Isotopic Fingerprint of Uranium Accumulation and Redox Cycling in Floodplains of the Upper Colorado River Basin.
Environ Sci Technol
; 53(7): 3399-3409, 2019 04 02.
Article
em En
| MEDLINE
| ID: mdl-30807121
ABSTRACT
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 (δ238U) 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 δ238U 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.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Poluentes Radioativos da Água
/
Água Subterrânea
/
Urânio
País/Região como assunto:
America do norte
Idioma:
En
Ano de publicação:
2019
Tipo de documento:
Article