Thermodynamic representation of aqueous sodium nitrate and nitric acid solution with electrolyte NRTL model

Abstract

Nitric acid solution has been widely used in nuclear waste treatment processes. To support heat and mass balance calculations and process simulation, a comprehensive thermodynamic model is developed for sodium nitrate–water binary, nitric acid–water binary, and nitric-acid–sodium nitrate–water ternary systems. Based on symmetric electrolyte NRTL (eNRTL) activity coefficient model, the present work takes into account complete dissociation of sodium nitrate and partial dissociation of nitric acid in aqueous solution. With up to three temperature coefficients for each eNRTL binary interaction parameter, the model provides an accurate and thermodynamically consistent representation for phase equilibrium properties such as vapor pressure, boiling point, dew point and salt solubility, calorimetric properties such as enthalpy and heat capacity, and speciation properties. The model is validated with data covering temperature up to 473.15K and sodium nitrate concentration up to saturation for the sodium nitrate–water binary system, temperature up to 379.15K and nitric acid concentration up to pure acid for the nitric acid–water binary system, and sodium nitrate concentration up to 0.21 mole fraction and nitric acid concentration up to 0.3 mole fraction for the nitric acid–sodium nitrate–water ternary system.