La précipitation est largement utilisée dans la chimie, l’hydrométallurgie, l’industrie pharmaceutique, le nucléaire ou de nombreuses autres activités industrielles. Les réactions de précipitation sont très sensibles à de nombreux paramètres de fonctionnement, tels que les concentrations de réactifs, la température, la sursaturation, l’hydrodynamique ou l'intensité du mélange. Ces paramètres jouent un rôle majeur pour contrôler la qualité physique du précipité. Dans l'industrie nucléaire, la précipitation est une opération très répandue, que ce soient dans l'extraction de l'uranium à partir de minerais d'uranium, dans le retraitement du combustible nucléaire irradié ou pour la gestion des effluents radioactifs. Dans cette étude, nous nous sommes intéressés à la précipitation de l'oxalate d’uranium IV. Seules quelques références bibliographiques liées à la précipitation de l'oxalate d'uranium tétravalent sont disponibles dans la littérature, elles concernent les fortes sursaturations (jusqu’à 2000). La présente étude a permis de proposer un modèle thermodynamique et des lois des cinétiques de précipitation à basse sursaturation à partir d’acquisitions expérimentales. De nouvelles mesures de solubilité de l’oxalate d’uranium à différentes acidités et différents excès oxaliques ont conduit à l’identification des constantes de complexation et du produit de solubilité. Les sursaturations sont calculées à partir des concentrations des ions libres. La comparaison avec l’approche basée sur les ions constitutifs montre que les deux concepts conduisent à des valeurs de sursaturations équivalentes. En ce qui concerne l’identification des cinétiques, de nombreux essais de précipitation de l’oxalate d’uranium IV en continu ont permis d’analyser l’influence des paramètres opératoires à la fois sur le rendement et les distributions de taille de particules. Les paramètres cinétiques sont obtenus par résolution du bilan de population selon la méthode des moments. Les lois de nucléation et d’agglomération sont exprimées à partir de la croissance cristalline. Le mécanisme de nucléation est de type secondaire et dépend de la puissance dissipée ainsi que de la concentration des cristaux. Quant au noyau d’agglomération, il a été identifié de type orthocinétique / Precipitation is widely used in many other industrial activities. Precipitation reactions are very sensitive to many operating parameters that play a major role in controlling the precipitate quality. In the nuclear industry, precipitation is a common operation, either in uranium extraction from uranium ore, nuclear fuel reprocessing or radioactive waste management. In this study we are interested in uranium IV oxalate precipitation. This study proposes a thermodynamic model and precipitation kinetics at low supersaturations on the basis of experimental acquisitions. New measures of uranium IV oxalate solubility at different acidities and oxalic excess led to the identification of the complexation constants and the solubility product. The supersaturation is calculated from free ions concentrations. The comparison with a constituent ions approach shows that the two concepts lead to equivalent supersaturation values. Regarding the identification of kinetics, many uranium IV oxalate precipitation continuous tests allowed the analysis of the influence of the operating parameters on efficiency and particle size distribution. Kinetic parameters are obtained by solving the population balance equation by the method of moments. Nucleation kinetics and agglomeration kernel are expressed from crystal growth kinetics. The nucleation mechanism corresponds to a secondary type and depends on the power dissipation and crystal concentration. As for the agglomeration kernel, it is identified of orthokinetic type

La carbonatation minérale est une technique alternative de capture et stockage du CO2 anthropique. L'abondance des matériaux carbonatables sur terre en fait une solution à fort potentiel. En particulier, la carbonatation directe en voie aqueuse a été présentée dans la littérature comme la voie la plus intéressante d'un point de vue énergétique pour la carbonatation minérale ex-situ, à la condition que les cinétiques naturellement lentes de dissolution des silicates magnésiens en phase aqueuse puissent être accélérées de plusieurs ordres de grandeur. Cette thèse étudie en détail les verrous et mécanismes de cette réaction en présence d'additifs organiques tels que l'oxalate, connus pour leur capacité à accélérer la dissolution des silicates magnésiens. Dans un premier temps, la carbonatation en voie aqueuse sans additif d'une olivine modèle est étudiée de manière à mettre en évidence la nature des phénomènes limitants. Ensuite le travail se concentre sur l'étude du rôle de l'additif oxalate à travers des essais spécifiques et une analyse fine de la phase solide. Il est démontré que pour différentes concentrations de suspension et sous 20 bar de CO2, cet additif conduit à la formation de complexes aqueux stables du magnésium avec l'oxalate et à la précipitation de MgC2O4,2H2O (glushinskite), qui empêchent toute précipitation quantitative de magnésite. La simulation géochimique complète du système a été réalisée et a permis d'expliquer les résultats des essais par un mécanisme de dissolution à grain rétrécissant. L'extension de l'étude à un autre silicate (harzburgite) et à d'autres ligands organiques accélérateurs de la dissolution des silicates tels que le citrate et l'EDTA n'a pas non plus permis d'obtenir la formation quantitative de carbonate, à cause d'une forte complexation en phase aqueuse du Mg extrait du minerai. Ces travaux remettent en doute la perspective de développement d'un procédé industrialisable de minéralisation du CO2 en présence d'additifs organiques. / Mineral carbonation is an interesting option for mitigation of anthropogenic CO2 emissions. Direct aqueous mineral carbonation has been presented by many as a promising strategy for ex-situ mineral carbonation, on the basis that organic additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. This thesis discusses and extends the current understanding of this process through geochemical modelling and detailed solid characterization. First, mineral carbonation is investigated in water alone, without additives, in order to understand and quantify the actual limitations of the process with specific magnesium silicate ores. Dissolution kinetics being critical with this process, the role of disodium oxalate as a dissolution accelerating agent is thoroughly examined with olivine, through dedicated experiments and comprehensive analysis of both solid and liquid phases. Under 20 bar of CO2, and irrespective of the conditions used, it is found that the formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of precipitating significant amounts of magnesium carbonate. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model. Other promising ligands from a dissolution perspective, namely citrate and EDTA, were also investigated. Contrary to oxalate, these do not form any solid by-products with magnesium, and yet they do not produce better carbonation results. The results and findings from this work cast strong doubts about the possibility of developing a viable direct aqueous mineral carbonation process using organic salts.

This thesis describes the convenient routes and the preparation conditions (temperature, oxygen partial presssure) which lead to the formation of single phase materials within the quaternary system Cu-Ni-Fe-O. The investigated compositions are the solid solutions CuxNi1-xFe2O4, the ferrites occurring in the phase triangle Cu0.5Ni0.5Fe2O4 -Cu0.9Fe2.1O4 - Cu0.5Fe2.5O4 and some copper-nickel oxide solid solutions. Three synthesis routes have been used, namely (i) the preparation and the thermal decomposition of freeze-dried carboxylate precursors, (ii) the preparation and the oxidation of intermetallic phases and (iii) the preparation and the heat treatment in air of mixed oxide/metallic powders. The thermal decomposition of freeze-dried Cu-Ni-Fe formate has been found as a suitable method for preparing single spinel phases within the Cu-Ni-Fe-O system. In comparison with the conventional solid state reaction, the required temperature is much lower. Concerning the solid solution CuxNi1-xFe2O4 , a single phase spinel is formed at 1000¢XC for x < 0.7; for CuO is identified as second phase. In this latter range the formation of a pure phase required an increase of the iron content in the mixture. The other single spinel phases in the phase triangle Cu0.5Ni0.5Fe2O4 - Cu0.9Fe2.1O4 - Cu0.5Fe2.5O4 have been synthesized under special synthesis p(O2)/T-conditions. For copper ferrites Cu1-xFe2+xO4 with x ?­ 0.1, 0.2, 0.33, 0.4 and 0.5, the change in the conductivity with the temperature is irreversible. The deviation from the linearity of the conductivity ?ã as a function of the temperature occurs due to the thermal history of these samples. The saturation magnetic moment (nB) at 5K, of some synthesized CuxNi1-xFe2O4 compounds has been determined. It has been found that nB increases with the nickel content in the ferrite sample.

Sodium oxalate is one of the many organics present in Bayer liquor. Due to its limited solubility, sodium oxalate can co-precipitate with alumina trihydrate during precipitation. This can have detrimental effects on the final product quality, especially if it occurs in the initial stages of precipitation.Quaternary amine type cationic surfactants can prevent sodium oxalate co-precipitation and increase the tolerable concentration of sodium oxalate in Bayer liquor. Their action is via the inhibition of nucleation or/and the inhibition of crystal growth. This study presents work detailing the effect of quaternary amines on sodium oxalate crystal growth in Bayer liquor.A series of quaternary amines were tested and classified as strong, medium or weak crystal growth inhibitors in plant liquor. The octadecyltrimethylammonium bromide was found to be the most effective under plant conditions.Results will show that while quaternary amines inhibit crystal growth in Bayer liquor, they have no effect on crystallization in synthetic liquor. It has been postulated that the presence of certain organic molecules is required for quaternary amines to crystallization and therefore stabilize the liquor. The inhibition of oxalate crystal growth in Bayer process liquors is due to the plant organics present, and the stabilizing effect of quaternary amines is the result of an interaction between quaternary amines and plant humic material on the oxalate surface. A series of organics, anionic macromolecules and anionic surfactants, have been tested to simulate the behaviour of plant humates, and their inhibitory effect on sodium oxalate crystal growth has been measured.A method for the analysis of the strongest quaternary amine has been adopted, improved and modified in order to fulfil experimental conditions.The CMC of quaternary amines has been determined in liquor. Surface tension ++ / measurements revealed relationships between certain liquor components and quaternary amines.Adsorption isotherms of quaternary amines have been successfully generated in Bayer liquor. Investigations with quaternary amines and plant humics reveal a synergy between the two. Co-adsorption of quaternary amines and plant humates onto the oxalate surface has been found, and the effect of the components on the adsorption behaviour will be discussed. The inhibitory effect and the adsorbed amount of components have been compared. Results revealed a relationship between the amount of plant humates on the surface and the crystal growth inhibition.The nature of the adsorption has been investigated with confocal laser scanning microscopy. These results will show that humic material adsorbs at the edges and in the corners of the crystals. In the presence of quaternary amines, the humic material occupies the main crystal faces as well. The nucleation of sodium oxalate from humic solution and from a mixture of humates and quaternary amine resulted in crystals with different morphology.Fourier Transform Infrared Attenuated Total Reflection Spectroscopy investigations will present the adsorption of quaternary amine on oxalate, and will indicate that the adsorption is pH dependent.

The broad aim of the work presented in this thesis was to examine the relationship between the mineral and organic phases of calcium oxalate monohydrate (COM) crystals, which are the principal components of human kidney stones. The results presented, clearly demonstrate the presence of some amino acids and urinary proteins in the crystals and suggest a role for intracrystalline proteins in urolithiasis. The adsorptive affinities of twenty amino acids to COM, calcium hydrogen phosphate, tricalcium phosphate and hydroxyapatite were assessed over the physiological urinary pH range (pH 5-8) in aqueous solutions. In all cases adsorption was strongest at pH 5 and decreased as the pH increased as a result of the increasing negative charge of both substrate and adsorbate. Binding was higher to COM than to the phosphate minerals, owing to differences in the surface charge or coordination-site availability. Aspartic acid (Asp), glutamic acid (Glu) and y- carboxyglutamic acid (Gla), which each have at least two carboxyl groups, exhibited the highest binding affinities, suggesting that binding occurs by chelation. Further, binding affinity was reasoned to result from the ability of the zwitterions of Asp, Glu and Gla to adopt favourable conformations in which two carboxyl groups, and possibly the amino group, can interact with the mineral surface without further rotation. Although free amino acids are unlikely to fulfil a prominent inhibitory role in stone pathophysiology, they could, nonetheless, fulfil an important function as terminal residues or as exposed components of calcium-binding domains of proteins involved in stone formation. The existence of intracrystalline proteins and amino acids in COM crystals was demonstrated by Synchrotron X-ray Diffraction (SXRD) analysis. / Non-uniform strains and crystallite sizes were derived from SXRD whole pattern line widths using Rietveld analysis, which showed an increase in average non-uniform strain and a decrease in average crystallite size. These were attributed to intracrystalline molecules. Occluded molecules were Glu, Gla, human prothrombin (PT) and to a lesser extent, human serum albumin (HSA), as well as crystal matrix extract (CME), which comprises a complex mixture of soluble organic molecules remaining after demineralization of COM crystals grown in centrifuged and filtered (CF) urine. COM grown in CF urine possessed greater non-uniform strain and smaller crystallite size than COM grown in ultrafiltered (UF) urine, indicating that the majority of intracrystalline macromolecules in crystals derived from CF urine were >10kDa in molecular mass. Asp, AspAsp, GluGlu and Tamm Horsfall glycoprotein (THG) were non-occluded molecules. Proteinase treatment of COM crystals grown in CF urine produced a marked decrease in non-uniform strain and an increase in crystallite size, suggesting that smaller crystallite material, more intimately associated with proteins than the bulk COM, was liberated during the treatment. A reciprocal relationship was found between non-uniform strain and crystallite size, which was dependent upon the type of molecule(s) in which the COM crystals were grown. For a given increment in non-uniform strain, the corresponding decrease in crystallite size was found to be considerably greater for occluded macromolecules, than for amino acids. This difference was attributed to the capacity of macromolecules, once incorporated into the crystal, to disrupt a larger volume of the mineral bulk than amino acids. Alternatively, unlike amino acids, macromolecules might possibly stabilise an amorphous phase. / Amorphous contributions resulting from the occlusion of PT and molecules from CF urine and UF urine in COM were found to range between 5-9%. The SXRD data derived from the COM crystals were further analysed for anisotropy using Williamson-Hall plots and individual peak analysis (SHADOW). Crystals grown in distilled water COM (distilled water) and COM (Asp, AspAsp, GluGlu, Gla, HSA, THG and PT) were isotropic with respect to both non-uniform strain and crystallite size. Although COM (Glu) and COM (UF) were isotropic with respect to non-uniform strain, the crystallite sizes were smaller along the (100) and (001) principal axes, respectively. COM (CF urine) and COM (CME) were also anisotropic, but with respect to crystallite size, with the shortest lengths occurring along the (100) and (001) axes. The absence of anisotropy in non-uniform strain was ascribed to experimental error. The data also showed that stacking faults contributed significantly to crystal disorder. Largest stacking faults, highest non-uniform strain and lowest crystallite sizes were generally found along the (13i) plane. Computer- generated models showed that molecules as large as proteins could not effectively be incorporated along the (13i) plane in COM. It was concluded therefore, that they transmit disorder from the principal (100,010, 001) planes in the crystal to the (13i) plane by diagonal sliding of one or more rows of oxalate ions, calcium ions and water molecules. SXRD single peak and whole pattern analysis of COM crystals grown in aqueous solutions of increasing concentrations of PT, HSA, CME and Gla showed that non- uniform strain increased, crystallite size decreased and stacking faults increased, to limiting values. / This was also found for crystals grown in UF urine containing CME and HSA. When crystals with occluded proteins were treated with proteinase K, their stacking faults and non-uniform strain decreased, and crystallite size increased, indicating that the non-crystalline material is more intimately associated with the protein and is physically removed or solubilised when the protein is destroyed. FESEM observations of the internal architecture of fractured CaOx crystals grown in human urine and synthetic solutions containing PT, revealed an inhomogeneous microstructure containing low density zones not observed in COM crystals grown in water or UF urine. Proteolytic treatment of the fractured crystals, created an internal honey combed structure that replaced the “low-density” zones. A timed growth study showed the internal ultrastructure of urinary COM crystals depended to a significant extent, upon the ratio of crystal-binding proteins to the available quantities of solute ions during growth. Dissolution studies of COM crystals showed that the process obeyed the Shrinking Core model and was therefore surface area-dependent. Pure COM dissolved more rapidly than crystals derived from UF urine, which dissolved at a faster rate than crystals precipitated from CF urine. This was attributed to shielding of the exposed COM surface by occluded molecules, which would reduce the effective surface area and slow dissolution. There is also the possibility that the macromolecules would have bound to the ions and retard their release into solution. The use of proteinase inhibitors verified the presence of proteinases in fresh urine and showed that they were capable of attacking proteins occluded in COM, in particular, proteins with Mr > 10kDa. / Although COM (CF) crystals were more difficult to dissolve than COM (UF) crystals in aqueous solutions, they were far more susceptible to endogenous proteolytic degradation in urine. Collectively, these findings have formed the basis of a novel hypothesis, which proposes that the type and concentration of urinary proteins incorporated inside CaOx crystals are fundamental to the disposal of CaOx crystals precipitated and retained within the renal system, and may therefore play an important role in the prevention of urolithiasis.

Bibliography: leaves 278-289. / xi, 324 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis reports on experimental investigation of the growth and aggregation of calcium oxalate mono-dydrate in metastable saline solutions using batch and continuous systems. The physical chemistry of calcium oxalate mono-hydrate in aqueous solutions is considered. A tubular crystalliser to be used as an in vitro system is described. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1996?

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [140]-152).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 174).

A tendência atual de simplificação de sistemas adesivos transformou-os em polímeros altamente hidrofílicos e prontamente susceptíveis à permeação de água através de sua estrutura. Estudos recentes têm demonstrado que os sistemas adesivos simplificados se comportam como membranas semipermeáveis, permitindo o movimento de fluidos através da sua estrutura. Soluções a base de oxalato de potássio são efetivos agentes de redução da condutividade hidráulica dentinária. Quando são aplicados na dentina após o condicionamento ácido, podem ser utilizados em associação com os sistemas adesivos sem o comprometimento da adesão. Este trabalho objetivou avaliar os efeitos dos sistemas adesivos AdheSE, One Up Bond F e Single Bond, associados ou não a uma solução a base de oxalato de potássio, na condutividade hidráulica da dentina. Foram realizados preparos de coroas totais em terceiros molares humanos que tiveram suas raízes secionadas e a polpa coronária removida. Os segmentos coronários obtidos foram conectados ao ?Medidor de Fluxo? (Flodec?System, De marco Engineering, Switzerland). A condutividade hidráulica dos espécimes foi mensurada antes e após a aplicação dos sistemas adesivos Single Bond -3M ESPE, One UP Bond F -Tokuyama Inc, AdheSe- Ivoclar- Vivadent. Os adesivos foram aplicados seguindo as recomendações do fabricante (grupos SBF, ADF e OBF), de forma experimental (grupos ADE e OBE), e em combinação com uma solução a base de oxalato de potássio (grupos SBO, ADO e OBO). Cada espécime teve seu valor de permeabilidade original ( smear layer) e máxima (após condicionamento ácido) medidos anteriormente, os quais serviram como parâmetros para o cálculo das respectivas alterações frente aos tratamentos, expressas em porcentagem. Após a determinação da condutividade hidráulica, os preparos foram moldados para obtenção de réplicas em resina, as quais foram examinadas em MEV (JEOL 2800, Japão) para qualificar a permeação de fluido através do adesivo. A Análise de variância a 2 critérios mostrou que apesar dos procedimentos adesivos causarem uma redução significante (p< 0.05) na condutividade hidráulica da dentina condicionada, nenhum foi capaz de eliminar completamente a passagem de fluidos através do adesivo polimerizado. Para os três adesivos testados, o tratamento com o oxalato de potássio foi o tratamento mais eficaz na redução da permeabilidade dentinária e esta diferença foi estatisticamente significante quando comparada aos outros tratamentos (p<0,05). Não houve diferença entre os três sistemas adesivos estudados com relação à redução da permeabilidade dentinária (p> 0,05). A análise das réplicas em MEV mostrou que mesmo após a polimerização do adesivo, a transudação de fluidos pôde ser identificada na superfície de todas réplicas examinadas. Nenhum dos sistemas adesivos testados foi capaz de eliminar a permeação de fluidos através da dentina, contudo a associação destes adesivos com uma solução a base de oxalato de potássio reduziu de forma significante a permeabilidade dentinária. / There is an ongoing trend to move away from classical multi-component bonding systems toward simplified adhesives. An immediate consequence of adhesive simplification is the intrinsic permeability to water that result from their increase in hydrophilicity. Current studies have demonstrated that single-step adhesives may act as semi-permeable membranes that allow water diffusion through its structure. Oxalate desensitizers are effective in reducing the hydraulic conductance of dentin. When oxalates are used after acid- etching they do not interfere with subsequent resin bonding. The objective of this study was to test the effects of adhesives systems with or without the application of an oxalate desensitizer on dentin permeability. Crown preparations were made from human extracted teeth. After the roots were sectioned and the coronal pulp removed, the crown segments were connected to an automatic flow-recording device (Flodec-System, De Marco Engineering, Switzerland). Fluid conductance was measured before and after the bonding procedures with the adhesives Single Bond -3M ESPE, One UP Bond F -Tokuyama Inc and AdheSe- Ivoclar Vivadent. Specimens were prepared and tested after the surface had been bonded according to manufacturer?s instructions (SBF,ADF and OBF groups) , in a experimental way (ADE and OBE groups) or integrating with a oxalate desensitizer gel (SBO, ADO and OBO groups). For each specimen, fluid flow across the smear-layer and bonded dentin was expressed as a percentage of acidetched dentin, which was assigned a value of 100% flow rate. After the hydraulic conductance measures, impressions were taken from the crown segments and epoxy resin replicas were produced for SEM examination. Two-Way ANOVA reveled that the adhesive systems reduced dentin permeability significantly (p< 0.05) compared to acid etched dentin, but no bonding system was able to eliminate the fluid flow though dentin. For the three bonding systems tested, treating the acid-etched dentin with potassium oxalate prior to the application of the adhesive was the most effective in reducing the hydraulic conductance of the specimens, and this difference was significant (p< 0.05) when comparing to the other treatments. There were no significant differences among the adhesives in their ability to reduce dentin permeability (p> 0.05). SEM micrographs of resin replicas showed that transudation of dentinal fluid droplets could be identified on the surfaces of all replicas examined.

No description available.