The role of mathematical models and simulators in describing the performance of mineral processing applications have had a large impact in optimising existing industrial plants and designing new plants over recent years. Before the development of sophisticated computer simulators, the design engineer used industrial “rules of thumb” to estimate the size and layout of plants. However, newly designed plants after commissioning, often do not meet the design product specification requirements and quite often years of “trial and error” optimisation is required. This process can be very costly especially with froth flotation processes where the complexity of the various stages of treatment makes “trial and error” optimisation very difficult to quantify and assess the benefits. Over the past 10 years, advances in the modelling of the flotation process have been conducted by many authors. The most significant flotation modelling advances in recent years have been provided by the AMIRA (Australian Mineral Industry Research Association) P9 project, whereby a new modelling methodology has been proposed. Within this methodology, the flotation response can be represented by a number of sub-processes including parameters describing the hydrodynamic, froth and ore characteristics. Although these parameters have been proposed, methods for measuring these parameters in large flotation cells are still developing, especially in the areas of the froth zone recovery and entrainment. In the light of this it was felt that the literature on froth recovery determination should be investigated to determine the most appropriate method for measuring froth recovery in large industrial flotation cells. It was found after the investigation of the literature that three techniques for measuring the froth recovery parameter stood out as potential methods for measurement within a large scale flotation cell. These were the methods decribed by Gorain et al (1998), Vera et al (1999) and Savassi et al (1997). It was decided that all three methods should be assessed on a quantitative and qualitative basis from data collected at the Mount Isa Mines (now Xstrata) Copper flotation circuit. In this assessment, all three methods were extensively trialed in a 2.8 m3 flotation cell which was operated in parallel to the main copper rougher flotation circuit. The cell could be operated at numerous operating conditions which allowed sufficient data to be collected. The conclusions from this work were that although the method proposed by Vera et al (1999) required significant amounts of data, the method appeared to be reliable in this scale of cell. The main recommendation from this work was to further test the Vera methodology in larger industrial flotation cells. A 100 m3 Outukumpu tank cell at the Mount Keith Nickel Concentrator was chosen for the further assessment of the Vera et al (1999) methodology and its applicability to large scale cells. This flotation cell was one of the largest flotation cells operating on a production scale at the time of the testwork. Numerous tests were conducted and data collected from this investigation showed that the Vera et al (1999) technique was applicable to this scale of flotation cell. Since the work at Mount Keith was conducted in a rougher flotation cell, it was decided to test the methodology with numerous cells of various sizes and duties at the Kambalda Nickel Concentrator. As with the previous investigation at Mount Keith, it was observed that the Vera method was able to measure froth recoveries in all cells measured at Kambalda (within typical operating ranges). However, the technique was not applicable at shallow froth depths since it does not take into account the effect of the pulp-froth interface within the froth recovery parameter estimation. The pulp froth interface and close to it is where a significant proportion of dropback occurs within the froth zone. In addition to this problem, the methodology required large numbers of samples and disturbed downstream processes which made the technique unpractical for operating industrial flotation plants. Hence, a new technique for measuring froth recovery in large flotation cells was required. For the technique to be successful on an industrial scale it required the following: • minimum disturbance on the process, • take into account the pulp froth interface within the froth recovery parameter, and • require a minimum amount of samples. To meet these needs a new technique was developed based on the Savassi et al (1997) technique and combining it with recent work by authors including Vera et al (2003). The methodology involves taking samples of the feed, concentrate and tail as per a typical flotation survey and combining them with two new samples: the air hold-up sample and the top of froth sample. With the addition of these samples, a mass balance across the pulp and froth phase could be conducted and the froth recovery parameter derived. In addition, the new method provided measurements of the pulp zone average bubble load and the amount recovered by the entrainment mechanism. The proposed method has a simple procedure which allows the technique to be used by academics and mill operators alike. The proposed froth recovery measurement technique was tested in numerous cells of various types (i.e. Wemco, Outokumpu, Dorr-Oliver etc), various sizes (up to 150 m3 in size), various duties (rougher, scavenger, cleaner, recleaner, etc) and various plants. In most cases the methodology proved to be a reliable measure of the froth recovery parameter. In addition, at the Century Zinc Operation, the methodology was compared directly with the original Vera et al (1999) technique and the results showed that there was a good comparison between the results with the off-set of the pulp-froth interface. A number of contributions to both the research and industrial areas have been provided from the outcomes of the thesis. The main contributions include: • A full assessment of the three current methods for measuring the froth recovery parameter within large flotation cells. With recommendations of developing a new technique. • The development of a froth recovery measurement technique which can be used in large cells to understand the impact of the froth zone in an individual cell, use within the AMIRA P9 modelling methodology and plant diagnostics. • The new method also allows the estimation of the average bubble load and quantifies the amount of material recovered by the entrainment mechanism which is invaluable to metallurgists in assessing the performance of a flotation circuit (plant diagnostics). Finally, the results of this thesis will provide practising metallurgists both within the research and operating fields, techniques to improve the profitability of flotation circuits worldwide. Metallurgists can quickly assess the performance of large flotation cells in terms of froth performance, bubble load and entrainment which has not been available before. In addition, the results from this thesis will also allow metallurgists to mathematically represent their plant through flotation models better and improve their understanding of their flotation circuits.

The role of mathematical models and simulators in describing the performance of mineral processing applications have had a large impact in optimising existing industrial plants and designing new plants over recent years. Before the development of sophisticated computer simulators, the design engineer used industrial “rules of thumb” to estimate the size and layout of plants. However, newly designed plants after commissioning, often do not meet the design product specification requirements and quite often years of “trial and error” optimisation is required. This process can be very costly especially with froth flotation processes where the complexity of the various stages of treatment makes “trial and error” optimisation very difficult to quantify and assess the benefits. Over the past 10 years, advances in the modelling of the flotation process have been conducted by many authors. The most significant flotation modelling advances in recent years have been provided by the AMIRA (Australian Mineral Industry Research Association) P9 project, whereby a new modelling methodology has been proposed. Within this methodology, the flotation response can be represented by a number of sub-processes including parameters describing the hydrodynamic, froth and ore characteristics. Although these parameters have been proposed, methods for measuring these parameters in large flotation cells are still developing, especially in the areas of the froth zone recovery and entrainment. In the light of this it was felt that the literature on froth recovery determination should be investigated to determine the most appropriate method for measuring froth recovery in large industrial flotation cells. It was found after the investigation of the literature that three techniques for measuring the froth recovery parameter stood out as potential methods for measurement within a large scale flotation cell. These were the methods decribed by Gorain et al (1998), Vera et al (1999) and Savassi et al (1997). It was decided that all three methods should be assessed on a quantitative and qualitative basis from data collected at the Mount Isa Mines (now Xstrata) Copper flotation circuit. In this assessment, all three methods were extensively trialed in a 2.8 m3 flotation cell which was operated in parallel to the main copper rougher flotation circuit. The cell could be operated at numerous operating conditions which allowed sufficient data to be collected. The conclusions from this work were that although the method proposed by Vera et al (1999) required significant amounts of data, the method appeared to be reliable in this scale of cell. The main recommendation from this work was to further test the Vera methodology in larger industrial flotation cells. A 100 m3 Outukumpu tank cell at the Mount Keith Nickel Concentrator was chosen for the further assessment of the Vera et al (1999) methodology and its applicability to large scale cells. This flotation cell was one of the largest flotation cells operating on a production scale at the time of the testwork. Numerous tests were conducted and data collected from this investigation showed that the Vera et al (1999) technique was applicable to this scale of flotation cell. Since the work at Mount Keith was conducted in a rougher flotation cell, it was decided to test the methodology with numerous cells of various sizes and duties at the Kambalda Nickel Concentrator. As with the previous investigation at Mount Keith, it was observed that the Vera method was able to measure froth recoveries in all cells measured at Kambalda (within typical operating ranges). However, the technique was not applicable at shallow froth depths since it does not take into account the effect of the pulp-froth interface within the froth recovery parameter estimation. The pulp froth interface and close to it is where a significant proportion of dropback occurs within the froth zone. In addition to this problem, the methodology required large numbers of samples and disturbed downstream processes which made the technique unpractical for operating industrial flotation plants. Hence, a new technique for measuring froth recovery in large flotation cells was required. For the technique to be successful on an industrial scale it required the following: • minimum disturbance on the process, • take into account the pulp froth interface within the froth recovery parameter, and • require a minimum amount of samples. To meet these needs a new technique was developed based on the Savassi et al (1997) technique and combining it with recent work by authors including Vera et al (2003). The methodology involves taking samples of the feed, concentrate and tail as per a typical flotation survey and combining them with two new samples: the air hold-up sample and the top of froth sample. With the addition of these samples, a mass balance across the pulp and froth phase could be conducted and the froth recovery parameter derived. In addition, the new method provided measurements of the pulp zone average bubble load and the amount recovered by the entrainment mechanism. The proposed method has a simple procedure which allows the technique to be used by academics and mill operators alike. The proposed froth recovery measurement technique was tested in numerous cells of various types (i.e. Wemco, Outokumpu, Dorr-Oliver etc), various sizes (up to 150 m3 in size), various duties (rougher, scavenger, cleaner, recleaner, etc) and various plants. In most cases the methodology proved to be a reliable measure of the froth recovery parameter. In addition, at the Century Zinc Operation, the methodology was compared directly with the original Vera et al (1999) technique and the results showed that there was a good comparison between the results with the off-set of the pulp-froth interface. A number of contributions to both the research and industrial areas have been provided from the outcomes of the thesis. The main contributions include: • A full assessment of the three current methods for measuring the froth recovery parameter within large flotation cells. With recommendations of developing a new technique. • The development of a froth recovery measurement technique which can be used in large cells to understand the impact of the froth zone in an individual cell, use within the AMIRA P9 modelling methodology and plant diagnostics. • The new method also allows the estimation of the average bubble load and quantifies the amount of material recovered by the entrainment mechanism which is invaluable to metallurgists in assessing the performance of a flotation circuit (plant diagnostics). Finally, the results of this thesis will provide practising metallurgists both within the research and operating fields, techniques to improve the profitability of flotation circuits worldwide. Metallurgists can quickly assess the performance of large flotation cells in terms of froth performance, bubble load and entrainment which has not been available before. In addition, the results from this thesis will also allow metallurgists to mathematically represent their plant through flotation models better and improve their understanding of their flotation circuits.

The role of mathematical models and simulators in describing the performance of mineral processing applications have had a large impact in optimising existing industrial plants and designing new plants over recent years. Before the development of sophisticated computer simulators, the design engineer used industrial “rules of thumb” to estimate the size and layout of plants. However, newly designed plants after commissioning, often do not meet the design product specification requirements and quite often years of “trial and error” optimisation is required. This process can be very costly especially with froth flotation processes where the complexity of the various stages of treatment makes “trial and error” optimisation very difficult to quantify and assess the benefits. Over the past 10 years, advances in the modelling of the flotation process have been conducted by many authors. The most significant flotation modelling advances in recent years have been provided by the AMIRA (Australian Mineral Industry Research Association) P9 project, whereby a new modelling methodology has been proposed. Within this methodology, the flotation response can be represented by a number of sub-processes including parameters describing the hydrodynamic, froth and ore characteristics. Although these parameters have been proposed, methods for measuring these parameters in large flotation cells are still developing, especially in the areas of the froth zone recovery and entrainment. In the light of this it was felt that the literature on froth recovery determination should be investigated to determine the most appropriate method for measuring froth recovery in large industrial flotation cells. It was found after the investigation of the literature that three techniques for measuring the froth recovery parameter stood out as potential methods for measurement within a large scale flotation cell. These were the methods decribed by Gorain et al (1998), Vera et al (1999) and Savassi et al (1997). It was decided that all three methods should be assessed on a quantitative and qualitative basis from data collected at the Mount Isa Mines (now Xstrata) Copper flotation circuit. In this assessment, all three methods were extensively trialed in a 2.8 m3 flotation cell which was operated in parallel to the main copper rougher flotation circuit. The cell could be operated at numerous operating conditions which allowed sufficient data to be collected. The conclusions from this work were that although the method proposed by Vera et al (1999) required significant amounts of data, the method appeared to be reliable in this scale of cell. The main recommendation from this work was to further test the Vera methodology in larger industrial flotation cells. A 100 m3 Outukumpu tank cell at the Mount Keith Nickel Concentrator was chosen for the further assessment of the Vera et al (1999) methodology and its applicability to large scale cells. This flotation cell was one of the largest flotation cells operating on a production scale at the time of the testwork. Numerous tests were conducted and data collected from this investigation showed that the Vera et al (1999) technique was applicable to this scale of flotation cell. Since the work at Mount Keith was conducted in a rougher flotation cell, it was decided to test the methodology with numerous cells of various sizes and duties at the Kambalda Nickel Concentrator. As with the previous investigation at Mount Keith, it was observed that the Vera method was able to measure froth recoveries in all cells measured at Kambalda (within typical operating ranges). However, the technique was not applicable at shallow froth depths since it does not take into account the effect of the pulp-froth interface within the froth recovery parameter estimation. The pulp froth interface and close to it is where a significant proportion of dropback occurs within the froth zone. In addition to this problem, the methodology required large numbers of samples and disturbed downstream processes which made the technique unpractical for operating industrial flotation plants. Hence, a new technique for measuring froth recovery in large flotation cells was required. For the technique to be successful on an industrial scale it required the following: • minimum disturbance on the process, • take into account the pulp froth interface within the froth recovery parameter, and • require a minimum amount of samples. To meet these needs a new technique was developed based on the Savassi et al (1997) technique and combining it with recent work by authors including Vera et al (2003). The methodology involves taking samples of the feed, concentrate and tail as per a typical flotation survey and combining them with two new samples: the air hold-up sample and the top of froth sample. With the addition of these samples, a mass balance across the pulp and froth phase could be conducted and the froth recovery parameter derived. In addition, the new method provided measurements of the pulp zone average bubble load and the amount recovered by the entrainment mechanism. The proposed method has a simple procedure which allows the technique to be used by academics and mill operators alike. The proposed froth recovery measurement technique was tested in numerous cells of various types (i.e. Wemco, Outokumpu, Dorr-Oliver etc), various sizes (up to 150 m3 in size), various duties (rougher, scavenger, cleaner, recleaner, etc) and various plants. In most cases the methodology proved to be a reliable measure of the froth recovery parameter. In addition, at the Century Zinc Operation, the methodology was compared directly with the original Vera et al (1999) technique and the results showed that there was a good comparison between the results with the off-set of the pulp-froth interface. A number of contributions to both the research and industrial areas have been provided from the outcomes of the thesis. The main contributions include: • A full assessment of the three current methods for measuring the froth recovery parameter within large flotation cells. With recommendations of developing a new technique. • The development of a froth recovery measurement technique which can be used in large cells to understand the impact of the froth zone in an individual cell, use within the AMIRA P9 modelling methodology and plant diagnostics. • The new method also allows the estimation of the average bubble load and quantifies the amount of material recovered by the entrainment mechanism which is invaluable to metallurgists in assessing the performance of a flotation circuit (plant diagnostics). Finally, the results of this thesis will provide practising metallurgists both within the research and operating fields, techniques to improve the profitability of flotation circuits worldwide. Metallurgists can quickly assess the performance of large flotation cells in terms of froth performance, bubble load and entrainment which has not been available before. In addition, the results from this thesis will also allow metallurgists to mathematically represent their plant through flotation models better and improve their understanding of their flotation circuits.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.

The role of mathematical models and simulators in describing the performance of mineral processing applications have had a large impact in optimising existing industrial plants and designing new plants over recent years. Before the development of sophisticated computer simulators, the design engineer used industrial “rules of thumb” to estimate the size and layout of plants. However, newly designed plants after commissioning, often do not meet the design product specification requirements and quite often years of “trial and error” optimisation is required. This process can be very costly especially with froth flotation processes where the complexity of the various stages of treatment makes “trial and error” optimisation very difficult to quantify and assess the benefits. Over the past 10 years, advances in the modelling of the flotation process have been conducted by many authors. The most significant flotation modelling advances in recent years have been provided by the AMIRA (Australian Mineral Industry Research Association) P9 project, whereby a new modelling methodology has been proposed. Within this methodology, the flotation response can be represented by a number of sub-processes including parameters describing the hydrodynamic, froth and ore characteristics. Although these parameters have been proposed, methods for measuring these parameters in large flotation cells are still developing, especially in the areas of the froth zone recovery and entrainment. In the light of this it was felt that the literature on froth recovery determination should be investigated to determine the most appropriate method for measuring froth recovery in large industrial flotation cells. It was found after the investigation of the literature that three techniques for measuring the froth recovery parameter stood out as potential methods for measurement within a large scale flotation cell. These were the methods decribed by Gorain et al (1998), Vera et al (1999) and Savassi et al (1997). It was decided that all three methods should be assessed on a quantitative and qualitative basis from data collected at the Mount Isa Mines (now Xstrata) Copper flotation circuit. In this assessment, all three methods were extensively trialed in a 2.8 m3 flotation cell which was operated in parallel to the main copper rougher flotation circuit. The cell could be operated at numerous operating conditions which allowed sufficient data to be collected. The conclusions from this work were that although the method proposed by Vera et al (1999) required significant amounts of data, the method appeared to be reliable in this scale of cell. The main recommendation from this work was to further test the Vera methodology in larger industrial flotation cells. A 100 m3 Outukumpu tank cell at the Mount Keith Nickel Concentrator was chosen for the further assessment of the Vera et al (1999) methodology and its applicability to large scale cells. This flotation cell was one of the largest flotation cells operating on a production scale at the time of the testwork. Numerous tests were conducted and data collected from this investigation showed that the Vera et al (1999) technique was applicable to this scale of flotation cell. Since the work at Mount Keith was conducted in a rougher flotation cell, it was decided to test the methodology with numerous cells of various sizes and duties at the Kambalda Nickel Concentrator. As with the previous investigation at Mount Keith, it was observed that the Vera method was able to measure froth recoveries in all cells measured at Kambalda (within typical operating ranges). However, the technique was not applicable at shallow froth depths since it does not take into account the effect of the pulp-froth interface within the froth recovery parameter estimation. The pulp froth interface and close to it is where a significant proportion of dropback occurs within the froth zone. In addition to this problem, the methodology required large numbers of samples and disturbed downstream processes which made the technique unpractical for operating industrial flotation plants. Hence, a new technique for measuring froth recovery in large flotation cells was required. For the technique to be successful on an industrial scale it required the following: • minimum disturbance on the process, • take into account the pulp froth interface within the froth recovery parameter, and • require a minimum amount of samples. To meet these needs a new technique was developed based on the Savassi et al (1997) technique and combining it with recent work by authors including Vera et al (2003). The methodology involves taking samples of the feed, concentrate and tail as per a typical flotation survey and combining them with two new samples: the air hold-up sample and the top of froth sample. With the addition of these samples, a mass balance across the pulp and froth phase could be conducted and the froth recovery parameter derived. In addition, the new method provided measurements of the pulp zone average bubble load and the amount recovered by the entrainment mechanism. The proposed method has a simple procedure which allows the technique to be used by academics and mill operators alike. The proposed froth recovery measurement technique was tested in numerous cells of various types (i.e. Wemco, Outokumpu, Dorr-Oliver etc), various sizes (up to 150 m3 in size), various duties (rougher, scavenger, cleaner, recleaner, etc) and various plants. In most cases the methodology proved to be a reliable measure of the froth recovery parameter. In addition, at the Century Zinc Operation, the methodology was compared directly with the original Vera et al (1999) technique and the results showed that there was a good comparison between the results with the off-set of the pulp-froth interface. A number of contributions to both the research and industrial areas have been provided from the outcomes of the thesis. The main contributions include: • A full assessment of the three current methods for measuring the froth recovery parameter within large flotation cells. With recommendations of developing a new technique. • The development of a froth recovery measurement technique which can be used in large cells to understand the impact of the froth zone in an individual cell, use within the AMIRA P9 modelling methodology and plant diagnostics. • The new method also allows the estimation of the average bubble load and quantifies the amount of material recovered by the entrainment mechanism which is invaluable to metallurgists in assessing the performance of a flotation circuit (plant diagnostics). Finally, the results of this thesis will provide practising metallurgists both within the research and operating fields, techniques to improve the profitability of flotation circuits worldwide. Metallurgists can quickly assess the performance of large flotation cells in terms of froth performance, bubble load and entrainment which has not been available before. In addition, the results from this thesis will also allow metallurgists to mathematically represent their plant through flotation models better and improve their understanding of their flotation circuits.

A produção de ferroníquel está intimamente ligada à indústria siderúrgica. Todas as operações pirometalúrgicas pertencentes à rota de processo (calcinação, redução e refino) visam o melhor aproveitamento energético e a menor quantidade de impurezas no produto final. A etapa de refino pirometalúrgico produz escória rica em ferro e níquel, que normalmente é processada para recuperação destes metais e reinserção no processo, na própria etapa de refino ou no forno de redução, dependendo da quantidade de impurezas. Ensaios realizados com a escória granulada da Mineração Morro Azul mostram que é possível recuperá-los por processos físicos, de maneira similar à existente no local, porém com resultados superiores, mediante algumas alterações propostas para o circuito. / Ferronickel production is intimately connected to the steel industry. All pyrometallurgical operations which comprise the process route (calcining, smelting, refining) aim at better energetic usage and smaller amount of impurities in the final product. The pyrometallurgical refining stage produces slag rich in iron and nickel, which is usually further processed for metal recovery and reinsertion back into the process, in the refining or smelting stages, depending on the amount of impurities. A series of tests carried out on the Mineração Morro Azul granulated refining slag shows that it is possible to recover the metallic particles through physical processing, similarly to the existing facility, but with improved results due to some alterations proposed for the circuit.

Os objetivos principais deste trabalho foram planejar, executar e analisar os resultados de uma campanha de ensaios de concentração de minerais em um jigue centrífugo. O programa de ensaios permitiu a análise da influência de variáveis operacionais do equipamento no desempenho metalúrgico do processo de concentração. As investigações tiveram por meta estabelecer o desempenho metalúrgico por faixas granulométricas discretas tanto em termos de recuperações como de enriquecimentos. Para tanto foi selecionado o rejeito de uma operação de concentração de minerais sulfetados polimetálicos. O método de trabalho consistiu na caracterização tecnológica do rejeito e execução dos ensaios de concentração no jigue centrífugo Kelsey variando três parâmetros principais: velocidade de rotação, freqüência e amplitude de pulsação. Os resultados dos ensaios foram analisados em termos de recuperações e enriquecimentos dos elementos de interesse, como níquel, cobre e enxofre, além de óxido de magnésio, principal contaminante dos concentrados. O desempenho da campanha de ensaios indicou valores significativos de recuperação e enriquecimento dos elementos de interesse, bem como redução importante de óxido de magnésio nos concentrados obtidos. / The present work describes an experimental program designed to assess the metallurgical performance of a centrifugal jig. The variations in the main operating conditions were analysed in terms of both metallurgical recovery and grades by size fraction in concentrates. The tailings of a sulphide mineral concentration plant were sampled, prepared and submited to technical characterization as a preparation for the testing campaign. A Kelsey centrifugal jig was used in the testing program which included variation in rotating speed, frequency and stroke of pulse. The results were analysed in terms of recovery and concentration of nickel, copper and sulphur, as well as magnesium oxide which was the main contaminant. The general performance of the tests indicated high values in recovery of the selected elements, as well as significant reductions of contaminant in the concentrates.

Flotation is an important and versatile mineral processing technique that is used to separate hydrophobic materials from hydrophilic. This technique makes it possible to mine complex ores that otherwise would have been regarded as uneconomic and non-beneficial. In this case flotation is used to separate copper from the unwanted gangue. The addition of lime is used to control the pH level in the flotation’s pulp, which governs the selectivity of the process, i.e. which minerals are recovered. Currently, fluctuating concentration grades of the produced metals have been observed in Boliden Aitik. Therefore, Boliden proposes a new control strategy which aims to maintain a constant ratio between the added lime and the incoming ore flow, but at the same time ensuring that the pH level is maintained within allowed limits. The aim of this thesis is to develop a model that captures the most essential dynamics of a process stage where lime is added, and then evaluate the suggested control strategy by studying suitable control structures. A linear model describing the system dynamics in a specific operating region is obtained by conducting step response experiments on the process. The model is then used to obtain a model describing the disturbances of the process, thereby yielding a complete model that describes the most important dynamics. The most promising control structure utilizes the concept of selective control, where a ratio controller is allowed to maintain a constant ratio as long as the pH level is within allowed boundaries. The pH level is maintained within the boundaries with upper and lower bound pH controllers that utilize the concept of an equivalent control objective (known as the strong acid equivalent) in order to achieve satisfying pH control. The results show that the control structure is able to maintain a constant ratio, and also ensure that the pH level is kept within the allowed limits. A cascade inspired pH ratio controller is also studied and evaluated. The results show that this pH ratio controller is only able to maintain a constant ratio as long as the incoming ore flow is constant. However, the outcomes also suggest that the concentration grades are either sensitive to variations in the ratio between added reagent and incoming ore flow, or that there is something else that causes them to vary.

Background Vanadium is an economically important mineral that is mined and processed at several international locations, including South Africa and the USA. Vanadium exists in several oxidative states, of which the pentavalent compounds are usually the most toxic. Vanadium pentoxide (V205) is pentavalent and is generated during various processing and metal alloy manufacturing processes. Occupational exposure may occur via inhalation of V205 fumes and particles, resulting primarily in adverse effects to the respiratory system. Currently, there is no evidence that vanadium is carcinogenic in humans, and it has never been reported in exposed humans. The International Agency for Research in Cancer (IARC) has classified V205 as possibly carcinogenic to humans, based on the increased incidence of bronchiolo-alveolar neo¬plasms observed in male and female mice and male rats in a study by the National Toxicology Program (NTP) of the US Department of Health and Human Services. The NTP study has prompted the international vanadium industry, embodied by Vanitec, the international association of vanadium producers, to request an epidemiological study with the aim of determining the potential association between cancer and occupational V205 exposure. Aim The aim of the study was to conduct a pilot retrospective case-control study to investigate the relationship between cumulative occupational exposure to V2O5 and the risk of developing cancer at two representative vanadium processing plants, one in SA and one in the USA. Methods All cases and controls were sourced from the industry’s current and past employee corps. Employees that could potentially have been exposed to V2O5 in the workplace for a period of at least 5 years were included in the study. Ethics approval for the study was obtained from the Ethics Committee of the University of Pretoria. Participation was on a voluntary basis, and all potentially eligible current workers were invited to participate. As many retirees and former employees as possible were traced and invited to participate, and eligible deceased employees that conformed to the inclusion and exclusion criteria were identified from lists provided by the companies involved. Potential participants were asked to grant informed consent to participate in the study. Health and lifestyle information, information on fuel use in the family home, and a personal job history were obtained by use of a structured questionnaire during a personal interview with a trained interviewer. Interviews were conducted from April to July 2004. The main inclusion criterion for both cases and controls was current or previous employment at the South African, or the USA vanadium processing facility included in the study. The disease case definition was histologically confirmed cancer. Exclusion criteria were: refusal of interview; less than 5 years in employment when V2O5 was produced at the plant; cause of death not ascertained, employment elsewhere in the vanadium industry, and exposure to a known carcinogenic agent during a period of employment elsewhere. Males and females were included and participants were not excluded on the basis of race or ethnicity. Employees of all ages were eligible. Exposure assessment at both plants was based on recorded V2O5 concentrations in personal air samples, the participant’s job history, the history of vanadium processing, the physical structure and work organisation at the processing plants. Historical V2O5 concentrations in air in the workplace were retrospectively estimated for those periods during which personal air sampling was not conducted. Historical concentrations were estimated by extrapolation from current (known) air concentrations, in conjunction with data on annual production volumes, personal experiences of occupational hygienists and plant managers at the plant, and historical records of plant upgrades, controls on emissions, changes in production processes and industrial incidents and accidents, where available at the plants. Exposure was expressed as the cumulative exposure (mg-years/m3) and the mean air concentration (mg/m3) of V2O5 to which participants had been exposed. Study participants were also classified into exposure categories based on their mean exposure concentrations. Results In total, 196 questionnaires were collected from eligible participants. The majority (94.4 per cent) were males. Smoking and the consumption of alcohol was fairly common amongst the study group, with 61 per cent of the participants being current or previous smokers, and 59.5 per cent indicating that they were drinking alcoholic drinks or beverages. The mean age (± SD) of the study group was 52.4 ± 10.2. The annual mean exposure of the study group during the period of employment was 0.02 ± 0.03 mg/m3 V2O5, and the mean cumulative exposure to V2O5 was 0.17 ± 0.46 mg-years/m3. Four (4) cancer cases were confirmed at the South African plant, and 6 at the USA plant: four adenocarcinomas (three each in the prostate and one in the colon); three squamous cell carcinomas (two each in the lung and one skin cancer); one renal cell cancer of the kidney, one seminoma of the testis, and one papillary urothelial cancer of the bladder. The occurrence of prostate and lung cancers were not unusual, giving the presence of risk factors such as relatively advanced age (for prostate cancer) and smoking (for lung cancer). The other types of cancer, and the ages at which cancer was most frequently diagnosed (the mean age at diagnosis of cancer was 58.5) were not remarkably different from those that were prominent in the cancer literature. An unusual cluster of specific types of cancer, or of any prominent and unusual organ involvement not associated with known non-occupational risk factors, was therefore not found in the case group. Conclusion The results of this study fail to indicate a statistically significant association between cancer and various indices of exposure to vanadium pentoxide. This conclusion is subject to a number of limitations and uncertainties arising from the small number of cases available for study, and limited follow-up of some participants. The potential association between exposure and cancer should be tested in a larger study group with more cancer cases, allowing more powerful statistical analyses, ideally multivariate logistic regression analysis. The study has confirmed the feasibility of the retrospective assessment of exposure to vanadium compounds in the vanadium processing industry, providing that the processing plant history covers detail of processing methodologies, physical structures, production volumes and work organisation, and providing that a detailed job history should be available for all potential participants. Confirmation of the cause of death and cancer status of previous employees was not practical in the South African scenario. An open case-control design nested in a prospective cohort should be more successful in the South African scenario, but also more expensive and results will only be available after an extended follow-up period. In the USA scenario tracing of previous employees, and access to cancer registries and death certificates should be more practical, and a retrospective case-control study should be possible. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / School of Health Systems and Public Health (SHSPH) / Unrestricted