(182b) Comprehensive Thermodynamic Model for Aqueous Nitric Acid and Sodium Nitrate Solution with Electrolyte NRTL Equation

Comprehensive Thermodynamic Model for Aqueous Nitric Acid and Sodium
Nitrate Solution with Electrolyte NRTL Model

Maximilian B. Gorensek ^a

Daniel P. Lambert ^a

Meng Wang ^b

Chau-Chyun Chen ^b

^aSavannah River National
Laboratory, Aiken, SC 29808

^bTexas Tech University,
Lubbock, TX 79409

Abstract

Nitric acid is widely used as a
solvent in reprocessing of spent nuclear fuel. It is typically neutralized with
sodium hydroxide, leading to significant amounts of sodium nitrate in nuclear
wastes. To support heat and mass balance calculations and process simulation
for nuclear waste treatment, a comprehensive thermodynamic model is developed
for the nitric-acid-sodium nitrate-water ternary system and its subsystems.
Based on the 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 a maximum of
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 such as molecular nitric acid content. The
model is validated with data covering temperatures up to 379.15 K and nitric
acid concentrations up to pure acid for the nitric acid-water binary, temperatures
up to 473.15 K and sodium nitrate concentrations up to saturation for the
sodium nitrate-water binary, and sodium nitrate concentrations up to 0.21 mole
fraction and nitric acid concentrations up to 0.3 mole fraction for the nitric
acid-sodium nitrate-water ternary system. The model is being extended to cover
additional ionic and organic species present in liquid waste at the Savannah
River Site.