A reactive transport approach
to predicting subsurface
uranium mobility:
Lessons from Rifle, Colorado
Jennifer Druhan,
Matt Bizjack ,
Noah Jemison,
Tom Johnson
Uranium
Recover y
Workshop
Denver, Colorado
6/7/2016
Rifle, Colorado
Previous site of
uranium mill
 ore → usable
uranium
Persistent U
contamination in
groundwater
Site of DOE
bioreduction
experiments
Google (2014)
US DOE (1999)
2
2010 Acetate Injection
Experiment
2 meters
Long et al. 2015
3
2010 Acetate Injection
Experiment
Long et al. 2015
4
U(VI) Reactive Transport
Complexation
Adsorption
Reduction
 Microbial
 Abiotic
 Oxidation
2+
O
U
[UO2(CO3)3]4 −
O
[(UO2)3(CO3)6]6−
Bernhard et al. 2001; Schlosser et al. 2010
5
U(VI) Reactive Transport
Complexation
Adsorption
Reduction
 Microbial
 Abiotic
 Oxidation
Lee and Yun (2013)
6
U(VI) Reactive Transport
Complexation
Adsorption
Ca2UO2(CO3)3(aq)
Ca2UO2(CO3)3(aq)
Ca2UO2(CO3)3(aq)
Reduction
Ca2UO2(CO3)3(aq)
Ca2UO2(CO3)3(aq)
Ca2UO2(CO3)3(aq)
 Microbial
 Abiotic
 Oxidation
Fox et al. 2006; Hyun et al. 2009
Mineral/Sediment surface
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U(VI) Reactive Transport
Complexation
Adsorption
Reduction
 Microbial
 Abiotic
 Oxidation
UO22+(aq)
e- donors
Org. C
H2S
2 e-
(Fe2+)
UO2(s)
Hyun et al. 2014; Williams et al. 2011; Bargar et al. 2013; Bao et al. 2014
8
U(VI) Reactive Transport
Complexation
Adsorption
Reduction
 Microbial
 Abiotic
UO22+(aq)
e- acceptors
O2
NO3-
2 e-
 Oxidation
UO2(s)
de Pablo et al. 1999
9
Conceptual model
10
Advective zone only
2 meters
11
Numerical model
CrunchTope
U Reactions
 Adsorption
>S(OH)2 + UO2++ → H+ + >S(OH)UO2+
logK = -7.92
>T(OH)2 + UO2++ → H+ + >T(OH)UO2+
logK = -3.52
 Microbial Reduction
=
Hyun et al. (2009)
[
]
[
+[
]
]
[
]
+[
]
12
Advective zone only
Model Results
Acetate Injection Active
Observations
Model
Bizjack et al. in prep
13
Advective zone only
Model Results
Sorption or
reoxidation?
Bizjack et al. in prep
14
U Isotopes
Two major effectively stable isotopes
 t ½ > 7×10 8 yr
 238 U (99.27%)
 235 U (0.72%)
Microbial reduction
preferentially uses
238 U
UO22+(aq)
Microbe
Basu et al. (2014)
UO2(s)
HCO3-(aq)
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U(VI) Reactive Transport
Factors affecting U
conc.
 Complexation
 Adsorption
 Reduction
Factors affecting field
scale U isotope ratios
 Complexation
 Adsorption
 Reduction
 Microbial
 Abiotic
 Microbial
 Abiotic
 Oxidation
 Oxidation
16
2010 Acetate Injection
Experiment
Long et al. 2015
17
2010 Acetate Injection
Experiment
Shiel et al. 2016
18
Advective zone only
Model Results
Bizjack et al. in prep
19
+ Diffusion Only Zones
with Gradient
Diffusion Only, 3% Porosity
Flow
Advection + Diffusion
25% Porosity
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+ Diffusion Only Zones
with Gradient
Bizjack et al. in prep
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Mass transport limitation
22
Distribution of solid phase U
after a bio-reduction event
Uraninite Volume
Fraction
Bizjack et al. in prep
Uraninite δ 238 U
23
A model for long-term U
accumulation
Jemison et al. in prep
24
Key Points
The reactive transport of U transport is a
complex, multi-component process
Numerical reactive transport models keep
track of these complexities and are a powerful
way of synthesizing observations to yield
predictive knowledge
U isotope ratios offer a unique constraint for
reactive transport models of U mobility
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