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Hani Khoury - One of the best experts on this subject based on the ideXlab platform.
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Natural Analogue approaches to prediction of long term behaviour of ca 2 uo 5 2 3h 2 o x phase case study from tulul al hammam site jordan
Arabian Journal of Geosciences, 2017Co-Authors: E.v. Sokol, Hani Khoury, S.n. Kokh, Yu.v. Seryotkin, S.v. Goryainov, S.a. Novikova, I.a. SokolAbstract:The Tulul Al Hammam area in central Jordan is an advantageous Natural Analogue site to study long-term U(VI) retention in ~ 1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~ 100 kyr. The marbles contain abundant grains of high-temperature (ca. 800–850 °C) primary double Ca-U(VI) oxides (mainly Ca3UO6 and CaUO4), which are commonly replaced by hydrated calcium uranates with various impurities (Si, Fe, Al and F). A more hydrous Natural Analogue of X-phase (Ca2UO5·2-3H2O) occurs as a predominant secondary U compound after primary Ca-U(VI) oxides. The phase was studied by single-crystal XRD, SEM/EDX and electron microprobe (EPMA) analyses and Raman spectroscopy. It is a non-crystalline phase with a specific finger-like microtexture consisting of thin (no wider than 1–2 μm) lamellar particles. Its Raman spectrum shows a single strong band at 706–713 cm−1, sometimes coexisting with up to three weak diffuse bands (ν ~ 390, ~ 540 and 1355–1400 cm−1). The find of the Natural X-phase (Ca2UO5·2-3H2O) is evidence of its long-term stability in a Natural environment. It proves explicitly that the compound Ca2UO5·nH2O is a solubility-limiting phase in aged cements. The results have implications for geological disposal of radioactive wastes.
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long term immobilisation of cd2 at the tulul al hammam Natural Analogue site central jordan
Applied Geochemistry, 2016Co-Authors: E.v. Sokol, Hani Khoury, S.n. Kokh, Yu.v. Seryotkin, S.v. GoryainovAbstract:Abstract The Tulul Al Hammam area in central Jordan is a Natural Analogue site where to study long-term Cd 2+ retention during the weathering of Cd-enriched combustion-metamorphic marbles with clinker-like mineralogy. Natural Cd-rich portlandite (Ca 0.67−0.45 Cd 0.33−0.55 )[OH] 2 was discovered and characterised by single-crystal XRD, SEM/EDS, and microprobe analyses, and Raman spectroscopy. The Ca[OH] 2 – Cd[OH] 2 solid solution ((Ca 1−x Cd x )[OH] 2 ) is isostructural with Ca[OH] 2 and β-Cd[OH] 2 crystals in the CdI 2 -type of structure. Cd-rich portlandite is a common secondary phase in slightly altered massive marbles, where it replaces and rims single-crystals of the high-temperature precursor (Ca 1−x Cd x )O. The Cd:Ca molar ratios of (Ca 1−x Cd x )[OH] 2 are inherited from the precursor phase (Ca 1−x Cd x )O. Reliable long-term immobilisation of Cd in (Ca 1−x Cd x )[OH] 2 is assumed for pore water pH values from 10.5 up to 12 buffered by C-S-Hs formed mainly during spurrite hydration. The Tulul Al Hammam site may have some bearing on long-term Cd 2+ retention in the concrete matrix.
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Cementation of kerogen-rich marls by alkaline fluids released during weathering of thermally metamorphosed marly sediments. Part I: Isotopic (C,O) study of the Khushaym Matruk Natural Analogue (central Jordan)
Applied Geochemistry, 2007Co-Authors: Serge Fourcade, Elias Salameh, Laurent Trotignon, Philippe Boulvais, I. Techer, Marcel Elie, Didier Vandamme, Hani KhouryAbstract:The Khushaym Matruk site in central Jordan may represent a Natural Analogue depicting the interaction of alkaline solutions with a clayey sedimentary formation or with clay-rich confining barriers at the interface with concrete structures in waste disposal sites. In this locality, past spontaneous combustion of organic matter in a clayey biomicritic formation produced a ca. 60 m-thick layer of cement-marble containing some of the high-temperature phases usually found in industrial cements (e.g., spurrite, brucite, and Ca-aluminate). A vertical cross-section of the underlying sediments was used in order to study the interaction between cement-marbles and neighbouring clayey limestones under weathering conditions. A thermodynamic approach of the alteration parageneses (calcitejenniteafwillitebrucite and CSH phases) in the cement-marbles constrains the interacting solutions to have had pH-values between 10.5 and 12. Over 3 m, the sediments located beneath the metamorphic unit were compacted and underwent carbonation. They display large C and O isotopic variations with respect to "pristine" sediments from the bottom of the section. Low d13C-values down to -31.4/PDB show the contribution of CO2 derived from the oxidization of organic matter and from the atmosphere to the intense carbonation process affecting that particular sedimentary level. The size of the C isotopic anomalies, their geometrical extent and their coincidence with the variations of other markers like the Zn content, the structure of organic matter, the mineralogical composition, all argue that the carbonation process was induced by the percolation of high pH solutions which derived from the alteration of cement-marbles. The temperature of the carbonation process remains conjectural and some post-formation O isotopic reequilibration likely affected the newly-formed carbonate. Carbonation induced a considerable porosity reduction, both in fractures and matrixes. The Khushaym Matruk site may have some bearing to the early life of a repository site, when water saturation of the geological formations hosting the concrete structures is incomplete, enabling simultaneous diffusion of alkaline waters and gaseous CO2 in the near field.
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propagation of high alkaline fluids in an argillaceous formation case study of the khushaym matruk Natural Analogue central jordan
Journal of Geochemical Exploration, 2006Co-Authors: Isabelle Techer, Hani Khoury, Elias Salameh, F Rassineux, Christelle Claude, Norbert Clauer, Maurice Pagel, Joel Lancelot, Bruno Hamelin, E JacquotAbstract:Abstract The Khushaym Matruk site in Central Jordan is investigated as a Natural Analogue of a deep geological repository for intermediate to high-level radioactive wastes to discuss the impact of high-alkaline solutions in an argillaceous formation. The studied site is characterised by Maestrichtian bituminous-rich marls, consisting of 66–83% of carbonates and 10–15% of clays of mixed-layers illite–smectite type (I–S), overlapped by a marble/cement unit formed by spontaneous in situ combustion of the sedimentary organic matter in sub-surface conditions. This high-temperature event produced marble and cementitious phases typical to those observed in industrial cements whose alteration generates high-alkaline solutions. Evidences of fluid circulations in Khushaym Matruk site are underlined by secondary minerals, mainly calcite and gypsum, neoformed in cracks and micro-cracks crosscutting the bituminous-rich marls, and in travertines capping them. The chemical and Sr isotopic data of these phases are characteristics of high-alkaline fluids generated by alteration of the cementitious phases and having percolated with partial equilibration in the underlying bituminous-rich marls. The propagation of these alkaline solutions by structural discontinuity paths in the clayey formation is underlined over distances greater than 5 m. Also, the mineralogical and petrographic characterisation of the bituminous-rich marls, far and close to the marble/cement unit, emphasizes slight variations in mineral contents, a few metres close to the marble/cement contact, with notably a decrease of I–S crystallinity, a change from beideillite to montmorillonite type and, calcite and zeolite recrystallisation. Together, textural disturbances of these rocks, underlined by micro-fissuration of the sedimentary matrix, are observed. A pervasive circulation of high-alkaline fluids in the argillaceous matrix is proposed to explain these changes and is underlined over a distance of a few metres under the contact with the marble/cement unit. Cathodoluminescence observations and U–Th radioactive disequilibrium dating applied on infilling calcite cracks indicate that these circulations were not continuous but occurred in several steps with a mean age of 110,000–130,000 years.
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The Maqarin (Jordan) Natural Analogue for 14C attenuation in cementitious barriers
Waste Management, 1994Co-Authors: Ian D. Clark, Ramesh Dayal, Hani KhouryAbstract:Carbonation reactions in portland cement grout examined in the laboratory suggest high attenuation of 14C in cementitious barriers for low- and intermediate-level radioactive waste repositories. Natural cementitious environments at two sites, Maqarin and Daba, in Jordan offer evidence that extensive carbonation can occur at field scales under both unsaturated and saturated conditions. Here, in situ spontaneous combustion of bituminous marl in the past has led to calcination and formation of calcium/silica/alumina-oxides typical of portland cement clinker. Retrograde alteration within these metamorphic zones began with hydration and precipitation of portlandite as a rock forming mineral along with ettringite, thaumasite, and other calcium-silica-hydrate-like phases. Metamorphism was a relatively recent event at the Maqarin site. Here hyperalkaline groundwater discharge from the alteration zones with two distinct geochemical facies: (a) higher TDSCaKNaOHSO4 groundwaters (pH > 12.5) apparently represent the earliest discharge following hydration, and (b) lower TDSCaOH groundwaters (pH 12.0 to 12.4) which appear to be later-stage leachates from the alteration zone. Subsequent carbonation has precipitated secondary calcite observed in the Eastern alteration zone. In central Jordan, travertines associated with the Daba marble record a third phase of porewater discharge where silica has been remobilized during carbonation of CSH-like phases. The unique geochemical features of the Maqarin site were examined to evaluate the validity of using it as a potential Natural Analogue for cement grout carbonation reactions studied under laboratory conditions.
Claudia Schutze - One of the best experts on this subject based on the ideXlab platform.
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an integrative hierarchical monitoring approach applied at a Natural Analogue site to monitor co2 degassing areas
Acta Geotechnica, 2014Co-Authors: U Sauer, Claudia Schutze, Carsten Leven, Stefan Schlomer, Peter DietrichAbstract:This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for Naturally occurring CO2 deposits (Analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects.
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diagnostic monitoring to identify preferential near surface structures for co2 degassing into the atmosphere tools for investigations at different spatial scales validated at a Natural Analogue site
International Journal of Greenhouse Gas Control, 2013Co-Authors: Claudia Schutze, Peter Dietrich, U SauerAbstract:Abstract Diagnostic monitoring tools applied at different scales are required to reliably detect and assess CO 2 leakages from storage formations in the shallow subsurface, as well as playing an important role in helping to establish a risk assessment strategy at carbon dioxide capture and storage facilities. These tools incorporate method developments and applications that will enable large spatial areas to be consistently covered in sufficient spatial and temporal resolutions. The use of remote sensing (open-path Fourier-transform infrared (OP-FTIR) spectroscopy) in combination with regional measurements (geophysics and chamber based soil CO 2 flux measurement) and local in situ measurements (Direct Push technology) enables a more reliable validation of risk, using a joint data interpretation approach. A promising tool currently in development for large-scale leakage detection and monitoring is Fourier transform infrared (FTIR) spectroscopy, which is used to determine spatial atmospheric CO 2 distribution in the near-surface atmosphere. Sufficient geophysical techniques for meso-scale monitoring include geoelectrical and self potential (SP) surveys. These methods are useful for characterizing fluid flow and transport processes in permeable near-surface sedimentary layers and can yield important information concerning CO 2 affected subsurface structures. The paper presents promising results achieved from measurements taken at a Natural Analogue site in the Czech Republic and indicates that the hierarchical monitoring approach represents a successful multidisciplinary modular concept to monitor physical and chemical processes taking place during CO 2 migration and seepage. The application of FTIR spectroscopy in combination with soil gas surveys and geoelectrical investigations results in a comprehensive site characterization, including the atmospheric and near-surface CO 2 distribution as well as subsurface structural features. Our data illustrate a correlation of higher CO 2 concentration in the atmosphere with increased CO 2 soil flux rates and soil CO 2 concentrations. These soil gas anomalies coincide with structural units characterized by a distinct negative SP anomaly and a zone of decreased resistivity in the ERT result.
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diagnostic monitoring to identify preferential near surface structures for co2 degassing into the atmosphere tools for investigations at different spatial scales validated at a Natural Analogue site
International Journal of Greenhouse Gas Control, 2013Co-Authors: Claudia Schutze, Pete Dietrich, U SaueAbstract:Abstract Diagnostic monitoring tools applied at different scales are required to reliably detect and assess CO 2 leakages from storage formations in the shallow subsurface, as well as playing an important role in helping to establish a risk assessment strategy at carbon dioxide capture and storage facilities. These tools incorporate method developments and applications that will enable large spatial areas to be consistently covered in sufficient spatial and temporal resolutions. The use of remote sensing (open-path Fourier-transform infrared (OP-FTIR) spectroscopy) in combination with regional measurements (geophysics and chamber based soil CO 2 flux measurement) and local in situ measurements (Direct Push technology) enables a more reliable validation of risk, using a joint data interpretation approach. A promising tool currently in development for large-scale leakage detection and monitoring is Fourier transform infrared (FTIR) spectroscopy, which is used to determine spatial atmospheric CO 2 distribution in the near-surface atmosphere. Sufficient geophysical techniques for meso-scale monitoring include geoelectrical and self potential (SP) surveys. These methods are useful for characterizing fluid flow and transport processes in permeable near-surface sedimentary layers and can yield important information concerning CO 2 affected subsurface structures. The paper presents promising results achieved from measurements taken at a Natural Analogue site in the Czech Republic and indicates that the hierarchical monitoring approach represents a successful multidisciplinary modular concept to monitor physical and chemical processes taking place during CO 2 migration and seepage. The application of FTIR spectroscopy in combination with soil gas surveys and geoelectrical investigations results in a comprehensive site characterization, including the atmospheric and near-surface CO 2 distribution as well as subsurface structural features. Our data illustrate a correlation of higher CO 2 concentration in the atmosphere with increased CO 2 soil flux rates and soil CO 2 concentrations. These soil gas anomalies coincide with structural units characterized by a distinct negative SP anomaly and a zone of decreased resistivity in the ERT result.
U Sauer - One of the best experts on this subject based on the ideXlab platform.
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an integrative hierarchical monitoring approach applied at a Natural Analogue site to monitor co2 degassing areas
Acta Geotechnica, 2014Co-Authors: U Sauer, Claudia Schutze, Carsten Leven, Stefan Schlomer, Peter DietrichAbstract:This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for Naturally occurring CO2 deposits (Analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects.
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diagnostic monitoring to identify preferential near surface structures for co2 degassing into the atmosphere tools for investigations at different spatial scales validated at a Natural Analogue site
International Journal of Greenhouse Gas Control, 2013Co-Authors: Claudia Schutze, Peter Dietrich, U SauerAbstract:Abstract Diagnostic monitoring tools applied at different scales are required to reliably detect and assess CO 2 leakages from storage formations in the shallow subsurface, as well as playing an important role in helping to establish a risk assessment strategy at carbon dioxide capture and storage facilities. These tools incorporate method developments and applications that will enable large spatial areas to be consistently covered in sufficient spatial and temporal resolutions. The use of remote sensing (open-path Fourier-transform infrared (OP-FTIR) spectroscopy) in combination with regional measurements (geophysics and chamber based soil CO 2 flux measurement) and local in situ measurements (Direct Push technology) enables a more reliable validation of risk, using a joint data interpretation approach. A promising tool currently in development for large-scale leakage detection and monitoring is Fourier transform infrared (FTIR) spectroscopy, which is used to determine spatial atmospheric CO 2 distribution in the near-surface atmosphere. Sufficient geophysical techniques for meso-scale monitoring include geoelectrical and self potential (SP) surveys. These methods are useful for characterizing fluid flow and transport processes in permeable near-surface sedimentary layers and can yield important information concerning CO 2 affected subsurface structures. The paper presents promising results achieved from measurements taken at a Natural Analogue site in the Czech Republic and indicates that the hierarchical monitoring approach represents a successful multidisciplinary modular concept to monitor physical and chemical processes taking place during CO 2 migration and seepage. The application of FTIR spectroscopy in combination with soil gas surveys and geoelectrical investigations results in a comprehensive site characterization, including the atmospheric and near-surface CO 2 distribution as well as subsurface structural features. Our data illustrate a correlation of higher CO 2 concentration in the atmosphere with increased CO 2 soil flux rates and soil CO 2 concentrations. These soil gas anomalies coincide with structural units characterized by a distinct negative SP anomaly and a zone of decreased resistivity in the ERT result.
R. De La Garza - One of the best experts on this subject based on the ideXlab platform.
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Final report of the Peña Blanca Natural Analogue project
2016Co-Authors: Schön S. Levy, Steven J. Goldstein, Amr I. Abdel-fattah, Mostafa Fayek, Patrick F. Dobson, Ronald S. Amato, Elizabeth Y. Anthony, Paul J. Cook, Diana French, R. De La GarzaAbstract:The Pena Blanca region, 50 km north of Chihuahua City, Chihuahua, Mexico, was a target of uranium exploration and mining by the Mexican government. After mining ceased in 1981, researchers became interested in this region as a study area for subsurface uranium migration with relevance to geologic disposal of nuclear waste. Many studies related to this concept were conducted at the Nopal I mine site located on a cuesta (hill) of the Sierra Pena Blanca. This site has geologic, tectonic, hydrologic, and geochemical similarities to Yucca Mountain, Nevada, a formerly proposed site for a high-level nuclear-waste repository in the unsaturated zone. The U.S. Department of Energy (U.S. DOE), Office of Civilian Radioactive Waste Management (OCRWM), sponsored studies at Nopal I in the 1990s and supported the drilling of three research wells – PB1, PB2, and PB3 – at the site in 2003. Beginning in 2004, the Pena Blanca Natural Analogue Project was undertaken by U.S. DOE, OCRWM to develop a three-dimensional conceptual model of the transport of uranium and its radiogenic daughter products at the Nopal I site.
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Heterogeneous seepage at the Nopal I Natural Analogue site, Chihuahua, Mexico
Hydrogeology Journal, 2011Co-Authors: Patrick F. Dobson, Paul J. Cook, Teamrat A. Ghezzehei, J. Alfredo Rodríguez-pineda, L. Villalba, R. De La GarzaAbstract:A study of seepage occurring in an adit at the Nopal I uranium mine in Chihuahua, Mexico, was conducted as part of an integrated Natural Analogue study to evaluate the effects of infiltration and seepage on the mobilization and transport of radionuclides. An instrumented seepage collection system and local automated weather station permit direct correlation between local precipitation events and seepage. Field observations recorded between April 2005 and December 2006 indicate that seepage is highly heterogeneous with respect to time, location, and quantity. Seepage, precipitation, and fracture data were used to test two hypotheses: (1) that fast flow seepage is triggered by large precipitation events, and (2) that an increased abundance of fractures and/or fracture intersections leads to higher seepage volumes. A few zones in the back adit recorded elevated seepage volumes immediately following large (>20 mm/day) precipitation events, with transit times of less than 4 h through the 8-m thick rock mass. In most locations, there is a 1–6 month time lag between the onset of the rainy season and seepage, with longer times observed for the front adit. There is a less clear-cut relation between fracture abundance and seepage volume; processes such as evaporation and surface flow along the ceiling may also influence seepage.
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Pena Blanca Natural Analogue Project: Summary of activities
Lawrence Berkeley National Laboratory, 2011Co-Authors: S. Levy, Steven J. Goldstein, P. F. Dobson, Philip C. Goodell, Amr I. Abdel-fattah, G. Saulnier, Mostafa Fayek, R. De La GarzaAbstract:The inactive Nopal I uranium mine in silicic tuff north of Chihuahua City, Chihuahua, Mexico, was studied as a Natural Analogue for an underground nuclear-waste repository in the unsaturated zone. Site stratigraphy was confirmed from new drill cores. Data from site studies include chemical and isotopic compositions of saturated- and unsaturated-zone waters. A partial geochronology of uranium enrichment and mineralization was established. Evidence pertinent to uranium-series transport in the soil zone and changing redox conditions was collected. The investigations contributed to preliminary, scoping-level performance assessment modeling.
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Heterogeneous seepage at the Nopal I Natural Analogue site, Chihuahua, Mexico
Vadose Zone Journal, 2008Co-Authors: Patrick F. Dobson, Paul J. Cook, Teamrat A. Ghezzehei, L. Villalba, J. Alfredo Rodriguez, R. De La GarzaAbstract:An integrated field, laboratory, and modeling study of the Pena Blanca (Chihuahua, Mexico) Natural Analogue site is being conducted to evaluate processes that control the mobilization and transport of radionuclides from a uranium ore deposit. One component of this study is an evaluation of the potential for radionuclide transport through the unsaturated zone (UZ) via a seepage study in an adit at the Nopal I uranium mine, excavated 10 m below a mined level surface. Seasonal rainfall on the exposed level surface infiltrates into the fractured rhyolitic ash-flow tuff and seeps into the adit. An instrumented seepage collection system and local automated weather station permit direct correlation between local precipitation events and seepage within the Nopal I +00 adit. Monitoring of seepage within the adit between April 2005 and December 2006 indicates that seepage is highly heterogeneous with respect to time, location, and quantity. Within the back adit area, a few zones where large volumes of water have been collected are linked to fast flow path fractures (0-4 h transit times) presumably associated with focused flow. In most locations, however, there is a 1-6 month time lag between major precipitation events and seepage within the adit, with longer residence timesmore » observed for the front adit area. Seepage data obtained from this study will be used to provide input to flow and transport models being developed for the Nopal I hydrogeologic system.« less
Yu.v. Seryotkin - One of the best experts on this subject based on the ideXlab platform.
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Natural Analogue approaches to prediction of long-term behaviour of Ca_2UO_5∙2-3H_2O X-phase: case study from Tulul Al Hammam site, Jordan
Arabian Journal of Geosciences, 2017Co-Authors: E.v. Sokol, S.n. Kokh, H.n. Khoury, Yu.v. Seryotkin, S.v. Goryainov, S.a. Novikova, I.a. SokolAbstract:The Tulul Al Hammam area in central Jordan is an advantageous Natural Analogue site to study long-term U(VI) retention in ~ 1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~ 100 kyr. The marbles contain abundant grains of high-temperature (ca. 800–850 °C) primary double Ca-U(VI) oxides (mainly Ca_3UO_6 and CaUO_4), which are commonly replaced by hydrated calcium uranates with various impurities (Si, Fe, Al and F). A more hydrous Natural Analogue of X-phase (Ca_2UO_5·2-3H_2O) occurs as a predominant secondary U compound after primary Ca-U(VI) oxides. The phase was studied by single-crystal XRD, SEM/EDX and electron microprobe (EPMA) analyses and Raman spectroscopy. It is a non-crystalline phase with a specific finger-like microtexture consisting of thin (no wider than 1–2 μm) lamellar particles. Its Raman spectrum shows a single strong band at 706–713 cm^−1, sometimes coexisting with up to three weak diffuse bands (ν ~ 390, ~ 540 and 1355–1400 cm^−1). The find of the Natural X-phase (Ca_2UO_5·2-3H_2O) is evidence of its long-term stability in a Natural environment. It proves explicitly that the compound Ca_2UO_5·nH_2O is a solubility-limiting phase in aged cements. The results have implications for geological disposal of radioactive wastes.
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Natural Analogue approaches to prediction of long term behaviour of ca 2 uo 5 2 3h 2 o x phase case study from tulul al hammam site jordan
Arabian Journal of Geosciences, 2017Co-Authors: E.v. Sokol, Hani Khoury, S.n. Kokh, Yu.v. Seryotkin, S.v. Goryainov, S.a. Novikova, I.a. SokolAbstract:The Tulul Al Hammam area in central Jordan is an advantageous Natural Analogue site to study long-term U(VI) retention in ~ 1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~ 100 kyr. The marbles contain abundant grains of high-temperature (ca. 800–850 °C) primary double Ca-U(VI) oxides (mainly Ca3UO6 and CaUO4), which are commonly replaced by hydrated calcium uranates with various impurities (Si, Fe, Al and F). A more hydrous Natural Analogue of X-phase (Ca2UO5·2-3H2O) occurs as a predominant secondary U compound after primary Ca-U(VI) oxides. The phase was studied by single-crystal XRD, SEM/EDX and electron microprobe (EPMA) analyses and Raman spectroscopy. It is a non-crystalline phase with a specific finger-like microtexture consisting of thin (no wider than 1–2 μm) lamellar particles. Its Raman spectrum shows a single strong band at 706–713 cm−1, sometimes coexisting with up to three weak diffuse bands (ν ~ 390, ~ 540 and 1355–1400 cm−1). The find of the Natural X-phase (Ca2UO5·2-3H2O) is evidence of its long-term stability in a Natural environment. It proves explicitly that the compound Ca2UO5·nH2O is a solubility-limiting phase in aged cements. The results have implications for geological disposal of radioactive wastes.
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long term immobilisation of cd2 at the tulul al hammam Natural Analogue site central jordan
Applied Geochemistry, 2016Co-Authors: E.v. Sokol, Hani Khoury, S.n. Kokh, Yu.v. Seryotkin, S.v. GoryainovAbstract:Abstract The Tulul Al Hammam area in central Jordan is a Natural Analogue site where to study long-term Cd 2+ retention during the weathering of Cd-enriched combustion-metamorphic marbles with clinker-like mineralogy. Natural Cd-rich portlandite (Ca 0.67−0.45 Cd 0.33−0.55 )[OH] 2 was discovered and characterised by single-crystal XRD, SEM/EDS, and microprobe analyses, and Raman spectroscopy. The Ca[OH] 2 – Cd[OH] 2 solid solution ((Ca 1−x Cd x )[OH] 2 ) is isostructural with Ca[OH] 2 and β-Cd[OH] 2 crystals in the CdI 2 -type of structure. Cd-rich portlandite is a common secondary phase in slightly altered massive marbles, where it replaces and rims single-crystals of the high-temperature precursor (Ca 1−x Cd x )O. The Cd:Ca molar ratios of (Ca 1−x Cd x )[OH] 2 are inherited from the precursor phase (Ca 1−x Cd x )O. Reliable long-term immobilisation of Cd in (Ca 1−x Cd x )[OH] 2 is assumed for pore water pH values from 10.5 up to 12 buffered by C-S-Hs formed mainly during spurrite hydration. The Tulul Al Hammam site may have some bearing on long-term Cd 2+ retention in the concrete matrix.
