Dataset Information

Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer.

ABSTRACT: The stimulation of bacterial activities that convert hexavalent uranium, U(VI), to tetravalent uranium, U(IV), appears to be feasible for cost-effective remediation of contaminated aquifers. However, U(VI) reduction typically results in the precipitation of U(IV) particles less than 5 nanometers in diameter, except for environmental conditions enriched with iron. Because these tiny particles are mobile and susceptible to oxidative dissolution after the termination of nutrient injection, in situ bioremediation remains to be impractical. Here we show that U(IV) nanoparticles of coffinite (U(SiO4)1-x(OH)4x) formed in fracture-filling calcium carbonate in a granitic aquifer. In situ U-Pb isotope dating demonstrates that U(IV) nanoparticles have been sequestered in the calcium carbonate for at least 1 million years. As the microbiologically induced precipitation of calcium carbonate in aquifer systems worldwide is extremely common, we anticipate simultaneous stimulation of microbial activities for precipitation reactions of calcium carbonate and U(IV) nanoparticles, which leads to long-term sequestration of uranium and other radionuclides in contaminated aquifers and deep geological repositories.

SUBMITTER: Suzuki Y

PROVIDER: S-EPMC4780221 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer.

Suzuki Yohey Y Mukai Hiroki H Ishimura Toyoho T Yokoyama Takaomi D TD Sakata Shuhei S Hirata Takafumi T Iwatsuki Teruki T Mizuno Takashi T

Scientific reports 20160307

The stimulation of bacterial activities that convert hexavalent uranium, U(VI), to tetravalent uranium, U(IV), appears to be feasible for cost-effective remediation of contaminated aquifers. However, U(VI) reduction typically results in the precipitation of U(IV) particles less than 5 nanometers in diameter, except for environmental conditions enriched with iron. Because these tiny particles are mobile and susceptible to oxidative dissolution after the termination of nutrient injection, in situ ...[more]

PMID: 26948389

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Project description:Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1-2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite-metatorbernite (Cu(UO2)2(AsO4)2-x (PO4) x ·8H2O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO2)2(SiO3OH)2·6H2O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO2)2(PO4)2·8H2O) were identified. The Cu(UO2)2(AsO4)2-x (PO4) x ·8H2O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed.

Dataset Information

Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer.

Publications

Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer.

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