Process method for recycling waste liquid of prussian blue analogue positive electrode material

Abstract

The application discloses a process method for recycling waste liquid of Prussian blue analogue positive electrode material, and belongs to the technical field of sodium ion battery positive electrode materials. The recycling method is mainly divided into synthesis filtering waste liquid and cleaning waste liquid: the synthesis waste liquid is stored in a storage tank after evaporation, iron removal by adding alkali, and cooling and crystallization of sodium sulfate; a small amount of sodium hydroxide and PAC and PAM are added to the cleaning waste liquid, so that the iron hydroxide generated by the reaction of the waste liquid is quickly flocculated and precipitated in lumps, and the supernatant is transferred to a low-concentration storage tank within a certain time; after the waste liquid in the two tanks is neutralized by sulfuric acid, sodium citrate and sodium sulfate are added, and deoxygenation is performed, the waste liquid is respectively reused to a premix kettle and a reaction kettle to participate in synthesis; the filter cake iron slag is reduced to ferrous sulfate, and the crystalline salt is recycled to mother liquor preparation. The whole process is protected by inert atmosphere to ensure the stability of the product, the mother liquor can be recycled, the by-product salt and iron raw material can be recycled, the output of waste water and hazardous waste is greatly reduced, the utilization rate of raw materials is improved, the production and environmental protection disposal cost is reduced, and green consumption reduction production is realized.

Description

Technical Field

[0001] This invention relates to the field of cathode materials for sodium-ion batteries, and specifically to a process for recycling waste liquid from a Prussian blue analog cathode material. Background Technology

[0002] Sodium-ion batteries, as potential chemical energy storage devices in the field of large-scale energy storage, rely heavily on the performance and cost of their cathode materials for industrialization. Currently, sodium-ion battery cathode materials are mainly classified into three categories: transition metal oxides, polyanionic compounds, and Prussian blue analogs. Among them, Prussian blue analogs, with their simple synthesis process, low raw material cost, and unique rigid open framework structure, offer significant advantages. They enable rapid insertion and extraction of sodium ions without lattice distortion, exhibit excellent cycle performance, and possess high theoretical capacity. Therefore, they occupy an important position among sodium-ion battery cathode materials and have become one of the current hot research directions for industrialization.

[0003] The industrial synthesis of Prussian blue analog cathode materials often employs a co-precipitation method, which generates a large amount of industrial wastewater. This wastewater mainly contains high concentrations of soluble salts (such as sodium sulfate), organic complexing agents (such as sodium citrate), and trace amounts of transition metal ions. Current technologies primarily treat this wastewater by evaporation crystallization or direct dilution into low-concentration salt solutions before discharge. However, evaporation crystallization processes are extremely energy-intensive, have high operating costs, and are prone to causing equipment scaling and corrosion. Direct discharge, on the other hand, leads to the waste of valuable resources such as salts and organic complexing agents in the wastewater, while also increasing the burden on environmental protection, which is inconsistent with the current industrial development concepts of green production, energy conservation and noise reduction, and resource recycling.

[0004] Therefore, how to efficiently treat the waste liquid generated during the synthesis of Prussian blue analog cathode materials, realize the recovery and recycling of useful resources in the waste liquid, reduce treatment costs, reduce resource waste and environmental pollution, and meet the needs of green industrial production has become an important research topic that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention proposes a waste liquid recycling synthesis process for Prussian blue analogue cathode materials used in sodium-ion batteries. The process primarily focuses on recovering and recycling the waste liquid generated during cathode material synthesis. The recovery method mainly involves two parts: synthesis filtration waste liquid and washing waste liquid. For the synthesis filtration waste liquid, evaporation is used to increase the concentration, and sodium hydroxide is added to precipitate ferrous ions, which are then filtered. The waste liquid, after removing ferrous ions, is cooled to crystallize and precipitate some sodium sulfate, and the supernatant is transferred to a storage tank. The washing waste liquid, due to its extremely low salt concentration and mainly consisting of trace amounts of sodium citrate, sodium sulfate, and ferrous sulfate, is similarly treated with small amounts of sodium hydroxide, PAC (polyaluminum chloride), and PAM (polyacrylamide). This causes the ferrous hydroxide produced in the reaction to rapidly flocculate and precipitate under the action of PAC and PAM, and the supernatant is transferred to a low-concentration storage tank within a certain time. Sulfuric acid is dripped into both storage tanks for neutralization, and small amounts of sodium citrate and sodium sulfate are added to adjust the concentration and deoxygenate the solution. This solution is then used as mother liquor for the next synthesis reaction and recycled.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A process for recycling waste liquid from a Prussian blue analogue cathode material includes the following steps:

[0008] (1) For the first reaction, in order to ensure the consistency of the positive electrode material produced, a certain concentration of sodium sulfate solution and sodium citrate solution are added to the premixing reactor 1, premixing reactor 2 and reaction vessel under the protection of nitrogen or argon. Ferrous sulfate and sodium ferrocyanide are added to the premixing reactor 1 and premixing reactor 2 respectively. Stir for 30 min - 120 min and add dropwise for 30 min - 720 min.

[0009] (2) After the addition is completed, stir and age the reaction solution, then transfer it to a stirred filter vessel. Keep the inert gas protection and filter under pressure in the stirred filter vessel. The filter cake is the positive electrode material of the target Prussian blue analogue and is retained in the stirred filter vessel. The synthesis waste liquid generated after filtration is transferred to the stirred vessel. Add deoxygenated deionized water to the stirred filter vessel and stir to wash the filter cake. The washing time is 10 min to 60 min. After the washing is completed, filter the washing liquid under pressure into a stirred precipitation vessel.

[0010] (3) Add sodium hydroxide solution to the stirred tank containing the synthesized waste liquid, and evaporate and concentrate it under normal pressure. The water vapor generated by evaporation is condensed and collected in the water storage tank. The system is in contact with trace air in an alkaline and high temperature environment. Ferrous ions are oxidized to ferric ions. Sodium hydroxide is used to convert ferrous ions in the waste liquid into ferric hydroxide precipitate.

[0011] After evaporation, the system is transferred to positive pressure filter one; the positive pressure filter one is pressurized to 0.1 MPa - 1.0 MPa to retain the ferric hydroxide filter cake, and the waste liquid is transferred to the crystallization kettle. The system is cooled and crystallized in the crystallization kettle at a temperature of 10℃-40℃. After sodium sulfate crystals precipitate, the supernatant is transferred to stirred storage tank one.

[0012] (4) Maintain inert gas protection, add sodium hydroxide, PAC and PAM to the cleaning solution in the stirred sedimentation tank in sequence, stir the cleaning solution for 10 min-60 min, age for 1 h-24 h, after aging, transfer the supernatant to the stirred storage tank 2, and treat the precipitated substances as hazardous waste after separation.

[0013] (5) The waste liquid in the stirred storage tank 1 and stirred storage tank 2 are uniformly adjusted: keep the inert gas protection, add sulfuric acid to the stirred storage tank for neutralization, and then add sodium citrate and sodium sulfate according to the standard concentration of the base solution of the first reaction; before the next synthesis begins, add the mother liquor in stirred storage tank 1 to the premixing kettle according to the calculated concentration and amount of mother liquor, and add the mother liquor in stirred storage tank 2 to the reaction kettle according to the calculated concentration and amount of mother liquor, so as to replace the fresh aqueous solution in the synthesis reaction and realize the mother liquor recycling;

[0014] (6) Mix the ferric hydroxide filter cake retained by the positive pressure filter with iron powder, and add sulfuric acid to react. The resulting ferrous sulfate is used as a raw material for the reaction.

[0015] The sodium sulfate precipitated from the crystallizer, after drying, can also be added to stirred storage tank 1 and stirred storage tank 2 as a control material for adjusting the concentration of the mother liquor.

[0016] Further, in step (1), the concentration of sodium sulfate solution is 0.01 mol / L-0.5 mol / L, and the concentration of sodium citrate solution is 0.05 mol / L-1.0 mol / L. The volume of sodium sulfate solution and sodium citrate solution added to premixing tank one and premixing tank two is 30L-5000L, and the volume of solution added to reaction tank is 10L-1000L. The amount of ferrous sulfate added is 3mol-10000mol, and the amount of sodium ferrocyanide added is 2.5-10000mol.

[0017] Furthermore, in step (2), the stirring is carried out for 10 min to 180 min, the aging is carried out for 1 h to 24 h, and the pressure of the pressure filter is 0.1 Mpa to 1.0 Mpa.

[0018] Furthermore, in step (3), the amount of sodium hydroxide added is 0.5-3400 mol, and the pH value in the system is controlled at 7.0-8.0.

[0019] Furthermore, in step (3), the evaporation and concentration temperature is 90℃-120℃, the evaporation amount is 10%-50% of the waste liquid volume, and after the concentration is completed, the stirring reaction continues for 30 minutes at a stirring speed of 5 r / min-100 r / min.

[0020] Furthermore, the amount of sodium sulfate crystals precipitated in step (3) is equivalent to the amount of sodium sulfate byproduct of the synthesis reaction. The cooling rate is controlled at 1℃ / h - 10℃ / h, the holding time for crystallization is 1h - 12h, and the crystallization is separated by a centrifuge.

[0021] Further, in step (4), the amount of sodium hydroxide added is 0.05-340 mol, the pH value is controlled at 7.0-8.0, the amount of PAC added is 5 g-5000 g, the amount of PAM added is 5 g-5000 g, and the pH value in the system is controlled at 7.0-8.0.

[0022] Further, in step (5), the system is neutralized to a pH of 6.8-7.5, and the amount of sulfuric acid added is 0.05-340 mol.

[0023] Furthermore, in step (6), the reaction temperature is 25℃-60℃, the amount of iron powder added is 0.5-3400mol, the amount of sulfuric acid added is 1-6800mol, and the stirring time is 1h-12h.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention employs a wastewater recycling synthesis process that significantly improves the effective utilization rate of raw materials while fully ensuring the core performance parameters and batch stability of the product, thereby reducing raw material consumption and preparation costs from the source of production. Simultaneously, the new process drastically reduces the generation of wastewater and waste salt during production, effectively lowering the company's environmental protection investment and hazardous waste disposal costs, and reducing resource waste. This invention combines economic efficiency with environmental friendliness, achieving the technical effects of maintaining production quality while reducing consumption and promoting green energy conservation, effectively solving the technical pain points of low raw material utilization and high environmental costs.

[0026] Other features and advantages of the present invention will be described in detail in part in the following detailed description. Attached Figure Description

[0027] Figure 1 This is a flow chart of the waste liquid recycling synthesis process provided in the embodiments of the present invention.

[0028] Figure 1The components are: 1. Premixing vessel one; 2. Reactor; 3. Premixing vessel two; 4. Stirred filter vessel; 5. Stirred sedimentation vessel; 6. Water storage tank; 7. Stirred vessel; 8. Positive pressure filter one; 9. Crystallization tank; 10. Stirred storage tank one; 11. Positive pressure filter two; 12. Stirred storage tank two; 13. Positive pressure filter three. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0030] Example 1

[0031] A waste liquid recycling synthesis process for Prussian blue analogue cathode materials used in sodium-ion batteries, such as... Figure 1 As shown, it includes the following steps:

[0032] (1) For the first reaction, in order to ensure the consistency of the produced cathode material, under the protection of nitrogen or argon, 3 mol of ferrous sulfate was added to a 50L premixing reactor one, and 2.5 mol of sodium ferrocyanide was added to a 50L premixing reactor two. 40L of sodium sulfate and sodium citrate solutions with a concentration of 0.1mol / L were added to premixing reactor one and premixing reactor two respectively, and stirred for 2h.

[0033] Add 20L of sodium sulfate and sodium citrate solutions, each with a concentration of 0.1mol / L, to a 150L reactor and stir for 2 hours;

[0034] The two premixing vessels began to add liquid to the reactor dropwise over a period of 120 minutes.

[0035] (2) After the dropwise reaction is completed, stir for 1 hour and age for 3 hours. Stir again and transfer the reaction solution to a stirred filter vessel. Keep inert gas protection and pressurize to 0.3 MPa in the stirred filter vessel for filtration. Transfer the waste liquid to the stirred vessel and leave the filter cake (positive electrode material) in the stirred filter vessel. Add 40 L of deoxygenated deionized water to the stirred filter vessel and stir to wash the filter cake for 30 min. After washing, pressurize the washing solution and filter it into a stirred precipitation vessel.

[0036] (3) Maintain inert gas protection, heat the stirred tank to 110°C, stir at 50 r / min, condense and collect the evaporated water vapor into the water storage tank. When the original liquid volume is 97 L and the solution in the stirred tank is 50 L, the evaporation rate is 48.45%. Add 10 L of sodium hydroxide solution prepared with 0.55 mol sodium hydroxide solid, stir for 30 min and then transfer to positive pressure filter one.

[0037] Pressurize the positive pressure filter to 0.3 MPa, transfer the waste liquid to the crystallization kettle, and the system comes into contact with air. Ferrous ions are oxidized to ferric ions, and the filter cake (ferric hydroxide) is collected. The crystallization is carried out in the crystallization kettle at a temperature of 15°C for 3 hours. After sodium sulfate is precipitated, the supernatant is transferred to the stirring storage tank.

[0038] (4) Maintain inert gas protection, add 1L of sodium hydroxide solution prepared with 0.05mol sodium hydroxide solid, 5g PAC, and 5g PAM to 40L of cleaning solution in the stirred sedimentation vessel, stir the cleaning solution for 30min, age for 12h, and transfer the supernatant to the stirred storage tank 2 after the end of the process.

[0039] (5) Maintain inert gas protection, gradually add 0.1 mol / L sulfuric acid solution to stirred tank one until the pH value is 7.0-7.2, and add 0.1 mol sodium citrate and 0.1 mol sodium sulfate in a specific ratio, and stir. Add 0.1 mol / L sulfuric acid solution to stirred tank two until the pH value is neutralized to 7.0-7.2, and stir. Before the next synthesis begins, add stirred tank one and stirred tank two to the premixing vessel and reaction vessel in sequence according to the calculated concentration and mother liquor volume;

[0040] (6) Mix the ferric hydroxide filtered out by the positive pressure filter with iron powder, add sulfuric acid, react at 60°C, use 0.5 mol of iron powder and 1 mol of sulfuric acid, stir for 3 hours, and filter under positive pressure at 0.3 MPa; the generated ferrous sulfate is used as a raw material for the reaction.

[0041] The sodium sulfate precipitated from the crystallization tank can be dried and then added as a control material to stirred storage tank 1 and stirred storage tank 2.

[0042] Example 2

[0043] A waste liquid recycling synthesis process for Prussian blue analog cathode material used in sodium-ion batteries includes the following steps:

[0044] (1) For the first reaction, in order to ensure the consistency of the produced cathode material, under the protection of nitrogen or argon, 9 mol of ferrous sulfate was added to a 50L premixing reactor one, and 8.5 mol of sodium ferrocyanide was added to a 50L premixing reactor two. 40L of sodium sulfate solution with a concentration of 0.2mol / L and sodium citrate solution with a concentration of 0.25mol / L were added to the two premixing reactors respectively, and stirred for 5h.

[0045] Add 20L of 0.2mol / L sodium sulfate solution and 0.25mol / L sodium citrate solution to a 150L reactor and stir for 5 hours;

[0046] The two premixing vessels began to add liquid to the reactor dropwise over a period of 240 minutes.

[0047] (2) After the dropwise reaction is completed, stir for 2 hours and age for 12 hours. Stir again and transfer the reaction solution to a stirred filter vessel. Keep inert gas protection and pressurize to 0.6 MPa in the stirred filter vessel for filtration. Transfer the waste liquid to the stirred vessel and leave the filter cake (positive electrode material) in the stirred filter vessel. Add 40 L of deoxygenated deionized water to the stirred filter vessel and stir to wash the filter cake for 30 min. After washing, pressurize the washing solution and filter it into a stirred precipitation vessel.

[0048] (3) Maintain inert gas protection, heat the stirred tank to 100°C, stir at 50 r / min, condense and collect the evaporated water vapor into the water storage tank. When the original liquid volume is 89.8 L and the solution in the stirred tank is 80 L, the evaporation rate is 10.91%. Add 10 L of sodium hydroxide solution prepared with 0.5 mol sodium hydroxide solid, stir for 30 min and then transfer to positive pressure filter one.

[0049] Pressurize the positive pressure filter to 0.3 MPa, transfer the waste liquid to the crystallization kettle, and the system comes into contact with air. Ferrous ions are oxidized to ferric ions, and the filter cake (ferric hydroxide) is collected. The mixture is cooled and crystallized in the crystallization kettle at 35°C for 1 hour. After sodium sulfate is precipitated, the supernatant is transferred to the stirring storage tank.

[0050] (4) Maintain inert gas protection, add 1L sodium hydroxide solution prepared with 0.1mol sodium hydroxide solid, 5g PAC, and 5g PAM to 40L of cleaning solution in the stirred sedimentation tank, stir the cleaning solution for 30min, age for 12h, and transfer the supernatant to the stirred storage tank 2 after the end of the process.

[0051] (5) Maintain inert gas protection, gradually add 0.1 mol / L sulfuric acid solution to stirred tank one until the pH value is 7.0-7.2, and add 0.3 mol sodium citrate and 0.1 mol sodium sulfate in a specific ratio, and stir. Add 0.1 mol / L sulfuric acid solution to stirred tank two until the pH value is neutralized to 7.0-7.2, and stir. Before the next synthesis begins, add stirred tank one and stirred tank two to the premixing vessel and reaction vessel in sequence according to the calculated concentration and mother liquor volume;

[0052] (6) Mix the ferric hydroxide filtered through the positive pressure filter with iron powder, add sulfuric acid, react at 60°C, use 0.5 mol of iron powder and 1 mol of sulfuric acid, stir for 3 hours, and filter under positive pressure at 0.3 MPa. The generated ferrous sulfate is used as a raw material for the reaction.

[0053] The sodium sulfate precipitated from the crystallization tank can be dried and then added as a control material to stirred storage tank 1 and stirred storage tank 2.

[0054] Example 3

[0055] A waste liquid recycling synthesis process for Prussian blue analog cathode material used in sodium-ion batteries includes the following steps:

[0056] (1) For the first reaction, in order to ensure the consistency of the produced cathode material, under the protection of nitrogen or argon, 6 mol of ferrous sulfate was added to a 50L premixing reactor one, and 6 mol of sodium ferrocyanide was added to a 50L premixing reactor two. 50L of sodium sulfate solution with a concentration of 0.15mol / L and sodium citrate solution with a concentration of 0.2mol / L were added to the two premixing reactors respectively, and stirred for 2h.

[0057] Add 20L of 0.15mol / L sodium sulfate solution and 0.2mol / L sodium citrate solution to a 150L reactor and stir for 2 hours;

[0058] The two premixing vessels began to add liquid to the reactor dropwise over a period of 180 minutes.

[0059] (2) After the dropwise reaction is completed, stir for 3 hours and age for 6 hours. Stir again and transfer the reaction solution to a stirred filter vessel. Keep inert gas protection and pressurize to 0.4 MPa in the stirred filter vessel for filtration. Transfer the waste liquid to the stirred vessel and leave the filter cake (positive electrode material) in the stirred filter vessel. Add 40 L of deoxygenated deionized water to the stirred filter vessel and stir to wash the filter cake for 20 minutes. After washing, pressurize the washing solution and filter it into a stirred precipitation vessel.

[0060] (3) Maintain inert gas protection, heat the stirred tank to 110°C, stir at 50 r / min, condense and collect the evaporated water vapor into the water storage tank. When the original liquid volume is 112.8 L and the solution in the stirred tank is 70 L, the evaporation rate is 37.94%. Add 10 L of sodium hydroxide solution prepared with 0.5 mol sodium hydroxide solid, stir for 30 min and then transfer to positive pressure filter one.

[0061] Pressurize the positive pressure filter to 0.3 MPa, transfer the waste liquid to the crystallization kettle, and the system comes into contact with air. Ferrous ions are oxidized to ferric ions, and the filter cake (ferric hydroxide) is collected. The mixture is cooled and crystallized in the crystallization kettle at 25°C for 1 hour. After sodium sulfate is precipitated, the supernatant is transferred to the stirring storage tank.

[0062] (4) Maintain inert gas protection, add 1L sodium hydroxide solution prepared with 0.1mol sodium hydroxide solid, 5g PAC, and 5g PAM to 40L of cleaning solution in the stirred sedimentation tank, stir the cleaning solution for 30min, age for 8h, and transfer the supernatant to the stirred storage tank 2 after the end of the process.

[0063] (5) Maintain inert gas protection, gradually add 0.1 mol / L sulfuric acid solution to stirred tank one until the pH value is 7.0-7.2, and add 0.2 mol sodium citrate and 0.1 mol sodium sulfate in a specific ratio, and stir. Add 0.1 mol / L sulfuric acid solution to stirred tank two until the pH value is neutralized to 7.0-7.2, and stir. Before the next synthesis begins, add stirred tank one and stirred tank two to the premixing vessel and reaction vessel in sequence according to the calculated concentration and mother liquor volume;

[0064] (6) Mix the ferric hydroxide filtered through the positive pressure filter with iron powder, add sulfuric acid, react at 40°C, use 0.5 mol of iron powder and 1 mol of sulfuric acid, stir for 6 hours, and filter under positive pressure at 0.3 MPa. The generated ferrous sulfate is used as a raw material for the reaction.

[0065] The sodium sulfate precipitated from the crystallization tank can be dried and then added as a control material to stirred storage tank 1 and stirred storage tank 2.

[0066] Comparative Example 1

[0067] A waste liquid recycling synthesis process for Prussian blue analog cathode material used in sodium-ion batteries includes the following steps:

[0068] (1) For the first reaction, in order to ensure the consistency of the produced cathode material, under the protection of nitrogen or argon, 9 mol of ferrous sulfate was added to a 50L premixing reactor one, and 8.5 mol of sodium ferrocyanide was added to a 50L premixing reactor two. 40L of 0.25mol / L sodium citrate solution was added to premixing reactor one and premixing reactor two respectively, and stirred for 5h.

[0069] Add 20L of 0.25mol / L sodium citrate solution to a 150L reactor and stir for 5 hours;

[0070] The two premixing vessels began to add liquid to the reactor dropwise over a period of 240 minutes.

[0071] (2) After the dropwise reaction is completed, stir for 2 hours and age for 12 hours. Stir again and transfer the reaction solution to a stirred filter. Pressurize the stirred filter to 0.6 MPa and filter. The filter cake (positive electrode material) remains in the stirred filter. Add 40 L of deoxygenated deionized water to the stirred filter and stir to wash the filter cake for 30 minutes. After washing, pressurize and filter the washing solution.

[0072] Waste liquid is evaporated and crystallized, while waste solid is treated or purified.

[0073] Table 1 shows the cumulative values ​​of main raw materials and waste materials after five batches of synthesis in Example 2.

[0074]

[0075] Table 2 shows the cumulative values ​​of main raw materials and waste after five batches of synthesis in Comparative Example 1.

[0076]

[0077] As can be seen from the comparison table, the raw material consumption of the waste liquid recycling synthesis process can be significantly reduced, including sodium citrate and deionized water. Although sodium sulfate is added in comparison example 1, the amount of sodium sulfate does not change with the production batch. As for the waste produced, apart from the recoverable sodium sulfate, the amount of other waste is basically zero.

[0078] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A process for recycling waste liquid from a Prussian blue analogue cathode material, characterized in that, Includes the following steps: (1) For the first reaction, in order to ensure the consistency of the positive electrode material produced, a certain concentration of sodium sulfate solution and sodium citrate solution are added to the premixing vessel 1, premixing vessel 2 and reaction vessel under the protection of nitrogen or argon. Ferrous sulfate and sodium ferrocyanide are added to the premixing vessel 1 and premixing vessel 2 respectively. Stir for 30min-120min and add dropwise for 30min-720min. (2) After the addition is completed, stir and age the reaction solution, then transfer it to a stirred filter vessel. Keep the inert gas protection and filter under pressure in the stirred filter vessel. The filter cake is the positive electrode material of the target Prussian blue analogue and is retained in the stirred filter vessel. The synthesis waste liquid generated after filtration is transferred to the stirred vessel. Add deoxygenated deionized water to the stirred filter vessel and stir to wash the filter cake. The washing time is 10 min to 60 min. After the washing is completed, filter the washing liquid under pressure into a stirred precipitation vessel. (3) Add sodium hydroxide solution to the stirred tank containing the synthesized waste liquid, and evaporate and concentrate it under normal pressure. The water vapor generated by evaporation is condensed and collected in the water storage tank. The system is in contact with trace air in an alkaline and high temperature environment. Ferrous ions are oxidized to ferric ions. Sodium hydroxide is used to convert ferrous ions in the waste liquid into ferric hydroxide precipitate. After evaporation, the system is transferred to positive pressure filter one; the positive pressure filter one is pressurized to 0.1 MPa - 1.0 MPa to retain the ferric hydroxide filter cake, and the waste liquid is transferred to the crystallization kettle. The system is cooled and crystallized in the crystallization kettle at a temperature of 10℃-40℃. After sodium sulfate crystals precipitate, the supernatant is transferred to stirred storage tank one. (4) Maintain inert gas protection, add sodium hydroxide, PAC and PAM to the cleaning solution in the stirred sedimentation tank in sequence, stir the cleaning solution for 10 min-60 min, age for 1 h-24 h, after aging, transfer the supernatant to the stirred storage tank 2, and treat the precipitated substances as hazardous waste after separation. (5) The waste liquid in the stirred storage tank 1 and stirred storage tank 2 are uniformly adjusted: keep the inert gas protection, add sulfuric acid to the stirred storage tank for neutralization, and then add sodium citrate and sodium sulfate according to the standard concentration of the base solution of the first reaction; before the next synthesis begins, add the mother liquor in stirred storage tank 1 to the premixing kettle according to the calculated concentration and amount of mother liquor, and add the mother liquor in stirred storage tank 2 to the reaction kettle according to the calculated concentration and amount of mother liquor, so as to replace the fresh aqueous solution in the synthesis reaction and realize the mother liquor recycling; (6) Mix the ferric hydroxide filter cake retained by the positive pressure filter with iron powder, and add sulfuric acid to react. The resulting ferrous sulfate is used as a raw material for the reaction. The sodium sulfate precipitated from the crystallizer, after drying, can also be added to stirred storage tank 1 and stirred storage tank 2 as a control material for adjusting the concentration of the mother liquor.

2. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (1), the concentration of sodium sulfate solution is 0.01mol / L-0.5mol / L, and the concentration of sodium citrate solution is 0.05mol / L-1.0mol / L. The volume of sodium sulfate solution and sodium citrate solution added to premixing tank one and premixing tank two is 30L-5000L, and the volume of solution added to reaction tank is 10L-1000L. The amount of ferrous sulfate added is 3mol-10000mol, and the amount of sodium ferrocyanide added is 2.5mol-10000mol.

3. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (2), stir for 10 min-180 min, age for 1 h-24 h, and pressurize and filter at a pressure of 0.1 MPa-1.0 MPa.

4. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (3), the amount of sodium hydroxide added is 0.5-3400 mol, and the pH value in the system is controlled at 7.0-8.

0.

5. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (3), the evaporation and concentration temperature is 90℃-120℃, the evaporation amount is 10%-50% of the waste liquid volume, and after concentration, the reaction is continued for 30 minutes with a stirring speed of 5r / min-100r / min.

6. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, The amount of sodium sulfate crystals precipitated in step (3) is equivalent to the amount of sodium sulfate by-product of the synthesis reaction. The cooling rate is controlled at 1℃ / h-10℃ / h, the crystallization time is 1h-12h, and the crystals are separated by centrifuge after crystallization.

7. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (4), the amount of sodium hydroxide added is 0.05-340 mol, the pH value is controlled at 7.0-8.0, the amount of PAC added is 5g-5000g, the amount of PAM added is 5g-5000g, and the pH value in the system is controlled at 7.0-8.

0.

8. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (5), the system is neutralized to a pH of 6.8-7.5, and the amount of sulfuric acid added is 0.05mol-340mol.

9. The process for recycling waste liquid from a Prussian blue analog cathode material according to claim 1, characterized in that, In step (6), the reaction temperature is 25℃-60℃, the amount of iron powder added is 0.5mol-3400mol, the amount of sulfuric acid added is 1mol-6800mol, and the stirring time is 1h-12h.

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