•Effect of ultrasound parameters on bulk and surface nanobubbles are reviewed.•Generation and stability mechanisms of nanobubbles in acoustic fields are discussed.•Future research focuses in the ...effect of ultrasound on nanobubbles are given.
The generation, and stability of nanobubbles are of particular interest for fundamental research and have potential application in numerous fields. Several attempts were made in the literature to produce nanobubbles through acoustic cavitation. However, the generation and stability mechanisms of nanobubbles in the acoustic field are unclear. Here, we review the effect of ultrasound parameters on bulk nanobubbles and surface nanobubbles. On this basis, we discuss the proposed generation and stability mechanisms of nanobubbles from the perspective of transient and stable acoustic cavitation. Moreover, we propose some future research directions for a deeper understanding of the role of ultrasound in the generation and stability of nanobubbles.
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•This review summarizes recent advances in dual-emission ratiometric fluorescence probes.•Categories, fabrication, chemo/biosensing and bioimaging applications for biomarker detection ...are introduced.•Current states, challenges and future perspectives of the probes are discussed.
A biomarker-based detection improves early diagnosis and subsequent treatment of diseases. Chemo/biosensing and bioimaging play a crucial role in biomarker detection. Ratiometric fluorescence (FL) probes provide built-in self-calibration for the correction of various target-independent factors and attract particular attention for analytical sensing and optical imaging. Based on the potential to provide a precise, quantitative, visual and real-time analysis, ratiometric FL probes are widely employed for chemo/biosensing and bioimaging detection of biomarkers. In this review, we systematically summarize the recent progress on dual-emission ratiometric FL probes. First, two general categories of ratiometric FL probes are introduced, involving ratiometric FL with one reference signal and two reversible signal changes. Then, fabrication methods of ratiometric FL probes are summarized in detail, including nanoparticle- or organic dye-embedded probes with dual-emission FL, fluorescent nanoparticles and organic dyes dual-embedded probes. Analytical applications of ratiometric FL probes are described overall, referring to different biomarker types and detection mechanisms, ratiometric FL chemo/biosensing in external samples and FL visual detection, ratiometric FL bioimaging in cells and tissues of small animals. Current states, probable challenges and future perspectives of ratiometric FL probes for biomarker detection are discussed rationally. This comprehensive review is attractive for numerous scientists from different areas, such as material science, chemistry, biomedicine, engineering, physics, etc. This review covers a wide range of scientific disciplines and benefits further development of functionalized optical materials, luminescent devices and bioimaging technique.
•Ultrasonic effects on flotation are observed and reviewed.•Mechanisms of ultrasonic effects are discussed from the perspectives of cavitation and acoustic radiation force.•Devices and methods of ...ultrasonic treatment are classified and compared.•Promising applications of ultrasound in flotation are proposed.
Ultrasound technology is widely applied in the flotation process. From the perspective of the theory of ultrasound, this article explains the effects and applications of ultrasound in the flotation process. To obtain a clear understanding of ultrasonic effects, we observe the phenomena of ultrasound using a high-speed camera and a CCD camera, and investigate potential applications in flotation. From these different phenomena, the ultrasonic effects are classified into three types of effect: the transient cavitation effect, stable cavitation effect, and acoustic radiation force effect. Based on these effects, the applications of ultrasound to mineral flotation are reviewed, including slime coating removal, oxidation film removal, desulfuration, tiny bubble generation, flotation reagent dispersion, and aggregation. In addition, the ultrasonic equipment and treatment methods applied in flotation are classified and compared based on their characteristics. Finally, we propose some potential directions in the study of the stable cavitation effect and acoustic radiation force effect, which are important, but are seldom mentioned in previous reports.
•Flotation of fine particles were improved by high-frequency ultrasonic standing wave.•Carrier bubbles can hardly be formed by low-frequency ultrasonic standing wave.•Increasing the frequency of USW ...could promote the formation of carrier bubbles.•Secondary acoustic radiation forces between carrier bubbles increased with frequency.•High-frequency ultrasonic standing wave was more likely to produce attraction instead of repulsion.
Froth flotation for mineral beneficiation is one of the most important separation techniques; however, it has several challenges for processing fine and ultrafine particles. Attractive mineralization between particles and bubbles by ultrasonic standing wave (USW) is a novel and high-efficiency method that could assist fine particle flotation. Frequency is an important ultrasound parameter, whose effectiveness mechanisms on the attractive mineralization did not compressively address. This study explored the effect of the USW field with various frequencies on the fine coal flotation for filling this gap. Herein, a high-speed camera and a focused beam reflectance measurement (FBRM) were used to analyze three sub-processes of the attractive mineralization, including the microbubbles’ formation, the conventional flotation bubbles (CFBs)’ dispersion, and the particles’ movement. It was found that the maximum flotation metallurgical responses were obtained under the highest examined USW frequency (600 kHz). However, the flotation outcomes by a low USW frequency (50 kHz) were even lower than the conventional flotation tests. Observation and theoretical calculation results revealed these results were originated from the influence of frequency on the carrier bubbles’ formation and the action of the secondary acoustic force during USW-assisted flotation. These outcomes demonstrated that frequency is a key factor determining the success of attractive mineralization for fine particles’ flotation.
In this study, experimental data for wet- and dry-ground coal samples under wet and dry grinding are characterized by commonly used distribution functions. First, both the R-R and Swrebec functions ...have superior fitting performances for cumulative particle size curves compared to the other studied functions. On this basis, a time-dependent expression is drawn to describe the cumulative particle size distribution. Second, the R-R function produces a significantly superior fit to the relative mass distributions of the ground products compared to those of the others at a short grinding time. The goodness of fit for all distribution functions studied performs marginally worse at approximately 3min, which can be associated with a change in the dominant breakage mechanisms from impact to abrasion-chipping. With an increase in the grinding time, the G-G-S function is the optimal function for characterizing the particle size probability mass distributions of wet grinding, whereas the G-M function provides the best fitting performance when applied to the experimental dry-grinding data. Further, the optimal particle size probability density functions are associated with the difference in breakage mechanisms between wet and dry grinding.
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•The R-R function fits the best to cumulative particle size curves compared to others.•A time-dependent expression is drawn to describe the cumulative particle size curve.•The proper probability distribution functions correlates with breakage mechanisms.
•Bulk micro-nanobubble solutions were prepared using a fine-bubble generator under different preparation times and aeration rates.•The dissolved oxygen contents of bulk micro-nanobubble water under ...different conditions were evaluated.•The bubble concentrations and sizes in bulk micro-nanobubble water under different conditions were evaluated.•The relationship between the dissolved oxygen concentration and the cavitation behaviors of bubbles was discussed.
Fundamental research on bulk micro-nanobubbles (BMNBs) has grown rapidly due to the demand for their industrial applications and potential role in interfacial sciences. This work focuses on examining properties of such bubbles, including the number, concentration, zeta potential, and surface tension in water. For this purpose, BMNBs were generated by the hydrodynamic cavitation (HC) mechanism. Distilled water and air in the experiments were the liquid and gas phases, respectively. The characterization of bulk microbubbles (BMBs) and bulk nanobubbles (BNBs) were performed through focused beam reflectance measurement (FBRM) and nanoparticle tracking analysis (NTA) techniques, respectively. Zeta potential and surface tension of aqueous solutions were measured at different time and aeration rates. The results showed that aeration rate and preparation time had an important role in the properties of BNBs (concentration, bubble size, and surface charge) and BMBs (number, and bubble size). The instability of BMBs led to the rapid changes in the dissolved oxygen (DO) content in the water. The number of BMBs decreased when preparation time and aeration rate increased, but their size remained constant. By enhancing the preparation time and aeration rate, the concentration of BNBs improved first and then reduced. Additionally, the surface tension of an aqueous solution containing BNBs was significantly lower than that of pure water.
Coal-series kaolin (CSK) in Xuzhou, Jiangsu Province of Eastern China was characterized by chemical analyses, X-ray diffraction (XRD) and zeta potential measurement as well as by scanning electron ...microscope equipped with an energy dispersive spectrometer (SEM-EDS). The authigenic ultrafine quartz grains (d90=15.8μm) closely associated with this CSK sample was the major impurity mineral, which cannot be separated from kaolin by screening and size classification process. This work investigated the separation of fine quartz from kaolin by flotation. Single mineral flotation tests indicated that effective separation of quartz from kaolin was possible with acidic pH value (pH=3), depressant of starch and collector of dodecyl amine (DDA). Rougher flotation tests of coal-series kaolin revealed that the SiO2/Al2O3 weight ratio of the concentrate was qualified for industrial applications in the presence of 160g/t starch and 100g/t DDA, at acidic pH pulp. A specially designed two-stage cleaner flotation flowsheet increased the concentrate recovery from 37.26% to 46.55% compared to a rougher flotation process.
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•The micron quartz grains closely are associated with kaolin in this ore.•Starch can selectively depress quartz in acidic solution.•A qualified product having a proper recovery was obtained in multi-stage flotation.
•Ultrasonic parameters of graphite flotation were optimized by Box–Behnken design.•Horn-type ultrasound produced a better flotation efficiency than that of bath-type.•Dual-frequency ultrasound was ...first employed for graphite flotation.•Related mechanisms are cavitation intensity and formed bubble-particle aggregates.
Ultrasound has emerged as a promising technique for improving the mineral flotation performance. However, limited research exists regarding the influence of different ultrasound types on the flotation process. Specifically, the impact of combined ultrasound and the comparison of horn- and bath-type ultrasounds on flotation have not been fully investigated. To address this knowledge gap, a comprehensive study to explore the effects of different ultrasonic pretreatments on the flotation of flake graphite was conducted. A Box-Behnken design is employed to analyze the effects of combined ultrasound on graphite flotation. By characterizing the properties of graphite samples before and after the ultrasonic treatment, the aim is to elucidate the mechanism underlying the impact of ultrasound on graphite flotation. The experimental results indicated that the ultrasonic cavitation intensity exerted a significant influence on the graphite flotation recovery. Both horn- and bath- type ultrasounds contributed to flotation, but horn-type ultrasound demonstrated a more pronounced effect, leading to a 7% increase in flotation recovery, whereas bath-type ultrasound resulted in only a 2% increase. Furthermore, the cavitation intensity of combined ultrasound was found to be higher than that of single-frequency ultrasound in the same duration. However, the performance of graphite flotation was better with short duration combined ultrasound pretreatment, while the opposite trend was observed for a long duration ultrasound pretreatment. These findings may inform the development of more efficient and effective ultrasonic pretreatments for flotation separation processes.
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•Ultrasound increased the impurity removal rate from ∼ 15 % (0 W input power) to ∼ 50 %.•The ash removal rate deteriorated at excessively high input power and temperature.•The maximum ...leaching kinetic parameters were obtained at 300 W ultrasonic power.•Ultrasound fractured particles, removed inertia layers, and improved mass transfer.
This study aimed to investigate the effect of ultrasonic power and temperature on the impurity removal rate during conventional and ultrasonic-assisted leaching of aphanitic graphite. The results showed that the ash removal rate increased gradually (∼50 %) with the increase in ultrasonic power and temperature but deteriorated at high power and temperature. The unreacted shrinkage core model was found to fit the experimental results better than other models. The Arrhenius equation was used to calculate the finger front factor and activation energy under different ultrasonic power conditions. The ultrasonic leaching process was significantly influenced by temperature, and the enhancement of the leaching reaction rate constant by ultrasound was mainly reflected in the increase of the pre-exponential factor A. Ultrasound treatment improved the efficiency of impurity mineral removal by destroying the inert layer formed on the graphite surface, promoting particle fragmentation, and generating oxidation radicals. The poor reactivity of hydrochloric acid with quartz and some silicate minerals is a bottleneck limiting the further improvement of impurity removal efficiency in ultrasound-assisted aphanitic graphite. Finally, the study suggests that introducing fluoride salts may be a promising method for deep impurity removal in the ultrasound-assisted hydrochloric acid leaching process of aphanitic graphite.
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•Homogenization, sonication, and their combination were assessed for preparing Pickering emulsions.•Optical microscopic images and chord length of emulsion droplets were ...evaluated.•Rotor-stator homogenizer had essential effects on emulsions when a chord length was greater than 20 μm.•Sonication method could disperse micro-scale aggregates of the nano-silica effectively.•Ultrasonic treatment was found superior over the rotor-stator homogenizer in reducing droplet size.
Pickering emulsions are eco-friendly, stabilized by solid particles, and have an essential role in leading industries. Although Pickering emulations have found several applications, surprisingly few investigations have attempted to explore the effectiveness of various mechanical processes for its production. To fill these gaps, the present investigation comprehensively examined the application of various Pickering emulsion preparation processes such as rotor-stator homogenization emulsification (R-SH), ultrasonic emulsification, and their combined processes by using nano-silica particles. The influences of emulsification time and intensity on emulsion droplets' distribution were analyzed as indicative factors. The kerosene/water nano-silica Pickering emulsion was utilized for all assessments. The obtained results demonstrated that the main distribution peak of the emulsion prepared by R-SH occurred where the chord length was greater than 40 μm. Micro-scale nano-silica-aggregates generated large droplets, while the fine-emulsion fraction was significantly increased after ultrasonic treatment. The experimental results showed that the emulsion prepared only by ultrasound needed substantial power to form a Pickering emulsion since the oil phase was difficult to disperse in the water phase. Finally, it was concluded that preprocessing by R-SH could form a stable and uniform emulsion speedily, which is essential for ultrasound emulsion preparation.
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