Thermodynamics of formation of ammonium, sodium and potassium alums and chromium alums

The Pitzer ion-interaction model has been used for thermodynamic simulation of the binary Cr2(SO4)3---H2O, KCr(SO4)2---H2O, and ternary (NH4)2SO4---Al2(SO4)3---H2O, Na2SO4---Al2(SO4)3---H2O, K2SO4---Al2(SO4)3---H2O, (NH4)2SO4---Cr2(SO4)3---H2O, Na2SO4---Cr2(SO4)3---H2O, and K2SO4---Cr2(SO4)3---H2O systems at T=298.15 K. The optimum values of the binary parameters of ionic interactions for chromium solutions have been calculated using osmotic data for unsaturated binary solutions. The mixing parameters have been chosen on the basis of the compositions of saturated ternary solutions and data on the binary solubility of the alums and chromium alums in water. Good agreement between experimentally determined and calculated solubilities has been found. 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.