Iron is often present in leach liquors produced in chemical and hydrometallurgical processes. It is known that voluminous iron precipitates with high impurity values are formed if the conditions during its formation are not controlled well. These products are also often difficult to treat in downstream processes. This study therefore focused on the determination of product quality parameters for the production of good quality iron precipitates from zinc-rich solutions. Special attention was given to the quality of metastable phases such as ferrihydrite and schwertmannite formed at elevated temperatures and in the pH range 1.5 to 3.5 in a continuous crystallizer. These phases are produced over a range of supersaturation levels with the best quality products formed at lower supersaturation. It was shown that most industrial processes are operated well above the metastability limit at relatively high supersaturation. However, stagewise precipitation of iron, even above the metastability limit, yielded better quality products. It was also shown that localized supersaturation levels could be controlled through changes in the micro and macromixing environments. The three-zone model approach was used to improve the quality of ferrihydrite and schwertmannite precipitates. Changes in the reactor design and the position of reagent feed points also impacted on the quality of the precipitates. Control over the localized supersaturation not only ensures the production of good quality nuclei, but also impacts on particle growth, which is required to make downstream processing of precipitates possible. In precipitation processes, growth mainly takes place through agglomeration as the rate of molecular growth is generally low. The final quality of iron precipitates is greatly influenced by the quality of the agglomerates formed during iron precipitation. A Hadamard matrix was used to indicate the relative importance of the most relevant operating parameters for the formation of good quality iron precipitates. / Thesis (PhD (Metallugical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

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Ziel der Arbeit war eine Steigerung der Wasseraufnahme und Harndilution durch Supplementierung von Natriumchlorid (NaCl) oder pH-Wert-Senkung durch Zugabe von Ammoniumchlorid (NH4Cl) zur Reduktion des Harnsteinbildungspotenzials. Durch die NaCl-Zulage wurde die Harnmenge signifikant gesteigert und das spezifische Gewicht des Harns gesenkt. Eine NaCl-Gabe stellt somit einen möglichen ergänzenden therapeutischen Ansatz für eine vermehrte Ausscheidung von Kristallen dar. Eine Ansäuerung des Harns durch Zulage von NH4Cl ließ sich nicht erreichen.

Une gestion groupée des actinides est envisagée afin d’améliorer les performances du combustible et de réduire le risque de prolifération. Dans le procédé COEXTM, l’étape de coprécipitation oxalique permet de former un oxalate mixte d’uranium et de plutonium, précurseur de l’oxyde mixte destiné à la fabrication de combustible MOX. Afin de déterminer les cinétiques de nucléation et de croissance de cet oxalate mixte, il est nécessaire de pouvoir calculer la sursaturation. Appliquée à la coprécipitation, différentes théories sont proposées dans la littérature, cependant aucune n’a été vérifiée expérimentalement. Une nouvelle expression de la sursaturation applicable à tous types de solutions solides est alors proposée. La détermination des cinétiques de nucléation primaire est basée sur le principe de Nielsen avec l’utilisation d’un appareil de nucléation assurant un très bon micromélange des réactifs. Les lois cinétiques des solutions solides vérifient la théorie de Volmer et Weber appliquée à la coprécipitation. La méthode de calcul de la sursaturation proposée permet de retrouver le comportement classique de la nucléation. Les résultats expérimentaux permettent de démontrer que la coprécipitation de la solution solide est favorisée par rapport à la précipitation des oxalates simples du fait d’une barrière énergétique plus faible pour la solution solide. La cinétique de croissance est déterminée à partir d’un suivi spectrophotométrique des concentrations des réactifs en solution et en utilisant une semence. La croissance est contrôlée par l’intégration au réseau cristallin selon un mécanisme en spirale / Current concepts for future nuclear systems aim at improving the fuel cycle with the co management of actinides in order to enhance the fuel performance and to reduce the proliferation risk. Actinides coconversion processes play an important role by producing mixed actinides compounds used as starting materials for fuel re-fabrication. Oxalic coprecipitation is one investigated way to synthesize solid solutions of actinides – lanthanides mixed oxalates which have to meet strict standards. The nucleation and growth kinetic laws involve a fundamental crystallization parameter such as the supersaturation. For the precipitation of solid solutions, different theories are developed in the literature, however none have been verified experimentally. A new suitable expression for the supersaturation ratio applicable is presented in order to determine a general model for the expression of nucleation and growth rates. The experimental study of the primary nucleation kinetics is based on a “stopped flow” apparatus which provides a very good micromixing of the reactants. The kinetic laws of solid solutions verify the theory of Volmer and Weber applied to the coprecipitation. The method of calculating the supersaturation developed allows to find the typical behavior of nucleation. The experimental results demonstrate that the coprecipitation of the solid solution is kinetically favored over the precipitation of simple oxalates due to a lower energy barrier for the solid solution. The crystal growth rate is determined from a spectrophotometric monitoring of the reactant concentrations using a seed charge. The crystal growth is controlled by the surface integration with a spiral mechanism

It is estimated that 90% of new chemical entities in development pipelines exhibit poor aqueous solubility. For compounds not limited by biological membrane permeability, this poor aqueous solubility is the limiting factor in bioavailability. Therefore, the formulation of such drugs has primarily been centered on improving dissolution properties. Traditional approaches for overcoming poor aqueous solubility include salt formation of the active ingredient, complexation, the use of surface active agents, formulation into oil based systems, particle size reduction, or a combination of these methods. More recently amorphous solid dispersions have been explored. Currently, the drug loading within solid dispersions is limited resulting in large quantities of the formulation being required for a therapeutically relevant dose. In the frame of the work herein, Thin Film Freezing was utilized to generate high drug loaded amorphous solid dispersions of the poorly water soluble drug phenytoin utilizing a hydrophilic polymer or an amphiphilic graft copolymer for system stabilization. Additionally a new solvent removal technique, atmospheric freeze drying, was investigated for removal of the solvents used during Thin Film Freezing. The Thin Film Freezing materials were subsequently incorporated into a polymeric carrier for solid dispersion formulation by a novel fusion production technique termed Kinetisol® dispersing. Studies of the solid dispersions produced by Thin Film Freezing revealed an amorphous system had been obtained for both stabilizing polymers. The formulation containing a hydrophilic carrier was capable of achieving supersaturation. Conversely, the amphiphilic graft copolymer demonstrated a phenytoin-polymer interaction resulting in poor dissolution. Atmospheric freeze drying of the Thin Film Freezing product demonstrated that the alternative drying technique generated powders with significantly improved handling properties as a result of reduced electrostatic interactions due to the increased pore size, reduced surface area, larger particle size, and higher, though acceptable, residual solvent levels. The use of Thin Film Freezing powders during Kinetisol Dispersing resulted in a single phase amorphous system while solid dispersions produced from physical mixtures of bulk materials were amorphous two-phase systems. This indicates that the use of amorphous drug compositions during solid dispersion production may increase drug loading in the final system while remaining single phase in nature. / text

Understanding the fundamentals of the growth of nanostructures is key to controlling their size and morphology. This thesis investigated the supersaturation effect as well as other effects on the growth of two one-dimensional nanomaterials - Magnesium hydroxide sulfate hydrate(MHSH) nanobelt and ZnO nanorod. It was found that the supersaturation for the growth of 1D nanomaterial had to be controlled at low level and it could be controlled through sparingly soluble carbonate salts. To examine the supersaturation effect on one-dimensional nanostructure growth, this study developed a quantitative kinetic model was developed to describe the one-dimensional nanostructure growth. The qualitative investigation and the quantitative model should provide more insight to the processes and some guide-lines for one-dimensional nanostructure growth in the future. This thesis also examines other factors such as agitation and temperature. Some other process parameters can have a significant effect on the growth process. The Zn(NO3)2 and HMT system was used as a model system to demonstrate that agitation had dramatic effects on the final morphology of the nanostructure. Spherical morphology could be obtained through mixing the reaction solution. The building blocks of the nanospheres were similar to those forming the nanorods. Thus, the spherical morphology was believed to result from the breakdown of the free diffusion of building blocks to the growing nanocrystal surface.

Le contrôle de la porosité des supports de catalyseurs est un enjeu important dans l'industrie du raffinage. L'objectif de cette thèse est de développer un nouveau procédé de précipitation afin d'obtenir des alumines γ présentant des propriétés texturales originales vis-à-vis de celles préparées de façon conventionnelle par précipitation de boehmite en réacteur agité. Pour cela, les influences combinées du précurseur, de la technologie de mélange et du temps de micromélange sur les propriétés physiques du produit final ont été étudiées. Ce travail de thèse propose donc une comparaison de trois technologies de mélange : un réacteur agité conventionnel, un réacteur à disque tournant et un disperseur rotor-stator. Les gammes de temps de micromélange accessibles avec chacun de ces réacteurs sont déterminées par la méthode iodure-iodate. L'étude porte sur la précipitation de deux précurseurs de l'alumine : la boehmite, classiquement utilisée, ainsi que la NH4-dawsonite, dont l'intérêt pour la préparation de supports de catalyseurs est plus récent. Leur solubilité est estimée dans la mesure du possible à l'aide des données thermodynamiques de la littérature. Dans le cadre de cette étude préliminaire, un modèle de suivi de la sursaturation en fonction du temps de micromélange est mis en place à l'aide des équations cinétiques de la précipitation de la boehmite. La caractérisation de la NH4-dawsonite précipitée en réacteur agité met en évidence l'intérêt de ce précurseur pour obtenir des alumines à forte porosité présentant des diamètres poreux moyens entre 10 et 30 nm. Une nuance est toutefois apportée aux fortes surfaces spécifiques généralement revendiquées sur ce matériau dans la littérature. Malgré tout, les propriétés texturales de l'alumine ex-dawsonite présentent une évolution thermique atypique lui permettant de se démarquer de l'alumine ex-boehmite. L'étude de la précipitation en mélangeur rapide met en évidence une grande différence de comportement entre les deux précurseurs. Contrairement à la boehmite, la forte sensibilité de la NH4-dawsonite au temps de micromélange permet d'obtenir une large gamme de propriétés texturales. Ce travail de thèse confirme donc l'intérêt de la NH4-dawsonite comme précurseur alternatif de l'alumine pour obtenir des propriétés texturales originales. L'utilisation de plusieurs systèmes précurseur / technologie de mélange s'avère également prometteuse pour couvrir une large gamme de propriétés texturales / Control of catalyst supports porosity is an important challenge for the refining industry. The aim of this thesis is to develop a new precipitation process in order to obtain γ-alumina supports exhibiting new textural properties compared with those prepared by the conventional boehmite precipitation route in stirred tank reactor. For that purpose, combined influences of precursor, mixing technology and micromixing time on the final product physical properties were studied.Three mixing technologies were compared: a classic stirred tank reactor, a sliding surface mixing device and a rotor-stator mixer. Micromixing time ranges achievable with each of these reactors were determined using the iodide-iodate method. The study focused on the precipitation of two alumina precursors: boehmite, usually used, and NH4-dawsonite, which interest for catalyst supports preparation is quite recent. A model was developed to simulate the supersaturation evolution as a function of the micromixing time, based on boehmite precipitation kinetic equations.Characterization of NH4-dawsonite precipitated in a stirred tank reactor confirmed this precursor interest in order to prepare high porosity aluminas with mean pore diameters ranging between 10 and 30 nm. Study of the precipitation conducted in fast contacting mixers highlighted a significant difference in the behaviour of both precursors. Contrary to boehmite, NH4-dawsonite high sensitivity to micromixing time led to a wide range of textural properties.This thesis work therefore confirms the NH4-dawsonite potential as an alternative alumina precursor in order to reach new textural properties. The use of several precursor / mixing technology systems has also proven promising to cover a wide range of textural properties

Dans la zone insaturée, l’altération des roches poreuses en condition de séchage est attribuée principalement aux sels qui cristallisent dans la solution porale lors de son évaporation. Ils exercent une pression (pression de cristallisation) contre les parois du pore dont le moteur est la sursaturation de la solution. Dans le même contexte, l’eau porale qui est retenue par capillarité dans les pores nanométriques est amenée sous pression négative. L’eau sous tension capillaire exerce une traction mécanique contre les parois du pore, mais aussi modifie les équilibres chimiques. Ces deux mécanismes, pression de cristallisation et traction capillaire, qui sont de nature physique, ont pour origine le déséquilibre chimique entre l’eau porale et l’air sec.Des expériences de cristallisation de sels (Na2SO4, NaCl) permettent 1/ de mettre en évidence des conditions favorables à l’expression de la pression de cristallisation, qui apparait comme un phénomène brutal et transitoire provoqué par la relaxation d’un état de déséquilibre (sursaturation), et 2/ de montrer que la tension capillaire, générée par une interface nanométrique, peut être transmise à un macrovolume dans un système géométrique particulier construit par les sels. L’état de tension y est métastable (l’eau est surchauffée) mais dure suffisamment longtemps pour observer les effets mécaniques (traction) et chimiques (dissolution) attendus. La relaxation brutale de l’état de surchauffe permet une rapide sursaturation, qui est le moteur de la pression de cristallisation.Ainsi, les cycles climatiques sont à l’origine d’évènements brutaux et transitoires qui marquent la relaxation d’un état de déséquilibre (surchauffe et sursaturation), contrôlés par la tension capillaire et la cristallisation des sels qui coopèrent pour altérer la roche en conditions de séchage. / The alteration of porous media in drying conditions is generally attributed to the pressure exerted by growing salts from the poral evaporating solution against the pore wall (crystallization pressure). In drying conditions, the water retained by capillarity in nanometric pores is under absolute negative pressure. Water under capillary tension exerts a mechanical traction against the pore walls but also modifies the chemical equilibria and so rock-fluid interactions. Crystallization pressure and capillary tension, which are physical processes, are both induces by the disequilibrium between poral water and dry air.Salt crystallization experiments in microtubes (Na2SO4, NaCl) show some favorable conditions for crystallization pressure - in terms of supersaturation and geometry – which is transient and brutal. A second series of experiments shows that capillary tension, generated by a nanometric liquid air interface, can be transmitted to a macrovolume of aqueous solution in a particular geometric system built with salts. The tensile state is metastable (superheated), but long enough to modify significantly the chemical budget of the system and to see mechanical effects. The brutal relaxation of the superheating state by vapor nucleation induces a rapid salt supersaturation which is the driving force of the crystallization pressure.The salt growth (during evaporation) and capillarity cooperate in drying conditions to alter porous media.During climate cycles (especially humidity) they control and induce transient and brutal events which mark the end of metastable states (superheating and salt supersaturation).