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[en] This paper presents a study in a qualitative and quantitative way of the acid-base and oxido-reducing properties of neptunium in solution in various molten alkaline chlorides. After a brief recall of some characteristics of the selected solvents and solutes (chapters I and II), the choice of the different experimental methods used during this work as well as their development are discussed in chapters III and IV. The following chapters include a quantitative study of acid-base and oxido-reducing properties of the different reactionary gas mixtures, and a quantitative study (by visible and near I.R. absorption spectro-photometry) of the behavior of neptunium solutions in different molten chlorides. A complementary study by Raman spectrometry then attempts to elucidate the nature of species present in solution. These results are completed by potentiometric measurements; all of these results are finally synthesized in the form of a potential-acidity diagram for neptunium.
[fr]Au cours de notre travail, nous etudierons de maniere qualitative et quantitative les proprietes acide-basiques et oxydo-reductrices du neptunium en solution dans divers chlorures alcalins fondus. Apres un rappel succinct de quelques caracteristiques des solvants et solutes utilises (chapitres I et II), nous discuterons du choix des differentes methodes experimentales utilisees au cours de ce travail ainsi que de leur mise au point (chapitres III et IV). Le chapitre V comportera l'etude quantitative des proprietes acido-basiques et oxydo-reductrices des differents melanges gazeux reactionnels utilises. L'etude quantitative, par spectro-photometrie d'absorption visible et proche I.R., du comportement des solutions de neptunium dans differents chlorures fondus fera l'objet du chapitre VI. Une etude complementaire par spectrometrie Raman tentera d'elucider la nature des especes presentes en solution (chapitre VII). Des mesures potentiometriques completeront utilement les resultats obtenus (chapitre VIII). L'ensemble de ces resultats sera enfin synthetise sous la forme d'un diagramme potentiel-acidite du neptunium (chapitre VIII)
[en] After some recalls on the liquid-liquid extraction and on the main extraction mechanisms, a presentation of the tributyl phosphate and of organic solutions and diluents used in this process, this research thesis highlights the role of water during the extraction of strong mineral mono-acids by the tributyl phosphate (study of the liquid-liquid extraction of water only by the tributyl phosphate, study of the gas-liquid extraction in anhydrous environment of the hydrochloric gas by the tributyl phosphate, study of the liquid-liquid extraction of hydrochloric acid by the tributyl phosphate). The second part proposes a generalisation of the obtained results with an application to the extractions of perchloric and nitric acids.
[en] This academic report addresses the study of the separation of plutonium, more precisely called 'U-Pu partition', which is performed by using the liquid-liquid extraction process in which plutonium transfer occurs from the organic phase to the aqueous phase through a reduction process. As reduction agent, uranium nitrate is generally used in the French industry in presence of hydrazine. The author first reports the measurement of the redox potential of different environments which may be present: a reducing environment (N2H4, U IV) and an oxidising environment (NO2) in absence of plutonium. The second part addresses the case of a presence of plutonium, and highlights some specific redox reactions. Then, by considering conditions close to that of industrial exploitation, the author reports the determination of the possible limitations of the method.