posted on 2021-07-29, 04:03authored byDiego Moreno Martinez, Eléonor Acher, Marin Vatin, Sandrine Dourdain, Dominique Guillaumont, Philippe Guilbaud
DEHCNPB
(butyl-N,N-di(2-ethylhexyl)carbamoyl-nonylphosphonate)
is an amido-phosphonic acid that has remarkable properties for the
separation of uranium from wet phosphoric acid. Despite previous studies,
a detailed description of the DEHCNPB organic solutions at the supramolecular
and molecular scales is missing. In the present work, we use classical
Molecular Dynamics (MD) combined with SANS and SAXS experimental data
in order to describe the aggregation of the bifunctional extractant
DEHCNPB as well as the speciation of uranium(VI) in such systems.
We provide a fine description of the molecular species in the organic
solution and of the interactions within the aggregates formed, shedding
light on solvent extraction mechanisms. Without uranium, the organic
phase is highly composed of dimers and trimers H-bonded through phosphonate
functions and without water molecules. With uranium, two to three
extractant molecules coordinate directly the uranyl cation by their
phosphonate groups. Uranyl is not fully dehydrated in this organic
solution, and the amide groups of the extractants are found to form
H-bonds with the water molecules bound to uranyl. These H-bond networks
around the metallic cation stabilize the complexes and facilitate
the extraction. These results underline the importance of considering
weak interactions in the understanding of extraction processes and
demonstrate how molecular simulations provide essential insights into
such complex organic phase chemistry with a high number of species.