Role Of Nanobubbles Research Articles

Effect of Nanobubbles on the Flotation Behavior of Microfine-Grained Serpentine

At present, scholars mainly study the relationship between nanobubbles and useful minerals, often ignoring the influence of bubbles on fine gangue minerals. When selecting nickel sulfide ore, scholars often faced with mudded and irrepressible serpentine, which seriously affects the quality of the concentrate. This mudded serpentine mineral often enters foam products with bubbles. In this study, the role of nanobubbles in the flotation behavior of hydrophilic serpentine was examined. Nanobubbles were successfully prepared via ultrasonic cavitation, with sizes ranging from 50 to 250 nm. The size and number of bubbles produced at 1 min and 2 min of sonication were significantly better than those of the prolonged test group, and it was found that longer sonication time did not produce better results. The stability of the nanobubbles produced via ultrasound was studied, and it was found that the nanobubbles were stable, with no change in size and only a slight decrease in number as the resting time increased. Nanobubbles were introduced into serpentine flotation, we found that the presence of nanobubbles significantly reduced the flotation recovery of serpentine. The presence of nanobubbles reduced the froth entrainment rate of microfine-grained serpentine, which in turn reduced its flotation rate. In the depressant group trials, it was found that the nanobubbles also reduced the amount of depressant. In short, the presence of nanobubbles can prevent the floating of fine hydrophilic gangues during flotation.

Role of nanobubbles on the fine lepidolite flotation with mixed cationic/anionic collector

Nanobubbles (NBs) have recently been used for fine particle flotation, and mixed cationic/anionic collectors have shown powerful effects in flotation of lepidolite. In this paper, the flotation tests, nano particle size analyses, contact angle tests, settling tests and high-speed camera observation was used to study the interaction between NBs and fine lepidolite particles with mixed cationic/anionic collectors. The results showed that the concentration of surface NBs and the presence of bulk NBs play an indispensable role in the promotion of lepidolite flotation by NBs. The size of NBs was larger near the isoelectric point and NBs were more stable by co-interaction with the mixed cationic/anionic collectors. The mechanism of the influence of NBs on the surface hydrophobicity of lepidolite was proposed, and the unstable effect of NBs on the flotation of fine-grained lepidolite was explained.

Exploring the Role of Nanobubbles in the Fate and Transport of Spilled Oil on Shorelines

Nanobubbles (NBs) generated by wave breaking and shearing are abundant and stable in the ocean. However, few studies have focused on the effects of NBs in the fate and transport of pollutants in the shoreline environment. In this study, the properties of NBs were determined, as well as the influencing factors. The role of NBs in the fate and transport of spilled oil were further investigated. The results showed that NBs significantly increased the concentration of dissolved oxygen as well as changed the pH, zeta potential, and surface tension of the water. Low salinity favored the generation of NBs, while high salinity inhibited this process. The surface active materials played a positive role in the generation and stabilization of NBs. With the assistance of external energy, the bulk NBs enhanced the efficiency in oil detachment from the surface of the substrate. At the same time, the surface NBs on the substrate obstructed the downward transport of oil colloids. Considering the behavior between the NBs in two different phases and the oil droplets, the oil droplets tended to bind to the NBs. This study demonstrates that NBs can play a significant role in the environmental behaviors of pollutants in the coastal areas.

Role of nanobubbles in the flotation of fine rutile particles

In this study, benzhydroxamic acid (BHA) was used as the collector for the flotation of fine rutile particles, and water with nanobubbles (NBs) was used to pretreat the particles. Adsorption capacity and zeta potential tests were used to elucidate the mechanism behind the interaction between the rutile and NBs. A high-speed camera was used to observe the collision and adhesion of the normal bubbles and samples. The flotation test results showed that, compared with the untreated group, the rutile treated with NBs had a higher recovery, lower collector demand, and higher flotation rate. The adsorption capacity test results suggested that pretreatment with NBs could reduce the amount of rutile collectors. The zeta potential test results indicated that using NBs could lead to a smaller electrostatic repulsive force for the corresponding rutile particles and an environment conducive to particle agglomeration, thereby enhancing the flotation performance. The images captured by the high-speed camera showed that the particles treated with NBs exhibited an obvious agglomeration effect and a higher adhesion probability, which was also reflected by the results of the flotation and zeta potential tests.

Formation of Water-Free Cavity in the Process of Nafion Swelling in a Cell of Limited Volume; Effect of Polymer Fibers Unwinding.

When Nafion swells in water, colloidal particles are repelled from the polymer surface; this effect is called the formation exclusion zone (EZ), and the EZ size amounts to several hundred microns. However, still no one has investigated the EZ formation in a cell whose dimension is close to the EZ size. It was also shown that, upon swelling in water, Nafion fibers “unwind” into the water bulk. In the case of a cell of limited volume, unwound fibers abut against the cell windows, and water is completely pushed out from the region between the polymer and the cell window, resulting in a cavity appearance. The temporal dynamics of the collapse of this cavity was studied depending on the cell size. It is shown that the cavity formation occurs due to long-range forces between polymer strands. It turned out that this scenario depends on the isotopic composition of the water, ionic additives and water pretreatment. The role of nanobubbles in the formation and collapse of the cavity were analyzed. The results obtained allowed us to conclude that the EZ formation is precisely due to the unwinding of polymer fibers into the liquid bulk.

Voltage gated inter-cation selective ion channels from graphene nanopores.

With the ability to selectively control ionic flux, biological protein ion channels perform a fundamental role in many physiological processes. For practical applications that require the functionality of a biological ion channel, graphene provides a promising solid-state alternative, due to its atomic thinness and mechanical strength. Here, we demonstrate that nanopores introduced into graphene membranes, as large as 50 nm in diameter, exhibit inter-cation selectivity with a ∼20× preference for K+ over divalent cations and can be modulated by an applied gate voltage. Liquid atomic force microscopy of the graphene devices reveals surface nanobubbles near the pore to be responsible for the observed selective behavior. Molecular dynamics simulations indicate that translocation of ions across the pore likely occurs via a thin water layer at the edge of the pore and the nanobubble. Our results demonstrate a significant improvement in the inter-cation selectivity displayed by a solid-state nanopore device and by utilizing the pores in a de-wetted state, offers an approach to fabricate selective graphene membranes that does not rely on the fabrication of sub-nm pores.

On the role of nanobubbles in particle–bubble adhesion for the flotation of quartz and apatitic minerals

This work evaluated the influence of nanobubbles (150–200 nm, mean diameter) on the visual adhesion of microbubbles (70 μm mean diameter) and macrobubbles (1 mm mean diameter) onto selected mineral particles (quartz and apatite) and on the flotation of both minerals, at bench scale. The adhesion of bubbles to high purity grains of quartz and apatite was monitored using a specially designed photographic technique. The results showed that the highest adhesion of bubbles onto the mineral grains occurred only after “conditioning” with nanobubbles. The nanobubbles appear to adhere to hydrophobic surfaces and confined to the rough surfaces of the grains, probably due to the dissipation of the free surface energy of the solids. As a result, the nanobubbles appear to serve as nuclei for enhanced adhesion of micro and/or macrobubbles, assisting the flotation of both minerals. In the case of quartz (D50 = 290 μm), the recovery increase was about 23% compared to a standard test of flotation with macrobubbles only. Furthermore, flotation kinetics was rapid and quartz recovery, at the first min, was double that obtained in the absence of nanobubbles. In the case of a fine apatitic ore (35% < 37 μm particles), best results were obtained with a combination of nano, micro and macrobubbles, with a 500–1000 g t−1 saponified soybean oil collector and a 300–600 g t−1 gelatinized corn starch depressant of iron bearing minerals. The P2O5 recoveries increased about 9% compared to flotation with macrobubbles only, and separation also occurred at a higher rate. The total recovered phosphate (4 min standard test) was obtained in the first 1.5 min, after conditioning with nanobubbles, followed by injection of and microbubbles. Results validated the reported high potential for nanobubbles in “surface conditioning”, the first stage of mineral flotation and were explained in terms of the solution and interfacial phenomena involved.

The Role of Nanobubbles in the Precipitation and Recovery of Organic-Phosphine-Containing Beneficiation Wastewater.

Dissolved air flotation (DAF) is broadly applied in wastewater treatment, especially for the recovery of organic pollution with low concentration. However, the mechanism of interaction between nanoscale gas bubbles and nanoparticles in the process of DAF remains unclear. Here, we investigated the role of nanobubbles in the precipitation of styryl phosphoric acid (SPA)-Pb particles and recovering organic phosphine containined in beneficiation wastewater by UV-vis (ultraviolet-visible) spectra, microflotation tests, nanoparticle tracking analysis, dynamic light scattering, and atomic force microscopy measurements. As suggested from the results, nanobubbles can inhibit the crystallization of SPA-Pb precipitation, which makes the sediment flotation recovery below 20%. After the precipitation crystallization is completed, nanobubbles can flocculate precipitated particles, which can promote the flotation recovery of precipitated particles to 90%. On the basis of the results, we proposed a model to explain the different roles of nanobubbles in the process of precipitation and flotation of SPA-Pb particles. This study will be helpful to understand the interaction between nanobubbles and nanoparticles in the application of flotation.

Bubble Formation at a Gas-Evolving Microelectrode

The electrolytic production of gas bubbles involves three steps--nucleation, growth, and detachment. Here the growth of hydrogen bubbles and their detachment from a platinum microelectrode of diameter 125 μm are studied using high-speed photography and overpotential frequency spectrum (noise) analysis. The periodic release of large <800 μm bubbles--gas oscillator behavior--was often observed, with a corresponding periodic oscillation of the overpotential which is reflected as a main peak and a series of harmonics in the power spectral density. The release frequency is inversely correlated with the bubble size and hydrogen production rate. When the coalescence of bubbles at the electrode surface is inhibited, either chemically with a surfactant or ethylene glycol or hydrodynamically by magnetically induced convection, swarms of small ∼50 μm bubbles are released in an aperiodic stream. The abrupt transition from periodic to aperiodic release occurs when the surface tension falls below 70 mN m(-1). Hydrogen bubble growth is also studied on a transparent platinum thin-film electrode, where the bubble coalescence can be observed directly. It leaves sessile droplets of electrolyte within the footprint of the growing bubble, showing that the growth involves scavenging smaller bubbles from solution due to hydrogen generated directly at the electrode. A possible role of nanobubbles in the lift-off process is discussed.

Boundary slip and nanobubble study in micro/nanofluidics using atomic force microscopy

The boundary condition at the solid–liquid interface on the micro/nanoscale is an important issue in micro/nanofluidic systems, where drag forces between fluids and solid walls need to be minimized. Recent studies have shown that on hydrophobic surfaces the fluid velocity near the solid surface is not equal to the velocity of the solid surface, a phenomenon called boundary slip. Theoretical and experimental studies suggest that at the solid–liquid interface, the presence of nanobubbles is responsible for boundary slip. In this review, various techniques for boundary slip investigation are described. We focus on the research performed using contact and tapping mode atomic force microscopy methods to study boundary slip on hydrophilic, hydrophobic, and superhydrophobic surfaces. The impact of surface roughness and hydrophobicity on measured slip length is discussed. The process of how to eliminate the influences of cantilever deflection and electrostatic forces on experimental measurement is discussed. Based on nanobubble imaging on a hydrophobic surface, the role of nanobubbles on boundary slip is discussed. Nanobubble movement and coalescence, as well as tip–nanobubble interactions, are discussed. The relationship between nanobubble immobility and surface structures on hydrophobic surfaces is discussed. Finally, a method to quantitatively measure sliding force on hydrophobic surfaces using atomic force microscopy is presented, and the effect of the presence of an electric field is discussed.