Thermodynamic study of quaternary systems with participation of ammonium and sodium alums and chromium alums

The Pitzer ion-interaction model has been used for thermodynamic simulation of the ternary NaCl-NH4Cl-H2O, NaBr-NH4Br-H2O, Na2SO4-(NH4)2SO4-H2O, NiSO4-Al2(SO4)3-H2O, and CuSO4-Al2(SO4)3-H2O systems at T=298.15 K. The mixing parameters have been chosen on the basis of the compositions of saturated ternary solutions taking into account the unsymmetrical mixing terms Eθ and Eθ′. The sodium-ammonium systems have been simulated simultaneously with a view to preserving a constant value of the binary θNa,NH4 mixing parameter. It was established that the zero values of θM,Me and ψM,Me,SO4 describe the properties of the ternary aqueous mixtures of 2-2 and 3-2 electrolytes with a sufficient accuracy. Important thermodynamic characteristics (thermodynamic solubility product, standard molar Gibbs energy of formation) of the solid phases (simple and double salts) crystallizing in the systems under consideration are determined. The calculated thermodynamic functions have been used for a thermodynamic study of the quaternary Na2SO4-(NH4)2SO4-Cr2(SO4)3-H2O, and Na2SO4-NiSO4-Al2(SO4)3-H2O systems. Good agreement between experimentally determined and calculated solubilities has been found.