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 and passing said flow Q.sub.IN 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; (b) passing said flow Q.sub.IN through a solid bed to obtain an outlet flow of treated water Q.sub.OUT; wherein the solid bed in step (b) comprises a magnesium ion source in the form of solid particles, wherein said magnesium ion source is natural or synthetic hydromagnesite.

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 total alkalinity (CaCO.sub.3) of from 5 to 200 mg/l.

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

5. The method according to claim 1, wherein the method further comprises a step of adjusting the pH of the feed water to a range of from 5.0 to 8.5, wherein said pH is adjusted by injecting an appropriate amount of carbon dioxide into inlet flow Q.sub.IN.

6. The method according to claim 1, wherein the method further comprises a step of adjusting the temperature of the feed water to a range of from 5 to 35° C.

7. The method according to claim 1, wherein the magnesium ion source is synthetic hydromagnesite.

8. The method according to claim 1, wherein the particles have a weight median particle size in the range of from 0.05 to 20 mm.

9. The method according to claim 1, wherein the contact time in step (b) between flow Q.sub.IN and the solid bed is: (i) at least 0.05 min; and/or (ii) less than 10 min.

10. The method according to claim 1, wherein the solid bed in step (b) is provided by a cavity of a flow reactor, said flow reactor having an inlet being configured to receive the inlet flow of feed water Q.sub.IN and an outlet being configured to release the outlet flow of treated water Q.sub.OUT.

11. The method according to claim 1, wherein the magnesium ion source is synthetic hydromagnesite and the particles have a weight median particle size in the range of from 0.5 to 1.5 mm, and the contact time in step (b) between flow Q.sub.IN and the solid bed is at least 0.05 min and less than 2 min.

12. The method according to claim 1, wherein the method further comprises a step of adjusting the pH of the outlet flow of treated water Q.sub.OUT to a range of from 4.5 to 9.5.

13. The method according to claim 1, wherein the feed water has a concentration of dissolved magnesium ions of 2 mg/l or less, a total alkalinity (CaCO.sub.3) of from 20 to 100 mg/l, and a Langelier Saturation Index (LSI) of from −1.0 to 0.7.

14. The method according to claim 1, further comprising adjusting the pH of the feed water to a range of from 6.0 to 7.5, the temperature of the feed water to a range of from 15 to 25° C., and the pH of the outlet flow of treated water Q.sub.OUT to a range of from 6.8 to 7.5.

15. The method according to claim 1, wherein the magnesium ion source is precipitated hydromagnesite particles having a weight median particle size in the range of from 0.5 to 1.5 mm.

16. 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; and (ii) a solid bed, the solid bed being configured to receive the inlet flow of feed water Q.sub.IN from said line 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, wherein said magnesium ion source is natural or synthetic hydromagnesite.

17. The water treatment system according to claim 16, wherein: (i) the magnesium ion source is synthetic hydromagnesite; (ii) the particles have a weight median particle size in the range from 0.05 to 20 mm; and/or (iii) the solid bed is provided by cavity of a flow reactor having an inlet being configured to receive the inlet flow of feed water Q.sub.IN and an outlet being configured to release the outlet flow of treated water Q.sub.OUT.

18. A flow reactor 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 an inlet flow of feed water Q.sub.IN; (ii) a solid bed, the solid bed being configured to receive the inlet flow of feed water Q.sub.IN 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, wherein said magnesium ion source is natural or synthetic hydromagnesite.

19. The flow reactor according to claim 18, wherein: (i) the magnesium ion source is precipitated hydromagnesite; (ii) the particles have a weight median particle size in the range from 0.05 to 20 mm; and/or (iii) the solid bed is provided by cavity of said flow reactor.

20. The flow reactor according to claim 18, wherein the flow reactor is a flow cartridge.

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.

(A) Analytical Methods

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

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

(4) 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.

(5) Carbon Dioxide Concentration

(6) The concentration of dissolved carbon dioxide in water was determined by titration using an aqueous sodium hydroxide standard solution as titrant and a DGi111-SC pH electrode (Mettler-Toledo).

(7) Particle Size Distributions

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

(9) Conductivity

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

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

(12) The total alkalinity was measured with a Mettler-Toledo T70 Titrator using the corresponding 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 pH standards (pH 4.01, 7.00 and 9.21).

(13) Turbidity

(14) 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.

(15) Solubility Limit

(16) 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.

(17) 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.

(B) Examples

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

(19) Equipment

(20) The following equipment was used in the trials:

(21) 1. Contactor system:

(22) 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 (not used in these trials), 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 the magnesium ion source as indicated below (filled to a bed height of about 200 mm) 2. 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. Feed water was run through the column for a period of at least two EBCT (empty bed contact time) to condition the column before taking samples for analysis from the outlet flow Q.sub.OUT 4. Trials were conducted with various flow rates to compare the impact of contact time
Materials

(24) The following magnesium minerals was tested as magnesium ion source in the trials:

(25) TABLE-US-00001 Mg Particle Origin ion source Chemical formula size or supplier PHM Mg.sub.5(CO.sub.3).sub.4(OH).sub.2•4H.sub.2O 500 gm As described in WO 2011/054831 A1 PHM = precipitated hydromagnesite.

(26) The chemical composition of PHM was confirmed by XRD (results not shown).

(27) Test Settings

(28) The following test settings were used in the trials using premineralized RO water which, however, was low in magnesium.

(29) TABLE-US-00002 Trial # 1 2 3 4 5 Premineralization Y Y Y Y Y Mg ion source PHM PHM PHM PHM PHM Bed height [mm] 200 200 41 41 41 Column Ø [mm] 68 68 68 68 68 CO.sub.2 dose [mg/l] 0 0 0 0 0 Flow [l/h] 21.8 43.6 12 18 36 Contact time [min] 2 1 0.75 0.5 0.25
Test Results

(30) The below table lists the results measured in Trials 1-5:

(31) TABLE-US-00003 Trial # 1 2 3 4 5 Sample point Q.sub.IN Q.sub.OUT Q.sub.IN Q.sub.OUT Q.sub.IN Q.sub.OUT Q.sub.IN Q.sub.OUT Q.sub.IN Q.sub.OUT pH value 6.75 10 6.76 9.8 7.06 9.66 7 9.6 7.06 9.49 T [° C.] 21.2 21.9 20.9 21.8 22.5 23.3 22.3 23.2 22.5 23.2 Conductivity [μS/cm] 137 296 140 253 208 279 208 273 205 259 TAC [mg/l CaCO.sub.3] 79 192 84 157 110 177 110 170 122 159 Free CO.sub.2 [mg/l] 11 0 11 0 4 0 4 0 4 0 Turbidity [NTU] 0.1 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Mg.sup.2+ [mg/l] <1 60 <1 46 <1 34.5 <1 29 <1 26

(32) The trials with hydromagnesite worked very effectively without injection of carbon dioxide. A large increase in the dissolved magnesium level, the alkalinity level, the pH level and full consumption of the carbon dioxide suggest a very rapid reaction rate.