Crandallites and Coffinite: Retardation of Nuclear Reaction Products at the Bangombé Natural Fission Reactor

Jensen, Keld Alstrup; Janeczek, Janusz; Ewing, Rodney C.; Stille, Peter; Gauthier-Lafaye, F.; Salah, Sonia

doi:10.1557/proc-608-525

Cited by 12 publications

(9 citation statements)

References 10 publications

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“…Coffinite USiO 4 is therefore expected to be one of the potential alteration phases precipitating from SNF alteration under reducing Si-rich conditions [10][11][12][13][14][15]. Indeed, this mineral is widely observed in uranium ore deposits as an alteration phase of uraninite (natural analog of SNF [16]), particularly at Oklo (Gabon) [13,[17][18][19] and Cigar Lake (Canada) [20][21][22][23]. Coffinite is also observed as primary uranium mineral in roll-front deposits where uranium precipitates in tight redox fronts as in Kazakhstan [24].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and characterization of coffinite

Pointeau

Deditius

Miserque

et al. 2009

Journal of Nuclear Materials

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Section: Introductionmentioning

confidence: 99%

Synthesis and characterization of coffinite

Pointeau

Deditius

Miserque

et al. 2009

Journal of Nuclear Materials

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“…Sulfate in bassetite from BAX03 most likely arises from contamination by the coexisting uranopilite. The bassetite grains are the unidentified Fe-uranyl phosphate hydroxide hydrate that was previously reported by [15,16,20].…”

Section: Uranyl Phosphatesmentioning

confidence: 53%

“…However, the oredeposit, as well as RZB, has been partially subjected to oxidative alteration during the past 350 000 years [14]. The alteration has resulted in the formation of U 6+ phases [15,16]. The alteration has occurred mainly during interaction with laterally moving oxidized groundwaters at the top of the FAsandstone (Fig.…”

Section: Geologymentioning

confidence: 99%

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U⁶⁺phases in the weathering zone of the Bangombé U-deposit: observed and predicted mineralogy

Jensen¹,

Palenik²,

Ewing³

2002

Radiochimica Acta

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Uraninite alteration / Uranyl phosphates / Uranyl sulfates / E h -pH diagrams / Natural fission reactor / Oklo / BangombéSummary. The mineralogy of the supergene-weathered Bangombé natural fission reactor (RZB) and surrounding uranium deposit has been analyzed and compared with the thermodynamically predicted minerals based on groundwater compositions. The primary U-minerals are uraninite UO 2+x and minor coffinite (U[SiO 4 ]·nH 2 O); sometimes with phosphorous. The U 6+ miner-has also been reported. Thermodynamic equilibrium modeling was completed using Geochemist's Workbench  with an expanded data base and the groundwater composition (−112 mV ≤ E h ≤ 143 mV; pH = 5.96) at the base of RZB in drill-hole BAX03. The new ∆G 0 f, 298.15 data were obtained from the literature or estimated using the polyhedral contribution method. Based on the updated database, E h −pH diagrams predict that coffinite, U(HPO 4 ) 2 ·H 2 O and UOF 2 ·H 2 O are the only stable U 4+ phases and that uranopilite, torbernite and bassetite will become stable during oxidative alteration. Except from UOF 2 ·H 2 O, this is in accord with mineralogical observations. The role of Cu was predicted from log a Cu -pH diagrams, which predicts that torbernite is stable at log a Cu = 3.98 × 10 −14 and pH ≥ 2.2 at E h = 143 mV in BAX03 groundwaters. At E h = −112 mV, torbernite is stable at pH > 5.5. Soddyite ((UO 2 ) 2 SiO 4 ·2H 2 O) was predicted to form at the expense of coffinite, but soddyite has not been identified at Bangombé. Previous blind prediction modeling, often omitting P and S, had only predicted soddyite and haiweeite (Ca(UO 2 ) 2 [Si 5 O 12 (OH) 2 ]·4−5H 2 O) and hence, failed to predict the U 6+ minerals observed at Bangombé. The results stress the importance of SO 4 2− and PO 4 3− resulting from dissolution of accessory apatite, monazite and sulfides in the retardation of U owing to the formation of U 6+ sulfates and phosphates.

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“…Thus, meta-uranopilite has remained as one of the insufficiently described uranyl minerals (Anthony et al, 2003). Some new not yet approved and published uranyl sulphate minerals have been also mentioned (Jensen et al, 1997;Jensen et al, 2000;Meisser et al, 2000;Jensen et al, 2002; (Burns, 2001). The mineral is of space group P 1 and consists of six distinct U 6+ cations forming part of a uranyl (UO 2 ) 2+ chains.…”

Section: Introductionmentioning

confidence: 97%

An XRD, SEM and TG study of a uranopilite from Australia

Frost¹,

Weier²,

Ayoko³

et al. 2006

Mineral. mag.

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A uranopilite from The South Alligator River, Northern Territory, Australia has been studied using X-ray diffraction, scanning electron microscopy with EDAX attachment and thermogravimetry in conjunction with evolved gas mass spectrometry. X-ray diffraction shows the mineral is a pure uranopilite with little or no impurities. SEM images show the uranopilite to consist of long elongated crystals up to 50 μm in length and 5 μm in width. Thermogravimetry combined with mass spectrometry shows that dehydration occurs around 31 °C resulting in the formation of metauranopilite. The first dehydration step over 20 -71 °C corresponds to the decrease of 5.4 wt %, equivalent to 6.076 H 2 O. The second dehydration step over 71-162.4 °C corresponds to a decrease of 4.7 wt % equivalent to 5.288 H 2 O making a total of 11.364 moles of H 2 O, close to 12 H 2 O for uranopilite. Dehydroxylation takes place over the temperature range 80 to 160 °C. The loss of sulphate occurs at higher temperatures in two steps at 622 and 636 °C. A mass loss also occurs at 755 °C accounted for by evolved oxygen.

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Crandallites and Coffinite: Retardation of Nuclear Reaction Products at the Bangombé Natural Fission Reactor

Cited by 12 publications

References 10 publications

Synthesis and characterization of coffinite

Synthesis and characterization of coffinite

U⁶⁺phases in the weathering zone of the Bangombé U-deposit: observed and predicted mineralogy

An XRD, SEM and TG study of a uranopilite from Australia

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Crandallites and Coffinite: Retardation of Nuclear Reaction Products at the Bangombé Natural Fission Reactor

Cited by 12 publications

References 10 publications

Synthesis and characterization of coffinite

Synthesis and characterization of coffinite

U6+phases in the weathering zone of the Bangombé U-deposit: observed and predicted mineralogy

An XRD, SEM and TG study of a uranopilite from Australia

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U⁶⁺phases in the weathering zone of the Bangombé U-deposit: observed and predicted mineralogy