To improve the mechanical properties of the most widely used Al-Si foundry alloys, small amounts of magnesium are often introduced. However, the effect of magnesium on the eutectic microstructure is unclear. The aim of the present work is to investigate the effect of magnesium on the eutectic microstructure and to clarify its role in the silicon solidification. / Experiments were performed on hypoeutectic and eutectic alloys (Al-7%Si, Al-11%Si, Al-13%Si and 413.2 alloys). Assessment of the eutectic microstructure was done using thermal analysis and metallography. The silicon phase was quantified by image analysis in terms of its perimeter, shape factor and aspect ratio. The results reveal that in hypoeutectic and eutectic synthetic alloys magnesium decreases the homogeneity of the microstructure. At about 1%Wt Mg, however, magnesium refines slightly the silicon phase. It was found that magnesium has a negative effect on strontium modification, that is, it changes the microstructure from well modified to partially modified. This is believed due to the presence of a complex intermetallic compound $ rm(Mg sb2SrAl sb4Si sb3)$ formed prior to the eutectic transformation. It is suggested that magnesium not be added in excess of 0.6 Wt% in strontium modified Al-Si alloys.

There is a great interest in the treatment of spent autocatalyst because, due to large amounts of PGM used by catalytic converters, the autocatalyst scrap is the largest and constantly growing source of PGM available for recycling. A hydrometallurgical method of PGM extraction from honeycomb type catalyst containing platinum (800-1200 ppm) and rhodium (50-60 ppm) using HCl-AlCl$ sb3$-HNO$ sb3$ or HCl-HNO$ sb3$ mixtures was studied. Experimental results of the leaches performed in a bench scale tubular reaction with recycled continuous flow of the leaching solution as well as 1000 cc stirred reactor are presented. The results suggest that Cl$ sp-$ single ion activity plays a decisive role in controlling the PGM dissolution. The extent of PGM recovery increased not by increasing HCl concentration to very high levels, but by keeping a relatively low total Cl$ sp-$ level (2.5 M) with a significant proportion present as AlCl$ sb3$. Rhodium extraction was always 5-10% lower than platinum, and it appears that increasing the AlCl$ sb3$/HCl ratio tends to increase rhodium recovery. High temperature (85-95$ sp circ$C) and an HNO$ sb3$ concentration around 3-3.5 M play very important roles in effectiveness of PGM extraction. The presented method of HCl-AlCl$ sb3$-HNO$ sb3$ tubular reactor leaching supplemented by solvent extraction (Kelex 100) of PGM from pregnant solution appears to be very attractive for small size (5-20 tonnes of catalyst/day) installations.

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No description available.

This thesis reports the effects of solids (hydrophobic and hydrophilic) on gas holdup, bubble size and water overflow rate with different frother types in a continuous flotation column setup. Four frothers were investigated: F150, 1-pentanol, 1-heptanol and DowFroth 250. The gas holdup, bubble size and water and solids overflow rate were measured as solids were added to the gas-water system. Solids used were talc (hydrophobic) and silica (hydrophilic). Measurements were taken at fixed froth depth and gas velocity. The following was found when talc was added: F150 - gas holdup decreased while bubble size increased; 1-pentanol - gas holdup increased while bubble size remained the same; gas holdup and bubble size remained the same with 1-heptanol and DowFroth 250. When silica was used as solids, no significant changes were observed in bubble size and gas holdup with all frothers tested. The observed behaviour of gas holdup and bubble size with F150 upon addition of talc is attributed to two factors: adsorption of frother by talc (an indirect effect) and talc promoting coalescence (a direct effect). The observed behaviour of gas holdup and bubble size with 1-pentanol upon addition of talc can be attributed to talc loading and slowing the rise velocity of bubbles which unlike the case with the other frothers, have not reached terminal velocity. Water overflow in 3-phase talc systems with 1-pentanol, 1-heptanol and DowFroth 250 increased with the addition of talc but in the case for F150 it fluctuated around an approximately constant value. Test results seem to show that the water overflow rate ranking for frothers in 2 phase is reversed in 3 phase with talc. Recommendations were made for future work. / L'on rapporte les effets de solides (aussi bien hydrophobiques que hydrophiliques) sur la rétention de gaz, la taille de la bulle, la vitesse d'écoulement du trop plein d'eau, par usage de différents types de moussants dans une colonne de flottation continue. Quatre moussants étaient étudiés: le F150, le pentanol-1, l'heptanol-1 et le DowFroth 250. La rétention du gaz, la taille de bulle et la vitesse d'écoulement du trop plein d'eau et des solides étaient mesurées en même temps que l'on procédait à l'ajout des solides dans le système gaz-eau. Les solides utilisés étaient le talc (hydrophobique) et la silice (hydrophilique). Les mesures étaient prises à des hauteurs de la mousse et à la vitesse du gaz determinées. Les résultats suivants étaient obtenus lorsque le talc était ajouté: pour le F150; la rétention du gaz avait diminué tandis que la taille de la bulle avait augmenté; pour le pentanol-1; la rétention du gaz avait augmenté alors que la taille de la bulle était invariable; pour l'heptanol-1 et DowFroth 250; la rétention de gaz et la taille de la bulle était restées inchangées. Lorsque la silice était utilisée, aucun changement majeur n'était observé, ni pour la taille de la bulle, ni pour la rétention du gaz et ce pour tous les types de moussants testés. Les changements observées pour la rétention de gaz et la taille de la bulle lors de l'utilisation du F150 comme moussant sont attribués à deux facteurs: l'adsorption du moussant par le talc (effet direct) et le talc qui fait la promotion de la coalescence (effet indirect). Le comportement observé dans la rétention du gaz et la taille de la bulle avec l'usage du pentanol-1 est dû à l'accroissement de la masse du talc qui ralentit du coup la vitesse de la bulle, laquelle à la différence des autres moussants, n'a pas encore atteint sa vitesse terminale. L'écoulement du trop plein d'eau dans le systè

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.