Measurements of the Mean Activity Coefficients of NaBr in NaBr–SrBr2–H2O Ternary Solutions at 318.15 K and Applications in Prediction of Phase Equilibria

The mean activity coefficients of NaBr in the NaBr–SrBr₂–H₂O ternary solution at 318.15 K were investigated by using the cell potential method. Sodium- and bromide-selective electrodes were used to measure the cell potentials of the NaBr–H₂O solutions. The standard cell potential (E⁰) and electrode response slope (κ) were derived from these measurements. Subsequently, the mean activity coefficients of NaBr in the NaBr–SrBr₂–H₂O system were determined for a total ionic strength range of 0.01 to 2.00 mol·kg^– 1. The ionic strength fraction of SrBr₂ (y_b) was set to 0.0, 0.2, 0.4, 0.6, or 0.8. Using mean activity coefficents and the Pitzer model, we used a programming solver to fit the Pitzer ion interaction parameters θ_{Na⁺,Sr²⁺} and ψ_{Na⁺,Sr²⁺,Br⁻}. The mean activity coefficients of SrBr₂, the osmotic coefficient Φ, the water activity a_w, and the excess Gibbs free energy G^E of the mixed solution were calculated. Additionally, the solubility of the ternary system was modeled using the Pitzer model. The predicted values were compared with experimental data at 308.2 and 323 K, confirming the reliability of the modeled results and the good adaptability of the mixed ion interaction parameters for solubility prediction.