| Autor: |
Gerber E; A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky Prospect, Moscow 119071, Russian Federation., Krot AD; A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky Prospect, Moscow 119071, Russian Federation.; Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory, Moscow 119991, Russian Federation., Chernyshev VV; A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky Prospect, Moscow 119071, Russian Federation.; Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory, Moscow 119991, Russian Federation., Trigub AL; National Research Centre 'Kurchatov Institute', Moscow 123182, Russian Federation., Sobolev NA; Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory, Moscow 119991, Russian Federation., Averin A; A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky Prospect, Moscow 119071, Russian Federation., Maksimov S; Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory, Moscow 119991, Russian Federation., Svetogorov R; National Research Centre 'Kurchatov Institute', Moscow 123182, Russian Federation., Nevolin IM; A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky Prospect, Moscow 119071, Russian Federation.; Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory, Moscow 119991, Russian Federation. |
| Abstrakt: |
The crystal structure of ammonium polyuranates x UO 3 · y NH 3 · z H 2 O has been investigated. Powder X-ray diffraction (PXRD) has been employed to define single-phase samples within a series of synthesized compounds, which are further characterized by elemental analysis to ascertain the stoichiometry, revealing compositions of 3UO 3 ·NH 3 ·5H 2 O and 2UO 3 ·NH 3 ·3H 2 O . Analysis using extended X-ray absorption fine structure and vibrational spectroscopy has elucidated that both 3UO 3 ·NH 3 ·5H 2 O and 2UO 3 ·NH 3 ·3H 2 O possess a local structure similar to the metaschoepite─layered U(VI) oxohydroxide UO 3 ·2H 2 O, but with H 2 O and NH 4 + groups in the interlayers. The structures of ammonium polyuranates are solved from PXRD data, revealing their relationship to the U(VI) oxohydroxide with the established composition of NH 4 [(UO 2 ) 3 O 2 (OH) 3 ]·3H 2 O and NH 4 [(UO 2 ) 2 O 2 (OH)]·2H 2 O for 3UO 3 ·NH 3 ·5H 2 O and 2UO 3 ·NH 3 ·H 2 O , respectively. These structures maintain the arrangement of U-O polyhedra as pentagonal bipyramids. However, disparities in lattice parameters, space group, and layer topology from UO 3 ·2H 2 O emphasize significant structural modifications resulting from the substitution of water by ammonium. Moreover, the anion topology of the NH 4 [(UO 2 ) 2 O 2 (OH)]·2H 2 O has no analogues among uranium oxohydroxide minerals. Notably, ammonium polyuranates, when compared, have minimal alterations in lattice parameters regardless of the presence of ammonia within the structure. The revealed results contribute valuable insights into the UO 3 -NH 3 -H 2 O system and hold potential applications in the field of nuclear power as ammonium polyuranates form during actinide precipitation in back-end of the nuclear fuel cycle and also serve as precursors in the fabrication of nuclear fuel. |
