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.     

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°.     

Yoon-Luttrell collision and attachment models analysis in flotation and their application on general flotation kinetic model

We theoretically used the models of Yoon and Luttrell for collision and attachment efficiencies to show the effect of fluid flow condition, the effect of bubble size and velocity and particle surface hydrophobicity in flotation system, and in order to demonstrate the effect of particle density on the attachment behavior we incorporate the correct expression for the maximum collision angle developed by Dukhin collision model in the Yoon-Luttrell attachment efficiency applied for two minerals species such as the quartz and chalcopyrite. Then we used the expression of the analytical model that enables the calculation of the flotation rate constant of particles derived by Pyke et al., developed under turbulent condition and with including the efficiency of collision using the generalized Sutherland equation (GSE), the attachment efficiency using modified Dobby-Finch model, and stability of bubble-particle aggregate includes the various forces acting between the bubble and the attached particle. Some results are obtained revealing the positive inertial effect for the quartz and galena particles under defined flotation data conditions by incorporating in the flotation rate constant mentioned above, the collision and attachment efficiency models of Yoon-Luttrell developed for potential flow condition with assuming that the bubble surface is completely mobile and the particle inertia is ignored. The results show also the influence of the increasing of the bubble velocity to determine the particle size range between the models considering the inertial effect and those who ignored the particle Inertia.     

The Limits of Fine and Coarse Particle Flotation

The flotation behaviour of quartz particles was studied over the particle size range from 0.5 µm to 1000 µm and for advancing water contact angles between 0° and 83°. Flotation was performed in a column and in a Rushton turbine cell. Particle contact angle threshold values, below which the particles could not be floated, were identified for the particle size range 0.5–1000 µm, under different hydrodynamic conditions. The flotation response of the particles, either in a column or in a mechanically agitated cell with a similar bubble size, was comparable. Turbulence plays a role, as does bubble‐particle aggregate velocity and bubble size. The stability of the bubble‐particle aggregate controls the maximum floatable particle size of coarse particles. For fine particles, the flotation limit is dictated by the energy required to rupture the intervening liquid film between the particle and bubble. Flotation of very fine and large particles is facilitated with small bubbles and high contact angles. These results greatly extend our earlier observations and theoretical predictions.     

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.     

Enhanced graphite recovery by optimising flotation energy input

This experimental work on graphite flotation investigated the effect of energy input on flotation performance of three particle size fractions. Results obtained from flotation tests indicated that the required energy input rate increases with the decreasing particle size. The maximum graphite recovery of coarse particles was obtained at 121 J/min, while the optimum recovery of fine particles was obtained at 330 J/min. However, the demand of energy for each coarse particle is slightly higher than that of the fine particle in collision process. Numerical analysis showed that the streamlines have little effect on the trajectories of coarse particles, which can significantly contribute to a higher recovery of coarse particles in comparison with fine particles at the same energy input rate.     

Optimization of some parameters in column flotation and a comparison of conventional cell and column cell in terms of flotation performance

In this study, a comparative evaluation was made between column and mechanical flotation cells for fine coal cleaning. In addition, the optimum values of operating parameters were examined, which are important to achieve a desired separation performance in column flotation, such as the frother concentration, the collector dosage, the froth thickness, the wash water rate, the air rate and the feeding rate. The coal sample was collected from a classifying cyclone overflow stream consisting of nominally −130 μm material. Ash, volatile mater, fixed carbon and total sulfur contents of the sample were found to be 47.50%, 20.80%, 31.70% and 0.75%, respectively. Comparison of the column and mechanical flotation results indicated that column flotation was considerably more efficient than mechanical flotation for fine coal cleaning. High froth thickness and wash water addition during column flotation made it possible to obtain cleaner coals. The column flotation produced a 15.60% product ash with a 50.92% clean coal yield and 81.85% combustible recovery.     

A flotation study of refuse pond coal slurry

The flotation behavior of a refuse pond fine coal slurry sample was studied using mechanical and column flotation techniques. Flotation parameters investigated included type and dosage of frother and collector, agitation speed, scrubbing time, slurry pH, etc. for the mechanical flotation cell, and air flow rate, feed flow rate, and wash water flow rate for the column flotation. Flotation kinetics was also studied in the mechanical flotation cell. The results showed that the coal sample was very difficult to clean by flotation. Low yield (5–15%) and low combustible recovery (6–23%) and high product ash (about 22%) were obtained when methyl-isobutyl-carbinol (MIBC) was used as frother and #2 fuel oil as collector. Adjustment of operating parameters such as agitation intensity showed limited effects. However, flotation yield was significantly improved when MIBC and #2 fuel oil were replaced with frother P948 and collector SPP. Mechanical scrubbing was unable to restore the floatability of the coal sample. ‘Ken-Flote’ column flotation was inferior to mechanical flotation for oxidized coal and possible reasons were given.     

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.     

高硫煤浮选脱硫实验研究

采用浮选法研究了磨矿粒度、捕收剂用量、起泡剂用量、抑制剂用量等因素对高硫煤脱硅效果的影响,结果表明,磨矿粒度-200目占48.48%,捕收剂用量1.4kg/t,起泡剂90g/t,抑制剂1.5g/L,浮选时间5min,浮选温度为室温,可获得较好的脱硫效果,脱硫率达到50%左右。论文的研究为高硫煤的浮选法脱硫提供一定的参考依据。     

Effect of insoluble amine on bubble surfaces on particle–bubble attachment in potash flotation

This study shows that in the potash flotation system, in which long‐chain amine collector appears in the form of colloidal particles, the hydrophobicity of sylvite surfaces critically depends on whether the amine is placed onto the solid surface or onto the surface of a bubble. The transportation of amine collector on the surface of bubbles was found to be beneficial for the bubble/KCl particle attachment.     

On the structure of collision and detachment frequencies in flotation models

New explicit analytical expressions are obtained for both the collision frequency and the bubble/particle detachment frequency which enter flotation separation models. The expression for the collision frequency takes into account both the particle settling velocity and the bubble rise velocity while that for the detachment frequency is motivated by analogous results for floc disruption in a turbulent flow field. In all the cases considered, it is shown that the inclusion of the particle settling velocity increases the collision frequency by a factor of approximately 1.5 and that the most significant factor affecting the collision frequency is the bubble radius.     

Removal of fine particles from aqueous medium by flotation: Sodium dodecylbenzenesulfonate-barium sulfate system

Insoluble barium sulfate particles were removed from water by a batch flotation technique using an anionic surfactant as a frother and collector. The measured particle concentrations are presented as a function of the elapsed time and compared with values predicted by a simple hydrodynamic collision model. The model predictions were in reasonable qualitative agreement with the experimental results. However, the attachment efficiency observed was found to be much smaller than unity, suggesting that an electrical repulsive force may affect the flotability. Accordingly, electrical mobilities for the air bubbles and the particles were measured by the electrophoresis method, and the energy barrier between the particles and the bubble surfaces was found to be relatively large.     

An experimental study of copper sulfide flotation in a packed cyclonic–static microbubble flotation column

A method using a cyclonic–static microbubble flotation column packed with fluid guiding media was proposed for improving flotation efficiency of copper sulfide. The installation of packed fluid guiding media in a cyclonic–static microbubble flotation column was for changing flow pattern in 10 the column by avoiding strong cyclonic flow in the upper region of the column, which can cause bubble-particle detachment. Therefore, the attached particles can be more likely to enter the froth zone instead of swirling in the column. The flow rectification contributed to a smaller bubble size in the column and significantly reduced the number of big bubbles with diameter above 1 mm. This scenario was caused by the damping of swirling liquid motion where bubbles tended to 15 concentrate and coalescence in the center of an eddy. The packed fluid guiding media changed the hydrodynamics in the upper column from a cyclonic flow to a gentle flow and as a result improve the column separation. The application of packed fluid guiding media can decrease the bubble-particle detachment and the flotation recovery of copper sulfide could constantly improve with the installation of packed fluid guiding media in the FCSMC column.     

新型煤泥浮选促进剂的制备及作用机理

介绍了棉籽油制备煤泥浮选促进剂的工艺,并进行浮选试验研究和机理分析。煤泥浮选试验表明：煤（柴）油中添加一定的促进剂可显著提高浮选精煤产率或大幅度降低捕收剂用量。FT-IR分析表明：棉籽油促进剂中含有极性较强的含氧官能团（如C=O,—C—O—C—,—OH）,有利于促进煤（柴）油在煤浆中更好地分散,增强煤粒与药剂的碰撞接触机会;同时还含有疏水性较强的长链烷烃和芳香结构官能团,有利于促进药剂在煤粒表面的吸附,提高煤粒表面疏水性。     

双流态微泡浮选机气液两相流测试结果分析

介绍了双流态微泡浮选机的特点,采用激光粒子动态分析仪测量了该浮选机矿化器内微泡发生器段和矿化管部分以及浮选槽内的微泡时均速度、脉动速度和粒径分布情况,分析了不同充气量与药剂量对微泡的影响;对比表明,该机在宏观流态、紊动特性以及形成的微气泡尺寸、粒径分布和浓度等方面为微细粒煤泥浮选创造了最佳的流体动力学环境。     

Flotation of Fine Gold Particles by the Assistance of Coal-Oil Agglomerates

This paper describes the use of coal-oil agglomerates in flotation to increase the gold recovery from an ore containing fine gold particles. The effects of operating parameters on gold flotation recovery such as oil type, particle size of agglomerating material, agglomerate/ore and oil/ore ratios were investigated. The studies showed that petroleum oils are more effective than vegetable oils in oil agglomeration of Kozlu coal and coal-oil assisted gold flotation. Gold recovery can be increased using a higher amount of agglomerates in the process; however, gold grade of the flotation concentrates is reduced significantly. The use of bridging oil at high concentrations in the agglomeration process provides high-grade gold concentrates, but lower recoveries. The utilization of coarser coal particles in the coal-oil agglomeration stage leads to higher selectivity and recovery values for gold particles.     

Air bubble-induced detachment of positively and negatively charged polystyrene particles from collector surfaces in a parallel-plate flow chamber

Electrostatic interactions between colloidal particles and collector surfaces were found to be important in particle detachment as induced by the passage of air bubbles in a parallel-plate flow chamber. Electrostatic interactions between adhering particles and passing air bubbles, however, were found to be less important. Regardless of the charge on the particles, detachment increased linearly with decreasing air bubble velocity and increasing liquid-air interfacial tension. Detachment efficiencies up to 75% could be achieved even for positively charged particles adhering to a negatively charged collector surface, provided that the velocity of the air bubble was low (2.37 mm s^-1) and the tension at the liquid-air interface was high (70.08 mJ m^-2). The detachment of positively charged particles was most sensitive to the air bubble velocity when adhering to a hydrophobic, negatively charged collector surface and least sensitive when adhering to a positively charged collector surface, but appeared equally sensitive to the liquid-air interfacial tension for all collector surfaces. On the other hand, the detachment of negatively charged particles was most sensitive to both the velocity of the air bubble and the tension at the liquid-air interface when adhering to a positively charged collector surface.     

系列药剂量分选超细粒煤试验研究

变化乳化药剂量进行超细粒煤的分选试验，贯穿运用3种细粒煤界面分选工艺方法；通过控制加药量，从少油量的泡沫浮选过渡到稍多油量的选择性疏水聚团，再逐渐增加油量，一直到大油量的油团聚，通过观察测量絮团大小，分析测定产物灰分、收率，寻找从小油量到大油量这整个过程所涉及的分选行为关系规律，此过程的研究对于细粒煤界面分选最佳条件的选择具有参考意义。     

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.