showing the calculated results have a good self-consistency between Pitzer ion interaction model and Gibbs−Duhem equation in the whole experimental molality range for NH 4 Cl−H 2 O system. Whereas for the NiCl 2 −H 2 O system, the Pitzer equation has its limitation of the molality range. Similarly, the osmotic coefficients of NiCl 2 −NH 4 Cl−H 2 O ternary system with different ionic strength can be obtained. Furthermore, the relative deviation between the experimental and calculated results indicated that the mixing parameters of Pitzer equation can be ignored in estimating the osmotic coefficients at the ionic strength of less than 2.5 mol•kg −1 , whereas it cannot be omitted at the higher ionic strength.
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