Imperial College London

DrKathrynHadler

Faculty of EngineeringDepartment of Earth Science & Engineering

Honorary Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 6510k.hadler

 
 
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Location

 

2.60Aston WebbSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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41 results found

Malone L, Cardin M-A, Cilliers JJ, Hadler Ket al., 2023, Exploring Novel Architectures in Lunar In-Situ Resource Utilisation, Brisbane, Australia, 26th World Mining Congress

Conference paper

Malone L, Cardin M-A, Cilliers J, Hadler Ket al., 2022, Development of a Comprehensive Lunar Mining Simulator to Study Design and Decision-Making under Uncertainty, Paris, France, International Astronautical Congress

Conference paper

Rasera JN, Cruise RD, Cilliers JJ, Lamamy J-A, Hadler Ket al., 2022, Modelling the tribocharging process in 2D and 3D, Powder Technology, Vol: 407, Pages: 1-12, ISSN: 0032-5910

Many discrete element method (DEM) tribocharging models presented in the literature rely on ill-defined or poorly quantified charging parameters. This work presents a straightforward experimental method to quantify key parameters, namely the charge transfer limit, Γ, and the charging efficiency, κc. These parameters are then used in both 2D and 3D DEM simulations to evaluate the applicability of faster 2D models to tribocharge modelling. Both the 2D and 3D models are found to perform well against the experimental data for single-contact and single-particle, multi-contact systems. However, the 2D model fails to produce good agreement with experimental data for multi-contact, multi-particle systems. This approach for determining experimentally the parameters for the DEM tribocharging model is found to be effective and produces good agreement between simulated and experimental data. This method will improve and simplify the DEM modelling of triboelectric charging in dry material handling processes.

Journal article

Cole K, Brito-Parada PR, Hadler K, Mesa D, Neethling SJ, Norori-McCormac AM, Cilliers JJet al., 2022, Characterisation of solid hydrodynamics in a three-phase stirred tank reactor with positron emission particle tracking (PEPT), Chemical Engineering Journal, Vol: 433, Pages: 1-13, ISSN: 1385-8947

It is challenging to measure the hydrodynamics of stirred tank reactors when they contain multiphase flows comprising liquid, gas bubbles and particles. Radioactive particle tracking techniques such as positron emission particle tracking (PEPT) are the only established techniques to determine internal flow behaviour due to the inherent opacity and density of fluid and the vessel walls. The profiles of solids flow are an important tool for robust reactor design and optimisation and offer insight into underlying transport processes and particle–fluid–bubble interactions for applications such as froth flotation. In this work, measurements with PEPT were performed with two tracer particles differing in surface hydrophobicity to characterise the solids hydrodynamics in a baffled vessel agitated with a Rushton turbine. The location data from PEPT were averaged with time to estimate the probability density function (PDF) of particle velocity in individual voxels. The peaks of these voxel distributions were used to produce profiles of solids flow in different azimuthal and horizontal slices. Bimodal vertical velocity distributions were observed in the impeller radial jet which suggest the particles experienced trajectory crossing effects due to inertia. Statistical tests were performed to compare the velocity distributions of the hydrophilic and hydrophobic tracer particles, which indicated similar average flow behaviour in the liquid or pulp phase of the vessel and differences near the air inlet, in the impeller discharge stream and pulp–froth interface. With tracers designed to represent gangue and valuable mineral species, the differences in velocity reveal interactions such as bubble–particle attachment and entrainment.

Journal article

Cole K, Barker DJ, Brito-Parada PR, Buffler A, Hadler K, Mackay I, Mesa D, Morrison AJ, Neethling S, Norori-McCormac A, Shean B, Cilliers Jet al., 2022, Standard method for performing positron emission particle tracking (PEPT) measurements of froth flotation at PEPT Cape Town, MethodsX, Vol: 9, Pages: 101680-101680, ISSN: 2215-0161

Positron emission particle tracking (PEPT) is a technique for measuring the motion of tracer particles in systems of flow such as mineral froth flotation. An advantage of PEPT is that tracer particles with different physical properties can be tracked in the same experimental system, which allows detailed studies of the relative behaviour of different particle classes in flotation. This work describes the standard operating protocol developed for PEPT experiments in a flotation vessel at PEPT Cape Town in South Africa. A continuously overflowing vessel with constant air recovery enables several hours of data acquisition at steady state flow and consistent flotation conditions. Tracer particles are fabricated with different coatings to mimic mineral surface hydrophobicity and size, and a data treatment derived from a rotating disk study is utilized to produce high frequency (1 kHz) location data relative to the tracer activity. Time averaging methods are used to represent the Eulerian flow field and occupancy of the tracer behaviour based on voxel schemes in different co-ordinate systems. The average velocity of the flow in each voxel is calculated as the peak of the probability density function to represent the peak of asymmetrical or multimodal distributions.•A continuously overflowing flotation vessel was developed for extended data acquisition at steady state flow.•The data treatment enabled the direct comparison of different particle classes in the flotation vessel.•The solids flow fields was described by the probability density function of tracer particle velocity measured in different voxel schemes.

Journal article

Cruise RD, Hadler K, Starr SO, Cilliers JJet al., 2022, The effect of particle size and relative humidity on triboelectric charge saturation, Journal of Physics D: Applied Physics, Vol: 55, Pages: 1-14, ISSN: 0022-3727

Triboelectric charging is present in numerous technologies and everyday processes, providing both problems and opportunities. Despite this, there is no generalised model for the amount of charge that will build up on surfaces in contact. Here, we develop a new model for the saturation charge on triboelectrically charged spherical insulators, accounting for both equalisation of surface potentials and electrical breakdown of the surrounding medium. Experiments are conducted under controlled temperature and humidity using two independent methods, measuring the saturation charge on polymer spheres contacting grounded stainless steel. The results verify our equalisation of surface potentials model which describes how saturation charge density increases for smaller particle sizes. Key triboelectric properties are calculated: The estimated saturation charge on a flat surface and the equalisation potential between different materials, which can be used to predict charge saturation and quantify a triboelectric series. The transition radius below which electrical breakdown will cause saturation of charge is also calculated theoretically. Limitations to the model are demonstrated experimentally. As particle size reduces, a point is reached at which the electrostatic adhesion of particles to the grounded charging surface prevents further charge build-up. Furthermore, it is found that the saturation charge for smaller particles in humid conditions is greatly reduced. These calculations, and the demonstrated procedure, can serve as a tool for the design of technologies and processes influenced by triboelectric charge build-up, including triboelectric nanogenerators and electrostatic mineral separators.

Journal article

Rasera J, Cilliers J, Lamamy J-A, Hadler Ket al., 2020, The beneficiation of lunar regolith for space resource utilisation: A review, Planetary and Space Science, Vol: 186, ISSN: 0032-0633

Space Resource Utilisation (SRU) technology will enable further exploration and habitation of space by humankind. The production of oxygen on the Moon is one of the first objectives for SRU; this can be achieved through the thermo-chemical reduction of the lunar regolith. Several techniques, such as hydrogen reduction and molten salt electrolysis, have been proposed. All reduction techniques require a consistent feedstock from the regolith to reliably and consistently produce oxygen. The preparation of this feedstock, known as beneficiation, is a critical intermediate stage of the SRU flowsheet, however it has received little consideration relative to the preceding excavation, and the subsequent oxygen production stage. This review describes the physics of the main beneficiation methods suitable for SRU. Further, we collate and review all of the previous studies on the beneficiation of lunar regolith.

Journal article

Hadler K, Martin DJP, Carpenter J, Cilliers JJ, Morse A, Starr S, Rasera JN, Seweryn K, Reiss P, Meurisse Aet al., 2020, A universal framework for Space Resource Utilisation (SRU), Planetary and Space Science, Vol: 182, Pages: 1-5, ISSN: 0032-0633

Space Resource Utilisation (SRU) or In Situ Resource Utilisation (ISRU) is the use of natural resources from the Moon, Mars and other bodies for use in situ or elsewhere in the Solar System. The implementation of SRU technologies will provide the breakthrough for humankind to explore further into space. A range of extraction processes to produce useable resources have been proposed, such as oxygen production from lunar regolith, extraction of lunar ice and construction of habitation by 3D printing. Practical and successful implementation of SRU requires that all the stages of the process flowsheet (excavation, beneficiation and extraction) are considered. This requires a complete ‘mine-to-market’ type approach, analogous to that of terrestrial mineral extraction.One of the key challenges is the unique cross-disciplinary nature of SRU; it integrates space systems, robotics, materials handling and beneficiation, and chemical process engineering. This is underpinned by knowledge of the lunar or planetary geology, including mineralogy, physical characteristics, and the variability in local materials. Combining such diverse fields in a coordinated way requires the use of a universal framework. The framework will enable integration of operations and comparison of technologies, and will define a global terminology to be used across all fields. In this paper, a universal SRU flowsheet and terminology are described, and a matrix approach to describing regolith characteristics specifically for SRU is proposed. This is the first time that such an approach has been taken to unify this rapidly-developing sector.

Journal article

Cilliers J, Hadler K, Rasera J, 2020, Estimating the scale of Space Resource Utilisation (SRU) operations to satisfy lunar oxygen demand, Planetary and Space Science, Vol: 180, Pages: 1-8, ISSN: 0032-0633

The production of oxygen from lunar regolith is analogous to metal production from ore in a terrestrial mine. The process flowsheets both include excavation, haulage and beneficiation of the regolith or ore to provide the feedstock for the chemical extraction of oxygen or metal. The production rate of oxygen depends on the mass rate of regolith treated and the efficiency of converting the regolith to oxygen. To date, the development of Space Resource Utilisation (SRU) has been concerned with the technological development of the process, particularly the excavation and oxygen extraction. However, the required operating mass rates of the mine operation and the oxygen extraction stage have not been considered in any great detail.Previous estimates of mining scale for lunar oxygen production are reviewed, and converted to a comparable regolith mining rate of kg/h. Beneficiation of the regolith before oxygen extraction is considered, and the effects of pre-sizing and removal of a specific component, agglutinates, are considered. The oxygen yield and operational availability are also included. It is estimated that the minimum mining rate to produce 1000 kg of oxygen per annum is at least five times higher than previous estimates, 30 kg/h, for equivalent efficiency assumptions.Monte-Carlo simulations were performed for statistical confidence in the estimates of the mining mass rate and the required oxygen extraction feedstock rate. To be 95% confident that the 1000 kg/y O2 will be met, the designed mining rate should be at least 65 kg/h, and the beneficiated feedstock rate 16 kg/h.This study has revised and increased the estimate of the lunar regolith mining scale required for the production of a given amount of oxygen. It has also estimated the mass rate of feedstock required for oxygen extraction, if the regolith is first beneficiated.The findings have a significant impact on the practical implementation of lunar mining and oxygen extraction, particularly the process des

Journal article

Rasera JN, Cilliers JJ, Lamamy JA, Hadler Ket al., 2019, The beneficiation of lunar regolith using electrostatic separation for space resource utilisation, 70th International Astronautical Congress, ISSN: 0074-1795

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Differences in the electrostatic properties of materials can be exploited for both the sizing and enrichment of minerals. In this study, the motion of silica particles falling through an electrostatic field was investigated to characterise a custom free-fall electrostatic separator. The motion was affected by varying the magnitude of the electrostatic field and the spacing of the electrodes. SiLibeads (spherical silica) were sized and tribocharged in a borosilicate glass beaker and fed into the separator. Fourteen electrostatic field strengths each generated at three different electrode spacings (75 mm, 150 mm, and 225 mm) were studied. The percentage of particles reporting to each electrode was measured. Analyses of the results indicate that the expected linear increase in the field strength does not increase proportionally the amount of material reporting to each electrode, indicating that additional underlying parameters must be characterised. Further, an analysis of the variance between the measurements indicates that there are almost no significant effects on the separator's operation due to changing either the field strength or electrode spacing. However, two statistically unique operating conditions were identified. The measurements collected at a field strength of 0.04 kV/mm with a 75-mm spacing were unique relative to other field strengths at that spacing and may indicate an optimal operating condition. Further, the data collected at each electrode spacing with a constant electric field strength of 0.06 kV/mm were also found to be unique. This implies that there may be a performance dependence on electrode spacing in addition to the field strength. Further analysis and experimentation are required to draw more detailed conclusions.

Conference paper

Owens CL, Nash GR, Hadler K, Fitzpatrick RS, Anderson CG, Wall Fet al., 2019, Apatite enrichment by rare earth elements: A review of the effects of surface properties, Advances in Colloid and Interface Science, Vol: 265, Pages: 14-28, ISSN: 0001-8686

Apatite subspecies depend on their halogen and hydroxyl content; chlorapatite, hydroxylapatite and fluorapatite, with additional substitution of other elements within the lattice such as rare earth elements (REE), sodium, strontium and manganese also possible. Rare earth elements are vital to green and emerging technologies, with demand set to outstrip supply. Apatite provides a possible future source of REE. Processing rare earth deposits is often complex, with surface behaviour having a significant effect on the optimization of a process flow sheet. The effect of enrichment of natural apatite and the doping of synthetic apatite on surface behaviour can be determined by measuring the zeta potential and the isoelectric point of the mineral. In this paper, we review zeta potential studies of natural and synthetic apatite to determine the effect of elemental enrichment on surface behaviour. Fifty three studies of natural apatite and forty four studies of synthetic apatite were reviewed. The isoelectric point of apatite varied from pH 1 to pH 8.7, with studies of apatite specified to be >90% pure reducing the variation to pH 3 to pH 6.5. Of the four studies of rare earth enriched apatite found, three had IEP values between pH 3 and pH 4. A study of synthetic apatite showing enrichment of between 1 and 10% by the REE europium does not affect surface behaviour. However, no studies were found that investigated the effect of common REE processing reagents on REE enriched apatite zeta potentials. Therefore, in addition to comparing previous studies we also therefore present new zeta potential measurements of apatite from a REE enriched deposit under water and common flotation collector conditions. The IEP value of this apatite under water conditions was at pH 3.6, shifting to <3.5 under both hydroxamic acid and betacol conditions. When compared to previous studies, the behaviour of REE enriched apatite under collector conditions is similar to non-REE apatite. This res

Journal article

Neethling SJ, Brito Parada P, Hadler K, Cilliers Jet al., 2019, The transition from first to zero order flotation kinetics and its implications for the efficiency of large flotation cells, Minerals Engineering, Vol: 132, Pages: 149-161, ISSN: 0892-6875

Flotation cells have traditionally been modelled using first order kinetics, often distributed over multiple floatable species. This description is valid as long as the kinetics are not restricted by the available bubble surface area. If this carrying capacity limit is approached, the behaviour will transition toward zero order kinetics with respect to the concentration of floatable species in the pulp, with this transition being associated with a significant degradation in performance. In this paper we develop a model which describes the transition from first to zero order kinetics. A dimensionless group is introduced, which is the ratio of the flotation rate under first order kinetics to the rate at maximum bubble carrying capacity. At values of this dimensionless group much less than 1 the kinetic equation reduces to the familiar k-Sb relationship, but with a progressive deviation away from first order kinetics as the value increases through 1, with zero order kinetics obtained for values of the dimensionless group much greater than one. This dimensionless group is a function of the cell size, being proportional to the ratio of the cell volume to its cross-sectional area.Since mechanical flotation cells continue to get larger, mainly due to the capital and operating cost benefits that they provide for a given residence time, the potential for deleterious zero order effects is likely to increase. This is also why zero order behaviour is virtually never encountered at the laboratory scale. The propensity for zero order kinetics also increases with both the floatability and concentration of floatable material in the pulp, as well as with the fineness of the grind. This means that cleaner cells are likely to be very susceptible to exhibiting zero order kinetics, while scavenger cells are likely to continue to exhibit first order kinetics for any foreseeable flotation cell size. The cell size at which zero order kinetics effects will degrade the performance of rougher

Journal article

Hadler K, Cilliers J, 2019, The effect of particles on surface tension and flotation froth stability, Mining, Metallurgy & Exploration, Vol: 36, Pages: 63-69, ISSN: 2524-3470

It is widely accepted that particles stabilise flotation froths and that stable froths result in improved flotation performance. Predicting the effect of particle addition on froth stability is, however, challenging. Dynamic surface tension measurement using maximum bubble pressure presents an attractive technique to investigate the effect of surfactant and particles at the air-water interface. The range of bubble lifetimes that can be studied (typically 0.1 to 60 s) is analogous to variations in air rate in flotation cells, and the corresponding changes in surface tension give an indication to the diffusion and adsorption rates of particles at the interface. In this paper, we use dynamic surface tension measurements to investigate the effect of particles on bubble surfaces at the microscale and link this to bulk froth stability measurements carried out using a froth column. Using the maximum bubble pressure method, the results show that the addition of particles results in lower surface tension, both at the dynamic (i.e. short) bubble lifetimes and towards equilibrium (i.e. 60 s bubble lifetime). This corresponds with the bulk froth stability measurements, where the three-phase system yielded more stable froths than the surfactant only system. Furthermore, increased particle loading at the air-water interface, whether through higher surfactant concentrations or lower air rates (longer bubble lifetimes), gave lower surface tension and higher froth stability. This demonstrates the link between bubble loading and froth stability. It is proposed that the maximum bubble pressure technique can be used to predict froth stability for two- and three-phase systems, enabling the effect of particle loading to be accounted for and quantified. Moreover, the technique has the potential to allow rapid determination of particle and surfactant diffusion at the air-water interface and prediction of the corresponding effect on bulk froth behaviour.

Journal article

Shean B, Hadler K, Neethling S, Cilliers JJet al., 2018, A dynamic model for level prediction in aerated tanks, Minerals Engineering, Vol: 125, Pages: 140-149, ISSN: 0892-6875

Stirred aerated tanks are a key unit operation in many industries, including froth flotation. Reliable and robust level control is of great importance in maintaining steady operation for successful implementation of higher level optimising control strategies, particularly when such tanks are arranged in series. When changes are made to the rate of aeration, there is a corresponding change in the pulp bubble size and gas holdup (the volume fraction of air in the tank), and consequently the pulp height. Stable operation of flotation tanks must, therefore, include the effect of air rate on pulp height in level control systems, especially if air rate is being actively controlled. In this paper, a model is developed from first principles to link the change in gas holdup with variation in air rate under dynamic conditions, accounting for the variability in gas holdup with height that results from differences in gas compressibility. This is validated experimentally. In order to test the model, experiments were carried out using a 70 L laboratory tank comprising water and reagent systems. For both simple and complex changes in air rate, the model showed good agreement with the experimental results when predicting the change in pulp height at steady state. Under dynamic conditions, the experimental system exhibited a slightly slower response than is predicted by the model; this is likely to be due to the well mixed assumption not being adequately met. This model provides a method to improve the operating stability of aerated tanks through better modelling of the dynamic pulp height changes that result from changes in air flowrate. In flotation tanks, this will enable greater control over froth height, which has been found to affect significantly mass pull, froth stability and flotation performance.

Journal article

Owens CL, Nash GR, Hadler K, Fitzpatrick RS, Anderson CG, Wall Fet al., 2018, Zeta potentials of the rare earth element fluorcarbonate minerals focusing on bastnäsite and parisite, Advances in Colloid and Interface Science, Vol: 256, Pages: 152-162, ISSN: 0001-8686

Rare earth elements (REE) are critical to a wide range of technologies ranging from mobile phones to wind turbines. Processing and extraction of REE minerals from ore bodies is, however, both challenging and relatively poorly understood, as the majority of deposits contain only limited enrichment of REEs. An improved understanding of the surface properties of the minerals is important in informing and optimising their processing, in particular for separation by froth flotation. The measurement of zeta potential can be used to extract information regarding the electrical double layer, and hence surface properties of these minerals. There are over 34 REE fluorcarbonate minerals currently identified, however bastnäsite, synchysite and parisite are of most economic importance. Bastnäsite-(Ce), the most common REE fluorcarbonate, supplies over 50% of the world's REE. Previous studies of bastnäsite have showed a wide range of surface behaviour, with the iso-electric point (IEP), being measured between pH values of 4.6 and 9.3. In contrast, no values of IEP have been reported for parisite or synchysite. In this work, we review previous studies of the zeta potentials of bastnäsite to investigate the effects of different methodologies and sample preparation. In addition, measurements of zeta potentials of parisite under water, collector and supernatant conditions were conducted, the first to be reported. These results showed an iso-electric point for parisite of 5.6 under water, with a shift to a more negative zeta potential with both collector (hydroxamic and fatty acids) and supernatant conditions. The IEP with collectors and supernatant was <3.5. As zeta potential measurements in the presence of reagents and supernatants are the most rigorous way of determining the efficiency of a flotation reagent, the agreement between parisite zeta potentials obtained here and previous work on bastnäsite suggests that parisite may be processed using similar

Journal article

Hadler K, 2017, Coke float: Using flotation to upgrade coal, Coal International, Vol: 265, Pages: 16-21, ISSN: 1357-6941

Journal article

Norori-McCormac A, Brito Parada P, Hadler K, Cole K, Cilliers JJet al., 2017, The effect of particle size distribution on froth stability in flotation, Separation and Purification Technology, Vol: 184, Pages: 240-247, ISSN: 1873-3794

Separation of particles of different surface properties using froth flotation is a widely-used industrial process, particularly in the minerals industry where it is used to concentrate minerals from ore. One of the key challenges in developing models to predict flotation performance is the interdependent nature of the process variables and operating parameters, which limits the application of optimising process control strategies at industrial scale. Froth stability, which can be quantified using air recovery (the fraction of air entering a flotation cell that overflows in the concentrate as unburst bubbles), has been shown to be linked to flotation separation performance, with stable froths yielding improved mineral recoveries. While it is widely acknowledged that there is an optimum particle size range for collection of particles in the pulp phase, the role of particle size on the measured air recovery and the resulting link to changes in flotation performance is less well understood. This is related to the difficulty in separating particle size and liberation effects.In this work, the effects of particle size distribution on air recovery are studied in a single species (silica) system using a continuous steady-state laboratory flotation cell. This allows an investigation into the effects of particle size distribution only on froth stability, using solids content and solids recovery as indicators of flotation performance. It is shown that, as the cell air rate is increased, the air recovery of the silica system passes through a peak, exhibiting the same froth behaviour as measured industrially. The air recovery profiles of systems with three different particle size distributions (d80 of 89.6, 103.5 and 157.1 μm) are compared. The results show that, at lower air rates, the intermediate particle size distribution (103.5 μm) yields the most stable froth, while at higher air rates, the finest particles (89.6 μm) result in higher air recoveries. This is subseq

Journal article

Shean B, Hadler K, Cilliers JJ, 2017, A flotation control system to optimise performance using peak air recovery, Chemical Engineering Research and Design, Vol: 117, Pages: 57-65, ISSN: 0263-8762

Automatic control of industrial flotation cells and circuits presents a set of significant challenges due to the number of variables, the sensitivity of flotation cells to variation in these variables and the complexity of predicting flotation performance and/or developing a strategy for optimisation. Air recovery, a measure of froth stability, has been shown to pass through a peak as flotation cell aeration increases. Furthermore, the air rate at which the peak air recovery (PAR) is obtained results in optimal flotation performance, whether improved concentrate grade, recovery or both grade and recovery. Peak air recovery, therefore, presents a clear optimising control strategy for the operation of flotation cells which is generic to all flotation cells regardless of position in the flotation circuit. In this study, a novel control system based on PAR is developed and demonstrated using a large continuous laboratory flotation cell.In this study, a direct search optimisation algorithm based on the GSS (generating set search) methodology was developed using a 70 l continuous flotation cell operating with a two-phase system (surfactant solution and air only). Characterisation of the laboratory system showed that it was stable for up to 6 h and exhibited a reproducible peak in air recovery. A dynamic model of the response of the system with regards to changes in air recovery was developed that allowed simulations of the proposed optimising control system to be carried out. The optimisation algorithm was then applied to the experimental system. The trialled GSS algorithm was shown to find the PAR air rate when starting above, below and at the PAR air rate, and additionally with a disturbance introduced into the system. While the direct search approach can be slow, it is simple and robust. This demonstrates an innovative approach to optimising control for froth flotation and is the first application of froth stability maximisation for flotation control.

Journal article

Hadler K, 2015, The link between froth surface grade and flotation feed grade, MINERALS ENGINEERING, Vol: 78, Pages: 32-37, ISSN: 0892-6875

Journal article

Morris G, Hadler K, Cilliers J, 2015, Particles in thin liquid films and at interfaces, Current Opinion in Colloid & Interface Science, Vol: 20, Pages: 98-104, ISSN: 1359-0294

The behaviour of small particles at interfaces and in thin liquid films has been studied for many years and recent advances in experimental and numerical techniques have allowed a wealth of new research to be conducted. This manuscript reviews the last five years of work investigating the effect of particle shape and packing density on their behaviour when attached to a thin liquid film or at an interface between two immiscible fluids. We discuss advances at the individual particle scale, covering shape and surface heterogeneity, as well as breakthroughs in experimental and numerical modelling of larger scale systems.

Journal article

Cole K, Brito-Parada PR, Morrison A, Govender I, Buffler A, Hadler K, Cilliers JJet al., 2014, Using positron emission tomography (PET) to determine liquid content in overflowing foam, Chemical Engineering Research & Design, Vol: 94, Pages: 721-725, ISSN: 1744-3563

Journal article

Norori-McCormac A, Hadler K, Cilliers JJ, 2014, Peak Air Recovery: An investigation into the effect of particle size

Air recovery, the fraction of air entering a flotation cell that overflows the cell lip, is linked to flotation performance, and it has been shown through industrial testwork that operating flotation cells at air rates that yield the Peak Air Recovery (PAR) results in high mineral recovery. For operating parameters over which flotation plants have little control, such as particle size, investigating the effect on the position of PAR, and the subsequent effect on flotation performance, proves more challenging. To this end, we have developed a bench scale flotation system that runs continuously and exhibits froth behavior similar to that found industrially, allowing the study of such parameters as particle size in addition to air rate. The bench scale system comprises a 4 l baffled cylindrical flotation cell, stirred by a Rushton impeller. The concentrate is recycled back into the pulp, allowing for continuous operation. Glass beads are used as solid particles, allowing a wide range of particle sizes to be tested, with TTAB as collector and MIBC as frother. The system allows operation at air rates typical of industrial flotation systems (1-2 cms<sup>-1</sup> superficial gas velocity), in addition to yielding a froth that coalesces and bursts and exhibits a peak in air recovery as cell air rate in increased. Solids and water recovery is also measured. The results show that air recovery is sensitive to changes in particle size. The intermediate size distribution showed a peak in air recovery (PAR) that corresponded with the maximum solids flowrate, as found industrially. It is shown that finer particles do result in more stable froths and higher recoveries, particularly at low air rates. The effect of particle size on the position of PAR is not yet unequivocally determined from these results.

Conference paper

Bhutani G, Brito-Parada PR, Hadler K, Cilliers JJet al., 2014, Modelling laminar multiphase dispersed flows using population balances in an adaptive mesh finite element framework, 6th European Conference on Computational Fluid Dynamics

Conference paper

Hu W, Hadler K, Neethling SJ, Cilliers JJet al., 2013, Determining flotation circuit layout using genetic algorithms with pulp and froth models, CHEMICAL ENGINEERING SCIENCE, Vol: 102, Pages: 32-41, ISSN: 0009-2509

Journal article

Bhutani G, Brito-Parada PR, Hadler K, Cilliers JJet al., 2013, Adaptive population balances using direct quadrature method of moments using a finite element framework, 5th International Conference on Population Balance Modelling

Mesh adaptivity has been applied to the external coordinates of a population balance system which is solved using the Direct Quadrature Method Of Moments (DQMOM). This is the first time adaptivity has been applied in the external coordinate space. The method has been implemented in Fluidity, a finite element, open source code. Use of adaptive anisotropic unstructured meshes results in a significant saving in computational time.

Conference paper

Hadler K, Greyling M, Plint N, Cilliers JJet al., 2012, The effect of froth depth on air recovery and flotation performance, MINERALS ENGINEERING, Vol: 36-38, Pages: 248-253, ISSN: 0892-6875

Journal article

Hadler K, Smith CD, Cilliers JJ, 2010, Flotation performance improvement by air recovery optimisation on rougher and scavengers, IMPC 2010

Froth stability is known to play a key role in affecting separation performance in mineral froth flotation. One measure of froth stability is air recovery, or the fraction of air entering a cell that overflows the cell lip as unburst bubbles. Recent work has shown that the air recovery passes through a peak as cell aeration is increased, and that by operating at the air rate that yields this peak air recovery, improved separation performance is obtained. Previous studies have been restricted in the number of cells for which air recovery has been measured and optimised. In this paper, the concept of air recovery optimisation is extended to a bank of eight cells, comprising rougher and scavengers. The testwork, carried out at an Australian copper mine, compared metallurgical performance for the ‘As Found’ air rate profile for the bank to the optimised ‘Peak Air Recovery (or PAR)’ air profile. Results showed that a peak in air recovery was obtained in all cells, including the scavengers at the end of the bank. Furthermore, operating at the PAR air profile yielded both an increase in concentrate grade and recovery. The improvement in flotation performance can explained by understanding the resulting changes in froth structure and stability that occur with changing aeration, specifically when operating at the peak air recovery.

Conference paper

Hadler K, Smith CD, Cilliers JJ, 2010, Recovery vs. mass pull: The link to froth stability, Minerals Engineering

In recent years, developments in control strategy for banks of flotation cells have included process control based on mass pull. Mass pull, or the flowrate of solids reporting to the concentrate, is affected by changes in froth structure and stability which are in turn affected by changes in operating parameters such as air flowrate and froth depth.Air recovery, or the fraction of air entering a cell that overflows the lip as unburst bubbles, is a robust, non-intrusive measure of froth stability that passes through a peak as cell air rate is increased. Furthermore, it has been shown that when operating a cell at the air rate that yields the ‘Peak Air Recovery’ (PAR), an improvement in flotation performance, particularly mineral recovery, can be obtained.In this paper, results from industrial experiments are reported that compare the effect of air rate on air recovery and flotation performance, and specifically the effect on mass pull and mineral recovery. The results show that an increase in mass pull does not necessarily yield an increased mineral recovery in all cases, since it is dependent on whether the air rate must be increased or decreased to obtain the ‘Peak Air Recovery’. This work shows the potential gain to be made from control using air recovery measurements and operating at PAR conditions.

Journal article

Smith CD, Hadler K, Cilliers JJ, 2010, Flotation bank air addition and distribution for optimal performance, Minerals Engineering

Recent studies have shown that varying the distribution of a set volume of air to a flotation bank significantly affects the performance of the bank. To date, however, the volume of air to be distributed has usually been arbitrarily set as that added with the ‘as found’ air rates, the typical operating air rates; not necessarily an optimum.Studies examining the effect of different total air additions, at a constant distribution, have shown the addition maximising air recovery typically yields the best performance. Air recovery is the fraction of the air added to a cell which overflows the lip of the cell as unburst bubbles and shows a peak with respect to cell aeration.In this work three experimental case studies are presented to examine of the role of aeration in flotation performance, with the aim of developing a generic technique to determine both the required total air addition and distribution of air to a bank of flotation cells.The first case study compares performance at three different total air additions. The air addition which gave the Peak Air Recovery (PAR) also gave the highest mineral recovery. Thus air recovery optimisation yields the optimum total air addition to a flotation bank. In the second case study the air recovery was optimised from each cell in a bank individually. The PAR air addition once more gave the highest mineral recovery from the bank. Therefore, air recovery optimisation determines the optimum total air addition to a bank and also provides a distribution for that air. The third case study compares a profile based on the PAR air rates with other distributions of the same total air. The results show the profile based on the PAR air rates gave a significantly higher cumulative mineral recovery than other distributions of the same volume of air, for the same cumulative grade.The results of the three case studies show air recovery optimisation of each cell in a bank is a robust and generic technique to simultaneously determin

Journal article

Smith CD, Hadler K, Cilliers JJ, 2010, The Total Air Addition and Air Profile for a Flotation Bank, International Symposium on Advances in Mineral Processing Science and Technology in honor of James Finch, Publisher: METALLURGICAL SOC-C I M, Pages: 331-336, ISSN: 0008-4433

Conference paper

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