Microanalysis (Micro-XRF, Micro-XANES, and Micro-XRD) of a Tertiary Sediment Using Microfocused Synchrotron Radiation

Abstract

Micro-focused synchrotron radiation techniques to investigate actinide elements in geological samples are becoming an increasingly used tool in nuclear waste disposal research. In this article, results using mu-focus techniques are presented from a bore core section of a U-rich tertiary sediment collected from Ruprechtov, Czech Republic, a natural analog to nuclear waste repository scenarios in deep geological formations. Different methods are applied to obtain various, complementary information. Elemental and element chemical state distributions are obtained from micro-XRF measurements, oxidation states of As determined from micro-XANES, and the crystalline structure of selected regions are studied by means of micro-XRD. We find that preparation of the thin section created an As oxidation state artifact; it apparently changed the As valence in some regions of the sample. Results support our previously proposed hypothesis of the mechanism for U-enrichment in the sediment. AsFeS coating on framboid Fe nodules in the sediment reduced mobile groundwater-dissolved U(VI) to less-soluble U(IV), thereby immobilizing the uranium in the sediment.

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

“…Two diffraction methods have been reported, namely X-ray diffraction (XRD) [78][79][80][81] and energy-dispersive X-ray diffraction tomography (EXDT) or alternatively called tomographic energy dispersive diffraction imaging (TEDDI) [82][83][84][85][86], where the former uses monochromatic X-ray while the latter makes use of polychromatic X-ray radiation. Despite the fact that diffraction itself does not give element-specific information, a recent study demonstrated its capability to monitor spatial distribution of specific chemical phases by recording diffraction and fluorescence signals simultaneously, and the distribution and composition of metal oxide species in CoMo/c-Al 2 O 3 catalyst have been elucidated [87].…”

“…A powerful method for investigating elemental composition and distribution is X-ray fluorescence spectroscopy (XRF) [88] and imaging (2D [79][80][81]89] and 3D [90]). Excellent spatial resolutions of 0.5-1 lm range for hard X-rays ([3 keV) and ca.…”

Laboratory-based micro-X-ray fluorescence setup using a von Hamos crystal spectrometer and a focused beam X-ray tube

“…Micro-X-ray fluorescence (μ-XRF) analysis 1 is applied in environmental sciences, 2,3 geological applications, 4,5 cultural heritage studies, 6 archeology, 7 and in the biomedical, 8,9 chemical, 10,11 and forensic 12 domains. Usually the related experiments are realized at advanced research facilities, i.e., third generation synchrotron sources, where the bright, coherent, polarized, energy-tunable, and monochromatic Xray beams can be used for fluorescence, scattering, diffraction, or absorption experiments.…”

Microscale analysis of metal uptake by argillaceous rocks using positive matrix factorization of microscopic X-ray fluorescence elemental maps

“…A recent review emphasizes the relevance of versatile micro-and nanoanalytical techniques for actinide environmental research [12]. Microscopic X-ray fluorescence (µ-XRF) spectroscopy combined with microscopic X-ray diffraction (µ-XRD) is a unique possibility to study these highly heterogeneous rocks [10,13]. The samples and the sorption concentrations must be in the good analytical performance domain of the used techniques.…”

“…Even though µ-XRF performed in air is not capable of detecting major light elements (O, Na, Mg, Al), information on the mineral phases responsible for the uptake of the radionuclide of interest can be derived from the data set if suitable mathematical methods are applied for data treatment. The assumptions derived from µ-XRF can be verified using µ-XRD phase analysis at representative selected positions [10,13]. One possibility is to examine inter-elemental correlations through scatter plots of the X-ray intensities of two selected elements.…”