Bubble Surface Research Articles

Hydrodynamic study of gas–liquid-solid mini-fluidization based on fluorescence PIV

The fluorescence-based tracer particle image velocimetry (fluorescence PIV) was used to obtain the flow regimes transition, bubble size and velocity, liquid and particle flow field characteristics of the 1 ∼ 3 mm GLSMFBs and 93 ∼ 195 μm glass beads. When the bed-to-particle diameter ratio increased, the bubble size and velocity distribution tended to be more concentrated. Bubble rose as straight line and S-shaped spiral trajectory. The divergence and vorticity of the flow field were preliminarily quantified. There showed a close relationship between the macroscopic hydromechanical behaviors such as bubble size and velocity and the mesoscopic behaviors such as the movement and development of vortices. The upward drag force of liquid and bubble on particles mainly affected the particle axial velocity, while the particle radial motion was mainly caused by bubble wake and surface force among particles. The results provide theoretical reference for the design and optimization of GLSMFB reactors.

Theoretical model of dynamics and stability of nanobubbles on heterogeneous surfaces

Surface nanobubbles have revealed a new mechanism of gas–liquid–solid interaction at the nanoscale; however, the nanobubble evolution on real substrates is still veiled, because the experimental observation of contact line motions at the nanoscale is too difficult. HypothesisThis study proposes a theoretical model to describe the dynamics and stability of nanobubbles on heterogeneous substrates. It simultaneously considers the diffusive equilibrium of the liquid–gas interface and the mechanical equilibrium at the contact line, and introduces a surface energy function to express the substrate’s heterogeneity. ValidationThe present model unifies the nanoscale stability and the microscale instability of surface bubbles. The theoretical predictions are highly consistent to the nanobubble morphology on heterogeneous surfaces observed in experiments. As the nanobubbles grow, a lower Laplace pressure leads to weaker gas adsorption, and the mechanical equilibrium can eventually revert to the classical Young-Laplace equation above microscale. FindingsThe analysis results indicate that both the decrease in substrate surface energy and the increase in gas oversaturation are more conducive to the nucleation and growth of surface nanobubbles, leading to larger stable sizes. The larger surface energy barriers result in the stronger pinning, which is beneficial for achieving stability of the pinned bubbles. The present model is able to reproduce the continual behaviors of the three-phase contact line during the nanobubble evolution, e.g., “pinning, depinning, slipping and jumping” induced by the nanoscale defects.

Effect of turbulence on the detachment between an air bubble and a glass bead with different hydrophobicity: Experiments and simulations

The effect of turbulence on the detachment between an air bubble and a glass bead (soda-lime) with different hydrophobicity was comprehensively researched. An experimental apparatus was designed to simulate the turbulent environment during the actual flotation process, which was used to research the detachment of different hydrophobic glass beads from bubble surfaces. It is indicated that three different hydrophobic glass beads detached from the bubble surfaces in the same way but at different speeds. The three-phase contact line (TPCL) shrank rapidly when the centrifugal detachment force of glass beads reached a critical value. The deformation of bubbles increased, and the three-phase contact (TPC) area continuously decreased. When the critical value was exceeded, the sliding and contraction speed around the TPCL further increased until a clear necking phenomena appeared near the TPC. Furthermore, the centrifugal detachment force, capillary force and total pressure force increased with increasing hydrophobicity in the detachment process.

Nanoengineering Scalephobic Surfaces for Liquid Cooling Enhancement

AbstractCrystallization fouling, a process where mineral scales form on surfaces, is of broad importance in nature and technology, negatively impacting water treatment and electricity production. However, a rational methodology for designing materials with intrinsic resistance to scaling and scale adhesion remains elusive. Here, guided by nucleation physics, this work investigates the effect of coating composition and surface structure on the nucleation and growth mechanism of scale on metallic heat transfer surfaces nanoengineered by large‐area techniques. This work observes that on hydrophilic nanostructured copper, despite its significantly enlarged surface area compared to smooth surfaces, scale formation is substantially suppressed leading to sustained, efficient cooling performance. This work reveals the mechanism through thermofluidic modeling coupled with in situ optical characterization and show that surface bubble formation through degassing is responsible for generating local hot spots enhancing supersaturation. This work then demonstrates a scalephobic nanostructured surface which reduces the accumulated surface scale mass 3.5× and maintains an 82% higher heat transfer coefficient compared to superhydrophobic surfaces with corresponding energy conversion savings. This work not only advances the understanding of fouling mechanisms but also holds promise for practical applications in industries reliant on efficient heat transfer processes.

Study of the interaction between a cavitation bubble and nearby biomimetic gas-entrapping microtextured surfaces and the potential damage effects on the wall using the compressible multiphases volume of fluid model

In the study, a compressible multiphase volume of fluid considering the phase change and thermal effect is presented, the interaction between a cavitation bubble and nearby biomimetic gas-entrapping microtextured surfaces is investigated using this model, and the potential damage effects on the wall are carefully analyzed. Based on this interaction, the standoff distance is classified into three types. For γ > 2.0, the cavitation bubble remains spherical during the expansion phase because it is not influenced by the entrapped gas cavities. However, during the contraction phase, it generates a jet directed away from the wall. For 1.0 < γ < 2.0, the cavitation bubble is affected by the cavities, causing it to lose its spherical shape during the expansion phase. For 0 < γ < 1.0, the cavitation bubble is close to the gas cavities, mixing with the gas cavities during the expansion phase. Two processes are identified as the main reasons for the potential damage to the wall. Furthermore, compared to a flat wall surface, the peak of the pressure impulse on the wall with entrapping gas cavities decreases by 33%, and the peak of the heat transfer quantity decreases by 59%, significantly reducing the damage to the wall.

Revealing the kinetic behaviors of hydrate formation on bubble surface with different pressure gradients in deep-sea methane seepage areas of the South China Sea

In the deep-sea methane seepage environment, hydrate formation on the methane bubbles is a crucial pathway for methane transformation, and plays an important role in determining whether seepage methane can enter the surface ocean. While how the pressure determines the hydrate formation process in different water depths remains unclear. In this study, we investigated the formation kinetic characteristics and microstructure evolution of methane hydrate on suspended gas bubbles within varied pressure conditions. The pressure range (4–14 MPa) was in the deep-sea methane seepage environment. The results indicated that pressure obviously affected the hydrate film formation characteristics. As pressure increased, the lateral growth rate of the hydrate film accelerated, the hydrate crystal particles became smaller, and the initial hydrate film surface became smoother. Raman spectroscopy results showed that pressure changes did not obviously alter the microporous evolution on the hydrate film surface, that the gas-phase/water-phase Raman peak area ratio exhibited similar trends. The dissolved methane concentration under different pressure conditions was not the primary factor affecting hydrate thickening, rather, it depended mainly on the driving force. This study is of great significance in revealing the characteristics of methane hydrate formation and methane transfer in the oceanic methane seepage environment.

Thin-film flow due to an asymmetric distribution of surface tension and applications to surfactant deposition

Thin-film equations are utilised in many different areas of fluid dynamics when there exists a direction in which the aspect ratio can be considered small. We consider thin free films with Marangoni effects in the extensional flow regime, where velocity gradients occur predominantly along the film. In practice, because of the local deposition of surfactants or input of energy, asymmetric distributions of surfactants or surface tension more generally, are possible. Such examples include the surface of bubbles and the rupture of thin films. In this study, we consider the asymmetric thin-film equations for extensional flow with Marangoni effects. Concentrating on the case of small Reynolds number $ Re $ , we study the deposition of insoluble surfactants on one side of a liquid sheet otherwise at rest and the resulting thinning and rupture of the sheet. The analogous problem with a uniformly thinning liquid sheet is also considered. In addition, the centreline deformation is discussed. In particular, we show analytically that if the surface tension isotherm $\sigma = \sigma (\varGamma )$ is nonlinear (surface tension $\sigma$ varies with surfactant concentration $\varGamma$ ), then accounting for top–bottom asymmetry leads to slower (faster) thinning and pinching if $\sigma = \sigma (\varGamma )$ is convex (concave). The analytical progress reported in this paper allows us to discuss the production of satellite drops from rupture via Marangoni effects, which, if relevant to surface bubbles, would be an aerosol production mechanism that is distinct from jet drops and film drops.

Dynamics of a single cavitation bubble near a cylindrical blind hole

Cavitation bubble dynamics, such as microjets and moving shock waves, are strongly influenced by their surroundings. We investigated the complex bubble behavior during the growth and collapse stages near a blind hole. The simultaneous study, which is a combination of experiment and numerical methods, was performed. The single bubble was induced by a laser focus beam near a blind hole in the cuvette and measured by a high-speed camera with an image processing method. Numerical predictions were conducted for a detailed further investigation of the pressure and velocity fields near and inside the bubble. A fully compressible two-phase Navier-Stokes solver based on the homogeneous flow assumption was used. Both experimental and numerical results showed good agreement with each other. Strong deformation of the bottom bubble surface evolution was observed at low standoffs above the hole entrance. An extremely high-velocity microjet with a mushroom cap-shaped bubble was predicted under high standoffs below the hole entrance. Secondary cavitation in the blind hole was observed experimentally, and we discussed the low-pressure region caused by the interaction among the shock wave, bubble, and blind hole. Consequently, the tendencies of maximum microjet velocity and time-dependent surface pressure in the collapse phase are suggested.

Anomalous diffusion of hydrocarbon vapor through an aqueous foam bubble structure

Hydrocarbons are known as “anti-foamers” because they cause bubble rupture, coalescence, and reduce foaming. We show that the dynamics of bubble structure allows hydrocarbon vapors permeate rapidly when an aqueous foam is placed on a hydrocarbon pool. Two distinct foam layers are formed. Vapor accumulates in an expanding bottom layer at the foam-pool interface where bubbles grow rapidly, rupture, and coalesce. Simultaneously, vapor diffuses through a top layer having small bubble structure, which changes slowly due to Ostwald-ripening. Very little vapor accumulates in the top layer, which has a constant thickness equal to the initial foam thickness. Surprisingly, both accumulation in the bottom layer and diffusion through top layer occur at constant rates, which are independent of time and initial foam thickness. The vapor diffusion rate in the top layer should have decreased, inversely proportional to the initial foam thickness, based on classical diffusion theory; only the fluorosurfactant containing foam (RefAFFF) placed on gasoline follows the classical theory where the bottom foam layer is absent. Therefore, we propose a theory to show a linear increase in diffusion time with initial foam thickness using an effective diffusion-coefficient. Experiments show that this variation could be because of increased liquid drainage, drying, and bubble coarsening, which are not considered explicitly in the theory. We also describe a theory for the expanding bottom layer to show that most vapor formed at the pool surface accumulates for very volatile hydrocarbons. The vapor diffusion controls foam ignition. We show that the measured foam ignition time also increases linearly with initial foam thickness, qualitatively consistent with the predicted diffusion time. By employing different hydrocarbons, we show that the measured foam ignition times decrease inversely proportion to square root of hydrocarbon vapor concentration for a given surfactant. This could be because a surfactant exhibits different degrees of oleophobicity towards different hydrocarbons that can reduce vapor adsorption, solubility, and diffusion at a bubble surface. Different surfactants also exhibit different degrees of oleophobicity towards a given hydrocarbon (n-pentane) and increase ignition times by a factor of six: RefAFFF having the longest ignition time, followed by siloxane-polyoxyethylene formulation, and its individual surfactant components.

Visualization investigation on heat and mass transfer of Al2O3 nanofluid in vapor chamber

As the vapor chamber (VC) moves towards ultra-thinness to meet the thermal management of microelectronic devices, achieving efficient heat transfer within a limited space poses severe challenges. In this study, a visualization VC with a thickness of only 0.9 mm was designed to investigate the heat transfer effect and boiling behavior of nanofluid applied on VC. The influences of Al2O3-deionized water (Al2O3-DW) with different mass concentrations and filling ratios on the heat transfer characteristics and flowing behavior were explored. The results indicated that the addition of nanoparticles improved the temperature uniformity and startup performance of VC. At 0.3 wt%, nanofluid promoted bubbles generation and growth, enhancing the phase-change process. The minimum thermal resistance was 1.46 K/W, representing a 13.6 % reduction compared to that of DW. However, at 0.6 wt% and under high filling ratios or heat load, excessive nanoparticles tended to accumulate on the surface of bubbles by surface tension during the boiling process and were pushed to the gas–liquid interface under the pressure gradient, resulting in deteriorated heat transfer. The results also found that deposition of nanoparticles further enhanced heat transfer. Nonetheless, the nanoparticles were detached from the substrate as the bubbles boiled, and the enhancement effect gradually diminished. The relevant research findings provide guidance for the application of nanofluids in ultra-thin VC.

How viscous bubbles collapse: Topological and symmetry-breaking instabilities in curvature-driven hydrodynamics

The duality between deformations of elastic bodies and noninertial flows in viscous liquids has been a guiding principle in decades of research. However, this duality is broken when a spheroidal or other doubly curved liquid film is suddenly forced out of mechanical equilibrium, as occurs, e.g., when the pressure inside a liquid bubble drops rapidly due to rupture or controlled evacuation. In such cases, the film may evolve through a noninertial yet geometrically nonlinear surface dynamics, which has remained largely unexplored. We reveal the driver of such dynamics as temporal variations in the curvature of the evolving surface. Focusing on the prototypical example of a floating bubble that undergoes rapid depressurization, we show that the bubble surface evolves via a topological instability and a subsequent front propagation, whereby a small planar zone that includes a singular flow structure, analogous to a disclination in elastic systems, nucleates spontaneously and expands in the spherically shaped film. This flow pattern brings about hoop compression and triggers another, symmetry-breaking instability to the formation of radial wrinkles that invade the flattening film. Our analysis reveals the dynamics as a nonequilibrium branch of "jellium" physics, whereby a rate-of-change of surface curvature in a viscous film is akin to charge in an electrostatic medium that comprises polarizable and conducting domains. We explain key features underlying recent experiments and highlight a qualitative inconsistency between the prediction of linear stability analysis and the observed "wavelength" of surface wrinkles.

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.

What are the mechanisms of functional monomers' effect on air entrainment of polycarboxylate superplasticizers in cement paste and mortar?

This study focuses on developing three kinds of polycarboxylate superplasticizers (PCEs), i.e., ether-type polycarboxylate superplasticizer (T-PCE), fluorine-type polycarboxylate superplasticizer (F-PCE), and phosphate-type polycarboxylate superplasticizer (P-PCE) synthesized respectively with three functional monomers, i.e., isopentenyl polyoxyethylene ether (TPEG3000), hexafluorobutyl methacrylate (HFBMA), and 2-hydroxyethyl methacrylate phosphate (HEMAP) for improved dispersion and low air entrainment in cementitious systems. The molecular structures of PCEs were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Gel Permeation Chromatography (GPC), and Proton Nuclear Magnetic Resonance (1H NMR). Further, the influence and mechanism of the functional monomers on the dispersion and air entrainment of PCEs in cement paste and mortar were investigated. Finally, the mechanisms of the functional monomers' effect on the air entrainment of PCEs in the cement paste and mortar were discussed. The results showed that T-PCE, F-PCE, and P-PCE were successfully synthesized, and P-PCE had the optimal effect on the fluidity (at W/C=0.35, 305.5 mm), the lowest foaming height (11.000 mm), and the fastest rate of defoaming of the cementitious systems, followed by F-PCE and T-PCE. Complexation, adsorption, surface activity, and polar hydrophobic mechanisms were identified. For unmodified T-PCE, there are more hydrophilic groups (-COOH), stronger surface activity. Therefore, T-PCE shows strong air entrainment; T-PCE has a high density of carboxylate and often forms a complex with 1 Ca2+ in the form of 4 carboxyl groups before reaching the adsorption equilibrium, so the concentration of free Ca2+ with foam stabilizing effect is high, which leads to strong air entrainment of T-PCE. The adsorption and complexation ability of F-PCE with Ca2+ is weaker than that of T-PCE. However, the hydrophobicity of F-PCE molecules is enhanced and the surface tension of F-PCE is reduced due to the ester group and C-F bonds in the structure of HFBMA, so the air entrainment of F-PCE is lower than that of T-PCE through Marangoni effect. P-PCE exhibited the lowest surface activity and the largest surface tension. Defoaming effect is promoted due to increased additional pressure on the bubble surface. Moreover, its adsorption and complexation with Ca2+ surpassed those of T-PCE and F-PCE due to the phosphate group has two negative charges, and the free Ca2+ is reduced, which also reduces the bubble stability. Therefore, P-PCE has minimal air entrainment in the cementitious systems.

Particle Tracking of Orientation and Velocity Of Arbitrary Shape

Dispersions or particulate systems are prevalent in numerous natural and practical applications. Characterisation of such multiphase systems usually involves measuring size, spatial location, velocity and number density, which is usually non-trivial. The 'Depth from Defocus' (DFD) technique provides an imaging-based volumetric approach for estimating the size and position of dispersed spherical particles using the blurring information from a shadowgraph image. The two-image DFD approach involves two cameras to capture simultaneous images at different degrees of blur, which, although simpler, requires a mandatory calibration procedure. This study proposes a single-image DFD technique that provides a calibration-free size estimation using theoretical functions while evaluating position requires a simple calibration. The efficacy of this technique is demonstrated for various sparse spherical dispersions, including target dots, dispersed glass beads, liquid droplets in sprays and surface bubble rupture, and pollen grains. The method further enables precise determination of the measurement volume, which is crucial, allowing for bias-free estimates of the size distribution and volume concentration. The simple optical configuration and semi-automatic calibration procedure make this method easily deployable and accessible for diverse applications. The pixelation effect on the limiting value of the degree of blur is also estimated theoretically and compared with experiments. This effect is of interest concerning any typical discrete sensor imaging system in general.

Abyss Aerosols: Drop Production from Underwater Bubble Collisions.

Over the past century, drops production mechanisms from bubble bursting have been extensively studied. They include the centrifugal fragmentation of liquid ligaments from the bubble cap during film rupture, the flapping of the cap film, and the disintegration of Worthington jets after cavity collapse. We show here that a dominant fraction of previously identified as "surface bubble bursting" submicron drops are, in fact, generated underwater, in the abyss, inside the bubbles themselves before they have reached the surface. Several experimental evidences demonstrate that these drops originate from the flapping instability of the film squeezed between underwater colliding bubbles. This finding, emphasizing the eminent role of bubble-bubble collisions, alters fundamentally our understanding of fine aerosol production and opens a novel perspective for transfers across water-air interfaces.

The effect of various crystalline forms of HFC 134a hydrate on the growth rate and desalination efficiency

Experimental studies on the synthesis of HFC 134a hydrate in the liquid HFC 134a – water system were performed. Despite today's lack of research on the use of HFC 134a hydrate for desalination of seawater and separation of harmful impurities by HFC 134a hydrate synthesis, this method has prospects for development: HFC 134a hydrate is synthesized at relatively high temperature and low pressure; it is poorly soluble in water, which simplifies gas hydrate separation from water–salt solution; it has high volumetric storage density and relatively high thermal conductivity. In spite of its low solubility in water, HFC hydrate exhibits relatively high growth rates. The growth of various crystalline forms and the peculiarities of their occurrence in pure water, aqueous salt solution, as well as with the addition of surfactant are considered. The use of SDS increases the HFC hydrate growth rate. For the first time, it was shown that the intensive growth of HFC 134a hydrate in the form of needles throughout the entire volume of the liquid allows increasing the efficiency of desalination. It is important to consider the desalination process comprehensively, taking into account the crystal forms, crystal growth rate, crystal defects, as well as taking into account the degree of salt removal. Simultaneously with the bubble growth, a thin gas hydrate film is shown to grow on the bubble surface. A detailed consideration of the stages of such hydrate growth is provided to explain the high-speed synthesis of porous HFC hydrate due to boiling of liquid HFC and vaporization.

Bubbling up in a Lab-on-a-Chip: A gravity-driven approach to the formation of polyelectrolyte multilayer capsules and foams

The generation of multi-functional capsules often requires the sequential deposition of different components on the surface of bubbles or drops. Batch-based methods lack fine control over the capsule sizes, including risk of fusion, and cannot ensure identical environments for each capsule. To overcome these issues, different micro/milli-fluidic methods have been developed in the past. However, a major challenge remains in combining an explicit and flexible control over the capsule generation and their residence time in the different solutions within the same device. Using for the first time the example of bubbles covered by layers of oppositely charged polyelectrolytes (PSS/PAH), we introduce an original millifluidic Lab-on-a-Chip device with two novel functions: (1) Size and separation of the bubbles are tuned at constant flow conditions via gas injection through a movible, circular dispense tip into the cross-flow of a rectangular channel. We provide a detailed exploration of the bubbling parameters together with physical justification of the observations. (2) The device exploits gravity to make the generated bubbles rise between horizontally stacked millifluidic chips containing each the controlled flow of a specific polyelectrolyte solution. In analogy with electric circuits, we show how the flow resistance of each chip can be adapted such that bubbles move smoothly between them while avoiding undesired mixing of the solutions. We show first examples of obtained multilayer capsules and discuss their peculiar features, in particular, their outstanding stability with respect to coalescence and dissolution. While our methods use polyelectrolyte assembly on bubbles, they can be readily transferred to other types of solutions or even to drops and particles.

Thermal analysis of the HTS transformer in the fault current condition considering the tape roughness effect

High temperature superconducting (HTS) transformers have many advantages over conventional transformers in terms of volume, weight, and total efficiency. However, fault conditions limit the electro-thermal performance of an HTS transformer. Based on this, we investigate the thermal modeling of the HTS transformer in the fault-current state. For thermal modeling, heat transfer and parameters affecting it such as surface roughness and bubble behavior have been considered. At first, an accurate thermal model for a 10 kVA HTS transformer has been prepared. Experimental results show that the penalty of this model is about 2.5 K in the hot-spot point (HSP) temperature in fault-current conditions. In a second step, the impact of a roughness on the heat transfer and mass transfer rate in nucleated boiling mode is investigated. Results show that surface roughness decreases the HSP temperature by more than 10 K in fault-current conditions. These results have significant impacts on protecting HTS windings against quenching.

The role of microbubble dose in combined microflotation of fine particles

Flotation of small particles is one of the global challenges facing the mineral raw materials processing industry. Large amounts of non-ferrous and rare metals are lost in the flotation tailings in the form of mineral particles below 15 µm in size as a result of the low effectiveness of their capture by coarse bubbles generated in conventional flotation machines. The method of combined microflotation, developed in recent years, uses conventional coarse bubbles (CB) and microbubbles (MB) produced in the stand-alone generator of air-in-water microdispersion, which serves as the flotation carriers. Depending on the MB dose, the effect of their application may be positive or negative. The theoretical analysis of various mechanisms of particle transfer onto the surface of coarse bubbles and further into the froth layer allowed to obtain the formula for the optimal MB dose f=d&lt;sub&gt;d&lt;/sub&gt;/2d&lt;sub&gt;p&lt;/sub&gt;r&lt;sub&gt;p&lt;/sub&gt;, where d&lt;sub&gt;d&lt;/sub&gt; is MB size; d&lt;sub&gt;p&lt;/sub&gt; and r&lt;sub&gt;p&lt;/sub&gt; respectively are the size and the density of particles. Experiments performed on the copper ore flotation tailings at the Atalaya Mining (Spain) and Chaarat Kapan (Armenia) concentrators showed that, besides the optimal MB dose in the range of 1-3 ml/g, there is another optimal MB dose in the range of 10-20 ml/g, where the copper recovery increases by several percent compared to the reference test (f = 0). The deep minimum in copper recovery is observed in the area between the optimal MB doses, which is by several percent lower than the value in the reference test.

Evaluation of separation by high shear mixing for per- and poly-fluoroalkyl substances (PFAS) treatment in water

Widespread per- and poly-fluoroalkyl substances (PFAS) contamination in water, sediments and soils has driven demand for scalable and cost-effective treatments suitable for application across a range of ∑PFAS concentrations from ng/L to mg/L. One promising class of treatment technology is based on PFAS accumulation at the surface of air bubbles. In this study, hydrodynamic cavitation induced by high shear mixing generated colloidal gas aphrons (CGAs) made of different surfactants (cationic, anionic and non-ionic) to facilitate separation of PFAS differing in carbon–fluorine chain length, head group and charge. Separation efficiency was evaluated for a 600 µg/L ∑PFAS mixture of 6 PFAS each at 100 µg/L, and also for a solution spiked to 1 mg/L ∑PFAS with an aqueous film forming foam (AFFF) mixture. The choice of surfactant produced CGAs with different bubble sizes and surface properties; the non-ionic surfactant produced significantly smaller bubbles, while the cationic and anionic surfactant varied principally by charge. The ∑PFAS separation efficiency varied from < 30 % to 86 % using different surfactants after a 30 s process. The non-ionic surfactant was most effective overall, and the cationic surfactant was most efficient for short-chain PFAS, and those with the carboxylic head group due to surface charge compatibility. Zwitterionic precursor PFAS and perfluoroalkyl sulfonic acids species tested in this study were removed with > 90 % efficiency when anionic and non-ionic surfactants formed the CGAs, while short-chain perfluoroalkyl acids PFAA were removed similarly effectively by cationic surfactant-derived CGAs. While separation efficiencies were lower than the > 95 % ∑PFAS reductions reported elsewhere, the effect was achieved with a treatment time of 30 s, in contrast to the significantly longer treatment cycles applied in other studies.