Device and method for recycling electrode liquid in electrodialysis by using nanofiltration membrane method

Abstract

The invention relates to separation of magnesium and lithium or concentration of lithium in salt lake brine by utilizing an electrodialysis method, in particular to a device and a method for recycling electrode liquid in electrodialysis by utilizing a nanofiltration membrane method, which comprises the following steps: when the magnesium ion content of the electrodialysis electrode liquid reaches 1.5 g / L, conveying high-magnesium electrode liquid to a high-magnesium electrode liquid tank; the high-magnesium electrode liquid is conveyed to a bag type filter for filtering and impurity removal; the filtered high-magnesium electrode liquid is guided into a nanofiltration membrane device to be separated, and a low-magnesium electrode liquid and a high-magnesium waste liquid are generated after separation; generated low-magnesium electrode liquid is guided into a recovery tank, and high-magnesium waste liquid is discharged to a salt pan tail liquid recovery pool for salt pan brine mixing; rO water is guided into a recovery tank to dilute the low-magnesium electrode liquid, the diluted solution is guided into electrodialysis equipment, and the PH of the diluted dialysate is within the range of 1.2-1.5; according to the present invention, RO water and concentrated hydrochloric acid are adopted to prepare the cleaning liquid in the cleaning tank to clean the filter membrane device, and the method has advantages of high chemical precipitation method cost reducing, complicated operation and process line improving, and the like.

Description

Technical Field

[0001] The invention relates to the use of electrodialysis for separation of magnesium and lithium from salt lake brine or concentration of lithium, and in particular to a device and method for recovering electrode liquid in electrodialysis by using a nanofiltration membrane method. Background Art

[0002] As one of the process technologies for extracting lithium from salt lake brine, the principle of electrodialysis is that under the action of DC electric field force, ions form directional migration, and the selective permeability of ion exchange membrane is used to achieve magnesium-lithium separation or lithium concentration. The electrode liquid in the electrodialysis equipment is the medium that provides current transfer. It is usually a 3% sodium nitrate solution, and the pH is adjusted to about 1.5 with 30% nitric acid. It is used as the electrode liquid. During the operation of the electrodialysis, the electrode liquid circulates between the positive and negative plates to protect the safe operation of the electrodialysis equipment. During the operation of the electrodialysis equipment, a large amount of OH is generated in the electrode liquid due to the dissociation of water during the electrolysis process. - In addition, as the running time of the electrodialysis equipment increases, the magnesium ion content in the electrode liquid will gradually increase. The magnesium ions in the electrode liquid will combine with the hydroxide ions to produce magnesium hydroxide, which will precipitate and adhere to the electrode membrane, causing the electrode membrane resistance to increase, the current to decrease, and continuous heat to cause the electrode membrane to burn.

[0003] To avoid the above situation, usually when the magnesium ion concentration in the electrode liquid reaches 1.5g / L, the newly prepared electrode liquid (sodium nitrate solution) will replace the high-magnesium electrode liquid to protect the safe and stable operation of the equipment. The replaced high-magnesium electrode liquid is generally discharged to the waste pool. Frequent replacement of the electrode liquid will cause the cost of its raw materials (sodium nitrate) to be too high. Therefore, the high-magnesium electrode liquid will be recycled in engineering applications, and the main process adopted is chemical precipitation. The use of chemical precipitation to recycle high-magnesium electrode liquid will add filter presses, reactors, multiple storage tanks, etc., with complex equipment structure, long recovery process, low degree of automation, and high labor intensity; and new chemical raw materials caustic soda must be introduced. The pH of the recovered electrode liquid is about 12, and nitric acid needs to be added to adjust the pH to about 6, and the amount of nitric acid increases. Therefore, this application proposes a device and method for recovering electrode liquid in electrodialysis using a nanofiltration membrane method, which reduces the high cost of the chemical precipitation method, improves the disadvantages of complex equipment structure, long recovery process, low degree of automation, and high labor intensity. Summary of the invention

[0004] The purpose of the present invention is to provide a device and method for recovering electrode liquid in electrodialysis by nanofiltration membrane method, which can reduce the high cost of chemical precipitation method and improve the disadvantages of complicated operation and process line. The specific technical scheme is as follows:

[0005] A method for recovering electrode liquid in electrodialysis by using a nanofiltration membrane method comprises the following steps:

[0006] S101 When the magnesium ion content of the electrodialysis electrode liquid reaches 1.5 g / L, the high magnesium electrode liquid is transported from the electrodialysis system to the high magnesium electrode liquid tank;

[0007] S102 transports the high magnesium cathode liquid from the high magnesium cathode liquid tank to a bag filter for filtering and impurity removal;

[0008] S103 introduces the filtered high-magnesium polar liquid into a nanofiltration membrane device for separation, and generates low-magnesium polar liquid and high-magnesium waste liquid after separation;

[0009] S104: the low-magnesium polar liquid generated in step S103 is introduced into a recovery tank, and the high-magnesium waste liquid generated is discharged to a salt field tail liquid recovery pool for salt field brine addition;

[0010] S105 introduces RO water into a recovery tank to dilute the low magnesium pole solution, and the diluted solution is introduced into an electrodialysis device, and the pH of the diluted solution is within the range of 1.2-1.5;

[0011] S106 prepares a cleaning solution using RO water and concentrated hydrochloric acid in a cleaning tank to clean the filter membrane device.

[0012] Through the above technical scheme, when the magnesium ion content of the electrodialysis electrode liquid is set to 1.5g / L, the subsequent process can ensure the safe operation of the electrodialysis equipment. By filtering and removing impurities from the high-magnesium electrode liquid in the pipeline, the solid particle impurities in the high-magnesium electrode liquid can be effectively removed, the physical blockage of the nanofiltration membrane can be reduced, the efficient flux of the membrane can be ensured, and the service life can be extended. The method of recovering the electrode liquid in the electrodialysis by nanofiltration membrane method makes the magnesium ion content of the recovered low-magnesium electrode liquid fully meet the feeding requirements of the electrodialysis equipment for the electrode liquid, and solves the problems of high cost, long process flow and complicated process flow in recovering high-magnesium electrode liquid by chemical precipitation method. Because its process flow is simple and easier to operate, it is easy to realize process automation control in actual production, which greatly reduces the labor intensity of personnel.

[0013] Furthermore, the filter medium of the filter device described in step S102 is a PP three-layer filter bag, and its filtering accuracy is 0.5um.

[0014] Through the above technical solution, the filtration medium of the filtration equipment uses a PP three-layer filter bag with a filtration accuracy of 0.5um; it can effectively remove solid particle impurities in the high-magnesium polar liquid, reduce the physical blockage of the nanofiltration membrane, ensure the efficient flux of the membrane, and extend the service life of the equipment.

[0015] Furthermore, the volume ratio of the low-magnesium polar liquid and the high-magnesium waste liquid generated after step S103 is adjusted to 6:1.

[0016] Through the above technical scheme, since the larger the volume ratio of low-magnesium anorthate liquid to high-magnesium waste liquid, the larger the volume of low-magnesium waste liquid recovered, the optimal volume ratio of the low-pressure nanofiltration membrane is adjusted by adjusting the volume ratio of low-magnesium anorthate liquid to high-magnesium waste liquid.

[0017] Furthermore, the turbidity of the high magnesium extreme liquid after filtration in step S102 is ≤0.5NTU.

[0018] Through the above technical solution, the turbidity of the high magnesium cathode liquid is required to be ≤0.5NTU after filtering and removing impurities through a bag filter. Low turbidity can ensure the removal rate of solid particle impurities to ensure the smoothness of subsequent processes.

[0019] Furthermore, in step S103, the magnesium ion content in the low-magnesium polar liquid at the outlet is ≤0.1 g / L, and the magnesium ion content in the high-magnesium waste liquid is ≥4 g / L.

[0020] Through the above technical scheme, the magnesium ion content of the low-magnesium pole liquid after the nanofiltration separation process is controlled to ≤0.1g / L to meet the feed requirements of the electrodialysis equipment; the magnesium ion content of the high-magnesium waste liquid is controlled to ≥4g / L. By detecting the magnesium ion content in the high-magnesium waste liquid, the performance of the nanofiltration membrane can be mastered.

[0021] Furthermore, the cleaning time of step S106 is set to 12-15 minutes.

[0022] Through the above technical scheme, during the operation of the device, when the nanofiltration membrane flux drops to a certain value, it needs to be cleaned, and the cleaning liquid is circulated to clean the nanofiltration membrane. The cleaning time is set to 12-15 minutes, which is the shortest time for the membrane flux to recover to the initial flux. After cleaning, the cleaning liquid remaining in the membrane shell is discharged into the ditch to save time and material costs.

[0023] A device for recovering electrode liquid in electrodialysis by nanofiltration membrane method, the device comprising a high-magnesium electrode liquid tank 1, a filter bag 2 and a nanofiltration membrane assembly 3, wherein the high-magnesium electrode liquid tank 1, the filter bag 2 and the nanofiltration membrane assembly 3 are sequentially connected by pipelines, a recovery tank 4 is provided at the discharge of the nanofiltration membrane assembly 3, a pressure pump 5 is provided at the feed port of the filter bag 2, and a cleaning tank 6 is provided in parallel with the nanofiltration membrane assembly 3.

[0024] Furthermore, the nanofiltration membrane assembly 3 includes two parallel nanofiltration membrane filter elements 7. One of the materials processed by the nanofiltration membrane filter elements 7 is nanofiltration low-magnesium waste liquid introduced into the recovery tank, and the other is nanofiltration high-magnesium waste liquid discharged to the salt field tail liquid recovery pool.

[0025] Furthermore, the cleaning tank 6 is provided with a cleaning pump 8 in series.

[0026] Through the above technical solution, a proper amount of RO water and concentrated hydrochloric acid are added to the cleaning tank, and the cleaning pump is started for internal circulation. The internal circulation can be performed to stir the internal solution so that the RO water and concentrated hydrochloric acid are fully mixed.

[0027] Compared with the prior art, the present invention has the following technical effects:

[0028] 1. The equipment structure is simple and easier to operate: The equipment required for the chemical precipitation method includes a filter press, a pressing system, a stirred reactor, multiple storage tanks, a delivery pump, a filter cake transport vehicle, etc.; while the main equipment for the nanofiltration membrane method only requires a nanofiltration membrane, a storage tank, and a delivery pump. The equipment structure is simple and easier to operate.

[0029] 2. Short recovery process and high recovery efficiency: The chemical precipitation method has a complex equipment structure and a long recovery process. In addition, the chemical precipitation method mainly uses filter cloth as the filter medium, and forms a filter cake on the surface of the filter cloth during the continuous solid-liquid separation cycle to separate the solid and liquid. In the early stage of the cycle, the filter cloth will have a filter penetration phenomenon, resulting in the inability to form a filter cake, and the solid-liquid separation efficiency is low. It takes a long time and multiple cycles to form a filter cake, thereby achieving solid-liquid separation. The time required to treat a unit volume of high-magnesium polar liquid is 1 hour; the nanofiltration membrane method uses the screening principle of membrane pore size. Due to the difference in the radius of ions of different valences, monovalent ions can pass through, and divalent and higher valence ions are intercepted, thereby achieving the separation of sodium ions and magnesium ions. The nanofiltration membrane method does not require multiple cycles, and the time required to treat a unit volume of high-magnesium polar liquid is 10 minutes. The recovery process is short and the efficiency is high.

[0030] 3. No additional auxiliary material input, low recovery cost: because the chemical precipitation method mainly uses Mg 2+ +2OH - —Mg(OH) 2 (Precipitation) principle is used to remove magnesium ions and recover the electrode liquid. Therefore, auxiliary material caustic soda needs to be added, and the pH of the recovered electrode liquid is 10-11, which is alkaline. Nitric acid needs to be added to adjust the pH to 1.2-1.5 to meet the electrodialysis feed requirements, and nitric acid needs to be consumed. When the nanofiltration membrane method is used for recovery, the radius of hydrogen ions in the high-magnesium electrode liquid is small and can all pass through the nanofiltration membrane into the low-magnesium waste liquid, resulting in the pH of the low-magnesium waste liquid being the same as that of the high-magnesium electrode liquid, and no pH adjustment is required. Therefore, the nanofiltration membrane method does not need to increase the amount of caustic soda and nitric acid, and the recovery cost is low.

[0031] 4. High degree of automation and low labor intensity: The chemical precipitation method requires manual operation for the preparation of caustic soda, calculation of the amount of caustic soda added, process sampling and testing, filter cake blowing, cake unloading and filter cake transportation, which has the disadvantages of low degree of automation and high labor intensity. The nanofiltration membrane method does not require the preparation of caustic soda solution, and the process is simple and can realize process automation control, which can reduce the labor intensity of personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the structure of a device and method for recovering electrode liquid in electrodialysis by using a nanofiltration membrane method provided by the present invention;

[0033] Figure 2 A flow chart of the present invention for recovering electrode liquid in electrodialysis by using nanofiltration membrane method;

[0034] Among them, 1. high magnesium pole liquid tank; 2. filter bag; 3. nanofiltration membrane assembly; 4. recovery tank; 5. pressure pump; 6. cleaning tank; 7. nanofiltration membrane filter element; 8. cleaning pump. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0036] Example 1

[0037] A method for recovering electrode liquid in electrodialysis by using a nanofiltration membrane method comprises the following steps:

[0038] S101 To ensure the safe operation of the electrodialysis equipment, when the magnesium ion content of the electrodialysis electrode liquid reaches 1.5 g / L, the high-magnesium electrode liquid is transported from the electrodialysis system to the high-magnesium electrode liquid tank;

[0039] In order to effectively remove solid particle impurities in the high-magnesium pole liquid, reduce the physical blockage of the nanofiltration membrane, and ensure the high-efficiency flux of the membrane, S102 transports the high-magnesium pole liquid from the high-magnesium pole liquid tank to the bag filter for filtration and impurity removal;

[0040] S103 introduces the filtered high-magnesium polar liquid into a nanofiltration membrane device for separation, and generates low-magnesium polar liquid and high-magnesium waste liquid after separation. During the process, the volume ratio of the low-magnesium waste liquid to the high-magnesium waste liquid is adjusted to 6:1 by adjusting the frequency and pressure of the high-pressure pump;

[0041] S104: the low-magnesium waste liquid generated in the process of step S103 is introduced into a recovery tank, and the high-magnesium waste liquid generated is discharged to the salt field tail liquid recovery pool for salt field brine addition;

[0042] S105 introduces RO water into the recovery tank to dilute the low-magnesium waste liquid. The volume ratio of RO water to the low-magnesium waste liquid is 1:1. The pH of the diluted low-magnesium waste liquid is measured. When the pH value = 1.2-1.5, it is judged to be qualified, which can ensure that the pH of the recovered low-magnesium waste liquid is the same as the pH of the high-magnesium pole liquid. There is no need to introduce an acid adjustment process, which reduces costs. The diluted low-magnesium waste liquid enters the electrodialysis equipment.

[0043] S106 uses RO water and concentrated hydrochloric acid to prepare the cleaning solution in the cleaning tank. During the use of the nanofiltration membrane, due to the influence of impurities and high-valent ions, the membrane pores will be physically and chemically blocked, causing the membrane flux to decrease. The flux drops to two-thirds of the initial flux. Too low a membrane flux will reduce the recovery efficiency and requires cleaning.

[0044] The best hydrochloric acid concentration for cleaning nanofiltration membranes is to prepare a 0.1 mol / L dilute hydrochloric acid solution with 31% concentrated hydrochloric acid. The cleaning time of 12-15 minutes is the shortest time for the membrane flux to recover to the initial flux. After a certain period of cleaning, the cleaning pump is turned off and the cleaning liquid remaining in the membrane shell is discharged into the ditch. When preparing the cleaning liquid, the conductivity and turbidity of the cleaning liquid will gradually increase during the recycling process due to the influence of high-valent impurity ions and solid impurities. When the upper limit of the conductivity of the cleaning liquid is 50ms / cm and the upper limit of the turbidity is 1NTU, the cleaning liquid needs to be discharged and re-prepared for the next nanofiltration membrane cleaning.

[0045] In order to effectively remove solid particle impurities in high-magnesium polar liquid, reduce physical blockage of nanofiltration membrane, ensure efficient flux of membrane, and extend the service life of equipment, the filter medium of the filtration equipment described in step S102 is a PP three-layer filter bag with a filtration accuracy of 0.5um.

[0046] Because low turbidity can ensure the removal rate of solid particle impurities, the turbidity of the high magnesium polar liquid is required to be ≤0.5NTU before the nanofiltration separation process. In order to meet the feeding requirements of the electrodialysis equipment, the magnesium ion content of the low magnesium waste liquid at the outlet after nanofiltration membrane filtration is ≤0.1g / L; the magnesium ion content of the high magnesium waste liquid is controlled at above 4g / L. The performance of the nanofiltration membrane can be mastered by detecting the magnesium ion content in the high magnesium waste liquid.

[0047] Example 2

[0048] Reference Figure 1 As shown, a device for recovering electrode liquid in electrodialysis by nanofiltration membrane method, the device comprises a high magnesium electrode liquid tank 1, a filter bag 2 and a nanofiltration membrane assembly 3, the high magnesium electrode liquid tank 1, the filter bag 2 and the nanofiltration membrane assembly 3 are connected in sequence by pipelines, the discharge of the nanofiltration membrane assembly 3 is provided with a recovery tank 4, the feed port of the filter bag 2 is provided with a high pressure pump 5, the pressure of the high pressure pump is 20-30 kg during operation, and the nanofiltration membrane assembly 3 is provided with a cleaning tank 6 in parallel.

[0049] Continue to refer to Figure 1 As shown, the nanofiltration membrane assembly 3 includes two parallel nanofiltration membrane filter elements 7. One of the materials treated by the nanofiltration membrane filter element 7 is nanofiltration low-magnesium waste liquid, which is introduced into a recovery tank. Then, the nanofiltration low-magnesium waste liquid in the recovery tank is diluted with RO water and enters the electrodialysis equipment; the other is nanofiltration high-magnesium waste liquid, which is discharged to the salt field tail liquid recovery pool.

[0050] Continue to refer to Figure 1 As shown, the cleaning tank 6 is provided with a cleaning pump 8 in series, and the cleaning pump 8 can perform internal circulation to stir the RO water and concentrated hydrochloric acid. A regulating valve is provided in series with the cleaning tank 6 and the cleaning pump 8 to control the mixing of the solution in the cleaning tank 6. A regulating valve is provided on the discharge pipe of the mixed cleaning liquid to adjust the flow rate of the cleaning liquid entering the nanofiltration membrane filter element 7 for cleaning. After cleaning, the cleaning liquid can be discharged or refluxed into the cleaning tank according to actual needs.

[0051] Example 3

[0052] Table 1 Chemical composition of materials for recovering high magnesium electrode solution in electrodialysis device using nanofiltration membrane method (unit: g / L)

[0053] project <![CDATA[Li + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[SO 4 2- ]]> <![CDATA[B 3+ ]]> <![CDATA[Na + ]]> pH Residual Chlorine High magnesium solution 0.3 1.5 1.24 0.51 0.052 8.5 1.35 0.04g / L Low magnesium wastewater 0.3 0.052 0.8 0.039 0.05 9.21 1.37 High magnesium waste liquid 0.22 4.17 1.95 0.94 0.043 7.34 1.51

[0054] From the above data, it can be seen that the magnesium ion content in the low-magnesium waste liquid is 52ppm, less than 0.1g / L; the sodium ion and hydrogen ion content in the low-magnesium waste liquid is not much different from that in the high-magnesium pole liquid. The chemical composition of the low-magnesium waste liquid obtained by recovering the high-magnesium pole liquid by nanofiltration membrane method fully meets the requirements of the electrodialysis equipment for the pole liquid.

[0055] Example 4

[0056] Table 2 Comparison of economic indicators of chemical precipitation method and nanofiltration membrane method for recycling electrode liquid of 6000 tons / year electrodialysis production unit

[0057]

[0058] Using chemical precipitation method to recycle electrodialysis high magnesium electrolyte, 20kg of caustic soda is consumed for each ton of lithium carbonate produced, and the unit price of caustic soda is 3,500 yuan / ton, and the cost of caustic soda is 70 yuan; 20L of nitric acid is consumed for acid adjustment for each ton of lithium carbonate produced, and the unit price of nitric acid is 3,000 yuan / m 3 The cost of nitric acid is 60 yuan; the power consumption of the recovery equipment for producing one ton of lithium carbonate is 15kwH, the unit price of electricity is 0.35 yuan / kwH, and the power consumption is 5.25 yuan; the consumption of filter cloth and other materials for producing one ton of lithium carbonate is 1.6 yuan; the depreciation cost of equipment for producing one ton of lithium carbonate is 4 yuan; the operating cost of producing one ton of lithium carbonate is 140.85 yuan by using chemical precipitation method to recover electrodialysis high magnesium cathode liquid.

[0059] The nanofiltration membrane method is used to recover the electrodialysis high-magnesium cathode liquid, and no auxiliary materials are consumed for each ton of lithium carbonate produced; the power consumption of the recovery equipment for producing each ton of lithium carbonate is 34kwH, the unit price of electricity is 0.35 yuan / kwH, and the power consumption is 12 yuan; the consumption of other materials such as nanofiltration membrane for producing each ton of lithium carbonate is 5 yuan; the depreciation cost of the equipment for producing each ton of lithium carbonate is 16 yuan; in summary, the chemical precipitation method is used to recover the electrodialysis high-magnesium cathode liquid, and the operating cost of producing each ton of lithium carbonate is 33 yuan.

[0060] Compared with the two recovery methods, the production cost of each ton of lithium carbonate produced by the nanofiltration membrane method is reduced by 107.85 yuan compared with the chemical precipitation method. Calculated based on an annual output of 6,000 tons of lithium carbonate, the nanofiltration membrane method can save 647,100 yuan in production costs each year compared with the chemical precipitation method, with significant economic benefits.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for recovering electrode liquid in electrodialysis using a nanofiltration membrane method, characterized in that: The steps include: S101 When the magnesium ion content of the electrodialysis electrode liquid reaches 1.5 g / L, the high magnesium electrode liquid is transported from the electrodialysis system to the high magnesium electrode liquid tank; S102 transports the high magnesium cathode liquid from the high magnesium cathode liquid tank to a bag filter for filtering and impurity removal; S103 introduces the filtered high-magnesium polar liquid into a nanofiltration membrane device for separation, and generates low-magnesium polar liquid and high-magnesium waste liquid after separation; S104: the low-magnesium polar liquid generated in step S103 is introduced into a recovery tank, and the high-magnesium waste liquid generated is discharged to a salt field tail liquid recovery pool for salt field brine addition; S105: introducing RO water into a recovery tank to dilute the dialysate, and introducing the diluted solution into an electrodialysis device, wherein the pH of the dialysate after dilution is within the range of 1.2-1.5; S106 prepares a cleaning solution using RO water and concentrated hydrochloric acid in a cleaning tank to clean the filter membrane device.

2. The method for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 1, characterized in that: The filter medium of the filter equipment described in step S102 is a PP three-layer filter bag, and its filtering accuracy is 0.5um.

3. The method for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 1, characterized in that: After step S103, the volume ratio of the low-magnesium polar liquid and the high-magnesium waste liquid is adjusted to 6:

1.

4. The method for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 1, characterized in that: The material turbidity at the feed inlet in step S103 is ≤0.5NTU.

5. The method for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 1, characterized in that: In step S103, the magnesium ion content in the low-magnesium extreme liquid at the outlet is ≤0.1 g / L, and the magnesium ion content in the high-magnesium waste liquid is ≥4 g / L.

6. The method for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 1, characterized in that: The cleaning time of step S106 is set to 12-15 minutes.

7. A device for recovering electrode liquid in electrodialysis by using a nanofiltration membrane method, the device comprising a high-magnesium electrode liquid tank (1), a filter bag (2) and a nanofiltration membrane assembly (3), wherein the high-magnesium electrode liquid tank (1), the filter bag (2) and the nanofiltration membrane assembly (3) are connected in sequence by a pipeline, characterized in that: The discharge port of the nanofiltration membrane assembly (3) is provided with a recovery tank (4), the feed port of the filter bag (2) is provided with a pressure pump (5), and the nanofiltration membrane assembly (3) is provided with a cleaning tank (6) in parallel.

8. The device for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 7, characterized in that: The nanofiltration membrane assembly (3) comprises two nanofiltration membrane filter elements (7) connected in parallel. One of the materials processed by the nanofiltration membrane filter elements (7) is nanofiltration dialyzate which is introduced into a recovery tank, and the other is nanofiltration high-magnesium waste liquid which is discharged to a salt field tail liquid recovery pool.

9. The device for recovering electrode liquid in electrodialysis by nanofiltration membrane method according to claim 7, characterized in that: The cleaning tank (6) is provided with a cleaning pump (8) in series.

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