Speaker
Description
Third-phase formation—an unintended splitting of the organic phase during solvent extraction—creates major operational issues and limits the metal loading that can be safely processed. This demixing arises from the self-assembly of extractant molecules into reverse aggregates whose attractive interactions eventually lead to macroscopic phase separation, but the underlying structural mechanisms remain only partly understood. Using uranium extraction by aliphatic amines (such as tri-octylamine in alkanes) as a model system, we combined SAXS, SANS, and ultra-small-angle scattering to probe the multiscale organization of both the light and third organic phases. The results reveal a hierarchy of structures: small reverse aggregates (4–6 extractant molecules) that cluster into larger uranium-rich domains, water-containing aggregates contributing to high water uptake, and previously unrecognized pockets of trapped diluent dispersed at the nanoscale. Together, the scattering analyses show the coexistence of distinct aggregate populations and dynamic concentration fluctuations, providing new insight into the physical chemistry driving third-phase formation and highlighting the key role of diluent composition and aggregate interactions in phase behavior.
