Flotation Machine Research Articles

Experiment and Research on the Concentration of Refractory Molybdenite Ore by Flotation Column

As certain refractory molybdenum with degree high oxidation and high argillization, on the premise of molybdenum concntrate recovery rate, in order to increase tenor of molybdenum concntrate, we use cyclonic static micro-bubble flotation column as concentration equipment. We used two concentrate courses to replace flotation machine eight concentrate courses. It showed that, in the condition of same recovery rate, tenor of molybdenum concntrate was 26.16%, rising by 8%. Using processes of flotation machine eight concentrate courses - concentrate regrinding - flotation column two concentrate courses, tenor of molybdenum concntrate was 39.33% and the recovery rate was of 8%. The results showed that, by increasing the degree of monomer dissociation of molybdenum ores, cyclonic static micro-bubble flotation column has higher capability in recovering and selecting ores of -400 mm size fraction. The high argillization resulting from the regrinding and unsuppressed gangue minerals are the main factors affecting the tenor of ore concentrate.

Hydrogen bubble flotation of silica

In this study the flotation recovery of silica using air, and molecular and electrolytically-generated hydrogen was investigated. For comparison of air and molecular hydrogen recoveries, a laboratory Denver, type D12, flotation machine was used. For both gases, pH of the suspension, gas flow rate, concentration of collector and frother, solids concentration, particle size and speed of impeller were kept constant. Almost identical recoveries were obtained for both gases, suggesting that gas composition played no significant role in silica flotation. Electroflotation experiments were carried out using 12.6 μm mean diameter silica particles. While fine particles had very poor recovery in the Denver cell, greater than 70% recoveries were achieved in the electroflotation cell. This was thought to be the result of the very small (less than 40 μm) bubbles generated by the electroflotation process. A population-balance model, incorporating the hydrogen generation process, supported the conclusion that increased recovery for electroflotation, for very fine silica particles at least, was attributed to the reduced bubble size and not by the composition of the gas.

New directions in flotation machine design

The theoretical background for flotation kinetics of ultrafine and coarse particles are explored. Recent advances in flotation technology for these difficult areas are reviewed, with a focus on improving the flotation rate of ultrafines, and extending the upper limit for coarse particle flotation. For ultra-fine particles, the theory suggests that the rate of flotation can be improved by increasing the rate of shear in the suspension of particles and bubbles. A new cell has been developed, the Concorde Cell, in which the pre-aerated feed is raised to supersonic velocities before passing into a high-shear zone in the flotation cell. The local dissipation rate is of the order of 100 kW/m 3, one to two orders of magnitude higher than is available in conventional mechanical cells. The Concorde Cell has been trialed on a finely ground PGM feed in South Africa, with excellent results. By recycling the tailings, and using the mass pull or solids recovery as the control variable, the Cell is capable of producing a high-grade concentrate at high recoveries, over a wide range of particle sizes. Theory for the upper limit of coarse particle flotation suggests that a quiescent flow field is necessary to prevent the particles from becoming detached from the bubbles. A liquid-fluidized bed provides a suitable environment. The flotation feed is introduced into the fluidized bed, and air bubbles are dispersed in the fluidizing water. Coarse particles attach to the bubbles rising through the bed and are lifted into the froth layer that is maintained on top of the cell in the usual way. Particles of galena up to 1 mm in diameter have been recovered in such a bed, while for particles of lower density such as quartz and coal, the upper limit for flotation has been extended to at least 2 mm and 5.6 mm respectively. The fluidized bed technology provides major advantages beyond the ability to recover coarse particles currently lost in existing operations. Thus, if the upper flotation limit can be extended, the top size for grinding can be raised, with significant reductions in energy costs. Liberation of the values is the key limitation. Also, a fluidized bed flotation cell can accept a feed with much higher percent solids, leading to significant reductions in water requirements.

Estimation of the actual bubble surface area flux in flotation

The bubble surface area flux, S B , defined as the ration between the superficial gas rate J G and the Sauter mean bubble diameter D 32, has been widely used to describe the gas phase dispersion efficiency in flotation machines, and from this predict flotation performance, notable mineral recovery to forecast plant economics. In this work, results of bubble size distribution (BSD) generated in a pilot column are analyzed. Using video and image analysis techniques, the impact of different sampling rates on the BSD was evaluated. Measurements were carried out for D 32 = 1–2 mm, J G = 0.5–1.5 cm/s and two frother concentration, with a maximum sampling rate of 100 fps. In addition, the bubble rise velocity in the bubble swarm was measured, as a function of the individual bubble diameter, for different operational conditions. The identification of the BSD depends on the proper selection of the visual field and sampling rate for acquisition and processing of bubble images. Distortion in the estimation occurs because a larger holdup of small bubbles is observed, relative to the overall data set, due to their lower velocity. The actual BSD was obtained by correcting the observed population, considering the effect of bubble rise velocity. Thus, the actual bubble surface area flux, S B , was calculated. The results were evaluated at a pilot scale (air–water system) as well as an industrial plant scale (air-pulp system).

Agerbruget i enkeltgravskultur – Senneolitikum og ældre bronzealder i Jylland belyst ud fra plantemakrofossil

Agerbruget i enkeltgravskultur – Senneolitikum og ældre bronzealder i Jylland belyst ud fra plantemakrofossil

Research on fine coal classified flotation process and key technology

In an attempt to resolve the problem of poor clean coal quality and low ash content of tailing in the mixed flotation technology, factors affecting flotation performance were studied by orthogonal experiments, sieve analysis, progressive release flotation test and statistical methods. The classification flotation technology based on 0.125mm as the classification size was introduced, in which the key technology was the application of classification cyclone to separate the flotation feed. The 0.125-0mm fine coal slime was processed by innovative cyclone micro-bubble flotation column and clean coal filter press, while the 0.5–0.125mm coarse coal slimes were dealt with flotation machines and disc vacuum filters. The research results show that a decrease of 1.12% in the ash content of flotation clean coal and an increase of 9.51% in the ash content of flotation tailing coincide with the application of the classification flotation technology. Meanwhile, the corresponding clean coal recovery increases by 2.61%.

Effect of ultrasound on separation selectivity and efficiency of flotation

The effect of the use of ultrasound in the froth phase on the flotation performance has been investigated in relation to the flotation rate of a complex sulphide ore. A series of kinetic flotation tests with and without ultrasound were conducted in a flotation machine with a 2-L cell, in which an ultrasonic probe is located in the froth zone. The results indicate that there is a considerable effect of ultrasound on separation selectivity and efficiency in the flotation of a complex sulphide ore at intermediate and high level airflow rates whereas, no significant differences in the separation performance were obtained from the flotation with and without ultrasound at low airflow rates. In addition, the results of the size-by-size analysis show that a much better cleaning action in the froth was promoted for coarse particles rather than fine particles as a result of the use of ultrasound. As a result of increase in the bubble coalescence, it was found that the use of ultrasound in the froth is more effective at shallow froths. Therefore, either effective pulp volume can be increased with a negligible loss of flotation performance or the pulp density can be decreased to obtain better product quality with the use of ultrasound in shallow froths.

A comparison of the critical impeller speed for solids suspension in a bench-scale and a pilot-scale mechanical flotation cell

This paper compares the critical impeller speed results for 6 L Denver and Wemco bench-scale flotation cells with findings from a study by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2007. Evaluation of solids suspension in a pilot-scale mechanical flotation cell: the critical impeller speed. Minerals Engineering 20, 233–240; Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621–629] conducted in a 125 L Batequip flotation cell. Understanding solids suspension has become increasingly important due to dramatic increases in flotation cell sizes. The critical impeller speed is commonly used to indicate the effectiveness of solids suspension. The minerals used in this study were apatite, quartz and hematite. The critical impeller speed was found to be strongly dependent on particle size, solids density and air flow rate, with solids concentration having a lesser influence. Liquid viscosity was found to have a negligible effect. The general Zwietering-type critical impeller speed correlation developed by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621–629] was found to be applicable to all three flotation machines. The exponents for particle size, solids concentration and liquid viscosity were equivalent for all three cells. The exponent for solids density was found to be less significant than that obtained by the previous authors, and to be consistent with values reported in the general literature for stirred tanks. Finally, a new dimensionless critical impeller speed correlation is proposed where the particle size is divided by the impeller diameter. This modified equation generally predicts the experimental measurements well, with most predictions within 10% of the experimental.

Bubble break-up and the role of frother and salt

Frothers are used in flotation to aid generation of small bubbles, but little is known about the mechanisms that take place in the flotation machine to produce such an effect. Coalescence prevention is the common explanation with less attention to a frother effect on bubble break-up. This communication presents a technique to study bubble coalescence and break-up. The technique is based on the exposure of a mono-size distribution of bubbles to a turbulent field generated by a three-bladed axial flow impeller. Analysis of bubble size distributions after contact with the turbulent field gives the coalescence and break-up fraction. The presence of frother shows a significant reduction of coalescence and an effect on break-up that increases the fraction of bubbles that are 90% of the original volume. A model relating uneven frother distribution on the stretching bubble prior to rupture is developed to explain the effect of frothers on bubble break-up. The work extends to salt (NaCl) which like frother can reduce bubble size.

An investigation of the flotation mechanism in the aerosol column flotation machine

It is shown that the induction time decreases as the temperature decreases if there is air bubble adhesion to hydrophobic and hydrophilic particles; if there isn’t, the time decreases where hydrophobic particles stick to one another and increases in the case of adhesion of hydrophilic particles. The established difference in the stability of wetting and symmetric films that depend on temperature can be explained by the fact that hydrophobic forces (involving those acting from a “hydrophobic” bubble) have a larger action radius of action than the forces of hydrophilicrepulsion. The revealed mechanisms allowed the development of a new flotation technique, namely, flotation with a steam-air mixture. The essence of this technique is that only a surface layer of the bubble, where the effect of structural forces is localized (rather than the entire slurry volume) is heated due to steam condensation. The efficiency of this technique is shown by the example of flotation concentration of minerals of different origins.

The Online Determination of Bubble Surface Area Flux Using the CiDRA GH-100 Sonar Gas Holdup Meter

In recent years it has been well documented that the bubble surface area flux plays a fundamental role in the performance of industrial flotation machines. Modern instrumentation is not yet capable of providing a robust direct measurement of this parameter, and the widespread industrial use of the available indirect methods have been hampered by the limitations of the available instruments and the complexity of the required calculations. This paper describes a reliable and maintenance-free method for online inference of bubble diameter and bubble surface area flux using CiDRA's GH-100 gas holdup meter. A method is presented for coding the iterative drift-flux analysis calculations for column cell bubble diameter and surface area flux using standard expert system or DCS programming language. An alternative empirical method applicable to mechanical cells is also demonstrated. Operating data from an industrial plant historian is presented.

Redesign of Mechanically Agitated Flotation Machine Based on Interior Flow Fields Simulation

In order to improve the flotation dynamical environment and efficiency of the mechanically agitated flotation machine,the numerical calculation on gas-solid-liquid three-phase three-dimension turbulent flow fields of the 165 m3 flotation is given with the computational fluid dynamics(CFD).The problems of the flow fields in prototype are analyzed,based on which the redesign is carried out on the basis of the flotation dynamical requirement.The flow fields meeting the flotation requirement is given by numerical simulation through changing the parameters of impeller setting angle,the relative position between guide vane and other flow passage components with the flotation cell.The flotation performances of the redesign are improved to meet the design requirements.The industrial experiments show that the redesign has higher efficiency than the prototype.The test results fit in with the simulation prediction result,which shows the validity of the redesign.

On-Line Bubble Size Analyzer for Collection Zone in Industrial Flotation Machines

Abstract Video cameras and image analysis software to measure the top of the froth parameters (velocity, stability, bubble size distribution, bubble load, color and texture) have been proposed to control and to enhance the metallurgical performance. Nevertheless, these measurements are based on a 2D image and empirical strategies, which are insufficient to interpret froth bed hydrodynamics and collection zone kinetics, being both aspects controlling factors in flotation. One of the variables directly related with flotation kinetics and fundamental models are the bubble size distribution in the collection zone (below froth interface). However, sampling and measuring bubble size in collection zone is complex due to the presence of dark particles and bubble clusters. To make possible an industrial measurement for control purposes, a new on-line analyzer based on McGill University bubble viewer , was developed and evaluated at industrial flotation machines. The device incorporates actuators and a PLC to automate: bubble sampling, image acquisition and a washing system. To increase reliability and accuracy of the measurement; new image analysis software is developed, which identifies single bubbles from cluster and eliminates dark area from an image. The prototype and software were evaluated in industrial flotation machines at Codelco-Chile, and has been awarded for the innovations incorporated. The results indicate that the device may be used at industrial scale and the bubble size distribution appears as a new control variable to improve metallurgical performance in industrial flotation machines.

Avaliação do efeito da granulometria no processo de flotação

A flotação é um dos principais processos de concentração, sendo empregado para diversas classes de minerais (sulfetos, óxidos, silicatos, fosfatos, etc.), como também para uma variedade de tamanhos de partículas. Estudos anteriores mostraram que a flotação pode ser empregada com sucesso para faixas granulométricas entre 10 e 300µm. A seletividade do processo de flotação torna-se muito baixa fora desses limites granulométricos, porque as condições hidrodinâmicas do sistema são incapazes de manter o nível de flotabilidade ideal das partículas. Diferentes tamanhos de partículas são encontrados nos atuais sistemas de flotação, que podem reduzir a seletividade do processo, devido às diferenças de comportamento. Esse trabalho avaliou a flotação em bancada das frações -150+45µm e -45µm em comparação com a fração global -150µm de um minério de ferro itabirítico, sob diferentes condições de pH, dosagens de reagentes e rotação de condicionamento. Os resultados obtidos mostram que essas frações apresentam diferentes comportamentos no processo de flotação, indicando que é possível aumentar a recuperação em massa e a seletividade, quando essas frações são flotadas separadamente.

Extraction of noble metals from the recycle slag of refining production

Results of investigations of concentration of metallurgical slag using electrical separators, jugs and flotation machines, sluices, concentration table, and Itomack centrifugal separator are presented. As a result, two production flowsheets are suggested, wet and dry, which provide recovery of ∼95% silver and ∼89% gold mixed with a ∼15.5% metal content.

Numerical simulation of gas-liquid two-phase jet flow in air-bubble generator

Air-bubble generator is the key part of the self-inspiration type swirl flotation machines, whose flow field structure has a great effect on flotation. The multiphase volume of fluid (VOF), standard k-ɛ turbulent model and the SIMPLE method were chosen to simulate the present model; the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation. The distributing law of the velocity, pressure, turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed. The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction, and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.

On lifetime costs of flotation operations

Overall economy of a flotation operation bears much more than investment costs. The lifetime operation and maintenance of a flotation machine may affect the economy of a project far more than a million saved in investment. Studying the long-term effects on investments is worthwhile as they often surpass any apparent savings in capital expenditure. The optimal solution does not even need to be more expensive. Besides, with high operating costs, time is never on one’s side. In the paper various flotation cell arrangements are compared in a simplified example. The example considers capital equipment investment costs, power delivery arrangements, energy costs, and maintenance costs throughout a 25-year ownership. Also effects on CO 2 emissions are discussed. The paper will illustrate how proper choice of equipment and modern power delivery and control methods will result in significant benefits in lifetime costs and profitability of flotation operations.

Design of the flotation machines and efficiency of their use

The designs of the most known flotation machines are compared, considering their design peculiarities that influence technological and economic parameters of the machines.

On the optimization of hydrodynamics in fine particle flotation

There is absolutely no question that a key role for an effective fine particle flotation plays the achievement of sufficiently high flotation velocities by means of large collision rates between the value mineral particles and bubbles in the strongly turbulent rotor (impeller) stream of the flotation machines. Therefore, a large ratio ε R m / ν F n has to be aimed at ( ε R is the local energy dissipation rate in the impeller stream; ν F is the kinematic viscosity of the fluid phase), i.e. ε R should be as large and ν F as small as possible. On the one hand, for that it is important to use an impeller–stator system having a large power number and an intensive internal slurry recirculation. On the other hand, a satisfactory dispersion state and thus advantageous rheological properties (low apparent viscosity) of the slurry must be aimed at. The latter effects a substantial reduction of the turbulence damping and with that not only an increase of ε R in the impeller stream but also a decrease of its volume contraction. Furthermore, an adequate control of the entrainment into the froth lamellae plays a role in optimization.

Numerical simulation of the residence time distribution in flotation cells

AbstractTwo methods for the numerical determination of residence time distributions (RTD) have been tested and proofed to be applicable. One has been used to obtain the RTD of solid particles in a laboratory size flotation machine. Emphasis has been laid on the influence of various parameters, e.g. numerical method, geometry or particle properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)