Influence of Mass Transfer on U(VI) Influence of Mass Transfer on U(VI) Microbial ReductionMicrobial Reduction

Influence of Mass Transfer on U(VI) Influence of Mass Transfer on U(VI) Microbial ReductionMicrobial Reduction

Chongxuan Liu1, Zheming Wang1, John M. Zachara1, James K. Fredrickson1, Byong-Hun Jeon1,2, Paul D. Majors1, James P. McKinley1, and Steve M. Heald1,3

1Pacific Northwest National Laboratory

DOE Environmental Remediation Sciences Division 2006 Meeting

3Argonne National Laboratory

2Yonsei University, Korea

2

Uranium Physical Location in Contaminated Uranium Physical Location in Contaminated SedimentsSediments

Uranium Physical Location in Contaminated Uranium Physical Location in Contaminated SedimentsSediments

Hanford 200 Area Sediments Hanford 300 Area Sediments

At Hanford site, sorbed U exists as U(VI) with complex speciation, physical location, and mineral association.

Sorbed U is commonly associated with intragrain regions.

U(VI)-silicateprecipitatesin graniticlithicfragment

U(VI) insecondary materials

3

Conceptual ModelConceptual ModelConceptual ModelConceptual Model

Dissolution

DiffusiveMass Transfer

e- donor

U(VI)

U(IV)

Porewater/Groundwater Microbial Activity

4

Characterization of Intragrain DiffusionCharacterization of Intragrain DiffusionCharacterization of Intragrain DiffusionCharacterization of Intragrain Diffusion

Tortuosity factor (Dp/DH2O): 0.66 fast region 0.006 slow region

A 1H nuclear magnetic resonance, pulse-field gradient spin echo (NMR-PGSE) approach was developed to measure intragrain diffusion properties using H2O as a tracer.

Diffusion time interval t (ms)

1 10 100 1000

App

aren

t Dif

fusi

vity

(m

m2 /s

)

10-6

10-5

10-4

10-3

10-2

high diffusivitylow diffusivity

H2O diffusivity in granitic lithic fragmentNMR image of H2O distribution

Slice image

2 mm

Projection image

5

Models of Ion Diffusion CoefficientsModels of Ion Diffusion CoefficientsModels of Ion Diffusion CoefficientsModels of Ion Diffusion Coefficients

Coupled electrodynamics-nonequilibrium thermodynamics

(EDNT) model: Dip = f(, c, Dj

p, Cj) c: surface charge density, Dj

p and Cj: diffusivity and concentration of ion j, respectively.

Geometrical model: Dip = Di

w Di

p: pore diffusivity, : tortuosity; Diw: diffusivity in water,

++

++

+-

-+

+

+

+

-

Distance

+++

++

+ -

-+

+-

Restricted ionsin double layers

Con

cent

ratio

n Non-restricted ion diffusion domain Cation

Anion

Schematic ion diffusion regions

KCl or NaCl Concentration (M)

0.001 0.01 0.1 1

Dif

fusi

vity

(x

10-6

cm

2 /s)

0.1

1

10

KCl, Malusis&Shackelford, 2002 ES&T

NaCl, Lake&Rowe, 2000, Geotext. Geomembr

KCl NaClGeometrical model

EDNT model

Ion diffusivity in clay matrix = 0.7 - 0.8

6

Microbial Reduction of Intragrain U(VI)Microbial Reduction of Intragrain U(VI)Microbial Reduction of Intragrain U(VI)Microbial Reduction of Intragrain U(VI) Coupling of Biogeochemical Processes: Synthetic System

Dissolved U(VI)

Alginate beads with synthetic Na-boltwoodite

Cell

+

Dissolution/ diffusion

Bioreduction

Time (day)0 10 20 30 40

Dis

solv

ed U

(VI)

(m

g/L

)

0

200

400

600

800

1000Cell spike (MR-1)

Time (day)0 10 20 30 40

Dis

solv

ed U

(VI)

(m

g/L

)

0

200

400

600

800

1000Cell spike (MR-1)

5x108 cells/mL

2x108 cells/mL

S. Oneidensis MR-1

R = 1 mm

7

Intrabead U(VI) speciation and DistributionIntrabead U(VI) speciation and DistributionIntrabead U(VI) speciation and DistributionIntrabead U(VI) speciation and Distribution

100 m100 m

A

12x106

10

8

6

4

2

0

Re

lativ

e I

nte

nsi

ty (

a.u

.)

600550500

Wavelength (nm)

Delay Time (s)

< 1

200

400

600

1000

< 1

a

b

c

d

e

f B

LIFS spectra LIFS image

No change of intrabead U(VI) speciation; U(VI) dissolved/diffused starting from bead edge to center.

8

U(IV) Precipitation on Bacterial SurfaceU(IV) Precipitation on Bacterial SurfaceU(IV) Precipitation on Bacterial SurfaceU(IV) Precipitation on Bacterial Surface

Time = 2 days Time = 7 days Time = 100 days

U(IV) accumulation on bacterial surfaces and periplasm

0.2 m

9

Modeling Coupled Biogeochemical ProcessesModeling Coupled Biogeochemical ProcessesModeling Coupled Biogeochemical ProcessesModeling Coupled Biogeochemical Processes

Time (day)0 10 20 30 40

Dis

solv

ed U

(VI)

(m

g/L

)

0

200

400

600

800

1000Data, 0.0 cells/mLData, 1x108 cells/mLData, 2x108 cells/mLData, 4x108 cells/mLData, 5x108 cells/mLModel, 0.0 cells/mLModel, 1x108 cells/mLModel, 2x108 cells/mLModel, 4x108 cells/mLModel, 5x108 cells/mL

Cell spike

Intragrain dissolution + Intragrain diffusion + Extragrain bioreduction

10

10

8

6

4

2

0R

elat

ive

Inte

nsity

600580560540520500480460

Wavelength (nm)

Synthetic system

Sediment system

UO2(CO3)3 4- reference

Ca2UO2(CO3)3 reference

Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)

Effects of Calcite Dissolution

Time (day)

0 10 20 30 40 50

Dis

solv

ed U

(VI)

(m

g/L

)

0

5

10

15

Control106 cells/mL MR-1107 cells/mL MR-1

Simulation

Cell spike

LIFS Spectra of Aqueous Solutions at liquid helium temperature

11

Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)

Coupling of Biogeochemical Processes

XRM analysis of Residual U

Time (day)

0 10 20 30 40 50 60

Dis

solv

ed U

(VI)

( m

ol/L

)

0

10

20

30

40

ControlMR-1 wild type = 1x108 cells/mLMR-1 OmcA(AB) = 1x108 cells/mL

Cell spike

MR-1 Mtrc/OmcA

12

Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)

U silicate

30 m

SEM analysis showed residual U silicate in occluded regions

13

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

17140 17150 17160 17170 17180 17190 17200 17210 17220

E (eV)

Nor

mal

ized

abs

orpt

ion

UO2

Uranyl

(-444,-7833)

(-1326,-8744)

(-492, -9044)

(-1084, -7795)

(-510, -8211)

XANES analysis found mixed valence distribution of U(IV) and U(VI) inside grains.

Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)Microbial Reduction of Hanford Intragrain U(VI)

Other Reduction Process?

14

ConclusionsConclusionsConclusionsConclusions An NMR-PGSE technique indicated that a dual region diffusion model was required to simulate ion diffusion in the intragrain fractures of the granitic lithic fragment in Hanford sediment.

Coupled electrodynamics and nonequilibrium thermodynamics (EDNT) model indicated that macroscopic ion diffusivity is a complex function of microscopic properties of mineral surface charges, ion exchange reactions, electrostatic double layers, and ion charge coupling.

Macroscopic aqueous U(VI) concentration was determined by the microscopic coupling of biogeochemical processes of dissolution/desorption, diffusion and microbial activity.

Microbial reduction of intragrain U(VI) in the contaminated Hanford sediment was complicated by the dissolution of calcite that released Ca to complex uranyl carbonates, which in turn slowed bioreduction rate and increased dissolution/diffusion rates. Some intragrain U(VI) in the contaminated Hanford 200 Area sediment was in occluded regions and might not be reactive due to mass transfer limitation.