Electrochemistry-based graded extraction process for calcium and magnesium in saline water

Abstract

The invention belongs to the technical field of water treatment brine reuse, and provides an electrochemistry-based brine calcium and magnesium graded extraction process, which comprises the following steps: brine enters a primary electrolysis device for electrochemical reaction, carbon dioxide is introduced, and calcium ions in the brine are precipitated; further entering a primary precipitation separation device, and intercepting and collecting precipitated calcium; then the brine enters a secondary electrolysis device, the density of current applied to an electrode is increased, and magnesium ions in the brine are precipitated; the solution enters a secondary precipitation separation device, and precipitated magnesium is intercepted and recycled; drying the separated calcium and magnesium precipitates to obtain a product; and finally, introducing the reacted effluent into an ion exchange resin chromatographic column to remove untreated calcium and magnesium ions, and applying the obtained hardness-free alkaline water to the hydrogen production industry. By regulating the current density and introducing CO2, calcium and magnesium in various kinds of saline water are respectively precipitated and extracted, and the device is suitable for salt-containing organic wastewater, seawater, seawater desalination concentrated solution, bitter brine and industrial circulating cooling water.

Description

Technical Field

[0001] The present invention belongs to water treatment and resource recovery technology, and relates to a process for extracting calcium and magnesium resources from brine by graded electrochemistry. Background Art

[0002] The existing brine resource recovery process has problems such as low resource utilization, difficulty in by-product treatment, and high energy consumption. For example, although the traditional chemical precipitation method can regulate the pH in the solution and achieve a certain degree of calcium and magnesium separation, it consumes a large amount of chemical agents, resulting in waste of resources and solid waste. This method is not environmentally friendly. For example, Jun-Hwan Bang first adjusted the pH of the seawater reverse osmosis concentrate to 10.5 to form suspended Mg(OH)2 particles, and then adjusted the solution to pH = 12 to generate Ca(OH)2 precipitates. The two were separated by adjusting the pH, and then CO2 mineralization was continuously exposed to the seawater desalination brine, and Mg(OH)2 was precipitated. 2+ and Ca 2+ The mineralization into magnesite and calcium carbonate respectively consumes a large amount of chemicals, and the excessive CO2 gas escape leads to a decrease in the CO2 conversion rate and the purity of the magnesite, and the particle size of the product cannot be guaranteed (Optimizing experimental parameters in sequential CO2 mineralization using seawater desalination brine). Boor Singh Lalia proposed a two-step electrochemical method for the selective separation, precipitation and recovery of Ca in the form of calcite and Mg in the form of brucite from brine with the assistance of CO2. In a single-cell reactor, electrolysis was carried out at 2.5V using a TiO2@C cathode and a graphite anode, and CO2 was introduced to purge the calcite. Subsequently, electrolysis was carried out at 3.5V using a graphite electrode to precipitate brucite, achieving a 100% recovery rate of magnesium (Selective electrochemical separation and recovery of calcium and magnesium from brine). However, this method requires electrolysis for more than 24 hours and remains only in the laboratory research stage. This method cannot ensure the size of the precipitate, and the traditional electrochemical precipitation technology causes serious cathode scaling problems.

[0003] At present, there is no mature process that matches the step-by-step extraction technology of calcium and magnesium. It is urgent to develop a full-process process for the graded extraction of calcium and magnesium resources from brine. By inputting brine and adjusting the process parameters, the calcium and magnesium precipitates can be separated from the brine, and alkaline water without hardness can be produced as a raw material for hydrogen production by electrolysis of water.

[0004] The present invention is based on the homogeneous nucleation technology (Ion migration mechanism of electrochemical water softening in dual-chamber reactors and their performance for realcirculating cooling water) to achieve uniform precipitation in the liquid phase and the use of anti-scaling cathodes (Scaling-Free Cathodes: Enabling Electrochemical Extraction of High Purity Nano-CaCO3 and-Mg(OH)2in Seawater). Through dynamic scale crystal balance, the problem of cathode scaling is avoided. By accurately controlling the current density, CaCO3 is precipitated in different pH ranges. 2+ and Mg 2+ , the separation efficiency is improved, and the purity of calcium and magnesium reaches more than 98%. This step-by-step precipitation mechanism not only realizes the precise control of product phase and particle size, but also can separate the solid and liquid phases in real time through separation technology, avoiding the heterogeneous nucleation problem caused by excessive supersaturation in traditional intermittent processes. Summary of the Invention

[0005] To address the lack of a matching process for producing nano-magnesium hydroxide and calcium carbonate by electrolysis of water, the present invention invents and designs an electrochemical-based process for the fractional extraction of calcium and magnesium from brine. This process is suitable for practical applications such as magnesium extraction from seawater for hydrogen production, fractional extraction of magnesium and lithium from salt lakes, softening of industrial circulating cooling water, and metal recovery from concentrated brine, thus achieving a circular economy of seawater desalination and seawater metal resources, as well as the reuse of various waste brine solutions.

[0006] The technical solution of the present invention:

[0007] The invention discloses an electrochemical-based calcium and magnesium fractionation extraction process of brine, which sequentially passes through a brine pretreatment unit, an electrolytic water calcium precipitation unit, a primary precipitation and separation unit, an electrolytic water magnesium precipitation unit, a secondary precipitation and separation unit, and a resin adsorption unit. The brine pretreatment unit is provided with different treatment units according to the water quality of the incoming brine, so that the brine pretreated by the brine pretreatment unit meets the electrolysis requirements, enters the electrolytic water calcium precipitation unit, and applies a suitable current while exposing CO2 into the reactor to remove the calcium in the brine. 2+ After precipitation in the form of CaCO3, the brine enters the primary precipitation separation unit to separate the CaCO3 precipitate from the brine and collect it; remove Ca 2+ The brine is pumped into the electrolytic magnesium precipitation unit, and a certain current density is applied to remove the Mg in the brine. 2+After precipitation in the form of Mg(OH)2, the brine enters the secondary precipitation separation unit to separate and collect the Mg(OH)2 precipitate; then remove most of the Ca 2+ Mg 2+ The brine is passed into the resin adsorption unit to adsorb the remaining unprecipitated Ca 2+ Mg 2+ , and obtain an alkaline solution without hardness for use in the chlor-alkali industry or alkaline water electrolysis hydrogen production field.

[0008] The brine pretreatment unit can be equipped with different treatment units according to the type of brine and the content of impurities. If the brine is high-salt organic wastewater (salt concentration is 10,000-50,000 mg / L, COD is 500-50,000 mg / L), the brine is sequentially pretreated through a coarse filtration device (grid, screen, sand filter, activated carbon filtration unit, etc.), a coagulation and flocculation unit, an air flotation sedimentation unit, and a fine filtration (microfiltration) unit to remove organic matter and suspended matter in the high-salt organic wastewater, so that the COD of the pretreated high-salt organic wastewater is reduced to below 100 mg / L, and the suspended matter content is reduced to below 50 mg / L. If the brine is industrial circulating cooling water, seawater, desalination concentrate, bittern, etc., which does not contain or contains a small amount of organic matter, the brine pretreatment unit is only equipped with a coarse filtration device and a fine filtration unit (microfiltration) to remove suspended matter in the water, so that the suspended matter content in the effluent is reduced to below 50 mg / L.

[0009] The electrolytic water precipitation unit is divided into an electrolytic water calcium precipitation unit and an electrolytic water magnesium precipitation unit. The reactor types include but are not limited to a sandwich structure double-cell reactor, a cylindrical reactor, a plate and frame reactor, a spiral reactor, a tubular reactor, a packed bed electrodialysis reactor, etc. The common feature of these reactors is that the cathode and anode regions are separated by an ion exchange membrane or a separator material, wherein the volume ratio of the cathode region to the anode region is 1:1 to 15:1, the residence time is 0.08 to 2 hours, the water inlet flow rate is 0.1 to 1000 L / h, and the applied current density is 1 to 300 mA / cm 2 .

[0010] The precipitation separation unit is divided into a primary precipitation separation unit and a secondary precipitation separation unit, which is mainly used to separate the precipitated solid from the solution, including but not limited to plate and frame filter press, vacuum drum filter, tripod centrifuge and disc centrifuge and other separation equipment. The cathode solution of the electrolytic water calcium precipitation unit and the electrolytic water magnesium precipitation unit are respectively introduced into the primary precipitation separation unit and the secondary precipitation separation unit, with a water inlet flow rate of 0.02 to 2000 L / h and a hydraulic retention time of 0.1 to 4 hours. Through different separation forces, including pressure, vacuum suction, Centrifugal force and other factors separate the solid and liquid in the solution, producing a solid precipitate with a water content not exceeding 95%. Among them, the applied pressure of the plate and frame filter press is between 0.4 and 1.6 MPa; the drum speed of the vacuum drum filter is between 0.1 and 10 rpm, and the vacuum degree is between -0.05 and 0.09 MPa; the speed of the tripod centrifuge is between 1000 and 6000 rpm, and the separation factor is between 300 and 5000; the speed of the disc centrifuge is between 1500 and 20000 rpm, and the number of discs is between 20 and 100.

[0011] Resin adsorption unit, after two-stage electrolysis and two-stage precipitation separation, the alkaline brine still contains a small amount of Ca 2+ Mg 2+ Ions are passed into a resin adsorption unit to remove these ions, including but not limited to fixed bed adsorption columns, moving bed adsorption columns, and fluidized bed adsorption columns. The types of loaded resins include but are not limited to sulfonic acid type sodium ion exchange resins, strong acid styrene cation exchange resins, and macroporous acrylic resins. The diameter of the resin column is 10 to 100 cm, the height of the resin column is 10 to 500 cm, the adsorption capacity of the resin is 2.6 to 4.6 mg / g, and the adsorption resins used are all renewable resins. The flow rate of water flowing through the resin column is 10 to 500 mL / min. Finally, the solution after adsorption by the adsorption column is discharged from the lower end of the adsorption column and transported to the alkali solution storage tank for storage by a conduit. These alkali solutions after removing the hardness can be used in subsequent chlor-alkali industry or electrolysis water hydrogen production system.

[0012] In the preferred embodiment, the treated brine includes but is not limited to seawater, seawater desalination concentrate, industrial circulating cooling water, bittern, preferably, Ca in brine 2+ The concentration is 100~1000mg / L, Mg 2+ Concentration is 100-2600 mg / L;

[0013] In the preferred embodiment, the electrolytic water calcium precipitation unit uses a sandwich structure electrolytic reactor, and the electrolytic water magnesium precipitation unit uses a cylindrical electrolytic reactor. The specific implementation methods are shown in Examples 1 and 2. Preferably, the electrolytic water calcium precipitation unit has a residence time of 0.1 to 2 hours, a water inlet flow rate of 0.1 to 1000 L / h, and an applied current density of 1 to 100 mA / cm2 The gas flow rate of carbon dioxide is 50-2000 mL / min, the residence time of the electrolytic magnesium precipitation unit is 0.08-1.5 h, the water flow rate is 0.2-1500 L / h, and the applied current density is 15-250 mA / cm 2 ;

[0014] In a preferred embodiment, the first-stage precipitation separation unit uses a plate and frame filter press for separation. Preferably, the inlet flow rate is 100 to 1000 mL / min, the hydraulic retention time is 2 to 4 h, the applied pressure is between 0.8 and 1.0 MPa, and the water content of the CaCO3 precipitate after filtration is below 95%;

[0015] Under the preferred embodiment, the secondary precipitation separation unit uses a drum centrifuge to separate the precipitate from the solution by centrifugal force. Preferably, the filter drum speed is 1 to 10 rpm, the vacuum degree is between -0.05 and 0.09 MPa, and the water content of the filtered Mg(OH)2 precipitate is below 95%.

[0016] Compared with the existing technology, the present invention has the following advantages: 1. The present invention proposes an electrochemical-based brine calcium and magnesium graded extraction process, which is applicable to a variety of brine, including high-salt organic wastewater, seawater, seawater desalination concentrate, industrial circulating cooling water, bittern, etc. In different usage scenarios, it only needs to change the operating parameters to adapt to different water qualities, and has a relatively broad application prospect; 2. Compared with traditional calcium and magnesium acquisition technologies, such as mining and chemical precipitation, the method of the present invention does not require the addition of chemicals, does not generate additional solid waste during the production process, and has a significantly reduced carbon emission compared with traditional methods, making it a green and environmentally friendly technology; 3. Compared with the existing technology, the existing technology produces micron-sized calcium carbonate and magnesium hydroxide products, while the method of the present invention can produce nano-sized products, which have higher industrial value; 4. The calcium carbonate and magnesium hydroxide powders produced by the method of the present invention can reach a purity of more than 98%; 5. The method of the present invention can produce alkaline water without hardness, which can be used in alkaline water hydrogen production process. The extracted acid can be used for backwashing of adsorption resin columns and neutralization and discharge of alkaline water at the alkaline end, with almost no wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process schematic diagram of the present invention;

[0018] Figure 2 It is a pipeline instrument flow chart of the present invention;

[0019] Figure 3 A schematic structural diagram of the sandwich structure electrolysis device according to the present invention;

[0020] Figure 4 A schematic structural diagram of the cylindrical electrolysis device according to the present invention;

[0021] In the figure, 1. water inlet tank; 2. pretreatment device; 3. water inlet pump; 4. check valve; 5. flow meter; 6. first electrolysis device; 7. precipitation separation device; 8. motor transmission device; 9. dryer; 10. second electrolysis device; 11. water outlet tank; 12. central control and power supply; 13. water inlet; 14. cathode; 15. anode; 16. screen; 17. water outlet; 18. reactor cavity; 19. acid extraction port; 20. electrode tank; 21. upper cover. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0023] like Figure 1 As shown, a unique electrochemical-based brine calcium and magnesium fractionation extraction process includes a pretreatment unit, an electrolytic water calcium precipitation unit, a primary precipitation and separation unit, an electrolytic water magnesium precipitation unit, a secondary precipitation and separation unit, and a resin adsorption unit;

[0024] Specifically, such as Figure 2 As shown, salt water or seawater is stored in a water inlet tank 1 and is first pretreated by a pretreatment device 2. A water pump 3 is installed after the pretreatment device to prevent solid impurities in the raw water from clogging the pretreatment device 2. Its function is to pump the raw water into the subsequent treatment unit. A check valve 4 is set after the water inlet pump to prevent water from the subsequent treatment unit from flowing back to the water inlet pump, causing damage to the water inlet pump 3. A flow meter 5 is then installed to monitor the water inlet flow rate. According to the detected flow rate, the opening of the water inlet pump is adjusted to adjust the water inlet flow rate to meet the requirements of the subsequent reaction unit. The water then enters the electrolytic water calcium precipitation unit 6 and is introduced into the CO2 gas for primary precipitation. The water then enters the primary precipitation separation unit 7 for primary precipitation. Separation, the precipitate is pushed out of the separation unit by the motor propulsion device 8 to obtain a CaCO3 solid with a water content of no more than 95%, and enters the dryer 9 to finally obtain nano-scale CaCO3 powder. The filtered alkaline brine is pumped into the electrolytic water magnesium precipitation unit 10 through the water inlet pump 3 for secondary electrolysis, and then enters the secondary precipitation separation unit 7 for secondary precipitation separation. The precipitate is pushed out of the separation unit by the motor propulsion device 8 to obtain a Mg(OH)2 solid with a water content of no more than 95%, and enters the dryer 9 to finally obtain micron-scale Mg(OH)2 powder. The filtered alkaline brine is pumped into the resin adsorption unit through the water inlet pump 3 to remove the unprecipitated Ca in the solution. 2+ Mg 2+Complete removal requires that the hardness of the effluent after resin adsorption reaches the inlet water quality standard for alkaline water hydrogen production, with a hardness not higher than 0.03 mmol / L (CaCO3). The alkaline water that meets the effluent standard enters the effluent tank 11 for storage through the third inlet pump 3, and is subsequently used for the chlor-alkali industry or the alkaline water hydrogen production industry. The inlet pump, flow meter, electrolysis device power supply, motor transmission device and other equipment of the entire process are inherited in an operation control center and equipped with an automated control system. The parameters are adjusted according to changes in the inlet water quality and process requirements to ensure stable operation of the entire process system.

[0025] The pretreatment unit includes different treatment units according to the different influent water qualities. For high-salt organic wastewater, the brine is first pumped into a coarse filtration device to remove large particles of suspended solids in the brine, and then pumped into a coagulation flotation unit to remove most of the soluble organic matter in the water. Then it enters the flotation sedimentation unit to blow out and scrape off the soluble organic matter in the high-salt organic wastewater adhering to fine bubbles, and then passes through a sedimentation tank to precipitate the solids. In order to ensure the purity of the product, it is further pumped into a fine filtration unit (microfiltration) to remove micron-level impurities in the solution. The brine after pretreatment is required to achieve a COD of less than 100 mg / L and a suspended matter content of less than 50 mg / L to ensure that the purity of the subsequently generated CaCO3 and Mg(OH)2 is above 98%; for brine containing no or a small amount of organic matter in seawater, seawater desalination concentrate, industrial circulating cooling water, and bittern, a coarse filtration unit and a fine filtration unit are set in the pretreatment to remove suspended solids in the brine, and the suspended matter content of the effluent is required to be less than 50 mg / L;

[0026] The pretreated brine enters the electrolytic water calcium precipitation unit, and the reactor of the electrolytic unit adopts a sandwich structure reactor, such as Figure 3 As shown, the sandwich structure reactor consists of a mesh cathode 14, a multi-layer separator material 16 and a mesh anode 15 to form a sandwich structure. Salt water enters the alkaline area in the reactor cavity 18 through the water inlet 13. The cathode 14 of the reactor is connected to the negative electrode of the power supply, and the anode 15 of the reactor is connected to the positive electrode of the power supply. 1-15 mA / cm 2 The current density is adjusted, and the acid liquid is extracted at a constant flow rate in the acidic area. The acid extraction speed is 1% to 10% of the water flow speed. The extracted acid liquid is stored in the acid liquid tank. The alkaline brine after electrolysis is discharged from the water outlet 17 and then pumped into the primary precipitation separation unit by the water inlet pump 3. In the primary precipitation separation unit 7, the solid CaCO3 precipitated in the solution is separated from the alkaline solution to obtain a solid with a moisture content of no more than 95%. The solid is then collected in the dryer 9 for drying. The completely dried solid becomes the product of this process.

[0027] Then the alkaline liquid after the first-level solid-liquid separation enters the electrolytic magnesium precipitation unit 10. The reactor of the electrolytic unit adopts a cylindrical reactor, such as Figure 4 As shown, the cylindrical reactor is composed of a cylindrical reactor shell 20, a cylindrical mesh cathode 14, a multilayer diaphragm material 16 for separating the cathode and anode, and a mesh coaxial anode 15 from the inside to the outside, wherein the mesh cathode 14, the multilayer diaphragm material 16 and the coaxial anode 15 are closely arranged, and the distance between the cathode and anode does not exceed 5 mm. A circular cylindrical cathode alkaline region is formed between the multilayer diaphragm material and the reactor shell, and a cylindrical anode acidic region is surrounded by the multilayer diaphragm material. The volume ratio of the cathode and anode regions is 2:1 to 10:1, and the water inlet and outlet adopts the bottom-in and top-out method. The water inlet 13 is installed 1 to 10 cm near the bottom of the reactor, and the water outlet 17 is installed 1 to 10 cm near the top of the reactor. The water inlet flow rate and the water outlet flow rate are the same, which is 200 to 2000 mL / h. The anode is connected to the positive pole of the power supply, and the cathode is connected to the negative pole of the power supply. 15 to 25 mA / cm is applied between the cathode and anode. 2 The current density is 0.5 to 2 hours, and the residence time in the reactor is 0.5 to 2 hours. After the reaction is complete, the alkaline brine flows out from the outlet and enters the secondary precipitation separation unit. The precipitation separation unit uses a three-legged centrifuge or a disc centrifuge to centrifuge the micron-sized Mg(OH)2 obtained by the secondary electrolysis unit and the alkaline brine to obtain a solid with a moisture content not exceeding 95%, and sends it to the dryer 9 for drying, and finally obtains micron-sized Mg(OH)2 powder with a purity greater than 98% as the final product.

Claims

1. A process for the fractional extraction of calcium and magnesium from brine based on electrochemistry, characterized in that: The brine is sequentially passed through the brine pretreatment unit, electrolytic water calcium precipitation unit, primary precipitation separation unit, electrolytic water magnesium precipitation unit, secondary precipitation separation unit and resin adsorption unit; the brine pretreatment unit is set with different brine pretreatment units according to the quality of the brine inlet, so that the brine pretreated by the brine pretreatment unit meets the electrolysis requirements, enters the electrolytic water calcium precipitation unit, applies appropriate current and exposes CO2 into the reactor at the same time, so as to remove the Ca in the brine. 2+ After precipitation in the form of CaCO3, the brine enters the primary precipitation separation unit, where the CaCO3 precipitate in the brine is separated and collected; Ca removal 2+ The brine is pumped into the electrolytic magnesium precipitation unit, and a certain current density is applied to remove the Mg in the brine. 2+ After precipitation in the form of Mg(OH)2, the brine enters the secondary precipitation separation unit to separate and collect the Mg(OH)2 precipitate; then remove most of the Ca 2+ Mg 2+ The brine is passed into the resin adsorption unit to adsorb the remaining unprecipitated Ca 2+ Mg 2+ , to obtain an alkaline solution that removes all hardness.

2. The salt water calcium and magnesium graded extraction process according to claim 1, characterized in that: The brine includes but is not limited to seawater, seawater desalination concentrate, industrial circulating cooling water, saline industrial wastewater, and bittern.

3. The salt water calcium and magnesium graded extraction process according to claim 1, characterized in that: The brine pretreatment unit is provided with different brine pretreatment units according to the type of brine and the content of impurities. If the brine is high-salt organic wastewater with a concentration of 10,000 to 50,000 mg / L and a COD of 500 to 50,000 mg / L, the brine is sequentially pretreated by a coarse filtration subunit for intercepting solid impurities with a particle size greater than 0.1 mm, a coagulation and flocculation subunit, an air flotation sedimentation subunit, and a fine filtration subunit for intercepting solid impurities with a particle size less than 10 μm, so as to remove organic matter and suspended matter in the high-salt organic wastewater, so that the COD of the pretreated high-salt organic wastewater is reduced to below 100 mg / L, and the suspended matter content is reduced to below 50 mg / L. If the brine is brine containing no or a small amount of organic matter, the brine pretreatment unit is only provided with a coarse filtration unit and a fine filtration unit to remove suspended matter in the water, so that the suspended matter content in the effluent is reduced to below 50 mg / L.

4. The salt water calcium and magnesium graded extraction process according to claim 1, characterized in that: The electrolytic water calcium precipitation unit and the electrolytic water magnesium precipitation unit both use ion exchange membranes or separator materials to separate the cathode area and the anode area, and the volume ratio of the cathode area to the anode area is 1:1 to 15:1; the electrolytic water calcium precipitation unit uses a sandwich structure electrolytic reactor with a residence time of 0.08 to 2 hours, a water inlet flow rate of 0.1 to 1000 L / h, and an applied current density of 1 to 100 mA / cm 2 The gas flow rate of carbon dioxide is 50-2000 mL / min; the electrolytic magnesium precipitation unit uses a cylindrical electrolytic reactor with a residence time of 0.08-1.5 h, a water flow rate of 0.2-1500 L / h, and an applied current density of 15-250 mA / cm 2 .

5. The salt water calcium and magnesium graded extraction process according to claim 1, characterized in that: The first-level sedimentation separation unit uses a plate and frame filter press for separation, with an inlet flow rate of 0.02 to 2000 L / h, a hydraulic retention time of 0.1 to 4 hours, an applied pressure of 0.8 to 1.0 MPa, and a water content of the CaCO3 precipitate after filtration below 95%.

6. The salt water calcium and magnesium graded extraction process according to claim 1, characterized in that: The secondary precipitation separation unit uses a rotary drum centrifuge, a tripod centrifuge or a disc centrifuge to separate the precipitate from the solution by centrifugal force. The rotary drum speed of the vacuum drum filter is 0.1 to 10 rpm, and the vacuum degree is between -0.05 and 0.09 MPa. The rotary drum speed of the tripod centrifuge is between 1000 and 6000 rpm, and the separation factor is between 300 and 5000. The rotary drum centrifuge has a rotary drum speed of 1500 to 20000 rpm, and the number of discs is between 20 and 100. The water content of the filtered Mg(OH)2 precipitate is below 95%.

7. The process for fractionated extraction of calcium and magnesium from brine according to claim 1, characterized in that: The resin adsorption unit, after two-stage electrolysis and two-stage precipitation separation, contains a small amount of Ca 2+ Mg 2+ Ions are passed into a resin adsorption unit to remove these ions, which includes but is not limited to a fixed bed adsorption column, a moving bed adsorption column, and a fluidized bed adsorption column. The types of resins loaded include but are not limited to sulfonic acid type sodium ion exchange resin, strong acid styrene type cation exchange resin, and macroporous acrylic resin. The diameter of the resin column is 10 to 100 cm, the height of the resin column is 10 to 500 cm, the adsorption capacity of the resin is 2.6 to 4.6 mg / g, and the adsorption resins used are all renewable resins. The flow rate of water flowing through the resin column is 0.1 to 2000 L / h. Finally, the solution after adsorption by the adsorption column is discharged from the lower end of the adsorption column and transported to the alkali solution storage tank for storage using a conduit.

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