The
aggregation of malonamide extractants diluted in an aliphatic
solvent phase has been studied in the presence of water by molecular
dynamics simulation. Using association criteria based on distances
between molecules and graphs theory, the aggregate distribution has
been computed and the corresponding Gibbs energy of aggregates and
mass action law constants have been determined. Finally, a model allowing
us to the compute critical micelle concentration and osmotic data
for a variable concentration of extractants, with or without a correction
of the organic phase activity, was developed. It appears however that
the accurate depiction of the aggregation allows modeling the thermodynamics
of the solution even without an explicit calculation of the activity:
both models give results in good agreement with the experiments.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.