Treatment device for wastewater containing oxalic acid and preparation device for sodium battery positive electrode precursor

Abstract

The utility model belongs to the technical field of sodium batteries, and relates to a treatment device for wastewater containing oxalic acid and a preparation device for a sodium battery positive electrode precursor. The treatment device for the wastewater containing the oxalic acid comprises a nanofiltration unit, a reverse osmosis unit, a two-compartment bipolar membrane unit and an acid-resistant reverse osmosis unit. The device provided by the utility model can realize effective separation of sodium sulfate and oxalic acid, so that not only can the sodium sulfate be recycled, but also the oxalic acid defined as a pollutant in the wastewater can be recycled to a production line.

Description

Technical Field

[0001] The present application belongs to the technical field of sodium batteries, and specifically relates to a treatment device for oxalic acid-containing wastewater and a preparation device for a sodium battery positive electrode precursor. Background Art

[0002] The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, and they mainly rely on the movement of sodium ions between the positive and negative electrodes to work. The material cost of sodium-ion batteries is 30-40% lower than that of lithium-ion batteries, and the cost advantage is mainly contributed by the positive electrode materials and the current collector structure. The battery systems of major sodium-ion battery R&D and production companies in the world have their own characteristics, among which the positive electrode technology routes are clearly differentiated, and layered transition metal oxides, anionic compounds and Prussian blue compounds are all used.

[0003] The mainstream manufacturing method for producing sodium battery positive electrode material precursors using the layered transition metal oxide technology route is the oxalic acid layered oxide method. In the process of making sodium battery positive electrode precursors using the oxalic acid layered oxide method, a mother liquor wastewater is generated, and the wastewater composition is 80g / L sodium sulfate and 20g / L oxalic acid. For this wastewater, the current traditional treatment method is chemical precipitation hardness removal combined with evaporation. The oxalate in the mother liquor is removed by two-step precipitation of lime and sodium carbonate, and then the mother liquor is evaporated into alum for sale. However, the process of using chemical precipitation hardness removal combined with evaporation has a high operating cost. A large amount of lime and sodium carbonate needs to be added during the chemical precipitation process, and the cost of adding reagents is high, which increases the operating cost; after adding the reagents, lime and calcium oxalate waste residues will be produced, which will be treated as hazardous waste in some areas with strict solid waste control, increasing the treatment cost and leading to an increase in overall costs. In addition, the overall process of this method only solves the problem from the perspective of governance, and can only recover sodium sulfate, while the oxalic acid in the wastewater is only treated as a pollutant. The higher-value oxalic acid in the wastewater is not recycled as a resource, and the oxalic acid pollutant is only removed by simple and crude excessive addition of drugs and precipitation, which is not in line with the concept of green environmental protection. Utility Model Content

[0004] One of the purposes of the present application is to overcome the defects of being unable to recover oxalic acid and having high operating costs when the existing chemical precipitation hardness removal combined with evaporation method is used to treat the wastewater generated in the process of preparing the positive electrode precursor of a sodium battery by the oxalic acid method, and to provide a new treatment device for oxalic acid-containing wastewater. When the device is used to treat the wastewater generated in the process of preparing the positive electrode precursor of a sodium battery by the oxalic acid method, oxalic acid and sodium sulfate can be recovered at the same time with low operating costs.

[0005] The second purpose of the present application is to provide a device for preparing a positive electrode precursor for a sodium battery.

[0006] Specifically, the treatment device for oxalic acid-containing wastewater provided in the present application includes a nanofiltration unit, a reverse osmosis unit, a two-compartment bipolar membrane unit, and an acid-resistant reverse osmosis unit;

[0007] The interception side of the nanofiltration unit is provided with an oxalic acid-containing wastewater inlet and a water source inlet, and the permeation side of the nanofiltration unit is provided with a sodium hydrogen oxalate solution outlet;

[0008] The interception side of the reverse osmosis unit is provided with a sodium hydrogen oxalate solution inlet and a high-concentration sodium hydrogen oxalate outlet, and the sodium hydrogen oxalate solution inlet on the interception side of the reverse osmosis unit is connected to the sodium hydrogen oxalate solution outlet on the permeation side of the nanofiltration unit;

[0009] The two-compartment bipolar membrane unit comprises a salt chamber and an alkali chamber; the salt chamber is provided with a salt chamber water inlet and a salt chamber water outlet, the salt chamber water inlet is connected to the high-concentration sodium hydrogen oxalate outlet on the interception side of the reverse osmosis unit; the alkali chamber is provided with an alkali chamber water inlet, and the alkali chamber water inlet is connected to a water source;

[0010] An oxalic acid source inlet and an oxalic acid outlet are arranged on the interception side of the acid-resistant reverse osmosis unit, and the oxalic acid source inlet is communicated with the salt chamber water outlet of the salt chamber of the two-compartment bipolar membrane unit.

[0011] The present application also provides a device for preparing a positive electrode precursor of a sodium battery, which includes a wastewater outlet, which is connected to an oxalic acid-containing wastewater inlet on the interception side of a nanofiltration unit in the above-mentioned oxalic acid-containing wastewater treatment device.

[0012] The key to the treatment device of oxalic acid wastewater provided by the present application is to cooperate the nanofiltration unit, the reverse osmosis unit, the two-compartment bipolar membrane unit and the acid-resistant reverse osmosis unit, so that the oxalic acid wastewater is sequentially subjected to nanofiltration treatment, reverse osmosis treatment, bipolar membrane conversion treatment and acid-resistant reverse osmosis treatment to achieve effective separation of sodium sulfate and oxalic acid, thereby not only realizing the recycling of sodium sulfate, but also realizing the reuse of oxalic acid defined as a pollutant in the wastewater to the production line, reducing production and operation costs. In addition, the treatment method of oxalic acid wastewater provided by the present application removes the drug addition precipitation link, saves the cost of using drugs in the drug addition precipitation process, saves the processing cost, and the overall process is a green and sustainable process, in line with the green environmental protection concept. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of a treatment device for oxalic acid-containing wastewater provided in this application;

[0014] Figure 2 Schematic diagram of a two-compartment bipolar membrane provided for this application.

[0015] Description of Reference Numerals

[0016] 100-nanofiltration unit; 200-reverse osmosis unit; 300-two-compartment bipolar membrane unit; 400-acid-resistant reverse osmosis unit. DETAILED DESCRIPTION

[0017] like Figure 1 As shown, the treatment device for oxalic acid-containing wastewater provided in the present application includes a nanofiltration unit 100 , a reverse osmosis unit 200 , a two-compartment bipolar membrane unit 300 , and an acid-resistant reverse osmosis unit 400 .

[0018] Nanofiltration unit

[0019] The interception side of the nanofiltration unit 100 is provided with an oxalic acid-containing wastewater inlet and a water source inlet, and the permeation side of the nanofiltration unit is provided with a sodium hydrogen oxalate solution outlet. Among them, the oxalic acid-containing wastewater inlet is used to introduce oxalic acid-containing wastewater, and the water source inlet is used to introduce water. The oxalic acid-containing wastewater is subjected to nanofiltration treatment in the nanofiltration unit 100, and water is added to the interception side during the nanofiltration treatment process so that the purity of the sodium sulfate solution on the interception side reaches more than 90%, and the permeation side contains sodium hydrogen oxalate solution.

[0020] The core component of the nanofiltration unit 100 is a nanofiltration membrane (NF membrane). A nanofiltration membrane is a filter membrane with a pore size between ultrafiltration and reverse osmosis. The nanofiltration membrane is preferably a disc-tube nanofiltration membrane. Compared with a roll-type or other operation modes, the disc-tube nanofiltration membrane has the characteristics of wide flow channel, short process and turbulent operation, and thus has the advantages of high recovery rate, simple pretreatment, pollution resistance, easy cleaning and long service life. The disc-tube nanofiltration membrane is preferably selected from at least one of a polyamide nanofiltration membrane, a triazine ring nanofiltration membrane, a sulfonated polymer nanofiltration membrane and a polyelectrolyte nanofiltration membrane, and is most preferably a polyamide nanofiltration membrane. In addition, the diaphragm in the disc-tube nanofiltration membrane preferably adopts a three-layer composite nanofiltration membrane, which has better anti-pollution performance, stable operation, and is relatively less affected by water quality fluctuations.

[0021] In a preferred embodiment, the nanofiltration unit includes a primary nanofiltration membrane, a secondary nanofiltration membrane and a tertiary nanofiltration membrane, the inlet of the oxalic acid-containing wastewater of the nanofiltration unit is arranged on the interception side of the primary nanofiltration membrane, the permeation side water outlet of the primary nanofiltration membrane is connected to the interception side water inlet of the secondary nanofiltration membrane, the permeation side water outlet of the secondary nanofiltration membrane is connected to the interception side water inlet of the tertiary nanofiltration membrane, and the sodium hydrogen oxalate solution outlet of the nanofiltration unit is arranged on the permeation side of the tertiary nanofiltration membrane, at this time, sodium sulfate and oxalic acid can be separated more thoroughly to obtain sodium sulfate and oxalic acid with higher purity. Furthermore, the molecular weight cutoff of the primary nanofiltration membrane, the secondary nanofiltration membrane and the tertiary nanofiltration membrane is preferably independently 100 to 200 Da, such as 100 Da, 120 Da, 140 Da, 160 Da, 180 Da, 200 Da or any value therebetween. In addition, when the above three-stage nanofiltration membrane is used to treat oxalic acid-containing wastewater, the conditions for the first-stage nanofiltration treatment preferably include a temperature of 25 to 35°C, such as 25°C, 28°C, 30°C, 32°C, 35°C or any value therebetween; a membrane inlet pressure of 25 to 35 bar, such as 25 bar, 28 bar, 30 bar, 32 bar, 35 bar or any value therebetween; a pH value of 2 to 3, such as 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. The conditions for the secondary nanofiltration treatment preferably include a temperature of 25 to 35°C, such as 25°C, 28°C, 30°C, 32°C, 35°C or any value therebetween; a membrane inlet pressure of 25 to 35 bar, such as 25 bar, 28 bar, 30 bar, 32 bar, 35 bar or any value therebetween; a pH value of 2 to 3, such as 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. The conditions for the three-stage nanofiltration treatment preferably include a temperature of 25 to 35°C, such as 25°C, 28°C, 30°C, 32°C, 35°C or any value therebetween; a membrane inlet pressure of 25 to 35 bar, such as 25 bar, 28 bar, 30 bar, 32 bar, 35 bar or any value therebetween; and a pH value of 2 to 3, such as 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. The pH value refers to the pH value of the solution to be treated by nanofiltration.

[0022] In a preferred embodiment, the primary nanofiltration membrane, the secondary nanofiltration membrane and the tertiary nanofiltration membrane are preferably each independently selected from at least one of a polyamide nanofiltration membrane, a triazine ring nanofiltration membrane, a sulfonated polymer nanofiltration membrane and a polyelectrolyte nanofiltration membrane, more preferably a polyamide membrane.

[0023] Reverse Osmosis Unit

[0024] The interception side of the reverse osmosis unit is provided with an inlet for a sodium hydrogen oxalate solution and an outlet for a high-concentration sodium hydrogen oxalate solution, and the inlet for the sodium hydrogen oxalate solution on the interception side of the reverse osmosis unit is connected to the outlet for the sodium hydrogen oxalate solution on the permeation side of the nanofiltration unit. The sodium hydrogen oxalate solution is subjected to reverse osmosis treatment in the reverse osmosis unit 200, and a high-concentration sodium hydrogen oxalate solution with a concentration of 0.2 to 0.3 mol / L is obtained on the interception side.

[0025] The reverse osmosis membrane used in the reverse osmosis treatment is preferably a polyamide membrane. In addition, the conditions for the reverse osmosis treatment preferably include a temperature of 25 to 35°C, such as 25°C, 28°C, 30°C, 32°C, 35°C or any value therebetween; and a membrane inlet pressure of 20 to 30 bar, such as 20 bar, 22 bar, 24 bar, 26 bar, 28 bar, 30 bar or any value therebetween.

[0026] Two compartment bipolar membrane unit

[0027] The two-compartment bipolar membrane unit 300 includes a salt chamber and an alkali chamber; the salt chamber is provided with a salt chamber water inlet and a salt chamber water outlet, and the salt chamber water inlet is connected to the high-concentration sodium hydrogen oxalate outlet on the interception side of the reverse osmosis unit; the alkali chamber is provided with an alkali chamber water inlet, and the alkali chamber water inlet is connected to a water source.

[0028] like Figure 2 As shown, the two-compartment bipolar membrane unit 300 generally includes an anode, a cathode, and a membrane assembly arranged between the anode and the cathode, the membrane assembly includes M bipolar membranes (BP membranes) and M-1 anion exchange membranes (C membranes) arranged alternately in sequence from the anode to the cathode, M is an integer greater than 2; the positive membrane side of the bipolar membrane faces the cathode, the negative membrane side (C layer) of the bipolar membrane and the anion exchange membrane form a salt chamber, and the positive membrane side (A layer) and the anion exchange membrane form an alkali chamber. A high-concentration sodium hydrogen oxalate solution is introduced from the water inlet of the salt chamber, and water is introduced from the water inlet of the alkali chamber. After the bipolar membrane conversion treatment, the sodium hydrogen oxalate in the salt chamber is converted into oxalic acid, and the water in the alkali chamber is converted into sodium hydroxide.

[0029] The conditions for the bipolar membrane conversion treatment using a two-compartment bipolar membrane unit are not particularly limited, as long as the sodium hydrogen oxalate in the salt chamber can be converted into oxalic acid. Preferably, the conditions for the bipolar membrane conversion treatment include a temperature of 25 to 35°C, such as 25°C, 28°C, 30°C, 32°C, 35°C or any value therebetween;

[0030] Acid-resistant reverse osmosis unit

[0031] The interception side of the acid-resistant reverse osmosis unit 400 is provided with an oxalic acid source inlet and an oxalic acid outlet, and the oxalic acid source inlet is connected to the salt chamber outlet of the salt chamber of the two-compartment bipolar membrane unit. The salt chamber product of the two-compartment bipolar membrane unit 300 is introduced into the acid-resistant reverse osmosis unit 400 for acid-resistant reverse osmosis treatment, and an oxalic acid solution with a concentration of 0.8 to 1 mol / L is obtained on the interception side.

[0032] The pressure-resistant reverse osmosis membrane is preferably a polyamide membrane. In addition, the conditions for the acid-resistant reverse osmosis treatment preferably include a temperature of 25 to 35°C, such as 25°C, 28°C, 30°C, 32°C, 35°C or any value therebetween; and a membrane inlet pressure of 50 to 60 bar, such as 50 bar, 52 bar, 54 bar, 56 bar, 58 bar, 60 bar or any value therebetween.

[0033] In a preferred embodiment, the treatment device for oxalic acid-containing wastewater also includes an evaporation and concentration unit, which is connected to the water outlet on the interception side of the nanofiltration unit. At this time, the sodium sulfate solution produced on the interception side of the nanofiltration unit can be evaporated and concentrated to produce alum, which can achieve resource utilization.

[0034] During operation, oxalic acid-containing wastewater is introduced from the inlet of oxalic acid-containing wastewater into the interception side of the nanofiltration unit for nanofiltration treatment, and water (introduced from the water source inlet) is continuously added to the interception side, and the amount of water used is such that the purity of the sodium sulfate solution on the interception side reaches more than 90%, and the permeate side is a sodium hydrogen oxalate solution; the sodium sulfate solution can be made into glauber powder for sale after evaporation and concentration; the sodium hydrogen oxalate solution is introduced from the inlet of the sodium hydrogen oxalate solution into the reverse osmosis unit for reverse osmosis treatment, and a high-concentration sodium hydrogen oxalate solution with a concentration of 0.2-0.3 mol / L is obtained on the interception side; the high-concentration sodium hydrogen oxalate solution and water are respectively introduced into the salt chamber and the alkali chamber of the two-compartment bipolar membrane for bipolar membrane conversion treatment to obtain a salt chamber product and an alkali chamber product; the salt chamber product is introduced into the acid-resistant reverse osmosis unit for acid-resistant reverse osmosis treatment to obtain an oxalic acid solution with a concentration of 0.8-1 mol / L.

[0035] Specifically, when the oxalic acid-containing wastewater treatment device provided in the present application is used to treat the wastewater generated in the process of preparing the positive electrode precursor of a sodium battery by the oxalic acid method, the corresponding treatment method includes the following steps:

[0036] S1. The oxalic acid-containing wastewater is subjected to nanofiltration treatment, and water is added to the interception side during the nanofiltration treatment process so that the purity of the sodium sulfate solution on the interception side reaches more than 90%, and the permeate side contains sodium hydrogen oxalate solution;

[0037] S2, subjecting the sodium hydrogen oxalate solution to reverse osmosis treatment to obtain a high-concentration sodium hydrogen oxalate solution with a concentration of 0.2 to 0.3 mol / L on the interception side;

[0038] S3, introducing a high concentration sodium hydrogen oxalate solution and water into the salt chamber and the alkali chamber of the two-compartment bipolar membrane respectively for bipolar membrane conversion treatment to obtain a salt chamber product and an alkali chamber product;

[0039] S4. The salt chamber product is subjected to acid-resistant reverse osmosis treatment to obtain an oxalic acid solution with a concentration of 0.8 to 1 mol / L on the interception side.

[0040] In the present application, oxalic acid-containing wastewater is wastewater generated in the process of preparing a sodium battery positive electrode precursor using the oxalic acid method. The specific process is well known to those skilled in the art and will not be described in detail here. Oxalic acid-containing wastewater contains oxalic acid and sodium sulfate. Among them, the content of oxalic acid is preferably 15 to 25 g / L, such as 15, 18, 20, 22, 25 g / L or any value therebetween. The content of sodium sulfate is preferably 70 to 90 g / L, such as 70, 72, 75, 78, 80, 82, 85, 88, 90 g / L or any value therebetween. In addition, the pH value of oxalic acid-containing wastewater is generally 11 to 12, such as 11, 11.2, 11.4, 11.6, 11.8, 12 or any value therebetween.

[0041] In the present application, oxalic acid and sodium sulfate in oxalic acid-containing wastewater cannot be separated by nanofiltration membrane. The present application skillfully adds water to the interception side, so that the existence form of oxalate radical changes, thereby realizing the separation of oxalate radical and sulfate radical. Wherein, the amount of water is based on the purity of the sodium sulfate solution on the interception side reaching more than 90% (specifically, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100% or any value therebetween). At this time, the sodium sulfate solution on the interception side has a higher purity and can be further concentrated by evaporation to be made into sodium sulfate and then sold to increase the value.

[0042] The preparation device of the positive electrode precursor of a sodium battery provided in the present application includes a wastewater outlet, and the wastewater outlet is connected to the oxalic acid-containing wastewater inlet on the interception side of the nanofiltration unit in the treatment device for oxalic acid-containing wastewater. The improvement of the present application is to use a specific device to treat the wastewater generated in the process of preparing the positive electrode precursor of a sodium battery by the oxalic acid method to recover sodium sulfate and oxalic acid, and the device for preparing the positive electrode precursor of a sodium battery by the oxalic acid method can be the same as the prior art, which is known to those skilled in the art and will not be described in detail here.

[0043] The present application will be described in detail below through examples.

[0044] In the following examples and comparative examples:

[0045] The primary nanofiltration membrane is made of polyamide with a molecular weight cutoff of 200Da;

[0046] The secondary nanofiltration membrane is made of polyamide with a molecular weight cutoff of 200Da;

[0047] The material of the third-stage nanofiltration membrane is polyamide, with a molecular weight cutoff of 200Da;

[0048] The reverse osmosis membrane is made of polyamide with a molecular weight cutoff of 200Da;

[0049] The two-compartment bipolar membrane is NEOSEPTA@BP-1E from ASTOM, Japan;

[0050] The acid-resistant reverse osmosis membrane is Industrial RO58040F35 produced by Beijing Shengda Weixin Technology Development Co., Ltd.

[0051] Example 1

[0052] The treatment device for oxalic acid-containing wastewater used in this embodiment includes a nanofiltration unit, a reverse osmosis unit, a two-compartment bipolar membrane unit, and an acid-resistant reverse osmosis unit. The interception side of the nanofiltration unit is provided with an oxalic acid-containing wastewater inlet and a water source inlet, and the permeation side of the nanofiltration unit is provided with a sodium hydrogen oxalate solution outlet; the interception side of the reverse osmosis unit is provided with a sodium hydrogen oxalate solution inlet and a high-concentration sodium hydrogen oxalate outlet, and the sodium hydrogen oxalate solution inlet on the interception side of the reverse osmosis unit is connected with the sodium hydrogen oxalate solution outlet on the permeation side of the nanofiltration unit; the two-compartment bipolar membrane unit includes a salt chamber and an alkali chamber; the salt chamber is provided with a salt chamber water inlet and a salt chamber water outlet, and the salt chamber water inlet is connected with the high-concentration sodium hydrogen oxalate outlet on the interception side of the reverse osmosis unit; the alkali chamber is provided with an alkali chamber water inlet, and the alkali chamber water inlet is connected with the water source; the interception side of the acid-resistant reverse osmosis unit is provided with an oxalic acid source inlet and an oxalic acid outlet, and the oxalic acid source inlet is connected with the salt chamber water outlet of the salt chamber of the two-compartment bipolar membrane unit.

[0053] When the above device is used to treat oxalic acid-containing wastewater, the specific steps include:

[0054] S1. The oxalic acid-containing wastewater (wastewater produced in the process of preparing the positive electrode precursor of the sodium battery by the oxalic acid method, which contains 15g / L oxalic acid and 70g / L sodium sulfate and has a pH value of 11) is subjected to three-stage nanofiltration treatment. During the nanofiltration treatment, water is added to the interception side of each nanofiltration membrane. The amount of water is such that the purity of the sodium sulfate solution on the interception side reaches 90%, and a sodium hydrogen oxalate solution is obtained at the water outlet. The sodium sulfate solution can be made into glauber powder for sale after evaporation and concentration. The nanofiltration membranes used in the three-stage nanofiltration treatment are all polyamide disc-tube nanofiltration membranes. The conditions for the first-stage nanofiltration treatment include a temperature of 25°C, a membrane pressure of 25bar, and a pH value of 2; the conditions for the second-stage nanofiltration treatment include a temperature of 35°C, a membrane pressure of 30bar, and a pH value of 2.5; the conditions for the third-stage nanofiltration treatment include a temperature of 30°C, a membrane pressure of 35bar, and a pH value of 3.

[0055] S2, subjecting the sodium hydrogen oxalate solution to reverse osmosis treatment to obtain a high-concentration sodium hydrogen oxalate solution with a concentration of 0.2 mol / L on the interception side. The reverse osmosis treatment conditions include a temperature of 30° C. and a membrane inlet pressure of 20 bar.

[0056] S3. Introduce a highly concentrated sodium hydrogen oxalate solution and water into the salt chamber and the alkali chamber of the two-compartment bipolar membrane respectively and perform bipolar membrane conversion treatment at 30° C. to obtain a salt chamber product and an alkali chamber product.

[0057] S4. Introducing the salt chamber product into an acid-resistant reverse osmosis unit for acid-resistant reverse osmosis treatment. The conditions of the acid-resistant reverse osmosis treatment include a temperature of 30° C. and a membrane inlet pressure of 50 bar, to obtain an oxalic acid solution with a concentration of 0.8 mol / L and a purity of 96%.

[0058] Example 2

[0059] The treatment device for oxalic acid-containing wastewater used in this embodiment includes a nanofiltration unit, a reverse osmosis unit, a two-compartment bipolar membrane unit, and an acid-resistant reverse osmosis unit. The interception side of the nanofiltration unit is provided with an oxalic acid-containing wastewater inlet and a water source inlet, and the permeation side of the nanofiltration unit is provided with a sodium hydrogen oxalate solution outlet; the interception side of the reverse osmosis unit is provided with a sodium hydrogen oxalate solution inlet and a high-concentration sodium hydrogen oxalate outlet, and the sodium hydrogen oxalate solution inlet on the interception side of the reverse osmosis unit is connected with the sodium hydrogen oxalate solution outlet on the permeation side of the nanofiltration unit; the two-compartment bipolar membrane unit includes a salt chamber and an alkali chamber; the salt chamber is provided with a salt chamber water inlet and a salt chamber water outlet, and the salt chamber water inlet is connected with the high-concentration sodium hydrogen oxalate outlet on the interception side of the reverse osmosis unit; the alkali chamber is provided with an alkali chamber water inlet, and the alkali chamber water inlet is connected with the water source; the interception side of the acid-resistant reverse osmosis unit is provided with an oxalic acid source inlet and an oxalic acid outlet, and the oxalic acid source inlet is connected with the salt chamber water outlet of the salt chamber of the two-compartment bipolar membrane unit.

[0060] When the above device is used to treat oxalic acid-containing wastewater, the specific steps include:

[0061] S1. The oxalic acid-containing wastewater (wastewater produced in the process of preparing the positive electrode precursor of the sodium battery by the oxalic acid method, which contains 25g / L oxalic acid and 90g / L sodium sulfate and has a pH value of 12) is subjected to three-stage nanofiltration treatment. During the nanofiltration treatment, water is added to the interception side of each nanofiltration membrane. The amount of water is such that the purity of the sodium sulfate solution on the interception side reaches 92%, and a sodium hydrogen oxalate solution is obtained at the water outlet. The sodium sulfate solution can be made into glauber powder for sale after evaporation and concentration. The nanofiltration membranes used in the three-stage nanofiltration treatment are all polyamide disc-tube nanofiltration membranes. The conditions for the first-stage nanofiltration treatment include a temperature of 35°C, a membrane pressure of 30bar, and a pH value of 3; the conditions for the second-stage nanofiltration treatment include a temperature of 25°C, a membrane pressure of 25bar, and a pH value of 2; the conditions for the third-stage nanofiltration treatment include a temperature of 30°C, a membrane pressure of 35bar, and a pH value of 2.5.

[0062] S2. The sodium hydrogen oxalate solution is subjected to reverse osmosis treatment to obtain a high-concentration sodium hydrogen oxalate solution with a concentration of 0.3 mol / L on the interception side. The reverse osmosis treatment conditions include a temperature of 30° C. and a membrane inlet pressure of 30 bar.

[0063] S3. Introduce a highly concentrated sodium hydrogen oxalate solution and water into the salt chamber and the alkali chamber of the two-compartment bipolar membrane respectively and perform bipolar membrane conversion treatment at 30° C. to obtain a salt chamber product and an alkali chamber product.

[0064] S4. Introducing the salt chamber product into an acid-resistant reverse osmosis unit for acid-resistant reverse osmosis treatment. The conditions of the acid-resistant reverse osmosis treatment include a temperature of 30° C. and a membrane inlet pressure of 60 bar to obtain an oxalic acid solution with a concentration of 1 mol / L and a purity of 95%.

[0065] Example 3

[0066] The treatment device for oxalic acid-containing wastewater used in this embodiment includes a nanofiltration unit, a reverse osmosis unit, a two-compartment bipolar membrane unit, and an acid-resistant reverse osmosis unit. The interception side of the nanofiltration unit is provided with an oxalic acid-containing wastewater inlet and a water source inlet, and the permeation side of the nanofiltration unit is provided with a sodium hydrogen oxalate solution outlet; the interception side of the reverse osmosis unit is provided with a sodium hydrogen oxalate solution inlet and a high-concentration sodium hydrogen oxalate outlet, and the sodium hydrogen oxalate solution inlet on the interception side of the reverse osmosis unit is connected with the sodium hydrogen oxalate solution outlet on the permeation side of the nanofiltration unit; the two-compartment bipolar membrane unit includes a salt chamber and an alkali chamber; the salt chamber is provided with a salt chamber water inlet and a salt chamber water outlet, and the salt chamber water inlet is connected with the high-concentration sodium hydrogen oxalate outlet on the interception side of the reverse osmosis unit; the alkali chamber is provided with an alkali chamber water inlet, and the alkali chamber water inlet is connected with the water source; the interception side of the acid-resistant reverse osmosis unit is provided with an oxalic acid source inlet and an oxalic acid outlet, and the oxalic acid source inlet is connected with the salt chamber water outlet of the salt chamber of the two-compartment bipolar membrane unit.

[0067] When the above device is used to treat oxalic acid-containing wastewater, the specific steps include:

[0068] S1. The oxalic acid-containing wastewater (wastewater produced in the process of preparing the positive electrode precursor of the sodium battery by the oxalic acid method, which contains 20g / L oxalic acid and 80g / L sodium sulfate and has a pH value of 11.5) is subjected to three-stage nanofiltration treatment. During the nanofiltration treatment, water is added to the interception side of each nanofiltration membrane. The amount of water is such that the purity of the sodium sulfate solution on the interception side reaches 95%, and the sodium hydrogen oxalate solution is obtained at the water outlet. The sodium sulfate solution can be made into glauber powder for sale after evaporation and concentration. The nanofiltration membranes used in the three-stage nanofiltration treatment are all polyamide disc-tube nanofiltration membranes. The conditions for the first-stage nanofiltration treatment include a temperature of 35°C, a membrane pressure of 25bar, and a pH value of 2; the conditions for the second-stage nanofiltration treatment include a temperature of 25°C, a membrane pressure of 35bar, and a pH value of 3; the conditions for the third-stage nanofiltration treatment include a temperature of 30°C, a membrane pressure of 30bar, and a pH value of 2.5.

[0069] S2, subjecting the sodium hydrogen oxalate solution to reverse osmosis treatment to obtain a high-concentration sodium hydrogen oxalate solution with a concentration of 0.25 mol / L on the interception side. The reverse osmosis treatment conditions include a temperature of 30° C. and a membrane inlet pressure of 25 bar.

[0070] S3. Introduce a highly concentrated sodium hydrogen oxalate solution and water into the salt chamber and the alkali chamber of the two-compartment bipolar membrane respectively and perform bipolar membrane conversion treatment at 30° C. to obtain a salt chamber product and an alkali chamber product.

[0071] S4. Introducing the salt chamber product into an acid-resistant reverse osmosis unit for acid-resistant reverse osmosis treatment. The conditions of the acid-resistant reverse osmosis treatment include a temperature of 30° C. and a membrane inlet pressure of 55 bar, to obtain an oxalic acid solution of 0.9 mol / L and a purity of 98%.

[0072] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application without departing from the principles and purpose of the present application.

Claims

1. A treatment device for oxalic acid-containing wastewater, characterized in that: It includes nanofiltration unit, reverse osmosis unit, two-compartment bipolar membrane unit and acid-resistant reverse osmosis unit; The interception side of the nanofiltration unit is provided with an oxalic acid-containing wastewater inlet and a water source inlet, and the permeation side of the nanofiltration unit is provided with a sodium hydrogen oxalate solution outlet; The interception side of the reverse osmosis unit is provided with a sodium hydrogen oxalate solution inlet and a high-concentration sodium hydrogen oxalate outlet, and the sodium hydrogen oxalate solution inlet on the interception side of the reverse osmosis unit is connected to the sodium hydrogen oxalate solution outlet on the permeation side of the nanofiltration unit; The two-compartment bipolar membrane unit comprises a salt chamber and an alkali chamber; the salt chamber is provided with a salt chamber water inlet and a salt chamber water outlet, the salt chamber water inlet is connected to the high-concentration sodium hydrogen oxalate outlet on the interception side of the reverse osmosis unit; the alkali chamber is provided with an alkali chamber water inlet, and the alkali chamber water inlet is connected to a water source; The interception side of the acid-resistant reverse osmosis unit is provided with an oxalic acid source inlet and an oxalic acid outlet, and the oxalic acid source inlet is communicated with the salt chamber water outlet of the salt chamber of the two-compartment bipolar membrane unit.

2. The treatment device for oxalic acid-containing wastewater according to claim 1, characterized in that: The nanofiltration membrane used in the nanofiltration unit is a disc-tube nanofiltration membrane.

3. The treatment device for oxalic acid-containing wastewater according to claim 2, characterized in that: The nanofiltration unit comprises a primary nanofiltration membrane, a secondary nanofiltration membrane and a tertiary nanofiltration membrane. The inlet of the wastewater containing oxalic acid of the nanofiltration unit is arranged on the retention side of the primary nanofiltration membrane, the water outlet on the permeate side of the primary nanofiltration membrane is communicated with the water inlet on the retention side of the secondary nanofiltration membrane, the water outlet on the permeate side of the secondary nanofiltration membrane is communicated with the water inlet on the retention side of the tertiary nanofiltration membrane, and the outlet of the sodium hydrogen oxalate solution of the nanofiltration unit is arranged on the permeate side of the tertiary nanofiltration membrane.

4. The treatment device for oxalic acid-containing wastewater according to claim 3, characterized in that: The primary nanofiltration membrane, the secondary nanofiltration membrane and the tertiary nanofiltration membrane are each independently selected from at least one of a polyamide nanofiltration membrane, a triazine ring nanofiltration membrane, a sulfonated polymer nanofiltration membrane and a polyelectrolyte nanofiltration membrane.

5. The treatment device for oxalic acid-containing wastewater according to claim 3, characterized in that: The molecular weight cutoffs of the primary nanofiltration membrane, the secondary nanofiltration membrane and the tertiary nanofiltration membrane are independently 100 to 200 Da.

6. The device for treating oxalic acid-containing wastewater according to any one of claims 1 to 5, characterized in that: The reverse osmosis membrane used in the reverse osmosis unit is a polyamide membrane.

7. The device for treating oxalic acid-containing wastewater according to any one of claims 1 to 5, characterized in that: The two-compartment bipolar membrane used in the two-compartment bipolar membrane unit includes an anode, a cathode and a membrane assembly arranged between the anode and the cathode, wherein the membrane assembly includes M bipolar membranes and M-1 anion exchange membranes arranged alternately in sequence from the anode to the cathode, where M is an integer greater than 2; the cation membrane side of the bipolar membrane faces the cathode, the anion membrane side of the bipolar membrane and the anion exchange membrane form a salt chamber, and the cation membrane side and the anion exchange membrane form an alkali chamber.

8. The device for treating oxalic acid-containing wastewater according to any one of claims 1 to 5, characterized in that: The acid-resistant reverse osmosis membrane used in the acid-resistant reverse osmosis unit is a polyamide membrane.

9. The device for treating oxalic acid-containing wastewater according to any one of claims 1 to 5, characterized in that: The device for treating oxalic acid-containing wastewater further comprises an evaporation concentration unit, and the evaporation concentration unit is connected to a water outlet on the interception side of the nanofiltration unit.

10. A preparation device for a sodium battery positive electrode precursor, characterized in that: The sodium battery positive electrode precursor preparation device comprises a wastewater outlet, which is connected to the oxalic acid-containing wastewater inlet on the interception side of the nanofiltration unit in the oxalic acid-containing wastewater treatment device according to any one of claims 1 to 9.

Images