title: 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.
authors.affiliation: Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yohey
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Mukai
authors.affiliation: National Institute of Technology, Ibaraki College, 866 Nakane, Hitachinaka-shi, Ibaraki 312-8508, Japan.
authors.forename: Toyoho
authors.initials: T
authors.lastname: Ishimura
authors.affiliation: Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Takaomi D
authors.initials: TD
authors.lastname: Yokoyama
authors.affiliation: Division of Earth &Planetary Sciences, Kyoto University, Kitashirakawa Oiwakesho, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Sakata
authors.affiliation: Division of Earth &Planetary Sciences, Kyoto University, Kitashirakawa Oiwakesho, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Hirata
authors.affiliation: Japan Atomic Energy Agency (JAEA), 1-64 Yamanouchi, Akeyo-cho, Mizunami, Gifu 509-6132, Japan.
authors.forename: Teruki
authors.initials: T
authors.lastname: Iwatsuki
authors.affiliation: Japan Atomic Energy Agency (JAEA), 1-64 Yamanouchi, Akeyo-cho, Mizunami, Gifu 509-6132, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizuno
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D060587:Groundwater / Q000382:microbiology*; D053758:Nanoparticles / Q000378:metabolism*; D055110:Radiometric Dating; D014501:Uranium / Q000378:metabolism*
chemical_list: D014501:Uranium