Bubble-particle Interaction Research Articles

Influence of Particle Size on Flotation Separation of Ilmenite and Forsterite

In addition to bubble–particle interaction, particle–particle interaction also has a significant influence on mineral flotation. Fine particles that coat the mineral surface prevent direct contact with collectors and/or air bubbles, thereby lowering flotation recovery. Calculating the particle interaction energy can help in evaluating the interaction behavior of particles. In this study, the floatability of coarse ilmenite (−151 + 74 μm) and different particle sizes (−45 + 25, −25 + 19, −19 μm) of forsterite with NaOL as a collector was investigated. The results showed that forsterite sizes of −45 + 25 and −25 + 19 μm had no effect on the ilmenite floatability, whereas −19 μm forsterite significantly reduced ilmenite floatability. A particle size analysis of artificially mixed minerals and a scanning electron microscopy (SEM) analysis of the flotation products showed that heterogeneous aggregation occurred between ilmenite and −19 μm forsterite particles. The extended DLVO (Derjaguin–Landau–Verwey–Overbeek) theory was applied to calculate the interaction energy between mineral particles using data from zeta potential and contact angle measurements. The results showed that the interaction barriers between ilmenite (−151 + 74 μm) and forsterite (−45 + 25, −25 + 19, and −19 μm) were 11.94 × 103 kT, 8.23 × 103 kT and 4.09 × 103 kT, respectively. Additionally, the interaction barrier between forsterite particles smaller than 19 μm was 0.51 × 103 kT. The strength of the barrier decreased as the size of the forsterite decreased. Therefore, fine forsterite particles and aggregated forsterite can easily overcome the energy barrier, coating the ilmenite particle surface. This explains the effect of different forsterite sizes on the floatability of ilmenite and the underlying mechanism of particle interaction.

Analysis of difficult flotation mechanisms for coarse low-rank coal: Comparing fluidized-bed and mechanical flotation technologies

Efficient flotation of coarse low-rank coal is essential for enhancing energy utilization in the mineral processing industry. As the beneficiation equipment scales up, the precision of particle size classification before flotation decreases, leading to a higher coarse particle content in the feed, which poses significant challenges to traditional flotation processes. Recent advancements in fluidized bed flotation technology have demonstrated considerable advantages in the flotation of coarse-grained metallic minerals; however, its application to coarse low-rank coal remains relatively unexplored. This study investigates the potential of fluidized bed flotation technology for coarse low-rank coal, employing various analytical methods to elucidate difficult flotation mechanisms. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were utilized to comprehensively characterize the surface morphology and chemical composition of coal samples. The influence of increasing particle size on flotation performance was systematically assessed through measurements of induction time and critical detachment amplitude. Comparative flotation experiments were conducted to evaluate the efficacy of traditional mechanical flotation against fluidized bed flotation technologies. Results indicate that the presence of cracks and oxygen-containing functional groups on the coal surface significantly enhances hydrophilicity, hindering flotation recovery rates. With increasing particle size, the induction time between particles and bubbles lengthens, while the critical detachment amplitude decreases, weakening the attachment and increasing detachment likelihood. Although high-efficiency collectors enhance coal particle hydrophobicity, they cannot fully mitigate the turbulence disrupting bubble-particle interactions in mechanical flotation. Conversely, fluidized bed flotation effectively minimizes turbulence interference, leading to an approximate 40 % increase in the recovery rate of coarse low-rank coal (0.25–1.00 mm) compared to traditional mechanical flotation. This study presents a novel technological approach for the efficient recovery of coarse low-rank coal, contributing to the clean utilization of low-rank coal resources.

Optimization of particle–bubble collision dynamics in turbulence via clustering algorithms and microscale vortex enrichment analysis

The interaction dynamics between particles and bubbles in turbulent flow fields are crucial for optimizing multiphase flow systems. In this work, direct numerical simulation is combined with advanced K-means++ clustering algorithms to quantify the spatial distribution and enrichment effects of particle–bubble clusters under different turbulence conditions. The results indicate that the Stokes number increases with particle and bubble size, demonstrating stronger inertial effects, but decreases with higher turbulence intensity. Radial relative velocity and collision frequency also exhibit a positive correlation with size and turbulence intensity. Clustering analysis reveals that larger particles and bubbles form more pronounced clusters, particularly in high turbulence conditions, leading to higher local densities and interaction frequencies. Overlap ratios suggest increased interactions with growing size and turbulence intensity. These findings highlight the importance of optimizing particle and bubble sizes to match specific turbulence conditions, enhancing interaction dynamics in multiphase flow systems. This research provides valuable insights for improving various industrial processes involving particle–bubble interactions.

Experimental analysis of particle dynamics influenced by cavitation bubbles near a rigid wall

This study utilized experimental methods involving high-speed cameras to observe the interaction between cavitation bubbles, generated by a low-voltage electric spark device, and particles near a rigid wall. The dynamic characteristics of the particles were analyzed under varying conditions, including different cavitation bubble sizes, particle sizes, and distances between the cavitation bubble and the wall. Two characteristic parameters were introduced: χ for the particle and cavitation bubble sizes, and λ for the cavitation bubble wall distance. Qualitative distinctions were made among types of particle–bubble interactions, and force analysis was conducted under conditions where χ exceeded the threshold χt. The findings reveal that when χ < χt, particle motion is primarily influenced by the jet effects produced by the cavitation bubble. Conversely, when χ > χt, particle motion is dominated by the radiation forces exerted by the cavitation bubble. Under jet-dominated conditions, particle trajectories were observed to be erratic and unpredictable. For cases where λ < 0, the high-speed jet directly impacts the particle. Conversely, for λ > 0, the jet's velocity decays rapidly upon reaching the particle. In scenarios dominated by radiation forces, the cavitation bubble drew particles away from the wall, followed by their free fall back toward it. The influence of gravity, buoyancy, bubble radiation force, fluid resistance, and virtual mass force on particles was studied when radiation forces prevailed. The acceleration formula for particles was derived through the application of the bubble dynamics equation and was refined based on experimental observations.

Effect of turbulence intensity on bubble-particle detachment mechanism in a confined vortex

Bubble-particle detachment induced by turbulence is the primary factor for the low recovery of coarse particles, which has attracted much attention in recent years. The prevailing centrifugal detachment theory has achieved broad consensus. However, due to the complexity of bubble-particle aggregate motion in the turbulent field, the influence of turbulence intensity on bubble-particle detachment mechanism remains unclear. In this study, a controlled rotating vortex was generated using a custom-made fluid channel to systematically investigate the effect of turbulence intensity on bubble-particle centrifugal detachment. Firstly, detachment behaviours of bubble-particle aggregates were captured using high-speed cameras, followed by flow field visualization of bubble-particle detachment processes using Computational Fluid Dynamics (CFD). Experimental results reveal three typical detachment modes of bubble-particle aggregates in the confined vortex: fluid shear, bubble oscillation, and particle centrifugal motion, with particle centrifugal detachment becoming dominant with increasing turbulence intensity. This shift is attributed to changes in turbulence intensity directly affecting the trajectories of bubble/aggregates and indirectly influencing the detachment mode of bubble-particle. Compared to low turbulence intensity, bubble-particle aggregates exhibit smaller rotational radii under high turbulence intensity, reducing the probability of fluid shear and bubble oscillation detachment by mitigating the influence of high-speed shear zones at the top of the cavity. Conversely, particles located at the edge of aggregates are more susceptible to acceleration by sidewall flow fields, favouring detachment through particle centrifugal motion. Moreover, unlike traditional centrifugal detachment theories, particles do not merely undergo independent circumferential motion on the bubble surface but participate as a whole with bubbles in centrifugal motion governed by vortices. These findings are expected to provide fundamental insights into the bubble-particle detachment mechanism in turbulent fields.

The role of interfacial nanobubbles in the flotation performance of microfine particles

The enhanced role of Interfacial nanobubbles (INBs) in microfine particles flotation is still unclear. In this study, the microfine particles with different sizes were functionalized to obtain different wettability. The temperature difference method was employed to produce the nanobubbles water. Atomic force microscopy (AFM) was utilized to investigate the formation of INBs. A temperature-controlled flotation system was devised to investigate the flotation performance of microfine particles in the presence and absence of INBs. Agglomeration experiments and attachment time tests were conducted to elucidate the enhanced effects of INBs on flotation from the perspectives of particle-particle and bubble-particle interactions. The results showed that both the number and size of INBs increased with the increase of surface hydrophobicity and level of air saturation in water. In the temperature-controlled flotation system, the flotation recovery and flotation rate of microfine particles were improved significantly in nanobubbles water compared to that in normal water. The optimal flotation result of −38 μm strongly hydrophobic particles was obtained in nanobubbles water at 25 ℃. The enhanced impact of INBs on flotation was more pronounced for more hydrophobic particles. The increase in the apparent size of particles and reduction in particle-bubble attachment time facilitated by INBs contributed to the flotation performance of microfine particles. This study underscores the pivotal effect of INBs on the flotation of microfine particles through enhancing particle-particle and bubble-particle interactions.

Role of oil droplet size on dynamic pore wetting of active carbon and particle-bubble interaction: New inspiration for enhancing the porous mineral floatability

The dynamic pore wetting plays a vital role in the flotation separation process of porous mineral particles, such as low-rank coal, fly ash and chrysocolla, etc. This paper investigated the dynamic pore wetting behavior of active carbon particles in the water-oil emulsion by 1H low-field nuclear magnetic resonance (1H LF-NMR). The influence of oil droplet size on pore wetting process was revealed. The change in the surface properties of particles before and after wetting was analyzed by contact angle and FTIR measurements. The particle-bubble attachment process in the emulsion and pure water was compared. The total pore wetting percentage of active carbon had a first-order kinetic relationship with the wetting time. The emulsion was beneficial to decrease the pore wetting percentage of particles compared with water. And the pore wetting percentage decreased with the decrease of oil droplet size in emulsion. The pores were easily filled by the oil droplet with small size and the hydrophobicity of sample surface was improved, which prevented the subsequent pore wetting by water. As a result, the detachment force of particle-bubble was increased with the help of micro-oil droplets. This work attempts to provide a new inspiration for the study of porous mineral flotation.

A case study of enhanced flotation of coal gasification fine slag by multiple compound collectors

ABSTRACT The flotation mechanism of multiple compound collectors called ZKC-I for coal gasification fine slag (CGFS) was revealed from the flotation kinetics, adsorption properties, bubble–particle interaction, and froth properties. The results were compared to dodecane, which represents the conventional nonpolar hydrocarbon oil collector. The flotation concentrates yield and rate constant of CGFS treated by ZKC-I were 2–3 times than those of CGFS treated by dodecane. Fourier transform infrared spectroscopy and wrap angle results showed that ZKC-I improved the hydrophobicity of residual carbon because of the synergistic adsorption of fatty acids, esters, and aromatic hydrocarbons in the ZKC-I on the heterogeneous surface of residual carbon particles, which enhanced the adhesion between residual carbon particles and bubble. Due to the strong carrying capacity of the bubble to residual carbon particles, the number of residual carbon particles in the froth treated by ZKC-I was more than that of the CGFS froth treated by dodecane. The high content of carbon particles in the froth resulted in great stability of the flotation froth, and the maximum height and half-life of the froth were higher than that of CGFS treated by dodecane. This study has practical and theoretical significance for the separation of coal-based solid waste.

A review of bubble collapse near particles

Bubble–particle interactions are of great importance in cavitation bubble dynamics, especially in the case of silt-laden flow. In this paper, a review of the physical mechanisms involved in bubble collapse near particles is presented, with an emphasis on the jet and shock wave phenomenon. First of all, the collapse of a bubble occurring close to a flat wall is introduced to provide a basis for understanding cavitation behavior near boundaries. Then, with the aim of revealing the physical processes that occur during bubble collapse near particles, this is followed by a detailed discussion, with plentiful examples, of the collapse process (the inception, growth, collapse, rebound, and final disappearance of the bubble) and the formation and behavior of jets (the inception jet, counter jet, and double jets) and shock waves (incident, reflected, jet-induced, and jet-split shock waves).

The effects of NaCl addition on the particle-bubble interactions of galena in the presence of xanthate

This work investigated the effects of NaCl addition on galena flotation in the presence of xanthate. The micro-flotation experiments were performed using NaCl solutions which also included xanthate, at pH 9 (±0.1). Our results indicated that galena recovery improved for higher NaCl as well as higher xanthate concentrations.A pH-dependent chemisorption model for the galena surface, with the addition of xanthate adsorption was calibrated using measured zeta potential values. We propose that xanthate adsorption on galena can take place via two separate mechanisms. The first mechanism involves direct xanthate chemisorption to specific surface sites. The second mechanism involves lead/xanthate complexes formed in the bulk solution. These lead/xanthate complexes attach on the galena surface as hydrophobic lead xanthate salts.The galena-air bubble interactions are repulsive in 1 mM NaCl, with or without xanthate, consistent with the lower galena recovery measured experimentally. An increase to 100 mM NaCl, irrespective of the xanthate addition, resulted in attractive galena-air bubble total interaction energies. The agreement with the experimental results shows the effectiveness of the charge regulated model for estimating the galena and air bubble behaviours during flotation in NaCl solutions.

Mixing/segregation characteristics and bubble behaviors of density-segregated binary particles in a pressurized fluidized bed

To enhance comprehension and achieve more targeted optimization of pressurized fluidized beds, experiments were carried out in a “cold” pseudo 2D pressurized fluidized bed with binary mixtures differing in densities via high-speed digital image analysis. The impacts of operating pressure and gas velocity on fluidization pattern, mixing/segregation characteristics, and bubble behaviors were comprehensively analyzed. Results show that the fluidization of binary mixtures is a gradual process which occurs within the range between the minimum fluidization velocity of flotsam and jetsam components. Particles with lighter density tend to produce larger size of bubbles, larger bubble fraction and increased fluctuation compared to the heavier ones when particle sizes are similar. Increasing the pressure results in an overall decreased bubble diameter and bubble fraction, which prohibits the bubble-particle interaction and ultimately deteriorates the mixing quality. The carried-out whole-field, non-intrusive measurements in this work would provide the much-needed database for validation of CFD models.

Dynamics of Bubble-Particle Interaction at Different Distances Under Ultrasonic Excitation

Dynamics of Bubble-Particle Interaction at Different Distances Under Ultrasonic Excitation

Influence of surface roughness of magnesite on bubble-particle energy barrier: Analysis based on a new simplified model

The surface roughness of mineral particles treated by different methods varies greatly, which will significantly affect flotation operations. In this investigation, magnesite particles with different surface roughness were obtained by ultrasonic treatment for different times. A new simplified mathematical model of rough particle-bubble interaction energy based on the extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory was formulated. Theoretical analysis shows that it is essentially consistent with the Wenzel wetting model. The parameters in the model were obtained by contact angle test, zeta potential test and AFM test. The interaction energy between a rough magnesite particle and a bubble at different NaOL concentrations was calculated. The results indicate that increasing the surface roughness of hydrophobic magnesite particles can significantly reduce the value of energy barrier (Em) that needed to be overcome for the adsorption between bubbles and magnesite particles. Meanwhile, it can push the location of energy barrier further away (that is, increase the critical hydration film thickness hcr when bubble-particle adhesion occurs), allowing magnesite particles to adhere to bubbles earlier and more easily, thereby improving the flotation performance of magnesite particles. However, the promoting effect of increasing surface roughness on the flotation of magnesite particles gradually weakened as the concentration of NaOL increased.

Numerical simulation of particle and bubble detachment process in turbulent flow environment using CFD-DEM

Three-dimensional discrete element method (DEM) models were developed to simulate particle-bubble interactions by utilizing the API function within the EDEM software platform. Geometric grids were constructed using FLUENT software to induce isotropic turbulence, and this turbulence environment was incorporated into the CFD-DEM framework. The simulations focused on the detachment of particles and bubbles, with particle sizes ranging from 0.10 to 0.30 mm, particle densities ranging from 1500 to 2500 kg/m³, and fixed bubble sizes of 1.00, 1.20, 1.60, and 2.00 mm. The detachment processes occurred within a turbulent flow field at distances of 1, 1.5, 2, and 3 mm from the grid. It is found that the particle-bubble bond required more capillary force to maintain attachment equilibrium as the particle density and size, bubble size, and flow field turbulence environment increased, the smaller the initial flow velocity to bring the bubble and particle to a critical desorption state, indicating the increase in all these factors were not conducive to attachment stability.

An investigation of nanobubble enhanced flotation for fly ash decarbonization

Froth flotation is often employed to remove unburned carbon in the fly ash produced as a coal combustion by-product before it can be utilized in the cement or similar industries. However, with the deterioration of coal quality and environmental regulations getting stricter, fly ash has become increasingly more difficult to be purified by the flotation process and the limitations of traditional flotation techniques have become more obvious for ultrafine particles such as fly ash. Nanobubbles have proven effective in enhancing the flotation performance with fine and ultrafine particles. In this study the effect of nanobubbles on fly ash flotation decarbonization and underlying mechanisms have been investigated with a flotation column under various experimental conditions using a Chinese fly ash sample. The results have demonstrated that nanobubbles are able to significantly improve the efficiency of decarbonization of fly ash flotation. Typically the use of nanobubbles increased the recovery of unburnt carbon by 3–15 % and reduced the fly ash LOI by 0.2 %–3.5 %. It has also been shown that nanobubble flotation reduced the required dosages of frother and collector by approximately one half. New mechanisms of nanobubbles improving fly ash decarbonization flotation performance were explored from the perspectives of bubble-particle interactions and solution surface tensions.

Particle-Bubble Interactions: an Investigation of the Three-Phase Contact Line by Atomic Force Microscopy.

The dynamics of the three-phase contact line during particle-bubble interactions determine the stability of particle-bubble aggregates in flotation. The interaction of particles and sessile gas bubbles can be studied by colloidal probe atomic force microscopy (CP-AFM). This paper demonstrates a method to obtain the contact angle, the position of the three-phase contact line on the particle, and the bubble profile by utilizing the full information contained in AFM force-distance curves, i.e., force and CP-position information as well as the work done to move the three-phase contact line on the CP-particle. The proposed method does not require any assumption of a constant contact angle or a constant opening angle. This is achieved by the combined solution of the particle force balance and an expression for the work required to move the three-phase contact line over the colloid probe. The applicability to AFM force-distance measurements was demonstrated for the interaction of a hydrophobic SiO2 or a hydrophobic Al2O3 colloidal probe particle with sessile gas bubbles having radii between 45 and 80 μm.

Fundamental role of surface roughness in bubble-particle interaction in flotation: A review

Fundamental role of surface roughness in bubble-particle interaction in flotation: A review

Rheology, bubble-particle interaction and air bubble system: A study of the influence of inorganic salts on air entrainment by bubble rising measurement

Rheological properties and the interaction between air bubbles and solid particles are important factors influencing the air bubble system in air-entrained concrete. The former may affect the bubble motion and the latter may influence the strength of bubbles. However, none of them were properly discussed by direct observation. In this study, we observe the rising behavior of various-sized bubbles in air-entrained cement paste. By a modified drag equation, the bubble-particle interaction is determined and represented by the interaction coefficient Ki. By Ki the bubble-particle interaction can be quantified and correlated with air entrainment properties. In combination with rheological properties and surface tension, the influence of inorganic salts on air entrainment is systematically studied. It is found that the content of bubbles <200 μm and the specific surface area of bubbles in the fresh mortar decrease with the increase of Ki, and the content of bubbles >1000 μm and the spacing factor increase with increasing Ki.

The effects of saline water on the recovery of lead and zinc sulfide during froth flotation

In this study, we investigated the effects of water salinity on the flotation performance of pure lead and zinc sulfide mineral samples as well as a Pb/Zn complex sulfide ore by means of micro-flotation and batch flotation experiments. Our results showed higher PbS and ZnS recoveries in more concentrated NaCl salt solutions. The results for the experiments using seawater demonstrated that in the presence of additional ions, such as Ca2+ and Mg2+, the recovery of PbS and ZnS was significantly reduced.As part of this investigation, we developed and implemented a surface complexation model for ZnS based on the presence of two differently charged surface sites. Zeta potential measurements of ZnS particles were used to optimise the parameters of our model. It was found that the surface potentials calculated using this model were in good agreement with the experimental zeta potentials, validating the model for predicting the zeta potential behaviour of ZnS particles over a broad range of pH and NaCl concentrations.Additionally, total interaction free energies were determined as a function of separation distance, representing particle–particle and particle-bubble interactions of our study in different NaCl concentrations. The theoretical analyses showed that asymmetric Pb/Zn particle–particle interactions were repulsive at lower NaCl concentrations, before becoming purely attractive at higher NaCl concentrations. For the case of the symmetric particle–particle interactions, attraction controlled all interactions, regardless of NaCl concentration. The calculated PbS-bubble interactions were repulsive in lower NaCl concentrations but became increasingly attractive in higher NaCl concentrations. Strong repulsions controlled all ZnS-bubble interactions, and these interactions remained repulsive with increasing NaCl concentration. The theoretical projections presented in this study were in good agreement with the measured saline water flotation phenomena.

Estimation of turbulent dissipation rates and its implications for the particle-bubble interactions in flotation

Increasing turbulence intensity has been traditionally applied to the beneficiation of fine particles for process intensification with higher flotation recovery. Nevertheless, quantifying turbulent dissipation rate directly from local velocity gradients is challenging as it requires measurements of flow fields down to the Kolmogorov length scales. Spatial resolution in velocity measurements using existing experimental techniques is insufficient. In this paper, we studythe effects of spatial resolution on the estimated turbulent dissipation rate and its effects on predicted particle-bubble interactions are further discussed. Direct numerical simulation of a homogeneous isotropic turbulence has been performed using the pseudo-spectral method. An instantaneous 3D velocity field is used to calculate true values of turbulent dissipation rate, which is used as benchmark to compare turbulent dissipation rates estimated from the same velocity fields of different resolutions. This velocity field is then coarsened to different levels relative to the Kolmogorov length scale, which are used to calculate turbulent dissipation rate from local velocity gradients of different spatial resolution. The underestimation of turbulent dissipation rate is quantified as a function of spatial resolution relative to the Kolmogorov length scales. This clarifies that special care should be paid to the understanding of turbulence effects on particle-bubble interactions.