Research
All members of the Nash group are actively involved in their own research projects. While all the projects revolve around lanthanide/ actinide separation techniques, the chemistry involved is still quite diverse. A brief summary of many of the ongoing projects are listed below.
Mikael Nilsson
As a Ph.D. student my research focused on liquid extraction and separation of long- and short-lived elements in spent nuclear fuel. The future goal for these EU-projects was to demonstrate a process for separating elements in spent nuclear fuel with the purpose of transmuting the long-lived isotopes into short-lived or stable isotopes. My areas of research as a post-doc still deal with chemical separation of elements in spent nuclear fuel; this time directed to the US scope of the fuel cycle, AFCI (Advanced Fuel Cycle Initiative). The research covers both basic understanding of the chemical processes that govern this separation, e.g. thermodynamics, kinetics, complexation and solution chemistry, as well as process chemistry, e.g. extraction profiles for different separation systems.
Peter Zalupski
The development of efficient liquid-liquid separation schemes for the treatment of spent nuclear fuel has relied heavily on studies of the thermochemistry of metal extraction. My research focuses on the development of a calorimetric methodology for the quantitative characterization of thermodynamic features for an array of solvent extraction processes. Our method for calorimetric investigation of heats of metal distribution in two-phase systems offers the flexibility of systematic thermodynamic dependency studies, where metal extraction can be studied in detail. Such thermochemical inquiry allows us to identify the driving force of a separation process, building a solid foundation for improvements and the development of more challenging separation schemes.
Mark Ogden
Owing to the chemical similarities of trivalent Ln and An, the mutual separation of the two groups is one of the most challenging tasks in separation science. Small differences in their solution chemistry must be exploited to acheive separation. The prior literature teaches us that donor atoms softer than oxygen, e.g. N, and S, are most effective for accomplishing this separation. It has also been shown that more sterically hindered ligands, which focus their donor groups in a favourable geometry, have an increased overall binding affinity. My current work has involved the design and synthesis of a series of tetradentate amine ligands containing both “soft” and “hard” nitrogen donors. All the ligands contain the 2-methylpyridyl moiety with increasing steric rigidity of the amine or imine back bone. This results in an increased steric orientation of the pyridyl and amine/imine moieties and eventual focusing of these moieties into an equatorial plane.
Thomas Shehee
The key to managing nuclear waste is the removal of high specific activity isotopes to reduce the radiation levels of high level waste. Dissolved spent nuclear fuel mixtures include U, Pu, trivalent actinides and lanthanides, and other fission products. Typical separation techniques such as PUREX and TRUEX cannot separate trivalent Am from the trivalent lanthanides. It has been suggested that carbonate complexation may significantly increase the solubility of Am(VI). This hypothesis is supported by studies that have shown the uranyl triscarbonate ion UO2(CO3)3-4 is unusually stable in carbonate media. One aspect of my project deals with developing an approach to the separation of Am from Cm and the lanthanides using a carbonate media. Am(III/VI) oxidation can be performed followed by the addition of carbonate to selectively precipitate Cm and lanthanides from Am.
Maria Kriz
My research project involves trying to understand the role of solvation effects in complexes and how solvation can impact the efficiency of analytical separations of lanthanides and actinides. I am studying the ligand alpha-hydroxyisobutyric acid in a variable water-dioxane media. This will help to determine the thermodynamic parameters ΔH, ΔG, and ΔS of the system. In addition the metal-complexation reactions are being looked at using calorimetry and potentiometry. I am also using spectroscopic methods to study hydration numbers and reaction dynamics of the system.
Melissa Ensor
Novel separation techniques are of interest in the separation of lanthanides and actinides due to the potential stabilization of unusual oxidation states, such as Am(VI). One such novel separation technique is cloud point extraction (CPE). CPE utilizes surfactants in an aqueous system to selectively extract metal-ligand complexes into a surfactant rich phase (SRP). This method has been widely applied to transition metals but only limitedly to the f-elements. In addition little has been reported in the literature about the mechanism of extraction or the physical properties of the SRP. In my research I am probing the system using spectroscopic and radiometric techniques to elucidate more about the structure and mechanism of CPE. An increased understanding of the fundamental science of the system will allow us to better exploit the system for separations.
Jenifer Shafer
The Department of Energy's Hanford Site, located in south central Washington, was the first facility to produce weapons grade Pu for use in nuclear weapons. The various separations processes employed at Hanford Site during 60 years of Pu production resulted in the creation of ~2x105 m3 of highly radioactive waste, stored in 177 underground waste tanks. During the remediation process, a significant decrease in radioactive waste volume could be acheived if the large volumes of Al(NO3)3 and CrO42- were removed through acidic treatments. Radioactive species, however, could be mobilized into the aluminum and chromium waste stream. The possibility of this radioactive migration necessitates the examination of extraction of europium, uranium and neptunium in varied Al(NO3)3 and acid conditions.
Travis Grimes
As an introduction to my scientific career, I am investigating the specific role of lactic acid in the TALSPEAK process. TALSPEAK, or Trivalent Actinide Lanthanide Separation by Phosphorous Extractants and Aqueous Komplexants, is an important solvent extraction process used for separating trivalent lanthanides from trivalent actinides in spent nuclear fuel. The TALSPEAK process is a proven process; however, the exact role of lactic acid, other than acting as a buffer, is not quite understood. I am trying to determine the complexation of all the different species present, namely the metal/lactate/extractant complex, which will allow eventual modeling of the system.
Derek Brigham
My research has varied from solvent extraction to the kinetics of complexation between vanadium pentoxide and peroxide using stopped flow techniques. My focus has now moved to the chemistry of phosphonates and phosphonic acids and their potential use as chelating agents.
John Freiderich
My research encompasses a new approach to the separation of actinides from spent nuclear fuel. Traditionally solvent extraction has been used for separation of lanthanides and actinides. This research proposes to contact the organic phase from a solvent extraction process with an ionic liquid (IL) phase post-extraction. The metal species would then be extracted into the IL phase. Once accomplished these metals in the IL phase will be oxidized with the goal of extracting different charged species from the IL. This may be an effective measure of separation as ionic liquids harness a large electrochemical window through which different chemistry can be conducted.
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