SURFACE-REACTED PRECIPITATED CALCIUM CARBONATE, PROCESS TO MAKE SAME, AND USES THEREOF

Abstract

The present invention relates to a process for the preparation of a surface-reacted precipitated calcium carbonate (PCC) pigment having an insoluble, at least partially crystalline calcium salt on its surface. In the process of the present invention, a PCC containing pigment is contacted with H.sub.3O.sup.+ ions and a solubilized anion in an aqueous medium in the presence of excess solubilized calcium ions to form the surface-reacted PCC having an insoluble, at least partially crystalline calcium salt of the anion formed on its surface.

Claims

1. A surface-reacted precipitated calcium carbonate (PCC) pigment prepared by the process comprising the following steps: a) providing at least one precipitated calcium carbonate (PCC)-comprising pigment; b) providing H3O+ ions; c) providing at least one anion being capable of forming water-insoluble calcium salts, said anion being solubilized in an aqueous medium; d) contacting said PCC-comprising pigment with said H3O.sup.+ ions and with said solubilized anions in an aqueous medium to form a slurry of surface-reacted PCC-comprising pigment, wherein said surface-reacted PCC comprises an insoluble, at least partially crystalline calcium salt of said anion formed on the surface of at least part of the PCC provided in step a); characterised in that an excess of solubilized calcium ions is provided during step d).

2. The surface-reacted PCC pigment according to claim 1, which is prepared by the process comprising the following steps: a) providing at least one precipitated calcium carbonate (PCC)-comprising pigment; and b) contacting the PCC-comprising pigment in an aqueous medium with at least one anion that is solubilized in an aqueous medium and forms water-insoluble calcium salts in the presence of excess solubilized calcium ions that are present in the aqueous medium, wherein the anion is in the form of a soluble neutral or acid salt, or is in the form of an acid, wherein the anion is a phosphate-comprising anion, PO.sub.4.sup.3, HPO.sub.4.sup.2, an oxalate anion (C.sub.2O.sub.4.sup.2), a carbonate-comprising anion in the form of CO.sub.3.sup.2, a phosphonate anion, a succinate anion or a fluoride anion, wherein the anion is added in a quantity corresponding to between 5 and 50% by weight, based on the weight of said PCC provided in step a), and wherein the PCC-comprising pigment in the aqueous medium, the at least one anion, and excess solubilized calcium ions are mixed so as to develop a laminar flow; to form a slurry of surface-reacted PCC comprising an insoluble, at least partially crystalline calcium salt of said anion formed on the surface of at least part of the PCC provided in step a), wherein the excess solubilized calcium ions are provided by the addition to the aqueous medium of: (i) H.sub.3O.sup.+ ions by addition of an acid or an acid salt that provides all or part of excess solubilized calcium ions in the aqueous medium, wherein the acid or acid salt is a sulphur-comprising acid, sulphuric acid, hydrochloric acid, perchloric acid, formic acid, lactic acid, acetic acid, or nitric acid, or an acid salt thereof, or a soluble calcium acid salt thereof, and/or (ii) a soluble neutral calcium salt that provides all or part of excess solubilized calcium ions in the aqueous medium.

3. The surface-reacted PCC pigment according to claim 2, wherein the H.sub.3O.sup.+ ions provide all or part of said excess solubilized calcium ions by dissolution of the PCC to liberate calcium ions.

4. The surface-reacted PCC pigment according to claim 2, wherein the acid or acid salt that provides all or part of the excess solubilized calcium ions is sulphuric acid, hydrochloric acid, acetic acid, or nitric acid, or an acid salt thereof, or a soluble calcium acid salt thereof.

5. The surface-reacted PCC pigment according to claim 2, wherein the anion of step b) is a phosphate-comprising anion, PO.sub.4.sup.3, or HPO.sub.4.sup.2.

6. The surface-reacted PCC pigment according to claim 2, wherein the anion of step b) is a carbonate-comprising anion that is generated in situ via the introduction of gaseous CO.sub.2 to the slurry.

7. The surface-reacted PCC pigment according to claim 2, wherein the anion in step b) is added in a quantity corresponding to between 15 and 30% by weight, based on the weight of said PCC provided in step a).

8. The surface-reacted PCC pigment according to claim 2, wherein the excess solubilized calcium ions are provided by addition of sulphuric acid, hydrochloric acid or acetic acid.

9. The surface-reacted PCC pigment according to claim 2, wherein the excess solubilized calcium ions are provided by addition of a soluble neutral calcium salt selected from the group consisting of CaCl.sub.2 and Ca(NO.sub.3).sub.2.

10. The surface-reacted PCC pigment according to claim 2, wherein H.sub.3O.sup.+ ions are provided by addition of hydrochloric acid, and the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO.sub.4.

11. The surface-reacted PCC pigment according to claim 2, wherein H.sub.3O.sup.+ ions are provided by addition of acetic acid, and the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO.sub.4.

12. The surface-reacted PCC pigment according to claim 2, wherein the H.sub.3O.sup.+ ions are provided by addition of sulphuric acid, and the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO.sub.4.

13. The surface-reacted PCC pigment according to claim 2, wherein the solubilized calcium ions are provided by addition of CaCl.sub.2, and the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO.sub.4.

14. The surface-reacted PCC pigment according to claim 2, wherein the solubilized calcium ions are provided by addition of Ca(NO.sub.3).sub.2, and the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO4.

15. The surface-reacted PCC pigment according to claim 2, wherein H.sub.3O.sup.+ ions are provided by addition of hydrochloric acid, and the anion of step b) is a phosphate-comprising anion provided by addition of Na.sub.3PO.sub.4 or Na.sub.4HPO.sub.4.

16. The surface-reacted PCC pigment according to claim 2, wherein H3O.sup.+ ions are provided by addition of hydrochloric acid, the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO.sub.4, and step b) takes place in the presence of NaCl.

17. The surface-reacted PCC pigment according to claim 2, wherein H3O.sup.+ ions are provided by addition of hydrochloric acid, the anion of step b) is a phosphate-comprising anion provided by addition of H.sub.3PO.sub.4, and step b) takes place in the presence of KNO.sub.3.

18. The surface-reacted PCC pigment according to claim 2, wherein the surface-reacted PCC so obtained in step b) has a calcium anion salt:calcium carbonate mass ratio of 20:80 to 60:40 as determined by thermogravimetric analysis.

19. The surface-reacted PCC pigment according to claim 2, which is in the form of a slurry.

20. The surface-reacted PCC pigment according to claim 2, which is dried to obtain a dry surface-reacted PCC product.

21. The surface-reacted PCC pigment according to claim 20, wherein the dry surface-reacted PCC product is treated with one or more fatty acids.

22. The surface-reacted PCC pigment according to claim 2, wherein the salt of the anion extends from the surface of at least part of the surface-reacted PCC pigment.

23. The surface-reacted PCC pigment according to claim 2, wherein the salt of the anion comprises one or more of octacalcium phosphate (OCP), hydroxyapatite (HAP) and tricalcium phosphate (TCP).

24. The surface-reacted PCC pigment according to claim 2, having a BET specific surface area that is at least three times greater than the BET specific surface area of the PCC in the PCC-comprising pigment provided in step a).

25. The surface-reacted PCC pigment according to claim 2, having a BET specific surface area of from 20 to 120 m.sup.2/g.

26. The surface-reacted PCC pigment according to claim 2, a pore volume of 1 to 2.2 cm.sup.3/g.

27. Paper, tissue paper, plastic, paint or water treatment comprising the surface-reacted PCC pigment according to claim 2 in the form of a slurry or a dried surface-reacted PCC.

Description

EXAMPLES

[0124] Measurement Methods

[0125] The following measurement methods are used to evaluate the parameters given in the examples and claims.

[0126] Hydrophilicity of a Material

[0127] Materials were classified as hydrophilic or not according to the following test. 50 ml of each of the following mixture of water:ethanol are prepared in 100 ml beakers: 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90, 0:100. Thereafter, 0.5 g of the material to be tested is passed through a sieve located over the mouth of the beaker (under slight agitation of this sieve to ensure that all of the material passes through it, said sieve openings being sized so as to allow the slowed passage of the material under slight agitation), and allowed to fall freely upon the liquid surface. As of the moment that sieving is completed, the behaviour of the material at the liquid surface is observed over a period of 5 minutes to assign a grade to the material in each beaker as follows:

[0128] 0=essentially all of the material sinks within 30 seconds;

[0129] 0.25=essentially all of the material sinks within 5 minutes;

[0130] 0.5=more than 50% of the material sinks within 5 minutes;

[0131] 0.75=more than 25% of the material sinks within 5 minutes;

[0132] 1=essentially none of the filler sinks within 5 minutes.

[0133] The grades assigned are plotted as a function of the water:ethanol ratio. Materials were classified as hydrophilic a zero value was observed for a water:ethanol mixture of 100:0 to 50:50.

[0134] Pore Volume of a Material

[0135] Tablets were made from suspensions of the material to be tested. The tablets are formed by applying a constant pressure to the suspension/slurry for several hours such that water is released by filtration through a fine 0.025 m filter membrane resulting in a compacted tablet of the pigment. The tablets are removed from the apparatus and dried in an oven at 80 C. for 24 hours.

[0136] Once dried, single portions from each of the tablet blocks were characterised by mercury porosimetry for both porosity and pore size distribution using a Micromeritics Autopore IV mercury porosimeter. The maximum applied pressure of mercury was 414 MPa, equivalent to a Laplace throat diameter of 0.004 m (i.e. nm). The mercury intrusion measurements were corrected for the compression of mercury, expansion of the penetrometer and compressibility of the solid phase of the sample. Further details of the measuring method are described in Transport in Porous Media (2006) 63: 239-259.

[0137] Specific Surface Area (SSA) of a Material

[0138] 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 110 C. in an oven for at least 12 hours.

[0139] Particle Size Distribution (Mass % Particles with a Diameter <X) and Weight Median Grain Diameter (d.sub.50) of a Particulate Material

[0140] Weight median grain diameter and grain diameter mass distribution of a particulate material 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.

[0141] 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.

[0142] X-Ray Diffraction (XRD)

[0143] Crystallographic structures of materials were identified based on the XRD analytical technique using Brucker AXS:D8 Advance instrumentation, scanning 2 to 70 2theta at a scanning speed of 0.5 seconds/step and a step size of 0.01 2theta. Analysis of the resulting spectra was based on the PDF 2 database of reference spectra issued by the International Centre for Diffraction Data.

[0144] pH of an Aqueous Slurry

[0145] The pH of the aqueous suspension is measured using a standard pH-meter at approximately 22 C.

[0146] pH Rise on Wet Grinding a Material

[0147] The pH rise observed on wet grinding a material is evaluated according to the following process:

[0148] 1) the aqueous phase of the slurry is replaced with deionised water to form a slurry featuring a solids content, as measured according to the measurement method provided in the Examples section herebelow, of 15% by weight;

[0149] 2) the slurry of Step 1) is ground in a grinding chamber using aluminium oxide grinding beads having a diameter of between 1.0 and 1.6 mm, added in an amount so as to fill approximately 80% of the volume of the grinding chamber, and at a grinding speed of 2500 rpm at 24 C. for 180 minutes, under a slurry re-circulation rate of 700 ml/minutes, and measuring the pH over time.

[0150] Solids Content of an Aqueous Slurry

[0151] 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.

[0152] Calcium Anion Salt:Calcium Carbonate Mass Ratio in a Sample of Material

[0153] Calcium anion salt:calcium carbonate mass ratio was evaluated based on the weight of calcium carbonate in a dried and washed sample of material, which is determined by thermogravimetric analysis (TGA) using a Mettler Toledo TGA 851 using a sample of 500+/50 mg and scanning temperatures as follows: [0154] 25 to 200 C. at a rate of 20 C./minute; [0155] 200 C. maintained 15 minutes; [0156] 200 to 400 C. at a rate of 20 C./minute; [0157] 400 C. maintained 15 minutes;

[0158] under an air flow of 80 ml/min and a nitrogen gas flow of 15 ml/min. This measurement provides a mass of CO.sub.2 gas released from the sample, relative to which a mass of calcium carbonate is calculated. The difference between this calculate mass of calcium carbonate and the mass of the sample provided corresponds to the mass of calcium anion salt

[0159] Preparation of PCC-Comprising Pigments of Step a)

[0160] The following is a description of the preparation of the PCC-comprising pigments of Step a) implemented in subsequent tests described hereafter.

[0161] Preparation of a Slurry of Undispersed, Scalenohedral and Calcitic PCC (PCC1)

[0162] PCC1 was synthesised by bubbling CO.sub.2 through a slurry of calcium hydroxide so as to obtain a product in slurry featuring the specific surface area and weight median particle diameter, as determined according to the measurement methods hereabove, given in Table 1, and formed of essentially the scalenohedral morphology of the calcite phase as determined by XRD analysis. The slurry solids was adjusted to 17% by weight. The pH of this slurry, as measured according to the measurement method given above, was between 8 and 9.5.

[0163] A sample of this PCC was subsequently wet ground to measure the pH evolution, according to the test method given above. During this grinding, the slurry pH was observed to rise by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0164] A sample of this PCC was also subjected to the hydrophilicity test given above, and determined to be hydrophilic.

[0165] Preparation of a Slurry of Dispersed, Scalenohedral and Calcitic PCC (PCC2)

[0166] PCC2 was synthesised by bubbling CO.sub.2 through a slurry of calcium hydroxide so as to obtain a product in slurry featuring the specific surface area and weight median particle diameter, as determined according to the measurement methods hereabove, given in Table 1, and formed of essentially the scalenohedral morphology of the calcite phase as determined by XRD analysis. The slurry solids was adjusted to 40% by weight in the presence of a polyacrylate-based dispersant. The pH of this slurry, as measured according to the measurement method given above, was between 8 and 9.5.

[0167] A sample of this PCC was subsequently wet ground to measure the pH evolution, according to the test method given above. During this grinding, the slurry pH was observed to rise by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0168] A sample of this PCC was also subjected to the hydrophilicity test given above, and determined to be hydrophilic.

[0169] Preparation of a slurry of undispersed, aragonitic PCC (PCC3) PCC3 was synthesised by bubbling CO.sub.2 through a slurry of calcium hydroxide so as to obtain a product in slurry featuring the specific surface area and weight median particle diameter, as determined according to the measurement methods hereabove, given in Table 1, and formed of essentially the aragonitic morphology as determined by XRD analysis.

[0170] The slurry solids was adjusted to 17% by weight. The pH of this slurry, as measured according to the measurement method given above, was between 8 and 9.5.

[0171] A sample of this PCC was subsequently wet ground to measure the pH evolution, according to the test method given above. During this grinding, the slurry pH was observed to rise by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0172] A sample of this PCC was also subjected to the hydrophilicity test given above, and determined to be hydrophilic.

[0173] Preparation of a Slurry of Undispersed, Rhombohedral PCC (PCC4)

[0174] PCC4 was synthesised by bubbling CO.sub.2 through a slurry of calcium hydroxide so as to obtain a product in slurry featuring the specific surface area and weight median particle diameter, as determined according to the measurement methods hereabove, given in Table 1, and formed of essentially the rhomobohedral morphology as determined by XRD analysis. The slurry solids was adjusted to 17% by weight. The pH of this slurry, as measured according to the measurement method given above, was between 8 and 9.5.

[0175] A sample of this PCC was subsequently wet ground to measure the pH evolution, according to the test method given above. During this grinding, the slurry pH was observed to rise by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0176] A sample of this PCC was also subjected to the hydrophilicity test given above, and determined to be hydrophilic.

Example 1

[0177] The following Example is illustrative the prior art, and involves contacting a PCC pigment with H.sub.3O.sup.+ and a phosphate-comprising anion in the absence of additional soluble calcium ions.

[0178] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of the PCC described in the Table herebelow, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at 70 C.

[0179] Under stirring such that an essentially laminar flow is established, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC weight and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to the PCC slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes.

[0180] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is the measured and reported in the Table below.

TABLE-US-00001 TABLE 1 Test 1 2 3 4 Prior Prior Prior Prior Art Art Art Art PCC type PPC1 PCC2 PCC3 PCC4 Weight median particle 2.0 1.8 2.7 1.1 diameter (m) SSA starting material (m.sup.2/g) 8 8 6.3 5.5 SSA final product (m.sup.2/g) 54 18 15 19

Example 2

[0181] The following Example is illustrative of the invention, and involves contacting PCC1 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt.

[0182] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC1 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0183] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0184] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC weight and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0185] The final solids of the obtained slurry was between 8 and 12% by weight.

[0186] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0187] Test 1 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00002 TABLE 2 Test 1 1A 1B 1C 1D Prior Inven- Inven- Inven- Inven- Art tion tion tion tion Tslurry ( C.) 70 70 70 95 70 Additive1 HCl HCl HCl Acetic acid Moles equivalents 5.5 2.7 5.5 6.6 H.sub.3O.sup.+ per gram PCC (10.sup.3)** Equivalent moles 2.7 1.4 2.7 3.3 Ca.sup.2+ ions per gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ 108 54 108 132 ions per gram PCC (10.sup.3) SSA (m.sup.2/g) 50 77 88 63 98 **assuming full dissociation of Additive1

[0188] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0189] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0190] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 3

[0191] The following Example is illustrative of the invention, and involves contacting PCC1 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt, and where said acid or acid salt is dosed at the same time as the phosphate-comprising anion.

[0192] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC1 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0193] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry, whiles simultaneously adding H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC weight and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0194] The final solids of the obtained slurry was between 8 and 12% by weight.

[0195] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0196] Test 1 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00003 TABLE 3 Test 1 1E Prior Art Invention Tslurry ( C.) 70 70 Additive1 H.sub.2SO.sub.4 Moles equivalents H.sub.3O.sup.+ per gram 4.0 PCC (10.sup.3)** Equivalent moles Ca.sup.2+ ions per 2.0 gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ ions per 80 gram PCC (10.sup.3) SSA (m.sup.2/g) 50 115 **assuming full dissociation of Additive1

[0197] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0198] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0199] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 4

[0200] The following Example is illustrative of the invention, and involves contacting PCC1 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are provided by the addition of a soluble neutral calcium salt.

[0201] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC1 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0202] Under stirring such that an essentially laminar flow is established, a soluble neutral calcium salt (Additive1) in an amount corresponding to a given mole equivalents Ca.sup.2+ ions per gram PCC (values being listed in the Table herebelow), is added to the PCC slurry.

[0203] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC weight and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0204] The final solids of the obtained slurry was between 8 and 12% by weight.

[0205] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0206] Test 1 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00004 TABLE 4 Test 1 1F 1G Prior Art Invention Invention Tslurry ( C.) 70 70 70 Additive1 CaCl.sub.2 Ca(NO.sub.3).sub.2 Equivalent moles Ca.sup.2+ ions per 1.4 1.2 gram PCC (10.sup.3)** Equivalent mass Ca.sup.2+ ions per 56 48 gram PCC (10.sup.3) SSA (m.sup.2/g) 54 80 90 **assuming full dissociation of Additive1

[0207] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0208] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0209] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 5

[0210] The following Example is illustrative of the invention, and involves contacting PCC1 with a phosphate-comprising anion (provided in the form of a salt), in the presence of excess soluble calcium ions, where the soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt.

[0211] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC1 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0212] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0213] Thereafter, Na.sub.(3-x)H.sub.xPO.sub.4 where x=0-1 (the value of x being indicated in the Table below) in an amount corresponding to approximately 310.sup.3 moles Na.sub.(3-x)H.sub.xPO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0214] The final solids of the obtained slurry was between 8 and 12% by weight.

[0215] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0216] Test 1 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00005 TABLE 5 X = 0 X = 1 Test 1 1H 1J Prior Art Invention Invention Tslurry ( C.) 70 70 70 Additive1 HCl HCl Moles equivalents H.sub.3O.sup.+ per 5.5 5.5 gram PCC (10.sup.3)** Equivalent moles Ca.sup.2+ ions 2.7 2.7 per gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ ions 108 108 per gram PCC (10.sup.3) SSA (m.sup.2/g) 50 55 108 **assuming full dissociation of Additive1

[0217] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0218] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0219] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 6

[0220] The following Example is illustrative of the invention, and involves contacting PCC1 or PCC2 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt, in the presence of a further additional additive which increases the ionic strength of the slurry.

[0221] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC1 or PCC2 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0222] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0223] Under continued stirring, a neutral, soluble salt capable of increasing the ionic strength of the slurry is added (Additive 2), in an amount listed in the Table herebelow.

[0224] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0225] The final solids of the obtained slurry was between 8 and 12% by weight.

[0226] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0227] Test 1 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00006 TABLE 6 PCC1 PCC2 1 1L 1M 2 2A 2B Test Prior Art Invention Invention Prior Art Invention Invention Tslurry 70 70 70 70 70 70 ( C.) Additive1 HCl HCl HCl HCl Moles 5.5 5.5 5.5 5.5 equivalents H.sub.3O.sup.+ per gram PCC (10.sup.3)** Equivalent 2.7 2.7 2.7 2.7 moles Ca.sup.2+ ions per gram PCC (10.sup.3) Equivalent 108 108 108 108 mass Ca.sup.2+ ions per gram PCC (10.sup.3) Additive2 NaCl KNO.sub.3 NaCl KNO.sub.3 % weight 0.1 0.1 0.1 0.1 Additive2 on PCC weight SSA (m.sup.2/g) 54 61 75 18 48 45 **assuming full dissociation of Additive1

[0228] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0229] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0230] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 7

[0231] The following Example is illustrative of the invention, and involves contacting PCC3 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt.

[0232] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC3 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0233] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0234] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0235] The final solids of the obtained slurry was between 8 and 12% by weight.

[0236] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0237] Test 2 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00007 TABLE 7 Test 3 3A Prior Art Invention Tslurry ( C.) 70 70 Additive1 HCl Moles equivalents H.sub.3O.sup.+ per 5.5 gram PCC (10.sup.3)** Equivalent moles Ca.sup.2+ ions 2.7 per gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ ions 108 per gram PCC (10.sup.3) SSA (m.sup.2/g) 15 49 **assuming full dissociation of Additive1

[0238] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0239] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0240] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 8

[0241] The following Example is illustrative of the invention, and involves contacting PCC2 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt.

[0242] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC2 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0243] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0244] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0245] The final solids of the obtained slurry was between 8 and 12% by weight.

[0246] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0247] Test 2 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00008 TABLE 8 Test 2 2C Prior Art Invention Tslurry ( C.) 70 70 Additive1 HCl Moles equivalents H.sub.3O.sup.+ per 5.5 gram PCC (10.sup.3)** Equivalent moles Ca.sup.2+ ions 2.7 per gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ ions 108 per gram PCC (10.sup.3) SSA (m.sup.2/g) 18 54 **assuming full dissociation of Additive1

[0248] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0249] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0250] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 9

[0251] The following Example is illustrative of the invention, and involves contacting PCC4 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt.

[0252] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC4 described hereabove, such that the slurry obtained has a solids content of 10% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0253] Under stirring such that an essentially laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0254] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0255] The final solids of the obtained slurry was between 8 and 12% by weight.

[0256] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0257] Test 2 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00009 TABLE 9 Test 4 4A Prior Art Invention Tslurry ( C.) 70 70 Additive1 HCl Moles equivalents H.sub.3O.sup.+ per 5.5 gram PCC (10.sup.3)** Equivalent moles Ca.sup.2+ ions 2.7 per gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ ions 108 per gram PCC (10.sup.3) SSA (m.sup.2/g) 19 87 **assuming full dissociation of Additive1

[0258] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0259] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0260] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.

Example 10

[0261] The following Example is illustrative of the invention, and involves contacting PCC1 with a phosphate-comprising anion (provided in the form of an acid), in the presence of excess soluble calcium ions, where soluble calcium ions are generated on contacting the PCC with an acid or an acid salt having a soluble corresponding calcium salt.

[0262] In a stainless steel reactor, an aqueous slurry is prepared by adjusting the solids content of the aqueous slurry of PCC1 described hereabove, such that the slurry obtained features a solids content of 20% by dry weight. The temperature of this slurry is thereafter brought to and maintained at a reaction temperature defined in the Table herebelow under Tslurry.

[0263] Under stirring such that laminar flow is established, an acid or an acid salt having a soluble corresponding calcium salt (Additive1) in an amount corresponding to a given mole equivalents H.sub.3O.sup.+ ions per gram PCC on contacting the precipitated calcium carbonate (which corresponds to a generation of a given mole equivalents of solubilised calcium ions, per gram PCC, both of these given values being listed in the Table herebelow), is added to the PCC slurry.

[0264] Thereafter, H.sub.3PO.sub.4 in an amount corresponding to 30% by weight on PCC weight and to approximately 310.sup.3 moles H.sub.3PO.sub.4 per gram PCC is added to this slurry over a period of 10 minutes. Following this addition, the slurry is stirred for an additional 5 minutes. During this period, the pH of the slurry was observed to decrease temporarily to a value of less than 6.0.

[0265] The final solids of the obtained slurry was between 8 and 12% by weight.

[0266] The resulting slurry is allowed to sit overnight before filtering and drying the obtained product. The final specific surface area of this dry product is measured and listed in the Table herebelow.

[0267] Test 1 of Example 1 is also listed in the Table herebelow as a reference.

TABLE-US-00010 TABLE 10 Test Invention Tslurry ( C.) 70 Additive1 HCl Moles equivalents H.sub.3O.sup.+ per 5.5 gram PCC (10.sup.3)** Equivalent moles Ca.sup.2+ ions 2.7 per gram PCC (10.sup.3) Equivalent mass Ca.sup.2+ ions 108 per gram PCC (10.sup.3) SSA (m.sup.2/g) 88 **assuming full dissociation of Additive1

[0268] In all case, when the product obtained according to the process of the invention was wet ground according to the method provided above, the pH during wet grinding rose by more than 2 and more than a corresponding slurry wherein the surface-reacted PCC was entirely replaced with GCC.

[0269] In all case, when the product obtained according to the process of the invention was analysed by TGA as described above, a calcium anion salt:calcium carbonate mass ratio of between 20:80 and 60:40 was observed.

[0270] XRD analyses of the products obtained according to the process of the invention indicated the presence of calcium phosphate minerals as well as calcium carbonate.