A recovery system and method for a sodium-ion battery cathode material production mother liquor

Abstract

The present invention relates to a recovery system and method for sodium ion battery positive electrode material production mother liquor, belonging to the field of waste liquid recovery technology. The system comprises a first sulfuric acid dosing device, a water washing system, a second sulfuric acid dosing device, a secondary nanofiltration system, and a concentration system. The sodium ion battery positive electrode material production mother liquor is treated by sulfuric acid added to the mother liquor through the first sulfuric acid dosing device until the mother liquor pH value reaches 5-6, and then enters the water washing system. After treatment by the water washing system, sodium sulfate is obtained at the concentrated water outlet of the water washing system. The water produced by the water washing system is treated by sulfuric acid added to the mother liquor pH value reach 2-3 through the second sulfuric acid dosing device, and then enters the secondary nanofiltration system. The water produced by the secondary nanofiltration system enters the concentration system, and after concentration, oxalic acid is obtained. After treatment by the system of the present invention, the purity of the oxalic acid reaches 90%, no waste liquid is generated, and the system has good application prospects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste liquid recovery, and particularly relates to a recovery system and method for mother liquor in production of sodium ion battery positive electrode material. BACKGROUND

[0002] Sodium ion batteries have the advantages of abundant resources, low cost and high performance-price ratio. The working principle of sodium ion batteries is similar to that of lithium ion batteries, and sodium ion batteries are highly compatible with lithium ion batteries, and have become an ideal substitute for lithium ion batteries. Sodium ion batteries mainly consist of positive electrode material, negative electrode material, separator and electrolyte. Among them, the positive electrode material as a component for storing active sodium not only directly determines the electrochemical performance of the battery, but also affects the final cost of the battery. The wastewater generated in the production process of the sodium oxalate positive electrode material contains sodium oxalate and sodium sulfate, and if the wastewater is directly discharged without treatment, it will not only harm the surrounding environment, but also waste a large amount of oxalic acid resources.

[0003] At present, the main oxalic acid recovery methods are distillation, resin adsorption, extraction, lead sulfate method and lime-gypsum method. However, the distillation method has high production cost and high energy consumption; the resin adsorption and extraction process chain is long, and the service life of the resin and the extractant is short; in the lead sulfate method, the activity of lead sulfate decreases with the increase of the use frequency, and lead-containing wastewater is generated; and in the lime-gypsum method, a large amount of reagent is added, and calcium-containing wastewater is generated.

[0004] The treatment methods for wastewater containing sodium sulfate mainly include adding a precipitant to form a sulfate precipitate, recrystallization or electrolysis. However, these methods can only obtain low-value industrial products, and have high energy consumption, low purity and high impurity content, and are difficult to be reused. The recovered sodium sulfate product cannot be utilized, and will cause secondary pollution to the environment. SUMMARY

[0005] (1) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a recovery system and method for mother liquor in production of sodium ion battery positive electrode material, which solves the technical problems of low recovery purity of oxalic acid and sodium sulfate in the mother liquor, large waste production, high cost and high energy consumption in the production of sodium ion battery positive electrode material.

[0007] (2) Technical solutions

[0008] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include:

[0009] In a first aspect, the present application provides a recovery system for mother liquor in production of sodium ion battery positive electrode material, comprising a first sulfuric acid adding device, a water washing system, a second sulfuric acid adding device, a secondary nanofiltration system and a concentration system.

[0010] The mother liquor of the sodium ion battery cathode material production is added with sulfuric acid by the first sulfuric acid adding device to pH=5-6, and then enters the water washing system;

[0011] The water washing system comprises a primary water washing device, a secondary water washing device and a tertiary water washing device, the concentrated water outlet side of the primary water washing device is connected with the water inlet side of the secondary water washing device, the concentrated water outlet side of the secondary water washing device is connected with the water inlet side of the tertiary water washing device, and the concentrated water outlet side of the tertiary water washing device obtains sodium sulfate;

[0012] The water produced by the primary water washing device, the secondary water washing device and the tertiary water washing device is added with sulfuric acid by the second sulfuric acid adding device to pH=2-3, and then enters the secondary nanofiltration system, the water produced by the secondary nanofiltration system enters the concentration system, and oxalic acid is obtained in the concentrated water after concentration by the concentration system.

[0013] The primary water washing device, the secondary water washing device and the tertiary water washing device of the application are all nanofiltration membrane devices, the permeate with a small amount of salt is the produced water, and the water with a high amount of salt is the concentrated water. After the mother liquor of the sodium ion battery cathode material production is adjusted to pH 5-6 by sulfuric acid, the solution containing oxalic acid will permeate the membrane, that is, the produced water contains oxalic acid, and the sodium sulfate will be intercepted by the membrane, that is, the concentrated water contains sodium sulfate. The application separates oxalic acid and sodium sulfate through the tertiary water washing device. With the increase of the washing multiple, the interception rate of the nanofiltration membrane to oxalic acid will increase, so the economic problem needs to be considered. The application sets the tertiary water washing device, so that the yield of sodium sulfate is 98wt%, and the purity can reach 96%, so more water washing devices do not need to be set. The application takes into account the economy and separation efficiency, and has more application value.

[0014] Optionally, a microfiltration system is further included, which can remove the suspended solids in the mother liquor of the sodium ion battery cathode material production; the microfiltration system comprises an adjusting tank and a microfiltration device, the mother liquor of the sodium ion battery cathode material production is connected with the water inlet side of the adjusting tank, the water outlet side of the adjusting tank is connected with the water inlet side of the microfiltration device, and the water outlet side of the microfiltration device is connected with the water washing system.

[0015] Optionally, the backwashing drainage side of the microfiltration device is further connected with the adjusting tank, so that the backwashing liquid generated by backwashing of the microfiltration device enters the adjusting tank for collection.

[0016] Optionally, the secondary nanofiltration system is a nanofiltration device, and the concentration system is a reverse osmosis device; the water produced by the primary water washing device, the secondary water washing device and the tertiary water washing device is connected to the water inlet side of the nanofiltration device, and the water outlet side of the nanofiltration device is connected to the water inlet side of the reverse osmosis device, so that the water produced by the nanofiltration device enters the reverse osmosis device for concentration treatment, and oxalic acid is obtained at the concentrated water outlet side of the reverse osmosis device.

[0017] Optionally, the concentrated water side of the nanofiltration device and the water outlet side of the reverse osmosis device are both connected to the water inlet side of the primary water washing device, the secondary water washing device and the tertiary water washing device; the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device enter the water washing system, so as to recover the solutes and reduce waste discharge.

[0018] Preferably, when the amount of nanofiltration concentrated water and reverse osmosis produced water is insufficient or the solute concentration is high, pure water can be supplemented as the water washing water source of the water washing system.

[0019] Optionally, the operating pressure of the primary water washing device, the secondary water washing device and the tertiary water washing device is 40-45 bar, and the average water production membrane flux is 12-15 LMH.

[0020] The membranes of the primary water washing device, the secondary water washing device and the tertiary water washing device are nanofiltration membranes, the membrane material is polyamide, and the pore size is 1 nm.

[0021] Optionally, the operating pressure of the nanofiltration device is 25-30 bar, and the average water production membrane flux is 14-15 LMH; the operating pressure of the reverse osmosis device is 60-70 bar, and the average flux is 14-15 LMH.

[0022] In a second aspect, the application provides a recovery method of a mother liquor for producing a sodium ion battery positive electrode material, which recovers oxalic acid and sodium sulfate in the mother liquor for producing the sodium ion battery positive electrode material by using the recovery system, and includes the following steps:

[0023] S1, the mother liquor for producing the sodium ion battery positive electrode material is collected in the adjusting tank and then enters a microfiltration device to remove suspended solids, and the backwashing water of the microfiltration device is returned to the adjusting tank;

[0024] S2, the water outlet of the microfiltration device is mixed with the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device in a volume ratio of 1:2-3, is adjusted to pH=5-6 by sulfuric acid, and then enters the primary water washing device;

[0025] S3, the water produced by the first water washing device enters the nanofiltration device, the concentrated water of the first water washing device is mixed with the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device at a volume ratio of 1:2-3, and then enters the second water washing device;

[0026] S4, the water produced by the second water washing device enters the nanofiltration device, the concentrated water of the first water washing device is mixed with the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device at a volume ratio of 1:2-3, and then enters the third water washing device;

[0027] S5, the water produced by the third water washing device enters the nanofiltration device, and the concentrated water of the third water washing device is sodium sulfate;

[0028] S6, the water produced by the first water washing device, the second water washing device and the third water washing device is mixed, the pH value is adjusted to 2-3 by sulfuric acid, and then enters the nanofiltration device;

[0029] S7, the concentrated water of the nanofiltration device returns to the water washing system, and the water produced by the nanofiltration device enters the reverse osmosis device;

[0030] S8, the water produced by the reverse osmosis device returns to the water washing system, and the concentrated water of the reverse osmosis device is oxalic acid.

[0031] Optionally, in addition to the nanofiltration device concentrated water and the reverse osmosis device water, additional washing water is also needed in the water washing system.

[0032] (Three) beneficial effects

[0033] The beneficial effects of the present application are: the present application adopts a full membrane method to recover oxalic acid and sodium sulfate in the sodium ion battery positive electrode material production mother liquor, can long-term and large-scale treat wastewater, only needs to maintain or replace the membrane regularly, has low cost and good effect. The present application adjusts the pH value of the sodium ion battery positive electrode material production mother liquor to 5-6, and then performs three water washing treatments, so that high-purity sodium sulfate can be obtained. By adjusting the pH value of the water produced by the water washing system to 2-3, and then performing a two-stage nanofiltration system treatment and a concentration system concentration, high-purity oxalic acid can be obtained. The present application only needs to add one kind of reagent, i.e. sulfuric acid, and the system water does not contain other substances, can be recycled, and has no pollution. By using the recovery system of the present application to recover oxalic acid and sodium sulfate, the yield of oxalic acid is 39wt%, and the purity can reach 90%; the yield of sodium sulfate is 98wt%, and the purity can reach 96%; the recovered oxalic acid and sodium sulfate have high purity and can be directly used for secondary use.

[0034] The concentrated water of the nanofiltration device and the product water of the reverse osmosis device can be recycled to the water washing system, and the system does not produce additional water that needs to be treated. The only product discharged by the system is sodium sulfate and oxalic acid that can be recycled, and there is no other waste.

[0035] The microfiltration system is arranged in front of the water washing system, which can remove the suspended solids in the mother liquor of the sodium ion battery positive material production, and avoid the membrane blockage of the water washing system, the secondary nanofiltration system and the concentration system caused by the suspended solids. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The figure is a schematic diagram of the recovery system of the mother liquor of the sodium ion battery positive material production of embodiment 1 of the application.

[0037]

Explanation of reference signs

[0038] 1: adjustment tank; 2: microfiltration device; 3: primary water washing device; 4: secondary water washing device; 5: tertiary water washing device; 6: secondary nanofiltration system; 7: reverse osmosis system; 8: first sulfuric acid adding device; 9: second sulfuric acid adding device. DETAILED DESCRIPTION

[0039] In order to better explain the application and facilitate understanding, the application will be described in detail below by specific embodiments in combination with the drawings.

[0040] In order to better understand the above technical solutions, the exemplary embodiments of the application will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the application are shown in the drawings, it should be understood that the application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer, more thorough understanding of the application and to fully convey the scope of the application to those skilled in the art.

[0041] Embodiment 1:

[0042] Reference Figure 1 The embodiment provides a recovery system of mother liquor of sodium ion battery positive material production, which comprises a first sulfuric acid adding device 8, a water washing system, a second sulfuric acid adding device 9, a secondary nanofiltration system and a concentration system.

[0043] The mother liquor of the sodium ion battery positive material production is added with sulfuric acid by the first sulfuric acid adding device 8 to pH=5-6 of the mother liquor, and then enters the water washing system.

[0044] The water washing system includes a primary water washing device 3, a secondary water washing device 4 and a tertiary water washing device 5. The concentrated water outlet side of the primary water washing device 3 is connected to the water inlet side of the secondary water washing device 4, and the concentrated water outlet side of the secondary water washing device 4 is connected to the water inlet side of the tertiary water washing device 5. The concentrated water outlet side of the tertiary water washing device 5 obtains sodium sulfate;

[0045] The produced water of the primary water washing device 3, the secondary water washing device 4 and the tertiary water washing device 5 is added with sulfuric acid through the second sulfuric acid dosing device 9 until the produced water pH is 2-3, and then enters the secondary nanofiltration system. The produced water of the secondary nanofiltration system enters the concentration system, and oxalic acid is obtained from the concentrated water after concentration by the concentration system.

[0046] Oxalic acid is a dibasic organic weak acid. It undergoes two-step ionization in water and exists in the form of oxalic acid, hydrogen oxalate and oxalate. Its electrolysis degree is different at different pH values, that is, the proportion of the three ions is different. Due to the characteristics of the nanofiltration membrane itself, it mainly intercepts divalent, high-valent ions and organic matter with larger molecular weight. When the pH of the washing water is adjusted to 5-6, the main anions in the water are SO4 2- 、C2O4 2- 、HC2O4 - Therefore, most of the sodium sulfate and part of the sodium oxalate are intercepted by the nanofiltration membrane, and oxalic acid and sodium hydrogen oxalate pass through the nanofiltration membrane; when the pH of the inlet water of the secondary nanofiltration system is adjusted to 2-3, oxalic acid is the main form of existence. At this time, the sodium sulfate in the water is intercepted by the nanofiltration membrane, while oxalic acid and sodium hydrogen oxalate pass through the nanofiltration membrane.

[0047] Using the above experimental data, most of the sulfate ions are removed during water washing, and the small part of the sulfate ions that pass through the nanofiltration membrane are removed during treatment in the secondary nanofiltration system. Therefore, the water produced by the secondary nanofiltration system is mainly oxalic acid.

[0048] The recovery system of this embodiment also includes a microfiltration system, which can remove suspended matter from the mother liquor produced by the production of sodium ion battery positive electrode materials;

[0049] The microfiltration system includes a regulating tank 1 and a microfiltration device 2. The mother liquor for producing the positive electrode material of the sodium ion battery is connected to the water inlet side of the regulating tank 1, the water outlet side of the regulating tank 1 is connected to the water inlet side of the microfiltration device 2, and the water outlet side of the microfiltration device 2 is connected to the water washing system.

[0050] The backwash drainage side of the microfiltration device 2 is also connected to the regulating tank 1, so that the backwash liquid generated by backwashing the microfiltration device 2 enters the regulating tank 1 for collection.

[0051] The function of regulating tank 1 is to collect the mother liquor produced by the positive electrode material of sodium ion battery.

[0052] After the filter screen of the microfiltration device 2 filters the suspended solids for a long time, the suspended solids will be concentrated on the filter screen to cause blockage, so the microfiltration device 2 needs to be periodically back-flushed, and the back-flushing water can be returned to the conditioning tank 1.

[0053] Further, the secondary nanofiltration system 6 is a nanofiltration device, and the concentration system 7 is a reverse osmosis device; the water produced by the primary water washing device 3, the secondary water washing device 4 and the tertiary water washing device 5 is connected to the water inlet side of the nanofiltration device, and the water produced by the nanofiltration device is connected to the water inlet side of the reverse osmosis device, so that the water produced by the nanofiltration device enters the reverse osmosis device for concentration treatment, and oxalic acid is obtained at the concentrated water outlet side of the reverse osmosis device.

[0054] Further, the concentrated water side of the nanofiltration device and the water outlet side of the reverse osmosis device are both connected to the water inlet side of the primary water washing device 3, the secondary water washing device 4 and the tertiary water washing device 5, so that the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device enter the water washing system.

[0055] Further, the operating pressure of the primary water washing device 3 is 40-45 bar, and the average water production membrane flux is 12-15 LMH; the operating pressure of the secondary water washing device 4 is 40-45 bar, and the average water production membrane flux is 12-15 LMH; the operating pressure of the tertiary water washing device 5 is 40-45 bar, and the average water production membrane flux is 12-15 LMH.

[0056] The operating pressure of the nanofiltration device is 25-30 bar, and the average water production membrane flux is 14-15 LMH; the operating pressure of the reverse osmosis device is 60-70 bar, and the average flux is 14-15 LMH.

[0057] Application Example 1

[0058] The method for recycling oxalic acid and sodium sulfate in the sodium-ion battery cathode material production mother liquor by using the sodium-ion battery cathode material production mother liquor recycling system described in Example 1; in this application example, the membrane type used by the primary water washing device, the secondary water washing device and the tertiary water washing device is ENCYCLO-ECTF, and the membrane type used by the nanofiltration device is ENCYCLO-ECNF.

[0059] Specifically, the following steps are included:

[0060] S1, the sodium-ion battery cathode material production mother liquor is collected by the conditioning tank and then enters the microfiltration device to remove suspended solids, and the back-flushing water of the microfiltration device is returned to the conditioning tank;

[0061] S2, the water outlet of the microfiltration device is mixed with the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device at a volume ratio of 1:2, then the pH is adjusted to 5 by sulfuric acid, and then the mixture enters the primary water washing device;

[0062] S3, the water produced by the primary water washing device enters the nanofiltration device, the concentrated water of the primary water washing device is mixed with the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device according to a volume ratio of 1:2, and then enters the secondary water washing device;

[0063] S4, the water produced by the secondary water washing device enters the nanofiltration device, the concentrated water of the secondary water washing device is mixed with the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device according to a volume ratio of 1:2, and then enters the tertiary water washing device;

[0064] S5, the water produced by the tertiary water washing device enters the nanofiltration device, and the concentrated water of the tertiary water washing device is sodium sulfate that can be recycled;

[0065] S6, the water produced by the primary water washing device, the secondary water washing device and the tertiary water washing device is mixed, adjusted to pH = 2 by sulfuric acid, and then enters the nanofiltration device;

[0066] S7, the concentrated water of the nanofiltration device returns to the water washing system, and the water produced by the nanofiltration device enters the reverse osmosis device;

[0067] S8, the water produced by the reverse osmosis device returns to the water washing system, and the concentrated water of the reverse osmosis device is oxalic acid that can be recycled.

[0068] In addition to the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device, additional washing water is also needed in the water washing system.

[0069] In the application example, the operating pressure, water production membrane flux and water inlet quantity of the primary water washing device, the secondary water washing device, the tertiary water washing device, the nanofiltration device and the reverse osmosis device, and the oxalate and sulfate contents in the water inlet, the water produced and the concentrated water of each part are shown in Table 1.

[0070] Table 1

[0071]

[0072] The recovery system of the sodium ion battery positive electrode material production mother liquor in Example 1 is used to process sodium ion battery positive electrode material production mother liquor containing oxalic acid and sodium sulfate, the concentration of oxalic acid in the mother liquor is 11.9 g / L, and the concentration of sulfate is 63.63 g / L. The parameters shown in Table 1 are used for processing, and the purity of the recovered oxalic acid can reach 90%, and the purity of the sodium sulfate can reach 96%.

[0073] In the recovery system of the sodium ion battery positive electrode material production mother liquor of the application, the concentrated water of the nanofiltration device and the water produced by the reverse osmosis device are recycled to the water washing system, which can be recycled, saves resources and does not produce additional water that needs to be treated. The products discharged by the system are only sodium sulfate and oxalic acid that can be recycled, without other waste water and waste, which is more environmentally friendly.

[0074] The effects of the membrane model and the influent pH of the water washing system and the nanofiltration device on the concentration and purity of oxalic acid and sodium sulfate were analyzed as shown in Table 2.

[0075] Table 2

[0076]

[0077] As can be seen, the water washing influent pH has a greater effect on the concentration of oxalic acid, that is, the lower the influent pH, the higher the concentration of oxalic acid, and the 10th group has the best effect, and the concentration and purity of oxalic acid and sodium sulfate are the highest compared with other groups.

[0078] In the description of the present application, it should be understood that the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can be explicitly or implicitly included one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0079] In the present application, unless otherwise specifically defined and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0080] In the present application, unless otherwise specifically defined and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. Moreover, the first feature is "above", "over" and "on" the second feature, which can be directly above or obliquely above the first feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature is "below", "under" and "under" the second feature, which can be directly below or obliquely below the first feature, or only indicates that the horizontal height of the first feature is lower than that of the second feature.

[0081] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an embodiment", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0082] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can modify, modify, replace and modify the above-described embodiments within the scope of the present application.

Claims

1. A recovery system for mother liquor produced from positive electrode materials for sodium ion batteries, characterized in that: It includes a first sulfuric acid dosing device (8), a water washing system, a second sulfuric acid dosing device (9), a secondary nanofiltration system (6), a concentration system (7) and a microfiltration system; The mother liquor produced by the sodium ion battery positive electrode material is added with sulfuric acid through the first sulfuric acid adding device (8) until the mother liquor pH value is 5-6, and then enters the water washing system; The water washing system comprises a primary water washing device (3), a secondary water washing device (4) and a tertiary water washing device (5); the concentrated water outlet side of the primary water washing device (3) is connected to the water inlet side of the secondary water washing device (4); the concentrated water outlet side of the secondary water washing device (4) is connected to the water inlet side of the tertiary water washing device (5); sodium sulfate is obtained from the concentrated water outlet side of the tertiary water washing device (5); The water produced by the primary water washing device (3), the secondary water washing device (4) and the tertiary water washing device (5) is doped with sulfuric acid by the second sulfuric acid dosing device (9) until the pH value of the produced water is 2-3, and then enters the secondary nanofiltration system (6). The water produced by the secondary nanofiltration system (6) enters the concentration system (7), and oxalic acid is obtained from the concentrated water after concentration by the concentration system (7); The microfiltration system comprises a regulating tank (1) and a microfiltration device (2); The secondary nanofiltration system (6) is a nanofiltration device, and the concentration system (7) is a reverse osmosis device; The concentrated water side of the nanofiltration device and the produced water side of the reverse osmosis device are both connected to the water inlet sides of the primary water washing device (3), the secondary water washing device (4) and the tertiary water washing device (5); the concentrated water of the nanofiltration device and the produced water of the reverse osmosis device enter the water washing system; The primary water washing device, the secondary water washing device and the tertiary water washing device are nanofiltration membrane devices.

2. The sodium ion battery positive electrode material production mother liquor recovery system according to claim 1, characterized in that: The microfiltration system can remove suspended matter in the mother liquor of sodium ion battery positive electrode material production; the mother liquor of sodium ion battery positive electrode material production is connected to the water inlet side of the regulating tank (1), the water outlet side of the regulating tank (1) is connected to the water inlet side of the microfiltration device (2), and the water outlet side of the microfiltration device (2) is connected to the water washing system.

3. The sodium ion battery positive electrode material production mother liquor recovery system according to claim 1, characterized in that: The backwash drainage side of the microfiltration device (2) is also connected to the regulating tank (1), so that the backwash liquid generated by backwashing the microfiltration device (2) enters the regulating tank (1) for collection.

4. The sodium ion battery positive electrode material production mother liquor recovery system according to claim 1, characterized in that: The water produced by the primary water washing device (3), the secondary water washing device (4) and the tertiary water washing device (5) is connected to the water inlet side of the nanofiltration device, and the water produced by the nanofiltration device is connected to the water inlet side of the reverse osmosis device, so that the water produced by the nanofiltration device enters the reverse osmosis device for concentration treatment, and oxalic acid is obtained at the concentrated water outlet side of the reverse osmosis device.

5. The sodium ion battery positive electrode material production mother liquor recovery system according to claim 4, characterized in that: The operating pressure of the nanofiltration device is 25-30 bar, and the average water production membrane flux is 14-15 LMH; the operating pressure of the reverse osmosis device is 60-70 bar, and the average flux is 14-15 LMH.

6. The sodium ion battery positive electrode material production mother liquor recovery system according to claim 1, characterized in that: The operating pressures of the primary water washing device (3), the secondary water washing device (4) and the tertiary water washing device (5) are all 40-45 bar, and the average water production membrane flux is all 12-15 LMH.

7. A method for recovering mother liquor from the production of sodium ion battery cathode materials, characterized in that: The recovery system according to any one of claims 1 to 6 is used to recover oxalic acid and sodium sulfate from the mother liquor of sodium ion battery positive electrode material production, comprising the following steps: S1, the mother liquor produced by the production of the positive electrode material of the sodium ion battery is collected in the regulating tank (1) and enters the microfiltration device (2) to remove the suspended matter, and the backwash water of the microfiltration device (2) is returned to the regulating tank (1); S2, the effluent from the microfiltration device (2) is mixed with the concentrated water from the nanofiltration device and the produced water from the reverse osmosis device in a volume ratio of 1:2-3, and then enters the primary water washing device (3) after adjusting the pH to 5-6 with sulfuric acid; S3, the produced water of the primary water washing device (3) enters the nanofiltration device, the concentrated water of the primary water washing device (3) is mixed with the concentrated water of the nanofiltration device and the produced water of the reverse osmosis device in a volume ratio of 1:2-3, and then enters the secondary water washing device (4); S4, the produced water of the secondary water washing device (4) enters the nanofiltration device, and the concentrated water of the primary water washing device (3) is mixed with the concentrated water of the nanofiltration device and the produced water of the reverse osmosis device in a volume ratio of 1:2-3, and then enters the tertiary water washing device (5); S5, the produced water of the tertiary water washing device (5) enters the nanofiltration device, and the concentrated water of the tertiary water washing device (5) is sodium sulfate; S6, the water produced by the primary water washing device (3), the secondary water washing device (4) and the tertiary water washing device (5) is mixed and adjusted to pH = 2-3 by sulfuric acid, and then enters the nanofiltration device; S7, the concentrated water of the nanofiltration device is returned to the water washing system, and the produced water of the nanofiltration device enters the reverse osmosis device; S8. The produced water of the reverse osmosis device is returned to the water washing system, and the concentrated water of the reverse osmosis device is oxalic acid.

8. The method for recovering mother liquor from production of sodium ion battery cathode materials according to claim 7, characterized in that: The washing water used in the water washing system requires additional washing water in addition to the concentrated water from the nanofiltration device and the water produced by the reverse osmosis device.

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