jjf flotation cell, flotation process, wemco flotation cell - xinhai
[Improvement]: Shallow groove, the stator lower than the impeller, large slurry circulation volume, low energy consumption; the stator is a cylinder with an elliptical hole which is conducive to the dispersion and mixing of pulp and air. Umbrella shaped dispersion cover with hole keeps the pulp surface stable.
When the JJF mechanical agitation flotation machine is working, vortexes are generated in the vertical tube and the draft tube. This vortex forms a negative pressure and sucks the air from the air inlet pipe. It is in the impeller and stator area with the slurry sucked in through the draft tube. mixing. The slurry-gas mixed flow is moved in a tangential direction by the impeller, and then converted into radial movement by the action of the stator, and is evenly distributed in the flotation cell. The mineralized bubbles rise to the froth layer and are scraped out unilaterally or bilaterally to form froth products.
flotation machine for mineral & metallurgy - jxsc machine
Application copper sulfide, gold sulfide, zinc, lead, nickel, antimony, fluorite, tungsten, and other non-ferrous metals, and also be used for coarse selection for ferrous metals and nonmetals. Type Agitating flotation machine, Self-priming, aeration flotation, flotation column. ModelXJK, SF, GF, CHF, XJC, etc. Contact us for specific & quick selection.
Flotation machine (floatation machine, planktonic concentrator) in the mineral processing plant, mainly used for separating copper, zinc, lead, nickel, gold, and other non-ferrous metal. TypeXJK series agitation impeller flotation machine (Seldom used, small capacity); SF flotation machine (Larger volume, better flotation effect); Pneumatic flotation machine (aeration and agitation, high capacity). Corollary equipmentIn front: one or two sets of mixing tank for flotation agent agitation and slurry pulp agitation. Behind: concentrate pond, thickener or filter Flotation cell According to the ore grade, mineral type and processing capacity to choose, determine the number of the flotation cells. It is recommended that carrying out the mineral flotation tests to obtain the best procedure plan, like pulp density, time, reagent selection, etc. Flotation reagentfoaming agent, collecting agent, activating agent, inhibitor, etc. BrandsWemco flotation unit, Fahrenwald Denver, Callow, BGRIMM, etc. How to select mining flotation machine1. According to the nature of the ore (washability, feed particle-size, density, grade, pulp, pH, etc.) and flotation plant scale choose the appropriate flotation machine. 2. The concentration operation is mainly to improve the ore concentrate grade. The flotation foam layer should be thin so that separates the gangue. It is not appropriate to use a flotation machine with a large aeration volume. Therefore, there are differences between the froth flotation machine of concentration, roughing and scavenging. 3. JXSC engineer team here to help do flotation mining machine selection, price inquiry, flowsheet design.
Flotation machine structureThe metallurgist flotation mainly made up of slurry tank, mixing device, aeration device, mineralized bubble discharging device and motor. Flotation machine working principleFlotation process refers to the flotation separation in mineral processing. In the flotation machine, the ore slurry treated with the added agent, by aeration and stir, some of the ore particles are selectively fixed on the air bubbles and floats to the surface of the slurry and is scraped out. The rest is retained in the pulp, thus achieve the purpose of separating different minerals. The complete froth flotation process in metallurgy consists of rougher flotation, concentrate flotation and scavenging flotation. Flotation methodFroth flotation of sulphide ores, mainly have differential flotation and bulk flotation process, improve the flotation recovery rate of fine - particle. Flotation cell manufacturerJXSC specializes in the production of a full set of mineral processing equipment, and cooperates with the Mining Research Institute to design a scientific and reliable mineral processing flowsheet, supply gold flotation, copper flotation, zinc flotation, and the like ore flotation units.
As pneumatic and froth separation devices are not commonly used in industry today, no further discussion about them will be given in this module. The mechanical machine is dearly the most common type of flotation machine currently used in industry, followed by the column machine which has recently experienced a rapid growth.
A mechanical machine consists of a mechanically driven impeller that disperses air into the agitated pulp. In normal practice this machine appears as a long tank-like vessel having a number of impellers in series. Mechanical machines can have open flow of pulp between the impellers or can be of cell-to-cell design with weirs between them. Below is a typical bank of flotation cells used in industrial practice.
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 feed to the mechanical flotation machine is usually introduced in the lower portion of the machine. At the very below is shown a typical flotation cell of each air delivery type (Agitair & Denver)
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 tomechanical cells. This type of machine provides a counter-current 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 the control of the feed rate to the column cell for such cells to be effective. Column cell use is often of limited value in the recovery of relatively coarse valuable particles; because of the long lifting distances involved, the bubbles can not carry large particles all the way to the top of the cell.
Probably the most significant area of change in mechanical flotation cell design has been the dramatic increase in machine cell volume with a single impeller. The idea behind this approach is that as machine size increases (assuming no loss of recovery performance with the larger machines), both plant capital and operating cost per unit of throughput decrease. In certain industrial applications today, cells of even a thousand cubic meters in volume (a large swimming pool) are being used effectively.
The throughput capabilities of various cell designs will vary with the flotation machines 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 cells volume and flotation efficiency is generally calculated from data gathered on a laboratory scale flotation using the same type of equipment for the same material mixture in question. This procedure is then followed by the application of semi-empirically derived 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 material of the various cell manufacturers. Flotation plants are built in multiple cell configurations (called banks), and the flow through the various banks is adjusted in order to optimize plant recovery of the valuable as well as the grade of the total recovered mass from flotation. Up above is a typical flotation bank scheme. The total layout of a given flotation plant (including all of the various banks) operating on a given feed is called a flotation circuit.
The application of the air-lift to flotation is not new, but the first attempts to make use of the principle were not successful because the degree of agitation in the machine was insufficient to enable the heavy oils then in use as collecting reagents to function effectively. The advent of chemical promoters, however, made agitation of secondary and aeration of primary importance, with the result that the application of the air-lift principle became practicable and led to the introduction of the Forrester and the Hunt matless machines. South western Engineering Corporation are the owners in most countries of the rights to license and manufacture these and other types operating on the air-lift principle, and they have developed a machine based chiefly on the Welsh and Hunt patents which may be considered as representative of the type that is now most commonly used.
The Southwestern Air-Lift Machine, as it is called, consists of a V-shaped wood or steel trough of any length but of the standard cross-section shown in Fig. 40, the area of which is 9.85 sq. ft. and the interior depth 36 in. Low- pressure air is delivered from a blower through a main supply pipe to an air-pipe or header which runs longitudinally over the top of the machine. The air enters the trough itself through a seriesof vertical down-pipes , which are screwed into sockets welded tothe underside of the header at 4-in. intervals along its length and are open at their lower ends. They are from to 1 in. in diameter for roughing machines and from to in. for cleaners, and they reach to within 6 in. of the bottom. The air-lift chamber is formed by two vertical partitions, one on each side of the line of down-pipes, both of which extend from one end of the trough to the other, forming a compartment 6 in. wide. The lower edges of the partitions are an inch or two above the ends of the down-pipes and their upper edges are about level with the froth overflow lips at each side of the machine. A few inches above the top of the air-lift chamber is a deflector cap which serves to direct the rising pulp outwards and downwards against two vertical baffles. These extend the length of the trough parallel to and outside the partitions, their loweredges being several inches below the normal pulp level. The spacebetween the baffles and the sides of the machine forms two spitzkasten- shaped zones of quiet settlement where the froth collects.
The feed enters near the bottom of one end of machine and the tailing is discharged over an adjustable weir at the other end. The air, issuing in a continuous stream from the open ends of the down-pipes, carries the pulp up the central chamber on the principle of an air-lift pump. The air is subdivided into minute bubbles and more completely mixed with the pulp as the rising mass hits the cap at the top and is deflected and cascaded on to the baffles at each side, which direct it downwards, distributing the bubbles evenly throughout the pulp in the body of the machine and giving them ample opportunity to collect a coating of mineral. Rising under their own buoyancy, the bubbles enter the spitzkasten zones, up which they travel without interference, dropping most of the gangue particles mechanically entangled between them as they ascend. They collect on the surface of the pulp at the top as a mineralized froth, which is voluminous enough to pass over the lip into the concentrate launders without the need of scrapers. The pulp, on the other hand, continues its downward passage and enters the air-lift chamber again. In this way a continuous circulation of the pulp is maintained, its course through the machine being more or less in the form of a double spiral.
The aeration is generally controlled by a single valve in the header of each machine, but for selective flotation the machine is sometimes divided by transverse partitions into sections 4 ft. long, the header over each section being provided with a separate air-valve. The depth of the froth is regulated by means of the adjustable gate of the tailing weir. If difficulty is likely to be experienced in making a clean tailing with the normal amount of aeration, it is preferable to use two machines. The second one is run as a scavenger with an excess of air as compared with normal requirements, the low-grade froth so produced being pumped back to the head of the primary or roughing machine, in which the aeration is more normal in order that a comparatively clean concentrate may be produced. It is often possible to take a concentrate off the first few feet of the rougher rich enough to be sent to the filters as a finished product, the froth from the rest of the machine being pumped back to the head. When this method of flotation is adopted, it is an advantage to have the header divided into sections, each with its own valve, so that the aeration can be varied along the length of the machine. By increasing the volume of air at the discharge end the froth can be given a slight flow towards the head of the machine, with the result that the minerals are concentrated there to the exclusion of partially floatable gangue which might otherwise enter any bubbles not fully loaded with mineral.
If the froth from the feed end of the rougher is not of high enough grade, it must be re-treated in a separate cleaning machine, the length of which usually varies from one-quarter to one-half of the total length ofthe roughing and scavenging machines according to the amount of concentrate to be handled. Should still further cleaning be necessary, it is performed in a recleaner, which is generally of the same length as the cleaner. The tailings from these operations are often, but not necessarily, returned to the head of the rougher.
It is usual to prepare the pulp for flotation by adding the reagents to the grinding circuit or in a conditioning tank ahead of the flotation section, but soluble frothers such as pine oil and quick-acting promoters such as the xanthates can be added at the head of the machine if desired, since the air-lift provides enough agitation to emulsify and distribute them throughout the pulp. It is not as a rule advisable to introduce reagents into the air-lift chamber itself ; should it be necessary to do so to obtain a satisfactory recovery of the minerals, it is best to employ separate roughing and scavenging machines and to make the extra additions at the head of the scavenger.
Southwestern Air-Lift Machines are made of standard cross-section, as already stated, and in a series of lengths ranging, for ordinary purposes, from 4 to 48 ft. There is no limit to the possible length, however, and 100-ft. machines are in actual use. The tonnage capacities under different conditions will be found in Table 26. The pressure of air needed at the machine is from 1.6 to 1.7 lb. per square inch, which under normal conditions requires a pressure of about 2 lb. per square inch at the blower. It is usual to allow 75 to 100 cu. ft. of free air per minute at this pressure per foot of rougher and 45 to 70 cu. ft. per minute per foot of cleaner and recleaner. From these figures the approximate volume of air required for a machine or machines of any given length can be calculated. The power necessary to supply the air can then be found from Table 30.
The Callow Cell consists of a shallow horizontal trough, the bottom of which is covered with a porous medium, usually termed a blanket, consisting of a few layers of canvas or of a sheet of perforated rubber. Air is introduced at low pressure under the blanket, and, in passing through it, is split up into minute bubbles, which rise through the pulp in the cell, collecting a coating of mineral in the process.
Fig. 41 shows a section of the type of cell commonly employed. Its width is usually from 24 to 36 in., and its interior depth from 18 to 22 in. measured from the overflow lip ; the length varies according to requirements and is generally a multiple of the width. On the bottom are placed, side by side, the square open-topped cast-iron blanket frames or pans . The blanket covering the top of each pan is securely held in place by flat iron strips bolted round the edges, while one or two pipe grid-bars across the top prevent it from bulging. This arrangement allows a blanket to be changed in a few minutes should it becomedamaged. The air inlet to each pan projects through the bottom of the cell and is connected by a pipe and regulating valve to a header, which is provided with a main control valve.
The pulp enters one end of the cell through a feed opening and is discharged over an adjustable weir at the other end. There is no agitation, but the continuously rising stream of air bubbles keeps the particles of ore in suspension and induces a certain amount of circulation as the pulp passes along the cell. In this way the minerals are given many chances of becoming attached to the bubbles and thus of being carried over into the concentrate launder. The froth that forms on the surfaceof the pulp, usually to a depth of 8 to 10 inches, is voluminous enough to overflow the lips on each side of the cell without the use of mechanical scrapers.
For estimating purposes the average capacity of a Callow Cell may be taken as 2.5 tons of feed per square foot of blanket area per 24 hours and the air consumption as 9 cu. ft. of free air per minute per square foot of blanket at a pressure of 4 lb. per sq. in. A greater pressure is likely to be required if the blankets become blinded .
The Callow Cell has proved satisfactory for many types of ores, but it has the disadvantage that coarse or heavy sand settles on the blankets, and can only be kept in motion by flogging the latter with short rubber-buffered poles. Moreover, if lime is employed in the circuit, the blankets become impregnated and clogged with calcium carbonate, which necessitates periodical acid treatment for its removal. The use of perforated rubber sheets in place of canvas in the Callow Cell mitigates without entirely curing these difficulties, which at one time were thought to be inherent in the use of a porous medium. They have been overcome, however, by the development of the Callow-Maclntosh Machine.
The Callow-Maclntosh, or the Macintosh Machine, consists of a shallow trough or cell at the bottom of which is a hollow revolving rotor covered with a porous medium. Fig. 42 shows its construction. The pulp enters through a feed opening at one end, and is discharged at the other in much the same way as in a Callow Cell. The rotor, made of seamless steel tubing with a cast-steel ring welded in each end, is perforated with -in. holes at 7-in. centres; it is about 8 in. shorter than the length of the cell and is usually 9 in. in diameter. Its weight is taken by two hollow shafts, each fitted with a flange, which are bolted to the ends of the rotor by means of four studs. This method of attachment enables the rotor to be changed and a new one inserted with little loss of time, usually not more than 15 minutes. The shafts project through the ends of this cell and are supported on self-aligning ball and socket bearings outside, so placed that the rotor itself is a few inches clear of the bottom of the trough. A rubber gasket, shown in Fig. 43, seals the opening at each end by simple pressure on a cone-faced disc mounted on the shaft. The joint is not completely watertight and a slight leakage takes place through it at the rate of about one quart per minute. At the discharge end this escaping pulp gravitates to the tailing launder, while at the feed end it is usually led to one of the pumps returning a middling product to the roughing circuit. The gasket is preferable to a stuffing-box, as it contains no grease and requires no gland water.
The rotor covering consists of a canvas sock or of a single sheet of perforated rubber. The latter is now far more commonly employed, since it lasts five times as long as the other, its life generally exceeding 18 months ; moreover it seldom becomes blinded withcalcium carbonate, and requires an air pressure of only 2 lb. per square inch instead of the 3-lb. pressure needed for canvas. The rubber sheets are made of pure gum about 5/64 in. thick with 225 holes per sq. in., the holes being made so as to allow the air to pass through while preventing the percolation of the pulp into therotor in the event of a temporary shut-down. Two scraper bars of angle iron, 1 by 1 in., are bolted to opposite sides of the rotor on the top of the covering. They project 2 in. beyond the ends of the rotor, and their purpose is to keep in circulation any sand that settles on the bottom of the cell, at the same timeprotecting the porous medium from undue wear by contact withsuch material. Air is introduced into the rotor through one or bothof the hollow shafts, which are connected by special inlet joints with themain supply. When both ends are employed for the admission of air,the rotor is usually divided into two sections by a central partitionto enable each half to be controlled separately. The rotor is driven ata speed of about 15 r.p.m. by an individual motor connected with theshaft at one end of the cell; either a worm drive directly coupled to themotor or a chain drive coupled to the motor through a speed reducercan be employed.
The principle on which theCallow-Maclntosh Machine worksis very similar to that of a CallowCell. The air bubbles actuallyissue from the top of the rotor,where the hydraulic pressure islowest, and spread out as theyrise, their distribution throughthe pulp being quite as even andeffective as when a flat blanket isused. The cell never needs flogging since the movementof the rotor prevents sand fromsettling on it, and the scraperbars keep in circulation theheavy particles that would otherwise settle on the bottom. Themachine can, if necessary, handle ore as coarse as 20 mesh at a W/Sratio of 1/1 without choking.
The control of a pneumatic cell is different from that of a machine of the mechanically agitated type, of which each cell is capable of performing the function of a high-speed conditioner. Little conditioning takes place once the pulp has entered a pneumatic cell, and provision must therefore be made for its proper preparation when employing heavy oils or chemical reagents which need a long contact period. The froth is usually maintained at a depth of 8 to 10 in., giving an effective pulp depth of 18 to 20 in. The very large volume of air bubbles released enables flotation to be effected more rapidly than in any other type of machine, the actual time required depending mostly on the degree to which the minerals have been rendered floatable. The upward stream of bubbles is so voluminous that, under ordinary conditions, the froth overflows the lips on both sides of the cell without the need of scrapers. For the same reason a considerable quantity of gangue is often carried over into the concentrate launder by mechanical entanglement with the bubbles, and one, sometimes two, subsequent cleaning operations are generally necessary in consequence. This, however, is by no means therule ; a concentrate of high enough grade to be sent to the filtering section as a finished product can sometimes be made in a single rougher- cleaner cell. When the Callow-Macintosh Machine is run in this way (counter-current operation) a partitioned rotor is employed, since, by increasing the volume of air at the tailing-discharge end, the froth can be made to flow towards the head of the cell with the result that the minerals are concentrated there to the exclusion of gangue particles. The same effect can be obtained in a Callow Cell by regulating the admission of air to the individual pans in a similar way. If is often the practice, especially in counter-current operation, for the rougher to be followed by a scavenging cell, which is run with an excess of air as compared with the former, the froth being returned to the head of the first cell.
Callow-Macintosh Machines are made in lengths of 10, 15, and 20 ft. and in widths of 24, 30, and 36 in. with a rotor 9 in. in diameter. The vertical distance from the centre-line of the rotor to the overflow lip is about 24 in. The design of the machine, however, lends itself to the construction of larger sizes for big scale operationsi.e., up to a 30-ft. cell 48 in. wide with one or two 9-in. rotors. The 30- and 36-in. cells are sometimes fitted with rotors up to 15 in. in diameter to meet special requirements.
The capacity of the standard machine varies considerably according to the grade and character of the ore. The average capacity of a rougher or rougher-cleaner cell is from 8 to 12 tons of dry feed per foot of rotor length per 24 hours. When cleaning is practised, the tonnage per foot of total rotor length (roughers, scavengers, and cleaners) may vary from 4 tons for a slow-floating ore needing double cleaning to 10 tons for an easily-floated ore with single cleaning, the average being about 6 tons per foot of total rotor length. The cleaning section usually amounts to between one-quarter and one-half of the combined length of the roughing and scavenging cells. The width of cell employed depends on the character of the ore, the time of treatment, and the tonnage.
The quantity of air necessary varies from 5 to 7 cu. ft. per minute per square foot of aerating surface at 2- to 2-lb. pressurethat is, from 12 to 16.5 cu. ft. per minute per linear foot of rotor. With a Roots type blower the power consumption in respect of the air supply is about 12 h.p. per 1,000 cu. ft. of free air per minute at a pressure of 2 lb. per square inch. The power needed to turn the rotor averages 0.5 h.p.
column and contact cell flotation | sgs
Flotation columns work on the same basic principle as mechanical flotation cells mineral separation takes place in an agitated and/or aerated water mineral slurry where the surfaces of selected minerals are made hydrophobic (water-repellent) by conditioning with selective flotation reagents. However, in column flotation, there is no mechanical mechanism causing agitation.As well, separation takes place in a vessel (known as a column) that is much taller than the width (or cross-section) of the cell. Air is introduced into the slurry in the column through spargers, which create a countercurrent flow of air bubbles.
The contact cell is mainly used in rougher flotation circuits. It is compact, highly efficient, simple to operate, and has low energy and maintenance costs. There are a number of other benefits and capital savings that can be obtained when installing contact cells including:
SGS is the most experienced and trusted organization in the mineral processing industry. We have conducted flowsheet design and pilot plant testing on thousands of flotation projects. Let our experts improve your flotation performance with our proven column and contact cell technologies.
More ores are treated using froth flotation cells than by any other single machines or process. Non-metallics as well as metallics now being commercially recovered include gold, silver, copper, lead, zinc, iron, manganese, nickel, cobalt, molybdenum, graphite, phosphate, fluorspar, barite, feldspar and coal. Recent flotation research indicates that any two substances physically different, but associated, can be separated by flotation under proper conditions and with the correct machine and reagents. The DRflotation machine competes with Wemco and Outotec (post-outokumpu) flotation cells but are all similar is design. How do flotation cells and machinework for themineral processing industry will be better understood after you read on.
While many types of agitators and aerators will make a flotation froth and cause some separation, it is necessary to have flotation cells with the correct fundamental principles to attain high recoveries and produce a high grade concentrate. The Sub-A (Fahrenwald) Flotation Machines have continuously demonstrated their superiority through successful performance. The reliability and adaptations to all types of flotation problems account for the thousands of Sub-A Cells in plants treating many different materials in all parts of the world.
The design of Denver Sub-A flotation cells incorporates all of the basic principles and requirements of the art, in addition to those of the ideal flotation cell. Its design and construction are proved by universal acceptance and its supremacy is acknowledged by world-wide recognition and use.
1) Mixing and Aeration Zone:The pulp flows into the cell by gravity through the feed pipe, dropping directly on top of the rotating impeller below the stationary hood. As the pulp cascades over the impeller blades it is thrown outward and upward by the centrifugal force of the impeller. The space between the rotating blades of the impeller and the stationary hood permits part of the pulp to cascade over the impeller blades. This creates a positive suction through the ejector principle, drawing large and controlled quantities of air down the standpipe into the heart of the cell. This action thoroughly mixes the pulp and air, producing a live pulp thoroughly aerated with very small air bubbles. These exceedingly small, intimately diffused air bubbles support the largest number of mineral particles.
This thorough mixing of air, pulp and reagents accounts for the high metallurgical efficiency of the Sub-A (Fahrenwald) Flotation Machine, and its correct design, with precision manufacture, brings low horsepower and high capacity. Blowers are not needed, for sufficient air is introduced and controlled by the rotating impeller of the Denver Sub-A. In locating impeller below the stationary hood at the bottom of the cell, agitating and mixing is confined to this zone.
2) Separation Zone:In the central or separation zone the action is quite and cross currents are eliminated, thus preventing the dropping or knocking of the mineral load from the supporting air bubble, which is very important. In this zone, the mineral-laden air bubbles separate from the worthless gangue, and the middling product finds its way back into the agitation zone through the recirculation holes in the top of the stationary hood.
3) Concentrate Zone:In the concentrate or top zone, the material being enriched is partially separated by a baffle from the spitz or concentrate discharge side of the machine. The cell action at this point is very quiet and the mineral-laden concentrate moves forward and is quickly removed by the paddle shaft (note direct path of mineral). The final result is an unusually high grade concentrate, distinctive of the Sub-A Cell.
A flotation machine must not only float out the mineral value in a mixture of ground ore and water, but also must keep the pulp in circulation continuously from the feed end to the discharge end for the removal of the froth, and must give the maximum treatment positively to each particle.
It is an established fact that the mechanical method of circulating material is the most positive and economical, particularly where the impeller is below the pulp. A flotation machine must not only be able to circulate coarse material (encountered in every mill circuit), but also must recirculate and retreat the difficult middling products.
In the Denver Sub-A due to the distinctive gravity flow method of circulation, the rotating impeller thoroughly agitates and aerates the pulp and at the same time circulates this pulp upward in a straight line, removing the mineral froth and sending the remaining portion to the next cell in series. No short circuiting through the machine can thus occur, and this is most important, for the more treatments a particle gets, the greater the chances of its recovery. The gravity flow principle of circulation of Denver Sub-A Flotation Cell is clearly shown in the illustration below.
There are three distinctive advantages of theSub-A Fahrenwald Flotation Machines are found in no other machines. All of these advantages are needed to obtain successful flotation results, and these are:
Coarse Material Handled:Positive circulation from cell to cell is assured by the distinctive gravity flow principle of the Denver Sub-A. No short circuiting can occur. Even though the ore is ground fine to free the minerals, coarse materials occasionally gets into the circuit, and if the flotation machine does not have a positive gravity flow, choke-ups will occur.
In instances where successful metallurgy demands the handling of a dense pulp containing an unusually large amount of coarse material, a sand relief opening aids in the operation by removing from the lower part of the cell the coarser functions, directing these into the feed pipe and through the impeller of the flowing cell. The finer fraction pass over the weir overflow and thus receive a greater treatment time. In this manner short-circuiting is eliminated as the material which is bled through the sand relief opening again receives the positive action of the impeller and is subjected to the intense aeration and optimum flotation condition of each successive cell, floating out both fine and coarse mineral.
No Choke-Ups or Lost Time:A Sub-A flotation cell will not choke-up, even when material as coarse as is circulated, due to the feed and pulp always being on top of the impeller. After the shutdown it is not necessary to drain the machine. The stationary hood and the air standpipe during a shutdown protects the impeller from sanding-up and this keeps the feed and air pipes always open. Denver Sub-A flotation operators value its 24-hour per day service and its freedom from shutdowns.
This gravity flow principle of circulation has made possible the widespread phenomenal success of a flotation cell between the ball mill and classifier. The recovery of the mineral as coarse and as soon as possible in a high grade concentrate is now highly proclaimed and considered essential by all flotation operators.
Middlings Returned Without Pumps:Middling products can be returned by gravity from any cell to any other cell. This flexibility is possible without the aid of pumps or elevators. The pulp flows through a return feed pipe into any cell and falls directly on top of the impeller, assuring positive treatment and aeration of the middling product without impairing the action of the cell. The initial feed can also enter into the front or back of any cell through the return feed pipe.
Results : It is a positive fact that the application of these three exclusive Denver Sub-A advantages has increased profits from milling plants for many years by increasing recoveries, reducing reagent costs, making a higher grade concentrate, lowering tailings, increasing filter capacities, lowering moisture of filtered concentrate and giving the smelter a better product to handle.
Changes in mineralized ore bodies and in types of minerals quickly demonstrate the need of these distinctive and flexible Denver Sub-A advantages. They enable the treatment of either a fine or a coarse feed. The flowsheet can be changed so that any cell can be used as a rougher, cleaner, or recleaner cell, making a simplified flowsheet with the best extraction of mineral values.
The world-wide use of the Denver Sub-A (Fahrenwald) Flotation Machine and the constant repeat orders are the best testimonial of Denver Sub-A acceptance. There are now over 20,000 Denver Sub-A Cells in operation throughout the world.
There is no unit so rugged, nor so well built to meet the demands of the process, as the Denver Sub-A (Fahrenwald) Flotation Machine. The ruggedness of each cell is necessary to give long life and to meet the requirements of the process. Numerous competitive tests all over the world have conclusively proved the real worth of these cells to many mining operators who demand maximum result at the lower cost.
The location of the feed pipe and the stationary hood over the rotating impeller account for the simplicity of the Denver Sub-A cell construction. These parts eliminates swirling around the shaft and top of the impeller, reduce power load, and improve metallurgical results.
TheSub-A Operates in three zones: in bottom zone, impeller thoroughly mixes and aerates the pulp, the central zone separates the mineral laden particles from the worthless gangue, and in top zone the mineral laden concentrate high in grade, is quickly removed by the paddle of a Denver Sub-A Cell.
A Positive Cell Circulation is always present in theSub-A (Fahrenwald) Flotation Machine, the gravity flour method of circulating pulp is distinctive. There is no short circulating through the machine. Every Cell must give maximum treatment, as pulp falls on top of impeller and is aerated in each cell repeatedly. Note gravity flow from cell to cell.
Choke-Ups Are Eliminated in theSub-A Cell, even when material as coarse as is handled, due to the gravity flow principle of circulation. After shutdown it is not necessary to drain the machine, as the stationary hood protects impeller from sanding up. See illustration at left showing cell when shut down.
No Bowlers, noair under pressure is required as sufficient air is drawn down the standpipe. The expense and complication of blowers, air pipes and valves are thus eliminated. The standpipe is a vertical air to the heart of the Cell, the impeller. Blower air can be added if desired.
The Sub-A Flexibility allows it tobe used as a rougher, cleaner or recleaner. Rougher or middling product can be returned to the front or back of any cell by gravity without the use of pumps or elevators. Cells can be easily added when required. This flexibility is most important in operating flotation MILLS.
Pulp Level Is Controlled in each Sub-A Flotation Cell as it has an individual machine with its own pulp level control. Correct flotation requires this positive pulp level control to give best results in these Cells weir blocks are used, but handwheel controls can be furnished at a slight increase in cost. Note the weir control in each cell.
High Grade Concentrate caused by thequick removal of the mineral forth in the form of a concentrate increases the recovery. By having an adjustment paddle for each Sub-A Cell, quick removal of concentrate is assured, Note unit bearing housing for the impeller Shaft and Speed reducer drive which operates the paddle for each cell
Has Fewer Wearing Parts because Sub-A Cells are built for long, hard service, and parts subject to wear are easily replaced at low cost. Molded rubber wearing plates and impellers are light in weight give extra long life, and lower horsepower. These parts are made under exact Specifications and patented by Denver Equipment Co.
TheRugged Construction of theSub-A tank is made of heavy steel, and joints are welded both inside and out. The shaft assemblies are bolted to a heavy steel beam which is securely connected to the tank. Partition plates can be changed in the field for right or left hand machine. Right hand machine is standard.
The Minerals Separation or M.S. Sub-aeration cells, a section of which is shown in Fig. 32, consists essentially of a series of square cells with an impeller rotating on a vertical shaft in the bottom of each. In some machines the impeller is cruciform with the blades inclined at 45, the top being covered with a flat circular plate which is an integral part of the casting, but frequently an enclosed pump impeller is used with curved blades set at an angle of 45 and with a central intake on the underside ; both patterns are rotated so as to throw the pulp upwards. Two baffles are placed diagonally in each cell above the impeller to break up the swirl of the pulp and to confine the agitation to the lower zone. Sometimes the baffles are covered with a grid consisting of two or three layers each composed of narrow wood or iron strips spaced about an inch apart. The sides and bottom of the cells in the lower or agitation zone are protected from wear by liners, which are usually made of hard wood, but which can, if desired, consist of plates of cast-iron or hard rubber. The section directly under the impeller is covered with a circular cast-iron plate with a hole in the middle for the admission of pulp and air. The hole communicates with a horizontal transfer passage under the bottom liner, through which the pulp reaches the cell. Air is introduced into each cell through a pipe passing through the bottom and delivering its supply directly under the impeller. A low-pressure blower is provided with all machines except the smallest, of which the impeller speed is fast enough to draw in sufficient air by suction for normal requirements.
The pulp is fed to the first cell through a feed opening communicating with the transfer passage, along which it passes, until, at the far end, it is drawn up through the hole in the bottom liner by the suction of the impeller and is thrown outwards by its rotation into the lower zone. The square shape of the cell in conjunction with the baffles converts the swirl into a movement of intense agitation, which breaks up the air entering at the same time into a cloud of small bubbles, disseminating them through the pulp. The amount of aeration can be accurately regulated to suit the requirements of each cell by adjustment of the valve on its air pipe.
Contact between the bubbles and the mineral particles probably takes place chiefly in the lower zone. The pumping action of the impeller forces the aerated pulp continuously past the baffles into the upper and quieter part of the cell. Here the bubbles, loaded with mineral, rise more or less undisturbed, dropping out gangue particles mechanically entangled between them and catching on the way up a certain amount of mineral that has previously escaped contact. The recovery of the mineral in this way can be increased at the expense of the elimination of the gangue by increasing the amount of aeration. The froth collects at the top of the cell and is scraped by a revolving paddle over the lipat the side into the concentrate launder. The pulp, containing the gangue and any mineral particles not yet attached to bubbles, circulates to some extent through the zone of agitation, but eventually passes out through a slot situated at the back of the cell above the baffles and flows thence over the discharge weir. The height of the latter is regulated by strips of wood or iron and governs the level of the pulp in the cell. The discharge of each weir falls by gravity into the transfer passage under the next cell and is drawn up as before by the impeller. The pulp passes in this way through the whole machine until it is finally discharged as a tailing, the froth from each cell being drawn off into the appropriate concentrate launder.
No pipes are normally fitted for the transference of froth or other middling product back to the head of the machine or to any intermediate point. Should this be necessary, however, the material can be taken by gravity to the required cell through a pipe, which is bent at its lower end to pass under the bottom liner and project into the transfer passage, thus delivering its product into the stream of pulp that is being drawn up by the impeller
Particulars of the various sizes of M.S. Machines are given in Table 21. It should be noted that the size of a machine is usually defined by the diameter of its impeller ; for instance, the largest one would be described as a 24-inch machine.
The Sub-A Machine, invented by A. W. Fahrenwald and developed in many respects as an improvement in the Minerals Separation Machine, from which it differs considerably in detail, particularly in the method of aerating the pulp, although the principle of its action is essentially the same. Its construction can be seen from Figs. 33 and 34.
In common with the M.S. type of machine, it consists of a series of square cells fitted with rotating impellers. Each cell, however, is of unit construction, a complete machine being built up by mounting the required number of units on a common foundation and connecting up the pipes which transfer the pulp from one cell to the next. The cells are constructed of welded steel. The impeller, which can be rubber-lined,if required, carries six blades set upright on a circular dished disc, and is securely fixed to the lower end of the vertical driving shaft. It is covered with a stationary hood, to which are attached a stand-pipe, a feed pipe, and the middling return pipes. The underside of the hood is fitted with a renewable liner of rubber or cast-iron. The pulp, entering the first cell through the feed pipe and sometimes through the middling pipes, falls on to the impeller, the rotation of which throws it outwards into the bottom zone of agitation. The suction effect due to the rotationof the impeller draws enough air down the standpipe to supply the aeration necessary for normal operation. A portion of the pulp, cascading over the open tops of the impeller blades, entraps and breaks up the entrained air, the resulting spray-like mixture being then thrown out into the lower zone of agitation, where it is disseminated through the pulp as a cloud of fine bubbles. Should this amount of aeration be insufficient, air can be blown in under slight pressure through a hole near the top of the stand-pipe, in which case a rubber bonnet is fastenedto the lower bearing and clamped round the top of the stand-pipe so as to seal the supply from the atmosphere.
The bottom part of the cell is protected from wear by renewable cast-iron or rubber liners. Four vertical baffles, placed diagonally on the top of the hood, break up the swirl of the pulp and intensify theagitation in the lower zone. The pumping action of the impeller combined with the rising current of air bubbles carries the pulp to the quieter upper zone, where the bubbles, already coated with mineral, travel upwards, drop out many of the gangue particles which may have become entangled with them, and finally collect on the surface of the pulp as a mineralizedfroth. One side of the cell is sloped outwards so as to form, in conjunction with a vertical baffle, a spitzkasten-shaped zone of quiet settlement, where any remaining particles of gangue that have been caught and held between the bubbles are shaken out of the froth as it flows to the overflow lip at the front of the cell. The baffle prevents rising bubbles from entering the outer zone, thus enabling the gangue material released from the froth to drop down unhindered into the lower zone. A revolving paddle scrapes the froth past the overflow lip into the concentrate launder.
Should the machine be required to handle more than the normal volume of froth, it is built with a spitzkasten zone on both sides of the cell. For the flotation of ores containing very little mineral the spitzkasten is omitted so as to crowd the froth into the smallest possible space, the front of the cell being made vertical for the purpose.
Circulation of the pulp through the lower zone of agitation is maintained by means of extra holes at the base of the stand-pipe on a level with the middling return pipes. An adjustable weir provides for the discharge of the pulp to the next cell, which it enters through a feed-pipe as before. Below the weir on a level with the hood is a small sand holeand pipe through which coarse material can pass direct to the next cell without having to be forced up over the weir. The same process is repeated in each cell of the series, the froth being scraped over the lip of the machine, while the pulp passes from cell to cell until it is finally discharged as a tailing from the last one. The middling pipes make it an easy matter for froth from any section of the machine to be returned if necessary to any cell without the use of pumps.
Table 22 gives particulars of the sizes and power requirements of Denver Sub-A Machines and Table 23 is an approximate guide to their capacities under different conditions. The number of cells needed
Onemethod of driving the vertical impeller shafts of M.S. Subaeration or Denver Sub-A Machines is by quarter-twist belts from a horizontal lineshaft at the back of the machine, the lineshaft being driven in turn by a belt from a motor on the ground. This method is not very satisfactory according to modern standards, firstly, because the belts are liable to stretch and slip off, and, secondly, because adequate protection againstaccidents due to the belts breaking is difficult to provide without making the belts themselves inaccessible. A more satisfactory drive, with which most M.S. Machines are equipped, consists of a lineshaft over the top of the cells from which each impeller is driven through bevel gears. The lineshaft can be driven by a belt from a motor on the ground, by Tex- ropes from one mounted on the frame work of the machine, or by direct coupling to a slow-speed motor. This overhead gear drive needs careful adjustment and maintenance. Although it may run satisfactorily for years, trouble has been experienced at times, generally in plants where skilled mechanics have not been available. The demand for something more easily adjusted led to the development of a special form of Tex-rope drive which is shown in Fig. 35. Every impeller shaft is fitted at the top with a grooved pulley, which is driven by Tex-ropes from a vertical motor. This method is standard on Denver Sub-A Machines, and M.S. Machines are frequently equipped with it as well, but the former type are not made with the overhead gear drive except to special order.
The great advantage of mechanically agitated machines is that every cell can be regulated separately, and that reagents can be added when necessary at any one of them. Since, as a general rule, the most highly flocculated mineral will become attached to a bubble in preference to a less floatable particle, in normal operation the aeration in the first few cells of a machine should not be excessive ; theoretically there should be no more bubbles in the pulp than are needed to bring up the valuable minerals. By careful control of aeration it should be possible for the bulk of the minerals to be taken off the first few cells at the feed end of the machine in a concentrate rich enough to be easily cleaned, and sometimes of high enough grade to be sent straight to the filtering section as a finished product. The level of the pulp in these cells is usually kept comparatively low in order to provide a layer of froth deep enough to give entangled particles of gangue every chance of dropping out, but it must not be so low that the paddles are prevented from skimming off the whole of the top layer of rich mineral. Towards the end of the machine a scavenging action is necessary to make certain that the least possible amount of valuable mineral escapes in the tailing, for which purpose the gates of the discharge weirs are raised higher than at the feed end, and the amountof aeration may have to be increased. The froth from the scavenging cells is usually returned to the head of the machine, the middling pipes of the Denver Sub-A Machine being specially designed for such a purpose. The regulation of the cleaning cells is much the same as that of the first few cells of the primary or roughing machine, to the head of which the tailing from the last of the cleaning cells is usually returned.
A blower is sometimes required with the M.S. Subaeration Machine. Since each cell is fitted with an air pipe and valve, accurate regulation of aeration is a simple matter. The Denver Sub-A, Kraut, and Fagergren Machines, however, are run without blowers, enough air being drawn into the machines by suction.
In the Geco New-Cell Flotation Cellthe pneumatic principle is utilized in conjunction with an agitating device. The machine, which is illustrated in Fig. 44, consists of a trough or cell made of steel or wood, whichever is more convenient, through the bottom of which projects a series of air pipes fitted with circular mats of perforated rubber. The method of securing the mat to the air pipe can be seen from Fig. 45. Over each mat rotates a moulded rubber disc of slightlylarger diameter at a peripheral speed of 2,500 ft. per minute. It is mounted on a driving spindle as shown in Fig. 46.
Each spindle is supported and aligned by ball-bearings contained in a single dust- and dirt-proof casting, and each pair is driven from a vertical motor through Tex-ropes and grooved pulleys, a rigid steel structure supporting the whole series of spindles with their driving mechanism. The machine can be supplied, if required, however, with a quarter-twist drive from a lineshaft over flat pulleys.
The air inlet pipes are connected to a main through a valve by which the amount of air admitted to each mat can be accurately controlled. The air is supplied by a low-pressure blower working at about 2 lb. per square inch. It enters the cell through the perforations in the rubber mat and is split up into a stream of minute bubbles, which are distributed evenly throughout the pulp by the action of the revolving disc. By this means a large volume of finely-dispersed air is introduced withoutexcessive agitation. There is sufficient agitation, however, to produce a proper circulation in the cell, but not enough to cause any tendency to surge or to disturb the froth on the surface of the pulp. All swirling movement is checked by the liner-baffles with which the sides of the cell are lined ; their construction can be seen in Fig. 44. They are constructed of white cast iron and are designed to last the life of the machine, the absence of violent agitation making this possible.The pulp must be properly conditioned before entering the machine. It is admitted through a feed box at one end at a point above the first disc, and passes along the length of the cell to the discharge weir without being made to pass over intermediate weirs between the discs. The height of the weir at the discharge end thus controls the level of the pulp in the machine. The froth that forms on the surface overflows the froth lip in a continuous stream without the aid of scrapers, its depth being controlled at any point by means of adjustable lip strips combined with regulation of the air.The Geco New-Cell is made in four sizesviz., 18-, 24-, 36-, and 48-in. machines, the figure representing the length of the side of the squarecell. Particulars of the three smallest sizes are given in Table 27. Figures are not available for the largest size.
Stawell gold mine in co-operation with Outotec Services completed a flotation circuit upgrade on time and on budget last year that, instead of the projected 3.5% improvement, resulted in an increase of 4.5% since the project was completed. Payback was also impressive, occurring within less than four months.
Flotation has been at the heart of the mineral processing industry for over 100 years, addressing the sulphide problem of the early 1900s, and continues to provide one of the most important tools in mineral separation today. The realisation of the effect of a minerals hydrophobicity on flotation all those years ago has allowed us to treat oxides, sulphides and carbonates, coals and industrial minerals economically, and will continue to do so in the future.
There have been a number of important changes in the industry over the years as flotation technology and equipment have advanced. Xstrata Technology considers the most noticeable has been the increase in sizes of the flotation machines, from the multiple small square cells that were initially used, to the 300 m round cells used today that are the norm in large scale plants.
Other changes have been more subtle, but equally as important. One of these has been the design of the flotation circuit to make the most of the liberation and surface chemistry effects of the minerals. In a lot of these situations it is not a matter of bigger is better, that will make the process work, but being smarter in the application of flotation technology.
Xstrata Technology is one company that believes the smarter use of flotation machines can deliver big improvements in plant performance. Through its use of the naturally aspirated Jameson Cell, Xstrata Technology has been making inroads into the processing of more complex ores. Having a small footprint, and using the high intensity mixing environment of slurry and naturally induced air in a simple downcomer, the Jameson Cell provides an ideal environment for the separation of hydrophobic particles and gangue, it says. The small footprint of the cells also makes them ideal to retrofit into a circuit especially where space is tight.
While the cell has been included in some flotation applications as the only flotation technology such as coal and SX-EW, the main applications in base metals have seen the cell operating in conjunction with conventional cells. The combination of the two technologies enables the Jameson Cell to target the quicker floating material, while the conventional cells target the slower floating material. Such a combination provides a superior overall grade recovery response for the whole circuit, than just one technology type on its own, Xstrata Technology says. Below are some of the duties for which the Jameson Cell can be used.
Jameson Cells in a scalping operation target fast floating liberated minerals, and produce a final grade concentrate from them. The wash water added to the Jameson Cell assists in obtaining the required concentrate grade due to washing out the entrained gangue. Scalping can be done at the head of the cleaner (also known as pre cleaning), or at the head of the rougher (also known as pre roughing), and minimises the downstream flotation capacity using conventional cells needed to recover the slower floating minerals.
Sometimes deleterious elements found in the orebody are naturally highly hydrophobic, and need to be removed at the start of flotation, otherwise they will report with the valuable minerals to the concentrate and effect concentrate grade. Mineral species such as talc, carbon and carbon associated minerals, such as carbonaceous pyrite, can all be difficult to depress in a flotation circuit. On the other hand, floating them off in a prefloat circuit before the rougher is an easier way to handle them. Jameson Cells acting as a prefloat cell at the head of a rougher circuit, or treating the hydrophobic gangue as a prefloat rougher cleaner, is an ideal way to produce a throw away product before flotation of the valuable minerals, minimising reagent use and circulating loads.
Jameson Cells can be used in cleaning circuits to produce consistent final grade concentrates. The ability of the cell to keep a constant pulp level, even with up stream disturbances or loss of feed, enables a constant grade to be obtained.
Xstrata Technology concludes: Importantly in a lot of these circuits, it is not the selection of one type of technology that produces therequired grade and recovery, but the selection of several technologies to get the best results. The interaction of slow floating and fast floating minerals, entrainment, hydrophobic gangue and a myriad of other variables make it rare for just one type of technology to prevail, but the combination of different flotation machines can achieve the required outcome more efficiently, as well as make the circuit robust enough to handle variations in feed quality.
Clariant Mining Solutions service engineers develop custom formulated reagents for each ore to be processed, while collectors and frothers are carefully selected for mutual compatibility. Clariant is investing considerably in mining chemicals and in support services for its customers all over the world.
The Jameson Cell has benefitted from over 20 years of continuous development. Early this year, the 300th cell was sold into Capcoals Lake Lindsay coal operation in the Bowen Basin of Australia. Around this time there were a number of coal projects taking in new Jameson Cells, including expansion projects for Wesfarmers Curragh and Gloucester Coals Stratford operations (both in Australia), Riversdales Benga project in Mozambique and Energy Resources Ukhaa Khudag coking coal project in Mongolia.
Le Huynh, Jameson Cell Manager, said the interest for coal preparation plants has remained strong, where operators needed dependable and reliable technology to treat fine coal, an important source of revenue. During 2010, the Jameson Cell business also found success in other applications, including recovering organic from a copper raffinate stream at Xstrata-Anglo Americans Collahuasi copper SX-EW plant in Chile.
Le said the consistent generation of very fine bubbles and the high intensity mixing in the Jameson Cell, was ideal for recovering very low concentrations of organic from raffinate streams, typically less than several hundred ppm. High throughput in a small footprint, simple operation and extremely low maintenance due to no moving parts in the cell are distinct advantages in this application.
The cell is designed with features specific to suit such hydrometallurgy applications including specialist materials, a flat-bottomed flotation tank with integrated pump box and tailings recycle system, and large downcomers. The Collahuasi cell was the first of its type in Chile, though there are many other large cells installed in SX-EW plants in Mexico, USA and Australia to treat both raffinate and electrolyte streams.
Dominic Fragomeni, Manager Process Mineralogy, Xstrata Process Support (XPS), notes that accurate, rapid development of a milling and flotation flowsheet for a new orebody is key to successful mine development. Time honoured conventional practice has typically favoured the extraction of a bulk sample of up to several hundred tonnes for conventional pilot plant campaigns which could operate at several hundred kilograms per hour. Where sample extraction is limited, much reliance has been placed on locked cycle tests alone to produce design basis criteria. These approaches can be lengthy, expensive, carry scale up risk, and have seen a wide range of successes and failures at commissioning and during life of a mine.
XPS has miniaturised the pilot plant process. At the same time, it has improved the representativeness of results from the pilot plant campaign by using exploration drill core to formulate the pilot plant sample. This Flotation Mini Pilot Plant (MPP) was developed in collaboration with Eriez subsidiary Canadian Processing Technologies (CPT) and operates in fully continuous mode either around the clock or can be made to demonstrate unit operations on a shift basis. The feed samples are in the range of 0.5-5 t and can consist of exploration NQ drill core which improves the sample representativeness. The MPP operates in the range of 7-20 kg/h, an order of magnitude lower in sample mass and typically at a lower cost when compared to conventional pilot plants.
XPS has developed and validated a representative sampling strategy, an appropriate quality control model for metallurgical results and has accurately demonstrated operations results using Raglan and Strathcona ores and flowsheets. These validation campaigns, in scale down mode from the full scale plants, have produced actual mill recoveries to within 0.5% at the same concentrate grade with internal material balance consistent with the
When designing a plant to recover copper, Scott Kay, Process Engineer with METS suggests (in METS Gazette, issue 32, October 2011) it would be prudent to perform some mineralogical analysis test work such as QEMSCAN (Quantitative Evaluation of Mineral by Scanning electron microscopy) to provide some knowledge on the proportion of sulphide and oxide minerals present, the grain sizes of each mineral and a suggested grind size before jumping into the bulk of the beneficiation test work.
Ideally, the characteristics of the copper bearing minerals should suggest an appropriate grinding circuit P80 of between 100 and 200 m (0.1 and 0.2 mm), which can be controlled by cyclones, or in some cases fine screens.
The Delkor BQR flotation machine (formally Bateman BQR) here at Messina Mowana Copper mine in Botswana. 15 x 50BQR and 16 x 200BQR flotation cells for Copper roughing, cleaning & re-cleaning. Oxide / Sulphide
Flotation reagent selection is paramount and test work is necessary to ensure the optimum reagent suite is utilised. If the ore contains a low amount of iron sulphides, xanthate collectors are often suitable to float copper sulphideminerals. If native gold is present, dithiophosphates can be used which are less selective to iron sulphides. Increasing and controlling the pH within the flotation vessel to between 10 and 12 causes the process to become more selective, away from iron sulphide gangue minerals such as pyrite to produce a cleaner copper mineral concentrate. Depending on the ore mineralogy, activators and depressants may be required to achieve the optimum reagent suite.
Recovery of copper oxide minerals can be achieved with flotation by sulphidising the ore. In essence, this creates a thin layer of copper sulphide (chalcocite) on the oxide grains which can then be activated and collected in the froth. When employed, this occurs after the sulphide flotation stage, however, this is not commonly used as other beneficiation processes, such as leaching and SX-EW are often more cost effective for copper oxide minerals.
A common flotation circuit usually includes a rougher/scavenger and a cleaner stage. As most copper orebodies exhibit an in-situ grade of less than 1% Cu, the mass pull to the rougher froth is often low. This means that the throughput of the cleaner stage is significantly less than the throughput of the rougher stage which imparts a relatively low capital and operating cost to the flotation circuit.
To counteract the possible absence of a scavenger stage, a slightly higher mass pull to the rougher froth is targeted (although still low overall) to increase overall copper recovery. The rougher froth can then be reground to increase the liberation of the copper sulphides from the iron sulphides before being fed to the cleaner flotation vessels. This results in a significant upgrade in copper in the cleaner froth whilst still achieving a high copper recovery. The final flotation concentrate usually contains between 25 and 40% Cu.
Alain Kabemba, Flotation Process Specialist at Delkor notes the major trend to treating lower-grade and more finely disseminated ores and lately the re-treatment of tailings. He also points to the broad applicability of size to below 10 m.
Real systems do not fulfil ideal conditions, mainly because of feed variation or disturbances. Before considering disturbances to flotation specifically, Kabemba says it is important to emphasise the interlock between grinding and flotation, not only with respect to particle size effects, but equally to flotation feed rate variations. The grinding circuit is usually designed to produce the optimum size distribution established in testing and given in the design criteria. When the product size alters from this optimum, control requires either changing feed tonnage to the circuit or changing product volume, with either causing changes in flotation feed rates.
While grindability changes due to the variation in ore properties are disturbances to the grinding circuit, they generate feed rate changes as disturbances to the flotation circuit. The variations in ore properties which affect flotation from those assumed in the design criteria must therefore necessarily include grindability changes.
This reflects important differences in flotation machine characteristics between the two processes. Grinding circuits are built and designed with fixed total mill volumes and energy input, so the grinding intensity is not a controllable variable, instead grinding retention time is changed by variation of feed rates. In contrast, the flotation circuit is provided both with adjustable froth and pulp volume for variation of flotation intensity by aeration rate or hydrodynamic adjustment. Reagent levels and dosages provide a further means for intensity control.
One recent trend has been towards larger, metallurgical efficient and more cost effective machines. These depart from the simpler tank/mechanism combination towards design which segregates and directs flow and towards providing an external air supply for types which had been self aerating and towards the application of hydrodynamic principles to cell design, like the Delkor BQR range of flotation machines, initially the Bateman BQR Float Cells.
Bateman has steadily developed the BQR flotation cells which have been in application for the past 30 years, and with its acquisition of Delkor in 2008, decided to rebrand the equipment into the Delkor equipment range. Kabemba explains that BQR cell capacities range from 0.5 to 150 m3 currently installed, and can be used in any application as roughers, scavengers and in cleaning and re-cleaning circuits.
Provide good contact between solid particles and air bubbles
Maintain a stable froth/pulp interface
Adequately suspend the solid particles in the slurry
Provide sufficient froth removal capacity
Provide adequate retention time to allow the desired recovery of valuable constituent.
Highest possible effective volume and reduced the froth travel distance
Improved metallurgical performances in terms of grade recovery and reduced capital and operating costs based on reduced fabrication material and ease of maintenance
Kabemba says there are not many differences in terms of design between BQR Flotation cells; however, from the BQR1000 upwards, the flotation cells have internal launders to maintain the design objectives and benefits highlighted.
Operating variables, such as impeller speed, air rate, pulp and froth depths have to be adjustable over a sufficient range to provide optimum results with a given ore, grind and chemical treatment, but adjustment should not extend beyond the hydrodynamic regime in which good flotation is possible.
The largest current BQR flotation machine is shown in the table. In the near future the BQR2000 (200 m3) and BQR3000 (300 m3) will be available to the market. Kabemba also explained that circular cells reduce the amount of dead volume when compared to square cells. This enables a much higher effective pulp volume, hence increasing the effective energy input into the flotation cell. In addition tank type cells offer enhanced froth removal due to the uniform shape of the circular launders. He concluded that fully automated flotation cells are becoming more and more common with the aid of smart control and advances in software in the marketplace.
FLSmidths flotation team notes that fundamental flotation models suggest that a relationship exists between fine particle recovery and turbulent dissipation energy1. Conversely, increased turbulence in the rotorstator region is theoretically related to higher detachment rates of the coarser size range2. Conceptually, the suggested modes of recovery for the extreme size distribution regions appear to be diametrically opposed.
Industrial applications have previously confirmed that imparting greater power to flotation slurries yields significant improvements in fine particle recovery. However, recovery of the coarser size class favours an opposing approach, the FLSmidthteam believe. An improvement in the kinetics of the fine and coarse size classes, provided there is no adverse metallurgical influence on the intermediate size ranges, is obviously beneficial to the overall recovery response. Managing the local energy dissipation, and hence the power imparted to the slurry, offers the benefit of targeting the particle size ranges exhibiting slower kinetics.
New concept, Hybrid Energy FlotationTM (HEFTM),was recently introduced by FLSmidth. In principle it decouples regimes where fine and coarse particles are preferentially floated. HEF includes three sections:
This subject will be expanded upon at the 5th International Flotation Conference (Flotation 11) in Cape Town, South Africa. The fundamental parameters that influence fine and coarse particle recovery will be reviewed. The potential dual recovery benefit is then presented in terms of its practical implementation in a scavenging application. HEF is proposed as the preferred methodology of recovering these slow-floating size ranges; a method that opposes the traditional approach of residence time compensation.
StackCell offers column-like performance in a substantially smaller footprint than conventional cells. These compact, stackable units provide considerable savings for new installations and are ideal for expanding capacity in an existing plant
Eriez Flotation Group introduced the StackCell flotation concept in 2009. This innovative technology recovers fine particles more efficiently than mechanical flotation cells. Weve taken the inherent advantages of mechanical flotation and adapted them to a new design that is significantly smaller and requires less energy, explained Eriez Vice President Mike Mankosa. We focused on reducing the retention time and energy consumption by implementing a completely different approach to the flotation process. This new approach provides all the performance advantages of column flotation while greatly reducing capital, installation and operation costs.
At the core of the StackCell technology is a proprietary feed aeration system that concentrates the energy used to generate bubbles and provides bubble/particle contacting in a relatively small volume. An impeller in the aeration chamber located in the centre of the cell shears the air into extremely fine bubbles in the presence of feed slurry, thereby promoting bubble/particle contact. Unlike conventional, mechanically agitated flotation cells, the energy imparted to the slurry is used solely to generate bubbles rather than to maintain particles in suspension. This leads to reduced mixing in the cell and shorter residence time requirements.
The StackCell sparging system operates with low pressure, energy efficient blowers that decrease power consumption by 50% compared to air compressors or multi-stage blowers used in other flotation devices.
The low-profile StackCell design features an adjustable water system for froth washing and also takes advantage of a cell-to-cell configuration to minimise short-circuiting and improve recovery rates. Space requirements for the StackCell design are approximately half of equivalent column circuits, with corresponding reductions in weight leading to reductions in installation costs. Units can be shipped fully assembled and lifted into place without the need for field fabrication.
This technology can provide recoveries and product qualities comparable to column flotation systems while using a low profile design. Not intended to replace the need forcolumn flotation, it does provide an alternative method to column-like performance where space and/or capital is limited. The small size and low weight of the new StackCell makes possible lower cost upgrades where a single cell or series of cells may be placed into a currently overloaded flotation circuit with minimal retrofit costs.
Steve Flatman, General Manager of Maelgwyn Mineral Services (MMS) also comments on the trend of moving towards a finer grind to improve mineral liberation. Unfortunately conventional tank flotation cells are relatively inefficient in recovering these metal fines below 30 m and very inefficient at the ultra fine grind sizes below 15 m. The incorporation of regrind mills on rougher concentrates has further exacerbated this problem. To date the conventional flotation tank cell manufacturers have attempted to counter this fall off in recovery of fine particles by inputting increasing amounts of energy (bigger agitation motors) into the system to improve bubble particle contact. Unfortunately this tends to compromise coarse particle recovery.
He says the solution is MMSs Imhoflot pneumatic flotation technology and specifically the Imhoflot G-Cell. Recent pilot plant test work at a nickel operation with a three stage Imhoflot G-Cell pilot plant enabled an additional 30% nickel to be recovered from the conventional flotation tank cell final plant tails. The recovery was predominantly associated with the minus-11 m fraction indicating that this improved recovery was not just related to additional residence time. The above results are in line with an earlier pilot plant trial using G-Cells on a zinc operation where an additional 10-20% zinc was recovered from cleaner tailings this time being associated with minus 7 m material.
It is postulated that the above improvements are related to the order of magnitude increase in terms of air rate (m/min/m pulp)for the G-Cells due to their principle of operation where forced bubble particle contact takes place in the aeration chamber rather than the cell itself with the cell merely acting as a froth separation chamber. Typically in percentage terms the G-Cell air rates are five to ten times that of conventional flotation although the overall or total air usage is approximately half.
When this additional targeted energy input is combined with the centrifugal action of the GCell and small bubbles benefits are obtained in both the flotation rate (kinetics) and overall recovery. The improved kinetics results in a much lower residence time than conventional flotation facilitating a double benefit of both reduced footprint and improved recovery.
Metso notes a main drawback of column cells being low recovery performance, typically resulting in bigger circulating loads. Its CISA sparger is derived from the patented MicrocelTM technology and enhances metallurgical performance by allowing flexibility on the graderecovery curve. Metso Cisa says the main advantages of its column technology include:
At the bottom of the column, the sparger system raises mineral recovery by increased carrying capacity due to finer bubble sizes. This maximises the bubble surface area flux which is a standard parameter in evaluating flotation device performance. It also provides maximum particle-bubble contacts within the static mixers and effective reagent activation from the mechanical operation of the pump.
It is well known that coarse particles behave poorly in a conventional flotation cell and were previously regarded as non-floatable. However, recent laboratory work demonstrates that Fluidised Bed Froth (FBF) flotation extends the upper size limit of flotation recovery by a factor of 2-3 resulting in significant concentrator performance benefits. AMIRAs P1047 project, Improved Coarse Particle Recovery by FBF Flotation, is expected to commence in 2012, and will be structured in two phases.
Early rejection of gangue with minimum mineral loss. Potential for significant increase in concentrator throughput or significant improvement in capital efficiency
Reduced energy consumption. Independent modelling predicts that if particles of 1 mm can be floated, comminution energy consumption will be lowered by at least 20%.
Better management of water requirement. FBF cells can take product straight from the milling circuit without dilution, and the feed to the FBF cell could be up to 80% w/w solids, which could lead to significant savings in process water demand.
Improve recovery of metallic and other dense minerals. In a continuous FBF Cell, dense mineral particles will tend to sink to the bottom and accumulate in the cell, thus they can be recovered in a concentrated form by emptying the cell periodically. This could be a significant benefit where the concentration of the heavy metallic material is too low to warrant a separate treatment plant to recover them.
In Australia, Northgate Minerals Stawell gold mine recently completed a project through which it aimed to increase recoveries by 3.5% by upgrading the flotation plant. This upgrade was implemented after Stawell changed its production profile to process lower grade ore at higher throughput rates.
Instead of the projected 3.5% improvement, the upgrade from Outotec Services has resulted in an increase of 4.5% since the project was completed on time and on budget last year, despite the wettest seasonal weather in recorded history. Payback was also impressive, occurring within less than four months. The projected payback was 5.5 months, so it was a pleasant surprise when it happened so soon explains Jodie Hendy, senior metallurgist at Stawell.
The project has also achieved payback in less than four months and has delivered further ongoing benefits, including easier operation and reduced maintenance costs, says Outotec Services, which worked in close partnership with Stawell Gold to ensure the site remained fully operational during
The mine, which has produced more than 2 Moz in its 26-year history, previously employed a flotation circuit consisting of a bank of eight mechanical trough cells in the rougher circuit, followed by two banks of 2 x OK3 Outotec cells as cleaners. The feed rate to the cells was between 90-105 t/h, at 50-55% solids. The overall flotation circuit was not performing at optimal rate due to entrainment problems in the rougher cells when feed density increased from 45% to 55% solids, typically at 105 t/h.
In anticipation of future production levels and as part of Stawells focus on operational excellence, it was decided to upgrade the flotation circuit. Following a site audit from Outotec Services, a 2 x TankCell -20 configuration equipped with larger TankCell -30 mechanisms was proposed to help optimise flotation. The larger mechanisms would allow operation at very high percent solids (50% and over).
The TankCell design also allows a much deeper froth depth and better concentrate grade through optimised launder lip length and surface area. These cells known for great performance, ease of operation and reduced power and air consumption. Outotec Services was commissioned to handle the complete turnkey solution of the new rougher circuit, including design, supply, installation and commissioning.
The schedule was demanding but achievable, in just 30 weeks. It was decided to adopt the partnering approach between Stawell and Outotec Services, because this collaborative method ensured open communication, with all parties having greater ownership of the project and its aims. This close teamwork resulted in meticulous planning and site remaining fully operational at all times. Pipework and electrical easement ducts, for example, were rerouted early in the project. Tie-in points for new cells and rerouting of pipework were also planned upfront in the project and all disruptive work was completed during shutdowns.
The project overcame a number of challenges, including an extremely limited footprint, which was adjacent to a gabion wall, close to the runof-mine pad and also close to a reagents shed, which could not be moved. Additionally, existing process requirements at Stawell required specific elevations for the new TankCells. Structural stability was the main issue when designing the tank support structure due to the height of the tanks and the limited footprint. Sufficient stiffness was required such that the operation frequencies of the TankCells would not interfere with the natural frequency of the tank support structure. Through FE modelling of the structure, section sizes and bracing orientations were optimised to produce the required stiffness.
Despite the challenges, the turnkey installation of the new rougher circuit, along with blowers for the complete flotation circuit, was completed within deadlines. Because all tie-in points had been already carefully planned upfront, commissioning was a seamless exercise.
Designed to cope with projected increases in production and considerably more operator friendly than its predecessor, the new TankCell 20 cells have quickly proved their worth at site. The air demand for the old rougher cells, for example, was estimated at over 3,000 Am3/h, whereas the estimated air demand on the Outotec TankCells is a maximum of 992 Am3/h.
The Outotec FloatForce rotor-stator mechanism, with its unique design, delivers enhanced flotation cell hydrodynamics and improved wear life and maintenance. Maintenance on the Outotec TankCells has also been minimal since the upgrade, Hendy commented. Basically we check the cells during shutdowns but there has been no maintenance required in the nine months since commissioning. The TankCells have really delivered on their reputation. Basically, they do exactly what they are supposed to do.
Turning to flotation reagents, Frank Cappuccitti, President of Flottec explains that Flottec and Cidra are working very hard jointly on developing instruments that will measure hydrodynamics in the flotation cell and circuit in a bid for better flotation control. This would be a great step forward in using a combination of reagents and sensors to optimise flotation systems. It brings together the knowledge we have developed in both how reagents effect hydrodynamics and measuring the hydrodynamics to maintain optimum conditions. He explains that back in the 1990s, when he worked at a well-known mining chemicals supplier, we spent most of our research on trying to find the best collectors. The thinking was that we could try to develop collectors with absolute specificity. In other words, we could develop a collector that would float only specific minerals and provide clients with an almost perfect flotation separation. This was our approach to flotation optimisation. Unfortunately, we discovered that there was no such thing as absolute specificity. In fact, we had trouble measuring any improvements in the circuits because they were multi-variant and highly complex. Every change made was always a trade off between grade, recovery and cost. Changing one thing in the circuit seemed to improve something but always got a negative response in some other variable. It was also very hard to measure the performance of the flotation circuit because the only real parameters you could measure on line were concentrate grades and tails of the circuits, which were always after the fact. There was little ability and understanding about what real time measurements we could take other than air rates, cell levels and flow rates. So even if we got an improvement or a response to a change, we never knew if that was a response to a change or a natural variation in the system. Every test needed long term statistical trials to get some confidence in any real change.
So, I wrote a paper in the 1990s that basically said that until we could measure the real time variables in a flotation system and learned to really understand and control the system, we were limited in our ability to work on continuous improvement in reagent optimisation. We needed new sensors that could measure the performance of the flotation circuit so we could learn to control it. Once we got this, then we could actually measure improvements and use this to develop reagents.
Fortunately, with the advent of strong computing power and software, we have moved forward tremendously in the last decade in understanding the flotation circuit. Froth cameras that tried to measure froth grade and velocity were one of the first new sensors developed to assist in optimising circuits. Through the work of universities such as McGill and organisations like JKtech, new sensors have been developed that could actually measure reliably and in real time the hydrodynamic parameters in the flotation cell. Flotation cell hydrodynamics (gas dispersion parameters) is critical to the performance of the cell. When we talk about these parameters, we are talking about measuring what is happening in a flotation cell. Flotation is really about making bubbles and using the surface area of the bubble to do the work of transporting hydrophobic minerals to the froth. In flotation cells, we add air, create bubbles of a certain size and speed that provide the surface area to do the flotation. The more bubbles and the smaller the bubble, the more surface area we have to do the work. This surface area we create is known as the surface bubble flux (Sb) and controls the kinetics of flotation. Now that we have instruments that can measure the air into a cell (known as Jg), measure the size of the bubble diameter (Db) and the gas hold up (Eg), we can figure out how the relationship between these parameters and how they affect the Sb and flotation circuit performance. We can also now do research on how reagents can be used to control these parameters as well.
Research of the last few years has shown that frothers actually play a much more important role in flotation hydrodynamics than once thought. Frothers perform two major functions. They create and maintain small bubbles in the pulp to transport the minerals and they create the froth on top of the cell to hold the minerals until they can be recovered. The froth is created because frothers allow a film of water to form on the bubbles which makes them stable enough not to break when they reach the surface of the cell. Fortunately, the water drains over a short period of time and the froth will eventually break down. Froth breakdown is essential for cleaning and transporting the concentrates. Small bubbles are essential in making flotation efficient. For the same volume of air in a cell, smaller bubbles give much higher surface area, which in turn gives much higher kinetics.
We now know that as you increase the concentration of frothers to the cell, the bubble size gets smaller, and the film of water on the bubble gets bigger. But bubble size does not keep getting smaller forever. The frother will reduce the bubble down to a certain size, which is about the same for all frothers in the same set of conditions. The concentration of frother where the bubble is at a minimum is known as the critical coalescence concentration or CCC.
Each frother has a different CCC. Each frother also has a different ability to add water to the bubble and hence provides different froth stability. This also changes with concentration. We have learned in the last few years that each frother has a hydrodynamic curve which relates the bubble size with the froth stability. Strong frothers give very high froth stability at the CCC, while weak frothers give very low stability of the froth at the CCC.
This new understanding of how frothers affect flotation cell hydrodynamics has lead to new methodologies to optimise flotation circuits. Flottec has worked on an optimisation system where a frother is added to a circuit at the CCC (which guarantees maximum kinetics or maximum Sb) and the performance is measured. Then frothers of different strength are added (always at the CCC) until the right strength for maximum performance is determined. Adding the frother at the CCC is the critical optimisation difference. By doing this you are always guaranteed to have maximum kinetics. If the frother used is too strong, the dosage will have to be cut back below the CCC or the froth will be too persistent. This lowers flotation kinetics. If the frother is too weak, too much has to be added to get the froth strength and this increases cost and likely reduces recovery. Flottec has been conducting research withMcGill University to develop the hydrodynamic curves and CCC for all families of frothers in order to implement the new methodology of frother optimisation in plants.
The next step in this research is to be able to use new sensor technology to measure and control the flotation system by controlling the hydrodynamics in the cell. With our current knowledge of how air rate, cell levels, and frother addition affect bubble size, water recovery and gas hold up, we can use these control variables to maintain the optimum hydrodynamics in the cell resulting in the optimum flotation circuit performance. Flottec is working with companies like Cidra to develop new sensors that can provide real time information on cell hydrodynamics (gas dispersion parameters) and on froth stability properties in order for us to optimise the reagents and operating strategies used in a plant. This will bring flotation performance to the next level.
Clariant Mining Solutions business is investing considerably in mining chemicals. It has opened a new laboratory at its US headquarters in Houston, Texas, dedicated to the development and optimisation of chemical solutions for North American customers. The laboratory is part of a planned multi-million dollar investment into Clariants global Mining Solutions business, which includes establishing several new Mining Solutions laboratories around the world. This network is intended to enable the business to better support customer needs and address regional challenges. Most recently, Clariant has opened new mining labs in South Africa (Johannesburg) and in China (Guangzhou). The new laboratories will complement existing facilities in Europe and Latin America.
As part of Clariant Mining Solutions global investment, new mining labs have been established in South Africa and China, to complement those already operating in Brazil, Chile, Peru, Australia, North America, Russia and Germany
Mining is a strategic focus area for Clariant, said Christopher Oversby, Global Head of Clariants Oil & Mining Services business unit. This investment further demonstrates Clariants ongoing commitment to providing innovative technologies and solutions for our mining customers around the world.
The Houston laboratory will process ore samples from customers in the USA and Canada. These samples were previously handled in Clariants mining laboratories located in South America and at the companys global research facility in Frankfurt, Germany. We are very excited about the new mining laboratory and the opportunity it provides us for offering our North American mineral processing customers even more localised services and attention, said Paul Gould, Global Head of Marketing and Application Development for Clariant Mining Solutions. The Houston lab will allow Clariant technicians to more efficiently develop optimised reagent solutions for our US and Canadian customers.
Additionally, Clariant is in the process of developing a new Innovation Center in Frankfurt at a cost of 50 million. Employing nearly 500 people and covering 30,000 m2, the facility will focus on customers using an integrated multidisciplinary approach to problem solving. Clariant says an open innovation approach on joint ventures with external partners will ensure the acceleration of the idea-to-market process. Mining research and development will also be part of this facility.
Axis House has been developing reagent technologies for the past 10 years, at its flotation laboratory in Cape Town, South Africa and more recently at it metallurgical labs in Sydney and Melbourne. These were acquired when Axis House bought the oxide flotation reagent technology from Ausmelt Chemicals. A practical application technology strategy was followed with Axis House providing a complimentary suite selection and optimisation service to its clients, who were then mainly interested in the Axis developed technology of combining fatty acids, hydroxamates and sulphidisation suites to effectively and economically float oxide minerals.
Early on the focus was on developing reagents to float complex ores which contained multiple minerals with varying flotation kinetics. Often the limiting factor was not only the sluggish flotation kinetics of the minerals but the process plants own equipment limitations, like flotation and conditioning times. Developing a reagent that floated a certain mineral was simply not enough. The solution was to develop suites of reagents which could function synergistically. By altering the types of collectors and the dosages, the company could optimise both the use of the processing equipment and the collecting power. It says this approach has successfully been applied to various types of base metal oxide ores.
It is now taking this innovative approach into the field of rare earth element (REE) flotation. This fits into the Axis House business plan as the chemistries are quite similar to what is in existence at Axis already. Of course some tweaks will have to be made to the reagents as well as the laboratories this process has already started, with the first batch of REE test material having arrived at Cape Town, and new reagent samples at the ready. There are a large number of REE projects coming online in the next few years. Most of these orebodies have not been previously treated at industrial level and so will face difficulties when scaling up. REO (Rare Earth Oxides) are often difficult to float and the development of multiple collector systems for these ore types would help increase the viability of these projects.
Jerry Sullivan, Global Marketing Manager-Mineral Processing, Cytec Industries Inc, discussed collectors, which contain mineralselective functional groups. They have a hydrophobic hydrocarbon tail. Changing the molecules functional group changes the preference for what mineral it will adsorb on to. Changing the length of the hydrocarbon chain changes the hydrophobicity of the molecule. This is related to the strength of the collector.
Within the collector molecule, there are donor atoms whose goal is to form bonds with acceptor atoms within the ore. Nitrogen, oxygen, and sulphur are the most important donor atoms in all reagent chemistry. Sulphur is the most important donor in sulphide collectors. Nitrogen and oxygen are additional donor atoms. Phosphorous and carbon are central atoms carrying the donors. They only have indirect participation in interactions. He noted the general characteristics of sulphide collectors to be:
Ionic collectors are stronger and less selective
Neutral, oily collectors are weaker, more selective
Higher homologues (more carbons) are stronger than lower homologues (fewer carbons)
Cytecs NCPs are very selective collectors
There is a strong case for formulated products (or blends), he continued That is because mineralogy is complex. Plant performance is also inherently variable. Mineralogy changes routinely. In addition, different minerals have different affinities for reagents. Various minerals will compete for a given reagent. Modifiers used will also influence reagent partitioning. Particle size distribution will also affect recoveries (recovery losses in coarse and fine size range). A single collector will not be sufficiently robust. Indeed, most plants use two or more collectors. The goal is to pick reagents that will get to the right minerals. Utilising a collector blend can balance cost and performance.
Cytec has multiple collectors and collector blends that are continuously being developed to tailor to the customers application. A few of the collector families that have recently been introduced to the market include the new XR Series Xanthate Replacement Collectors, developed to meet the desire to replace xanthates. This new series of collectors are cost competitive with xanthates and are strong collectors but with high selectivity. In addition, they are safer and vastly improves handling and level of toxic exposure of the personnel to product, stock safety management and simplifies plant operations.
The XD 5002 blends were developed to operate in a broad pH range 8-12 and be highly selective in Cu/Mo, Cu/Au sulphide ores, enhance Mo recovery in Cu/Mo bulk float and enhance Au recovery in Cu/Au ores. The MAXGOLDTM blends were introduced to float primary Au ores; auriferous pyrite, arsenopyrite, and tellurides and are also capable of enhancing recovery in Cu/Au ores.
It is now possible to use measurement devices based on impedance tomography to create realtime 3D images. The technology opens up entirely new possibilities in controlling flotation processes. With Flotation Watch the operator can see what takes place underneath the surface. Flotation Watch measures several parameters at the same time, on-line. The sensor can measure the stiffness of the froth, the thickness of the froth, analyse the interface area between the froth and the slurry and it can analyse the slurry too depending on the customer needs, says Jukka Hakola, Numcores Vice President of Sales and Marketing.
With Numcore measurement devices, the size and quantity of air bubbles and the solid matter content of the froth bed can be monitored by means of electric conductivity distribution. With Flotation Watch the stiffness of the flotation froth can be measured and this helps to keep the recovery in higher level. The signals for the production failures, such as hardening and collapse of the froth bed, can be seen beforehand and avoided. This way we can help to minimise the losses in the flotation process, says Hakola.
Real-time characteristics are a key in this technology; in other words, the system continuously provides the operator with factual data on what is happening in the flotation cells, for example the location of minerals and the bottom surface of the froth bed. Because it has not been possible to look inside tanks, controlling a mineral concentration process has largely been based on experience-derived knowhow. Now that operators can look inside the process, it is possible for them to maintain an optimal mix all the time, says Hakola.
Numcore has, in close co-operation with a few key customers, developed measurement technology to better serve everyday work. We have now delivered several Flotation Watch sensors to flotation cells in several markets and for different metals such as copper, zinc and gold. One of the main benefits is that contamination of the probe is taken into account in mathematical formula and the measurement probe does not need to be cleaned. Our sensor has been in a zinc rougher flotation cell for nine months and is giving accurate results to the operator. We can now offer automated control for flotation process with Flotation Watch and see that this can bring new benefits for our customers, he promises.
Numcores measurement technology is currently in test use at Inmets Pyhsalmi copper-zinc mine (IM, April 2010, pp10-18), among others. According to Seppo Lhteenmki, Processing Mill Manager, the system has provided accurate information on the condition of the froth bed, and the technology has functioned reliably. We have tested the device for a few months, and it has provided clear benefits for those operators who have received operator training for it and actively monitored the data provided by the system. The device appears to be so useful, in fact, that we are seriously considering buying it after the test period, he says.
Mettler Toledo notes that pH greatly determines the efficiency of the flotation, which minerals will float, or even if there will be any flotation at all. The critical pH value for efficient flotation depends on the mineral and the collector. Below this value the mineral will float, above it, it will not (or, in some cases, vice versa).
In a recent white paper www.mt.com/pro-phflotation, the company says in order to overcome difficulties with the hostile environment in flotation cells, sensor manufacturers are very creative in their choice of sensor design. It is possible to find pH electrodes with a ceramic, plastic, rubber or even a wood reference diaphragm. Still, their performance can be severely limited as the colloidal particles and sulphides interfere almost instantly with the reference system. The sensors maintenance requirement is therefore high, requiring very frequent cleaning and calibration, and usually sensor life is short.
Mettler Toledo has acknowledged this issue and to combat it has designed the InPro 4260i pH electrode with Xerolyt Extra solid polymer electrolyte. The InPro 4260i does not have a diaphragm and instead features an open junction, which is an opening that allows direct contact between the process medium and the electrolyte. Contrary to the miniscule capillaries of any other type of diaphragm in conventional pH electrodes, the diameter of the open junction is extremely large and much less susceptible to clogging or fouling. Another significant difference is in the choice of polymer electrolyte. Xerolyt Extra was designed specifically for service in tough environments to provide a strong and lasting barrier against sulphide poisoning.
The companys Intelligent Sensor Management (ISM) is a platform based on sensors with embedded digital technology for better pH management. The integrated system consists of a digital sensor and ISM-compatible transmitter. The key to the technology is a microprocessor which is contained within the sensor head and is powered by and read through the transmitter. Critical sensor information such as identification, calibration data, time in operation and process environment exposure are all recorded and used to continuously monitor the health of the sensor.
By constantly keeping track of process pH value, temperature and operating hours, ISM calculates when sensor calibration, cleaning or replacement will be needed. Any need for maintenance is recognised at an early stage.
In recent years, researchers at Imperial College have been focusing on measuring air recovery in industrial flotation cells and have found that a peak in metallurgical performance (improvements in both grade and recovery) corresponds well with a peak in air recovery. Major platinum and copper operations have already observed the benefits of using this methodology as developed by the researchers. JKTech is now licensed by Imperial Innovations to commercially provide this methodology and associated benefits to the global minerals industry.
The PAR technique comprises two stages evaluation and implementation. The evaluation stage involves determining the effect of the technology at a mine site, typically determining the peak air recovery for a bank (or banks) of flotation cells and evaluating the resultant metallurgical performance. The implementation stage involves setting the air rates to those that maximise the air and/or metal recovery, and support and training of site personnel including operating manuals. The implementation stage requires an end-user license to be obtained by the sites through Imperial Innovations.
GIW Industries has launched its new High Volume Froth (HVF) pump. Unlike any other pump on the market, GIW says, the HVF pump can pump froth without airlocks. It provides continuous operation without shutdown or operator intervention. The new hydraulic design actually removes air from the impeller eye while the pump is running, so you can keep
Designed for air-entrained slurries, the pump can be used in phosphate mining, hard rock mining and oil sands. The pump offers improved efficiency and is environmentally friendly and cost effective, GIW reports
The GIW HVF can be retrofit into many existing froth applications. The pumps deaeration system includes a patent-pending vented impeller and airlock venting. This helps to eliminate sump overflow due to pump airlock; reduce downtime; and allow water use to be restricted to the bare minimum. Fewer pumps are required for less capital expense, requiring less water and power usage.
The HVF pump has been fully tested on froth and viscous liquids. The pump exceeded expectations at a large phosphate company in Finland. The companys existing pumps were not able to provide the required flow and were airlocking at only one-third of process design capacity. After installing an HVF pump, the company achieved a flow of 415 m3/h.
Traditional slurry pumps are prone to airlock when working with slurries that incorporate froth. A pump works by pulling in a liquid at a certain pressure and adding mechanical force to expel the liquid at a higher pressure. The air in the froth does not want to move to a higherpressure zone, and it is prone to build up at the lower-pressure pump entrance. The accumulation of air can eventually block the pump entrance completely, leading to airlock, which requires pump shutdown or operator intervention to avoid sump overflow.
How is GIWs HVF pump different? The main innovation is in the impeller design. Typically, air bubbles gather at the centre of the impeller as the heavier fluids are spun to the outer edges. The HVF pumps de-aeration system includes the vented impeller and airlock venting. In the HVF pump, small holes in the centre of the impeller allow air bubbles to pass through to a separate port. The port vents air up and out of the pump to normal atmospheric pressure.
flotation machines & flotation cells
In small plants, it is common practice to include conditioners following the last stage of grinding. Additional conditioners are normally required between flotation operations which produce individual mineral concentrates. Each conditioner stage should consist of a minimum of two separate agitated tanks. Provision must be made to drain and clean conditioner tanks to appropriate flowsheet locations. This is particularly important in the case of conditioners which follow the grinding circuit since these tanks tend to accumulate oversize material produced during grinding circuit upsets.
Conditioners provide positions in the plant flowsheet wherein changes to the ore slurry are brought about by the addition of reagents and pH modifiers. Conditioners must always be designed to provide adequate time for chemical or physical changes induced by reagent additions to proceed to completion. Conditioners also serve a useful function in that swings in ore grade, particle size distribution, or other flotation variable tend to be partially homogenized and dampened during the conditioning unit operation. For example, in small installations it is not unusual to experience wide swings in feed grade. The conditioning unit operation provides the operator an opportunity to modify reagent additions in order to maximize recovery during periods of process instability. If possible, conditioner tanks should be arranged in tiers so that slurry overflows between sequential tanks under the influence of gravity.
The selection of flotation cell size and configuration can have a substantial influence upon installed cost and can contribute to operational efficiency. Two possible flotation configurations for a 500 metric ton per day installation are presented in Figure 5. The computational basis assumes 30 percent solids in rougher flotation, 20 percent solids in cleaner, recleaner and cleaner-scavenger flotation, a ratio of concentration in rougher flotation of 3.07 an overall ratio of concentration of 5.0, and an ore specific gravity of 2.9. This representation indicates that the flotation bay layout employing the larger flotation cells, in this case 2.83 cubic meter (100 cubic feet) machines, occupies less area and reduces installed capital cost by about 25 percent. However, there are instances when the first illustration (selection of small flotation cells) would be chosen for reasons of compactness and symmetry.
Complex multiple product flotation installations usually require a high degree of sophistication regarding operational control. Many times, in small flotation concentrators this level of sophistication is not available. If the facility is located in a remote area, experienced operational personnel may be impossible to acquire. Consequently, the flotation circuits should be as simple as possible. For an installation producing a single mineral product, the flotation scheme illustrated in Figure 6 is recommended. This system, which is compatible with configuration 2 on Figure 5, is simple to operate and eliminates the build-up of a large circulating load of scavenger concentrate. This system is also flexible in that various produced concentrates can be subjected to regrinding should changes in mineralogy or primary grind so dictate.
It must be recalled that the weight of rougher and cleaner concentrates produced from high-grade ores can be substantial. Provision to remove froth by the use of froth paddles on all flotation cells should be included in the original design. The additional capital cost required for froth paddles is a reasonable investment since these devices tend to negate errors in flotation pulp level or frother addition. The open circuit flotation system presented can be operated by individuals having minimal training. The advice of Taggart regarding the inclusion of a small pilot table as a visual sample on rougher tailings is still legitimate.
In almost all new flotation installations, the use of launders fabricated from sheet rubber is recommended. Care must be taken to insure that all launders are sloped properly. In addition, launders must be provided with appropriate sprays and sluice lines to facilitate concentrate transport. The launder water system must be carefully designed to insure functionality without excessive concentrate dilution.
In recent years it has become popular to use vertical pumps for both concentrate and tailing transport in smaller circuits. It is usually possible to employ only one, or at the most two, pump sizes for all of the required flotation pumping installations. The same size vertical pump may also be used in various locations about the plant for cleanup duty. The usage of vertical pumps reduces seal water requirements, and eliminates concrete pump bases, fabricated sumps, and the valving associated with horizontal pumps.
For the past 35 years Sub-A Flotation Machines have been serving faithfully in all parts of the world. Anniversaries of progress such as this make reminiscing very interesting and we thought you would enjoy seeing some of the Firsts in the flotation machine industry as pioneered by the Sub-A.
1928was a pioneer in the use of V-belt drives in the flotation industry. This high-head machine also had wide-spaced greaseless lower bearings. At one time this was the largest flotation machine in the world.
1930 First steel tank flotation machine. Earlier machines had wood tanks. Steel tanks met great opposition at first, later became standard. This high-head, all-steel Sub-A marked the introduction of anti-friction lower bearings.
1932 First low-head flotation machine marked a radical departure from the then accepted principle that the space between bearings must be greater than the distance beyond the lower bearing. This machine was of the cell-to-cell pulp flow design and used a quarter-turn flat belt line-shaft drive.
1933 First steel tank low-head, low-level flotation machine. It had an individual motor and a V-belt drive. This design became very popular with mill operators and thousands of cells were sold similar to those pictured above.
Laboratory Flotation Machines have made progress, too. In our early days the cast-iron tank machine with its round-belt mule drive was the latest word. Contrast it with todays modern Sub-A Laboratory Flotation Machine with its heavy glass tank and stainless steel parts.
1961 Todays demands for Sub- A Flotation Machines keep our modern factory busy. Today more Sub- A Flotation Machines are specified than all competitive makes and is the unquestioned First Choice in Flotation.