Picobubble Enhanced Fine Coal Flotation

Abstract

Froth flotation is widely used in the coal industry to clean ?28 mesh fine coal. A successful recovery of particles by flotation depends on efficient particle‐bubble collision and attachment with minimal subsequent particle detachment from bubble. Flotation is effective in a narrow size range beyond which the flotation efficiency drops drastically. It is now known that the low flotation recovery of particles in the finest size fractions is mainly due to a low probability of bubble‐particle collision while the main reason for poor coarse particle flotation recovery is the high probability of detachment. A fundamental analysis has shown that use of picobubbles can significantly improve the flotation recovery of particles in a wide range of size by increasing the probability of collision and attachment and reducing the probability of detachment.

A specially designed column with a picobubble generator has been developed for enhanced recovery of fine coal particles. Picobubbles were produced based on the hydrodynamic cavitation principle. They are characterized by a size distribution that is mostly below 1 µm and adhere preferentially to the hydrophobic surfaces. The presence of picobubbles increases the probability of collision and attachment and decreases the probability of detachment, thus enhancing flotation recovery. Experimental results with the Coalberg seam coal in West Virginia, U.S.A. have shown that the use of picobubbles in a 2″ column flotation increased fine coal recovery by 10–30%, depending on the feed rate, collector dosage, and other flotation conditions. Picobubbles also acted as a secondary collector and reduced the collector dosage by one third to one half.     

Contact angle and vacuum floatability of ultrafine size particles

The contact angle of ultrafine size particles has been evaluated using 1 µm monosize SiO₂ particles of various degrees of wettability. The contact angle was determined by film flotation and Zisman plots. Chlorotrimethylsilane (CTS) was used to methylate the SiO₂ particle surface and establish the level of surface wettability. Also, the vacuum floatability of the methylated ultrafine SiO₂ particles was assessed to correlate it to the contact angle. This vacuum floatability was very low below 40º and increased monotonically above this contact angle value because of favorable bubble nucleation and a greater stability of the bubbles on the hydrophobic surface. Free energy of bubble nucleation on the hydrophobic surfaces has been estimated and correlated to the vacuum floatability of the ultrafine particles.     

Effect of flotation on the dioxin distribution in size-fractioned fly ash of hospital solid waste incineration

After the flotation of hospital solid waste incinerator (HSWI) fly ash, two types of solid products, froths and tailings, are produced. This paper reports the effect of flotation on the dioxins distribution patterns in different particle size fractions (?25, ?38, +25, ?75, +38, ?106, +75 and +106 µm) of fly ash. The results showed that the froths had a higher small-size particle distribution than that of the raw fly ash. The dioxin content with particle size in the flotation products depended on the partition behavior of powder-activated carbon (PAC). The dioxin content in the fine particles of the froths was higher than that in the coarse particles, and the highest content was in the finest particles (?25 µm). The dominant dibenzo-p-dioxins and dibenzofurans (PCDD/F) congeners in the froths and tailings were similar to those in the raw fly ash. A positive correlation between carbon removal and PCDD/F removal with different size fractions was observed. The carbon removal efficiencies of the fractions of ?25 and ?38, +25 µm were evidently higher than those of the other particle size fractions. Similarly, the PCDD/F removal efficiencies in fractions of ?25 and ?38, +25 µm could reach 156.9% and 115.0%, respectively.     

Bubble size distribution in cyclonic zone of a novel flotation column

In order to investigate bubble size distribution (BSD) in the cyclonic flotation column, a series of tests were conducted to study flow velocity distribution (FVD) and BSD by using the method of particle image velocimetry (PIV). Foaming performance of the n-octyl alcohol is more applicable than both of n-butyl alcohol and terpenic oil. At different circulation volume conditions, BSD range lies in 0–800 μm, and a large number of tiny bubbles (<90 μm) are generated. Besides, the curve presents a normal distribution in 90–180 μm. With the increase in circulation volume, bubble size decreases. BSD determined by cyclonic flow effect plays a crucial role on bubble mineralization with fine particle in cyclonic zone of the flotation column.     

The Effect of Adding Phosphate on the Size of Extremely Fine Needle‐like Lepidocrocite Particles Prepared by Oxidizing an Aqueous Suspension of Ferrous Hydroxide

Extremely fine particles of needle‐like lepidocrocite (γ‐FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature of 30°C, and the effects of the reaction conditions or the oxidation rate were investigated in order to determine the parameters that control the particle size. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of a needle‐like particle decreased from 0.7 µm to 0.4 µm with increasing oxidation rate. By adding of NaH₂PO₄ to an aqueous Fe(OH)₂ suspension, in concentrations up to 1.0 mol/m³ during the air oxidation, and up to 0.9 mol/m³ during the oxidation with 30% and 50% O₂, the major axis could be reduced to ca. 0.3 µm with the minor axis and the oxidation rate remained almost unchanged.     

The influence of frother types and concentrations on fine particles’ entrainment using column flotation

Entrainment which is the characteristic feature of fine particles is closely related to water recovery. It is based on the changes depending on the establishment of linear relationship between water recovery and solid recovery. This paper deals with the investigation of the effect of frother types and concentrations on fine particles’ entrainment using column flotation. Entrainment of fine particle using a mixture of artificial ore (celestite:calcite; 1:1) was investigated in column flotation. In a two-phase system (water/air), the variation of bubble diameters and gas hold-up with a superficial air rates using different frother types and concentrations were tested. The results showed that the frother types and concentrations had significant effect on the grade and recovery, superficial air rate, gas hold-up and fine gangue entrainment. Entrainment factors for frother types and concentrations were compared in flotation column. Kirjaveinen^[11] model was used for describing the specific entrained factor (P_i) of hydrophilic particles. It has been found that Kirjaveinen model supports the results of this study.     

Effect of aggregate size on liquid absorption characteristics of konjac glucomannan superabsorbent

In this article, four kinds of konjac glucomannan based superabsorbent polymers (KSAPs) with different aggregate sizes were obtained by sieving the KSAP powders manually. They were characterized by scanning electronic microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and optical contact angle (OCA), and the effects of aggregate size on liquid absorption characteristics of KSAP were studied in detail. The results show that the coarse KSAP particles were aggregated by many microspheres, while the fine particles were well dispersed with 50–150 µm particle size. OCA dynamic images showed the enhanced hydrophilicity for the finer particles. The liquid absorption measurements demonstrated that water and physiological saline absorption velocity of KSAP increased for the finer particles, while their ultimate water holding capacity decreased accordingly. The liquid absorption capacity of the finest sample (75 µm) could reach its maximum value (332.5 ± 5.6 g/g) in 0.5 min, while the coarsest sample (850 µm) reached the maximum value (532.5 ± 1.2 g/g) in 16 min. The reason for this phenomenon was discussed, and a new model was proposed to explain it. We believe that the results of this article would be meaningful in application of KSAP as superabsorbent materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45416.     

The Effect of Copper Bearing Particles Liberation on Copper Recovery from Smelter Slag by Flotation

The impact of the liberation of copper bearing particles on copper recovery in the flotation has been the subject of research in this paper. Tests have shown that grinding of material highly impacts the recovery rate in the flotation process. Results of flotation of smelter slag samples with different contents of grain size fraction ?74 µm: 50%, 60%, 70%, 80%, and 90%, have shown that by an increasing the content of the ?74 µm fraction in the feed, the recovery of copper was increasing as well. The highest recovery rate of copper was obtained with 90% of grain size fraction ?74 µm in the feed. The microscopic analysis of concentrates have shown that increased content of grain size fraction ?74 µm, was followed by increased contribution of liberated particles in the 0 to 70 µm fraction, while the contribution of middlings had been decreasing.     

浮选柱在淮北选煤厂涡北分厂的适用性分析

淮北选煤厂涡北分厂浮选系统存在煤泥量大、设备腐蚀和磨损严重、处理能力不足等问题,通过分析浮选柱在细粒、高灰煤泥分选方面的适用性,提出采用FCMC-4000型微泡浮选柱代替传统的机械搅拌式浮选机的方案,改造后将提高浮选精煤产率,降低电耗。     

Experimental testing of the hydrodynamic collision model of fine particle flotation

Flotation rates of glass beads and of latex particles have been measured as a function of particle size using very small bubbles. With glass beads the observed rate versus size relationship agreed quite well with the prediction of a simple hydrodynamic collision model, but that found with latex particles did not. It is suggested that electrical forces may have to be taken into account when the particles have a significant zeta potential. With both types of particle, the relationship between flotation rates measured at two different bubble sizes is consistent with the model's predictions.     

Microsphere tensiometry to measure advancing and receding contact angles on individual particles

In this paper, a method to measure the advancing and receding contact angles on individual colloidal spheres is described. For this purpose, the microspheres were attached to atomic force microscope cantilevers. Then the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble was measured. From these distances the contact angles were calculated. To test the method, experiments were done with silanized silica spheres (4.1 μm in diameter). From the experiments with drops, an advancing contact angle of 101 ± 4° was determined. A receding contact angle of 101 ± 2° was calculated from the jump-in distance into a bubble. Both experimental techniques gave the same contact angle. In contrast, on similarly prepared planar silica surfaces, a clear hysteresis was measured with the sessile drop method; contact angles of 104.5 ± 1° and 93.8 ± 1° were determined for the advancing and receding contact angles, respectively.     

Bubble–particle collision and attachment probability on fine particles flotation

Particle size is an important parameter in flotation and has been the focus of flotation research for decades. The difficulty in floating fine particles is attributed to the low probability of bubble–particle collision. In this research, the influence of hydrodynamic parameters on collision probability of fine particles was investigated. Collision probability was obtained using Stokes, intermediate I and intermediate II and potential equations. Maximum collision probability was 5.65% obtained with impeller speed of 1100 rpm, air flow rate of 30 l/h and particle size of 50 μm. Also, attachment probability under Stokes flow, turbulent and potential flow conditions was calculated 100, 99.49 and 81.87% respectively. Maximum attachment probability was obtained with impeller speed of 700 rpm, contact angle of 90°, particle size of 20 μm and air flow rate of 15 l/h. Collision angles were obtained between 60.71° and 60.18° and attachment angles were obtained between 9.15° and 59.83°.     

Erodent size effect on the erosion of polyphenylene sulfide composite

The effect of erodent particle size on solid particle erosion of randomly oriented short glass fiber and mineral particle reinforced polyphenylene sulfide (PPS) was investigated. To examine the effect of erodent size on the erosion resistance of the PPS composite, aluminum oxide particles at three different sizes, namely, 300–425 μm, 150–212 μm, and 45–75 μm, were used. The erosion tests were performed at six different contact angles of 15°, 30°, 45°, 60°, 75°, and 90°, respectively. The results showed a strong relationship between the erodent particle size and erosion rates of PPS composite. Maximum erosion rate for the erodent particles with sizes of 45–75 μm and 150–212 μm occurred at contact angle of 30°, on the other hand maximum erosion rate for particles having 300–425 μm size occurred between 45° and 60°. The morphologies of eroded surfaces were characterized by the scanning electron microscopy (SEM). Possible erosion mechanisms were discussed. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

A perspective on flotation: a review

The problem of fine particles processing has become important both in mineral processing and also for water and wastewater engineering. It is accepted, on the other hand, that the bubble–particle collection efficiency increases with decreasing bubble size. A decrease in bubble size can be obtained using different methods (dispersed‐air, where electroflotation is included, and/or dissolved‐air flotation), as discussed. Following an introduction of the subject, older laboratory results are presented in this review paper (based on 4 decades of experience), explaining the above, giving further ideas and possibly, assisting future researchers in the area. Examples given are: separation of fine mineral particles (such as pyrite and magnesite), and of metal ions (as chromium, arsenic, copper, zinc, germanium and so on); among the various available techniques, mention is given to ion, precipitate, adsorbing colloid, sorptive and biosorptive flotation ‐ including certain comparisons for the same application. The metal ion flotation application deserves further study and work, mainly for selective removal. © 2017 Society of Chemical Industry     

Flotation behaviour of fine particles with respect to contact angle

The flotation behaviour of methylated quartz particles of different size, but within the size range from 0.2 to 50 μm, and varying contact angle, was probed in a mechanical flotation cell. Results suggest that particles of a given size need to possess a minimum critical contact angle (θ_crit) for flotation to occur. This behaviour is shown not to be solely dependent on fine particles having lower collision efficiency with bubbles, but rather due to a combination of low collision efficiency and particles not having enough kinetic energy at collision with bubbles to form the three phase line of contact and initiate the attachment process. In the particle size range investigated, the critical contact angle increases with a decrease in particle size.     

团聚液雾化气泡粒径分布特性的可视化研究

泡沫团聚法是有效脱除细颗粒物PM_2.5的方法。本文对团聚液的雾化粒径进行了研究,筛选出适于团聚PM_2.5的气泡粒径的溶液及喷雾条件。文中首先对气泡粒径与团聚颗粒物的能力进行估算,进而通过CCD拍摄精细雾化喷嘴喷出的团聚液泡沫的流动过程,利用MATLAB处理图片,得出雾化气泡粒径和密度大小。实验结果表明,发泡剂会使团聚液的雾化液滴形成气泡,增大雾化颗粒直径;PAM团聚液形成的气泡粒径偏小,且雾化颗粒密度大,粒径主要分布在小于200μm范围;XTG团聚液气泡粒径偏大,CMC团聚液气泡粒径介于两者之间;0.2% CMC团聚液气泡粒径均匀,颗粒数量大;在距喷口轴向20cm处,气泡破碎和聚合趋于稳定;喷口直径0.5mm时,气泡雾化粒径大多分布在100~300μm粒径范围内,符合团聚脱除PM_2.5的气泡条件;随着温度的升高,直径在0~300μm内的气泡颗粒数量增大明显。     

Removal of toxic metal ions from aqueous systems by biosorptive flotation

Biosorptive flotation was used as a combined operation for the simultaneous abstraction of nickel, copper and zinc ions from aqueous streams. Laboratory‐scale batch experiments, as well as pilot‐scale continuous experiments, have been conducted. Grape stalks, a by‐product of the winery industry, were used as sorbent material. The experimental procedure consisted of two consecutive stages: (i) biosorption, and (ii) flotation. The possibility of reusing biomass, after appropriate elution, was also examined. The main parameters examined were biomass concentration, particle size of sorbent, surfactant concentration, pH and flocculation. Flotation removals, following laboratory‐scale experiments, were found to be in the order of 100, 85 and 70% for copper, zinc and nickel, respectively. In pilot‐scale experiments, biomass sorption capacities were determined as 25 for copper, 81 for zinc and 7 µmol dm^?3 for nickel. The order of biomass affinity regarding the studied metals was Cu > Zn > Ni. Short retention time and high effectiveness suggest that biosorptive flotation is a promising treatment process for the removal of toxic metals from contaminated aqueous solutions. © 2002 Society of Chemical Industry     

Effect of microbubbles and particle size on the particle collection in the column flotation

Particle-bubble collection characteristics from microbubble behavior in column flotation have been studied theoretically and experimentally. A flotation model taking into account particle collection has been developed by particle-bubble collision followed by the particle sliding over the bubble during which attachment may occur. Bubble size and bubble swarm velocity were measured as a function of frother dosage and superficial gas velocity to estimate the collision and collection efficiency. Separation tests were carried out to compare with theoretical particle recovery. Fly ash particles in the size range of <38, 38-75, 75-125, >125 mm were used as separation test particles. Theoretical collision and collection efficiencies were estimated by experimental data on the bubble behavior such as bubble size, gas holdup and bubble swarm velocity. Collection efficiency improved with an increase of the bubble size and particle size but decreased in the particle size up to 52 mm. Also, flotation rate constants were estimated to predict the optimum separation condition. From the theoretical results on the flotation rate constant, optimum separation condition was estimated as bubble size of 0.3-0.4 mm and superficial gas velocity of 1.5-2.0 cm/s. A decrease of bubble size improved the collection efficiency but did not improve particle recovery.     

Separation Characteristics of Inorganic Particles from Rainfalls in Dissolved Air Flotation: A Korean Perspective

Abstract

Many reservoirs have been constructed in Korea to store water resources utilizing the terrain of the land. In general, dam source waters contain algae species that have densities close to that of water. Consequently algae are difficult to remove by conventional gravity sedimentation (CGS), while dissolved air flotation (DAF) is known to be an effective process for the purpose. The same source waters usually also have high turbidities due to mineral soil particles in the wet summer season. Systematic studies on the effect of high turbidity on the DAF process are very limited. In this work, DAF and CGS experiments were carried out to investigate water treatment characteristics and removal efficiencies under various COD/SS and chlorophyll‐a/SS ratios. A kinetic DAF process model was employed to describe bubble‐floc collision and agglomeration, as well as the rising velocity of bubble‐floc agglomerate. Our results showed that the initial collision‐attachment efficiency for the clay floc size range of 100?400 µm was a relatively low value of 0.3. The removal efficiency by DAF was greater than by CGS when chlorophyll‐a/SS ratio was high. It was also found that sedimentation prior to flotation is required for the effective separation of large clay flocs caused by runoff. Our experimental and theoretical results also suggest that the DAF process requires carefully operation in Korea, especially, in the rainy summer season.     

Polymer derived SiC environmental barrier coatings with superwetting properties

Surfaces with superwetting capabilities can be used for corrosion protection, self-cleaning and bio-fouling protection amongst other applications. In this work, we present a method to produce a SiC coating with an almost superhydrophobic behavior exhibiting water contact angles of 145±3°. Ceramic coatings were produced by the pyrolysis of polycarbosilane as a preceramic precursor of SiC. Aluminum and carbon powders were used as active and passive fillers to compensate for the volume shrinkage of polycarbosilane during pyrolysis. The effects of particle size (Al particles ranging from 0.8 to 10 µm) and concentration 10–30% wt.) C and Al of both fillers were studied to produce defect-free ceramic coatings. We have observed that the fillers used not only affected the microstructure but also the surface roughness. We show that the addition of carbon fillers can increase the water contact angle of the ceramic from 42° up to 141°. The combination of carbon and aluminum fillers resulted in water contact angles up to 145°.