Radiolytic stability of metal (IV) phosphonate sorbents designed for minor actinide-lanthanide separations
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Date
2024-09-01
Journal Title
Journal ISSN
Volume Title
Publisher
CEA
Abstract
Nuclear power is an intrinsically clean source of energy. However, improvements in nuclear waste treatment are required. The minor actinide (MA) elements in nuclear waste are problematic due to their radiotoxicity and long half-lives. In principle, minor actinides (MAs) in nuclear waste could be recycled. However, the chemical similarity of MAs and the lanthanide fission products also found in nuclear waste means that separating and recycling MAs is extremely challenging. Hence, there is a need for materials that can selectively separate MAs from lanthanides in nuclear waste, whilst also possessing the necessary acid and radiation resistance required to function in nuclear waste conditions.
Metal (IV) phosphonates, such as titanium or zirconium phosphonates, are a type of material with promising potential for MA-lanthanide separation applications. Metal phosphonates are a coordination polymer: a material in which inorganic metal cations are structurally joined together by organic ligands via coordinate bonds. The hybrid inorganic-organic nature of metal phosphonates allows for a variety of chemical and physical properties. In the context of MA-lanthanide separations, the phosphonate component allows for the intramolecular incorporation of organic ligands that provide selectivity and efficiency for MA sorption. Furthermore, the strong M(IV)–O–P bonding of the inorganic component provides stability and resistance to acid and radiation damage. Post-synthesis, metal phosphonates are collected as a porous, solid powder; hence, they can be employed as a solid-phase phase sorbent in MA-lanthanide separations. Previous studies on zirconium (IV) phosphonate materials have demonstrated promising sorption capacity, selectivity for MA over lanthanides, and excellent stability1,2,3. Therefore, further study and optimization of these materials presents a potential pathway for solving the challenges of MA separation and recycling.
In this study, a zirconium phosphonate sorbent that intramolecularly incorporates the MA-selective 2,6-bis(1,2,3-triazol-4-yl)pyridine (PTP) ligand was synthesised. The sorbent (ZrPTP) was irradiated with high energy electron radiation to doses of 2 MGy to study its radiation stability. Since ZrPs are highly amorphous, synchrotron light sources were employed to accurately assess the average local structure before and after irradiation using x-ray absorption spectroscopy (XAS) and atomic pair distribution function (PDF). Gas chromatography, solid-state NMR and infrared spectroscopy were also used to support the characterisation. Lastly, the MA-selectivity of ZrPTP before and after irradiation was compared using americium and europium. It was found that ZrPTP possessed excellent radiation stability for doses up to 2 MGy. Characterisation of ZrPTP exhibited only small amounts of radiation damage to its Zr-O bonds, aliphatic C-H bonds, and its N bonds in the triazole groups. Furthermore, ZrPTP demonstrated maintained selectivity for americium over europium even after a 2 MGy dose. Overall, the results extensively demonstrate the viability of metal phosphonate sorbents for nuclear waste treatment applications in terms of their radiation stability. © The Authors
Description
Keywords
Metals, Phosphonates, Actinides, Separation processes, Rare earths, Energy, Fission, Radioactive wastes, Titanium, Zirconium, Americium
Citation
Cataldo, T., Veliscek-Carolan, J., Bedford, N., & Le Caër, S. (2025). Radiolytic stability of metal (IV) phosphonate sorbents designed for minor actinide-lanthanide separations. Presentation to the 6th International ATALANTE Conference on Nuclear Chemistry for Sustainable Fuel Cycles (ATALANTE-2024) Avignon, France, September 1-6, 2024. In Book of Abstracts ATALANTE 2024 nuclear chemistry for sustainable fuel cycles, September 1-6, 2024 - Avigon, France, (pp. 73-74). Retrieved from: https://atalante2024.org/ATALANTE-2024-talks-BoA.pdf