Impact of branching position and degree on uranium extraction by amines: A supramolecular and thermodynamic study

• Published in: Journal of molecular liquids 2024-06, Vol.403, p.124820, Article 124820
• Main Authors: Guerinoni, E., Giusti, F., Dourdain, S., Dufrêche, J.-F., Motokawa, R., Ueda, Y., Aoyagi, N., Zemb, T., Pellet-Rostaing, S.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemical Sciences
• ISSN: 0167-7322
• DOI: 10.1016/j.molliq.2024.124820

[Display omitted] •Suitable modification of tertiary amines alkyl chain structures enhances uranium extraction by 2 orders of magnitude.•Intermediate branching, as one or two short branched alkyl chains, yields optimal uranium extraction and limits third-phase formation.•Effect of branching on third phase formation and uranium extraction can be rationalized by considering that tertiary amines form reverse micelle-type aggregates.•The Gibbs free energy of transfer is monitored by the film term which is impacted by the packing parameter of the molecules and by the penetration of the diluent into the apolar shell of the aggregates. In uranium production, liquid–liquid extraction using the AMEX (AMine EXtraction) process employs tertiary amines solubilized in an aliphatic diluent. Practical constraints as phase stability problems and co-extraction of competitive elements highlight the need for in-depth investigation and optimization. Modifying gradually the alkyl chain structure of tertiary amines, we investigate here the large variation in extraction performance in terms of Gibbs free energy of transfer using the ienaic decomposition taking into account long-range interactions. We show hereby that structuration of the solvent phase can change uranium distribution by 2 orders of magnitude, which is incompatible with standard complexation theory of liquid–liquid extraction. We observe that co-extraction of water and aggregation number higher than four are required to obtain uranium extraction. We conclude that the film term in the ienaic decomposition of the Gibbs energy of transfer, is the one that governs extraction performance. It shows that metal transfer is beyond complexation, and that organization of the solvent phase must be considered to quantitatively interpret the distribution coefficients.