Thermodynamic modeling of calcium carbonate scale precipitation: aqueous Na+-Ca2+-Cl–-HCO3–-CO32–-CO2 system

To allow for accurate calculations of calcium carbonate scaling in highly saline produced waters, we present a comprehensive thermodynamic model based on the electrolyte nonrandom two-liquid (eNRTL) activity coefficient equation for the aqueous Na+-Ca2+-Cl–-HCO3–-CO32–-CO2 system. The eNRTL binary interaction parameters for the H2O:(Na+-CO32–) pair, the H2O:(Na+-HCO3–) pair, the (Na+-Cl–):(Na+-CO32–) pair, and the (Na+-Cl–):(Na+-HCO3–) pair are identified in this work via the regression of thermodynamic, calorimetric, and phase equilibria experimental data. The binary interaction parameters associated with the H2O:(Na+-Cl–) pair, the CO2:(Na+-Cl–) pair, the H2O:(Ca2+-Cl–) pair, and the (Na+-Cl–):(Ca2+-Cl–) pair are retrieved from the literature. The remaining binary interaction parameters are retrieved from Aspen Plus or set to zero. In addition, the solubility product constants are identified for Na2CO3•10H2O(s), Na2CO3•7H2O(s), Na2CO3•H2O(s), Na2CO3•NaHCO3•2H2O(s), Na2CO3•3NaHCO3(s), and CaCO3(s) via regression of solubility data. The model is capable of accurately calculating all phase equilibria and calorimetric properties at temperatures up to 473.15 K and salt concentrations up to saturation.