Coupling Raman spectroscopy and DFT study for enhanced description of nitrosyl nitrato nitrite ruthenium(III) complexes
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Coupling Raman spectroscopy and DFT study for enhanced description of nitrosyl nitrato nitrite ruthenium(III) complexes in nitric acid Thomas Dirks1 · Thomas Dumas1 · Dominique Guillaumont1 · Marie‑Christine Charbonnel1 Received: 15 June 2020 / Accepted: 19 September 2020 / Published online: 10 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Dissolution of spent nuclear fuel in nitric acid forms diverse octahedral complexes of the ruthenium fission product with one nitrosyl and a variable number of nitrate, nitrite, hydroxide and water ligands. Some of these ruthenium complexes can trouble uranium and plutonium extractions by TBP and their purifications. In this study, we analyze the effect of gamma radiation on the structure of ruthenium(III) nitrosyl complexes in 5 M nitric acid solution and highlight the necessity to take into account the nitrato–nitrite complexes [RuNO(NO3)x(NO2)y(H2O)5−x−y]3−x−y. Accordingly, we performed a parametric study to analysis the influence of varying nitrous acid concentrations on ruthenium nitrosyl complexes in 1 M and 5 M nitric acid solutions. Raman spectra show that nitrites from nitrous acid replace nitrate ligands in ruthenium complexes. Resulting nitrite complexes were characterized by comparing the experimental Raman spectra to DFT calculations. This comparison supports a successive formation of mono-, cis- and potentially mer-ruthenium nitrite complexes with increasing nitrous acid concentrations. The degradation of such nitrite complexes has been followed by Raman measurements and the reverting to nitrate complexes occurs within several weeks. The radiolytic formation and the slow degradation shows a relevance of nitrite complexes to understand and hence control ruthenium in solvent extraction processes. Keywords Ruthenium · Raman · Radiation · Speciation · Nitrite · Nitric acid
Introduction Despite its rareness on earth, the platinum metal ruthenium has numerous applications in electronic, catalytic and radiochemical purposes. Increasing demands will challenge ruthenium production, purification and recycling in the future. In the process of nuclear fuel recycling, this challenge is already addressed. The Plutonium and Uranium Reduction Extraction process (PUREX) using the extractant tri-n-butyl phosphate (TBP) can extract parts of fission product ruthenium from nitric acid solution of nuclear fuel [1, 2]. Currently, extracted ruthenium is removed from uranium Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10967-020-07402-3) contains supplementary material, which is available to authorized users. * Thomas Dumas [email protected] 1
CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, France
and plutonium extractions in purification (called scrubbing) cycles. An efficient scrub of ruthenium is a key aspect to limit solvent degradation due to the β−- and γ-radiation of the isotope 106Ru (T1/2 ≈ 1 year), and to ensure a recovery of pure uranium and plutonium [3]. To improve ruthenium scrubbings operation
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