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CIRC Seminar – Michael Servis
February 19, 2019 @ 4:10 pm - 5:00 pm
The Center for Institutional Research Computing’s February seminar will be given by Michael Servis, from WSU’s Department of Chemistry.
Coffee and light refreshments will be served.
Molecular structure and phase behavior in atomistic simulation of liquid/liquid extraction with applications to the nuclear fuel cycle
Liquid/liquid extraction is the predominant chemical separations technique implemented in the nuclear fuel cycle to recover fissile nuclides from used nuclear fuel. In the industry standard Plutonium Uranium Reduction EXtraction (PUREX) process, a kerosene-based organic phase with an extractant molecule, tributyl phosphate (TBP), is contacted with an aqueous phase containing the used fuel dissolved in nitric acid. The amphiphilic TBP selectively extracts actinides into the organic phase as a charge neutral nitrate salt, e.g., UO2(NO3)2(TBP)2. Under high metal or acid loading into the organic phase, the deleterious phenomenon of third phase formation can occur, wherein the organic phase splits into a solute-rich and solvent-rich phase. This represents a chemical processing complication and, potentially, a criticality risk. This presentation will cover molecular simulation studies of the nanoscale structures which govern the efficiency and phase behavior of these complex molecular solutions. Simulation force fields are optimized to macroscopic thermodynamic properties for extractant/solvent mixtures and quantum potential energy surfaces for extractant/metal solvates. A graph theoretic framework is used to quantify solution phase speciation of extractant/water/acid hydrogen bonded clusters in the absence of extracted metal ions. Then, upon the extraction of U(VI), the role of solvent and extractant molecular structure in the association of UO2(NO3)2(TBP)2 solvates is studied. Percolation theory is applied to interpret the third phase formation phase transition for systems with and without UO2(NO3)2(TBP)2 solvates, identifying a different phase transition mechanism for each case. Lastly, the effect of extractant adsorption at the liquid/liquid interface on the interfacial water hydrogen bonding network is studied to identify the mechanism by which TBP extracts water from the interface into the organic phase.