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Speciation and reactivity of uranium products formed during in situ
bioremediation in a shallow alluvial aquifer
#MMPMID25265543
Alessi DS
; Lezama-Pacheco JS
; Janot N
; Suvorova EI
; Cerrato JM
; Giammar DE
; Davis JA
; Fox PM
; Williams KH
; Long PE
; Handley KM
; Bernier-Latmani R
; Bargar JR
Environ Sci Technol
2014[Nov]; 48
(21
): 12842-50
PMID25265543
show ga
In this study, we report the results of in situ U(VI) bioreduction experiments at
the Integrated Field Research Challenge site in Rifle, Colorado, USA. Columns
filled with sediments were deployed into a groundwater well at the site and,
after a period of conditioning with groundwater, were amended with a mixture of
groundwater, soluble U(VI), and acetate to stimulate the growth of indigenous
microorganisms. Individual reactors were collected as various redox regimes in
the column sediments were achieved: (i) during iron reduction, (ii) just after
the onset of sulfate reduction, and (iii) later into sulfate reduction. The
speciation of U retained in the sediments was studied using X-ray absorption
spectroscopy, electron microscopy, and chemical extractions. Circa 90% of the
total uranium was reduced to U(IV) in each reactor. Noncrystalline U(IV)
comprised about two-thirds of the U(IV) pool, across large changes in microbial
community structure, redox regime, total uranium accumulation, and reaction time.
A significant body of recent research has demonstrated that noncrystalline U(IV)
species are more suceptible to remobilization and reoxidation than crystalline
U(IV) phases such as uraninite. Our results highlight the importance of
considering noncrystalline U(IV) formation across a wide range of aquifer
parameters when designing in situ remediation plans.
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