The main factors affecting the indexes of dry magnetic separator are ore properties (grade, magnetism, particle size and moisture), equipment performance and operation level. Under certain conditions, the operation adjustment should be determined according to the properties of the ore and the requirements of the product index. The operation adjustment factors mainly include roller speed, baffle position and ore feeding quantity. Reasonable adjustment of these three factors can improve the magnetic separation index.

The adjustment of the roller speed determines the centrifugal force on the surface of the cylinder and the strength of the magnetic overturning effect of the magnetic particles. With the increase of the roller speed, the centrifugal force increases and the magnetic overturning effect increases, which is beneficial to improve the concentrate grade and ore handling capacity. However, with the increase of rotating speed, a lot of tailings will be thrown out, and the tailings grade will be improved correspondingly; on the contrary, the effect of reducing rotating speed is just the opposite, and the concentrate grade and tailings grade will be reduced.

The adjustment of the baffle mainly refers to the upper and lower tailings baffles. Adjusting the position of the baffle can control the tailings grade (or tailings volume). The closer the baffle is to the cylinder skin, the more tailings, the higher the grade of tailings. At the same time, the amount of middlings will be reduced and the grade of middlings will be improved; the farther the baffle is from the cylinder surface, the opposite effect will be achieved. Of course, the change of middling quantity and middling grade will inevitably affect the concentrate grade. When the middling quantity of the upper roller is small and the grade is high, the concentrate grade of the lower roller is also easy to improve, which is especially obvious when dealing with coarse-grained ores.

The adjustment of feeding quantity determines the thickness of feeding layer on the roller. When the feeding quantity is large, the feeding layer is thick, and the magnetic force on the surface of the feeding layer is small, so it is easy to be thrown into the tailings and increase the grade of tailings. When the fine grade is treated, the grade of concentrate will be reduced. At this time, the ore feed should be reduced to ensure the required separation index.

The particle size also has a great influence on the separation index of dry double drum permanent magnet separator, and the index of coarse particle grade is better than that of fine particle grade. This is mainly because when dealing with the coarse grade, because the material is coarse, with less water and mud content, it is easy to disperse on the cylinder, which is conducive to the separation of magnetic and non-magnetic ore particles, and also conducive to improving the processing capacity. Moreover, the fluctuation of ore feed has little influence on the separation effect. The ore is coarse and heavy, and the centrifugal force on the roller is also large, so the roller speed must be strictly controlled. And pay attention to adjust the baffle position in time with the change of speed. When the speed is high, the baffle should be far away from the cylinder skin, and when the speed is low, it can be near. When dealing with the fine grade, due to the fine particle size of the material, more water and mud content, it is easy to agglomerate, and it is difficult to disperse on the surface of the cylinder. The agglomerated ore particles are thrown into the tailings under the action of centrifugal force, so that the tailings grade is on the high side. The fine ore particles form magnetic chain under the action of magnetic field, and the bonding of water and slime makes it difficult for the magnetic chain to disperse and discharge slime in the process of magnetic overturning. In addition, the weight of fine ore is small and the centrifugal force is smaller than that of coarse ore, so the tailings throwing belt is narrow and it is not easy to intercept ore by baffle. In order to reduce this effect, the ore can be pre classified according to the size, and the coarse and fine grades can be treated separately according to different conditions. When dealing with the fine grade, the feeding amount should not be too large, and the rotation speed of the roller should be appropriately increased, so as to reduce the thickness of the material layer, strengthen the centrifugal force and magnetic overturning, destroy the magnetic agglomeration, and throw the gangue into the tailings. Because the fine grade tailings throwing belt is narrow, and the distance between the grade of tailings belt and the barrel is not obvious, the baffle can be close to the barrel, so the tailings grade does not increase much, which is beneficial to the improvement of concentrate grade.

Production practice has proved that, because the size of the selected ore has a great influence on the dry magnetic separation index, in order to reduce this influence, the actual operation should be determined according to the specific situation. Beijing Iron Mine divides the ore with 200 mesh size accounting for 25% into coarse grade with - 200 mesh content of 5% - 8% and fine grade with - 200 mesh content of 50% - 60%. The two grades are selected respectively to obtain better separation index.

The moisture content of ore has a certain influence on the dry magnetic separation, especially for the fine grade separation. Because moisture can improve the adhesion of "magnetic mass", which makes the "magnetic mass" bond more firmly. Moreover, it is easy to stick to the cylinder skin. Although the centrifugal force is increased, the index can not be improved, and sometimes it is worse. Therefore, when the moisture content of ore is large in rainy season, the proportion of lump ore can be appropriately increased to reduce the water content and mud content of ore. when the moisture content greatly affects the separation index, the method of reducing ore feed and ensuring qualified concentrate products can be adopted for adjustment. When the moisture content of coarse ore is less than 2%, it has no significant effect on the separation index; when the moisture content of fine ore is less than 2.5%, it has no significant effect on the separation index.

When the magnetic rate is high, the tailings grade should be reduced as much as possible to improve the recovery rate on the basis of ensuring the concentrate quality. When the magnetic rate is low, the operation should focus on ensuring the concentrate grade and reducing the tailings grade.