f-Element Electrochemistry in RTIL Solutions: Electrochemical Separation of Lanthanides and Actinides

Electrochemical methods can be used to effectively separate actinide and lanthanide species from complex mixtures. This is based on the unique electrochemical properties of each specific target species. In studies it has been found that, with the exception of Ce, aqueous solutions provide unsuitable electrochemical windows to effectively evaluate the thermodynamic properties that are useful for chemical separations. Therefore, a more novel approach was examined which eliminated the aqueous solution with a room temperature ionic liquid (RTIL) solution. RTIL solutions do not suffer from the side reactions that are prominent in aqueous environments. In addition, the potential window is much larger for the RTIL solutions. They are a new starting point for the electrochemical separation of individual species from a mixture. The ultimate goal is to fully characterize the oxidation/reduction of f-elements in RTILs to establish the baseline thermodynamic and kinetic data for these systems. The data will be used to critically evaluate the ability to use electrochemical methods for controlled, potential mediated, separation of f-elements by electroplating on electrodes surfaces. Factors that will influence the ability to measure the redox processes in f-elements in RTIL solutions and electroplating on electrode surfaces include the structure, solubility, and stability of the target species in these solutions

The Electrochemical Separation of Curium and Americium: Quaterly Report August-December 2004

This research report outlines the current status and progress associated with the electrochemical separation of Curium and Americium. The following pages outline the progress on our project to date. We have been actively performing research on this project for three months and are currently on schedule in terms of the proposed timelines. The initial focus of the project involved setting up the laboratories for the studies outlined in the grant proposal. The instrumentation needed included an electrochemical work station that will perform the bulk of the electrochemical studies. This instrument will complement the electrochemical instrumentation in Dr. Hatchett’s laboratory and will be housed in Dr. Czerwinski’s laboratory. In addition the required electrodes, electrochemical glassware, side apparatus including nitrogen degassers and the chemicals for the initial studies were obtained

The Electrochemical Separation of Curium and Americium: Quaterly Report January - March, 2006

This research report outlines the current status and progress associated with the electrochemical separation of Curium and Americium. For two and a half years, research has been actively performed on this project, and is currently on schedule for the proposed timelines. Progress: • The electrochemical characterization of Ce and Eu complexed with EDTA, NTA, and Citrate has been completed. • Synthesis of the polymer substrate and the chelating ligand is underway. Approximately 50 grams of disulfide has been produced to produce the chelating thiol group required for the last set of studies. • Gold substrates have been prepared to perform the 2-D surface chelation using the chelating disulfide and thiol. The goal is to determine the potentials required for chelation. • Polymer gold composite systems have been prepared and characterized for use with the chelating ligands

Electrochemical Separation of Curium and Americium

The objective of this project is to use electrochemical techniques to develop a thermodynamic understanding of actinide and lanthanide species in aqueous solution and use this data to effectively separate species with very similar chemical properties. In consultation with a national laboratory collaborators, electrochemical methods and materials will be evaluated and used to exploit the thermodynamic differences between similar chemical species enhancing the ability to selectively target and sequester individual species from mixtures. This project is in its third year and has successfully completed Phases 1 and 2. The following were specific goals for this year: To develop a fundamental understanding of the thermodynamic properties of actinide and lanthanide species such as Cm, Am, Ce, Nd, Eu, and Sm after complex formation. To examine how chelation influences the thermodynamic properties of waste form species. To use systematic studies to distinguish the thermodynamic signatures and ability to shift thermodynamic potentials using chelation to enhance separation properties

f-Element Electrochemistry in Room Temperature Ionic Liquids

This proposal focuses on f-element electrochemistry in room temperature ionic liquids (RTILs). The ultimate goal is to fully characterize the oxidation/reduction of elements in RTILs to establish the baseline thermodynamic and kinetic data for these systems. The data will be used to critically evaluate the ability to use electrochemical methods for controlled, potential mediated, separation off-elements by electroplating on electrodes surfaces. Factors that will influence the ability to measure the redox processes in f-elements in RTIL solutions and electroplating on electrode surfaces include the structure, solubility, and stability of the target species in these solutions. These factors will be addressed using a multidisciplinary research approach with techniques including UV/Vis, and FTIR spectroscopy which will provide structural and stability information. These studies will provide a comprehensive study of the use of RTIL systems in the electrochemical analysis and potential dependent separation of f-elements by electroplating. This research will address the need to demonstrate, by 2015, progress in understanding, modeling and controlling chemical reactivity and energy transfer processes in solutions at electrochemical interfaces using non-aqueous solutions comprised entirely of organic cations and inorganic/organic anions. Electrochemical studies will examine the interfacial electron transfer processes of f-elements and the potential dependent deposition of f-elements at electrode surfaces. These studies will probe the ability to use RTIL systems in the controlled, potential dependent, separation of f-elements species from complex mixtures

Influence of NaBH4 reduction on the hydrogen storage properties of aniline/Pd composite materials

The characterization and chemical synthesis of composites containing aniline and N-Phenylenediamine (NPPD), synthesized with palladium, will be analyzed according to recent studies [1] to confer hydrogen storage capabilities. The palladium metal will be introduced as either PdCl4 2- or PdCl2 2-. The experiments will be carried out under both acidic and non-acidic conditions forming a total of 8 different compounds. Each compound will be reduced with NaBH4 and analyzed using gas chromatography to measure hydrogen storage. Infrared spectroscopy and ultraviolet visible spectroscopy will also be used to gather data concerning each compound

The Electrochemical Separation of Curium and Americium: Quaterly Report April - June, 2005

This research report outlines the current status and progress associated with the electrochemical separation of Curium and Americium. Results • We have completed the electrochemical investigation in of the Ce3+/Ce4+ redox couple and have determined the optimum experimental conditions. • Computer modeling of the cerium using the JChess speciation-modeling program has been completed for the Ce redox couple. Traditional complexing ligands such as EDTA, oxalate, NTA, phosphate, acetate, and sulfate have been purchased and will be used to initiate the complexation and electrochemical characterization. • Electrochemical investigations have continued on the Eu2+/Eu3+ redox system in HClO4 supporting electrolyte at a glassy carbon working electrode. The redox couple has been electrochemically resolved using cyclic voltammetry and square wave voltammetry. The data suggests that the couple is stable with reversible oxidation/reduction occurring. • Complex formation has been initiated and theoretical calculations regarding the stability of species has been used to target the solution conditions required to view the oxidation/reduction processes

The Electrochemical Separation of Curium and Americium: Quaterly Report January - March 2004

This research report outlines the current status and progress associated with the electrochemical separation of Curium and Americium. Data collection and analysis of the Ce3+/Ce4+ redox couple in various supporting electrolytes has continued. All electrolyte systems were investigated at Pt, Au, and Glassy Carbon working electrodes. Analysis of these data was accomplished by performing appropriate background subtractions to reveal net peaks due to Ce redox behavior. Successful identification of the Ce redox couple was achieved with all electrolyte/electrode systems, although a decline in peak resolution was observed with increasing acid concentration. Optimal conditions in this experiment were realized with a 6.0 mM Ce concentration, 0.1 M H2SO4 supporting electrolyte, and scan rate of 0.02 V/s. An investigation into ionic strength is being conducted for the Ce system, using varying concentrations of K2SO4 in place of the H2SO4 supporting electrolyte solutions. The data suggests that acidity is the key variable in the system with higher resolution and lower splitting of the Ce3+/Ce4+ redox couple. Finally, the investigation of the Sm redox couple was initiated by employing the conditions determined as optimal for the Ce experiment. Successful resolution of the Sm redox couple was accomplished using this system. Future work on this species will include further experiments, similar to those conducted for Ce, which will vary the working electrode and supporting electrolyte

Electrochemical Separation of Curium and Americium

The objective of this project is to develop a method for the separation of Am from Cm based on electrochemical techniques. Electrochemical systems that allow the thermodynamics of actinide and lanthanide complexes to be systematically evaluated and tuned will be examined. The influence of complex formation on the ability to selectively isolate a given species electrochemically will be evaluated. Metal-ligand complex formation provides a useful derivation technique to increase solubility in solution environments that favor precipitation. In addition, the thermodynamic properties of a complex relative to the isolated species may be shifted to more suitably measurable electrochemical separation regimes. Electrochemical sorption methods are well suited for use in the separation of similar chemical species where the applied potential provides the thermodynamic selectivity required. Traditional separation techniques will be evaluated using common electrodes such as Hg, Au/Hg film, and glassy carbon. In addition, conductive polymer such as polypyrrole will examined to provide a more novel method of separating and sequestering of actinide and lanthanide chemical species. The polymer composite electrodes will be chemically modified with chelating and the separation of chemical species based on the adsorption/desorption thermodynamics of the polymer relative to the complex or isolate species will be probed. The proposed experiments will provide a comprehensive survey of the effect of complex formation and species on the ability to separate complex mixtures of actinide and lanthanide complexes in aqueous environments using electrochemical methods and modified polymer electrodes. Year one of the project will develop the lab facilities required for the electrochemical experiments. The electrochemical workstation will be acquired and necessary electrodes, reagents, and supplies will be purchased. The year one goals are to prepare and electrochemically evaluate the complexes and species of interest in this study or species that closely resemble more hazardous counterparts. These studies will be important for the future studies of polypyrrole membranes providing the required thermodynamic data concerning the complexes formed and possible separation of complex mixtures

Hydrogen-Induced Embrittlement of Candidate Target Materials for Applications in Spallation-Neutron-Target Systems

Spallation-neutron-sources, such as those under investigation for use in accelerator-driven transmutation systems, generate neutrons through the collision of high-energy protons, or charged hydrogen atoms, with heavy metal targets such as lead. As a result, these systems also tend to deposit a significant amount of hydrogen in the materials of the transmuter target and superstructure. This can result in accelerated corrosion and changes in the properties of the exposed materials. Of particular importance is a phenomenon called hydrogen embrittlement, in which materials lose their ductility (ability to deform under stress) and become brittle (more susceptible to fracture) after reacting with hydrogen. Given the extreme temperature ranges and large quantities of hydrogen expected in the accelerator-driven transmutation systems, these phenomena are of particular importance to the transmutation program. This research program will examine the effects of hydrogen on hydrogen embrittlement, environment-induced stress corrosion cracking (SCC), and other hydrogen induced/ enhanced corrosion phenomena in target materials. The UNLV research group will also examine the effectiveness of various surface and heat treatments in minimizing the impact of these phenomena in candidate materials. It is hoped that establishing a baseline performance of these materials in a hydrogen rich environment (analogous to the expected in-proton-beam environment of the target systems) will pave the way for conducting in-proton-beam radiation experiments and eventually support the materials qualification needed for facility design and operation