Thermodynamic Properties of Aqueous Sodium Nitrate Solutions Under Superambient Conditions

Use has been made of the Pitzer ion-interaction or virial coefficient approach to estimate the pressure dependence of the osmotic and activity coefficients of aqueous solutions of sodium nitrate (NaNO3) up to 423.15 K and 6.0 mol·kg−1 using published volumetric data on NaNO3(aq). In particular, volumetric Pitzer ion-interaction parameters have been evaluated from a mathematical fit of published apparent molar volume data with the appropriate Pitzer equation. The Pitzer parameters were then fitted as a function of temperature and pressure. These results were then used to calculate the change in the osmotic and activity coefficients in going from the state of an initial pressure p1 to one of a final pressure p2. These pressure dependences have been combined with the osmotic and activity coefficient values of NaNO3(aq) at 0.1 MPa or vapor-saturation pressures (psat) obtained from the model of Archer to yield a comprehensive set of thermodynamic parameters for NaNO3(aq) at temperatures from 293.15 K through 423.15 K, at pressures of (5, 10, 15, 20) MPa, and molalities to 6.0 mol·kg−1.