Method and system for multi-stage nanofiltration treatment of chemical waste liquid

Abstract

The invention relates to the technical field of water treatment, and discloses a method and a system for treating chemical polishing waste liquid through multistage nanofiltration, and the method sequentially comprises the following steps: mixing chemical polishing washing water with tank liquor, removing suspended impurities through a microfiltration membrane, intercepting aluminum ions through an acid-resistant nanofiltration membrane, circularly treating concentrated water through multistage nanofiltration, and carrying out negative pressure evaporation and concentration. Through cascade combination of micro-filtration and multi-stage nano-filtration, the transmittance of the acid liquor and the removal rate of foreign ions are effectively improved, and concentration and recycling of the acid liquor are realized through an evaporation link.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, in particular to a method and system for treating chemical polishing waste liquid by multi-stage nanofiltration. BACKGROUND

[0002] Aluminum and aluminum alloy chemical polishing process is widely used in the metal surface treatment industry, but a large amount of chemical polishing waste acid liquid is generated in the production process, which mainly includes phosphoric acid and sulfuric acid, and is rich in aluminum ions, iron ions and other impurities. With the recycling, the metal impurities in the acid gradually accumulate, not only leading to the decrease of polishing efficiency and the increase of acid consumption, but also increasing the difficulty of waste acid treatment. If directly discharged, it will cause environmental pollution and resource waste. To solve the above problems, the common chemical polishing waste acid treatment methods currently include neutralization precipitation method, evaporation crystallization method, diffusion dialysis, electrodialysis and membrane separation method, etc. The neutralization precipitation method will produce a large amount of sludge, and the treatment cost is high; the evaporation crystallization method can recover part of the acid, but the energy consumption is large; the diffusion dialysis and the electrodialysis have limited removal capacity for impurity ions. Membrane separation technology gradually attracts attention due to its advantages of normal temperature and pressure operation, simple operation, etc., among which nanofiltration membrane has high rejection rate for divalent and multivalent ions, and is considered as a potential process for chemical polishing waste acid recycling. But the existing single-stage nanofiltration still has limitations under the condition of strong acid and high aluminum ions: it is difficult to balance the acid permeation rate and the metal ion rejection rate, the membrane pollution and concentration polarization phenomenon are obvious, and the operation stability is insufficient.

[0003] For the recycling of acidic waste liquid, some published patents have proposed the application ideas of nanofiltration or multi-stage nanofiltration. For example, patent CN110217931A discloses a resourceful treatment process of waste acid, which realizes acid recovery by combining acid-resistant nanofiltration with diffusion dialysis, and assists with precipitation and calcination to recover alumina, but it mainly combines single-stage nanofiltration with other units, and does not involve the operation parameter design of multi-stage nanofiltration in high-aluminum chemical polishing waste acid system. Patent CN216472254U discloses a membrane integrated resourceful treatment system for dilute waste acid of sulfuric acid method titanium dioxide, which sets up multi-stage nanofiltration membrane unit and is connected in series with pre-concentration and evaporation device to realize the purification and concentration of dilute waste acid. Although this scheme proposes multi-stage nanofiltration, its object is dilute waste acid of titanium dioxide, which has obvious differences in acidity and impurity characteristics from chemical polishing waste acid.

[0004] It can be seen that although the existing technology has explored the application of nanofiltration and multi-stage nanofiltration in waste acid treatment, under the condition of high aluminum in chemical polishing waste acid, how to realize the balance of acid permeation rate and metal removal rate through multi-stage nanofiltration cascade is still lack of effective solutions. SUMMARY

[0005] The purpose of the present application is to provide a method and system for treating chemical polishing waste liquid by multi-stage nanofiltration, in order to solve the problems of low acid recovery rate, insufficient aluminum ion rejection rate and poor operation stability.

[0006] To achieve the above object, the present application provides the following scheme: A multi-stage nanofiltration treatment method for chemical polishing waste liquid, comprising the following steps: Step 1, mixing chemical polishing water washing water with tank liquid: mixing the first water washing water after chemical polishing with the chemical polishing tank liquid in proportion, and the specific gravity of the mixture is 1.10-1.15; Step 2, removing impurities by microfiltration membrane: passing the mixed chemical polishing waste acid containing phosphoric acid, sulfuric acid and aluminum ions through a microfiltration membrane box to remove suspended colloids and solid particles; Step 3, first-stage nanofiltration: treating the chemical polishing waste acid treated in step 2 by nanofiltration membrane under the operating pressure of 30-35 bar, controlling the first-stage water recovery rate to be 70%-75%, and the obtained first-stage water is sent to the subsequent evaporation process, and the first-stage concentrated water is collected for standby; Step 4, second-stage nanofiltration: diluting the first-stage concentrated water obtained in step 3 with pure water and sending it to a second-stage nanofiltration membrane group, operating under the operating pressure of 35-45 bar, the second-stage water is sent to the subsequent evaporation process, and the second-stage concentrated water is discharged or continuously diluted to enter the third-stage nanofiltration membrane group when the set recovery rate of 60%-70% is reached; Step 5, third-stage nanofiltration: diluting the second-stage concentrated water and sending it to a third-stage nanofiltration membrane group, operating under the operating pressure of 45-50 bar, the third-stage water is sent to the subsequent evaporation process, and the third-stage concentrated water is discharged when the recovery rate of 50%-70% is reached; Step 6, negative pressure evaporation concentration: transferring the first-stage water in step 3, the second-stage water in step 4 and the third-stage water in step 5 to a negative pressure evaporation concentration device for negative pressure evaporation concentration treatment to obtain finished product recycling acid.

[0007] Further, when mixing the first water washing water after chemical polishing with the chemical polishing tank liquid in step 1, displacement water is also added to adjust the specific gravity of the chemical polishing waste acid to 1.10-1.15.

[0008] Further, the microfiltration membrane in step 2 is a hollow fiber microfiltration membrane.

[0009] Further, the nanofiltration membrane in steps 3, 4 and 5 is an acid-resistant nanofiltration membrane, and the membrane area is 6m 2 , and the operating frequency is 30-40 Hz.

[0010] Further, the negative pressure evaporation concentration device in step 6 provides a negative pressure environment through a vacuum pump set.

[0011] On the other hand, the present application also provides a multi-stage nanofiltration treatment system for chemical polishing waste liquid for the above method, which comprises: polishing tank liquid storage tank, washing water storage tank, tank liquid pump, washing water pump, waste acid storage tank, microfiltration membrane liquid inlet pump, microfiltration membrane pool, microfiltration membrane water storage tank, microfiltration membrane concentrated water discharge pump, microfiltration membrane concentrated water storage tank, nanofiltration feed pump a, nanofiltration membrane group a, nanofiltration water storage tank, primary concentrated water storage tank, primary concentrated water discharge pump, nanofiltration feed tank a, nanofiltration feed pump b, nanofiltration membrane group b, secondary concentrated water storage tank, secondary concentrated water discharge pump, nanofiltration feed tank b, nanofiltration feed pump c, nanofiltration membrane group c, tertiary concentrated water storage tank, evaporator liquid inlet pump, negative pressure evaporator, acid discharge pump, finished acid storage tank; The water outlet of the polishing tank liquid storage tank is connected with the liquid inlet of the waste acid storage tank through a tank liquid pump, the water outlet of the washing water storage tank is connected with the liquid inlet of the waste acid storage tank through a washing water pump, the water outlet of the waste acid storage tank is connected with the liquid inlet of the microfiltration membrane pool through a microfiltration membrane liquid inlet pump, the water outlet of the microfiltration membrane pool is connected with the liquid inlet of the microfiltration membrane water storage tank through a pipeline, and the liquid inlet of the microfiltration membrane concentrated water storage tank is connected with the concentrated water outlet of the microfiltration membrane pool through a pipeline. The water outlet of the microfiltration membrane water storage tank is connected with the liquid inlet of the nanofiltration membrane group a through a nanofiltration feed pump a, the water outlet of the nanofiltration membrane group a is connected with the liquid inlet of the nanofiltration water storage tank through a pipeline, and the concentrated water outlet of the nanofiltration membrane group a is connected with the liquid inlet of the primary concentrated water storage tank through a pipeline. The water outlet of the primary concentrated water storage tank is connected with the liquid inlet of the nanofiltration feed tank a through a primary concentrated water discharge pump, the liquid outlet of the nanofiltration feed tank a is connected with the liquid inlet of the nanofiltration membrane group b through a nanofiltration feed pump b, the water outlet of the nanofiltration membrane group b is connected with the liquid inlet of the nanofiltration water storage tank through a pipeline, and the concentrated water outlet of the nanofiltration membrane group b is connected with the liquid inlet of the secondary concentrated water storage tank through a pipeline. The water outlet of the secondary concentrated water storage tank is connected with the liquid inlet of the nanofiltration feed tank b through a secondary concentrated water discharge pump, the liquid outlet of the nanofiltration feed tank b is connected with the liquid inlet of the nanofiltration membrane group c through a nanofiltration feed pump c, the water outlet of the nanofiltration membrane group c is connected with the liquid inlet of the nanofiltration water storage tank through a pipeline, and the concentrated water outlet of the nanofiltration membrane group c is connected with the liquid inlet of the tertiary concentrated water storage tank through a pipeline. The water outlet of the nanofiltration water storage tank is connected with the liquid inlet of the evaporator through an evaporator liquid inlet pump, and the water outlet of the negative pressure evaporator is connected with the liquid inlet of the finished acid storage tank through an acid discharge pump.

[0012] Compared with the prior art, the beneficial effects of the present application are as follows: 1. The multi-stage nanofiltration treatment process and its supporting system for chemical polishing waste liquid can significantly improve the resource recovery level of chemical polishing waste acid by building a stable process balance between the acid system, impurity accumulation and nanofiltration membrane operation conditions through the comprehensive coupling of microfiltration pretreatment, multi-stage acid-resistant nanofiltration series operation and negative pressure evaporation concentration. 2、The application adopts a three-stage acid-resistant nanofiltration membrane progressive separation structure, and different concentrations of acid liquid are treated in different pressure sections, so that monovalent ions such as phosphoric acid and sulfuric acid achieve high permeability in the low concentration section, and high-valence aluminum ions are strongly intercepted in the high pressure section. By setting the recovery rate in sections (70%-75% for the first stage, 60%-70% for the second stage, and 50%-70% for the third stage), the concentration polarization in the nanofiltration process is effectively alleviated, the acid permeability and aluminum ion interception rate form a controllable separation gradient, and the separation effect that cannot be achieved by single-stage nanofiltration is realized.

[0013] 3、The colloidal aluminum, aluminum phosphate complex and fine particles in the waste pickling acid are easy to block the surface of the nanofiltration membrane. The hollow fiber microfiltration membrane is arranged before nanofiltration in the application, which can effectively remove suspended and colloidal impurities, so that the solid content of the acid liquid entering the nanofiltration section is significantly reduced. This step not only reduces the risk of generating a compact layer on the membrane surface, but also reduces the strength of the concentration polarization, so that the stable flux of the nanofiltration membrane is significantly prolonged, thereby reducing the cleaning frequency and prolonging the service life of the membrane module.

[0014] 4、The traditional single-stage nanofiltration concentrated water has high concentration and large viscosity, which easily leads to increased membrane pollution. In the application, the first-stage and second-stage concentrated water are diluted and then enter the next nanofiltration stage, so that the membrane group operates in a lower viscosity and controllable ionic strength range, which is beneficial to maintaining a higher effective filtration flux. At the same time, the concentrated water of each stage is fully utilized, so that the acid resources in the system are maximized, the amount of waste liquid is reduced as a whole, and the economic efficiency and environmental protection benefits are improved.

[0015] 5、The nanofiltration operating pressure is divided into three sections of 30-35 bar, 35-45 bar and 45-50 bar in the application, so that acid liquids of different concentrations are operated in the appropriate pressure range, avoiding the decrease of permeability due to insufficient pressure or membrane damage due to excessive pressure. Combined with the matching relationship of 6 m² membrane area and 30-40 Hz operating frequency, the membrane module can maintain a stable operating window in a strong acid and high aluminum system, improving the controllability and reliability of the system.

[0016] 6、The nanofiltration product water needs to be further concentrated due to the low concentration of permeable acid liquid. The application uses negative pressure evaporation to volatilize and concentrate the acid at a lower boiling point, which not only reduces energy consumption, but also reduces the risk of acid decomposition or equipment corrosion at high temperatures. The final finished acid can be reused in the pickling process, realizing real acid recycling and significantly reducing the consumption of newly purchased acid.

[0017] 7. The system's storage tanks, pump sets, and membrane modules are connected in sequence, enabling continuous treatment of chemical polishing waste acid through dilution, filtration, separation, and concentration. The buffering effect of multiple storage tanks and feed tanks gives the nanofiltration system the ability to resist fluctuations, maintaining stable water quality even when faced with changes in feed concentration and load. The modular design allows for flexible adjustment of the number of membrane modules, pump configuration, and pressure range, making it easy to adapt to chemical polishing production lines of different scales.

[0018] 8. Acid reuse is achieved through a combination of multi-stage nanofiltration and negative pressure evaporation, reducing the amount of concentrated liquid discharged. Metal impurities such as aluminum ions are concentrated into a smaller volume of concentrated water, which can be further processed for resource recovery or integrated with the company's existing treatment system, thus reducing the overall amount of waste acid discharged. Compared with evaporation crystallization, neutralization precipitation, and other solutions, this method has lower energy consumption and produces less sludge, resulting in a significant reduction in overall operating costs. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The flowchart illustrates a multi-stage nanofiltration method for treating chemical waste liquid, as provided in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of a multi-stage nanofiltration system for treating chemical waste liquid, provided in an embodiment of the present invention.

[0022] Among them, 1-polishing tank liquid storage tank, 2-wash water storage tank, 3-tank liquid pump, 4-wash water pump, 5-polishing waste acid storage tank, 6-microfiltration membrane feed pump, 7-microfiltration membrane tank, 8-microfiltration membrane permeate storage tank, 9-microfiltration membrane concentrate discharge pump, 10-microfiltration membrane concentrate storage tank, 11-nanofiltration feed pump a, 12-nanofiltration membrane module a, 13-nanofiltration permeate storage tank, 14-primary concentrate storage tank, 15- 16-Nanofiltration feed tank a, 17-Nanofiltration feed pump b, 18-Nanofiltration membrane module b, 19-Secondary concentrate storage tank, 20-Secondary concentrate discharge pump, 21-Nanofiltration feed tank b, 22-Nanofiltration feed pump c, 23-Nanofiltration membrane module c, 24-Tertiary concentrate storage tank, 25-Evaporator inlet pump, 26-Negative pressure evaporator, 27-Acid discharge pump, 28-Finished acid storage tank. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] See Figure 1 As shown, this embodiment of the invention provides a multi-stage nanofiltration method for treating chemical waste liquid, including: Step 1, mixing the chemical polishing rinse water with the bath solution: Mix the first rinse water after chemical polishing with the chemical polishing bath solution in a certain proportion, and the specific gravity after mixing is 1.10-1.15; Step 2, Microfiltration membrane separation of impurities: The mixed chemical polishing waste acid is passed through a microfiltration membrane box to remove suspended colloids and solid particulate matter. The chemical polishing waste acid contains phosphoric acid, sulfuric acid and aluminum ions. Step 3, primary nanofiltration: The chemical waste acid treated in step 2 is processed through a nanofiltration membrane and operated at a pressure of 30-35 bar. The primary permeate recovery rate is controlled at 70%-75%. The resulting primary permeate enters the subsequent evaporation process, and the primary concentrate is collected for later use. Step 4, Secondary nanofiltration: The primary concentrate produced in Step 3 is diluted with pure water and then sent to the secondary nanofiltration membrane module. It is operated at an operating pressure of 35-45 bar. The secondary permeate is incorporated into the subsequent evaporation process. The secondary concentrate is discharged after reaching the set recovery rate of 60%-70% or is further diluted and sent to the tertiary nanofiltration membrane module. Step 5, tertiary nanofiltration: The secondary concentrate is diluted and then enters the tertiary nanofiltration membrane module, which operates at a pressure of 45-50 bar. The tertiary permeate enters the subsequent evaporation process, and the tertiary concentrate is discharged after the recovery rate reaches 50%-70%. Step 6, negative pressure evaporation and concentration: The primary product water from step 3, the secondary product water from step 4, and the tertiary product water from step 5 are transferred to a negative pressure evaporation and concentration device for negative pressure evaporation and concentration treatment to obtain the finished product, recycled acid. In some embodiments of this application, when the first rinse water after chemical polishing is mixed with the chemical polishing tank liquid in a proportional manner in step 1, replacement water is also added to adjust the specific gravity of the chemical polishing waste acid to 1.10 to 1.15.

[0026] In some embodiments of this application, the microfiltration membrane described in step 2 is a hollow fiber microfiltration membrane.

[0027] In some embodiments of this application, the nanofiltration membrane described in steps 3, 4, and 5 is an acid-resistant nanofiltration membrane with a membrane area of ​​6m². 2 The operating frequency is 30-40Hz.

[0028] In some embodiments of this application, the negative pressure evaporation and concentration device in step 6 provides a negative pressure environment through a vacuum pump unit.

[0029] Specifically, the washing water is treated using the above process, and its main components are shown in Table 1:

[0030] The phosphoric acid recovery rate was 76.82%, the sulfuric acid recovery rate was 82.41%, and the aluminum ion removal rate was 98.26%. After initial dilution, the concentrate was treated by nanofiltration. The nanofiltration high-pressure pump frequency was modulated at 30Hz, the initial pressure was 35 bar, and the concentrate discharge pressure was 45 bar. The concentrate was discharged when the recovery rate reached 70%. The concentrations of each component before and after nanofiltration membrane treatment are shown in Table 2.

[0031] The phosphoric acid recovery rate was 52.74%, the sulfuric acid recovery rate was 54.64%, and the aluminum ion removal rate was 99.07%. After dilution of the secondary concentrate, it was treated by nanofiltration. The nanofiltration high-pressure pump frequency was modulated at 30Hz, the initial pressure was 45 bar, and the concentrate discharge pressure was 50 bar. The concentrate was discharged when the recovery rate reached 70%. The concentrations of each component before and after nanofiltration membrane treatment are shown in Table 3.

[0032] The phosphoric acid recycling rate was 32.64%, the sulfuric acid recycling rate was 29.74%, and the aluminum ion removal rate was 99.2%. Therefore, the overall process achieved a phosphoric acid recycling rate of 92.62%, a sulfuric acid recycling rate of 94.39%, and an aluminum ion removal rate of 96.57%.

[0033] See Figure 2 As shown, this embodiment of the invention provides a multi-stage nanofiltration system for treating chemical waste liquid, comprising: 1. Polishing tank liquid storage tank; 2. Washing water storage tank; 3. Tank liquid pump; 4. Washing water pump; 5. Chemical polishing waste acid storage tank; 6. Microfiltration membrane feed pump; 7. Microfiltration membrane tank; 8. Microfiltration membrane permeate storage tank; 9. Microfiltration membrane concentrate discharge pump; 10. Microfiltration membrane concentrate storage tank; 11. Nanofiltration feed pump a11; 12. Nanofiltration membrane assembly a12; 13. Nanofiltration permeate storage tank; 14. Primary concentrate storage tank; 15. Primary concentrate discharge pump; 16. Nanofiltration feed tank a16; 17. Nanofiltration feed pump b17; 18. Nanofiltration membrane assembly b18; 19. Secondary concentrate storage tank; 20. Secondary concentrate discharge pump; 21. Nanofiltration feed tank b21; 22. Nanofiltration feed pump c22; 23. Nanofiltration membrane assembly c23; 24. Tertiary concentrate storage tank; 25. Evaporator feed pump; 26. Negative pressure evaporator; 27. Acid discharge pump; 28. Finished acid storage tank.

[0034] The outlet of the polishing tank liquid storage tank 1 is connected to the inlet of the chemical polishing waste acid storage tank 5 via a pipeline through a tank liquid pump 3. The outlet of the washing water storage tank 2 is connected to the inlet of the chemical polishing waste acid storage tank 5 via a washing water pump 4. The outlet of the chemical polishing waste acid storage tank 5 is connected to the inlet of the microfiltration membrane tank 7 via a pipeline through a microfiltration membrane inlet pump 6. The product water outlet of the microfiltration membrane tank 7 is connected to the inlet of the microfiltration membrane product water storage tank 8 via a pipeline. The inlet of the microfiltration membrane concentrate storage tank 10 is connected to the concentrate outlet of the microfiltration membrane tank 7 via a pipeline through a microfiltration membrane concentrate discharge pump 9. The outlet of the microfiltration membrane permeate storage tank 13 is connected to the inlet of the nanofiltration membrane module a12 via a pipeline through the nanofiltration feed pump a11. The permeate outlet of the nanofiltration membrane module a12 is connected to the inlet of the nanofiltration permeate storage tank 13 via a pipeline. The concentrate outlet of the nanofiltration membrane module a12 is connected to the inlet of the primary concentrate storage tank 14 via a pipeline. The outlet of the primary concentrate storage tank 14 is connected to the inlet of the nanofiltration feed tank a16 via the primary concentrate discharge pump 15. The outlet of the nanofiltration feed tank a16 is connected to the inlet of the nanofiltration membrane module b18 via the nanofiltration feed pump b17. The permeate outlet of the nanofiltration membrane module b18 is connected to the inlet of the nanofiltration permeate storage tank 13 via a pipeline. The concentrate outlet of the nanofiltration membrane module b18 is connected to the inlet of the secondary concentrate storage tank 19 via a pipeline. The outlet of the secondary concentrate storage tank 19 is connected to the inlet of the nanofiltration feed tank b21 via the secondary concentrate discharge pump 20. The outlet of the nanofiltration feed tank b21 is connected to the inlet of the nanofiltration membrane module c23 via the nanofiltration feed pump c22. The permeate outlet of the nanofiltration membrane module c23 is connected to the inlet of the nanofiltration permeate storage tank 13 via a pipeline. The concentrate outlet of the nanofiltration membrane module c23 is connected to the inlet of the tertiary concentrate storage tank 24 via a pipeline. The outlet of the nanofiltration permeate storage tank 13 is connected to the inlet of the negative pressure evaporator 26 via a pipeline through the evaporator inlet pump 25, and the outlet of the negative pressure evaporator 26 is connected to the inlet of the finished acid storage tank 28 via a pipeline through the acid discharge pump 27.

[0035] The negative pressure evaporator 26 provides a negative pressure environment through a vacuum pump unit.

[0036] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0037] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for multi-stage nanofiltration treatment of a polishing effluent, characterized in that, The method comprises the following steps: Step 1, mixing the first water washing water after chemical polishing with the tank liquid: the first water washing water after chemical polishing is mixed with the chemical polishing tank liquid in proportion, and the specific gravity of the mixture is 1.10-1.15; Step 2, removing impurities by microfiltration membrane: the mixed chemical polishing waste acid containing phosphoric acid, sulfuric acid and aluminum ions is passed through a microfiltration membrane tank to remove suspended colloids and solid particles; Step 3, primary nanofiltration: the chemical polishing waste acid treated in step 2 is treated by nanofiltration membrane under the operating pressure of 30-35 bar, and the primary water recovery rate is controlled to be 70%-75%; the obtained primary water is sent to the subsequent evaporation process, and the primary concentrated water is collected for standby; Step 4, secondary nanofiltration: the primary concentrated water obtained in step 3 is diluted with pure water and then sent to the secondary nanofiltration membrane group under the operating pressure of 35-45 bar; the secondary water is sent to the subsequent evaporation process, and the secondary concentrated water is discharged or continuously diluted to enter the tertiary nanofiltration membrane group when the set recovery rate of 60%-70% is reached; Step 5, tertiary nanofiltration: the secondary concentrated water is diluted and then sent to the tertiary nanofiltration membrane group under the operating pressure of 45-50 bar; the tertiary water is sent to the subsequent evaporation process, and the tertiary concentrated water is discharged when the recovery rate of 50%-70% is reached; Step 6, negative pressure evaporation and concentration: the primary water in step 3, the secondary water in step 4 and the tertiary water in step 5 are transferred to a negative pressure evaporation and concentration device for negative pressure evaporation and concentration treatment to obtain finished product recycling acid.

2. The method of claim 1, wherein the multi-stage nanofiltration process for treating chemical polishing waste solution is characterized by, In step 1, displacement water is added when the first water washing water after chemical polishing is mixed with the chemical polishing tank liquid in proportion to adjust the specific gravity of the chemical polishing waste acid to 1.10-1.

15.

3. The method of claim 1, wherein the multi-stage nanofiltration process for treating chemical polishing waste solution is characterized by, The microfiltration membrane in step 2 is a hollow fiber microfiltration membrane.

4. The method of claim 1, wherein the multi-stage nanofiltration process for treating chemical polishing waste solution is characterized by, The nanofiltration membrane described in steps 3, 4 and 5 is an acid-resistant nanofiltration membrane, and the membrane area is 6 m 2 , and the operating frequency is 30-40 Hz.

5. The method of claim 1, wherein the multi-stage nanofiltration process for treating chemical polishing waste solution is characterized by, The negative pressure evaporation and concentration device in step 6 provides a negative pressure environment through a vacuum pump set.

6. A multi-stage nanofiltration system for treating chemical polishing waste liquid, which is used to realize the method of any one of claims 1-5, and comprises: a polishing tank liquid storage tank, a water washing water storage tank, a tank liquid pump, a water washing water pump, a chemical polishing waste acid storage tank, a microfiltration membrane liquid inlet pump, a microfiltration membrane tank, a microfiltration membrane water storage tank, a microfiltration membrane concentrated water discharge pump, a microfiltration membrane concentrated water storage tank, a nanofiltration feed pump a, a nanofiltration membrane group a, a nanofiltration water storage tank, a primary concentrated water storage tank, a primary concentrated water discharge pump, a nanofiltration feed tank a, a nanofiltration feed pump b, a nanofiltration membrane group b, a secondary concentrated water storage tank, a secondary concentrated water discharge pump, a nanofiltration feed tank b, a nanofiltration feed pump c, a nanofiltration membrane group c, a tertiary concentrated water storage tank, an evaporator liquid inlet pump, a negative pressure evaporator, an acid discharge pump and a finished product acid storage tank; the water outlet of the polishing tank liquid storage tank is connected to the liquid inlet of the chemical polishing waste acid storage tank through the tank liquid pump via a pipeline, the water outlet of the water washing water storage tank is connected to the liquid inlet of the chemical polishing waste acid storage tank through the water washing water pump via a pipeline, the water outlet of the chemical polishing waste acid storage tank is connected to the liquid inlet of the microfiltration membrane tank through the microfiltration membrane liquid inlet pump via a pipeline, the water outlet of the microfiltration membrane tank is connected to the liquid inlet of the microfiltration membrane water storage tank via a pipeline, and the liquid inlet of the microfiltration membrane concentrated water storage tank is connected to the concentrated water outlet of the microfiltration membrane tank through the microfiltration membrane concentrated water discharge pump via a pipeline; The water outlet of the microfiltration membrane water production tank is connected to the inlet of the nanofiltration membrane group a through a nanofiltration feed pump a and a pipeline, the water outlet of the nanofiltration membrane group a is connected to the inlet of the nanofiltration water production tank through a pipeline, and the concentrated water outlet of the nanofiltration membrane group a is connected to the inlet of the primary concentrated water tank through a pipeline; The water outlet of the primary concentrated water tank is connected to the inlet of the nanofiltration feed tank a through a primary concentrated water discharge pump, the outlet of the nanofiltration feed tank a is connected to the inlet of the nanofiltration membrane group b through a nanofiltration feed pump b and a pipeline, the water outlet of the nanofiltration membrane group b is connected to the inlet of the nanofiltration water production tank through a pipeline, and the concentrated water outlet of the nanofiltration membrane group b is connected to the inlet of the secondary concentrated water tank through a pipeline; The water outlet of the secondary concentrated water tank is connected to the inlet of the nanofiltration feed tank b through a secondary concentrated water discharge pump, the outlet of the nanofiltration feed tank b is connected to the inlet of the nanofiltration membrane group c through a nanofiltration feed pump c and a pipeline, the water outlet of the nanofiltration membrane group c is connected to the inlet of the nanofiltration water production tank through a pipeline, and the concentrated water outlet of the nanofiltration membrane group c is connected to the inlet of the tertiary concentrated water tank through a pipeline; The water outlet of the nanofiltration water production tank is connected to the inlet of the negative pressure evaporator through an evaporator feed pump and a pipeline, and the water outlet of the negative pressure evaporator is connected to the inlet of the finished acid tank through an acid discharge pump and a pipeline.

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