Solubility Modeling of the Systems Ni(NO₃)₂–H₂O and Fe(NO₃)₃–Ni(NO₃)₂–H₂O with the Extended Universal Quasichemical (UNIQUAC) Model

Thermodynamic modeling of the binary systems Ni(NO₃)₂–H₂O and Ni(NO₃)₂–H₂O and of the ternary system of Fe(NO₃)₃–Ni(NO₃)₂–H₂O along the 30 °C isotherm are presented. The extended UNIQUAC model was applied for the thermodynamic assessment of the investigated systems, the model parameters were regressed simultaneously using the available databank but with additional experimental data recently published in the open literature. A revision for previously published parameters for the nickel ion, new parameters for the iron(III) nitrate system, and interaction parameters for the Ni²⁺–Fe³⁺ interaction are presented. Based on this set of parameters, the equilibrium constants of hydrates were determined. The model represents the experimental data with good accuracy from the freezing point region to the boiling points of the solutions.