A seletividade e eficiência do processo de flotação não estão fundamentadas tão somente nas diferenças das propriedades físico-químicas das superfícies dos minerais, mas também na hidrodinâmica do sistema de concentração. Via de regra, a eficácia da flotação diminui quando o tamanho de partícula ultrapassa 150 micrômetros. Esta pesquisa visou estudar a influência de variáveis hidrodinâmicas sobre mecanismos de flotação de partículas grossas em células mecânicas e suas implicações cinéticas. Os ensaios utilizaram células com agitação mecânica e cada situação experimental esteve associada a um conjunto de variáveis hidrodinâmicas: números de hidrodinâmicos adimensionais, características geométricas do impelidor, velocidade mínima de suspensão da polpa, energia dissipada média e energia de preservação do agregado partícula-bolha. Desta forma, a influência dos parâmetros hidrodinâmicos na flotação de apatita e esferas de vidro (diâmetro médio248 micrômetros) foi determinada na presença de oleato de sódio e acetato de eteramina em pH 10. Em condições hidrodinâmicas pouco turbulenta, a recuperação de partículas grossas decresce em função da falta de suspensão de partículas, por outro lado para condições hidrodinâmicas mais severas a recuperação foi quase nula devido à destruição do agregado partícula/bolha. A cinética de flotação da apatita foi estudada em escala de laboratório sob severas condições de turbulência, os resultados indicaram que partículas grossas de apatita têm flotabilidade inferior a finas, corroborando que a flotação dessas partículas grossas não se ajustou ao modelo de primeira ordem. Estes resultados evidenciaram que grossas demandam um ambiente hidrodinâmico apropriado para flotar eficientemente. / Coarse particles badly float mostly because the bubbleparticle aggregates are not strong enough to prevent the particle detachment from the bubble surface caused by the particle weight and turbulence eddies during the rise of the aggregates in the pulp phase to the froth phase and then to the froth launder. The aim this work was to determine effects and degrees of significance of hydrodynamic variables on coarse particle flotation and their kinetic implications. The tests were carried out in flotation cells with mechanical stirring system and each experimental condition was related to group of hydrodynamic variables: hydrodynamic dimensionless numbers, impeller geometries, minimum impeller rotational speed, energy dissipation rate and detachment energy. The influence of hydrodynamic parameters on flotation of the apatite and glass spheres (diameter average248 micrometers) was determined in the presence of sodium oleate and etheramine acetate at pH 10. For more quiescent hydrodynamic conditions, recovery of coarse particles decreased due to a lack in particle suspension, on the other hand, in the most severe hydrodynamic conditions the recovery was almost nil because the bubbleparticle aggregates detachment. Flotation kinetics of apatite was studied in laboratory scale under strong hydrodynamic conditions, the results indicated that coarse particles of apatite float at a lower rate than finer particles and the flotation kinetics of coarse particles did not fit to first order model. Those results evidenced that coarse particles demand a suitable hydrodynamic environment to float efficiently.

This thesis involves the design, synthesis and testing of organic hydrophobic ligands. They would act as co-collectors in froth flotation processes to enhance the recovery of sulfidic minerals which have undergone some oxidation on processing and are not efficiently collected by the commercial reagents used in froth flotation. Strong and selective binding to iron(III) oxide/hydroxide surfaces, e.g. goethite, over unwanted silicaceous material was considered essential criteria for such new cocollectors. A general overview of froth flotation processes is given in Chapter 1 as well as a description of the analytical techniques used in this thesis and the features that the ligands must have to act as co-collectors. On the basis of the strong binding to iron(III) surfaces of the organic ligand Irgacor 419®, used commercially as a corrosion inhibitor for iron, this compound was studied as a potential co-collector. Adsorption isotherms were determined by UV-Vis spectroscopy for two carboxylic acids that may also bind strongly to goethite, the results of which are discussed in Chapter 2. Chapter 3 involves the measurement of the strength of binding of one the most widely used type of collectors for sulfide ores, potassium ethyl xanthate. Complications in the analysis of materials in solution by both ICP-OES and UV-Vis spectroscopy arose due to the instability of potassium ethyl xanthate in solution, making determination and interpretation of isotherms difficult. The determination of adsorption isotherms for 2-mercaptobenzothiazole, which showed weak binding to goethite as well as to silica, and the mode of binding of 2-mercaptobenzothiazole on copper(I) surfaces is reported in Chapter 4. A crystal structure was obtained in which four units of 2-mercaptobenzothiazole bridge two nickel atoms through the nitrogen atom and the exocyclic sulfur and is considered as a model for binding to sulfidic minerals. Chapter 5 looks at the strength of binding to goethite and silica of various hydroxamic acids. Benzohydroxamic acid was initially selected for study since hydroxamates are known to act as collectors for oxidized materials. Unpredictably, benzohydroxamic acid showed strong binding to a goethite surface and did not release any iron from the surface into solution, which would have been predicted due to its known strong chelating abilities to iron(III). The X-ray structure determination of the first example of a dinuclear Fe(III) hydroxamate complex showed this to have -oxo bridge formed by the hydroxamate unit and supports multisite attachment between this ligand and the surface, as suggested by adsoption isotherms. Simple models based on this dinucleating motif provide plausible modes of multisite attachment to a goethite surface. Competitive binding studies provided a way of ranking the ability to bind to goethite of acetohydroxamic acid, which was not suitable for analyses by either ICP-OES or UV-Vis spectroscopy. Of the ligands studied in this chapter acetohydroxamic acid was found to bind most strongly to goethite followed by benzohydroxamic acid. In Chapter 6, the attachment to goethite and silica of a series of phosphonic acids is investigated. All show a very high binding strength to goethite. Froth flotation experiments at a laboratory scale are described in Chapter 7. The types of ligand that showed strong binding to goethite in adsorption isotherms experiments were tested as co-collectors in different ores and conditions. There is not a simple correlation between adsorption isotherm data and flotation performance as co-collectors because other factors, besides strength of binding, affect the system. Benzohydroxamic acid was the ligand that increased the grade/recovery of the process in all the cases studied. Irgacor 419® enhances the grade/recovery curve for Palabora ore and phenyl malonic acid for Kennecott ore. These results support the original proposition that it may be possible to increase the recovery of oxidized particles substantially by using a blend of collectors which includes a compound to target the oxidized sites.

Multiphase systems (containing solid, liquid and gas) are increasingly common in a number of industries, with the most complex manifestation being three-phase froth. The interstitial suspension has to navigate tortuous channels and its transport is affected by drag, capillary and gravitational forces. Particle properties such as wettability, size, shape, and morphology results in a number of different types of interactions with the liquid-air interface and can have a significant effect on froth composition and stability. The effect of particle size and shape on its transport through these confined channels is thus of great interest for a number of industrial applications and is the focus of this work. This transport behavior is studied using a three phase transient froth that is produced in the froth flotation process for mineral separation. In this system, hydrophilic non-value particles present in the interstitial liquid phase do not attach to air bubbles, and their removal is desirable. The original hypothesis was that as particles become more anisotropic in shape, there is an increase in the froth interstitial viscosity, which results in reduced drainage rate of particles through the froth. Flotation experiments, froth sampling experiments, and rheological experiments were conducted to test this hypothesis. Froth zone sampling experiments were conducted using mixtures of sized platy mica, needle-like wollastonite, and fibrous chrysotile, all mixed with low aspect ratio silica in varying amounts. The froth zone suspension compositions were then used to prepare the froth interstitial suspension ex-situ, and bulk rheological measurements were conducted on the suspensions. The data showed that while the relative viscosities of the suspensions were much higher at even low concentrations of the fibrous ore in the mixture, there was no significant difference when mica was substituted for silica in the mixture at high concentrations (~50 wt%) at the solids volume fraction of interest (~7.5%). The bulk rheological measurements thus could not fully account for the difference in transport behavior between mica and silica. Flotation experiments were conducted with a copper mineral-containing ore augmented with additional hydrophilic minerals mica, silica (low aspect ratio), wollastonite or chrysotile. The results suggest increasing aspect ratios of the added non-value particles result in increased net transport (transport accounting for loss due to drainage) through the froth zone; mica transport is faster than silica. Froth zone sampling experiments (using pure mixtures of above minerals) confirmed that mica net transport was greater than that of silica. It was then hypothesized that this increase was due to increased drag experienced by high aspect ratio mica compared to low aspect ratio silica. The doped ore flotation data also suggested a decrease in transport as size of added platy mica increased until a local transport minimum was reached, beyond which another increase in transport was observed. It was further hypothesized that this was related to confinement of coarse mica particles in the plateau borders when the size of the constriction was comparable to particle size. Froth sampling experiments under high drag (upward flow dominated) conditions were compared with those under conditions where drag and drainage were more balanced (steady state froths). Under high drag conditions, mica mixtures showed more hydrophilic mineral mass in the froth zone compared to silica mixtures. Under drag and drainage-balanced conditions when the size of mica approached the size of the measured channel size, platy mica was found to be accumulating in the froth. This was not the case for silica particles with settling being more efficient for silica than for mica. The key parameters driving transport of particles through the froth are the bulk rheology of the interstitial suspension (driven by particle size and shape distributions and solids concentration), the size of constrictions in the plateau borders and vertices and the resulting confinement effects, and the mobility or elasticity of the interfaces (driven largely by the hydrophobic particles attached at the interface).

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The differential lead-zinc flotation process has been practised since 1912, yet selectivity in the process remains a significant technical issue in many operations. The minerals processing operation at Zinifex Limited's Century Mine, which uses differential flotation, began in November 1999 and the flotation behavior of the ore remains a major research interest. The present study was aimed to determine the possible mechanisms of sphalerite recovery during carbon pre-flotation and lead flotation in this operation including identification of the variables that affect these two flotation stages and also identify depressants for sphalerite that offer better selectivity during these stages. To achieve this aim, the study was undertaken in two stages: a review of literature related to selectivity during lead-zinc flotation, and an experimental program consisting of bench-scale flotation tests wherein the various experimental variables were systematically varied. A comparison between the data generated to those of the plant was also undertaken. The review of literature revealed four basic mechanisms of sphalerite recovery: activation of the sphalerite surface, composite particle flotation with galena and gangue, graphitic inclusions in the mineral surface and entrainment in the froth. The depression or rejection of sphalerite on the other hand could be affected by grinding, froth washing and the use of chemical depressants including cyanides, zinc sulfate, abraded iron and iron sulfate, sodium sulfide, sodium sulfite and metabisulfite, and organic depressants derived from selective collectors. / The results from the experimental program indicate that: (a) activation of the sphalerite surface as a mechanism of sphalerite recovery during lead flotation was not significant at the Century Mine concentrator, (b) the recovery of sphalerite during the carbon pre-flotation was predominantly due to a bulk flotation action and entrainment in the froth, (c) composite particle recovery was a significant contributing factor in the recovery of sphalerite in lead flotation, and (d) mineral oxidation was only significant for galena and occurred mostly during pre-flotation, but the use of cyanide adequately counters any effect on sphalerite recovery. The investigation on the variables that affect the pre-flotation and lead flotation circuits revealed that: (a) reducing the pulp density and the amount of frother added during pre-flotation significantly reduced the bulk flotation action and entrainment of sphalerite in the froth, b) grinding the ore finer (P80 = 40 μm) reduced the recovery of sphalerite as composite particles during lead flotation, and (c) the pulp pH was best maintained at natural pH during pre-flotation and at an elevated alkaline pH (pH 9.5) during lead flotation for optimal selectivity. In terms of depressants it was found that zinc sulfate specifically depressed sphalerite during lead flotation.

The present research is focused on investigating particle interactions between valuable and gangue materials, and the effect of these interactions on selectivity in flotation. This is a very important issue to operations at several mines across the world (e.g., at Century Mine operated by Zinifex Ltd in Australia). Particle interactions between valuable and gangue minerals with subsequent aggregation have significant impact on flotation performance. Valuable minerals may be depressed if heavily covered with hydrophilic gangue minerals and/or gangue minerals may misreport to the concentrate.

Canada has the largest known reserve of oil in the world in the form of oil sands: an estimated 1.7 to 2.5 trillion barrels of oil are deposited in combination of the sand, water and clay. The presented research is devoted to bubble-solid surface interaction, which is one of the critical areas of the oil sand processing and it is also a key point for many other processing technologies, such as mineral recovery, froth flotation, soil remediation, de inking of paper, heat transfer in boilers tube, biological and medical sciences. The goal of this work was to investigate new theoretical and practical approaches, which would help in better understanding of fundamentals of the flotation process in oil sands extraction. Among many achievements of this research are: 1)development of the method for generation of a single micro bubble. Dependence of this process on micropipette tip size and inclination, gas type, taper length and other parameters has also been studied (Chapter 3); 2)study of gas bubble - flat surface interactions based on a practical approach of determination of two dynamic parameters, sliding velocity and induction time of a gas bubble. Various types of gas bubbles (CO2, Air, H2, and O2) and collector surfaces (bitumen, treated hydrophobic and hydrophilic silica) were used in sliding velocity and induction time measurements. The sliding velocity of gas bubbles under an inclined collector surface was found to be in a strong dependence of water chemistry, type of gases, temperature, initial separation between bubble and collector surface (Chapter 4); 3)developing an analytical model for predicting bubble sliding velocity based on previously developed models. The model was in a good agreement with experimental results (Chapter 5); 4)establishing a new method for bubble zeta potential measurements. The measurements were in a good agreement with previously studies reported in literature (Chapter 6). Summarized above findings from this research represent valuable advances in understanding oil sands processing. The prospects of future work are provided in Chapter 8. / Chemical Engineering

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No description available.

No description available.