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Electro-volatilisation du ruthénium en milieu nitrique. - Influences de la nature des formes chimiques du ruthénium et de la composition des solutions modèles de dissolution

Abstract : Ruthenium is one of the fission products in the reprocessing of irradiated fuels that requires a specific processing management. Its elimination, upstream by the PUREX process, has been considered. A process, called electro-volatilization, which take advantage of the RuO4 volatility, has been optimised in the present study. It consists in a continuous electrolysis of ruthenium solutions in order to generate RuO4 species that is volatilized and easily trapped. This process goes to satisfying ruthenium elimination yields with RuNO(NO3)3(H2O)2 synthetic solutions but not with fuel dissolution solutions. Consequently, this work consisted in the speciation studies of dissolved ruthenium species were carried out by simulating fuel solutions produced by hot acid attack of several ruthenium compounds (Ru(0), RuO2,xH2O, polymetallic alloy). In parallel with dissolution kinetic studies, the determination of dissolved species was performed using voltammetry, spectrometry and spectro-electrochemistry. The results showed the co-existence of Ru(IV) and RuNO(NO2)2(H2O)3. Although these species are different from synthetic RuNO(NO3)3(H2O)2, their electro-oxidation behaviour are similar. The electro-volatilisation tests of these dissolution solutions yielded to comparable results as the synthetic RuNO(NO3)3(H2O)2 solutions. Then, complexity increase of models solutions was performed by in-situ generation of nitrous acid during ruthenium dissolution. Nitrous acid showed a catalytic effect on ruthenium dissolution. Its presence goes to quasi exclusively RuNO(NO2)2(H2O)3 species. It is also responsible of the strong p-bond formation between Ru2+ and NO+. In addition, it has been shown that its reducing action on RuO4 hinders the electro-volatilization process. Mn2+ and Ce3+ cations also reveal, but to a lesser extent, an electro-eater behaviour as well as Pu4+ and Cr3+ according to the thermodynamics data. These results allow one to purpose a dissolution mechanism of RuO2,xH2O species in nitric acid as well as quantify, thanks to the determination of oxidation and volatilization apparent constants, the baneful effect of nitrous acid on the electro-volatilization process. An explanation of the low yield of ruthenium electro-volatilization from irradiated fuel solutions has been proposed.
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Submitted on : Friday, September 10, 2010 - 3:23:14 PM
Last modification on : Tuesday, September 22, 2020 - 3:38:14 AM
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  • HAL Id : pastel-00002223, version 1

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Francois Mousset. Electro-volatilisation du ruthénium en milieu nitrique. - Influences de la nature des formes chimiques du ruthénium et de la composition des solutions modèles de dissolution. Chimie. Chimie ParisTech, 2004. Français. ⟨pastel-00002223⟩

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