82 results found
Zhang H, Brito-Parada PR, Neethling SJ, et al., 2022, Yield stress of foam flow in porous media: The effect of bubble trapping, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 655, Pages: 1-12, ISSN: 0927-7757
Foam behaves as a yield-stress fluid as it flows in a porous medium. Quasi-static analysis suggests that the yield stress arises from the non-smooth motion of foam films, denoted as lamellae, in pores. In order to study the effect of trapped lamellae on the motion of a moving lamella and consequently on the yield stress of foam, we conduct numerical simulations in the quasi-static limit. We propose a new method utilizing the surface energy minimization algorithm, which explicitly considers the connectivity of pores in a porous medium. We consider two different shapes of pore and vary the number of nearby trapped lamellae to investigate the effects of bubble trapping on the non-smooth and the smooth motion of a single lamella passing through a pore, respectively. We find that the trapped lamellae lead to the increased volume-averaged pressure drop and thus the increased yield stress. Notably, the motion of a lamella through a pore with rounded corners in the pore body becomes non-smooth, due to the presence of trapped lamellae. The results contribute to a better understanding of the yield stress of foam in porous media.
Deveci M, Brito-Parada PR, Pamucar D, et al., 2022, Rough sets based Ordinal Priority Approach to evaluate sustainable development goals (SDGs) for sustainable mining, RESOURCES POLICY, Vol: 79, ISSN: 0301-4207
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Morley JD, Myers RJ, Plancherel Y, et al., 2022, A database for the stocks and flows of sand and gravel, Resources, Vol: 11, Pages: 1-17, ISSN: 2079-9276
Increasing demand for sand and gravel globally is leading to social, environmental, and political issues that are becoming more widely recognised. Lack of data and poor accessibility of the few available data contribute to exacerbating these issues and impair evidence-based management efforts. This paper presents a database to store stocks and flows data for sand and gravel from different sources. The classification system underlying within it builds on the Universal Materials Information System (UMIS) nomenclature, which is used to construct hierarchical order in the data and in the same manner as the Yale Stocks and Flow Database (YSTAFDB), a common data format. To illustrate how the database is built and used, a case study using UK data is presented. The UK is chosen owing to relatively better access to data compared to other locations. Quantitative analyses of the data show the supply chain of these materials to be currently stable for the UK as indigenous extraction contributes 95.6% to UK sand and gravel production, with imports accounting for the rest of the inputs, of which 50% is reliant on only one nation.
Deveci M, Gokasar I, Brito-Parada PR, 2022, A comprehensive model for socially responsible rehabilitation of mining sites using Q-rung orthopair fuzzy sets and combinative distance-based assessment, Expert Systems with Applications, Vol: 200, Pages: 117155-117155, ISSN: 0957-4174
Mining companies play a critical role in developing mineral wealth across the globe. Interacting effectively with local communities is yet another potential source of long-term profitability, because of the opportunities that are not accessible if community engagement is not achieved. The financial advantages of a positive company image can be linked to attracting and retaining employees, as well as sustaining or even enhancing the capacity to do business with local suppliers. The socially responsible rehabilitation of a site after mine closure can facilitate access to new or former jobs for the mine workers. This study focuses on how to identify the best rehabilitation strategy after the closure of a mining site. In particular, a q-rung orthopair fuzzy sets (q-ROFSs) based CODAS (COmbinative Distance-based ASsessment) model is developed to support the evaluation of socially responsible rehabilitation activities in mining sites. To test and validate the model, the proposed methodology is compared to the ARAS (Additive Ratio Assessment) method. The results show that rehabilitation and social transition subsidy is the best alternative among those considered. Implementation of this alternative benefits the mining companies and also brings social benefits to the mine workers and the wider communities within the mining site.
Morley JD, Myers RJ, Plancherel Y, et al., 2022, A Database for the Extraction, Trade, and Use of Sand and Gravel (Retraction of Vol 11, art no 38, 2022), RESOURCES-BASEL, Vol: 11
Singh DK, Brito-Parada PR, Bhutani G, 2022, An open-source computational framework for the solution of the bivariate population balance equation, Computers & Chemical Engineering, Vol: 161, Pages: 107780-107780, ISSN: 0098-1354
The bivariate population balance equation (PBE) is a mathematical framework to explain the evolution of polydisperse multiphase systems. In this work, the direct quadrature method of moments (DQMOM) is implemented in an open-source CFD code, Fluidity, for the numerical solution of bivariate PBE. This efficient numerical framework is a highly-parallelised finite element (FE) CFD code that allows for the use of mesh adaptivity on fully-unstructured meshes. Various test cases to solve spatially homogeneous bivariate PBEs with aggregation, breakage, growth and dispersion were simulated and verified against analytical solutions, resulting in excellent agreement. Benchmarking, by comparison with the Monte Carlo method solutions from the literature, with realistic kernels in a gas–liquid system for simultaneous bivariate aggregation and breakage was also performed to show the feasibility of this implementation for realistic applications. This open-source framework demonstrates its impressive potential in the case of bivariate PBE and can be exploited for the simulation of complex polydisperse multiphase systems.
Morley JD, Myers RJ, Plancherel Y, et al., 2022, A Database for the Extraction, Trade, and Use of Sand and Gravel, RESOURCES-BASEL, Vol: 11
Cole K, Brito-Parada PR, Hadler K, et 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.
Cole K, Barker DJ, Brito-Parada PR, et 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.
Wang P, Brito-Parada PR, 2022, Dynamics of a particle-laden bubble colliding with an air-liquid interface, Chemical Engineering Journal, Vol: 429, Pages: 1-10, ISSN: 1385-8947
The collision, bouncing and potential bursting of air bubbles with air-liquid interfaces are key processes involved in the initial stage of foam formation. While fundamental studies of these processes, especially for gas-liquid-solid froth systems, are very valuable for a better understanding of various chemical engineering separation systems, these are scarce. This paper investigates the dynamics of rising bubbles, without particles attached and with various particle coverages, as they collide with an air-liquid interface. For uncoated bubbles, an increase in distance from the bubble releasing point to the air-liquid interface resulted in higher bubble approach velocities, although with minor changes in the velocity fluctuation frequency. This increase in approach velocity was not observed for bubbles with relatively high particle coverage. For particle-laden bubbles, the collision with the interface is associated with movement of the particles over the surface of the decelerating bubble. This particle motion on the bubble surface, combined with bubble shape pulsation, contributes to the kinetic energy dissipation of the approaching bubble. A damped oscillation model was derived to represent the velocity of the bubble interacting with the interface, which shows that the amplitude of the velocity decreases gradually with the increase in particle coverage. The damping coefficient in the model, introduced to quantify the influence of attached particles, is shown to increase with particle coverage, confirming the key role that particles play in bubble collision dynamics at an air-liquid interface and allowing, for the first time, the prediction of their behavior.
Aksoy DO, Ozdemir S, Celik PA, et al., 2022, Fusion of the microbial world into the flotation process, Mineral Processing and Extractive Metallurgy Review, Vol: 43, Pages: 1068-1082, ISSN: 0273-3706
The depletion of high-grade ore deposits, as well as the generation of large quantities of tailings by mining and metallurgical activities, necessitates an urgent search for not only more cost-effective, but also more eco-friendly methods of recovering minerals from low-grade deposits and secondary resources. Research in the bioflotation process appears to be an answer to this search, thanks to the contribution of the microbial world. This study constitutes the first systematic and the most comprehensive review on bioflotation. The bioflotation studies in the literature were examined in a certain chronological order and by classifying the reagents in terms of both their origin and their use in flotation. Aside from the benefits of bioreagents to the mining industry, the review attempted to reveal the issues that prevent the transition to industrial application. This review aims to raise awareness of future research opportunities for mining and biology researchers while also presenting current bioflotation studies.
Marmiroli B, Rigamonti L, Brito-Parada PR, 2021, Life Cycle Assessment in mineral processing – a review of the role of flotation, The International Journal of Life Cycle Assessment, Vol: 27, Pages: 62-81, ISSN: 0948-3349
PurposeThe aim of this literature review is to investigate the role of the beneficiation stage in the Life Cycle Assessment (LCA) of metals and minerals with a focus on the flotation process.MethodsThe systematic literature search included LCA studies comprising the beneficiation stage in their system boundaries and resulted in 29 studies that met the criteria requirements and were analysed. First, the system boundaries are investigated, along with the level of detail in the description of the sub-processes (e.g. flotation) and data granularity. Then, the life cycle inventories are scrutinised: data transparency and the relation between system granularity and data availability is commented. Of particular relevance, the way in which the functional unit is dealt with is examined. Finally, studies impact assessments are compared and discussed, and key parameters are highlighted.Results and discussionFor system boundaries, beneficiation is generally embedded into the mining stage. Even when described on its own, important sub-processes (e.g. flotation) are not considered, except for eight cases analysed. Functional unit definition is hindered by the output of the system being an intermediate product. Indeed, most studies use a declared functional unit but fail to provide its relevant characteristics, which is essential for a correct interpretation of results and for comparisons. Most studies rely on secondary data, not always presented transparently, to describe beneficiation. Results on the role of beneficiation in the metal value chain environmental impacts are conflicting, partly because of its site dependency. Site-dependent parameters found to be determining are ore grade, energy mix, mining technique, concentrate grade and ore mineralogy.ConclusionsThe flotation process, and more generally the beneficiation stage, is typically overlooked in LCA studies despite its growing relevance. Beneficiation not being assessed as a standalone stage, detailed in its subprocess
Mesa D, Cole K, van Heerden MR, et al., 2021, Hydrodynamic characterisation of flotation impeller designs using Positron Emission Particle Tracking (PEPT), Separation and Purification Technology, Vol: 276, Pages: 1-19, ISSN: 0950-4214
Impellers play a key role in flotation cells, as the turbulence generated through agitation aids particle suspension, air dispersion and particle–bubble collision. Therefore, it is important to understand the effect that different impeller designs have on flotation hydrodynamics, as small variations could enhance flotation performance. The study of flotation hydrodynamics is, however, a complex task due to the nature of flotation systems, which are opaque, multiphase, and polydisperse. In this paper, the impact of impeller design modifications on the hydrodynamics of a flotation cell was quantified for the first time in a three-phase system. Two different impeller designs, with and without a stator, were assessed using positron emission particle tracking (PEPT), a technique that allows the position and velocity of radioactive particle tracers within an opaque vessel to be determined. A novel PEPT data analysis strategy, as well as a statistical analysis on the basis of the Jensen–Shannon distance, were used. This statistical analysis, applied for the first time to PEPT data, facilitated the comparison of the different designs, by generating a robust quantification of their hydrodynamic differences. The experimental results showed that the stator significantly modified the hydrodynamics within the flotation cell, distorting the lower mixing loop that is characteristic of radial impellers. The use of a stator also resulted in the reduction of particle velocity and swirling outside of the impeller–stator region, both at the level of the impeller and, notably, at the pulp–froth interface. These findings have important implications for impeller–stator design, evidencing that the impeller has a direct effect on the hydrodynamics of the pulp and froth.
Promentilla MA, Beltran A, Orbecido A, et al., 2021, Systems approach toward a greener eco-efficient mineral extraction and sustainable land use management in the Philippines, Chemical Engineering Transactions, Vol: 88, Pages: 1171-1176, ISSN: 1974-9791
As the world transition towards a low-carbon future through renewable energy, mining of minerals and metals to attain this goal is substantial. The Philippines will play an important role in such global economy as it is the world’s fifth most mineral-rich country. However, their exploitation has not been maximized to benefit society. Benefits from the mineral resources sector remain less than 2 % of the country’s GDP since 2006, and the mining and mineral processing, including abandoned or legacy mines, are perceived negatively by the public. In low- and middle-income countries with weak implementation of mining and environmental legislation, the mining industry still operates in a linear system which is considered unsustainable. The mining, mineral extraction and processing, and metal extraction are designed to maximize profits with little plan on how to effectively manage mine wastes, protect the environment, transform post-mining land for beneficial use and empower impacted communities. This paper, thus, proposes a systems approach toward greener eco-efficient mineral extraction and sustainable land use management (SAGES). This approach will facilitate a paradigm shift, which is necessary to manage the country’s mineral endowments sustainably without compromising future land use of mining areas while at the same time supporting the needs and aspirations of the impacted host communities. It envisions extending the usability of mining areas beyond the life of the mine and integrating circular economy principles in addressing holistically mine waste management problems. The multi-R framework, originally developed in waste management (Reduce, Reuse, Recycle) and extended to circular economy strategies, has potential applications in mine waste management in the Philippines. An illustrative case study is then presented that employs a multi-R framework to address the mine waste in an operating Ni-laterite mining site.
Quintanilla P, Neethling SJ, Navia D, et al., 2021, A dynamic flotation model for predictive control incorporating froth physics. Part I: Model development, Minerals Engineering, Vol: 173, Pages: 1-23, ISSN: 0892-6875
It is widely accepted that the implementation of model-based predictive controllers (MPC) ensures optimal operation if an accurate model of the process is available. In the case of froth flotation, modelling for control purposes is a challenging task due to inherent process instabilities. Most models for control have only focused on the pulp phase rather than the froth phase, which is usually oversimplified or even neglected. Despite the fact that froth stability can significantly affect the overall performance of flotation cells, there is still a gap in literature regarding flotation models for control purposes that properly include froth physics.In this paper we describe the development of a dynamic flotation model suitable for model predictive control, incorporating equations that describe the physics of flotation froths. Unlike other flotation models for control in the literature, the model proposed here includes important variables related to froth stability, such as bursting rate and air recovery, as well as simplified equations to calculate froth recovery and entrainment. These model equations allow estimating the amount of valuable material reporting to the concentrate, which can be used as a proxy to estimate grade and recovery. Additionally, pulp-froth interface physics was also included in our model, which enables a more accurate prediction of relevant flotation variables.A sensitivity analysis of the parameters showed that two out of seven parameters were highly sensitive. The highly sensitive parameters are the exponential factor n of the equation for the overflowing bubble size, and the constant value a of the equation for the bursting rate. Although the other parameters showed a reasonably lower sensitivity than n and a, the results also revealed that there is a significant difference in the prediction accuracy if the parameters are poorly estimated. Further simulations of important variables for control exhibited a good adaptability to changes in typ
Quintanilla P, Neethling SJ, Mesa D, et al., 2021, A dynamic flotation model for predictive control incorporating froth physics. Part II: Model calibration and validation, Minerals Engineering, Vol: 173, Pages: 1-15, ISSN: 0892-6875
Modelling for flotation control purposes is the key stage of the implementation of model-based predicted controllers. In Part I of this paper, we introduced a dynamic model of the flotation process, suitable for control purposes, along with sensitivity analysis of the fitting parameters and simulations of important control variables. Our proposed model is the first of its kind as it includes key froth physics aspects. The importance of including froth physics is that it improves the estimation of the amount of material (valuables and entrained gangue) in the concentrate, which can be used in control strategies as a proxy to estimate grade and recovery.In Part II of this series, experimental data were used to estimate the fitting parameters and validate the model. The model calibration was performed to estimate a set of model parameters that provide a good description of the process behaviour. The model calibration was conducted by comparing model predictions with actual measurements of variables of interest. Model validation was then performed to ensure that the calibrated model properly evaluates all the variables and conditions that can affect model results. The validation also allowed further assessing the model’s predictive capabilities.For model calibration and validation purposes, experiments were carried out in an 87-litre laboratory scale flotation tank. The experiments were designed as a randomised full factorial design, manipulating the superficial gas velocity and tailings valve position. All experiments were conducted in a 3-phase system (solid-liquid–gas) to ensure that the results obtained, as well as the behaviour of the flotation operation, are as similar as possible to those found in industrial flotation cells.In total, six fitting parameters from the model were calibrated: two terms from the equation for overflowing bubble size; three parameters from the bursting rate equation; and the number of pulp bubble size classes. After the mode
Moore KR, Moradi S, Doyle K, et al., 2021, Sustainability of switch on-switch off (SOSO) mining: Human resource development tailored to technological solutions, Resources Policy, Vol: 73, Pages: 1-13, ISSN: 0301-4207
Adaptable, mobile, modularised technical solutions were piloted for switch on-switch off (SOSO) mining at test sites in the west Balkans. Pre-training occurred at the site of module construction and on the mine site in order to transfer knowledge relating to the rapid deployment, commissioning and operation of mining and processing units, in a mature health and safety culture. Translation of extensive documentation, describing operation of the equipment, into local languages and visual aids supported communication. Consideration of the activities required to deploy and operate prototype solutions revealed how characteristics of a SOSO workforce differed from other types of mining. Deployment of modularised plant employed fewer workers than traditional stick-build of a processing plant, but selective mining and processing of complex and variable deposits limited the potential for automation and required operator control. A workforce with mixed levels of experience was most amenable to development of a mature health and safety culture. The total number of employees was small at an individual site and might remain small, even in a multi-deposit, regional business model. However, employment is higher per unit of production than for conventional large-scale mining. The duration of employment is shorter than for large-scale mining but employment can nevertheless be important where there are few alternative opportunities and where it can increase the skills-base to support a more diversified local economy. SOSO mining constitutes a new relationship between society and the mining industry, which needs further consideration for greater resilience in the local community and increased social sustainability.
Beylot A, Muller S, Segura-Salazar J, et al., 2021, Switch on-switch off small-scale mining: Environmental performance in a life cycle perspective, Journal of Cleaner Production, Vol: 312, ISSN: 0959-6526
A switch on-switch off (SOSO) approach to mining relies on an integrated modular and mobile plant. It is appropriate for rapid start-up and cessation of production from ore deposits that have economic viability dependent on fluctuating commodity prices. This study aims at assessing the environmental performance of the SOSO approach in a life cycle perspective, using evidence collected during its pilot-scale implementation on a high-grade lead deposit located in Bosnia-Herzegovina. The deployed modules include: i) a selective mining tool, ii) a comminution module with crusher and screen, and iii) a gravity separation module with screen, spirals and a shaking table. The Life Cycle Inventory is based on a comprehensive and transparent set of data, drawn from the on-site pilot tests, completed with additional calculations (including process simulation with USIM-PAC®), scenarios (regarding energy), and some generic data and assumptions. The potential environmental impacts are calculated considering 13 impact categories of the EF 2.0 impact assessment method. The production of one tonne of Pb concentrate, with a Pb-content of 58.7%, induces in particular the potential generation of 897 kg CO2-eq. Moreover, the contribution analysis enables identification of the environmental hotspots, including the consumption of electricity supplied by on-site diesel generators that contributes to more than 90% of the total impacts in seven impact categories. Finally, this article discusses i) how advantageous the SOSO approach is compared to large-scale lead mining regarding some of its associated key environmental hotspots, ii) the potential for reduction of the impacts associated with electricity consumption, in particular through the implementation of a renewable electricity supply mix (solar photovoltaics and biomass-based), iii) the contributions of equipment and tailings to the total impacts, and iv) the contribution of the SOSO approach to resource accessibility and depletion
Wang H, Brito-Parada PR, 2021, Shape deformation and oscillation of particle-laden bubbles after pinch-off from a nozzle, Chemical Engineering Journal, Vol: 412, Pages: 1-10, ISSN: 1385-8947
The rise of bubbles in liquid is a common phenomenon in chemical engineering applications. Bubble dynamics, however, are not fully understood, particularly at the early stages after bubbles are released from submerged nozzles, or when particles coat the bubble surface. In this work, a detailed investigation of microparticle-laden bubbles rising in water after being released from a nozzle was carried out to determine the influence of bubble surface coverage on the interface dynamics after pinch-off. The use of high-speed photography, at up to 25170 frames per second, allowed two regimes to be systematically investigated for the first time, i.e. an initial bubble shape deformation and shape oscillations. Surface pressure analysis shows that microparticles reduce the apparent surface tension of the interface by generating surface pressure during the initial bubble deformation. In contrast, during shape oscillations, little effect was observed on the period of the dominant harmonic, indicating that surface tension does not change during the oscillations. Harmonic analysis also showed that microparticles at bubble surfaces significantly increase the damping rate of the dominant harmonic, with a dependency on the bubble surface coverage. By quantifying the effect of particles on bubble dynamics, this work contributes to a better understanding of gas–liquid–solid reactors in which particle attachment plays a key role.
Quintanilla P, Neethling SJ, Brito-Parada PR, 2021, Modelling for froth flotation control: A review, Minerals Engineering, Vol: 162, ISSN: 0892-6875
Flotation is a conceptually simple operation; however, as a multiphase process with inherent instability, it exhibits complex dynamics. One of the most efficient ways to increase flotation performance is by implementing advanced controllers, such as Model Predictive Control (MPC). This type of controller is very dependent on the model that represents the dynamics of the process. Although model development is one of the most crucial parts in MPC, flotation models have been mainly developed for simulation purposes (i.e. analysis and design) rather than control purposes. This paper presents a critical literature review on modelling for froth flotation control. Models reviewed have been sub-classified as empirical, phenomenological and hybrid according to their characteristics. In particular, it is highlighted that models have so far primarily focused on the pulp phase, with the froth phase often neglected; when the froth phase is included, kinetics models such as those used for the pulp phase, are commonly used to represent it. Froth physics are, however, dominated by processes such as coalescence, liquid motion and solids motion, which have been previously modelled through complex, steady-state models used for simulation purposes, rather than control purposes. There remains a need to develop appropriate models for the froth phase and more complex models for the pulp phase that can be used as part of MPC strategies. The challenges associated with the development of such models are discussed, with the aim of providing a pathway towards better controlled froth flotation circuits.
Segura-Salazar J, Brito-Parada PR, 2021, Stibnite froth flotation: A critical review, Minerals Engineering, Vol: 163, Pages: 1-23, ISSN: 0892-6875
Antimony has a long and diverse history of applications, and concerns about its future supply have emerged in recent years. Stibnite-bearing ores continue to be the main source of this critical element, although its sourcing from secondary resources (e.g. mine tailings) is becoming increasingly relevant yet technically challenging. In this sense, froth flotation plays a key role in the recovery of stibnite from both sources. In view of this, a comprehensive review of technical and environmental aspects related to the flotation of stibnite across scales (microflotation, bench-scale and industrial-scale) has been carried out. One of the major topics reviewed is stibnite flotation reagents; while the overall practice has been mostly conservative, relying on the use of xanthate collectors and lead nitrate as an activator, less common (bio)reagents for the flotation of stibnite ores of varying complexity have been shown to be a promising alternative. Other challenges identified from the literature are discussed, highlighting areas of opportunities for further research to enhance stibnite flotation, minimise antimony losses throughout the mine life cycle and thus make antimony more available for future generations.
Wang H, Brito-Parada PR, 2021, Deformation dynamics of particle-laden bubbles: The effect of surfactant concentration and particle contact angle, Minerals Engineering, Vol: 160, Pages: 1-6, ISSN: 0892-6875
The pinch-off dynamics of bubbles coated with silica particles in deionised water and in dodecylamine (DDA) solution, at 0.2 μM and 20.0 μM, was studied using high-speed photography. Surface pressure generated at the deforming particle-laden interface during bubble pinch-off was obtained based on the fitting to a pinch-off model. It was observed that the pinch-off dynamics of these particle-laden bubbles remained almost unchanged at the low DDA concentration of 0.2 μM, while the dynamics slowed down significantly at the DDA concentration of 20.0 μM. Notably, both the 0.2 μM and 20.0 μM DDA concentrations have a negligible effect on the surface tension and pinch-off dynamics of uncoated bubbles. The difference in DDA concentration, however, is known to change the contact angle of silica particles from approximately 27° to 45°. It can be concluded that it is the change in particle contact angle that affects the pinch-off dynamics of particles-laden bubbles. Indeed, at a concentration of 0.2 μM DDA there is no significant change in contact angle of the silica particles with respect to that in DI water only, resulting in similar dynamics. It is suggested that the increase in the particle contact angle changes particle interactions, leading to a change in the surface pressure and apparent surface tension of particle-laden bubbles, which in turn slows down the pinch-off process. The findings in this work are relevant to our understanding of fundamental aspects of deforming particle-laden interfaces, such as those in the coalescence of flotation froths.
Wang H, Brito-Parada PR, 2020, The role of microparticles on the shape and surface tension of static bubbles, Journal of Colloid and Interface Science, Vol: 587, Pages: 14-23, ISSN: 0021-9797
HYPOTHESIS: Surface tension is a critical parameter in bubbles and foams, yet it is difficult to assess when microparticles are attached at the interface. By considering the interaction force between an air-liquid interface and microparticles, modified equations for sessile bubble tensiometry can be derived to determine the surface tension and shape of static microparticle-laden bubbles. EXPERIMENTS: A modified sessile bubble method, in which the forces between microparticles and the air-liquid interface are considered, was developed and used to analyse the surface tension of bubbles fully coated by a monolayer of silica microparticles of different sizes. The results are compared to those obtained using classical sessile bubble tensiometry. The new method is also used to investigate the contours of particle-laden bubbles of varying particle radius and contact angle. FINDINGS: While the classical sessile bubble method overestimates the surface tension, results obtained using the modified sessile bubble method show that the surface tension of static microparticle-laden bubbles remains the same as that of uncoated bubbles, with no dependency on the particle size. The discrepancy is due to the fact that microparticles attached to the air-liquid interface deform a bubble in a similar way that changes in surface tension do for uncoated bubbles.
Vega-Garcia D, Cilliers JJ, Brito-Parada PR, 2020, CFD modelling of particle classification in mini-hydrocyclones, Separation and Purification Technology, Vol: 251, Pages: 1-9, ISSN: 1383-5866
This work presents validated Computational Fluid Dynamics (CFD) predictions of the effect that changes in vortex finder and spigot diameters have on the classification performance of mini-hydrocyclones. Mini-hydrocyclones (e.g. 10 mm in diameter) have been applied successfully to the separation of micron-sized particles since their bypass fraction is larger than the water recovery, which results in a high particle recovery to the underflow, as well as low water recovery. However, a larger bypass fraction can be a disadvantage when the purpose of the hydrocyclone is particle classification, because of the large amount of fine particles that are misplaced in the underflow. Although it is well known that changes in the outlets of the hydrocyclone affect its performance, there is limited research on the effect of these design parameters in mini-hydrocyclones, in particular with regard to particle classification. The aim of this study is to computationally explore the influence of spigot and vortex finder on the classification process. To this end, CFD simulations were carried out and the predictions experimentally validated in a 3D printed mini-hydrocyclone using glass beads (below 20μm) as the particulate system. The numerical results showed very good agreement with the experimental data for recovery of solids, concentration ratio, pressure drop and particle size distribution. A trade-off was observed between the solids recovery and concentration ratio, while the solids recovery was found to be inversely proportional to the pressure drop when vortex finder diameters were kept constant. It was found that the design that yielded the lowest recovery among those tested also resulted in a particle size distribution furthest away from that of the feed. We show how the model can be used to assess changes in design parameters in order to inform the selection of designs that exhibit lower energy requirements without compromising separation performance.
Mesa Pena D, Morrison AJ, Brito Parada PR, 2020, The effect of impeller-stator design on bubble size: implications for froth stability and flotation performance, Minerals Engineering, Vol: 157, ISSN: 0892-6875
The impeller in a mechanical flotation tank plays a key role in keeping particles in suspension, dispersing and breaking-up air bubbles, and promoting particle-bubble collision. However, the turbulent regime generated by the impeller can also affect the pulp-froth interface, destabilising the lower regions of the froth and affecting the overall flotation performance. The effects that pulp zone design modifications have on the froth are, however, poorly understood and have not been well-studied.In this work, we study the impact of impeller-stator design on the performance of a large laboratory-scale flotation tank. Two different impeller designs, with and without a stator, were assessed under a range of air flow rates to determine changes in pulp bubble size, froth stability, and metallurgical recovery. The results allow us to quantify, for the first time, the reduction in bubble size in a three-phase flotation system and the improvement in froth stability due to the use of a stator, and thus the enhancement in flotation performance. An inverse relationship is found between the pulp bubble size and froth stability. It is shown that the impeller designs that exhibited smaller bubble sizes resulted in higher froth stability values and also higher flotation recoveries. These findings provide insights into the links between pulp and froth zone phenomena, paving the way for improvements in flotation tank design that lead towards flotation optimisation.
Wang H, Brito-Parada PR, 2020, The pinch-off dynamics of bubbles coated by microparticles, Journal of Colloid and Interface Science, Vol: 577, Pages: 337-344, ISSN: 0021-9797
HypothesisWhile the pinch-off dynamics of bubbles is known to be influenced by changes in surface tension, previous studies have only assessed changes due to liquid properties or surfactant effects at the air-liquid interface but not due to the presence of particles. The current study proposes that particles at the air-liquid interface play an important role in changing the surface tension and thus the pinch-off dynamics of particle-laden bubbles.ExperimentsHigh-speed photography was used to study the pinch-off dynamics of air bubbles coated by a monolayer of silica microparticles. The influence of bubble surface coverage and particle size classes on the bubble pinch-off dynamics were explored.FindingsWe identify that although the scaling exponent of the power law that governs the pinch-off of coated and uncoated bubbles is the same, the pinch-off dynamics is distinctly different when particles are present at the air-liquid interface due to a decrease in surface tension with time in the neck region. We suggest that the surface pressure generated by particle interaction reduces the pinch-off speed by reducing the apparent surface tension. We observe that the apparent surface tension is dependent on particle size but not on the percentage of bubble surface coated by particles.
Sommer A-E, Ortmann K, Van Heerden M, et al., 2020, Application of Positron Emission Particle Tracking (PEPT) to measure the bubble-particle interaction in a turbulent and dense flow, Minerals Engineering, Vol: 156, Pages: 1-10, ISSN: 0892-6875
In a flotation cell, turbulence influences the motion of solid particles relative to the bubble surface, and, thus,affects the recovery rate. But, the impact of turbulence on the probability of a bubble-particle aggregationis still difficult to measure, especially in a dense flow. Therefore, the focus of this work was to applyPositron Emission Particle Tracking (PEPT) as a method to investigate the effect of turbulence on theparticle movement and bubble-particle interaction in an opaque flow. Single air bubbles (db = 2.5 mm) weregenerated on a needle in a water flow channel. Upstream, a grid produced an isotropic turbulent flow with5 % to 15 % turbulence intensity and a Kolmogorov microscale of 20 µm. Depending on the distance to thegrid, the flow near the captive bubble (Reb ≈ 450) was characterized by eddies of different length scalesand magnitude with tomographic Particle Image Velocimetry (PIV). The solid suspension contained up to0.3 % polymethylmethacrylate (PMMA) particles (dp = 200 µm–400 µm) and up to six radiolabelled particles(dp = 300 µm–400 µm) coated with PMMA. The trajectories of the labelled particles were used to determinethe average particle distribution in the turbulent field and describe the bubble-particle interactions. Theseresults provide valuable information on the applicability of PEPT in turbulent and dense flow fields as wellas on particle trajectories close to bubbles, enhancing our understanding of key flotation phenomena.
Mesa Pena D, Brito Parada P, 2020, Bubble size distribution in aerated stirred tanks: Quantifying the effect of impeller-stator design, Chemical Engineering Research and Design, Vol: 160, Pages: 356-369, ISSN: 0263-8762
Bubble size is an important variable in aerated stirred tanks as it determines the surface area available for reactions. In the bubble break-up process, impellers play a key role. Despite this importance, research into the effect of impeller design on bubble size is scarce. In this work we study the effect of two impellers, with and without a stator, as well as the effect of airflow rate, impeller speed and surfactant concentration on bubble size.Results show that there is a critical impeller speed above which bubble size is not further decreased, regardless of the airflow. Operating at this critical speed results in the smallest bubble size possible without additional turbulence. The reduction in bubble size caused by a stator was quantified for the first time and, interestingly, it was found that the stator also reduced the critical coalescence concentration. The implications of these findings for the design, evaluation and optimisation of impellers are discussed.
Sitorus F, Brito-Parada PR, 2020, A multiple criteria decision making method to weight the sustainability criteria of renewable energy technologies under uncertainty, Renewable and Sustainable Energy Reviews, Vol: 127, Pages: 1-11, ISSN: 1364-0321
Selecting the most suitable renewable energy technology among feasible alternatives considering conflicting criteria is a Multiple Criteria Decision Making (MCDM) problem. One of the essential stages in the methods used to solve such problems is determining the appropriate weight of each criterion to be considered. The Shannon Entropy method is a frequently used MCDM method to calculate the criteria weights, however it is not suitable to solve problems for which uncertainty in the input data exists. This paper presents a new extended Shannon Entropy method: the Integrated Constrained Fuzzy Shannon Entropy (IC-FSE) method, by which criteria weights are obtained from uncertain input data. To show the applicability of IC-FSE, an illustrative example for the selection of a renewable energy technology in the mining industry is presented, in which three alternative renewable energy technologies, onshore wind, solar photovoltaic and concentrated solar power, were evaluated with respect to technical, social, economic and environmental categories. The results show that IC-FSE can effectively provide appropriate fuzzy solutions for weighting the sustainability criteria for renewable energy technologies. The superiority of this method is showcased by demonstrating that IC-FSE results are more robust than those obtained using other existing methods. The methodology presented can be applied broadly in the renewable energy sector to ensure better informed decision making processes.
Wang H, Brito-Parada PR, 2020, Coalescence dynamics of particle-laden bubbles., Langmuir: the ACS journal of surfaces and colloids, Vol: 36, Pages: 5394-5399, ISSN: 0743-7463
Understanding the coalescence of particle-laden bubbles is crucial to our understanding of the role of particles in stabilizing liquid foams. In this work, the coalescence of microparticle-laden bubbles is studied experimentally using high-speed photography. In particular, the interparticle forces in the neck region during the early stage of bubble coalescence are calculated. The results indicate that a monolayer of silica particles coating the bubble surfaces hinders the growth dynamics of the air neck formed between the coalescing bubbles. We postulate that the decrease in the growth dynamics is due to the surface pressure caused by the particle interaction after the initiation of bubble coalescence. We identify that the apparent surface tension in the neck region increases with time for particle-laden bubbles and is lower for larger particle sizes. These findings enhance our understanding of the role of particles on the dynamics of fast deforming interfaces.
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