Oily Bubble Flotation 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.

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%.

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.

Application of the Oily-Bubble flotation of Shengli lignite and its optimization

ABSTRACT The upgrading of low-rank coal is important for its utilization. The lignite used in this study had extremely low surface hydrophobicity and responded poorly to the conventional flotation process. Therefore, to enhance its flotation, a laboratory device known as oily-bubble flotation was used. With this device, the combustible matter recovery at a collector dosage of 6.4 kg/t reached 32.94% which was comparable to that of the conventional flotation at the collector dosage of 50 kg/t. For improving recovery, utilization of electrochemical conditions for pulp, i.e., pH, and NaCl and CaCl2 solutions, was used to further enhance the oily-bubble flotation performance. Based on the response-surface methodology, a functional model for combustible matter recovery was established, and the regulator scheme in oily-bubble flotation was optimized to achieve a combustible recovery of 59.19% with pH and NaCl and CaCl2 concentrations of 6.03, 61.26 mmol/L, and 80 mmol/L, respectively. Results showed that an increased combustible matter recovery of 78.69% could be obtained using this optimization scheme.

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.

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.

A study on novel reactive oily bubble technology enhanced collophane flotation

Collophane is an important phosphate mineral, which has proven to be difficult to float from gangue. In this work, the novel application of reactive oily bubbles to enhance collophane flotation is reported. Three different types of bubbles, conventional air bubble, oily bubbles (kerosene only) and reactive oily bubbles (kerosene containing fatty acids) approaching collophane particles were studied by measurements of zeta potential, induction time and contact angle. The reactive oily bubble shows negligible effects on the zeta potential of collophane particles. A shorter induction time of reactive oily bubble was found at pH6.0 and/or at pH9.0 relative to the conventional air bubbles and the oily bubbles. This suggests a strong collection power of reactive oily bubble. Advancing contact angles of the reactive oily bubble on collophane increased dramatically with pH. At pH9.0, a contact angle of 120 degrees was observed where the reactive oily bubble flotation is anticipated. Micro-flotation results demonstrate the superiority of reactive oily bubbles over air bubbles for collophane flotation. A concentrate containing 35.67% of P2O5 and 0.39% of MgO was obtained using reactive oily bubble flotation at pH9.0. Micro-flotation results also show that Ca2+ and Mg2+ ions have a negative effect on the collophane flotation, but the effect of reactive oily bubble system is smaller than that of air bubble system.

Enhancing flotation performance of low rank coal by improving its hydrophobicity and the property of oily bubbles using 2-ethylhexanol

In this paper, the influence of 2-ethylhexanol used as a modifier/emulsifier on the surface chemical property of low rank coal and its flotation performance was investigated. According to the FTIR analysis, it showed an obvious decline in the hydrophilic groups while an increase in the hydrophobic groups on the surface of coal after pretreatment by 2-ethylhexanol solution for 12 h, resulting in the increase of contact angle from 74.9° to 95.4°. Whereas the induction time showed a significant decrease from 246.0ms down to 85.4ms, which meant the better hydrophobicity and floatability of coal particles after the pretreatment. As a result, a better flotation efficiency of low rank coal was attained after the pretreatment. Additionally, the oily bubble flotation combining 2-ethylhexanol was employed to enhance the flotation of coal samples. The results indicated that the mixture of diesel oil and 2-ethylhexanol improved the collecting power and selectivity of oily bubbles, with the oil contact angle for coal samples decreasing from 17.8° to 14.5° and the induction time from 50ms down to 19.7ms. The performance of oily bubble flotation, especially using the mixed diesel oil bubbles, was much better than that of conventional flotation, and the recovery of combustible matter and flotation efficiency index increased from 43.42% and 29.52% up to 89.27% and 59.91% respectively. Consequently, the flotation performance of low rank coal may be enhanced by the surface modification of 2-ethylhexanol as well as the novel oily bubble flotation technology.

Comparison of flotation performances of low rank coal in air and oily bubble processes

Low rank coal is typically difficult to float using traditional flotation processes. In this study, a novel flotation process, oily bubble flotation, was proposed and evaluated using samples of low rank coal. X-ray photoelectron spectrometer (XPS) and scanning electron microscope (SEM) were used to characterize the surface chemical and morphology properties of coal samples. Induction time tests were used to compare the mineralization degree between air or oily bubble and low rank coal particle surfaces. It was found that flotation selectivity in the oily bubble flotation process was considerably higher than that in the traditional flotation process. With the increase of collector dosage, the combustible matter recovery in the oily bubble flotation process increased from 62.92% to 82.65% while the ash content of the concentrate slightly increased from 7.43% to 8.21%. Moreover, the ash content of concentrate obtained from the oily bubble flotation process was slightly lower than that in the air bubble flotation process. Therefore, a comparison of the performances of air and oily bubble flotation indicated that the oily bubble flotation process was feasible for upgrading low rank coal.

Flotation Performances of Different Size Fractions of Low-Rank Coal in Air- and Oily-Bubble Processes

ABSTRACTXPS results of different size fractions indicated that the content of oxygen-containing functional groups on the 0.500–0.250 mm and -0.074 mm size-fraction surfaces are much higher than that of other size fractions. Furthermore, both the 0.500–0.250 mm and -0.074 mm size fractions account for 63.35% of the raw coal. Therefore, the low-rank coal is extremely difficult to float in an air-bubble-flotation process. In order to efficiently float low-rank coal, a novel flotation process is proposed in this article that was named the oily-bubble-flotation process. Induction Timer 2015 was also used to compare the mineralization degree of different size particles between air and oily bubbles. The flotation results of low-rank coal in air- and oily-bubble processes indicated that the combustible matter recovery in the oily-bubble-flotation process for low-rank coal increased with increasing the diesel oil dosage and decreases in the particle-size fraction, especially for the -0.074 mm size fraction. Meanwhile, the oily-bubble flotation can obtain a better selectivity of finer particles flotation, which can effectively reduce the occurrence of entrainment. Therefore, the flotation performance of different size fractions of Da Liuta low-rank coal may be enhanced by oily-bubble flotation.

A Study of Kinetics on Oily-Bubble Flotation for a Low-Rank Coal

ABSTRACTThe flotation performance and kinetics for a low-rank coal were investigated using air bubbles and oily bubbles. Five flotation kinetic models were applied to the test data to estimate the relationships between the flotation rate constant, the maximum recovery, and the collector dosage. The results showed that the oily-bubble flotation (OBF) obtained lower ash content and higher combustible recovery with less collector dosage than the air-bubble flotation (ABF). But this advantage of OBF gradually diminished with the collector dosage. It was found that the flotation of a low-rank coal in ABF and OBF can be best described with the second-order kinetic model and classical first-order model, respectively. The OBF had higher maximum combustible recovery values and lower maximum ash recovery values. The flotation rate constants of OBF were higher in all the models except the fully mixed reactor model. Furthermore, the effect of collector dosage on the low-rank coal flotation kinetics was evaluated. It was indicated that the maximum recovery values and modified rate constants increased with the collector dosage. The similar trend was observed in the flotation rate constants for all of the models except the fully mixed reactor model.

Application of reactive oily bubbles to bastnaesite flotation

Reactive oily bubble, defined as air bubbles covered with a thin layer of kerosene containing collectors, was used to float a major rare earth mineral, bastnaesite from rare earth ores. Both fatty acid and hydroxamic acid were used to generate reactive oily bubbles. The flotation of bastnaesite with reactive oily bubble was investigated by zeta potential, zeta potential distribution and induction time measurement and micro-flotation tests. The results showed a quicker attachment to bastnaesite and a stronger collecting power of reactive oily bubbles containing 100ppm fatty acid than conventional air bubbles, resulting in an enhanced bastnaesite recovery. The flotation recovery of bastnaesite by reactive oily bubbles containing hydroxamic acid is lower than that by conventional air bubble flotation where the bastnaesite was pre-conditioned by hydroxamic acid in aqueous phase. During induction time measurement, no attachment is observed between bastnaesite particles and reactive oily bubbles containing hydroxamic acid, illustrating the importance of collector type in reactive oily bubble flotation technology. These findings suggest the superior performance of reactive oily bubble technique than conventional bastnaesite flotation method only when proper collector is used to generate the reactive oily bubbles.

Experimental design of oily bubbles in oxidized coal flotation

Oxidized coal is difficult to float using oily collectors in the conventional flotation process. This study was aimed at designing the flotation process, namely the oily bubble flotation process, to float oxidized coal efficiently. The flotation process using oily bubbles is thoroughly described. The study compared using oily bubbles and air bubbles to float oxidized coal. some properties of oxidized coal are similar to lignite. Therefore, oxidized coal should also be recovered efficiently. The flotation collectors have a great effect on the flotation process of oxidized coal. The float ability of Taixi oxidized coal can be improved by surface activation or grinding. The microwave pretreatment can improve the hydrophobicity of oxidized coal by decreasing the moisture content of oxidized coal. The flotation results show that the oily bubble flotation process can obtain higher combustible matter recovery than the conventional flotation process. The flotation efficiency index using oily bubbles is also higher than that using air bubbles.

Role of oily bubbles in enhancing bitumen flotation

A recognized challenge in bitumen extraction is the reduced bitumen recovery when processing high-fine ores or “weathered” oil sand ores, collectively called poor processing ores. Preliminary lab tests demonstrated that bitumen flotation recovery from these ores could be greatly enhanced by using oily bubbles (air bubbles coated with a thin layer of oil or solvent) instead of air bubbles. In this study, dynamic contact angle of air/oily bubbles on bitumen surface and induction time of bitumen–air/oily bubble attachment in aqueous solution were measured to investigate the mechanisms of how oily bubbles help improve bitumen recovery and to justify the use of oily bubbles while processing poor oil sand ores. Oily bubbles showed a marginal effect on the contact angle values compared to air bubbles. However, the spreading of oily bubbles on a bitumen surface was found to be much faster than that of air bubbles. The induction time for bubble–bitumen attachment in the process water from poor processing ores was found to be much shorter for oily bubbles than for air bubbles. The reduced induction time for kerosene-coated air bubble–bitumen attachment correlates well with the improved bitumen recovery from poor processing ores using kerosene-coated oily bubble flotation technology.

Fundamental study of reactive oily-bubble flotation

A novel concept of reactive oily bubbles (i.e., bubbles covered by a thin layer of oil containing oil-soluble collectors) as a carrier in flotation is proposed. In addition to the role of fine particle agglomeration by oily films, the surface properties of air bubbles coated with a thin oil film can be better controlled for the desired selectivity by adding certain types and concentrations of water insoluble collectors into the oil phase. Oily bubbles attain a much higher contact angle than air bubbles, ensuring a strong collecting power, favorably for floating both coarse and fine particles. The reactive oily bubble flotation can eliminate the addition of collector to the aqueous phase, avoid undesired synergetic interactions among collectors, activators, depressants and dispersants present in slurry, minimize undesired activation of gangue particles and significantly reduce the amount of collectors needed. The electrokinetics of kerosene droplets in aqueous collector solutions was measured as a function of solution pH. The results clearly showed that the surface charge and hence the surface properties of oil droplets can be finely tuned by controlling the type of the collectors to suit the desired flotation needs. The attachment of collector-containing oily bubbles on silica, sphalerite and galena surfaces was investigated with contact angle measurement. The concept of using reactive oily bubble to achieve selective flotation was demonstrated in microflotation tests.