Process to prepare a surface-reacted calcium carbonate implementing a weak acid, resulting products and uses thereof
The present application relates to a process for preparing a surface-reacted calcium carbonate in an aqueous environment. The process according to the present invention aims at avoiding the mandatory implementation of medium-strong to strong acids. Another aspect of the present invention is directed to an aqueous suspension of surface-reacted calcium carbonate which is Obtainable by the inventive process.
1. An aqueous suspension of surface-reacted calcium carbonate obtained according to the process comprising the following steps:
a) providing at least one ground natural calcium carbonate (GNCC);
b) providing at least one water-soluble acid in the form of an aqueous solution having an acid concentration, determined as the equivalent weight of pure acid on the weight of the total solution, corresponding to from 25 to 75%;
c) providing gaseous CO 2 ;
d) contacting the GNCC of step a) with the acid of step b) and with the CO 2 of step c); wherein:
(i) the at least one acid of step b) has a pK a of greater than 2.5 and less than or equal to 7, when measured at 20° C., and is associated with the ionisation of the first available hydrogen, and a corresponding anion formed on loss of the first available hydrogen that is capable of forming water-soluble calcium salts;
(ii) following contacting the at least one acid with the GNCC, at least one water-soluble salt is additionally added, wherein the water-soluble salt is a hydrogen-containing salt having a pK a of greater than 7, when measured at 20° C., and is associated with the ionisation of the first available hydrogen, and a salt anion is capable of forming water-insoluble calcium salts.
2. The aqueous suspension according to claim 1 , wherein the GNCC comprises marble, chalk, calcite, dolomite, limestone, or any mixture thereof.
3. The aqueous suspension according to claim 1 , wherein the suspension has a solids content of 10 wt.-% and 80 wt.-%, based on the weight of the suspension.
4. The aqueous suspension according to claim 1 , wherein the suspension is stabilized by the addition of dispersants.
5. The aqueous suspension according to claim 1 , wherein the at least one water-soluble acid of step b) has a pKa of between 2.6 and 5.
6. The aqueous suspension according to claim 1 , wherein the at least one water-soluble acid is acetic acid, formic acid, propanoic acid or any mixture thereof.
7. The aqueous suspension according to claim 1 , wherein the at least one water-soluble acid is acetic acid.
8. The aqueous suspension according to claim 1 , wherein the at least one water-soluble acid is dosed in a total amount corresponding to at least 1.5×10 −4 mol of hydrogen atoms in the acid/m 2 GNCC provided in step a).
9. The aqueous suspension according to claim 1 , wherein the at least one water-soluble acid of step b) is dosed in a total amount corresponding to 5 to 40 wt.-% equivalent pure acid based on the dry weight of GNCC provided in step a).
10. The aqueous suspension according to claim 1 , wherein the at least one water-soluble acid of step b) is provided in the form of an aqueous solution having an acid concentration, determined as the equivalent weight of pure acid on the weight of the total solution, corresponding to from 25 to 75%.
11. The aqueous suspension according to claim 1 , wherein the cation of the at least one water-soluble salt is selected from the group consisting of potassium, sodium, lithium, and any mixture thereof.
12. The aqueous suspension according to claim 1 , wherein the cation of the at least one water-soluble salt is sodium.
13. The aqueous suspension according to claim 1 , wherein the anion of the at least one water-soluble salt is selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, oxalate, silicate, hydrates thereof, and any mixture thereof.
14. The aqueous suspension according to claim 1 , wherein the anion of the at least one water-soluble salt is selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, hydrates thereof, and any mixture thereof.
15. The aqueous suspension according to claim 1 , wherein the anion of the at least one water-soluble salt is dosed in a total amount corresponding to at least 5×10 −5 mol of anion/m 2 GNCC provided in step a).
16. The aqueous suspension according to claim 1 , wherein in step d) the addition of the at least one water-soluble salt takes place in an aqueous environment having a temperature of above 50° C.
17. The aqueous suspension according to claim 1 , wherein the aqueous suspension is concentrated following step d).
18. The aqueous suspension according to claim 1 , having a pH, measured at 20° C., of greater than 6.0.
19. The aqueous suspension according to claim 1 , having a pH, measured at 20° C., of greater than 7.5.
20. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a specific surface area of more than 20 m 2 /g.
21. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a specific surface area of more than 30 m 2 /g.
22. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a specific surface area of more than 80 m 2 /g.
23. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a specific surface area within the range of 20 m 2 /g to 200 m 2 /g.
24. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a specific surface area within the range of 30 m 2 /g to 150 m 2 /g.
25. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a specific surface area within the range of 20 to 200 m 2 /g and a median grain diameter within the range of 0.1 to 50 μm.
26. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a median grain diameter of from 0.1 to 50 μm.
27. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a median grain diameter of from 3 to 15 μm.
28. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has a median grain diameter of from 5 to 12 μm.
29. The aqueous suspension according to claim 1 , wherein the surface-reacted calcium carbonate has an intra-particle porosity within the range of 20% vol to 40% vol, measured by mercury porosimetry.
30. Paper, tissue paper, plastic, paint, a controlled release or a water treatment agent comprising the surface-reacted calcium carbonate of the aqueous suspension of claim 1 , a dried surface-reacted calcium carbonate thereof, or a dried surface-reacted calcium carbonate treated with one or more fatty acids or another hydrophobising/oleophilising agent.
31. A surface-reacted calcium carbonate obtained by drying the aqueous suspension of claim 1 .
32. A treated surface-reacted calcium carbonate obtained by treating the surface-reacted calcium carbonate of claim 31 with one or more fatty acids or another hydrophobising/oleophilising agent.