A novel method for preparing magnetic carriers, the functionalization of magnetic particles by molecular self-assembly, is described. Oriented and stable monolayers of a dibenzoic acid diamide bolaamphiphile were prepared on the surface of nanosized maghemite (gamma-Fe2O3) particles. The nature of the monolayer was characterized by X-ray photoelectron spectroscopy (XPS), while the structure and stability were characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the bolaamphiphile anchors on the surface through chemical bonding between one of the carboxylic head groups and the iron of the maghemite, leaving a pendant carboxylic moiety reactive. A density of the self-assembled films on gamma-Fe2O3 was assessed from potentiometric titration studies of the coated particles in dimethylformamide (DMF). Modification of the carboxy-terminated carriers through a reaction with the ligand diethylenetriamine (DETA), using a typical carbodiimide, enabled the preparation of highly selective magnetic carriers. Potentiometric titration of the reacted carriers indicates a 50% yield of DETA-reacted surfaces. An application of the prepared magnetic carriers in the recovery of metals, such as Cu2+ ions from dilute streams, is demonstrated. The efficiency of carriers in the chelation of copper ions was assessed by complexometric titration. Imaging of the prepared magnetic carriers, using an advanced Pt/C replica technique of transmission electron microscopy (TEM), is presented.

Na, Sr and Sb are the elements commercially used to modify the silicon phase in Al-Si foundry alloys. Interactive effects which occur during modification resulting from the mixing of modifiers in alloy melts are studied from many different aspects to identify the conditions for the occurrence of negative effects on modification, to study the modifier interaction mechanisms, and to devise ways to eliminate negative effects. / Metallographic studies have shown that antimony exerts deleterious effects on sodium or strontium modification of both A356 and A413 alloys. The deleterious effect of antimony has been quantified for various levels of sodium and strontium. The effect of antimony is more severe at higher antimony concentrations in the melt. No negative effects on modification occur in the combined presence of sodium and strontium. / Modifier interaction mechanisms were investigated by means of electron beam analysis, and the results were analyzed from the viewpoint of thermodynamics and crystallization. Certain antimony compounds are found in antimony treated Al-Si alloys. These antimony compounds play an important role in modifier interactions. Many interaction mechanisms are possible between antimony and strontium. The interactions may result in the formation of ternary or binary compounds. Duplex particles often form by the heterogeneous nucleation of Al$ sb4$Sr on the substrate of antimony compounds. In the study of sodium and antimony interaction mechanisms, similar duplex particles are also found. Other products from sodium and antimony interactions are a sodium-antimony binary compound and its oxide. When all three modifying elements are mixed together, all of the above interaction mechanisms are possible. Al$ sb4$Sr can heterogeneously nucleate on Na$ sb3$Sb forming an inclusion containing all three of the modifying elements. / Negative effects arising from antimony can be eliminated by using a suitable excess of sodium or strontium. Orthogonal tests show that a combination of sodium and strontium is preferable to overcome the influence of antimony on modification. Mechanical property tests have shown that the influence on mechanical properties from the interactions of antimony with other modifiers can be overcome. Improved mechanical behaviour is guaranteed under relatively long periods of melt holding when using the optimum combination of sodium and strontium to treat antimony containing melts.

Metal ion production by minerals alone and in pairs was studied by solution analysis, extraction with ethylene diamine tetraacetate (EDTA) and laser ion mass spectroscopy (LIMS) for combinations of pyrite, pyrrhotite, galena, and sphalerite. The effect of grinding, pH, and the presence of xanthate was studied. Metal ion transfer between sulphide minerals was determined. / Metal ion production with minerals in pairs was different from that for single minerals. The amount of metal ion in solution followed a galvanic interaction model, increasing for the anodic mineral and decreasing for the cathodic mineral. However, from the EDTA extraction technique, the concentration of metal ions on the mineral surface increased for both minerals. The mechanism of additional metal ion production on the cathodic mineral is unclear, but may be related to reaction between the mineral and OH ions formed on the surface as a result of galvanic interaction. / Metal ions transferred between two minerals in contact. In the case of pairing with pyrite, the larger proportion of Fe remained on pyrite, while 50% or more of Zn (from sphalerite) and Pb (from galena) transferred to pyrite. / The effect of Pb ions on pyrite in the presence of xanthate, and diethylene triamine (DETA) was investigated by cyclic voltammetry, ex situ spectroelectrochemical analysis and zeta potential measurements. / Once pyrite was contaminated by Pb ions, uptake of xanthate was promoted at pHs 9.2 and 10.5 with lime as pH modifier. The source of Pb--from solution or from contact with galena--was not a factor, and the effect was evident at Pb concentrations as low as 1 ppm. With soda ash as pH modifier, the effect of Pb was suppressed, perhaps due to formation of lead carbonate. The only xanthate product detected was dixanthogen, unless an initial potential less than $-$800 mV/SCE was imposed (when Pb$ sp{2+}$ is reduced to Pb$ sp0)$ and lead xanthate formed. / Xanthate adsorption on Pb-contaminated pyrite was suppressed by DETA, but relatively large concentrations were required. DETA decreased the potential at the mineral/solution interface, which retarded oxidation of xanthate to dixanthogen. / A mechanism of Pb "activation" of pyrite was proposed: adsorption of Pb(OH)$ sp+$ on pyrite provided sites for xanthate adsorption forming Pb(OH)X, on which xanthate ions were attached by hydrophobic interaction and oxidised to dixanthogen.

This research involved numerous team based industrial campaigns to measure hydrodynamic conditions (superficial gas velocity (Jg), gas hold-up (g), bubble diameter (Db) and frother concentration) in industrial flotation cells. The primary focus of this thesis is the data collected at Agnico-Eagle Mines Ltd.’s LaRonde concentrator and Inmet Mining Corp’s Troilus concentrator. These campaigns helped identify key measurements and required steps toward controlling hydrodynamic characteristics for cells and banks of cells. This research sought to investigate the dependence of bank performance on the setting of profiles for both gas velocity and frother concentration. Some cell characterization and frother analysis work is described. The difficulty of manipulating frother addition rates on the plant scale identified laboratory opportunities to study the interaction of frothers to link hydrodynamic characteristics and froth quality. The laboratory experimental set up involved the use of a laboratory scale flotation column. This set up was used to investigate independent addition of a bubble size controlling frother (e.g., pentanol) with a froth quality controlling frother (e.g., Flottec F150) to test for independent control over the two functions. / Cette recherche a inclus plusieurs visites en équipe aux usines industrielles pour mesurer les conditions hydrodynamiques (vélocité de gaz superficiel (Jg), rétention de gaz (g), diamètre de bulles (Db) et concentration de moussant) dans les cellules de flottation industrielles. Cette thèse vise principalement les données enregistrer au concentrateur de la mine Agnico-Eagle Ltd. LaRonde et le concentrateur de la mine Troilus de Inmet Mining Corp. Ces campagnes ont aidé à identifier les mesures importantes et étapes requis pour contrôler les caractéristiques hydrodynamiques dans les cellules et bancs de cellules. On a essayé d’investiguer la dépendance de la performance des bancs en fixant des profiles de vélocité de gaz superficiel et de concentration de moussant. Du travail en caractérisation de cellules et analyse de moussant sont décrits. La difficulté de manipuler l’addition de moussant au niveau de l’usine a mené à l’opportunité d’étudier l’interaction entre moussants pour trouver un lien entre les conditions hydrodynamiques et la qualité de l’écume. Le plan d’expériences a utilisé une colonne de flottation d’échelle laboratoire. On a examiné l’addition indépendante d’une moussant qui contrôle la taille de bulles (pentanol) avec une moussant qui a un effet sur l’écume (Flottec F-150) pour examiner le contrôle indépendant sur ces deux fonctions.

A technique for on-line simultaneous determination of gas and solids holdup, based on a combination of conductivity and pressure difference measurements, was developed and tested in a laboratory flotation column (10 cm in diameter and 447 cm in height). The actual holdup was determined by an isolating technique. / It was found that the shape of dispersed particles could significantly affect the conductivity of the dispersion. For flake-shaped particles, this resulted in unacceptable estimates of solids holdup in solid-water systems when the classical models for a spherical dispersed phase (e.g., Maxwell (1892) and Bruggeman (1934)) were used. Fricke's model (1924), which accounts for particle shape, was found suitable. / A critical ratio of dispersed to continuous phase conductivity, CCR, was introduced beyond which the dispersion conductivity is insensitive to the dispersed phase conductivity. Two equations to approximate CCR for any given dispersion were proposed. / The effect of concentration, size and type of solid particles on gas holdup was investigated. The presence of solids significantly decreased the gas holdup, by up to 40% relative. Possible mechanisms to explain the effect of solid particles were evaluated based on bubble coalescence, slurry density/viscosity changes, radial profiles and wake structure effects. It was experimentally shown that bubble coalescence was not responsible for the gas holdup reduction. It was proposed that the effect of solids on reducing gas holdup is a combination of an increase in the rise velocity of bubbles due to stabilization of the bubble wake and a change in the gas holdup profile from flat to saddle-shaped.

This study compares zirconium extraction from hydrochloric acid solutions using either Cyanex 923 or Cyanex 925 in kerosene. While both are mixtures of trialkyl phosphine oxides, the trialkyl groups in the former have straight chains, while those in the latter have branched chains. / The major variables studied were hydrochloric acid, extractant and zirconium concentrations, and phase ratio. With both reagents, zirconium is extracted rapidly. Extraction increases with increasing hydrochloric acid concentration, and zirconium is loaded as its neutral tetrachloride complex by a solvation reaction. The loaded zirconium forms a di-solvate, except at high excess extractant concentrations, where solvation numbers greater than 2 are found. At a constant total chloride concentration, the zirconium extraction level is maintained if hydrochloric acid is partially replaced by lithium chloride, provided sufficient hydrochloric acid is retained to prevent zirconium hydrolysis. Distribution coefficients decease with increasing zirconium concentration, suggesting that polymerization occurs in the aqueous phase. / For given conditions, zirconium extraction into Cyanex 923 is higher than for Cyanex 925. However, loading selectivity for zirconium over other metals has not been studied. A few preliminary experiments have shown that aqueous solutions of ammonium carbonate are potential stripping agents.

Computer programs were developed to perform creep tests on three microalloyed steels, with the aim of determining the precipitation kinetics of VN in austenite in one of the steels. This was a commercial 0.01% Ti- 0.12% V- 0.25% Mo steel. The other two were niobium steels with low (0.04% Nb) and high (0.07% Nb) niobium levels, respectively. / The Ti-V-Mo steel was tested at various stresses between 30 and 50 MPa in the temperature range 850-900$ sp circ$C. A mathematical equation was fitted to the creep strain vs. time curves and the creep strain was expressed as a function of time. The strain rate was determined by differentiating the equation with respect to time and log(strain rate) vs. log(creep strain) or creep strain curves were then plotted for each testing condition. At 850$ sp circ$C and 900 seconds, the strain rate was observed to decrease at a faster rate. This time decreased to 700 seconds at 875$ sp circ$C at the same stress of 36MPa. This effect is attributed to the occurrence of VN precipitation in austenite, which reduces the creep rate. However, precipitation could not be detected by the creep technique at 900$ sp circ$C in this steel. / The 0.07% Nb steel was tested at 950$ sp circ$C under stresses of 42 and 32 MPa. At 32MPa, the strain rate was found to decrease at a faster rate at 250 seconds. The 0.04% Nb steel was tested under stresses of 50 and 40 MPa at 875$ sp circ$C, and under 50 MPa at 850$ sp circ$C. In this steel too, a behaviour similar to that shown by the Ti-V and high Nb steels was observed at 375 seconds, 40MPa (875$ sp circ$C) and at 460 seconds, 50MPa (850$ sp circ$C). This is believed to be due the precipitation of NbCN.

The Niobec concentrator recovers niobium minerals (principally pyrochlore) from carbonate and silicate gangue. In the process some 15% of the Nb is rejected in a slimes ($-$10 $ mu$m) product. Recovery of pyrochlore from the slimes was studied. The study was performed using plant water which contained about 200 ppm Ca, 100 ppm Mg and variable quantities of organics as the main contaminants. Selective pyrochlore collectors and selective silicate depressants were evaluated. Four possible routes to float pyrochlore selectively were found. All routes required prior carbonate flotation. Carbonate flotation was attempted using fatty acids and sodium silicate dispersant (as conducted at Niobec) in a flotation column. However, pyrochlore also floated as a result of inadequate dispersion of the slimes. Therefore, new dispersants were tested, which proved effective only at high concentration, because reaction with Ca and Mg cations in the water. High dispersant concentration caused carbonate depression. / An additional problem in the flotation column was bubble coalescence and collapse of the froth. This was caused by the fatty acids, enhanced by the high dispersant concentration. / A novel method of quantifying coalescence using the change in gas holdup in the column was developed. A stable froth could be made at high fatty acid emulsifier concentration, but his promoted unselective flotation. Only by working at high percent solids (10% vs 1%) could sufficient emulsifier be introduced into solution without exceeding the dosage (per unit mass of solids) above which flotation is unselective. For such high percent solids work must be conducted at plant site. Preliminary plant column work was encouraging. / Extensive testwork on very fine feeds (80% $-$20 $ mu$m) at Niobec, and at Mt Isa Mines (Australia) confirmed that column flotation is ideal for selective flotation of fines principally due to reduced gangue entrainment.

Ferrite grain refinement is one of the best methods to improve the mechanical properties of low carbon steels. / The present work is a continuation of this past research and was conducted using a torsion machine. The aim was to improve the understanding of the strain levels and deformation temperatures required for UFF formation, as well as the influence of silicon addition. Two steels were studied: a low silicon (LSi) steel containing 0.09% C-0.02%Si-1.3%Mn-0.07%Al-0.036%Nb and a high silicon (HSi) steel containing 0.09%C-0.48%Si-1.2%Mn-0.02%Al-0.038%Nb. In the hot torsion tests, both steels were deformed to 5 true strain levels: 2, 2.5, 3.2, 3.5 and 4 at a strain rate of 3/s. The Ar3 temperatures for the two steels were measured as 758°C for LSi and 776°C for HSi. It was found that at a strain level of 4 or above, UFF was formed. The optimum deformation temperature was just above the Ar3 and the higher the strain, the finer the ferrite grain size achieved. The results indicated that silicon addition impedes ferrite grain size refinement.

The ternary Mg-Mn-Ce phase diagram was experimentally studied and thermodynamically calculated at the Mg-rich corner. More than twenty binary and ternary alloys were synthesized and heat-treated at both ambient and elevated temperatures. The microstructures and lattice parameters of the samples were studied via XRD, SEM/EDS and EPMA to determine phase equilibria. The ternary phase diagram was also calculated via thermodynamic calculation software FactSage. The results from both experiment and the assessment were compared and discussed. The binary phase diagrams were re-examined, especially the Mg-Ce system. In order to investigate the composition range of the intermetallic compounds Mg12Ce and Mg41Ce5, and to clarify data in the existing phase diagram, both the solid-liquid diffusion couple method and alloys synthesized with target phases were analyzed. The binary phase diagram study was also extended to the Ce-rich side of Mg-Ce system. A modified phase diagram was suggested to accommodate the stoichiometry of Mg11Ce, Mg39Ce5, and Mg3Ce. The experimental study on the ternary phase diagram was conducted on three isopleths: 0.6, 1.8 and 2.5wt% Mn, respectively, and Ce varied between 0 and 25wt%. Finally, the phase diagram calculation with FactSage program was conducted and the small disagreement between the modeling results and present experimental data were found. / Le diagramme de phase ternaire Mg-Mn-Ce a été étudié expérimentalement et calculé thermodynamiquement à son extrémité riche en magnésium. Plus de 20 alliages binaires et ternaires ont été synthétisés et traités thermiquement à température pièce et températures élevées. La microstructure et les paramètres de maille des échantillons ont été étudiés via XRD, SEM/EDS et EPMA pour déterminer les phases à l'équilibre. Le diagramme de phase ternaire a aussi été calculé à l'aide du logiciel de calcul thermodynamique Factsage. Les résultats provenant des expériences ainsi que de l'évaluation thermodynamique ont été comparés et discutés. Les diagrammes de phase binaires ont été re-examinés, spécialement pour le système Mg-Ce. Dans le but d'évaluer l'étendue de composition des composés intermétalliques Mg12Ce et Mg41Ce5, ainsi que de clarifier les données des diagrammes de phase existants, les méthodes de couple de diffusion solide-liquide et de synthèse d'alliages aux phases ciblées ont été utilisés. L'étude du diagramme de phase binaire a été prolongée à l'extrémité riche en Ce du système Mg-Ce. L'étude expérimentale du diagramme de phase ternaire a été conduite sur trois isoplèthes: 0.6, 1.8 et 2.5wt% Mn, respectivement, et Ce a été varié entre 0 et 25wt%. Finalement, les calculs de diagramme de phase provenant du logiciel FactSage ont été fait et de petites divergences entre les résultats modélisés et ceux expérimentaux ont été observées.