Permanent magnetic drum separator

Wet magnetic drum separator structure and magnetic field characteristics

The structure of this magnetic separator is shown in Figure 1. It is composed of three main parts: Magnetic drum 1, magnetic system 2 and bottom tank 3.

The magnetic drum is made of rolled and welded stainless steel plate with thickness of 2 to 3 mm. The end cover of the magnetic drum is a cast aluminum piece, connected to the drum with stainless steel screws. The reason why use stainless steel (or copper) or aluminum for the drum is because these materials are non-conductive materials, with good permeability, so that the magnetic lines of force and the drum does not form a magnetic short circuit. The surface of the magnetic drum is also covered with a layer of wear-resistant rubber so that the drum surface is not worn. At the same time, it is conducive to the adhesion of magnetic particles on the drum surface, which strengthens the carrying effect of the drum on the magnetic particles, and the drum rotation is driven by the motor.

The magnetic system 2 in Figure 1 is a three-pole permanent magnet system, but there are also four-pole or multi-pole ones. The polarities of the magnetic poles are alternately arranged along the rotation direction of the drum and are fixed during operation. When the magnetic particles are attracted to the surface of the drum and rotate together with the drum, the magnetic tumbling (also called magnetic stirring) phenomenon occurs due to the alternating polarity, and a part of the non-magnetic particles mechanically entrapped in the magnetic particles are removed, which can improve the quality of magnetic products.
Figure 1 Semi-counterflow type permanent magnetic drum separator
1.Magnetic drum 2. magnetic system 3. Bottom tank 4. magnetic conductive plate 5. structure 6. Spray system 7. feeding box 8. discharge water pipe 9. bottom plate 10. adjusting device 11. frame

As seen in Figure 2, the distribution of magnetic field intensity along the radial direction is saddle-shaped, and the farther away from the surface of the drum, the smaller the magnetic field intensity is. On the surface of the drum, the magnetic field strength at the edge of the pole is higher than the magnetic field strength at the center of the pole surface and the center between the poles. 20 mm away from the surface of the drum, the magnetic field strength is similar at all points except for the two outermost points of the pole.

Figure 2 Magnetic field characteristics of CYT600×1800mm semi-counterflow type permanent magnetic drum separator

Wet magnetic drum separator sorting procedures

The sorting process is (refer to Figure 1) after the slurry is fed into the bottom tank 3 through the feeding box 7, the ore particles enter the feed area at the bottom of the box in a loose state under the action of the water flow from the feed water spray system 6. Due to the magnetic field, the magnetic particles are magnetically agglomerated and form “magnetic clusters” or “magnetic chains”, and overcome mechanical forces such as gravity to the magnetic poles, and are attracted to the surface of the magnetic drum 1. Then it rotates upward together with the drum. Due to the alternating polarity of the magnetic system, the ore particles are magnetically stirred so that the mechanically entrapped vein stones fall off, thus improving the concentrate grade. The magnetic particles rotate with the drum to the weakest point at the edge of the magnetic system. It is discharged into the concentrate tank under the action of the flushing water jet from the discharge water pipe 8. The non-magnetic or weakly magnetic ore particles are discharged into the tailing pipe through the tailing holes in the bottom plate 9 under the action of the fast flowing slurry flow in the tank.

Types & features of permanent magnetic drum separator

The permanent drum magnetic separator can be divided into three types: down-flow, counter-flow and semi-counter-flow according to the structure of the bottom box. The type of the bottom tank has a great impact on the separation index and operation.

(1) Downstream type permanent magnetic drum separator

The feeding direction is consistent with the direction of drum rotation or the direction of movement of magnetic products, as shown in Figure 3 and Figure 4 (a). The slurry is fed directly from the feed box 3 to the bottom of the magnetic system of magnetic drum 1. Non-magnetic particles and very weak magnetic particles are discharged from the gap between the two bottom plates below the drum, and magnetic particles are sucked to the surface of the drum and rotate with the drum to the weaker magnetic field at the edge of the magnetic system, and are discharged to the concentrate tank by the discharge hose.
Figure 3 Downstream type permanent magnetic drum separator
1. Magnetic drum 2. Bottom tank 3. feeding box 4. transmission part 5. discharge water pipe 6.discharge adjusting device 7. Frame 8. Steering device

Downstream type magnetic separator has a large capacity, suitable for handling coarse particles (greater than 6 mm) of the strong magnetic materials of the coarse separation and selection operations, or for the recovery of magnetic heavy media, can also be used for multiple tandem work.

However, the sorting index of this magnetic separator is affected by the amount of ore feed, and the response is sensitive. When the feed amount is large, the magnetic particles are easily lost in the tailings, so the operation should be strengthened to control the lower slurry level.

(2) Counter-current magnetic separator

The feeding direction is opposite to the rotation direction of drum 1 or the movement direction of magnetic products [as shown in Figure 5 and Figure 4(b)]. The slurry is fed directly from the feed box 3 to the bottom of the magnetic system of drum 1, and the non-magnetic particles and very weak magnetic particles are discharged from the tailing hole on the bottom plate below the left edge of the magnetic system, and the magnetic particles are taken to the concentrate end with the drum against the direction of feeding and discharged into the concentrate tank.

This kind of magnetic separator is suitable for the roughing and sweeping operation of fine particles of strong magnetic minerals with particle size less than 0.6 mm. This is because the tailings discharge outlet is far from the feed end. Separation time is longer, the recovery rate is higher, while the concentrate discharge end is closer to the feed end, the magnetic flip effect is poor, so the concentrate grade is lower. Counter-current magnetic separator is not suitable for handling coarse-grained ore, because the size is coarse, the ore particles are easy to deposit and thus block the separation space.

Figure 4 different types of permanent magnetic drum separators


Figure 5 Counter stream flow permanent magnetic drum separator
1. Magnetic drum 2. Bottom tank 3. frame 4. transmission part 5. steering device

(3) Semi-counter-current magnetic separator

The direction of ore feeding is basically the same as the direction of magnetic attraction, and the slurry enters the separation space from the bottom of the tank, and the magnetic particles are easily attracted to the surface of the magnetic drum, and are discharged to the concentrate tank along with the drum to the weakest magnetic field at the edge of the magnetic system. Non-magnetic ore particles or very weak magnetic particles flow through the left edge of the magnetic system against the direction of cylinder rotation and are discharged through the rectangular hole on the bottom plate. Thus, the slurry in the bottom tank can be leveled and maintained, and the gap between the bottom plate and the drum can be adjusted within a certain range of 30 to 40 mm.

This type of magnetic separator can obtain higher quality iron ore concentrate, and also get better recovery rate, so the semi-counter current magnetic separator is widely used in production practice. It is suitable for processing the coarse and selective operations of strong magnetic minerals with fine grains less than 0.2 mm, and it can work in tandem with multiple units to achieve the role of multiple selection.

Factors that affecting the sorting

There are many factors affecting the work of permanent magnetic drum separator, besides the bottom tank type, magnetic system structure, magnetic field characteristics, there are also magnetic system deflection angle, working gap, sorting concentration and drum rotation speed, etc..

1. If the magnetic system deflection angle is not appropriate, it will obviously affect the sorting index. The so-called magnetic system declination is the angle between the center line of the magnetic system arc and the vertical line of the drum center. The grade of the tailing is low after the magnetic system deviation, but when it is too deviated, the grade of the tailing will be increased because the concentrate cannot be lifted to the concentrate end. If the magnetic system is biased in front, the concentrate will be lifted too high and the sweeping area will be shortened, so the grade of the tailings will be higher, so the angle of the magnetic system should be adjusted to a moderate position.

2. The distance between the surface of the magnetic drum and the bottom plate of the roughing area is called the working gap, and the size of the working gap should affect the effect of sorting. The gap is large, the flow of slurry is also large, which is conducive to improving the processing capacity, but because the surface of the drum is farther away, the magnetic field strength is lower, so it will make the tailing grade higher and reduce the metal recovery rate. On the contrary, if the working gap is small, increasing the magnetic field force will make the concentrate grade lower, but the recovery rate can be higher. If the working gap is too small, the slurry flow rate will be too fast, so that the ore particles can not be sucked to the surface of the drum before the slurry flow to the tailings, which will cause the tailings grade to rise, and even make it difficult to discharge the tailings, and the phenomenon of “full slot”. Therefore, the installation and maintenance of the magnetic separator should pay attention to ensure that the appropriate working clearance.

3. The size of the sorting concentration determines the slurry flow rate of a certain amount of ore, which affects the sorting time of the ore particles. High concentration, slow flow rate, high resistance, easy to entrain veinstone in the concentrate, reducing the quality of the concentrate. However, due to the longer sorting time, it is beneficial to the recovery rate. Conversely, if the sorting concentration is low, the concentrate grade can be higher, and the tailing grade will also increase, so that the recovery rate is reduced.

4. The drum rotation speed also has an impact on the sorting index, low speed, low yield. High rotational speed, the centrifugal force on the ore particles is large, the magnetic flip effect per unit time increases, the concentrate grade and processing capacity are high, while the recovery rate is reduced.

In practice, it is important to adjust the blowing water of the feed ore and the rinsing water of the concentrate. If the blowing water is too large, the slurry flow rate will be too fast, which will increase the tailing grade. On the contrary, if the blowing water is small, the ore particles will not be fully loosened and the sorting effect will be affected, so that the tailing grade will be higher and the concentrate grade will be lower. Concentrate flushing is mainly used to unload the concentrate from the drum skin, the size of the flushing water should be able to ensure the unloading of concentrate.