Magnetic separation and electrostatic separation

First, the basic principle of magnetic separation

Magnetic separation is a mineral processing method that uses the magnetic differences between minerals to separate different minerals in an uneven magnetic field. It is mainly used for the separation of ferrous metal ores and the selection of nonferrous and rare metal ores. Magnetic separation of nonmetallic minerals is to remove magnetic impurities such as iron from nonmetallic mineral raw materials, so as to achieve the purpose of purifying nonmetallic minerals.

After the ore enters the sorting area of magnetic separation equipment, the mineral particles are subjected to the combined action of magnetic force and mechanical force (including gravity, centrifugal force, hydrodynamic force, etc.). ), mineral particles with different magnetic properties are subject to different magnetic forces. Strong magnetic mineral particles are magnetized under the action of uneven magnetic field. Because the resultant force of magnetic force and mechanical force acting on each mineral particle is different, the magnetic separation between strong magnetic minerals and weak magnetic minerals (nonmagnetic minerals) is realized.

The magnetism of minerals is the basic property of minerals and the basis of magnetic separation. The magnetism of various minerals in nature can be divided into paramagnetism, diamagnetism and ferromagnetism (ferrous magnetism and antiferromagnetism). Paramagnetic minerals are weakly magnetic in magnetic field, and the representative minerals are rutile, wolframite, amphibole, chlorite, olivine, garnet and pyroxene. The diamagnetic minerals are also weakly magnetic in the magnetic field, and the representative minerals are galena, diamond, gypsum, fluorite, corundum, kaolin, coal, Yingshi and feldspar. Ferromagnetic minerals have strong magnetism in magnetic field, and the representative minerals are magnetite, maghemite, hematite, titanomagnetite and pyrrhotite.

The magnetic field of minerals is mostly expressed by their specific magnetization coefficient, which can be divided into three categories, as shown in Table 2-8.

Table 2-8 Mineral Magnetism and Classification

Second, magnetic separation equipment

Magnetic separation equipment has a variety of structures and classification methods. For example, there are weak magnetic fields and strong magnetic fields according to the magnetic induction intensity; According to the magnetic source, it can be divided into permanent magnet and electromagnetic; According to the operation mode, it is divided into dry type and wet type; According to the shape of the separator, there are belt, cylinder, drum, ring and so on. According to the feed particle size, it can be divided into coarse and fine magnetic separation equipment.

In the process of selecting magnetic separation equipment, it should be selected according to mineral magnetism and feed particle size, and the content of magnetic substances should also be considered in the magnetic separation of metal ore itself. Non-metallic minerals themselves are mostly non-magnetic minerals, but they often contain some magnetic minerals or weak magnetic minerals. Therefore, high gradient magnetic separators are widely used.

(1) weak magnetic field magnetic separator

The weak magnetic field magnetic separator is mainly used for the separation of strong magnetic iron ore. There are magnetic rollers and permanent magnet drum magnetic separators related to the separation of nonmetallic minerals. The former is used for dry separation of large coarse-grained ore, while the latter is used for wet separation of fine-grained ore.

1. magnetic roller (magnetic pulley)

Its structure is shown in Figure 2-23. It is a roller made of non-magnetic materials such as stainless steel, copper and aluminum. It is equipped with a circumferential magnetic system. The polarities of magnetic poles alternate along the axial direction N and S, and remain unchanged along the circumferential direction. The magnetic system is fixed on the shaft. Its magnetic system is formed by embedding permanent magnets. Its structure is simple, and it can be directly installed on the head of belt conveyor or configured as a separate dry magnetic separator.

The ore is evenly conveyed to the conveyor belt. When the ore passes through the magnetic roller, the non-magnetic or weakly magnetic lump ore leaves the belt surface under the action of centrifugal force and gravity and is thrown into the non-magnetic ore. Strong magnetic lump ore is attracted to the belt by magnetic force and moves with the belt until the belt at the lower part of the drum leaves the drum and straightens, and falls into the magnetic product tank due to the decrease of magnetic field strength. See Figure 2-23 (b) for the magnetic separation process.

Figure 2-23 Schematic Diagram of Permanent Magnet Roller Structure (A) and Schematic Diagram of Magnetic Separation Process (B)

Magnetic roller is mostly used for magnetic separation of lump ore, with the feeding granularity of 75 ~ 10 mm, and the feeding granularity of bulk magnetic roller can reach 300 mm It is a preliminary enrichment equipment, which can obtain coarse concentrate and final tailings that need further treatment, and can also be used for iron removal.

2. Permanent magnet cylinder magnetic separator

Permanent magnet drum magnetic separator is a widely used wet weak magnetic field magnetic separation equipment. It mainly consists of a magnetic system, a cylinder, a sorting tank, a transmission device and a feeding, discharging and overflow device. Magnetic separators have three tank structures: downstream (S), countercurrent (N) and semi-countercurrent. Semi-countercurrent is widely used. Its magnetic system consists of 3 ~ 5 magnetic poles composed of ferrite magnets and magnetic plates, which are fixed on the cylinder shaft and do not rotate when working. The polarity of magnetic poles changes alternately in the circumferential direction and remains unchanged in the axial direction, and the magnetic system envelope angle is 106 ~ 1 17. The magnetic system is biased towards the ore discharge end of concentrate, and the magnetic system deflection angle (the included angle between the magnetic system center line and the vertical line) is 15 ~ 20. Semi-countercurrent (CTB, as shown in Figure 2-24) means that the slurry is transported from the lower part of the tank to the lower part of the cylinder, and the movement direction of non-magnetic products is the same as the rotation direction of the cylinder. CTS means that the feeding direction is consistent with the rotating direction of the cylinder or the moving direction of the magnetic product. Countercurrent (CTN) means that the feeding direction is opposite to the rotating direction of the cylinder or the moving direction of the magnetic product.

Working principle and process: When the pulp enters the separation zone, it is in a loose suspension state under the action of blowing water. Due to the different specific magnetization coefficients of minerals, under the action of magnetic field force, strong magnetic minerals are adsorbed on the surface of the cylinder and rotate with the cylinder. In the process of rotation, due to the alternation of magnetic polarity, magnetic stirring is generated, so that the gangue mixed in the magnetic group or flux linkage is washed out, the grade of magnetic products is improved, and magnetic ore particles are transferred out of the magnetic system with the cylinder. Non-magnetic (weakly magnetic) minerals flow into the tailings pipe from the tailings hole on the bottom plate under the action of slurry flow in the box, and separation is realized.

Application characteristics: Semi-countercurrent magnetic separator, because the pulp is suspended and enters the separation space from bottom to top, magnetic particles are easily adsorbed on the surface of the cylinder, and the recovery rate is high. The flow direction of tailings is opposite to the rotation direction of the cylinder, and magnetic minerals have more opportunities to be attracted. At the same time, the non-magnetic minerals mixed in the concentrate are also easy to be washed away, and the magnetic products are of high grade, which is suitable for roughing and cleaning fine-grained strong magnetic minerals of 0. 0. 15 ~1.0mm 0.0mm ..

In the downstream magnetic separator, magnetic particles are attracted to the cylinder and pass through the arc length of the whole magnetic system, and the magnetic stirring times are more, and the magnetic product grade is higher, but the slurry flow rate is higher, which will take away a small amount of magnetic particles, so the recovery rate is lower. It is suitable for cleaning and roughing 6 ~ 10 mm high magnetic ore.

In the counter-current magnetic separator, the discharge end of magnetic ore particles is close to the ore feeding place, and the magnetic stirring effect is not strong, so the grade of magnetic products is low. However, the discharge port of non-magnetic products is far from the ore feeding place, and the recovery rate of magnetic products is high because the ore particles pass through a long separation area. Suitable for roughing or scavenging with particle size of 0. 6 ~ 1.0 mm .. is not suitable for processing coarse-grained ore, because it is easy to block the separation space.

Figure 2-24 CTB semi-countercurrent permanent magnet drum magnetic separator structure

(2) High intensity magnetic separator

High-intensity magnetic separators are widely used in mineral processing and purification of nonmetallic minerals.

1. Dry disc high intensity magnetic separator

At present, most of the products produced in China and applied to production practice are single (? Ф ф885mm) and double disk (Ф? 580 mm) dry high-intensity magnetic separator. Its structure is shown in Figure 2-25. The structure is mainly composed of magnetic system, induction disk, vibration tank, feeding cylinder and transmission device. Its magnetic system is mountain-shaped, and it forms a closed magnetic circuit with the disk through the vibration groove (or belt). The separation process is carried out in the gap between the groove surface and the disk tip edge, and the gap spacing can be adjusted. In order to prevent strong magnetic materials from interfering with the magnetic separation process, there is a weak magnetic field magnetic separator at the feeding end, which can pre-select strong magnetic materials. After the sorting work starts, the preliminarily sorted minerals enter the feed hopper, the magnetic substances are separated by the weak magnetic field roller, and the rest fall evenly on the running conveyor belt in the form of thin layers. When minerals are sent under the magnetic disk, the magnetic disk sucks out weakly magnetic minerals and is brought into the non-magnetic field with the rotating magnetic disk, so the weakly magnetic minerals leave the magnetic disk and fall into the concentrate hopper under the action of gravity and centrifugation, and the minerals that are not sucked out continue to fall into the tailings hopper with the belt running, thus achieving the purpose of separation.

Application features: The magnetic separator is suitable for separating weakly magnetic ores with specific magnetization coefficient greater than 5. 0× 10-7m3/kg, the particle size is less than 2 mm, and because it belongs to suction type, it has strong selectivity and can obtain relatively pure concentrate. But also can obtain a variety of products with different magnetism, and the work is stable and reliable. It is usually used to select minerals such as iron, titanium, zircon, rutile and monazite.

2. Dry double-roll high-intensity magnetic separator

Magnetic separators can be divided into permanent magnet type and electromagnetic type. It is mainly composed of a magnetic drum, an induction unloading drum, a weak magnetic feed drum, a feed hopper and a receiving hopper. There are two magnetic rollers, which are arranged oppositely to form a closed magnetic circuit. Each magnetic roller consists of two groups of three-pole permanent magnets with the same polarity. The structure of CGR -54 double-roll magnetic separator is shown in Figure 2-26.

Fig. 2-25 Structural Schematic Diagram of Double-disc Dry High Intensity Magnetic Separator

Figure 2-26 CGR-54 double drum magnetic separator

Working process: the selected materials first enter the weakly magnetic feeding drum from the feed hopper, and the strongly magnetic ore particles are selected. And then enters three strong magnetic fields between two magnetic rollers through an ore separation tank and an adjustable feed hopper. Non-magnetic mineral particles are not affected by magnetic force, but directly fall into hopper D under the action of gravity. Magnetic particles are attracted to the magnetic poles by magnetic force and rotate together with the magnetic roller. With the change of the rotation angle of the magnetic roller, the magnetic field intensity gradually weakens, minerals with different magnetism fall into hoppers C and B one after another, and a small amount of minerals with strong magnetism are discharged to concentrate hopper A by the induction discharge roller.

Application features: The magnetic separator has short magnetic circuit and high magnetic field intensity, so it has large production capacity and good separation effect. It is suitable for the separation of metallic minerals and non-metallic minerals with different magnetic properties with particle size below 3 mm, and can be used for the purification of non-magnetic substances to obtain higher purity. But it is not suitable for handling very fine materials.

3.CS- 1 and CS-2 high-intensity magnetic separators.

The structure of CS-L high intensity magnetic separator is shown in Figure 2-27. It is a strong magnetic field electromagnetic induction drum magnetic separator. It is mainly composed of a feed box, a sorting roller, an electromagnetic core and a frame. The main part of the magnetic separator is a magnetic system consisting of an electromagnetic core, a magnetic pole head and an induction roller. The electromagnetic iron core and the induction roller are symmetrically arranged in parallel, the ends of the two iron cores are connected with four magnetic pole heads to form a closed magnetic circuit with the induction roller, and four sorting belts (sorting gaps) are formed between the two induction rollers and the four magnetic pole heads.

Figure 2-27 CS- 1 Electromagnetic Induction Drum High Intensity Magnetic Separator

Sorting process: the selected minerals enter the feed box and are led out from the peach-shaped hole on the side wall of the box by the feed roller. After the magnetic mineral particles enter the separation gap between the induction roller and the magnetic pole head along the sliding plate and corrugated plate, they are attracted to the teeth of the induction roller under the action of magnetic force and rotate with the induction roller. When they leave the magnetic field, they are separated from the teeth under the action of gravity and centrifugal force and discharged into the concentrate box. Non-magnetic mineral particles flow into the tailings box with the pulp through the comb gap to realize separation.

4.SHP wet double-disk high-intensity magnetic separator

It is mainly composed of frame, magnetic sorting system, transmission system, cooling system, power supply and signal. The magnetic system consists of two U-shaped magnetic poles welded on the upright post, an excitation coil and a turntable mounted on the spindle. The magnetic pole and turntable are made of pure iron, and the excitation coil is energized with direct current to form four symmetrical magnetic poles. The separation system consists of toothed plate group, movable gland, ore outlet box, gland, ore disturbing ring, ore receiving groove, cleaning nozzle and ore feeding nozzle.

Figure 2-28 SQC-6-2770 Wet High Intensity Magnetic Separator

Working process: during the rotation of the turntable, the sorting box enters the magnetic field area and the toothed plate is magnetized. At this time, after the feed nozzle sends the pulp into the sorting box, the weakly magnetic minerals are adsorbed on the upper tooth tips of the toothed plates, and the nonmagnetic minerals are gradually discharged into the tailings tank at the lower part of the sorting box through the gaps between the toothed plates. When the sorting box is turned to the lower part of the middle flushing nozzle, the washing water will flush the minerals adsorbed on the upper part of the toothed plate to the lower part of the toothed plate, and at this time, the gangue and a small amount of minerals will be discharged into the middle trough. When the sorting box is turned to the position perpendicular to the center line of the magnetic pole, it is in the neutral zone, and the fine concentrate washing nozzle sprays high-pressure water to flush the concentrate into the concentrate receiving tank to complete the mineral separation process.

Features and application: this model has the advantages of low noise, power saving, small size and convenient installation and adjustment; Equipped with automatic alarm system, the equipment runs safely and reliably. It is mainly used to separate weakly magnetic iron minerals, such as hematite, limonite, specularite and ilmenite.

5. SQC and SZC wet flat ring magnetic separators with high and medium magnetic fields

The structure of SQC-6-2770 wet high intensity magnetic separator is shown in Figure 2-28. It is an annular chain closed magnetic circuit, and the copper tube is wound with an excitation coil, which is excited by low voltage and high current and cooled by water. Magnetic permeable stainless steel is used as magnetic concentrating medium. It is mainly composed of ore feeding device, sorting rotary ring, magnetic system, concentrate and middling washing device, ore receiving device and transmission mechanism.

Sorting process: the sorting ring with sorting chamber rotates slowly under the drive of transmission mechanism. After the separation chamber enters the magnetic field, the toothed plate medium is magnetized and the material enters the separation chamber from the separation point. Magnetic ore particles are attracted to the tip of the toothed plate by magnetic force and rotate together with the separating ring. When they are transferred to the cleaning position of middling, a small amount of cleaning water is supplied to wash away gangue and slime mixed in magnetic ore particles, and it is discharged into the tailings tank. When the sorting chamber is turned to the concentrate washing position (magnetic neutral point between adjacent poles), it is washed into the concentrate tank by pressure water, and non-magnetic pulp enters the tailings tank under the action of gravity and pulp flow.

Structural features and application features: the magnetic system is composed of an inner and outer concentric circular yoke and an iron core, forming an annular chain-like closed magnetic circuit (the excitation coil is wound with a special-shaped copper tube and sheathed on the iron core with insulation layer, close to the magnetic pole head), with short magnetic circuit, small magnetic leakage, high field strength, low power consumption, good separation effect, simple structure and reliable operation, and is suitable for the separation of fine and weakly magnetic minerals in black, colored and nonmetallic minerals, such as hematite, limonite and so on. The lower limit of the recovered particle size is 20 micron meters.

6. Strong magnetic field wet double vertical ring magnetic separator

This model is a vertical ring high-intensity magnetic separator successfully developed in China in the late 1970s. It is mainly composed of ore feeder, sorting ring, magnetic system, tailings tank, concentrate tank, water supply system and transmission device.

Sorting process: the sorting ring with medium rotates slowly in the magnetic field. Coarse particles and impurities are removed from the pulp through a fine screen, and then the pulp is sent into a sorting chamber in a magnetic field along a circular ring. Under the action of gravity, non-magnetic mineral particles flow into the tailings pond with the pulp through the gaps between spherical media. Magnetic mineral particles are attracted to the surface of spherical medium by strong magnetic force, leave the magnetic field area with the rotation of the sorting ring, and then flow into the concentrate tank after being washed by pressure water.

Structural features and uses: The main feature is that the spherical medium can be well loosened by the vertical operation of the sorting ring. The blockage of the medium is well solved; It has demagnetization effect and is convenient for ore unloading; Strong adaptability, wide sorting granularity and wide application. It can be used for the separation of nonferrous metals and rare metal minerals, and also for the iron removal and purification of nonmetallic minerals. The lower limit of effective recovery particle size is 20μm m. ..

(3) High gradient magnetic separator

The high gradient magnetic separator is also a kind of wet magnetic separator with strong magnetic field, and it obtains large magnetic field gradient through two ways. Gradient is due to the use of special magnetic medium steel wool, which greatly improves its magnetic field force, many times higher than that of wet high-intensity magnetic separator, and the lower limit of effective treatment particle size can be reduced to10 μ m. In the purification of nonmetallic minerals, high gradient magnetic separator is more commonly used. At present, it can be used for the separation and purification of kaolin, talc, graphite, mica, feldspar, timely, calcite, fluorite, coal gangue, molding sand, nonmetallic minerals and raw materials containing sulfur, arsenic and bismuth. This is especially important for the purification of kaolin. The purification of kaolin is the main object of application of high gradient magnetic separator at present.

When working, the current is switched on first, and the coil generates a magnetic field, so that the steel velvet is magnetized. Then, the feed valve, the discharge valve and the flow control valve are automatically opened, and the slurry enters the sorting box. After the magnetized steel wool, the magnetized substance is intercepted by the steel wool, and the remaining unmagnetized pulp passes through the discharge valve. Open the flushing valve to flush the non-magnetic slurry on the steel wool, then turn off the power supply, the magnetism of the steel wool disappears, and then flush the magnetized magnetic minerals with water. The whole process is automatically controlled according to the program.

Features: simple process, low cost, no pollution, good effect and strong adaptability. Different grades of products can be produced by adjusting the operating parameters of magnetic separation, and the production cost can be controlled according to the demand.

1. continuous flat ring Sala high gradient magnetic separator

Its structure is shown in Figure 2-29. Sala high gradient magnetic separator is an early and widely used magnetic separator. Made by Sara Magnetic Company, the performance is constantly improving, especially the blockage of steel velvet. It is mainly composed of sorting ring, saddle solenoid coil, armored solenoid iron shell and sorting box filled with ferromagnetic medium. The sorting ring is installed on the central shaft and driven by the motor to rotate. Determine the number of revolutions according to the sorting needs. The ring body is made of nonmagnetic material. The sorting ring is divided into several sorting chambers, which are filled with corrosion-resistant soft magnetic media (metal calendered mesh or stainless steel cotton). The diameter, width and height of the sorting ring are designed into different specifications according to the sorting needs. Magnets of continuous equipment retain the characteristics of periodic equipment magnets, namely armored solenoid magnets. This is the main part that distinguishes other wet high-intensity magnetic separators. In order to generate a uniform magnetic field in the ring magnetic separator, the magnet consists of two independent saddle-shaped coils, so that the ring body filled with medium can rotate through the coils. Generally, saddle solenoid coil can be wound with hollow square soft copper tube, charged with low voltage and high current, and cooled with water. The armored annular frame surrounds the solenoid electromagnet and acts as a magnetic pole. The magnetic field direction is parallel to the pulp flow direction, and the axial direction of the separation medium is perpendicular to the magnetic field direction. Therefore, the magnetic force on the upper and lower surfaces of the dielectric element is the largest, and the fluid resistance is the smallest, so it is easy to collect magnetic particles on the upper and lower surfaces of the dielectric element.

Figure 2-29 Sarah -HGMS continuous high gradient magnetic separator

Sorting process: the pulp flows through the long hole of the upper magnetizer in the magnetized separation chamber, and the weak magnetic particles are trapped on the magnetized magnetic aggregate medium, and the non-magnetic particles flow to the bottom of the separation chamber with the pulp flowing through the gap of the medium and are discharged as tailings. The weakly magnetic particles trapped in the magnetic aggregate medium rotate with the sorting ring, are taken to the cleaning section of the magnetized area, then washed away and leave the magnetized area, and the trapped weakly magnetic particles are discharged into concentrate under the action of cleaning water.

Structural characteristics and application characteristics: the high gradient magnetic separator is a continuous operation with large capacity, which is suitable for separating fine-grained materials with high magnetic mineral content (above 50%); The magnetic field direction is parallel to the pulp direction, and the pulp flow does not directly scour the medium, so the magnetic circuit structure is reasonable, the rotating ring is not a part of the magnetic circuit, and the magnetic leakage is small. It is mostly used to separate weakly magnetic iron, titanium, tungsten ore and non-metallic ore, and reduce the ash and sulfur content of coal.

2. Continuous vertical ring Slon pulsating high gradient magnetic separator

It is mainly composed of rotary ring, rotary ring driving mechanism, excitation coil, iron yoke, pulsation mechanism, feed hopper, tailings hopper, concentrate hopper, concentrate washing device and frame. Magnetic conductive stainless steel medium (steel mesh or steel wool) is installed in the vertical ring. Its structure and appearance are shown in Figure 2-30 (a) and (b) respectively.

Working process: During mineral processing, the rotating ring rotates clockwise, and the pulp enters from the feed hopper and flows through the rotating ring along the gap of the upper iron yoke. The magnetic medium in the rotating ring is magnetized in the magnetic field, forming a high gradient magnetic field on the surface of the magnetic medium, and the magnetic particles in the pulp are attracted to the surface of the magnetic medium. It is carried to the top non-magnetic field area by the rotating ring, washed into the concentrate hopper by backwashing water, and non-magnetic particles flow into the tailings hopper along the gap of the lower yoke and are taken away, and mineral processing is repeated.

Structural characteristics Application characteristics: the rotating ring rotates vertically, the concentrate is backwashed, the magnetic medium is not easy to be blocked (especially the large-particle minerals), and the pulsating mechanism can eliminate the mechanical wrapping phenomenon, with large enrichment ratio and high recovery rate; Reliable operation and strong adaptability to the fluctuation of feed granularity, concentration and grade. This machine is mainly used to separate weakly magnetic metallic minerals, such as hematite,

Beneficiation of limonite, siderite and colored titanium, etc. For nonmetallic minerals, it is used for iron removal, mineral processing and purification of feldspar, quartz, nepheline, andalusite and kaolin. The lower limit of separation particle size can reach 65438 0μ m. ..

Figure 2-30 Structure Diagram (A) and Appearance Photo (B) of SLON Magnetic Separator

3.CAD high gradient magnetic separator

This kind of magnetic separator works periodically and is mostly used to filter the suspension containing magnetic particles, also known as high gradient magnetic filter. It is also suitable for the purification of nonmetallic minerals such as kaolin.

The machine is mainly composed of magnetic pole, water-cooled excitation coil, medium box and magnetic medium (steel wool, etc.). ) Fill it in the box. Sorting process: after the magnetic field is turned on, the particles to be separated pass through the magnetic medium in the separation medium box, and the magnetic particles are attracted and captured on the steel wire. After the suspension is purified, it is discharged from the separation device. When the medium reaches the saturated adsorption capacity, the ore feeding is stopped, the magnetic field is turned off, and the adsorbed particles are washed away with washing water to realize the separation of magnetic particles from water.

Fig. 2-3 1 main structure of drum superconducting magnetic separator

(4) Superconducting magnetic separation method

It is suitable for treating several extremely weak paramagnetic minerals of micron or submicron level. It consists of superconducting magnet (made of niobium titanium wire or niobium tin wire) and ultra-low temperature cooling system (liquid helium is used for refrigeration, and the superconducting magnet of niobium titanium or niobium tin reaches the superconducting state of magnet without DC at 4 o'clock. 2K), sorting tube or sorting device (separating magnetic minerals and non-magnetic minerals from pulp in superconducting magnetic field), etc. See figure 2-3 1 for the main structure.

Features: It can run for a long time. Compared with the conventional magnetic separator, the power consumption is reduced by 80% ~ 90%, the floor space is 34% of the original area, and the weight is 47% of the high gradient magnetic separator with the same production capacity. It has the ability of rapid excitation and demagnetization, which can reduce the time required for equipment sorting, demagnetization and impurity washing, thus improving the mineral processing ability.

For example, Bell Telephone Laboratory in the United States has built an electromagnet with 654.38+ million gauss, which consumes 654.38+0.600 kWh of electricity and needs to be cooled by 4. 5t water per minute. 1976, a superconducting magnet of 175000 gauss was manufactured in Japan, which is the strongest superconducting magnet in the world, and the total power consumption is only 15 kW. Superconductors, as wires, can flow through hundreds of thousands of amperes per square centimeter, producing a strong magnetic field of hundreds of thousands of gauss, while ordinary electromagnets can only produce a strong magnetic field as high as 20 thousand gauss.

Third, the basic principle of electrical separation

Electroseparation is a mineral separation method which uses the electrical differences of various minerals to realize mineral separation in high voltage electric field. Widely used in the separation of nonferrous metals, ferrous metals and nonmetallic minerals.

1. Electrical properties of minerals

The electrical properties of minerals include conductivity, dielectric constant and specific conductivity.

The conductivity of minerals indicates the ability of minerals to conduct electricity, that is, the difficulty of electrons moving in the crystal lattice of mineral objects. The greater the conductivity, the stronger the conductivity of minerals. According to the conductivity value, minerals can be divided into three categories:

1) conductor minerals, such as native copper, graphite and other minerals.

2) Semiconductor minerals, such as sulfide minerals and metal oxides.

3) Non-conductor minerals, such as silicate and carbonate minerals.

The electrical conductivity of minerals is related to temperature, crystal structure and surface state of minerals.

Dielectric constant of minerals: It indicates the ability of an object to isolate the interaction between charges. The larger the dielectric constant, the stronger the ability to isolate the interaction between charges.

Specific conductivity of minerals: the electrical properties of mineral particles (that is, whether they are conductive or not) are related to the interfacial resistance between particles and electrodes, and the interfacial resistance is related to the potential difference of high-voltage electric field. When the voltage of the electric field is large enough, the interfacial resistance decreases, and minerals with poor conductivity can also act as conductors. That is, all minerals have potential differences from non-conductor to conductor. When graphite acts as a conductor, the ratio of the required potential difference between each mineral and graphite is called specific conductivity. The greater the difference in electrical conductivity between two minerals, the easier it is to separate them.

2. The charging method of minerals

The main charging methods of electrostatic separation minerals are direct conduction charging, induction charging, corona charging and friction charging.

Conductive charging: when mineral particles are in direct contact with the electrode, mineral particles with good conductivity can directly obtain the same polarity charge from the electrode, that is, direct conductive charging. When the mineral is charged, it will be polarized by the electrode to produce bound charges, and the end near the electrode will produce charges opposite to the electrode, which will be attracted by the electrode and have different conductivity, so the behavior on the electrode will be different.

Induction charging: ore particles are not in contact with charged bodies or electrodes, but are induced in an electric field. The ore particles with good conductivity are induced by the electrode at one end close to the electrode, and the same charge is generated at the other end, so that the charge on the ore particles can be removed, thus charging the ore particles. Minerals with poor conductivity can only be polarized by electrodes, and their charges are not removed, resulting in different electrical behaviors.

Corona charging: If enough voltage is applied to two electrodes with different radii of curvature, the electric field intensity near the thin electrode will greatly exceed that of the other electrode. The air near the fine electrode will collide and ionize, producing a large number of electrons and positive and negative ions.

Move to the electrode with opposite sign to form corona current. This phenomenon is called corona discharge. In the corona electric field, different mineral particles adsorb air ions to obtain the same sign but different amounts of charges, showing different electrical effects, thus realizing separation.

Triboelectric charging: Mineral particles with different properties rub against each other or the surface of feeding equipment, so that mineral particles with different properties have opposite signs and sufficient charges, thus charging minerals.

In the process of electrical separation, conductive charging and corona charging are often combined.

3. Mineral electrostatic separation process

Electrical separation is carried out in the electric field of the electrical separator. After the mineral particles are fed into the electric field, due to the different conductivity, the mineral particles have different properties or different amounts of charges in some way. So as to be separated by different electric field forces.

Four, electrical separation equipment

There are many types of electric separators.

According to the electric field characteristics, it can be divided into electrostatic concentrator, corona electrostatic separator and corona-electrostatic composite electric field electrostatic separator; See Figure 2-32 for the trajectory of particles with different electrode structures.

According to the structural characteristics, it can be divided into drum, plate and belt electrostatic separators.

According to the charging mode of ore particles, it can be divided into contact charged electrostatic separator, friction charged electrostatic separator and corona charged electrostatic separator.

1.YD high-pressure roller electrostatic separator

This is a kind of electrostatic separation equipment developed by our country, which is mainly composed of main engine, heater and high voltage DC power supply. The main machine part consists of rotating drum, corona electrode, electrostatic electrode, brush and ore separator. The host structure is shown in Figure 2-33.

Figure 2-33 YD-3A High Voltage Electrostatic Separator

Figure 2-32 Schematic diagram of particle trajectory under different electrode structures

Sorting process: This machine adopts a composite electric field combining corona electrode and static electrode (polarized electrode). After the high-voltage direct current passes through the corona electrode and the static electrode, a large number of electrons are released to the drum due to the small diameter of the corona electrode. These electrons ionize air molecules, and positive ions fly to the negative electrode and negative electrons fly to the drum (grounded positive electrode). The space near the drum is negatively charged, and the electrostatic electrode only generates high-voltage electrostatic field without discharging. When mineral particles enter the electric field with the rotating drum, both conductors and non-conductors have the same charge. Because of the different electrical properties of ore particles, the trajectory of movement and falling is also different. After receiving the negative charge, the conductor particles can be quickly transferred through the rotating drum, and at the same time they are induced by the electrostatic field generated by polarization. A positive charge is induced at one end close to polarization, and a negative charge is induced at the other end far away from polarization, and the negative charge is quickly transferred away from the drum, leaving only the positive charge. Due to the attraction of positive and negative phases, the conductive particles are polarized and attracted to the negative electrode (electrostatic electrode), and the particles themselves are subjected to tangential components of centrifugal force and gravity, which leads to the transfer of the conductive particles from the roller. For non-conductor minerals, although negative charges are also obtained, due to their poor conductivity, the obtained charges are difficult to transfer through the drum, so the charges are induced by the surface of the drum and tightly adsorbed on the surface of the drum 5. The higher the voltage (the greater the electric field intensity), the greater the attraction. The tailings (non-conductor) are brought to the back of the roller with a roller and forcibly brushed down with a platen brush. The coal between the conductor and the non-conductor falls into the corresponding coal bucket.

Figure 2-34 Single-roller electrostatic separator

2. Single-roller electrostatic separator for diamond dressing

It is mainly composed of grounding electrode, corona electrode, bias electrode, ore feeder, brush, product separator and transmission device. The grounding electrode is a brass roller with a diameter of 200mm and a length of 400mm, and the corona electrode has a diameter of 0. 15 mm, length 400 mm, deflection electrode is brass tube with diameter 40 mm, and the structure of single-roll electrostatic separator is shown in Figure 2-34.

The corona electrode and the bias electrode are connected with a power supply with a voltage of 15 ~ 20kV. By changing the spatial position of corona electrode and deflection electrode, the distance between electrodes can be adjusted.

Single-roller electrostatic separator for diamond dressing is also used to separate according to the difference of mineral conductivity under the action of composite electric field.

3. American Capco high voltage electrostatic separator

The electrostatic separator is also a drum-type composite electric field electrostatic separator, which is mainly composed of a feed hopper, a drum electrode, a separation plate and a receiving hopper, as shown in Figure 2-35 and Figure 2-36.

Figure 2-35 Electrode structure of CAPCO electrostatic separator

Figure 2-36 Capco industrial electrostatic separator

Features: the high-voltage power supply reaches 40 kV, and the separation effect is significantly improved; Adopt large rollers with diameters of 200mm, 250mm, 300mm and 350 mm, which are replaceable and adaptable; The processing capacity is large, and the roller length per cm can reach 18 kg per hour, but the circulation of middle coal is large, about 20% ~ 40%.

Electrostatic separators are widely used in the purification and separation of nonmetallic minerals, especially in the beneficiation of diamonds, coastal placers, graphite and asbestos. The electrostatic separation system of some common oxide minerals and silicate minerals is briefly described as follows:

Barite-silicate, graphite-timing, limestone-timing, garnet-ilmenite, kaolin-iron minerals, monazite-cassiterite, kyanite-rutile and iron minerals, monazite-ilmenite, feldspar-mica, rutile-monazite, rutile-seashore sand, rutile-zircon.