Determination of fictive binary data for uranium(IV) nitrate: preliminary results

Abstract

The concept of simple solutions is applied to a quaternary system of U(NO3)4, HNO3, N2H5NO3 and H2O in order to determine fictive binary data for U(NO3)4. Hydrazinium nitrate solutions were used at low concentrations relative to the nitric acid and uranium(IV) nitrate concentrations, allowing this system to be considered as a ternary (U(NO3)4, HNO3, H2O) system. The simple behavior of the system allowed fictive binary data (osmotic coefficient and density) to be calculated from water activity and density measurements. The results were then used to calculate the coefficients related to Pitzer´s model and to specific interaction theory, used to model the deviation of the concentrated solution from ideality. The results were also used to calculate the activity coefficient of uranium(IV) nitrate in the presence of uranyl(VI) nitrate and nitric acid. The binary data obtained for uranium(IV) nitrate were found to differ significantly from the data for plutonium(IV) nitrate.