Froth Flotation Of Minerals Research Articles

Compression and reconstruction of flotation foam images based on generative adversarial networks

The froth flotation is a beneficiation method that utilizes the differences in the physical and chemical properties of the surface of mineral particles to achieve the effective separation of different minerals. Recently, with the development of image processing and computer technology, machine vision has been widely used in mineral froth flotation. However, due to the high pixels of the flotation froth image and the limited storage space of the industrial computer, it is difficult to save a large amount of image data at the industrial site. To this end, a flotation foam image compression and reconstruction method is presented in this work. First, a lossless froth image is collected from the flotation cell in a gold hydrometallurgical plant. Then, the JPEG image compression algorithm compresses the original images to one in dozens. Under this situation, low-quality and small-volume images can be stored in an industrial computer easily. To reconstruct the compressed image, the generative adversarial networks (GAN) is used in this work, and RRDB and VGG19 are employed as the generative and discriminative models of the network, respectively. The loss function of the model is the sum of three losses, which are L1 loss, perceptual loss, and adversarial loss. Three methods for testing the texture features of the froth image are selected to verify the efficiency of the proposed method. The results show that the reconstructed image can effectively restore the details of the bubbles, reflect the image features, and has less noise and high visual similarity with the original image. The reconstructed images generated by low-resolution images with different compression qualities mostly maintain a restoration degree of more than 90% compared with the original images in three texture features.

Interaction mechanisms between sub-bituminous coal particle and air bubble: Impact of collector adsorption

The interaction between air bubbles and minerals surface plays essential role in mineral froth flotation. In this work, an atomic force microscope (AFM) colloidal probe technique was employed to directly measure the interaction forces between an air bubble and sub-bituminous coal (SBC) particle modified with polar (1-dodecanol)/nonpolar (dodecane) collectors, respectively. And the SBC particle-bubble attachment efficiency measurement was used to verify the AFM force measurement results. The adhesion force was found to be stronger for the air bubble-SBC particle modified with 1-dodecanol, which makes particle-bubble attachment efficiency higher than the dodecane-modified condition. The interaction forces between SBC particles and collectors were determined, and the adsorption behavior of the collector on the coal surface was studied by molecular dynamics (MD) simulation, aiming to reveal the underlying mechanism for the variation of collector-modified SBC particle-bubble interaction force. It was found that 1-dodecanol and SBC have stronger adhesion, which helps it to be more easily adsorbed on the SBC surface. The contact angle test and MD simulation results showed that the hydrophobicity of the SBC surface improved the most after the modification with 1-dodecanol, which in turn finally promoted the interaction between SBC surface and air bubble. This work may offer an interesting strategy for the targeted selection of collectors in the flotation process of SBC.

Effects of surfactants combination on iron ore flotation

Frothing plays a crucial role in mineral froth flotation. However, the use of only frothing reagents is not common in the reverse cationic flotation of iron ores because etheramines, the commonly applied collectors, also play this role. In alkaline aqueous solution, etheramines dissociate as ionic (collector) and molecular (frother) species, simplifying the chemical system. Despite practical and functional, this practice is limited once etheramines are less efficient to form foam and more expensive than conventional frothers, e.g., alcohols and polyglycols. This study investigated the comparative effects between non-ionic frothers and cationic etheramines on foam properties in two phase systems, and the combination of these etheramines and frothers in three phase systems in comparison to single etheramines and their mixtures. The results show that the frothers DF1012 and MIBC produce smaller bubbles and more stable foams than the single ethermonoamine or etherdiamine. The partial replacement of etheramines by non-ionic frothers reduced the silica content in the concentrate, improving flotation selectivity at specific mixture condition of collector substitution for each frother type, despite decreasing the iron metallurgical recovery. The substitution of etherdiamine by polyglycol at 10 % w/w produced the best result in the cationic/non-ionic surfactants comparison, although the mixture of etherdiamine and ethermonoamine yielded the highest selectivity, because of the synergistic effect on froth stability and mineral surface adsorption.

Standard method for performing positron emission particle tracking (PEPT) measurements of froth flotation at PEPT Cape Town

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.

Nano-Silica based mineral flotation frother: Synthesis and flotation of Platinum Group Metals (PGMs)

We report the synthesis and application of nanomaterials in the field of mineral processing. Nanotechnology is a potentially disruptive technology with a huge potential to open up new avenues of enhancing mineral recovery and grades in the domain of mineral froth flotation. In this investigation a solid, nano-silica (NS) based frother was synthesized using the sol–gel method for test works involving Platinum Group Metals (PGMs) and associated base metals. The nano flotation reagent was characterized using Fourier Transform Infrared Spectroscopy for chemical structure analysis (FTIR), Powder X-Ray Diffraction (P’XRD) for structural analysis and Field Emission Scanning Electron Microscopy (FESEM) for surface morphology and particle size distribution, Energy Dispersive Spectroscopy (EDS) for elemental analysis. X-ray fluorescence (XRF) was used for mineral assaying after flotation. The generated nano-silica had an average particle size distribution of 35–41 nm. The flotation performance of the nano-frother was benchmarked with a commercial conventional frother (SasFrother). At an optimum nano-frother dosage of 20 g/t a recovery of 73.8%, 77.0%, 84.0% and 78.2% platinum, palladium, nickel and copper respectively was realized. However, the associated grades were lower when compared with the conventional frother. On the other hand, increasing nano-silica dosage above the optimal dosage resulted in a reduction of the actual recovery for all the metals. Interestingly, the dosage requirement for the nano-frother required for optimal mineral recover was much lower than that of the conventional frother. Based on these findings, opportunities at nano scale can proffer numerous novel materials with exceptional properties for application in mineral froth flotation.

Unlocking the potential of sustainable chemicals in mineral processing: Improving sphalerite flotation using amphiphilic cellulose and frother mixtures

The transition towards cleaner production of primary minerals demands technologies that improve productivity while lowering their environmental impact. The present study explores a novel approach to support this transition by partially substituting a commercial froth stabilization reagent in mineral froth flotation (DowFroth200) with an amphiphilic cellulose derivative (namely, hydroxypropyl methyl cellulose) that is nontoxic, biodegradable and can be produced from sustainable sources. The performance of the cellulose-frother mixture is explored using sphalerite as case study.In the first place, the interaction between the two frother molecules was studied from the perspective of two-phase foam characteristics. The use of the polymer-surfactant (PS) mixture studied reported an increased foam stability and small bubble sizes, attributed to a combination of liquid film drainage prevention and steric effects of cellulose macromolecules. As a result, when used as frothers in the flotation of sphalerite, the PS-mixture exhibited a robust behavior resulting in advantages such as: i) improved separation efficiencies; ii) consistent recovery values, even under highly alkaline pH, iii) maintaining high recoveries when the collector dosage was reduced down to 25% of typical values used in the industry; and iv) faster flotation kinetics. The results obtained aim to demonstrate that properly designed green chemical systems can have a positive impact in the mining sector.

Cationic collector conformations on an oxide mineral interface: Roles of pH, ionic strength, and ion valence

The adsorption of collectors at the solid–liquid interface to impart and enhance a mineral’s hydrophobicity is essential to mineral froth flotation. During adsorption, collectors must conform on the mineral surface with their nonpolar tails facing the aqueous phase to enhance the mineral’s hydrophobicity. This conformation is subject to conditions prevailing in the aqueous phase, such as the pH and nature of ions present. Since this conformation can affect the degree of hydrophobicity, molecular-level understanding of this phenomenon also is beneficial to improve hydrophobicity via adsorption layer manipulation. In this study, the structural conformational changes of cationic collector behenyl trimethyl ammonium chloride on a silica surface were studied using an in situ quartz crystal microbalance with dissipation (QCM–D) coupled with contact angle measurements. Two electrolytes, NaCl and CaCl2, were used to investigate the effects of ionic strength (IS) and ion valence. The QCM–D data at different pHs, both with and without a background electrolyte, revealed complex changes in the collector conformations and structure of the adsorption layer. Two distinct adsorption characteristics were also observed depending on ion valence: the presence of NaCl led to a thin, rigid layer (low dissipation), while a thick, soft layer (high dissipation) formed in the presence of CaCl2. Meanwhile, the increase in the IS of NaCl resulted in a more rigid adsorbed layer on the silica at both pHs. For CaCl2, the adsorbed layer became softer and highly dissipated at pH 5.7, whereas it became less soft at pH 10. This inconsistency in the rigidity with IS in the presence of CaCl2 was likely due to the strong sorption of Ca(OH)+ at a high pH. Interestingly, the imparted hydrophobicity decreased as the IS increased, with a greater extent of reduction at a high pH regardless of ion type. Moreover, it had a strong relationship with the ratio of dissipation and frequency change, with a lower contact angle at a higher ratio due to greater imbibition of water molecules and/or hydrated cations. These findings have implications for silica flotation systems wherein Ca2+ and Na+ cations are present in appreciable amounts.

Hetero-difunctional Reagent with Superior Flotation Performance to Chalcopyrite and the Associated Surface Interaction Mechanism.

Surface modification by chemical reagents is of profound importance to modulate the surface characteristic and functionality of materials, which has attracted tremendous interest in many research fields and industrial applications, such as froth flotation of minerals. In this work, a new reagent S-[(2-hydroxyamino)-2-oxoethyl]- O-octyl-dithiocarbonate ester (HAOODE) with heterodifunctional ligands was designed and synthesized to improve the flotability of chalcopyrite (CuFeS2). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed the co-adsorption of heterodifunctional ligands (i.e., dithiocarbonate and hydroxamate groups) of HAOODE on chalcopyrite via Cu(I)-S and Cu(II)-O covalent bonds. The bubble probe atomic force microscopy (AFM) technique was employed to quantitatively measure the air bubble-chalcopyrite interactions with and without the reagent adsorption. AFM force results revealed that the bubble could be more readily attached to flat chalcopyrite after HAOODE treatment under different hydrodynamic conditions because of the enhanced hydrophobic interaction, with the decay length D0 increasing from 0.65 to 1.20 nm. The calculated bubble-particle interaction forces also demonstrated the critical influence of HAOODE treatment, hydrodynamic conditions, and bubble size on the interaction behavior and thin-film drainage process in flotation. In froth flotation, HAOODE exhibited superior recovery for chalcopyrite over pH 3-12 and excellent selectivity for chalcopyrite against pyrite (FeS2) above pH 10.5, as compared to the conventional reagent sodium isobutyl xanthate. This work provides a useful approach to develop effective reagents that could selectively adsorb on desired mineral surfaces through heterodifunctional ligands and to quantitatively evaluate the role of reagent adsorption in the interactions between air bubbles and mineral surfaces at the nano- and microscale. Our results show implications on developing molecular design principles of novel reagents for surface modifications of materials in a wide range of engineering and biological applications.

A review of temperature-responsive polymers as novel reagents for solid-liquid separation and froth flotation of minerals

Over the past few decades, the study of temperature-responsive polymers has unlocked a vast array of potential applications in various research areas, including biological systems, wastewater treatment, and gel actuation. These dynamic materials are able to exhibit reversible hydrophilic-hydrophobic transitions in a sharp and rapid manner, under a change in temperature in aqueous solutions. This property can be used to reversibly change particle-particle interactions between attractive and repulsive states. Recent studies have demonstrated that the temperature-responsive properties of these materials can be utilised to enhance water recovery and increase solids concentration in dewatering processes, as well as improve the recovery of minerals in flotation operations. This review explores the nature of temperature-responsive polymers, and the mechanisms behind their use as flocculants in solid-liquid separation and tuneable collector/depressants in froth flotation. The polymers and minerals investigated will be considered in detail, as well as the factors influencing the dewatering and flotation capabilities of thermo-responsive materials. The challenges and considerations in the development of new temperature-responsive polymers and their potential applications in minerals processing will also be discussed.

Mapping the Nanoscale Heterogeneity of Surface Hydrophobicity on the Sphalerite Mineral

Hydrophobic effect plays an important role in a wide range of natural phenomena and engineering applications, such as mineral froth flotation. In this work, atomic force microscope (AFM) force mapping was employed, for the first time, to probe the nanoscale heterogeneity of surface hydrophobicity and surface interactions on the sphalerite mineral surface before/after conditioning treatment (activated by copper sulfate and then treated by amyl xantahte). The AFM force mapping demonstrates that adhesion on sphalerite falls in a narrow range with a peak centered at 16.4 mN/m and adhesion on conditioned sphalerite falls in a wide range with a small peak centered at 15.5 mN/m and a large peak centered at 58.1 mN/m. It is evident that the sphalerite surface is hydrophilic with homogeneous surface hydrophobicity whereas conditioned sphalerite exhibits a heterogeneous distribution of surface hydrophobicity due to the nonuniform adsorption of xanthate. The significantly enhanced adhesion after conditioning treatme...

Probing Surface Interactions of Electrochemically Active Galena Mineral Surface Using Atomic Force Microscopy

Colloidal stability governed by various surface interactions finds wide application in many engineering processes, such as mineral froth flotation. In this work, electrochemical atomic force microscopy (EC-AFM) was employed to modulate the interfacial chemical reaction and simultaneously probe the evolution of surface characteristics (i.e., morphological changes and surface interactions) of electrochemically active galena mineral surface at the nanoscale. Successive potentials (i.e., −0.7, −0.3, 0, 0.1, 0.2, 0.3, and 0.45 V), referred to the Ag/AgCl/3.4 M KCl reference electrode (0.206 V vs standard hydrogen electrode), were respectively held for 20 s on the galena surface. The in-situ topographic imaging demonstrates homogeneous electrochemical oxidation across the mineral surface, leading to slight surface roughening at the potential of 0 V and more pronounced surface roughening at higher potentials (e.g., 0.3 and 0.45 V). The direct force measurements with an octadecyltrichlorosilane (OTS)-functionaliz...

Predicting bubble size and bubble rate data in water and in froth flotation-like slurry from computational fluid dynamics (CFD) by applying deep neural networks (DNN)

Accurate characterization of two phase bubbly flows is crucial in many industrial processes such as fluidized reactors, ore froth flotation, etc. The bubble size determines the rate at which components present in the gas phase are transferred to the surroundings and vice versa while bubble rate defines the appropriate bubbly flow regime occurring in the heterogeneous system. This research work employs deep neural networks (DNNs) to predict bubble size and bubble rate using data obtained from validated computational fluid dynamics (CFD) computations. Pure water and slurry (in conditions similar to those employed in mineral froth flotation) case studies are evaluated. It is found that the DNN can predict the CFD results accurately when using four hidden layers, describing discontinuities in the bubbly flow regime. The relative errors computed between the CFD data and the prediction obtained by the DNN is as low as 8.8% and 1.8% for bubble size and bubble rate, respectively. These results confirm that the DNN can be applied to sophisticated fluid dynamics systems and allow developing better control process strategies since once the DNN is trained critical variables can be computed very efficiently. The slurry case study, although restricted to the application of mineral froth flotation, can also be generalized to other industrial operations keeping the exact same procedure.

Probing the interaction between air bubble and sphalerite mineral surface using atomic force microscope.

The interaction between air bubbles and solid surfaces plays important roles in many engineering processes, such as mineral froth flotation. In this work, an atomic force microscope (AFM) bubble probe technique was employed, for the first time, to directly measure the interaction forces between an air bubble and sphalerite mineral surfaces of different hydrophobicity (i.e., sphalerite before/after conditioning treatment) under various hydrodynamic conditions. The direct force measurements demonstrate the critical role of the hydrodynamic force and surface forces in bubble-mineral interaction and attachment, which agree well with the theoretical calculations based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. The hydrophobic disjoining pressure was found to be stronger for the bubble-water-conditioned sphalerite interaction with a larger hydrophobic decay length, which enables the bubble attachment on conditioned sphalerite at relatively higher bubble approaching velocities than that of unconditioned sphalerite. Increasing the salt concentration (i.e., NaCl, CaCl2) leads to weakened electrical double layer force and thereby facilitates the bubble-mineral attachment, which follows the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory by including the effects of hydrophobic interaction. The results provide insights into the basic understanding of the interaction mechanism between bubbles and minerals at nanoscale in froth flotation processes, and the methodology on probing the interaction forces of air bubble and sphalerite surfaces in this work can be extended to many other mineral and particle systems.

Factors involving the solids-carrying flotation capacity of microbubbles

Dissolved air flotation (DAF) is a technique used extensively for separating fine particles in water and wastewater treatment, but, unfortunately, its use is still limited for froth flotation of minerals. This appear to be due to the very low lifting power of the microbubbles (40–70μm) and low airflow rate because of the low solubility of air in water. Thus, the efficiency of DAF in treating mineral particles has shown to be poor and as a solid/liquid separation technology is limited to slurries with no more than 3% solids. This work presents results showing (measuring) the limits of DAF as a function of particle size distribution, solids content and air superficial velocity. Interestingly, the microbubbles were found to be not selective with respect to particle size, floating both fine and coarse particles, which is most likely due to the existence of several mechanisms acting on the flotation of particles by these minute bubbles.

A Novel Property of DNA – As a Bioflotation Reagent in Mineral Processing

Environmental concerns regarding the use of certain chemicals in the froth flotation of minerals have led investigators to explore biological entities as potential substitutes for the reagents in vogue. Despite the fact that several microorganisms have been used for the separation of a variety of mineral systems, a detailed characterization of the biochemical molecules involved therein has not been reported so far. In this investigation, the selective flotation of sphalerite from a sphalerite-galena mineral mixture has been achieved using the cellular components of Bacillus species. The key constituent primarily responsible for the flotation of sphalerite has been identified as DNA, which functions as a bio-collector. Furthermore, using reconstitution studies, the obligatory need for the presence of non-DNA components as bio-depressants for galena has been demonstrated. A probable model involving these entities in the selective flotation of sphalerite from the mineral mixture has been discussed.

Effect of Environmental Humidity on Static Foam Stability

The quality of foaming products (such as beer and shampoo) and the performance of industrial processes that harness foam (such as the froth flotation of minerals or the foam fractionation of proteins) depend upon foam stability. In this study, experiments are performed to study the effect of environmental humidity on the collapse of static foams. The dependency of the rate at which a foam collapses upon humidity is demonstrated, and we propose a hypothesis for bubble bursting due to Marangoni instability induced by nonuniform evaporation to help explain the dependency. This hypothesis is supported by direct experimental observations of the bursting process of isolated bubbles by high speed video recording and the thinning of isolated foam films under different values of humidity and temperature by microinterferometric methods.

Study of Microemulsified Systems Applied to Mineral Flotation

An investigation of calcite and fluorite microflotation using microemulsified systems is reported. Several reagents that are commonly used in mineral froth flotation, such as sodium silicate, quebracho, and pH modifiers, were tested. The main objective of this research was to simplify the conventional flotation process by the use of microemulsions. This application is based on their capacity to contain variable amounts of water, oil, and surface-active material in a single phase and their ability to decrease interfacial tension, a fact that favors their application in separation processes. The microflotation assays were accomplished in a modified Hallimond tube under specific operating conditions. The results obtained are pioneer and demonstrated the viability of the use of microemulsions in mineral flotation, leading to an improvement of the conventional process.

Visualisation of plant disturbances using self-organising maps

Ill-defined processes such as the froth flotation of minerals are mostly controlled in an empirical way by using rules of thumb. These processes involve so many variables that the plant operator finds it difficult to visualise or even observe a change in process conditions. In froth flotation the operator is supposed to visually observe process changes from the appearance of the froth, which is an unreasonable demand under industrial conditions. An on-line computer vision system based on a textural analysis of the froth phase has been developed in South Africa and has been in operation on two industrial plants since early 1995. Textural parameters are determined on-line, and disturbances in process conditions, such as a change in reagent addition or froth depth, are visualised via a Self-Organizing Map (SOM) neural net.

The effect of dissolved hydrocarbon gases in surfactant solutions on froth flotation of minerals

Hydrocarbon gases are known to dissolve in surfactant solutions and affect the solution/gas interfacial properties. In this study, their effect on the froth flotation of various minerals was investigated. Also, solubility of these gases in collector solutions and the resultant surface tension changes were simultaneously determined for elucidating the mechanisms responsible for the effects on flotation. Methane dissolved in sodium dodecylsulfonate collector solutions was found to increase the flotation of alumina by 10–30%. Corresponding increase obtained due to the dissolution of butane was 10–50%. Flotation of hematite or quartz was not affected by the presence of dissolved methane or butane. Dissolution studies using a new automated constant-pressure apparatus showed the solubility of gases to be lower in surfactant solutions than in water when the surfactant concentration was low and higher than in water when the concentration was high. This is explained on the basis of the predominance of the “salting-out” effect at lower surfactant concentrations and that of hydrophobic bond formation between the hydrocarbon molecule and the surfactant chains at higher concentrations. Measurements of surface tension properties of these hydrocarbon saturated solutions have indicated adsorption of the gas molecules at the solution/air interface. The selective effects of the dissolved hydrocarbons on froth flotation of minerals are discussed on the basis of possible changes in the properties of the solution surface and the mineral/solution interface.