NEW INSIGHTS IN THIRD PHASE FORMATION IN THE U(Ⅵ)-HNO_3, TBP-ALKANE SYSTEM

摘要

In this work, the system U(Ⅵ)-HNO_3-tributylphosphate (TBP)-n-dodecane has been revisited with the objective of gaining coordination chemistry and structural information on the species that are formed in the organic phase before and after third phase formation. Chemical analyses, spectroscopic and EXAFS data indicate that U(Ⅵ) is extracted as the UO_2(NO_3)_2·2TBP adduct, while the third phase species has the composition UO_2(NO_3)_2·2TBP·HNO_3. Small-angle neutron scattering (SANS) data reveal the presence in the organic phase, both before and after phase splitting, of ellipsoidal aggregates whose formation seems to depend more on the extraction of HNO_3 than that of U(Ⅵ).