In this research work, three types of flotation models (discrete, mean rate and the gamma function models) are modified based on the relationship between mass recovery and recovery. The modified models can be used to calculate both the recovery and grade of concentrate. Experimental work was carried out by using three different samples, which are chalcopyrite, coal and complex sulphide. In the chalcopyrite and coal flotation, air flow rate (AFR) was varied and different size fractions were considered in coal flotation. In complex sulphide flotation, the impeller speed (IPS) and air flow rate were varied, different size fractions were also considered individually. From the experimental results, the effect of air flow rate, impeller speed and particle size on the recovery and grade of concentrate are obtained, it is shown that an increase in air flow rate does not significantly increase recovery but reduce the grade of concentrate. High impeller speed can increase the recovery of fine and medium size, but it has very little effect on the coarse size. The effect of particle is that the medium size has the highest recovery in Fe minerals but the fine has the highest recovery in Zn and Cu minerals. The air flow rate, impeller speed and particle size affect on the kinetics of flotation is discussed from the model results. Where the modified models are used, the results show that an increase in air flow rate will increase the flotation rate of all size fraction, but an increase in impeller speed can only increase the flotation rate of the fine and medium size. The medium size has the highest flotation rate in most of the case.

A first principle flotation model has been derived from the basic mechanisms involved in the bubble-particle and bubble-bubble interactions occurring in flotation. It is a kinetic model based on the premise that the energy barrier (E1) for bubble-particle interaction can be reduced by increasing the kinetic energy (Ek) for bubble-particle interaction and by increasing the hydrophobic force in wetting films. The former is controlled by energy dissipation rate (𝜀), while the latter is controlled by collector additions. The model consists of a series of analytical equations to describe bubble generation, bubble-particle collision, attachment and detachment, froth recovery, and bubble coalescence in froth phase. Unlike other flotation models that do not consider role of hydrophobic force in flotation, the first principle model developed at Virginia Tech can predict flotation recoveries and grades from the chemistry parameters such as 𝜁-potentials, surface tension (𝛾), and contact angles (𝜃) that may represent the most critical parameters to control to achieve high degrees of separation efficiencies. The objectives of the present work are to i) validate the flotation model using the experimental data published in the literature, ii) incorporate a froth model that can predict bubble coarsening due to coalescence in the absence of particles, iii) develop a computer simulator for a froth model that can predict bubble coarsening in the presence of particles, and iv) study the effects of incorporating a regrinding mill and using a stronger collector in a large copper flotation circuit. The model validation has been made using the size-by-class flotation rate constants (kij) obtained from laboratory and pilot-scale flotation tests. Model predictions are in good agreement with the experimental data. It has been found that the flotation rate constants obtained for composite particles can be normalized by those for fully liberated particles (kmax), which opens the door for minimizing the number of flotation products that need to be analyzed using a costly and time-consuming liberation analyzer. A bubble coarsening froth model has been incorporated into the flotation model to predict flotation more accurately. The model has a limitation, however, in that it cannot predict bubble-coarsening in the presence of particles. Therefore, a new computer simulator has been developed to predict the effects of particle size and particle hydrophobicity on bubble coarsening in froth phase. In addition, the first principle flotation model has been used to simulate flotation circuits that are similar to the Escondida copper flotation plant to study the effects of incorporating a re-grinding mill and using a more powerful collector to improve copper recovery. The flotation model developed from first principles is useful for predicting and diagnosing the performance of flotation plants under different circuit arrangements and chemical conditions. / Master of Science

A realização deste estudo teve por objetivo caracterizar o funcionamento de uma célula pneumática de flotação e comparar o seu desempenho às diferentes tecnologias [células mecânicas e colunas de flotação] já instaladas e em operação nos circuitos industriais da Samarco Mineração - no Circuito de Grossos e no Circuito de Finos. Utilizou-se, para a realização dos ensaios e/ou das análises, uma célula mecânica laboratorial [modelo Wemco®], uma célula pneumática piloto [modelo MBE®] e um medidor de tamanho de bolhas e de velocidade superficial do ar [modelo APBS®]. Neste estudo, utilizaram-se amostras coletadas na alimentação dos dois referidos circuitos industriais de flotação - executando-se, posteriormente, etapas complementares de caracterização mineralógica, levantamento de dados e análise estatística dos resultados. Como conclusões, em maior relevância, citam-se: a) Para as células pneumáticas, maiores aplicabilidades industriais foram identificadas para o modelo Pneuflot®, processando carvão e em operações na China. Foram mapeadas células de 4,1 a 5,0 m de diâmetro processando volumes de polpa superiores a 1.000 m3/h; b) Em análise de influência das variáveis, foi identificado que o percentual de sólidos da alimentação e a velocidade da polpa no distribuidor possuem elevada influência sobre as variáveis respostas do processo de flotação; c) Em célula pneumática, em escala piloto e em regime batch, observou-se que: para a flotabilidade de sílica, a constante cinética (k) foi fortemente influenciada pela granulometria, sendo de 0,719 min-1 para a amostra CG e de 0,237 min-1 para a amostra CF; d) Utilizando-se de modelos cinéticos, dimensionaram-se circuitos de células pneumáticas. Conforme especificações atualmente praticadas e sem otimizações, seriam necessárias 8 células para o Circuito de Grossos e 11 células para o Circuito de Finos. e) Em comparativos entre células mecânicas e colunas de flotação [em escala industrial], constataram-se maiores eficiências de circuitos contendo células pneumáticas [dimensionados a partir de resultados em escala piloto]; e f) Em análise de dispersão do ar, realizaram-se medições e/ou identificação das correlações existentes entre as variáveis velocidade superficial do ar (Jg), diâmetro médio de bolhas ou diâmetro de Sauter (d32), hold-up do ar (Eg) e fluxo superficial de área de bolhas (Sb). / This study aimed to characterize the operation of pneumatic cells and compare their performance to other different technologies [mechanical cells and columns] already installed and in operation in the industrial circuits of the company Samarco Mineração - Circuit of Coarse materials and Circuit of Fine materials. It was used, for the tests and/or assays, a laboratorial mechanical cell [Wemco® model], a pilot pneumatic cell [MBE® model] and a bubbles size and superficial air velocity measurer [APBS® model]. For these, feed samples of both industrial flotation circuits were taken - followed by complementary steps of mineralogical characterization, data collection and statistical analyzes of results. As conclusions, in higher relevance, have been noted: a) For the pneumatic cells, larger industrial applications were identified for the Pneuflot® model, processing coal and in operation in China. Cells measuring from 4,1 to 5,0 m of diameter were listed processing volumes higher than 1.000 m3/h; b) In an analysis of the influence of variables, it was identified that the percentage of solids in the feed and the velocity of slurry in the distributor have high influence on the process responses of flotation; c) In a pneumatic cell, on a pilot scale and under batch regime, for the floatability of silica, the kinetic constant (k) was strongly influenced by the size of particles, of 0,719 min-1 for the sample CG [from Coarse Circuit] and of 0,237 min-1 for the sample CF [from Fine Circuit]; d) Using kinetic models, circuits of pneumatic cells have been designed. According to the current specifications and without optimizations, 8 cells would be necessary for the Coarse Circuit and 11 cells for the Fine Circuit; e) In comparisons between mechanical cells and columns [on an industrial scale], greater efficiencies were noted for circuits containing pneumatic cells [designed from results on a pilot scale]; and f) In an analysis of the air dispersion, measurements and/or identification of existing correlations between the variables superficial air velocity (Jg), bubble size diameter (d32), air hold-up (Eg) and superficial area bubble flux (Sb) have been done.

A realização deste estudo teve por objetivo caracterizar o funcionamento de uma célula pneumática de flotação e comparar o seu desempenho às diferentes tecnologias [células mecânicas e colunas de flotação] já instaladas e em operação nos circuitos industriais da Samarco Mineração - no Circuito de Grossos e no Circuito de Finos. Utilizou-se, para a realização dos ensaios e/ou das análises, uma célula mecânica laboratorial [modelo Wemco®], uma célula pneumática piloto [modelo MBE®] e um medidor de tamanho de bolhas e de velocidade superficial do ar [modelo APBS®]. Neste estudo, utilizaram-se amostras coletadas na alimentação dos dois referidos circuitos industriais de flotação - executando-se, posteriormente, etapas complementares de caracterização mineralógica, levantamento de dados e análise estatística dos resultados. Como conclusões, em maior relevância, citam-se: a) Para as células pneumáticas, maiores aplicabilidades industriais foram identificadas para o modelo Pneuflot®, processando carvão e em operações na China. Foram mapeadas células de 4,1 a 5,0 m de diâmetro processando volumes de polpa superiores a 1.000 m3/h; b) Em análise de influência das variáveis, foi identificado que o percentual de sólidos da alimentação e a velocidade da polpa no distribuidor possuem elevada influência sobre as variáveis respostas do processo de flotação; c) Em célula pneumática, em escala piloto e em regime batch, observou-se que: para a flotabilidade de sílica, a constante cinética (k) foi fortemente influenciada pela granulometria, sendo de 0,719 min-1 para a amostra CG e de 0,237 min-1 para a amostra CF; d) Utilizando-se de modelos cinéticos, dimensionaram-se circuitos de células pneumáticas. Conforme especificações atualmente praticadas e sem otimizações, seriam necessárias 8 células para o Circuito de Grossos e 11 células para o Circuito de Finos. e) Em comparativos entre células mecânicas e colunas de flotação [em escala industrial], constataram-se maiores eficiências de circuitos contendo células pneumáticas [dimensionados a partir de resultados em escala piloto]; e f) Em análise de dispersão do ar, realizaram-se medições e/ou identificação das correlações existentes entre as variáveis velocidade superficial do ar (Jg), diâmetro médio de bolhas ou diâmetro de Sauter (d32), hold-up do ar (Eg) e fluxo superficial de área de bolhas (Sb). / This study aimed to characterize the operation of pneumatic cells and compare their performance to other different technologies [mechanical cells and columns] already installed and in operation in the industrial circuits of the company Samarco Mineração - Circuit of Coarse materials and Circuit of Fine materials. It was used, for the tests and/or assays, a laboratorial mechanical cell [Wemco® model], a pilot pneumatic cell [MBE® model] and a bubbles size and superficial air velocity measurer [APBS® model]. For these, feed samples of both industrial flotation circuits were taken - followed by complementary steps of mineralogical characterization, data collection and statistical analyzes of results. As conclusions, in higher relevance, have been noted: a) For the pneumatic cells, larger industrial applications were identified for the Pneuflot® model, processing coal and in operation in China. Cells measuring from 4,1 to 5,0 m of diameter were listed processing volumes higher than 1.000 m3/h; b) In an analysis of the influence of variables, it was identified that the percentage of solids in the feed and the velocity of slurry in the distributor have high influence on the process responses of flotation; c) In a pneumatic cell, on a pilot scale and under batch regime, for the floatability of silica, the kinetic constant (k) was strongly influenced by the size of particles, of 0,719 min-1 for the sample CG [from Coarse Circuit] and of 0,237 min-1 for the sample CF [from Fine Circuit]; d) Using kinetic models, circuits of pneumatic cells have been designed. According to the current specifications and without optimizations, 8 cells would be necessary for the Coarse Circuit and 11 cells for the Fine Circuit; e) In comparisons between mechanical cells and columns [on an industrial scale], greater efficiencies were noted for circuits containing pneumatic cells [designed from results on a pilot scale]; and f) In an analysis of the air dispersion, measurements and/or identification of existing correlations between the variables superficial air velocity (Jg), bubble size diameter (d32), air hold-up (Eg) and superficial area bubble flux (Sb) have been done.

A first-principle flotation model was derived at Virginia Tech from the basic mechanisms involved in the bubble-particle and bubble-bubble interactions occurring in a flotation cell (Yoon and Mao, 1996; Sherrell and Yoon, 2005; Do, H, 2010). The model consists of a series of analytical equations for bubble generation, bubble-particle collision, attachment, detachment, and froth phase recovery. The process of bubble-particle attachment has been modelled on the premise that bubble-particle attachment occurs when the disjoining pressure of the thin liquid in a wetting films formed between particle and bubble is negative, as was first suggested by Laskowski and Kitchener (1969). These provisions allow for the flotation model to incorporate various chemistry parameters such as zeta-potentials, contact angles, surface tension in addition to the physical and hydrodynamic parameters such as particle size, bubble size, and energy dissipation rate. In the present work, the effects of both hydrodynamic and chemistry parameters have been studied using the model-based computer simulator. A series of laboratory batch flotation experiments carried out on mono-sized glass beads validated the simulation results. The flotation feeds were characterized in terms of particle size, contact angle, and Hamaker constant, and the flotation experiments were conducted at different energy dissipation rates, gas rates, froth heights. The flotation tests were also carried out on mixtures of hydrophobic silica and hydrophilic magnetite particles, so that the grades of the flotation products can be readily determined by magnetic separation. The experimental results are in good agreement with the model predictions both in terms of grade and recovery. / Master of Science

Previous mineralogical investigations (QemSCAN) performed on all effluent flotation streams of Mimosa mine (Zimbabwe) indicated the presence of appreciable amounts of platinum group minerals (PGMs), which are not recovered. Most, generally in excess of 70%, of the liberated PGMs in these streams belonged to the Pt-Pd-Bi-Te class in all the samples investigated. In the first part of this work, electrochemical investigations, electrochemically-controlled contact angle measurements and Raman spectroscopy have been employed to investigate the interaction of ethyl xanthate with Pd-Bi-Te and PtAs2. Impedance measurements showed lower capacitance values in solutions containing KEX indicating the formation of a continuous surface layer. Anodic and cathodic polarization diagrams show the mixed potential to be higher than the reversible potential of the xanthate-dixanthogen equilibrium reaction, hence the formation of dixanthogen on the surface is possible. Electrochemically controlled in situ Raman spectroscopy has confirmed the co-presence of xanthate with dixanthogen indicating that xanthate retains its molecular integrity when it adsorbs on the surface of the Pd-Bi-Te. The result of this investigation has shown dixanthogen to be present on both the minerals (PtAs2 and Pd-Bi-Te) when the surfaces are anodically polarized. Chemisorbed xanthate could be identified within 120 seconds yielding a hydrophobic surface as indicated by electrochemically-controlled contact angle measurements. Maximum contact angles of 63o were measured in the case Pd-Bi-Te. As a result the mineral surface is expected to be hydrophobic and a lack of collector interaction with the mineral is not the reason for low PGM recoveries experienced. Secondly, the flotation recovery of synthetically prepared Pd-Bi-Te was compared with that of chalcopyrite (a typical fast-floating mineral) and pyrrhotite (a typical slow-floating mineral), with microflotation tests. These indicated Pd-Bi-Te to be a fast-floater with flotation rates exceeding that of chalcopyrite. Predicted flotation rate constants (from the Ralston model) were significantly lower for small particles (with diameters similar to those lost to the effluent streams) compared with those of particle with intermediate sizes. This supports the suggestion that losses to effluent streams are caused by particle size effects. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted