From EXAFS of reference compounds to U(VI) speciation in contaminated environments

Area of Science:

• Environmental Science
• Geochemistry
• Nuclear Chemistry

Background:

• Understanding technogenic uranium speciation is vital for assessing migration, bioavailability, and remediation of contaminated sites.
• Reference data from well-characterized uranium compounds are essential for accurate analysis of environmental samples.
• Minimizing synchrotron measurement errors requires comparing environmental data with standards acquired under identical conditions.

Purpose of the Study:

• To establish reliable reference data for technogenic uranium compounds using X-ray absorption spectroscopy (XAS).
• To accurately determine uranium speciation in a radioactively contaminated soil sample.
• To improve the reliability of uranium speciation analysis in nuclear legacy sites.

Main Methods:

• Characterization of reference uranium compounds (uranyl oxyhydroxides, phosphates, carbonates, uranates) using Raman spectroscopy and powder X-ray diffraction.
• Acquisition and analysis of X-ray Absorption Fine Structure (XAFS) spectra for reference compounds and a contaminated soil sample.
• EXAFS fitting to determine bonding nature, interatomic distances, and coordination numbers for uranium species.

Main Results:

• Distinct XAFS parameters were identified for various uranium compounds, enabling differentiation.
• The speciation of uranium in the contaminated soil sample was determined to be a mixture of uranium oxyhydroxide and carbonate phases.
• The study successfully differentiated local molecular environments of U(VI) in model compounds.

Conclusions:

• The developed methodology using well-characterized standards and XAFS provides reliable uranium speciation data.
• Accurate uranium speciation is achievable even in complex environmental matrices like contaminated soil.
• This research contributes to better risk assessment and effective remediation planning for uranium-contaminated nuclear legacy sites.