A comparison of hafnium solvent extraction from hydrochloric acid solutions using either Cyanex 923 or 925 (organic extractants) diluted in kerosene was established. Since understanding of the hafnium-hydrochloric acid solution is important, development of a speciation diagram for such a solution was carried out. While both Cyanex 923 and 925 are mixtures of trialkyl phosphine oxides, the trialkyl group in the former have straight chains, while those in the latter have branched chains. / Experimentally, the major variables studied were hydrochloric acid, hafnium and Cyanex concentrations. Hafnium is rapidly loaded as the tetrachloride complex by a solvation reaction forming a disolvate with the extractant (923 or 925). While extraction increases with increasing acid concentration, it decreases with increasing hafnium concentration due to polymerization. Total chloride level is the controlling factor provided there is enough acid to prevent hafnium hydrolysis and polymerization. Cyanex 923 is a more powerful extractant than Cyanex 925 for given conditions. A few experiments have shown that a very dilute hydrochloric acid solution is suitable as a stripping agent. / The main objective is to evaluate the potential of Cyanex 923 (or 925) as an alternative to MIBK due to the problems associated with the latter. MIBK is the conventional extractant for hafnium and zirconium extraction and separation from hydrochloric acid/thiocyanate solutions. Thus, preliminary studies of hafnium and zirconium (existing separately or together) extraction from hydrochloric acid/thiocyanate solutions were also performed. When existing separately, hafnium and zirconium are similarly extracted into either Cyanex reagents, but when both metals coexist in the same solution, preferential separation of hafnium is observed.

Canadian Electrolytic Zinc in Valleyfield, Quebec utilizes the conventional Roast-Leach-Electrowin process to produce zinc metal. Iron removal is carried out in the jarosite conversion circuit which consists of ten continuous stirred tank reactors in series. / In this study, the first five tanks of the jarosite conversion circuit were piloted and process identification experiments were carried out. Step changes in the flows of the raw acid, spent acid, jarosite slurry and zinc ferrite slurry streams were performed. The goal of these experiments was to collect transient response data which could be used to validate a dynamic conversion circuit model. The process was found to be most sensitive to changes in the flow of the raw acid stream. / The zinc ferrite dissolution rate constant calculated from the experimental data agrees with literature values. Using a jarosite precipitation rate expression from the literature, it was found that jarosite precipitation is negligible in the first reactor but cannot be ignored in the second tank. / The dynamic model provides a good representation of the first two tanks of the jarosite conversion circuit and can be used for both process control and optimization studies on a full-scale facility.

Interactions between diffusing impurity atoms and dislocations can occur during or following the deformation of metals. These interactions cause dislocation pinning, leading to strain aging. At lower temperatures (<400°C), the relevant solutes are interstitial (in particular, carbon and nitrogen). At higher temperatures (>800°C), substitutional impurities are expected to be most influential. The same mechanisms that result in the yield drops, increased flow stresses and increased work hardening associated with strain aging at low temperatures should result in significant modification of recovery and recrystallization behaviour at higher temperatures. / The present work involves the deformation of austenitic (304) stainless steel at high temperatures (800°C to 1280°C) in 1-hit and 2-hit high-temperature compression and multi-hit hot torsion testing. Experimental variables include the strain rate, temperature and interpass time. / Significant anomalies in the static softening kinetics are observed; under certain deformation conditions, the normal relationship between temperature and fractional softening is reversed. This effect is attributed to the non-equilibrium segregation of phosphorus during the interpass holding time. Analysis of dynamic recrystallization (DRX) in the material has revealed retardation of the initiation of recrystallization; this effect is explained in terms of the segregation of substitutional elements to the boundaries of new DRX grains.

Flotation is a multivariable process that can be considered the output of at least four interacting factors: chemical (frother, collector), physical (particle size, percent solids), machine and circuit arrangement. These factors combine with the aim of producing the best conditions for particle collection. / Gas dispersion defines the characteristics of a bubble population generated from a continuous stream of air. Gas Dispersion parameters include superficial gas velocity, gas holdup, bubble size and bubble surface-area flux. Gas distribution defines the spread of the air bubbles throughout the cell volume. It is intuitive that best metallurgical results are likely associated with uniform distribution of gas. The measurement of gas distribution is the focus of this thesis, achieved by simultaneous measurements of gas velocity at several radial distances at a common depth in flotation cells. A distribution deviation index (DDI) is proposed to quantify the distribution. / La flottation est un processus multivariable que l'on peut considérer le résultat d'au moins quatre facteurs : le produit chimique (moussant, collecteur), les aspects physiques (taille des particules, proportion de solides), l'équipement disponible et le circuit de flottation. Ces facteurs se réunissent pour produire les meilleures conditions pour la séparation de particules. / La dispersion du gaz définit les caractéristiques d'une population de bulles produites dans un courant continu d'air. Parmi les paramètres de dispersion, il y a la vitesse superficielle du gaz, la charge gazeuse, la taille des bulles et le flux de superficie des bulles. La distribution du gaz définit la diffusion des bulles d'air partout dans le volume d'une cellule de flottation. Il est intuitif de croire que les meilleurs résultats métallurgiques seraient associés à une distribution uniforme du gaz. La mesure de la distribution du gaz est le sujet de cette thèse, réalisée par mesures simultanées de vitesse du gaz à plusieurs distances radiales à une profondeur commune dans une cellule de flottation. On propose un indice de déviation de distribution (DDI) pour évaluer quantitativement la distribution du gaz.

Arsenic disposal is one of the most important environmental issues the mining and metallurgical industries are faced with. This problem has worsened in recent years because of the increasing arsenic content of the low-grade and complex ores currently processed by the mining industry and the introduction of stricter environmental regulations. / This Ph.D. thesis sought to develop a novel concept for arsenic fixation suitable for the long-term safe disposal of arsenic generated and disposed by the minerals industry. In particular this research project investigates the encapsulation of scorodite, a well characterized Fe(III)-As(V) compound having the following formula FeAsO4·2H2O, with phosphate coatings, materials potentially not prone to reductive decomposition. Reductive decomposition is known to be responsible for the release of arsenic into the environment form arsenate solids such as scorodite. / The subject matter of this thesis is the application of heterogeneous crystallisation techniques to produce stable phosphate coatings on scorodite particles. The experimental work reported in this thesis involved three different types of studies, namely (1) production of a number of synthetic minerals; (2) evaluation of their stability; and (3) encapsulation of scorodite with two of these synthetic minerals. The synthesis work involved the production of aluminium and calcium phosphates via homogeneous, heterogeneous and seeded crystallisation. The stability work involved the study of the dissolution of hydrated aluminium phosphate (AlPO4·1.5H2O), dicalcium phosphate dihydrate (CaHPO4·2H2O), and calcium-deficient hydroxyapatite (Ca10-x(HPO 4)x(PO4)6- x(OH)2-x, x <2). Finally, the encapsulation work involved the deposition of hydrated aluminium phosphate and calcium-deficient hydroxyapatite on scorodite particles and the evaluation of their stability in simulated oxic and anoxic environments. / The directed deposition of phosphate on scorodite particles was achieved via the control of supersaturation. For the directed deposition of aluminium phosphate, the supersaturation was controlled via pH adjustment. On the other hand, for the controlled deposition of calcium-deficient hydroxyapatite on scorodite particles supersaturation was controlled via regulated mixing of two Ca(II) and P(V) solutions at constant pH. Both encapsulation techniques appeared to enhance scorodite stability under simulated oxic and anoxic environments by reducing the arsenic release rate up to one order of magnitude.

Zirconium oxide is a barrier against corrosion. The oxidation behavior of zirconium alloys is believed to be related to the properties of the substrate and the zirconium oxide grown on this substrate. Both monoclinic and tetragonal phases of the oxide grown on Zr-2.5Nb and Zircaloy-4 are strongly textured. The volume fraction of tetragonal phase in zirconium oxide was investigated. The tetragonal phase percentage gradually decreases with an increase of the oxide thickness. / The oxidation kinetics of Zr-2.5Nb and Zircaloy-4 was investigated and the results demonstrate that the oxidation rate is related to the volume fraction of tetragonal phase. No texture evolution was observed in both alloys as the oxidation time varied. It was found that the higher the volume fraction of tetragonal phase, the higher oxidation resistance. / The texture formation of the oxide is related to the texture of the substrate. A model of crystal orientation relationship between alpha-Zr and the monoclinic phase was applied to explain the formation of oxide textures on substrates having different textures. Good agreement between the results predicted from the model and the experimental results were obtained. A crystallographic orientation relationship between the monoclinic and tetragonal oxide phases is proposed based on the texture investigation of both phases. Various methods were applied to modify the texture of Zr-2.5Nb. Heat treatment at 560°C caused decomposition of the beta-Zr phase. This heat treatment only slightly increased the sharpness of texture of the alpha-Zr phase and heat treatment improved the oxidation resistance of Zr-2.5Nb. The improvement is attributed to a change of morphology of the beta-Zr phase. High temperature heat treatment at 855°C significantly changes the microstructure and texture of the substrate. A needle shape second phase formed inside the alpha-Zr phase is responsible for the increase of oxidation rate. Cold deformation causes the texture in the Zr-2.5Nb substrate to change from (1120)[1100] to (11 23)[1100]. The change of the texture degrades the oxidation resistance of Zr-2.5Nb.

The evolution of texture and microstructure during the deformation of two Mg-based (+Al, Mn, Zn) alloys has been studied under various conditions of temperature and strain rate. The tested materials were taken from AZ31 and AM30 extruded tubes. The mechanism of recrystallization was investigated by using uniaxial compression, while twinning was studied under uniaxial tension testing. Optical metallography, X-ray analysis and EBSD techniques were employed to study the texture and grain scale development. The first part of the investigation focused on the misorientations that apply to the different mechanisms of new grain formation during the hot compression of magnesium alloy AM30. This approach led to the identification of three types of microstructural features produced during deformation at high temperature (350°C at a strain rate of 0.001s-1). In the first, microbands were produced in grain interiors due to the accumulation of basal dislocations. Their orientation changes involve rotations of the basal planes to a more favorable orientation for glide, leading to geometric softening. In the second, two different types of DRX nuclei were observed, i.e. those formed i) by bulging and ii) by continuous dynamic recrystallization. Although visually distinct, the two mechanisms are formed as a result of dislocation-based processes that produce c-axis rotations toward the loading axis. For low misorientation angles, the boundary character is consistent with the accumulation of basal dislocations. Once nuclei of the latter two types have formed, however, only those orientations belonging to the RD-TD fibre are able to grow. In this way, recrystallization leads to the retention of the main characteristics of the initial RD-TD texture. The second part focused on the mechanisms associated with variant selection during contraction and double twinning. These twins are of practical interest since they have a high potential for texture randomization. For this purpose, magn / L'évolution des orientations cristallographiques préférentielles et de la microstructure de deux alliages de magnésium, soit AZ31 et AM30, a été étudiée à des températures et à des vitesses de déformation différentes. Les échantillons des deux alliages utilisés ont été prélevés sur des tubes extrudés. Des essais de traction et de compression uniaxiales ont été effectués dans le but de comprendre les mécanismes à l'origine de la formation des macles et des grains recristallisés. L'effet de la recristallisation sur les macles primaires (ou de contraction) et secondaires (ou d'extension) a finalement été étudié. La première partie de l'étude porte sur les relations de désorientation qui sont associées aux joints de grain qui se forment durant la compression de l'alliage de magnésium AM30 à haute température (soit 350 °C, et à une vitesse de déformation de 0.001s-1). Cette méthode de caractérisation a permis l'identification de trois types de composantes structurales. Premièrement, des microbandes se forment au centre des grains par l'accumulation de dislocations basales. Ces bandes produisent des rotations qui positionnent les plans de glissement basal de façon à faciliter le glissement des dislocations. Ainsi, un adoucissement géométrique est généré, ce qui a pour effet de diminuer la contrainte d'écoulement. Deuxièmement, la recristallisation engendre la formation de nouveaux grains aux joints des grains initiaux. Deux mécanismes de recristallisation sont observés : les nouveaux grains sont créés soit par la migration des joints de grain ou par recristallisation continue. Bien que visuellement distincts, ces deux mécanismes sont tout deux initiés par une accumulation de dislocations. Les résultats ont démontré que les nouveaux grains ayant une orientation similaire à celle des grains initiaux sont avantagés au niveau de la croissance. Ainsi, la recristallisation a tendance à retenir les orientations

The effect of modern mechanized girth welding on high strength line pipe has been investigated. The single cycle grain coarsened heat affected zone in three grade 690 line pipe steels and a grade 550 steel has been simulated using a Gleeble thermo-mechanical simulator. The continuous cooling transformation diagrams applicable to the grain coarsened heat affected zone resulting from a range of heat inputs applicable to modern mechanized welding have been established by dilatometry and metallography. The coarse grained heat affected zone was found to transform to lath martensite, bainite, and granular bainite depending on the cooling rate. The impact toughness of the steels was measured using Charpy impact toughness and compared to the toughness of the grain coarsened heat affected zone corresponding to a welding thermal cycle. The ductile to brittle transition temperature was found to be lowest for the steel with the highest hardenability. The toughness resulting from three different thermal cycles including a novel interrupted intercritically reheated grain coarsened (NTR ICR GC HAZ) that can result from dual torch welding at fast travel speed and close torch spacing have been investigated. All of the thermally HAZ regions showed reduced toughness that was attributed to bainitic microstructure and large effective grain sizes. Continuous cooling transformation diagrams for five weld metal chemistries applicable to mechanized pulsed gas metal arc welding of modern high strength pipe steel (SMYS>550 MPa) have been constructed. Welds at heat inputs of 1.5 kJmm-1 and 0.5 kJmm-1 have been created for simulation and analysis. Dilatometric analysis was performed on weld metal specimens cut from single pass 1.5 kJmm-1 as deposited beads. The resulting microstructures were found to range from martensite to polygonal ferrite. There is excellent agreement between the simulated and as deposited weld metal regions. Toughness testing indicates improved energy absorption at -20 °C with increased cooling time. / L'effet des méthodes modernes de soudage circonférentiel mécanisé sur des aciers à forte résistance utilisés pour les tubes de canalisation a été investigué. La zone affectée thermiquement ayant subi une croissance de grain lors d'un cycle thermique simple de soudage a été simulée pour trois grades d'acier à tubes de canalisation 690 et un grade d'acier 550 à l'aide d'un appareil de simulation thermomécanique Gleeble. Les diagrammes de transformation en refroidissement continu pour la zone affectée thermiquement ayant subi une croissance de grains ont été établis pour un spectre de chaleur induite représentatif du procédé de soudage mécanisé en utilisant la dilatométrie ainsi que des analyses métallographiques. Il résulte que la zone affectée thermiquement ayant subi une croissance de grain connaît un changement de phase vers une martensite massive, une bainite ou une bainite granulaire selon le taux de refroidissement rencontré. La résistance des aciers étudiés a été mesurée par essais Charpy et comparée à la résistance obtenue pour la zone affectée thermiquement ayant subi une croissance de grains correspondant à un cycle thermique de soudage. Le plus bas température de transition ductile-fragile a été obtenue pour les grades d'acier ayant la plus grande aptitude à la trempe. La résistance résultante des structures obtenues pour trois différents cycles thermique, notamment un nouveau cycle thermique interrompu par recuit intercritique similaire à l'effet que peut avoir un soudage à double torche à déplacement rapide et espacement réduit, a été étudié. Toutes les zones affectée thermiquement montrent une baisse de résistance causée par l'apparition d'une structure bainitique et la croissance des grains.Les diagrammes de transformations en refroidissement continu ont été établis pour 5 alliages de soudage applicable pour le soudage pulsé à l'arc sous gas des aciers à tube modernes à haute résistance. Des soudures avec un apport de chaleur de 1,5 kJmm-1 et 0,5 kJmm-1 ont été utilisées pour les simulations et les analyses. Des essais de dilatométrie ont été faits sur des échantillons prélevés des cordons de soudure déposés en une passe à 1,5 kJmm-1. L'observation métallographique des échantillons présente une structure allant de la martensite à la ferrite polygonale. Une excellente concordance a été établie entre la structure du métal obtenu par simulation et telle que déposé. Les tests de résistance indiquent une amélioration de l'énergie absorbée à -20°C lorsque le temps de refroidissement est plus long.

The performance characteristics of a tundish, such as the flotation of inclusions and of slag entrainment, are largely influenced by the fluid flow phenomena. Physical and mathematical modeling in water is widely used to understand fluid flows in a tundish, and as a tool to improve, control and design procedures for high quality steel processing operations. These approaches were used to study the performance of fluid flow for a new design of ladle shroud. The new "Dissipative Ladle Shroud" (DLS) was studied, using a one third scale, delta shaped, four-strand tundish. The results were compared with those achieved with the standard ladle shroud. The standard k-ε turbulence model, together with the continuity and momentum equations, were employed in order to analyze, and visualize, the velocity fields generated within the tundish operating at steady state. Different cases have been analyzed, including a conventional ladle shroud (LS) with a bare tundish, and a tundish furnished with an impact pad. Similarly, the new design of the shroud (DLS) was studied under equivalent conditions. The physical experiments included the use of Particle Image Velocimetry (PIV) and conductivity tracer techniques. The PIV measured the instantaneous velocities at the outlet of the DLS and the LS at different flow rates, showing the detailed jetting characteristics of water leaving the two types of ladle shroud. Residence Time Distribution (RTD) curves were also obtained for the different flow arrangements previously mentioned, and the dispersion of a colored dye tracer was observed at different intervals of time during tundish operation, and analyzed using the video visualization technique. / Les caractéristiques de performance d'un répartiteur telles la flottaison des inclusions et de la scorie sont largement influencées par les phénomènes d'écoulement des fluides. Les modèles physiques et mathématiques sont communément utilisés pour comprendre la dynamique des fluides dans un répartiteur et pour améliorer, contrôler et concevoir les procédés de traitement d'acier de haute qualité. Cette approche a été utilisée pour étudier la performance de la dynamique des fluides avec un nouveau design de poche de couleé. La nouvelle "Dissipative Ladle Shroud" (DLS) a été étudiée en utilisant une échelle d'un tiers de répartiteur, en forme delta et possédant quatre drains de couleé. Les résultats ont été comparés avec ceux obtenues avec le poche de couleé normal. Le modèle de turbulence k-ε, avec les équations de conservation des masses et de quantité de mouvement, a été utilisé pour analyser et visualiser les champs de vitesse générés par l'opération du répartiteur en conditions stables. Différents cas ont été analysés, incluant un "conventional ladle shroud" (CLS) avec un répartiteur vide, et un répartiteur muni d'un bloc d'impact. De même, le nouveau design de poche de couleé (DLS) a été étudié sous des conditions équivalentes. Les expériences physiques incluent l'utilisation du "Particle Image Velocimetry" (PIV) et de techniques de traceur de conductivité. Le PIV mesure la vitesse instantanée à l'issue du DLS et du CLS à différents taux de flux, en montrant les caractéristiques détaillées du jet d'eau quittant les deux types de poche de couleé. Des courbes de Distribution des Temps de Résidence (RTD) ont également été obtenues pour les différents arrangements de flux précédemment mentionnés, et la dispersion d'un traceur de teinture colorée a été observée et analysé à différent intervalles de temps pendant l'opération du répartiteur en utilisant une vidéo de visualisation technique.

The aqueous chemistry of the reduction of selenious species by sodium dithionite, sodium sulfide, stannous chloride and sulfur dioxide/sulfite was studied. The resultant precipitates were characterized using different techniques, including scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. In the case of sodium dithionite, the research showed that, at initial pH below 1.7 and dithionite stoichiometric excess above three, less than 0.5 ug/L remained in solution less than a minute after the addition of the reagent. However, it was found that the precipitate, mainly composed of red amorphous selenium, was not stable in the presence of the dithionite decomposition by-products and partially redissolved after several hours. In the case of the reaction involving selenious acid and sulfide ions, the results showed that, below a pH of approximately 7.0, the precipitation reaction was complete in less than 10 minutes at a sulfide to selenium ratio above 1.8 with less than 5 ug/L of soluble selenium remaining in solution. The precipitate was deduced to be a Se-S solid solution consisting of ring molecules of the following SenS8−n formula. However, above pH 7 the removal of selenium was incomplete due to formation of a stable colloidal suspension. In the case of industrial solutions, high dissolved sulfur dioxide content (> 5g/L) decreases the effectiveness of the precipitation reaction. Concerning the removal of Se(IV) by tin(II), at an initial pH below 1.3 and molar ratios above two, less than 5 ug/L of selenium(IV) remained in solution after reduction. The reaction products, were determined to be composed of approximately equal amounts of tin selenide and tin dioxide with a small amount of selenium(IV) being adsorbed on the latter. Finally, it was found that Se(IV) can be reduced quantitatively at ambient temperature via a combination of sulfite reduction and ultra-acidification to a colloidal form that can be determined using turbidimetry. The developed technique was shown to be equally effective with real Se(IV)-bearing industrial solutions generated in a zinc concentrate roasting operation hence making the method particularly useful as on-line process monitoring and control tool. / La chimie aqueuse des réactions de réduction entre les ions sélénieux et le dithionite de sodium, le sulfure de sodium et les ions stanneux ont été étudiées. Les précipités résultant de cette réaction ont été caractérisés par différentes techniques comme la microscopie électronique à balayage, la diffraction à rayons X et la spectrométrie de photoélectrons induits par rayons X. Dans le cas du dithionite de sodium, ce projet a démontré que, pour un pH initial inférieur à 1.7 et un ratio stœchiométrique de dithionite supérieur à trois, moins de 0.5 ug/L de sélénium(IV) restait en solution moins d'une minute après l'addition du réactif. Par contre, le précipité, formé en majorité de sélénium rouge amorphe, n'était pas stable en présence des composés issus de la réaction de décomposition du dithionite et était partiellement re-dissous après quelques heures. Dans le cas de la réaction entre l'acide sélénieux et le sulfure de sodium, les résultats indiquaient que pour un ratio molaire sulfur/sélénium plus grand que 1.8 et un pH sous 7.0 la réaction de précipitation était complète et moins de 5 ug/L de sélénium (IV) restait en solution. Aucune précipitation n'a été constatée pour un pH plus élevé que 9.5 et la réaction était incomplète pour un pH entre 7 et 9.5. Le précipité semblait être composé d'une solution solide Se-S formé de molécules circulaires répondant à la formule SenS8−n. Par contre, pour un pH plus élevé que 7, la précipitation du sélénium était incomplète à cause de la formation d'un précipité de sélénium colloïdal. De plus, dans le cas des solutions industrielles, de hautes concentrations de dioxyde de souffre dissous (> 5g/L) diminuait l'efficacité de la réaction de précipitation.En ce qui concerne la réaction entre le sélénium(IV) et l'étain, pour un pH initial sous 1.3 et un ratio molaire étain/sélénium plus grand que deux, moins de 5 ug/L de sélénium restait en solution après la réaction. Les analyses ont révélé que le précipité était composé de parts approximativement égales de séléniure d'étain et de dioxyde d'étain et que ce dernier pouvait adsorber une petite quantité d'ions sélénieux. Finalement, ce projet a démontré que le sélénium(IV) peut être réduit, à la température ambiante, par une solution ultra-acide riche en sulfites. Une fois le sélénium précipité sous forme colloïdale, la concentration originale de celui-ci peut ensuite être déterminée par turbidimétrie. Par ailleurs, cette méthode est aussi efficace sur des solutions industrielles contenant du sélénium(IV) et peut donc être appliquée pour l'analyse en temps réel de cet élément.