Solubility Studies on the Na - F - PO4 system in Sodium Nitrate and in Sodium Hydroxide Solutions

The thesis investigates the solubility of various sodium salts present in the waste tanks at the Hanford nuclear site. The experiments were conducted in different concentrations of caustic and in water at 25°C and 50°C. The results obtained from these studies will be used to improve existing databases for the Environmental Simulation Program (ESP, available from OLI Systems, Inc.), thereby increasing its accuracy in predicting waste behavior under high ionic strength conditions. Experiments were performed on the following systems: 1) NaF - NaNO3 - NaOH, 2) Na3PO4 - NaNO3 - NaOH, 3) NaF - Na3PO4 - 1m NaNO3 - NaOH, and 4) NaF - Na3PO4 - 3m NaNO3 - NaOH. The results obtained from these experiments were then compared to the ESP predictions and the available literature data. Comparision of the experimental work with the available literature data revealed that the data obtained from this study is in agreement with previous studies for the NaF - NaOH, NaNO3 - NaOH, and Na3PO4 - NaOH systems. This is the first report on solubilities for the Na - F - PO4 - OH system with added nitrate. The presence of sodium hydroxide was found to lower the solubility of natrophosphate, Na7F(PO4)2.19H2O. The solubility of this double salt was also significantly lowered in the presence of sodium nitrate. Error analysis of the experimental data was performed and indicated that the experimental molalities were accurate to within an average of + 0.02