Реферат: The widespread use of atomic technologies has made the issues surrounding the disposal of radioactive waste a concern for nearly every country today. One of the promising methods for the long-term management of radioactive waste is deep geological disposal in stable geological formations, utilizing both engineered and natural barriers. To ensure the safety of disposal sites, it is essential to understand the migration behavior of radionuclides at a molecular level. Phosphate anions and alkali metal cations are integral components of natural environments. Therefore, the investigation of the structure and properties of double phosphates of actinides is one of the key tasks. The chemical behavior of Pu is complex as it possesses seven oxidation states, four of which (Pu(III), Pu(IV), Pu(V), and Pu(VI)) may coexist under environmental conditions and can easily transform from one to another depending on the conditions. Here, we investigate the formation patterns of Pu-containing particles in aqueous media, focusing on their interactions with vital inorganic phosphate ligands. Given Pu complex redox chemistry and high radiotoxicity, our study also includes their less radioactive monovalent thorium (Th) analogue and non-radioactive cerium (Ce) for comparison. We aim to establish the relationship between actinide particle formation conditions, size, structure, and thermodynamic properties. A traditional method for determining the structure of compounds is X-ray diffraction (XRD). Synchrotron X-ray diffraction allows for the investigation of small quantities of substances, which is particularly important in the context of working with radionuclides. In addition to X-ray diffraction, X-ray absorption spectroscopy (XAS) enables the determination of the oxidation state of actinides as well as their local environment. Together, these methods provide comprehensive data on the structure of double phosphates of actinides, allowing for a thorough description of new compounds that were previously unknown in the literature. Double phosphates of Pu, Th and Ce were synthesised by by aging process of PuO2, ThO2 or CeO2 nanoparticles in Na2HPO4/NaH2PO4 media for up to 4 years. Additionally, the dioxide’s aging process was studied under mild hydrothermal treatment (HT) conditions (< 150 °С) in K2HPO4/KH2PO4 or (NH4)2HPO4/NH4H2PO4 solutions. The structure features and phase composition of the samples were investigated by synchrotron XRD and absorption spectroscopy (XAS) and electronic microscopy (SEM and HRTEM). Under long-term storage and HT treatment conditions in a phosphate buffer medium, PuO2, CeO2, and ThO2 nanoparticles are crystallized into the phosphates phase. Their second-generation phase structure depends on the pH value and the composition of the initial phosphate buffer. The HT treatment of dioxides in a NaH2PO4/Na2HPO4 buffer solution leads to the formation of a nanocrystalline Ce(IV) phase. In contrast, thorium and plutonium generate a phase characterized by the local structure of NaTh2(PO4)3. Additionally, Pu(IV) double phosphates with K+ or NH4+ can be synthesized when PuO2 undergoes HT treatment in potassium phosphate or ammonium phosphate buffers. Using synchrotron radiation techniques enable to decode the structures of K2Pu(PO4)2 and (NH4)2Pu(PO4)2 for the first time. pages:93-94 funding:This work was supported by the Ministry of Science and Higher Education of the Russian Federation, grant number 075-15-2021-1353.

Библиографическая ссылка: Plakhova T.V. , Kuzenkova A.S. , Romanchuk A.Y. , Kalmykov S.N.
Synthesis and structural elucidation of Pu, Ce, and Th double phosphates using synchrotron radiation
В сборнике Synchrotron Radiation Techniques for Catalysts and Functional Materials. III International Conference : Abstracts. – BIC SB RAS., 2024. – C.93-94. – ISBN 978-5-906376-58-9.

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