Browsing by Author "Franzidis, Jean-Paul"
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- ItemOpen AccessBeneficiation of fine coal using the air-sparged hydrocyclone(1992) Breed, Ashley Wayne; Franzidis, Jean-PaulThe Air-Sparged Hydrocyclone (ASH) is a high capacity flotation device which is alleged to be more efficient for the flotation of fine particles than conventional flotation equipment. The principal aims of this thesis were to investigate the use of an ASH in the flotation of South African coal ultrafines (-150 micron), and to determine the effect of various design and operating parameters on the performance of the process, in terms of the product yields and grades obtainable. The testwork was carried out on a typical Witbank coal, from the Kleinkopje Colliery, with an ash content of 23.7 %. The coal was characterised by means of size, ash-by-size and float-and-sink analyses. Batch flotation experiments were carried out to provide a benchmark against which the ASH could be compared. Preliminary ASH work was carried out to determine the required collector and frother dosages and the optimal slurry feed rate.
- ItemOpen AccessCharacterising the acid mine drainage potential of fine coal wastes(2013) Kotelo, Lerato Olga; Broadhurst, Jennifer Lee; Becker, Megan; Harrison, STL; Franzidis, Jean-PaulAcid mine drainage (AMD) is one of the major environmental challenges facing the South African mining sector. Acid mine drainage has received significant public attention in recent years. South Africa's long mining history has led to a growing concern that coal-related AMD from these mines (both operational and defunct) will continue for centuries to come. Pyrite bearing fine waste, generated during coal preparation and beneficiation, is thought to carry a significant amount of AMD pollution risk. Coal-related AMD generation has not been afforded the same exposure as AMD generation from high sulphide minerals such as gold and copper ores. This is exacerbated by the growing concern over water quality degradation in the Mpumalanga region of South Africa. The development of integrated solutions to address the management of coal-related AMD requires an understanding of the principle causes behind coal-related AMD. To date, most of the prediction methods described in literature have been derived for the prediction of AMD in metal bearing ores. Furthermore, some of these methods are based on assumptions and do not take into consideration the various sulphur species present. Additionally, some of these methods have limited applicability to coal due to the high total organic carbon content (TOC) of the material. This research project attempts to address these short comings and uncertainties by developing a systematic and meaningful framework for the characterisation of South African coal and coal waste. The research project contributes to the knowledge of coal-related AMD with particular emphasis on the characterisation methods responsible for sulphur speciation and mineralogy for coal. The approach entails carrying out a case study assessment aimed at empirically assessing a coal tailings sample according to: particle size distribution, textural reference, mineralogical characteristics, and how the aforementioned factors influence the acid potential in coal. The approach intends to address key factors which include: identifying the sulphur bearing organic and inorganic constituents related AMD generation in coal, assessing how the mineralogy, texture and particle size distribution contribute to AMD potential in coal tailings, and then identifying suitable analytical techniques and test methods which can provide data. The combination of these key outcomes will seek to provide a systematic and meaningful framework for the characterisation of coal and coal waste streams. The characterisation methods used in this case study outlined a framework focusing on four main areas of acid mine drainage characterisation for coal wastes, these included: chemical characterisation, mineralogical characterisation, sulphur speciation and AMD prediction. This comprehensive approach employed a suite of techniques, including: petrography, quantitative x-ray diffraction (QXRD) and quantitative evaluation of minerals by scanning electron spectrometry (QEMSCAN).
- ItemOpen AccessCombining froth flotation and reflux classification to mitigate ARD generating potential of the Waterberg and Witbank coal ultrafines via sulfide removal(2014) Iroala, Onyinye Judith; Franzidis, Jean-Paul; Harrison, STLIn South Africa, over 10 million tons of ultrafine coal wastes are discarded every year, typically in the form of ultrafine slurries. These fines have a high calorific value, and contain sulfur minerals, particularly pyrite. The high calorific value of these discards leads to a waste of energy that could be harnessed and used, while the high sulfur content contributes to adverse environmental effects such as acid rock drainage (ARD). The University of Cape Town (UCT) has developed a two-stage flotation process, which involves coal flotation in the first stage and pyrite flotation of the tailings in the second stage, for mitigating the ARD potential of ultrafine wastes. Research has shown that this two stage froth flotation process was sufficient to render the tailings non-acid forming. At the same time, North West University (NWU) has been carrying out research on coal fines using the recently invented reflux classifier. The reflux classifier is claimed to be capable of separating particles down to 38 ìm in size; however, no work has been done using the reflux classifier to separate pyrite from coal. This dissertation investigates the effectiveness of combining flotation and reflux classification for removing sulfide minerals from two South African coal ultrafines, whilst recovering valuable coal, and compares the results to those obtained using the UCT two-stage flotation process. As no previous work has been done using reflux classification to remove sulfide minerals from coal, this is the first time that the reflux classifier will be investigated for this purpose. Two process routes were investigated: (i) froth flotation followed by reflux classification of the tailings (process route 1), and (ii) reflux classification followed by froth flotation of the overflow (process route 2). Coal flotation, sulfide flotation and reflux classification were conducted on samples of Waterberg and Witbank coals, using a 3 L Leeds-type flotation cell and a 10 L batch reflux classifier constructed at NWU. Acid base accounting (ABA) and net acid generating (NAG) static characterization tests were performed on the products and feeds from all three process routes.
- ItemOpen AccessDeveloping a mechanistic model for flow through a perforated plate with application to screening of particulate materials(2016) Ogunmodimu, Olumide; Mainza, Aubrey; Govender, Indresan; Franzidis, Jean-PaulScreening in mineral processing is the practice of separating granulated ore materials into multiple particle size fractions, and is employed in most mineral processing plants. Models of screening performance have been developed previously with the aim of improving process efficiency. Different methods have been used, such as physical modelling, empirical modelling, and mathematical modelling including the discrete element method (DEM). These methods have major limitations in practice, and experimental data to validate the models have been difficult to obtain. Currently, the design and scale-up of screens still relies on rules of thumb and empirical factor methods rather than a fundamentally based understanding of the behaviour of the granular system. To go beyond the current state-of-the-art in screen modelling requires a clear understanding of the particle motion along a dynamic (vibrating) inclined plane. Central to this understanding is the notion that granular systems exhibit a unique rheology that is not observed in fluids; i.e. neither Newtonian nor non-Newtonian. It is thus imperative to fully quantify the granular rheology, which is determined by the depth of the particle bed along the screen, the solids concentration, and the average velocity of the granular avalanche on the screen. The concept of granular rheology is important. Existing empirical models of vibrating screens tend to be extremely dependent on boundary conditions of a particular machine design. The concept of granular rheology is important because, akin to fluid flow, granular flow exhibits different flow regimes depending on the extent of energy input in the system. This work employed DEM to quantify the granular rheology of particles moving along a vibrating inclined screen in order to begin the development of a phenomenological model of screening. The model extends the visco-plastic rheology formation of Pouliquen et al. (2006) to capture the kinetic and turbulent stresses obtained in granular flow on an inclined vibrating screen. In general, DEM was employed to develop a mechanistic model of screening which includes a description of the rheology of granular flow on a vibrating screen. Microscopic properties of granular flow were used in DEM to simulate screening of particulate materials. Granular mixtures of two particle constituents (3 mm and 5 mm) were simulated on an inclined vibrating screen of 3.5 mm apertures. For the base case, frequency and amplitude are 4 Hz and 1 mm, respectively. While microscopic properties were employed for the simulation, the properties extracted from the simulations are macroscopic fields which are consistent with the continuum equations of mass, momentum and energy balance. From the continuum equations, a micro-macro transition method called the coarse-graining approach was employed to obtain the volume fraction and the tangential velocity as a function of the depth of flow along the inclined surface. This approach is suitable for this work because the produced fields satisfy the equations of continuum mechanics; even near the base of the flow. The continuum analysis of the flowing layer reveals a coexistence of flow regimes- (i) quasi-static, (ii) dense (liquid-like), and (iii) inertial. The regimes are consistent with the measured solids concentrations spanning these regimes on inclined vibrating screens. The quasi-static regime is dominated by frictional stress and corresponds to low inertial number (I). Beyond the quasi-static regime, the frictional stress chains break and the collisional-kinetic and turbulent stress begin to dominate. The variation of the effective frictional coefficient with the inertial number (I) characterises the flow. Finally, an effective frictional coefficient model that is based on frictional, collisionalkinetic and turbulent stress was developed. Data analyses for this model were done at a steady flow in the base case where a coexistence of three flow regimes were observed. It was observed that each regime of flow is dominated by corresponding shear stresses. While the quasi-static regime is dominated by frictional stress, the kinetic and the inertial regimes are dominated by kinetic and turbulent shear stresses, respectively. This model was tested by varying the intensity of vibration in the base case and it was observed that at higher frequencies and amplitudes, the quasi-static regime gradually disappeared. Furthermore, the inertial number at which transition occurs to different regimes varies in response to the intensity of vibration. This is an important step in developing a phenomenological model of screening. The model presents a fundamental understanding of the mechanisms governing transport of granular matter on an inclined vibrating screen.
- ItemOpen AccessDevelopment of a fine coal beneficiation circuit for the Twistdraai Colliery(1997) Bunt, John Reginald; Franzidis, Jean-Paul; Harris, MartinThe principal aim of this thesis was to develop a fine coal beneficiation circuit for the Twistdraai Colliery capable of achieving.a saleable 10.0% ash (28 MJ/kg CV) product. Gravity circuit testing involved a comparative study of a conventional double-stage Spiral circuit and a Stokes upward-current washer when treating Twistdraai <850J.1m x 106J.1m fine coal. In addition, froth flotation technologies, in the form of the Microcel column and the Jameson cell were also tested in order to ascertain whether they can be suitably applied · to the Twistdraai naturally fine coal to produce a 10.0% ash steam coal export product. In this investigation, the Twistdraai fine coal surface was characterised by size as well as by density. Functional group determination included the measurement of the coals hydroxyl, carboxylic and total acid groups, since these exert the most important influence on the properties of the coal surface. These are supported by contact angle measurements, petrographic analysis and washability measurements in orde:r to determine the oil wettability of the coal fractions prior to flotation testing. The results described and discussed in this thesis show that it was possible to recover the desired quality of product by employing split-stream processing of the (850J.1m x 0) Twistdraai fine coal circuit feed. This was achieved by application of both gravity concentration and froth flotation technologies treating specific particle size ranges.
- ItemOpen AccessDreams come true: youth entrepreneurs in eSikhawini township, Richards Bay(2016) Manqoyi, Ayanda; Fuh, Divine; Broadhurst, Jennifer Lee; Franzidis, Jean-PaulThis research project examines the emergence of youth entrepreneurs in the moments just before mining and industrial activities develop within a community. It focuses on how young people engage with the hopes and promise of opportunities engendered by the expansion of mines and industry within a particular place. Using ethnography as methodology, it looks at how young people's dreams and desires in eSikhawini, a township in the Richards Bay area within the uMhlathuze Municipality, are activated by the coming of mining activities and how they use these to create entrepreneurs. In the context of mining and industrial expansion, young people use the promise of opportunity and the pursuit of dreams and desires to create particular kinds of entrepreneurs who attempt to stabilize their lives and that of their community in the face of precarity. It argues that the interrelations emergent in the daily enterprise of creating a stable future are key resources and insurance against uncertainty that sustain "community" in the context of eSikhawini. Overall, the thesis attempts to demonstrate that by recognising and strengthening youth entrepreneurs' capacity to aspire and realise their dreams can entrepreneurship interventions and programmes foster and sustain empowering relationships amongst marginalized people living in areas affected by mining and mineral beneficiation.
- ItemRestrictedAn economic analysis of coal desulpharisation by froth flotation to prevent acid rock drainage (ARD) and an economic review of capping covers and ARD treatment processes(2013) Jera, Melody Kudzai; Franzidis, Jean-Paul; Harrison, STLAcidic drainage as a result of mining and mineral processing activities is a growing concern. The effects of Acid Rock Drainage (ARD) include environmental pollution in the affected areas and beyond. As South Africa has water challenges, the potential threat of continual depletion of useable water resources through their contamination by ARD and other mining activities may affect economic productivity, as well as quality of life. Currently used ARD remediation measures are variable and costly, not only in South Africa but worldwide. End of pipe approaches such as treatment by neutralisation fail to reduce the risk of ARD generation and provide long term solutions. Further it fails to address the limited resource utilisation of the byproduct materials, currently disposed of as ARD forming wastes. The Department of Chemical Engineering, at UCT, has focused research onto the prevention of ARD generation and minimisation of waste. One approach proposed is the two stage froth flotation process for separating sulphides, responsible for ARD formation, from the remaining tailings, leaving these benign with respect to ARD. Testwork results have proven its technical feasibility using porphyry copper tailings, fine coal and more recently gold tailings. Historically, ultrafine coal was not treated by most collieries in South Africa, but disposed as waste. Oxidation of the pyrite in the coal leads to generation of acidic water. In this project, an economic analysis of the coal two stage flotation process for the mitigation of ARD formation is considered. This project proposes ARD prevention by desulphurisation of sulphide rich waste coal material as an in-process approach which can be incorporated into mineral process flowsheets or as an add-on process for desulphurisation of old workings. The two stage flotation may yield a valuable mineral or coal product, as well as a low volume sulphide rich fraction which can be processed further to yield sulphuric acid or disposed of with containment and a benign tailings fraction which can be used as cover material or disposed conventionally.
- ItemOpen AccessThe effect of conditioning on froth flotation(1995) Henwood, Daryl; Franzidis, Jean-PaulThe method and extent to which mineral slurries are conditioned have been shown to greatly affect flotation grades and recovery. Most of this work is very mineral specific and centres around one or two operating variables. One of the major obstacles to understanding the effects of such pretreatment more fully, and to developing a global understanding of conditioning, is the system specific nature of the procedures applied to each mineral, and the apparently conflicting results across a range of mineral types. This thesis sets out to define conditioning both broadly enough to encompass almost all aspects of conditioning, as well as specifically enough to be useful in the study of single mineral-collector systems. Having done this, a measure of the efficiency or effectiveness of conditioning is devised and used to evaluate the relative effects of variables of conditioning, as well as to gain some insight into the mechanisms affecting the results. The work is completed by relating these observations to expected results in industrial applications and their implications on plant procedures. Most forms of conditioning for flotation were found to fit into two basic categories, which if they both take place in the same process, follow one another sequentially. In this thesis, these were termed "primary" and "secondary" conditioning, and were defined as follows: Primary Conditioning relates to the physical preparation of the surface of the particles, including comminution, oxidation, acid leaching and bacterial pretreatment. Secondary Conditioning is the process whereby prepared particles are rendered hydrophobic or hydrophilic through mixing, control of the environment and contacting with reagents.
- ItemOpen AccessEffect of HPGR on platinum bearing ores and the flotation response as compared to the conventional ball mill(2011) Solomon, Nomonde; Mainza, Aubrey; Becker, Megan; Petersen, Jochen; Franzidis, Jean-PaulThis thesis focuses on the application of the high pressure grinding rolls (HPGR) on platinum bearing ores Merensky, UG2 and Platreef. Conventional tumbling mills such as the ball mill that are typically applied on these ore types are highly energy intensive with a small percentage of the input energy being used for actual breakage. Rapidly increasing energy costs have contributed to the rising interest of the HPGR in the platinum industry, particularly in plants processing UG2 and Platreef ores. Therefore, this thesis seeks to determine if the HPGR can be used as an alternative to the ball mill. Key aspects of interest are throughput, energy efficiency, PGE grade and recovery and PGM liberation.
- ItemOpen AccessHydrodynamics and gas dispersion in industrial flotation cells(1999) Egya-Menash, Daniel; Franzidis, Jean-PaulSolids suspension and gas dispersion studies were performed on a total of 40 industrial flotation cells of various types, sizes and duties in a Platinum Group Metal (pgm) concentrator in the North West Province of South Africa. The wide variety of cells studied included a Bateman 3-m³ cell, Outokumpu 16-m³ conventional and 50-m³ TankCells, WEMCO 84, 120, 144 cells and WEMCO 144 with 164 mechanism and high-power motor. The gas phase properties of bubble size, superficial gas velocity, air holdup and bubble surface area flux were used in characterising these cells. The bubble size was measured at six different locations in the cells using the UCT Bubble Size Analyser. The superficial gas velocity and gas holdup were measured similarly with other special designed devices. The bubble surface area flux, a new parameter for characterising the hydrodynamics and gas dispersion in flotation cells, was calculated from the ratio of the superficial gas velocity to the Sauter mean bubble size. The results of these measurements were analysed in terms of key variables including air flowrate, impeller speed and location in the cell. The bubble size was found to increase with increasing air flowrate and decreasing impeller speed. Bubbles in the impeller zone were found to be smaller than bubbles in the quiescent zone due to significant bubble coalescence in this region. The bubble size was also found to be inversely related to the power consumption provided that this was expressed on an impeller-swept-volume basis. The superficial gas velocity was found to increase with increasing air flowrate and impeller speed and was significantly affected by location in the cell. Differences in superficial gas velocities were observed at constant air flowrates and at different impeller speeds. This unexpected finding was attributed to differences in flow patterns in the cells. Air holdup was found to be largely insensitive to changes in air flowrate and impeller speed in cells operating at their normal conditions. Differences in air holdup in the quiescent and turbulent zones were observed but these were more noticeable in smaller cells. The bubble surface area flux in industrial flotation cells was found to be in the range of 50-60 m²/m²/s irrespective of the type, size and duty of cell. However, it was observed that the bubble surface area flux could be varied by manipulating certain key cell variables such as the impeller speed and the air flowrate. The bubble surface area flux was found to increase with increasing air flowrate until reaching an optimum at sufficiently high air flowrates.
- ItemOpen AccessImproving the selectivity of the radio-labelling of ion exchange resin tracers for positron emission particle tracking(2015) Van Heerden, Michael Rudi; Franzidis, Jean-Paul; Buffler, AndyPositron emission particle tracking (PEPT) is a technique which non-invasively tracks tracer particles labelled with a positron emitting radionuclide in a system of flow. The tracers are tracked through the detection in a PET scanner, of the two nearly collinear 511 keV gamma rays resulting from the annihilations of the positrons. For this technique to be effective, the tracer must be representative of the media in the system under study, and labelled with a sufficient activity of radionuclides. Organic ion exchange resins are suitable tracer materials for PEPT experiments, and are usually labelled with ⁶⁸Ga at the laboratories of PEPT Cape Town. The labelling performance relies on the chemical and physical properties of organic strongly acidic cation exchange resins and the nuclear chemistry of ⁶⁸Ga. The objective of this study is to obtain consistent tracer labelling throughout, or even beyond, the lifespan of the SnO₂ ⁶⁸Ge/⁶⁸Ga generator which degrades over time. The objective 1s achieved by integrating a purification technique into a "standard" radiolabelling method used at iThemba LABS. A small 0.5 ml Amberchrom CG-71 column is loaded with the ⁶⁸Ga generator eluent in 7 M HCl, then rinsed of most the contaminants before eluting the product with distilled water and used in the radiolabelling method. Using a 1-year-old 30 mCi SnO₂ ⁶⁸Ge/⁶⁸Ga generator eluent that has been purified by this method improved the radiolabelling performance by an average of at least 10% when compared to the performance of the un-purified product. Purifying the generator eluent will enable PEPT experiments of longer duration, and in highly shielded systems where tracers with high activity are required, such as granular and fluid flow in engineering applications.
- ItemOpen AccessInvestigating depressant behaviour in the flotation of selected Merensky ores(2009) Wiese, Jennifer Gael; Bradshaw, Dee; Franzidis, Jean-Paul; Harris, PeterThis study utilised laboratory batch flotation tests to characterise the flotation performance, with respect to sulfide and gangue minerals, of two Merensky ores with different mineralogy, in the presence of depressants; and contributes to the increased understanding of depressant behaviour in the flotation of Merensky ores. The ores were obtained from the southern section of the Merensky reef in the Bushveld Igneous Complex.
- ItemOpen AccessAn investigation of particle collection efficiency in different particle-bubble contacting environments in flotation(1995) Breytenbach, Jacobus Nicolaas; Franzidis, Jean-Paul; Harris, Martin; O'Connor, CyrilThe collection efficiency of quartz particles in four different particle-bubble contacting environments was investigated during this thesis. Flotation experiments were carried out in a hybrid flotation column that could be modified into three different cell configurations (a quiescent column cell, an agitated column cell and a Jameson-type cell), while the fourth cell environment comprised a laboratory batch subaeration flotation cell. High purity quartz was used as a probe ore in conjunction with a cationic collector and a commercial frother blend. The quartz was initially contaminated with organic material and needed to be cleaned by calcination. The cleaned quartz was divided into four narrow particle size fractions to determine the effect of particle size on particle collection efficiency. The quartz was floated over a wide range of collector dosages and frother dosage was kept constant during experiments. The flotation was conducted using tap water at neutral pH. Froth depth was kept shallow during all experiments in the hybrid column cell configurations to enable the investigation to focus specifically on the collection zone. The effect of contacting environment (cell type) on particle collection efficiency was investigated by considering the effect of particle hydrophobicity, particle size and agitation speed (turbulence) on flotation recovery in the different cell types. The unique particle-bubble contacting environments resulted in different particle collection efficiencies and it was found that increased contacting intensity generally led to increased efficiency of collection. Increased particle hydrophobicity generally resulted in increased particle collection efficiency, although the overdosing of collector led to decreased flotation recovery which was probably caused by combined collector double layer and flocculation effects. The effect of particle size on flotation recovery exhibited classical n-curve behaviour at intermediate collector dosages and the optimum particle size range as reported in the literature was confirmed. Intense contacting between particles and bubbles followed by relatively quiescent disengagement (such as the mechanism employed in the Jameson cell configuration) proved to be beneficial to collection of both fine and coarse particles.
- ItemOpen AccessInvestigation of particles with high crack density produced by HPGR and its effect on the redistribution of the particle size fraction in heaps(Elsevier, 2013) Ghorbani, Yousef; Petersen, J; Becker, Megan; Mainza, Aubrey Njema; Franzidis, Jean-Paul; Kalala, JTThe application of comminution technology such as the High-pressure grinding rolls (HPGR), which is able to generate a high density of cracks in the ore particles, is favourable for leaching processes. Extraction of metallic values by the heap leach process, can take place on the particles with partial exposure of mineral grains, if it can provide sufficient surface front for chemical attack by leaching solution. The aim of this study was to assess the benefits of high crack density in the ore particles produced using the HPGR and how it could diminish due to inadequate percolation of the leaching agent. A zinc ore was comminuted using HPGR at three different pressure settings and with a cone crusher for the control experiment. Subsamples from the (+23/-25, +14/-16, +5.25/-6.75 mm) size fractions were characterized and packed into leach reactors. The reactors were stopped from time to time to investigate the progress of crack and micro-crack growth and its effect on metal extraction using the X-ray computed tomography (CT). The results are validated with those obtained using traditional techniques such as SEM and QEMSCAN. Investigation of the leach reactors residue indicated significant changes in the particle size distribution (PSD) of initial feed toward the fine size fraction. The residues from the reactors leaching the material prepared using the HPGR product contained more fine particles than the reactors, which were fed by cone crusher product. These differences were up to 10.3%.
- ItemOpen AccessInvestigation of the effect of different frother blends on the flotation of selected PGM bearing ores(2015) Ngoroma, Faustine; Franzidis, Jean-Paul; Wiese, JennyConcentrators processing platinum group mineral (PGM) bearing ores use polysaccharide depressants to reduce the recovery of the naturally floatable gangue minerals (mainly silicates) present in the ores. Recent work has shown that high depressant dosage can completely depress the naturally floatable gangue from reporting to the concentrate. Unfortunately, this high dosage of depressant can have a negative effect on the recovery of valuable minerals present in the ore by reducing the stability of the froth. In order to counterbalance the negative effects of depressant addition, frothers are normally added. The optimum frother provides a balance between the pulp kinetics and the froth recovery (through the effect of the frother on the bubble size and froth stability, respectively) over the range of frother addition. Usually one frother is added to accomplish this but using only one frother gives only one unique hydrodynamic relationship. It would be preferable to have independent control over the bubble size and froth stability, but unfortunately this cannot be achieved because changing the concentration of the frother changes both responses. An alternative strategy for gaining more independent control over the froth characteristics and bubble size would be to use a blend of frothers, such as a weak and a stronger frother. Such a system would give an additional degree of freedom so that changing the ratio of the two frothers would provide more independent control of bubble Sauter mean diameter and froth stability. Little research work has been conducted on frother blends and none suggests the mechanism of blended frother action. This study investigates through the use of batch flotation tests how blending low molecular weight alcohols with commercially available high molecular weight frothers impacts the solids and water recovery, as well as the valuable mineral recovery and concentrate grade, in different PGM ores. The results are compared with laboratory batch flotation tests using single frothers only. Two ores from the Merensky Reef in the Bushveld Igneous Complex, South Africa, were used .The frothers were selected to cover a range of polyglycols and alcohols, and included Senfroth 516, DOW 200 and DOW 250 (all polyglycols), and 1-butanol, 1-pentanol, 1-hexanol and MIBC (all low molecular weight alcohols). The frothers were used individually and as v blends at a total dosage of 50 g/t. Two phase tests were also carried out to measure the bubble sizes produced at different concentrations of both single frother and blends.
- ItemOpen AccessInvestigation of the effect of mineralogy as rate-limiting factors in large particle leaching(Elsevier, 2013-10) Ghorbani, Yousef; Becker, Megan; Petersen, J; Franzidis, Jean-PaulAlthough heap leaching is by now well established in the mining industry, the process remains limited by low recoveries with different rate-limiting factors that are not clearly understood. In this study, three large particle size classes (+19/-25, +9.5/-16, +4.75/-5 mm) were prepared from a sphalerite ore by two different methods of comminution (HPGR and cone crusher). The particles were then packed into leach reactors that were operated continuously for eleven months with well-mixed internal circulation of the leach solution. Characterization of the residue of the leach reactors indicated that there are areas within the ore particles where although sphalerite grains are accessible to the solution, they remain unreacted. X-ray tomography and QEMSCAN® analysis of the selected samples before, during and after leaching, showed increased leaching of sphalerite grains associated with pyrite due to galvanic interactions. Mineral chemistry (Fe, Mn content of sphalerite) and jarosite precipitation were also investigated as factors influencing sphalerite leaching.
- ItemRestrictedLarge particle effects in chemical/biochemical heap leach processes - A review(Elsevier, 2011) Yousef, Ghorbani; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, JochenThe application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-of-mine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
- ItemRestrictedLarge particle effects in chemical/biochemical heap leach processes – A review(Elsevier, 2011) Ghorbani, Yousef; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, JochenThe application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-ofmine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
- ItemOpen AccessThe liberation characteristics of Greenside No. 2 seam coal(1987) Harris, Martin Colquhoun; Franzidis, Jean-PaulIn South Africa, ever increasing quantities of fine (-0,5 mm) coal are being produced as a result of the increased use of mechanised mining methods. Very few mines beneficiate the fines; in most cases they are discarded. However the fine size of this material suggests that it should be well liberated, with the potential to produce a low ash product. This thesis forms part of an ongoing research program examining the use of flotation to beneficiate coal fines to produce a low ash product. Coal is a highly heterogeneous material, consisting of a number of both organic (maceral) and inorganic (mineral) components with different physical and technological properties. Therefore in order to evaluate and interpret flotation results, an understanding of the liberation characterist ics of both the organic and inoganic components is required. This thesis presents a liberation study on fine coal from the Greenside Colliery, a typical colliery in the Witbank Coalfield which is the most important source of South African low ash coal. The study was performed by mining a run of mine coal sample to varying degrees of fineness (from 30 % finer than 150 micron to 90 % finer than 150 micron), screening, and assessing the liberation of each size fraction. These results were compared to those obtained from a sample of naturally arising fines (thickener underflow). Liberation was assessed by float and sink analysis, and for this purpose a new technique was developed that enables rapid and accurate float and sink analysis of coal down to a few micron in size. Petrographic analyses were performed to determine the liberation of the organic coal components.
- ItemOpen AccessA liberation study on ultrafine South African coals(1989) Buys, Irmtraud Erna; Franzidis, Jean-PaulSouth African coal mines generate large quantities of fines as a result of the increased use of mechanised mining methods. Generally, these fines are discarded. They do however contain relatively large proportions of high grade material, which provides a considerable incentive for their beneficiation. The increasing demand for low-ash and superlow- ash coals is an added price incentive for fines beneficiation. As coal is a highly heterogeneous substance, it is necessary, in order to optimize beneficiation processes, to have a good understanding of its liberation characteristics. The aim of this thesis is to extend the liberation study of Harris (1987) on Greenside (Witbank No.2 Seam) coal to finer sizes and to investigate the liberation characteristics of two other South African coals, one from the Rietspruit Colliery (Witbank Coalfield) and the other from the Grootegeluk Colliery (Waterberg Coalfield).