Process to prepare a surface-reacted calcium carbonate implementing a weak acid, resulting products and uses thereof

Abstract

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.

Claims

1. A process for preparing a surface-reacted calcium carbonate in an aqueous environment comprising the following steps: a) providing at least one ground natural calcium carbonate (GNCC); b) providing at least one water-soluble acid; c) providing gaseous CO.sub.2; d) contacting the GNCC of step a) with the acid of step b) and with the CO.sub.2 of step c); wherein: (i) the at least one acid of step b) has a pK.sub.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.sub.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 of which is capable of forming water-insoluble calcium salts.

2. The process according to claim 1, wherein the GNCC comprises marble, chalk, calcite, dolomite, limestone, or any mixture thereof.

3. The process according to claim 1, wherein the GNCC of step a) has a weight median diameter of 0.01 to 10 m.

4. The process according to claim 1, wherein the GNCC of step a) has a weight median diameter of 0.5 to 2 m.

5. The process according to claim 1, wherein the GNCC is provided in the form of an aqueous GNCC suspension.

6. The process according to claim 5, wherein the suspension has a pH of less than 11.

7. The process according to claim 5, wherein the suspension has a pH of less than 10.5.

8. The process according to claim 5, wherein the suspension has a solids content of greater than or equal to 10 wt.-%, based on the weight of the suspension.

9. The process according to claim 5, wherein the suspension has a solids content of 10 wt.-% and 80 wt.-%, based on the weight of the suspension.

10. The process according to claim 5, wherein the suspension has a solids content of 16 wt.-% and 60 wt.-%, based on the weight of the suspension.

11. The process according to claim 5, wherein the suspension has a solids content of 16 wt.-% and 40 wt.-%, based on the weight of the suspension.

12. The process according to claim 5, wherein the suspension is stabilized by the addition of dispersants.

13. The process according to claim 1, wherein the at least one water-soluble acid of step b) has a pKa of between 2.6 and 5.

14. The process according to claim 1, wherein the at least one water-soluble acid is acetic acid, formic acid, propanoic acid or any mixture thereof.

15. The process according to claim 1, wherein the at least one water-soluble acid is acetic acid, formic acid, or any mixture thereof.

16. The process according to claim 1, wherein the at least one water-soluble acid is acetic acid.

17. The process according to claim 1, wherein the at least one water-soluble acid is dosed in a total amount corresponding to at least 1.510.sup.4 mol of hydrogen atoms in the acid/m.sup.2 GNCC provided in step a).

18. The process according to claim 1, wherein the at least one water-soluble acid is dosed in a total amount corresponding to from 210.sup.4 to 1210.sup.4 mol of hydrogen atoms in the acid/m.sup.2 GNCC provided in step a).

19. The process according to claim 1, wherein the at least one water-soluble acid is dosed in a total amount corresponding to from 310.sup.4 to 1010.sup.4 mol of hydrogen atoms in the acid/m.sup.2 GNCC provided in step a).

20. The process 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).

21. The process according to claim 1, wherein the at least one water-soluble acid of step b) is dosed in a total amount corresponding to 10 to 30 wt.-% equivalent pure acid based on the dry weight of GNCC provided in step a).

22. The process according to claim 1, wherein the at least one water-soluble acid of step b) is dosed in a total amount corresponding to 15 to 25 wt.-% equivalent pure acid based on the dry weight of GNCC provided in step a).

23. The process 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%.

24. The process 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 40 to 60%.

25. The process according to claim 1, wherein during step d), the at least one acid of step b) is added, in one or more steps, to the GNCC.

26. The process 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.

27. The process according to claim 1, wherein the cation of the at least one water-soluble salt is sodium.

28. The process according to claim 1, wherein the anion of the at least one water-soluble salt is selected from the group consisting of, dihydrogen phosphate, monohydrogen phosphate, hydrates of oxalate, hydrates of silicate, and any mixture thereof.

29. The process 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.

30. The process 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 510.sup.5 mol of anion/m.sup.2 GNCC provided in step a).

31. The process according to claim 1, wherein the anion of the at least one water-soluble salt is dosed in a total amount corresponding to 510.sup.5 to 5010.sup.5 mol of anion/m.sup.2 GNCC provided in step a).

32. The process according to claim 1, wherein the anion of the at least one water-soluble salt is dosed in a total amount corresponding to 1010.sup.5 to 3010.sup.5 mol of anion/m.sup.2 GNCC provided in step a).

33. The process according to claim 1, wherein the at least one water soluble salt is added in one step.

34. The process according to claim 1, wherein in step d) the addition of the at least one water-soluble salt take place in a stirred reactor under stirring conditions such as to develop a laminar flow.

35. The process 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.

36. The process 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 60 C.

37. The process according to claim 1, wherein the aqueous suspension is concentrated following step d).

Description

EXAMPLES

Measurement Methods

(1) The following measurement methods are used to evaluate the parameters given in the examples and claims.

(2) Specific Surface Area (SSA) of a Material

(3) The specific surface area is measured via the BET method according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample is filtered, rinsed and dried at 90-100 C. in an oven for at least 12 hours before being broken down in a mortar and pestle, and then placed in a mass balance at 130 C. until a constant weight is observed.

(4) Particle Size Distribution (Mass % Particles with a Diameter<X) and Weight Median Grain Diameter (d.sub.50) of Non-Surface Reacted Calcium Carbonate Particulate Material (ie. GNCC)

(5) Weight median grain diameter and grain diameter mass distribution of a particulate material, such as GNCC, are determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph 5120.

(6) The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and ultrasonic.

(7) Median Grain Diameter (d.sub.50) of Surface-Reacted Calcium Carbonate

(8) Median grain diameter of surface-reacted calcium carbonate is determined using a Malvern Mastersizer 2000 Laser Diffraction System.

(9) pH of an Aqueous Slurry

(10) The pH of the aqueous suspension is measured using a standard pH-meter at approximately 25 C.

(11) Solids Content of an Aqueous Slurry

(12) The slurry solids content (also known as dry weight) is determined using a Moisture Analyser HR73 commercialised by Mettler-Toledo with the following settings: temperature of 120 C., automatic switch off 3, standard drying, 5-20 g of slurry.

Example 1

(13) The following Example is illustrative of the prior art, and involves contacting GNCC with phosphoric acid.

(14) A calcium carbonate suspension is prepared by adding water and undispersed chalk (having a d.sub.50 of 1 m, wherein 90% of particles have a diameter of less than 2 m (Sedigraph)) to a 20-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(15) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, phosphoric acid in the form a 10% solution is added to the calcium carbonate suspension through a peristaltic pump over a period of 10 minute in an amount corresponding to 10% by weight on dry calcium carbonate weight and approximately 310.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(16) The suspension is stirred for an additional 5 minutes.

(17) The resulting suspension is allowed to sit overnight. The product has an SSA=24.0 m.sup.2/g and a d.sub.50=3.5 m (Malvern).

Example 2

(18) The following Example is illustrative of the prior art, and involves contacting GNCC with phosphoric acid.

(19) A calcium carbonate suspension is prepared by adding water and undispersed chalk (having a (d.sub.50 of 3 m, wherein 33% of particles have a diameter of less than 2 m (Sedigraph)) to a 100-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(20) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, phosphoric acid in the form a 30% solution is added to the calcium carbonate suspension through a peristaltic pump over a period of 10 minute in an amount corresponding to 25% by weight on dry calcium carbonate weight and approximately 2.610.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(21) The suspension is stirred for an additional 5 minutes.

(22) The resulting suspension is allowed to sit overnight. The product has an SSA=34.5 m.sup.2/g and a (d.sub.50=7.9 m (Malvern).

Example 3

(23) The following Example is illustrative of the prior art, and involves contacting GNCC with phosphoric acid.

(24) A calcium carbonate suspension is prepared by adding water and dispersed marble (having a d.sub.50 of 0.7 m, wherein 90% of particles have a diameter of less than 2 m (Sedigraph)) in a 20-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(25) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, phosphoric acid in the form a 10% solution is added to the calcium carbonate suspension through a peristaltic pump over a period of 10 minute in an amount corresponding to 30% by weight on dry calcium carbonate weight and approximately 910.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(26) The suspension is stirred for an additional 5 minutes.

(27) The resulting suspension is allowed to sit overnight. The product has an SSA=35.0 m.sup.2/g and a (d.sub.50=3.9 m (Malvern).

Example 4

(28) The following Example is illustrative of the invention.

(29) A calcium carbonate suspension is prepared by adding water and undispersed chalk (having a d.sub.50 of 3 m, wherein 33% of particles have a diameter of less than 2 m (Sedigraph)) in a 20-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(30) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, acetic acid in the form a 50% solution is added to the calcium carbonate suspension through a separation funnel over a period of 1 minute in an amount corresponding to 18.4% by weight on dry calcium carbonate weight and 310.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(31) Subsequently, NaH.sub.2PO.sub.4.2H.sub.2O in the form of a 30% solution is added via a peristaltic pump to the calcium carbonate suspension over a period of 10 minutes in an amount corresponding to 47.8% by weight on dry calcium carbonate weight and 310.sup.4 mol H.sub.2PO.sub.4 anion/m.sup.2 GNCC. Following this addition, the suspension is stirred for an additional 5 minutes.

(32) The resulting suspension is allowed to sit overnight. The product has an SSA=72.4 m.sup.2/g and a d.sub.50=7.1 m (Malvern).

Example 5

(33) The following Example is illustrative of the invention.

(34) A calcium carbonate suspension is prepared by adding water and dispersed marble (having a (d.sub.50 of 0.7 m, wherein 90% of particles have a diameter of less than 2 m) in a 20-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(35) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, acetic acid in the form a 50% solution is added to the calcium carbonate suspension through a separation funnel over a period of 1 minute in an amount corresponding to 18.4% by weight on dry calcium carbonate weight and 310.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(36) Subsequently, NaH.sub.2PO.sub.4.2H.sub.2O in the form of a 30% solution is added via a peristaltic pump to the calcium carbonate slurry over a period of 10 minutes in an amount corresponding to 47.8% by weight on dry calcium carbonate weight and 310.sup.4 mol H.sub.2PO.sub.4 anion/m.sup.2 GNCC. Following this addition, the suspension is stirred for an additional 5 minutes.

(37) The resulting suspension is allowed to sit overnight. The product has an SSA=81.6 m.sup.2/g and a d.sub.50=6.8 m (Malvern).

Example 6

(38) The following Example is illustrative of the invention.

(39) A calcium carbonate suspension is prepared by adding water and undispersed chalk (having a d.sub.50 of 3 m, wherein 33% of particles have a diameter of less than 2 m (Sedigraph)) in a 20-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(40) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, acetic acid in the form a 50% solution is added to the calcium carbonate suspension through a separation funnel over a period of 1 minute in an amount corresponding to 36.8% by weight on dry calcium carbonate weight and 610.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(41) Subsequently, Na.sub.2HPO.sub.4 in the form of a 30% solution/slurry is added via a peristaltic pump to the calcium carbonate suspension over a period of 10 minutes in an amount corresponding to 43.5% by weight on calcium carbonate weight and 310.sup.4 mol HPO.sub.4 anion/m.sup.2 GNCC. Following this addition, the suspension is stirred for an additional 5 minutes.

(42) The resulting suspension is allowed to sit overnight. The product has an SSA=69.6 m.sup.2/g and a (d.sub.50=7.5 m (Malvern).

Example 7

(43) The following Example is illustrative of the invention.

(44) A calcium carbonate suspension is prepared by adding water and undispersed chalk (having a (d.sub.50 of 3 m, wherein 33% of particles have a diameter of less than 2 m (Sedigraph)) in a 20-L stainless steel reactor, such that the aqueous suspension obtained has a solids content corresponding to 16% by dry weight relative to the total suspension weight. The temperature of this suspension is thereafter brought to and maintained at 70 C.

(45) Under stirring at approximately 1000 rpm such that an essentially laminar flow is established, acetic acid in the form a 50% solution is added to the calcium carbonate suspension through a separation funnel over a period of 1 minute in an amount corresponding to 6.1% by weight on dry calcium carbonate weight and 110.sup.4 mol equivalent hydrogen/m.sup.2 GNCC. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(46) Subsequently, NaH.sub.2PO.sub.4.2H.sub.2O in the form of a 30% solution is added via a peristaltic pump to the calcium carbonate slurry over a period of 10 minutes in an amount corresponding to 15.9% by weight on calcium carbonate weight and 110.sup.4 mol H.sub.2PO.sub.4 anion/m.sup.2 GNCC. Following this addition, the suspension is stirred for an additional 5 minutes.

(47) The resulting suspension is allowed to sit overnight. The product has an SSA=33.5 m.sup.2/g and a d.sub.50=6.0 m (Malvern).

(48) TABLE-US-00001 TABLE 1** Example 1 2 3 4 5 6 7 Prior art PA PA PA IN IN IN IN (PA)/ invention (IN) Acid H.sub.3PO.sub.4 H.sub.3PO.sub.4 H.sub.3PO.sub.4 CH.sub.3COOH CH.sub.3COOH CH.sub.3COOH CH.sub.3COOH TLV <1 ppm <1 ppm <1 ppm 10 ppm 10 ppm 10 ppm 10 ppm pKa 2.12 2.12 2.12 4.76 4.76 4.76 4.76 Amount 3 10.sup.4 2.6 10.sup.4 9 10.sup.4 3 10.sup.4 3 10.sup.4 6 10.sup.4 1 10.sup.4 acid mol mol mol mol mol mol mol added Water- none none none NaH.sub.2PO.sub.42H.sub.2O NaH.sub.2PO.sub.42H.sub.2O Na.sub.2HPO.sub.4 NaH.sub.2PO.sub.42H.sub.2O soluble salt Amount n/a n/a n/a 3 10.sup.4 3 10.sup.4 3 10.sup.4 1 10.sup.4 salt added mol mol mol mol Total 3 10.sup.4 7.7 10.sup.4 9 10.sup.4 9 10.sup.4 9 10.sup.4 9 10.sup.4 3 10.sup.4 equivalent mol mol mol mol mol mol mol H atoms added*** SSA of 24.0 34.5 35.0 72.4 81.6 69.6 33.5 final product (m.sup.2/g) **all amounts acid are given in mol equivalent hydrogen/m.sup.2 GNCC and all amounts salt are given in mol corresponding anion/m.sup.2 GNCC ***equivalent hydrogen atoms in all of the acid and salt added to GNCC in mol equivalent hydrogen/m.sup.2 GNCC