Browsing by Author "Deglon, David A"

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    Open Access
    Development of a heuristic methodology for designing measurement networks for precise metal accounting
    (2016) Bepswa, Paul Aaron; Deglon, David A
    This thesis investigates the development of a heuristic based methodology for designing measurement networks with application to the precise accounting of metal flows in mineral beneficiation operations. The term 'measurement network' is used to refer to the 'system of sampling and weight measurement equipment' from which process measurements are routinely collected. Metal accounting is defined as the estimation of saleable metal in the mine and subsequent process streams over a defined time period. One of the greatest challenges facing metal accounting is 'uncertainty' that is caused by random errors, and sometimes gross errors, that obtain in process measurements. While gross errors can be eliminated through correct measurement practices, random errors are an inherent property of measured data and they can only be minimised. Two types of rules for designing measurement networks were considered. The first type of rules referred to as 'expert heuristics' consists of (i) Code of Practice Guidelines from the AMIRA P754 Code, and (ii) prevailing accounting practices from the mineral and metallurgical processing industry which were obtained through a questionnaire survey campaign. It was hypothesised that experts in the industry design measurement networks using rules or guidelines that ensure requisite quality in metal accounting. The second set of rules was derived from the symbolic manipulation of the general steady-state linear data reconciliation solution as well as from an intensive numerical study on the variance reduction response of measurements after data reconciliation conducted in this study. These were referred to as 'mathematical heuristics' and are based on the general principle of variance reduction through data reconciliation. It was hypothesised that data reconciliation can be used to target variance reduction for selected measurements by exploiting characteristics of entire measurement networks as well as individual measurement characteristics.
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    Development of a protocol to determine the sorting potential of particulate ore material
    (2016) Duncan, Michael Graeme; Deglon, David A
    The objective of this research was to develop a protocol/ methodology to determine the potential for an ore to be sorted using sensor-based sorting. The research builds upon previous methodologies in literature to determine ore sortability. The first attempt to create a standard methodology to assess the amenability of an ore to sorting at a pilot-scale was developed by Fitzpatrick (2008). Tong (2012) developed a methodology to assess the amenability of an ore to sensor-based sorting on an ideal laboratory-scale. These methodologies focus on determining the upgrading potential of an ore based on ore sorting amenability tests. In order to gain further acceptance of sorting technology in the mining industry, Lessard et al. (2015) developed a method to determine the impact of ore sorting on an operation from an economic perspective. The protocol, developed during the current research, is used to determine the potential ore sortability based, firstly, on intrinsic particle properties and, secondly, based on laboratory-scale sensor sortability tests using ideal and industrial sensor measurement parameters. The intrinsic sortability results represent the ideal/ best- case sortability if a perfect separator existed and are calculated based on particle-by-particle ore characterisation. Ore that is intrinsically sortable is further assessed based on ideal laboratory-scale sensor sort ability tests using selected sensors. Ore sorting sensors that show potential based on the ideal sensor tests are further assessed by determining the sort ability of the ore using sensor measurement parameters similar to those used on industrial-scale ore sorting machines
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    Open Access
    The effect of energy input on flotation kinetics
    (2018) Safari, Mehdi; Deglon, David A
    SYNOPSIS Energy/power input in a flotation cell is an important parameter which, if optimised, can increase the flotation rate. The optimum energy/power input within a flotation cell is still a matter of conjecture and there is a need for a better understanding of the effect of energy input on flotation kinetics. This study investigates the effect of energy/power input on flotation kinetics in an oscillating grid flotation cell (OGC). The OGC decouples the processes of solid suspension and bubble generation as well as producing relatively isotropic and homogeneous turbulence with zero mean flow. Due to this, oscillating grids provide a potentially ideal environment for investigating the effects of energy input on flotation kinetics, which cannot be achieved in a mechanical flotation cell. The first objective of this thesis was to determine the effect of energy/power input on the flotation kinetics of sulphide minerals (galena, pyrite & pentlandite) and oxide minerals (apatite & hematite) in a laboratory scale oscillating grid flotation cell. The second objective was to compare the results from the laboratory OGC to comparative studies in the flotation literature and to fundamental models for particle-bubble contacting. The third objective was to determine whether the experimental results from the laboratory OGC are consistent with those from a pilot-scale OGC operating on a platinum ore. Galena, pyrite, pentlandite (-150 μm), apatite (-650 μm) and hematite (-75 μm) were floated in the laboratory OGC at energy inputs from 0.1 to 5.0 W/kg, using 0.13, 0.24, 0.58 and 0.82 mm bubble sizes (d₁₀), and at three collector dosages. Platinum ore (-75 μm) was floated in the pilot-scale OGC at energy inputs from 0 to 2.5 W/kg, using 0.71 and 1.47 mm bubble sizes (d₁₀). The effect of energy input on flotation kinetics was interpreted through trends in experimental flotation rate constants, simulated flotation rate constants and attachment-detachment flotation rate constants. Here, simulated flotation rate constants were calculated using a literature fundamental model for flotation in turbulent systems. This model is based on suitable expressions for the collision frequency, collision efficiency, attachment efficiency and stability efficiency, Attachment-detachment flotation rate constants were calculated using a kinetic model which allows for the two separate processes of bubble-particle collision/attachment and detachment. This model is based on kinetic expressions using empirical correlations for the attachment and detachment rate constants. Experimental flotation results show that the effect of energy input on the flotation rate is strongly dependent on the particle size and particle density and less dependent on bubble size and contact angle. Flotation rates generally increase with increasing particle size, decreasing bubble size and increasing contact angle, as is commonly found in the literature. Increasing energy input generally leads to an increase in the flotation rate for fine particles, an optimum flotation rate for intermediate particles and a decrease in the flotation rate for coarse particles. The optimum in the flotation rate for minerals with higher density is at a lower energy input than that for lower density minerals. The changes (increases/decreases) in the flotation rate with increasing energy input are very large for most of the conditions, indicating that this is an important parameter in flotation. Pilot scale results generally support the trends observed in the laboratory OGC. These findings are attributed to the effect of energy/power input on bubble-particle collection which is a balance between two competing effects, those of bubble-particle collision/attachment and those of bubble-particle detachment. Increasing energy input generally leads to significant increases in the flotation rate of fine particles, due to increased bubble-particle collision/attachment. Increasing energy input generally leads to an optimum flotation rate for intermediate particles, due to a combination of increased bubble-particle collision/attachment and detachment. For coarse particles, increasing energy input leads to significant increases in bubble-particle detachment. The relationship between the flotation rate and energy input is often described as k  ɛᴺ, in the absence of significant bubble-particle detachment. The typical values of N are in the range of 0.44-0.75 for theoretical studies and 0.7-1 for experimental studies. The values of N found in the current study are in the range of 0.7-1, which suggests that bubbleparticle collision/attachment has a stronger dependence on energy input than theory suggests. Simulated flotation results for fine particles compare well to the experimental data in terms of both trends and magnitude. This suggest that the turbulent collision model used is appropriate for fine particles. For intermediate particles there are differences between the simulated flotation rate constants and the experimental data, primarily in terms of trends. For coarse particles there are very large differences between simulated flotation rate constants and the experimental data. This is attributed to under prediction of the collision frequency/efficiency and incorrect prediction of the stability efficiency. Here, the stability efficiency is considered to be under predicted at low energy inputs and over predicted at high energy inputs. This suggests that the stability efficiency has a much stronger dependence on energy input than theory suggests. Attachment-detachment results show that the attachment rate constant has a stronger dependence on energy input than theory suggest, supporting finding from the experimental results and simulated results for coarser particles. In addition, the detachment rate constant has a much stronger dependence on energy input than theory suggests, supporting findings from both the experimental and simulated results. Based on the objectives of this study and literature reviewed, the following hypotheses were made at the outset 1) Increasing energy/power input will increase the rate of flotation of fine particles but will result in an optimum for intermediate and coarse particles. The position of this optimum will depend on the particle density, bubble size and contact angle. 2) Fundamental models based on the RMS turbulent velocity will be appropriate for describing flotation kinetics as turbulence in the oscillating grid cell is relatively homogeneous and isotropic and 3) Trends in flotation results for a laboratory and pilot-scale oscillating grid flotation cell will be comparable as the distribution of turbulence in OGCs at equivalent specific power inputs is scale independent. Hypothesis 1 was found to be valid for both fine and intermediate particles, but for coarse particles increasing energy input resulted in sharp decreases in the flotation rate. In addition, the increase in the flotation rate with increasing energy input was found to be more dependent on the particle size and particle density than the bubble size and contact angle. Hypothesis 2 was found to be valid for fine particles but not for intermediate or coarse particles. Here, it was found that the processes of bubble-particle collision/attachment and detachment have a stronger dependence on energy input than theory suggests. Hypothesis 3 was supported by general trends in results for the laboratory and pilot-scale oscillating grid flotation cells, but was not convincingly demonstrated.
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    Open Access
    The effect of energy input on precipitation in an oscillating grid reactor
    (2010) Mokgethi, Botlhe Tshimologo; Deglon, David A; Lewis, Alison Emslie
    The move to cleaner production has led to the process industry aiming at producing chemicals in a pure form and at the lowest possible cost. In practice this has resulted in a shift from treating processes as "black boxes" towards developing more concise models which reveal what happens within these "black boxes". This shift can be discerned at plant level for better control mechanisms, at a reactor design level to incorporate the effect of hydrodynamics and even at a molecular level when designing a tailor-made catalyst.
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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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    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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    Water minimisation at Skorpion zinc
    (2009) Bhikha, Harshad; Lewis, Alison Emslie; Deglon, David A
    This work proposes a systemic optimisation of the water balance of the Skorpion Zinc refinery, the case study selected for this work. The Skorpion process is located in Rosh Pinah in Namibia and was selected due to its location on an ecologally sensitive region where water is scarce. The project proposes that peocess optimisation cannot occure through focus on unit operations in isolation, but rather to use the interactions between the different operations to optimise the process systematically.