Understanding the behaviour of actinide species is of importance when removing and processing all nuclear waste. Examples include the safe clean-up of contaminated waste ponds and aspects of the TALSPEAK (Trivalent Actinide-Lanthanide Separation by Phosphorus Reagent Extraction from Aqueous Komplexes) process. The chemistry of the ponds and the TALSPEAK process has been studied by probing the aqueous solution behaviour of Ln(III), Am(III), Cm(III) and Th(IV) ions in the presence of organic (EDTA4- (ethylenediamine tetraacetate), DTPA5- (diethylenetriamine pentaacetate) and lactate) and inorganic (CO32- (carbonate) and OH- (hydroxide)) ligands by a variety of techniques including Nuclear Magnetic Resonance (NMR), Ultra Violet-Visible (UV-Vis) and luminescence spectroscopies, as well as potentiometry. Various ternary complexes have been shown to exist, including [M(EDTA)(CO3)]3-(aq), (where M = LnIII, AmIII or CmIII) and [Th(EDTA)(CO3)2]4-(aq), which form approximately over the pH range 8 to 11, and also [M(EDTA)(lactate)]2-(aq) (where M = Ln(III) or Am(III)) and [Th(EDTA)(lactate)]-(aq), which predominantly occur over the pH range 4 to 6. The nature of lactate interaction with [M(DTPA)]2-(aq) complexes (where M = Ln(III) or Am(III)) is unclear, as it may be possible that lactate can coordinate directly to the metal ion or to the acetate groups of DTPA5- (via a H-bonding interaction). The knowledge gained in this research has given a deeper insight into the nature of lanthanide and actinide coordination chemistry in mixed-ligand environments. For example, the increasing solubility of actinide metal ions in the contaminated waste ponds is probably due to the ability of organic ligands present in the ponds to solubilise metal ions at high pH, and also under TALSPEAK conditions of pH 3.5, there is likely to be minimal interaction of lactate with the [Ln(DTPA)]2-(aq) complexes. The determination of metal ion speciation using a combination of NMR, UV-Vis and luminescence spectroscopies, coupled with potentiometry, could be applied to new characterisation challenges faced in the future of the nuclear industry.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:553431 |
| Date | January 2012 |
| Creators | Griffiths, Tamara Lloyd |
| Contributors | Sharrad, Clint |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/investigations-of-ternary-complexes-relevant-to-the-nuclear-fuel-cycle(80e2192f-a0d4-4d7b-92a2-c366a36fc175).html |
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