Phosphatian coffinite with rare earth elements and Ce-rich françoisite-(Nd) from sandstone beneath a natural fission reactor at Bangombé, Gabon

Janeczek, Janusz; Ewing, Rodney C.

doi:10.1180/minmag.1996.060.401.14

Cited by 38 publications

(39 citation statements)

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“…A previous study of REE isotopes of the Bangombé reactor showed that the elemental abundances of non-fissiogenic REE in the Bangombé RZ are very low (⌺REE Ͻ 500 ppm) despite its high U concentration (29.5-45.0 wt.%; Hidaka and Gauthier-Lafaye, 2000). In addition, REE patterns (Hidaka and Gauthier-Lafaye, 2000) and mineralogical observation (Janeczek and Ewing, 1996b;Jensen and Ewing, 1998) suggest that uraninite in the Bangombé RZ has been partially dissolved and affected by supergene alteration. In particular, Stille et al (2003) described the enrichment of LREE in groundwater that passes through the Bangombé uranium deposit.…”

Section: U and Ree Differentiationmentioning

confidence: 91%

“…Among the four thin sections, the samples 1225 and 1290 are the same samples in which REE-bearing françoisite, (REE)(UO 2 ) 3 O(OH)(PO 4 )6H 2 O, and Uenriched goethite, FeOOH were previously discovered, respectively (Janeczek and Ewing, 1996b;Janeczek, 1999). Although mineral observation and chemical analysis of major elements of françoisite and goethite were previously carried out by Janeczek and Ewing (1996b), the isotopic measurements were not performed. Besides the françoisite and goethite, in this study we found several phosphorus coffinite grains in BAX03.1225 and 1240, and uraninite grains in 1215 and 1290 that were subjected for isotopic analyses.…”

Section: Samplesmentioning

confidence: 98%

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Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

Hidaka

Janeczek

Skomurski

et al. 2005

Geochimica et Cosmochimica Acta

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To study geochemical processes for migration and fixation of fissiogenic rare earth elements (REE) in association with uranium dissolution, in situ isotopic analyses using an ion microprobe were performed on U-and REE-bearing secondary minerals, such as coffinite, françoisite, uraniferous goethite, and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at Bangombé, Gabon. Phosphate minerals such as phosphatian coffinite and françoisite with depleted 235 U ( 235 U/ 238 U ϭ 0.00609 to 0.00638) contained large amount of fissiogenic light REE, while micro-sized uraninite grains in a solid bitumen aggregate have normal U isotopic values ( 235 U/ 238 U ϭ 0.00725) and small amount of fissiogenic REE components. The proportions of fissiogenic and non-fissiogenic REE components in four samples from the core of BAX03 vary in depth ranging from 30 cm to 130 cm beneath the reactor, which suggests mixing between fissiogenic isotopes from the reactor and non-fissiogenic isotopes from original minerals in the sandstone. Significant chemical fractionation was observed between Ce and the other REE in the secondary minerals, which shows evidence of an oxidizing atmosphere during their formation. Pb-isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of U-Pb decay system due to recent geologic alteration. However, systematic Pb-isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes, Pb and U from the reactor in association with dolerite dyke intrusion ϳ0.798 Ga ago and the formation of the secondary minerals by mixing event between 2.05 Ga-old original minerals and reactor materials due to recent alteration.

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Section: U and Ree Differentiationmentioning

confidence: 91%

Section: Samplesmentioning

confidence: 98%

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

Hidaka

Janeczek

Skomurski

et al. 2005

Geochimica et Cosmochimica Acta

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“…Stable U(IV) minerals, which could form as secondary phases, would impart lower uranium solubility to such systems. Thus, knowledge of coffinite thermodynamics is needed to constrain the solubility of U(IV) in natural environments and would be useful in repository assessment.In natural uranium deposits such as Oklo (Gabon) (4,7,11,12,14,17,18) and Cigar Lake (Canada) (5, 13, 15), coffinite has been suggested to coexist with uraninite, based on electron probe microanalysis (EPMA) (4,5,7,11,13,17,19,20) and transmission electron microscopy (TEM) (8, 15). However, it is not clear whether such apparent replacement of uraninite by a coffinite-like phase is a direct solid-state process or occurs mediated by dissolution and reprecipitation.…”

mentioning

confidence: 99%

“…In natural uranium deposits such as Oklo (Gabon) (4,7,11,12,14,17,18) and Cigar Lake (Canada) (5,13,15), coffinite has been suggested to coexist with uraninite, based on electron probe microanalysis (EPMA) (4,5,7,11,13,17,19,20) and transmission electron microscopy (TEM) (8,15). However, it is not clear whether such apparent replacement of uraninite by a coffinite-like phase is a direct solid-state process or occurs mediated by dissolution and reprecipitation.…”

mentioning

confidence: 99%

Thermodynamics of formation of coffinite, USiO ₄

Guo

Szenknect

Mesbah

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

107

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Coffinite, USiO 4 , is an important U(IV) mineral, but its thermodynamic properties are not well-constrained. In this work, two different coffinite samples were synthesized under hydrothermal conditions and purified from a mixture of products. The enthalpy of formation was obtained by high-temperature oxide melt solution calorimetry. Coffinite is energetically metastable with respect to a mixture of UO 2 (uraninite) and SiO 2 (quartz) by 25.6 ± 3.9 kJ/mol. Its standard enthalpy of formation from the elements at 25°C is −1,970.0 ± 4.2 kJ/mol. Decomposition of the two samples was characterized by X-ray diffraction and by thermogravimetry and differential scanning calorimetry coupled with mass spectrometric analysis of evolved gases. Coffinite slowly decomposes to U 3 O 8 and SiO 2 starting around 450°C in air and thus has poor thermal stability in the ambient environment. The energetic metastability explains why coffinite cannot be synthesized directly from uraninite and quartz but can be made by low-temperature precipitation in aqueous and hydrothermal environments. These thermochemical constraints are in accord with observations of the occurrence of coffinite in nature and are relevant to spent nuclear fuel corrosion.uranium | coffinite | USiO 4 | U(IV) minerals | calorimetry I n many countries with nuclear energy programs, spent nuclear fuel (SNF) and/or vitrified high-level radioactive waste will be disposed in an underground geological repository. Demonstrating the long-term (10 6 -10 9 y) safety of such a repository system is a major challenge. The potential release of radionuclides into the environment strongly depends on the availability of water and the subsequent corrosion of the waste form as well as the formation of secondary phases, which control the radionuclide solubility. Coffinite (1), USiO 4 , is expected to be an important alteration product of SNF in contact with silica-enriched groundwater under reducing conditions (2-8). It is also found, accompanied by thorium orthosilicate and uranothorite, in igneous and metamorphic rocks and ore minerals from uranium and thorium sedimentary deposits (2,4,5,(8)(9)(10)(11)(12)(13)(14)(15)(16). Under reducing conditions in the repository system, the uranium solubility (very low) in aqueous solutions is typically derived from the solubility product of UO 2 . Stable U(IV) minerals, which could form as secondary phases, would impart lower uranium solubility to such systems. Thus, knowledge of coffinite thermodynamics is needed to constrain the solubility of U(IV) in natural environments and would be useful in repository assessment.In natural uranium deposits such as Oklo (Gabon) (4,7,11,12,14,17,18) and Cigar Lake (Canada) (5, 13, 15), coffinite has been suggested to coexist with uraninite, based on electron probe microanalysis (EPMA) (4,5,7,11,13,17,19,20) and transmission electron microscopy (TEM) (8, 15). However, it is not clear whether such apparent replacement of uraninite by a coffinite-like phase is a direct solid-state process or occurs mediated by dis...

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“…In recent years "natural analogues" for both the repository environment (e.g., the Oklo natural reactors) and nuclear waste form behavior (e.g., corrosion and alteration of uraninite, UO 2+x ) have been cited as a fundamental means of achieving confirmation of long-term extrapolations (Ewing and Jercinovic, 1987;Ewing, 1991Ewing, , 1992Ewing, , 1993aEwing, , 1993bEwing, , 1999b. In particular, considerable effort has already been made to establish that uraninite, UO 2+x , with its impurities, is a good structural and chemical analogue for the analysis of the long-term behavior of the UO 2 in SNF (Fayek et al, 1997a;Janeczek and Ewing, 1991aJaneczek et al, 1993Janeczek et al, , 1996aJaneczek et al, , 1996bMurphy, 1993;Pearcy et al, 1994). …”

Section: Introductionmentioning

confidence: 99%

Corrosion of Spent Nuclear Fuel: The Long-Term Assessment

Ewing¹

2004

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Spent nuclear fuel (SNF), essentially UO 2 , accounts for over 95% of the total radioactivity of all of the radioactive wastes in the United States that require disposal, disposition or remediation. The UO 2 in SNF is not stable under oxidizing conditions and may also be altered under reducing conditions. The alteration of SNF results in the formation of new uranium phases that can cause the release or retardation of actinide and fission product radionuclides. Over the long term, and depending on the extent to which the secondary uranium phases incorporate fission products and actinides, these alteration phases become the near-field source term.This research program has been a broadly based effort to understand the long-term behavior of SNF and its alteration products in a geologic repository. 4. Are the corrosion products accurately predicted from geochemical codes (e.g., EQ3/6 or Geochemist's Workbench) that are used in performance assessments? Can these codes be tested by studies of natural analogue sites (e.g., Oklo, Cigar Lake or Pena Blanca).As detailed in the summary of results, we have made substantial progress in addressing each of the above issues.4

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Phosphatian coffinite with rare earth elements and Ce-rich françoisite-(Nd) from sandstone beneath a natural fission reactor at Bangombé, Gabon

Cited by 38 publications

References 6 publications

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

Thermodynamics of formation of coffinite, USiO ₄

Corrosion of Spent Nuclear Fuel: The Long-Term Assessment

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Phosphatian coffinite with rare earth elements and Ce-rich françoisite-(Nd) from sandstone beneath a natural fission reactor at Bangombé, Gabon

Cited by 38 publications

References 6 publications

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

Thermodynamics of formation of coffinite, USiO 4

Corrosion of Spent Nuclear Fuel: The Long-Term Assessment

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Thermodynamics of formation of coffinite, USiO ₄