Process for the production of precipitated calcium carbonate, precipitated calcium carbonate and uses thereof
The present invention relates to a process for the production of precipitated calcium carbonate, comprising the following steps: a) providing a reaction vessel containing an aqueous phase at an initial temperature; b) injecting a carbon dioxide generating compound into the aqueous phase until the pH of the aqueous phase is in the range of around 5 to around 7; and c) subsequently adding a calcium hydroxide slurry at an initial temperature to the reaction vessel while continuing the injection of the carbon dioxide generating compound, in order to obtain an aqueous slurry of the precipitated calcium carbonate. The addition rate of the calcium hydroxide slurry to the reaction vessel in step c) is such that an average electrical conductivity of the reaction contents in the reaction vessel during the reaction is in a range of 100 to 6,000 μS/cm.
1. Prismatic, scalenohedral or colloidal precipitated calcium carbonate obtained by the process comprising the following steps:
(a) providing a reaction vessel containing an aqueous water phase at an initial temperature;
(b) injecting a carbon dioxide generating compound into the aqueous water phase until the pH of the aqueous phase is in the range of pH 5 to pH 7; and
(c) subsequently adding a calcium hydroxide slurry at an initial temperature to the reaction vessel while continuing the injection of the carbon dioxide generating compound, in order to obtain an aqueous slurry of precipitated calcium carbonate having a solids content of 5 to 20% by weight and a weight median grain diameter (d 50 ) in a range of 2.5 to 7.5 μm,
wherein in step (c) the addition rate of the calcium hydroxide slurry to the reaction vessel is such that an average electrical conductivity of the reaction contents in the reaction vessel during the reaction is in a range of 100 to 6000 μS/cm,
and wherein (i) prismatic precipitated calcium carbonate is obtained when the average electrical conductivity of the reaction contents in the reaction vessel during the reaction is in a range of 100 to 1200 μS/cm, (ii) scalenohedral precipitated calcium carbonate is obtained when the average electrical conductivity of the reaction contents in the reaction vessel during the reaction is in a range of 1200 to 6000 μS/cm, and (iii) colloidal precipitated calcium carbonate is obtained when the average electrical conductivity of the reaction contents in the reaction vessel during the reaction is in a range of 1200 to 6000 μS/cm and the aqueous water phase contains at least one additive to facilitate production of colloidal precipitated calcium carbonate.
2. The precipitated calcium carbonate according to claim 1 , wherein the pH of the aqueous slurry of the precipitated calcium carbonate is in the range of pH 7 to pH 13.
3. The precipitated calcium carbonate according to claim 1 , wherein the pH of the aqueous slurry of the precipitated calcium carbonate is in the range of pH 7 to pH 12.
4. The precipitated calcium carbonate according to claim 1 , wherein the addition rate of the calcium hydroxide slurry in step (c) is at least 0.02 fold/minute per volume of carbonated aqueous phase.
5. The precipitated calcium carbonate according to claim 1 , wherein the addition rate of the calcium hydroxide slurry in step (c) is in the range of 0.02 to 0.25 fold/minute per volume of carbonated aqueous phase.
6. The precipitated calcium carbonate according to claim 1 , wherein the addition rate of the calcium hydroxide slurry in step (c) is in the range of 0.025 to 0.10 fold/minute per volume of carbonated aqueous phase.
7. The precipitated calcium carbonate according to claim 1 , wherein the carbon dioxide generating compound in step (c) is introduced in the reaction vessel at a rate of 0.05 to 2 kg CO 2 /h per kg of dry Ca(OH) 2 .
8. The precipitated calcium carbonate according to claim 1 , wherein the carbon dioxide generating compound in step (c) is introduced in the reaction vessel at a rate of 0.2 to 0.8 kg CO 2 /h per kg of dry Ca(OH) 2 .
9. The precipitated calcium carbonate according to claim 1 , wherein the carbon dioxide generating compound is selected from the group consisting of gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide and a gas containing carbon dioxide.
10. The precipitated calcium carbonate according to claim 1 , wherein the carbon dioxide generating compound is a gaseous mixture of carbon dioxide and air.
11. The precipitated calcium carbonate according to claim 1 , wherein the carbon dioxide generating compound is a gaseous mixture of carbon dioxide and nitrogen.
12. The precipitated calcium carbonate according to claim 1 , wherein the aqueous suspension of the aqueous slurry of the precipitated calcium carbonate obtained in step (c) has a solids content of 7% to 20% by weight.
13. The precipitated calcium carbonate according to claim 1 , wherein the aqueous suspension of the aqueous slurry of the precipitated calcium carbonate obtained in step (c) has a solids content of 10% to 20% by weight.
14. The precipitated calcium carbonate according to claim 1 , wherein the precipitated calcium carbonate has a weight median grain diameter (d 50 ) in a range of 3.3 to 6.9 μm.
15. The precipitated calcium carbonate according to claim 1 , wherein the precipitated calcium carbonate has a BET specified surface area in a range of 1.0 to 25.0 m 2 /g.
16. The precipitated calcium carbonate according to claim 1 , wherein the precipitated calcium carbonate has a BET specified surface area in a range of 1.3 to 23.5 m 2 /g.
17. The precipitated calcium carbonate according to claim 1 , wherein the precipitated calcium carbonate has a BET specified surface area in a range of 1.3 to 5.0 m 2 /g.
18. The precipitated calcium carbonate according to claim 1 , wherein after step (a) or after step (b) but prior to step (c) an additive is added to the reaction vessel.
19. The precipitated calcium carbonate according to claim 18 , wherein the additive is one selected from the group consisting of a slaking additive, a precipitation additive and a dispersing agent.
20. The precipitated calcium carbonate according to claim 19 , wherein the additive is one selected from the group consisting of a sugar; a sugar alcohol; citric acid; a sodium, potassium, calcium or magnesium salt of citric acid; and a polyacrylic acid in neutralized or partly neutralized form.
21. The precipitated calcium carbonate according to claim 1 , wherein the average electrical conductivity is controlled in a range of 100 to 1200 μS/cm.
22. The precipitated calcium carbonate according to claim 1 , wherein the average electrical conductivity is controlled in a range of 200 to 1010 μS/cm.
23. The precipitated calcium carbonate according to claim 1 , wherein the average electrical conductivity is controlled in a range of greater than 1200 to 6000 μS/cm.
24. The precipitated calcium carbonate according to claim 1 , wherein the average electrical conductivity is controlled in a range of 1300 to 3000 μS/cm.
25. The precipitated calcium carbonate according to claim 1 , wherein the average electrical conductivity is controlled in a range of 1300 to 2500 μS/cm.
26. The precipitated calcium carbonate according to claim 1 , further comprising drying the precipitated calcium carbonate to form dried precipitated calcium carbonate.
27. The precipitated calcium carbonate according to claim 1 , wherein the at least one additive to facilitate production of colloidal precipitated calcium carbonate is a sugar.
28. The precipitated calcium carbonate according to claim 1 , wherein the at least one additive to facilitate production of colloidal precipitated calcium carbonate is sucrose.
29. The precipitated calcium carbonate according to claim 1 , which is in the form of prismatic precipitated calcium carbonate.
30. The precipitated calcium carbonate according to claim 1 , which is in the form of scalenohedral precipitated calcium carbonate.
31. The precipitated calcium carbonate according to claim 1 , which is in the form of colloidal precipitated calcium carbonate.
32. The precipitated calcium carbonate according to claim 1 , which is in the form of an aqueous suspension.
33. The precipitated calcium carbonate according to claim 1 , which is dried.
34. A paper coating formulation or filler comprising the precipitated calcium carbonate according to claim 1 , in the form of an aqueous suspension or in a dried form.
35. A paint, rubber, plastic, building material, ink, water treatment product, food, feed or cosmetic comprising the precipitated calcium carbonate according to claim 1 , which is dried.