Kinetics and Mechanism\nof Ce(IV) Phase Transfer by\nthe Neutral Extractants Tributyl Phosphate and <i>N,N</i>-Di(2-ethylhexyl)isobutyramide

Tributyl phosphate and <i>N</i>,<i>N</i>-di(2-ethylhexyl)isobutyramide\n(DEHiBA) are uranium-selective extractants that could be used to recover\nlow-enriched uranium from commercial used nuclear fuel. The economic\nviability of liquid–liquid extraction processes for chemical\nseparations depends on both thermodynamic and kinetic considerations.\nWe used microfluidic droplet extraction to measure interfacial phase\ntransfer rate constants for the extraction and stripping of Ce(IV),\na nonradioactive actinide surrogate. The Damköhler numbers\nfor each system were calculated and the phase transfer processes were\ndetermined to be diffusion-limited under all conditions, contrary\nto prior studies using constant interface stirred cells and single\ndrop methods. A well-extracted 2:1 DEHiBA/Ce(IV) complex in the organic\nphase was determined from batch distribution studies, suggesting a\ndifferent extraction mechanism for Ce(IV) compared with poorly extracted\nPu(IV). Finally, phase disengagement rates were found to be rapid\nin both systems, in agreement with other studies.