While all flotation processes are selective or differential in that one mineral or group of minerals is floated away from accompanying gangue, bulk flotation generally refers to separation of unlike mineral types such as sulfides from non-sulfides. Differential flotation(exemplified, for instance, by the concentration and subsequent successive removal of Cu, Pb, Zn and Fe sulfides from a single ore) on the other hand, is restricted to operations involving separation of similar mineral types.
Batch Froth flotation Testing is a means of treating a pulp of finely ground ore so that it yields the valuable or desired mineral in a concentrate that will be amenable to further processing. The process involves the imparting of a water repellent (hydrophobic) character to the wanted mineralparticles by chemicals that are called collectors or promoters. Under favorable conditions, these chemically coated particles become attached to the air that is bubbled through the pulp, and will thus float on the surface.
If the surface tension of the pulp is then reduced by a second chemical, called a frother, a stabilized froth containing the wanted mineral particles will form on the surface of the pulp. This froth can then be skimmed off to yield a concentrate in which the desired mineral is present in a much higher percentage than in the original ore.
The test objectives and therefore information required from the results should be established (e.g. sizings, assays, rates of flotation and treatment of products, etc). Knowing the information that is required, the test can be planned with regard to the following:
All reagents to be used during the test should be prepared at the required strengths prior to commencement. The freshness of some reagents is important. Remember the more dilute the reagent, the more accurate is the addition rate but the higher the volume addition to the cell.
It is sometimes helpful to gain information from previous tests of a similar type or performed on the same feed source, to become aware of any problems which may occur during the test (e.g. amount and nature of sulphides, feed size distribution, frothing problems, etc.)
Every mine large enough to justify the installation of a concentrating mill should be able to increase its profits by installing a conveniently arranged ore dressing laboratory. The laboratory may consist of a few essential items or of a very complete installation, depending upon the size of the mine and the complexity of the ore dressing problems encountered.
The Batch Laboratory Test Plant makes it possible to conduct tests for flotation, gravity concentration, amalgamation, cyanidation, or any combination of these processes. Batch laboratory machines can be supplied to suit the customers individual requirements as necessity at various times dictates. Mining companies frequently install a nucleus of equipment to which various additions are made as the value of testwork becomes increasingly apparent.
Many mining schools throughout the world have practically standardized on Batch Laboratory Equipment and have made complete installations of Batch Laboratory TestPlants. This wide acceptance is due not only to dependablemetallurgical results, but also to the fact that LaboratoryMachines demonstrate the principles of standard commercial machines. Government and private testing laboratories use Laboratory Machines because they require units from which standard, accurate results can be obtained and results which can be duplicated in commercial practice.
The installation and operation of a commercial plant may involve problems which should be studied under small scale continuous operating conditions. The results secured from such study willeliminate the need for costly experimentation with large tonnages of ore when the commercial plant is placed in operation, and assures selection of the proper size and type of equipment. The Continuous Laboratory Test Plant offers ample opportunity for the study of many complex problems and thousands of tests have been conducted on widely varying types of materials and ores from customers throughout the world. Following are examples:
Recent advances in the art of flotation have broadened the scope of flotation testwork to include materials not previously considered. Besides the metallic minerals, industrial materials and products are now being successfully treated. Coal, cryolite, bauxite, phosphates, apatite, feldspars, syenite, ilmenite, and salt are being concentrated; also milkweed, resins, and grain.
Continuous Laboratory Test Plants are used extensively by universities and government bureaus for research in ore dressing, and by mining companies to determine method of treatment and layout for new projects. With the development of the No. 8 Sub-A Laboratory Flotation Machine, continuous testing in parallel with standard mill circuits has become mechanically practical. This allows changes in grinding, conditioning, emulsifying, and reagents to be made under identical mill feeding and mill operating conditions without interruptions or fluctuations in the main circuit.
Using as a basis the three sizes of Sub-A Laboratory Flotation Machines available, namely the Nos. 5, 7 and 8, these plants can be furnished to fit each particular requirement. The No. 5 has a capacity of 50 to 150 pounds an hour, the No. 7 of 200 to 500 pounds an hour, while the No. 8 will handle 1,500 to 2,500 pounds an hour. These capacities depend, of course, on the material being treated.
The full name of the flotation is called froth flotation. It is the process of selecting minerals from the pulp by means of the buoyancy of the bubbles, depending on the difference in the surface properties of the various minerals. Where to buy flotation machines?
The specific process of flotation is to add various flotation reagents to a certain concentration of slurry, and a large number of diffuse bubbles are generated by stirring and aeration in the flotation machine. At this time, the suspended ore collides with the bubbles, and some of The floatable ore particles adhere to the bubbles, and float up to the surface of the ore to form a foam product, which is the concentrate; the non-floating mineral remains in the slurry and becomes the tailings. Thereby, achieve the purpose of mineral sorting.
Froth Flotation machine plays an indispensable role in the mineral beneficiation process, flotation is susceptible to a number of factors during the process, including grinding fineness, slurry concentration, pulp pH, pharmaceutical system, aeration and agitation, flotation time, water quality and other process factors. The factors that affect the flotation process are detailed below.
Both large ore particles (larger than 0.1mm) and small ore particles (less than 0.006mm) affect flotation efficiency and mineral recovery. In the case of flotation coarse particles, due to the heavyweight, it is not easy to suspend in the flotation machine, and the chance of collision with the bubbles is reduced. Further, after the coarse particles adhere to the air bubbles, they are easily detached from the air bubbles due to the large dropout force. Therefore, the coarse particles have a poor flotation effect under the general process conditions.
During the fine particles flotation separation process, the fine particles are small in volume and the possibility of collision with the bubbles is small. The fine grain quality is small, and when it collides with the bubble, it is difficult to overcome the resistance of the hydration layer between the ore particle and the bubble, and it is difficult to adhere to the bubble.
The content of the coarse-grained monomer must be less than the upper limit of the particle size of the mineral flotation. At present, the upper limit of flotation particle size is generally 0.25-0.3 mm for sulfide minerals; 0.5-1 mm for natural sulfur; and the upper limit of particle size for coal is 1-2 mm.3.Avoid muddy as much as possible. When the flotation particle size is less than 0.01 mm, the flotation index will decay significantly.
The most appropriate grinding fineness must be determined by testing and reference to production practice data. For some ores, the stage grinding and stage selection process are often used to avoid over-grinding of the ore, so that the dissociated ore particles are selected in time.
If the froth machine contains much ore slurry, it will bring a series of adverse effects on flotation cells mineral processing. The main influences are as follows 1 Easy to be mixed in the foam product, so that the concentrate grade is reduced. 2 Easy to cover the coarse grain surface, affecting the flotation of coarse particles. 3 Adsorption of a large number of agents, increase drug consumption. 4 The pulp is sticky and the aeration conditions are deteriorated.
The type and quantity of the agent added during the flotation process, the dosing place and the dosing method are collectively referred to as the drug system, also known as the prescription. It has a major impact on flotation indicators.
In the ore dressing, it is necessary to pass the ore selectivity test in order to determine the type and quantity of the agent, and in practice, the number, location and mode of dosing should be constantly revised and improved.
In addition to oxygen, nitrogen and inert gases, there are carbon dioxide and water vapor in the air. The gas has a selective effect on the surface of the mineral, oxygen is the most important factor affecting the surface of minerals. Oxygen is beneficial to the hydrophobicity of sulphide ores/ sulfine flotation, however, if the action time is too long, the mineral surface will return to hydrophilicity. When the gas adsorption conditions are appropriate, the mineral surface will be drained, the flotation mineral processing can be done even without a flotation agent. The Galena mine can only float up with the action of xanthate through the initial action of oxygen.
Stirring the slurry can promote the suspension of the ore particles and evenly disperse in the tank, thus promote the good dispersion of the air and make it evenly distributed in the tank, further can promote the enhanced dissolution of air in the high-pressure area of the tank, and strengthen the precipitation in the low-pressure area. Enhanced aeration and agitation are advantageous for flotation separation, but not excessively, as excessive aeration and agitation can have the following disadvantages: (1) Promoted the merger of bubbles (2) Reduced concentrate quality (3) Increased power consumption (4) Increased wear of various parts of the flotation machine (5) The volume of the slurry in the tank is reduced (this is because the volume of the tank is increased by the portion occupied by the bubble) (6) Excessive agitation may also cause the ore particles attached to the bubbles to fall off. The optimum amount of aeration and agitation in production should be determined by experimentation depending on the type and structural characteristics of the flotation machine.
Inflation and agitation are carried out simultaneous in the flotation machine. Strengthening them is beneficial to increase the flotation index, but if it is determined too much, it will cause shortcomings such as bubble merger, degraded quality, increased electric energy consumption, and mechanical wear. Therefore, aeration and agitation must be appropriate.
The slurry concentration can affect the following technical and economic indicators: (1) Recovery rate. When the slurry concentration is small, the recovery rate is low. As the concentration of the slurry increases, the recovery rate also increases, but the recovery rate exceeds the limit. The main reason is that the concentration is too high, which destroys the aeration condition of the flotation machine. (2) Quality of concentrates. The general rule is that the quality of the concentrate is higher in the flotation of the leaner slurry, and the quality of the concentrate is reduced in the flotation of the richer slurry. (3) Consumption of pharmaceuticals. When the slurry is thicker, the amount of treatment per ton of ore is less, and when the concentration of the slurry is thinner, the amount of treatment per ton of ore is increased. (4) The production capacity of the flotation equipment. As the concentration of the slurry increases, the production capacity of the froth flotation machine calculated according to the treatment amount also increases. (5) Water and electricity consumption. The thicker the pulp, the smaller the water and electricity consumption per ton of ore processed. In short, when the concentration of the slurry is thick, it is beneficial to the flotation process. However, if the slurry and bubbles do not flow freely, the aeration will deteriorate, thereby reducing the quality and recovery. In this case, the various ore sections of the flotation should determine the appropriate concentration of the slurry according to the nature of the ore and relevant technical requirements.
The most suitable ore pulp concentration during the flotation process is related to the ore property and the flotation processing conditions. The general rules as flow: (1) Pulp Density. The mineral with large flotation density uses a thicker slurry, while the mineral with a small flotation density uses a thinner slurry. Flotation of coarse-grained materials with thicker slurry, flotation of fine-grained and muddy materials with thinner ore. (2) Pulp PH Value. The pH of the pulp refers to the concentration of OH and H+ in the slurry, which is generally expressed by the PH value. Various minerals have a floating and non-floating pH when using different flotation agents for flotation, The pH of the critical pH. By controlling the critical pH, it is possible to control the effective sorting of various minerals. Therefore, controlling the pH value of the slurry is one of the important measures to control the flotation process. (3) Flotation Time. The flotation time directly affects the quality of the indicator. The time is too long, the grade of the concentrate is reduced; the time is too short and the grade of the tailings is increased. Therefore, the flotation time required for various Minerals must be determined by experimentation. (4) Water Quality. Floating water should not contain a large number of suspended particulates, nor can it contains soluble substances and various microorganisms that may interact with minerals or flotation reagents. This problem should be specially noticed when using backwater, pit water, and lake water. (5) Pulp Temperature. Flotation is generally carried out at room temperature, but sometimes it is necessary to warm the slurry in order to obtain a good sorting effect. The specific heating or not needs to be determined according to the actual situation. If it is heated, it is best to adapt to local conditions and use waste heat and exhaust gas as much as possible.
The main effects of pulp quality score on froth flotation process in metallurgy are as follows: (1) Recovery rate. Within a certain range, when the pulp mass fraction is low, the recovery rate is low; the pulp mass fraction is increased, and the recovery rate is correspondingly increased. However, the mass fraction of the slurry should not be too large. If it is too large, the flotation machine is difficult to inflate normally in the slurry, which in turn reduces the recovery rate.
(2) Concentrate grade. The general rule is that the concentrate grade is higher when ore flotation is carried out in a leaner slurry, while the concentrate grade is reduced when it is floated in a thicker slurry.
(3) The dosage of the agent. The flotation agent should maintain a certain mass fraction in the pulp to have a good flotation effect. When the pulp is thicker, the mass fraction of the medicament is correspondingly increased, that is, the required medicament mass fraction can be achieved with fewer chemicals, and the amount of medicament per tan ore is correspondingly reduced. Conversely, when the pulp is thinner, the amount of the agent increases.
Thats all 7 main variables affecting froth flotation. Contact us to know more info about industrial gold mining equipment, get free froth flotation PDF, flotation process flow chart, and related industry cases of gold froth flotation, zinc froth flotation, copper flotation, ore flotation.
Since the content of useful components in the ore that needs flotation treatment is getting lower and lower, the particle size of the impregnation is getting finer and finer, and the composition is more and more complicated and difficult to separate. Therefore, how to design an efficient mineral flotation flow is of the utmost importance.
The 911MPELMFTM20 is an ultra modern and versatile Laboratory Flotation Bench Test Station whichoutdoes the classicMetso/Denver D12 flotation machine as it has been designed to provide an accurate reliable means of reproducing test results. It is ideally suited in duplicating plant processes and operations.
You must select the flotation tank sizes and shape as well as the rotor diameter. Baseline Model starts includes an agitatorrotor for cells of 1.75 to 3.5 liters in volume and one 3 liter square tank.(Free exchange for another rotor/tanks of any capacity/size).
Introduce Small Flotation XFDIII Single cell Laboratory flotation machine is widely used in geology, metallurgy, building materials, chemicals and other research institutions and laboratories for mining stirring, scrub, separation, and selection of a small number of ore samples and so on. XFD floatation machine is Froth Flotation Equipment, uses inverter technology, variable speed impeller, digital display, and also change from the outside air to intake inflated with the precise adjusted, clear and stable display. According to user needs, FX Model Continuous Mechanical Flotation Machine can be equipped with a heater, temperature control device to control, display tank mine fluid temperature at any time. Small Flotation Machines can be equipped with additional water level automatically adjusts automatically administration and other devices can achieve a higher level of automation. The flotation machines have a frame member, spindle transmission parts, locking parts, wiper parts, flotation tanks, outside the inflatable devices and electrical control components. Gas of pump tank supply to the rotor agitation, and mix with ore fluid, the stator is cut to produce tiny bubbles mineralization. Rotor speed is stepless and can be adjusted by the inverter. Fixed flotation tank fasten by hand wheel drive screw clamp. Shaving foam body, its trajectory is a circular motion. click to know the Industrial flotation separation machine.
Working Principle of Small Single Cell FlotationSingle cell flotation machine is an important device to realize the flotation process with only one cell. Single groove flotation machine is suitable for the separation of colored ferrous metals, but also for non-metallic materials such as coal-sparkling stone, talc. The single groove flotation machine is driven by the motor triangle drive impeller rotation, resulting in centrifugal action to form negative pressure, on the one hand, adequate air and slurry mixing, on the one hand, mixing pulp and medicine, and at the same time refine the foam, Above the mineral-bonded foam, the mineral floats to the surface of the ore pulp to form mineralized foam. Adjust the height of the gate to control the liquid level so that the useful foam is scraped out of the scraper. The basic performance of single tank flotation machine requires good inflatable action, stirring effect, stable foam zone, continuous operation, and easy adjustment.
Industrial flotation machines can be divided into four classes: (1) mechanical, (2) pneumatic, (3) froth separation, and (4) column. The mechanical machine is clearly the most common type of flotation machine in industrial use today, followed by the rapid growth of the column machine. Mechanical machines consist of a mechanically driven impeller, which disperses air into the agitated pulp. In normal practice, this machine appears as a vessel having a number of impellers in series. Mechanical machines can have open flow of pulp between each impeller or are of cell-to-cell designs which have weirs between each impeller. The procedure by which air is introduced into a mechanical machine falls into two broad categories: self-aerating, where the machine uses the depression created by the impeller to induce air, and supercharged, where air is generated from an external blower. The incoming slurry feed to the mechanical flotation machine is introduced usually in the lower portion of the machine.Figure 7 shows a typical industrial flotation cell of each air delivery type.
The most rapidly growing class of flotation machine is the column machine, which is, as its name implies, a vessel having a large height-to-diameter ratio (from 5 to 20) in contrast to mechanical cells. The mechanism behind this machine to is provide a countercurrent flow of air bubbles and slurry with a long contact time and plenty of wash water. As might be expected, the major advantage of such a machine is the high separation grade that can be achieved, so that column cells are often used as a final concentrate cleaning step. Special care has to be exercised in the generation of fine air bubbles and controlling the feed rate to column cells.
Good mixing of pulp. To be effective, a flotation machine should maintain all particles uniformly in suspension within the pulp, including those of relatively high density and/or size. Good mixing of pulp is required for maximizing bubble-particle collision frequency.
Appropriate aeration and dispersion of fine air bubbles. An important requirement of any flotation machine is the ability to provide uniform aeration throughout as large a volume of the machine as is possible. In addition, the size distribution of the air bubbles generated by the machine is also important, but experience has shown that the proper choice of frother type and dosage generally dominates the bubble size distributions being produced.
Sufficient control of pulp agitation in the froth zone. As mentioned earlier, good mixing in the machine is important; however, equally important is that near and in the actual froth bed at the top of the machine, sufficiently smooth or quiescent pulp conditions must be maintained to ensure suspension of hydrophobed (collector coated) particles.
Efficient mass flow-mechanisms. It is also necessary in any flotation machine that appropriate provisions be made for feeding pulp into the machine and also for the efficient transport of froth concentrate and tailing slurry out of the machine.
Probably the most significant area of change in mechanical flotation machine design has been the dramatic increase in machine size. This is typified by the data ofFig. 8, which shows the increase in machine (cell) volume size that has occurred with a commonly used cell manufactured by Wemco. The idea behind this approach is that as machine size increases, both plant capital and operating costs per unit of throughput decrease.
The throughput capabilities of various cell designs will vary with flotation residence time and pulp density. The number of cells required for a given operation is determined from standard engineering mass balance calculations. In the design of a new plant, the characterization of each cell's volume and flotation efficiency is generally calculated from performing a laboratory-scale flotation on the same type of equipment on the ore in question, followed by the application of empirically derived design (scale-up) factors. Research work is currently under way to improve the understanding and performance of commercial flotation cells. Currently, flotation-cell design is primarily a proprietary function of the various cell manufacturers.
Flotation plants are built in multiple cell configurations (called banks), and the flow through various banks is adjusted in order to optimize plant recovery of the valuable as well as the valuable grade of the total recovered mass from flotation. This recovery vs grade trade-off is economically important in flotation, as increased recovery of the valuable is associated with decreased grade. For example, a 95% recovery of copper in the feed ore might give a concentrate grade of 18% Cu in the total recovered mass, while 80% Cu recovery might give a grade of 25% in the concentrate. Obviously, the higher the valuable recovery is, the higher the potential income, but if this higher recovery requires a great deal more grinding and/or expensive downstream processing (including further flotation) in order to upgrade the concentrate for metal refining such as smelting, the increase in potential recovery income may actually cause a net loss of total income. This grade-recovery optimization is generally worked out by individual flotation operators in each plant (and each mineral) and sets the operating philosophy of that plant.Figure 9 shows a typical industrial recovery vs grade trade-off curve for a copper sulfide ore containing pyrite. The higher the copper recovery is, the greater the amount of undesired pyrite contained in the concentrate.
The various banks of flotation cells in an industrial plant are given special names to denote the particular purpose of the banks. The rougher bank is the first group of cells that the pulp sees after size reduction. The goal of the roughers is to produce a concentrate with as high a recovery of valuable as possible with generally low grade of the valuable. The rejected gangue material from any bank of cells is commonly denoted as the tails or tailings. Usually, rougher tails are discarded so that valuable mineral not recovered in the rougher bank is lost. The concentrate of the rougher bank can be further concentrated, sometimes after additional grinding, in banks of cells called cleaners or recleaners. The tailings from the cleaners or recleaners can be recirculated to a bank of cells known as scavengers in order not to lose any valuable material in the upgrading process. Various banks of cells are also sometimes known by the particle size of the particular pulps being floated. Coarse particles, fine or slime particles, and middle-sized particles, denoted as middlings, can all be treated in separate banks.
As to overall capacities of flotation plants, the range is quite variable, depending on the type and value of the mineral being processed, the amount of valuable mineral in the feed ore to flotation, the degree and cost of size reduction involved, and the relative response of the valuable(s) to the flotation process. Smaller plants ranging in size from 500 to 5000 metric tons of feed per day are common, with feed materials having high amounts of valuable per ton of feed ore (>40%), such as coal, phosphate, and oxide ores. On the other hand, the sulfide minerals that are typically a small percentage of the ore (<10% and often less than 1%) require much greater capacity in order to achieve a reasonable economic return on investment. Thus, typical copper sulfide plants have capacities in the range of 20,000 to more than 60,000 metric tons of feed ore per day.
Conventional flotation machines house two functions in a single vessel: an intense mixing region where bubbleparticle collision and attachment occurs, and a quiescent region where the bubbleparticle aggregates separate from the slurry. The reactor/separator machines decouple these functions into two separate (or sometimes more) compartments. The cells are typically considered high-intensity machines due to the turbulent mixing in the reactor (see Section 12.9.5). The role of the separator is to allow sufficient time for mineralized bubbles to separate from the tailing stream which generally requires relatively short residence time (when compared to mechanical cells or columns).
Some of the earliest machine designs were of the reactor/separator-type. Figure 12.80 shows a design from a patent by Hebbard (1913). Feed slurry was mixed with entrained air in an agitation box (reactor) and flowed into the separation vessel where froth was collected as overflow. The design would be the basis for the Minerals Separation Corporation standard machine and early flotation cells used in the United States (Lynch et al., 2010).
The Davcra cell (Figure 12.81) was developed in the 1960s and is considered to be the first high-intensity machine. The cell could be thought of as a column or reactor/separator device. Air and feed slurry are contacted and injected into the tank through a cyclone-type dispersion nozzle, the energy of the jet of pulp being dissipated against a vertical baffle. Dispersion of air and collection of particles by bubbles occurs in the highly agitated region of the tank, confined by the baffle. The pulp flows over the baffle into a quiescent region designed for bubblepulp disengagement. Although not widely used, Davcra cells replaced some mechanical cleaner machines at Chambishi copper mine in Zambia, with reported lower operating costs, reduced floor area, and improved metallurgical performance.
Several attempts have been made to develop more compact column-type devices, the Jameson cell (Jameson, 1990; Kennedy, 1990; Cowburn et al., 2005) being a successful example (Figure 12.82). The Jameson cell was developed in the 1980s jointly by Mount Isa Mines Ltd and the University of Newcastle, Australia. The cell was first installed for cleaning duties in base metal operations (Clayton et al., 1991; Harbort et al., 1994), but it has also found use in coal plants and in roughing and preconcentrating duties. The original patent refers to the Jameson cell as a column method, but it can also be considered a reactor/separator machine: contact between the feed and the air stream is made using a plunging slurry jet in a vertical downcomer (the reactor), and the airslurry mixture flows downwards to discharge and disengage into a shallow pool of pulp in the bottom of a short cylindrical tank (the separator). The disengaged bubbles rise to the top of the tank to overflow into a concentrate launder, while the tails are discharged from the bottom of the vessel. Air is self-aspirated (entrained) by the action of the plunging jet. The air rate is influenced by jet velocity and slurry density and level in the separator chamber.
The Jameson cell has been widely used in the coal industry in Australia since the 1990s. Figure 12.83 shows a typical cell layout where fine coal slurry feeds a central distributor which splits the stream to the downcomers. Clean coal is seen overflowing as concentrate from the separation vessel. The major advantage of the cell in this application is the ability to produce clean concentrates in one stage of operation by reducing entrainment, especially when wash water is used. It also has a novel application in copper solvent extraction/electrowinning circuits, where it is used to recover entrained organic droplets from electrolyte (Miller and Readett, 1992).
The Contact cell (Figure 12.84) was developed in the 1990s in Canada. The feed slurry is placed in direct contact with pressurized air in an external contactor which comprises a draft tube and an orifice plate. The slurryair mixture is fed from the contactor to the column-type separation vessel, where mineralized bubbles rise to form froth. Contact cells employ froth washing similar to conventional flotation columns and Jameson cells. Contact cells have been implemented in operations in North America, Africa, and Europe.
The IMHOFLOT V-Cell (Figure 12.85(a)) was developed in the 19801990s and evolved from earlier designs developed in Germany in the 19601970s (Imhof et al., 2005; Lynch et al., 2010). Conditioned feed pulp is mixed with air in an external self-aeration unit above the flotation cell. The airslurry mixture descends a downcomer pipe and is introduced to the separation vessel via a distributor box and ring pipe with nozzles that redirect the flow upward in the cell. The separation vessel is fitted with an adjustable froth crowding cone which can be used to control mass pull. The concentrate overflows to an external froth launder, while the tailings stream exits at the base of the separation vessel. The V-Cell has been used to float sulfide and oxide ores with the largest operation being an iron ore application (Imhof et al., 2005).
The IMHOFLOT G-Cell (Figure 12.85(b)) was introduced in 2001 and employs the same external self-aerating unit as the V-Cell. The airslurry mixture which exits the aeration unit is fed to an external distributor box (located above the separation vessel) where pulp is split and fed to the separation vessel tangentially via feed pipes. The cell is unusual as an internal launder located at the center of the vessel collects froth. The centrifugal motion of the slurry enhances froth separation with residence times being ca. 30s.
The Staged Flotation Reactor (SFR) (Figure 12.86) is a recent development in the minerals industry. By sequencing the three processesparticle collection, bubble/slurry disengagement, and froth recoveryand assigning each to a purpose-built chamber, the SFR aims to optimize each of the three processes independently.
The SFR incorporates an agitator in the first (collection) chamber designed to provide high energy intensity (kWm3) and induce multiple particle passes through the high shear impeller zone, hence giving high collection efficiency. Slurry flows by gravity through the reactor stages, that is, there is no need to apply agitation to suspend solids, only for particle collection. As such, impeller speed can be adjusted online in correlation with desired recovery without sanding. The second tank is designed to deaerate the slurry (bubble disengagement) and rapidly recover froth to the launder without dropback. The froth recovery unit is tailored for use of wash water and for high solids flux. Efficient particle collection and high froth recovery translate into fewer, smaller cells, resulting in a smaller footprint and building height, with lower power consumption, and the potential for good selectivity in both roughing and cleaning applications.
Induced air flotation machines have gained a degree of popularity within certain sections of the minerals processing industry because of their ability to produce small bubbles at relatively high energy efficiency. The most common of such machines is the Jameson Cell. A downcomer protrudes out of the bubbly liquid in which is housed a plunging jet. Because this jet is at high velocity the pressure within the downcomer is low due to the Bernoulli equation, and air is induced into the downcomer creating a plume of bubbles within the liquid, which rise to form a foam. There are major problems with operating Jameson Cells because their high demand for surfactant causes downstream residual frother issues. (It is noted, as an aside, that frother strippers are being developed to remove residual frother in flotation circuits, and these are identical to foam fractionation units.) Notwithstanding that Jameson Cell technology has failed to live up to its promise, it has been successfully used as a pilot-scale foam reactor to effect the autothermal thermophilic aerobic digestion (ATAD) of high strength wastewater sludge produced at a chicken processing factory. The advantage that induced gas systems have over alternative pneumatic foam systems is their very high gasliquid surface area per unit volume of foam due to their small bubbles. This feature of the foams would also be an advantage in foam fractionation because it creates high flux of gasliquid surface. However, to the authors knowledge, no attempt has ever been made to use induced gas systems as foam fractionators.
The Denver DR flotation machine, which is an example of a typical froth flotation unit used in the mining industry, is illustrated in Figure 1.47. The pulp is introduced through a feed box and is distributed over the entire width of the first cell. Circulation of the pulp through each cell is such that, as the pulp comes into contact with the impeller, it is subjected to intense agitation and aeration. Low pressure air for this purpose is introduced down the standpipe surrounding the shaft and is thoroughly disseminated throughout the pulp in the form of minute bubbles when it leaves the impeller/diffuser zone, thus assuring maximum contact with the solids, as shown in Figure 1.47. Each unit is suspended in an essentially open trough and generates a ring doughnut circulation pattern, with the liquid being discharged radially from the impeller, through the diffuser, across the base of the tank, and then rising vertically as it returns to the eye of the impeller through the recirculation well. This design gives strong vertical flows in the base zone of the tank in order to suspend coarse solids and, by recirculation through the well, isolates the upper zone which remains relatively quiescent.
Froth baffles are placed between each unit mechanism to prevent migration of froth as the liquid flows along the tank. The liquor level is controlled at the end of each bank section by a combination of weir overflows and dart valves which can be automated. These units operate with a fully flooded impeller, and a low pressure air supply is required to deliver air into the eye of the impeller where it is mixed with the recirculating liquor at the tip of the air bell. Butterfly valves are used to adjust and control the quantity of air delivered into each unit.
Each cell is provided with an individually controlled air valve. Air pressure is between 108 and 124 kN/m2 (7 and 23 kN/m2 gauge) depending on the depth and size of the machine and the pulp density. Typical energy requirements for this machine range from 3.1 kW/m3 of cell volume for a 2.8 m3 unit to 1.2 kW/m3 for a 42 m3 unit.
In the froth flotation cell used for coal washing, illustrated in Figure 1.48, the suspension contains about 10 per cent of solids, together with the necessary reagents. The liquid flows along the cell bank and passes over a weir, and directly enters the unit via a feed pipe and feed hood. Liquor is discharged radially from the impeller, through the diffuser, and is directed along the cell base and recirculated through ports in the feed hood. The zone of maximum turbulence is confined to the base of the tank; a quiescent zone exists in the upper part of the cell. These units induce sufficient air to ensure effective flotation without the need for an external air blower.
Most of the industrial flotation machines used in the coal industry are mechanical, conventional cells. These machines consist of a series of agitated tanks (usually 48 cells) through which fine coal slurry is passed. The agitators are used to ensure that larger particles are kept in suspension and to disperse air that enters down through the rotating shaft assembly (Fig. 11.13). Air is either injected into the cell using a blower or drawn into the cell by the negative pressure created by the rotating impeller. For coal flotation, trough designs that permit open flow between cells along the bank are more common than cell-to-cell designs that are separated by individual weirs.
Some of the major manufacturers of flotation equipment include Wemco (FLSmidth), Metso, Svedala, and Outokumpu. The commercial units are very similar in basic design and function, although some slight variations exist in terms of cell geometry and impeller configuration. Machines with large specific surface areas are generally preferred for coal flotation, due to the fast flotation kinetics of coal and the large froth solids loadings. Flotation machines with individual cell volumes of up to 28m3 are commonly used due to advantages in terms of capital, operating and maintenance costs. Some manufacturers also offer tank machines, which consist of relatively short cylindrical tanks equipped with conventional impellers. The simplified structural design, which allows these machines to be much larger, can offer significant savings in terms of capital and power costs for some installations. Tank cells with volumes as large as 100m3 are already in operation at coal plants in Australia.
Unlike conventional, mechanically agitated flotation machines, which tend to use relatively shallow rectangular tanks, column cells used in the coal industry are usually tall vessels with heights typically ranging from 7 to 16m depending on the application. Unlike conventional flotation machines, columns do not use mechanical agitation and are typically characterized by an external sparging system, which injects air into the bottom of the column cell. The absence of intense agitation promotes higher degrees of selectivity and can aid in the recovery of coarse particles.
In general, feed slurry enters the column at one or more feed points located in the upper third of the column body and descends against a rising swarm of fine bubbles generated by the air sparging system (Fig. 11.14). Hydrophobic particles that collide with, and attach to, the bubbles rise to the top of the column, eventually reaching the interface between the pulp (collection zone) and the froth (cleaning zone). The location of this interface, which can be adjusted by the operator, is held constant by means of an automatic control loop that regulates a valve on the column tailings line. Varying the location of the interface will increase or decrease the height of the froth zone. The froth is transported from the froth zone into the product launder via mass action.
Methods of sparging in columns are numerous and include air lances, porous tubes, eductors, static mixers, and Cavitation-TubesTM. The air rate used in a column is selected according to the feed rate and concentrate-production requirements. This parameter typically has the largest effect on the operating point of the column with respect to the ash/yield curve. The bubbles generated by the air sparging system are sized to provide the maximum amount of bubble surface area given a constant energy input. In other words, the designs of the various sparging devices are engineered to provide the smallest size and largest number of bubbles possible.
For an equivalent volumetric capacity, the cross-sectional surface area of a column cell is much smaller than that of a conventional cell. This reduced area is beneficial for promoting froth stability and allowing deep froth beds to be formed. This is an important aspect of column flotation, as a deep froth bed facilitates froth washing for the removal of unwanted impurities from the float product. Wash water, added at the top of the column, percolates through the froth zone displacing dirty process water and non-selectively entrained particles trapped between the bubbles. In addition, froth wash water serves to stabilize and add mobility to the froth. Sufficient water must be added to ensure that all of the feed water that would otherwise normally report to the froth product is replaced with fresh or clarified water. It has been reported that less than 1% of the feed pulp and associated clays will report to the froth in a well-operated column (Luttrell et al., 1999). The ability to maintain and wash a deep froth layer is the main reason cited for the improved product grades when comparing column cells to conventional cells.
In contrast, conventional mechanical cells do not operate with deep froths. Therefore, these devices allow some portion of the ultrafine mineral slimes to be recovered with the water that reports to the froth. Consequently product quality is reduced by this non-selective hydraulic conveyance (i.e., entrainment) of gangue into the product launder. In fact, fine particles (<0.045mm) have a tendency to report to the froth concentrate in direct proportion to the amount of product water recovered. As such, the flotation operator is often forced to make the decision to either pull hard on the cells to maintain yield (e.g., wet froth), or run the cells less aggressively to maintain grade (e.g., dry froth).
The primary advantage of utilizing wash water is the ability to provide a superior product grade when compared to conventional flotation processes. This capability is illustrated by the test data summarized in Fig. 11.15, which compares column flotation technology with an existing bank of conventional cells. As shown, the separation data for the column cells utilizing wash water are far superior to those obtained from the conventional flotation bank. In fact, the data for the column cells tend to fall just below the separation curve predicted by release analysis (Dell et al., 1972). A release analysis is an indication of the ultimate flotation performance and is often regarded as wash-ability for flotation. This figure suggests that columns provide a level of performance that would be difficult to achieve even after multiple stages of cleaning by conventional machines.
There are a significant number of full-scale column installations currently in commercial service around the world. The most popular brands of columns include the CPT CoalPro (Eriez), Jameson, and Microcel columns. Although the Jameson cell does not have the traditional column geometry, it is included since it typically uses wash water to improve ash rejection. Details related to the specific design features of the various column technologies are available in the literature (McKay et al., 1988; Finch and Dobby, 1990; Yoon et al., 1992; Manlapig et al., 1993; Davis et al., 1995; Rubinstein, 1995; Wyslouzil, 1997). The primary difference between the various columns used in the coal industry is the type of air sparging system employed. These include porous bubblers, static mixers, and dynamic air injectors. Details related to the features and operation of these systems have been discussed extensively in the literature (Dobby and Finch, 1986a; Xu and Finch, 1989; Huls et al., 1991; Groppo and Parekh, 1992; Yoon et al., 1992; Finch, 1995). Ideally, the spargers should produce small, uniformly sized bubbles at a desired aeration rate. Other factors, such as equipment costs, mechanical reliability, wear resistance, and serviceability also need to be carefully considered prior to selecting an industrial sparging system.
Due to economy of scale, recent trends in the coal industry have shifted away from the installation of large numbers of smaller units toward fewer, large units with diameters up to 5m or more. Although most column installations involve the treatment of particles finer than 0.150mm, several recent column operations have been installed to treat coarser particles, such as minus 1mm feeds or deslimed 0.1500.045mm feeds. Additionally, a move to more economical cells in terms of energy efficiency has been realized as manufacturers focus on the generation of the required air bubble dispersions while using significantly less power than traditional approaches. One such device is the Eriez StackCell, which utilizes both pre-aeration methods in conjunction with traditional froth washing (Davis et al., 2011) to maximize efficiency with regard to both installation and operating cost.
The two most important requirements of laboratory flotation machines are reproducibility and performance similar to commercial operations. These two criteria are not always satisfied. The basic laboratory machines are scaled down replicas of commercial machines such as Denver, Wemco and Agitair. In the scale down, there are inevitable compromises between simplification of manufacture and attempts to simulate full scale performance. There are scaling errors, for example, in the number of impeller and stator blades and various geometric ratios. Reproducibility in semi-batch testing requires close control of impeller speed, air flow rate, pulp level and concentrate removal.
Until now, deaeration tanks always had to be placed underneath the flotation machine and also frequently in the cellar of a facility in order to ensure a sufficient height difference for the conveyance of foam. In addition, the tanks are open on top and can overflow with excess foam. That is now a thing of the past with the Deaeration Foam Pump (DFP) 4000. The new pump can be linked directly to the deinking machine and forms a clean and closed disposal system. Because it can be placed at the same level as the flotation cells, the entire flotation system saves more space than previous systems. A cellar or an additional floor height for the flotation is no longer required. The deaeration results are very impressive with the DFP 4000 from Voith Paper. The air content of the foam mass is reduced when passing through the pump from 80% to an average of 8%. Conventional deaeration systems offer approximately 12%. In addition, by using the DFP 4000, upstream foam destroyers, downstream long piping as well as pumps with high head pressures to overcome the floor height can be dispensed. With the DFP 4000, it is possible to deaerate and convey the foam, which is loaded with inks and other impurities, within a single machine. As a compact unit, it fully replaces the foam destroyer, foam tank stirring unit, and pump of previous deaeration systems. This means a clear reduction in investment costs for the tank, stirring unit, pipes, pumps, and floor space.
The DFP 4000, developed by Voith, is a compact unit that integrates several elements of the flotation deinking system. This combines the pump and deaeration machine into one unit. The deaeration foam pump replaces the foam destroyer, foam tank, stirring unit, and pump and costs less than the current suite of equipment. The DFP 4000 achieves better deaeration of the foam than conventional systems.
The DFP 4000 has two parts. In the upper part, foam is predeaerated by a mechanical foam destroyer. In the lower part, centrifugal force produced by a quick rotational movement further deaerates the foam. The resulting low-air-content suspension is brought to the required pressure so that it can be conveyed out of the machine to the next process stage. The air released during deaeration is conveyed out of the machine through a special air chamber on the side so that the airflow does not prevent the foam entering from above (Dreyer,2010).
The new pump can be linked directly to the deinking machine, forming a clean and closed disposal system. Because the deaeration pump can be placed at the same level as the flotation cells, the entire system requires less space than previous systems, so a cellar (or additional floor height) is no longer required to accommodate the system. When the foam mass passes through the DFP 4000, the foams air content is reduced from 80% to an average of 8% (Voith,2011a). Conventional deaeration systems reduce the air content to approximately 12%. The first DFP 4000 operating in a paper mill has been in service since September 2009 (Dreyer,2010). The benefits of the DFP 4000 are summarized in Table11.9 (Dreyer,2010; Voith,2011a).
Batch testing has been carried out using a specially designed 21 tumbler for mixing, and a standard Denver flotation machine for separation. A typical charge of the soil sample ranged from 200 to 600g, and the amount of coal varied depending on the contaminant concentration.
Figure 1 shows the block diagram of the 6T/day continuous unit. A slurry of contaminated soil and coal is fed at optimal solids concentration to a specially designed tumbler. In the front section of the tumbler, as a result of rotary motion, the solids are mixed and dispersed. In another section of the tumbler, layering, compaction and abrasion take place. After being discharged from the tumbler, the contents are screened into two streams. The 1mm particle size stream is directed to a high shear mixer where the oil-wetted coal particles are conditioned. The slurry is then transfered to flotation cells, where the coal microagglomerates, in the form of froth, are separated from clean soil. To facilitate dewatering and improve handleability of the combustible product, the froth can be subsequently fed into the low shear mixer for further agglomeration.
Flotation has progressed and developed over the years; recent trends to achieve better liberation by fine grinding have intensified the search for more advanced means of improving selectivity. This involves not only more selective flotation agents but also better flotation equipment. Since the froth product in conventional flotation machines contains entrained fine gangue, which is carried into the froth with feed water, the use of froth spraying was suggested in the late 1950s to eliminate this type of froth contamination. The flotation column patented in Canada in the early 1960s and marketed by the Column Flotation Company of Canada, Ltd., combines these ideas in the form of wash water supplied to the froth. The countercurrent wash water introduced at the top of a long column prevents the feed water and the slimes that it carries from entering an upper layer of the froth, thus enhancing selectivity.
The microbubble flotation column (Microcel) developed at Virginia Tech is based on the basic premise that the rate (k) at which fine particles collide with bubbles increases as the inverse cube of the bubble size (Db), i.e., k1/Db3. In the Microcel, small bubbles in the range of 100500m are generated by pumping a slurry through an in-line mixer while introducing air into the slurry at the front end of the mixer. The microbubbles generated as such are injected into the bottom of the column slightly above the section from which the slurry is with drawn for bubble generation. The microbubbles rise along the height of the column, pick up the coal particles along the way, and form a layer of froth at the top section of the column. Like most other columns, it utilizes wash water added to the froth phase to remove the entrained ash-forming minerals. Advantages of the Microcel are that the bubble generators are external to the column, allowing for easy maintenance, and that the bubble generators are nonplugging. An 8-ft diameter column uses four 4-in. in-line mixers to produce 56 tons of clean coal from a cyclone overflow containing 50% finer than 500 mesh.
Another interesting and quite different column was developed at Michigan Tech. It is referred to as a static tube flotation machine, and it incorporates a packed-bed column filled with a stack of corrugated plates. The packing elements arranged in blocks positioned at right angles to each other break bubbles into small sizes and obviate the need for a sparger. Wash water descends through the same flow passages as air (but countercurrently) and removes entrained particles from the froth product. It was shown in both the laboratory and the process demonstration unit that this device handles extremely well fine below 500-mesh material.
Another novel concept is the Air-Sparged Hydrocyclone developed at the University of Utah. In this device, the slurry fed tangentially through the cyclone header into the porous cylinder to develop a swirl flow pattern intersects with air sparged through the jacketed porous cylinder. The froth product is discharged through the overflow stream.
The process is carried out in a flotation cell or tank, of which there are two basic types, mechanical and pneumatic. Within each of these categories, there are two subtypes, those that operate as a single cell, and those that are operated as a series or bank of cells. A bank of cells (Fig. 8) is preferred because this makes the overall residence times more uniform (i.e., more like plug flow), rather than the highly diverse residence times that occur in a single (perfectly mixed) tank.
FIGURE 8. Flotation section of a 80,000t/d concentrating plant, showing the arrangement of the flotation cells into banks. A small part of the grinding section can be seen through the gap in the wall. [Courtesy Joy Manufacturing Co.]
The purpose of the flotation cell is to attach hydrophobic particles to air bubbles, so that they can float to the surface, form a froth, and can be removed. To do this, a flotation machine must maintain the particles in suspension, generate and disperse air bubbles, promote bubbleparticle collision, minimize bypass and dead spaces, minimize mechanical passage of particles to the froth, and have sufficient froth depth to allow nonhydrophobic (hydrophilic) particles to return to the suspension.
Pneumatic cells have no mechanical components in the cell. Agitation is generally by the inflow of air and/or slurry, and air bubbles are usually introduced by an injector. Until comparatively recently, their use was very restricted. However, the development of column flotation has seen a resurgence of this type of cell in a wider, but still restricted, range of applications. While the total volume of cell is still of the same order as that of a conventional mechanical cell, the floor space and energy requirements are substantially reduced. But the main advantage is that the cell provides superior countercurrent flow to that obtained in a traditional circuit (see Fig. 11), and so they are now often used as cleaning units.
Mechanical cells usually consist of long troughs with a series of mechanisms. Although the design details of the mechanisms vary from manufacturer to manufacturer, all consist of an impeller that rotates within baffles. Air is drawn or pumped down a central shaft and is dispersed by the impeller. Cells also vary in profile, degree of baffling, the extent of walling between mechanisms, and the discharge of froth from the top of the cell.
Selection of equipment is based on performance (represented by grade and recovery), capacity (metric tons per hour per cubic meter); costs (including capital, power, maintenance), and subjective factors.
Flotation is the most widely used beneficiation method for fine materials, and almost all ores can be separated by flotation. Another important application is to reduce ash in fine coal and to remove fine pyrite from coal. The flotation machine is mechanical equipment for realizing the froth flotation process and separating target minerals from ore. At present nearly 2 billion tons of ore in the world are treated by the froth flotation process. According to rough statistics, about 90% of non-ferrous minerals are recovered by the flotation method, accounting for 50% proportion in the field of ferrous metal mineral separation.
Suitable material Sulfide minerals, oxide minerals, non-metallic minerals, silicate minerals, nonmetallic salt minerals, soluble salt minerals, rare earth minerals, etc., including gold, silver, copper, lead, zinc, galena, zinc blende, chalcopyrite, pyroxene, molybdenite, nickel pyrite, malachite, cerussite, smithsonite, hematite, cassiterite, wolframite, Ilmenite, beryl, spodumene, brimstone, graphite, diamond, quartz, mica, feldspar, fluorite, apatite, barite, and so on.
The flotation machine is composed of single or multiple flotation cells, by agitating and inflating the chemical reagent treated slurry, some mineral ore particles are adhered to the foam and float up, and then be scraped out, while the rest remains in the slurry.
Industrial flotation machines can be divided into 5 classes, mechanical agitation flotation machine, pneumatic flotation machines, flotation column, airlift flotation machine, froth separation flotation machines. At present, the mechanical flotation machine is the most commonly used in industry, followed by the column flotation which has recently set off hot spot, the pneumatic type and froth separation are not common.
Commonly used flotation models TankCell series, Wemco series, Agitair series, SuperCells, RCS(reactor cell system), Denver laboratory flotation, KYF, and XCF series flotation devices, laboratory flotation machine. Well-known flotation machine manufacturers have Outotec, Flsmidth, Metso, BGRIMM, JXSC flotation machine china; column flotation manufacturers or models have Jameson, CPT, Counter-flow inflatable flotation column.
Main parts: slurry tank, agitator device, mineralized froth discharging system, electromotor, etc. 1. Slurry tank: mainly consist of a slurry inlet, slurry tank and a gate device for controlling the slurry volume, welded with steel plate. 2. Agitator: slurry tank have a series of the mechanically driven impeller that disperses the air into the agitated pulp. 3. Mineralized forth discharging: the useful minerals are enriched in the foam, scraped out, dehydrated, and dried into concentrate products.
Whatever flotation machines design is selected, it must accomplish a series of complicated industrial requirements. 1. Good mixing function. a qualified flotation machine should mix the slurry uniformly and maintain the particles especially the target mineral particle in suspension with the pulp, maximum the froth-mineral probability. 2. Adequate ventilation and distribution of fine bubbles. Except for the flotation machine performance, the frother type and dosage also matter to the distribution of the bubbles. 3. Appropriate agitation control in the froth beds. It is should pay importance to keep froth zones smoothly, which ensures the suspension of collector coated particle.
1. The throughput capabilities of various cell designs will vary with the ore property (beneficiability, size, density, grade, pulp, PH, etc.). In the case of ore easy separated, and a small amount of air inflation required, may choose a mechanical flotation machine; if the minerals with coarse size, proper to choose the KYF, BS-F, ore CLF type; what's more, when in case of ore easy separated, fine particles, high grade, low PH, flotation column is the best, especially in the concentrating process. 2. There is a difference between the process of concentrating, rough selecting. Thin froth layer is better for separate mineral particles, thus may not choose a large air inflation flotation machine.
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