Measurements and calculations of solid-liquid equilibria in the ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O at 348 K

According to the compositions of the underground brine resources in the west of Sichuan Basin, solubilities of the ternary systems NaBr–Na 2 SO 4 –H 2 O and KBr–K 2 SO 4 –H 2 O were investigated by isothermal method at 348 K. The equilibrium solid phases, solubilities of salts, and densities of the solutions were determined. On the basis of the experimental data, the phase diagrams and the density-composition diagrams were plotted. In the two ternary systems, the phase diagrams consist of two univariant curves, one invariant point and two crystallization fields. Neither solid solution nor double salts were found. The equilibrium solid phases in the ternary system NaBr–Na 2 SO 4 –H 2 O are NaBr and Na 2 SO 4 , and those in the ternary system KBr–K 2 SO 4 –H 2 O are KBr and K 2 SO 4 . Using the solubilities data of the two ternary subsystems at 348 K, mixing ion-interaction parameters of Pitzer’s equation θxxx, Ψxxx and Ψxxx were fitted by multiple linear regression method. Based on the chemical model of Pitzer’s electrolyte solution theory, the solubilities of phase equilibria in the two ternary systems NaBr–Na 2 SO 4 –H 2 O and KBr–K 2 SO 4 –H 2 O were calculated with corresponding parameters. The calculation diagrams were plotted. The results showed that the calculated values have a good agreement with experimental data.