Confocal Micrometer-Scale X-ray Fluorescence and X-ray Absorption Fine Structure Studies of Uranium Speciation in a Tertiary Sediment from a Waste Disposal Natural Analogue Site

Denecke, Melissa A.; Janssens, Koen; Proost, K.; Rothe, J.; Noseck, Ulrich

doi:10.1021/es048644k

Cited by 53 publications

(25 citation statements)

References 17 publications

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“…Further, secondary uranium mineral phases of U(IV) predominantly, were identified: uraninite (UO 2 ), ningyoite (U, Ca, Ce) 2 (PO 4 ) 2 .1-2H 2 O, tristamite (Ca, U, Fe)(PO 4 , SO 4 ).2H 2 O. According to µ-XRF maps of element distribution, U seems to be accumulated close to Fe nodules where it is associated with As [6]. Content of U in these phases is high, forming major part of U-mineralisation.…”

Section: Uranium Mineral Formsmentioning

confidence: 99%

“…Mineral phases were studied either using classical methods (XRF, microprobe) and modern microscale surface methods, i.e., micrometer scale X-ray fluorescence and X-ray absorption (µ-XRF and µ-XAFS) [6]. Firstly, detrital immobile uranium phases were found, originated probably from granite source (monazite, rhabdophane, xenotime, zircon).…”

Section: Uranium Mineral Formsmentioning

confidence: 99%

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Geochemical study of uranium mobility in tertiary argillaceous system at ruprechtov site, Czech Republic

et al. 2006

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The natural analogue study at the Ruprechtov site is aimed to investigate and understand the behaviour of natural radioelements in plastic clay formation. Uranium is present predominantly in U(+IV) form, either in secondary uranium minerals (uraninite, ningyoite) or in detrital immobile phases (monazite, rhabdophane, xenotime, zircon) and in hardly characterisable non-crystalline forms as well. Process of uranium accumulation probably proceeded via reduction of U(VI) and U(IV) precipitation with involvement of As. Sorption also played important role in U accumulation formation. The sequential extraction experiments were performed in order to specify phases causing uranium retention and accumulation. The isotopic exchange tests with 233 U were used to determine the amount of exchangeable uranium. The contradictions in the extraction schema used for the Ruprechtov sediment samples were found. The results prompt careful approach and potential sequential schema modification.

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Section: Uranium Mineral Formsmentioning

confidence: 99%

Section: Uranium Mineral Formsmentioning

confidence: 99%

Geochemical study of uranium mobility in tertiary argillaceous system at ruprechtov site, Czech Republic

et al. 2006

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“…For this reason it is important to identify, which mineral phases are responsible for the UO 2 2+ uptake on the microscale, complementing the wet chemistry studies. The spatial distribution of uranium was successfully studied on thin sections using synchrotron-radiation microbeam X-ray fluorescence (micro-XRF) in investigating rocks from a natural analogue site for radioactive waste disposal (Denecke et al 2005) and for cementitious materials after diffusion experiments (Wieland et al 2010). Although information concerning spatial heterogeneity in uptake mechanism would be essential, studies involving petrographic thin sections after sorption experiments are very limited and dealing only with other elements such as Np (e.g.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of uranium uptake of Boda Claystone Formation as the candidate host rock of high level radioactive waste repository in Hungary

et al. 2014

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In Hungary two geological sites of the Boda Claystone Formation (BCF) located in the W-Mecsek Mountains (South Hungary) have been selected for the study of potential host rocks for high level radioactive waste (HLW), Gorica (G) Block and W-Mecsek Anticline (WMA) Block. The aim of the study was to obtain information on the uranium uptake characteristics of both sites. Our results revealed that in the sample, taken from WMA Block, where dolomites have ankerite rims and U-bearing rings, newly formed FeOOH precipitations were observed, which partly replaced the ankerite at near neutral pH (6.8). UO 2 2+ ions were adsorbed easily due to the enhanced specific surface area and high adsorption capacity of FeOOH formed from the dissolution of ankerite. The oxidation of Fe 2+ leads to the formation of FeOOH parallel to partial reduction of U 6+ to U 4+ . 75% of uranium was taken up by clay minerals and 25% by FeOOH although the ankerite concentration is as low as 6% in WMA Block of BCF. In G Block, the argillaceous matrix was found to be mainly responsible for the UO 2 2+ uptake. The study demonstrated that the U retention capacity of different BCF locations was significantly influenced by the mineralogy of these sites.

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“…These experiments are necessary but will not give the final answer to the questions: which minerals retain the radionuclides and how reversible the processes are (type of chemical bonds involved). With the revolutionary development of X-ray sources (synchrotrons) and optics such questions can be answered by micro scale resolution spectroscopy and diffraction techniques [7,8,9,10,11]. A recent review emphasizes the relevance of versatile micro-and nanoanalytical techniques for actinide environmental research [12].…”

Section: Introductionmentioning

confidence: 99%

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

Osán

Kéri

Breitner

et al. 2014

Spectrochimica Acta Part B: Atomic Spectroscopy

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Argillaceous rocks are considered in most European countries as suitable host rock formations for the deep geological disposal of high-level radioactive waste (HLW). The most important chemical characteristic in this respect is their generally strong radionuclide retention property due to the high sorption capacity. Consequently, the physico-chemical parameters of these processes have to be studied in great detail. Synchrotron radiation microscopic X-ray fluorescence (SR µ-XRF) has sufficient sensitivity to study these processes on the microscale without the necessity of the application of radioactive substances. The present study focuses on the interaction between the escaped ions and the host-rock surrounding the planned HLW repository. SR µ-XRF measurements were performed on thin sections subjected to sorption experiments using 5 µm spatial resolution. Inactive Cs(I), Ni(II), Nd(III) and natural U(VI) were selected for the experiments chemically representing key radionuclides. The thin sections were prepared on high-purity silicon wafers from geochemically characterized cores of Boda Claystone Formation, Hungary. Samples were subjected to 72-hour sorption experiments with one ion of interest added. The µ-XRF elemental maps taken usually on several thousand pixels indicate a correlation of Cs and Ni with Fe-and K-rich regions suggesting that these elements are predominantly taken up by clay-rich phases. U and Nd was found to be bound not only to the clayey matrix, but the cavity filling minerals also played important role in the uptake. Multivariate methods were found to be efficient tools for extracting information from the elemental distribution maps even when the clayey matrix and fracture infilling regions were examined in the same measured area. By using positive matrix factorization as a new approach the factors with higher sorption capacity could be identified and with additional mineralogical information the uptake capacity of the different mineral phases could be quantified. The results were compared with cluster analysis when the regions dominated by different mineral phases are segmented. The multivariate approach based on µ-XRF to identify the minerals was validated using microscopic X-ray diffraction. Keywords: micro-XRF; sorption; positive matrix factorization; radioactive waste; argillaceous rock IntroductionIn most European countries, clay-rich rocks are considered as suitable host rock formations for isolation of the radionuclides generated by the nuclear industry from the biosphere for thousands of years. During this time period the radionuclides might migrate from the engineered barriers and the safety is determined by the retention capability of the host rock. Following water intrusion into the repository, radionuclide contaminants can be released. Clay rocks have very good retention capability due to their high sorption capacity. Sorption depends on the water/solid compositions, porewater properties such as pH and Eh, as well as the presence of complexing anions as they determine t...

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Confocal Micrometer-Scale X-ray Fluorescence and X-ray Absorption Fine Structure Studies of Uranium Speciation in a Tertiary Sediment from a Waste Disposal Natural Analogue Site

Cited by 53 publications

References 17 publications

Geochemical study of uranium mobility in tertiary argillaceous system at ruprechtov site, Czech Republic

Geochemical study of uranium mobility in tertiary argillaceous system at ruprechtov site, Czech Republic

Characteristics of uranium uptake of Boda Claystone Formation as the candidate host rock of high level radioactive waste repository in Hungary

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

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