Multiple batch system for the preparation of a solution of calcium hydrogen carbonate suitable for the remineralization of desalinated water and of naturally soft water

Abstract

The invention relates to a multiple batch system for the preparation of a solution of calcium hydrogen carbonate and the use of such a dual batch system for the preparation of a solution of calcium hydrogen carbonate.

Claims

1. A multiple batch system for the preparation of a solution of calcium hydrogen carbonate, the multiple batch system comprising: a) at least one dosing unit for dosing a suspension of calcium carbonate into the master batch line and the at least one slave batch line, b) a master batch line comprising in circular communication: (i) at least one gas dosing inlet for dosing carbon dioxide gas, (ii) at least one mixing unit provided with at least one inlet and at least one outlet, and iii) at least one tank provided with at least one inlet and at least one outlet, c) at least one slave batch line comprising in circular communication: (i) at least one gas dosing inlet for dosing carbon dioxide gas, (ii) at least one mixing unit provided with at least one inlet and at least one outlet, and (iii) at least one tank provided with at least one inlet and at least one outlet, d) a control unit for measuring one or more of pH, turbidity, conductivity, temperature and calcium ion concentration of the calcium carbonate suspension and/or the solution of calcium hydrogen carbonate, and e) a storage tank comprising carbon dioxide in gaseous or liquid form, wherein the master batch line and the at least one slave batch line are independently connected to the at least one dosing unit, and wherein the master batch line is in a separate loop from the at least one slave batch line.

2. The multiple batch system according to claim 1, wherein the at least one dosing unit is connected to a water reservoir and a storage container for solid material.

3. The multiple batch system according to claim 1, wherein the at least one gas dosing inlet of the master batch line and/or the at least one slave batch line is located before the at least one mixing unit.

4. The multiple batch system according to claim 1, wherein the master batch line and/or the at least one slave batch line comprises one mixing unit.

5. The multiple batch system according to claim 1, wherein the master batch line and/or the at least one slave batch line comprises at least two mixing units.

6. The multiple batch system according to claim 1, wherein the master batch line and/or the at least one slave batch line comprises at least two mixing units connected in series.

7. The multiple batch system according to claim 1, wherein the at least one mixing unit of the master batch line and/or the at least one slave batch line is a vertical and/or horizontal mixing unit.

8. The multiple batch system according to claim 1, wherein the at least one mixing unit of the master batch line and/or the at least one slave batch line is a vertical mixing unit.

9. The multiple batch system according to claim 1, wherein the at least one mixing unit of the master batch line and/or the at least one slave batch line is at least one static mixer.

10. The multiple batch system according to claim 1, wherein the at least one mixing unit of the master batch line and/or the at least one slave batch line is located between the at least one gas dosing inlet and the at least one tank.

11. The multiple batch system according to claim 1, wherein the at least one mixing unit of the master batch line and/or the at least one slave batch line is at least one dynamic mixer.

12. The multiple batch system according to claim 11, wherein the at least one mixing unit of the master batch line and/or the at least one slave batch line is located between the at least one gas dosing inlet and the at least one tank or integrated in the at least one tank.

13. The multiple batch system according to claim 1, wherein the master batch line comprises at least one control unit monitoring at least one of pH, turbidity, conductivity, temperature and calcium ion concentration.

14. The multiple batch system according to claim 1, wherein the master batch line comprises at least one control unit monitoring a calcium ion concentration by an ion sensitive electrode.

15. The multiple batch system according to claim 1, further comprising at least one membrane filtration unit.

16. The multiple batch system according to claim 1, further comprising a cross flow or dead-end membrane microfiltration device and/or a cross flow or dead-end membrane ultrafiltration device.

Description

EXAMPLES

(1) The following examples present different ways of preparing aqueous solutions of calcium hydrogen carbonate, known as calcium bicarbonate, using the multiple batch system comprising a master batch line and at least one slave batch line. 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 using the multiple batch system were performed using different calcium carbonate products as raw material for the preparation of said solutions of calcium hydrogen carbonate.

(2) All trials were performed under room temperature, i.e. at a temperature of from 15 to 25 C. It is to be noted that the RO (reverse osmosis) water provided at the beginning of each trial had a temperature of about room temperature, i.e. of from 15 to 25 C.

(3) The following Table 1 summarizes the different calcium carbonate products used during the remineralization pilot trials using the multiple batch system.

(4) TABLE-US-00001 TABLE 1 Calcium carbonate d.sub.50 CaCO.sub.3 HCl insoluble Samples.sup.[1] rock [m] [wt.-%] [wt.-%] A Limestone 3.0 99.3 0.1 B Marble 3.5 98.0 0.2 .sup.[1]All calcium carbonates used in the present invention are commercially available from Omya International AG, Switzerland.

(5) The respective micronized calcium carbonate is poured in a funnel placed at the top of the dosing unit allowing a precise dosing of the powder into the dosing unit by means of a dosing screw connecting the bottom part of the funnel to the top of the dosing unit. The calcium carbonate suspension is prepared in the dosing unit by mixing the micronized calcium carbonate powder to RO (reverse osmosis) water. The RO water was produced on-site using a reverse osmosis unit, BWT PERMAQ Pico, provided by Christ and had the average quality as outlined in the following Table 2.

(6) TABLE-US-00002 TABLE 2 Alkalinity Conductivity Turbidity pH (mg/l as CaCO.sub.3) (S/cm) (NTU) RO water 5.4-5.6 5-10 10-20 <0.1

(7) The filling up of the dosing unit with RO water and the corresponding amount of micronized calcium carbonate is programmed and set according to the level switches placed inside the tank of the dosing unit. The initial solid content of the calcium carbonate suspension in the dosing unit varies within the range of 0.01-2 g/l as CaCO.sub.3. The RO water is added by the means of a pump and introduced by a pipe connected to the top of the dosing unit, while the calcium carbonate powder is added to the dosing unit from the dosing screw placed at the top of the dosing unit. Both the RO water and the micronized calcium carbonate are dosed proportionally accordingly to a previously pre-programmed ratio allowing a constant solid content of the aqueous suspension of calcium carbonate in the dosing unit.

(8) In the start-up procedure the dosing unit is filled up completely with the calcium carbonate suspension at a defined starting solid content. Then, the calcium carbonate suspension is pumped out of the dosing unit to feed one or more mixing units each having a volume of 100 l of the multiple batch system.

(9) Impact of the CO.sub.2 Stoichiometric Ratio

(10) Different CO.sub.2 stoichiometric ratios compared to the initial calcium carbonate solid content were tested using the inventive multiple batch system. The CO.sub.2 stoichiometric ratios are the x-fold ratio of the CaCO.sub.3 molar concentration of the aqueous starting slurry and varied from 2- to 6-fold, giving 24 to 72 l of CO.sub.2 (injected at a pressure of 2 bars) dosed per batch line into the 100 l mixing unit of the multiple batch system. These tests were performed on the CaCO.sub.3 sample A (limestone, d.sub.50=3.0 m) at an initial solid content in the CaCO.sub.3 slurry of 500 mg/l by using the single batch mode with a time-controlled setting.

(11) The following Table 3 shows the parameters measured for the resulting aqueous calcium hydrogen carbonate solutions obtained by using the single batch mode at different tested CO.sub.2 stoichiometric ratios dosed with a constant CO.sub.2 flow rate of 2.5 l/min (injected at a pressure of 2 bars) with time-controlled batches of 90 minutes.

(12) TABLE-US-00003 TABLE 3 CO.sub.2 stoichiometric Conductivity Turbidity Trials # ratio [x-fold] (S/cm) (NTU) pH 1 2 605 220 6.5 2 3 645 120 6.2 3 5 710 83 6.1

(13) The following Table 4 shows the parameters measured for the aqueous calcium hydrogen carbonate solutions obtained by using the single batch mode at different tested CO.sub.2 stoichiometric ratios dosed with a constant CO.sub.2 flow rate of 5 l/min (injected at a pressure of 2 bars) with time-controlled batches of 70 minutes.

(14) TABLE-US-00004 TABLE 4 CO.sub.2 stoichiometric Conductivity Turbidity Trials # ratio [x-fold] (S/cm) (NTU) pH 4 3 685 155 6.2 5 4 740 100 6.0 6 5 800 50 6.0

(15) These two sets of examples show that if the CO.sub.2 stoichiometric ratio relative to the CaCO.sub.3 initial solid content of the aqueous starting slurry is increased, the conductivity increases proportionally thereto, while the turbidity as well as the pH values decreases. Accordingly, it can be concluded that the more CO.sub.2 is dosed into the corresponding batch line the more calcium carbonate is dissolved in the liquid phase of the calcium carbonate suspension and thus forming a solution of calcium hydrogen carbonate.

(16) Impact of the CO.sub.2 Dosing Rate

(17) Different CO.sub.2 dosing rates of a defined volume of CO.sub.2 to be added to the initial calcium carbonate suspension were tested using the inventive multiple batch system. The CO.sub.2 stoichiometric ratios are kept constant to a pre-defined value between 2- to 6-fold in respect to the CaCO.sub.3 molar concentration of the aqueous starting suspension of calcium carbonate, giving 24 to 72 l of CO.sub.2 (injected at a pressure of 2 bars) dosed per batch line into the 100 l mixing unit of the multiple batch system. The pre-defined volume of CO.sub.2 was then dosed at different dosing rates into each batch line varying between 1 and 6.2 l/min (injected at a pressure of 2 bars), with 4 to 5 l/min of CO.sub.2 usually being the upper limit for the pumps to work properly. The maximum CO.sub.2 dosing rate also depends on the temperature at which the trials are performed, because the solubility of CO.sub.2 into the aqueous phase is reversely proportional to the temperature. In general, lower temperature allows better dissolution of CO.sub.2 and therefore allows in this case a higher CO.sub.2 dosing rate. In this regard, trials performed on the multiple batch system showed that the maximum CO.sub.2 dosing rate was 5 l/min (injected at a pressure of 2 bars) for trials run at 15 C. and a maximum of 4 l/min (injected at a pressure of 2 bars) for trials run at 20 C. All the below mentioned trials were performed by using the single batch mode and calcium carbonate sample A as outlined above (limestone, d.sub.50=3.0 m) at an initial solid content in the calcium carbonate suspension of 500 mg/l with a time-controlled setting.

(18) The following Table 5 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate obtained by using the single batch mode at different tested CO.sub.2 dosing rates for a constant 5-fold CO.sub.2 stoichiometric ratio (corresponding to an added volume of CO.sub.2 of 60 l, injected at a pressure of 2 bars) with time-controlled batches of 70-90 minutes.

(19) TABLE-US-00005 TABLE 5 CO.sub.2 dosing rate Conductivity Turbidity Trials # [l/min] (S/cm) (NTU) pH 7 1 690 100 6.1 3 2.5 710 83 6.1 8 4 785 85 5.9 6 5 800 50 6.0

(20) From Table 5, it can be gathered that if the CO.sub.2 dosing rate increases the conductivity increases proportionally, while the turbidity as well as the pH values decrease. Thus, it can be concluded that the more CO.sub.2 is dosed at once in the corresponding batch line, the more calcium carbonate is dissolved in the liquid phase of the calcium carbonate suspension and thus forming a solution of calcium hydrogen carbonate. This trend has generally been observed in the other performed trials.

(21) Impact of Starting Solid Content of the CaCO.sub.3 Aqueous Slurry

(22) The initial solid content of the aqueous calcium carbonate suspension has been studied through various trials using the multiple batch system in order to produce a highly concentrated solution of calcium hydrogen carbonate with a minimum of CO.sub.2 excess, and in the meanwhile trying to achieve turbidity levels as low as possible. The following trials were performed using the CaCO.sub.3 sample A as outlined above (limestone, d.sub.50=3.0 m) at an initial solid content in the calcium carbonate suspension of 500 mg/l, 700 mg/l and 1,000 mg/l with corresponding CO.sub.2 stoichiometric ratio varying between 3 and 6-fold the molar concentration of the calcium carbonate present in the starting calcium carbonate suspension. The trials were performed by using the single batch mode with time-controlled batches of between 30 and 90 minutes.

(23) The following Table 6 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate obtained by using the single batch mode at constant CO.sub.2 dosing rate of 4 l/min (injected at a pressure of 2 bars) for different starting solid contents of the calcium carbonate suspension and its corresponding CO.sub.2 stoichiometric ratios.

(24) TABLE-US-00006 TABLE 6 Initial slurry Time- solid CO.sub.2 Tur- controlled Trials content stoichiometric Conductivity bidity setting # [mg/l] ratio [x-fold] (S/cm) (NTU) pH (min) 9 500 5 704 38 5.9 60 8 500 5 785 85 5.9 70 10 500 6 800 30 5.9 90 11 700 3.6 860 147 6.1 60 12 700 4.3 887 330 6 30 13 700 4.3 972 120 6 90 14 1,000 3 1,050 670 6.2 30 15 1,000 3 900 790 6.1 30 16 1,000 3 1,100 445 6.1 80

(25) From Table 6, it can be gathered that increasing the initial solid content of the calcium carbonate solid content leads to a higher conductivity measured for the resulting solution of calcium hydrogen carbonate; even with a proportionally lower CO.sub.2 stoichiometric ratio. However, it should be noted that a good portion of the calcium carbonate is not dissolved in the aqueous phase of the calcium carbonate suspension and, thus, remains as a suspension of calcium carbonate inducing a turbidity increase. When trials are performed at high starting solid content in the calcium carbonate suspension, for instance 1,000 mg/l CaCO.sub.3, turbidity can reach values above 400 NTU.

(26) In addition thereto, the corresponding batch time shows a significant impact on the characteristics of the final solution of calcium hydrogen carbonate. In general, if the batch times are longer, a decrease of turbidity and an increase of conductivity are observed.

(27) In order to decrease or remove turbidity from the solution of calcium hydrogen carbonate obtained during trials #13 and #16, the solutions were filtered by using an ultrafiltration membrane. The resulting filtered solutions of calcium hydrogen carbonate had turbidity levels below the detection limit, i.e. <0.1 NTU, for conductivity up to 950 and 1,050 S/cm for trials #12 ([CaCO.sub.3].sub.slurry=700 mg/l) and for trials #15 ([CaCO.sub.3].sub.slurry=1,000 mg/l) respectively.

(28) Impact of the Starting CaCO.sub.3 Product

(29) The following pilot trials were performed using two calcium carbonate samples of different geological sources, being a limestone containing 99.3 wt.-% calcium carbonate, based on the total weight of the calcium carbonate sample, and with a mean particle size d.sub.50=3.0 m (sample A), and a marble containing 98 wt.-% calcium carbonate, based on the total weight of the calcium carbonate sample, and with a mean particle size d.sub.50=3.5 m (sample B). Both calcium carbonate samples were tested by using the single batch mode and with CO.sub.2 dosing at 4 l/min, for an initial solid content of the aqueous CaCO.sub.3 slurry of 500 mg/l and 700 mg/l, with 5-fold or 3.6-fold CO.sub.2 stoichiometric ratios, respectively.

(30) The following Table 7 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate obtained in the single batch mode at constant CO.sub.2 dosing rate of 4 l/min (injected at a pressure of 2 bars) during 15 minutes for different calcium carbonate samples at two different solid contents of the calcium carbonate suspension and its corresponding CO.sub.2 stoichiometric ratios.

(31) TABLE-US-00007 TABLE 7 Initial slurry solid Time- Trials CaCO.sub.3 content Conductivity Turbidity controlled # source [mg/l] (S/cm) (NTU) pH setting (min) 9 Sample A 500 704 38 5.9 60 17 Sample B 500 735 30 6.0 60 11 Sample A 700 860 147 6.1 60 18 Sample B 700 911 80 6.0 65

(32) From Table 7, it can be gathered that trials #17 and #18, using the marble geological source (sample B), presented higher conductivity and lower turbidity of the resulting solution of calcium hydrogen carbonate than the obtained solutions from limestone geological source (sample A) as used in trials #9 and #11.

(33) Impact of the Value Controlled Batches

(34) The multiple batch system allows the preparation of the solution of calcium hydrogen carbonate controlled by the monitored parameters of the master batch line, such as pH, turbidity or conductivity. When the set value is reached, for instance, the target conductivity being 1,000 S/cm, the corresponding batch is completed and the obtained solution of calcium hydrogen carbonate is then discharged. The batch time to reach this target value within the master batch line is then implemented to the at least one slave batch line, and the solution of calcium hydrogen carbonate obtained for any slave batch line is also discharged after this defined batch time has been reached. The batch time of the master batch line to reach the set value is then updated for each single run.

(35) Various trials have been performed in value-controlled mode with either conductivity or turbidity values, or both conductivity and turbidity values. The following trials were performed using the calcium carbonate sample A (limestone, d.sub.50=3.0 m) at different initial solid content in the calcium carbonate suspension with defined CO.sub.2 stoichiometric ratio (injected at a pressure of 2 bars).

(36) The following Table 8 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate obtained by using the single batch mode under different value controlled settings. It is appreciated that the corresponding values set out in the column value controlled must be reached before the resulting aqueous solution of calcium hydrogen carbonate is released from the system.

(37) TABLE-US-00008 TABLE 8 Initial slurry Process setting: Process solid content CO.sub.2 ratio, Value Conductivity Turbidity batch time Trials # [mg/l] CO.sub.2 dosing rate controlled (S/cm) (NTU) (min) 20 500 6-fold, 3 l/min <150 NTU 860 150 26 21 500 7.5-fold, 3 l/min <150 NTU 800 150 20 22 1000 3-fold, 4 l/min >1,000 S/cm, 1,303 700 44 <700 NTU 23 1000 3-fold, 4 l/min >1,000 S/cm, 1,200 800 28 <800 NTU 24 1000 3-fold, 4 l/min >1,000 S/cm, 1,210 800 31 <800 NTU 25 1200 3.3-fold, 3 l/min >1,000 S/cm 1,000 442 26 26 1800 2.2-fold, 3 l/min <800 NTU 1,450 800 65 27 >2000 2-fold, 3 l/min >1,000 S/cm 1,720 2,970 N/A

(38) From Table 8, it can be gathered that the calcium carbonate suspension having an initial solid content of 500 mg/l reached a turbidity of lower than 150 NTU within 20 or 26 minutes according to the CO.sub.2 stoichiometric ratio used, i.e. 7.5-fold or 6-fold respectively. Higher solid contents of the calcium carbonate slurry were tested with values controlled for turbidity lower than 700 or 800 NTU. Calcium carbonate slurries having initial solids contents of more than 1,000 mg/l may be further treated afterwards by using filtration means, such as ultrafitration or microfiltration.

(39) Impact of the Number of Static Mixers

(40) Further testing using the multiple batch system has been performed implementing only one static mixer instead of the two static mixers in series used for all the previous trials for the preparation of the solution of calcium hydrogen carbonate. The following trials were performed using the calcium carbonate sample A (limestone, d.sub.50=3.0 m) at an initial solid content of 500 mg/l in the calcium carbonate suspension and a 6-fold CO.sub.2 stoichiometric ratio dosed at 4 l/min (injected at a pressure of 2 bars).

(41) The following Table 9 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate by using constant process settings and the single batch mode. Furthermore, the master batch line was equipped with one static mixer.

(42) TABLE-US-00009 TABLE 9 Number of Time- static Conductivity Turbidity controlled Trial # mixers (S/cm) (NTU) pH setting (min) 28 1 1,022 88 6.1 60

(43) From Table 9, it can be seen that high conductivity can also be achieved while using only one static mixer meaning that the solution of calcium hydrogen carbonate was formed. The obtained pH value also fits with the expected values.

(44) Impact of a Closed Tank

(45) The following pilot trials were performed on a multiple batch system comprising a closed tank. The closed tank has a pressure-released valve at I bar. The calcium carbonate sample used for these trials were samples A (limestone, d.sub.50=3.0 m) and B (marble, d.sub.50=3.5 m) at an initial solid content of the aqueous CaCO.sub.3 slurry of 500 mg/l of CaCO.sub.3. The CO.sub.2 dosing was performed at 4 l/min (injected at a pressure of 2 bars) for testing with a 5-fold CO.sub.2 stoichiometric ratio and dosed using only one static mixer. It is to be noted that the trials with the closed tank were performed under room temperature, i.e. of around 25 C., while the trials performed with the open tank were performed at a temperature of around 15 C.

(46) The following Table 10 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate obtained in the single batch mode at constant CO.sub.2 dosing rate of 4 l/min (injected at a pressure of 2 bars) during 15 minutes for different calcium carbonate samples at initial solid contents of the calcium carbonate suspension of 500 mg/l and its corresponding CO.sub.2 stoichiometric ratios.

(47) TABLE-US-00010 TABLE 10 Time- controlled Conductivity Turbidity Trials # Sample Vessel setting (min) (S/cm) (NTU) pH 9 A open 60 704 38 5.9 29 A closed 30 485 22 5.6 30 A closed 60 660 22 5.8 31 A closed 50 665 55 5.9 9 B open 60 735 30 6.0 32 B closed 40 720 21 5.8 33 B closed 55 615 12 5.9

(48) From Table 10, it can be gathered that both open and closed systems reach the expected values for conductivity, pH and turbidity.

(49) Impact of the Consecutive Runs

(50) The multiple batch system allows consecutive runs to be done in every individual batch of the multiple batch system, i.e. in the master batch line and each slave batch line, with specifically selected process settings. During this continuous mode each run of the master batch line is monitored and the process parameters such as conductivity, turbidity, pH and temperature are recorded.

(51) The following Table 11 shows the parameters measured for the resulting aqueous solution of calcium hydrogen carbonate obtained by using the continuous batch mode under different process conditions. The CO.sub.2 was injected at a pressure of 2 bars.

(52) TABLE-US-00011 TABLE 11 Initial Process slurry setting: solid CO.sub.2 ratio, CaCO.sub.3 content CO.sub.2 dosing Value Number of Conductivity Turbidity Trials # source [mg/l] rate controlled runs (S/cm) (NTU) 9 Sample A 500 5-fold, 55 min Run 1 704 38 4 l/min Runs 2-5 722 22 29 2 20 Sample A 500 6-fold, 150 NTU Run 1 730 150 3 l/min Runs 2-6 860 35 28 Sample A 500 6-fold, 60 min Run 1 1022 88 4 l/min Runs 2-4 1,099 13 53 2 17 Sample B 500 5-fold, 55 min Run 1 735 30 4 l/min Runs 2-6 849 33 34 7 11 Sample A 700 3.6-fold, 50 min Run 1 860 147 4 l/min Runs 2-4 919 7 156 11 12 Sample A 700 4.3-fold, 30 min Run 1 887 334 4 l/min Runs 2-4 935 13 224 13 18 Sample B 700 5-fold, 60 min Run 1 911 80 4 l/min Runs 2-6 979 18 80 27 15 Sample A 1,000 3-fold, 30 min Run 1 900 790 4 l/min Runs 2-3 1,025 35 725 21 14 Sample A 1,000 3-fold, 30 min Run 1 1050 670 4 l/min Runs 2-4 1,208 12 794 84

(53) From Table 11, it can be gathered that the first run leads to lower conductivity levels than the following runs, however no specific trend could be observed for turbidity between the first run and the following runs.

Pilot Unit Examples

(54) The following examples present the way of preparing aqueous solutions of calcium hydrogen carbonate, known as calcium bicarbonate, using the inventive system for continuous pilot-scale trials. 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, or rain water. The trials using the inventive system were performed using one calcium carbonate product as raw material, namely Sample A listed in Table 1 above, for the preparation of a calcium carbonate suspension, hereafter slurry, and the resulting solution of calcium hydrogen carbonate obtained after the dosing of carbon dioxide.

(55) The respective micronized calcium carbonate powder is poured from the storage container for solid material (42) into the dosing unit (44) by means of a dosing screw that allows a precise dosing of the powder into the dosing unit (44). The RO (reverse osmosis) water from the water supply (40) is added to the dosing unit (44) to which the micronized calcium carbonate is dosed to prepare a calcium carbonate suspension by mixing. The RO water was produced on-site using a reverse osmosis unit and had the average quality as outlined in the following Table 12.

(56) TABLE-US-00012 TABLE 12 Conductivity Turbidity pH (S/cm) (NTU) RO water 6.4-6.6 10-25 <0.1

(57) The filling up of the dosing unit with RO water and the corresponding amount of micronized calcium carbonate runs automatically according to the defined settings. The solid content of the calcium carbonate suspension in the dosing unit (44) was 400 mg/L of CaCO.sub.3.

(58) The calcium carbonate suspension was first prepared in the dosing unit (44) and then the resulting 800 L of suspension were injected into the mater batch line (50) through the slurry supply (2 of FIG. 1 or 46 of FIG. 3). The master batch line comprises a gas dosing inlet (4), where carbon dioxide can be introduced into the aqueous suspension of calcium carbonate. The dissolution of calcium carbonate out of the aqueous suspension of calcium carbonate occurs in the presence of carbon dioxide to form the solution of concentrated calcium hydrogen carbonate within the master batch line (50). The CO.sub.2 dosage consisted in dosing 1.05 g/L CO.sub.2 into the calcium carbonate suspension, representing a stoichiometric excess of 6-fold of CO.sub.2 in comparison to the calcium carbonate present in the suspension. The batch time for these pilot trials were set to 100 minutes in order to follow the dissolution of calcium carbonate by this process.

(59) Table 13 summarizes the process settings for this 11-day pilot trial.

(60) TABLE-US-00013 TABLE 13 Target CO.sub.2/ Target CaCO.sub.3 Concentrate concentration CO.sub.2 stoichiometric Recirculation batch volume (mg/L dosage ratio batch time (L) as CaCO.sub.3) (g/L) (x-fold) (min) 800 400 1 6 100

(61) Samples of the resulting solution of concentrated calcium hydrogen carbonate were taken at 0, 30, 60 and 100 minutes in respect to the batch time, and parameters such as pH, conductivity, turbidity were analysed. On the final concentrated calcium hydrogen carbonate, sampled at 100 minutes both the alkalinity and the acidity were measured in addition to the other measured parameters.

(62) Table 14 summarizes the average manually measured parameters of the obtained concentrated calcium hydrogen carbonate according to the process settings set for the long-run pilot trial.

(63) TABLE-US-00014 TABLE 14 Samples Average manually measured values Batch time Conductivity Turbidity (min) (S/cm) pH (NTU) 0 177 7.6 600 30 647 6.2 57 60 698 6.2 20

(64) Table 15 summarizes the average manually measured parameters of the obtained concentrated calcium hydrogen carbonate according to the process settings set for the long-run pilot trial.

(65) TABLE-US-00015 TABLE 15 Samples Average manually measured values Batch time Temperature Conductivity Turbidity Alkalinity Acidity (min) ( C.) (S/cm) pH (NTU) (mg/L as CaCO.sub.3) (mg/L as CO.sub.2) 100 16.5 719 6.4 8.2 420 45