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

TitleIsotopic and geochemical tracers for U(VI) reduction and U mobility at an in situ recovery U mine
Publication TypeJournal Article
Year of Publication2015
AuthorsBasu A., Brown S.T, Christensen J.N, DePaolo D.J, Reimus P.W, Heikoop J.M, Wodegabriel G., Simmons A.M, House B.M, Hartmann M., Maher K.
JournalEnvironmental Science & Technology
Volume49
Pagination5939-5947
Date Published2015/05
Type of ArticleArticle
ISBN Number0013-936X
Accession NumberWOS:000355058300013
Keywordsfractionation factors; fresh-water; Groundwater; heavy-elements; riparian zone; sediment; stable-isotopes; th-series nuclides; transport; u-238/u-235; uranium deposits
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 U-238/U-235 (delta U-238), U-234/U-238 activity ratio, and S-34/S-32 (delta S-34), 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 delta U-238 in Rosita groundwater varies from +0.61 parts per thousand to -2.49 parts per thousand, with a trend toward lower delta U-238 in downgradient wells. The concurrent decrease in U(VI) concentration and delta U-238 with an epsilon of 0.48 parts per thousand +/- 0.08 parts per thousand is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic U-234/U-238 activity ratio and delta S-34 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.

DOI10.1021/acs.est.5b00701
Short TitleEnviron. Sci. Technol.
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