Aggregation of Bifunctional Extractants Used for Uranium(VI) Separation

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Nuclear Chemistry

Background:

• Butyl-N,N-di(2-ethylhexyl)carbamoyl-nonylphosphonate (DEHCNPB) is an effective extractant for uranium from wet phosphoric acid.
• A detailed molecular-level understanding of DEHCNPB organic solutions and uranium speciation is lacking.
• Understanding these interactions is crucial for optimizing solvent extraction processes.

Purpose of the Study:

• To elucidate the supramolecular and molecular-scale behavior of DEHCNPB in organic solutions.
• To describe the aggregation of DEHCNPB and the speciation of uranium(VI) during extraction.
• To reveal the underlying molecular interactions governing the solvent extraction mechanism.

Main Methods:

• Classical Molecular Dynamics (MD) simulations.
• Small-Angle Neutron Scattering (SANS) and Small-Angle X-ray Scattering (SAXS) experiments.
• Integration of simulation and experimental data for comprehensive analysis.

Main Results:

• In the absence of uranium, DEHCNPB forms hydrogen-bonded dimers and trimers via phosphonate groups, excluding water.
• In the presence of uranium, 2-3 DEHCNPB molecules coordinate the uranyl cation through their phosphonate groups.
• Water molecules bound to uranyl form hydrogen bonds with DEHCNPB amide groups, stabilizing the complex and facilitating extraction.

Conclusions:

• Molecular simulations provide critical insights into the complex organic phase chemistry of DEHCNPB.
• Weak interactions, particularly hydrogen bonding, play a vital role in the uranium extraction mechanism.
• The study clarifies the molecular speciation and aggregation behavior of DEHCNPB in solvent extraction systems.