RU2351398C1 - Electro-dynamic separator - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention refers to concentrating minerals and can be implemented for separation of small metallic inclusions, particularly, gold from flow of bulk solids, specifically, from sand of placer and anthropogenic deposits. The electro-dynamic separator of conducting particles contains a coil with a power source for generating pulse magnet field, a facility for supplying mixture in magnet field zone, an intake capacity for conducting particles, and an intake capacity for non-conducting particles. Additionally the separator contains the second coil with power source assembled coaxially to the first one. Pulses of magnet field of the second coil are retarded relative to pulses of magnet field of the first coil for the period of ΔT=0.1÷0.4T_puls, where T_puls is duration of pulse of magnet field.

EFFECT: increased efficiency of separation due to extraction of small and thin metal fractions which can not be extracted by gravitation methods because of physical-chemical properties of particle surface.

1 cl, 3 dwg

Description

The invention relates to the field of mineral processing and can be used for the separation of small metal inclusions, in particular gold, from the flow of bulk material, in particular sand, placer and man-made deposits.

It is known that the main losses of placer and ore gold occur in primary beneficiation operations, in which mainly thin, lamellar and pulverized gold with a particle size from a millimeter to several microns are lost. In connection with the depletion of most deposits, more and more poor, difficult to process, and complex in composition raw materials are involved in processing. Over the many decades of gold mining, the country has also accumulated a significant amount of man-made placers, which often compete in the content and reserves of gold with the deposits involved in processing today [1]. However, high-quality enrichment of refractory and technogenic placers is possible only with the help of new technological processes.

Gravity methods and extraction apparatuses used in modern gold mining have apparently reached the limit of their physical capabilities. Despite the huge number of inventions and improvements, metal with a size of less than 0.2 mm is poorly captured by these devices [2]. According to experts, there are about as much fine and thin gold left in Russian placers as has already been mined [3]. About 10,000 tons of gold lies in technogenic deposits located on the surface of the Earth, most often in the vicinity of already equipped areas. But in order to extract this gold, new primary enrichment technologies are necessary, which would make it possible to efficiently extract gold in the range of size classes - 0.2 - 0.01 mm.

Devices implementing new mining methods should have, in comparison with gravitational, better extraction capacity in the range of particle size classes - 0.2-0.01 mm., Higher productivity, and in comparison with leaching methods, be environmentally friendly and have the potential for further improvement and improvement their technical and technological characteristics.

Alluvial deposits are natural mixtures of minerals in which particles of free metal differ from the host rocks in high electrical conductivity. If an alternating magnetic field is applied to such a mixture, then Foucault eddy currents will be induced in all particles of the minerals. In metallic particles, due to the high conductivity, eddy currents will be much stronger than the currents in the host rocks. Foucault currents interact with an external magnetic field so that the conductive body is pushed out of the amplified field region. As a result of this interaction, a metal particle acquires a certain momentum, which allows one to separate conductive particles from non-conductive ones. This method is used in the magnetic separation of bulk minerals in high-gradient separators with permanent magnets, but the field created by moving permanent magnets allows you to separate only relatively large particles. The difficulty lies in the fact that the force acting on a conductive particle placed in a gradient magnetic field depends on the ratio of the particle size R to the thickness of the skin layer (the depth of penetration of the magnetic field into the metal) λ. If the particle size is less than the skin layer thickness, then the mechanical momentum acquired by the particle turns out to be very small, and the final particle velocity rapidly decreases with decreasing R / λ ratio.

There are a significant number of patents devoted to improving the methods of electrodynamic separation of conductive particles. In US patent No. 4743364 and No. 6095337 [4, 5] describes a method of separation of electrically conductive particles from a non-conductive material, based on the use of a high-frequency magnetic field excited by a magnetic coil in the core gap made of ferromagnetic material. A stream of material containing conductive particles is fed into the core gap, where the conductive particles acquire a momentum proportional to their size and can be separated from the stream of non-conductive particles. The disadvantage of this method is that in the described devices, a particle acquires an impulse sufficient for separation only if its size is comparable with the thickness of the skin layer, which in turn is related to the field frequency by the relation

,

,

where μ ₀ = 4π · 10 ^-7 GN / m is the magnetic constant, ω-circular frequency of the field, ρ-specific conductivity of the particle material. For the case of gold, a skin layer thickness of 1 mm will be achieved at a field frequency of about 20 kHz, and to reduce the skin layer by half, it is necessary to increase the field frequency by four times. The creation of high-frequency fields of high tension is a very difficult technical task and requires a large expenditure of energy, therefore, the minimum particle size that can be extracted by these methods is about 0.5 mm.

Bypass many difficulties that are insurmountable for both conventional and superconducting electromagnets, allows the technique of pulsed magnetic fields. Pulsed magnetic systems consume significantly less energy, making them easier to cool. The windings of pulse coils can be made from a thin conductor and receive fields in their working area with characteristics unattainable for permanent magnets, ordinary and superconducting electromagnets.

A separator using pulsed magnetic fields is described in a device that is a prototype of this application [6]. The separator contains a loading hopper, a receiving tank for conductive particles, a receiving tank for non-conducting particles, a solenoid (coil) with a source of current pulses and means for supplying the mixture to the magnetic field formation zone. The principle of operation of the separator is based on the fact that when a current pulse is passed through a coil, a pulsed high-gradient magnetic field is generated near it, exciting Foucault currents in a conducting particle located in this magnetic field. The interaction of Foucault currents with an increasing magnetic field leads to the ejection of the particle into the region of a weaker field, which allows us to obtain the effect of spatial separation of conductive and non-conductive particles.

The disadvantage of the prototype is that although in the process of increasing the magnetic field even a small metal particle acquires a speed sufficient for separation, when the field decays to zero at the end of the pulse, the particle speed also decreases to zero, since when the sign of the derivative of the field changes, the direction of the magnetic moment of the particle also changes sign and the particle accelerated at the leading edge of the field pulse will be inhibited at its trailing edge. As a result, the particle will have only a very small speed due to the final displacement of the particle during a short current pulse in the coil. Therefore, it is not possible to communicate a large momentum to a small particle using a single induction coil, in which the current rises and falls to zero. This is confirmed by numerical calculations that made it possible to determine the particle velocity depending on its size and field parameters.

Figure 1 shows a graph of the calculated particle velocity versus time for one half-cycle of the sinusoidal current of the coil, consisting of 10 turns (the radius of the inner coil is 2 mm and the outer one is 10 mm). The following quantities were taken for the calculation: particle material density ρ = 15000 kg / m ³ particle specific conductivity σ = 5 · 10 ^-7 (Ohm · m), particle radius R = 0.1 mm, pulse duration 120 μs, current amplitude 3 kA. Moreover, the maximum magnetic field strength on the axis of the coil is 3 · 10 ⁶ A / m, and the gradient of the intensity of 1.5 · 10 ⁹ A / m ² . It can be seen that during the action of the field pulse the particle acquires a velocity of the order of 1 cm / s, but by the end of the pulse it slows down to very low velocities, which do not allow the effective separation of the particle from the flow. The use of the asymmetric shape of the current pulse proposed in the prototype will not lead to a drastic change in the situation, since during the growth of the field the particle will not have time to significantly change its position, moving to the area of the weak field, so the particle will be inhibited almost to zero speed even by a slowly decreasing field.

The technical result achieved in this separator is to increase the separation efficiency due to the separation of fine and fine metal fractions, as well as metal particles that are not emitted by gravitational methods due to the physicochemical features of the particle surface.

The specified technical result is achieved by the fact that in the known electrodynamic separator containing a coil with a power source for generating a pulsed magnetic field, means for supplying the mixture to the magnetic field, a receiving tank for conductive particles, a receiving tank for non-conducting particles, according to the invention, an additional second coil with a power source located coaxially with the first, and the magnetic field pulses of the second coil have a delay relative to the magnetic field pulses of the first coil mja ΔT = 0,1 ÷ 0,4T _pulses, where T _imp - the duration of the pulse magnetic field.

The proposed device is shown in FIG. 2. As in the prototype, the separator contains a loading hopper 1, a receiving tank for conductive particles 2, a receiving tank for non-conducting particles 3, a solenoid (coil) 4 with a current pulse source 5 and means for supplying the mixture to the magnetic field formation zone 6. But the proposed the device also contains a second coil 7 with a power source 8.

The device operates as follows. A mixture comprising metal particles, for example gold, is loaded into the loading hopper, which, through the supply means 6, enters the zone between coils 4 and 7. Current coils are supplied to coils 4 and 7 from pulse generators 5 and 8 with a certain frequency, and the current pulse in the coil 7 is delayed relative to the current pulse in coil 4. In this case, the change in sign of the derivative of the magnetic induction will be simultaneously accompanied by a change in the sign of the gradient of the induction, and the force acting on the particle will not change sign until both current pulses end. As a result, the particle at this moment will retain a high speed of motion. Under the influence of a traveling magnetic field pulse, the metal particles will acquire a speed directed towards the second coil and during the fall they will be released from the non-conductive particles stream and fall into the receiving hopper for the useful product 2. The current pulses may have a shape close to one sinusoid period, as shown in figure 3, but may also have the form of a half period of a sinusoid, or have a duration of nT / 2, where n is an integer, T is the duration of the period.

1.6 см/с. Если сдвиг между импульсами тока варьировать, то максимальная скорость будет меняться, и оптимальный режим наблюдается при сдвиге между импульсами Δt≈Т/3 (именно этот случай и демонстрируется на фиг. 3).In FIG. 3 shows the results of calculations of the particle velocity in the field of two coils with the same parameters as in FIG. 1. It can be seen that the particle is always accelerated in a pulsed traveling magnetic field formed by two coils. The maximum particle velocity is reached by the end of the second pulse V _max

1.6 cm / s. If the shift between current pulses varies, then the maximum speed will change, and the optimal mode is observed with a shift between pulses Δt≈Т / 3 (this is the case that is shown in Fig. 3).

An experimental verification of the principle of operation of the proposed device was carried out on a layout assembled according to the scheme shown in figure 2. Coils 4 and 7 were made of a copper bus 0.2 thick and 5 mm wide. The internal diameter of the coils was 5 mm, the external diameter was 18 mm, the number of turns in the coils was 20. The coils were connected to generators 5 and 8, which generate current pulses in the coils with a shape close to one sinusoid period. The amplitude of the current pulses was 2.5 kA, and the pulse duration was 200 μs. As conductive particles, copper particles with a diameter of 0.25 mm were used. Instead of receiving bins 2 and 3, a receiving plane was located, which allows fixing the distribution of particles along the axis of the coils. The distance from the feeder 6 to the receiving plane was 0.25 m, which ensured a particle transit time of 0.22 seconds. In the experiments, the average deviation of the particles from the point of vertical incidence from the feed device was recorded, from which the speed that the particle acquires in the separator in the approximation of its constancy during incidence was determined.

Three experiments were conducted: with a current pulse passing only through coil 4 and with a current passing through both coils. The experimental results are given below.

Experiment 1 Parameter Value Amplitude of current in coil 4 2500 A The amplitude of the current in the coil 7 0A Average particle displacement not fixed The average particle velocity acquired in the separator 0 Experiment 2 Parameter Value Amplitude of current in coil 4 2500 A The amplitude of the current in the coil 7 2500 A The delay time between the current pulse in coil 4 and the current pulse in coil 7 40 μs Average particle displacement 5 mm The average particle velocity acquired in the separator 2.3 cm / sec Experiment 3 Parameter Value Amplitude of current in coil 4 2500 A The amplitude of the current in the coil 7 2500 A The delay time between the current pulse in coil 4 and the current pulse in coil 7 45 μs Average particle displacement 13 mm The average particle velocity acquired in the separator 6 cm / sec

Thus, experiments prove that the use of a system of two coils in a device can significantly improve the efficiency of separation of fine and fine metal fractions.

Information sources

1. Technogenic deposits of mineral raw materials. / Makarov A.B. // Soros educational journal, volume 6, No. 8, 2000.

2. Benevolsky B.I. Gold of Russia: problems of the use and reproduction of the mineral resource base. // M .: "Geoinformtsentr". 2002.446 s.

3. On the main issues of the study of clastic matter of sedimentary rocks and placer gold deposits. / Surkov AV, Khotylev OV // Mater. Scientific Seminar System "Planet Earth" (Unconventional issues of geology) February 4-6, 2004, Moscow, Moscow State University, pp.103-114.

4. US patent US 4743364, May 10, 1988

5. US patent US 6095337, August 1, 2000

6. Patent for utility model RU, by application No. 2006116399, May 12, 2006, positive decision dated June 13, 2007

Claims (1)

An electrodynamic separator of conductive particles, comprising a coil with a power source for generating a pulsed magnetic field, means for supplying the mixture to the magnetic field zone, a receiving tank for conducting particles, a receiving tank for non-conducting particles, characterized in that it further comprises a second coil with a power source located coaxially the first, and 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 - duration imp pulse of the magnetic field.

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