For coated paper, paperboard and high-grade paint coatings, plastics and rubber, kaolin particle size and its distribution is a crucial index.
Some high-quality kaolin, especially hard kaolin or Kaolin, still need to be pulverized.
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According to the requirements of the final product and the fine grinding method, the grinding process of kaolin can be divided into two kinds: dry method and wet method.
1. Kaolin dry grinding
The dry method is mostly used for grinding hard kaolinite or kaolinite, especially for processing kaolinite directly into ultrafine powder to meet the requirements of users.
At present, the product fineness that can be achieved by domestic dry method is generally D90≤10 m, that is, the final product is about 1250 mesh.
The dry processing equipment mostly uses the air flow pulverizer, the cyclone self-grinder, the high speed mechanical impact type superfine pulverizer, the vibration grinder and so on.
In order to control the product particle size distribution, especially the maximum particle content, it is often necessary to configure fine classification equipment. Currently, turbine type air centrifugal classifier is generally configured, such as LHB type, ATP type, MS type and MSS type dry centrifugal classifier.
2. Kaolin wet grinding
Kaolin wet milling is mostly used for ultra-fine grinding of soft and arenaceous kaolin after sand removal and impurity removal, especially for D80≤2 m or D90≤2 m coating kaolin products, which is also the industrial hard kaolin or kaolin processing D80≤2 m or D90≤2 m coating kaolin products must be used grinding processing method.
Because the flaky crystal type of kaolin is an excellent property for its application in some fields, the wet ultra-fine pulverization of kaolin is also known as stripping, which means that the thicker lamellar kaolin is shelled into the thinner small flakes, so as to maintain its original crystal characteristics.
The stripping methods include wet grinding, extrusion, chemical soaking and joint process.
(1) Grinding method
With the help of the relative movement of grinding medium, the kaolin particles are subjected to shearing, impingement and grinding stripping, which make them peel into thin and flaky fine particles along the interlayer.
The commonly used equipment is grinding and peeling machine, mixing ball mill, sand mill, etc.
Grinding media commonly used glass beads, alumina beads, corundum beads, zirconia beads, natural quartz sand, particle size 0.8m-3mm.
The smaller the particle size of the grinding medium is, the finer the product will be. However, attention should also be paid to the relationship between the diameter of the medium ball and the diameter of the material to be ground. The diameter of the grinding medium should be more than 10 times the average particle size of the feed.
(2) Extrusion
The working principle is that the kaolin slurry in the homogenizer barrel is pressurized to 20-60mpa by a piston pump, and the high-pressure slurry is extrudated and ejected from the nozzle of the homogenizer (the surface is hardened through a very narrow gap) at a linear speed of more than 950m/s.
Due to the sudden and sharp decrease in pressure, the kaolin crystal lamination in the slurry becomes "loose", and the slurry ejected at high speed onto the impeller in the atmospheric region, suddenly changing the direction of motion and producing a strong cavitation effect.
The loosened crystal lamination was exfoliated along the interlaminar layer by cavitation erosion.
(3) Chemical soaking
Kaolin was soaked by chemical agent solution. When the agent was immersed into the crystal planes which were bonded by hydrogen bond, the binding force between the crystal planes became weak, and the crystal layers were loosened. At this time, a small external force was applied to peel off the crystal layers.
Chemical immersion method used in the pharmaceutical urea, benzidine, amine acetate, etc.
This is the most promising and effective method to prepare nanometer kaolin.
(4) Intercalation grinding
The method of intercalation grinding and stripping can achieve remarkable peeling effect in a short time, and the technology can be applied to ultra-fine kaolin in industry.
In addition, scanning electron microscope analysis showed that intercalation grinding did little damage to the crystal shape of kaolinite, and many of the lamellar particles still appeared as complete hexagonal flaky crystals after grinding.
China's kaolin ore reserves are rich, good quality, but the quality products are quite few, still need to import a lot of high-quality kaolin from abroad every year.
With the increasing demand for high-quality kaolin in China, it is urgent to improve the quality of domestic kaolin products and accelerate the development of fine processing technology of kaolin. Ultra-fine pulverizing of kaolin will become one of the key directions of research and application in the future.
PUDA Kaolin packing machine:
After the analysis of the special bulk density, air content , water content, PUDA will recommend screw feeder type machine for kaolin, we have valve bag and open bag machines.
