Pertechnetate/perrhenate-capped Zr/Hf-Dihydroxide Dimers: Elucidating Zr-TcO 4 Co-Mobility in the Nuclear Fuel Cycle

• Published in: Chemistry : a European journal Vol. 30; no. 10; p. e202303218
• Main Authors: Shohel, Mohammad, Bustos, Jenna, Roseborough, Alexander, Nyman, May
• Format: Journal Article
• Language: English
• Published: Germany 16-02-2024
• Subjects: Zirconium; Technetium; Nuclear Fuel; Hafnium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202303218

Spent nuclear fuel contains heavy element fission products that must be separated for effective reprocessing for a safe and sustainable nuclear fuel cycle.
Zr and
Tc are high-yield fission products that co-transport in liquid-liquid extraction processes. Here we seek atomic-level information of this co-extraction process, as well as fundamental knowledge about Zr
(and Hf
) aqueous speciation in the presence of topology-directing ligands such as pertechnetate (TcO
) and non-radioactive surrogate perrhenate (ReO
). In this context, we show that the flat tetrameric oxyhydroxyl-cluster [M
(OH)
(H
O)
]
(and related polymers) is dissociated by perrhenate/pertechnetate to yield isostructural dimers, M
(OH)
(XO
)
(H
O)
 ⋅ 3H
O (M=Zr/Hf
; X=Re/Tc
), elucidated by single-crystal X-ray diffraction. We used these model compounds to understand the pervasive
Zr-
Tc coextraction with further speciation studies in water, nitric acid, and tetrabutylphosphate (TBP) -kerosene; where the latter two media are relevant to nuclear fuel reprocessing. SAXS (small angle X-ray scattering), compositional evaluation, and where experimentally feasible, ESI-MS (electrospray ionization mass spectrometry) showed that perrhenate/pertechnetate influence Zr/Hf
-speciation in water. In Zr-XO
solvent extraction studies to simulate fuel reprocessing, we provide evidence that TcO
enhances extraction of Zr
, and compositional analysis of the extracted metal-complexes (Zr-ReO
study) is consistent with the crystallized Zr
(OH)
(Re
O
)
(H
O)
⋅dimer.