Froth Flotation Cell Research Articles

Artificial neural network (ANN) modelling to estimate bubble size from macroscopic image and object features

Bubble size measurements in aerated systems such as froth flotation cells are critical for controlling gas dispersion. Commonly, bubbles are measured by obtaining representative photographs, which are then analyzed using segmentation and identification software tools. Recent developments have focused on enhancing these segmentation tools. However, the main challenges around complex bubble cluster segmentation remain unresolved, while the tools to tackle these challenges have become increasingly complex and computationally expensive. In this work, we propose an alternative solution, circumventing the need for image segmentation and bubble identification. An Artificial Neural Network (ANN) was trained to estimate the Sauter mean bubble size (D<sub>32</sub>) based on macroscopic image features obtained with simple and inexpensive image analysis. The results showed excellent prediction accuracy, with a correlation coefficient, R, over 0.998 in the testing stage, and without bias in its error distribution. This machine learning tool paves the way for robust and fast estimation of bubble size under complex bubble images, without the need of image segmentation.

Economic model predictive control for a rougher froth flotation cell using physics-based models

The development of an economic model predictive control (E-MPC) strategy is presented. The strategy uses a novel dynamic flotation model that incorporates the physics of the froth phase in a flotation cell. The dynamic model was previously calibrated and validated using experimental data.Sensitivity analyses were conducted to select a suitable objective function that accounted for both process economics and control variable sensitivities. While the ultimate goal of a rougher flotation cell is to maximise the metallurgical recovery at a steady state for a specified minimum grade, it was evident that the incorporation of air recovery dynamics (which can be measured in real-time) and concentrate grade dynamics (calculated through first-principle models) led to the best results. The addition of a dynamic variable that can be easily measured online, i.e. air recovery, offers great potential to improve plant performance in existing froth flotation systems. Furthermore, a minimum concentrate grade was imposed in the E-MPC strategy. This acts as an economic constraint as it allows the metallurgical recovery to be optimised while ensuring that concentrate grade requirements are met.The dynamic optimisation problem for the E-MPC strategy was discretised using orthogonal collocations, and was implemented in Matlab using automatic differentiation via CasADi. Two typical manipulated variables were considered: air flowrate and pulp height setpoints. Based on laboratory-scale data, the implementation of the E-MPC strategy resulted in improvements ranging from +8 to +22 % in metallurgical recovery, while maintaining the specified grade. This is therefore an encouraging control strategy to explore in larger flotation systems.

X-ray Particle Tracking Velocimetry in an Overflowing Foam

In mineral processing, froth flotation is based on recovering valuable mineral particles by means of the overflowing froth. Industrial-scale froth flotation cells are typically equipped with optical measurement systems, which monitor the bubble sizes and flow velocities at the froth surface. However, the velocity profile of the overflowing froth underneath its free surface is not accessible by optical observation. The present study combines X-ray radiography and particle tracking velocimetry in a laboratory-scale experiment aiming to measure local flow velocities within an optically opaque foam at a weir, which here describes a one-sided horizontal overflow. For this purpose, we prepared custom-tailored tracer particles: small 3D-printed polymer tetrahedra with tiny metal beads glued to the tetrahedral tips. In parallel to the velocity measurements by means of X-ray particle tracking, we determined the liquid fraction of the overflowing foam by electric conductivity measurements using electrode pairs. The experiment was performed with aqueous foams of two different surfactant concentrations but similar bubble size range and superficial gas velocity, yielding around 10% liquid fraction near the weir. Employing the particles as tools for flow tracing in X-ray image sequences, we measured the velocity profile in vertical direction above the weir crest and found that the maximum velocity is reached underneath the free surface of the overflowing foam.

Hydrodynamics in a three-phase flotation system – Fluid following with a new hydrogel tracer for Positron Emission Particle Tracking (PEPT)

Understanding the hydrodynamics of three-phase stirred tanks, such as froth flotation cells, is paramount for the characterisation of turbulence, stability and performance. Although positron emission particle tracking (PEPT) is known for its effectiveness in measuring the hydrodynamics of particles in opaque, high solid content systems, it has not been widely used for characterising the liquid phase. This work presents a new, neutrally buoyant, alginate hydrogel tracer, designed to emulate the density of the liquid phase, which is suitable for high-speed tracking with PEPT.PEPT experiments were conducted in a bench-scale flotation cell, comparing the new tracer to ion-exchange resin tracers previously used in this system. Results showed statistically significant differences in pathlines, residence time and velocity distribution among the tracers. Moreover, the hydrodynamics of the new tracer agree with existing CFD predictions for the liquid phase. This methodology enables the comprehensive study of relative flow behaviour in complex multiphase systems.

An integrated multi-mode model of froth flotation cell based on fusion of flotation kinetics and froth image features

Froth flotation is the most commonly used technology in minerals separation and beneficiation. A comprehensive and precise flotation model is the foundation for optimizing the recovery rate and grade of valuable minerals. In this paper, a phenomenological model is built to describe the underlying physicochemical principles of the flotation process. To account for the influence factors not explicitly included in the phenomenological model, a data-driven model based on Long Short-Term Memory (LSTM) is proposed for error compensation by learning from the sequentially collected froth images. Considering the time-varying nature of flotation dynamics, a multi-mode modeling framework is established in the context of comprehensive state space (CSS) description system. In the framework, the dynamics of the flotation cell is described using a twofold integration. For each working condition, the phenomenological model and the compensation model are integrated to describe the process dynamics. The process dynamics is formulated as an integration of the sub-models of each working condition. In order to follow the evolution of working condition, the weights of the sub-models vary with the location of the working point in the CSS, which are calculated using a SAE(Stacked Auto Encoder)-KD(K-dimensional tree)-TAN(Tree Augmented Naive Bayes) approach. The proposed approach utilizes both kinetics knowledge and froth image features, and can be adapted to the variation of working conditions. A case study illustrates the stability and accuracy of the proposed approach.

Beneficiation of Talc-Magnesite Ore with Cu-Co Mineralization

Magnesite ore with a low chalcopyrite – cobaltite mineralization was subjected to a series of separations designed to evaluate thepossible concentration of the two accessory minerals. Although the Cu-Co grade in the ore (> 0.01% Co, > 0.1% Cu) is significantlylower than the typical economic grades, content of the main valuable mineral for which the ore is mined and processed incombination with a listing of cobalt as a critical raw material, coupled with their higher price might compensate for the additionalbeneficiation stages. The ore was first crushed and subsequently classified to -100 μm and +100 -400 μm size fractions. The finefraction was upgraded by froth flotation processing in laboratory froth flotation cell. The coarser fraction was processed in severalseparation stages including gravity separation on shaking table, magnetic separation and corona electrostatic separation. The sameprocedure was also repeated with a higher-grade sample as a verification of the procedures. Preliminary results suggest that theaccessory minerals can be separated from the talc-magnesite ore and individual mineral concentrates with about 19% Co and 28%Cu were prepared. However, further work must be done to achieve desirable recoveries for the processing to be economically viable.

Froth Flotation Beneficiation a Sure Way to Value Addition to Arufu (Nigeria) Zinc Ore Towards Smelting Grade Concentrate Production

Froth flotation of Arufu ore was carried out at varying particle sizes after characterization. Fifty (50) kilogram crude sample of the ore was sourced from Arufu zinc mine in Arufu town of Nassarawa state, Nigeria. The whole sample was crushed out of which five (5) kilogram was sampled out using random sampling method. One kilogram each of the resulting sample was then ground and sieved to three particle sizes viz; 63 µm, 90 µm and 125 µm. Chemical analysis of the representative sample of the sourced ore was carried out using Energy Dispersive X-Ray Fluorescence Spectrometer (ED –XRF). 250 grams of the 63 µm sample was charged into Froth flotation cell mixed with water at a ratio of 1:4 to form slurry. The Slurry formed was condition to a pH of 9, while other froth flotation reagents were added one after the other. This resulted in froth and depressed samples, which were dewatered after 24 hours and samples picked for compositional analysis. The procedure was repeated for 90 µm and 125 µm. The characterization of head sample revealed that the ore contains predominantly 36.80%ZnO (26.29% Zn), 31.1 % SiO2 alongside other trace mineral as gangue in the ore. However, Froth flotation studies of the ore at varying particle size revealed that, appreciable amount of mineral of interest (ZnO) was lost to the tailing at sieve sizes 63 µm and 90 µm. This was attributed to over-grinding above the ore’s liberation size phenomenon which has been proven to have adverse effect on the mineral’s quality and overall separation efficiency. It was concluded that the froth flotation is best carried out at a particle size of 125 µm, pH of 9, using potassium ethyl xanthate (PEX) as frother to yield concentrate grade of 50.21 % ZnO (35.93 % Zn) at a recovery of 46.3%. This was re – cleaned to yield high grade of 82.36%ZnO (66.42%Zn). The re – cleaned concentrate produced falls within the standard requirement of 65 % Zn needed as a charge into the blast furnace for Zinc metal production.

Froth Flotation Beneficiation a Sure Way to Value Addition to Arufu (Nigeria) Zinc Ore Towards Smelting Grade Concentrate Production

Froth flotation of Arufu ore was carried out at varying particle sizes after characterization. Fifty (50) kilogram crude sample of the ore was sourced from Arufu zinc mine in Arufu town of Nassarawa state, Nigeria. The whole sample was crushed out of which five (5) kilogram was sampled out using random sampling method. One kilogram each of the resulting sample was then ground and sieved to three particle sizes viz; 63 µm, 90 µm and 125 µm. Chemical analysis of the representative sample of the sourced ore was carried out using Energy Dispersive X-Ray Fluorescence Spectrometer (ED –XRF). 250 grams of the 63 µm sample was charged into Froth flotation cell mixed with water at a ratio of 1:4 to form slurry. The Slurry formed was condition to a pH of 9, while other froth flotation reagents were added one after the other. This resulted in froth and depressed samples, which were dewatered after 24 hours and samples picked for compositional analysis. The procedure was repeated for 90 µm and 125 µm. The characterization of head sample revealed that the ore contains predominantly 36.80%ZnO (26.29% Zn), 31.1 % SiO2 alongside other trace mineral as gangue in the ore. However, Froth flotation studies of the ore at varying particle size revealed that, appreciable amount of mineral of interest (ZnO) was lost to the tailing at sieve sizes 63 µm and 90 µm. This was attributed to over-grinding above the ore’s liberation size phenomenon which has been proven to have adverse effect on the mineral’s quality and overall separation efficiency. It was concluded that the froth flotation is best carried out at a particle size of 125 µm, pH of 9, using potassium ethyl xanthate (PEX) as frother to yield concentrate grade of 50.21 % ZnO (35.93 % Zn) at a recovery of 46.3%. This was re – cleaned to yield high grade of 82.36%ZnO (66.42%Zn). The re – cleaned concentrate produced falls within the standard requirement of 65 % Zn needed as a charge into the blast furnace for Zinc metal production.

State controllability of a froth flotation cell

Abstract The control goals for a froth flotation cell are to maintain a stable pulp level and maximise the separation between valuable minerals to the concentrate and gangue to the tailings. Only a limited set of manipulated variables are available to achieve a target concentrate grade and tailings grade for a specific pulp level. The froth flotation cell can be represented by a non-linear phenomenological state-space model. The states of the model are the concentration of minerals in the froth and the pulp, and the volume of liquid in the froth and pulp. A state controllability analysis of the model indicates that the states are controllable using air flow-rate, tailings flow-rate, and feed-rate as manipulated variables. Therefore, given these three manipulated variables, a controller should be able to maximise the separation between minerals in the concentrate and tailings, while maintaining a pulp level within acceptable bounds.

Multivariate image analysis of realgar–orpiment flotation froths

ABSTRACTMultivariate image analysis was used to estimate the arsenic concentrations in froths resulting from the flotation of different mixtures of realgar and orpiment particles in a laboratory batch flotation cell. The realgar floated rapidly and in excess of 90% of the mineral could be recovered after 2 minutes, whereas only 48–75% of the orpiment could be recovered in the same time. Textural features, based on grey level co-occurrence matrices (GLCMs), local binary patterns (LBPs), steearable pyramids and textons were used in the analysis. Random forest models could explain approximately 71–77% of the variance in the arsenic using either of the texton, steerable pyramid or LBP features. This was considerably better than what could be obtained with the GLCM features. Monitoring of froth flotation cells was simulated with the batch data. The texton textural features were the most discriminatory with regard to detecting changes in the arsenic content of the froth.

Flotation Froth Image Analysis by Use of a Dynamic Feature Extraction Algorithm

Abstract: Froth image analysis has been well established as a means to infer the performance of froth flotation cells in real time. Apart from linking the appearance of the froth to the behavior of the flotation system, the dynamic behaviour of the froth is also an important determinant of the performance of the flotation cell, and ideally, this information should also be taken into consideration. In this investigation, the dynamic behaviour of the froth was incorporated implicitly in the features extracted from the images. As a case study, mineral mixtures consisting of realgar, orpiment and quartz were floated in a laboratory batch flotation cell. Videographic mages of the froths generated by the experiments and a dynamic local binary pattern algorithm (LBP-TOP) was used to extract features from the video data. A random forest model could subsequently be built to reliably classify the conditions prevailing in each of the batch runs. The dynamic LBP algorithm did not perform significantly better than its 2D equivalent that did not incorporate the temporal behaviour of the froth, as both approaches could very reliably identify the different froth classes.

The dynamic behaviour of coarse particles in flotation froths. Part III: Ore particles

A froth separating device was tested in which heavy, hydrophobic particles break froth films and sink to the bottom, while light, hydrophilic particles are supported by the froth to form a top tailings product. Two potential industrial applications for the reverse froth flotation process were evaluated. As a coarse particle flotation technique for sulphide bearing ores, it was found that xanthate pre-conditioning of the ore results in concentrating the sulphur bearing particles to the concentrate. By increasing the xanthate addition, the relative mass recovery as well as sulphur recovery increases. This increase in mass and sulphur recovery is not linear. These results were promising in terms of finding a coarse particle flotation technique for the pre-concentration of sulphide bearing minerals. Preliminary tests indicated that the reverse froth flotation process is not suitable for the replacement of grease belts for fine (−3 mm) diamond recovery. The major concern is the high potential losses of valuable material to the tailings. These losses are mainly due to the fact that the major separation process in the reverse froth flotation cell is based on particle mass beyond a certain critical value. The surface properties of the particle account only for a secondary separation process. Nevertheless, this technique still offers the potential to be applied to coarse coal flotation and recycling waste separation within certain operating limits.

Quasi-one-dimensional foam drainage

Foam drainage is considered in a froth flotation cell. Air flow through the foam is described by a simple two-dimensional deceleration flow, modelling the foam spilling over a weir. Foam microstructure is given in terms of the number of channels (Plateau borders) per unit area, which scales as the inverse square of bubble size. The Plateau border number density decreases with height in the foam, and also decreases horizontally as the weir is approached. Foam drainage equations, applicable in the dry foam limit, are described. These can be used to determine the average cross-sectional area of a Plateau border, denoted A, as a function of position in the foam. Quasi-one-dimensional solutions are available in which A only varies vertically, in spite of the two-dimensional nature of the air flow and Plateau border number density fields. For such situations the liquid drainage relative to the air flow is purely vertical. The parametric behaviour of the system is investigated with respect to a number of dimensionless parameters: K (the strength of capillary suction relative to gravity), α (the deceleration of the air flow), and n and h (respectively, the horizontal and vertical variations of the Plateau border number density). The parameter K is small, implying the existence of boundary layer solutions: capillary suction is negligible except in thin layers near the bottom boundary. The boundary layer thickness (when converted back to dimensional variables) is independent of the height of the foam. The deceleration parameter α affects the Plateau border area on the top boundary: weaker decelerations give larger Plateau border areas at the surface. For weak decelerations, there is rapid convergence of the boundary layer solutions at the bottom onto ones with negligible capillary suction higher up. For strong decelerations, two branches of solutions for A are possible in the K = 0 limit: one is smooth, and the other has a distinct kink. The full system, with small but non-zero capillary suction, lies relatively close to the kinked solution branch, but convergence from the lower boundary layer onto this branch is distinctly slow. Variations in the Plateau border number density (non-zero n and h) increase individual Plateau border areas relative to the case of uniformly sized bubbles. For strong decelerations and negligible capillarity, solutions closely follow the kinked solution branch if bubble sizes are only slightly non-uniform. As the extent of non-uniformity increases, the Plateau border area reaches a maximum corresponding to no net upward velocity of foam liquid. In the case of vertical variation of number density, liquid content profiles and Plateau border area profiles cease to be simply proportional to one another. Plateau border areas match at the top of the foam independent of h, implying a considerable difference in liquid content for foams which exhibit different number density profiles.

The `Grab and Run' revisited — improving selectivity between organic and inorganic components in conventional coal froth flotation

Conventional coal froth flotation has been used for decades to upgrade the finest fraction of coal (0.60 mm×0 or 0.147 mm×0) in commercial coal cleaning plants. While this fraction amounts to a modest 5–10% of the plant feed in typical U.S. coal cleaning plants, it can amount to over half of the feed to pond fine recovery circuits. Proper operation of the froth flotation circuit becomes critical, especially for these pond fine circuits. Much has been made of column flotation cell performance. However, the high capital cost, the requirement for large amounts of compressed air for some cell designs, and the often higher reagent cost, cannot often be justified in the overall economics of a typical coal cleaning plant and, especially, for pond fine recovery. By selecting operating conditions that improve the selectivity between the organic and inorganic fractions of the coal, conventional coal flotation cell performance can approach the performance of column flotation cells. Operators can successfully accomplish this by selecting circuitry like the `Grab and Run' circuit, with operating conditions that allow for the increased drainage of ash-forming and sulfur-bearing minerals from the froth. This paper provides a review of data regarding flotation circuitry that gives coal flotation operators guidance in selecting the best operating conditions for conventional coal froth flotation cells.

Geotechnical characterization of blended coal tailings for construction and rehabilitation work

Abstract Coarse and fine refuse is produced by various coal processing equipment. For instance, fine tailings (100-500µm) are produced by froth flotation cells, whereas coarse fractions (up to 50 mm) constitute cyclone rejects. The relatively wet fine tailings have limited use in construction activities and they are generally pumped as slurries into tailings ponds. The coarse rejects have a greater engineering applicability and are utilized in the construction of tailings dams, mine access roads as well as for landfill and ballast. This study investigates the fundamental engineering properties of blended tailings, where- by appropriate fractions of flotation tailings are mixed with cyclone rejects to produce an acceptable construction or rehabilitation fill. In particular, a practical procedure to optimize the blended ratios is proposed on the basis of fundamental geotechnical testing. The applications of relevant tests are described, including Proctor compaction, California Bearing Ratios, triaxial and consolidation tests. The results confirm that blending of fines with coarse rejects enables enhanced dry densities associated with reduced permeabilities, higher shear and compressive strengths, lower consolidation settlements and increased bearing capacities. The addition of a small quantity of cement (2-5%) further improves the engineering properties of the blended matrix. The practical findings of this study should encourage coal processing plants to modify their existing disposal methods to adopt more efficient co-disposal schemes. Optimization of procedures for discarding fine and coarse rejects together would generate substantial savings, with regard to dewatering of wet tailings and rehandling of distinctly different waste gradations.

Design and operation characteristics of an improved laboratory flotation cell

An improved laboratory froth flotation cell has been designed which eliminates many of the inadequacies of previous cells, and also allows the study of froth effects in flotation. Details of its design and functional features are discussed herein.The performance of the new cell is evaluated from results of replicate batch flotation tests, carried out by using china clay slurries. This evaluation indicates that reproducibility of results is satisfactory, the maximum deviation of cumulative recovery from the mean being only about six percent in the replicate tests.Hydrodynamic collision theories suggest that to float fine or colloidal particles, eg. china clay particles, it is necessary, first of all, to flocculate the particles so that optimum-size flocs form for attachment to bubbles in a flotation cell, which are typically 1–2 mm in diameter.Equilibrium floc size in a flotation cell depends on the shear rate distribution introduced by the impeller. Hence the shear rate distribution has been computed based on a three-zone distributed shear rate model, using measured value of power input to the cell. The results demonstrates that shear rates decline rapidly away from the impeller tip, allowing the formation of stable flocs.

A froth ultra-fine model for the selective separation of coal from mineral in a dispersed air flotation cell

A Denver D-12 Laboratory froth flotation cell was used to investigate the effect of froth structure on the kinetics and selectivity of the separation of ultra-fine coal from its associated mineral. A mathematical model was developed which was capable of predicting flotation performance in terms of the flux of bubble surface area up the column and the thickness of the interbubble lamellar liquid. A lamellar probe was constructed and film thicknesses were measured for two-and three-phase froths. For three-phase froths, the limiting lamellar thickness at the top of the froth column correlated with the d 95 size of the particles in the froth. Selectivity predictions using the model were experimentally confirmed. Predictions for tests in which the feed-pulp was diluted and in which the concentrate was refloated were also confirmed experimentally.

Effective desliming of froth flotation cell feed at Elk Run Coal Co.

This paper focuses on the −½ mm cleaning at Elk Run Coal. The original circuitry incorporated desliming cyclones. Problems with slimes entrainment in the cyclone underflow (froth cell feed) resulted in poor froth cell selectivity. Laboratory test work led to the installation of high frequency desliming screens. Consequently, great improvement in cell performance was brought about by enhanced desliming with the ability to use split flotation. The modifications resulted in significant improvement in total plant performance and overall yield while maintaining clean coal quality.

Froth flotation: The adhesion of solid particles to flat interfaces and bubbles

The adhesion of a spherical particle to a liquid-air interface has been investigated experimentally, and equations derived for the force and work required to detach the particle from the interface as functions of the solid and liquid densities, the surface tension and the angle of contact. The critical centrifugal force required to detach and submerge siliconed glass beads (radii 0·02–0·1 cm) from air-liquid interfaces was in good agreement with theory. The liquids used were water, and 10 per cent and 25 per cent ethanol in water. Similar measurements with aggregates of approximately equal sized beads showed that the adhesive strength of the aggregate decreased as the number of beads increased, reaching a limiting value of about 50 per cent of the adhesive strength of the individual beads, when ten beads were present in the aggregate. The bearing of the results on the process of attachment and the adhesion of mineral particles to air bubbles in froth flotation cells is discussed.