Speaker
Yulia Podkovyrina
(Southern Federal University)
Description
Deep understanding of mobilization/immobilization mechanisms of uranium in the environment is essential for safety assessment of a long-term nuclear waste repository. For example the soluble in groundwater U(VI) can be immobilized by sorption or incorporation into minerals [1]. Iron oxide nanoparticles are abundant in the environment and play a major role in sorption and redox behavior of U. Magnetite (Fe3O4) is a ferrous bearing oxide and a corrosion product of steel used in storage containers of nuclear waste.
High-energy resolution X-ray absorption near edge structure (HR-XANES) spectroscopy at the actinide (An) L3 and M4,5 edges is currently developing technique providing new insights into the An electronic and coordination structure [2,3]. We present the U L3/M4 HR-XANES experimental spectra of U sorbed on magnetite or maghemite (U-magnetite, U-maghemite) nanoparticles and U M4 HR-XANES spectra of UO3, meta-autunite (Ca(UO2)2PO4)210-12•(H2O)) and torbernite (Cu(UO2)2(PO4)2•12(H2O)). The HR-XANES spectra are analyzed on the basis of theoretical simulations to investigate local coordination structure of U in the magnetite/maghemite nanoparticles. Theoretical spectra are calculated by applying a self-consistent field (SCF) full multiple scattering (FMS) method implemented in the FEFF9.6 code [4]. Phase shifts of the photoelectron are calculated in the framework of self-consistent crystal muffin-tin (MT) potential scheme with 15% overlapping MT spheres. Best agreement of energy positions and intensities of spectral features between theoretical and experimental spectra is achieved for spectra calculated with the Hedin-Lundquist potential with non-screened core-hole (final state rule). FMS calculations of U L3-edge HR-XANES spectra of the U-magnetite and U-maghemite nanoparticles is performed for two types of substitution, i.e., uranium replaces iron in octahedral or tetrahedral sites. Comparison of experimental and theoretical spectra suggest that U is incorporated in octahedral magnetite sites for the specific experimental conditions. The FEFF9.6 program is found to be an adequate tool for analysis of U L3 –edge and M4,5 edges HR-XANES of U containing compounds.
Acknowledgments
This work is supported by the German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DADD)(Project P-2014a-1).
References
[1] Riley, R. G.; Zachara, J. M. Chemical Contaminants on DOE Lands and Selection of Contaminant Mixtures for Subsurface Science Research; U.S. Department of Energy,Office of Energy Research:Washington, DC, 1992.
[2] Vitova T et al. 2010 PRB 82 235118
[3] Kvashnina K O, Butorin S M and Glatzel P 2011 J. Anal. At. Spectrom. 26 1265
[4] JRehr J J, Kas J J, Prange M P, Sorini A P, Takimoto Y and Vila F 2009 C. R. Physique 10 548 59
Primary author
Yulia Podkovyrina
(Southern Federal University)
Co-authors
Prof.
Alexander Soldatov
(Southern Federal University)
Mr
Ivan Pidchenko
(Institute for Nuclear Waste Disposal)
Dr
Kristina Kvashnina
(European Synchrotron Radiation Facility)
Mr
Tim Pruessmann
(Karlruhe Institute of Technology)
Dr
Tonya Vitova
(Karlsruhe Institute of Technology)
