Mean activity coefficients of KCl in the KCl + SrCl2 + H2O solutions at 278.15 K determined by cell potential method and their application to the prediction of solid-liquid equilibria of the KCl + SrCl2 + H2O system

The cell potentials were determined by the cell without liquid junction K-ISE vertical bar KCl (m0) vertical bar Cl-ISE firstly. Using Nernst equation and the measured cell potentials, the response slope j of the single-salt electrode and the standard cell potential E-0 were fitted well. The total ionic strengths range from 0.0100 to 1.0000 mol.kg(-1), the cell without liquid junction K-ISE vertical bar KCl (m1), SrCl2 (m(2)) vertical bar Cl-ISE is used to determine the mean activity coefficients of KCl in the KCl + SrCl2 + H2O solutions, the ionic strength fractions yb of SrCl2 are 0.8, 0.6, 0.4, 0.2 and 0. According to the measured cell potentials, the mean activity coefficients of KCl in the KCl + SrCl2 + H2O solutions were calculated by Nernst equation, and the relationship diagrams between the mean activity coefficients and total ionic strengths of the mixed solutions are drawn at 278.15 K. The mixed interaction parameters hK,Sr, and wK, Sr,Cl in the Pitzer model were also obtained by regression of the mean activity coefficients of KCl in the mixed solutions. The mean activity coefficients of SrCl2, the osmotic coefficients, the water activities, and the excess Gibbs free energies of the mixed solutions were also calculated by Pitzer equations. Additionally, in order to verify the mixed ion parameters of Pitzer model fitted in this work, the isothermal dissolution equilibrium method is used to measure experimentally the phase equilibria of the mixed solutions at 278.15 K, and then the Pitzer equations and the mixed ion parameters are used to predict the solubilities of the salts in the mixed solutions at 278.15 K. The experimental and predicted phase diagrams are good agreement. (C) 2022 Published by Elsevier B.V.

Automated summary

In this study, the average activity coefficients and interaction parameters of KCl in mixed solutions were investigated by measuring cell potentials. By fitting the Nernst equation and Pitzer model, the activity coefficients, osmotic coefficients, and solubilities of KCl in the mixed solutions were predicted and showed good agreement with experimental results.