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.     

浮选柱气泡发生器的研究

通过对新型浮选柱气泡发生器的研究,目的在于对工业生产浮柱中出现的具体问题提供解决的途径,并对静态混合器的研究提供可靠的理论依据。     

Application of Statistical Analysis on the Bubble Surface Area Flux in a Column Flotation Cell

Flotation is a widely used separation process with applications from mineral separation to de-inking of recycled paper, waste water treatment, and solid remediation. In flotation column, bubble surface area flux (S_b) has been reported to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. No information is available regarding S_b for coal flotation in column cell. This paper describes the effects of hydrodynamic parameters on S_b by means of a 2³ factorial experimental design in designed flotation column using coal slurry. The results showed that S_b increased with increasing superficial gas velocity and frother concentration, but decreased with increasing solid concentration. The main and interaction effects of operating parameters on S_b were evaluated using Yates’ analysis. The statistical model was developed to predict S_b in column flotation cell using experimental data. This paper also presents the development of the statistical model and the validation using a number of additional data sets. There is a good agreement between experimental results and predicted results from the developed model.     

Double-sensor conductivity probe applied in a flotation system

This study proposed a new approach for measuring bubble size distribution, bubble mean diameter, Sauter mean bubble diameter, and gas holdup using a double-sensor conductivity probe in an air/water two-phase system bubble column. The results for the two-phase system were compared and calibrated using analyses from bubble images taken by a digital camera from the side of the column wall. Good agreement was observed between the two techniques. The same double-sensor conductivity was used in an air/water/solids three-phase system. The conductivity probe captured the change in bubble dynamic behaviour inside the pulp phase; however, the presence of the solids made it more challenging to measure. As a result, the VisioFroth commercial package, using images taken from the top of the froth layer, could be used in conjunction with the double-sensor conductivity probe to show the dynamic evolution of mineralized bubbles from the pulp zone to the froth zone in a flotation process.     

浮选设备流体力学特征参数研究现状

浮选设备是矿物加工工程领域一种重要的气液反应装置，主要包括浮选机和浮选柱。浮选设备应用已有百年历史，随着选矿技术水平的提高，浮选设备逐渐向自动化、大型化的方向发展。近年来对浮选设备内流体力学特征参数的研究解析越来越多，进一步促进了设备的合理放大和优化。本工作在简要介绍目前浮选设备的发展和应用现状后，总结了国内外学者对浮选设备内气泡尺寸、气含率和气泡速度3个重要流体力学特征参数的检测方法和研究现状，提出了在今后研究中，开发以机器视觉为核心的检测技术和强化侵入式检测装置的适用性是流体力学特征参数检测手段的发展方向之一。     

Effect of pulp fibres on gas holdup in a flotation column

Column flotation is an emerging technology in the deinking of recycled paper. Deinking efficiency depends primarily on the effect of four physical variables: gas and accepts flowrates, bubble size distribution, and pulp consistency. Experiments to establish operating ranges for these variables by determining their effect on gas holdup were conducted in a laboratory column installed at Bowater's Gatineau (Quebec) mill which processes a pulp (70% ONP/30% OMG) with about 1% consistency. The results showed the general trends expected from a review of previous studies: gas holdup increases with gas and accepts flowrates and with smaller bubble size, and decreases for higher pulp consistencies. However, the review also demonstrated that the published information is of limited application as the bubble size was much larger than that encountered in industrial flotation practice, primarily because of the use of pure water. Industrial pulps contain in most cases surface active agents which have a substantial effect on forming and preserving a small size bubble population.     

Flow characterization of a flotation column

The flow characteristics of a froth flotation column have been experimentally studied using air and aqueous surfactant solutions without the presence of solids. The hold-up behaviours of the bubbly and the froth zones of the column were linked together using the drift-flux model. The ratio of the gas drift-flux, j_gf, to the bubble terminal velocity, V, for both the bubbly and the froth zones was found to be well correlated by the Richardson–Zaki equation:      

Bubble size distribution in a flotation column

The bubbles that were generated in a flotation column were measured. The bubble size distributions were obtained both for air-water and air-water-coal systems. The size distribution pattern was fitted to different equations. It was found that the bubble size distribution in both the flotation and cleaning zones follows the Rosin-Rommler equation used to describe the particle size distribution in crushing. This study indicates that bubbles in the cleaning zone are always larger than those of the flotation zone and finer bubbles are generated when a mixture of frothers is used instead of individual frothers.     

The effect of bubble size on oil-water separation efficiency for a novel oil-water separation column

Bubble size is a key factor in froth flotation for oil-water separation. In this paper, the bubble size which impacts on oil removal efficiency for a novel oil-water separation column was researched systematically. The bubble size distribution was researched by using the photographic method and Matlab software. In addition, several operating parameters which impact on the bubble size were investigated, including circulating pressure, aeration rate, and the foaming agent. Based on the results of experimental data and image analysis, the frother consumption and aeration rate has important influence on the bubble size. The bubble size can be controlled by adjusting the operation conditions including the circulating pressure, aeration rate, and the frother consumption. The optimum operating conditions for the oil-water separation column were determined. Furthermore, the mathematical model of oil removal efficiency for the oil-water separation column was established.     

运用CFD模拟浮选柱内的流体流动

根据浮选柱内气液流动的特点,在气速与气含率的径向分布一致的基础上,建立了通用的计算浮选柱内流体流动模型,简便且较准确地模拟出了浮选柱内气液的流动状况,为浮选柱内气体发生器设计以及柱内返混的研究提供了依据和方法。     

Performance,mixing and kinetics study in the flotation column reactor using coal

ABSTRACT

A flotation column has been designed and characterized with respect to gas velocity, slurry velocity, frother concentration, gas holdup, bubble surface area flux for the study of the mixing property, liquid phase residence time distribution, flotation recovery and rate constant. The study was performed using coal as solid. A strategy of integrating chemical kinetics into the flotation process to test the floatability behaviour of coal and to estimate floatability parameter of coal has been developed. The results indicate that the coal floatability parameter is 3.05 × 10^?4. A relationship between gas holdup and bubble surface area flux was developed.     

Role of Frothers in Bubble Generation and Coalescence in a Mechanical Flotation Cell

Two frothers covering a very broad range from weak and selective (DF‐200) to powerful (DF‐1012) flotation performance were chosen to test the effect of frothers on bubble generation and bubble coalescence in a laboratory scale flotation cell. In two‐phase, gas‐liquid systems, the experiments showed that the frothers affect both the bubble breaking process and the coalescence of bubbles. While the DF‐200 frother, characterized by much larger critical coalescence concentration (CCC) values than DF‐1012, has the ability to produce finer bubbles at concentrations exceeding the CCC value, the bubbles generated in the DF‐1012 solutions at concentrations exceeding CCC are much larger.     

一种新型浮选柱的数值模拟及性能研究

自主研制了一种新型多级规整填料浮选柱,应用计算流体力学软件FLUENT6.3.26进行数值模拟计算,对其内部的气液两相流动进行了考察,采用了欧拉-欧拉多相流模型,对气相的模拟采用单一气泡尺寸,液相湍流采用了标准k-ε模型,两相之间的动量传输仅考虑曳力作用。通过模拟,获得了不同实验条件下浮选柱内部的气液速度场分布、气含率分布等,对部分模拟结果进行了定量比较。结果表明随着气相流量的增大,浮选柱内部气含率增大,液体循环速度增大,从而气液之间混合更加充分,这对于提高浮选柱的分选效率和设备的放大有重要意义。在唐山钱家营开滦煤矿选煤厂进行了以其煤浆为原料的浮选性能的测试,在气体1.25 m³/h,进料0.05 L/h条件下20 min停留时间获得了精煤灰分10.28%,尾煤灰分43.39%,精煤产率52.53%的指标,与该厂浮选精煤灰分10.58%相接近。     

Effect of Frothers on Bubble Size and Foam Stability in Potash Ore Flotation Systems

The objective of this project was to compare the effect of a selective flotation frother (MIBC) and powerful frothers (DEMPH and DF‐1012) on bubble size and foamability in water and in brine. In water, the bubble size is clearly reduced by flotation frothers which prevent bubbles from coalescing. The present study shows that the bubbles do not coalesce in brine and, therefore, frothers do not affect the size of bubbles in brine. The dynamic foamabality index measured in brine is much lower than that in water for weak frothers (e.g. MIBC); for both tested strong frothers the foamability measurements in brine reveal formation of meta‐stable foams.     

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.     

Hydrodynamics and mass transfer in an upward venturi/bubble column combination

The hydrodynamics and mass transfer characteristics of a venturi/bubble column combination were studied at high liquid superficial velocities of up to 0.35 m/s. The gas hold-up was increased by 50% to 150% and the overall volumetric mass transfer coefficient was tripled when the venturi was used as “gas distributor” instead of a porous distributor. A correlation of the overall volumetric mass transfer coefficient (K_La) with the gas hold-up, valid for gas hold-ups as high as 0.3, was proposed for the cylindrical bubble column section. The energy consumption per mole of oxygen transferred was lower than with most distributors and the oxygen transfer rate per unit of reactor volume was higher than in a bubble column with a porous distributor. The venturi/bubble column combination is a compact and efficient system which does not have the operating problems of systems which require internals.     

Non-newtonian two-phase circulation in bubble columns

Gas-liquid and gas-slurry bubble columns are widely used in the mineral and engineering industries, particularly for aeration (oxidation), synthesis of oil and flotation of mineral fines. Even though gas may be introduced into a bubble column evenly through a distributor plate over the whole column floor, undesirable circulation patterns generally develop in the column. This paper extends a force balance approach (originally used for turbulent systems) to predict circulation in non-Newtonian gas-liquid mixtures and demonstrates how the rheological properties will affect a single circulation pattern in a column.     

环流浮选塔用于含油污水处理的实验研究

以空气/含柴油污水为模拟介质体系,在环流浮选塔(外筒体内径100 mm,高932 mm;导流筒内径59 mm,高780 mm)上考察了操作气速、液相流量及浮选塔上部空间填料设置对油-水分离效率的影响. 结果表明,分离效率随操作气速增大先增后降,随液体流量增大而降低;与传统空筒式浮选塔相比,环流浮选塔的分离效率比常规空筒式浮选塔有显著提高. 实验确定的最佳操作气速为0.015~0.02 m/s,最佳液相流量为20 L/h,在环流浮选塔上部设置填料的情况下,油-水分离效率最高可达57.3%. 基于实验数据建立了涉及气泡特性、液相物性、气液相流量及油滴返混影响因素在内的分离效率的经验模型,与实验值吻合较好.     

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.     

Drift Flux Modelling for a Two‐Phase System in a Flotation Column

Using different two‐phase systems, a laboratory flotation column was operated over a wide range of bubble size from 250 to 1100 µm. The drift flux analysis for the tests was used to obtain a new correlation to relate the characteristic exponent m in the drift flux equation j_gf = U_tα_g(1 — α_g)^m, to bubble Reynolds number, where j_gf is the drift flux, U_t is the terminal velocity of an individual bubble, α_g is the gas volume fraction, and m is an exponent that depends on flow conditions. m = 20.26 + 1.89 Re_b/4.38 + Re_b.