期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 53, 期 7, 页码 3399-3409出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.8b05593
关键词
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资金
- DOE-BER Climate and Environmental Sciences Division through the SLAC Groundwater Quality Science Focus Area (SFA) program
- DOE-BES [DE-AC02-76SF00515]
- Lawrence Berkeley National Laboratory's Genomes-to-Watershed Scientific Focus Area [DE-AC02-05CH11231]
Uranium (U) groundwater contamination is a major concern at numerous former mining and milling sites across the Upper Colorado River Basin (UCRB), USA, where U(IV)-bearing solids have accumulated within naturally reduced zones (NRZs). Understanding the processes governing U reduction and oxidation within NRZs is critical for assessing the persistence of U in groundwater. To evaluate the redox cycling of uranium, we measured the U concentrations and isotopic compositions (delta U-238) of sediments and pore waters from four study sites across the UCRB that span a gradient in sediment texture and composition. We observe that U accumulation occurs primarily within fine-grained (low-permeability) NRZs that show active redox variations. Low permeability NRZs display high accumulation and low export of U, with internal redox cycling of U. In contrast, within high permeability NRZs, U is remobilized under oxidative conditions, possibly without any fractionation, and transported outside the NRZs. The low delta U-238 of sediments outside of defined NRZs suggests that these reduced zones act as additional U sources. Collectively, our results indicate that fine-grained NRZs have a greater potential to retain uranium, whereas NRZs with higher permeability may constitute a more-persistent but dilute U source.
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