Battery-grade iron phosphate synthesis wastewater treatment method and system

Abstract

The application discloses a battery-grade iron phosphate synthesis wastewater treatment method and system, and belongs to the technical field of wastewater treatment. After filtering the phosphorus iron washing water, pure water is obtained through two-stage RO membrane groups; after filtering the phosphorus iron mother liquor, the concentrated water side of the first-stage RO membrane group is mixed, and then the mixture is subjected to a first-stage nanofiltration membrane group and a concentrated RO membrane group. The concentrated water side of the concentrated RO membrane group obtains an acid solution; the insoluble substances filtered by the two routes are iron phosphate dihydrate; the concentrated water side of the first-stage nanofiltration membrane group is mixed with the water production side of the concentrated RO membrane group and then enters a second-stage nanofiltration membrane group; the water production side of the second-stage nanofiltration membrane group is connected to the concentrated RO membrane group; and the concentrated water side of the second-stage nanofiltration membrane group is mixed into a water distribution mixture or is neutralized with calcium hydroxide to obtain calcium slag. The scheme sets differentiated treatment paths for two types of wastewater generated in the synthesis of iron phosphate, and simultaneously adopts a multi-stage membrane group circulation reflux and a material combined flow process. The overall process cooperates with each other, effectively solves the problems of large water quality fluctuation, resource loss and system fault in the original process.

Description

Technical Field

[0001] This invention relates to a method and system for treating battery-grade iron phosphate synthesis wastewater, belonging to the field of wastewater treatment technology. Background Technology

[0002] With the rapid development of my country's new energy battery industry, battery production scale is constantly expanding. In the production process of iron phosphate, the precursor for battery cathode materials, the synthesis and washing processes generate large amounts of iron phosphate mother liquor and washing water. Due to issues such as filter breakage and material loss during pressure filtration, the iron phosphate solid content in the wastewater fluctuates significantly. The wastewater has a relatively low acid concentration and contains harmful impurities such as aluminum, making it unsuitable for direct reuse. Direct neutralization or membrane treatment after neutralization not only results in a significant waste of water, sulfate, and phosphorus resources but also in high disposal costs. Furthermore, fluctuations in influent water quality can lead to unstable operation of the treatment system, frequently causing abnormal conditions such as tank cleaning and membrane clogging.

[0003] Therefore, in the existing phosphorus and iron wastewater discharge treatment process, how to make the system withstand water quality shocks, ensure stable operation, recover useful resources, and reduce disposal costs are problems that urgently need to be improved and solved. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a method and system for treating battery-grade iron phosphate synthesis wastewater, aiming to solve problems such as unstable system operation caused by fluctuations in influent water quality, high treatment and discharge costs, and resource waste in existing iron phosphate synthesis wastewater treatment technologies.

[0005] The technical solution adopted by this invention to solve its technical problem is: In a first aspect, this application provides a method for treating battery-grade iron phosphate synthesis wastewater. After filtering out insoluble matter, the iron phosphate washing water is passed sequentially through a primary RO membrane group and a secondary RO membrane group to obtain pure water. The concentrate side of the secondary RO membrane group is refluxed back into the primary RO membrane group. After filtering out insoluble matter, the phosphorus iron mother liquor is mixed with the concentrate side of the first-stage RO membrane group, and then passed sequentially through the first-stage nanofiltration membrane group and the concentrated RO membrane group. The concentrate side of the concentrated RO membrane group yields acid solution. The insoluble matter filtered from the ferric phosphorus washing water and the insoluble matter filtered from the ferric phosphorus mother liquor are combined to obtain ferric phosphate dihydrate; The concentrate side of the primary nanofiltration membrane module is mixed with the permeate side of the concentrated RO membrane module, and the resulting mixed solution enters the secondary nanofiltration membrane module. The permeate side of the secondary nanofiltration membrane module is then re-circulated to the concentrated RO membrane module, and the concentrate side of the secondary nanofiltration membrane module is either mixed with the mixed solution or neutralized with calcium hydroxide to obtain calcium sludge.

[0006] The battery-grade iron phosphate synthesis wastewater treatment method provided in this application sets differentiated treatment paths for the two types of wastewater generated from iron phosphate synthesis. It is also combined with a multi-stage membrane module circulation and reflux process and a material merging process. The overall process works together to effectively solve the problems of large fluctuations in water quality, resource loss and easy system failure in the original process.

[0007] Furthermore, in the step of mixing and distributing water, the mixing ratio of the concentrate side of the primary nanofiltration membrane module to the permeate side of the concentrated RO membrane module is 1:1~2.

[0008] This formulation is well-matched with the screening characteristics of the secondary nanofiltration membrane module, optimizing the component concentration and flow state of the water after mixing, and enhancing the operational efficiency of subsequent treatment stages. The concentrate from the primary nanofiltration membrane module has a relatively high overall ion concentration, while the permeate from the concentrated RO membrane module is low-ion-concentration clean water. Mixing these two types of water in a defined ratio dilutes the excessively high ion concentration in the concentrate, reducing the probability of salt precipitation and membrane pore blockage, and extending the continuous operating time of the membrane module. After the mixed water undergoes screening in the secondary nanofiltration membrane module, the permeate is returned to the concentrated RO membrane module. The stable feed water concentration ensures a stable concentration ratio for the concentrated RO membrane module, preventing significant fluctuations in acid enrichment.

[0009] Furthermore, during the process of the water mixture entering the secondary nanofiltration membrane module, the concentrate side of the primary nanofiltration membrane module stops supplying the water mixture, while the permeate side of the concentrated RO membrane module continues to supply the water mixture to keep the volume of the water mixture constant.

[0010] After stopping the replenishment of concentrate from the primary nanofiltration membrane module, the total amount of impurities entering the secondary nanofiltration membrane module will no longer increase. The secondary nanofiltration membrane module can perform circulating screening for a limited number of impurities, avoiding material accumulation caused by continuous feeding. The concentrated RO membrane module continuously replenishes the water body, thereby maintaining the inlet water pressure and flow rate of the secondary nanofiltration membrane module within a constant range, avoiding fluctuations in screening accuracy.

[0011] Further, the step of mixing the concentrate side of the secondary nanofiltration membrane module with the water distribution mixture or neutralizing it with calcium hydroxide includes: when the water distribution mixture begins to enter the secondary nanofiltration membrane module, the concentrate side of the secondary nanofiltration membrane module is completely mixed with the water distribution mixture; when the sulfate concentration in the concentrate side of the secondary nanofiltration membrane module is 1 / 10 to 1 / 12 of the sulfate concentration in the concentrate side of the primary nanofiltration membrane module, the permeate side of the concentrated RO membrane module stops being supplied with the water distribution mixture, and the concentrate side of the secondary nanofiltration membrane module is completely neutralized with calcium hydroxide.

[0012] The two operating stages of the concentrate from the secondary nanofiltration membrane module are based on the sulfate concentration threshold, with the concentrate flow direction switching accordingly. The flow direction settings at different stages are coordinated with the front-end water distribution and makeup processes to achieve an orderly connection between deep component recovery and harmless treatment of impurities. When the mixed water first enters the secondary nanofiltration membrane module, the concentrate recirculation can enrich sulfate. When the sulfate concentration in the secondary nanofiltration membrane module concentrate drops to one-tenth to one-twelfth of the sulfate concentration in the primary nanofiltration membrane module concentrate, further enrichment becomes more difficult. At this point, the flow direction is switched to reduce the inefficient operation of the membrane module and conveying equipment, reduce energy consumption, and ultimately accurately divert harmful wastewater, reducing the volume of materials and reagents required for subsequent neutralization. This balances resource recovery efficiency and wastewater treatment costs, and also prevents high-impurity water from contacting the membrane module for extended periods, thus preventing fouling.

[0013] Furthermore, during the continuous replenishment of the product water side of the concentrated RO membrane module to the water mixture, when the product water side of the concentrated RO membrane module is insufficient to maintain the constant volume of the water mixture, the product water side of the primary RO membrane module is replenished to the water mixture.

[0014] The permeate from the concentrated RO membrane module mainly comes from the permeate from the primary nanofiltration membrane module. The permeate flow rate fluctuates due to the influent wastewater volume and the membrane module's permeate efficiency. When the permeate supply is insufficient, the volume of the mixed solution decreases continuously, altering the influent pressure and flow state of the secondary nanofiltration membrane module, thus affecting the screening effect. The cleanliness and ion concentration of the permeate from the primary RO membrane module are similar to those of the concentrated RO membrane module. Using it to supplement the water supply will not significantly change the component ratio and concentration of the mixed solution, maintaining the original screening conditions of the secondary nanofiltration membrane module. This supplementation pathway establishes a material connection between the two-stage RO filtration and the secondary nanofiltration, making the water management of the entire system more flexible, improving the overall process's ability to cope with water volume fluctuations, and enhancing the system's operational continuity.

[0015] Furthermore, when the amount of permeate from the concentrated RO membrane module exceeds a preset threshold, the excess portion enters the primary RO membrane module.

[0016] The concentrated RO membrane module continuously produces purified water, and its total output is affected by the permeate flow rate of the upstream nanofiltration system. When the influent flow rate is too high, the permeate will accumulate. If all of it is sent to the secondary nanofiltration influent tank, it will disrupt the specific water distribution ratio and constant-volume secondary nanofiltration cycle. Diverting excess permeate to the primary RO membrane module quickly solves the problem of excess concentrated RO permeate. The excess purified water sent to the primary RO membrane module participates in the purification process of both RO membranes, becoming pure water that can be reused for washing. This water diversion measure balances the influent load of each membrane module unit in the entire system, preventing any single membrane module unit from operating at high load for extended periods. This slows down membrane element aging, reduces the probability of membrane clogging and shutdown, and ensures that the water flow of each treatment unit is matched, further enhancing the system's ability to withstand fluctuations in influent flow rate and water quality.

[0017] Secondly, this application provides a battery-grade iron phosphate synthesis wastewater treatment system, characterized in that it includes an iron phosphate washing tank and an iron phosphate mother liquor tank. The effluent from the iron phosphate washing tank is connected to a washing ceramic membrane module. The product water side of the washing ceramic membrane module is connected to a first-stage RO feed tank. The effluent from the first-stage RO feed tank is connected to a first-stage RO membrane module. The concentrate side of the first-stage RO membrane module is connected to a first-stage nanofiltration feed tank. The product water side is connected to a second-stage RO feed tank. The effluent from the second-stage RO feed tank is connected to a second-stage RO membrane module. The product water side of the second-stage RO membrane module is connected to a pure water tank, and the concentrate side is returned to the first-stage RO feed tank. The effluent from the phosphorus and iron mother liquor tank is connected to the mother liquor ceramic membrane module. The product water side of the mother liquor ceramic membrane module is connected to the first-stage nanofiltration feed water tank. The effluent from the first-stage nanofiltration feed water tank is connected to the first-stage nanofiltration membrane module. The product water side of the first-stage nanofiltration membrane module is connected to the concentrated RO feed water tank, and the concentrate side is connected to the first-stage nanofiltration concentrate tank. The effluent from the concentrated RO feed water tank is connected to the concentrated RO membrane module. The product water side of the concentrated RO membrane module is connected to the concentrated RO product water tank, and the concentrate side is connected to the acid tank. The effluent from the primary nanofiltration concentrate tank and the effluent from the concentrated RO permeate tank are both connected to the secondary nanofiltration feed tank. The effluent from the secondary nanofiltration feed tank is connected to the secondary nanofiltration membrane module. The permeate side of the secondary nanofiltration membrane module is connected to the concentrated RO feed tank, and the concentrate side is connected back to the secondary nanofiltration feed tank and to the neutralization reaction tank via a three-way valve.

[0018] The battery-grade iron phosphate synthesis wastewater treatment system of this application is laid out with equipment and pipelines along two main lines: iron phosphate washing water and iron phosphate mother liquor. The equipment is connected and the functions are complementary. From the hardware level, the first aspect of the process flow is realized, and the entire process of solid-liquid separation, multi-stage membrane filtration, component recovery, and wastewater diversion and treatment is achieved.

[0019] Each water tank in the entire system plays a role in buffering water volume and stabilizing water quality, mitigating the impact of fluctuations in the quality and volume of incoming water. Each membrane module sequentially completes functions such as solid-liquid separation, water purification, component concentration, and impurity separation. The upstream and downstream equipment work together in a coordinated manner, with solid impurities being intercepted and collected step by step, useful resources being recycled in a targeted manner, and harmful impurities being centrally disposed of. This is conducive to significantly improving the recovery rate of water resources, phosphorus, and sulfate, while reducing the probability of system failure and overall operation and maintenance costs.

[0020] Furthermore, the concentrate side of the washing ceramic membrane assembly is returned to the ferrophosphorus washing tank, the bottom of the ferrophosphorus washing tank is connected to the washing sludge discharge tank, the washing sludge discharge tank is connected to the washing filter press, and the filtrate of the washing filter press is connected back to the ferrophosphorus washing tank. The concentrate side of the mother liquor ceramic membrane module is returned to the phosphorus iron mother liquor tank. The bottom of the phosphorus iron mother liquor tank is connected to the mother liquor sludge discharge tank. The mother liquor sludge discharge tank is connected to the mother liquor hydraulic filter. The filtrate of the mother liquor hydraulic filter is connected back to the phosphorus iron mother liquor tank.

[0021] The concentrated water retained by the ceramic membrane washing unit is returned to the ferric phosphate washing tank. The intercepted ferric phosphate solid particles return to the original water tank and do not flow downstream to the membrane unit. When the solid particles inside the tank accumulate to a certain amount, the high-solids-content water at the bottom is directly discharged into the washing sludge tank and then sent to the washing filter press for filtration. The filtrate after filtration is returned to the ferric phosphate washing tank to continue participating in the treatment process. The filter residue is collected as ferric phosphate dihydrate, completing the solid raw material recovery. The treatment of the ferric phosphate mother liquor is similar.

[0022] Furthermore, the primary RO feed tank is connected to the washing ceramic membrane assembly in reverse via a washing ceramic membrane backwash pump, and the concentrate side of the washing ceramic membrane assembly is also connected to the washing sludge discharge tank. The primary nanofiltration feed tank is connected to the mother liquor ceramic membrane module in reverse via a mother liquor ceramic backwash pump, and the concentrate side of the mother liquor ceramic membrane module is also connected to the mother liquor sludge discharge tank.

[0023] Regular backwashing flushes away solid ferric phosphate particles adhering to the membrane pores and surface, relieving pore blockage, restoring the filtration flux of the ceramic membrane, and allowing it to maintain stable filtration capacity over a long period. The backwash wastewater generated by the ceramic membrane unit is directly discharged into the wash sludge tank, where it mixes with the high-solids water discharged from the bottom of the water tank and is then sent to a wash filter press for treatment. The treatment of the ferric phosphate mother liquor follows the same principle.

[0024] Furthermore, the outlet water of the secondary RO inlet tank is also connected to the secondary nanofiltration inlet tank, and the outlet water of the concentrated RO product water tank is also connected to the primary RO inlet tank.

[0025] Two material conveying pipelines connect the secondary RO feed tank, the concentrated RO permeate tank, the secondary nanofiltration feed tank, and the primary RO feed tank, optimizing the overall system's water volume management capabilities and improving water circulation flexibility and resource utilization. Multiple interconnected pipelines allow for flexible water flow between different treatment units, enabling adjustments to water volumes in some tanks and membrane modules, preventing unit shutdowns due to localized water inflow or permeate imbalances. The coordinated operation of these pipelines perfects the overall system's water circulation network, ensuring independent operation of each process section while achieving water exchange and complementarity, further enhancing the system's overall stability, water volume regulation capabilities, and comprehensive water recovery rate.

[0026] The beneficial effects of this invention are as follows: Based on the composition and concentration characteristics of two types of wastewater, namely ferric phosphate washing water and ferric phosphate mother liquor, this invention first treats the two types of wastewater in parallel and then partially mixes them for treatment. The system has strong operational stability, can recover ferric phosphate dihydrate, recover pure water for reuse in washing ferric phosphate, recover acid for reuse in the leaching process, and recover sulfate ions in calcium slag, thereby effectively recovering a variety of useful resources and helping to reduce wastewater treatment costs.

[0027] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a battery-grade iron phosphate synthesis wastewater treatment system provided in an embodiment of this application.

[0029] Attached reference numerals: 1. Phosphorus iron wash water tank; 2. Wash water ceramic membrane feed pump; 3. Wash water ceramic membrane module; 4. Wash water ceramic membrane backwash pump; 5. First-stage RO feed water tank; 6. First-stage RO feed water pump; 7. First-stage RO membrane module; 8. Second-stage RO feed water tank; 9. First-stage RO permeate transfer pump; 10. Second-stage RO feed water pump; 11. Second-stage RO membrane module; 12. Pure water tank; 13. Wash water filter press; 14. Wash water sludge pump; 15. Wash water filter press feed pump; 16. Wash water sludge tank; 17. Mother liquor ceramic membrane backwash pump; 18. First-stage nanofiltration feed water tank; 19. First-stage nanofiltration feed water pump; 20. First-stage nanofiltration membrane module; 21. Concentrated RO 21. Inlet tank; 22. Concentrated RO inlet pump; 23. Concentrated RO membrane module; 24. Acid tank; 25. Phosphorus iron mother liquor tank; 26. Mother liquor ceramic membrane feed pump; 27. Mother liquor ceramic membrane module; 28. Secondary nanofiltration inlet tank; 29. ​​Secondary nanofiltration inlet pump; 30. Secondary nanofiltration membrane module; 31. Concentrated RO permeate transfer pump; 32. Concentrated RO permeate tank; 33. Mother liquor hydraulic filter; 34. Mother liquor sludge discharge pump; 35. Mother liquor hydraulic filter feed pump; 36. Mother liquor sludge discharge tank; 37. Primary nanofiltration concentrate tank; 38. Primary nanofiltration concentrate transfer pump; 39. Neutralization reaction tank; 40. Calcium slag filter press feed pump; 41. Calcium slag filter press. Detailed Implementation

[0030] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0031] The following disclosure provides many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0032] This application provides a method for treating battery-grade iron phosphate synthesis wastewater. After filtering out insoluble matter, the iron phosphate washing water is passed sequentially through a primary RO membrane group and a secondary RO membrane group to obtain pure water. The concentrate side of the secondary RO membrane group is refluxed back into the primary RO membrane group. After filtering out insoluble matter, the phosphorus and iron mother liquor is mixed with the concentrate side of the first-stage RO membrane group, and then passed sequentially through the first-stage nanofiltration membrane group and the concentrated RO membrane group. The concentrate side of the concentrated RO membrane group yields acid solution. The insoluble matter filtered from the ferric phosphate washing water and the insoluble matter filtered from the ferric phosphate mother liquor were combined to obtain ferric phosphate dihydrate; The concentrate side of the primary nanofiltration membrane unit is mixed with the permeate side of the concentrated RO membrane unit. The resulting mixture enters the secondary nanofiltration membrane unit. The permeate side of the secondary nanofiltration membrane unit is then fed back to the concentrated RO membrane unit. The concentrate side of the secondary nanofiltration membrane unit is either mixed with the mixture or neutralized with calcium hydroxide to obtain calcium sludge.

[0033] The phosphate and ferric phosphate wash water first removes internal solid impurities, then flows sequentially through two-stage RO membrane modules. The second-stage RO membrane module produces pure water that meets reuse standards. The water retained by the second-stage RO membrane module is returned to the first-stage RO membrane module, forming a loop. This loop can repeatedly retain residual salts and trace solid impurities in the water, preventing impurities from penetrating during a single membrane treatment. It also improves the water purification level, ensuring that the final pure water consistently meets the requirements for phosphate and ferric phosphate washing. Furthermore, the recirculation reduces wastewater discharge, gradually increasing the overall water recovery rate.

[0034] After solid-liquid separation, the phosphorus-iron mother liquor is directly combined with the concentrated water retained by the first-stage RO membrane unit. These two types of high-impurity water are then uniformly fed into the subsequent nanofiltration and RO treatment units, eliminating the need for separate back-end separation systems and simplifying the overall piping and equipment layout. The first-stage nanofiltration membrane unit performs component screening on the mixed water. The permeated water is sent to the concentrated RO membrane unit, which continuously enriches the acidic substances in the water. The enriched concentrated water is directly collected as acidic solution that can be reused in production, achieving targeted recovery of sulfate and acidic resources and changing the previous process where acidic solutions were lost with wastewater.

[0035] Solid impurities separated from the ferric phosphate washing water and ferric phosphate mother liquor by filtration are collected to form ferric phosphate dihydrate. This solid material is directly returned to the ferric phosphate production process, so that the raw materials are fully recovered and the raw material loss is reduced.

[0036] The concentrate retained by the primary nanofiltration membrane unit is mixed with the purified water produced by the concentrated RO membrane unit. This mixed water then enters the secondary nanofiltration membrane unit. The water that passes through the secondary nanofiltration membrane unit is then sent back to the concentrated RO membrane unit, where it merges with the upstream water to participate in the concentration and acid extraction process, allowing any remaining acid to be enriched and recovered. The concentrate retained by the secondary nanofiltration membrane unit has two separate flow paths: one part is returned to the water distribution stage for further nanofiltration screening, and the other part is sent for neutralization.

[0037] This solution recovers a wide variety of materials with a high recovery rate. Only water containing high concentrations of harmful impurities is neutralized, significantly reducing the amount of chemicals used and wastewater treatment costs. The multi-stage membrane module combined with a local small-circulation process can also buffer fluctuations in influent water quality, ensuring the continuous and stable operation of the entire treatment process.

[0038] Accordingly, refer to Figure 1This application provides a battery-grade iron phosphate synthesis wastewater treatment system, comprising: an iron phosphate washing tank 1, a washing ceramic membrane feed pump 2, a washing ceramic membrane module 3, a washing ceramic membrane backwash pump 4, a primary RO feed tank 5, a primary RO feed pump 6, a primary RO membrane module 7, a secondary RO feed tank 8, a primary RO permeate transfer pump 9, a secondary RO feed pump 10, a secondary RO membrane module 11, a pure water tank 12, a washing filter press 13, a washing sludge pump 14, a washing filter press feed pump 15, a washing sludge tank 16, a mother liquor ceramic membrane backwash pump 17, a primary nanofiltration feed tank 18, a primary nanofiltration feed pump 19, a primary nanofiltration membrane module 20, a concentrated RO feed tank 21, a concentrated RO feed pump 22, a concentrated RO membrane module 23, and an acid tank 24. The system includes: 25. Phosphorus iron mother liquor tank; 26. Mother liquor ceramic membrane feed pump; 27. Mother liquor ceramic membrane module; 28. Secondary nanofiltration feed water tank; 29. ​​Secondary nanofiltration feed water pump; 30. Secondary nanofiltration membrane module; 31. Concentrated RO permeate transfer pump; 32. Concentrated RO permeate tank; 33. Mother liquor hydraulic filter; 34. Mother liquor sludge discharge pump; 35. Mother liquor hydraulic filter feed pump; 36. Mother liquor sludge discharge tank; 37. Primary nanofiltration concentrate tank; 38. Primary nanofiltration concentrate transfer pump; 39. Neutralization reaction tank; 40. Calcium slag filter press feed pump; 41. Calcium slag filter press; 42. Phosphorus iron washing water tank 1 is equipped with a synthetic washing water inlet pipe at the top. Phosphorus iron washing water tank 1, washing water ceramic membrane feed pump 2, and washing water ceramic membrane module 3 are connected in sequence by pipes. The concentrate pipe of washing water ceramic membrane module 3 is connected to the top of phosphorus iron washing water tank 1. The washing water ceramic membrane module 3 produces... The water pipe is connected to the top of the primary RO inlet tank 5. The primary RO inlet tank 5, the washing ceramic membrane backwash pump 4, and the washing ceramic membrane module 3 are connected in sequence by pipes. The backwash water discharge pipe of the washing ceramic membrane module 3 is connected to the top of the washing sludge tank 16. The washing sludge tank 16, the washing filter press feed pump 15, and the washing filter press 13 are connected in sequence by pipes. The filtrate pipe of the washing filter press 13 is connected to the top of the phosphorus iron washing water tank 1. The primary RO inlet tank 5, the primary RO inlet pump 6, and the primary RO membrane module 7 are connected in sequence by pipes. The concentrate pipe of the primary RO membrane module 7 is connected to the top of the primary nanofiltration inlet tank 18. The permeate pipe of the primary RO membrane module 7 is connected to the top of the secondary RO inlet tank 8. The secondary RO inlet tank 8 is connected to the primary RO permeate transfer pump 9 by pipes. The outlet pipe of the permeate transfer pump 9 is connected to the top of the secondary nanofiltration inlet tank 28. The secondary RO inlet tank 8, the secondary RO inlet pump 10, and the secondary RO membrane module 11 are connected in sequence by pipes. The concentrate pipe of the secondary RO membrane module 11 is connected to the top of the primary RO inlet tank 5. The permeate pipe of the secondary RO membrane module is connected to the top of the pure water tank 12. The top of the ferric phosphate mother liquor tank 25 is equipped with a synthetic mother liquor inlet pipe. The ferric phosphate mother liquor tank 25, the mother liquor ceramic membrane feed pump 26, and the mother liquor ceramic membrane module 27 are connected in sequence by pipes. The concentrate pipe of the mother liquor ceramic membrane module 27 is connected to the top of the ferric phosphate mother liquor tank 25. The permeate pipe of the mother liquor ceramic membrane module 27 is connected to the top of the primary nanofiltration inlet tank 18. The primary nanofiltration inlet tank 18, the mother liquor ceramic membrane backwash pump 17, and the mother liquor ceramic membrane module 27 are connected in sequence by pipes.The backwash water drain pipe of the mother liquor ceramic membrane module 27 is connected to the top of the mother liquor sludge discharge tank 36. The mother liquor sludge discharge tank 36, the mother liquor hydraulic filter feed pump 35, and the mother liquor hydraulic filter 33 are connected in sequence by pipes. The filtrate pipe of the mother liquor hydraulic filter 33 is connected to the top of the phosphorus iron mother liquor tank. The first-stage nanofiltration water inlet tank 18, the first-stage nanofiltration water inlet pump 19, and the first-stage nanofiltration membrane module 20 are connected in sequence by pipes. The concentrate pipe of the first-stage nanofiltration membrane module 20 is connected to the top of the first-stage nanofiltration concentrate tank 37. The permeate pipe of the first-stage nanofiltration membrane module 20 is connected to the top of the concentrated RO water inlet tank 21. The concentrated RO water inlet tank 21, the concentrated RO water inlet pump 22, and the concentrated RO membrane module 23 are connected in sequence by pipes. The concentrate pipe of the concentrated RO membrane module 23 is connected to the top of the acid tank 24. The permeate pipe of the concentrated RO membrane module 23 is connected to the top of the concentrated RO permeate tank 32. The concentrated RO permeate tank 32 and the concentrated RO permeate transfer pump 31 are connected by pipes. The outlet pipe of the concentrated RO permeate transfer pump 31 is connected to the top of the secondary nanofiltration inlet tank 28. Simultaneously, a branch pipe from the outlet of the concentrated RO permeate transfer pump 31 connects to the top of the primary RO inlet tank 5. The primary nanofiltration concentrate tank 37 is connected to the primary nanofiltration concentrate transfer pump 38 via a pipe. The outlet pipe of the primary nanofiltration concentrate transfer pump 38 connects to the top of the secondary nanofiltration inlet tank 28. The secondary nanofiltration inlet tank 28, the secondary nanofiltration inlet pump 29, and the secondary nanofiltration membrane module 30 are sequentially connected via pipes. The permeate pipe of the secondary nanofiltration membrane module 30 connects to the top of the concentrated RO inlet tank 21. The concentrate pipe of the secondary nanofiltration membrane module 30 branches into two lines, connecting to the top of the secondary nanofiltration inlet tank 28 and the top of the neutralization reaction tank 39, respectively. The top of the neutralization reaction tank 39 has a calcium hydroxide dosing port. The neutralization reaction tank 39, the calcium slag filter press feed pump 40, and the calcium slag filter press 41 are sequentially connected via pipes.

[0039] Figure 1 In the diagram, A represents the source of ferrophosphate washing wastewater, B represents the source of ferrophosphate mother liquor wastewater, C represents ferrophosphate dihydrate obtained by filtration in washing filter press 13, D represents ferrophosphate dihydrate obtained by filtration in mother liquor filter press 33, E represents the addition of calcium hydroxide, F represents the recycled pure water reused for washing ferrophosphate, G represents the recycled acid solution reused in the leaching process on the production line, H represents calcium slag obtained by filtration in calcium slag filter press 41, and I represents the filtrate obtained by filtration in calcium slag filter press as the final residual wastewater, which is discharged externally.

[0040] Preferably, the bottom of the ferric phosphate washing tank 1 is designed in a conical shape, and the bottom of the cone is connected to the top of the washing water sludge pump 14 and the washing water sludge tank 16 in sequence by pipes, so as to timely extract the ferric phosphate deposited in the ferric phosphate washing tank 1 and reduce the ferric phosphate concentration in the ferric phosphate washing tank 1.

[0041] Preferably, the inlet pipe of the washing ceramic membrane feed pump 2 is located above the transition zone between the cylinder and the cone bottom of the phosphate washing tank 1, to prevent the phosphate deposited at the bottom from entering the washing ceramic membrane group 3 and to extend the backwashing cycle of the washing ceramic membrane group 3.

[0042] Preferably, the bottom of the ferric phosphate mother liquor tank 25 is designed in a conical shape, and the bottom of the cone is connected to the top of the mother liquor sludge pump 34 and the mother liquor sludge tank 36 in sequence by pipes, so as to timely extract the ferric phosphate deposited in the ferric phosphate mother liquor tank 25 and reduce the concentration of ferric phosphate in the ferric phosphate mother liquor tank 25.

[0043] Preferably, the water inlet pipe of the mother liquor ceramic membrane feed pump 26 is located above the transition zone between the cylinder and the cone bottom of the phosphate mother liquor tank 25, to prevent the phosphate deposited at the bottom from entering the mother liquor ceramic membrane 27 group and to extend the backwashing cycle of the mother liquor ceramic membrane group 27.

[0044] Preferably, the ceramic membrane module 27 uses a 50nm zirconium dioxide tubular ceramic membrane, which has strong corrosion resistance, is not easily fouled, and is less affected by fluctuations in the iron phosphate content of the raw water during operation.

[0045] Preferably, the washing water discharge tank 16, the mother liquor discharge tank 36, and the neutralization reaction tank 39 are equipped with agitators to prevent ferric phosphate from depositing inside the tanks.

[0046] The working process of this system can be summarized as follows: Add ferric phosphate wash water to the ferric phosphate wash water tank. When the tank level is above 1 / 2, start the ceramic membrane feed pump to pump the ferric phosphate wash water into the ceramic membrane module. The clarified liquid after filtration through the ceramic membrane flows into the primary RO feed tank. Ferric phosphate trapped by the ceramic membrane and the ferric phosphate wash water that has not permeated through the ceramic membrane are returned to the ferric phosphate wash water tank. The permeate rate of the ceramic membrane module can be adjusted according to the SS concentration of the influent, with a control range of 50%-95% and permeate SS ≤ 0.1 m³. g / L; When the SS (suspended solids) concentration in the ferric phosphate washing tank is ≥15%, start the washing water sludge pump to discharge the high-concentration ferric phosphate washing water in the ferric phosphate washing tank into the washing water sludge tank. After the washing ceramic membrane module has been running for a period of time, it will be backwashed once with the clear liquid in the first-stage RO inlet tank. The backwash water will also be discharged into the washing water sludge tank. When the liquid level in the washing water sludge tank is higher than 1 / 2, the washing water filter press feed pump can be started to pump the water to the washing water filter press for filtration. The filtrate flows back to the ferric phosphate washing tank, and the filter residue is ferric phosphate dihydrate.

[0047] When the liquid level in the primary RO feed tank is higher than 1 / 2, the primary RO feed pump is started to pump the phosphorus and iron washing water into the primary RO membrane module. The phosphorus and iron washing water flows into the secondary RO feed tank after being filtered by the primary RO membrane. The primary RO concentrate generated on the concentrate side of the primary RO membrane module flows into the primary nanofiltration feed tank. The water production rate of the primary RO membrane module is controlled within the range of 85%-95%.

[0048] When the level in the secondary RO feed tank is higher than 1 / 2, the secondary RO feed pump is started to pump the primary RO permeate into the secondary RO membrane module. The secondary RO permeate, after being filtered by the secondary RO membrane, flows into the pure water tank. The secondary RO concentrate generated on the concentrate side of the secondary RO membrane module flows back to the primary RO feed tank. The permeate rate of the secondary RO membrane module is controlled within the range of 90%-95%. The conductivity of the pure water in the pure water tank is tested to be ≤100μs / cm, which can be used for washing ferric phosphate dihydrate during the ferric phosphate synthesis process.

[0049] Add ferric phosphate mother liquor to the ferric phosphate mother liquor tank. When the tank level is above 1 / 2, start the ceramic membrane feed pump to pump the ferric phosphate mother liquor into the ceramic membrane module. The clear liquid after filtration through the ceramic membrane flows into the primary nanofiltration feed tank. The ferric phosphate trapped by the ceramic membrane and the ferric phosphate mother liquor that has not permeated through the ceramic membrane return to the ferric phosphate mother liquor tank. The permeate rate of the ceramic membrane module can be adjusted according to the SS concentration of the influent, with a permeate rate control range of 50%-90% and permeate SS ≤ 0.1 mg / L. When the S concentration is ≥15%, start the mother liquor discharge pump to discharge the high-concentration ferric phosphate mother liquor from the ferric phosphate mother liquor tank to the mother liquor discharge tank. After the mother liquor ceramic membrane module has been running for a period of time, it will be backwashed once with the clear liquid in the first-stage nanofiltration inlet tank. The backwash water will also be discharged into the mother liquor discharge tank. When the liquid level in the mother liquor discharge tank is higher than 1 / 2, the mother hydraulic filter feed pump can be started to pump the mother hydraulic filter for pressure filtration. The filtrate flows back to the ferric phosphate mother liquor tank. The filter residue is ferric phosphate dihydrate, which enters the ferric phosphate production process together with the filter residue produced by the wash water filter press to make ferric phosphate products.

[0050] When the liquid level in the primary nanofiltration feed tank is higher than 1 / 2, the primary nanofiltration feed pump is started to pump the material into the primary nanofiltration membrane module. The primary nanofiltration permeate after filtration by the primary nanofiltration membrane flows into the concentrated RO feed tank. The primary nanofiltration concentrate generated on the concentrate side of the primary nanofiltration membrane module flows into the primary nanofiltration concentrate tank. The permeate rate of the primary nanofiltration membrane module is controlled within the range of 85%-95%.

[0051] When the liquid level in the concentrated RO feed water tank is higher than 1 / 2, the concentrated RO feed water pump is started to pump the nanofiltration permeate into the concentrated RO membrane module. The concentrated RO permeate after filtration by the concentrated RO membrane flows into the concentrated RO permeate tank. The concentrated RO concentrate generated on the concentrate side of the concentrated RO membrane module flows into the acid tank. The concentration ratio of the concentrated RO membrane module can be adjusted according to the required concentration of feed acid and concentrate acid. The sulfate content in the concentrated RO concentrate is controlled at 1.6-1.8 mol / L. The mixed acid in the acid tank is used in the leaching section of ferric phosphate production.

[0052] When the levels in both the primary nanofiltration concentrate tank and the concentrated RO permeate tank are above 1 / 2, start the primary nanofiltration concentrate transfer pump to pump the primary nanofiltration concentrate into the secondary nanofiltration feed tank. Simultaneously, start the concentrated RO permeate transfer pump to pump the concentrated RO permeate into the secondary nanofiltration feed tank. The ratio of primary nanofiltration concentrate to concentrated RO permeate can be controlled at 1:(1-2) according to production needs. When the level in the secondary nanofiltration feed tank reaches 3 / 5-3 / 4, shut down both the primary nanofiltration concentrate transfer pump and the concentrated RO permeate transfer pump to complete water distribution. Start the secondary nanofiltration feed pump to pump the material into the secondary nanofiltration membrane module. The secondary nanofiltration permeate, filtered by the secondary nanofiltration membrane module, flows into the concentrated RO feed tank. The secondary nanofiltration concentrate generated on the concentrate side of the secondary nanofiltration membrane module flows back into the secondary nanofiltration feed tank. The permeate production rate of the secondary nanofiltration membrane module is controlled within the range of 50%-66%. When the level in the secondary nanofiltration feed tank begins to drop, start the concentrated RO permeate transfer pump to replenish the secondary nanofiltration feed tank, and control the concentrated RO permeate flow rate to keep the level in the secondary nanofiltration feed tank constant. When the sulfate concentration in the secondary nanofiltration membrane concentrate is measured to be 1 / (10-12) of the sulfate concentration in the primary nanofiltration concentrate, shut down the concentrated RO permeate transfer pump, switch the secondary nanofiltration membrane concentrate flow to the neutralization reaction tank, and shut down the secondary nanofiltration feed pump when the material in the secondary nanofiltration feed tank reaches a low level. If the level in the concentrated RO permeate tank is insufficient during operation, the primary RO permeate transfer pump can be started to replenish the secondary nanofiltration feed tank with primary RO permeate. If the level in the concentrated RO permeate tank is high, the concentrated RO permeate transfer pump can also be started to transfer water to the primary RO feed tank.

[0053] Turn on the agitator in the neutralization reaction tank, add calcium hydroxide into the neutralization reaction tank, control the pH value to 8-9 and carry out the neutralization precipitation reaction for 1-2 hours. After the reaction is completed, start the feed pump of the calcium slag filter press to feed the calcium slag filter press for filtration. The filtrate produced by the calcium slag filter press is discharged after passing the test. The filter residue produced by the calcium slag filter press is handed over to a qualified unit for disposal.

[0054] This invention uses ceramic membrane modules instead of conventional precision filters, flat sheet membranes, ultrafiltration, and other conventional treatment devices. It can effectively withstand fluctuations in the iron phosphate solid content of raw water, ranging from 10 ppm to 75,000 ppm, and is less prone to clogging. After treatment by this invention, the water recovery rate in iron phosphate washing water can reach over 98.5%, and the water recovery rate in iron phosphate mother liquor can reach over 95%.

[0055] This invention employs a two-stage nanofiltration concentrate reflux dialysis combined with membrane concentration technology. It leverages the advantages of nanofiltration in separating acids while effectively overcoming the retention problems of sulfate and phosphorus in nanofiltration membranes. This significantly improves the separation and recovery of sulfate, phosphorus, and other impurities. After treatment with this device, the sulfate recovery rate in the ferrophosphate washing water can reach over 99%, and the phosphorus recovery rate can reach over 95%. In the ferrophosphate mother liquor, the sulfate recovery rate can reach over 98%, and the phosphorus recovery rate can reach over 95%.

[0056] Compared with conventional treatment processes such as "direct neutralization and discharge" and "neutralization + membrane recovery + discharge", the present invention has a more obvious advantage in operating cost, the process is easier to stabilize and control, and it is easier to achieve automatic treatment.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0058] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for treating battery-grade iron phosphate synthesis wastewater, characterized in that, After the insoluble matter is removed by filtering the phosphate and iron washing water, it is passed through a primary RO membrane group and a secondary RO membrane group in sequence to obtain pure water. The concentrate side of the secondary RO membrane group is refluxed back into the primary RO membrane group. After filtering out insoluble matter, the phosphorus iron mother liquor is mixed with the concentrate side of the first-stage RO membrane group, and then passed sequentially through the first-stage nanofiltration membrane group and the concentrated RO membrane group. The concentrate side of the concentrated RO membrane group yields acid solution. The insoluble matter filtered from the ferric phosphorus washing water and the insoluble matter filtered from the ferric phosphorus mother liquor are combined to obtain ferric phosphate dihydrate; The concentrate side of the primary nanofiltration membrane module is mixed with the permeate side of the concentrated RO membrane module, and the resulting mixed solution enters the secondary nanofiltration membrane module. The permeate side of the secondary nanofiltration membrane module is then re-circulated to the concentrated RO membrane module, and the concentrate side of the secondary nanofiltration membrane module is either mixed with the mixed solution or neutralized with calcium hydroxide to obtain calcium sludge.

2. The method for treating battery-grade iron phosphate synthesis wastewater according to claim 1, characterized in that, In the step of mixing and distributing water, the mixing ratio of the concentrate side of the primary nanofiltration membrane module to the permeate side of the concentrated RO membrane module is 1:1~2.

3. The method for treating battery-grade iron phosphate synthesis wastewater according to claim 2, characterized in that, During the process of the water mixture entering the secondary nanofiltration membrane module, the concentrate side of the primary nanofiltration membrane module stops supplying the water mixture, while the permeate side of the concentrated RO membrane module continues to supply the water mixture to keep the volume of the water mixture constant.

4. The method for treating battery-grade iron phosphate synthesis wastewater according to claim 3, characterized in that, The steps of mixing the concentrate side of the secondary nanofiltration membrane module with the water distribution mixture or neutralizing it with calcium hydroxide include: when the water distribution mixture begins to enter the secondary nanofiltration membrane module, the concentrate side of the secondary nanofiltration membrane module is completely mixed with the water distribution mixture; when the sulfate concentration in the concentrate side of the secondary nanofiltration membrane module is 1 / 10 to 1 / 12 of the sulfate concentration in the concentrate side of the primary nanofiltration membrane module, the permeate side of the concentrated RO membrane module stops being supplied with the water distribution mixture, and the concentrate side of the secondary nanofiltration membrane module is completely neutralized with calcium hydroxide.

5. The method for treating battery-grade iron phosphate synthesis wastewater according to claim 3, characterized in that, During the continuous replenishment of the product water side of the concentrated RO membrane module to the water mixture, when the product water side of the concentrated RO membrane module is insufficient to maintain the constant volume of the water mixture, the product water side of the primary RO membrane module is replenished to the water mixture.

6. The method for treating battery-grade iron phosphate synthesis wastewater according to claim 1, characterized in that, When the amount of permeate on the concentrated RO membrane module exceeds a preset threshold, the excess portion enters the primary RO membrane module.

7. A battery-grade iron phosphate synthesis wastewater treatment system, characterized in that, The system includes a phosphorus iron washing water tank (1) and a phosphorus iron mother liquor tank (25). The outlet of the phosphorus iron washing water tank (1) is connected to the washing water ceramic membrane group (3). The product water side of the washing water ceramic membrane group (3) is connected to the first-stage RO inlet tank (5). The outlet of the first-stage RO inlet tank (5) is connected to the first-stage RO membrane group (7). The concentrate side of the first-stage RO membrane group (7) is connected to the first-stage nanofiltration inlet tank (18). The product water side is connected to the second-stage RO inlet tank (8). The outlet of the second-stage RO inlet tank (8) is connected to the second-stage RO membrane group (11). The product water side of the second-stage RO membrane group (11) is connected to the pure water tank (12). The concentrate side is returned to the first-stage RO inlet tank (5). The effluent from the phosphorus and iron mother liquor tank (25) is connected to the mother liquor ceramic membrane group (27). The product water side of the mother liquor ceramic membrane group (27) is connected to the first-stage nanofiltration feed water tank (18). The effluent from the first-stage nanofiltration feed water tank (18) is connected to the first-stage nanofiltration membrane group (20). The product water side of the first-stage nanofiltration membrane group (20) is connected to the concentrated RO feed water tank (21), and the concentrate side is connected to the first-stage nanofiltration concentrate tank (37). The effluent from the concentrated RO feed water tank (21) is connected to the concentrated RO membrane group (23). The product water side of the concentrated RO membrane group (23) is connected to the concentrated RO product water tank (32), and the concentrate side is connected to the acid tank (24). The outlet water of the primary nanofiltration concentrate tank (37) and the outlet water of the concentrated RO product water tank (32) are both connected to the secondary nanofiltration inlet tank (28). The outlet water of the secondary nanofiltration inlet tank (28) is connected to the secondary nanofiltration membrane module (30). The product water side of the secondary nanofiltration membrane module (30) is connected to the concentrated RO inlet tank (21). The concentrate side is connected back to the secondary nanofiltration inlet tank (28) and connected to the neutralization reaction tank (39) through a three-way valve.

8. The battery-grade iron phosphate synthesis wastewater treatment system according to claim 7, characterized in that, The concentrate side of the washing ceramic membrane assembly (3) returns to the phosphorus iron washing tank (1), the bottom of the phosphorus iron washing tank (1) is connected to the washing sludge discharge tank (16), the washing sludge discharge tank (16) is connected to the washing filter press (13), and the filtrate of the washing filter press (13) is connected back to the phosphorus iron washing tank (1). The concentrate side of the mother liquor ceramic membrane assembly (27) returns to the ferric phosphorus mother liquor tank (25), the bottom of the ferric phosphorus mother liquor tank (25) is connected to the mother liquor sludge discharge tank (36), the mother liquor sludge discharge tank (36) is connected to the mother hydraulic filter (33), and the filtrate of the mother hydraulic filter (33) is connected back to the ferric phosphorus mother liquor tank (25).

9. The battery-grade iron phosphate synthesis wastewater treatment system according to claim 8, characterized in that, The primary RO inlet tank (5) is connected to the washing ceramic membrane assembly (3) in reverse via the washing ceramic membrane backwash pump (4), and the concentrate side of the washing ceramic membrane assembly (3) is also connected to the washing sludge discharge tank (16). The primary nanofiltration feed tank (18) is connected to the mother liquor ceramic membrane module (27) in reverse via the mother liquor ceramic backwash pump (17), and the concentrate side of the mother liquor ceramic membrane module (27) is also connected to the mother liquor sludge discharge tank (36).

10. The battery-grade iron phosphate synthesis wastewater treatment system according to claim 7, characterized in that, The outlet water of the secondary RO inlet tank (8) is also connected to the secondary nanofiltration inlet tank (28), and the outlet water of the concentrated RO product water tank (32) is also connected to the primary RO inlet tank.

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