Method for increasing the magnesium ion concentration in feed water

Abstract

The present invention relates to a method for increasing the magnesium ion concentration of feed water. The method comprises the steps of providing an inlet flow of feed water (Q.sub.IN), increasing the concentration of carbon dioxide in said inlet flow Q.sub.IN to obtain a flow of carbon dioxide-containing feed water (Q.sub.CO2), and passing said flow Q.sub.CO2 through a solid bed comprising a magnesium ion source to obtain an outlet flow of treated water (Q.sub.OUT) having an increased concentration of magnesium ions. The invention further relates to a water treatment system for increasing the magnesium ion concentration of feed water and a corresponding flow reactor.

Claims

1. A method for increasing the magnesium ion concentration of feed water, the method comprising the following steps: (a) providing an inlet flow of feed water Q.sub.IN, wherein the feed water has a total alkalinity (CaCO.sub.3) of from 5 to 200 mg/L; (b) increasing the concentration of carbon dioxide in said inlet flow Q.sub.IN to obtain a flow of carbon dioxide-containing feed water Q.sub.CO2; and (c) passing the carbon dioxide-containing feed water of flow Q.sub.CO2 through a solid bed to obtain an outlet flow of treated water Q.sub.OUT; wherein the solid bed in step (c) comprises a magnesium ion source in the form of solid particles having a solubility limit in water of 10 g/L or less, measured at 20° C. and 100 kPa; wherein in step (b) the concentration of carbon dioxide in the carbon dioxide-containing feed water of flow Q.sub.CO2 is adjusted to a concentration of from 20 to 100 mg/L; wherein the magnesium ion source comprises one or more sources selected from the group consisting of brucite and hydromagnesite; wherein the particles have a weight median particle size in the range of from 0.5 to 1.5 mm; and wherein a contact time in step (c) between the carbon dioxide-containing feed water of flow Q.sub.CO2 and the solid bed is at least 0.1 min and less than 5 min.

2. The method according to claim 1, wherein the feed water has a concentration of dissolved magnesium ions of 10 mg/L or less.

3. The method according to claim 1, wherein the feed water has a Langelier Saturation Index (LSI) of from −2.0 to 1.0.

4. The method according to claim 1, wherein in step (b) the concentration of carbon dioxide is increased by injecting gaseous carbon dioxide into the inlet flow Q.sub.IN.

5. The method according to claim 1, wherein in step (b) the pH of the carbon dioxide-containing feed water of flow Q.sub.CO2 is adjusted to a range of from 5.0 to 8.5 by injecting carbon dioxide into inlet flow Q.sub.IN.

6. The method according to claim 1, wherein in step (b) the temperature of the carbon dioxide-containing feed water of flow Q.sub.CO2 is adjusted to a range of from 5 to 35° C.

7. The method according to claim 1, comprising the brucite being selected from the group consisting of natural brucite, partially calcined brucite, and fully calcined brucite or the hydromagnesite being selected from the group consisting of natural hydromagnesite, partially calcined hydromagnesite, fully calcined hydromagnesite, and synthetic hydromagnesite.

8. The method according to claim 1, wherein the solubility limit of the particles in water is 5 g/L or less, measured at 20° C. and 100 kPa.

9. The method according to claim 1, wherein the solid bed in step (c) is provided in a cavity of a flow reactor, said flow reactor having an inlet being configured to receive the flow of carbon dioxide-containing feed water Q.sub.CO2 and an outlet being configured to release the outlet flow of treated water Q.sub.OUT.

10. The method of claim 1, wherein the magnesium ion source comprises brucite.

11. The method of claim 1, wherein the magnesium ion source comprises hydromagnesite.

12. A water treatment system for increasing the magnesium ion concentration of feed water, the system comprising: (i) a line, the line being configured to receive an inlet flow of feed water Q.sub.IN; (ii) a pretreatment device connected to said line, the pretreatment device being configured to increase the concentration of carbon dioxide in said inlet flow of feed water Q.sub.IN to obtain a flow of carbon dioxide-containing feed water Q.sub.CO2; and (iii) a solid bed located downstream from the pretreatment device, the solid bed being configured to receive the flow of carbon dioxide-containing feed water Q.sub.CO2 from said pretreatment device to obtain an outlet flow of treated water Q.sub.OUT; wherein the solid bed comprises a magnesium ion source in the form of solid particles having a solubility limit in water of 10 g/L or less, measured at 20° C. and 100 kPa; and wherein the magnesium ion source comprises one or more sources selected from the group consisting of brucite and hydromagnesite.

13. The water treatment system according to claim 12, wherein said pretreatment device is an injection device being configured to inject gaseous carbon dioxide into said inlet flow Q.sub.IN.

14. The water treatment system according to claim 12, wherein: (i) the particles have a weight median particle size in the range of from 0.01 to 15 mm; (ii) the solubility limit of the particles in water is 2 g/L or less at 20° C. and 100 kPa; and/or (iii) the solid bed is provided by cavity of a flow reactor having an inlet being configured to receive the flow of carbon dioxide-containing feed water Q.sub.CO2 and an outlet being configured to release the outlet flow of treated water Q.sub.OUT.

15. The system of claim 12, wherein the magnesium ion source comprises brucite.

16. The system of claim 12, wherein the magnesium ion source comprises hydromagnesite.

17. A flow reactor system for use in a water treatment system for increasing the magnesium ion concentration of feed water, said flow reactor comprising: (i) an inlet, the inlet being configured to receive a flow of carbon dioxide-containing feed water Q.sub.CO2 and in flow communication with means to increase the concentration of carbon dioxide in the flow of feed water; (ii) a solid bed, the solid bed being configured to receive the flow of carbon dioxide-containing feed water Q.sub.CO2 from said inlet and to obtain an outlet flow of treated water Q.sub.OUT; and (iii) an outlet being configured to release the outlet flow of treated water Q.sub.OUT; wherein the solid bed comprises a magnesium ion source in the form of solid particles having a solubility limit in water of 10 g/L or less, measured at 20° C. and 100 kPa; and wherein the magnesium ion source comprises one or more sources selected from the group consisting of brucite and hydromagnesite.

18. The flow reactor according to claim 17, wherein: (i) the particles have a weight median particle size in the range of from 0.01 to 15 mm; (ii) the solubility limit of the particles in water is 2 g/L or less measured at 20° C. and 100 kPa; and/or (iii) the solid bed is provided by cavity of said flow reactor.

19. The flow reactor according to claim 17, wherein the flow reactor is a flow cartridge.

20. The reactor of claim 17, wherein the magnesium ion source comprises brucite.

Description

EXAMPLES

(1) The scope and interest of the invention may be better understood on basis of the following examples which are intended to illustrate embodiments of the present invention.

(2) (A) Analytical Methods

(3) All parameters defined throughout the present application and mentioned in the following examples are based on the following measuring methods:

(4) Metal Ion Concentrations (e.g. Ca.sup.2+ or Mg.sup.2+)

(5) The metal ion concentrations indicated in this application, including the magnesium and calcium ion concentration were measured by ion chromatography using a Metrohm 882 Compact IC plus instrument. All samples were filtered (RC—0.20 μm) prior to analysis.

(6) Carbon Dioxide Concentration

(7) The concentration of dissolved carbon dioxide in water was determined by titration using an aqueous sodium hydroxide standard solution as titrant and a DGi11-SC pH electrode (Mettler-Toledo).

(8) Particle Size Distributions

(9) For determining the weight media particle size of solid particles, fractional sieving according to the ISO 3310-1:2000(E) standard was used.

(10) Conductivity

(11) The electrical conductivity was measured using a SevenMulti pH meter from Mettler-Toledo (Switzerland) equipped with an InLab 741 probe from Mettler-Toledo (Switzerland).

(12) Total Alkalinity (CaCO.sub.3)

(13) The total alkalinity was measured with a Mettler-Toledo T70 Titrator using the corresponding LabX Light 2016 Titration software. A DGi111-SC pH electrode was used for this titration according to the corresponding Mettler-Toledo method 40 of the application brochure 37 (water analysis). The calibration of the pH electrode was performed using Mettler-Toledo pH standards (pH 4.01, 7.00 and 9.21).

(14) Turbidity

(15) The turbidity was measured with a Hach Lange 2100AN IS Laboratory turbidity meter. Calibration was performed using StabCal turbidity standards (formazin) of having <0.1, 20, 200, 1000, 4 000 and 7 500 NTU.

(16) Solubility Limit

(17) The solubility limit is determined by the shake flask method known to the skilled person. According to this method, excess compound (e.g. the magnesium ion source) is added to the solvent (e.g. water, preferably deionized water) and shaken at 20° C. and 100 kPa ambient pressure for at least 24 h. The saturation is confirmed by observation of the presence of undissolved material. After filtration of the slurry, a sample of the solution having a defined volume is taken for analysis. Filtration is performed under the conditions used during dissolution (20° C., 100 kPa) to minimize loss of volatile components. The solvent of the sample was then evaporated and the mass concentration of dissolved compound was determined based on the mass of the residual compound after evaporation of the solvent and the sample volume.

(18) In many cases, solubility limits of active ingredients are available in public databases generally known to the skilled person. In case of any differences or inconsistencies, the solubility limit determined according to the method described hereinabove shall be preferred.

(19) (B) Examples

(20) The following examples are not to be construed to limit the scope of the claims in any manner whatsoever.

(21) Equipment

(22) The following equipment was used in the trials: 1. Contactor system: A contactor column constructed from DN80 clear PVC equipped with barrel union end connectors to allow for changing of filter material within the column Pump with variable speed control to deliver feed water at required flow rate Carbon dioxide dosing sparger to dissolve carbon dioxide into feed water Flow measurements with online flow meter Flow control with rate tube and needle valve to column Online measurement of pH, turbidity, and conductivity on inlet and outlet of column 2. Carbon dioxide dosing system, consisting of: Carbon dioxide bottle Pressure regulator to decrease pressure from bottle at 50 bar to 5 bar Mass flow meter and control valve to regulate and measure the dosing of carbon dioxide Dosing connection to dissolution sparger in feed pipework to column
Procedure

(23) The following procedure was used to run the trials: 1. Contactor columns were filled with different magnesium ion sources as indicated below (filled to a bed height of 200-600 mm) 2. Both, water from reverse osmosis (RO water) and water that had been treated with reverse osmosis and then stabilized using a calcite contactor was used as feed water Q.sub.IN and pumped through the contactor column (the mineral composition and quality of feed water is indicated hereinbelow) 3. Before entering the column, the water was dosed with carbon dioxide from the carbon dioxide cylinder at different dose rates to produce a flow of carbon dioxide containing feed water Q.sub.CO2 (the mineral composition and quality of carbon dioxide-containing feed water is indicated hereinbelow) 4. Before taking samples for analysis from the outlet flow Q.sub.OUT, feed water was run through the column for a period of at least two EBCT (empty bed contact time) to condition the column 5. Trials were conducted with varying dosages of carbon dioxide, various flow rates to compare the impact of contact time, and different magnesium ion sources as indicated hereinafter
Materials

(24) The following magnesium minerals were tested as magnesium ion sources in the trials:

(25) TABLE-US-00001 Mg ion Chemical Particle Origin or source formula size supplier BR1 Mg(OH).sub.2 3-8 mm China BR2 Mg(OH).sub.2 500 μm China BR3 Mg(OH).sub.2 1 mm China HBD CaCO.sub.3•MgO 2.5-4.5 mm Dolomitwerk Jettenberg PHM Mg.sub.5(CO.sub.3).sub.4(OH).sub.2•4H.sub.2O 500 μm As described in WO 2011/054831 A1 BR1 = Brucite 1 BR2 = Brucite 2 BR3 = Brucite 3 HBD = Half-burned dolomite PHM = precipitated hydromagnesite.

(26) The chemical composition of the different magnesium ion sources was confirmed by XRD (results not shown).

(27) Test Settings

(28) The following test settings were used during the trials. Initial trials were performed using RO water which had almost no calcium, magnesium or alkalinity content, but a high dissolved carbon dioxide content. Following these initial tests, further tests were performed with premineralized RO water which, however, was low in magnesium.

(29) TABLE-US-00002 Mg Bed Column CO.sub.2 Contact Trial Preminer- ion height Ø dose Flow time # alization source [mm] [mm] [mg/l] [l/h] [min] 1 N BR1 600 56 0 5 17.7 2 N BR1 600 56 0 7.5 11.8 3 N BR1 600 56 0 10 8.9 4 N BR1 600 56 0 15 5.9 5 Y BR1 350 56 20 25.9 2 6 Y BR2 400 68 43 43.6 2 7 Y BR2 400 68 30 87.2 1 8 Y PHM 200 68 49 21.8 2 9 Y PHM 200 68 31 43.6 1 10 Y HBD 350 68 26 38.1 2 11 Y HBD 350 68 28 76.3 1 12 Y BR2 110 68 23 24 1 13 Y BR2 110 68 16 35.8 0.67 14 Y BR3 110 68 23 12 2 15 Y BR3 110 68 16 24 1 16 Y BR3 110 68 22 35.8 0.67 17 Y BR3 110 68 17 35.8 0.67 18 Y BR2 110 68 23 24 1
Test Results

(30) The below table lists the results measured in Trials 1-18:

(31) TABLE-US-00003 Trial Sample pH T Conductivity TAC Free CO.sub.2 Turbidity Mg.sup.2+ # point value [° C.] [μS/cm] [mg/l CaCO.sub.3] [mg/l] [NTU] [ppm] 1 Q.sub.IN 5.7 21.8 25 16 42 0.4 1.2 Q.sub.OUT 9.3 21.9 145 70 0 1.2 27 2 Q.sub.IN 5.6 21.9 24 13 42 0.1 1.2 Q.sub.OUT 8.8 22.2 131 64 0 2 23 3 Q.sub.IN 5.7 20.8 26 13 42 0.1 1.2 Q.sub.OUT 6.8 21.4 119 58 3 0.7 20 4 Q.sub.IN 5.8 22.2 23 12 42 0.1 1.2 Q.sub.OUT 6.5 21.0 95 56 12 1.2 17 5 Q.sub.IN 7.65 20.9 186 123 5 0.2 <1 Q.sub.CO2 6.6 26 Q.sub.OUT 7.4 21.3 217 102 11 0.1 6 6 Q.sub.IN 7.5 21.4 155 91 8 0.2 <1 Q.sub.CO2 6.4 50 Q.sub.OUT 9.5 22.1 275 172 0 0.15 38 7 Q.sub.IN 7.5 21.2 268 99 7 0.2 <1 Q.sub.CO2 6.5 38 Q.sub.OUT 9.4 22.6 233 140 0 0.1 29 8 Q.sub.IN 6.9 21.5 160 93 8 0.16 <1 Q.sub.CO2 6.4 57 Q.sub.OUT 9.8 22.3 519 400 0 0.2 122 9 Q.sub.IN 6.9 21.3 165 97 8 0.25 <1 Q.sub.CO2 6.5 39.5 Q.sub.OUT 9.9 22.3 442 323 0 0.15 89 10 Q.sub.IN 6.8 21.6 151 86 11 0.2 <1 Q.sub.CO2 6.5 38 Q.sub.OUT 9.5 22.5 271 130 0 0.15 21 11 Q.sub.IN 6.8 21.4 153 91 11 0.3 <1 Q.sub.CO2 6.5 38 Q.sub.OUT 7.8 22.3 201 112 3 0.2 17 12 Q.sub.IN 7.6 22.7 188 102 4 0.1 <1 Q.sub.CO2 6.6 27 Q.sub.OUT 9.3 23.2 231 136 0 0.1 18.5 13 Q.sub.IN 7.5 22.6 190 102 4 0.1 <1 Q.sub.CO2 7.0 27 Q.sub.OUT 7.8 23.4 225 125 2 0.1 8.5 14 Q.sub.IN 7.0 22.6 190 102 4 0.1 <1 Q.sub.CO2 6.8 20 Q.sub.OUT 7.9 23.3 220 120 0.2 0.1 8.5 15 Q.sub.IN 7.0 22.8 205 108 4 0.1 <1 Q.sub.CO2 6.75 27 Q.sub.OUT 8.4 23.0 237 132 0 0.05 13 16 Q.sub.IN 7.0 23.0 200 107 4 0.05 <1 Q.sub.CO2 6.8 20 Q.sub.OUT 7.5 22.8 227 125 2 0.05 8 17 Q.sub.IN 7.1 23.0 205 107 4 0.1 <1 Q.sub.CO2 6.7 26 Q.sub.OUT 7.3 22.8 227 121 12 0.05 5.5 18 Q.sub.IN 7.1 22.5 205 108 4 0.1 <1 Q.sub.CO2 6.7 21 Q.sub.OUT 7.5 22.9 223 120 8 0.05 5.5

(32) The trials with brucite 1 to 3 worked effectively, in particular when particle sizes were decreased to 1 mm or 500 μm or when higher dosages of carbon dioxide were utilized. The trials with hydromagnesite worked very effectively yielding the largest quantities of dissolved magnesium. A large increase in the dissolved magnesium level, the alkalinity level, the pH level and full consumption of the carbon dioxide suggests a very rapid reaction rate of the product. Likewise, the application with half burned dolomite works very effectively.