Thermodynamics of multicomponent, miscible, ionic solutions. 2. Mixtures including unsymmetrical electrolytes

Model equations for the excess Gibbs energy and solvent and solute activity coefficients (given previously for symmetrical salt systems) are here developed for mixtures containing an indefinite number of ions of arbitrary charge, over the entire concentration range. The equations are expressed on a mole fraction basis and comprise a Debye-Hückel term extended to include the effects of unsymmetrical mixing, and a Margules expansion carried out to the four suffix level. The model is tested using activity coefficient and salt solubility data for the systems H-(Al,Mg,Ca,Sr)-Cl-H₂O, H-(La,Ca)-NO₃-H₂O, Na-Mg-Cl-SO₄-H₂O, Mg-Ca-K-Cl-HA and Na-K-Mg-SO₄-H₂O at 298.15 K. Thermodynamic properties of quaternary aqueous solutions are predicted using only parameters determined from binary and ternary mixtures. Salt solubilities in both systems involving HNO₃ are satisfactorily represented from aqueous salt solution to pure liquid HNO₃. © 1992 American Chemical Society.