FY-2011 Status Report for Thermodynamics and Kinetics of Advanced Separations Systems

Abstract

This report presents a summary of the work performed in the area of thermodynamics and kinetics of advanced separations systems under the Fuel Cycle Research and Development (FCR&D) program during FY 2011 at the INL. On the thermodynamic front, investigations of liquid-liquid distribution of lanthanides at TALSPEAK-related conditions continued in FY11. It has been determined that a classical ion-exchanging phase transfer mechanism, where three HDEHP dimers solvate the metal ion in the organic phase, dominates metal extraction for systems that contain up to 0.1 M free lactate in solution. The correct graphical interpretation of the observed data in those regions relied on incorporating corrections for non-ideal behavior of HDEHP dimer in aliphatic diluents as well as sodium extraction equilibria. When aqueous conditions enter the complex regions of high lactate concentrations, slope analysis is no longer possible. When normalized metal distribution ratios were studied along the increasing concentration of free lactate, a slope of -1 was apparent. Such dependency either indicates aqueous complexing competition from lactate, or, a more likely scenario, a participation of lactate in the extracted metal complex. This finding agrees with our initial assessment of postulated changes in the extraction mechanism as a source of the lactate-mediated loss of extraction efficiency. The observed shape in the lanthanide distribution curve in our studies of TALSPEAK systems was the same for solutions containing no lactate or 2.3 M lactate. As such we may conclude that the mechanism of phase transfer is not altered dramatically and remains similarly sensitive to effective charge density of the metal ion. In addition to these thermodynamics studies, this report also summarizes the first calorimetric determination of heat of extraction of 248Cm in a bi-phasic system. The heat of extraction measured by isothermal titration calorimetry is compared to that determined using van't Hoff calculations. Further investigations on the kinetics of extraction in TALSPEAK with macro quantities of lanthanides present in the initial aqueous phase composition have been performed. These results have been summarized and compared to previous work performed for FCR&D. In addition, the effects of HDEHP concentration in the organic phase on europium extraction have been studied.