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Title: Acid-switched Eu(III) coordination inside reverse aggregates: Insights into a synergistic liquid-liquid extraction system

Determining the structure of complex solutions bearing metal ions is challenging, but crucial for developing important technologies such as liquid-liquid extraction for metal refining and separation purposes. Herein, the structure of an organic Eu(III) solution consisting a binary mixture of lipophilic ligands di-2-ethylhexyl phosphoric acid (HDEHP) and tetraoctyl diglycolamide (TODGA) in dodecane is studied using synchrotron small angle X-ray scattering (SAXS) and X-ray absorption fine structure spectroscopy (EXAFS). This system is of technological importance in f-element separation for nuclear fuel cycle applications, where extraction is controlled by varying nitric acid concentration. Extraction is promoted at low and high concentration, but is retarded at intermediate concentration, leading to a U-shaped function; the structural origins of which we investigate. At the nanoscale, the solution is apparently comprised of reverse micelles with polar cores of approximately 1 nm in size, and these remain virtually unchanged as acid concentration is varied. Inside the polar cores, the coordination environment of Eu(III) switches from a 9-coordinate [Eu(TODGA) 3] 3+ motif at high acid, to a 6-coordinate HDEHP-dominated complex resembling Eu(HDEHP·DEHP) 3 at low acid. The results show that extraction is controlled within the coordination sphere, where it is promoted under conditions that favor coordination of eithermore » one of the two organic ligands, but is retarded under conditions that encourage mixed complexes. Lastly, our results link solution structure with ion transport properties in a technologically-important liquid-liquid ion extraction system.« less
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Inorganica Chimica Acta
Additional Journal Information:
Journal Name: Inorganica Chimica Acta; Journal ID: ISSN 0020-1693
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; solvent extraction; EXAFS; SAXS; solution structure; solvation; lanthanide
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1396660