Narrow particle size distribution calcium carbonate and methods of making same
View Patent ↗Calcium carbonate particles having very narrow particle sizes with a controlled D 98 and minimal ultrafines (very small particles) are described. The particles are prepared by grinding a feedstock in a centrifugal grinding mill, which utilizes very high centrifugal forces to impact the particles with each other or grinding media.
1. A method for preparing alkaline earth metal carbonate particles, comprising: grinding an alkaline earth metal carbonate feedstock in a centrifugal grinding mill to produce ground alkaline earth metal carbonate particles having a median particle size (D 50 ) of from 1 to 3 microns; wherein the ratio of D 50 to D 98 , D 50 :D 98 , is at least 36:100; and wherein the alkaline earth metal carbonate feedstock is of sedimentary origin.
2. The method of claim 1 , wherein the alkaline earth metal carbonate feedstock is calcium carbonate (CaCO 3 ).
3. The method of claim 1 , wherein grinding comprises pneumatically conveying initially ground particles into a size classifier and subsequently re-grinding any particles rejected by the size classifier in the centrifugal grinding mill.
4. The method of claim 1 , further comprising coating the feedstock with an aliphatic carboxylic acid while the feedstock is being ground in the centrifugal grinding mill.
5. The method of claim 1 , further comprising coating the feedstock with an aliphatic carboxylic acid comprising stearic acid, palmitic acid, behenic acid, montanic acid, capric acid, lauric acid, myristic acid, isostearic acid, cerotic acids, or a mixture thereof, while the feedstock is being ground in the centrifugal grinding mill.
6. The method of claim 1 , wherein the feedstock is micritic limestone comprising at least 95% calcium carbonate (CaCO 3 ).
7. The method of claim 1 , wherein at least 55% by weight of the ground particles have a size of from 1 to 3 microns.
8. The method of claim 1 , wherein D 20 is from 0.8 to 1.2 microns.
9. The method of claim 1 , wherein no more than 10% of the ground particles by weight have a size smaller than 0.5 microns.
10. The method of claim 1 , wherein the ground particles are further characterized by a D 20 of from 0.8 to 1.2 microns, and wherein at least 55% by weight of the ground particles have a size of from 1 to 3 microns, and no more than 10% of the ground particles by weight have a size smaller than 0.5 microns.
11. The method of claim 1 , wherein the method further comprises a step of pre-grinding the alkaline earth metal carbonate feedstock using a roller mill, ball mill, or hammer mill, prior to grinding the alkaline earth metal feedstock in the centrifugal grinding mill.
12. A method for preparing alkaline earth metal carbonate particles, comprising: grinding an alkaline earth metal carbonate feedstock in a centrifugal grinding mill to produce ground alkaline earth metal carbonate particles having a median particle size (D 50 ) of from 1 to 3 microns; wherein:
grinding comprises impacting the alkaline earth metal carbonate feedstock with itself and a grinding media in the centrifugal grinding mill;
the ground particles have a ratio of D 50 to D 98 , D 50 :D 98 , of at least 36:100; and
the alkaline earth metal carbonate feedstock is of sedimentary origin.
13. The method of claim 12 , wherein the grinding media comprises a ceramic material.
14. The method of claim 12 , wherein the alkaline earth metal carbonate feedstock comprises calcium carbonate (CaCO 3 ).
15. The method of claim 14 , wherein:
at least a portion of the ground particles are coated with an aliphatic carboxylic acid comprising stearic acid, palmitic acid, behenic acid, montanic acid, capric acid, lauric acid, myristic acid, isostearic acid, a cerotic acid, or a mixture thereof; and
the aliphatic carboxylic acid constitutes from 0.5% to 1.5% by weight of the ground particles.
16. The method of claim 14 , wherein the ground particles are further characterized by a D 20 of from 0.8 to 1.2 microns, and wherein at least 55% by weight of the ground particles have a size of from 1 to 3 microns, and no more than 10% of the ground particles by weight have a size smaller than 0.5 microns.
17. The method of claim 14 , wherein the method further comprises a step of pre-grinding the alkaline earth metal carbonate feedstock using a roller mill, ball mill, or hammer mill, prior to grinding the alkaline earth metal feedstock in the centrifugal grinding mill.
18. The method of claim 14 , wherein grinding further comprises pneumatically conveying initially ground particles into a size classifier and subsequently re-grinding any particles rejected by the size classifier in the centrifugal grinding mill.
19. The method of claim 14 , further comprising coating the feedstock with an aliphatic carboxylic acid while the feedstock is being ground in the centrifugal grinding mill.
20. A method for preparing alkaline earth metal carbonate particles, comprising: grinding an alkaline earth metal carbonate feedstock in a centrifugal grinding mill capable of accelerating the feedstock in a range from 30 G to 50 G to produce ground alkaline earth metal carbonate particles having a median particle size (D 50 ) of from 1 to 3 microns; wherein:
the alkaline earth metal carbonate feedstock comprises calcium carbonate (CaCO 3 ); and
the ground particles have a ratio of D 50 to D 98 , D 50 :D 98 , of at least 36:100.
21. The method of claim 20 , wherein the centrifugal grinding mill comprises a nutating bearing capable of rotating at from 760 to 960 rpm.