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.     

Effect of frothers and dodecylamine on bubble size and gas holdup in a downflow column

Bubble size and gas holdup were characterized in a two phase gas–water system in a laboratory downflow column. The effect of the cationic surfactant dodecyl amine (MW 185, HLB 10.7) and the frothers MIBC (MW 102, HLB 6.05) and polyglycol F507 (MW 425, HLB 8.63) on the bubble size and gas holdup were investigated. In addition, the effect of blends of MIBC-dodecyl amine (DDA) and F507-DDA on these parameters was assessed. The bubble Critical Coalescence Concentration (CCC) followed the order MIBC > DDA > F507. When blending the frothers with DDA at a concentration below its CCC, the frother CCC decreased and bubbles of finer size were obtained below and above the frother CCC. Static surface tension measurements of aqueous solutions with frothers and DDA as well as with frothers-DDA blends show coadsorption of DDA at the air/aqueous solution interface. The surface tension of aqueous solutions prepared with the blends decreased with the addition of DDA and varied linearly with the frother concentration within the concentration range studied. The gas holdup in the downflow column was determined by the bubble size and decreased with the bubble size. It is shown that frother-DDA blends gave the lowest gas holdup in the downflow column. This work is relevant for the reverse flotation of quartz from iron ores using amine collectors in cells with downflow systems.     

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.     

Critical coalescence concentration of inorganic salt solutions

Critical coalescence concentration (CCC) was determined in a laboratory-scale mechanical flotation cell for a series of coalescence inhibiting inorganic salts (KCl, NaCl, Na₂SO₄, CaCl₂ and MgSO₄) compared to two commercial frothers (methyl isobutyl carbinol, Dowfroth 250C). The salt CCC values ranged from 0.07 M (MgSO₄) to 0.31 M (KCl and NaCl) and correlated with ionic strength. The CCC values are compared to transition concentrations in the literature. The effect of salts on gas dispersion in flotation systems is discussed.     

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.     

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.     

Effect of impeller rotational speed on the size dependent flotation rate of galena in full scale plant cells

The first three rougher cells in the lead circuit of the Elura concentrator (formerly Pasminco Australia Limited) were selected as the plant cells for investigation. Metallurgical surveys were performed and various hydrodynamic measurements taken, allowing the galena flotation rate constant and the bubble surface area flux (S_b) in these cells to be calculated over a wide range of gas flow rates, and at two impeller rotational speeds. It was determined that altering the impeller rotational speed did not significantly change the rate constant dependency on S_b when flotation was considered on an unsized basis.The analysis was further extended to examine the same cells parameters on a size-by-size basis. The results obtained have been used to identify differences in the flotation behaviour of the various particle size fractions, independently of surface hydrophobicity. It is shown that the physical conditions for effective flotation of fine (<9 μm) and coarse (>53 μm) particle size fractions differ substantially, suggesting that a specific hydrodynamic environment will favour a high flotation rate for fine galena, which may be detrimental to the recovery of coarse galena, and vice versa. These observations are in accord with metallurgical practice that suggest that it is difficult to improve fine particle flotation without also compromising coarse particle stability efficiency simply by modifying the cell hydrodynamics alone. A fundamental flotation model was applied to quantify differences in the flotation rate of the various particle size fractions with impeller rotational speed.     

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.     

Effect of ball size distribution on milling rate

This paper focuses on the determination of the selection function parameters α, a, μ, and Λ together with the exponent factors η and ξ describing the effect of ball size on milling rate for a South African coal.A series of batch grinding tests were carried out using three media single sizes, i.e. 30.6, 38.8, and 49.2 mm. Then two ball mixtures were successively considered. The original manufacturer’s recommended ball mixture was used to investigate the effect of ball size distribution on the selection function whereas the equilibrium ball mixture was used to validate the model.Results show that with the six parameters abovementioned, the charge mixture is fully characterized with about 5% deviation. Interestingly, the estimated parameters can be used in the simulator model allowing one to find the optimal ball charge distribution for a set of operational constraints.     

730A与松醇油两种起泡剂在昆钢大红山铁矿150万t/a选矿厂的生产应用

介绍了730A和松醇油两种起泡剂在昆钢大红山铁矿150万t/a选矿厂的生产应用。生产实践表明,根据不同的矿石性质、工艺流程、设备性能使用两种起泡剂, 可以增强起泡剂的适应性,稳定浮选泡沫层,提高选矿指标,降低药剂成本。     

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.     

Micro- and nano-scale phenomena effect on bubble size in mechanical flotation cell

The micro/nano-scale phenomena affecting the bubble size observed in a mechanical flotation cell were investigated using an extensive dynamic surface property study with commercial laboratory instruments. The results highlighted two distinct dynamic surface properties: a rapid adsorption/desorption rate leading to undetectable dilatation surface elasticity, and a slow adsorption/desorption process taking place within minutes and leading to a significant increase in the dilatation elasticity of the interface. The latter is observed in highly surface-active reagent grade Polypropylene Glycol and in commercial Dowfroth 250 frothers while the rapid adsorption/desorption rate is a characteristic of weakly surface-active reagent grade 1-Pentanol and commercial Dowfroth 200.The bubble size distribution and therefore the Sauter mean diameter results also highlighted the unambiguous similarity in the effect of frother on bubble size between the I-Pentanol and the Dowfroth 200 and indeed between the Polypropylene Glycol and the Dowfroth 250. The present paper examines the similarity between the two groups in order to gain understanding on how the dynamic surface properties affect the bubble size in two-phase systems.     

Determining frother-like properties of process water in bitumen flotation

In oil sands flotation, bitumen is known to release natural surfactants into the process water following the addition of NaOH. These surfactants appear to replace the need for frother. Measuring the Sauter mean diameter (D₃₂) vs. dilution, it was possible to characterize the frother-like properties of process waters as an equivalent concentration of a known frother commonly used in mineral flotation, DF-250. Process water samples from the thickener overflow at the Shell Albian plant were examined. The study showed equivalent concentrations up to 60 ppm DF-250 and variations between samples. Reasons for the variability are discussed. A gas holdup vs. D₃₂ correlation was established which reduced the experimental effort.     

On the effect of van der Waals attractions on the critical salt concentration for inhibiting bubble coalescence

The coalescence of gas bubbles in many salt solutions such as NaCl is significantly inhibited if the salt concentration exceeds a critical concentration which is unique for each salt. It has been predicted as a function of the Hamaker constants of van der Waals attractions between two bubbles. In this paper, the Lifshitz theory on the van der Waals interaction energy and the available spectrum for water dielectric permittivity are applied to determine the Hamaker constants for liquid films between bubbles in pure water and salt solutions. Using the new values for Hamaker constants for thin films of saline solutions, we show that the effect of van der Waals attractions on the critical salt concentration is significantly weaker than previously hypothesized. The predictions based on van der Waals attractions significantly under-estimate the experimental critical concentrations. The failure of the van der Waals attraction in predicting the critical salt concentration highlights the urgent need of revising the available theories on bubble coalescence in salt solutions and saline water.     

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.     

Boundary conditions for gas rate and bubble size at the pulp–froth interface in flotation equipment

This paper describes the effective boundary conditions for the gas dispersion parameters of bubble size, superficial gas velocity and bubble surface area flux, in mechanical and column flotation cells. Using a number of previously derived correlations, with appropriate simplifying assumptions, and experimental data reported from plant practices, the boundary conditions were identified. Thus, it was shown that these constraints typically allow for a mean bubble diameter range of d_b = 1–1.5 mm and superficial gas rate of J_g = 1–2 cm/s, in order to maximize the bubble surface area flux, S_b = 50–100 s⁻¹. Under these conditions there is no carrying capacity limitation, while keeping a distinctive pulp–froth interface.     

浮选机叶轮排布方式对叶轮流体动力学的影响

基于计算流体力学(Computational Fluid Dynamics)方法,分析叶轮排布方式对KYF型浮选机叶轮流体动力学参数的影响。对两种排布方式的叶轮承受流体激励力进行傅里叶变换,分析其波动频率及其成分。从流体激励力时域和频域角度分析叶轮叶片排布对其振动特性的影响。     

气泡、油泡和活性油质气泡在浮选中的应用和机理探讨

浮选是高效回收矿产资源应用最广泛的技术方法。气泡作为浮选载体在浮选过程中有着举足轻重的作用。以气泡-油泡-活性油质气泡为线索,对比了传统气泡与改性后油泡(气泡表层包裹一薄层油性捕收剂)、活性油质气泡(气泡表层包裹一薄层含有捕收剂的中性油)的浮选特性。通过浮选动力学分析了气泡与油泡、活性油质气泡浮选的区别,传统气泡浮选与改性后的油泡浮选均为2步反应,而活性油质气泡实现了1步浮选,大大降低了气泡与矿物颗粒间的黏附功,提高了浮选效率。从油-水界面表面活性剂解离度这个角度分析了活性油质气泡的表面性质,指出活性油质气泡的表面电性由表层中性油中添加的捕收剂和p H决定。通过DLVO理论计算了不同气泡与矿物颗粒间的相互作用能,从理论上解释了活性油质气泡浮选指标更好的原因。活性油质气泡在选矿中的成功应用表明,活性油质气泡与矿物表面的作用均强于传统气泡与矿物表面的作用,即活性油质气泡对矿物具有更强的捕收能力,相较于气泡和油泡的浮选,活性油质气泡浮选有利于提高浮选效率,降低捕收剂用量。活性油质气泡作为浮选载体从气泡这一特殊视觉为浮选行业开辟了一个崭新的研究领域。