Browsing by Author "Harris, Martin"

Now showing 1 - 12 of 12
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    An automated camera tracking system for single bubble velocity profiling
    (2007) Reid, Stewart Charlton; Wilkinson, Andrew John; Harris, Martin
    An apparatus has been developed for the automated velocity profiling of single bubbles in aqueous solutions. Using a mobile IEEE 1394 camera and a control algorithm, the apparatus can automatically track a bubble as it rises in a Perspex column. The resulting video footage is then post-processed to obtain the velocity profile of the bubble, amongst other data. This apparatus is to be used in research relevant to the minerals processing industry. The software components were developed in Matlab and Microsoft Visual C++ and implemented in Visual C++. The methodology used to develop the apparatus is presented, and typical examples of velocity profiles are given. An analysis to determine the effect of error of parrallax is also performed.
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    Developing a framework for the design of the milling and rougher circuits for a platinum-bearing UG2 ore
    (2012) Steyn, Johannes Jakobus; Harris, Martin
    In the western limb of the Bushveld Igneous Complex, platinum is mined predominantly from two reefs – Merensky and UG2. Most of the platinum group minerals (PGM’s) in Merensky ore are associated with base metal sulphides (BMS), and thus Merensky concentrators will usually resemble simple BMS circuits. However, the mineralogy of UG2 ore is more complicated, and thus UG2 circuits are also more complex. The UG2 reef is a chromitite layer in the critical zone of the Bushveld Igneous Complex, which results in high chromite content. Chromite causes significant complications in the downstream smelter process, and therefore chromite constraints are imposed on UG2 concentrators. A further aspect complicating the treatment of UG2 ore is that PGM’s are not only associated with BMS, but ultra-fine PGM’s are also locked in gangue minerals. This affects the milling and flotation characteristics of the circuits, as it is not possible to efficiently target the liberation and recovery of relatively large BMS and ultra-fine PGM’s in the same circuit. As a result UG2 circuits have evolved to deal with these issues in a number of ways. This thesis focuses on the design of milling and flotation circuits to optimise the recovery of coarse BMS (with associated PGM’s) and ultra-fine PGM’s contained in associated siliceous gangue minerals. In order to achieve this, UG2 circuits usually feature more than one milling and flotation stage.
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    Development of a fine coal beneficiation circuit for the Twistdraai Colliery
    (1997) Bunt, John Reginald; Franzidis, Jean-Paul; Harris, Martin
    The 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.
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    The development of a flotation simulation methodology towards an optimisation study of UG2 platinum flotation circuits
    (2001) Harris, T A; Harris, Martin
    The design of new flotation plants is still based substantially on experience obtained from prior plant designs. Design criteria are typically based on rule of thumb procedures that often prove to be highly ineffective. The development of appropriate models of the flotation process is a means of addressing these problems so that flotation plant simulations can be performed to identify the true potential of existing plants as well as in the design of new flotation plants. This thesis addresses the complex issue of developing a robust methodology for use in flotation circuit modelling and simulation, based on the operation of pilot-scale flotation equipment. The investigation is focussed on the processing of platinum bearing ores from the UG2 reef in South Africa. The UG2 reef is of considerable economic importance, containing a substantial proportion of the world wide reserves of platinum group metals. However, UG2 ore has very complex mineralogy, and a high degree of association with chromite, which renders processing of this ore relatively difficult. Consequently, optimising the design of flotation circuits to treat this ore has proved challenging, and has been the focus of much attention by major platinum producers over the last 10 to 20 years.The primary aim of this thesis is to identify, evaluate and refine appropriate flotation models and modelling procedures reported in the literature, and use these models to develop a flotation circuit simulation procedure that can be used to provide a sound basis for the evaluation of current UG2 circuit design trends, and as an optimisation tool for the design of UG2 circuits in the future. The processing of UG2 ore from three different locations is evaluated, using two continuous pilot plants of different size, each operated in a variety of different configurations. The investigation required extensive modification of the pilot plant facility that was used, to facilitate the acquisition of the data required by the selected models.The basis and implications of these modifications with respect to the design and operation of pilot plants as a tool for design and optimisation is extensively covered. The modelling approach adopted in this study is based on the separation of the factors affecting flotation into those arising from the characteristics of the ore (floatability) and those arising owing to the hydrodynamics in the equipment, in both the pulp and froth zones of the cell. It is proposed that the pulp zone performance can best be related to the bubble surface area flux based on the work of Gorain et al (1997), while ore floatability is modelled using a distributed floatability model, based on the approach developed by Runge et al (1997) and Harris (1997). The performance of the froth phase with respect to minerals recovered by true flotation is modelled based on the approach proposed by Harris (1997) and Gorain et al (1998), while entrainment in the froth is modelled using the approach proposed by Savassi et al (1998).
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    The development of frother optimisation techniques in full scale flotation plants
    (2013) Venkatesan, Luke; Mcfadzean, Belinda; Harris, Martin
    In 2012, Anglo American Platinum assembled a technical task team of metallurgists for their concentrator operations. Although there has been extensive research in literature regarding the flotation response and behaviour of reagents, there still exists a gap between fundamental laboratory scale research and plant scale application. This thesis will focus on the development of techniques for optimising and characterising frother on a full scale plant using the Anglo American Platinum Bubble Sizer (AAPBS) which is a commonly used tool by the plant metallurgist. The techniques developed have been based on the application of fundamental research of frothers in literature. This thesis consists of three main focus areas: 1) Developing a technique for measuring the relationship between sauter mean bubble diameter and frother concentration on a full scale plant. 2) Developing a technique for estimating frother concentrations in process streams in full scale plant 3) Establishing whether the relationship between sauter mean bubble diameter and superficial gas velocity in a flotation bank of identical cells in series in a plant operating at frother concentration above the CCC is identical, and whether this can be used to detect the decrease of frother concentration to below the CCC at any point in the bank. Furthermore, the metallurgical performance of a bank with a decrease in frother concentration below the CCC midway through the bank was determined before and after the addition of frother, which was added as such that all the cells in the bank operate with a frother concentration above the CCC. There were two techniques investigated for measuring the relationship between sauter mean bubble diameter and frother concentration. Both techniques involved using the AAPBS and the use of forced air mechanically agitated tank cells. Technique 1 involved using the first rougher cell on a flotation plant, dosing frother at different rates into the cell to target different frother concentrations and then measuring the resultant bubble size whilst operating at a fixed air rate. The coalescence mechanism here was occurring in a three phase solids/aqueous/air system occurring in a continuous stirred tank. Similarly Technique 2 involved using the first rougher cell; however, the first cell was depleted of frother by bypassing the frother dosage line into the next cell. This was done to isolate the first rougher cell and to minimise disturbance to the rest of the rougher bank. Known concentrations offrother were made up in potable water and these were added into the AAPBS. Bubbles from the pulp phase enter the bubble riser tube which is long and narrow (3m x 25mm diameter) which is representative of two phase aqueous/air “plug flow” system. These bubbles coalesce to different degrees based on the known frother concentration. The resulting bubble size distribution was then be measured by taking photographs at the viewing pane of the AAPBS. The air rate in the cell was kept constant to within 0.7-0.9 cm/s and the photographs were analysed using software provided by stone three to determine the sauter mean bubble diameter and the bubble size distribution. Technique 1 was applied to Plant A UG2 concentrator which was using a polyglycol type frother called Betafroth 206C which has an undisclosed composition and a molecular weight of approximately 200 g/mol. The first rougher cell used was an Outokumpu 70 m3 forced air mechanically agitated tank cell. The results showed no clear relationship between sauter mean bubble diameter and frother concentration. Furthermore, the sauter mean bubble diameter was already very small and it appeared that the changes in between runs were more strongly linked to the superficial gas velocity than frother concentration. The fact that the sauter mean bubble diameter obtained was already small implied that the frother concentration in the cell was already high. This could have been due to an additional source of frother due to spillage or in the process water that potentially elevated the actual frother concentrations in the cell. Technique 1 also resulted in significant disturbances to the entire rougher bank because it involved changing the frother dosages to the bank. This would affect the flotation performance of the bank for a prolonged period and affect plant performance. Hence it was decided that technique 1 would not be suitable.
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    The effect of energy input on flotation kinetics in an oscillating grid flotation cell
    (2012) Changunda, K; Deglon, David; Harris, Martin
    Energy is known to play an important role in particle-bubble contacting in flotation. This thesis investigates the effect of energy input (or agitation) on the flotation kinetics of quartz in a novel oscillating grid flotation cell. The effects of bubble size and particle size have been recognized as important variables affecting particle-bubble contacting in turbulent systems and are investigated in this thesis. The research work done in this thesis is a continuation of the work done by the Centre for Minerals Research by Deglon (1998) who investigated the effects of energy in a batch mechanical flotation cell. However, this system has a very complex hydrodynamic environment, resulting from the large disparities in turbulence intensity. Previously Breytenbach (1995) had constructed a hybrid flotation column cell, which was essentially a column flotation cell that could be modified into a Jameson cell or a mechanically agitated column cell. He used this to compare particle collection efficiency in these different particle-bubble contacting environments. The third phase of the work was the oscillating baffle column (OBC), a novel flotation column that attains agitation by oscillating a set of orifice baffles through the slurry, thereby producing a more uniform shear rate distribution than would be obtained in an impeller driven system (Anderson, 2008). The OBC unfortunately has significant oscillatory flow and has high shear rates, which often result in detachment effects becoming appreciable. Oscillating grids generate near ideal hydrodynamic environments, characterised by turbulence that is relatively homogeneous and isotropic. The oscillating grid flotation cell used in this study was based on the oscillatory multi-grid mixer used by Bache and Rasool (2001). The oscillatory multi-grid mixer was purchased from these authors and retrofitted to produce the oscillating grid flotation cell. The novel oscillating grid cell consists of a 10 litre tank agitated by 19 grids with a mesh size of 8 mm and grid spacing of 18 mm. The grids were oscillated at a fixed amplitude, equal to the grid spacing, and over a range of frequencies, using a variable speed drive. Frother was added at 100 ppm to be consistent with the work of Deglon (2002) and Ahmed and Jameson (1985). A low gas flow-rate (100 ml/min) and solids concentration were specifically chosen in order that there was minimal influence on the structure of turbulence in the oscillating grid cell, as Bache and Rasool (2001) took measurements in water. Flotation tests were performed on methylated quartz particles (P80 = 100 μm) over a range of power intensities (0.015–0.60 W/kg) and using three different bubble sizes, generated by sintered glass discs (0.13, 0.24 and 0.82 mm). The flotation rate constant was found to increase approximately linearly with increasing particle size for all three bubble sizes. This was due to the increased probability of collision for larger particles and is well established in the flotation literature. A number of researchers have found that the flotation rate constant for quartz particles increases almost linearly with particle size, at low power intensities. An inverse power relationship was observed between bubble size and flotation rate constant for all fine, middling and coarse particle size ranges. This inverse power relationship was due to the increased probability of collision for smaller bubbles and is also well established in the flotation literature. More significantly, the flotation rate constant was found to increase almost linearly with increasing power intensity for all particle and bubble sizes used in this study. The majority of theoretical and experimental studies have found energy input to have less of an effect than the proportional/linear dependence observed in this study. In addition, the increase in the flotation rate constant with increasing power intensity was observed to depend on particle size, but to be less dependent on bubble size. These findings suggest that energy input and bubble size may respectively play more and less of a role in promoting particle-bubble contacting in turbulent environments than was noted in the flotation literature. However, a recent study by Newell and Grano (2006) done using a stirred tank also noted this linear dependence. Given the findings of this thesis, it is strongly recommended that further work be done to investigate the OGC at higher energy intensities (~3W/kg) and to scale it up so that it can be more comparable to the widely used mechanical flotation cells. The homogeneous and nearly isotropic turbulence generated by the OGC also makes it an ideal environment to characterize floatability for different ores.
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    Flotation in a novel oscillatory baffled column
    (2008) Anderson, Christopher James; Deglon, David; Harris, Martin
    This thesis presents an evaluation of an Oscillatory Baffled Column as a novel flotation device and as a research tool for investigating the role which hydrodynamics play in promoting particle-bubble contacting. The cell differs from a conventional cell design in that bubble generation is decoupled from the power input. This allows the hydrodynamic environment to be optimised for effective particlebubble contacting. The design also incorporates a novel mechanism of agitation which provides a more even distribution of shear rate than would be obtained in a stirred system and allows considerably more variation of the power input to the cell. Based on these properties it is hypothesised that the OBC would provide an effective hydrodynamic environment for fine particle flotation, particularly in highly viscous, non-Newtonian slurries. It is also hypothesised that the development of such a cell technology will facilitate an improved understanding of the role which hydrodynamics play in promoting particle-bubble contacting. To investigate these hypotheses, the OBC was first characterised in terms of key flotation parameters, such as bubble size, gas hold-up and mixing. The cell was then flotation tested on quartz, in order to benchmark the study against previous studies on hydrodynamics and particle-bubble contacting in stirred systems. Finally, the OBC was tested in application to a highly viscous, non-Newtonian nickel ore slimes slurry which is difficult to treat using conventional cell technologies. This study gave context to the potential future role of OBC technology in the minerals processing industry. The results of this thesis clearly show that the OBC is a promising novel technology for the treatment of fine mineral slurries. The cell has been demonstrated to significantly improve flotation kinetics by a factor of between 1.4 and 1.6 relative to a standard column. Optimal flotation conditions were obtained at power dissipations as low as 10 W/m3. The advantages of the OBC as a novel device include its ability to decouple bubble generation and particle-bubble contacting, its even distribution of shear rate in the cell as well as the additional fluctuating fluid motion produced under oscillatory flow. Furthermore, the flotation kinetics in the cell were shown to be unaffected by slurry rheology indicating the cell is best suited to niche application in the processing of ore types exhibiting highly viscous non-Newtonian behaviour.
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    Investigating the effect of energy dissipation on flotation kinetics in an oscillating grid flotation cell
    (2011) Massey, Wesley Thomas; Deglon, David A; Harris, Martin
    This thesis investigates the effect of energy dissipation on the flotation kinetics of quartz in an oscillating grid flotation cell. Oscillating grids exhibit relatively isotropic and homogeneous turbulence, which cannot be achieved in standard impeller agitated flotation cells. Due to this they provide a potentially ideal environment in which to investigate the effects of energy dissipation on flotation kinetics. Previous work in an oscillating grid flotation cell was limited to energy dissipations of up to 0.6 kW/m³, which is low when compared to 0.6 - 3 kW/m³ commonly used in both flotation literature and industry. The current work uses a new oscillating grid cell which can operate at energy dissipations of up to 5 kW/m³. Quartz (sub 100 μm) has been floated in the new cell at energy dissipations ranging from 0.5 - 5 kW/m³ and using three discrete bubble sizes (0.13 mm, 0.24 mm and 0.82 mm). Characterisation experiments show that the new cell operates in a similar manner to the oscillating grid cell used by Changunda et al. (2008), and produces repeatable results. The effect of changing bubble and particle size on flotation kinetics is in agreement with literature findings, indicating that as a flotation device the oscillating grid cell is operating as expected.
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    An investigation of particle collection efficiency in different particle-bubble contacting environments in flotation
    (1995) Breytenbach, Jacobus Nicolaas; Franzidis, Jean-Paul; Harris, Martin; O'Connor, Cyril
    The 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.
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    Relationship between froth behaviour and the properties of particles
    (2011) Tesh, Ditend Kanyik; Franzidis, Jean-Paul; Harris, Martin
    The aim of this project was to gain an insight into how the properties of particles entering the froth affect the performance of the froth phase. In platinum group mineral (PGM) flotation, gangue minerals are known to have a stabilizing effect on the froth phase; in this project, their hydrophobicity was changed by the addition of depressant and the performance of the froth phase was measured in terms of froth recovery.
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    Rheological effects on gas dispersion in a pilot scale mechanical flotation cell
    (2013) Shabalala, Ntokozo Zinhle Precious; Deglon, David A; Harris, Martin
    Froth flotation is a separation method used for the beneficiation of a considerable portion of the world's mineral ores. The majority of flotation occurs in mechanical flotation cells, where effective gas dispersion is a primary requirement for particle-bubble contacting. Due to the mineralogical complexity of ores, it is required that particles be ground even finer to liberate valuable minerals. Mining operations tend to run flotation circuits at fairly high solids concentrations in order to maximise residence time, accommodate higher tonnages and limit water consumption. Mineral slurries processed at fine particle sizes and high solids concentrations have been shown to exhibit non-Newtonian rheological behaviour. The effect of slurry rheology on gas dispersion in a 100 litre mechanical flotation cell was investigated by varying the solids concentration. The study was conducted using kaolin, Bindura nickel and Platreef slurries. All three ores displayed typical non- Newtonian rheological behaviour where the slurry yield stress and viscosity increased exponentially with solids concentration. Bubble size varied from 0.55 to 1.10 mm for all the ores tested. At low solids concentration bubble size was found to decrease with impeller speed, a characteristic trend that was expected. At moderate solids concentrations bubble size was found to either increase/remain relatively constant with impeller speed; this trend was also expected. Unexpectedly, at the highest solids concentration, a dramatic decrease in bubble size was observed. This unexpected drop in bubble size was attributed to slurry rheology. It was also observed that there was a slight increase in bubble size at the highest solids concentration with increasing impeller speed. This increase was attributed to a trade-off relationship between the rheology of the slurries and the existing hydrodynamics (as a result of the rotating impeller). Gas hold-up varied from 2 to 15% across all the ores tested. At low solids concentrations gas hold-up increased with impeller speed as expected. At moderate solids concentration gas hold-up was viewed to either increase/remain relatively constant with impeller speed. A significant drop in gas hold-up was observed at the highest solids concentration. The gas hold-up however still increased with impeller speed albeit at a lower rate at the highest solids concentrations. This drop in gas hold- up at the highest solids concentration (along with the decrease in bubble size) was attributed to the effect of slurry rheology. At high solids concentrations, all three slurries (kaolin, Bindura nickel and Platreef) exhibit non-Newtonian behaviour illustrated by means of high viscosities and yield stresses. High viscosities result in turbulence damping in the cell which inhibits bubble break-up, resulting in larger bubbles and correspondingly lower gas hold-up. It was concluded in this study that the yield stress is the dominant rheological property due to the significant changes observed with increasing solids concentration. High yield stresses resulted in the formation of a 'cavern' of slurry around the impeller region. Within this 'cavern', high power intensities exist around the impeller where small bubbles are formed. However due to the formation of the 'cavern', the slurry in the bulk cell remains relatively stagnant. As a result small bubbles formed around the impeller remain localised in the 'cavern' and cannot be dispersed throughout the cell. This localization and poor dispersion of bubbles resulted in low gas hold-ups.
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    The use of machine vision to describe and evaluate froth phase behaviour and performance in mineral flotation systems
    (2010) Morar, Sameer Harish; Bradshaw, Dee; Harris, Martin
    Within froth flotation, it is widely acknowledged that froth stability affects flotation performance. As a result, it is expected that through the effective management of froth stability, it would be possible to both control and optimise a flotation cell and bank. However, for this to be possible, the relationships between the operating conditions, froth stability behaviour and flotation performance attributes need to be well understood. In addition, froth stability would need to be measured using a robust method suitable for on-line operation. Within the literature, no robust methods are available to measure either the concentration of solids on the froth surface, or froth stability in a manner suitable for on-line operation. Thus, two novel non-intrusive machine vision measurements have been developed in this work to quantify these attributes.