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Structural correspondence between uranyl chloride complexes in solution and their stability constants.

L Soderholm¹, S Skanthakumar, Richard E Wilson

¹Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States. ls@anl.gov

The Journal of Physical Chemistry. A

|April 30, 2011

Summary

Chloride ions directly bind to uranyl in solution, replacing water molecules and decreasing the uranyl coordination number. This study confirms uranyl chloride complex structures and their stability constants using high-energy X-ray scattering.

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Area of Science:

Inorganic Chemistry
Solution Chemistry
X-ray Scattering

Background:

Uranyl ions (UO2^2+) are crucial in nuclear fuel cycles and environmental remediation.
Understanding uranyl speciation in chloride solutions is vital for predicting its behavior.

Purpose of the Study:

To elucidate the structural details of uranyl chloride complexes in aqueous solutions.
To quantify the coordination changes and stability constants of uranyl chloride complexes.

Main Methods:

High-energy X-ray scattering (HEXS) was employed to collect pair-distribution function (PDF) data.
Solutions were analyzed across varying chloride concentrations and at constant ionic strength.
Stability constants were determined and compared with literature values.

Main Results:

Chloride ions form inner-sphere complexes with uranyl, displacing water molecules.
Uranyl coordination number decreases with increasing chloride concentration.
Stability constants (β1, β2, β3) were determined and found to agree with previous studies.
Structural models for mono-, di-, and trichlorouranyl species were proposed based on coordination numbers.

Conclusions:

HEXS data confirm the existence of direct uranyl-chloride interactions, not just solvent-ion effects.
The study provides a detailed structural model for uranyl chloride complexes in solution.
The findings contribute to a better understanding of uranyl chemistry in chloride-containing environments.