title: Isotopic and Geochemical Tracers for U(VI) Reduction and U Mobility at an in Situ Recovery U Mine.
abstract: In situ recovery (ISR) uranium (U) mining mobilizes U in its oxidized hexavalent form (U(VI)) by oxidative dissolution of U from the roll-front U deposits. Postmining natural attenuation of residual U(VI) at ISR mines is a potential remediation strategy. Detection and monitoring of naturally occurring reducing subsurface environments are important for successful implementation of this remediation scheme. We used the isotopic tracers (238)U/(235)U (δ(238)U), (234)U/(238)U activity ratio, and (34)S/(32)S (δ(34)S), and geochemical measurements of U ore and groundwater collected from 32 wells located within, upgradient, and downgradient of a roll-front U deposit to detect U(VI) reduction and U mobility at an ISR mining site at Rosita, TX, USA. The δ(238)U in Rosita groundwater varies from +0.61‰ to -2.49‰, with a trend toward lower δ(238)U in downgradient wells. The concurrent decrease in U(VI) concentration and δ(238)U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic (234)U/(238)U activity ratio and δ(34)S values may also be used to trace the mobility of the ore zone groundwater after mining has ended. These results support the use of U isotope-based detection of natural attenuation of U(VI) at Rosita and other similar ISR mining sites.
authors.affiliation: †Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, California 94720, United States.
authors.forename: Anirban
authors.initials: A
authors.lastname: Basu
authors.affiliation: †Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, California 94720, United States.|‡Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Shaun T
authors.initials: ST
authors.lastname: Brown
authors.affiliation: ‡Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: John N
authors.initials: JN
authors.lastname: Christensen
authors.affiliation: †Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, California 94720, United States.|‡Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: DePaolo
authors.affiliation: §Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Reimus
authors.affiliation: §Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Heikoop
authors.affiliation: §Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Giday
authors.initials: G
authors.lastname: Woldegabriel
authors.affiliation: §Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Ardyth M
authors.initials: AM
authors.lastname: Simmons
authors.affiliation: §Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.|∥Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, United States.
authors.forename: Brian M
authors.initials: BM
authors.lastname: House
authors.affiliation: ⊥Uranium Resources, Inc., 6950 S. Potomac Street, Suite 300, Centennial, Colorado 80112, United States.
authors.forename: Matt
authors.initials: M
authors.lastname: Hartmann
authors.affiliation: #Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, United States.
authors.forename: Kate
authors.initials: K
authors.lastname: Maher
mesh_terms: D052918:Environmental Restoration and Remediation; D005843:Geography; D060587:Groundwater / Q000737:chemistry; D008906:Mining; D010084:Oxidation-Reduction; D013460:Sulfur Isotopes; D013781:Texas; D014501:Uranium / Q000032:analysis*; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D013460:Sulfur Isotopes; D014875:Water Pollutants, Radioactive; D014501:Uranium