A Pitzer Interaction Model for the NaNO 3 –NaNO 2 –NaOH–H 2 O System from 0 to 100 °C

The solubility relations and water activities in NaNO 3, NaNO 2, and NaOH solutions are used in many applications, including the management of alkaline high-level nuclear waste. Only limited water activity data is available at temperatures above ambient for NaNO 3 and NaNO 2 aqueous solutions, so water activity was measured by isopiestic methods at 50 and 100 °C in this study. The results are consistent with the limited experimental data previously available. These data are used to parameterize the Pitzer electrolyte solution model for these electrolytes and NaOH in water between 0 and 100 °C. Neutral ion pairs between Na + and NO 3 – as well as Na + and NO 2 – were required in order to fit the data adequately. Ternary Pitzer ion interaction parameters for the interactions between the electrolytes were also required and developed to model solubility in mixtures of the electrolytes. These results provide a strong foundation for modeling the effect of NaNO 2, NaNO 3, and NaOH on the solubility of other key electrolytes of interest to the management of high-level nuclear waste.