Effect of gas rate and impeller speed on bubble size in frother-electrolyte solutions

In a flotation cell, bubble size is a function of both coalescence and breakup phenomena. Two phase tests, conducted in a conventional 5.5 L Denver mechanical flotation cell, studied the effect of impeller speed, gas flow rate and frother concentration on bubble size in various electrolyte-frother solutions. The addition of frother to a synthetic sea salt did reduce the measured bubble size (at certain mechanical conditions); whereas the effect of frother addition to NaCl was too small (when compared to measurement errors) to make significant conclusions. This led to more detailed CCC curves (0–50 ppm MIBC) for NaCl, NaCl + MgCl₂, NaCl + CaSO₄, and NaCl + KCl solutions, at constant electrolyte concentrations, to be conducted. They showed an increase in bubble size with the addition of MIBC. This was attributed to the saturation of frother at the air-water interface, reducing local surface tension gradients that help produce smaller bubbles. This occurrence is typically masked in traditional CCC curves due to the dominance of coalescence effects at low frother concentrations.     

Indirect estimation of bubble size using visual techniques and superficial gas rate

In this paper, an indirect method for determining the Sauter mean diameter of a bubble population is presented. The technique relies on the estimation of the percent area occupied by bubbles in a 2D image as well as on the superficial gas rate. The percent area was defined as the quotient between the black pixels (bubble representation) divided by the total pixels in a binary image. A linear model to describe the Sauter diameter as a function of the percent area and the superficial gas rate was proposed. The regressions showed a fairly good predictive capacity in laboratory and industrial flotation machines under bubbly regime, which makes the proposed methodology a promising tool for monitoring and controlling gas dispersion in real time.     

Influence of particles on the formation of bubbles from a submerged capillary

This paper will explore the possibility of using colloidal particles as a bubble stabilising agent in froth flotation. Nearly monodisperse 300 nm silica particles were subjected to surface modification through an esterification reaction using a long chain alcohol to create an advancing contact angle of 73.5 °. To study the influence of particles on the growth and departure of a single bubble, experiments were performed with a capillary tube submerged in the hydrophobised silica suspension. A high-speed camera was used to capture the bubbling phenomena in real time. The acquired videos were then analysed to extract the parameters such as bubble size, departure frequency, and growth time through an image-processing software. Experiments were also carried out with MIBC (methyl isobutyl carbinol) and a polyglycol type surfactant (poly(propylene glycol)), PPG) for comparison. The results showed that an increase in the particle concentration resulted in a decrease in mean bubble size produced at the tip of capillary. The same trend was also observed with both frothers.     

Estimation of the bubble size and bubble loading in a flotation froth using electrical resistance tomography

Flotation process is widely used in mineral industry for the separation of valuable minerals from low-grade ore slurry. There are several parameters such as the bubble size and bubble loading that predict the efficiency of the flotation process. These parameters can be used for the control of the flotation process. There are already some techniques that can be used for online monitoring of these parameters, for example, the high-speed video imaging and a probe sensor based on electrical resistance tomography (ERT). These methods, however, suffer for some limitations. The high speed video imaging gives information only on the surface of the froth and in the previously proposed ERT based techniques the conductivity of the froth is typically modeled to be smoothly varying. However, in reality the froth is composed of different size of bubbles having highly conductive surface and very low conductive interior which configuration cannot be modeled with smoothly varying conductivity distribution. In this paper, we propose a computational approach in which the structure of the froth is modeled and both the bubble size and the conductivity of the boundary of the bubbles are estimated. The proposed approach utilizes data measured with the standard ERT probe. The estimated bubble size and conductivity of the boundary of the bubbles are compared to online measured camera based estimates of the bubble size and bubble loading. The proposed approach is evaluated with simulated measurements and real data from Pyhäsalmi Mine. The results show that there is a high correlation between the camera based and the ERT based estimates of the bubble size. Furthermore, some of the parameters obtained from the ERT based method correlate well with the camera based estimate of the bubble loading.     

Breakup and re-formation of bubble clusters in a flotation cell

This study is concerned with the behavior of bubble clusters in a well-controlled turbulent flow. We used a specially designed cell where the bubble aggregates could be formed and exposed to breakage by a rotating impeller. The effects of impeller speed and the concentration of collector on cluster behavior were studied. It was found that the size of the clusters increases with the concentration of collector used. We also found that although the clusters could easily be destroyed under the action of impeller, they could reform, especially at lower impeller speeds. It was observed that the size of the bubbles arriving into the impeller region in the absence of particles before breakage was considerably higher than the size of the clusters formed at the same impeller speed. It appears that both cluster breakage and re-formation take place simultaneously, and the extent of formation and regrowth is mainly determined by the hydrophobicity of the particles and the impeller speed.     

Froth flotation of sphalerite: Collector concentration,gas dispersion and particle size effects

This experimental work on sphalerite flotation investigated the effect on flotation performance of three particle size fractions, namely, coarse (d₈₀ = 100 μm), medium (d₈₀ = 39 μm) and fine (d₈₀ = 15 μm), bubble size distribution, superficial air velocity, and collector dosage. Bubble size distributions were characterized with the image analysis technique. The two-phase (liquid–gas) centrifugal pump and frother addition (MIBC, 5–30 ppm) allowed generating bubble diameters between 150 and 1050 μm, and air holdup ranging from 0.2% and 1.3%. Main results showed that each particle-size distribution required an optimal bubble-size profile, and that sphalerite recovery proceeded from mechanisms involving true flotation (when J_g = 0.04 cm/s and 1.9 × 10⁻⁴ M SIPX). However, cluster-flotation occurs at high collector dosage (when J_g = 0.04 cm/s and d₃₂ between 285 and 1030 μm), and requiring further investigation.     

Effect of entrainment in bubble load measurement on froth recovery estimation at industrial scale

Froth recovery was calculated in a 130 m³ mechanical cell of a rougher flotation circuit. This was done by bubble load determinations along with mass balance surveys. Valuable grade in the bubble load decreased in the −38 μm due to fine particles entrained to the chamber of the device. The effect of fine particle entrainment on froth recovery was evaluated. A comparison between results from the raw bubble load data (assuming all particles were transported by true flotation) with those from corrected bubble load information (subtracting fine particle entrainment) was carried out. Entrainment occurred due to hydraulic transport in the bubble rear, which corresponds to the worst case scenario for froth recovery estimation. Results showed that the relative error was less than 0.3%, which allowed validation of the bubble load measurement as an effective methodology for froth recovery estimation at industrial scale.     

Influence of gas flow rate and frothers on water recovery in a froth column

Froth plays an important role in the froth flotation separation of minerals. In froth and foam liquid drains away due to gravity until equilibrium is reached and at the same time is carried upwards by the moving gas phase. This paper aims at better understanding of the influence of the superficial gas velocity and frothers on the liquid drainage in foam and liquid recovery rate from the froth column. The obtained experimental data shows that the available standard drainage theory does not properly describe the influence of gas flow rate and Dowfroth 250 frother on the liquid recovery rate. The theory overpredicts the liquid recovery rate from the froth column. The improvement of the standard theory by inclusion of the contribution of the vertex geometry to the liquid drainage in foam does not resolve this problem. It appears that the liquid drainage process in the froth column is controlled by the interfacial properties of the adsorbed surfactants at the gas–liquid interface.     

Controlling bubble size using a frit and sleeve sparger

This paper describes a frit and sleeve sparger designed to control the size of bubbles produced. The design comprises a porous ring (frit) surrounded by a sleeve through which water is passed to generate shear. A prototype is described and results confirm that bubble size can be controlled independent of gas velocity and is governed by the shear in the annular gap between the frit and sleeve independent of gap size.     

Examination of NaCl and MIBC as bubble coalescence inhibitor in relation to froth flotation

With scarcity of fresh water resources, flotation plants are increasingly under pressure to supply their water needs from other sources such as bore water, seawater or recycled plant water. This water generally contains a high concentration of inorganic electrolytes which may have a substantial influence on the performance of the flotation operation. In this study, the stabilisation mechanism of bubbles by salt was investigated using a specifically designed experimental set-up. Two bubbles of approximately the same size were produced at the tip of two adjacent capillaries in concentrated solutions of an inorganic electrolyte (NaCl). Their coalescence behaviour was recorded using high speed video imaging in which information such as coalescence time and deformation of the resultant bubble upon coalescence could be extracted. The results were then compared against a similar system using MIBC. It was found that delayed coalescence in NaCl required a relatively concentrated solution in the order of 0.1-0.5 M to achieve coalescence times comparable to MIBC. Unlike NaCl, it appears that a small amount of MIBC, in the order of 10⁻⁵ M, is sufficient to delay the coalescence of bubbles, which reach a maximum at a concentration of 3 × 10⁻³ M. The analysis of oscillation patterns during the coalescence process revealed that the oscillation is noticeably damped in the presence of MIBC at high concentrations, although this is not the case in NaCl solutions. Results are discussed in terms of bubble stability, froth stability and their possible implications on particle recovery.     

Determination of sampling pipe (riser) diameter for a flotation bubble load measuring device

This work explores the determination of an optimum riser (pipe) diameter for a newly-developed bubble load measuring device. Stimulus response experiments using NaCl as a tracer were carried out to measure the intensity of axial mixing as a function of riser diameter and frother concentration (bubble size). Three riser diameters (20, 30 and 50 mm) were tested and conductivity probes were used to sense salt concentration at three levels above the bottom of the tube (300, 770 and 1380 mm). Results indicate that the intensity of axial mixing increases with increase in riser diameter. It was concluded that the intensity of axial mixing in the 50 mm riser was strong enough to compromise the bubble load quality. A general increase in NaCl concentration with increase in frother concentration at each conductivity probe was seen for all the tested riser diameters. A model based on the tanks-in-series approach was developed. Simulink was used to fit the model to measured data. It was found that 16 tanks in series and an additional parameter that accounts for salt adsorbed on the bubble surfaces adequately fitted the data.     

Frother function–structure relationship: Dependence of CCC95 on HLB and the H-ratio

Although the number and diversity of commercial frothers has steadily increased to meet flotation industry demands, frother selection is still mainly empirical. As part of a general structure–property study, the paper presents a correlation between the critical coalescence concentration (CCC95) and H-ratio for surfactants used as flotation frothers. The CCC95 were determined in 0.8 m³ mechanical flotation cell. The H-ratio was a substitution of hydrophile-lipophile balance (HLB) and determined through high resolution proton nuclear magnetic resonance (¹H NMR) spectrometry. A large data set, consisting of 45 surfactants from four frother families, was used to develop the correlation. It is shown that the H-ratio can substitute for HLB. The potential of NMR both to identify the frother family and to derive the H-ratio in predicting CCC95 for commercial frothers is discussed.     

胺类捕收剂对异极矿等4种矿物浮选行为的影响

考察了不同碳链长度的胺类捕收剂对异极矿、石英、白云石和褐铁矿浮选行为的影响,讨论了胺的碳链长度对捕收异极矿的影响。结果表明,在pH为9~11的条件下,异极矿的浮选回收率最高,胺对异极矿的选择性随着脂肪胺碳链长度的增加而增加,其中,十八胺对异极矿具有较好的捕收能力和选择性。     

On the relationship between hydrodynamic characteristics and the kinetics of column flotation. Part I: Modeling the gas dispersion

Modeling of flotation has been the subject of many investigations aiming at better understanding the process behavior per se, and as well for process design, control and optimization purposes. With this regard, the importance of hydrodynamic characteristics, either as manipulated or measured variables, are paramount. The interfacial area of bubbles (I_b) is introduced in Part 1 of this paper as a hydrodynamic variable providing more information about the size distribution than the commonly used bubble surface area flux (S_b). Experimental evidence shows that the bubble size distribution can exhibit normal, lognormal, and even multi-modal shape. Unlike the Sauter mean diameter (d₃₂) and S_b, the interfacial area of bubbles is derived from the complete bubble size distribution, and takes into account these specific characteristics. Fundamental expressions are proposed to allow characterising I_b using the population mean and standard deviation. Experimental results indicate that for lognormal bubble size distributions, I_b correlates well with the gas hold-up and d₃₂. Part 2 of the paper analyzes the correlation of gas dispersion characteristics with flotation rate constant.     

Study of gas holdup and pressure characteristics in a column flotation cell using coal

Present work has been carried out to observe the effect of process variables (gas flow rate, feed flow rate, solid concentration and frother concentration) on gas holdup and pressure characteristics in flotation column using coal. Gas holdup has been estimated using phase separation method while piezometers have been used to obtain column’s axial pressure profile. It was observed that gas holdup in collection zone was affected by both air as well as feed flow rates. Up to 6% change in gas holdup may occur when the feed flow rate changes from 1–2 cm/s. It was also observed that addition of coal decreased the gas holdup while addition of methyl isobutyl carbinol (MIBC) had opposite effect. Almost linear variation in columns axial pressure characteristics has been observed with gas flow rate. An empirical relationship between gas holdup in the flotation column with column’s axial pressure difference was developed.     

Effect of slurry rheology on gas dispersion in a pilot-scale mechanical flotation cell

This paper investigates the effect of slurry rheology on gas dispersion in a 100 l pilot-scale Batequip mechanical flotation cell. The study is conducted using Kaolin, Bindura nickel and Platreef slurries. All three ores display typical non-Newtonian rheological behaviour. The slurry yield stress and viscosity increase exponentially with solids concentration. Bubble size and gas hold-up vary from 0.60 to 1.10 mm and 2% to 15%, respectively. At low/moderate solids concentrations, bubble size and gas holdup display characteristic trends, as noted in numerous literature studies. At high solids concentrations, both bubble size and gas holdup decrease significantly, which is an unexpected finding. This is attributed to the formation of a ‘cavern’ of slurry around the impeller, due to the very high slurry yield stresses. This ‘cavern’ results in the generation of small bubbles in the impeller zone, but poor dispersion of these bubbles throughout the cell, resulting in low gas hold-ups.     

Maximum size of floating particles in different flotation cells

Two flotation models, particle at the liquid-gas interface and particle-bubble aggregate, both based on balance of forces, were used for evaluation of experimental data relating the maximum size of floating particles d_max and their advancing contact angle. It was noticed, by comparing the experimental and model data, that for a given flotation device and material the maximum size of floating particle d_max increases with increasing particle hydrophobicity and at the same time the acceleration a, experienced by the d_max particle at the moment of rupture, decreases with particle hydrophobicity. The acceleration values change with cell dynamics and type of flotation device and are usually not available, therefore empirical apparent cell constants A, which characterize flotation dynamics and relate particle acceleration with advancing contact angle have been proposed instead. The values of A were determined by evaluation of experimental data relating d_max and advancing (detachment) contact angle for constant: particle density, medium density, surface tension, and flotation cell dynamics. Since A depends on particle density, a tentative formula was proposed to link A with density-independent flotation cell constant A_o. The values of A_o for selected flotation cells were calculated and presented.Using quartz as an example, it was shown in the paper that a positive advancing contact angle does not guarantee flotation because a prerequisite for flotation is non-zero receding contact angle.     

煤泥柱浮选的承载能力与气含率轴向分布

为优化柱浮选设备的处理能力和分选效果,采用压差法测定柱体内部的气含率,同时通过调整入料浓度和流速,分析煤泥柱浮选承载能力和气含率轴向分布的变化规律,并探索两者之间的内在联系及对煤泥分选效果的影响。结果表明：入料流速小于临界流速时,气含率在轴向上从底部到顶部依次增大;流速达到临界流速或以上时,气含率轴向分布发生逆变;临界流速随入料浓度的升高逐渐减小。承载能力随入料流速的增大先增大后减小,拐点为气含率轴向分布逆变的临界流速;一定范围内浓度的升高有利于提高承载能力和可燃体回收率。建立了煤泥柱浮选的承载能力预测模型,线性拟合的相关系数R 2=0.873,达到了较高的预测精度。     

某氟碳铈矿型稀土矿石的浮选试验研究

以某氟碳铈矿型稀土矿石为研究对象 ,在矿石工艺矿物学性质及其对氟碳铈矿浮选分离性能影响研究的基础上 ,通过分选条件试验和药剂作用机理研究 ,采用磨矿脱泥全浮选工艺 ,在以 FX为捕收剂的浮选药剂制度下 ,获得良好选别指标。为该类稀土资源提供了较好的开发利用技术     

广东某钼矿浮选试验研究

采用由广州有色金属研究院研发的高效选钼新药剂MS,对含Mo0.093%的原矿石进行浮选,回收其中的辉钼矿,最终获得钼精矿品位47.23%、回收率90.73%的较好指标。