Patent ID: 7757976

Claim:
The method of converting granular igneous rock feedstock with a hardness of at least about 6 Mohs and a grain size profile to an ultra-fine grain finished product for subsequent commercial use, said ultra-fine grain product having a maximum grain size of less than about 6 microns, said method comprising: (a) providing a dry preprocessed feedstock with a maximum particle size greater than about 20 microns and less than about 100 microns; (b) grinding said feedstock in a dry state by passing said feedstock vertically downward through a continuous, high-speed stirred ball mill having stirring arms rotated at a selected high speed in a vertically extending chamber filled with a grinding media whereby said feedstock is ground into an intermediate powder by the action of said media as said media is moved at high speed by said rotating stirring arms, said intermediate powder having a drastically reduced grain size profile than the grain size profile of said feedstock; (c) passing said intermediate powder through an air classifier using a rapidly moving high speed air stream traveling along a given path to convey said ultra-fine grain product along said path and from said classifier and to allow coarse particulate material including particles larger than said ultra-fine product to be separated from said intermediate powder by centrifugal force and then expelled from said classifier; (d) collecting said ultra-fine product; and, (e) returning said coarse material to said high speed stirred ball mill for regrinding.