Oily Bubbles Research Articles

Oily Bubble Flotation of Coal Macerals of Shendong Jurassic Coal

The comprehensive quality enhancement and grading of coal are crucial methods for unlocking the high value-added and low-carbon utilization of coal resources. In this work, the influence of oily bubbles on the flotation of Shendong Jurassic vitrinite-rich coal and inertinite-rich coal was studied via flotation tests, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle detection, and induction time measurements. FT-IR and XPS analyses demonstrated that the surface of inertinite-rich coal contains more hydrophilic oxygen-containing functional groups. Contact angle and induction time measurements showed that the vitrinite-rich coal is more hydrophobic than inertinite-rich coal, and that for both air and oily bubbles, the induction time on the surface of vitrinite-rich coal is shorter than that on the surface of inertinite-rich coal. In addition, rather remarkably, the induction times for both vitrinite-rich coal and inertinite-rich coal are significantly reduced by oily bubbles. Finally, a better flotation performance for oily bubble flotation of vitrinite-rich coal and inertinite-rich coal was found. It appears that oily bubble flotation is an efficient method for enhancing the recovery of vitrinite-rich coal and inertinite-rich coal.

Influence of oil film on the interaction between bubble and bubble/lignite particle

ABSTRACT The floatability of low-rank coal is poor because of its low metamorphosis, and the oily bubble flotation is an effective means to collect coal particles. In this paper, adhesion angles and forces between watery/oily bubbles and coal surfaces were measured to analyze the influence of oil film on adhesion behavior between bubble and particle. The properties of watery/oily bubbles were analyzed by dynamic foam analyzer (DFA) to reveal the influence of oil film on the bubbles further. The results showed that in the dynamic environment, the maximum adhesion angle of the oily bubble was 36.55°, while the angle of the watery bubble was 31.29°, and the adhesion kinetic constant for oily bubble-particle and watery bubble-particle were 0.0295 and 0.0174, respectively. The measured maximum adhesion forces of the watery bubble and oily bubble were 19.2 μN and 86.8 μN, respectively, indicating that oily bubbles were more prone to attach to the coal surface and were beneficial to flotation. The calculated normalized contact line indicated that the oil film could squeeze a lot of water out from the coal surface, increasing the actual contact area and strengthening the attachment. The results of DFA showed that with the oil film, the oily bubbles could be more stable with a smaller size and lower liquid content than the watery bubbles. The results of the above study show that the oil film covering the watery bubble could improve the adhesion between bubble and particle and reduce the bubble size, which is conducive to promoting the sorting efficiency and thus enhancing the flotation of lignite.

Study on inhibition mechanisms of detachment of coal particles from oily bubbles in flotation column

The cyclonic microbubble flotation column is an efficient separation equipment in the beneficiation process of metallic and non-metallic minerals. However, the higher detachment rate of coarse particles in the pulp, pulp-froth interfacial zone, and froth zone is an issue that needs to be addressed urgently in column flotation. Compared with traditional air-water bubbles, oily bubbles have higher hydrophobicity, which is beneficial for strengthening the bubble-particle attachment and inhibiting the bubble-particle detachment. Therefore, oily bubbles were introduced into the cyclonic microbubble flotation column to reduce the particle detachment rate. Firstly, an improved cyclonic microbubble flotation column was set up, and traditional air-water bubbles were placed by oily bubbles through the combined use of an atomizer and a bubble generator during experiments. Subsequently, we investigated the feasibility of using oily bubbles as a flotation carrier to regulate the particle detachment rate, improve the particle recovery, and explore the mechanism behind this. Column flotation results showed that recovery rates generated from experiments with oily bubbles are higher than those with air-water bubbles under different operation conditions, and the particle detachment rate in the interfacial region was significantly reduced with the use of oily bubbles. Recoveries and flotation rate constants generated from collection zones for each particle size range indicated that the use of oily bubbles can increase the upper limit of flotation particle size compared with the use of air-water bubbles. Calculated detachment rates showed that the use of oily bubbles can effectively reduce the detachment probability of particles with different sizes in the collection zone. Combined with the observation of ultrasonic-assisted oscillation, it is proved that the oil coating film on the oily bubble significantly improves the resistance of oily bubbles to turbulent disturbance. In addition, the increase in hydrophobic force between oily bubbles and particles and the growth of the three-phase contact periphery are beneficial to reducing the particle detachment probability due to turbulent disturbance in the collection zone. Results from bubble coalescence experiments showed that the existence of oily bubbles significantly reduced bubble coalescence time and increased the damping coefficient. Compared with air-water bubbles, oily bubbles have a stronger damping effect on the oscillation caused by bubble coalescence, inhibiting the violent bubble surface deformation and the induced particle detachment during bubble coalescence. Therefore, the introduction of oily bubbles is a promising idea to reduce the detachment probability of coarse particles and increase the upper limit of particle size in column flotation.

Comparison of attachment process of particles to air and oily bubbles in flotation

The attachment between particles and bubbles is a very important basic unit for mineral flotation. In the present study, methylation processing for glass spheres with trimethylchlorosilane was used to prepare particles with different surface hydrophobicity, and a visualization setup was assembled based on high-speed camera technology to investigate the dynamic attachment process of particles onto air/oily bubbles. More importantly, the difference in the attachment process between particles and air/oily bubbles was successfully quantified with the software Image Pro Plus 6.0. It was found that the wetting film ruptured at about 36 ms during the attachment between the hydrophobic glass sphere M2 and air bubbles, while it occurred at about 28 ms during the attachment between M2 and oily bubbles. Moreover, the formed three-phase contact line between hydrophobic particles and oily bubbles was larger than that between hydrophobic particles and air bubbles, suggesting a more stable attachment of the former. In contrast, no successful attachment of the hydrophilic glass sphere M0 onto air or oily bubbles was observed. These findings strongly demonstrated that oily bubbles had both strong collecting power and excellent selectivity for hydrophobic particles in flotation. This study improved the understanding of the difference between oily-bubble and conventional flotations.

Effect of oily bubbles on the detachment behavior between bubbles and coarse particles

Coarse particle flotation provides significant advantages in terms of reducing grinding costs and improving the throughput of the flotation process. However, the high probability of the detachment of coarse particles during flotation is a significant challenge. In this study, we explored the feasibility of using oily bubbles to reduce the detachment of coarse particles from the bubbles. Specifically, the effect of oily bubbles on the attachment stability of bubble–particle aggregates from the perspective of attachment force was theoretically analyzed and compared to that of air bubbles, and the effect of oily bubbles on the detachment probability of spherical glass beads with different contact angles was investigated experimentally using a home-built experimental system. Both the theoretical and experimental results proved that it is feasible to apply oily bubbles to reduce the detachment probability of coarse particles. However, there are limitations to this method. The influence of oily bubbles on the detachment behavior was mainly governed by changes in the contact angle and interfacial tension, which is not the case with air bubbles. Therefore, the oily bubbles were effective in reducing the detachment probability only for particles in which the influence of the increase in contact angle on the particle detachment exceeded that of the decrease in interfacial tension. The results of this study advance our understanding of the effect of oily bubbles on the detachment behavior of coarse particles, such as in the flotation separation of valuable minerals using oily bubbles.

A novel method for evaluating the hydrophobic interaction between coal particles and air bubbles and its role in flotation

Among surface forces, the non-Derjaguin-Landau-Verwey-Overbeek hydrophobic force between hydrophobic surfaces is critical to bubble-particle attachment and, as a result, mineralization in flotation. However, it brings challenge to study the hydrophobic interaction between coal particles and air bubbles due to lack of the hydrophobic interaction constant. In this study, a novel method was proposed to evaluate the hydrophobic interaction between coal particles and air bubbles, which comprehensively combines the extended Derjaguin-Landau-Verwey-Overbeek theory, the Stefan-Reynolds model and the experimentally measured attachment time. It was found that the attachment time between coal particles and air/oily bubbles was respectively 246 and 50 ms. The decay length for hydrophobic interactions was about 25 nm. Then, according to the obtained attachment time and decay length, the derive Stefan-Reynolds model was solved and the hydrophobic interaction energy constant between air bubbles and coal particles was determined to be −4.19 mJ/m2, about 1/7 of that between oily bubbles and coal particles. These findings clearly demonstrated the significant difference between conventional and oily-bubble flotations, and the critical role of the hydrophobic interaction in coal flotation was confirmed.

Investigation of adhesion behavior between reactive oily bubble and low-rank coal

Reactive oily bubble, defined as air bubble covered with a thin layer of diesel oil containing surfactants, was used in low-rank coal flotation. Both the cationic surfactant dodecyl amine (DDA) and the anionic surfactant palmitic acid (HPa) were used to generate the reactive oily bubble. The strengthening mechanism of the reactive oily bubble was investigated by a series of flotation tests and the adhesion force measurements. The results showed that at low concentrations (0.5, 2.5, and 5.0 mM), the effect of the reactive oily bubble with DDA to enhance adhesion and promote separation was not significant. When the concentration of DDA increased to 50 mM, the coalescence of bubbles deteriorated separation. In addition, the competitive adsorption between oil and DDA (reverse orientation) reduced the hydrophobicity of the coal surface and weakened the adhesion force between the bubble and coal surface. While for HPa, the synergistic adsorption between HPa and diesel oil played an important role in promoting separation and the concentration of HPa in the oily bubble and the flotation efficiency was positively correlated. The values of normalized contact line (x) could be used to represent the expansion of the three-phase contact line which indicated that the reactive bubble containing HPa could squeeze more water out from grooves of coal surface than that of bubble containing DDA. These findings suggest that using the reactive oily bubble is conducive to promoting the separation efficiency only when proper concentration and type surfactant is used to generate the reactive oily bubble.

Comparison of the adhesion kinetics between air or oily bubble and long flame coal surface in flotation

Flotation is an effective separation technology with a wide range of applications, and oily bubbles have recently been shown to be more effective than air bubbles at separating low-rank coal. However, the differences in the spreading behaviours of oily and air bubbles at the microscale have not yet been clarified. In this study, high-speed camera technology was used to characterise the interaction process of air and oily bubbles with low-rank coal particles. The three-phase contact (TPC) line formation behaviours of air and oily bubbles on the low-rank coal surface were observed in a deionised solution. At 0–20 ms, the oily bubbles spread more quickly on the low-rank coal surface than the air bubbles; the TPC spreading completion percentages of the oily and air bubbles were 97.58% and 70.73%, respectively. At 20–100 ms, the oily bubbles spread more slowly than the air bubbles because they respectively had 2% and 30% of the TPC spreading process to complete. The results indicated that the oily bubble surface was more hydrophobic than the air bubble surface.

Effect of pH on surface hydration of coal particles and its attachment with oily bubbles in flotation

ABSTRACT The pH of flotation slurry directly affects the surface potentials of mineral particles and bubbles, and therefore the hydration of coal surface and the mineralization process of flotation. In this paper, the effect of pH on the surface potential, hydration degree, and floatability of lignite particles was studied, wherein Einstein’s dispersion viscosity theory was adopted to calculate the hydration degree, and DLVO theory was used to estimate the interaction between coal particles and oily bubbles. The effect of pH on the lignite floatability was evaluated in terms of induction time and oily-bubble flotation results. The results showed that with increasing pH, the zeta potentials of coal particles and oily bubbles decrease, causing a 37.89% increase in the coal surface hydration from pH 3 to pH 11. As a result, the energy barrier for attachment between the coal particles and oily bubbles reaches the maximum value of 2.669 × 10−16 J at pH 11, resulting in low attachment efficiency. Correspondingly, the combustible matter recovery of oily-bubble flotation is significantly decreased from 57.76% to 28.00%.

Variability of a natural hydrocarbon seep and its connection to the ocean surface

Natural hydrocarbon seeps are ubiquitous along continental margins. Despite their significance, we lack a basic understanding of the long-term temporal variability of seep dynamics, including bubble size, rise velocity, composition, and upwelling and entrainment processes. The shortcoming makes it difficult to constrain the global estimates of oil and gas entering the marine environment. Here we report on a multi-method approach based on optical, acoustic, satellite remote sensing, and simulations, to connect the characteristics of a hydrocarbon seep in the Gulf of Mexico to its footprint on the sea surface. Using an in-situ camera, bubble dynamics at the source were measured every 6 h over 153 days and the integrated total hydrocarbon release volume was estimated as 53 m3. The vertical velocity was acoustically measured at 20 m above bed (mab) and found to be approximately 40% less than the dispersed-phase at the source, indicating that the measured values are reflecting the plume continuous-phase flow. Numerical simulations predict that the oily bubbles with diameters larger than 8 mm reach the surface with a small footprint, i.e. forming an oil slick origin, deflection of which with wind and surface current leads to the formation of an oil slick on the surface. Nineteen SAR images are used to estimate the oil seepage rate from GC600 for 2017 giving an average discharge of 14.4 cm3/s.

Comparison of flotation performances of low-rank coal with lower ash content using air and oily bubbles

The attachment interaction in a flotation process is critical because it controls the recovery of mineral particles and is dominated by the interaction energy barrier between bubbles and solid particles. In this investigation, the surface properties of coal particles and oily bubbles were evaluated via the X-ray photoelectron spectroscopy (XPS) analysis, zeta potential measurement and induction time tests. The results proved that the classical Derjagin–Landau–Verwey–Overbeek (DLVO) theory did not adequately predict the flotation performances of oily bubble flotation. The attractive interaction or hydrophobic force induced by the hydrophobic force should be considered in the extended DLVO (EDLVO) theory. Throughout this paper, therefore, it is significant to consider the attractive interaction or hydrophobic force between low-rank coal particles and oily bubbles when comparing the advantages of the flotation response using air and oily bubbles.

Effects of NaCl/CaCl2 on the surface hydration and flotation of lignite particles

ABSTRACT This study focused on the mechanisms of NaCl and CaCl2 enhancing the oily-bubble flotation of lignite. The degree of surface hydration of coal particles before and after conditioning with NaCl/CaCl2 was evaluated with the Einstein theory of dispersion viscosity, while the effect of these two electrolytes on lignite floatability was evaluated via attachment time and flotation tests. The results indicated the adsorption amount of Ca2+ on the coal sample was more than that of Na+ in the same electrolyte concentration. Owing to the cationic adsorption, the zeta potential of lignite particles increased with increasing NaCl and CaCl2 concentrations, which thus decreased the electrostatic repulsion between coal particles and oily bubbles. Moreover, the hydration of the coal surface decreased when NaCl/CaCl2 was added to flotation pulp, meaning the surface hydrophilicity of the coal sample was reduced. As a result, the attachment time between coal particles and oily bubbles decreased significantly, and the combustible-matter recovery correspondingly increased up to a maximum of 50.97% and 90.06% with increasing NaCl and CaCl2 solutions concentration, respectively. However, it is necessary to keep the electrolyte solution concentration within a reasonable range for a good selectivity during the oily-bubble flotation.

Use of “oily bubbles” and dispersants in flotation of molybdenite in fresh and seawater

Molybdenite - as all inherently hydrophobic minerals – is floated with the use of water-insoluble oily collectors. Such collectors can be used in flotation either after emulsification in water, but can also be brought to the point of particle-to-bubble attachment on the surface of bubbles (as oily-bubbles). In this paper we are testing the effect of oily-bubbles and the dispersants sodium hexametaphosphate (SHMP) and sodium silicate (SS) on the flotation of moleybdenite in seawater in alkaline environment. The results show that molybdenite recovery increases when kerosene is supplied on the surface of bubbles which was particularly important in the flotation of molybdenite at pH > 9.5 in seawater. SHMP dispersant had a strong positive effect on the recovery of molybdenite at pH > 9.5, the pH range known to cause depression of the molybdenite flotation when pH is raised to depress pyrite and magnesium species precipitate as hydroxo-complexes/hydroxide. The combined effect of the oily bubbles and dispersants allows for the molybdenite recoveries to reach to similar values to those achieved when using fresh water. The results of induction time measurements indicate that the attachment of bubbles to molybdenite is significantly improved when the bubbles are coated with a layer of kerosene.

Janus membrane emulsification for facile preparation of hollow microspheres

Hollow microspheres have aroused considerable interests in the materials community owing to their numerous potential applications; however, scalable, facile, low-cost production of hollow microspheres has not yet been demonstrated. Here, inspired by the idea that a hydrophilic surface allows the rapid detachment of gas bubbles to reduce the bubble size significantly, a novel and feasible approach to preparing gas-in-oil-in-water (G/O/W) emulsions on a large scale using Janus membrane emulsification is presented. A Janus membrane with asymmetric wettability, rather than a fully hydrophilic or a fully hydrophobic membrane, is employed in the emulsification system, in which the hydrophobic side allows gas/oil permeation and the hydrophilic side achieves fast release of oily bubbles. The wetting and chemical properties of each side of the membrane were investigated by contact angle and spectroscopy measurement. It was observed that the stability of the emulsions increased with increasing solution pH values. The variation of droplet size and distribution with the gas flow rate was also studied. The outer diameters of double emulsion drops are in the order of 100–300 μm. These droplets are further exposed to UV light to obtain hollow polymeric microspheres through solidification of the oil layers. Hollow structures of the microspheres were verified by HIM observations. This simple strategy opens a new avenue for generating double emulsions and hollow microspheres at scale with relatively narrow polydispersity.

Experimental Simulation of the Zones Characteristics Considering Oily Bubble Behavior During in Situ Combustion

A linear combustion tube experiment with halfway fire extinguishing was utilized to reconstruct the combustion region distributions based on apparent characteristics of burnt oil-bearing quartz, temperature profile, and oil saturation field distribution between a gas injection well and a production well, etc. The gas composition and fluid composition in each region could be obtained. Following, a high-temperature-high-pressure visualization system was utilized to simulate experimentally the flue-gas flow in the crude oil. A flow characteristics simulation using such process parameters as system injected fluid composition and temperature condition based on the above test results of the combustion tube was conducted. The characteristics of each region were qualitatively described, the flow characteristics of the flue gas was visualized, and the oil bubble enhancement mechanism causing crude oil movement with flue gas was semiquantitatively determined. The results of the combustion tube simulation showed tha...

A novel method for measuring film thickness of oily bubbles and its effect on attachment time in oily-bubble flotation

Oily-bubble flotation technology has been proven to be an effective separation method for low rank/oxidized coals, and difficult-to-float minerals, in which oily bubbles as a carrier replacing air bubbles are the key. This study proposed a novel method for measuring the film thickness of oily bubbles, which is based on the light interference combining with an ultraviolet light spectrophotometer. Moreover, the effect of oil film thickness on the mineralization was investigated with an induction time instrument. The results indicated that the increase in oil film thickness caused the decrease in attachment time, and was thereby conducive to the attachment of the coal particles on oily bubbles. This work may enrich the knowledge in the branch of coal flotation.

Attachment interactions between low-rank coal particles and air/oily bubbles in a microflotation cell

ABSTRACTThe separation of particles by flotation is achieved based on the difference in their surface properties. The controlling step for successful flotation is bubble–particle attachment. The time required for attachment of a particle to an air bubble is defined as the attachment time. Given that attachment times cannot be measured in flotation cells due to the presence of a large number of bubbles and particles which are in motion, the only possibility is to calculate attachment times using the fundamental flotation model. The focus of this paper is to determine the attachment times of low-rank coal in the presence of air bubbles and oily bubbles. The flotation recovery, the rate constant and the attachment efficiency for the oily bubble–coal flotation system were found to be higher than those for the air bubble–coal flotation system. The difference between the flotation rate constants for the air bubble–coal flotation system and that for the oily bubble–coal flotation system was small. However, when considering the difference between the attachment efficiency results, the opposite was true. The relationship between the attachment efficiencies and the attachment times was found to be an exponential decay. The similar trend was also observed for the curve showing the relationship between the flotation rate constants and the attachment times. This work shows the importance of determination of attachment times in coal flotation research.

Comparison of air and oily bubbles flotation kinetics of long-flame coal

This paper focuses on the difference in kinetics of air and oily bubbles flotation of long-flame coal. Six flotation kinetic models were taken to fit the air and oily bubbles flotation results by the software MATrix LABoratory. The findings indicated that the conventional flotation was greater than the oily-bubble flotation in flotation rate in the early stage, and these two flotation processes exhibited different variation laws in cumulative concentrate yield with flotation time. Additionally, it was found that the classical first-order model could provide an excellent fit to the experimental data for the conventional flotation, yet all the studied kinetic models showed a great deviation in fitting to oily-bubble flotation data. Consequently, an improvement for flotation kinetic models was conducted by subtracting the delay constant in the oily-bubble flotation to attain an excellent fitting. Finally, the delay constant for the oily-bubble flotation was determined to be about 0.7500 min, while the improved classical first-order model was found to give the best fit to the oily-bubble flotation data. This study may contribute to a better understanding of the oily-bubble flotation characteristics.

Oily bubble flotation technology combining modeling and optimization of parameters for enhancement of flotation of low-flame coal

There are abundant low-medium rank coal resources in China that provide an important guarantee for China's economic and social development as well as security of energy supply. However, it is difficult to achieve the economic recovery of low-medium rank coals by conventional flotation owing to its high natural surface hydrophilicity. In this study, the characteristics of low-medium rank coal samples were comprehensively investigated based on their size/density distributions, XPS, BET, and SEM analyses. An improved oily bubble flotation combining modeling and optimization of technological parameters was employed to enhance the flotation of low-medium rank coal samples. The results indicated that the studied samples were rich in oxygenated functional groups, pores, and cracks that existed on the surfaces of the coal samples, thereby making it difficult for them to float. As a result, the collector dosage was maintained at a high level ranging from 10 to 50 kg/t in the conventional flotation of the coal sample. However, the oily bubble flotation technology showed much better flotation efficiency in the case of low-medium rank coal, achieving a higher combustible matter recovery at a much smaller collector dosage. Additionally, various parameters, such as the collector dosage, impeller speed, flotation pulp concentration, and air flow rate, had a profound effect on the flotation performance in the oily bubble flotation of the coal samples. An optimization of the technological parameters was conducted regarding the flotation of oily bubbles of low-medium rank coals, and a quadratic function model for the combustible matter recovery was established. Finally, an optimization scheme was established attaining a combustible matter recovery of 86.32% for oily bubble flotation of coal samples, where the frother dosage, collector dosage, impeller speed, pulp concentration, and air flow rate were 0.4 kg/t, 2.32 kg/t, 2198.53 rev/min, 52.47 g/L, and 0.23 m3/h, respectively. As a consequence of the optimization scheme, the collector dosage was decreased by 95.36%.

Exploration on the mechanism of oily-bubble flotation of long-flame coal

The interaction between long-flame coal particles and oily bubbles controls the crucial processes of attachment and mineralization in oily-bubble flotation thus dominates the recovery of coal. In this study, the interaction energy between long-flame coal particles and diesel oily bubbles was estimated by both DLVO and EDLVO theories, while the attachment of coal particles to oily bubbles was evaluated by induction time measurements and oily-bubble flotation tests. The results indicated that the isoelectric points of oily bubbles and coal particles were observed at about pH 3.5 and 2.3, respectively. Over the entire range of pH 2–11, the attachment between coal particles and oily bubbles was confirmed by the results of the induction time and oily-bubbles flotation tests. Additionally, it was found that the flotation recovery of coals was inversely related to the induction time. The attachment could be accurately predicted by the EDLVO theory over the tested pH range. On the contrary, it showed a great deviation for the DLVO theory to predict the attachment over the tested pH range except at pH 3. The reason for the deviation in prediction may be that the hydrophobic force on the interface of coal particles and oily bubbles is too great to be ignored.