Experimental study and modelling of saturation molality of NaCl in quaternary aqueous electrolyte solutions at various temperatures

Saturation molality of sodium chloride in mixed aqueous electrolyte solutions containing NaCl, CaSO4 and Na2SO4 was measured at atmospheric pressure over the wide range of temperatures using an equilibrium cell equipped with an accurate temperature control system. The measurements were carried out at different CaSO4 and Na2SO4 concentrations. In order to check the repeatability of the experimental data for the saturation molality of NaCl, the experiments were replicated three times and the values reported were the average of the replicas. To model the data generated in this work, the PDH+UNIFAC-Dortmund activity coefficient model was used. The model used to predict the mean ionic activity coefficients of NaCl at the saturation molality at various temperatures and at different concentrations for CaSO4 and Na2SO4. The PDH term of the model accounts for the long range interactions between ionic species in solutions, while the modified UNIFAC-Dortmund activity coefficient model was used to account for the short range interactions between the species in solutions. It is worth noting that no new adjustable parameters were introduced into the model and the previously reported values for the interaction parameters of the binary and ternary electrolyte systems were directly used to predict the experimental data of the mean ionic activity coefficients of NaCl at saturation molality. The results showed that the PDH+UNIFAC-Dortmund activity coefficient model can accurately predict the mean ionic activity coefficients for the quaternary electrolyte solutions studied in this work.

Research Highlights
► Mixed aqueous electrolyte solution contains NaCl, CaSO4 and Na2SO4.
► NaCl saturation molality in mixed aqueous electrolyte solutions was measured.
► The PDH+UNIFAC-Dortmund model was used to predict the solubility.
► To predict the experimental data, the previously reported values were used.
► The model can predict the mean ionic activity coefficients for mentioned solutions.