Probing Covalency in the UO3 Polymorphs by U M4 edge HR- XANES

Local atomic and electronic structure investigations of uranium trioxide (UO3) crystalline phases performed by the U M4 edge HR-XANES technique is presented. The experimental U M4 edge HR-XANES spectra of α-UO3, β-UO3 and γ-UO3 polymorphic phases are compared with spectra of uranate (CaU2O7) and uranyl (UO3•1-2(H2O)) compounds. We describe a finger print approach valuable for characterization of variations of U-O axial bond lengths. Theoretical calculations of spectra using full-multiple-scattering theory (FEFF9.6 code) are performed. We have tested and selected input parameters, which provide best agreement between experimental and calculated spectra

U redox state and speciation of U in contact with magnetite nanoparticles : High resolution XANES, EXAFS, XPS and TEM study

Long-term storage of high-level radioactive waste is associated with potential radioecological hazards. One chemical element of high interest is uranium (U), which can mainly exists as a mobile U(VI) (oxidizing conditions) and sparingly soluble U(IV) (reducing conditions) species. It is expected that the main inorganic reducing agent for U(VI) in the environment are ferrous species in magnetite, formed on the steel canisters surface as an intermediate iron (Fe) corrosion product [1]. Results obtained from laboratory experiments for the interaction of U(VI) with magnetite nanoparticles point to partial reduction of U(VI) [2] or the formation of ~3 nm uranium dioxide (UO₂) particles on the surface layer [3]. The evidence for U(VI) reduction to intermediate U(V) state was found with no direct evidence of U(IV), which is in contradiction with thermodynamic calculations [4]. Continuous interaction and related phase dissolution/recrystallization processes can also lead to U redox changes and structural U incorporation into Fe oxides, resulting in U immobilization [5]. U redox state and speciation analyses are still very challenging due to simultaneous formation of several different species in such mineral systems. New advanced spectroscopic methods for characterization of such systems will provide more precise results from speciation studies. The main goal of our investigation is to assess the U M4 edge high energy resolution X-ray absorption near edge structure (HR-XANES) spectroscopy technique for detection of U(V) possibly co-existing with U(IV) and U(VI) under reducing conditions on/in Fe containing minerals. The U M4 edge HR-XANES has an advantage compared to the conventional U L3 edge XANES, as the measured spectra are less dominated by corehole lifetime broadening effects and therefore have narrower spectral features [6-8]. This technique facilitates the detection of minor contribution of one oxidation state in mixtures. We have investigated the U redox states and speciation in a set of samples where U coprecipitated with magnetite nanoparticles (~ 20 nm) with U concentrations varying in the 1000-10000 ppm range (1000, 3000, 6000 and 10000 ppm). In addition to U M4 edge HR-XANES, U L3 edge extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques have been applied. The studied system models the interaction of U(VI) with magnetite in aqueous solution, important for the understanding of the retarding effect of Fe corrosion products on U in the context of deep geological spent nuclear fuel disposal. These spectroscopic results can be compared with thermodynamic calculations and geochemical models describing this interaction. After 10 days U interaction with magnetite U M4 edge HR-XANES results indicate the formation of U(IV), U(V) and U(VI) mixtures in varying ratios, depending on the initial U loading. Going from 10000 to 3000 ppm, the U(VI) content decreases continuously and is no longer found in the 1000 ppm sample. At the same time the U(IV) and U(V) fractions increase. U(V) is stabilized as the main U redox state in the 1000 ppm sample along with a smaller U(IV) contribution. After 20 days of contact time XPS data show the predominance of U(IV) and U(V) species in the 6000 ppm sample. However, mostly U(V) and some U(IV) is found for the 1000 ppm sample. For all samples aged for 240 days U L3 XANES and EXAFS strongly suggest the formation of a UO₂ phase, UO₂ is the dominating species in the 10000 ppm sample with U-O bond distance 2.33. Å as determined by EXAFS. UO₂ crystalline clusters with about 5 nm size formed on the surface of the magnetite nanoparticles are also found by TEM in the 10000 and 3000 ppm samples. The major and minor contributions of U(V) and U(IV), respectively, for the 1000 ppm sample after 240 days confirm the assumption that the U redox kinetics has completed within less than 10 days at this U concentration. EXAFS analyses reveal U(V)-Fe interaction in the second U coordination sphere, which substantially increases from the 10000 to 1000 ppm sample and is the dominating species in the 1000 ppm sample

Epidemiological Significance of Hantavirus Infection in Crimea

Objective of this work was to determine epidemiological significance of Hantaviruses, circulating in Crimea, on the basis of retrospective data and taking into account the results obtained over the monitoring period of 2015–2018.Materials and methods. The study of small mammals and blood sera of donors was carried using enzyme-linked immunosorbent assay.Results and discussion. Held in 1985–1989 studies of hemorrhagic fever with renal syndrome (HFRS) suggested that Hantaviruses, circulating among the voles of the genus Microtus in the territory of Crimea, do not have etiological significance in the structure of HFRS incidence. A 2008 study found the circulation of Hantaviruses of the Tula serotype among Microtus arvalis (obscurus). Studies on the natural focality of Hantavirus infection in Crimea during 2015–2018 showed circulation of Hantaviruses among small mammals: Microtus socialis, Mus musculus, Sylvaemus witherbyi, Crocidura suaveolens, which are not the main reservoirs of pathogenic Hantaviruses. Also, seropositive to hantavirus donors were detected – 0.4 %. Local cases of HFRS infection for the entire observation period were not registered. To confirm the positive findings and determine the epidemiological significance of circulating pathogens, samples with positive for Hantaviruses findings were sent to the reference center for HFRS in 2017. The results of the investigation did not confirm the presence of antibodies to human pathogenic Hantaviruses in the blood sera of donors; in the biological material from mouse-like rodents, the antigen of pathogenic for humans serotypes of Hantavirus was not detected. Thus, in the natural foci of Crimea in 2015–2018, the circulation of Hantaviruses which do not belong to pathogenic for humans serotypes of Hantavirus Puumala, Hantaan, Dobrava was registered. Detection of seropositive donors testifies to natural immunization of the population through circulation of Hantaviruses that are non-pathogenic for humans or Hantaviruses of other serotypes

Aqueous U(VI) interaction with magnetic nanoparticles in a mixed flow reactor system: HR-XANES study

The redox variations and changes in local atomic environment of uranium (U) interacted with the magnetite nanoparticles were studied in a proof of principle experiment by the U L3 and M4 edges high energy resolution X-ray absorption near edge structure (HR-XANES) technique. We designed and applied a mixed flow reactor (MFR) set-up to maintain dynamic flow conditions during U-magnetite interactions. Formation of hydrolyzed, bi- and poly-nuclear U species were excluded by slow continuous injection of U(VI) (10-6 M) and pH control integrated in the MFR set-up. The applied U HR-XANES technique is more sensitive to minor changes in the U redox states and bonding compared to the conventional XANES method. Major U(VI) contribution in uranyl type of bonding is found in the magnetite nanoparticles after three days operation time of the MFR. Indications for shortening of the U-Oaxial bond length for the magnetite compared to the maghemite system are present too

A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany

Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1–2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite–metatorbernite (Cu(UO$_{2}$)$_{2}$(AsO$_{4}$)$_{2-x}$(PO$_{4}$)$_{x}$·8H$_{2}$O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO$_{2}$)$_{2}$(SiO$_{3}$OH)$_{2}$·6H$_{2}$O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO$_{2}$)$_{2}$(PO$_{4}$)$_{2}$·8H$_{2}$O) were identified. The Cu(UO$_{2}$)$_{2}$(AsO$_{4}$)$_{2-x}$(PO$_{4}$)$_{x}$·8H$_{2}$O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed