Reuse of high salinity produced waters in oil and gas production is a major concern due to high treatment cost and regulations on disposal in the environment . To support development of novel separation techniques and process innovations, we report development of a comprehensive engineering thermodynamic model for the aqueous hexary system of Na+
, and SO42â
, the major ionic species present in high salinity produced waters. Based on the electrolyte NRTL theory , the model accurately predicts thermodynamic and phase equilibrium properties with two binary interaction parameters per water-electrolyte pair and electrolyte-electrolyte pair sharing a common ion. The model is validated with the electrolyte concentrations up to salt saturation and temperatures from 273 to 473 K. This paper presents the methodology to identify the binary interaction parameters from the literature data. Furthermore, it presents the model predictions for wide varieties of thermophysical and phase equilibrium properties including salt solubilities for selected binary, ternary, and quaternary subsystems. The model should be a very useful tool in process research, development, and simulation of novel treatment processes for high salinity produced waters.
 D.L. Shaffer, L.H. Arias Chavez, M. Ben-Sasson, S. R.-V. CastrillÃ³n, N.Y. Yip, M. Elimelech, Environ. Sci. Technol. 2013, 47:9569-9583.
 Y. Song, C.-C. Chen, âSymmetric Electrolyte Nonrandom Two-Liquid Activity Coefficient Model,â Ind. Eng. Chem. Res. 2009, 48:7788-7797.