Extraction of Radioactive Cesium

1
Extraction of Radioactive Cesium
from Nuclear Waste
Mary Ditto Knox College - Galesburg,
IL (mditto_at_knox.edu) SULI/GLCA ORSS ORNL - CSD -
Chemical Separations Group
2
Basis for Research

• High Level waste clean up at Savannah River Site
• Need for removal of 137Cs from caustic media
• Extracting 137Cs from supernate using
  Caustic-Side Solvent Extraction (CSSX)
• Want to vitrify waste into glass canisters

Glass Storage
Solvent
Supernate
Extraction
Sludge
3
Five Approaches to Use of Ion Hosts

• Co-extraction of cation or anion

B. A. Moyer, P. V. Bonnesen, C. K. Chambliss, T.
J. Haverlock, A. P. Marchand, H-S. Chong, A. S.
McKim, K. Krishnudu, K. S. Ravikumar, V. S.
Kumar, and M. Takhi, in Nuclear Site Remediation
First Accomplishments of the Environmental
Science Program, ACS Symposium Series, Vol. 778,
P. G. Eller and W. R. Heineman, Eds., American
Chemical Society, Washington, DC, 2001.
4
Extraction Cycle
Extraction
Stripping
OH-
Acid
OH-
OH-
Waste
OH-
5
Distribution Ratios

• DCs Cs in organic phase divided by Cs in
  aqueous phase

DCs gtgt 1
DCs ltlt 1
Org
Org
Org
Org
Org
Org
Org
Aq
Aq
Aq
Extraction Organic calixarene grabs Cs out of HL
waste
Strip Acid removes Cs from organic layer
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New Stripping Solution?

• Boric Acid Advantages
• Preliminary results show promisingly low DCs
  values
• Boric acid already has boron for glass storage
• -no extra element added to the waste form

?

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Cesium Extraction Equations
Ion Pair Complexation in Organic Phase
Kex
B Extractant
Cs X- B
CsBX-
CsBX-
DCs Cs org
Kex
CsX-B
Cs aq
DCs
Kex
DCs ?X-
X-B
? constant

• Shows DCs is dependent on the concentration of
  the anion

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Extraction of Cesium from Nitric Acid

• DCs increases with NO3-, therefore ion pair
  complex

• Extract at high concentrations, Strip at low
  concentrations

9
Boric Acid Extraction and Strip

• Same conditions
• Extraction CSSX and SRS simulant
• Strip 1 mM H3BO3

Extraction
Strips

• Preliminary results show excellent low DCs values
  with only 3 strips.

• These results were non-reproducible, even after 6
  strips and two experiments.

Recipe given by the Savannah River Site
Personnel
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Extraction of Cesium from Boric Acid

• Slope Analysis Since slope 0, DCs not
  dependent upon H3BO3

• Changing conditions only varied DCs by 0.004

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Experiments and Conclusions
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Cesium Extraction Equations
Dissociation of Ion Pair
Kex
B Extractant
Cs X- B
CsB X-
CsBX-
CsB X-
Kex
CsX-B
Cs X-
DCs2
DCs Cs org
Kex
Cs aq
B
DCs constant Slope 0

• Shows DCs is independent of the concentration of
  the anion

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Cesium Extraction Through Anion Host

• New idea Extracting an anion with the cation
  coming along

• Extractions performed in nitrobenzene
• Very polar solvent
• Expect complete dissociation effect upon
  extraction
• True for most anions but not for all (Br- and
  Cl-)

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CsCl Results

• Points are mostly in line with previous results
• Evidence that the cation and anion are not
  completely dissociated

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Anion Host Conclusions

• Confirmed that chloride and bromide interact
  with the cesium cation
• Discovered that iodide behaves similarly to the
  other halides
• Confirmed that nitrate is dissociated from the
  cesium cation
• Something special going on with halides
• calix4pyrrole preorganized by the anion
  through complexation Good receptor for Cs?

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Impact of Research

• Helped determine that boric acid would not be an
  improvement on the current CSSX stripping
  solution
• Confirmed results for extraction of cesium
  anions using calix4pyrrole as an anion receptor
• Found new results for iodide

17
Acknowledgments
Lætitia H. Delmau - Supervisor Bruce Moyer -
Group Leader Maryna G. Gorbunova Jonathan L.
Sessler - UT-Austin Tatiana G. Levitskaia Chemical
Separations Group Chemical Sciences Division Oak
Ridge National Laboratory United States
Department of Energy SULI and ORSS sponsored by
GLCA