Isopiestic Measurements of Osmotic and Activity Coefficients of NiCl2–NH4Cl–H2O Systems at 308.15 K

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In this work, the osmotic coefficients and water activities of NiCl2–NH4Cl–H2O ternary system and its two subsystems were obtained by isopiestic measurements at 308.15 K. The mean ion activity coefficients of NiCl2–H2O and NH4Cl–H2O 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 NH4Cl–H2O system. Whereas for the NiCl2–H2O system, the Pitzer equation has its limitation of the molality range. Similarly, the osmotic coefficients of NiCl2–NH4Cl–H2O 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.