Modeling of Liquid-Liquid Extraction (LLE) Equilibria Using Gibbs Energy Minimization (GEM) for the System TBP–HNO₃–UO₂–H₂O–Diluent

Abstract

Liquid-liquid extraction (LLE) is a widely used separation method for an extensive range of metals including actinides. The Gibbs energy minimization (GEM) method is used to compute the complex chemical equilibria for the LLE system HNO₃–H₂O–UO₂(NO₃)₂–TBP plus diluent at 25°C. The nonelectrolyte phase is treated as an ideal mixture defined by eight tri-n-butyl phosphate (TBP) complexes plus the inert diluent. The Pitzer method is used to capture nonidealities in the concentrated electrolyte phase. The generated extraction isotherms are in very good agreement with reported experimental data for various TBP loadings and electrolyte concentrations demonstrating the adequacy of this approach to analyze complex multiphase multicomponent systems. The model is robust and yet flexible allowing for expansion to other LLE systems and coupling with computational tools for parameter analysis and optimization.

Keywords:

• Gibbs Energy Minimization (GEM)
• Liquid-Liquid Extraction (LLE)
• Chemical Equilibria
• Electrolyte
• Organic Liquid

ACKNOWLEDGMENTS

This research is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.