The Froth Flotation Process is about taking advantage of the natural hydrophobicity of liberated (well ground) minerals/metals and making/playing on making them hydrophobic (water-repel) individually to carefully separate them from one another and the slurry they are in. For this purpose we use chemicals/reagents:
The froth flotation process was patented by E. L.Sulman, H. F. K. Pickard, and John Ballot in 1906, 19 years after the first cyanide process patents of MacArthur and the Forests. It was the result of the intelligent recognition of a remarkable phenomenon which occurred while they were experimenting with the Cattermole process. This was the beginning. When it became clear that froth flotation could save the extremely fine free mineral in the slime, with a higher recovery than even gravity concentration could make under the most favorable conditions, such as slime-free pulp, froth flotation forged ahead to revolutionize the nonferrous mining industry. The principles of froth flotation are a complex combination of the laws of surface chemistry, colloidal chemistry, crystallography, and physics, which even after 50 years are not clearly understood. Its results are obtained by specific chemical reagents and the control of chemical conditions. It not only concentrates given minerals but also separates minerals which previously were inseparable by gravity concentration.
This new process, flotation, whose basic principles were not understood in the early days, was given to metallurgists and mill men to operate. Their previous experience gave them little guidance for overcoming the serious difficulties which they encountered. Few of them knew organic chemistry. Those in charge of flotation rarely had flotation laboratories. Flotation research was done by cut and try and empirical methods. The mining industry had no well equipped research laboratories manned by scientific teams.
Froth flotation, as pointed out previously, was a part of the evolution of milling during the first quarter of the 20th centurya period during which the progress of milling was greater than in all of its previous history. It marks the passing of the stamp battery, after 400 years service to the mining industry, and the beginning of grinding with rod mills, ball mills, and tube mills without which neither the cyanide process nor the froth flotation process would have reached full realization. More than all of these, it was the time when custom and tradition were replaced by technical knowledge and technical control.
This volume, then, is dedicated to those men who, with limited means, made froth flotation what it is today. It is designed to record the impact of this great ore treatment development on the mining industry both present and future.
The single most important methodused for the recovery and upgrading ofsulfide ores, thats howG. J. Jameson described the froth flotation process in 1992. And its true: this process, used in several processing industries, is able to selectively separatehydrophobic fromhydrophilic materials,by taking advantage of the different categories of hydrophobicity that areincreased by using surfactants and wetting agents during the processalso applied to wastewater treatment or paper recycling.
The mining field wouldnt be the same without this innovation, considered one of the greatest technologies applied to the industry in the twentieth century. Its consequent development boosted the recovery of valuableminerals like copper, for instance. Our world, full of copper wires usedfor electrical conduction and electrical motors, wouldnt be the same without this innovative process.
During the froth flotation process, occurs the separation of several types ofsulfides,carbonatesandoxides,prior to further refinement.Phosphatesandcoalcan also be purified by flotation technology.
Flotation can be performed by different types of machines, in rectangular or cylindrical mechanically agitated cells or tanks, columns, aJameson Flotation Cellor deinking flotation machines. The mechanical cells are based in a large mixer and diffuser mechanism that can be found at the bottom of the mixing tank and introduces air, providing a mixing action.The flotation columnsuse airspargersto generate air at the bottom of a tall column, while introducing slurry above and generating a mixing action, as well.
Mechanical cells usually have a higher throughput rate, but end up producing lower quality material, while flotation columns work the other way around, with a lower throughput rate but higher quality material.The Jameson cell just combines the slurry with air in a downcomer: then, a high shear creates the turbulent conditions required for bubble particle contacting.
Advantages of froth flotation: first of all, almostallmineralscan be separatedbythis process. Then, the surface propertiescan be controlledandaltered by the flotationreagent. Finally, this technique is highly appropriate for the separation ofsulfideminerals.
To help towards an understanding of the reasons for the employment of specific types of reagents and of the methods of using them, an outline of the principal theoretical factors which govern their application may be of service. For a full discussion of the theory of flotation the various papers and text-books which deal with this aspect should be consulted.
The physical phenomena involved in the flotation of minerals, those, for example, of liquid and solid surface-tensions, interfacial tension, adsorption, flocculation, and deflocculation, are the manifestations or effects of the surface-energies possessed by all liquids and solids in varying degree. These, in turn, arise from the attractions which exist between the interior molecules of every substance and are responsible for their distinctive propertiesform, fluidity, cohesion, hardness, and so on. It follows, therefore, that every substance must exhibit some degree of surface-energy.
All the solids normally present in an ore i.e., metallic, non-metallic, and rock-forming mineralshave their particular contact-angle and hysteresis values and therefore tend to be wetted in varying degrees in accordance with such values. These differences, however, are not usually sufficient to allow of the effective separation of the mineral and gangue constituents from each other. It is the function of the flotation reagents employed to accentuate or magnify these differences to a degree which renders separation by flotation practicable. Some reagents (modifiers) are added with the object of decreasing the contact-angle and so increasing the degree of wetting of the unwanted particles, which are usually more prone to become wetted than the wanted minerals. Others (promoters) are added to increase the tendency toward non-wetting shown by the valuable minerals by coating them with a film of yet higher contact-angle value. Such films are said to be adsorbed in respect of the water.
In this connection reference to Fig. 28 will indicate that a reagent which decreases the surface-tension of water tends thereby to increase wetting of the solid, since, if the value of S1 and therefore of its horizontal component, is lessened, the water-edge, as at P, will tend to extend over the solid surface, making therewith a smaller contact-angle.
The reagents added to promote the separation of the wanted minerals by increasing the water/solid contact-angle consist of substances whose molecules or minute suspensions have a markedly lower attraction for water molecules than the latter exert between themselves. Finely divided oil emulsions in water, dissolved xanthates, and other promoters are typical of such reagents. Substances of such nature, when dissolved in or disseminated through water, are pre-eminently adsorbed, or thrust towards the water boundaries, where the intra-molecular attractions are less uniformly balanced. Normally, this would occur at the free or air/water surface. In a pulp, however, from which air surfaces are absent, but in which mineral particles are suspended, the same thing takes place at the water/solid boundaries, adsorption being most pronounced at those faces where the interfacial tension is greatest viz., those with the highest contact-angle value and lowest adhesion for water. The minute particles of oil or xanthate molecules are thus virtuallythrust into adherence with the more floatable solids, whose surfaces they therefore film, increasing the contact-angles to their own high values and so rendering the solid more floatable. Experimental work indicates that the film so formed is of the order of one molecule in thickness.
Adsorption can be both positive and negative. Substances whose molecules have less attraction for water than the water molecules have for each other are concentrated at the water boundaries as explained in the foregoing paragraph ; this is termed positive adsorption, but substances whose molecules have a greater attraction for water molecules than the latter have for each other will tend to be dragged away from the surface layers, at which their concentration thus becomes less than in the interior of the liquid ; this is negative adsorption. Substances that are negatively adsorbed are those which tend to form chemical compounds or definite hydrates with water, such as sulphuric acid. In froth flotation we are concerned more with positive than with negative adsorption.
In some cases a chemical reaction between the solid and the reagent occurs at the interface ; for instance, in the activation of sphalerite by copper sulphate a film of copper sulphide is deposited on the mineral following adsorption of the copper salt at its surface. In many cases there is no evidence of any chemical change, but, whether chemical action takes place or not, there is no doubt that the filming of the mineral is due primarily to the adsorption property of the liquid itself, by virtue of which the promoting reagent dissolved or suspended in it is concentrated at the interface.
The chemical action of flotation reagents has been and still is the subject of a great deal of research work, which is bringing the various theories into common agreement, but there are still too many doubtful points and unexplained phenomena to make a simple explanation possible in these pages.
The foregoing paragraphs can be summarized by stating that the reagents employed in froth flotation can be classified into three general groups, comprising frothers, promoters, and modifiers, respectively, the purposes of each class being as follows :
The operation of flotation is not always confined to the separation of the valuable constituents of an ore in a single concentrate from a gangue composed of rock-forming minerals. It often happens that two classes of floatable minerals are present, of which only one is required. The process of floating one class in preference to another is termed selective or preferential flotation , the former being perhaps the better term to use. When both classes of minerals are required in separate concentrates, the process by which first one and then the other is floated is often called differential flotation , but in modern practice the operation is described as two-stage selective flotation .
Selective flotation has, therefore, given rise to two other classes of reagents, each of which may be regarded as falling within one of the classes already mentioned. They are known as depressing and activating reagents.
The use of these reagents has been extended in recent years to three- stage selective flotation. For example, ores containing the sulphide minerals of lead, zinc, and iron, can be treated to yield three successive concentrates, wherein each class of minerals is recovered separately more or less uncontaminated by the others.
Although the flotation of the commoner ores, notably those containing copper and lead-zinc minerals, has become standardized to some extent, there is nevertheless considerable variation in the amount and nature of the reagents required for their treatment. For this reason the running costs of the flotation section of a plant are somewhat difficult to predict accurately without some test data as a basis, more especially as the cost of reagents is usually the largest item. Tables 32 and 33 can therefore only be regarded as approximations. Table 32 gives the cost of the straightforward treatment in air-lift machines of a simple ore such as one containing easily floated sulphide copper minerals, and Table 33 that of the two-stage selective flotation of a lead-zinc or similar complex ore.
From Table 32 it will be seen that the reagent charge is likely to be the largest item even in the flotation of an ore that is comparatively easy to treat, except in the case of a very small plant, when the labour charge may exceed it. At one time the power consumption in the flotation section was as expensive an item as that of the reagents, but the development of the modern types of air-lift and pneumatic machines has made great economies possible in expenditure under this heading. As a ruleCallow-Maclntosh machines require less power than those of the air-lift type to give the same results, while subaeration machines can seldom compete with either in the flotation of simple ores, although improvements in their design in recent years have resulted in considerable reductions in the power needed to drive them. It should be noted that the power costs given in the table include pumping the pulp a short distance to the flotation machines, as would be necessary in an installation built on a flat site, and the elevation of the rougher and scavenger concentrates as in circuits such as Nos. 9 and 10.
The power costs decrease with increasing tonnage because of the greater economy of larger units and the lower price of power when produced on a large scale. The cost in respect of reagents and supplies also decreases as the size of the plant increases, due to better control and organization and to lower first cost and freight rates of supplies when purchased in bulk. The great disadvantage of a small installation lies in the high labour cost. This, however, shows a rapid reduction with increase of tonnage up to 1,000 tons per day, the reason being that with modern methods a flotation section handling this tonnage requires few more operators than one designed for only 200 tons per day. For installations of greater capacity the decrease is comparatively slight, since the plant then generally consists of parallel 1,000-ton units, each one requiring the same operating force ; the reduction in the cost of labour through increase of tonnage is then due chiefly to the lower cost of supervision and better facilities for maintenance and repairs. Provided that the installation is of such a size as to assure reasonable economy of labour, research work and attention to the technical details of flotation are generally the most effective methods of reducing costs, since improved metallurgy is likely to result in a lower reagent consumption if not in decreased power requirements.
The costs given in Table 33 may be considered as applying to a plant built on a flat site for the two-stage selective flotation of a complex ore in subaeration machines with a tank for conditioning the pulp ahead of each stage and one cleaning operation for each rougher concentrate. It is evident that the reagent charge is by far the largest item of cost. This probably accounts for the more or less general use of machines of the mechanically agitated type for complex ores in spite of their higher power consumption and upkeep costs, since the high-speed conditioning action of the impellers and provision for the accurate regulation of each cell offer the possibility of keeping the reagent consumption at a minimum. As in the case of single-stage flotation, the charge for labour falls rapidly as the capacity of the plant increases to 1,000 tons per day ; beyond this point the rate of decrease of this and all other items of cost with increase of tonnage is less rapid. The remarks in the previous paragraph concerning the importance of research work and attention to technical details apply with added force, because of the possibility through improved metallurgy of reducing the much higher reagent and power costs which a complex ore of the class in question has to bear.
Optimal mineral recovery in a flotation circuit depends on the capacity to adapt to metallurgical variability in the ore being processed. Recognizing the need for a solution that addresses these challenges, Metso has made several advances in flotation design and technology.
Combining the benefits of circular cells with the unique features of the patented DV mechanism, the RCS (Reactor Cell System) flotation technology has been developed to create ideal conditions to maximize flotation performance for all roughing, cleaning and scavenging duties. The cell can be modified to handle high density slurries.
Maximize bubble-particle contact within the mechanism and the flotation tank leads to enhanced performance. Effective air dispersion and distribution throughout the cell volume helps in smooth froth surface and removal.
Our RCS flotation machines are built with efficient air and level controls with controlled aeration rate at each cell. The pneumatically operated dart valves help in effective pulp level control followed by accurate measurement with ultrasonic level sensor and float.
Metso offers the innovative circular tank concept to minimize slurry short circuiting as well as simplifying froth handling process. The compact and modular design proves to be very beneficial for quick construction, shipment and installation. Our internal dart valves also help to minimize footprint requirements.
Metso RCS flotation machines have extended wear life due to minimized local high velocity zones inside the tank. Impellers and diffusors supplied in high abrasion-resistant elastomers, and the impeller profile is design to minimize adsorbed power.
The mechanism design produces powerful radial slurry pumping to the cell wall and gives strong return flows to the underside of the impeller to minimize sanding. Additionally, it is the only mechanism to give maximum slurry recirculation to the upper part of the impeller.
The modular dart valve design provides flexibility to capacity changes without disturbances.Full suspension of the DV mechanism from the cell superstructure leads to very simplified routine maintenance. Along with our robust design, the RCS flotation machines are built to work for you!
Metso RCS flotation machines also are found as an essential piece to a regrind circuit. Rougher cells extract majority of the valuable mineral from the fresh ore. Meanwhile, scavenger cells are going to capture the remaining valuable mineral.
Revolutionary image analysis system for live measurement of multiple froth properties such as velocity, color, bubble size distribution, texture, stability and more. Higher froth recovery with continuous monitoring and analysis of flotation cells.
Ore is reduced in size, chemicals are added and minerals separated and upgraded to produce a marketable product. You need to make sure these metallurgical processes are operating as efficiently as possible. We have a range of metallurgical lab equipment to meet your process testing demands easy to operate and built to last
Essa metallurgical testing equipment gives you complete confidence in the quality of sample preparation and analysis. Not only that, its also built to last. Strong and simple designs keep your maintenance, replacement and downtime costs to an absolute minimum.
We designed all our metallurgical testing equipment with you, the user, in mind. This means you can expect efficient handling that protects against workplace injury. We use the best materials to make sure all products last.
Ball and rod mills have been around a long time, so you can expect any modern design to be fine-tuned to perform consistently over long periods of time. Essa Laboratory Ball and Rod Mills can be trusted. Use them to grind soft, hard, brittle and fibrous materials. Theyre quick, efficient and deliver reliable results. We offer a range of barrel volumes, so youre sure to find an Essa ball or rod mill to suit your laboratory application.
The best way to describe Essa Bottle Rollers is robust and uncomplicated by design. Use them for batch wet leaching and wet or dry grinding or blending of a wide variety of ores and minerals. If youre looking for a machine that can operate non-stop in tough conditions while delivering accurate results, youve found it here. You can also be sure that the strong build will stand the test of time.
Essa Certified Pressure Filters are newly designed to give you the highest standard of compliance and precision. They come in two standard sizes to suit either small or large volume test work and batch processing either the small to mid-size CPF015 or the large volume CPF035. Both are recognised for filtering samples quickly and for being easy to load, unload and operate. Theyre cleverly designed to reduce risk of contamination or loss of sample. We believe these to be one of the most superior pressure filters on the market today.
Essa FTM101 Flotation Test Machine is a versatile addition to any laboratory. It gives you full and thorough processing for a range of applications. Use the Essa Flotation Test Machine to establish the percentage of reagents in a production flotation cell, as well as to perform batch froth, agitation, attrition, scrubbing and blending tests that can be replicated in a production environment.
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Turbulence as an important factor to flotation has been reviewed.Techniques measuring fluid flows have been reviewed according to their categories.The strengths and weakness of each technique has been analysed.Suitable techniques for three phase flow turbulence measurements were identified.
Flotation is one of the most important primary separation processes in the minerals industry. As far as the mechanism of flotation is concerned, turbulence is one of the key parameters determining flotation performance because it affects three main processes: suspension of particles, air dispersion and particle-bubble collision, attachment and detachment. To study turbulence in industrial flotation cells, both numerical simulation and experimental measurement can be performed. Development of turbulence models and validation of Computational Fluid Dynamic (CFD) numerical simulation need experimental data obtained from turbulence measurement techniques that can be used in the three phase abrasive opaque environment present in a flotation cell. In this paper, the different techniques which have been used to characterise turbulence in the literature are reviewed in terms of their basic principles, system structure, range of application and limitations. Laser Doppler Anemometry (LDA), Particle Image Velocimetry (PIV), Constant Temperature Anemometer (CTA) and the Aeroprobe are all techniques that have been widely used to characterise the turbulence created in flotation machines operating with only fluid (or fluid and air). They cannot however be used when the concentration of solids is high as commonly occurs in a flotation machine. Techniques that have been identified that have the potential to be used to produce accurate measurements in three phase flows include Positron Emission Particle Tracking (PEPT), Piezoelectric Vibration Sensor (PVS) and Electrical Resistance Tomography (ERT). It is envisaged that applications of PEPT in three phase flotation cells will mostly be confined to studies at the laboratory scale. ERT has been tested in flotation cells filled with water and air but needs more development before it can be applied confidently in industrial scale flotation units. PVS, on the other hand, has been validated at laboratory scale and has been applied successfully for measuring turbulence in large scale operating flotation machines.
The last few decades have seen major advances in instrumentation and technology, and simplifications and modifications of new flotation plant designs. This has allowed for significant developments in process control. In particular, the development of base level process control (control of pulp levels, air flowrates, reagent dosing, etc.) has seen significant progress. Long-term, automated advanced and optimising flotation control strategies have, however, been more difficult to implement. It is hoped that this will change as a result of the development of new technologies such as machine vision and the measurement of new control variables, such as air recovery.
This review looks at each of the four essential levels of process control (instrumentation, base level flotation control, advanced flotation control and optimising flotation control) and examines current and future trends within each sub-level.
Literature of instrumentation used in flotation control. A review of base-level (regulatory) process control in froth flotation processes. A review of stabilising flotation control, and optimising flotation control methods. Review of implementation of newer technologies into flotation process control including machine vision and froth stability.