Determination of mean activity coefficients and prediction of phase equilibria of the NaCl-SrCl2-H2O solution at 318.15 K

In this work, the cell potential method is used to measure activity coefficients of NaCl-SrCl2-H2O mixed solution at 318.15 K. The potential values of NaCl in NaCl-H2O single salt solution were measured, and the standard cell potential E-0 and electrode response slope k were fitted with linear regression. Subsequently, the results show that the ion-selective electrode has a good Nernst response. The mean activity coefficients NaCl in NaCl-SrCl2-H2O solution are also determined with Nernst equation, and the total ionic strength in the mixed solution range is from 0.1000 similar to 0.8000 mol.kg(-1), the ionic strength fraction of SrCl2 with y(b) = (0.0, 0.2, 0.4, 0.6, 0.8). Using the mean activity coefficients data and Pitzer model, the Pitzer ion interaction parameters theta(Na,Sr) and psi(Na,Sr,Cl) of Pitzer equations at 318.15 K are fitted. Furthermore, the mean activity coefficients of SrCl2, permeability coefficient Phi, water activity a(w), and excess Gibbs free energy G(E) were also calculated by Pitzer's equations. The phase equilibria of the NaCl-SrCl2-H2O solution at 318.15 K are predicted, and corresponding phase diagram of the ternary solution is plotted according to the calculated solubilities in this work, and comparison of phase equilibria at different temperatures is also presented. The results show that the ion interaction parameters of Pitzer equations obtained in this work can be used for calculation of thermodynamic parameters and prediction of phase equilibria of salt-water solutions containing strontium.

Automated summary

The cell potential method was used to measure the activity coefficients of a NaCl-SrCl2-H2O mixed solution. The Nernst response of the ion-selective electrode was determined and used to calculate the mean activity coefficients of NaCl in the solution. The Pitzer ion interaction parameters were then fitted using the mean activity coefficients and used to calculate various thermodynamic parameters and predict the phase equilibria of the solution.