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Title: Direct monitoring of speciation for minor actinide separations
Author: Stuber, Wanda
ISNI:       0000 0004 6494 4297
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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One of the major challenges in the development of future generations of nuclear reprocessing procedures is the separation of the minor actinides from the chemically similar trivalent lanthanide ions. In this thesis, the potential of two purely N-donor ligands for minor actinide separations is evaluated and behaviour in aqueous and extraction conditions investigated. Of two chosen ligands, 12N4Py4 and 9N3Py3, only the larger 12N4Py4 was found to be able to complex lanthanide ions; however, both bind readily to divalent calcium ions. In comparison to earlier published properties of Ln(III)- 12N4Py4 complexes, the cerium complex was found to show differences based on greater d-orbital mixing. Conjugated acid dissociation constants and metal binding constants were determined using newly developed fitting functions in several conditions and found to be comparable to those of other extractants. As the investigation was performed in aqueous conditions, side reactions such as hydroxide formation and precipitation had to be considered and included into fitting procedures. Studies on U(IV) and Am(III) were conducted, but due to unfavourable conditions complexation by 12N4Py4 could not be verified beyond reasonable doubt. Extraction of ligand species and metal complexes was studied in various conditions and in the presence of various anions. Beside the main target cations, Ln(III) and An(III), 12N4Py4 is also capable of complexing and extracting protonated ligand species and Na+ with considerably higher partition coefficients than those observed for species with higher charge. Low solubilities of potassium, sodium and protonated species involving 12N4Py4 in presence of lipophilic anions such as pertechnetate, perrhenate and triiodide lead to precipitation. Formation of solids is of considerable concern in minor actinide separations, but could also offer novel pathways for iodine trapping.
Supervisor: Faulkner, Stephen ; Stuber, Wanda Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available