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Title: Speciation of actinides and lanthanides with ligands proposed for next generation partitioning processes
Author: Whittaker, Daniel Mark
ISNI:       0000 0004 5364 0992
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2014
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Lanthanide(III) and actinide complexes with the N-donor extractants which are proposed for se in next generation separation processes, CyMe4-BTPhen and CyMe4-BTBP, have been synthesised and characterised in idealised synthetic and real extraction conditions. Next generation spent nuclear fuel reprocessing is necessary in order to reduce the longevity of activity (from 100,000’s to 100-1,000’s years) through re-use as fuel in GenIV reactor programs. The N donor extractants have been previously shown to preferentially extract the trivalent An ions over the Ln ions in biphasic acidic extraction processes, a necessary task due to the large neutron capture crosssections of the lanthanides, and the reasons behind this selectivity have been investigated here. Proposed processes that use these extractants are called SANEX and GANEX. The SANEX process is undertaken after a PUREX-style process where only the trivalent minor actinides and the lanthanides are present during the separation. Whereas, in the GANEX process the organic phase contains the N-donor molecule and another extractant, such as TBP, with the aqueous phase containing the entire An series in various oxidation states. Speciation of the Ln3+ ions with the N-donor molecules has been shown to be dominated by 1:2 (M:L) complexes in the bulk organic phase post extraction and coordination is completed by a small ligand, either H2O or NO3-. Spectrophotometric titration yielded logβ values for the 1:2 (M:L) complexes of Pr3+, Eu3+ and Tb3+ nitrate salts. In all cases it was shown that the CyMe4-BTPhen molecule has a greater affinity than the CyMe4-BTBP molecule for the Ln3+ ions, as expected given the ‘locked’ design of CyMe4-BTPhen. The uranyl ion was shown to only form 1:1 (M:L) complexes in solution with the N-donor molecules but structural characterisation showed it to also form 2:1 (M:L) complexes with the metal ions bridged by a peroxide anion. The formation of this species was found to require a protic solvent, light and molecular dioxygen. Again, binding was shown, by spectrophotometric titration, to be stronger with CyMe4-BTPhen than CyMe4-BTBP.The speciation of the tetravalent An ions, Pu4+ and Th4+ was studied using 1H NMR and X-ray absorption spectroscopy in GANEX style conditions. When the organic phase contains TBP and the N donor extractants, complexation is completed by TBP in the post extraction organic phase and the extraction of Th4+ is exclusively completed by TBP but by both extractants for Pu4+. In both cases, the major bulk species was identified as Pu/Th(NO3)4.3TBP, although complexes of the N donor extractants and the An4+ have been observed in idealised conditions, in both 1:1 and 1:2 (M:L) stoichiometries, depending on the solution composition. U4+ was shown to form a variety of complexes of a myriad of M:L stoichiometries.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: purex ; ganex ; sanex ; uranium ; uranyl ; CyMe4-BTPhen ; CyMe4-BTBP ; plutonium ; separation ; nuclear waste ; actinide ; lanthanide ; GenIII ; GenIV