A chemical equilibrium model of solution behavior and solubility in the H-Na-K-Ca-OH-Cl-HSO4-SO4-H2O system to high concentration and temperature

This paper describes a chemical model for calculating solute and solvent activities and solid-liquid equilibria in the H-Na-K-Ca-OH-Cl-HSO₄-SO₄-H₂O system from low to high solution concentration within the 0° to 250°C temperature range. The solubility modeling approach of Harvie and Weare (1980) and Harvie et al. (1984), and their implementation of the Pitzer (1973) specific interaction equations are employed. This model expands the variable temperature H-Na-K-OH-Cl-HSO₄-SO₄-H₂O model of Christov and Moller (2004) by evaluating the Ca²⁺-acid/base binary and ternary solution parameters and the chemical potentials of three basic calcium solid phases: Ca(OH)₂(s), CaCl₂.Ca(OH)₂.H₂O(s), and CaCl₂.3Ca(OH)₂.13H₂O and three calcium chloride hydrates (CaCl₂.nH₂O; n = 6, 4, 2). Comparisons of solubility and activity predictions with experimental data used and not used in model parameterization are given. Limitations of the model due to data insufficiencies are discussed.