REE mobility in groundwater proximate to the natural fission reactor at Bangombé (Gabon)

Stille, Peter; Gauthier-Lafaye, F.; Jensen, Keld Alstrup; Salah, Sonia; Bracke, Guido; Ewing, Rodney C.; Louvat, D.; Million, D.

doi:10.1016/s0009-2541(03)00035-4

Cited by 47 publications

(37 citation statements)

References 30 publications

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“…Aqueous REEs frequently become immobilized in phosphate minerals by the consumption of apatite or they are simply bound to aqueous P during alteration processes [27,64]. Under typical environmental conditions, the hydrated RE phosphates observed in the present study are expected to initially form at nanoscale sizes.…”

Section: Discussionmentioning

confidence: 68%

Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature

Ochiai

Utsunomiya

2017

Minerals

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Abstract:In order to understand the crystal chemical properties of hydrous rare-earth (RE) phosphates, REPO 4,hyd , that form at ambient temperature, we have synthesized REPO 4,hyd through the interaction of aqueous RE elements (REEs) with aqueous P at room temperature at pH < 6, where the precipitation of RE hydroxides does not occur, and performed rigorous solid characterization. The second experiment was designed identically except for using hydroxyapatite (HAP) crystals as the P source at pH constrained by the dissolved P. Hydrated RE phosphate that precipitated at pH 3 after 3 days was classified into three groups: LREPO 4,hyd (La → Gd) containing each REE from La-Gd, MREPO 4,hyd (Tb → Ho), and HREPO 4,hyd (Er → Lu). The latter two groups included increasing fractions of an amorphous component with increasing ionic radius, which was associated with non-coordinated water. RE all PO 4,hyd that contains all lanthanides except Pm transformed to rhabdophane structure over 30 days of aging. In the experiments using HAP, light REEs were preferentially distributed into nano-crystals, which can potentially constrain initial RE distributions in aqueous phase. Consequently, the mineralogical properties of hydrous RE phosphates forming at ambient temperature depend on the aging, the pH of the solution, and the average ionic radii of REE, similarly to the well-crystalline RE phosphates.

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Section: Discussionmentioning

confidence: 68%

Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature

Ochiai

Utsunomiya

2017

Minerals

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“…Reactors 1-9 and the Bangombé reactor, which are all located near the surface of the ore bodies, were significantly weathered for extended periods of time after the cessation of reactor criticality. For example, the Bangombé reactor zone is affected by supergene weathering and by chemical exchange with groundwater (Stille et al, 2003). On the other hand, Oklo Reactor Zone 10 is the deepest reactor zone and is therefore the best preserved in terms of post-reaction alteration.…”

Section: Discussionmentioning

confidence: 99%

“…The REE data suggest that significant amounts of fissiogenic LREE such as La, Ce, and Pr were re-distributed by alteration of uraninite, and that REE distribution primarily occurred by strong water-rock interaction during the U ore formation. Stille et al (2003) studied fissiogenic REE mobilities in groundwater around the Bangombé reactor. Their data suggest that actinides and REE were re-distributed by supergene weathering and rapidly incorporated into secondary REEbearing minerals.…”

Section: The Oklo-bangombé Natural Reactorsmentioning

confidence: 99%

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The role of mass spectrometry to study the Oklo–Bangombé natural reactors

Laeter

Hidaka

2007

Mass Spectrometry Reviews

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The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the (235)U/(238)U ratio of certain U ore samples indicated a depletion in (235)U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2 x 10(9) years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo-Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years.

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“…Aside from primary minerals, secondary minerals (colloids) and organic matters are also important factors affecting the mobilization and fractionation of trace elements and REEs (Stille et al, 1999;Aubert et al, 2001;Sun et al, 2012). As weathering proceeds, Fe, Al, and Mn were released from primary mineral and formed secondary minerals and colloids.…”

Section: Factors Controlling Trace Elements and Rees Mobilization/framentioning

confidence: 99%

Geochemistry of trace and rare earth elements during weathering of black shale profiles in Northeast Chongqing, Southwestern China: Their mobilization, redistribution, and fractionation

Ling

Ren

et al. 2015

Geochemistry

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REE mobility in groundwater proximate to the natural fission reactor at Bangombé (Gabon)

Cited by 47 publications

References 30 publications

Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature

Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature

The role of mass spectrometry to study the Oklo–Bangombé natural reactors

Geochemistry of trace and rare earth elements during weathering of black shale profiles in Northeast Chongqing, Southwestern China: Their mobilization, redistribution, and fractionation

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