Дисертації з теми "Mineral ion exchanger"

The principal objective of the research was to model the outflow results of multiple tracer outflow dilution (M.T.O.D.) techniques from the canine tibia so as to obtain a more precise understanding of the physiological mechanisms underlying mineral exchange in bone. To date, M.T.O.D. techniques have been performed on the tibiae of greyhound dogs but the subsequent outflow results have produced information mainly at the capillary level for the diffusible tracers concerned such as capillary permeability-surface area PSC products from the widely used Crone-Renkin formulation. Back diffusion and heterogeneous capillary flow rates lacking from the formulation, however, have impaired the accuracy of PS(C). Outflow results from two series of previously performed M.T.O.D. experiments were modelled. In the first experimental series, outflow results from the ipsilateral femoral vein concerning l25l-albumin reference and 85Sr (Ca analogue), 86Rb (K analogue) diffusible tracers were used ; the tracers having being injected into the tibial nutrient arteries. In the second experimental series, 125l-albumin and 85Sr outflow results were used from parathyroidectomised dogs in which both tracers had been injected together before and after a dose of 0.0005 mg bovine parathyroid hormone (PTH). The problem of back diffusion was alleviated by optimising a homogeneous flow model to M.T.O.D. data. The model produced informative parameter estimates for 85Sr and 86Rb concerning fluid spaces and associated boundaries in Haversian systems largely comprising the diaphyseal cortex. Exchange was assumed to take place there by virtue of injecting the tracers into the tibial nutrient artery. Blood flow rates, known to be influential in governing the extent of tracer exchange in the diaphysis, were investigated using the microsphere technique. Flow rate heterogeneity was found to be substantial, as adjudged by distributions of relative deposition densities of microspheres in 40 pieces of cortex and 10 marrow samples in 6 tibiae. For the cortex, the distributions were positively skewed with a relative dispersion of around 40%. Additional work involving light microscopy suggested that the distribution of cortical flow rates were not attributable to particular changes in capillary density, which were relatively uniform at 2682 + 510 capillaries/cm2 (4 tibiae ; 240 observations). The findings concerning flow rate heterogeneity, together with the deduction that the cortex and marrow respectively received 65% and 35% of tibial nutrient artery flow, prompted the development of a parallel multicapillary model in which 4 capillary systems were alloted to the cortex and 1 such system to the marrow. Input to the model was a suitable form of the reference tracer outflow profile which describes the large vessel transport behaviour assumed identical for all tracers concerned. Parameter estimates (mean + s.d.) found by optimisation for 85Sr and 86Rb (n=6) were PSC = 0.045 + 0.021 and 0.047 + 0.022 ml/s respectively. Apparent volumes of distribution (n=5) for the interstitial fluid were 0.90 + 0.36 (85Sr) and 0.69 + 0.22 ml of diaphysis (86Rb). Additional studies involving gamma variates showed that model inputs were robust in terms of varying degrees of large vessel dispersion. Furthermore, simulation studies involving the effect of asymmetric transport on the resulting parameter estimates in the context of modelling the PTH data provided speculative evidence for the concept of a bone-lining cell membrane controlling uptake to bone surfaces.

Les alumino, titano et zircono-silicates zéolithiques sont des matériaux présentant des propriétés intéressantes pour de nombreuses applications dans la pétrochimie, l'agriculture, le médical, le stockage d'énergie ainsi que la décontamination d'effluents. Dans le domaine du traitement des effluents radioactifs, leurs propriété d'échange d'ions font de ces matériaux des extractants de radionucléides efficaces avec de bonnes sélectivités (e.g. césium ou strontium). Leurs compositions (le ratio Al/Si, Ti/Si, Zr/Si… ; la nature et la charge des métaux ; la nature, la charge, la concentration et la taille de l'ion échangeable) ainsi que la structure cristalline (amorphe, 2D lamellaire, 3D cage ou tunnel) vont avoir des effets sur les mécanismes d'échange ionique (cinétique, spécificité, stabilité). Ces paramètres vont aussi influencer la capacité de sorption ainsi que la sélectivité que le matériau a pour un ion. Lors de cette thèse, les relations structure/propriété de différents silicates seront étudiées dans le but d'appréhender les mécanismes de sorption. A cette fin, les synthèses de plusieurs silicates seront menées et optimisées. Par la suite, différentes techniques de caractérisation seront misent en place afin d'analyser les propriétés structurales, morphologiques et la composition des silicates. Enfin, ces matériaux seront mis en œuvre pour le traitement d'effluents modèles et d'effluents réels simulés, afin d'évaluer leurs performances et les mettre en lien avec leurs caractéristiques structurales et texturales
Alumino, titano and zircono-silicates zeolitic materials exhibit good performances in applications such as catalysis, gas separation and confinement. In addition, these kind of materials has been successfully used in different fields like petrochemistry, agriculture, medical, energy storage and nuclear decontamination. Their ion exchange properties make them very selective for radionuclides extraction (e.g. cesium or strontium) from wastewater treatment. Their composition (Al/Si, Ti/Si, Zr/Si ratio; “metal” nature and charge; labile ion nature, charge, size and concentration) and their framework structure (amorphous, 3D cage or tunnel) affect the ion exchange mechanism (i.e. kinetics, specificity, stability). These parameters may also modify the sorption capacity and the ion selectivity. In the present PhD, the relationship between structure and properties of several silicates will be studied in order to better understand their sorption mechanisms. To this end, the synthesis of different silicates will be performed and optimized. Then, their structures, morphologies and compositions will be analyzed by the application of different characterization techniques. Finally, this materials will be implemented to effluent treatments (i.e. model effluent and simulate real effluent) to evaluate their performances and find the connection between the structural and textural properties

Premilere partie: la plupart des phases du titre ont une structure en couches voisine de celle de zrp-alpha. Le traitement en milieu acide des phases en couches km**(i)(po::(4))::(2), m=sb, ta permet d'obtenir les acides correspondant hm**(v)(po::(4))::(2)xh::(2)o. Un autre acide, hta(po::(4))::(2) 3d, peut etre obtenu directement par voie seche, description de sa structure tridimensionnelle. Determination de la teneur en eau, de la structure et du comportement thermique de ces differents acides dont la thermolyse conduit a des phases originales qui sont etudiees. Seconde partie: dans la premiere famille, les phases (m'**(iii)::(1/2)m**(v)::(3/2)) (po::(4))::(3) sont de type nasicon ou sc::(2)(no::(4))::(3) ou d'un nouveau type structural, dans la seconde, les phases m'**(iii)::(1/2)m**(v)::(1/2))p::(2)o::(7) presentent des structures voisines de celle de zrp::(2)o::(7)

L'application de la rmn **(129)xe permet de suivre l'evolution du libre parcours moyen du xenon adsorbe utilise comme sonde en fonction de la concentration en eau d'une zeolite nay. De plus, l'adsorption de l'ammoniac sur la zeolite y modifiee par echange de cations metalliques, a montre que la rmn-**(1)h permet de suivre la reconstitution des complexes ammoniaques en fonction de la temperature de pretraitement du solide et de la concentration en nh::(3) adsorbe ou desorbe

Made available in DSpace on 2014-12-17T15:42:08Z (GMT). No. of bitstreams: 1 FranciscoCBS_DISSERT.pdf: 2327685 bytes, checksum: 7ea91ee570c997cb17e15b80242eeaa3 (MD5) Previous issue date: 2013-07-30
The present work was to carry out a study on the adsorption of hydrogen sulfide (H2S) in arrays synthesized from a commercial clay mineral formed by a mixture of dolomite and quartz. To produce the ion exchange matrix were made using aqueous solutions of salts of cobalt II chloride hexahydrate (CoCl2.6H2O) II cadmium nitrate tetrahydrate (Cd (NO3)2.4H2O) I mercuric chloride (HgCl) nitrate and chromium III pentahydrate (Cr (NO3)3.5H2O). The arrays were subjected to hydrogen sulphide gas passage for one hour. To check the amount of gas adsorbed was used gravimetric process. The best result was in the adsorption matrix doped with cadmium and the solution retained for a longer time than the largest amount of H2S was the cobalt matrix. The matrix unmodified exhibited poor adsorption capacity. The characterization of the matrices were used XRD, XRF and IV. Mother with cadmium showed a high capacity in ion exchange, because the percentage of cadmium increased from 0% to 81.38% by replacing atoms of calcium and silicon which increased from 96.54% to 17.56% and 15, 72% to 0.32%, respectively, but also the best performance in adsorption of H2S adsorbing 11.89507 mg per gram of matrix
O presente trabalho teve como finalidade realizar um estudo sobre a capacidade de adsor??o de g?s sulf?drico(H2S) em matrizes sintetizadas a partir de um argilomineral comercial formado por uma mistura de dolomita e quartzo. Para produzir as matrizes foram feitas trocas i?nicas utilizando as solu??es aquosas dos sais: cloreto de cobalto II hexaidratado(CoCl2.6H2O), nitrato de c?dmio II tetraidratado (Cd(NO3)2.4H2O), cloreto de merc?rio I (HgCl) e nitrato de cromo III pentaidratado(Cr(NO3)3.5H2O). As matrizes foram submetidas a passagem de g?s sulf?drico durante uma hora. Para verificar a quantidade de g?s adsorvido foi utilizado o processo de gravimetria. O melhor resultado na adsor??o foi com a matriz dopada com a solu??o de c?dmio e a que reteve por mais tempo a maior quantidade de H2S, foi a matriz com cobalto. A matriz n?o modificada apresentou uma fraca capacidade de adsor??o. Na caracteriza??o das matrizes foram utilizadas an?lises de DRX, FRX e IV. A matriz com c?dmio apresentou uma alta capacidade na troca i?nica, pois a porcentagem de c?dmio passou de 0% para 81,38%, substituindo ?tomos de c?lcio e de sil?cio que passaram de 96,54% para 17,56% e de 15,72% para 0,32%, respectivamente, como tamb?m, o melhor desempenho na adsor??o, adsorvendo 11,89507mg de H2S por grama de matriz

The focus of this work is to investigate the dissolution of MW25, a non-radioactive simulant of UK high-level nuclear waste borosilicate glass, and to predict its performance in the near field of a geological repository. A single-pass flow-through (SPFT) experimental system was used to measure the forward dissolution rates of MW25. Experiments were conducted in two parts. Experiment Part 1 considers the dissolution of the waste glass in deionised water at 40 and 90 oC and circum-neutral pH. Experiment Part 2 considers the dissolution of the waste glass in simulant groundwaters, with similar compositions to groundwaters of Callovo-Oxfordian clay (lower-strength sedimentary rock (LSSR)) and Borrowdale Volcanic Group rocks (higher-strength rock (HSR)), at 40 oC and pH 7. The forward dissolution rate measured in deionised water was found to be approximately one order of magnitude higher at 90 oC than at 40 oC. A similar release was observed for Si, Mg and Al at 40 oC and 90 oC, whereas the B, Cs, Na, Li and Mo showed an order of magnitude increase when the temperature was increased from 40 to 90 oC for low q/S values. The activation energy (Ea) of the reactions shows that the dissolution process is a surface phenomenon. At 90 oC the net effect of the processes governing MW25 dissolution led to the preferential release of boron and alkali metals relative to the release of Si during the transient dissolution stage, accompanied by an increase in the concentration of silicic acid. This suggests that the solution activity of silicic acid at a higher temperature has a weak influence on the release of the mobile elements. The forward dissolution rate measured in LSSR simulant groundwater was found to be slightly higher than that measured in HSR simulant groundwater. The dissolution behaviour of MW25 in both groundwaters is consistent with its behaviour in deionised water at 40 oC, with the dissolution rates of elements increasing as flow rates were increased. However, forward dissolution rates measured in the simulant groundwaters were lower than the forward dissolution rates measured in deionised water under these experimental conditions. This is attributable to the interaction of the components of the simulant groundwaters with the glass, as revealed by post-reaction surface analyses, and a consequential lower alkalinity of the leachates collected in the experiments with simulant groundwater than in deionised water. Reactive chemical transport simulations of waste glass dissolution and radionuclide release in a hypothetical near field were conducted over a time span of a million years with GoldSim. The results showed that enclosing the waste glass in a steel canister covered by a copper canister and emplacing the waste package in a granite host rock is optimal for the long-term isolation of the radionuclides. The waste glass was found to play a significant role in the overall performance of the near field. This study features a new method for estimating the surface area of reacted glass powder more accurately than the geometric surface area estimate, which is the preferred standard method among researchers.

Les schémas actuels de traitement des minerais et des concentrés de chalcopyrite aboutissent à la formation du SO2 dont le rejet partiel ou complet dans l'atmosphère pose des problèmes pour l'environnement. Suite aux nouvelles réglementations sur l'environnement et à la pression de l'opinion publique, de nombreuses recherches se poursuivent afin de trouver d'autres alternatives qui auraient l'avantage de produire le soufre élémentaire. Dans ce contexte, cette étude porte sur la dissolution électrochimique sélective de la chalcopyrite à partir d'un minerai naturel et d'un concentré de flottation. Différents types de réacteurs électrochimiques et notamment un réacteur à lit granulaire E3P, une cellule à diaphragme poreux et une cellule à membrane échangeuse d'ions ont été testés. Des techniques de caractérisation physico-chimique telles que la DRX, le MEB, la Microscopie Optique, la Spectroscopie Raman, l'Analyse chimique, etc. , ont été utilisées pour caractériser les échantillons initiaux et les produits des réactions chimiques et/ou électrochimiques. L’oxydation du minerai dans le réacteur E3P permet une dissolution préférentielle des composés du fer autres que la chalcopyrite, tandis que la réduction favorise la solubilisation du fer de la chalcopyrite. Cependant, dans les deux cas, la cinétique est lente et le rendement faradique est faible. L’utilisation de la cellule à diaphragme poreux n'a pas sensiblement amélioré les résultats de la dissolution. Les meilleurs résultats ont été obtenus en utilisant la cellule électrochimique à membrane échangeuses d'ions. La dissolution de la chalcopyrite est essentiellement réalisée par les ions ferriques et cuivriques générés électrochimiquement in-situ. Un taux d'extraction de cuivre atteignant 98% a été obtenu. Dans les conditions optimales, les rendements faradiques sont proches de 100%. La chalcopyrite est dissoute sélectivement et la majorité du soufre est obtenue sous forme élémentaire

Etude en laboratoire du comportement de la bentonite green-bond dont on envisage l'usage dans les remblais de forages de sites de stockage de dechets radioactifs. On etudie en particulier le gonflement de l'argile avec de l'eau, son erosion par un ecoulement d'eau demineralisee. On procede a la reconnaissance de l'influence des processus chimiques sur le comportement de l'argile, les phenomenes d'erosion n'apparaissant que pour des forces ioniques faibles et donc des conductivites faibles

Le projet de thèse s’inscrit dans le Projet Investissement d’Avenir (PIA) DEMETERRES, dont l’objectif est le développement de méthodes et de technologies pour la décontamination et la remédiation des sols et effluents contaminés après un accident nucléaire. L’objectif de cette thèse est de mieux appréhender les interactions de 137Cs et 90Sr avec les différentes composantes des terres agricoles et ainsi être capable de prédire l’état chimique dans lequel ces éléments se trouveraient dans les sols en cas d’accident nucléaire. Une base de données dans le formalisme des échangeurs d’ions multi-sites a été mise en place, représentant les comportements d’adsorption de Cs+ et Sr2+ dans les illites et smectites (deux des principaux minéraux argileux) vis-à-vis des cations majeurs environnementaux H+, Na+ et Ca2+. Cette base de données a par la suite été utilisée pour tenter de prédire le comportement d’adsorption de Cs+ et Sr2+ dans des échantillons de sols agricoles français (Pusignan, Etoile-sur-Rhône et Herqueville). De bonnes simulations du comportement d’adsorption de Cs+ et Sr2+ ont été obtenues sur Pusignan et Etoile-sur-Rhône. Dans le cas d’Herqueville, la suppression de la MON n’a pas amélioré l’accord entre les simulations et les expériences, tandis que l’élimination de l’aluminium échangeable a lui permis une meilleure simulation de l’adsorption de Sr2+, mais pas de Cs+. Ces travaux permettent de simuler efficacement le comportement d’adsorption de Cs et Sr dans des sols et ainsi d’appuyer les stratégies de décontamination et remédiation après un accident nucléaire
This study is part of the DEMETERRES project, which aims to develop new methods and technologies in the field of decontamination and remediation of contaminated soils and effluents after a nuclear accident. The objective of this PhD is to obtain a better knowledge of 137Cs and 90Sr interactions onto agricultural soils and to better predict the chemical state of these elements in soils after a nuclear accident. A database in the multi-sites ion exchanger formalism has been built, reflecting the adsorption behaviours of Cs+ and Sr2+ onto illite and smectite (two major clay minerals) with regards to major environmental cations: i.e. H+, Na+, and Ca2+. It was used to predict the adsorption of Cs+ and Sr2+ onto French agricultural soil samples (Pusignan, Etoile-sur-Rhône and Herqueville). Good simulations of the adsorption of Cs+ and Sr2+ onto Pusignan and Etoile-sur-Rhône are obtained. In the case of Herqueville, the removal of NOM does not improve the agreement between experimental results and simulations, but the removal of exchangeable aluminum allows a better representation of the adsorption results of Sr2+ onto Herqueville, but not for Cs+. This work allows efficiently simulating the adsorption of Cs and Sr onto soils and support decontamination and remediation strategies after a nuclear accident

Preparation de polymeres mixtes en ajoutant un heteroelement a de l'acide antimonique frais. Les composes molybdoantimoniques se presentent sous la forme de particules octaedriques cristallisees dans le systeme pyrochlore ayant une charge de surface relativement elevee. Les composes silicoantimoniques conservent aussi la structure pyrochlore de l'acide antimonique

Comparaison des avantages et des inconvenients de l'extraction a l'aide de resines et de l'extraction liquide-liquide en vue de preciser leur domaine respectif d'utilisation en hydrometallurgie. Etude de la separation du gallium contenu dans les solutions d'attaque des minerais de zinc. Utilisation de la resine duolite es467 et pour l'extraction liquide-liquide de l'hydroxy-8 quinoleine et d'une alpha-hydroxy-oxime

Les interactions chimiques entre des solutions utilisées dans les boues de forage, et différents types d'argiles ont été étudiées dans des conditions P, T proches de celles des forages (150°C) afin de déterminer les conséquences éventuelles sur la stabilité des argilites. Le travail a été conduit essentiellement de manière expérimentale, en utilisant différentes solutions: eau pure, NaOH (pH 8, 10, 12), KCl (0,1, 1, 2 mol. /l), eau de mer et K₂CO₃, et des argiles à forte et faible proportion de feuillets gonflants (smectite (Na, Na-Ca, Ca) interstratifiés illite-smectite). Les produits de réaction ont été étudiés par diffraction des rayons X, et microsonde électronique. Les feuillets de smectites montrent une série de transformations (échange en site interfoliaire, fermeture de feuillets, hydrolyse), qui ne conduisent pas cependant à la formation de nouveaux minéraux sauf dans le cas de traitement en présence de K₂CO₃ à 150°C (formation de zéolites). L’échange du cation interfoliaire est fonction de la nature du cation, de la concentration des cations dans les solutions, des constantes d'échange et du rapport liquide/solide. Dans les solutions diluées (<1 mol. /l), l'échange est partiel et a pour conséquence l'obtention de smectites à garnitures interfoliaires mixtes qui présentent des états d'hydratation variés. L'hydrolyse, plus forte pour la smectite sodique que la calcique, conduit à une perte du fer octaédrique

Obtention des composes a structure mixte par echange ionique en sel fondu d'ions lanthanides trivalents sur les cristaux d'aluminogallate de sodium, na::(1+y)(al::(1-x)ga::(x))::(11) o::(17+(y/2)), obtenus par la methode du fondant, avec 0,5y1 et 0x0,5. Caracterisation par des mesures de susceptibilite magnetique et conductivite electrique. Analyse des spectres rpe pour localiser les ions lanthanides dans les structures de type alumine beta ou mixte, pour lesquelles les etudes d'absorption optique, de fluorescence et de declin de fluorescence indiquent des proprietes optiques differentes des ions ce**(3+), nd**(3+), eu**(2+) et eu**(3+)

Extraction de cd et zn a partir des milieux aqueux, perchlorate, nitrate et sulfate par des melanges de phenyl-1 methyl-3 benzoyl-4 pyrazolone-5 et de sels d'ammonium lipophiles. Le pyrazolonate de nh::(4) est l'agent reel de synergie. Mecanisme de transport de cuivre par des acyl-4 pyrazolones-5 a travers une membrane liquide epaisse

I. Etude des mécanismes de relaxation mis en jeu dans Cl2, Br2, I2 isolés en matrice, après excitation en UV proche ou lointain : émission structurée (transitions vibroniques) pour Cl2en UV proche et transitions électroniques avec interaction Rydberg-Valence en UV lointain; émission dans le visible pour Br2 et I2 quelle que soit l'énergie d'excitation; étude théorique des processus de relaxation. II. Observation d'ions moléculaires simplement ou doublement chargés, formés par échange de charge simple ou double étudié par spectrométrie de translation; analyse des règles de sélection : conservation du spin et observation des seuls états singlets pour Cl2, influence croissante du couplage spin-orbite lorsqu'on passe de Cl2, à Br2 puis I2.

Caracterisation et quantification des equilibres chimiques qui regissent un nouveau systeme d'extraction dont l'apport est de pouvoir operer a partir du milieux fortement acides avec des cinetiques d'extraction tres rapides. Des substitutions de coordinats sont prealablement operees en phase aqueuse. L'extraction elle-meme est realisee par des echangeurs cationiques formant des micelles inverses dans les diluants utilises. Cas de l'acide dinonylnaphtalenesulfonique

Au cours de ces dernières décennies, des études ont étés menées pour identifier plusieurs traceurs des matériaux du cycle du combustible nucléaire, dans le cadre de la lutte contre la prolifération nucléaire. Ces matériaux sont généralement collectés lors d’inspections dans des installations nucléaires, ou saisis lors de contrôles de trafics illicites. Les informations fournies par ces traceurs sont parcellaires et ne permettent pas de déterminer avec exactitude la provenance et l’historique industriel de ces matériaux.Le but de ce travail de thèse est de démontrer le potentiel de l’utilisation des isotopes du molybdène pour le traçage des matériaux du cycle du combustible nucléaire. Le choix s’est porté sur le molybdène car en raison de la similarité de leurs propriétés chimiques, le molybdène et l’uranium sont étroitement associés dans les minerais d’uranium et tout au long de la chaîne de purification de l’uranium. L’étude s’est focalisée sur une partie de l’amont du cycle du combustible, depuis l’extraction des minerais d’uranium jusqu’à la production des concentrés miniers d’uranium : divers procédés physiques et chimiques sont appliqués, à la fois pour purifier l’uranium et abaisser la concentration en molybdène.Au cours de cette étude, une nouvelle méthode de séparation du molybdène a été développée pour caractériser sa composition isotopique dans des minerais, minéraux et concentrés miniers d’uranium. La variabilité des compositions isotopiques du molybdène dans un gisement d’uranium est principalement due aux mécanismes d’adsorption et/ou de précipitation du molybdène. Les gisements magmatiques et sédimentaires ont des compositions isotopiques différentes, ce qui permet ainsi leurs distinctions. Les concentrés miniers d’uranium produits à partir de ces deux types de gisements ont des compositions isotopiques similaires aux minerais. Ces résultats soulignent ainsi le potentiel des isotopes du molybdène comme traceur des origines des concentrés miniers d’uranium. Cependant, un fractionnement des isotopes du molybdène a été établi lors de la production des concentrés miniers d’uranium pour deux usines au Niger. Les procédés de purification de l’uranium tels que la lixiviation, l’extraction par solvant et la précipitation ont été reproduits en laboratoire sur des échantillons réels pour expliquer le fractionnement isotopique du molybdène lors de la production des concentrés miniers. Au cours de ces procédés, le fractionnement peut être positif (lixiviation), négatif (extraction par solvant, précipitation à l’eau oxygénée) ou nul (précipitation à l’ammoniaque). Dans le cas des échantillons du Niger, la somme de ces procédés est négative, dans le sens des données expérimentales que nous avons obtenues, démontrant ainsi également le potentiel de l’utilisation des isotopes du molybdène comme traceur des procédés de transformations des matériaux du cycle du combustible nucléaire
Nuclear forensics aims at determining the age, provenance as well as industrial or storage history of uranium ores and uranium ore concentrates that are part of the nuclear fuel cycle. Several potential tracers have already been identified for this purpose. However, these tracers are not providing always unambiguous information. This study is focused on establishing Mo isotopes as a new tracer of uranium ore provenance and of ore processing for its application in nuclear forensics. Molybdenum and uranium share a number of common geochemical properties. In the nuclear fuel cycle, molybdenum is an impurity that is difficult to separate during uranium extraction and purification processes, while its concentration is required to be lower than some specification limits. We focused this study on the first part of the nuclear fuel cycle, from the uranium ores extraction to the production of uranium ore concentrates.We developed an enhanced separation method for Mo from a uranium-rich matrix (uranium ores, uranium minerals, uranium ore concentrates) in order to analyze the mass fractionation induced by processes typical of the nuclear fuel cycle. Molybdenum isotopic compositions in uranium ores depend of adsorption and precipitation processes. The δ98Mo values of sedimentary uranium ores is shifted to negative values relative to magmatic ores. This provides a means of distinguishing these types of uranium ores. Uranium ores concentrates produced from both uranium ore natures (magmatic and sedimentary) have Mo isotope compositions similar to the uranium ores. These results suggest that molybdenum isotopes have a strong potential of as a tracer for identifying the origin of the uranium ore concentrates. However, Mo isotopes fractionations were established during the production of uranium ore concentrates in the both Niger mills. We reproduced in laboratory the lixiviation, solvent extraction and precipitation processes to explain these observations. The Mo isotopes fractionation is positive for the lixiviation process, negative for the solvent extraction and precipitation with hydrogen peroxide, and null for ammonia precipitation. In the case of the Niger samples, the sum of these processes is negative and agrees with our experimental data. Mo isotopes have a strong potential as a tracer for identifying the origin and transformation of uranium in the nuclear fuel cycle, in the framework of nuclear forensics

Marine clay deposits are characterized by very soft to soft consistencies (undrained strength 1-50 kPa), presence of saline pore solution and low-swelling clays. Besides, loss of metastable structure on disturbance, poor undrained strengths of soft clays is contributed by high water contents. Presence of saline pore solution and low-swelling clays (illite, chlorite, kaolinite) play an important role in developing metastable structure of soil sediments deposited in marine environment. The pore solution salinity regulates the “physico-chemical (A - R) stress” that in turn has significant bearing on development of the metastable structure. Metastable structure refers to edge-face, edge-edge associations in card-house arrangement of platy/elongate particles that develop during deposition. Loss of metastable structure of soft marine clays upon disturbance leads to excessive settlements and slope failures. Besides A - R forces, metastable structure of marine clays is contributed by cementation bonds, thixotropic hardening, ion leaching, formation or addition of dispersing agents and chemical weathering. Secondary compression also causes bonding of micro-structural units that increase stiffness and strength of the metastable structure. Review of literature brings out that majority of studies examining the role of physico-chemical factors on the engineering behavior of marine clays have focused on illite rich sediments. However, non-swelling clay, namely, kaolinite is also encountered in marine deposits (example, Pusan clay, Singapore clay, Sarapui soft clays). Kaolinites differ from illites in being 1:1 mineral (unit layer comprises of 1 silica sheet bonded to 1 gibbsite sheet) and having strong hydrogen bonding between unit layers. Consequently, kaolinite particles are thick (0.3 to 3 ìm thickness) with low surface area (10 to 20 m2/g). Also the hydrogen bonding between unit layers do not allow them to separate on hydration. Combination of very low isomorphous substitution (Al for Si 1 in 400), low cation exchange capacity (3 meq/100g), and low surface area, lead to negligible development of diffuse double layer repulsion forces between kaolinite particles. Strong positive edge (developed on broken bonds at particle edges from adsorption of hydrogen ions) negative face attraction between kaolinite particles, encourages flocculation of particles at range of water contents. It was therefore considered of interest to examine the engineering response of kaolinites to changes in pore solution salinity from leaching effects. The focus of the thesis is hence to gain better understanding of physico-chemical (pore solution salinity, A - R forces) and mechanical (secondary compression, loss of overburden) factors towards development of metastable structure of kaolinite clays deposited in synthetic seawater environments in the context of their compressibility and undrained strength characteristics. Laboratory experiments are performed with kaolinites that are slurry consolidated in conventional consolidometers in saline and synthetic seawater solutions. The metastable structure developed by consolidated specimens is relevant to alluvial marine sediments that contain kaolinite (example, Pusan clay, Singapore clay, Sarapui soft clays). The structure of the thesis is as follows: Chapter 1 gives an introduction to the thesis. Chapter 2 provides a detailed review of literature on the role of chemical factors (pore solution composition, A - R forces, osmotic suction) and mechanical processes (secondary compression and overconsolidation) in developing metastable structure of kaolinite specimens subjected to slurry consolidation and the consequent influence of metastable structure on compression, undrained strength and sensitivity characteristics of clay specimens. The Chapter also defines the scope and objectives of the study. Chapter 3 details the experimental program undertaken to bring out the role of chemical factors and mechanical processes in influencing the 1-dimensional compression and undrained strength characteristics of slurry consolidated kaolinites prepared in saline medium. Chapter 4 delineates the role of chloride salt solutions (sodium, magnesium and calcium) and synthetic seawater solution in contributing to the metastable structure developed by slurry consolidated kaolinites at various vertical effective stress (óv’) and the consequent influence of metastable structure on 1-dimensional compression, undrained strength and sensitivity characteristics of the clay. Chapter 5 examines influence of secondary compression on metastable structure developed by kaolinites that were slurry consolidated in 24.53 g/L sodium chloride and synthetic seawater solutions and the consequence of the developed metastable structure on undrained strength and sensitivity. The chapter also examines the consequences of secondary compression experienced by soft overconsolidated kaolinites on their undrained strength and sensitivity characteristics. Chapter 6 examines the relative influence of differential osmotic stress and electrochemical stress on the consolidation behaviour of kaolinite specimens that are slurry consolidated in sodium chloride solutions. The osmotic efficiencies (á) of kaolinite were obtained using the Fritz-Marine Membrane Model. Chapter 7 summarizes the major conclusions of the thesis.

Marine clay deposits are characterized by very soft to soft consistencies (undrained strength 1-50 kPa), presence of saline pore solution and low-swelling clays. Besides, loss of metastable structure on disturbance, poor undrained strengths of soft clays is contributed by high water contents. Presence of saline pore solution and low-swelling clays (illite, chlorite, kaolinite) play an important role in developing metastable structure of soil sediments deposited in marine environment. The pore solution salinity regulates the “physico-chemical (A - R) stress” that in turn has significant bearing on development of the metastable structure. Metastable structure refers to edge-face, edge-edge associations in card-house arrangement of platy/elongate particles that develop during deposition. Loss of metastable structure of soft marine clays upon disturbance leads to excessive settlements and slope failures. Besides A - R forces, metastable structure of marine clays is contributed by cementation bonds, thixotropic hardening, ion leaching, formation or addition of dispersing agents and chemical weathering. Secondary compression also causes bonding of micro-structural units that increase stiffness and strength of the metastable structure. Review of literature brings out that majority of studies examining the role of physico-chemical factors on the engineering behavior of marine clays have focused on illite rich sediments. However, non-swelling clay, namely, kaolinite is also encountered in marine deposits (example, Pusan clay, Singapore clay, Sarapui soft clays). Kaolinites differ from illites in being 1:1 mineral (unit layer comprises of 1 silica sheet bonded to 1 gibbsite sheet) and having strong hydrogen bonding between unit layers. Consequently, kaolinite particles are thick (0.3 to 3 ìm thickness) with low surface area (10 to 20 m2/g). Also the hydrogen bonding between unit layers do not allow them to separate on hydration. Combination of very low isomorphous substitution (Al for Si 1 in 400), low cation exchange capacity (3 meq/100g), and low surface area, lead to negligible development of diffuse double layer repulsion forces between kaolinite particles. Strong positive edge (developed on broken bonds at particle edges from adsorption of hydrogen ions) negative face attraction between kaolinite particles, encourages flocculation of particles at range of water contents. It was therefore considered of interest to examine the engineering response of kaolinites to changes in pore solution salinity from leaching effects. The focus of the thesis is hence to gain better understanding of physico-chemical (pore solution salinity, A - R forces) and mechanical (secondary compression, loss of overburden) factors towards development of metastable structure of kaolinite clays deposited in synthetic seawater environments in the context of their compressibility and undrained strength characteristics. Laboratory experiments are performed with kaolinites that are slurry consolidated in conventional consolidometers in saline and synthetic seawater solutions. The metastable structure developed by consolidated specimens is relevant to alluvial marine sediments that contain kaolinite (example, Pusan clay, Singapore clay, Sarapui soft clays). The structure of the thesis is as follows: Chapter 1 gives an introduction to the thesis. Chapter 2 provides a detailed review of literature on the role of chemical factors (pore solution composition, A - R forces, osmotic suction) and mechanical processes (secondary compression and overconsolidation) in developing metastable structure of kaolinite specimens subjected to slurry consolidation and the consequent influence of metastable structure on compression, undrained strength and sensitivity characteristics of clay specimens. The Chapter also defines the scope and objectives of the study. Chapter 3 details the experimental program undertaken to bring out the role of chemical factors and mechanical processes in influencing the 1-dimensional compression and undrained strength characteristics of slurry consolidated kaolinites prepared in saline medium. Chapter 4 delineates the role of chloride salt solutions (sodium, magnesium and calcium) and synthetic seawater solution in contributing to the metastable structure developed by slurry consolidated kaolinites at various vertical effective stress (óv’) and the consequent influence of metastable structure on 1-dimensional compression, undrained strength and sensitivity characteristics of the clay. Chapter 5 examines influence of secondary compression on metastable structure developed by kaolinites that were slurry consolidated in 24.53 g/L sodium chloride and synthetic seawater solutions and the consequence of the developed metastable structure on undrained strength and sensitivity. The chapter also examines the consequences of secondary compression experienced by soft overconsolidated kaolinites on their undrained strength and sensitivity characteristics. Chapter 6 examines the relative influence of differential osmotic stress and electrochemical stress on the consolidation behaviour of kaolinite specimens that are slurry consolidated in sodium chloride solutions. The osmotic efficiencies (á) of kaolinite were obtained using the Fritz-Marine Membrane Model. Chapter 7 summarizes the major conclusions of the thesis.