Granted Patent B2

US 7,757,976 · App. 12/009,693 · Granted Jul 20, 2010

Abstract

Claims (29)

1. 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.

2. The method as defined in claim 1 wherein said granular igneous rock feedstock is nepheline syenite particulate feedstock.

3. A method as defined in claim 2 wherein said feedstock has a particle size of 99% particles less than about 50 microns.

4. A method as defined in claim 2 wherein said selected speed is 200-450 rpm.

5. A method as defined in claim 2 wherein said media is particles having a size of less than 5 mm.

6. A method as defined in claim 2 wherein said media is particles having a size of 2.0-2.5 mm.

7. A method as defined in claim 2 wherein said media has a hardness number of Mohs 9.

8. A method as defined in claim 2 wherein said media is ceria-stabilized zirconium oxide.

9. A method as defined in claim 2 wherein said media is selected from the class consisting of stabilized zirconium oxide, aluminum oxide and tungsten carbide.

10. A method as defined in claim 2 wherein substantially no grinding aid is used in grinding of said feedstock.

11. A method as defined in claim 2 wherein said stirred ball mill has a water cooling jacket.

12. A method as defined in claim 2 wherein said media fills about 50-80% of said grinding chamber.

13. A method as defined in claim 2 wherein said air classifier is a side draft classifier including a main classifying chamber with a vertical blade rotor rejector operated at a high rotating speed below an outlet hood and a lower expansion chamber, said rejector separating said ultra-fine product by allowing said product to pass radially through said rejector together with said high speed air stream, whereby said coarse material is collected in and by said lower expansion chamber.

14. A method as defined in claim 13 wherein said high rotating speed is greater than about 1400 rpm.

15. A method as defined in claim 2 wherein said feed rate of said stirred ball mill is 0.5-2.3 kg/min.

16. A method as defined in claim 2 wherein said feedstock has about 20-30% particles with a grain size of less than about 5-6 microns and said intermediate powder has about 35-40% particles with a grain size of less than about 5-6 microns.

17. A method as defined in claim 2 wherein said stirred ball mill has an adjustable discharge grate with an opening or slot of 0.5 to 1.5 mm.

18. A method as defined in claim 2 wherein the D50 size of said final product is in the range of 1.5 to 2.0 microns.

19. The method of converting a pre-processed nepheline syenite particulate feedstock with a grain size profile to an ultra-fine grain finish product for subsequent commercial use, said ultra-fine grain product having a grain size of less than about 6 microns, said method comprising:

(a) providing a dry feedstock with a controlled 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 through a ball mill whereby said feedstock is ground into an intermediate powder, said intermediate powder having a drastically reduced grain size profile than the grain size profile of said feedstock;

(c) passing said intermediate powder in a dry state 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 feedstock by centrifugal force and then expelled from said classifier, wherein said air classifier is a side draft classifier including a main classifying chamber with a vertical blade rotor rejector operated at a high rotating speed below an outlet hood and a lower expansion chamber, said rejector separating said ultra-fine product by allowing said product to pass radially through said rejector together with said high speed air stream, whereby said coarse material is collected in and by said lower expansion chamber;

(d) collecting said ultra-fine product; and,

(e) returning said coarse material to said high speed stirred ball mill for regrinding.

Assignments (10)