Bauxite is heterogeneous mineral containing aluminum hydroxide minerals such as gibbsite, boehmite and disapore.  It is a sedimentary rock mixed with kaolinite clay that might have some iron oxide minerals mixed in. 

Bauxite is used as a source of Aluminum Oxide (Al2O3) which is used in ceramics or as an abrasive (or for abrasion resistance).  Bauxite is also the main source for Aluminum Metal production. 

Aluminum Hydroxide minerals (gibbsite, boehmite and disapore)and Kaolinite Clay both have a relatively low Mohs hardness with Aluminum Hydroxide ranging from 2.5 – 3 and Kaolinite Clay ranging from 2 – 2.5 on the Mohs hardness scale. However, Bauxite has varying levels of abrasive materials such as haematite (iron oxide) or quartz / sand.   

One of the standard methods of milling Bauxite is with the Hosokawa Mikro® ACM Air Classifying Mill .   To verify that the Mikro ACM® is a good fit, the amount of abrasive impurities needs to be determined (should be 3% or less).  

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 < 10 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.

For highly abrasive applications (> 3% abrasive impurities), or for ultra-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.

Contact Hosokawa’s mineral applications department to learn more about Bauxite Milling.