Este estudo foi feito a partir de uma amostra de carvão extraído na mina da Vale- Moçambique, localizada no distrito de Moatize, Província de Tete. O trabalho visa analisar o sistema de reagentes na flotação de finos de carvão mineral pertencente à camada UCB. Dentre os métodos de beneficiamento de carvão, a flotação se destaca como um dos mais importantes para a concentração deste material, em particular no tratamento de partículas finas. A alimentação total da planta de processamento da Vale- Moçambique é de 8000 tph de carvão, onde 10% dessa alimentação corresponde a fração fina que alimenta o circuito de flotação. O material utilizado nesse estudo apresentou uma granulometria 96% menor do que 0,25 mm. Os reagentes utilizados nos ensaios de flotação foram betacol e óleo diesel como agentes hidrofobizantes e MIBC como espumante. O intervalo de concentrações de betacol na primeira fase de ensaios foi de 200 g/t a 500 g/t, e na segunda fase foi de 200 g/t a 500g/t de óleo diesel e manteve-se constante o MIBC em 300 g/t. Os resultados mostraram que é possível, a partir de uma alimentação com o teor de cinzas em torno de 22,84%, obter produtos com teores abaixo de 10% de cinzas, com uma recuperação mássica em torno de 50%. A recuperação de matéria carbonosa também foi avaliada e apresentou resultados positivos. Complementando esse estudo, foi avaliado o efeito da recuperação de H2O e foi observado que para as concentrações de betacol as recuperações variaram de 6 a 9%, e para óleo diesel mais MIBC foram de 4 a7%. / This study was done from a sample of coal mined at the Vale-Mozambique mine, located in Moatize district, Tete Province. The aim of this work is to analyze the reagent system in the flotation of coal fines belonging to the UCB layer. Among coal processing methods, flotation stands out as one of the most important for the concentration of this material, in particular in the treatment of fine particles. The total feed of the Vale-Mozambique processing plant is 8000 tph of coal, where 10% of this feed corresponds to the fine fraction that feeds the flotation circuit. The material used in this study had a particle size of 96% smaller than 0.25 mm. The reagents used in the flotation tests were betacol and diesel oil as hydrophobizing agents and MIBC as frother. The range of betacol concentrations in the first test phase was 200 g / t at 500 g / t, and in the second phase 200 g / t at 500 g / t of diesel oil and MIBC were kept constant at 300 g / t. The results showed that it is possible, from a feed with the ash content around 22.84%, to obtain products with levels below of 10% ash, with a mass recovery around 50%. The recovery of carbonaceous matter was also evaluated and presented positive results. Complementing this study, the effect of H2O recovery was evaluated and it was observed that for the concentrations of betacol the recoveries ranged from 6 to 9%, and for diesel oil plus MIBC were 4 to 7%.

Bubble size is considered to be one of the most important parameters affecting the performance of froth flotation cells. However, monitoring, controlling and predicting bubble size is a very challenging task. This dissertation presents results obtained from a comprehensive pilot- and industrial-scale experimental investigation of gas dispersion performance of two commercially available flotation cells. To facilitate this investigation, a continuous pilot-scale flotation system was developed and tested. The results of the hydrodynamic and metallurgical testing conducted on the pilot-scale flotation circuit are presented. In addition, an assessment of the impact of two commercially available rotor/stator mechanism designs on bubble generation was performed under non-coalescing conditions. Based on obtained results, the mechanisms of gas dispersion throughout the flotation cell and gas cavity formation behind the impeller blades have been presented and discussed. A new in-situ optical bubble sampling method was also developed as part of this investigation. The new system allowed an accurate estimation of local bubble sizes and determination of overall gas dispersion patterns within the cell. The new method was compared to the existing ex-situ bubble sampling method commonly used in industry. Two image analysis techniques were also evaluated, i.e., a template matching BubbleSEdit technique and the edge detection Northern Eclipse technique. Significant variations in bubble size as a function of the sampling method, sampling location, operating condition, machine type and image analysis method were observed. Generally, bubbles observed with the in-situ sampling method appeared to be larger than bubbles recorded with the ex-situ method. Furthermore, the mean bubble size determined by the Northern Eclipse bubble sizing method was smaller than the BubbleSEdit value. The experimental tests also revealed that sampling location had a strong effect on measured local mean bubble size and bubble size distribution in both vertical and horizontal directions. In addition, aeration rate was found to have a profound impact on the gas dispersion pattern in the cell and on local bubble size. Agitation rate also had a significant effect on bubble size, although the degree of impact strongly depended on the agitation level, chemical conditions in the cell and the machine type. / Ph. D.

Froth Flotation is an industrial separation process commonly used in the primary enrichment of run-of-mine mineral material. Over the past 100 years, much of the process's development has come from empirical evolution, rather than fundamental understanding. While many of the governing sub-processes are still poorly understood, the primary influential factors lie within the chemical, equipment, and operational variables unique to each flotation system. This investigation focuses on the phenomenological investigation of the equipment variables, particularly the rotor design, at the laboratory scale. During this study, several small-scale flotation systems were developed, including various rotor and stator designs, tank sizes, and flow conditions. Experimental techniques were also developed to identify operational performance in four criteria: power consumption, gas dispersion, operational robustness, and flotation kinetics. Evaluation of the various rotors was conducted in two campaigns: (1) an exploratory campaign which featured 14 rotors in limited operational conditions (2) a detailed campaign which featured three rotors in an exhaustive set of conditions. The results show that different rotors exhibited varying degrees of performance when judged by the aforementioned performance criteria. In general, excessive fluid pumping leads to an increase range of stable operation at the expense of greater power consumption. However, this increased power consumption does not necessarily correspond to increased flotation performance, as the data generally confirms the linearly proportional relationship of flotation rate and bubble surface area flux. Consequently, enhanced flotation kinetics can be achieved by rotors which disperse high rates of gas while retaining a small bubble size. / Master of Science

Between two neighboring air bubbles in a froth (or foam), a thin liquid film (TLF) is formed. As the bubbles rise upwards, the TLFs thin initially due to the capillary pressure created by curvature changes. As the film thicknesses (H) reach approximately 200 nm, the disjoining pressure created by surface forces in the films also begins to control the film drainage rate and affect the waves motions at the air/water interfaces. If the disjoining pressure is negative, both the film drainage and the capillary wave motion accelerate. When the TLF thins to a critical film thickness (Hcr), the amplitude of the wave motion grows suddenly and the two air/water interfaces touch each other, causing the TLF to rupture and bubbles to coalesce. In the present work, a new model that can predict Hcr has been developed by considering the film drainage due to both viscous film thinning and capillary wave motion. Based on the Hcr model, bubble-coarsening in a dynamic foam has been predicted by deriving the geometric relation between the thickness of the lamella film, which controls bubble-coalescence rate, and the Plateau border area, which controls liquid drainage rate. Furthermore, a model for predicting bubble-coarsening in froth (3-phase foam) has been developed by developing a film drainage model quantifying the effect of particles on pc. The parameter pc is affected by the number of particles and the local capillary pressure around particles, which in turn vary with the hydrophobicity and size of the particles in the film. Assuming that films rupture at free films, the pc corrected for the particles in lamella films has been used to determine the critical rupture time (tcr), at which the film thickness reaches Hcr, using the Reynolds equation. Assuming that the number of bubbles decrease exponentially with froth height, and knowing that bubbles coalesce when film drains to a thickness Hcr, a bubble coarsening model has been developed. The model predictions are in agreement with the experimental data obtained using particle of varying hydrophobicity and size. / Ph. D.

No description available.

Esta tese investiga o efeito de dissipação de energia (energy input) sobre a cinética de flotação de apatita em meio básico (pH 10,5) utilizando oleato de sódio (40 mg/L e 80 mg/L) como coletor. Uma célula de flotação com agitação promovida por grades oscilantes (OGC - Oscilating Grid Flotation Cell), desenvolvida especialmente para avaliação do efeito de energia dissipada na flotação, foi adotada para o estudo devido à célula apresentar uma turbulência praticamente isotrópica, enquanto que as células mecânicas convencionais de flotação geram regiões com diferentes níveis de turbulência, visto que, próximo ao rotor a turbulência é muito maior que nas regiões mais afastadas. A agitação gerada pelo impelidor interfere em todos os sub-processos da flotação: colisão entre bolhas e partículas, adesão e destacamento (detachment). A macroturbulência na célula de flotação suspende as partículas no interior da célula, enquanto a microturbulência dispersa as bolhas e promove as colisões entre as bolhas e as partículas. Todos estes fenômenos podem influenciar a cinética do processo. Além disso, pelo fato das partículas muito grossas (+150µm) e finas (-44µm) de apatita apresentarem recuperações mais baixas do que uma faixa de tamanho ótimo, é importante estudar a influência da dissipação de energia na cinética dessas partículas. Os resultados mostraram que a cinética de flotação de apatita é fortemente influenciada pela dissipação de energia, pelo tamanho das partículas e pela concentração de coletor (ângulo de contato). As partículas finas (-44µm) exigem um elevado nível de energia (2 kW.m-3), devido ao aumento das frequências de colisão entre bolhas e partículas, esse aumento de energia não destruiu o agregado bolha/partícula para fração fina. Por outro lado, a cinética de flotação de partículas grossas (+150µm) foi fortemente afetada pelo aumento da energia transferida, os maiores valores da constante cinética para os grossos foram obtidos com o menor nível de dissipação de energia testado (0,1 kW.m-3), qualquer aumento na turbulência apresentou uma redução na taxa de flotação de no mínimo 40%, devido à destruição do agregado de partículas/bolha. O efeito da hidrofobicidade da apatita foi avaliado através de testes de flotação com duas concentrações de coletor (40 e 80g/L). A alta concentração de coletor (80g/L) apresentou resultados mais elevados de constante cinética para todos os níveis de dissipação de energia e para qualquer tamanho de partícula. Estes resultados evidenciam a influência da hidrofobicidade na adesão e na estabilidade do agregado partícula/bolha. / This thesis investigates the effect of energy dissipation (also called energy input) on the flotation kinetics of apatite in basic medium (pH10.5) with sodium oleate (40mg/L and 80mg/L) as collector. A special equipment called Oscillating Grid Flotation Cell (OGC) was adopted because the movement of the grids inside OGC creates a near isotropic turbulence, whereas the conventional mechanical flotation cells generate regions with different levels of turbulence: the intensity of turbulence is strongly higher close to the impeller and is very low far from it. The agitation created by the impeller influences all flotation sub process: particle/bubble collision, adhesion and detachment. Macroturbulence promotes the particle suspension inside the cell, whilst microturbulence disperses the bubbles and promotes collisions between bubbles and particles. All these phenomena influence the kinetics of the process. Moreover, because very coarse (+150µm) and fine (-44µm) particles of apatite show lower recovery than an optimum size range, it is important to study the influence of energy input on the kinetics of these sort of particles. The results showed that flotation kinetics of apatite is strongly influenced by the energy input, particle size and collector concentration (contact angle). Fine particles (-44µm) require high energy input (2 kW.m-3) probably to promote collision and the increase of energy input did not destroy the bubble/particle aggregate. Conversely, the flotation kinetics of coarse particles (+150µm) was strongly affected by energy input: 0,1 kW.m-3 promoted high flotation rate, but increasing the energy input to any higher level the flotation kinetics exhibits a clear decay, probably due to the destruction of the aggregate particle/bubble. The effect of hydrophobicity is evaluated testing two collector concentrations. With high collector concentration the flotation rate increased for all levels of energy input, these results evidenced the influence of hydrophobicity on the attachment and stability of the aggregate particle/bubble.

Rare earth elements (REE) are considered as critical and non-substitutable metals for electronics and green technology. A greater diversity of supply is needed and the REE occur in a wide range of REE- and REE-bearing minerals within different ore deposit types. The beneficiation processes for REE ores can vary widely based on their mineralogy and texture. It is, therefore, essential to understand the mineralogical characteristics when designing processing routes. Little research was carried out on this topic until the last few years, apart from bastnäsite, monazite, and xenotime, and most REE minerals in deposits currently under exploration are poorly understood in terms of processing characteristics. This geometallurgical study brings together the results of process mineralogy and minerals processing to recover synchysite-(Ce) and apatite from the carbonatite at Songwe Hill, Malawi. This deposit is unusual because it is a potential carbonatite source of both LREE and HREE. Results from previous flowsheet development studies on this deposit suggest that flotation is the most promising processing route and therefore this study concentrated on testing this hypothesis. It sought to understand the mineralogy better in order to predict processing response and carried out a series of flotation experiments to improve the processing efficiency. It also investigated the fundamental magnetic properties of the rare earth fluorcarbonate minerals (including synchysite) and established for the first time that there is a systematic variation in their properties that can be applied to minerals processing. Eight samples of REE carbonatite drill core, crushed to 1700 μm, and a composite sample ground to 53 μm and 38 μm were used throughout this research. Automated mineralogy (QEMSCAN®) was applied to determine the mineralogical characteristics of the ore deposit. This utilised a novel species identification protocol (SIP) for REE minerals in carbonatites, which was validated by electron microscopy (SEM-EDS), and electron probe microanalysis (EPMA). The principal REE minerals at Songwe are the REE fluorcarbonates, synchysite-(Ce) and also parisite-(Ce). These are challenging minerals for automated mineralogical techniques owing to their chemical similarity and common occurrence either as bladed (needle-like) crystals, which is the main textural type at Songwe Hill, or as syntaxial intergrowths. However, using the SIP developed in this study, the QEMSCAN® can distinguish between these minerals based on the Ca content and can also recognise syntaxial intergrowths on a scale of about > 20 μm. The Songwe Hill carbonatite hosts about 6 wt% to 10 wt% of REE- and REE-bearing minerals. Apatite hosts the more valuable HREE in addition to P2O5, followed by synchysite-(Ce)/parisite-(Ce) (mainly synchysite-(Ce)), and minor florencite-(Ce), which host the LREE. These minerals are commonly associated with the predominant gangue minerals, ankerite and calcite, and, to a lesser extent Fe- Ox/CO3 and K-feldspar, strontianite and baryte. Fundamental magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) were determined. The magnetic susceptibility is highly dependent on the mineral composition. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) in this deposit was experimentally determined by magnetic separation and behaved as a diamagnetic mineral. This can be explained by the layered structure common to the REE fluorcarbonate series minerals. Selected laboratory scale mineral processing experiments including magnetic separation and froth flotation were performed. Pre-concentration tests by magnetic separation showed a recovery of 84% for P2O5, 80% for Y2O3, and 76% for Ce2O3 in the non-magnetic product, with gangue minerals rejection of about 49% for ankerite and 48% for Fe-Ox/CO3 to the magnetic product. Apatite and synchysite-(Ce) loss to the magnetic product is mainly the result of their association with the paramagnetic minerals i.e. ankerite and Fe-Ox/CO3 as indicated by automated mineralogy. A spectrophotometer was utilised to measure the solubility of the organic chemical reagents including fatty acids and lignin sulphonate in different alkaline solutions and to determine the appropriate operating parameters for bench flotation tests. The results indicated that the solubility of fatty acids increased with increasing the pH value from 8.5 to 10.5, while the opposite was observed for lignin sulphonate. 35 bench-scale froth flotation tests under a wide range of chemical and operating conditions including pH modifiers and dosages, soluble and insoluble collectors, depressants, temperature, and conditioning time were performed. The results demonstrated that fatty acids and lignin sulphonate are sensitive to changes in pH, conditioning time, and temperature. These factors significantly affected flotation efficiency. A recovery of 86% for P2O5 and 74% for both of Y2O3 and Ce2O3 with TREO upgrading from 1.6 wt% to 3.8 wt% at a mass pull of 31% were achieved under a constant pulp pH of 9.5, elevated temperature, and long conditioning time. This study suggests that combining magnetic separation and froth flotation techniques to pre-concentrate and upgrade the REE- and REE-bearing minerals, should be considered further to minimise the cost of the chemical reagents used in froth flotation and gangue leaching.

Os processos envolvidos no beneficiamento do carvão produzem efeitos nocivos para o meio ambiente, principalmente pela quantidade e natureza dos rejeitos que são gerados. Estes rejeitos comumente denominados piritosos, mesmo não apresentando altos conteúdos de pirita, constituem um material ácido que causa efeitos nocivos ao meio ambiente, principalmente aos corpos dágua. Estes rejeitos geralmente são depositados em barragens de rejeitos. Operações de beneficiamento como a flotação, consagrada na recuperação de finos, podem desempenhar um importante papel no processo de recuperação destes rejeitos de partículas ultrafinas. O rejeito carbonoso estudado nesta pesquisa provém da barragem de rejeitos El Cantor, localizada na Colômbia, na mina El Cerrejón. O processo de beneficiamento envolve ciclones de meio denso e espirais. A caracterização revelou que o material possuim teor de cinzas de 56% e poder calorífico de 5.800 BTU/lb, o teor de enxofre é 1,2%. Em termos de granulometria o material é considerado ultrafino já que 63% é menor que 0,014 mm. O conteúdo de matéria carbonosa deste rejeito é facilmente recuperado por flotação, como se demonstra neste trabalho. É possível recuperar 74% da matéria carbonosa e obter um produto com 7,3% de cinzas e poder calorífico de 14.225 BTU/lb em base seca. / The processes involved in coal preparation generate harmful effects to the environment, mainly due to the quantity and nature of the wastes that are generated. These tailings generally called pyritic, not even showing high content of pyrite are an acid material, harmful to the environment. These tailings are usually disposed of in tailings dams. Froth flotation will be important as a coal preparation process to recover these ultrafine particles. The tailings, studied in this work come from a process involving dense medium cyclones and spirals. They have an ash content of 56% and a calorific value of 5,800 BTU / lb, the sulfur content is 1.2%. In terms of size the material is considered as ultrafine as 63% is less than 0.014 mm. The coal matter content of these tails is easily recovered by froth flotation, as evidenced in this work. It is possible to recover 74% of the coal matter and to obtain a product with 7.3% ash and calorific value of 14,225 BTU / lb in dry basis.

The main area of research delineated in this thesis provides instances when Computer vision based technology has shown tremendous productivity gains in the Oil sands industry in Fort McMurray, Alberta, Canada. Specifically, the interface between Bitumen-froth (crude oil) and the Middlings (Sand) in separation cells (during the extraction process) is estimated in real time from camera video and used for automatic control of the interface level. Two original algorithms have been developed which solve the interface estimation problem using techniques ranging from image analysis, estimation theory (Particle filters) and probabilistic reasoning. These ideas are discussed in chapters three and four. The first chapter of this thesis discusses the broad area of Computer vision research as a knowledge basis for the current work. Computer vision (automatic image analysis) has been presented starting from the basics and culminating in advanced algorithms that are used frequently. The methods described in this chapter form the foundation of the work that follows in the subsequent chapters. After the introduction to automatic image analysis, a set of Monte Carlo simulation based methods called Particle filters are introduced in the second chapter. These Monte Carlo filters assume importance in the current work as they are used to derive one of the main results of this thesis. A large part of this chapter though is devoted to the introduction of the concept of measure theoretic probability which is used in proving the convergence of Particle filters. Another application of Computer vision techniques is also developed in this thesis (in chapter five) to treat the problem of automatic interface and boundary detection in X-ray view cell images. These images are typically used to observe liquid-liquid and liquid-vapour phase behaviour of heavy oils such as Bitumen in chemical equilibrium investigations. The equilibrium data would then be used to enhance Bitumen separation technologies. Manual tracking of the interfaces between these phases for different mixtures and conditions is time consuming when a large set of such images are to be analysed. A novel algorithm is developed that is based on state-of-the-art in Computer vision techniques and automates the entire task. / Process Control

No description available.