Evidence of a pre-transitional phase in third-phase formation using neutron and small-angle X-ray scattering

As part of a study of the AMEX process for uranium extraction in sulfuric media, new mechanisms for third-phase formation have been uncovered by small-angle X-ray and neutron scattering. The demixing of the organic phase, known as 3^rd phase, leads to major complications for industry, such as solvent losses, and even criticality problems when radioactive materials are involved. It is generally accepted that this demixing is linked to the structuring of the organic phase into inverted micelle-type aggregates, which attract and collapse until they demix. The result of a collaboration between ICSM and the Japan Atomic Energy Agency, analysis of the diffusion data suggested the involvement of other phenomena, such as depletion forces, as well as the formation of sub-nanometer nanodroplets of pre-third phase before demixing. A pre-transitional structure was thus identified, calling into question the sticky hard sphere models conventionally applied to fit diffusion data.

^{Credit: S. Dourdain / ICSM}

Authors: E. Guerinoni, S. Dourdain, O. Tache, R. Motokawa, Y. Ueda, S. Pellet Rostaing, T. Zemb

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Molecular and supramolecular mechanisms of uranium extraction by tertiary amines and quaternary ammoniums. E. Guerinoni. PhD thesis, University of Montpellier (2023)