ABSTRACT In the continuous casting process, the tundish not only serves as an intermediate buffer, but it also acts as a useful reactor for liquid steel refining. Modern tundishes are now designed to carry out different metallurgical operations, such as inclusion separation and flotation, alloy trimming, calcium doped inclusion modification, and thermal homogenization. To carry out such operations effectively, fluid flow inside a tundish plays an important role. It is now a proven fact that the insertion of different types of flow modifying devices can alter flow patterns within the tundish and thus affect the performance of the tundish significantly. Due to adverse operating conditions, direct experimental investigations are difficult to carry out. For that reason, physical and mathematical modeling is predominantly used to study tundish performance. Parameters like 'Residence Time Distribution' (RTD), tracer dispersion, velocity distribution, inclusion separation, etc. were mostly used to study and predict the performance of a tundish. Slag entrainment, though, is a vital problem during ladle changing that has been given less attention. In this research, it is intended to form a physical and mathematical modeling framework, to study and predict the performance of a 12 t, delta shaped, four strand, billet casting tundish. A full scale water model was studied both physically and mathematically. The phenomenon of slag entrainment occurring during a ladle changing operation was used as the key parameter to assess tundish performance. The amount of slag entering the 'Submerged Entry Nozzle' during a ladle change was measured to quantify the performance of different flow modifying arrangements. It is believed that the results of tests carried out under transient conditions can give a fairly good idea about tundish performance at steady state. To strengthen this belief, mathematical modeling of inclusion s / RÉSUMÉDans les procédés de coulées continu, les paniers répartiteurs ne servent pas seulement comme interface tampons, mais aussi comme un réacteur efficace pour raffiner l'acier. Les paniers répartiteurs modernes sont maintenant conçus pour effectuer différentes opérations métallurgiques comme la séparation des inclusions et leur flottation, l'ajustement fin de la nuance, le contrôle de la température de surfusion, la modification des inclusions par ajout de calcium et l'uniformisation de la température.Pour y arriver efficacement, l'écoulement du fluide dans le panier joue un rôle majeur. Il est maintenant prouvé que l'ajout de différents systèmes pour modifier les écoulements peut altérer les patrons d'écoulement dans le panier et en changer significativement la performance. Due aux conditions d'opérations difficiles, des investigations par expérimentation directe sont très difficiles. Pour cette raison la modélisation physique et mathématique est largement utilisée pour étudier la performance des paniers répartiteurs. Des paramètres comme la «Distribution des temps de résidence (RTD)», la dispersion d'éléments traceurs, le champ de vélocité, la séparation des inclusions, etc. sont largement utilisés pour étudier et prédire les performances d'un panier. L'entrainement du laitier, quoiqu'un problème vital lors du changement de creuset, a pourtant reçu moins d'attention. Dans cette recherche, le but est de développer une méthodologie de modélisation physique et mathématique pour étudier et prédire la performance d'un panier répartiteur de douze tonnes de forme triangulaire à quatre jets de coulée. Un modèle aquatique de grandeur nature fut étudié physiquement et mathématiquement. Le phénomène d'entrainement de laitier durant les opérations de changement de creuset fut utilise comme paramètre clé pour quantifier la performance du panier. La$

The hydrolysis of iron(III) from sulphate bearing aqueous solutions was investigated to significantly improve the neutralization of acidic mineral effluents. Both theoretical and experimental studies were undertaken. A literature review and a thermodynamic analysis of the Fe(III)-SO$ sb4$-H$ sb2$O system were performed. / The thermodynamic analysis determined that Fe(III)-sulphato complexes dominate in the acidic pH range (pH $<$ 4) while at neutral to mild alkaline pH range Fe(OH)$ sb3 sp circ sb{ rm (aq)}$ is the dominant species. It was found that a relationship exists between the precipitation pH and the sulphate content of the precipitate (17% at pH 3, 7-9% at pH 6 and 1-2% at pH 9) and it was attributed in part to the existence of the precursor Fe(III)-sulphato complexes and in part to SO$ sb4 sp{2-}$ adsorption on the Fe(III) oxyhydroxide solid phase. / Several variables were examined for their influence on the properties of the iron(III) hydrolysis products, such as: pH, neutralization rate, temperature, agitation rate, sulphate concentration and ionic strength. Tests were performed in a batch reactor and NaOH was selected as the most effective neutralizing reagent. Treatment sludges were characterized physically (e.g., solids content, settling rate, etc.), chemically and morphologically, while the treated effluent was examined for residual iron(III) content. These tests proved only partially successful as the precipitates produced were highly amorphous with low solids content (${<8 %}$) and poor settling (${<3}$ m/hr). However, exceptionally good precipitates were produced when the hydrolysis tests were performed under supersaturation control. This work led to the development of a novel approach to neutralization of effluents involving sludge recycling and staged neutralization in order to maintain a low and controlled supersaturation level. Via this novel method partially crystallized precipitates of excellent properties were produced at 50$ sp circ$C after eight recycles. (Abstract shortened by UMI.)

A quantitative texture analysis has been done on silicon steel specimens having different precipitate distribution in order to understand the texture development and the role of precipitates during secondary recrystallization. / To improve the size and distribution of precipitates, several annealing treatments were done on specimens obtained at different stages in the production of silicon steel. Tests for magnetic properties such as core loss and permeability, were done on final product specimens which had different precipitate distribution before secondary recrystallization. It is proposed that good precipitate distribution in the sheet before secondary recrystallization leads to a higher quality final product. / Grain size distribution and orientation distribution function (ODF) were obtained for the primary recrystallized specimens and for the annealed specimens, just before and just after, secondary recrystallization. From the ODF data, the probability of coincidence site lattice (CSL) boundaries were calculated up to $ Sigma$27b. The probability of CSL boundaries in specimens having good precipitate distribution was different from the probability observed in specimens having poor precipitate distribution. / An etch-pit method was used to give a more detailed, quantitative analysis of the texture development. An image analyzer was used to digitize the etch pit shapes, as well as the shape of grains. A computer program was developed to calculate the grain size of different texture components, the frequency of CSL boundaries between all grains, and the frequency of CSL boundaries between Goss grains and neighbouring grains. (Abstract shortened by UMI.)

This basic research project was aimed at assessing the potential of wash water for mechanical flotation machines. Test work at laboratory scale first examined the nature of entrainment; froth structures with and without wash water; and the location, geometry, and flowrate of wash water addition. The relationship between slurry, total water recovery and gangue recovery was characterized. Confirmatory work at pilot plant was completed. / The effect of wash water on metallurgical performance was tested with various streams from the Falconbridge Strathcona mill at laboratory and pilot and full plant scale, and with the secondary cleaner stage at the Eastmaque Kirkland Lake mill. / Results show that mechanical entrainment is the major means of gangue transport up to the slurry-froth interface. Transport into the froth is mostly hydraulic, although entrapment becomes dominant at low water recoveries. Free gangue recovery was closely related to slurry water recovery at all three scales. Wash water at an optimum superficial rate of 0.03 to 0.07 cm/s reduced entrainment by anywhere from 30 to 70%, typical values being around 50%. / Wash water can be further assisted by mechanical and ultrasonic vibration of the froth, difficult to achieve at plant scale, or with warm wash water, which becomes attractive if a waste heat source is available. A further rejection of 10 to 20% then becomes possible. / Distributor geometry was aimed at washing the entire froth surface at laboratory and pilot scale. It was observed that the recovery of hydrophobic minerals generally increased because the froth was stabilized. At plant scale, two perforated pipes close to the concentrate weir yielded the most reject. Froth stabilization was lost, and recoveries decreased.

Constant true strain rate (2 s$ sp{-1})$ compression tests with one or two interruptions were carried out on a series of steels over the temperature range 900-1050$ sp circ$C. Based on a 0.07% C, 1.25% Mn and 0.006% N reference steel, the three microalloyed steels contained the following: (i) 0.08% Al, (ii) 0.04% Nb, or (iii) 0.045% Nb and 0.08% Al. The degree of fractional softening during the interpass was used to assess recrystallization start (R$ sb{ rm s})$ and finish (R$ sb{ rm f})$ times as well as those for the onset (P$ sb{ rm s})$ and termination (P$ sb{ rm f})$ of precipitation. / Relative to a plain C steel, the static recrystallization kinetics show that the single solute retarding effect of Al is small but measurable while that of Nb is substantially larger. The influence of each element is enhanced when they are present jointly. The retardation effects observed at 1000$ sp circ$C are due solely to the presence of these elements in solution. Additional delays observed at or below 950$ sp circ$C in the two Nb bearing steels are ascribed to strain induced precipitation of Nb(CN). / The P$ sb{ rm s}$ times were estimated from the fractional softening data as well as from stress relaxation type tests. The presence of high levels of Al retarded the onset of Nb(CN) precipitation while it accelerated its progress. The Nb precipitates were cube shaped and heterogeneously distributed, suggesting that they were formed on dislocation networks. / A thermodynamic model was developed for the alloy system studied. The calculations indicated that there is a higher chemical driving force for precipitation in the Nb steel than in the Nb-Al steel at a given temperature. Consequently, this produces a higher equilibrium mole fraction of Nb(CN) in the former. The P$ sb{ rm s}$ times calculated based on the classical nucleation theory are in good agreement with the values observed. / Three hit test results further showed that increased hold times between the first two hits decrease the rate of softening between the second and third hits. Residual strain in the partially recrystallized structure is more effectively accumulated at lower temperature due to slower softening rates. These data enabled the development of a model for calculation of residual strains following a hold in a partially recrystallized structure. (Abstract shortened by UMI.)

Three microalloyed steels were tested under continuous and interrupted loading conditions. These materials consisted of a base steel containing 0.06%C and 1.31%Mn and two further alloys containing single additions of 0.29%Mo and 0.04%Nb. / Double hit compression tests were performed on cylindrical specimens of the three steels at 820, 780 and 740$ sp circ$C within the $ alpha$ + $ gamma$ field. A softening curve was determined at each temperature using the offset method. It was observed that, in the base steel, $ alpha$ recrystallizes more slowly than $ gamma$. The addition of Mo steel retards the recrystallization of the base material; it has a greater influence on $ gamma$ than on $ alpha$ recrystallization. Nb addition has an even greater effect on the recrystallization of the two phases. In this steel, the recrystallization of ferrite was incomplete at the three intercritical temperatures. Furthermore, the austenite remained completely unrecrystallized up to the maximum time involved in the experiments (1 hr). / The progress of ferrite recrystallization was followed on quenched specimens of the three steels by means of quantitative metallography. Most of the data fit an Avrami equation with exponents in the range 2 to 2.5. A departure from this equation was observed for the final stages of the recrystallization process. Growth rate analysis showed that the average growth rate decreased with time for all the experimental materials, this decrease being greatest for the base steel and least for the Nb-containing grade. The nucleation of recrystallization was observed to occur heterogeneously in the microstructure. The interface between ferrite and austenite was the preferred site for nucleation. Measurement of the number and size of recrystallized ferrite grains showed that some grains begin to recrystallize very early, growing to a large size by the end of the process. The total number of grains increased continuously until almost 80% of the volume fraction was recrystallized. After that, due to coalescence, the number of recrystallized grains decreased very rapidly. (Abstract shortened by UMI.)

One critical issue in chloride hydrometallurgy is the regeneration of the lixiviant HCl that is commonly achieved by pyrohydrolysis. It is the scope of this thesis to investigate a low temperature HCl regeneration process, which regenerates HCl and produces saleable gypsum. Experiments were performed to determine the optimum conditions of the chemical reaction that involved the reactive mixing of calcium chloride (CaCl2) solution with sulfuric acid (H2SO4) solution at low temperature and atmospheric pressure. / The results showed that the crystallization chemistry of the CaCl 2-H2SO4 reaction can be controlled in such away that favors the production of well grown gypsum crystals with the simultaneous regeneration of practical strength HCl. High strength HCl (= 4 M) was regenerated by the reaction of (3.5 M) CaCl2 leach solutions with (8 M) sulfuric acid in the temperature range of 20-60°C. Acid addition in stages to simulate the titration procedure, seeding and recycling, and increasing temperature were found to favor crystal growth and filterability. Finally, this research showed that there is negligible metal uptake with the exception of lead, making the production of marketable gypsum possible.

This thesis reports the results of an investigation of scorodite long-term solubility and stability conducted at fixed pH (5-9) and temperature (22°C, 50°C and 75°C). The decomposition of scorodite at 22°C was found to be extremely slow. At neutral pH, the arsenic concentration stabilized at 5.8 mg/L. As scorodite dissolved, the iron reprecipitated as 2-line ferrihydrite. The growth and re-crystallization of ferrihydrite was delayed by apparent arsenate adsorption. The solubility product of scorodite was calculated as 10-25.5. The dissolution rate of scorodite in a pure system was modeled with a decreasing exponential equation. The pre-exponential factor approached first order vis-a-vis OH- concentration and the activation energy suggested that scorodite dissolution is chemically controlled. A thermodynamic investigation indicated that the stability field of scorodite extends up to pH 6.75 for a molality of the aqueous species of 6.7x10 -5 (5 mg/L As) when in equilibrium with ferrihydrite but only up to pH 2.3 when in equilibrium with goethite. The presence of gypsum led to lower arsenic concentrations; this was attributed to the formation of calcium-iron-arsenate compounds, such as yukonite (Ca2Fe3(AsO4) 4(OH)·12H2O).

Nonoriented electrical steels are mainly used as the core materials in motors and generators. The magnetic properties required for these materials are low core loss, high magnetic induction and high magnetic permeability. These magnetic properties of nonoriented electrical steels are mainly influenced by grain size and crystallographic texture. All research to improve the magnetic properties so far has focused on grain growth through the control of chemical compositions and various processing parameters. However, in the manufacturing techniques of nonoriented electrical steels, the control of grain size is approaching its limit. Since there is still enough room to improve the magnetic properties through the control of texture, future research in nonoriented electrical steels should be concentrated on the optimization of crystallographic texture. / Recrystallization texture itself has long been a subject of research because the origin of recrystallization texture provides a high level of scientific interest. Despite much research on recrystallization texture, the mechanism of the formation of recrystallization texture is still disputed. This dispute is associated with the complexity of microstructural inhomogeneity formed in the deformed state, different nucleation rates for different orientations of deformed grains and different growth rates of nuclei into the neighboring deformed matrix. However, the advent of Orientation Imaging Microscopy (OIM) has contributed to a remarkable progress in the area of recrystallization texture, and stimulated research on the annealing texture in low carbon and interstitial free steels. Conversely, no systematic research on the evolution of the annealing texture in nonoriented electrical steels has yet been done. / The mechanism of texture evolution during recrystallization in the nonoriented electrical steels containing 1% and 2% Si respectively, a main objective of this thesis, is investigated from electron backscatter diffraction (EBSD) measurements on the materials with different recrystallization fractions. Based on obtained results, the mechanism for the formation of the recrystallization texture is proposed. The behavior of deformed grains of specific orientations is also discussed in terms of image quality value introduced by EBSD techniques. In addition, the origin of nuclei of specific orientations is suggested from observed EBSD results. / The texture development during grain growth, another main objective of this thesis, is investigated. Furthermore, a mechanism of texture development during grain growth is proposed based on the misorientation angle distribution with adjacent grains and the average size of grains of specific orientations. / Some useful means to optimize the magnetic properties through texture control in nonoriented electrical steels are studied. The effect of initial grain size prior to cold rolling on texture evolution during both the recrystallization stage and the grain growth stage is clarified. In addition, the effects of temper rolling reduction and annealing time on texture development during final annealing are examined. A mechanism of texture transformation by strain induced boundary migration (SIBM) is suggested by means of the introduction of image quality value in EBSD techniques. Finally, the effect of heating rate on texture development during final annealing is investigated, and the reason for texture change due to different heating rates is discussed.

In flotation, bubbles are the transport medium of mineral particles and water. The recovery of fine hydrophilic gangue is related to the recovery of water, which impacts the grade of the concentrate. In the solution (pulp) phase, water is transported as a layer on the bubble surface and as a trailing wake. The amount of water depends on bubble size, gas rate and, it is hypothesized, frother type. / Frothers are surface-active reagents that reduce bubble size by retarding coalescence. To isolate the effect of frother type (chemistry) on water transport from that of bubble size and gas rate an appropriate independent variable had to be established. Bubble surface area flux and gas holdup were proposed and correlated against the overflow rate of water from a bubble column at a given foam depth which was used as a measure of water carrying rate. / Gas holdup is established as the independent variable and it is shown that the common frothers can be grouped into families based on the gas holdup-carrying rate relationship. No relation was found between water carrying rate and bubble surface area flux. Possible reasons are considered.