Production of surface-reacted calcium salts by grinding induced conversion

Abstract

The present invention relates to a process for producing an aqueous suspension of surface-reacted calcium salt particles by mixing a calcium salt excluding monocalcium phosphate and dicalcium phosphate, a calcium phosphate selected from monocalcium phosphate and/or dicalcium phosphate, with water, and grinding the obtained aqueous suspension at a pH value of at least 4.2 to form an aqueous suspension of surface-reacted calcium salt particles.

Claims

1. A process for producing an aqueous suspension of surface-reacted calcium salt particles comprising the steps of: a) providing a calcium salt excluding monocalcium phosphate and dicalcium phosphate, b) providing a calcium phosphate, wherein the calcium phosphate is dicalcium phosphate and is produced by contacting a calcium ion source and a phosphate ion source, c) forming an aqueous suspension by mixing the calcium salt of step a), and the calcium phosphate of step b) with water, and d) grinding the aqueous suspension of step c) at a pH value from 4.2 to 14 and at a temperature of 0 C. to 100 C. to form an aqueous suspension of surface-reacted calcium salt particles, wherein the calcium salt of step a) and the calcium phosphate of step b) in combination have a calcium ion to a phosphate ion molar ratio (Ca.sup.2+: PO.sub.4.sup.3) in the range from 2.2:1 to 100:1; wherein grinding of step d) is carried out: (1) in a ball mill, a rod mill, a vibrating mill, a centrifugal impact mill, a vertical bead mill, an attrition mill, a sand mill, or combinations thereof; and (2) at a specific grinding energy from 50 to 500 kWh per dry metric ton of (2) surface-reacted calcium salt particles.

2. The process of claim 1, wherein the calcium salt of step a) is selected from a calcium carbonate-comprising material, calcium oxide, calcium hydroxide, calcium chloride, calcium nitrate, calcium chlorate, calcium bromide, calcium iodide, calcium acetate, calcium sulphate, calcium citrate, or mixtures thereof.

3. The process of claim 2, wherein the calcium carbonate-comprising material is selected from natural ground calcium carbonate, precipitated calcium carbonate, dolomite, or mixtures thereof.

4. The process of claim 1, wherein the calcium salt of step a) is in form of particles having a weight median particle size d.sub.50(wt) from 0.05 to 500 m.

5. The process of claim 1, wherein the calcium salt of step a) and the calcium phosphate of step b) in combination have a calcium ion to phosphate ion molar ratio (Ca.sup.2+: PO.sub.4.sup.3) in the range from 2.5:1 to 10:1.

6. The process of claim 1, wherein the calcium phosphate of step b) is dicalcium phosphate dihydrate and is provided in an amount from 1.7 to 230 wt.-%, based on the total weight of the calcium salt excluding monocalcium phosphate and dicalcium phosphate.

7. The process of claim 1, wherein the calcium phosphate of step b) is anhydrous dicalcium phosphate and is provided in an amount from 1.4 to 181 wt.-%, based on the total weight of the calcium salt excluding monocalcium phosphate and dicalcium phosphate.

8. The process of claim 1, wherein the aqueous suspension formed in step c) has a solids content from 1 to 90 wt.-%, based on the total weight of the aqueous suspension.

9. The process of claim 1, wherein step d) is carried out at a pH value from 4.5 to 14.

10. The process of claim 1, wherein the dicalcium phosphate of step b) is produced by the following steps: i) providing the calcium ion source excluding dicalcium phosphate, ii) providing the phosphate ion source selected from phosphoric acid, a salt thereof, or a mixture thereof, and iii) contacting the calcium ion source of step i) and the phosphate ion source of step ii) in the presence of water to form dicalcium phosphate, wherein the calcium ion source of step i) and the phosphate ion source of step ii) in combination are provided in a calcium ion to phosphate ion molar ratio from 1:2 to 5:1.

11. The process of claim 10, wherein the calcium ion source of step i) is the same as the calcium salt of step a) of claim 1 and/or the phosphate ion source of step ii) is phosphoric acid.

12. The process of claim 10, wherein the phosphate ion source is phosphoric acid, a hydrogen-free salt of phosphoric acid, a monohydrogen salt of phosphoric acid, Na.sub.2HPO.sub.4, or a dihydrogen salt of phosphoric acid, or a mixture thereof.

Description

EXAMPLES

1. Measurement Methods

(1) In the following, measurement methods implemented in the examples are described.

1.1 Particle Size Distribution

(2) Volume determined median particle size d.sub.50(vol) and the volume determined top cut particle size d.sub.98(vol) was evaluated using a Malvern Mastersizer 2000 Laser Diffraction System (Malvern Instruments Plc., Great Britain). The d.sub.50(vol) or d.sub.98(vol) value indicates a diameter value such that 50% or 98% by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement was analyzed using the Mie theory, with a particle refractive index of 1.57 and an absorption index of 0.005. The methods and instruments are known to the skilled person and are commonly used to determine particle size distributions of fillers and pigments. The sample was measured in dry condition without any prior treatment.

(3) The weight determined median particle size d.sub.50(wt) and the weight determined top cut particle size d.sub.98(wt) was measured by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement was made with a Sedigraph 5120 of Micromeritics Instrument Corporation, USA. The method and the instrument are known to the skilled person and are commonly used to determine particle size distributions of fillers and pigments. The measurement was 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 supersonicated.

1.2. Specific Surface Area (SSA)

(4) The specific surface area was measured via the BET method according to ISO 9277:2010 using nitrogen and a ASAP 2460 instrument (Micromeritics GmbH, Germany), following conditioning of the sample by heating at 100 C. for a period of 30 minutes. Prior to such measurements, the sample was filtered within a Bchner funnel, rinsed with deionised water and dried at 110 C. in an oven for at least 12 hours.

1.3. Specific Grinding Energy (SGE)

(5) The specific grinding energy (SGE) was determined through first recording simultaneously the electrical power consumption (P) of the grinding device, given in kW, and the volumetric flow rate (v.sub.s) of the feeding slurry, given in m.sup.3/h, and as indicated in the respective monitoring displays. Further, the total solids (TS) content of the feeding slurry, given in wt.-% was determined using a Moisture Analyzer HR73 from Mettler-Toledo (T=120 C., automatic switch off 3, standard drying) with a sample size of 5 to 20 g. Assuming the density of water (.sub.w) to be 1.00 T/m.sup.3 and the density of the applied dry calcium carbonate/marble/chalk (pc) to be 2.71 T/m.sup.3, the SGE can be calculated as the function of the given quantities, as expressed in equations (1), (2) and (3).
SGE=P/((TS).Math.m.sub.s)Eq. (1)
m.sub.s=.sub.s.Math.v.sub.sEq. (2)
.sub.s=[.sub.c.Math..sub.w]/[.sub.c.Math.(1(TS))+.sub.w.Math.(TS)]Eq. (3)

2. Examples

2.1. Example 1 (In-Situ Production of Dicalcium Phosphate)

(6) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m and a weight determined top cut particle size d.sub.98(wt) of 50 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 20% by dry weight relative to the total suspension weight.

(7) Under stirring such that essentially laminar flow is established, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 10% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(8) Mixing in the high-speed tank mixer was continued until no gas bubbles were observed and the pH of the slurry was at least 7.0. Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 75 L/h through a 25 L vertical bead mill filled with 21 kg of ZrO.sub.2 based grinding medium having a bead material density of 3.8 g/cm.sup.3 and run at a mill-rotor tip speed of 5.3 m/s resulting into a specific grinding energy (SGE) of 189 kWh/T. The product was collected after at least 25 L of slurry was pumped through the mill.

(9) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 50 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 4.2 m, and a volume determined top cut particle size d.sub.98(vol) of 10.5 m.

2.2. Example 2 (In-Situ Production of Dicalcium Phosphate)

(10) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m and a weight determined top cut particle size d.sub.98(wt) of 50 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 20% by dry weight relative to the total suspension weight.

(11) Under stirring such that essentially laminar flow is established, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 15% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(12) Mixing in the high-speed tank mixer was continued until no gas bubbles were observed and the pH of the slurry was at least 7.0. Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 75 L/h through a 25 L vertical bead mill filled with 21 kg of ZrO.sub.2 based grinding medium having a bead material density of 3.8 g/cm.sup.3 and run at a mill-rotor tip speed of 7.5 m/s resulting into a specific grinding energy (SGE) of 260 kWh/T. The product was collected after at least 25 L of slurry was pumped through the mill.

(13) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 62 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 3.3 m, and a volume determined top cut particle size d.sub.98(vol) of 7.2 m.

2.3. Example 3 (In-Situ Production of Dicalcium Phosphate)

(14) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m and a weight determined top cut particle size d.sub.98(wt) of 50 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 20% by dry weight relative to the total suspension weight.

(15) Under stirring such that essentially laminar flow is established, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 10% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(16) Mixing in the high-speed tank mixer was continued until no gas bubbles were observed and the pH of the slurry was at least 7.0. Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 75 L/h through a 25 L vertical bead mill filled with 36 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-rotor tip speed of 5.3 m/s resulting into a specific grinding energy (SGE) of 290 kWh/T. The product was collected after at least 25 L of slurry was pumped through the mill.

(17) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 48 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 2.9 m, and a volume determined top cut particle size d.sub.98(vol) of 7.0 m.

(18) 2.4. Example 4 (in-situ production of dicalcium phosphate)

(19) Fine chalk powder (Aero chalk), from Omya SAS Omey France having a weight determined median particle size d.sub.50(wt) of 4 m and a weight determined top cut particle size d.sub.98(wt) of 16 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 20% by dry weight relative to the total suspension weight.

(20) Under stirring such that essentially laminar flow is established, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 10% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(21) Mixing in the high-speed tank mixer was continued until no gas bubbles were observed and the pH of the slurry was at least 7.0. Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 75 L/h through a 25 L vertical bead mill filled with 21 kg of ZrO.sub.2 based grinding medium having a bead material density of 3.8 g/cm.sup.3 and run at a mill-rotor tip speed of 5.3 m/s resulting into a specific grinding energy (SGE) of 233 kWh/T. The product was collected after at least 25 L of slurry was pumped through the mill.

(22) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 47 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 3.6 m, and a volume determined top cut particle size d.sub.98(vol) of 8.5 m.

2.5. Example 5 (In-Situ Production of Dicalcium Phosphate)

(23) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m and a weight determined top cut particle size d.sub.98(wt) of 50 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 20% by dry weight relative to the total suspension weight.

(24) Under stirring such that essentially laminar flow is established, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 10% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(25) Mixing in the high-speed tank mixer was continued until no gas bubbles were observed and the pH of the slurry was at least 7.0. Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 15.8 L/h through a 6 L vertical bead mill filled with 10 kg of ZrO.sub.2 based grinding medium having a bead material density of 3.8 g/cm.sup.3 and run at a mill-rotor tip speed of 5.0 m/s resulting into a specific grinding energy (SGE) of 254 kWh/T. The product was collected after a temporally constant temperature platform (max.2 C. fluctuation range at steady state) was reached.

(26) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 50 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 3.3 m, and a volume determined top cut particle size d.sub.98(vol) of 7.8 m.

2.6. Example 6 (Separate Production of Dicalcium Phosphate)

(27) Batch 1

(28) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m and a weight determined top cut particle size d.sub.98(wt) of 50 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 40% by dry weight relative to the total suspension weight.

(29) Under essentially turbulent stirring, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 98% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension. Mixing in the high-speed tank mixer was continued until no gas bubbles were observed.

(30) Batch 2

(31) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m and a weight determined top cut particle size d.sub.98(wt) of 50 m was diluted with water at ambient temperature (20 C.2 C.) in a second high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 19% by dry weight relative to the total suspension weight.

(32) Mixing and Grinding

(33) Under stirring such that essentially laminar flow is established, Batch 1 was added into Batch 2 such that the total added marble in the combined slurry corresponds to 20% by dry weight relative to the total suspension weight, excluding the weight of added aqueous solution of H.sub.3PO.sub.4.

(34) Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 75 L/h through a 25 L vertical bead mill filled with 21 kg of a ZrO.sub.2 based grinding medium having a bead material density of 3.8 g/cm.sup.3 and run at a mill-rotor tip speed of 5.3 m/s resulting into a specific grinding energy (SGE) of 211 kWh/T. Product was collected after at least 25 L of slurry was pumped through the mill.

(35) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 54 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 4.0 m, and a volume determined top cut particle size d.sub.98(vol) of 9.2 m.

2.7. Example 7 (Separate Production of Dicalcium Phosphate)

(36) Batch 1

(37) Fine chalk powder (Aero chalk), from Omya SAS Omey France having a weight determined median particle size d.sub.50(wt) of 4 m and a weight determined top cut particle size d.sub.98(wt) of 16 m was diluted with water at ambient temperature (20 C.2 C.) in a high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 40% by dry weight relative to the total suspension weight.

(38) Under essentially turbulent stirring, an aqueous solution having 75 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate over the period of 90 to 120 seconds in an amount corresponding to 98% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension. Mixing in the high-speed tank mixer was continued until no gas bubbles were observed.

(39) Batch 2

(40) Fine chalk powder (Aero chalk), from Omya SAS Omey France having a weight determined median particle size d.sub.50(wt) of 4 m and a weight determined top cut particle size d.sub.98(wt) of 16 m was diluted with water at ambient temperature in a second high-speed tank mixer such that the aqueous suspension obtained has a solids content corresponding to 19% by dry weight relative to the total suspension weight.

(41) Mixing and Grinding

(42) Under stirring such that essentially laminar flow is established, Batch 1 was added into Batch 2 such that the total added chalk in the combined slurry corresponds to 20% by dry weight relative to the total suspension weight excluding the weight of added aqueous solution of H.sub.3PO.sub.4.

(43) Subsequently, the slurry was transferred to a storage tank equipped with a slow mixing device to keep the solid particulate material suspended. The slurry was then pumped at a rate of 75 L/h through a 25 L vertical bead mill filled with 21 kg of ZrO.sub.2 based grinding medium having a bead material density of 3.8 g/cm.sup.3 and run at a mill-rotor tip speed of 5.3 m/s resulting into a specific grinding energy (SGE) of 204 kWh/T. Product was collected after at least 25 L of slurry was pumped through the mill.

(44) The obtained surface-reacted calcium salt particles presented a specific surface area (SSA) of 42 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 4.0 m, and a volume determined top cut particle size d.sub.98(vol) of 9.6 m.

(45) The described process parameters of Examples 1 to 7, together with the respective SSA, d.sub.50(vol) and d.sub.98(vol) values of the obtained products are summarized in Table 1 below.

2.8. Example 8 (Monohydrogen Salt as Phosphate Ion Source)

(46) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m, a weight determined top cut particle size d.sub.98(wt) of 50 m, and a specific surface area (SSA) of 1.1 m.sup.2/g, was diluted with water at ambient temperature (20 C.2 C.) in a 15 L bucket with an overhead stirrer such that the aqueous suspension obtained has a solids content corresponding to 40% by dry weight relative to the total suspension weight.

(47) Under stirring such that essentially laminar flow is established, an aqueous mixture having 6.8 wt.-% of Na.sub.2HPO.sub.4.Math.2H.sub.2O, based on the total weight of the aqueous mixture, was added to the calcium carbonate suspension over the period of 45 to 60 seconds in an amount corresponding to 18.2% by weight Na.sub.2HPO.sub.4.Math.2H.sub.2O salt on dry calcium carbonate weight such that the aqueous suspension obtained has a solids content corresponding to 20% by dry calcium carbonate weight relative to the total suspension weight.

(48) Mixing in the bucket with an overhead stirrer was continued at least 10 min. The slurry was then pumped at a rate of 17.7 L/h through a 0.6 L horizontal bead mill filled with 1.070 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-agitator tip speed of 14 m/s. The product was collected after at least 5 L of slurry was pumped through the mill.

(49) The obtained surface-reacted calcium salt particles presented SSA of 20.6 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 7.9 m, and a volume determined top cut particle size d.sub.98(vol) of 19.2 m.

2.9. Example 9 (Dihydrogen Salt as Phosphate Ion Source)

(50) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m, a weight determined top cut particle size d.sub.98(wt) of 50 m, and a specific surface area (SSA) of 1.1 m.sup.2/g, was diluted with water at ambient temperature (20 C.2 C.) in a 15 L bucket with an overhead stirrer such that the aqueous suspension obtained has a solids content corresponding to 40% by dry weight relative to the total suspension weight.

(51) Under stirring such that essentially laminar flow is established, an aqueous mixture having 6.0 wt.-% of NaH.sub.2PO.sub.4.2H.sub.2O, based on the total weight of the aqueous mixture, was added to the calcium carbonate suspension over the period of 45 to 60 seconds in an amount corresponding to 15.9% by weight NaH.sub.2PO.sub.4.2H.sub.2O salt on dry calcium carbonate weight such that the aqueous suspension obtained has a solids content corresponding to 20% by dry calcium carbonate weight relative to the total suspension weight.

(52) Mixing in the bucket with an overhead stirrer was continued at least 10 min. The slurry was then pumped at a rate of 18.1 L/h through a 0.6 L horizontal bead mill filled with 1.070 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-agitator tip speed of 14 m/s. The product was collected after at least 5 L of slurry was pumped through the mill.

(53) The obtained surface-reacted calcium salt particles presented SSA of 34.1 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 9.4 m, and a volume determined top cut particle size d.sub.98(vol) of 22.8 m.

2.10. Example 10 (Dihydrogen Salt as Phosphate Ion Source)

(54) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m, a weight determined top cut particle size d.sub.98(wt) of 50 m, and a specific surface area (SSA) of 1.1 m.sup.2/g, was diluted with water at ambient temperature (20 C.2 C.) in a 15 L bucket with an overhead stirrer such that the aqueous suspension obtained has a solids content corresponding to 40% by dry weight relative to the total suspension weight.

(55) Under stirring such that essentially laminar flow is established, an aqueous mixture having 4.9 wt.-% of Ca(H.sub.2PO.sub.4).sub.2.Math.H.sub.2O, based on the total weight of the aqueous mixture, was added to the calcium carbonate suspension over the period of 45 to 60 seconds in an amount corresponding to 12.9% by weight Ca(H.sub.2PO.sub.4).sub.2.H.sub.2O salt on dry calcium carbonate weight such that the aqueous suspension obtained has a solids content corresponding to 20% by dry calcium carbonate weight relative to the total suspension weight.

(56) Mixing in the bucket with an overhead stirrer was continued at least 10 min. The slurry was then pumped at a rate of 18.6 L/h through a 0.6 L horizontal bead mill filled with 1.070 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-agitator speed of 14 m/s. The product was collected after at least 5 L of slurry was pumped through the mill.

(57) The obtained surface-reacted calcium salt particles presented SSA of 46.9 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 8.0 m, and a volume determined top cut particle size d.sub.98(vol) of 20.2 m.

2.11. Example 11 (Dihydrogen Salt as Phosphate Ion Source)

(58) Ground marble, from Omya SPA Carrara Italy having a weight determined median particle size d.sub.50(wt) of 10 m, a weight determined top cut particle size d.sub.98(wt) of 50 m, and a specific surface area (SSA) of 1.1 m.sup.2/g, was diluted with water at ambient temperature (20 C.2 C.) in a 15 L bucket with an overhead stirrer such that the aqueous suspension obtained has a solids content corresponding to 40% by dry weight relative to the total suspension weight.

(59) Under stirring such that essentially laminar flow is established, solid KH.sub.2PO.sub.4 crystals, were added to the calcium carbonate suspension over the period of 15 to 25 seconds in an amount corresponding to 13.9% by weight KH.sub.2PO.sub.4 salt on dry calcium carbonate weight such that the aqueous suspension obtained has a solids content corresponding to 20% by dry calcium carbonate weight relative to the total suspension weight.

(60) Mixing in the bucket with an overhead stirrer was continued at least 10 min. The slurry was then pumped at a rate of 20.1 L/h through a 0.6 L horizontal bead mill filled with 1.070 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-agitator speed of 14 m/s. The product was collected after at least 5 L of slurry was pumped through the mill.

(61) The obtained surface-reacted calcium salt particles presented SSA of 27.1 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 8.1 m, and a volume determined top cut particle size d.sub.98(vol) of 19.7 m.

2.12. Example 12 (Lime Stone as Calcium Ion Source)

(62) Ground lime stone, from Omya SAS Orgon France having a weight determined median particle size d.sub.50(wt) of 3.5 m, a weight determined top cut particle size d.sub.98(wt) of 10.5 m, and a specific surface area (SSA) of 1.5 m.sup.2/g, was diluted with water at ambient temperature (20 C.2 C.) in a 15 L bucket with an overhead stirrer such that the aqueous suspension obtained has a solids content corresponding to 20% by dry weight relative to the total suspension weight.

(63) Under stirring such that essentially laminar flow is established, an aqueous mixture having 85 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate suspension over the period of 25 to 35 seconds in an amount corresponding to 10% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(64) Mixing in the bucket with an overhead stirrer was continued at least 10 min, until no gas bubbles were observed and the pH of the slurry was at least 7.0. The slurry was then pumped at a rate of 20.4 L/h through a 0.6 L horizontal bead mill filled with 1.070 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-agitator tip speed of 14 m/s. The product was collected after at least 5 L of slurry was pumped through the mill.

(65) The obtained surface-reacted calcium salt particles presented SSA of 47.1 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 8.7 m, and a volume determined top cut particle size d.sub.98(vol) of 25.0 m, as measured right after the process.

2.13. Example 13 (Scalenohedral Precipitated Calcium Carbonate (S-PCC) as Calcium Ion Source)

(66) A 20% slurry of scalenohedral precipitated calcium carbonate, from Omya GmbH Hausmening Austria having a volume determined median particle size d.sub.50(wt) of 3.3 m and specific surface area (SSA) of 5.5 m.sup.2/g was stirred at ambient temperature (20 C.2 C.) in a 15 L bucket with an overhead stirrer.

(67) Under stirring such that essentially laminar flow is established, an aqueous mixture having 85 wt.-% of H.sub.3PO.sub.4, based on the total weight of the aqueous solution, was added to the calcium carbonate suspension over the period of 25 to 35 seconds in an amount corresponding to 10% by weight active phosphoric acid on dry calcium carbonate weight. Following this addition, CO.sub.2 gas bubbles were observed to form and pass upwards through the suspension.

(68) Mixing in the bucket with an overhead stirrer was continued at least 10 min, until no gas bubbles were observed and the pH of the slurry was at least 7.0. The slurry was then pumped at a rate of 18.3 L/h through a 0.6 L horizontal bead mill filled with 1.070 kg of ZrO.sub.2 based grinding medium having a bead material density of 6.2 g/cm.sup.3 and run at a mill-agitator tip speed of 14 m/s. The product was collected after at least 3 L of slurry was pumped through the mill.

(69) The obtained surface-reacted calcium salt particles presented SSA of 36.0 m.sup.2/g, a volume determined median particle size d.sub.50(vol) of 1.95 m, and a volume determined top cut particle size d.sub.98(vol) of 15.5 m, as measured right after the process.

(70) TABLE-US-00001 TABLE 1 Process parameters and characteristics of obtained surface-reacted calcium carbonates. Example 1 2 3 4 5 6 7 Calcium salt Marble Marble Marble Chalk Marble Marble Chalk Calcium phosphate in-situ in-situ in-situ in-situ in-situ separate separate production Amount calcium 40 (batch 1) 40 (batch 1) salt (wt.-%, based 20 20 20 20 20 19 (batch 2) 19 (batch 2) on total weight of 20 (mixture) 20 (mixture) aqueous suspension) Added H.sub.3PO.sub.4 or 10 15 10 10 10 98 (batch 1) 98 (batch 1) phosphate salt 10 (mixture) 10 (mixture) amount (wt.-%, based on total weight of calcium salt) Molar ratio 9.79:1 6.53:1 9.79:1 9.79:1 9.79:1 1.0:1 (batch 1) 1.0:1 (batch 1) Ca.sup.2+:PO.sub.4.sup.3 9.79:1 (mixture) 9.79:1 (mixture) Mill volume (L) 25 25 25 25 6 25 25 Grinding medium A* A* B** A* A* A* A* Bead diameter 1.0/1.6 mm 1.0/1.6 mm 1.2/1.4 mm 1.0/1.6 mm 0.7/1.4 mm 1.0/1.6 mm 1.0/1.6 mm Amount 21 kg 21 kg 36 kg 21 kg 10 kg 21 kg 21 kg Flow rate (L/h) 75 75 75 75 15.8 75 75 Tip speed (m/s) 5.3 7.5 5.3 5.3 5.0 5.3 5.3 SGE (kWh/T) 189 260 290 233 254 211 204 SSA (m.sup.2/g) of SRCC 50 62 48 47 50 54 42 d.sub.50 (m) of SRCC 4.2 3.3 2.9 3.6 3.3 4.0 4.0 d.sub.98 (m) of SRCC 10.5 7.2 7.0 8.5 7.8 9.2 9.6 *A: Specific bead density = 3.8 g/cm.sup.3; Composition: 66% ZrO.sub.2, 1% HfO.sub.2, 5% Al.sub.2O.sub.3, 27% SiO.sub.2, 1% others Origin: France. **B: Specific bead density = 6.2 g/cm.sup.3; Composition: 80% ZrO.sub.2, 2% HfO.sub.2, 0.4% Al.sub.2O.sub.3, <200 ppm SiO.sub.2, 16.5% CeO.sub.2, 1.1% others; Origin: China

(71) TABLE-US-00002 TABLE 2 Process parameters and characteristics of obtained surface-reacted calcium carbonates. Example 8 9 10 11 12 13 Calcium salt Marble Marble Marble Marble Lime stone S-PCC Phosphate source Na.sub.2HPO.sub.42H.sub.2O NaH.sub.2PO.sub.42H.sub.2O Ca(H.sub.2PO.sub.4)H.sub.2O KH.sub.2PO.sub.4 H.sub.3PO.sub.4 H.sub.3PO.sub.4 Calcium phosphate in-situ in-situ separate in-situ in-situ in-situ production Amount calcium 20 20 20 20 20 20 salt (wt.-%, based on total weight of aqueous suspension) Added H.sub.3PO.sub.4 or 18.2 15.9 12.9 13.9 10 10 phosphate salt amount (wt.-%, based on total weight of calcium salt) Molar ratio Ca.sup.2+:PO.sub.4.sup.3 9.79:1 9.79:1 9.79:1 9.79:1 9.79:1 9.79:1 Mill volume (L) 0.6 0.6 0.6 0.6 0.6 0.6 Grinding medium A* A* A* A* A* A* Bead diameter 0.6/1.0 mm 0.6/1.0 mm 0.6/1.0 mm 0.6/1.0 mm 0.6/1.0 mm 0.7/1.4 mm Amount 1.070 kg 1.070 kg 1.070 kg 1.070 kg 1.070 kg 1.070 kg Flow rate (L/h) 17.7 18.1 18.6 20.1 20.4 18.3 Tip speed (m/s) 14 14 14 14 14 14 SSA (m.sup.2/g) of SRCC 20.6 34.1 46.9 27.1 47.1 36.0 d.sub.50 (m) of SRCC 7.9 9.4 8 8.1 8.7 1.95 d.sub.98 (m) of SRCC 19.2 22.8 20.2 19.7 25 15.5 *A: Specific bead density = 3.8 g/cm.sup.3; Composition: 66% ZrO.sub.2, 1% HfO.sub.2, 5% Al.sub.2O.sub.3, 27% SiO.sub.2, 1% others; Origin: France.