Mean activity coefficients of KCl in the KCl–K2B4O7–H2O solutions at 288.15 K determined by cell potential method and their application to the prediction of solid–liquid equilibria of the KCl–K2B4O7–H2O system

Abstract

• The unreported mixed ion interaction of Pitzer parameters in KCl–K 2 B 4 O 7 –H 2 O solutions at 288.15 K were obtained in this work. • The experimental and predicted solubilities were compared to verify the rationality of fitting parameters. After measuring the cell potential of the cell without liquid junction K-ISE | KCl ( m 1 ), K 2 B 4 O 7 ( m 2 ) | Cl-ISE with the calibrated potassium ion and chloride ion selective electrode, the mean activity coefficients of KCl in KCl–K 2 B 4 O 7 –H 2 O solutions are calculated by the Nernst equation. The single parameters β (0) , β (1) , C Φ of K 2 B 4 O 7 , and the mixed ion interaction parameters θ Cl, B 4 O 5 (OH) 4 and ψ K,Cl, B 4 O 5 (OH) 4 of the Pitzer model were determined by programming solver and mean activity coefficients in this work. Furthermore, Pitzer equation is also used to evaluate the mean activity coefficient of potassium tetraborate in the KCl–K 2 B 4 O 7 –H 2 O solutions, as well as the osmotic coefficients, water activity and excess Gibbs free energy of the mixed solutions. Additionally, the experimental measurements of phase equilibria in the ternary system KCl–K 2 B 4 O 7 –H 2 O at 288.15 K are investigated in this work. The solubilities of the salts in the ternary system at 288.15 K are predicted by using Pitzer equation and the obtained ion parameters. The comparision of experimental and calculated phase diagram is presented in detail. The prediction results show that the predicted data are in accordance with the experimental data.