Title  Fundamental Chemistry of U and Pu in the TBP-Dodecane-Nitric Acid System	Researchers K. Czerwinski , B. Bennett Collaborators George Vandegrift, Argonne National Laboratory Thomas Albrecht-Schmitt, Auburn University
Background  The extraction of tetravalent Pu and hexavalent uranyl in nitric acid solution by tributylphosphate (TBP), based on the formation of organic phase neutral complexes such as Pu(NO3)4•2TBP and UO2(NO3)2•2TBP, has been the foundation of actinide purification for a number of decades. Upon reduction of Pu(IV), Pu(III) is back extracted into an aqueous phase.  However, the data needed for detailed modeling of Pu extraction is not available for all conditions of concern to the Advanced Fuel Cycle Research and Development program.  This proposal was developed with Dr. George Vandegrift of Argonne National Laboratory to obtain the necessary data for Pu extraction modeling.  Understanding the role of nitrate in actinide speciation is important for determining the necessary data for extraction modeling.  Difficulties in modeling Pu extraction under some nitrate conditions may be due to ill-defined constants of formation for the dinitrate and trinitrate species of U and Pu.  The influence of pertechnetate on the speciation of U and Pu in the TBP-dodecane-nitric acid system is still poorly understood.  Since pertechnetate is capable of reoxidizing reduced Pu species, it may have a profound impact on the extraction of Pu.  In the uranium extraction process, acetohydroxamic acid (AHA) is expected to be used.  AHA can complex and reduce Pu, decreasing its extraction into the organic phase; the effect of uranyl-AHA on U extraction has not been quantified.  AHA can reduce pertechnetate as well, initiating a redox cycle with both U and Pu.  In a solvent extraction system using AHA, it is necessary to determine the complexation kinetics, redox reactions, and thermodynamics of AHA interactions with these elements. Crystal Structure of Uranyl-AHA The measured concentrations in the organic and aqueous phases of 10 mM uranyl, 100 mM AHA extracted with TBP.   The measured concentrations of uranyl, nitrate, and acid in the organic phase extracted from 0.02 M U, 1.0 M HNO3, and varied initial nitrate.	Research Objectives and Methods The research objective is to experimentally evaluate the fundamental speciation of Pu and U in the TBP-dodecane-nitric acid-AHA system and the effect of pertechnetate, specifically:  · To determine the influence of nitrate on the speciation of U and Pu in the TBP-dodecane-nitric acid system.  The aqueous and organic speciation of U and Pu are examined as a function of the nitric acid concentration, nitrate concentration, actinide ion concentration, temperature, and time. · To determine the speciation of U and Pu with AHA in the presence and absence of TBP-dodecane organic phase.  The aqueous and organic speciation of U and Pu are evaluated as a function of AHA concentration, metal ion concentration, metal ion redox state, pH, and temperature. · To determine the interaction of AHA with pertechnetate, and the effect on the interaction of AHA and pertechnetate with U and Pu. · To incorporate thermodynamic and kinetic data into existing modeling codes.  All of the initial experiments were performed with uranyl, UO22+. The results obtained from U are the basis for further experiments with Pu. In extraction experiments, the aqueous and organic phases are contacted in equal volumes from 0.3 to 5.0 mL.
Students  Amber Wright G   Wendy Pemberton G   Jeanette Daniels G  Jeremy Maute U Trent Ohman U	Department Mechanical Engineering
Final Report	Annual Report
Proposal 05/07/04	Quarterly Reports  10/01/04-12/31/04  01/01/05-03/31/05  04/01/05-06/30/05   01/01/06-03/31/06