Browsing by Author "Deglon, David"

Now showing 1 - 14 of 14
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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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    The effect of ore blends on the mineral processing of platinum ores
    (2011) Van Tonder, Erika; Deglon, David
    This thesis investigates the effect of ore blends on milling and flotation performance. Anglo Platinum's Waterval UG2 concentrator in Rustenburg processes ore from various shafts.
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    The effect of phyllosilicate mineralogy and surface charge on the rheology of mineral slurries
    (2013) Ndlovu, Bulelwa; Deglon, David; Becker, Megan; Forbes, Elizaveta
    Phyllosilicate minerals exist as common gangue components in many low grade ores. Often broadly classified as ‘clays’, this group of minerals is closely associated with several processing issues. Despite many good studies on the physico-chemical properties of phyllosilicates, there still remains a poor understanding of their suspension flow behaviour. The primary objective of this thesis was to characterise the colloidal behaviour of three commonly occurring phyllosilicates, namely muscovite, vermiculite and chrysotile in terms of their surface charge, mineralogical and resultant rheological properties. The thesis was initiated in order to gain a better understanding of the flow behaviour of these minerals within well-defined model mineral systems, with a longer term view to understanding their impact in complex mineral systems found in mineral processing circuits.
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    Evaluation of an Attachment–Detachment Kinetic Model for Flotation
    (2020-11-02) Safari, Mehdi; Deglon, David
    This paper compares model predictions from a novel kinetic model with data from five fundamental single-mineral literature flotation datasets. The empirical correlations proposed by Safari and Deglon (2018) are modified to improve their robustness, requiring only a single best-fit regression coefficient per mineral type. Experimental and model-predicted rate constants were compared on a parity chart where a reasonable linear correlation was observed, with a gradient of 0.95 and an overall R2 value of 0.97. Thereafter experimental and model-predicted trends from the flotation datasets were compared for particle size, contact angle, agitation, and gas flow rate. Model-predicted trends were reasonably accurate for most of the flotation datasets, but under-predicted the rate constant for larger particles for the data of Pyke (2004). In general model predictions were reasonably accurate, which is considered quite good, as these were obtained by fitting a single parameter per mineral type to several large flotation datasets, totaling 330 rate constants.
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    The evaluation of solids suspension in a pilot scale mechanical flotation cell
    (2004) Van der Westhuizen, Andries P P; Deglon, David
    The central step in flotation is particle collection, with solids suspension together with gas dispersion and reagent mixing as necessary preconditions for particle collection. Solids suspension is therefore often identified as an important subprocess for effective flotation. Yet, surprisingly little work has been published on solids suspension in mechanical flotation cells, especially more recent studies since the advent of round mechanical flotation cells and the subsequent dramatic increases in maximum cell sizes are largely lacking.
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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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    A hydrodynamic investigation of platinum flotation in a pilot flotation plant
    (2003) Lewis, Jonathan Stretton; Deglon, David; O'Connor, Cyril
    The aim of this thesis was to determine the effect of impeller speed and air flowrate on the flotation of platinum in mechanical flotation cells.
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    Investigating the rheological behavior of Witbank coal water mixtures
    (2016) Owusu Gyebi, Prince; Deglon, David
    South Africa has large low-grade coal reserves. With the prospect of expanding its coal demands for exports and power generation, it is important that the beneficiation and transport of coal in the country are economical. The current mode of transporting coal has some drawbacks, which include inefficient rail infrastructure, long distances, and several environmental concerns related to air pollution, water pollution, and traffic risks. It is, therefore, important to investigate efficient means of coal transportation, which will also reduce environmental impacts. The transport of highly concentrated coal-water slurries through pipelines has attracted the attention of many researchers as an efficient and economical means of fine coal utilization. The primary objectives of this study are to investigate the importance of surface charge, solids concentration and particle size on the stability and rheological behaviour of Witbank coal. This work was carried out to arrive at a sounder discernment of the function of dispersion addition on coal-water mixtures rheology and stability.
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    A Methodology to Determine the Potential for Particulate Ore Sorting Based on Intrinsic Particle Properties
    (2022-05-16) Duncan, Michael; Deglon, David
    Sensor-based particulate ore sorting is a pre-concentration technique that sorts particles based on measurable physical properties, resulting in reduced energy consumption by removing waste prior to grinding. This study presents an integrated methodology to determine the potential for ore sorting based on intrinsic particle properties. The methodology first considers the intrinsic sortability based on perfect separation. Only intrinsically sortable ore is further assessed by determining the sensor-based sortability. The methodology is demonstrated using a case study based on a typical copper porphyry comminution circuit. The sorting duty identified for the case study was the removal of low-grade waste material from the pebble crusher stream at a suitable Cu cut-off grade. It was found that the ore had the potential to be sorted based on the intrinsic and ideal laboratory sensor sortability results but showed no potential to be sorted using industrial-scale sensors. The ideal laboratory XRF sensor results showed that around 40% of mass could be rejected as waste at copper recoveries above 80%. An economic analysis of the sortability tests showed that, at optimum separation conditions, the intrinsic, ideal sensor and industrial sensor sortability would result in an additional annual profit of ~$30 million, $21 million and $−7 million (loss), respectively.
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    Modeling of flow in impeller stirred tanks using computational fluids dynamics
    (2004) Siwale, Namwawa Alice; Meyer, Chris; Deglon, David
    The efficiency of mixing processes in impeller agitated tanks depends highly on the hydrodynamics. Computational fluids dynamics (CFD) provides a method of predicting the complex flow structures in stirred tanks. As with any approximate numerical method, CFD methods are subject to errors due to assumptions in the underlying mathematical models, as well as errors due to the numerical solution procedures. The aim of this thesis was to present a CFD method that accurately models the hydrodynamic properties of the 110w in stirred tanks. The general purpose CFD software Fluent 6. 1 was used to develop the model of a laboratory scale stirred tank. Numerical experiments were conducted to investigate the effects of the computational grid density, discretization schemes, turbulence models and impeller modelling method on the accuracy of the simulated flow. The results were validated with Laser Doppler Velocimetry data from the literature. It was found that the density of the numerical grid had more influence on the predicted turbulent quantities than on the mean velocity components. For the mean velocity components, reasonable agreement with the experimental data was observed even on relatively coarse grids. The choice of discretization scheme was found to have significant effect on the predicted turbulent kinetic energy and Power numbers. Very good agreement with experimental data was achieved for both these flow variables when higher order discretization schemes were used on fine grids. This is an important finding as it suggests that the generally reported underestimation of turbulence in literature is caused by numerical errors in the CFD simulation as opposed to inadequacies in the turbulence models as suggested by most researchers. Steady-state and time-dependent impeller models were compared and found to have little effect on the mean velocity and turbulent kinetic energy. However impeller Power numbers calculated from the time-dependent simulations were found to be in better agreement with the experimental values. A comparison was also made between the standard k-s and RNG models. It was found that the standard k-s turbulence model gave better predictions of the flow than the RNG- k-s turbulence model.
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    Multiphase CFD modelling of stirred tanks
    (2007) Appa, Harish; Deglon, David; Meyer, CJ
    Stirred tanks agitated with Rushton turbines are commonly used in industry, for instance mixing processes and flotation systems. The need for more efficient systems in industries has led to the study of fluid flow within the tanks upon agitation; so that a better understanding of the phenomena can help in the optimisation of the tanks. In the recent years, efforts have been made towards the development of predictive methods using computational fluid dynamics (CFD). Among the various numerical works presented, emphasis was laid mainly on single phase systems. However, due to the various processes involving gas-liquid systems, the need for multiphase modelling of stirred tanks became increasingly important. This has led to more research studies involving multiphase flows. Most of the work reported showed good prediction of the velocity data and the power draw, reasonable turbulence parameters. But, the prediction of the gas hold-up was rarely well established. Therefore, the aim of this thesis, based on the numerical work presented by Engelbrecht (2006), is to investigate the discrepancies reported and to develop a multiphase model of a stirred tank agitated by a Rushton turbine. The commercially available CFD code FLUENT@ was used to model the agitated gas-liquid system. The results were validated with the numerical work of Engelbrecht (2006) and the experimental work presented by Deglon (1998). Two main cases were investigated, with a steady state and a transient approach. The QUICK scheme was used for the discretisation of the volume fraction and momentum and the first order upwind scheme for the discretisation of the turbulent kinetic energy and dissipation rate. The standard k - E turbulence model was used to account for the turbulent flow regime. A steady state MRF model was used for the investigation of the discrepancy reported by Engelbrecht (2006). The author reported that no convergence was achieved with such models. Solving the problem would have resulted in a good modelling approach for the prediction of gas dispersion, since steady state models are not computationally intensive. Three different boundary conditions, namely, a pressure outlet, an outflow and a velocity inlet, were used to model the outlet of the tank. The Euler-Euler multiphase model was used to simulate the gas-liquid system for the steady state model.
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    Numerical modelling of hydrodynamics, gas dispersion and mass transfer in an autoclave
    (2012) Appa, Harish; Deglon, David; Meyer, CJ
    Includes abstract. Includes bibliographical references.
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    Process Evaluation of an Iron Ore Operation Using the Floatability Component Model
    (2021-05-31) Geldenhuys, Stefan; Pinto, Thiago Souza; Filho, Laurindo Leal; Deglon, David
    The Brucutu iron ore mine (Minas Gerais, Brazil) is Vale‘s largest iron producing operation achieving around 21 million tons per annum. Evaluation of flotation performance is of high importance as even small gains can lead to large monetary benefits. Cell-by-cell samples of the froth products, selected feed and pulp-products were analyzed for flow rate, particle size distribution and chemical composition. In addition, certain samples were analyzed on an assay-by-size basis and hydrodynamic measurements of certain flotation cells were also performed. This detailed experimental dataset was then used to calibrate a floatability component model of the process. Longer mainline residence time resulted in significant Fe2O3 losses while yielding little benefit in terms of SiO2 product grade. Scavenger 2 has twice the residence time of scavenger 1 while having to treat only 10% of the SiO2, resulting in high Fe2O3 recoveries to the froth and poor separation. In addition, it is shown that the Fe2O3 exhibits true flotation behavior resulting in increased Fe2O3 losses. Simulations using the floatability component model identified avenues of process improvement to address the identified behavior. The insight provided by the simulations into the dynamics of the flotation process is invaluable for process engineers.
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    Study on the thermodynamics and kinetics of the stripping of palladium from a typical palladium organic
    (2005) Brits, Johannes Hendrik Wilhelmus Machiel; Deglon, David
    The aim of this thesis was to investigate the thermodynamics and the kinetics of the stripping of palladium from a typical palladium organic. The thesis firstly characterizes the thermodynamic effects of temperature and strip acid normality on the stripping of palladium and secondly investigates the kinetics of the palladium stripping reaction by exploring the effect of impeller speed and type on the overall volumetric mass transfer coefficient. which was the major focus of this thesis.