Complexation des actinides (III, IV et V) par des acides organiques

L acquisition de données structurales et thermodynamiques relatives à des systèmes actinides (An(III), Pu(IV) Pa(V)) acides organiques polyfonctionnels (citrique, NTA, DTPA), en solution aqueuse, vise à une meilleure compréhension des interactions actinides-ligands essentielle à l optimisation de procédés de séparation, de décorporation, et également à l évaluation de la sûreté des sites de stockage de déchets radioactifs. Le comportement du protactinium pentavalent à l échelle des traces en présence des anions citrates et NTA a fait l objet d études systématiques par extraction liquide-liquide dans le système TTA/Toluène/HClO /NaClO /Pa(V)/ligands. Après avoir déterminé l ordre limite des complexes (3 pour Pa(V)-Cit et 2 pour Pa(V)-NTA), les constantes de formation associées à chaque espèce ont pu être calculées. L étude multi-technique (électrophorèse capillaire et spectrofluométrie laser) sur la complexation des An(III) par le DTPA, réalisée à plusieurs pH, a permis de mettre en évidence la coexistence des complexes mono-protoné (AnHDTPA ) et déprotoné. (AnDTPA ) pour des solutions acides et faiblement acides. Une réinterprétation des données de la littérature, en considérant les deux complexes, a permis de faire converger les valeurs des constantes de complexation des espèces qui étaient jusqu à maintenant dispersées. L étude thermodynamique a ensuite été complétée par une étude théorique (calculs DFT). La structure des complexes protoné et non protoné et le mode de coordination du Curium ont ainsi été établis. L étude exploratoire sur la complexation du Pu(IV) par le DTPA dans des conditions de pH proches du milieu biologique a nécessité le développement d un protocole expérimental en trois étapes : protection de Pu(IV) contre l hydrolyse avec NTA (pH faible), augmentation du pH vers des conditions neutres, compétition entre la complexation de Pu(IV) par le NTA et le DTPA. Les expériences préliminaires réalisées entre pH 1,5 et 3,5 par électrophorèse capillaire (EC-ICP-MS), semblent indiquer l existence d effet cinétique ou/et l existence d un complexe mixte. Les interprétations faites lors de cette étude exploratoire sont à confirmer.A thorough knowledge of the chemical properties of actinides is now required in a wide variety of fields: extraction processes involved in spent fuel reprocessing, groundwater in the vicinity of radioactive waste packages, environmental and biological media in the case of accidental release of radionuclides. In this context, the present work has been focused on the complexation of Am(III), Cm(III), Cf(III), Pu(IV) and Pa(V) with organic ligands: DTPA, NTA and citric acid. The complexation of pentavalent protactinium with citric and nitrilotriacetic acids was studied using liquid-liquid extraction with the element at tracer scale (CPa < 10-10M). The order and the mean charge of each complex were determined from the analysis of the systematic variations of the distribution coefficient of Pa(V) as function of ligand and proton concentration. Then, the apparent formation constants related of the so-identified complexes were calculated. The complexation of trivalent actinides with DTPA was studied by fluorescence spectroscopy (TRLFS) and capillary electrophoresis (CE-ICP-MS). The coexistence of the mono-protonated and non-protonated complexes (AnHDTPA and AnDTPA ) in acidic media (1.5 <= pH <= 3.5) was shown unambiguously. Literature data have been reinterpreted by taking into account both complexes and a consistent set of formation constants of An(III)-DTPA has been obtained. The experimental study was completed by theoretical calculations (DFT) on Cm-DTPA system. The coordination geometry of Cm in CmDTPA - and CmHDTPA- including water molecules in the first coordination sphere has been determined as well as interatomic distances. Finally, a study on the complexation of Pu(IV) with DTPA was initiated in order to more closely mimic physiological conditions. A three-step approach was proposed to avoid plutonium hydrolysis: i/ complexation of Pu(IV) with (NTA) in order to protect Pu(IV) from hydrolysis (at low pH) ii/ increase of pH toward neutral conditions and iii/ competition between the complexation of Pu with NTA and with DTPA. The preliminary experiments performed with CE-ICP-MS in the pH range 1.5 - 3.5 tend to indicate kinetic effect or/and the presence of mixed complex.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Etude des interactions entre les éléments transuraniens et quelques ligands environnementaux par le couplage électrophorèse capillaire

Dans ces travaux, les capacités du couplage entre une électrophorèse capillaire et un ICP-MS sont mises à profit pour améliorer les connaissances sur la spéciation des éléments transuraniens dans le cadre environnemental (gestion des déchets radioactifs) et dans le cadre du retraitement du combustible irradié. Des données thermodynamiques essentielles sur les interactions du plutonium à l état d oxydation 5+ (forme soluble majoritaire du Pu dans la plupart des eaux de surface) en milieu inorganique environnementale (chlorure, nitrate, sulfate, carbonate) ont été déterminées pour la première fois. Cette étude permet de corriger les modèles existant basés sur les données thermodynamiques du neptunium pentavalent (analogue du Pu pentavalent). Par ailleurs, le couplage EC-ICP-MS a également été appliqué à l étude des interactions entre le DTPA, molécule chélatante très utilisée dans l industrie du nucléaire, et les éléments à l état d oxydation 3+ (Pu, Am, Cm, Cf) et 4+ (Pu, Np, Th). Les résultats obtenus mettent pour la première fois en évidence la formation d espèces mixtes An(IV)/DTPA/OH susceptibles de jouer un rôle important sur le comportement des actinides dans le cadre de la gestion des déchets. L étude concernant les éléments trivalents confirme, quant à elle, la sélectivité du DTPA vis-à-vis des actinides trivalents dans le cadre de la séparation des actinides et des lanthanides mais indique que le caractère covalent de la liaison, responsable de la sélectivité, est moins marqué que le caractère ionique.In this work, the capabilities of the hyphenated Capillary Electrophoresis-ICP-MS technique are used to improve the kwnowledge on the transuranic element speciation in the environment (nuclear waste management) and in the framework of spent fuel reprocessing. Essential thermodynamical data have been determined for the first time for the interactions of the plutonium at the 5+ oxydation state (main soluble species of Pu of the surface water) in inorganic media (chloride, nitrate, sulfate, carbonate). This study enables to correct the existing model, based on the thermodynamical data of the neptunium at the 5+ oxydation state (analogue of the pentavalent plutonium). Furthermore, the hyphenated CE-ICP-MS technique has also been applied to study the interactions between DTPA, widely used in the nuclear industry, and the elements at the 3+ oxydation state (Pu, Am, Cm, Cf) and at the 4+ oxydation state (Pu, Np, Th). The results show for the first time the formation of mixed An(IV)/DTPA/OH complexes likely to play a key role on the actinide behavior in the field of the waste management. The study on the trivalent elements confirms the selectivity of DTPA versus the actinide in the framework of the actinide/lanthanide separation but proves that the covalency, responsible of the selectivity, are less important than the ionicity in the binding.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Analyse et spéciation du tritium dans des matrices environnementales

Cette étude s'inscrit dans le domaine de la surveillance de l'environnement. Elle consiste à optimiser et valider la procédure analytique de détermination du tritium sous forme organique, et à identifier les molécules organiques, porteuses de tritium, responsables de son transfert de l'environnement à l'homme. La démarche s'est organisée en trois temps. Une procédure analytique a d'abord été mise en place pour déterminer, la teneur en hydrogène des échantillons, élément clé, utilisée pour le calcul des activités de tritium organique. L'impact de la séparation des fractions de tritium organique (l'échange labile) sur la détermination de l'activité de la fraction représentative du niveau de tritium environnemental a ensuite été évalué. Pour cela, les quantités d'échantillon solubilisées ont été estimées. Enfin, la spéciation du tritium dans des échantillons environnementaux a été abordée. Pour cela, les familles de molécules, puis les composés organiques solubilisés lors des échanges labiles ont été identifiés. Les résultats montrent que la répartition du tritium dans les organismes dépend à la fois des propriétés de la liaison chimique dans laquelle il est impliqué et des propriétés des molécules organiques le portant. Les composés identifiés appartiennent aux familles de molécules constitutives (glucides, acides aminés) de la matière vivante. Il serait à présent intéressant d'étudier la répartition du tritium au sein d'un échantillon de l'environnement pour cibler les molécules d'intérêt et étudier de manière plus approfondie la distribution du tritium dans l'environnement et son impact, de l'environnement à l'homme.This study deals with environmental monitoring. The main aims are (i) the optimisation of the analytical procedure for the tritium in organic form determination, and (ii) the identification of the tritium bearing molecules which are responsible for its transfer from the environment to man. The study was divided into three stages. First an analytical method was developed to determine hydrogen content of several samples, which is a key element to calculate accurate organically bound tritium activities. Secondly, the impact of the organically bound tritium fractions separation (labile exchange) for the determination of the representative fraction of the level of environmental tritium activity was then evaluated. For that, the amount of solubilised sample was estimated. Finally, the speciation of tritium in environmental samples was investigated. Several molecules classes and organic compounds dissolved in the labile exchanges solvent were identified. The results show that the distribution of tritium in organisms depends on both properties of the chemical bond in which it is involved and chemical properties of tritium bearing molecules. The identified compounds belong to the molecules classes such as carbohydrates or amino acids, constitutive of living organisms. It would now be of interest to study the tritium distribution in an environmental sample to target molecules of interest and study the impact of tritium from the environment to man.PARIS-JUSSIEU-Bib.électronique (751059901) / SudocSudocFranceF

Determination of the stability constants of Pu(VI) carbonate complexes by capillary electrophoresis coupled with inductively coupled plasma mass spectrometer

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The speciation of protactinium since its discovery: a nightmare or a path of resilience

International audienceAbstract This review concerns the speciation of protactinium in aqueous solution under its both oxidation states +IV and +V. Emphasis is placed on experimental data obtained at trace level but also in macroscopic amount leading to the determination of thermodynamic and structural data. Thus, the complexation of Pa(V) with mineral acids and organic acids, mainly polyaminocarboxylic acids (iminodiacetic acid [IDA], nitrilotriacetic acid [NTA], ethylenediaminetetraacetic acid [EDTA] and diethylenetriaminepentaacetic acid [DTPA]) are highlighted and compared. The review also includes the actual knowledge about the Pa(IV) aqueous chemistry pinpointing its spectroscopic features.</jats:p

Quantum molecular dynamics investigations of protactinium (V) fluoro and oxofluoro complexes in solution

International audienceQuantum Molecular Dynamics simulations of protactinium (V) fluoro and oxofluoro complexes in solution were undertaken using density functional theory with generalised gradient approximation (and the ABINIT software package). The complexes were studied in the gas phase (at 0 K) and in solution (at 298 K) with water molecules as the solvent. We characterised all of the systems, taking into account their structures, dissociation energies, bond lengths and formation enthalpies in solution, and explained their relative stabilities. At ambient temperature, the hydrated species PaF 5 , P a F 4 + $Pa{F}_{4}^{+}$ , P a O F 5 2 − $PaO{F}_{5}^{2-}$ , P a O F 4 − $PaO{F}_{4}^{-}$ and PaOF 3 were found to be the most stable (and to exhibit similar stabilities). The calculated formation enthalpies of the complexes are in close agreement with measurements made elsewhere

Individual differences in the long-distance vocalizations used during pair bonding in European quail (Coturnix coturnix)

WOS:000078223500002International audienceIn European quail, individual birds can be discriminated by using only three parameters describing the long-distance vocalizations used during pair bonding. In the male vibrate these parameters are: the total duration of the vibrate, the duration of the second syllable and the highest energy component of the fundamental. For the male triplet, the necessary parameters are: the interval between the highest frequency points of syllables 1 and 2, of syllables 2 and 3, and the frequency of the inflexion point of the third syllable. Individual females can usually be identified by three rally call parameters; these being the interval between syllables 1 and 2, the interval between the lowest frequency points, and the frequency of maximal amplitude in the second syllable of the rally call. Comparison based on these three parameters for each form of vocalization showed that more than 80% of individuals were correctly discriminated thus permitting fairly reliable counts of populations in the field. Intra-individual variations of parameters of male triplets linked with sexual development or age could permit sexual selection of singing males by females. Comparisons between the sexual calls of the European quail and the Grey partridge lead to evolutionary suggestions about the structure of vocalizations in these two related sympatric species

Kinetics of incongruent dissolution of carbonates in a Chalk aquifer using reverse flow modelling

International audiences u m m a r y Water–rock interactions are major processes that control the solute transfer (from natural or anthropo-genic sources) in aquifers. In carbonate aquifers, these water–rock interactions are mainly characterised by the incongruent dissolutions of carbonates. The in situ quantification of these reactions is few studied. In the present paper, we provide a new quantification of the kinetic rates of simultaneous incongruent dissolution of composite carbonate and dolomite in a Chalk aquifer. The approach is based on a mass-balance model used to calculate the rates of mineral dissolution and precipitation along a 500 m to 4 km flow path starting at the groundwater divide line. The groundwater transfer times between the groundwater divide line and the wells are calculated thanks to flow and transport modelling, used in a backward particle tracking mode. The uncertainties on porosity, dispersivity and transmissivity are taken into account. The rates are found ranging between 1.5 Â 10 À5 and 1.5 Â 10 À4 mol C5 chalk L À1 w yr À1 for the composite carbonate dissolution, between 1.0 Â 10 À7 and 3.0 Â 10 À6 mol dolomite L À1 w yr À1 for the dolomite dissolution and between 1.0 Â 10 À5 and 1.5 Â 10 À4 mol calcite L À1 w yr À1 for the calcite precipitation. The results highlight the importance of physical and geological properties of the aquifer