(59h) Thermodynamic Modelling of Ca2+-Na+- Cl--CO2 Quaternary System with Electrolyte NRTL Model

Calcium carbonate (CaCO₃) is one of the most important solutes that can lead to scale formation in produced water processing equipment and in desalination water treatment. A scientific model that provides quantitative thermodynamic predictions for different conditions is useful and when used with models of the thermodynamics of other important ions can form a complete model of scaling and precipitation in such equipment. In this study symmetric electrolyte nonrandom two liquid (eNRTL) activity coefficient model is used to model the aqueous Ca²⁺-Na⁺- Cl^−-CO₂ quaternary system. The model requires only molecule-electrolyte and electrolyte-electrolyte binary interaction parameters. The temperature dependence of these interaction parameters is described via Gibbs-Helmholtz equation including up to three temperature coefficients. Experimental data including the osmotic coefficient, mean ionic activity coefficient, vapor pressure, heat capacity, excess enthalpy, and salt solubility at different temperatures and electrolyte concentrations up to saturation are used to identify the model parameters. The model provides accurate representation for all thermodynamic properties and phase equilibria for the aqueous quaternary system. The model of carbonate thermodynamics is coupled with the thermodynamics of other important electrolytes to evaluate scaling and precipitation in typical saline waters including brackish groundwater, seawater and examples of produced waters.