Phase Equilibrium Studies of Savannah River Tanks and Feed Streams for the Salt Waste Processing Facility

A chemical equilibrium model is developed and used to evaluate supersaturation of tanks and proposed feed streams to the Salt Waste Processing Facility. The model uses Pitzer's model for activity coefficients and is validated by comparison with a variety of thermodynamic data. The model assesses the supersaturation of 13 tanks at the Savannah River Site (SRS), indicating that small amounts of gibbsite and or aluminosilicate may form. The model is also used to evaluate proposed feed streams to the Salt Waste Processing Facility for 13 years of operation. Results indicate that dilutions using 3-4 M NaOH (about 0.3-0.4 L caustic per kg feed solution) should avoid precipitation and reduce the Na{sup +} ion concentration to 5.6 M.