RU2452582C1 - Method of generating travelling magnetic field in electrodynamic separator working zone and device to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates dressing of minerals and may be used for extraction of fine conducting particles, e.g. gold, silver, platinoids from metal-containing gravel deposits of various genesis. Proposed method consists in that single magnetic field pulses are generated to shape travelling magnetic field pulse groups. Note here that said pulses are synchronised in said group while pulse amplitude and group repetition rate are selected to ensure required extraction of valuable particles from bulk flow.

EFFECT: higher efficiency, power savings, expanded range of extracted particles.

4 cl, 4 dwg

Description

The group of inventions relates to the field of mineral processing, in particular for the extraction of small conductive particles, such as gold, silver, platinoids from metal-containing placer deposits of various genesis, as well as for their extraction from ores, concentrates and tailings. More specifically, the invention relates to a method for electrodynamic separation of metal-bearing sands and a device for implementing this method.

The essence of electrodynamic separation is that eddy currents are induced in the particles of materials to be separated using an alternating magnetic field, due to which the induced magnetic moments appear in the particles, and thus their magnetic properties change. The greater the eddy currents excited, the greater the magnetic moments of the particles, the greater the differences in their magnetic properties. The eddy currents in the particles, according to the law of electromagnetic induction, are determined by their electrical conductivity and the rate of change of the magnetic field induction

,

,

where I is the eddy current in the particle; σ is the electrical conductivity of the particle; B - magnetic field induction.

Since the electrical conductivity of metal particles is large, eddy currents in them are always large, and metal particles interact with an external magnetic field more strongly than particles of host rocks.

Known methods for generating an alternating magnetic field in the working area of electrodynamic separators, such as: by movement in the immediate vicinity of the working area of permanent magnets, and by generation of electromagnets, also located in the immediate vicinity of the working area and powered by alternating current (US 4743364, class B03C 1 / 22, published on 05/10/1988 and US 6095337, class B03C 1/23, published on 08/01/2000).

The intensity and rate of change of the magnetic field in the working zone obtained by such methods is limited either by the magnitude of the permanent magnetization of the permanent magnets and their speed of movement relative to the separated material, or by the amount of energy consumed by the electromagnets and the saturation induction of the core material. The field strength obtained by such methods does not exceed ~ 1.5 · 10 ⁴ G. The frequency of changes in the magnetic field in electromagnets is also, most often, limited by the frequency of changes in industrial variable currents - 50 (60) Hz. Therefore, commercially available electrodynamic separators from transporting streams only metal particles larger than 15 mm are well recovered. Commercially available electrodynamic separators are not used to extract finer metal. An obstacle to this is the insufficient magnitude of the magnetomotive force in their working area. This is the main disadvantage of the known methods.

A device for magnetic separation of finely divided raw materials is known, comprising a vibratory feeder equipped with a dielectric cone, a separation chamber in the form of a hollow perforated dielectric cylinder with staggered holes thereon provided with ribs helically wound along the location of the holes. A rotating magnetic system, which is a hollow vertically oriented cylinder of dielectric material, containing on the outer side alternating in polarity rows of blocks of permanent magnets radially along the cylinder axis of the same polarity in a row (RU 2295392, class B03C 1/24, published March 20, 2007 g.).

The mentioned device allows the separation of ferromagnetic, paramagnetic and diamagnetic impurities and can be used, for example, to extract gold from certain types of gold-containing sands in grain size classes +1 mm. The device extracts large (+1 mm) ferromagnetic and paramagnetic particles, and the diamagnetic fraction, together with the host inert material, small ferro- and paramagnets, goes into tails.

The main disadvantages of the known device are the low efficiency of extraction of a valuable component of mineral particles with a particle size of 1 mm, and the inability to isolate the diamagnetic fraction from the containing material (i.e., the device does not separate, for example, fine gold and inert containing material). This disadvantage is especially pronounced when trying to enrich sand, in which the starting material is almost completely composed of an inert dielectric material and contains diamagnets only in small quantities (for example: metal-bearing sands with a low content of ferromagnets and a fine and fine gold content of ~ 1 ÷ 0.1 g / m ³ ). In this case, all the gold (diamagnet) during separation by the criticized device remains together with the host rocks, i.e. not shared.

The closest in technical essence to the proposed method and device is the device of an electromagnetic separator for mineral processing, using a generated traveling magnetic field in which the magnetic system is made in the form of two coils with power supplies located coaxially. The pulses of the magnetic field of the second coil have a delay relative to the pulses of the magnetic field of the first coil for a time ΔT = 0.1 ÷ 0.4 T _imp , where T _imp is the duration of the magnetic field pulse (RU 2351398, class B03C 1/02, published on April 10, 2009) .

The disadvantage of this device is its low productivity, so the extraction of useful components from the mass flow of the material to be separated is milligrams per minute, so this device is not suitable for industrial use.

It should be emphasized that a metal particle will change its trajectory only when the sum of the forces acting on it from the side of the magnetic field becomes greater than the sum of the forces holding it inside the particle stream of the host rocks. The force acting on a mineral particle in the working volume of an electrodynamic separator can be conveniently estimated using the formula (see Dyadin V.I., Kozhevnikov V.Yu., Kozyrev A.V., Podkovyrov V.G., Sochugov N.S. Electrodynamic method separation of small conductive particles // Physico-technical problems of the development of minerals. 2008. No. 3. S.132-139):

where R is the radius of the metal particle;

σ is the particle conductivity;

H is the magnetic field strength;

B - magnetic field induction in the particle material.

It follows from the formula that it is possible to extract metal particles with a particle size of less than 1 mm from the transporting mass flow of non-conductive particles only in a large amplitude, rapidly changing in time and space field. A magnetic field with the necessary characteristics can only be obtained with the help of electromagnets. But the continuous generation of magnetic fields with such characteristics requires an extremely large energy consumption. Therefore, the creation of power sources and working units for electrodynamic separators, which allow efficiently extracting metal particles with a particle size of less than 1 mm, is a difficult technical task.

The technical result of the invention for an object of the device is to increase its productivity and significantly reduce energy consumption, and for both claimed objects is to increase the efficiency of extraction of small fractions of a useful component by creating conditions for increasing the intensity, rate of change and gradient of the magnetic field, which gives an increase in magnetomotive force in the working separator zone and allows you to expand the range of particle size classes of recoverable metal particles due to small and thin x fractions, including those having a flat shape.

The named technical result is achieved in the proposal due to the use of a pulsed traveling magnetic field and a fundamentally different organization of the mass flow of the material to be separated.

The pulsed generation method allows one to obtain fields with parameters that are fundamentally unattainable during continuous generation, in which a huge amount of energy is consumed to obtain the field, which ultimately turns into heat, capable of not only remelting the material to be separated, but also the installation itself.

To obtain a pulsed field with parameters sufficient to separate small particles, the energy needs to be tens of times less, so it is much easier to cool such a device. As a result, it becomes possible to generate sufficiently powerful fields and create facilities for the separation of small particles.

The essence of the proposed method for generating a traveling magnetic field in the working area of an electrodynamic separator is that to generate eddy currents required to extract metal particles with a particle size of less than 1 mm, single magnetic field pulses are generated, from which form trains of a traveling magnetic field, while magnetic field pulses they are synchronized inside the train, and the pulse amplitude and the train repetition rate are selected from the condition of ensuring the required degree of extraction of enriched particles from the mass flow about the class size of the useful component.

The main advantage of the proposed method is the possibility of generating at a low energy consumption in the working space of magnetic field separators with characteristics that are fundamentally unattainable for continuous generation systems. Due to this, the range of recoverable size classes of the useful component is expanded due to small and thin size classes, and, thereby, the overall efficiency of the enrichment process increases.

Verification of the proposed method was carried out in a laboratory setup, a diagram of which is shown in figure 1.

For the experiments, K ₁ and K ₂ coils were used, each having 24 turns, made of a copper bus 0.2 mm thick and 5 mm wide. Inter-turn insulation is made of a polyimide film 50 microns thick. The inner diameter of the coils is 5 mm, the outer is 24 mm, their inductance is 12 μH. Coils are rigidly fixed at a distance of 6 mm from each other. The current pulses in them, close in shape to one sinusoidal period, are formed using an LC circuit including a storage capacitance C ₁ (C ₂ ) with a nominal value of 80 μF, a protective inductance L ₁ (L ₂ ) with a nominal value of 7 μH, and a coil K ₁ ( K ₂ ). The circuit was switched by fast pulse thyristors T ₁ (T ₂ ) brand TBI243-500. The first half-cycle of the current pulse flows through the thyristors, when the current direction changes in the second half period, the diodes D ₁ (D ₂ ) of the ДЧ143-500 brand open, and the second half of the pulse flows through them. The storage capacities were charged by chargers ZU1 and ZU2 to voltages from 500 to 2000 V, which ensured the receipt of current pulses in coils with an amplitude of up to 2 kA. The impedance of the discharge circuit was 1 Ohm; therefore, the amplitude of the pulse current was numerically equal to the charging voltage. The control system, indicated in FIG. 2 by block 14, could generate both single pulses and pulses with a repetition rate of up to 100 Hz, but only single pulses were used in the experiments described.

As model particles, pieces of copper wire with a diameter of 0.05 to 0.4 mm were used. The length of the particles was approximately equal to their diameter. Each particle was fed into the space between the coils from the reset system, indicated in block 2 by block 15, by opening the electromagnetic shutter of the outlet. After a delay time τ ₁ equal to the passage of the particle from the outlet of the discharge system to the center of the coils and amounting to about 40 μs, the thyristor T _{1 was} started and a current pulse was formed in the first coil. After a delay time τ ₂ relative to the start of the first thyristor, the thyristor T _{2 was} started and a current pulse was formed in the second coil. The delay time τ ₂ could vary from 0 to 100 μs and was one of the experimental parameters. The generation of two biased current pulses in the coils led to the formation of a pulsed traveling magnetic field between the coils, directed from the first coil to the second.

The falling particles fell on the receiving plane, located 25 cm lower from the center of the coils and representing a surface coated with a layer of oil with a millimeter grid. A layer of oil prevented the rebound of falling particles, allowing you to fix the true location of the fall of the particle. By measuring the distance L from the point of vertical incidence of particles in the absence of a field to the point of incidence of particles in the presence of a field, we determined the horizontal velocity acquired by the particle in the separator in the approximation of its constancy during incidence, which was also taken constant in the approximation of uniformly accelerated particle motion in the gravitational field and equal to 0.22 from.

It should be noted that the particles had a complex shape and fell into the zone of influence of the pulse. In addition, the moment a particle reaches a point between the centers of the coils could vary within a few milliseconds due to the scatter of the moment they fall out of the outlet of unit 15. These features led to the fact that the particle was exposed to a traveling magnetic field pulse not necessarily exactly at the point between the centers coils, and in some neighborhood around this point. As a result, the particle acquired various velocities, and a particle distribution was formed on the receiving plane, the result of which was their spread over the calculated acquired velocities.

Figure 2 presents a graph of the experimentally measured and theoretically calculated speed acquired by a particle on its diameter, for two values of the charging voltage: 1 - 1500 V; 2 - 2000 V. From the graph it follows that, within the limits of the change in the experimental parameters, only the deviation of particles with a diameter of 0.05 mm was not recorded, i.e. their deviation was less than a reliably measurable quantity. Already particles with a diameter of 0.1 mm acquired a speed of 1-2 cm / s, which suggests the possibility of separation of such particles in a pulsed traveling magnetic field formed by phase-shifted currents of two coils. In the range of diameters less than 0.2 mm, an acceptable agreement was observed between the experimental data and the calculated values obtained for the same conditions. Underestimated experimental values of velocities obtained with particle diameters greater than 0.2 mm are associated with the design features of the separator: the displacement by a distance of L ~ 2 cm is limiting, since at large angles of deviation of the particle from the vertical, it is able to touch the elements of the separator design and change the direction of motion. This is manifested in an increase in the dispersion of particles on the receiving surface and an underestimation of the average deviation.

Figure 3 presents a graph of the dependence of the particle velocity on the pulse delay of the second coil relative to the first pulse. Charging voltage 1500 V; 1 - particle diameter 0.4 mm, 2 - 0.25 mm. Based on the graph, the traveling field effect is visible: when the coils are turned on simultaneously, the particle speed is close to zero, the maximum speed is achieved when the second coil is turned on for about 50 μs, which corresponds to about 0.2 of the oscillation period, as predicted by theoretical calculations, based on which the speed acquired by a particle is inversely proportional to the square of its size, but directly proportional to the square of the field (i.e., the square of the current in the coils and the square of the charging voltage). Therefore, to maintain a constant particle velocity, while reducing its size, it is necessary to proportionally increase the current in the coils.

It is important to note that the parameters used in the experiment are not limiting for modern power semiconductor devices. A multiple increase in operating voltages and currents is possible. Thus, in a pulsed traveling magnetic field formed by phase-shifted currents of two coils, it is quite possible to accelerate particles with sizes of 50 μm or less to speeds of about 1-2 cm / s.

Based on the foregoing, we can conclude that the possibility of separation of small particles (of the order of 0.1 mm) in a pulsed traveling magnetic field generated by phase-shifted currents of two coils is theoretically justified and experimentally confirmed, and the proposed method can be used to create technologies for extracting small and fine gold from placer and man-made deposits.

The separator that implements the proposed method, allows you to effectively extract metal particles that are lost when the sand is enriched by existing methods (particle size -0.5 mm, +0.1 mm).

The proposed method of using a pulsed traveling magnetic field is implemented in an electrodynamic separator designed for the industrial enrichment of metal-bearing sands.

The separator contains a loading tank with a cone distributor, the output annular opening of which is connected to a means of supplying conveying material (metal-bearing sands) to the working area. This tool is made in the form of an annular chamber. The separator also contains a complex inductor consisting of several coaxial coils, at least two of which are located on the inner side of the annular chamber and are configured to push the conductive particles of the transporting material to the outer wall of this chamber, and at least one coil is located on the outside of the chamber and configured to attract these particles to the outer wall of the chamber.

The coils are connected to the corresponding sources of voltage pulses, the operation of which is synchronized in such a way that they feed successive magnetic field pulses into the windings of the inductor, forming trains of a traveling magnetic field. Under the annular chamber is a means of separating the conductive particles from the remaining particles of the transporting material, made in the form of a cone cutter.

In the separator, a system of forced liquid (oil) cooling is used, including containers for coolant located on the inside and outside relative to the coils of the complex inductor.

As a cooling agent, transformer oil can be used. To reduce the energy consumption of the proposed separator, liquefied gases such as liquid nitrogen or hydrogen can also be used as a cooling agent.

Figure 4 schematically shows the design of the proposed separator, consisting of: a loading tank 1 with a cone distributor 2, a complex inductor consisting of a set of voltage pulses connected each to a separate source, coaxial, flat, frameless coils 3.1, 3.2 and 3.3, separated by distance washers 4, coupling flanges 5 and 7, containers 6 for coolant, current leads 8, a hollow cone cutter 9 separating the extracted material 10 from non-conductive particles 11, coupling screws 12 and installed between the coils kami complex inductor annular chamber 13.

The device operates as follows.

Classified, with a separated magnetic fraction, the source material is fed uniformly into the loading container 1 to a cone distributor 2 and through the annular chamber 13 it enters the working area of the inductor coils under the influence of a pulsed traveling magnetic field generated by sources and coils 3.1, 3.2, 3.3. Moreover, coils 3.1 and 3.2 are pushed out, and coil 3.3 attracts conductive particles to the outer wall of the annular chamber. As a result of interaction with a pulsed traveling magnetic field, the conductive particles 10 are removed from the mass flow and fall outside the edge of the cutter 9. The non-conductive inert material 11 with the magnetic field practically does not interact and freely falls into the gap between the cylindrical surface of the container for cooling liquid 6 of the inductors 3.1 and 3.2 and the cutter 9. This is the spatial separation of the components of the source material.

The described separator allows the efficient extraction of metal particles of particle size class -0.5 mm, +0.1 mm.

Claims (4)

1. A method of generating a traveling magnetic field in the working area of an electrodynamic separator, which consists in generating single pulses of a magnetic field from which trains of a traveling magnetic field are formed, while the pulses of the magnetic field inside the train are synchronized, and the pulse amplitude and pulse repetition rate are selected from conditions for ensuring the required degree of extraction from the mass flow of particles of the enriched particle size class of the useful component. 2. An electrodynamic separator for the enrichment of metal-bearing sands, containing a loading container for conveying material with a cone distributor, an outlet ring opening of which is connected to a conveyor material supply means in the form of an annular chamber, a complex inductor consisting of several coaxial coils of at least at least two of which are located on the inner side of the annular chamber and are configured to eject conductive particles transporting material to the outer wall of this chamber, and at least one coil is located on the outside of the chamber and is configured to attract these particles to the outer wall of the chamber, while the coils are connected to the corresponding voltage pulse sources, the operation of which is synchronized so that they are in the inductor windings the magnetic field pulses following one after another form the trains of the traveling magnetic field, and a means for separating the conductive particles from the transporting material is located under the annular chamber. 3. The separator according to claim 2, characterized in that the means for separating the conductive particles from the conveying material is made in the form of a cone cutter. 4. The separator according to claim 2, characterized in that it is equipped with containers for coolant located on the inside and outside relative to the coils of the complex inductor.

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