Process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate and its use

Abstract

The present invention refers to a process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate and its uses. The process is carried out in a reactor system that comprises a tank (1) equipped with a stirrer (2) and at least one filtering device (4).

Claims

1. A process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, the process comprising the steps of: a) providing water, b) providing at least one substance comprising at least one earth alkali carbonate, the at least one substance being in a dry form or in an aqueous form, wherein the at least one substance is selected from the group consisting of marble, limestone, chalk, dolomite, and precipitated calcium carbonate, and wherein the at least one substance has a specific surface area (SSA) in the range of 1.0 to 200 m.sup.2/g, and a weight median particle size (d.sub.50) in the range of 0.1 μm to 50 μm, c) providing CO.sub.2, d) combining the at least one substance of step b) with the CO.sub.2 of step c) in the water of step a) at a temperature in a range of 5 to 55° C. in order to obtain a resulting suspension S having a pH of between 6 and 9, a solids content of from 1 to 35 wt.-% based on the total weight of the resulting suspension S, and containing particles that represent a total particle surface area (SSA.sub.total) that is greater than 20,000 m.sup.2/tonne of the resulting suspension S, and e) filtering at least a part of the resulting suspension S that is obtained in step d) by passing the resulting suspension S through a filtering device in order to obtain an aqueous solution comprising at least one earth alkali hydrogen carbonate.

2. The process according to claim 1, wherein the particles of the resulting suspension S represent a total particle surface area (SSA.sub.total) that is in the range of 25,000-2,000,000 m.sup.2/tonne of the resulting suspension S.

3. The process according to claim 1, wherein the particles of the resulting suspension S represent a total particle surface area (SSA.sub.total) that is in the range of 50,000-5,000,000 m.sup.2/tonne of the resulting suspension S.

4. The process according to claim 1, wherein the particles of the resulting suspension S represent a total particle surface area (SSA.sub.total) that is in the range of 200,000-600,000 m.sup.2/tonne of the resulting suspension S.

5. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate of step b) has a weight median particle size (d.sub.50) in the range of 0.5 μm to 5 μm.

6. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate of step b) has a specific surface area (SSA) in the range of 1 to 100 m.sup.2/g.

7. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate of step b) has an HCl insoluble content from 0.02 to 90 wt.-%, based on the total weight of the dry substance.

8. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate of step b) has an HCl insoluble content from 0.05 to 15 wt.-%, based on the total weight of the dry substance.

9. The process according to claim 1, wherein the water of step a) is distilled water, tap water, desalinated water, brine, treated wastewater, ground water, surface water, or rainfall.

10. The process according to claim 1, wherein the CO.sub.2 of step c) is gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide, or a gaseous mixture of carbon dioxide and at least one other gas.

11. The process according to claim 1, wherein the CO.sub.2 of step c) is gaseous carbon dioxide.

12. The process according to claim 1, wherein the amount of CO.sub.2 used, in mol, to produce 1 mol of the at least one earth alkali hydrogen carbonate in the aqueous solution is from 0.5 to 4 mol of CO.sub.2.

13. The process according to claim 1, wherein the amount of CO.sub.2 used, in mol, to produce 1 mol of the at least one earth alkali hydrogen carbonate in the aqueous solution is from 0.5 to 2.5 mol of CO.sub.2.

14. The process according to claim 1, wherein the amount of CO.sub.2 used, in mol, to produce 1 mol of the at least one earth alkali hydrogen carbonate in the aqueous solution is from 0.5 to 1.0 mol of CO.sub.2.

15. The process according to claim 1, wherein the amount of CO.sub.2 used, in mol, to produce 1 mol of the at least one earth alkali hydrogen carbonate in the aqueous solution is from 0.5 to 0.65 mol of CO.sub.2.

16. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a hardness from 5 to 130 °dH.

17. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a hardness from 10 to 60 °dH.

18. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a hardness from 15 to 50 °dH.

19. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate and that is obtained in step e) has a pH in the range of 6.5 to 9 at 20° C.

20. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a pH in the range of 6.7 to 7.9 at 20° C.

21. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a pH in the range of 6.9 to 7.7 at 20° C.

22. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a calcium concentration, as calcium carbonate, from 70 to 630 mg/l.

23. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is dolomite, and the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a magnesium concentration, as magnesium carbonate, from 1 to 200 mg/l.

24. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is dolomite, and the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a magnesium concentration, as magnesium carbonate, from 2 to 150 mg/l.

25. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is dolomite, and the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a magnesium concentration, as magnesium carbonate, from 3 to 125 mg/l.

26. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a turbidity value of lower than 0.5 NTU.

27. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a turbidity value of lower than 0.3 NTU.

28. The process according to claim 1, wherein at least step d) is carried out at a temperature that is in a range of 20 to 45° C.

29. The process according to claim 1, which is a continuous process.

30. The process according to claim 1, wherein the filtering device of step e) is a membrane filter.

31. The process according to claim 30, wherein the filtering device is a tube membrane filter with a pore size of between 0.02 μm and 0.5 μm.

32. The process according to claim 30, wherein the filtering device is a tube membrane filter with a pore size of between 0.05 μm and 0.2 μm.

33. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is marble.

34. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is limestone.

35. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is chalk.

36. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is dolomite selected from dolomitic limestone or calcareous dolomite.

37. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is dolomite.

38. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is precipitated calcium carbonate.

39. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate that is obtained in step e) has a turbidity value of lower than 1.0 NTU and has a calcium concentration, as calcium carbonate, from 50 to 650 mg/l.

40. The process according to claim 1, wherein the at least one earth alkali hydrogen carbonate comprises Mg(HCO.sub.3).sub.2 formed in the presence of Ca(OH).sub.2.

41. The process according to claim 1, wherein the aqueous solution comprising at least one earth alkali hydrogen carbonate comprises a calcium concentration of 80 to 120 mg/l as calcium carbonate and a magnesium concentration of 20 to 30 mg/l as magnesium carbonate.

42. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is dolomitic limestone.

43. The process according to claim 1, wherein the at least one substance comprising at least one earth alkali carbonate is calcareous dolomite.

44. A continuous process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, the process comprising: combining at least one substance comprising at least one earth alkali carbonate with CO.sub.2 in water at a temperature in a range of 5 to 55° C. to obtain a resulting suspension having a pH of between 6 and 9, a solids content of from 1 to 35 wt.-% based on the total weight of the resulting suspension, and containing particles that represent a total particle surface area (SSA.sub.total) that is greater than 20,000 m.sup.2/tonne of the resulting suspension; and passing the resulting suspension through a filtering device to obtain the aqueous solution comprising at least one earth alkali hydrogen carbonate; wherein the at least one substance is selected from the group consisting of marble, limestone, chalk, dolomite, and precipitated calcium carbonate and has a specific surface area (SSA) in the range of 1.0 to 200 m.sup.2/g, and a weight median particle size (d.sub.50) in the range of 0.1 μm to 50 μm.

Description

(1) FIG. 1 is meant to illustrate the process according to the present invention.

(2) FIG. 1 exemplifies one embodiment of the present invention. The process according to the present invention is preferably carried out in a reactor system that comprises a tank (1) that is equipped with a stirrer (2), at least one inlet (not shown) for the water, the carbon dioxide and the at least substance comprising at least one earth alkali carbonate and the optional at least one earth alkali hydroxide as well as a pH measuring device (not shown). The at least one substance comprising at least one earth alkali carbonate and the optional at least one earth alkali hydroxide in a minor amount in respect to earth alkali carbonate can be introduced into the tank either in a dry or in an aqueous form. Connected to the reactor, there is at least one filtering device (4) that has an outlet for the aqueous solution comprising at least one earth alkali hydrogen carbonate. When there is more than one filtering device present, then they can be either arranged in a parallel, or an in-line (serial), or a parallel and an in-line manner. The filtering device (4) is preferably a membrane filter. The filtering device (4) is connected to the tank (1) in such a way that a recirculation of a part of the suspension from the filtering device (4) into the tank (1) is possible, if required.

(3) The at least one substance comprising at least one earth alkali carbonate and the optional at least one earth alkali hydroxide (6) in a minor amount in respect to earth alkali carbonate, the water (14) and the CO.sub.2 are introduced into the tank (1) via the at least one inlet (not shown) and are stirred with stirrer (2) in order to obtain the resulting suspension S having a pH of between 6 and 9. Then, the resulting suspension S is fed (8) to the filtering device (4), where coarse particles, i.e. all particles having a size of at least 0.2 μm, that are contained in the suspension are retained in the filtering device (4), and a clear aqueous solution comprising at least one earth alkali hydrogen carbonate is obtained. At least a part of the clear aqueous solution comprising at least one earth alkali hydrogen carbonate is discharged (10) from the filtering device (4).

(4) The flow rate of the suspension S through the filtering device (4) is at least 1 m/s, and preferably in the range of 1.5 to 10 m/s, and most preferably in the range of 3 to 6 m/s.

(5) Optionally, further treatments (16) can be carried out, such as for example a mechanical treatment or the addition of biocides or other additives in order to change the pH of the solution (e.g. addition of a base such as NaOH), the conductivity of the solution, or the hardness of the solution. As a further option, the clear aqueous solution comprising at least one earth alkali hydrogen carbonate discharged from the filtering device can be diluted with further water (14). The coarse particles contained in the suspension and that are retained in the filtering device can optionally be recirculated (12) to the reactor in order to be available for further conversion.

(6) According to one embodiment the flow rate of the feed water is 20 000 to 500 000 m.sup.3 per day.

(7) The inventive process may be used to produce drinking water, recreation water such as water for swimming pools, industrial water for process applications, irrigation water, or water for the production of purified earth alkali carbonates.

(8) According to one embodiment the earth alkali hydrogen carbonate solution obtained by the inventive process has a calcium concentration from 1 to 700 mg/l, as CaCO.sub.3, preferably from 50 to 650 mg/l, as CaCO.sub.3, and most preferred from 70 to 630 mg/l, as CaCO.sub.3. In case the slurry comprises a further magnesium salt such as magnesium hydrogen carbonate, or magnesium sulfate, the earth alkali hydrogen carbonate solution obtained by the inventive process may have a magnesium concentration from 1 to 200 mg/l, as MgCO.sub.3, preferably from 2 to 150 mg/l, as MgCO.sub.3, and most preferably from 3 to 125 mg/l, as MgCO.sub.3.

(9) According to one embodiment of the present invention the earth alkali hydrogen carbonate solution has a turbidity of lower than 1.0 NTU, preferred lower than 0.3 NTU.

EXAMPLES

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

(11) The specific surface area (SSA) was measured using a Malvern Mastersizer 2000 (based on the Fraunhofer equation).

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

(13) Weight median grain diameter and grain diameter mass distribution of a particulate material were determined using a Malvern Mastersizer 2000 (based on the Fraunhofer equation).

(14) pH of an Aqueous Suspension

(15) The pH was measured using a Mettler-Toledo pH meter. The calibration of the pH electrode was performed using standards of pH values 4.01, 7.00 and 9.21.

(16) Solids Content of an Aqueous Suspension

(17) The suspension solids content (also known as “dry weight”) was determined using a Moisture Analyser HR73 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120° C., automatic switch off 3, standard drying, 5 to 20 g of suspension.

(18) Turbidity

(19) The turbidity was measured with a Hach Lange 2100AN IS Laboratory Turbidimeter and the calibration was performed using StabCal turbidity standards (formazine standards) of <0.1, 20, 200, 1000, 4000 and 7500 NTU.

(20) Determination of the Hardness (German Hardness; Expressed in “°dH”)

(21) The hardness refers to the total amount of earth alkali ions in the aqueous solution comprising the earth alkali hydrogen carbonate, and it is measured by complexometric titration using ethylene-diamine-tetra-actetic acid (EDTA; trade name Titriplex III) and Eriochrome T as equivalent point indicator.

(22) EDTA (chelating agent) forms with the ions Ca.sup.2+ and Mg.sup.2+ soluble, stable chelate complexes. 2 ml of a 25% ammonia solution, an ammonia/ammonium acetate buffer (pH 10) and Eriochrome black T indicator were added to 100 ml of a water sample to be tested. The indicator and the buffer is usually available as so-called “indicator-buffer tablet”. The indicator, when masked with a yellow dye, forms a red colored complex with the Ca.sup.2+ and Mg.sup.2+ ions. At the end of the titration, that is when all ions are bound by the chelating agent, the remaining Eriochrome black T indicator is in its free form which shows a green color. When the indicator is not masked, then the color changes from magenta to blue. The total hardness can be calculated from the amount of EDTA that has been used.

(23) The table below shows a conversion for the different units of the water hardness.

(24) TABLE-US-00001 Conversion for the different units of the water hardness.sup.[1] °dH °e °fH ppm mval/l mmol/l German Hardness 1° dH = 1 1.253 1.78 17.8 0.357 0.1783 English Hardness 1° e = 0.798 1 1.43 14.3 0.285 0.142 French Hardness 1° fH = 0.560 0.702 1 10 0.2 0.1 ppm CaCO.sub.3 (USA) 1 ppm = 0.056 0.07 0.1 1 0.02 0.01 mval/l Earth alkali ions 1 mval/l = 2.8 3.51 5 50 1 0.50 mmol/l Earth alkali ions 1 mmol/l = 5.6 7.02 10.00 100.0 2.00 1 .sup.[1]In this regard the unit ppm is used in the meaning of 1 mg/l CaCO.sub.3.

(25) The carbon dioxide used in the examples is commercially available as “Kohlendioxid 3.0” from PanGas, Dagmarsellen, Switzerland. The purity was ≥99.9 Vol.-%.

Examples

The Prior Art Examples were Prepared in the Following Way

(26) The prior art examples show different slurries with various concentrations of calcium carbonate which were prepared from different carbonate rocks and dosed to feed water in a batch mode.

(27) The feed water was obtained from a reverse osmosis desalination process and was acidified with about 50 mg/l CO.sub.2. The slurries were prepared by mixing an appropriate amount of calcium carbonate with 100 ml feed water at room temperature using a magnetic stirrer, with stirring between 1000 and 1500 rpm and a mixing time of between 3 and 5 min.

(28) The remineralization was performed by adding the slurry in small amounts to about one liter of the acidified feed water, wherein the slurry and the feed water were mixed using a magnetic stirrer, with stirring between 1000 and 1500 rpm and a mixing time of 2 minutes. After every slurry addition, a sample was taken from the treated feed water to control the alkalinity, turbidity, conductivity, pH, temperature. A final calcium concentration of 125 mg/l as CaCO.sub.3 was chosen as target for remineralization of the feed water. 125 mg CaCO.sub.3/l represent a concentration of 0.0125 wt.-%. For each sample the turbidity of the remineralized water was measured directly after mixing and after a settling period of minimum 60 minutes. The turbidity measured on the settled samples was performed in order to observe the impact of sedimentation in the remineralization process.

(29) The turbidity was measured with a Hach Lange 2100AN IS Laboratory Turbidimeter and the calibration was performed using StabCal turbidity standards (formazin standards) of <0.1, 20, 200, 1000, 4000 and 7500 NTU.

(30) The total alkalinity was measured with a Mettler-Toledo T70 Titrator using the related LabX Light Titration software. A DGi111-SG pH electrode was used for this titration according to the corresponding Mettler-Toledo method M415 of the application brochure 37 (water analysis). The calibration of the pH electrode was performed using Mettler-Toledo standards of pH values 4.01, 7.00 and 9.21.

Example 1

Slurry A

(31) Two slurries having a calcium carbonate concentration of 0.5 and 5 wt.-% based on the total weight of the slurry were prepared from marble (Salses, France) derived micronized calcium carbonate having a medium particle size of 3.5 μm and a HCl insoluble content of 0.2 wt.-% based on the total weight of the calcium carbonate.

(32) The results compiled in Table 1 show similar turbidity values for both remineralization processes with 0.5 wt.-% and 5 wt.-% CaCO.sub.3 slurries. After a settling period, the samples presented turbidity values lower than 0.5 NTU.

Example 2

Slurry B

(33) Three slurries having a calcium carbonate concentration of 0.5, 1 and 10 wt.-% based on the total weight of the slurry were prepared from marble (Bathurst, Australia) derived micronized calcium carbonate having a medium particle size of 2.8 μm and a HCl insoluble content of 1.5 wt.-% based on the total weight of the calcium carbonate.

(34) The results compiled in Table 1 show similar turbidity values for all three remineralization processes. However the turbidity values measured for the settled samples taken after two minutes of remineralization are higher than those of example 1, which may be due to the difference in the HCl insoluble content of the marble calcium carbonate.

Example 3

Slurry C

(35) A slurry having a calcium carbonate concentration of 5 wt.-% based on the total weight of the slurry was prepared from limestone (Orgon, France) derived micronized calcium carbonate having a medium particle size of 3 μm, a specific surface area (SSA) of 2.6 m.sup.2/g, and a HCl insoluble content of 0.1 wt.-% based on the total weight of the calcium carbonate.

(36) The results compiled in Table 1 show that the turbidity value measured for the settled sample is much lower in comparison to the values of example 1 and 2, which may be due to the different geological structures of the carbonate rocks.

(37) TABLE-US-00002 TABLE 1 Slurry Alkalinity concentration Turbidity (NTU) fresh sample Slurry (wt.-%) Fresh sample Settled sample (mg/l CaCO.sub.3) A 0.5 35 0.44 100 A 5.0 32 0.45 120 B 0.5 26 3.90 115 B 1.0 25 3.50 112 B 10.0 24 3.30 119 C 5.0 20 0.21 117

(38) The results compiled in Table 1 show a strong turbidity of the fresh samples and for most of the samples even after settlement.

Example 4

Different Particle Sizes

(39) Three slurries having a calcium carbonate concentration of 5 wt.-% based on the total weight of the slurry were prepared from marble derived micronized calcium carbonate having a particle size of 3.5, 9, and 20 μm, respectively, and a HCl insoluble content of 0.2 wt.-% based on the total weight of the calcium carbonate.

(40) The results compiled in Table 2 show that after a settling period the turbidity of the water remineralized with a larger particle size, i.e. 20 μm, has a lower turbidity value in comparison with the turbidity of the water remineralized with smaller particle size, i.e. 3.5 μm what is logic due to the fact that the coarse particles settled much faster versus fine particles.

(41) TABLE-US-00003 TABLE 2 Mean particle size (μm) Turbidity (NTU) Alkalinity SSA (m.sup.2/g) Fresh Settled fresh sample SSA (m.sup.2/m.sup.3) sample sample (mg/l CaCO.sub.3) 3.5 2.61 32 0.45 120 326 9 1.75 22 0.36 78 219 20 0.94 27 0.31 67 118

(42) The results compiled in Table 2 show a strong turbidity for the fresh samples. After a settling period he water that was remineralized with a larger particle size, i.e. 20 μm, shows a lower turbidity value compared to the water that was remineralized with a smaller particle size, i.e. 3.5 μm, what is somehow logic due to the fact that coarse particles settle much faster than fine ones, but which will increase the turbidity of the sample immediately if the sample is shaken.

(43) Marble based calcium carbonate having a weight median diameter (d.sub.50) of 3.5 μm represents approximately a total particle surface of 2.61 m.sup.2/g corresponding to 326.3 m.sup.2/tonne of suspension at 0.0125 wt.-% solids.

(44) Marble based calcium carbonate having a weight median diameter (d.sub.50) of 9 μm represents approximately a total particle surface of 1.75 m.sup.2/g corresponding to 218.8 m.sup.2/tonne of suspension at 0.0125 wt.-% solids.

(45) Marble based calcium carbonate having a weight median diameter (d.sub.50) of 20 μm represents approximately a total particle surface of 0.94 m.sup.2/g corresponding to 117.5 m.sup.2/tonne of suspension at 0.0125 wt.-% solids.

(46) It can be derived from the above information that the dissolution rate of calcium carbonate is reduced by the reduced specific surface of the calcium carbonate particles that are present in the suspension.

Examples Relating to the Invention

(47) A general process flow sheet of the process according to the present invention is shown in FIG. 1.

(48) The feed water used in the inventive examples was obtained from an ion exchange equipment of Christ, Aesch, Switzerland Typ Elite 1BTH, the feed water having the following water specification after the ion exchanger:

(49) TABLE-US-00004 Sodium 169 mg/l  Calcium  2 mg/l Magnesium <1 mg/l ° dH 0.3

(50) The following different process routes were used to exemplify the process according to the present invention: Process A (FIG. 1) The suspension of the reactor passes a mill without grinding beads in the mill. This process is sought to exemplify the embodiment of the invention.

Example 5

Microdol A Extra (Dolomite)

(51) In the present example, Microdol A extra a dolomite obtained from the Company Norwegian Talc, Knarrevik, was used as the at least one earth alkali carbonate. The reaction and the operation conditions are given in Table 3.

(52) Process A, 23° C. (Tank Temperature)

(53) TABLE-US-00005 TABLE 3 l/h of CO.sub.2 Permeate at d.sub.10 Feed ml/min 10° dH Mem- l/h/m.sup.2 d.sub.50 solids g/h °dH l/h of Mol brane Permeate pH d.sub.90 wt.-% Mol/h Permeate Permeate CaCO.sub.3/h pressure at 10° dH permeate SSA 15 100 25 63 158 1 264 7.4 0.35 μm 11.8 0.282 2.67 μm 0.268 10.23 μm 2.24 m.sup.2/g 15 150 30 55 165 1.5 276 7.35 17.7 15 200 32 51 162 1.5 270 7.25 23.6 15 200 32.5 47 151 2 252 7.14 23.6

(54) The total mineral surface of the particles in the suspension of this trial represents 336 000 m.sup.2/tonne of suspension.

(55) The ratio of produced mol CaCO.sub.3 to used mol CO.sub.2 in this example is 1:0.54

Example 6

Marble

(56) In the present example, a marble sold under the trade name “Omyacarb 10 AV” from the company Omya International, Switzerland, was used as the earth alkali carbonate. The HCL insoluble content was 0.7 wt.-%. The reaction and the operation conditions are given in Table 4.

(57) Process A, 27° C. (Tank Temperature)

(58) TABLE-US-00006 TABLE 4 l/h of CO.sub.2 Permeate at d.sub.10 Feed ml/min 10° dH Mem- l/h/m.sup.2 d.sub.50 solids g/h °dH l/h of Mol brane Permeate pH d.sub.90 wt.-% Mol/h Permeate Permeate CaCO.sub.3/h pressure at 10° dH permeate SSA 15 50 32.5 35 115 1.5 192 6.55 0.48 μm 5.9 0.205 5.42 μm 0.134 16.98 μm 1.52 m.sup.2/g

(59) The total mineral surface of the particles in the suspension of this trial represents 228 000 m.sup.2/tonne of suspension.

(60) The ratio of produced mol CaCO.sub.3 to used mol CO.sub.2 in this example is 1:0.65

Example 7

Marble, Norway

(61) Process A, 20° C. (Tank Temperature)

(62) Fine ground Norwegian marble (Molde, Norway) was dispersed in tap water (3°dH, pH 7.4) at a solids content of 35 wt.-% using 0.72 wt. %, based on dry weight of the marble, of sodium polyphosphate, and 0.21 wt.-% of phosphoric acid to form a suspension. The suspension had a conductivity of 2 580 μS/cm.

(63) The suspension was pumped in circulation mode at a rate of 3200 l/h from the reactor passing a membrane module of 0.2 m.sup.2 (Microdyn-Modul MD 063 TP 2N) and was then recirculated into the tank. CO.sub.2 was dosed after the pump, but before the membrane module.

(64) The pump was driven by a mix of solar electrical power (Solarcenter Muntwiler, Switzerland, www.solarcenter.ch) and nuclear power plant. The solar power station comprises approximately 25 m.sup.2 of solar panels. The total electrical power used in this trail was 5.5 kWh; the part of solar power was 1.5 kWh. (1.1 to 1.9 kWh).

(65) TABLE-US-00007 l/h of Permeate at d.sub.10 Feed 10° dH Mem- l/h/m.sup.2 d.sub.50 solids CO.sub.2 °dH Mol brane Permeate pH d.sub.90 % wt.-% ml/min Permeate CaCO.sub.3/h pressure at 10° dH permeate SSA Solar power 35 50 13 49.8 1 249 7.1 0.33 μm 27% 0.089 0.87 μm 1.92 μm 3.40 m.sup.2/g

(66) The total mineral surface of the particles in the suspension of this trial represents 1 197 385 m.sup.2/tonne of suspension.

Example 8

Pilot Scale Trials

(67) This examples presents trials for the preparation of aqueous solutions of calcium hydrogen carbonate in pilot scale. The obtained solution of calcium hydrogen carbonate is then used for the remineralization of soft water, which could be for instance natural soft water from ground water or surface water sources, desalinated water from reverse osmosis or distillation, rain water. The trials were performed using different calcium carbonate products as raw material for the preparation of calcium carbonate suspension, hereafter slurries, and the resulting solutions of calcium hydrogen carbonate obtained after the dosing of carbon dioxide.

(68) The following Table 5 summarizes the properties of the calcium carbonate used during the remineralization pilot trials with an initial slurry volume of 1200 L.

(69) TABLE-US-00008 TABLE 5 Calcium carbonate d.sub.50 CaCO.sub.3 HCl insoluble Samples.sup.[1] rock [μm] [wt.-%] [wt.-%] A Marble 13.7 96.6 0.6 B Marble 2.7 96.0 1.0 C Limestone 7.8 99.5 0.1 D Limestone 4.3 99.5 0.1 .sup.[1]It has to be noted that all of the above listed calcium carbonates are commercially available from Omya, Switzerland.

(70) The following Table 6 summarizes the properties of the slurries of the calcium carbonate products that have been used for the present trials.

(71) TABLE-US-00009 TABLE 6 Starting slurry composition Target slurry Mean particle size (μm) concentration SSA (m.sup.2/g) Slurry Product (wt.-%) Expected total SSA (m.sup.2/t) 1 A 2 13.7  1.3 26′600 2 B 2 2.7 3.9 78′000 3 C 2 7.8 1.7 34′800 4 D 7 4.3 2.3 162′400 

(72) The in Table 6 mentioned calcium carbonate suspensions (or “slurries”) were prepared by mixing the micronized calcium carbonate powder and reverse osmosis water (RO water). The RO water was produced on-site using a reverse osmosis unit and had the average quality as outlined in the following Table 7.

(73) TABLE-US-00010 TABLE 7 Conductivity Turbidity pH (μS/cm) (NTU) RO water 6.4-6.6 10-25 <0.1

(74) The tank was filled up completely with the respective calcium carbonate suspension. Then, the calcium carbonate suspension was pumped from the tank towards the mill (without grinding beads in the mill), and from there to the membrane filtering device for filtration. The mill was used as dosing point for the carbon dioxide that is required for the dissolution of the calcium carbonate into the water. The obtained dissolved hydrogen carbonate then passed through the membrane, while the undissolved calcium carbonate was fed back to the tank. Amongst different water parameters, the conductivity was used as a proxy for measuring the amount of dissolved hydrogen carbonate obtained by this process.

(75) The conditions for the carbon dioxide and calcium carbonate dosing can be derived from Table 8.

(76) TABLE-US-00011 TABLE 8 Target Target CO.sub.2/concen- Concentrate concentration CO.sub.2 CO.sub.2/CaCO.sub.3 trate ratio flowrate (mg/L as flowrate stoechiometric (L CO.sub.2/L (L/h) CaCO.sub.3) (L/min) ratio (x-fold) concentrate) 500 500 5 5 0.6

(77) The following Table 9 summarizes the results obtained at the end of full days of testing (6-7 hours per day) over 1 to 3 days of slurry 1 (with a solids content of 2 wt.-% of sample A) and slurry 2 (with a solids content of 2 wt.-% of sample B).

(78) TABLE-US-00012 TABLE 9 Start Final d.sub.50 Final start Testing d.sub.50 f SSA.sub.f total SSA.sub.f conductivity Test Slurry [μm] days [slurry].sub.f [μm] (m.sup.2/g) (m.sup.2/t) (μS/cm) 1 Slurry 1 13.7 2 1.2% 15.8 1.1 14′124 995 2 Slurry 1 13.7 1 1.7% 10.7 1.4 28′764 1060 3 Slurry 2 2.7 3 1.7% 3.4 2.3 39′100 1100 4 Slurry 2 2.7 1 1.6% 3.2 3.2 61′440 1225

(79) This set of tests shows that the conductivity is increasing proportionally to the specific surface area, i.e. SSA.sub.f (m.sup.2/g), and to the total surface area available in the slurry, i.e. SSA total (m.sup.2/t) for a given constant solid content of the slurry, i.e. [slurry].sub.f of around 2 wt %.

(80) The results presented in Table 10 were performed using the slurry 2 (with a solids content of 2 wt.-% of sample B). The two tests were performed using the same CO.sub.2 dosing ratio of 0.3 L CO.sub.2/L concentrate and the results presented the values obtained at the end of a full day of testing (6-7 hours) over 1 to 2 days.

(81) TABLE-US-00013 TABLE 10 Start Final d.sub.50 Final start Testing SSA.sub.f total SSA.sub.f conductivity Test Slurry [μm] days [slurry].sub.f (m.sup.2/g) (m.sup.2/t) (μS/cm) 5 Slurry 2 2.7 2 1.9% 3.0 62′700 825 6 Slurry 2 2.7 1 2.2% 3.5 92′400 930

(82) The outcome of this set of trials shows that the conductivity is increasing proportionally to the specific surface area, i.e. SSA.sub.f (m.sup.2/g) and to the total surface area available in the slurry, i.e. SSA total (m.sup.2/t).

(83) Continuous Testing Period

(84) It is believed that the inventive process requires time to reach a steady-state, therefore long testing period have been initiated with a testing period from 10 to 22 days. The surface area of the solids present in the slurry has a direct impact on the dissolution of the calcium carbonate into the water and therefore on the final concentration of the dissolved hydrogen carbonate, measured as final conductivity.

(85) The results presented in Table 11 were performed using two slurries made of different products. The slurry 3 contains the coarser product (Sample C: d.sub.50=7.8 μm, SSA=1.7 m.sup.2/g) and the slurry 4 the finer product (Sample D: d.sub.50=4.3 μm, SSA=2.3 m.sup.2/g). Both slurries have a different the solid content, 2 wt.-% for slurry 3 and 7 wt.-% for slurry 4, respectively. The tests were performed using the same CO.sub.2 dosing ratio of 0.3 L CO.sub.2/L concentrate and the results present the values obtained at the end of 8 days of testing when the system can be considered to have reached a steady-state.

(86) TABLE-US-00014 TABLE 11 Start Final d.sub.50 Final start Day of results (d)/ SSA.sub.f total SSA.sub.f conductivity Test Slurry [μm] Testing period (d) [slurry].sub.f (m.sup.2/g) (m.sup.2/t) (μS/cm) 7 Slurry 3 7.8 8/22 1.7% 0.7 14′908 670 8 Slurry 3 7.8 8/10 1.9% 0.7 16′450 710 9 Slurry 4 4.3 8/12 6.8% 1.4 116′345  792