efficient dry magnetic separator power consumption

magnetic separators

magnetic separators

The science of magnetic separation has experienced extraordinary technological advancements over the past decade. As a consequence, new applications and design concepts in magnetic separation have evolved. This has resulted in a wide variety of highly effective and efficient magnetic separator designs.

In the past, a process engineer faced with a magnetic separation project had few alternatives. Magnetic separation was typically limited and only moderately effective. Magnetic separators that utilized permanent ferrite magnets, such as drum-type separators, generated relatively low magnetic field strengths. These separators worked well collecting ferrous material but were ineffective on fine paramagnetic particles. High intensity magnetic separators that were effective in collecting fine paramagnetic particles utilized electromagnetic circuits. These separators were large, heavy, low capacity machines that typically consumed an inordinate amount of power and required frequent maintenance. New developments in permanent magnetic separation technology now provide an efficient alternative for separation of paramagnetic materials.

Technological advances in the field of magnetic separation are the result of several recent developments. First, and perhaps most important, is the ability to precisely model magnetic circuits using sophisticated multi-dimensional finite element analysis (FEA). Although FEA is not a new tool, developments in computing speed over the last decade have made this tool readily accessible to the design engineer. In this technique, a scaled design of the magnetic circuit is created and the magnetic characteristics of the individual components quantified. The FEA model is then executed to determine the magnetic field intensity and gradient. Using this procedure, changes to the magnetic circuit design can be quickly evaluated to determine the optimum separator configuration. This technique can be applied to the design of both permanent and electromagnetic circuits. As a consequence, any type of magnetic separator can be developed (or redesigned) with a high level of confidence and predictability.

Equally important has been the recent development of rare-earth permanent magnets. Advances in rare-earth magnet materials have revolutionized the field of magnetic separation. The advent of rare-earth permanent magnets in the 1980s provided a magnetic energy product an order of magnitude greater than that of conventional ferrite magnets. Rare-earth magnetic circuits commonly exhibit a magnetic attractive force 20 to 30 times greater than that of conventional ferrite magnets. This development has provided for the design of high-intensity magnetic circuits that operate energy-free and surpass the strength and effectiveness of electromagnets.

Finally, the materials of construction used in the fabrication of magnetic separators have advanced to a point that significantly extends service life while decreasing maintenance. Advanced materials, such as fiber composites, kevlar, ultra high molecular weight polyester, and specialty steel alloys are now commonly used in contact areas of the separator. These materials are lightweight, abrasion resistant, and comparatively inexpensive resulting in significant design advantages as compared to previous construction materials.

The evolution of high strength permanent rare-earth magnets has led to the development of high-intensity separators that operate virtually energy free. The use of rare-earth magnetic separators for beneficiation of industrial minerals has become the industry standard with literally hundreds of separators placed in recent years. The following sections present an overview of the most widely used permanent magnetic separators: rare-earth drum and rare-earth roll-type separators.

Of the roll separators, there are at least fourteen manufacturers. Most of the different makes are based on the original Permroll design concept originated by this author. Various enhancements have been mainly focused on the belt tracking methods. New magnetic roll configurations and optimization of roll designs are relatively recent innovations. Additional optimization efforts are in progress.

At last count, seven manufacturers have commercially available drum separators, most based on magnet circuits derived from the use of conventional ferrite magnet. Two unique designs have been developed with one clearly offering advantages over older configurations.

Rare-earth elements have some unique properties that are used in many common applications, such as TV screens and lighters. In the 1970s, rare-earths began to be used in a new generation of magnetic materials, that have very unique characteristics. Not only were these stronger in the sense of attraction force between a magnet and mild steel (high induction, B), the coercivity (Hc) is extremely high. This property makes the magnetization of the magnet body composed of a rare-earth element alloy very stable, i.e., it cannot easily be demagnetized.

It was a well known fact that permanent magnets positioned on both sides of a flat steel body can magnetize the steel to a high level, if the magnet poles were the same on each side, i.e., the magnets would repel each other. However, in the past, large magnet volumes were required to achieve any substantial magnetization. With the new powerful magnets, the magnet volume could be relatively small to generate high steel magnetization. In 1981 this author determined the optimum ring size for samarium-cobalt magnets. Maximum steel magnetization (near saturation) could be obtained if the rings were stacked to make a roll using a 4:1 ratio of magnet to steel thickness, see Figure 1. Since magnetized particles are attracted to the magnetized steel surface on the roll periphery, this means that 20% of the exposed roll surface would collect such material. This collection area is an order of magnitude greater than what could be achieved with prior art magnets, making the magnetic roll useful for mineral separation.

Although one of the first prototype rare-earth magnetic rolls was calculated to have about 14,000 gauss steel magnetization, it was found in comparative testing with electromagnetic induced roll (IMR) separators operating at about 21,000 gauss, that similar performance was obtained in fine particle processing (smaller than 1 mm). When processing coarser particles an improved performance was established (e.g., less weakly magnetic contaminants remaining in the upgraded product and fewer separation passes to achieve high quality). The improvement results because the magnetic force acting on the particles is high, due to a high flux gradient. An electromagnetic induced magnetic roll separator has an air gap, which must be increased to accommodate the processing of larger particles. The rare-earth magnetic roll (REMR) magnetic separator has no such air gap. Consequently, the magnetic force does not decline in the manner of an IMR set with a large air gap.

As the name implies, suspended magnets are installed over conveyors to lift tramp iron out of the burden. Suspended magnets have been more frequently applied as conveyor speeds have increased. Suspended type magnets are capable of developing very deep magnetic fields and magnet suspension heights as high as 36 are possible.

Suspended magnets are of two basic types (1) circular and (2) rectangular. Because of cost considerations, the rectangular suspended magnet is nearly always used. Magnet selection requires careful analysis of the individual system to insure adequate tramp iron removal. Factors that must be considered include:

The position in which the magnet must be mounted will also influence the size of magnet required. The preferred position is at an angle over the head pulley of the conveyor where the load breaks open and the tramp iron is free to move easily to the magnet face. When the suspended magnet must be mounted back from the head pulley parallel to the conveyor, tramp iron removal is more difficult and a stronger magnet is required.

Magnetic drum separators come in many different styles. Tramp iron drum separators usually use a magnet design referred to as a radial type. In such a unit the magnet poles alternate across the width of the drum and are of the same polarity at any point along the drums circumference. The magnet assembly is held stationary by clamp bearings and the drum shell is driven around this magnet assembly.

Drum-separators lend themselves to installation in chutes or at the discharge point of bucket elevators or screen conveyors.The capacity and type of tramp iron to be removed will determine the size selection of a drum separator. They are available in both permanent and electro magnetic types.

Standard drum diameters are 30 and 36. General guide lines, in diameter selection, are based on (1) feed volume (2) magnetic loadings and (3) particle size. The 30 diameter drum guide lines are roughly maximum of 75 GPM per foot feed volume, 8 TPH per foot magnetic loading and 10 mesh particle size. The 36 guide lines are 125 GPM per foot feed volume, 15 TPH per foot magnetic loading and 3/8 inch particle size.

For many years, wet magnetic drum separator magnet rating has been on the basis of a specified gauss reading at 2 from the drum face. The gauss reading is an average of readings taken at the centerline of each pole and the center of the magnet gap measured 2 inches from the drum surface. This rating tends to ignore edge of pole readings and readings inside of the 2 inch distance, particularly surface readings which are highly important in effective magnetic performance.

We have previously discussed dry drum separators as used for tramp iron removal. A second variety of drum separator is the alternating polarity drum separator. This separator is designed to handle feeds having a high percentage of magnetics and to obtain a clean, high grade, magnetic concentrate product. The magnet assembly is made up of a series of poles that are uniform in polarity around the drum circumference. The magnet arc conventionally covers 210 degrees. The magnet assembly is held in fixed operating position by means of clamp bearings and the cylinder is driven around this assembly.

Two styles of magnet assemblies are made up in alternating polarity design. The old Ball-Norton type design has from 8 to 10 poles in the 210 arc and develops a relatively deep magnetic field. This design can effectively handle material as coarse as 1 inch while at the same time imparting enough agitation in traversing the magnetic arc to effectively reject non-magnetic material and produce a clean magnetic concentrate product. The 30 diameter alternating polarity drum is usually run in the 25 to 35 RPM speed range.

Application of the high intensity cross-belt is limited to material finer than 1/8 inch size with a minimum amount of minus 200 mesh material. The cost of this separator is relatively high per unit of capacity approaching $1000 per inch of feed width as compared to $200 per inch of feed width on the induced roll separator.

This investigation for an improved separator is a continuation of the previously reported pioneering research of the Bureau of Mines on the matrix-type magnetic separator. When operated with direct current. or a constant magnetic field, the matrix-type magnetic separator has several disadvantages, which include incomplete separation of magnetic and nonmagnetic components in one pass and the retention of some of the. magnetic fraction at the discharge quadrant. Since the particle agitation that results from pulsed magnetic fields may overcome these factors, operation with an alternating current would be an improvement. Another possibility is the separation of dry feeds, which may have applications where the use of water must be avoided.

The effects of an alternating field were first described by Mordey and later by others of whom Doan provides a bibliographical resume. The significant feature to note in the description by Mordey is the change from a repulsion in weak fields to an attraction in strong fields, in addition to a difference in response with different minerals. The application by Mordey was with wet feeds using launders and inclined surfaces, although applications by others are with both wet and dry feeds.

Except for occasional later references the interest in alternating current for magnetic separation has almost disappeared. Lack of interest is probably due to the apparent high power consumption required to generate sufficiently intense magnetic fields, a problem that warrants further consideration.

The matrix separator differed somewhat from the slotted pole type described in a previous report in that the flux passed into the matrix from only one side, the inverted U-shaped magnet cores 4 and 7 illustrated in figure 1. Figure 1 shows a front view, side view, and a bottom view of the matrix-type magnetic separator. By this arrangement, an upward thrust could be exerted on the matrix disk during each current peak; the resulting induced vibration would accelerate the passage of the feed as well as the separation of the magnetic particles from the nonmagnetic particles since the applied field during the upward thrust preferentially lifts

The matrix disk 5 rotates successively through field and field-free quadrants. Where a given point on the disk emerges into a field quadrant, feed is added from a vibrating feeder; nonmagnetic particles fall through the matrix, and magnetic particles are retained and finally discharged in the succeeding field-free quadrant.

Two types of disks were used, a sphere matrix illustrated in top and cross-sectional views in figure 2 and a grooved plate type similarly illustrated in figure 3. Both the spheres and grooved plates were mounted on a nonmagnetic support 1 of optimum thickness for vibration movement (figs. 2-3). The sphere matrix disk, similar to that of the earlier model, had a matrix diameter 8 of 8.5 inches and spokes 7 spaced 45 apart; the spheres were retained by brass screens 4 (fig. 2).

The grooved plate disk was an assemblage of grooved steel plates that tapered so that one edge 5 was thinner than the other 6 (fig. 4) to provide a stack in the form of a circle having an outside diameter 9 of 7.9 inches (fig. 3). The plates were retained by two split aluminum rings 8 and 3 clamped in two places 1 and 11. They were stacked so that the vertically oriented grooves of one plate touched the flat side of the second plate. As illustrated in figure 4, two slots 3 and 4 were added to reduce eddy current losses.

Both disks 5 illustrated in figure 1 were rotated by a pulley 1 through a steel shaft 8 held by two aluminum bars 2 and which in turn were fastened to aluminum bars 3 and steel bars 6. The magnetic cores 4 and 7 were machined from 10- by 12-inch E-shaped Orthosil transformer laminations. For wet feeds,

With the information derived from the performance of this separator, a cross-belt-type separator was also constructed as illustrated in figure 5, which shows a front view and a cross-sectional view through the center of the magnet core. The cross-belt separator mentioned here differs somewhat from the conventional cross-belt separator in that the belt 5 moves parallel to the feed direction instead of 90 with the feed direction. The magnetic core, composed of parts 17, 19, 21 and 22 that were machined from 7--by 9 inch E-shaped Orthosil transformer laminations, supplies a magnetic field between one magnetic pole 6, which has grooves running parallel to the feed direction, and the other magnetic pole 14. Owing to the higher intensity field at the projection from the grooves, magnetic particles are lifted from feeder 15 to the belt 5. By movement on flat-faced pulleys 3 supported by bearings 4 the belt 5 carries the particles to the discharge chute 7. Nonmagnetic particles fall from the feeder edge and are discharged on the chute 8. A special 0.035-inch-thick Macarco neoprene-dacron endless belt permits a close approach of the feeder surface to the magnet pole 6. The feeder 15 constructed of plexiglass to prevent vibration dampening by eddy currents, is fastened to a vibration drive at 16 derived from a small vibrating feeder used for granular materials. A constant distance between poles 6 and 14 was maintained by acrylic plastic plates 9 on each side of the poles 6 and 14 with a recessed portion 13 to provide room for the belt 5 and feeder 15. The structural support for the separator, which consisted of parts 1, 2, 11, 18, and 20, was constructed of 2- by 2- by -inch aluminum angle to form a rectangular frame, and part 10 was machined from angular stock to form a support for the magnet core.

Each U-shaped magnet core in figure 1 was supplied with two 266-turn coils and two 133-turn coils of No. 10 AWG (American wire gage) heavy polythermaleze-insulated copper wire. With alternating current excitation, the current and voltage are out of phase so that the kilovolt-ampere value is very high even though the actual kilowatt power is low. This difference may be corrected with either series capacitors to reduce the input voltage or parallel capacitors to reduce the input current. However, the circuit that was selected is illustrated in figure 6 in which the two 266-turn coils are connected in series with the capacitor 2. Power is supplied by the 133-turn drive coil 7 that is connected in series with the 133-turn drive coil 9 on the other U-shaped magnet core. Coils 4 and 6 and the capacitor 2 form a circuit that resonates at 60 hertz when the capacitor 2 has a value of 49 microfarads in accordance with the equation

For the capacitance in the power input circuit, the value is calculated on the basis of the equality of equations 2-3. When the input at point 10 is 10 amperes at 126 volts or 1.26 kilovolt-amperes, the current at point 3 and the voltage at

point 1 are 10 amperes and 550 volts, respectively, or a total of 11.0 kilovoIt-amperes for the two magnet cores, which provides a 5,320-ampere- turn magnetization current. The capacitors, a standard power factor correction type, had a maximum rating of 600 volts at 60 hertz.

Application of alternating current to the cross-belt separator is not successful. In contrast to the matrix-type separator in which the feed is deposited on the magnetized matrix, the feed for the cross belt is some distance below a magnet pole where the field is weaker and the force is a repulsion. Even though the magnetic force with the matrix-type separator may be a repulsion instead of an attraction, it would result in the retention of the magnetic fraction in the matrix. Replacement of the alternating current with an intermittent current eliminates the repulsion effect but still retains the particle vibration characteristics.

For an intermittent current the circuit shown in figure 7 is used. A diode 5 supplies the current to a coil 4, which can be the magnetizing coil for the cross-belt separator, or for one magnet core of the matrix-type separator that is connected in parallel or series with the coil for the other core. A coil 2 is supplied with half-wave-rectified current from a diode 6 but is out of phase with the other coil 4 and is only applicable to a second separator. However, the circuit illustrates the reduction of the kilovolt-ampere load of intermittent magnetizing currents. As an example, measurements were, made with the two magnet cores of figure 1; each core had 532 turns of wire. When the capacitor 9 has a value of 72 microfarads, the current at point 8 is 13 amperes, and the voltages at points 10, 1, and 7 are 75, 440, and 390 volts, respectively. The kilovoIt-ampere input at point 11 is therefore 0.98, and the kilovolt-amperes supplied to the coils is 5.07. This circuit is not a simple resonance circuit, as shown in figure 6, but a circuit in which the correct value of the capacitor 9 depends on the current. At currents lower than 13 amperes, the 72-microfarad value is too large.

However, separations with intermittent current were confined to a simple one-diode circuit. With the matrix-type separator, each magnet core carried 10.5 amperes at 240 volts through 399 wire turns or a total of 21 amperes since the two cores were connected in parallel. For the cross-

belt separator illustrated in figure 5, five 72-turn coils and one 96-turn coil wound with No. 6 AWG heavy polythermaleze-insulated square copper wire were used in series connection. Current-carrying capacity is approximately 40 amperes with an input of approximately 80 volts of half-wave-rectified 60-hertz current. At 40 amperes, the average number of ampere turns would be 18,240. Intermittent current and voltage were measured with the same dynamometer meters used for alternating current; these meters measure an average value.

It is possible to increase the magnetizing current for the matrix-type separator without excessive vibration by increasing the thickness of the plate 1 (figs. 2-3). Another alternative is a combination of intermittent and constant magnetic fields. Although a variety of circuits are possible, the combination of fields was accomplished with the simple adaptation of the stray field losses in a U-shaped magnet core using the circuit of figure 8. The power drawn is full-wave rectification, or half wave for each leg of the magnet core with the flux, from the coils 3 and 4 adding. Owing to magnetic leakage, the flux from the coil nearest to the magnet pole tested predominates. When the magnetic field is measured with a Bell model 300 gaussmeter and observed with a Tektronix type 547 oscilloscope with a type 1A1 amplifier, the results of figure 9 represent a pulsating magnetic field on top of a constant magnetic field plateau.

Although it is known that minerals in water suspension may be separated in the constant-field matrix-type separator at fine sizes, some tests were conducted to investigate if any beneficial effects exist with an intermittent field. One advantage that was found with a minus 325-mesh feed was an increase in the completeness of the discharge of the magnetic fraction with an intermittent field as illustrated in tables 1-2. Both tests had the same average current of 10.5 amperes through the magnetizing coils of each magnet core illustrated in figure 7. The matrix consisted of 1/16-inch-diameter steel spheres.

In the two short-period comparative tests, the wash water for removing the magnetic fraction was the same and was of a quantity that permitted complete discharge with the intermittent field and partial removal with the constant field. After the test was completed, magnetic particles retained with the constant field were determined by a large increase in the intensity of flow of wash water, a flow volume that would not be practical for normal operation. For separation efficiency, the intermittent field had no advantage over the constant field probably because of a lack of vibration response with minus 325-mesh particles at 60 hertz. This will be described later with dry feeds.

Dry magnetic separation at coarse sizes is not a problem because it may be accomplished with a variety of separator types. Difficulty at fine sizes is twofold. First, the feed rate capacity decreases in the separators with moving conveyor surfaces such as the induced roll and cross-belt separators in which the attracted magnetic particles would have to move at nominal feed rates through a thick layer of nonmagnetic particles; second, an agglomeration effect is present that increases with decrease in particle size.

Results of the separation of several mineral combinations in the size range of minus 200 plus 325 mesh are summarized in tables 3-5. Table 3 illustrates the separation of -Fe2O3 from quartz in an ore with one pass through a matrix of 1/8-inch-diameter steel spheres using the alternating current circuit of figure 6.

Application of an intermittent field with a matrix of 75 percent 1/16-inch-diameter steel spheres and 25 percent 1/8-inch-diameter steel spheres is illustrated in table 4 in a one-pass separation of pyrrhotite from quartz using the circuit of figure 7. Unlike table 3, no attempt was made to obtain an intermediate fraction, which would have resulted in raising and lowering the iron compositions of the magnetic and nonmagnetic fractions, respectively, and provided a fraction for repass with increased recovery.

Table 5 gives the results of the application of a partially modulated field using the circuit of figure 8 and the grooved plate matrix of figure 3 in a one-pass separation of ilmenite from quartz. The advantage of the grooved plate over the spheres is that the particles pass through the matrix in a shorter time. The high flow rate obtained using the grooved plate could be increased further, particularly if water is used, by attaching suction chambers under the disk in a manner similar to applications with continuous vacuum filters. Although the grade and recovery of ilmenite are very high, this need not necessarily be attributed to the grooved-plate matrix since the ampere turns are higher than in any of the other tests. Increased ampere turns is a prerequisite for successful application of alternating current separators and intermittent current separators.

When a minus 325-mesh fraction is tested, a separation sometimes occurs, but in most cases the feed passes through without separation. Response at higher frequencies was investigated with a smaller -inch-cross section U-shaped magnet core 1 (fig. 10). Separation was performed with a nonmagnetic nonconducting plane surface 3 moved manually across the magnet pole as illustrated by the direction arrow 4. When separation occurred, the nonmagnetic mineral 5 would move with the plane, and the magnetic mineral would separate from the nonmagnetic mineral by remaining attached to the magnet pole. When no separation occurred, the entire mixture of magnetic and nonmagnetic minerals would either move with the plane or adhere to the magnet pole.

Four magnetising coils of 119 turns each of No. 14 AWG copper wire were used; three were connected in series with a capacitor as in figure 6, and one was connected to a variable-frequency power supply. The current in the resonant circuit is approximately 5 amperes. When the capacitor has a value of 49 microfarads, the resonant frequency is 130 hertz, and no separation occurs. With the capacitor reduced to 10 microfarads to provide a resonant frequency of 300 hertz, a separation occurs. In the case of a minus 325-mesh -Fe2O3-quartz mixture, most of the quartz moves with the plane, and the -Fe2O3 remains attached to the magnet pole. Similar results are obtained with pyrrhotite-quartz. Indications are that the separation may be improved with preliminary treatment of the feed by dry grinding aids.

frequencies, the time per cycle is too short to permit initial magnetization; at very low frequencies, the magnetization is in phase with the field. The frequencies reported here are between these two extremes and probably near, and just above, the low frequency limit. Experimental values on particles in the size range of minus 35 plus 65 mesh were previously published. These data indicate that 0.16 second, the time required to traverse a magnetizing field distance of 0.9 inch at 5.5 inches per second, is adequate time for the magnetization of minerals, but 0.02 second, the time required to traverse approximately 0.1 inch at the same rate, is too short. Time lag has been reported in the literature for magnetic alloys and has been classified, to the exclusion of the eddy current lag, into a lag that is dependent on impurities and a Jordan lag that is independent of temperature.

From evidence derived from the Barkhausen effect, the magnetization does not proceed uniformly and simultaneously throughout a specimen but is initiated in a limited region from which it spreads in a direction parallel to the field direction at a finite velocity. In a changing magnetic field, the number of initiating nuclei is proportional to the cross-sectional area perpendicular to the direction of the field. For a specimen in the form of a cube, the rate of energy W transferred to the cube would therefore be proportional to the aforementioned cross-sectional area so that for a cube of side s,

Application of intermittent current to the cross-belt separator arose from the need for the dry separation of an iron composition material from the copper in a product submitted by personnel of a Bureau of Mines chalcopyrite vacuum decomposition project. Although this product was of a relatively coarse size, the matted mass resulting from the needle shape or fiber form of the copper and the magnetic field coagulation effects of the magnetic particles prevented use of commercial dry separators such as the induced roll separator and constant-field cross-belt separator. The pulsating magnetic field had a separation effect similar to the pulsations in a hydraulic jig; the pulsating magnetic field permits the nonmagnetic fibers to sink back to the vibrating feeder and allows the magnetic particles to rise to the belt. Other applications would include fibrous minerals such as tremolite, actinolite, and chrysolite, and matted and fibrous secondary materials.

Application of alternating and intermittent current to magnetic separation at a relatively high number of ampere turns was made possible by special electronic circuits. Actual power losses are low and include the IR loss, which is the same that occurs in direct-current magnetic separation, and the core loss, which has a magnitude corresponding to the IR loss. Minerals may be dry-separated close to the minus 325-mesh size at 60-hertz frequency and possibly at smaller particle sizes at higher frequency. In the wet separation of minus 325-mesh feeds, intermittent current provides for complete release of the magnetic fraction during the discharge cycle. For matted fibrous and magnetically coagulating feeds, a cross-belt separator with an intermittent magnetizing current provides efficient separations.

magnetic separator - an overview | sciencedirect topics

magnetic separator - an overview | sciencedirect topics

As magnetic separators progress toward larger capacity, higher efficiency, and lower operating costs, some subeconomic iron ores have been utilized in recent years. For example, magnetite iron ore containing only about 4% Fe (beach sands or ancient beach sands) to 15% Fe (iron ore formations) and oxidized iron ore of only about 10% Fe (previously mine waste) to 20% Fe (oxidized iron ore formations) are reported to be utilized. They are first crushed and the coarse particles pretreated using roll magnetic separators. The magnetic product of roll magnetic separators may reach 2540% Fe and then is fed to mineral processing plants.

As shown in Figure5, slurry is fed from the top of an inclined screen in a low-intensity magnetic field, with the mesh size of screen sufficiently larger than those of particles in slurry. As the slurry flows down the above surface of screen, magnetic particles agglomerate with the size of agglomerations increasingly growing and roll down as magnetic concentrate at the lower end of screen. The less- or nonmagnetic particles pass through the screen as tailings. Figure5 shows the operation of screen magnetic separators for cleaning of magnetite.

Commercial magnetic separators are continuous-process machines, and separation is carried out on a moving stream of particles passing into and through the magnetic field. Close control of the speed of passage of the particles through the field is essential, which typically rules out free fall as a means of feeding. Belts or drums are very often used to transport the feed through the field.

As discussed in Section 13.4.1, flocculation of magnetic particles is a concern in magnetic separators, especially with dry separators processing fine material. If the ore can be fed through the field in a monolayer, this effect is much less serious, but, of course, the capacity of the machine is drastically reduced. Flocculation is often minimized by passing the material through consecutive magnetic fields, which are usually arranged with successive reversals of the polarity. This causes the particles to turn through 180, each reversal tending to free the entrained gangue particles. The main disadvantage of this method is that flux tends to leak from pole to pole, reducing the effective field intensity.

Provision for collection of the magnetic and nonmagnetic fractions must be incorporated into the design of the separator. Rather than allow the magnetics to contact the pole-pieces, which then requires their detachment, most separators are designed so that the magnetics are attracted to the pole-pieces, but come into contact with some form of conveying device, which carries them out of the influence of the field, into a bin or a belt. Nonmagnetic disposal presents no problems; free fall from a conveyor into a bin is often used. Middlings are readily produced by using a more intense field after the removal of the highly magnetic fraction.

Conventional magnetic separators are largely confined to the separation or filtration of relatively large particles of strongly magnetic materials. They employ a single surface for separation or collection of magnetic particles. A variety of transport mechanisms are employed to carry the feed past the magnet and separate the magnetic products. The active separation volume for each of these separators is approximately the product of the area of the magnetised surface and the extent of the magnetic field. In order for the separators to have practical throughputs, the magnetic field must extend several centimetres. Such an extent implies a relatively low magnetic field gradient and weak magnetic forces.

To overcome these disadvantages HGMS has been developed. Matrices of ferromagnetic material are used to produce much stronger but shorter range magnetic forces over large surface areas. When the matrices are placed in a magnetic field, strong magnetic forces are developed adjacent to the filaments of the matrix in approximately inverse proportion to their diameter. Since the extent of the magnetic field is approximately equal to the diameter of the filaments the magnetic fields are relatively short range. However, the magnetic field produced is intense and permits the separation and trapping of very fine, weakly magnetic particles (Oberteuffer, 1979).

The transport medium for HGMS can be either liquid or gaseous. Dry HGMS processing has the advantage of a dry product although classification of the pulverised coal is required to ensure proper separation. Small particles tend to agglomerate and pass through the separator. It has been shown that individual particles of coal in the discharge of a power plant pulveriser flow freely and hence separate well only if the material below about 10 m is removed (Eissenberg et al., 1979). Even then drying of that part of run of mine coal to be treated by HGMS may be required to ensure good flow characteristics.

A schematic representation of a batch HGMS process is shown in Figure 11.5 (Hise, 1979, 1980; Hise et al., 1979). It consists of a solenoid, the core cavity of which is filled with an expanded metal mesh. Crushed coal is fed to the top of the separator. Clean coal passes through while much of the inorganic material is trapped to be released when the solenoid is later deactivated.

Data from a batch HGMS process of one size fraction of one coal are plotted in Figure 11.6 as weight per cent of material trapped in the magnetic matrix, the product sulphur and the product ash versus the independent variable of superficial transport velocity. At low superficial transport velocities the amount of material removed from the coal is high partly due to mechanical entrapment. As the velocity is increased the importance of this factor diminishes but hydrodynamic forces on the particles increase. These hydrodynamic forces oppose the magnetic force and the amount of material removed from the coal decreases (Hise, 1979).

For comparison, Figure 11.7 shows data from a specific gravity separation of the same size fraction of the same coal. While the sulphur contents of the products from the two separation processes are similar the ash content of the HGMS product is considerably higher than that of the specific gravity product. It should be emphasised that this comparison was made for one size fraction of one coal.

More recently dry HGMS has been demonstrated at a scale of 1 t/h on carousel type equipment which processes coal continuously (Figure 11.8; Hise et al., 1981). A metal mesh passes continuously through the magnetised cavity so that the product coal passes through while the trapped inorganics are carried out of the field and released separately.

Wet HGMS is able to treat a much wider range of coal particle sizes than dry HGMS. The efficiency of separation increases with decreasing particle size. However, depending on the end use a considerable quantity of energy may have to be expended in drying the wet, fine coal product. Wet HGMS may find particular application to the precleaning of coal for use in preparing coal water mixtures for subsequent combustion as both pulverising the coal to a fine particle size and transporting the coal in a water slurry are operations common to both processes.

Work at Bruceton, PA, USA has compared the pyrite reduction potential of froth flotation followed by wet HGMS with that of a two stage froth flotation process (Hucko and Miller, 1980). Typical results are shown in Figures 11.9 and 11.10. The reduction in pyritic sulphur is similar in each case although a greater reduction in ash content is achieved by froth flotation followed by HGMS than by two stage froth flotation. However, Hucko (1979) concludes that it is highly unlikely that HGMS would be used for coal preparation independently of other beneficiation processes. As with froth flotation there is considerable variation in the amenability of various coals to magnetic beneficiation.

In the magnetic separator, material is passed through the field of an electromagnet which causes the retention or retardation of the magnetic constituent. It is important that the material should be supplied as a thin sheet in order that all the particles are subjected to a field of the same intensity and so that the free movement of individual particles is not impeded. The two main types of equipment are:

Eliminators, which are used for the removal of small quantities of magnetic material from the charge to a plant. These are frequently employed, for example, for the removal of stray pieces of scrap iron from the feed to crushing equipment. A common type of eliminator is a magnetic pulley incorporated in a belt conveyor so that the non-magnetic material is discharged in the normal manner and the magnetic material adheres to the belt and falls off from the underside.

Concentrators, which are used for the separation of magnetic ores from the accompanying mineral matter. These may operate with dry or wet feeds and an example of the latter is the Mastermag wet drum separator, the principle of operation of which is shown in Figure 1.43. An industrial machine is shown in operation in Figure 1.44. A slurry containing the magnetic component is fed between the rotating magnet drum cover and the casing. The stationary magnet system has several radial poles which attract the magnetic material to the drum face, and the rotating cover carries the magnetic material from one pole to another, at the same time gyrating the magnetic particles, allowing the non-magnetics to fall back into the slurry mainstream. The clean magnetic product is discharged clear of the slurry tailings. Operations can be co- or counter-current and the recovery of magnetic material can be as high as 99.5 per cent.

An example of a concentrator operating on a dry feed is a rotating disc separator. The material is fed continuously in a thin layer beneath a rotating magnetic disc which picks up the magnetic material in the zone of high magnetic intensity. The captured particles are carried by the disc to the discharge chutes where they are released. The nonmagnetic material is then passed to a second magnetic separation zone where secondary separation occurs in the same way, leaving a clean non-magnetic product to emerge from the discharge end of the machine. A Mastermagnet disc separator is shown in Figure 1.45.

The removal of small quantities of finely dispersed ferromagnetic materials from fine minerals, such as china clay, may be effectively carried out in a high gradient magnetic field. The suspension of mineral is passed through a matrix of ferromagnetic wires which is magnetised by the application of an external magnetic field. The removal of the weakly magnetic particles containing iron may considerably improve the brightness of the mineral, and thereby enhance its value as a coating or filler material for paper, or for use in the manufacture of high quality porcelain. In cases where the magnetic susceptibility of the contaminating component is too low, adsorption may first be carried out on to the surface of a material with the necessary magnetic properties. The magnetic field is generated in the gap between the poles of an electromagnet into which a loose matrix of fine stainless steel wire, usually of voidage of about 0.95, is inserted.

The attractive force on a particle is proportional to its magnetic susceptibility and to the product of the field strength and its gradient, and the fine wire matrix is used to minimise the distance between adjacent magnetised surfaces. The attractive forces which bind the particles must be sufficiently strong to ensure that the particles are not removed by the hydrodynamic drag exerted by the flowing suspension. As the deposit of separated particles builds up, the capture rate progressively diminishes and, at the appropriate stage, the particles are released by reducing the magnetic field strength to zero and flushing out with water. Commercial machines usually have two reciprocating canisters, in one of which particles are being collected from a stream of suspension, and in the other released into a waste stream. The dead time during which the canisters are being exchanged may be as short as 10 s.

Magnetic fields of very high intensity may be obtained by the use of superconducting magnets which operate most effectively at the temperature of liquid helium, and conservation of both gas and cold is therefore of paramount importance. The reciprocating canister system employed in the china clay industry is described by Svarovsky(30) and involves the use a single superconducting magnet and two canisters. At any time one is in the magnetic field while the other is withdrawn for cleaning. The whole system needs delicate magnetic balancing so that the two canisters can be moved without the use of very large forces and, for this to be the case, the amount of iron in the magnetic field must be maintained at a constant value throughout the transfer process. The superconducting magnet then remains at high field strength, thereby reducing the demand for liquid helium.

Micro-organisms can play an important role in the removal of certain heavy metal ions from effluent solutions. In the case of uranyl ions which are paramagnetic, the cells which have adsorbed the ions may be concentrated using a high gradient magnetic separation process. If the ions themselves are not magnetic, it may be possible to precipitate a magnetic deposit on the surfaces of the cells. Some micro-organisms incorporate a magnetic component in their cellular structure and are capable of taking up non-magnetic pollutants and are then themselves recoverable in a magnetic field. Such organisms are referred to a being magnetotactic.

where mpap is the inertial force and ap the acceleration of the particle. Fi are all the forces that may be present in a magnetic separator, such as the magnetic force, force of gravity, hydrodynamic drag, centrifugal force, the friction force, surface forces, magnetic dipolar forces, and electrostatic forces among the particles, and others.

Workable models of particle motion in a magnetic separator and material separation must be developed separately for individual types of magnetic separators. The situation is complicated by the fact that many branches of magnetic separation, such as separation by suspended magnets, magnetic pulleys, or wet low-intensity drum magnetic separators still constitute highly empirical technology. Hesitant steps have been taken to develop theoretical models of dry separation in roll and drum magnetic separators. Alternatively, open-gradient magnetic separation, magnetic flocculation of weakly magnetic particles, and wet high-gradient magnetic separation (HGMS) have received considerable theoretical attention. A notable number of papers dealing with the problem of particle capture in HGMS led to an understanding of the interaction between a particle and a matrix element. However, completely general treatment of the magnetostatic and hydrodynamic behavior of an assembly of the material particles in a system of matrix elements, in the presence of a strong magnetic field, is a theoretical problem of considerable complexity which has not been completed, yet. Detailed description of particle behavior in various magnetic separators can be found in monographs by Gerber and Birss (1983) and Svoboda (1987, 2004).

The brick material ratio was: Slag(1.0mm<): Grog (3.0mm<): Ceramic Gravel (1.0mm<): Clay (1.0mm<) at 20 : 35 : 25 : 20. To this mixture, 2% of pigment were added. Kneading and blending was done by a Mller mixer for 15 minutes. Molding was done by a 200 ton friction press, and the bricks were loaded onto the sintering truck.

This paper presents preliminary results using the Magnetic Micro-Particle Separator, (MM-PS, patent pending) which was conceived for high throughput isothermal and isobaric separation of nanometer (nm) sized iron catalyst particles from Fischer-Tropsch wax at 260 oC. Using magnetic fields up to 2,000 gauss, F-T wax with 0.30.5 wt% solids was produced from 25 wt% solids F-T slurries at product rates up to 230 kg/min/m2. The upper limit to the filtration rate is unknown at this time. The test flow sheet is given and preliminary results of a scale-up of 50:1 are presented.

Most loads for flap valves, conveyors, vibrating feeders, crushers, paddle feeders, magnetic separators, fans and trash screens generally are supplied at 415 V three-phase 50 Hz from the 415 V Coal Plant Switchboard, although 3.3 kV supplies may be used when the duty demands. Stacker/reclaimer machines are supplied at 3.3 kV. Electrical distribution is designed to safeguard the independent operational requirements of the duplicated coal plant facilities and to ensure that an electrical fault will not result in the total loss of coal supplies to the boilers.

The first step in any form of scrubbing unit is to break the lumpy materials and remove tramp elements by a magnetic separator. The product is then led into the scrubbing unit. The dry scrubbing principle is to agitate the sand grains in a stream of air so that the particles shot-blast each other. A complete dry scrubbing plant has been described in a previous book of this library in connection with sodium silicate bonded sands.* For clay-bonded sands the total AFS clay content in the reclaimed sand varies from 05% to 25% clay depending on the design of the plant.

non - metallic minerals high gradient magnetic separator machine for quartz

non - metallic minerals high gradient magnetic separator machine for quartz

High Gradient Magnetic Separator Vertical Ring for Swivel Outer Diameter 2000mm Product characteristic Vertical ring magnetic separator come over the technical problem that the magnetic media of high gradient flat ring magnetic separator is easy to block up. The separator possesses many advantages such as high magnetic field intensity, high gradient magnetic field, big concentration ratio, having a wide range in the particle size of feeding ore and the thickness of slurry, intelligent control operation, get a satisfactory mineral processing result when separate the low intensity magnetic ores. Operation process When mineral processing, firstly, filled the separation cavity with water, open the pulsating equipment, then feeding the raw ore from the feed box. The magnetic particle in the separation cavity separate from the non-magnetic particle by the different magnetic force, pulsating fluid force and gravity which those particles are acted on. The magnetic particles are absorbed on the magnetic media, the nonmagnetic particle will discharge from the iron discharge. several minutes later, magnetic cutting, then flushing the magnetic particle from the magnetic media. Technical parameter Model WD-1250 WD-1500 WD-1750 WD-2000 Swivel outer diameter(mm) 1250 1500 1750 2000 Ore size(mm), (-200 mesh%) -1.2(30-100) -1.2(30-100) -1.2(30-100) -1.2(30-100) Ore density(%) 10-40 10-40 10-40 10-40 Ore pulp transit capability(m/h) 20-50 50-100 75-150 100-200 Dry ore throughput(t/h) 10-18 20-30 30-50 50-80 Rated background magnetic field(T) 1.0 1.0 1.0 1.0 Rated energizing current(A) 850 950 1200 1200 Rated energizing voltage(V) 23 29 31 35 Rated exciting power(Kw) 19 27 37 40 Swivel rotating power(Kw) 1.5 3 4 5.5 Rotating pulsation power(Kw) 2.2 4 4 7.5 Pulse stroke(mm) 0-20 0-30 0-30 0-30 Pulse speed(times/min) 0-300 0-300 0-300 0-300 Water consumption(Mpa) 0.15-0.3 0.2-0.3 0.2-0.3 0.2-0.3 Water consumption(m/h) 30-45 60-90 80-120 100-150 Cooling water processing(m/h) 2.5-3 3-4 4-5 5-6 Weight of biggest parts(T) 4 5 11 14 dimension(length x width x height,mm) 3200x2340x2700 3600x2900x3200 3900x3300x3800 4200x3550x4200 Application scope It is used to purify the non-metallic minerals and separate the low intensity magnetic minerals. The non-metallic minerals includes quartz, feldspar, nepheline, fluorite,spodumene,kaolin. The low intensity magnetic minerals includes hematite, limonite, ilmenite, wolframite and tantalum-niobium ores.

The separator possesses many advantages such as high magnetic field intensity, high gradient magnetic field, big concentration ratio, having a wide range in the particle size of feeding ore and the thickness of slurry, intelligent control operation, get a satisfactory mineral processing result when separate the low intensity magnetic ores.

The magnetic particle in the separation cavity separate from the non-magnetic particle by the different magnetic force, pulsating fluid force and gravity which those particles are acted on. The magnetic particles are absorbed on the magnetic media, the nonmagnetic particle will discharge from the iron discharge. several minutes later, magnetic cutting, then flushing the magnetic particle from the magnetic media.

It is used to purify the non-metallic minerals and separate the low intensity magnetic minerals. The non-metallic minerals includes quartz, feldspar, nepheline, fluorite,spodumene,kaolin. The low intensity magnetic minerals includes hematite, limonite, ilmenite, wolframite and tantalum-niobium ores.

dry electromagnetic separator

dry electromagnetic separator

Its been difficult to make an iron separation of grain size under 0.1mm due to particle attraction and adhesion to the separator. CG directs the magnetic flux to the center of unit and enhances higher flux density without magnetic leakage. Vibration of the filters ensures effective removal of iron to improve screen flow rate and maximize good product recovery.

Our new CG-Mini reduces the footprint by 32%, 20% smaller coil casing, 25% less weight, half the screens, and still offers 50% of the Magnetization power. With honeycomb screens it is expected to trap 81% of contamination of its big brother.

Electromagnetic screens capture fine ferrous material in the micron range. Vibrators ensure effective and smooth flow of the material through the screens. Eight styles of screens are available to achieve the best results based on the materials flow characteristics and desired purity level.

Three sizes are available in the basic unit with four levels of magnetic strength in each, up to 12,000 Gauss. Options for additional impact vibrators for cleaning are also available. Several screen types and pitches are available.

The model CG-xxx-X series is our new series of ultra-high Gauss magnetic separators. This series has 7% increase in Gauss strength, is bigger and better than even our highest strength standard units. This unit is designed to meet the needs of ultra-high purity requirements in a high production environment. Coupled with our new honeycomb or micropitch screens, this unit captures more than 95% of SUS304. The CG-xxx-X is targeted to the lithium processing market sector but is also useful in pharmaceuticals, chemical and carbon black markets.

The model CG-mini series is our new series of ultra-small footprint magnetic separators. This unit is targeted at application where size is more important than Gauss strength. Many times, purification or separation is an after thought in production and there is little room to add a massive separator. This little guy is smaller and shorter but still packs a punch with

dry magnetic separator - magnets by hsmag

dry magnetic separator - magnets by hsmag

Introduction and function of Dry magnetic separator BY HSMAG The dry magnetic separator is commonly used iron ore and manganese ore beneficiation equipment. It is the mainstream strong magnet separator, which is specialized in processing dry magnetic minerals. The wet type magnetic separator use liquid diluents to improve separation efficiency. The dry type magnetic separator requires that the material must be dry, and can move freely between the particles. Or it will affect the separation result, and even cannot separate materials.

The magnetic system of dry type magnetic separator adopts high quality ferrite or using the composite material by rare earth and magnetic steel. The average magnetic induction strength of tube surface is 100-600mT. According to the requirements of users, we can offer downstream, semi-countercurrent and countercurrent and other types of magnetic separators. The advantages of this magnetic separator are: simple structure, large capacity, easy to operate and easy to maintain.

Dry magnetic separator equipment is commonly used iron and manganese equipment, mainstream intensity magnetic separator mineral processing equipment. Dry magnetic separator for dry magnetic separation of magnetic minerals beneficiation machinery, as opposed to wet magnetic separator to use when sorting mineral liquid as a diluent to improve separation efficiency, the dry magnetic separator is required to be separation of the mineral drying, particles can move freely, into independent free state, otherwise it will affect the magnetic effect, or even result in non-separation of the consequences. Dry magnetic separator for particle size below 3mm magnetite, pyrrhotite, roasted ore, ilmenite and other materials, wet magnetic separation, but also for coal, non-metallic minerals, building materials and other materials in addition to iron work .

Working principle and Characteristic of Dry magnetic separator Dry magnetic separator is the successful development of our new high-performance magnetic separation equipment. Department of all the magnetic are made by rare-earth Nd-Fe-B high-performance materials and high-quality ferrite materials. After a cleverly designed open-circuit, tube scale constituencies can achieve the maximum magnetic induction more than 0.8T, the magnetic field strength of conventional magnetic machine 3 -5 times that of the magnetic field strength at the constituency up to Electromagnetic Separator strong magnetic level. Cylinder separation refined by the use of wear-resistant stainless steel. Mineral sorting through the vibration feeder evenly separate of the upper tube, rotate the cylinder to cylinder behind that of non-magnetic materials, magnetic materials by the strong magnetic field force suction to the cylinder, with sub-ore easily board, accurate to the magnetic separation of non-magnetic materials. Strong magnetic field strength with Drum Magnetic separator for sub-select, weak magnetic minerals into a reality. Equipment to deal with a large amount of sorting a wide range of mineral grain size, separation of high precision, non-blocking; simple structure, easy maintenance, strong electromagnetic power consumption of only 20% of magnetic separator.wet magnetic separator

Dry Permanent magnet drum magnetic separator is my new company successfully developed highly efficient magnetic separation equipment. Department of the use of high-performance magnetic NdFeB rare-earth materials and high quality ferrite materials production, a cleverly open magnetic circuit design, tube highest breakdown constituency 0.8T magnetic induction to reach more than conventional magnetic field strength in the magnetic machine 3 -5 Times the sub-constituency of the magnetic field strength can be achieved strong electromagnetic Magnetic Separator the level of magnetic force. Sorting using wear-resistant stainless steel cylinder from refined; mineral sorting through the vibration feeder evenly to the separation of the upper part of the cylinder, the cylinder of rotating non-magnetic materials out-stripped the cylinder, magnetic materials by the strong magnetic field force To the suction tube, with sub-plate mine easily and accurately be magnetic, non-magnetic material separation.

Strong magnetic field strength used to drum Magnetic Separator at selected weak magnetic minerals into a reality. Handle amounts of equipment, sorting a wide range of mineral grain size, high precision, isolated, non-plug; simple structure, easy maintenance, power consumption is only strong electromagnetic Magnetic Separator of 20%. CTG Dry Magnetic Separator main purpose: the election of the regional water iron work; refractories and other materials in addition to the iron work.

HSMAG is a professional magnetic separator manufacturer. Its dry type magnetic separator has the following features: 1, dressing without water: because it belongs to dry type separator, it doesnt need water. Compared with wet type separator, it can save water and has no sludge and water pollution. Take the HSCTB primary dressing machine as an example, this machine can save at least 600 thousand tons of water every year. 2, good sorting effect: because this machine has dynamic magnetic system, the materials can slide and move in the surface of roller without stick up to the rotary drum, which is good for sorting the materials. The primary grade can be increased 1-4 times. The concentrate grade can reach 60% or more in the primary dressing process. 3, large capacity: the machine has open magnetic system and has no clogging. The capacity of single machine can reach 50 tons or more. Multi-parallel machines can increase the capacity in times. 4, wide range of applications: our dry type magnetic separator has four categories, and over 20 kinds of specifications and models. It can meet the requirements of many industries such as iron ore, river sand, tailings, slag, steel ash, abrasives, refractoriness, rubber and agriculture. Some of the equipments have multipurpose. 5, high efficiency: because it is not restricted by water resources, it can increase 100-150 workdays every year and improve the utilization rate of equipment in the waterless regions, seasonal water shortage areas and alpine regions.

Half Magnetic Drum, Magnetic Drum Systems, Half Magnetic Drum Roller, Drum Magnets, automated separating system, Permanent Magnetic Drum Rotating Magnet, Magnetic Rotary Separator China Supplier Half Magnetic Drum, also named half magnetic roller, has a half disc(180 degree) stationary magnetic section that is covered by a revolving round stainless steel shell with rotation axis. It []

Permanent Magnetic Drum, Rotating Drum Magnet, Magnetic Head Roller, Permanent Drum type Magnetic Separators, Magnetic Drum Pulley, Rare Earth NdFeB and Ceramic Drum Separation Magnets China Supplier Factory Permanent Drum type Magnetic Separator is most useful for separating tramp iron from non magnetic material processed in bulk quantity, for the purity of end products, recovery []

Magnetic Drum Separators, Drum Magnets, Magnetic Drum Roller, Head Pulley Magnet, Drum Magnetic Dry / Wet Separators, Permanent magnetic separation drums, Ceramic and Rare Earth-Neodymium Magnet Drum China Supplier Magnetic Drum Separators, Drum magnets, also called separation drums, contain two sectors one magnetic and the other not. There is a drum which rotates around []

Magnetic Drum Roller, Drum Magnet Systems, magnetic pulleys, Magnetic Head Roller, Rotating Drum Magnets, Permanent Magnetic Drums China Supplier We are offering our clients with Magnetic Drum Roller Systems that are manufactured using high grade raw material and latest technology. Our automatic systems have the capability to cover a magnetic field of over 180 at []

new highly efficient dry separation technologies of fine materials | springerlink

new highly efficient dry separation technologies of fine materials | springerlink

During cleaning of high-ash coal mainly wet processes are used which require 510tonnes water consumption per 1tonne of coal. Arrangement of recycling water supply reduces demand in fresh water, but transportation of huge volumes of water slurry requires high-energy consumption. Dry cleaning of low-rank coal which has not been exposed to preliminary preparation is inefficient. It was suggested that to provide dry cleaning of high-ash coal it would be reasonable to expose it to chemical heat treatment first, and then to direct the treated coal mass for physical and mechanical cleaning to get the low-ash high-caloric product. It has been determined that in black coal exposed to medium temperature pyrolysis, as well as in brown coal, improvement of incombustible mineral fraction liberation is observed that facilitates further beneficiation with the use of a combination of high-intensity magnetic separation and triboelectrostatic separation. It has been determined that cleaned semicoke substantially exceeds both initial and cleaned coal by its qualities as a solid fuel, and tailings of semicoke dry cleaning can be utilised.

Mined coal is exposed to long processing flowsheet ending with its use as a fuel in the energy industry, metallurgy or chemical industry. There are several stages in this processing flowsheet at which the largest economic waste occurs and the environment is subjected to damage. For example, during coal cleaning mainly wet processes are used which require 510 tonnes water consumption per 1 tonne of coal. Arrangement of recycling water supply reduces demand in fresh water, but transportation of huge volumes of water slurry requires high-energy consumption.

Long-distance transportation of commercial coal is associated with expenses occurring due to movement of a relatively low-caloric product containing in addition from 15 to 25% of ballasting ash fraction.

On the basis of the above, one may suggest that to provide for dry cleaning of high-ash coal, it is reasonable to expose it first to heat treatment, and then direct the treated coal mass for physical and mechanical cleaning to get the low-ash high-caloric product (coal char fuel).

For the liberation of ash fractions in high-ash coal, it is usually required to grind material up to particle size less than 1mm. To separate ash fractions with such particle size, it is possible to use pneumatic separation, magnetic separation and triboelectrostatic separation. The use of pneumatic separation for extraction of ash fraction out of coal has been studied rather well [9, 10] and has not been considered in this study. Studies on the use of magnetic and triboelectrostatic separation for extraction of ash fraction from coal proved their prospectivity [10, 11, 12, 13, 14]. The main difficulty for the processes of separation of mineral powders with the particle size less than 1mm by their magnetic and electrical properties is provided by the availability of internal friction forces in powders which hinder effective separation of mineral particles. Studies proved that to overcome the internal friction forces in mineral powders, one may use the effect of vibrofuidization occurring during overlapping of certain vibrations [15]. The use of this effect allowed the creation of effective separators for separation of fine mineral powders by magnetic and electrical properties described in [16] and used in this study.

Pyroysis of the coal sample under test at a laboratory unit showed that at t=550C, semicoke yield makes 63.8%, the yield of pyrolysis oil is 11.4%, pyrolysis gas20%, pyrogenetic water4.7%, that is in good correspondence with the results received by Fishers method.

Magnetic separation of raw coal and semicoke grinded up to particle size 00.5mm was conducted in a laboratory magnetic separator in two stepsthe first was at magnetic field induction of 0.35 T, the secondat 1.7 T.

The results received to prove the practicability of using thermochemical modification of high-ash black coal to increase the efficiency of its dry cleaning with the use of physical and mechanical processes.

It has been determined that in black coal exposed to medium temperature pyrolysis, as well as in brown coal [8], improvement of incombustible mineral fraction liberation is observed that facilitates further beneficiation.

Final tailing of semicoke dry cleaning containing more than 50% of combustible mineral fractions is raw material for the production of a binding agent for construction, i.e. cement analogue, which can be derived by means of their combustion without additional fuel and used for back filling of coal mines.

Cleaning high-ash coal without using water requires a new approach to the organisation of its conversion. To create conditions providing the possibility of dry cleaning of high-ash coal requiring its fine grinding for exposure non-combustible mineral fractions, it is reasonable to perform thermochemical modification of coal before cleaning. Medium temperature pyrolysis at t=450600C is an effective method of modification of high-ash coal providing possibility of dry cleaning derived semicoke with the use of high-intensity magnetic separation and triboelectrostatic separation.

Research being carried out with the financial support of the state represented by the Ministry of Education and Science of the Russian Federation. Agreement No. 14.579.21.0023. 05. Jun 14. Unique project Identifier: REMEF 157914X0023.

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magnetic separation technology can improve grinding circuit efficiency | e & mj

magnetic separation technology can improve grinding circuit efficiency | e & mj

The presence of grinding ball fragments in the milling circuit can impact two critical areas in minerals processing. One is the crushing circuit where companies have observed damage to crushers, unscheduled downtime and loss of production. Grinding ball fragments, for example, can cause damage to a cone crusher mantle.

The second is the grinding circuit where ball fragments have resulted in wear to pumps and damage to pump impellers, as well as sumps, piping, hydrocyclones and liners. Fragments can also lead to inefficient grinding, increased power consumption and less-than-optimal throughput.

There are several proven magnetic separation techniques available today to reduce or eliminate grinding ball fragments, depending upon the application and circuit location. Each has its own set of challenges, and each is approached in a different manner.

SUSPENDED ELECTROMAGNET IN PEBBLE CRUSHER CIRCUITSSuspended electromagnets (SE) are designed to capture pieces of tramp metal with a large mass (e.g., steel scats) rather than smaller metal pieces. The larger the mass, the more likely the SE will pick up the object in spite of maximum burden depth.

However, in a pebble crusher application, the majority of the metal is typically minus 45 in. To effectively separate 100% of +1/2-in. chips, at least two magnets and a metal detector or three magnets in a series are recommended. The first magnet can be crossbelt, but the second and third are recommended to be positioned in-line.

SEs are typically mounted in the crossbelt or in-line position over a pebble crusher conveyor belt, mostly depending upon belt speed. If belt speed is fairly slow (300 ft/min or less), then pulling tramp metal out of burden depth should not be an issue. When the belt is traveling faster, its better to have the SE mounted just over the stream of material leaving the head pulley; material coming off faster-moving belts results in a higher trajectory free-fall off the head pulley, clear of any burden. The SE can also capture the tramp metal as it flies off the head pulley; however, a non-magnetized head pulley is recommended in this case.

Be aware that properly sized magnets for pebble crusher circuits do not follow conventional magnet selection norms. Through experience, companies like Eriez have adopted new selection norms to ensure the pebble crusher circuits operate continuously and trouble-free.

As material reaches the end of the screen, the magnetic field lifts and holds ferrous chips and scats on the drum shell. As the drum revolves, it carries the material through the stationary magnetic field to the top of the drum onto a separate discharge. The nonmagnetic material falls freely from the screen onto a conveyor belt.

A heavy-duty magnetic drum separator is commonly used in minerals processing. The drum consists of a stationary, shaft-mounted magnetic circuit completely enclosed by a rotating drum. The magnetic circuit has segments of alternating rare-earth magnets and steel pole pieces that span an arc of 120. The steel poles are induced and project a high-intensity, high-gradient magnetic field.

The nonmagnetic material discharges in a natural trajectory from the screen. The magnetic material is attracted to the drum shell by the magnetic circuit and is rotated out of the nonmagnetic particle stream. The drum separator treats relatively coarse material in a high-capacity, severe-duty application.

TRUNNION MAGNET WITH BALL MILL DISCHARGEThe trunnion magnet is an enhanced system for separation and removal of balls, chips or scats in a typical ball or SAG mill operation. The trunnion magnet is mounted at the SAG ball mill discharge point and is used in place of a trommel screen.

The trunnion magnet consists of a barrel or blind trommel that is mechanically attached to the trunnion or discharge of a ball mill. The barrel rotates around a fixed assembly of ferrite and rare-earth magnets, positioned on the outside of the barrel. The stationary magnetic assembly, approximately 28 in. long, covers an arc of about 210, and attracts chips and scats to the inside diameter of the barrel. As the ball mill slurry discharges through the barrel, eight strategically placed lifters inside the barrel carry the ball fragments to the top, where they fall onto a sloping discharge chute.

In a typical grinding mill application, the grinding media eventually fractures and wears into a fine metallic powder because of the heavy recirculating load in the mill. Fragments of grinding media eventually accumulate in the ore being processed and can cause serious damage to other equipment in the grinding circuit such as pumps and hydrocyclones.

The foremost reason to use a trunnion magnet system in a ball mill is to replace the deadweight of ball fragments with fresh ore. The effective removal of chips and scats from a ball mill leads to lower power consumption from the mill drive. Eriez trunnion magnet can provide the solutiona powerful and efficient magnetic separator that can effectively remove as much as 80% or more of the worn/broken media.

One example of the trunnion magnets effectiveness was recorded at the Kemess mine in British Columbia, an open-pit copper and gold operation. There, the effect of a trunnion magnet system on the ball mill was significant: Total mill feed remained essentially unchanged, averaging approximately 1,300 t/h; however, total mill power consumption dropped 8% from an average of 7,600 kW to 7,000 kW. The mill work index dropped 10% from an average of 5.5 kW-hr/T to 5 kW-hr/T.

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