The method of producing the metal manganese powder mechanically pulverizing method can be divided into chemical and physical methods milling, the table below.
Physical chemical milling
Cutting and grinding
Vertical mill pulverization
Organic solvent method
Metal manganese is divided into metal manganese produced by fire reduction and electrolytic manganese metal produced by wet electrowinning. The fire metal manganese is block-shaped and difficult to pulverize; the wet-processed metal manganese is flake-shaped, easily pulverized, and has high purity. At the same time, the production scale of manganese metal powder is generally large, and the added value of metal manganese powder is not high. These factors determine that the mechanical pulverization method is suitable for the production of manganese metal powder, and the raw material used is electrolytic manganese metal. Industrial application methods include ball milling, ultrafine pulverization, roll crushing, and vertical mill pulverization. The basic principle of the mechanical pulverization method is to pulverize the manganese sheet into manganese powder by shearing, impacting, bending, pressing, grinding, etc., using the brittleness of the manganese sheet.
1. Ball milling to produce manganese metal powder
1. Metal Manganese Powder Production Process Ball mill is the oldest grinding machine and is still widely used in the preparation of ultrafine powders such as chemical raw materials, ceramic raw materials and coatings. The ball mill is characterized by large crushing ratio, simple structure, strong mechanical reliability, easy to inspect and replace worn parts, mature technology, standardization, and can be adapted to operations under different conditions, such as pulverization and drying, pulverization and mixing, etc. It can be used for dry pulverization and wet pulverization. However, the ball mill has low pulverization efficiency, high energy consumption per unit output, cannot be continuously operated, the grinding medium is easily worn, and the noise is large during operation.
The principle of ball-milling method for producing manganese powder is that when the ball mill is running, the grinding medium and the material are lifted to a certain height under the action of centrifugal force and friction force, and then fall off the wall along the parabolic trajectory due to gravity, and then they are lifted again. At a certain height, it falls along the parabolic trajectory. In this way, the material between the grinding media is crushed by the impact; at the same time, the particles are ground by grinding, rubbing, shearing, etc. due to the rolling and sliding of the grinding media.
The principle flow of metal manganese powder production is shown in Figure 1.
2. Process operation 1) The coarse-grained metal manganese is easy to accumulate bridge, the fluidity is poor, and it is easy to form the grinding along the side of the manganese sheet during the ball milling process, and the crushing efficiency is low; especially for the long electro-storage time and large thickness Manganese flakes, this phenomenon is particularly prominent, so the manganese flakes before the scoring mill generally need to be coarsely crushed. The coarse crushing is carried out in a roll crusher . Mars emerges from time to time during the crushing of the manganese sheet by the roller. Therefore, the inert gas protection is applied. The fine powder is not produced much in the coarse crushing process, but a small amount of dust is still generated, and a dust collecting facility is required.
2) Ball Milling Ball mill is the main equipment for preparing manganese powder by ball milling. Due to the high hardness of manganese metal and the strict requirements of iron content in manganese powder products, corundum lining and ball mill material should be selected.
The working parameters of the ball mill, such as the amount of ball loading, the amount of charge, the speed of the mill, etc., are selected according to the conventional ball mill. The grinding balls, coarse crushed materials and the materials on the sieve are added into the ball mill to prevent the explosion of high concentration metal manganese dust in the ball mill. After the completion, the air in the ball mill should be taken out, filled with nitrogen, then sealed, turned the ball mill, and started timing.
Since the fine metal manganese powder is easily oxidized, the customer generally requires -0.05 mm manganese powder to be less than 20% and up to 25%. Therefore, the ball milling time should not be too long, generally grinding about 3h to discharge the sieve.
The unloading operation is the most prone to fire. The dust concentration is high, and the powder is also increased due to the ball milling temperature. The collision between the ball and the ball during the unloading, between the ball and the barrel of the mill, and between the ball and the receiving device may cause sparks, which may cause an explosion. For this purpose, the discharge must be carried out under the protection of an inert gas and a special discharge device must be designed.
The advantage of ball milling for the production of manganese powder is that there is no dust spillage during the grinding process, and the explosion can also be controlled; the disadvantage is intermittent operation and low production efficiency.
3) Screening Screening is critical to producing a qualified micronized product. During the grinding process, the particle size gradually decreases with the extension of time; at the same time, the specific surface area of â€‹â€‹the material gradually increases, and the specific surface energy also increases gradually, so the tendency of the fine particles to reunite with each other is gradually enhanced. In order to improve the pulverization efficiency and reduce the energy consumption, in addition to improving the pulverizer and adding the grinding aid in the pulverization, the most important point is to timely separate the qualified fine-grain grade products, so as to avoid the qualified fine-grain grade materials in the mill. "Over-grinding", for this purpose, high-efficiency grading equipment must be installed in the ultra-fine pulverization process. For the screening of metal manganese powder, the high-frequency vibrating screen is a suitable equipment. When the screening, some dust is generated, and dust-proof and dust-removing treatment is required.
4) Packaging Because the electrolytic manganese metal powder is active, especially the newly prepared manganese powder is easily oxidized in the air, it is important to ensure the quality of the manganese powder and the packaging quality. In general, the packaging for the two layers, the inner layer is a plastic film bag or aluminum foil pouch, and evacuated, packaging for the drum. The packaging specifications range from 50, 100, 250, 500kg per barrel.
Second, the jet mill produces manganese metal powder
High pressure jet mill is a relatively mature superfine crushing technology. It utilizes the energy of high-speed airflow (300~500m/s) to cause the particles to impact, collide and rub against each other, resulting in particle comminution.
Figure 2 shows a metal manganese jet mill.
The high-speed airflow is generated by rapidly expanding the high-pressure air after being sprayed through a nozzle installed around the mill. Due to the high velocity gradient near the nozzle, most of the comminution occurs near the nozzle. In the milling chamber, the frequency of collision between particles and particles is much higher than the collision of particles with the walls, ie the main comminution in the jet mill is the impact or collision between the particles. Jet mill is one of the most commonly used ultra-fine pulverizing equipment. The fineness of the product is generally 1~5Î¼m. The upper limit of the product size depends on the solid content in the mixed gas stream and is inversely proportional to the unit energy consumption. The lower the solids content, the finer the particle size of the product. The product of jet milling has the characteristics of narrow particle size distribution, smooth particle surface, regular particle shape, high purity, high activity and good dispersibility. And the process is carried out in a closed system, with high automation, simple operation, inert gas protection, few fires, explosions, and less dust, which is better for environmental protection. The disadvantage is that the feed particles are required to be fine, the productivity is low, and the cost is relatively high.
The pulverization is carried out by a jet mill. In addition to the jet mill itself, there are auxiliary equipment including airflow generating equipment, airflow purifying equipment and processing equipment, feeding equipment, finished product collecting equipment, and collection and recovery equipment for exhaust gas entrained materials. Dust removal equipment, etc. Because metal manganese powder is flammable and explosive, it must be pulverized by inert gas flow. The characteristics of the process arrangement should ensure the recovery and utilization of inert gas.
3. High-pressure roll grinding method The production of metal manganese powder high-pressure roll mill is a relatively new crushing equipment. It has the advantages of high efficiency, low energy consumption, light wear, low noise, easy operation and wide application range. Compared with the conventional roller mill, the unit energy consumption is reduced by 10% to 20%, which is used for grinding cement clinker, and the wear is only 1.5g/t, which is about 1% of the ball mill (200g/t).
The high-pressure roller mill is mainly composed of a feeding device, a material level control device, a roller (a fixed roller, a moving roller), a transmission device (motor, a pulley, a gear shaft), a hydraulic system, and a lateral leakage preventing device.
The working principle of the high pressure roller mill is shown in Figure 3. The material is fed by a feeding device (gravity or pre-pressing screw feeder). Between the two rollers rotating opposite each other, the particles are pulverized by mutual extrusion, and most of them are crushed under the compressive stress of 50 MPa or more. The material is effectively crushed by the minimum gap S between the two rolls.
One of the two rollers is a fixed roller supported on the bearing, and the other is a moving roller. The abrasive roller F is applied to the material layer by the moving roller. The two rollers rotate at opposite speeds at the same speed, and the two ends of the roller are sealed by a sealing device. Leakage from the lateral gap of the roller under the action of high pressure. Due to the unique working principle of the high-pressure roller mill, it is suitable for crushing brittle materials of various hardnesses such as hard, medium hard and soft.
The manganese metal is hard and brittle, and is suitable for crushing with a high-pressure roller mill. The manganese powder is produced by a high-pressure roller, which not only has high production efficiency, but also is convenient for system sealing and dustproof and explosion-proof.
4. Stirring mill to produce manganese powder
Stirring mill generally needs to have liquid medium, which is more suitable for preparing manganese powder slurry. When manganese powder is used in the next stage of production of chemical products, it needs to be treated by wet method, and stirring medium is often used, and there is water medium. Pay attention to the safety hazard of eliminating hydrogen. Because manganese powder reacts with water, hydrogen is released. Especially in the grinding process, the newly formed manganese powder reacts more strongly with water. The workshop should be strictly prohibited from fireworks and well ventilated.
5. Production of anti-oxidation manganese powder
Anti-oxidized manganese powder forms an anti-oxidation film on the surface of ordinary electrolytic manganese powder to prevent it from being further oxidized by contact with air.
The key steps in the production of anti-oxidation manganese powder have three aspects: one is the production of low-oxygen electrolytic manganese powder; the other is anti-oxidation treatment, that is, the surface passivation treatment of manganese powder; the third is drying, the drying temperature should not be too high, and inert gas is required. protection.
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