The objective of this work was to investigate the behaviour of malleable metals in tumbling mills. Much of the work focused on lead: shots, flattened shots and fragments were ground in three different laboratory mills. Testwork with fragments was repeated in the presence of a brittle and harder mineral phase (95% silica, 5% lead) and for copper (100% copper). The transfer of particles across size classes and the loss of weight because of smearing on the mill shell and grinding media were measured. Microhardness tests confirmed that lead did not work-harden during grinding. / The transfer across size classes was modelled with various first order differential equations describing flattening, folding, cold-welding and actual breakage. Model parameters were estimated using a least-square minimization criterion. When more than one model was fitted to a given data set, the one whose phenomenological basis was closest to the dominant transfer mechanisms observed almost always yielded the best data fit. The dominant mechanism was very dependent on the type of metal ground, its particle size and shape, the grinding intensity generated by the tumbling mill and the presence of a hard, brittle phase. Flattening, responsible for the transfer to coarser size classes, generally dominated over folding, the mechanism accountable for the transfer to finer size classes (other than breakage). Breakage was favoured over flattening and folding when grinding finer and softer particles,in a high impact environment, or in the presence of a hard, brittle mineral phase. Loss of weight due to smearing significantly increased when grinding a softer mineral in a mill with a rough inner shell, or when particle breakage took place. / A methodology based on the Laboratory Knelson Concentrator was developed and tested to estimate the breakage function and gravity recoverability of gold flakes. Progeny from the breakage of gold particles was shown to be highly gravity recoverable, more than 90% above 0.025 mm. The breakage function was non-normalizable, with a large b$ sb{ rm i+1,i}$ component, because of folding.

A numerical modelling study has been undertaken to analyze transport phenomena in various steel casters. During the course of this work, a general three-dimensional parabolic heat flow model was developed for casters of arbitrarily shaped mould using a body-fitted coordinate transformation technique. The heat flow model was specifically applied to a beam blank caster as well as to an industrial slab caster of regular rectangular cross section, so as to analyze solidification within casters. / Furthermore, a fully coupled turbulent flow and solidification model was developed to describe the turbulent transport processes in the upper part of a steel slab caster as well as to evaluate the process variables affecting the casting. Solidification modelling was carried out using a fixed grid enthalpy method while the mushy zone was modelled based on a Darcy-porosity approach. A modified low-Reynolds number version of the $ kappa$-$ epsilon$ model of turbulence was employed to calculate eddy viscosity within the liquid and mushy regions. A control volume based on finite difference method was used to solve the transport equations, wherein a SIMPLER algorithm was adopted to resolve the velocity-pressure coupling in the momentum equations. In order to verify the turbulent flow model, a water modelling study was performed for fluid flow in the mould region of a slab caster. Reasonable agreement was obtained between the mathematical model's predictions, and water modelling experiments. / Macrosegregation of carbon in a steel billet caster was also modelled based on a continuum formulation, in which the conservation equations are derived in terms of mixture dependent variables. The effect of turbulence on the transport of solute in the liquid and mushy regions was taken into account using the $ kappa$-$ epsilon$ model adopted in this work. / Various parametric studies have been preformed on different casting systems, and their effects on temperature distributions and velocity fields within the strand, solidification profiles, and trajectories of inclusions were predicted. Typical predicted results of the models have been compared against the experimental measurements on operating casters reported in the literature and relatively good agreement was obtained.

The commercial applications of cast Al-Si alloys depend to an important extent on controlling the morphology of the eutectic silicon through thermal modification in the solid state and/or chemical modification of the melt before the production of the casting. The effects of modification and/or heat treatment on the microstructure and the mechanical properties of 356 alloy have been investigated on both permanent mold and sand cast samples. Strontium (0.02%) and sodium (0.01%) were used to produce well modified microstructures. The importance of the amount of modifier used was also examined in producing castings with 0.002% Sr and 0.08% Sr. Production parameters such as solution heat treatment time and artificial aging time were examined. / Microstructural assessment was done by quantitative metallography using image analysis coupled to SEM while mechanical testing comprised tensile testing, hardness and microhardness measurements as well as impact tests. / The greatest improvement in mechanical properties obtained with modification was observed for the lower rates of solidification, i.e sand casting. The effect of modification on the heat treatment response of 356 alloy was investigated. The differences between unmodified and modified microstructures were more important in sand cast samples than in permanent mold cast samples. After one hour of solution heat treatment at 540$ sp circ$C, both permanent mold unmodified and modified microstructures became similar in terms of silicon particle size and sphericity. The processes which led to this were different. Silicon platelets in the unmodified structures segmented while silicon particles in the modified alloy coarsened. The final result was however the same. In sand cast alloy, the initial microstructural differences persisted after up to 12 hours of solution treatment. The coarser the initial as-cast microstructure, the greater the improvements associated with modification and heat treatment. / It was also found that porosity caused by modification can negate many of the microstructural benefits by decreasing tensile strength and percent elongation. It was demonstrated that modification also has an influence on the aluminum matrix. The hardness of modified alloy was found to be less after the T6 temper than in unmodified alloy. This was reflected in a lower yield strength of modified 356 alloy. / Quantitative microstructure-mechanical property relationships were established for the permanent mold samples. The best silicon-structure characteristics to predict the tensile properties were found to be the particle count per unit area and the particle area. / It was also determined that hardness can be a simple and inexpensive means whereby ultimate tensile strength and yield strength of 356 alloy in the T4 condition or T6 condition can be estimated.

The present work represents a study of the mixing and slag entrainment behaviour of metallurgical processes. Two immiscible fluids were mixed in a model reactor, equipped with a single centrally located tuyere, through which air was blown. / For low energy input systems, it was found that the thickness of the second liquid phase can significantly affect the mixing time of the bulk phase by altering the fluid flow pattern of the liquid. The entrainment of the upper phase into the lower phase was also affected by the thickness of the upper phase, as well as by the intensity of bath agitation. At low flowrates, the number density of entrained droplets was constant with time, increasing with increasing agitation and thickness of the layer. The air flow required for the transition in the entrainment behaviour increased with an increase in the thickness of the upper phase.

Non-metallic inclusions in steel such as alumina, silicates, etc. are detrimental to many steel properties. Elimination of these inclusions has long been a major target in steelmaking. / In this investigation, attempts have been made to remove these non-metallic inclusions by passing the liquid steel through a ceramic filter. It was found that this approach is very effective for removing solid non-wetting inclusions such as alumina. It appeared that liquid silicates could also be removed to some degree.

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.

No description available.

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