Imperial College London

Professor Jan Cilliers

Faculty of EngineeringDepartment of Earth Science & Engineering

Chair in Mineral Processing
 
 
 
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Contact

 

+44 (0)20 7594 7360j.j.cilliers

 
 
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Location

 

RSM 1.46BRoyal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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136 results found

Harrison STL, Kotsiopoulos A, Stevenson R, Cilliers JJet al., 2020, Mixing indices allow scale-up of stirred tank slurry reactor conditions for equivalent homogeneity, Chemical Engineering Research and Design, Vol: 153, Pages: 865-874, ISSN: 0263-8762

© 2019 The Institution of Chemical Engineers The influence of reactor scale, impeller tip speed and specific power on the overall homogeneity (multi-phasic mixing) of two dimensionally similar stirred tanks of 50 mm and 220 mm internal diameter (ID) are compared using data collected from electrical resistance tomography for 5 and 15% v/v 600–800 μm particle suspensions. The data collected is used to quantify the suspension quality of the system by defining mixing indices in the axial MIz and radial MIr directions as well as the overall mixing index MIo. Analyses across the vessels indicated that axial and radial homogeneity improved with increasing impeller tip speed for both large and small vessels with more consistent suspensions observed in the former. Improved homogeneity was consistently found in the 10–20% (v/v) solids loading range (data only shown for 15%) than at 5%, across both reactors. In either vessel, optimum homogeneity was achieved at impeller tip speeds ca. 20% lower than the critical suspension speed, as shown previously. Analysis of the local concentration of particles in the lowest region of the vessels indicated that absolute homogeneity was unattainable as the decreasing local concentration displayed an asymptotic character with increasing power per unit volume. The suspension quality during reactor scale-up was relatively consistent with specific power ratios P/V, while the same degree of homogeneity was not achieved when the impeller tip speed was kept constant.

Journal article

Fernando F, Cilliers J, Brito Parada PR, 2019, An integrated constrained fuzzy stochastic analytic hierarchy process method with application to the choice problem, Expert Systems with Applications, Vol: 138, Pages: 1-25, ISSN: 0957-4174

The ability of the analytical hierarchy process (AHP) when applied to the choice problem in the context of group decision making under uncertainty has been often criticised. AHP is not able to fully capture the various opinions and the uncertainty associated with the lack of information. This work develops an integrated constrained fuzzy stochastic analytic hierarchy process (IC-FSAHP) method in order to deal with the aforementioned drawbacks. IC-FSAHP combines two existing fuzzy AHP (FAHP) methods and further extends its applicability by implementing stochastic simulations. A case study has been conducted in order to assess the ability of IC-FSAHP; the results showed that IC-FSAHP is able to capture the uncertainty and multiple DMs' opinions. This paper also discusses the effect that the number of DMs has in enhancing rank discrimination. Besides, the possibility of the occurrence of rank reversal because of the use of IC-FSAHP has been analysed. The results showed that the ranking of alternatives was preserved throughout the changes in the number of alternatives, however, rank reversal occurred in the case of changes in judgements scales. By comparing the U-uncertainty in fuzzy global priorities obtained using IC-FSAHP to that obtained using an existing FSAHP method, we show that our method is capable of minimising the risk of losing important knowledge during the computations. We also discuss how IC-FSAHP can decrease the uncertainty and increase the reliability of the decisions by means of robust computations.

Journal article

Wang P, Reyes F, Cilliers J, Brito Parada PRet al., 2019, Evaluation of collector performance at the bubble-particle scale, Minerals Engineering, ISSN: 0892-6875

Particle attachment and detachment in froth flotation are complex processes and their measurement presents many challenges. Of particular interest is the effect of collectors at the bubble-particle scale, in order to assess the strength or collecting ability of these reagents. However, studies of the effect of collectors on particle attachment at the bubble-particle scale are scarce. In this work, we propose a methodology to characterise collector strength by measuring the attachment rate of particles to a capillary-pinned bubble. An image processing technique was developed to quantify bubble surface coverage over time, which was then used to determine particle attachment kinetics. The image analysis strategy is based on the sessile drop method and uses curve fitting to determine accurately the particle coverage. The methodology was used to assess the collecting ability of three chalcopyrite collectors. Interestingly, although very similar contact angle measurements were found for two of the collectors, they showed distinctly different particle attachment kinetics. It is proposed that this particle-bubble attachment method can be used to gain additional information not currently available from either contact angle measurements or bulk collector performance tests.

Journal article

Hadler K, Martin DJP, Carpenter J, Cilliers JJ, Morse A, Starr S, Rasera JN, Seweryn K, Reiss P, Meurisse Aet al., 2019, A universal framework for Space Resource Utilisation (SRU), Planetary and Space Science, Pages: 104811-104811, 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, Estimating the scale of space resource utilisation (SRU) operations to satisfy lunar oxygen demand, Planetary and Space Science, 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 ratesof the mineoperation and the oxygen extraction stage havenot 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 removalof 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 1000kg of oxygen per annum is at least five times higher than previous estimates, 30 kg/h, for equivalent efficiency assumptions. Monte-Carlosimulationswere performed forstatistical confidence in the estimates of the miningmass rateand the required oxygen extraction feedstock rate. To be 95% confident that the 1000 kg/y O2will be met, the designed mining rate should beat least 65 kg/h, and the beneficiated feedstock rate 16 kg/h. This study has revisedand increased the estimate of the lunar regolith mining scale required for the productionof 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 miningand oxygen extraction, particularlythe process designand whethe

Journal article

Wang P, Cilliers JJ, Neethling SJ, Brito-Parada PRet al., 2019, The behavior of rising bubbles covered by particles, Chemical Engineering Journal, Vol: 365, Pages: 111-120, ISSN: 1385-8947

A systematic investigation of the influence of particle coverage on the dynamics of rising bubbles was carried out using high-speed photography and image analysis techniques to study bubble behavior in terms of changes in velocity and aspect ratio. The buoyancy force and drag force exerted on the bubbles and the effect of particles were calculated to further understand their behavior. Results show that particles attached on the bubbles strongly dampen the oscillations observed in bubble aspect ratio and decrease its velocity and acceleration. The particles also render the bubbles more spherical and slow their velocity. It was found that the overall velocity of a bubble is directly correlated to its aspect ratio and inversely correlated to its particle coverage, while the acceleration and the aspect ratio and its change are inversely correlated. Interestingly, the trend observed in the oscillation and the oscillation period of particle-laden bubbles is similar for different levels of particle coating. A drag modification factor ηp, which quantifies the drag influence of particles on bubble velocity, was identified from force analysis. A modified drag coefficient for uncoated and particle-laden bubbles was introduced, which allows, for the first time, to predict the behavior of rising bubbles in gas-liquid-particle systems.

Journal article

Sitorous F, Cilliers JJ, Brito Parada PR, 2019, Multi-criteria decision making for the choice problem in mining and mineral processing: applications and trends, Expert Systems with Applications, Vol: 121, Pages: 393-417, ISSN: 0957-4174

Despite the fact that the potential of multi-criteria decision making (MCDM) to overcome a variety of problems in mining and mineral processing has been widely recognised, no literature review in these fields has been conducted. This manuscript addresses this issue by providing a comprehensive overview of the applications and trends of MCDM methods for the choice problem (i.e., determining the best option from a set) in mining and mineral processing. 90 articles published between 1999 and 2017 were selected following a searching methodology and eligibility criteria detailed in this manuscript. In addition, for the purpose of the survey, different types of selection problems were identified. The results show that there are two phases of growth in the application of MCDM techniques to the choice problem in mining and mineral processing. The first phase, from 1999 to 2007, shows a very low number of publications with only a moderate increase by the end, whereas the second phase, from 2007 to 2017, shows a significant growth in the number of published articles. The review also shows that the most addressed problem has been the selection of mining methods, while the Analytical Hierarchy Process (AHP) has been the most used MCDM method. The rise in the application of hybrid MCDM methods is also discussed. This review paper provides insight into the current state of applications of MCDM in mining and mineral processing and discusses pathways for future research directions in the development of MCDM methods that would benefit these fields.

Journal article

Wang P, Cilliers JJ, Neethling SJ, Brito-Parada PRet al., 2019, Effect of particle size on the rising behavior of particle-laden bubbles, Langmuir, Vol: 35, Pages: 3680-3687, ISSN: 0743-7463

The rising behavior of bubbles, initially half and fully coated with glass beads of various sizes, was investigated. The bubble velocity, aspect ratio, and oscillation periods were determined using high-speed photography and image analysis. In addition, the acting forces, drag modification factor, and modified drag coefficient were calculated and interpreted. Results show that the aspect ratio oscillation of the rising bubbles is similar, irrespective of the attached particle size. As the particle size is increased, the rising bubbles have a lower velocity and aspect ratio amplitude, with the time from release to each aspect ratio peak increasing. Higher particle coverage is shown to decrease the bubble velocity and dampen the oscillations, reducing the number of aspect ratio peaks observed. The highest rise velocities correspond to the lowest aspect ratios and vice versa, whereas a constant aspect ratio yields a constant rise velocity, independent of the particle size. Force analysis shows that the particle drag modification factor increases with the increased particle size and is greatest for fully laden bubbles. The modified drag coefficient of particle-laden bubbles increases with the increased particle size, although it decreases with the increased Reynolds number independent of the particle size. The drag force exerted by the particles plays a more dominant role in decreasing bubble velocities as the particle size increases. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations will enhance the modeling of industrial applications.

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 rough

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

Cilliers JJ, Harrison STL, 2019, Yeast flocculation aids the performance of yeast dewatering using mini-hydrocyclones, SEPARATION AND PURIFICATION TECHNOLOGY, Vol: 209, Pages: 159-163, ISSN: 1383-5866

Journal article

Morrison A, Brito-Parada P, Cilliers J, 2019, Developing a design modification for improved froth flotation performance through minimising turbulence at the pulp-froth interface, Pages: 1739-1747

© IMPC 2018 - 29th International Mineral Processing Congress. All rights reserved. The separation of valuable and gangue minerals according to their surface hydrophobicity in a froth flotation tank occurs in both its pulp and froth phases. In the pulp phase, hydrophobic particles must be brought into contact with rising bubbles introduced at or near the bottom of the tank. In a mechanical froth flotation tank, this is primarily achieved through the agitation of the pulp by an impeller or by a rotor-stator system. However, the turbulent and mixing effects of such an impeller or rotor-stator system, necessary to promote bubble-particle interactions in the pulp, are not confined to the pulp zone, but are transmitted into the froth zone at the pulp-froth interface. This impeller-induced turbulence at the pulp-froth interface is compounded by the impulse of buoyant bubbles entering the base of the froth phase, reducing the stability, and thus separation performance, of the resulting froth. Hence, turbulence improves separation performance if it occurs deep in the pulp phase, but diminishes it if it occurs close to the pulp-froth interface. For this work, a performance-enhancing pulp phase insert was designed to isolate the impeller-induced turbulence from the pulp-froth interface in a laboratory-scale, continuously-operated froth flotation tank. The result was a shifted grade-recovery curve that allows the insert to be designed to maximize the recovery from the system without sacrificing the grade of the concentrate, or vice versa, along a spectrum of improved performance. This paper will present the insert design and development process that resulted in this improved grade-recovery curve, as well as a set of heuristics that could be used to design a similar insert for pilot- and industrial-scale validation and deployment.

Conference paper

Vega D, Brito-Parada PR, Cilliers JJ, 2019, Small hydrocyclones for classiffication of particles in the micron range, Pages: 2398-2405

© IMPC 2018 - 29th International Mineral Processing Congress. All rights reserved. Small diameter (10 mm) hydrocyclones have been applied successfully for the separation of particle suspensions in the micron size range. These hydrocyclones are attractive because they show a bypass fraction larger that the water recovery, resulting in a high particle recovery to the underflow as well as low water recovery. However, this is a disadvantage when the purpose of the hydrocyclone is classification because of the large amount of fine particles that are misplaced in the underflow. The aim of this study is to explore, experimentally and computationally, the influence of design parameters on the classification process. In this work, a full factorial experimental design was defined to carry out comprehensive experimental tests using glass beads (0-20 µm) as the particulate system. We show that the dimensions of spigot and vortex finder diameter can be effectively manipulated to change the separation performance of the system and the energy consumption. A CFD model was developed that is able to predict particle size distribution. The numerical results for the partition curves showed very good agreement with the experimental data.

Conference paper

Reyes F, Cilliers JJ, Neethling SJ, 2019, Quantifying mineral liberation by grade and surface exposure using X-ray micro-tomography for flotation processes, Pages: 1570-1579

© IMPC 2018 - 29th International Mineral Processing Congress. All rights reserved. Liberation is a key driver in all mineral separation processes as it limits the maximum possible grade for a given recovery. In flotation, this is further complicated by the fact that it is surface exposure of the floatable minerals that determines the ultimate performance. Liberation, grade and surface exposure are commonly quantified using Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM/EDX) analysis of polished sections. The intrinsically 2D nature of this technique can result in significant sampling errors and stereological effects that can affect the quantification of the ore's textural characteristics. X-ray micro-Tomography (XMT) is an imaging method that can non-invasively and non-destructively delineate ore fragments in 3D, thus providing an alternative method that eliminates the need for stereological corrections and readily provides surface exposure. A methodology and automated algorithm were designed for extracting this information from images of closely packed particles, thus allowing samples containing a large number of particles to be assessed. The main drawback of XMT is that, unlike SEM/EDX, it cannot directly measure the mineralogy of the sample, instead producing a 3D X-ray attenuation map. We therefore also present an algorithm for calibrating the thresholding of the XMT images based on SEM/EDX images of sections through the same sample, thus allowing the liberation analysis to be carried out on a 3D mineral map in which the uncertainty in the mineral assignment is small and statistically quantified. The methodology was tested on low grade porphyry copper ore as this is both an industrially relevant and traditionally difficult system to quantify using XMT due to the similarity in the X-ray attenuation of the sulphide species, especially the pyrite and chalcopyrite. As each 3D volume imaged contain 100-1000s of grains, large da

Conference paper

Reyes F, Cilliers JJ, Neethling SJ, 2019, Quantifying mineral liberation by grade and surface exposure using X-ray micro-tomography for flotation processes, Pages: 3985-3994

© IMPC 2018 - 29th International Mineral Processing Congress. All rights reserved. Liberation is a key driver in all mineral separation processes as it limits the maximum possible grade for a given recovery. In flotation, this is further complicated by the fact that it is surface exposure of the floatable minerals that determines the ultimate performance. Liberation, grade and surface exposure are commonly quantified using Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM/EDX) analysis of polished sections. The intrinsically 2D nature of this technique can result in significant sampling errors and stereological effects that can affect the quantification of the ore's textural characteristics. X-ray micro-Tomography (XMT) is an imaging method that can non-invasively and non-destructively delineate ore fragments in 3D, thus providing an alternative method that eliminates the need for stereological corrections and readily provides surface exposure. A methodology and automated algorithm were designed for extracting this information from images of closely packed particles, thus allowing samples containing a large number of particles to be assessed. The main drawback of XMT is that, unlike SEM/EDX, it cannot directly measure the mineralogy of the sample, instead producing a 3D X-ray attenuation map. We therefore also present an algorithm for calibrating the thresholding of the XMT images based on SEM/EDX images of sections through the same sample, thus allowing the liberation analysis to be carried out on a 3D mineral map in which the uncertainty in the mineral assignment is small and statistically quantified. The methodology was tested on low grade porphyry copper ore as this is both an industrially relevant and traditionally difficult system to quantify using XMT due to the similarity in the X-ray attenuation of the sulphide species, especially the pyrite and chalcopyrite. As each 3D volume imaged contain 100-1000s of grains, large da

Conference paper

Mackay I, Cilliers JJ, Videla AR, Brito-Parada PRet al., 2019, Optimising froth stability of copper flotation tailings, Pages: 1730-1738

© IMPC 2018 - 29th International Mineral Processing Congress. All rights reserved. Linking results from laboratory scale experiments to industrial flotation behaviour is challenging. Typically, such experiments involve batch tests in which the system does not operate at steady-state, making it difficult to infer the effects that operating conditions have on flotation performance. In order to overcome this limitation a 4-litre recirculating tank was previously developed at Imperial College London. This tank is capable of reaching, and operating at, steady-state by recycling overflowing concentrate back into the feed. As well as instruments to control operating conditions, it is fitted with a system of sensors that allow the surface of the froth to be dynamically monitored. From this information, it is possible to measure the air recovery-a proxy for froth stability. Thus, this bench-scale tank can be used to understand the effect of differing operating conditions on flotation performance at steady state. However, so far, this cell has only been used to investigate idealised systems with only one or two species. Reprocessing of tailings dams is not only environmentally desirable but also increasingly economically feasible due to the declining head grades of primary deposits. There is also the added benefit of no further milling being required prior to flotation. However, the effects of fine and ultrafine particles on froth stability are not yet fully understood. In this work, the bench-scale continuous tank has been used for the first time to determine the flotation response of a complex feed, consisting of samples from a copper tailings dam, to changes in operating conditions. It was shown that the froth stability in the system is comparable to that of previous work and industrial tests, with a peak in air recovery being found at a superficial gas velocity of 1.13 cm/s. There is scope to optimise the froth stability of tailings flotation for enhanced metallurgic

Conference paper

Cilliers J, Hutahaean J, Brito Parada PR, 2018, A multi‐criteria decision framework for the selection of biomass separation equipment, Chemical Engineering and Technology, Vol: 41, Pages: 2346-2357, ISSN: 0930-7516

For the first time, a two‐stage decision support framework for equipment selection, applied to biomass separation, is presented. In the first stage, the framework evaluates from a number of equipment based on the process requirements and outputs only those that offer a technically feasible separation. In the second stage, the analytic hierarchy process is applied for performing a multicriteria decision analysis to select amongst the feasible equipment based on separation performance and energy consumption criteria. This approach systematically considers the relative importance of those different alternatives and selection criteria by pairwise comparisons. The output of the framework is an overall ranking of equipment as well as a sensitivity analysis of the results for different weighting of the criteria. These results can be used to equip practitioners in the field of bioseparations with a tool for making more consistent and better‐informed equipment selection decisions.

Journal article

Brito Parada P, Dewes R, Vega Garcia D, Cilliers Jet al., 2018, The influence of design parameters on the separation of biomass in mini-hydrocyclones, Chemical Engineering and Technology, Vol: 41, Pages: 2323-2330, ISSN: 0930-7516

Small hydrocyclones are an attractive technology for biomass separation from fermentation processes. The interactive effect of design parameters on the performance of mini‐hydrocyclones is, however, not fully explored and studies are often limited by the challenges in manufacturing such small units. Here, 10‐mm mini‐hydrocyclones are produced by 3D printing and the impact of spigot diameter, vortex finder diameter and height on separation performance is studied. A central composite rotatable design was adopted to obtain information on the relation between the variables and their influence on concentration ratio and recovery of yeast from a highly diluted system. A Pareto front for separation performance was generated and shown to be suitable to select an optimal design for a set of process constraints.

Journal article

Vega-Garcia D, Brito Parada P, Cilliers JJ, 2018, Optimising small hydrocyclone design using 3D printing and CFD simulations, Chemical Engineering Journal, Vol: 350, Pages: 653-659, ISSN: 1385-8947

The use of small hydrocyclones for the separation of particles in the micron range is of growing interest. However, these hydrocyclones are typically limited to conventional shapes or restricted to specific outlet sizes, which can lead to sub-optimal performance. The aim of this study is to present a method for the optimisation of small hydrocyclone design. This method consists of four steps that combine designing, Computational Fluid Dynamics (CFD) simulations, 3D printing and experimental testing. A 3D printed 10 mm hydrocyclone was shown first to match the performance of a ceramic equivalent, followed by factorial experiments with a set of printed hydrocyclones of different spigot and vortex finder diameters. A CFD model for small hydrocyclones was implemented and, following validation with the experimental data, used to simulate small hydrocyclone designs with parabolic walls. The model predicted improved separation performance compared to the conventional conic wall designs. In a novel development, a 10 mm hydrocyclone with parabolic walls was 3D printed and the prediction confirmed experimentally. The solids recovery and concentration ratio were increased by 10 percentage points and 0.2, respectively, for a 0.5 g/L yeast suspension and at an equivalent pressure drop. The use of 3D printing to manufacture small hydrocyclones of various designs has been proven in this study to be practical and to allow rapid prototyping design informed by CFD simulations. This is a significant improvement in the cost, time and versatility associated to hydrocyclone design and can lead to enhanced separation performance.

Journal article

Reyes F, Lin Q, Cilliers JJ, Neethling SJet al., 2018, Quantifying mineral liberation by particle grade and surface exposure using X-ray microCT, Minerals Engineering, Vol: 125, Pages: 75-82, ISSN: 0892-6875

Liberation is a key driver in all mineral separation processes as it limits the maximum possible grade for a given recovery. In flotation, this is further complicated by the fact that it is surface exposure of the floatable minerals that determines the ultimate performance. Liberation, grade and surface exposure are commonly quantified using Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectroscopy (SEM/EDX) analysis of polished sections. The intrinsically 2D nature of this technique can result in significant sampling errors and stereological effects that can affect the quantification of the ore's textural characteristics. X-ray microCT (XMT) is an imaging method that can non-invasively and non-destructively delineate ore fragments in 3D, thus providing an alternative method that eliminates the need for stereological corrections and readily provides surface exposure. A methodology and automated algorithm were developed for extracting this information from images of closely packed particles. By dividing these particles into classes based on both their surface exposure and grade, the extent to which there is preferential breakage of the particles can be assessed—an important consideration if sufficient surface liberation for good flotation performance is to be achieved at coarser particle sizes. Using low energy scanning simple 3D mineral maps can be obtained via XMT, allowing for the assessment of liberation and surface exposure for each mineral species. The methodology was tested on low grade porphyry copper ore as this is representative of the most commonly treated ore types for copper production.

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

Mackay I, Mendez E, Molina I, Videla AR, Cilliers JJ, Brito Parada PRet al., 2018, Dynamic froth stability of copper flotation tailings, Minerals Engineering, Vol: 124, Pages: 103-107, ISSN: 0892-6875

In this work, dynamic froth stability is used for the first time to investigate the flotation behaviour of copper tailings. Reprocessing of material from tailings dams is not only environmentally desirable, but also increasingly economically feasible as head grades can be high compared to new deposits. Flotation tailings, however, usually contain a large proportion of fine (10–50 m) and ultra fine (<) material and the effect of these particle sizes on froth stability is not yet fully understood.For this study, samples were obtained from the overflow and underflow streams of the primary hydrocyclone at a concentrator that reprocesses copper flotation tailings. These samples were combined in different ratios to assess the dynamic froth stabilities at a wide range of particle size distributions and superficial gas velocities. The findings have shown that the effect of particle size on dynamic froth stability can be more complex than previously thought, with a local maximum in dynamic froth stability found at each air rate. Moreover, batch tests suggest that a local maximum in stability can be linked to improvements in flotation performance. Thus this work demonstrates that the dynamic froth stability can be used to find an optimum particle size distribution required to enhance flotation. This also has important implications for the reprocessing of copper tailings as it could inform the selection of the cut size for the hydrocyclones.

Journal article

Dobson KJ, Harrison STL, Lin Q, Bhreasail AN, Fagan-Endres MA, Neethling SJ, Lee PD, Cilliers JJet al., 2017, Insights into ferric leaching of low grade metal sulfide-containing ores in an unsaturated ore bed using x-ray computed tomography, Minerals, Vol: 7, ISSN: 2075-163X

The distribution of the metal-bearing mineral grains within a particulate ore prepared for leaching, and the impact of this spatial heterogeneity on overall extraction efficiency is of key importance to a mining industry that must continuously target ever-reducing grades and more complex ore bodies. If accessibility and recovery of the target minerals is to be improved, a more detailed understanding of the behaviour of the system must be developed. We present an in situ analysis using X-ray computed tomography to quantify the rates of volume reduction of sulfide mineral grains in low grade agglomerated copper bearing ores during a miniature laboratory scale column leaching experiment. The data shows the scale of the heterogeneity in the leaching behaviour, with an overall reduction of sulphide mineral grains of 50%, but that this value masks significant mm3 to cm3 scale variability in reduction. On the scale of individual ore fragments, leaching efficiency ranged from 22% to 99%. We use novel quantitative methods to determine the volume fraction of the sulfide that is accessible to the leachate solution.

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

Tong M, Cole K, Brito-Parada PR, Neethling S, Cilliers JJet al., 2017, Geometry and Topology of Two-Dimensional Dry Foams: Computer Simulation and Experimental Characterization, LANGMUIR, Vol: 33, Pages: 3839-3846, ISSN: 0743-7463

Pseudo-two-dimensional (2D) foams are commonly used in foam studies as it is experimentally easier to measure the bubble size distribution and other geometric and topological properties of these foams than it is for a 3D foam. Despite the widespread use of 2D foams in both simulation and experimental studies, many important geometric and topological relationships are still not well understood. Film size, for example, is a key parameter in the stability of bubbles and the overall structure of foams. The relationship between the size distribution of the films in a foam and that of the bubbles themselves is thus a key relationship in the modeling and simulation of unstable foams. This work uses structural simulation from Surface Evolver to statistically analyze this relationship and to ultimately formulate a relationship for the film size in 2D foams that is shown to be valid across a wide range of different bubble polydispersities. These results and other topological features are then validated using digital image analysis of experimental pseudo-2D foams produced in a vertical Hele–Shaw cell, which contains a monolayer of bubbles between two plates. From both the experimental and computational results, it is shown that there is a distribution of sizes that a film can adopt and that this distribution is very strongly dependent on the sizes of the two bubbles to which the film is attached, especially the smaller one, but that it is virtually independent of the underlying polydispersity of the foam.

Journal article

Fagan-Endres MA, Cilliers JJ, Sederman AJ, Harrison STLet al., 2017, Spatial variations in leaching of a low-grade, low-porosity chalcopyrite ore identified using X-ray mu CT, Minerals Engineering, Vol: 105, Pages: 63-68, ISSN: 0892-6875

This study presents an investigation, using 3D X-ray micro computed tomography (μCT), into the effect of sulfide mineral position within an ore particle on leaching efficiency. Three sections of an unsaturated mini-leaching column that had been packed with agglomerated low-grade, low-porosity chalcopyrite ore and leached with an acidified ferric iron solution were imaged at different stages of a 102 day experiment. Image analysis was used to quantify changes in the mineral content and the influence on this of the mineral distance from the ore particle surface, local voidage and radial position within the column. The main factor affecting the mineral recovery was identified to be proximity of the mineral to the ore particle surface, with recovery decreasing with increasing distance from the ore surface. A maximum leaching penetration was observed to exist at 2 mm from the surface, beyond which no recovery was achieved. Higher recoveries at the column wall indicated that preferential flow in this higher voidage had an additional, albeit smaller, impact on leaching efficiency.

Journal article

Kiziroglou M, boyle D, Yeatman E, Cilliers Jet al., 2016, Opportunities for sensing systems in mining, IEEE Transactions on Industrial Informatics, Vol: 13, Pages: 278-286, ISSN: 1551-3203

Pervasive sensing - the capability to deploy large numbers of sensors, to link them to communication networks, and to analyze their collective data - is transforming many industries. In mining, networked sensors are already used for remote operation, automation including driverless vehicles, health and safety, and exploration. In this paper, the state-of-the-art sensing and monitoring technologies are assessed as solutions against the main challenges and opportunities in the mining industry. Localization, mapping, remote operation, maintenance and health and safety are identified as the main beneficiaries, from rapidly developing technologies such as 3D visualization, augmented reality, energy autonomous sensor nodes, distributed sensing, smart network protocols and big data analytics. It is shown that the identification and management of ore grade in particular, which transcends each stage of the mining process, may critically benefit from certain arising sensing technologies, where major efficiency improvements are possible in exploration, extraction, haulage and processing activities.

Journal article

Boucher D, Jordens A, Sovechles J, Langlois R, Leadbeater TW, Rowson NA, Cilliers JJ, Waters KEet al., 2016, Direct mineral tracer activation in positron emission particle tracking of a flotation cell, Minerals Engineering, Vol: 100, Pages: 155-165, ISSN: 0892-6875

Understanding the complex interplay of physics and chemistry inside a flotation cell is the ultimate goal of most flotation research. Key to the development of a model of flotation is the ability to validate it from measurements of a real flotation system. This work uses positron emission particle tracking (PEPT) to track directly activated mineral particles, hydrophobic and hydrophilic, in a lab-scale flotation cell. In contrast to other particle activation methods the direct activation technique allows mineral particles with their original surface characteristics to be used in PEPT experiments. In this work the flotation separation investigated was the separation of hematite from quartz from a synthetic ore using a combination of an oleic acid collector and sodium silicate depressant. This work represents the first time in which particles of typical flotation size (−106 + 90 μm diameter) with real bulk mineral properties and surface chemistry have been tracked in a flotation cell. The results illustrate small particles flow behaviour in the cell for a hydrophilic particle. The trajectory and velocities of the tracer particle are shown as it is transported inside the flotation cell.

Journal article

Shean B, Hadler K, Cilliers JJ, 2016, A flotation control system to optimise performance using peak air recovery, Chemical Engineering Research & Design, Vol: 117, Pages: 57-65, ISSN: 1744-3563

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 strategyfor theoperation offlotation cellswhich 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, adirect search optimisation algorithm based on the GSS (generating set search) methodologywasdeveloped 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 hours and exhibited a reproducible peak in air recovery. Adynamic 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 startingabove,belowand atthe PAR air rate, andadditionallywith a disturbance introduced into the system.While the direct search approach can be slow, it is simple and robust.This demonstratesan innovative approach to optimising control for froth flotation and isthe first applicationof froth sta

Journal article

Bhutani G, Brito Parada PR, Cilliers JJ, 2016, Polydispersed flow modelling using population balances in an adaptive mesh finite element framework, Computers and Chemical Engineering, Vol: 87, Pages: 208-225, ISSN: 1873-4375

An open-source finite element framework to model multiphase polydispersed flows is presented in this work. The Eulerian–Eulerian method was coupled to a population balance equation and solved using a highly-parallelised finite element code—Fluidity. The population balance equation was solved using DQMOM. A hybrid finite element–control volume method for solving the coupled system of equations was established. To enhance the efficiency of this solver, fully-unstructured non-homogeneous anisotropic mesh adaptivity was applied to systematically adapt the mesh based on the underlying physics of the problem. This is the first time mesh adaptivity has been applied to the external coordinates of the population balance equation for modelling polydispersed flows. Rigorous model verification and benchmarking were also performed to demonstrate the accuracy of this implementation. This finite element framework provides an efficient alternative to model polydispersed flow problems over the other available finite volumeCFD packages.

Journal article

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