Publications Details

Thermodynamic modeling of liquid-liquid extraction (LLE) for the system TBP-HNO3-UO2(NO3)2-H 2O-diluent

Jove Colon, Carlos F.; Moffat, Harry K.; Rao, Rekha R.

The PUREX process is one of the most widely adopted approaches of industrial-scale liquid-liquid extraction (LLE) methods for the separation and recovery of U and Pu from dissolved used nuclear fuel. This paper documents the application of chemical equilibrium approaches to the modeling of LLE for the PUREX process at 25°C. In this work, we focus on modeling the extraction of HNO3 and UO2(NO3)2 by the non-electrolyte organic liquid phase Tri-n-butyl Phosphate (TBP) plus a diluent (Amsco 125-82). Six chemical reactions representing the equilibria between the concentrated HNO3-UO2(NO3)2 electrolyte and TBP-diluent organic phase is sufficient to accurately generate the extraction isotherms for the extracted components for a wide range of TBP and acid concentrations in the non-electrolyte and electrolyte phases, respectively. The Pitzer approach is used to compute the activity coefficients of the HNO3 electrolyte phase. No activity coefficient model is adopted for TBP organic complexes where these were assigned unity values. Even with this assumption, the predicted isotherms are in very good agreement with the experimental data and such result serves as a preamble to extend this modeling approach to more compositionally complex systems relevant to LLE of radionuclides.