Characterizing the structure of bacteriogenic uranium oxides
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Characterizing the Structure of Bacteriogenic Uranium Oxides. Jonathan Stahlman, Carnegie Mellon University John Bargar, Stanford Linear Accelerator Center Eleanor Schofield, Stanford Linear Accelerator Center. Outline. Motivation Overall project This summer’s work Final results.

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Characterizing the structure of bacteriogenic uranium oxides
Characterizing the Structure of Bacteriogenic Uranium Oxides

  • Jonathan Stahlman, Carnegie Mellon University

  • John Bargar, Stanford Linear Accelerator Center

  • Eleanor Schofield, Stanford Linear Accelerator Center


Outline
Outline

  • Motivation

  • Overall project

  • This summer’s work

  • Final results


A big problem
A BIG Problem

  • Our Cold War Legacy:

    • 1.7 trillion gallons of contaminated groundwater

    • 40 million m3 of contaminated soils

    • 3 million m3 of buried waste

  • Contaminants: radionuclides, metals, hydrocarbons

How do we manage these threats?


One possible solution

O2

2 e-

One Possible Solution

U(VI)

Shewanella oneidensis MR-1

2 e-

Nanoparticulate UO2

Uranium - green ; Oxygen - red


Hypothesis
Hypothesis

  • Incorporation of other cations present in groundwater into the UO2 structure will result in a more stable crystalline structure

We will look at:

Ca

Mg

Mn


A structured approach
A Structured Approach

  • Ecole Polytechnique Fédérale de Lausanne (EPFL)

    • Sample preparation

  • Washington University in St. Louis

    • Dissolution studies

  • Stanford Synchrotron Radiation Laboratory

    • Structural studies (EXAFS, WAXS)


This summer s work
This Summer’s Work

  • Wide angle x-ray scattering (WAXS) to examine lattice contraction

  • Experimental Setup

  • Compton Subtraction

  • Background Subtraction

  • Le Bail Fitting

  • Results

a


Wide angle x ray scattering
Wide Angle X-ray Scattering

  • Challenges:

    • Wet Samples

    • Radioactive Concerns

    • Anaerobic Conditions



Compton subtraction

2Θ = 10°

2Θ = 120°

Compton Subtraction

  • Compton - inelastically scattered x-rays

  • Can be easily separated at high angle due to difference in energy

    • Not true at lower angles


Compton fits
Compton Fits

2Θ = 10°

2Θ = 120°


Background subtraction
Background Subtraction

  • XRD-BS:

    • Subtract the capillary reflections

    • Correct for absorption in the sample


Le bail fitting
Le Bail Fitting

  • A derivative of the Rietveld Refinement

  • Used to extract the lattice constant

  • Parameters: Space Group, Particle Size, Background, Lattice Constant


Magnesium results
Magnesium Results

Undoped Sample: 5.4307 ± .0016 Å

10 mM Mg Doped Sample: 5.4405 ± .0045 Å

Sample pH: 8.0 Cleaning Method: NaOH


Calcium results
Calcium Results

Undoped Sample: 5.4437 ± .0029 Å

10 mM Ca Doped Sample: 5.4353 ± .0022 Å

Sample pH: 6.0 Cleaning Method: NaOH


Manganese results
Manganese Results

Undoped Sample: 5.4331 ± .0016 Å

Mn Doped Samples:

.1 mM : 5.3956 ± .0061 Å

1 mM : 5.4387 ± .0016 Å

5 mM : 5.4018 ± .0022 Å

Sample pH: 6.3 Cleaning Method: NaOH


Cleaning method results
Cleaning Method Results

No Dopants Added


Conclusions
Conclusions

  • Possible lattice contraction in Mn samples

  • NaOH cleaning process is affecting the structure of bacteriogenic UO2

  • Future Work:

    • Rietveld Refinement for more structural information

    • Possibly design new cleaning method


Acknowledgments
Acknowledgments

  • Funding:

    • Department of Energy, SULI

  • Software:

    • Sam Webb: XRD-BS

    • A.C. Larson and R.B. Von Dreele: GSAS

    • B. H. Toby: EXPGUI

    • Nita Dragoe: Powder 4

  • Other:

    • Apurva Mehta

    • John Bargar and Eleanor Schofield


Summary
Summary

  • Long term sequestration of bacteriogenic UO2 depends on incorporation of cations

  • WAXS provides structural information about bacteriogenic UO2 samples

  • Le Bail fitting reveals:

    • Possible lattice contraction for Mn doped sample

    • NaOH cleaning method causing lattice contraction


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