Kaolin or kaolinite mineral is alumina silicate clay that was formed from the weathering of igneous rocks in moist and warm climate regions.
Kaolin is used in paper filler and coatings, in cosmetics, in ceramics as well as ceramic proppants, in addition to many filler or absorbent applications.
Pure kaolin is a relatively soft mineral, with a Mohs hardness of 2 – 2.5. However, mined kaolinite may have a minor portion of abrasive impurities such as quartz / sand. Upon heat treatment, kaolin will transform into various stages of hardness until it reaches a ceramic stage.
One of the standard methods of milling kaolin is with the Hosokawa Mikro ACM Air Classifying Mill. The ACM has a rotating rotor disc with hammers which rotates with speeds up to 23,000 feet per minute. The particle size is controlled by the internal air classifier, to provide sharp particle size distributions. Various classifier designs are available, to produce from coarse (100 mesh) product down to a fineness of 400 mesh product or a D50 of less than 5 microns. Abrasion Resistant options are available, including tungsten carbide tipping, Ni-Hard or Ceramic liners to assist with abrasive impurities and to assist with long life of mill components. Warm air can also be used to dry the product while milling.
An alternate to the Hosokawa ACM for coarser grade Kaolin is the Hosokawa Mikro Pulverizer Hammer & Screen Mill. The Mikro Pulverizer uses swing-hammers with interchangeable screen liners to produce a variety of products from 50 mesh to 150 mesh products. The Mikro Pulverizer needs less air (less ancillary equipment) than the ACM and is a lower cost options for the coarser grind Kaolin products.
For ulta-fine (D50 < 5 microns) milling, the Hosokawa Alpine Super Orion Ball Mill and Air Classifier are the best option. These units come in a variety of sizes to meet your application needs.