Minor actinide recycling by means of spent nuclear fuel partitioning and subsequent transmutation is a challenging but indispensable step, in order to reduce the long-term radiotoxicity of the spent fuel and thus the burden for future generations. Among the different hydrometallurgical processes proposed so far for MA partitioning, the 1c-SANEX stands out for its conceptual simplicity. The present thesis work was focused on the study of three newly synthesized lipophilic ligands to substitute the current ligand of reference in the 1c-SANEX process. Two of them, named PTID and PTTO, boasted the promising 2,6-bis-triazolyl-pyridine (PyTri) complexing core, already proven to be selective for An in the PTEH ligand of the same family, functionalized with different alkyl chains at the 1-position of the triazoles, while the third one incorporated three PyTri units in a calixarene preorganized structure. Their solubility in various organic diluents was studied, along with their efficiency and selectivity properties towards An(III) through liquid-liquid extraction tests with actinide and lanthanide radiotracers. In addition, to comprehend the complex formation and extraction mechanism, ad hoc monophasic solutions containing the ligands and stable cations (La and Eu) at different ratios as well as organic phases from extraction experiments were analyzed by electrospray ionization mass spectrometry. Designed to be improvements of the PTEH ligand, PTID and PTTO showed promising solubility and selectivity, however, differences in extraction efficiency were observed. PTTO is slightly more efficient with respect to PTEH, while PTID exhibits too low extraction efficiency, despite having the same complexing core. The macrocyclic ligand proved to be adequately soluble and the preorganization of its coordinating PyTri units on the calixarene scaffold leads to satisfactory efficiency and remarkable selectivity for Am over Eu. The experimental results strengthen the belief that PyTri ligands can actually be a viable alternative for the selective actinide separation in SANEX-like processes.
Il riciclo degli attinidi minori, mediante partitioning dal combustibile nucleare e loro trasmutazione, è un processo necessario per ridurre la radiotossicità a lungo termine del combustibile esausto. Attualmente, uno dei processi idrometallurgici proposti per il partitioning di MA è il 1c-SANEX che si contraddistingue per la sua semplicità concettuale. Il progetto di tesi si è focalizzato sullo studio di tre leganti lipofili di nuova sintesi quali possibili alternative all'attuale legante di riferimento nel processo 1c-SANEX. Due di questi, PTID e PTTO, sono costituiti dal core complessante 2,6-bis-triazolil-piridina (PyTri) funzionalizzato con diverse catene alchiliche laterali, core che ha già dimostrato la sua selettività per gli An(III) tramite il legante PTEH della stessa famiglia. Il terzo legante è costituito da una struttura preorganizzata quale un calix[4]arene funzionalizzato con tre unità chelanti PyTri. Per ciascun legante è stata studiata sperimentalmente la solubilità in solventi organici, insieme alla loro efficienza e selettività verso An(III) mediante test di estrazione con solvente in presenza di radiotraccianti (Am-241 e Eu-152). Inoltre, per comprendere il meccanismo di complessazione, sono state analizzate tramite spettrometria di massa a ionizzazione elettrospray sia soluzioni monofasiche contenenti i leganti e cationi stabili (La ed Eu) a diversi rapporti che fasi organiche derivanti dai test di estrazione. I leganti PTID e PTTO, progettati come miglioramento del PTEH, hanno mostrato promettente solubilità e selettività, ma una diversa efficienza di estrazione. Il PTTO risulta leggermente più efficiente rispetto al PTEH, mentre il PTID ha un’efficienza molto bassa, nonostante tutti abbiano lo stesso core complessante. Il legante macrociclico si è dimostrato adeguatamente solubile e la preorganizzazione delle unità chelanti PyTri sul macrociclo ha permesso di ottenere un’efficienza e una selettività per Am(III) ancor più elevate. I risultati sperimentali ottenuti rafforzano la convinzione che i leganti PyTri possano essere una valida alternativa per la separazione selettiva degli attinidi nei processi di tipo SANEX.
Lipophilic 2,6-bis-triazolyl-pyridine derivatives for minor actinide recycling : a comparative study
GRIVAS, SYMEON
2020/2021
Abstract
Minor actinide recycling by means of spent nuclear fuel partitioning and subsequent transmutation is a challenging but indispensable step, in order to reduce the long-term radiotoxicity of the spent fuel and thus the burden for future generations. Among the different hydrometallurgical processes proposed so far for MA partitioning, the 1c-SANEX stands out for its conceptual simplicity. The present thesis work was focused on the study of three newly synthesized lipophilic ligands to substitute the current ligand of reference in the 1c-SANEX process. Two of them, named PTID and PTTO, boasted the promising 2,6-bis-triazolyl-pyridine (PyTri) complexing core, already proven to be selective for An in the PTEH ligand of the same family, functionalized with different alkyl chains at the 1-position of the triazoles, while the third one incorporated three PyTri units in a calixarene preorganized structure. Their solubility in various organic diluents was studied, along with their efficiency and selectivity properties towards An(III) through liquid-liquid extraction tests with actinide and lanthanide radiotracers. In addition, to comprehend the complex formation and extraction mechanism, ad hoc monophasic solutions containing the ligands and stable cations (La and Eu) at different ratios as well as organic phases from extraction experiments were analyzed by electrospray ionization mass spectrometry. Designed to be improvements of the PTEH ligand, PTID and PTTO showed promising solubility and selectivity, however, differences in extraction efficiency were observed. PTTO is slightly more efficient with respect to PTEH, while PTID exhibits too low extraction efficiency, despite having the same complexing core. The macrocyclic ligand proved to be adequately soluble and the preorganization of its coordinating PyTri units on the calixarene scaffold leads to satisfactory efficiency and remarkable selectivity for Am over Eu. The experimental results strengthen the belief that PyTri ligands can actually be a viable alternative for the selective actinide separation in SANEX-like processes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/173322