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Title: Isotopic and geochemical tracers for U(VI) reduction and U mobility at an in situ recovery U mine

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. Post-mining 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 ²³⁸U/²³⁵U (δ²³⁸U), ²³⁴U/²³⁸U activity ratio, and ³⁴S/³²S (δ³⁴S), 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 δ²³⁸U in Rosita groundwater varies from 0.61‰ to -2.49‰, with a trend toward lower δ²³⁸U in downgradient wells. The concurrent decrease in U(VI) concentration and δ²³⁸U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic ²³⁴U/²³⁸U activity ratio and δ³⁴S 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:
 [1] ;  [2] ;  [3] ;  [2] ;  [4] ;  [4] ;  [4] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Univ. of California, Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, San Diego, La Jolla, CA (United States)
  6. Uranium Resources, Inc., Centennial, CO (United States)
  7. Stanford Univ., Stanford, CA (United States)
Publication Date:
OSTI Identifier:
1193681
Report Number(s):
LA-UR--15-21333
Journal ID: ISSN 0013-936X
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 49; Journal Issue: 10; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES