Phase Equilibria and Thermodynamic Properties of Phases in the H2O–Gd(NO3)3 System

Solid–liquid equilibria in the system H 2 O–Gd(NO 3 ) 3 were measured from –20 to 70°C using the isothermal saturation method. The Pitzer–Simonson–Clegg thermodynamic model was implemented to obtain the temperature dependence of Gd(NO 3 ) 3 ⋅6H 2 O solubility constant, to calculate salt solubility and to construct a phase diagram of the system from eutectic point to hydrate melting. Thermochemical properties of gadolinium nitrate aqueous solutions, such as dilution enthalpies and heat capacities, were assessed also. The model has shown to be reliable for phase equilibria calculation from –35 to 90°C and from 0 up to ~15 mol % of salt as well as the thermodynamic properties of Gd(NO 3 ) 3 aqueous solutions at room temperature and around it.