Solubility in the Na + F + NO3 and Na + PO4 + NO3 Systems in Water and in Sodium Hydroxide Solutions

Solubilities of the Na + F + NO3 and Na + PO4 + NO3 systems in aqueous solution and in sodium hydroxide solutions have been measured at (25 and 50) °C. Natrophosphate, the double salt of sodium fluoride and sodium phosphate, has been identified in the tank waste at the Hanford site (Richland, Washington, USA). The brine in these tanks is often saturated in nitrate. Solubility experiments were undertaken to better understand the chemistry in the Na + F + PO4 + NO3 + OH system. As the initial part of this effort, measurements of solubility in the constituent binary systems, NaF + NaNO3 and Na3PO4 + NaNO3, with and without the presence of sodium hydroxide, were performed and are reported herein. The presence of nitrate in the solution resulted in a decrease in the solubility of either sodium fluoride or trisodium phosphate. The presence of hydroxide in the solution also resulted in decreased solubility for each component.