(257az) Thermodynamic Model for Aqueous Na+–K+– Mg2+– Ca2+–SO42- Quinary System

We present a comprehensive thermodynamic model based on the electrolyte Non-Random Two Liquid theory (eNRTL) for the aqueous quinary system containing Na⁺, K⁺, Mg²⁺, Ca²⁺ and SO₄²⁻ ions. In the thermodynamic framework of eNRTL, the concentration dependency of the solution nonideality is accounted for with two binary interaction parameters for each of the water−electrolyte pairs and the electrolyte–electrolyte pairs. Many of the binary interaction parameters required in modeling this quinary system have been reported in the literature. In this study, we obtain values for the binary parameters for the (Na⁺ SO₄²⁻):(Ca²⁺ SO₄²⁻) pair, the (K⁺ SO₄²⁻):(Ca²⁺ SO₄²⁻) pair, and the (Mg²⁺ SO₄²⁻): (Ca²⁺ SO₄²⁻) pair by regressing experimental thermodynamic and solubility data from the literature. With the binary parameters retrieved from the literature and obtained in this study, the eNRTL model accurately represents various thermodynamic properties of the Na⁺–K⁺– Mg²⁺– Ca²⁺–SO₄²⁻ quinary system and its subsystems with temperatures from 273.15 K to 473.15 K and concentrations up to salt saturation. The model is being extended to cover Ba²⁺, Sr²⁺, Cl⁻ and HCO₃⁻ ions with the goal to support simulation and development of novel water desalination processes for high salinity produced water in oil and gas productions.