Impurity removal and decolorization method and system for surface treatment of waste acid

Abstract

The invention provides an impurity removal and decolorization method for surface treatment of waste acid, which improves the filtering efficiency, improves the waste acid recovery efficiency and saves the production cost. The method comprises the following steps: S1, filtering; suspended matter impurities in waste acid are removed through a self-cleaning filter, and filtrate is formed; s2, extracting; adding tributyl phosphate into the filtrate, uniformly mixing, and standing for layering to obtain a bottom solution and a top solution; s3, reverse extraction; water is added into the top solution, after uniform mixing, standing and layering are carried out, an upper-layer solution and a lower-layer solution are obtained, the lower-layer solution comprises strip liquor for back extraction of phosphoric acid, and the upper-layer solution comprises a tributyl phosphate solution obtained after back extraction; taking the tributyl phosphate subjected to reverse extraction as an extracting agent to be continuously used for extracting and decolorizing; the lower-layer solution is used for repeated reverse extraction until the concentration of the mixed acid meets the requirement, and bottom raffinate acid is obtained; and S4, complexing. And S5, re-filtering. The invention also provides an impurity-removing and decolorizing system for surface treatment of waste acid.

Description

Technical Field

[0001] The invention relates to the technical field of industrial waste acid treatment, and in particular to a method and system for removing impurities and decolorizing surface treated waste acid. Background Art

[0002] Aluminum plate is an important structural material, and generally there will be some dirt and oxide layer on its surface, which will not only affect the performance of the aluminum plate itself, but also reduce its service life. Therefore, the surface treatment of aluminum plate can be carried out by pickling with polishing liquid, which mainly removes the dirt and oxide layer on the surface of aluminum plate, thereby improving the quality and performance of the surface of aluminum plate. Conventional waste acid is a mixed acid of phosphoric acid and sulfuric acid. Scrapped waste acid has high content of phosphoric acid, sulfuric acid, and metal salts, and its appearance is brown or reddish brown. The direct discharge of this waste acid greatly increases the operating cost of the back-end water treatment. Therefore, the environmentally friendly and economical approach is to recycle the waste acid after treatment, and re-obtain the mixed acid solution with low impurity content after the waste acid treatment, which is further used for the surface treatment of aluminum plate.

[0003] Existing waste acid treatment method "Study on the process of extracting and purifying low-concentration wet-process phosphoric acid using tributyl phosphate in sulfuric acid-phosphoric acid system" In the sulfuric acid-phosphoric acid system, the use of kerosene as a diluent mixed with tributyl phosphate to extract low-concentration wet-process phosphoric acid has a good purification effect. The removal rates of Fe2O3 and Al2O3 can reach more than 99%, and SO4 2－ The removal rate of P2O5 is nearly 80%, and the recovery rate of P2O5 after one stripping purification is about 40%. However, the stripping solution after water stripping is dilute phosphoric acid with a low phosphoric acid content. If the phosphoric acid concentration needs to be unified for reuse, an additional distillation process is required and the water consumption is large, resulting in low efficiency and high cost of waste liquid recycling.

[0004] Existing waste acid treatment methods usually include a filtration process. The filter used in the existing filtration process, such as patent CN201811625839.9, proposes a self-cleaning filter. When it is necessary to filter sewage, the discharge pipe and the through hole are misaligned, and the sewage enters the filter element from the through hole for filtration. When the filter element needs to be cleaned, the motor reducer drives the rotating tube to rotate, so that the discharge pipe and the through hole are aligned, and the dirt generated after the filter element is cleaned is discharged from the automatic sewage pipe. However, the solid particles in the waste acid generated after the polishing liquid is used are relatively sticky. During filtration, the solid particles will adhere to the filter screen and are difficult to completely scrape off, which can easily block the filter screen, causing difficulty in filtration and generating more inferior waste. The filter screen needs to be replaced frequently, resulting in reduced filtration effect, thereby reducing the waste acid recovery efficiency. Summary of the invention

[0005] In view of the shortcomings of low waste liquid recycling efficiency and high cost in existing waste acid treatment methods, the present invention provides a method and system for removing impurities and decolorizing waste acid by surface treatment, which improves filtration efficiency, improves waste acid recovery efficiency, and saves production costs.

[0006] The present invention adopts the following technical scheme: a method for removing impurities and decolorizing waste acid by surface treatment, characterized in that it comprises the following steps: S1: Filtration: The waste acid passes through a self-cleaning filter to remove suspended impurities in the waste liquid to form a filtrate; S2: extraction; adding tributyl phosphate to the filtrate, mixing evenly and then standing to separate into a bottom solution and a top solution, wherein the bottom solution includes a decolorized mixed acid solution, and the top solution includes a solution after tributyl phosphate absorption and a phosphoric acid solution; S3: stripping; adding water to the top solution, mixing evenly, standing and stratifying into an upper solution and a lower solution, wherein the lower solution comprises a stripping solution of stripping phosphoric acid, and the upper solution comprises a stripping tributyl phosphate solution, and the pigment is deposited on the top; the stripped tributyl phosphate is used as an extractant for extraction and decolorization until too much pigment is deposited and there is no decolorization effect, and then discharged into activated carbon for adsorption and decolorization and reuse; the lower solution is used for repeated stripping until the mixed acid concentration reaches the requirement to obtain the bottom residual acid; S4: complexation; adding a complexing agent to the bottom residual acid after stripping, stirring and reacting to form a solid-containing mixed solution; S5: re-filtration; filtering the solid-containing mixed solution to obtain a mixed acid solution after impurities are removed, and the mixed acid after impurities are removed is used for surface treatment of aluminum plates.

[0007] It is further characterized by: In S1, suspended impurities in the self-cleaning filter are enriched on the inner wall of the self-cleaning filter to form a mud cake layer, and the mud cake layer is dispersed by backwashing liquid and scraped off with the assistance of a scraper, and the backwashing liquid includes the filtrate; In S2, the volume ratio of the mixed acid to tributyl phosphate is 1:0.5-1, and after being mixed evenly, the mixture is allowed to stand for 15-30 minutes to separate into layers; In S3, the volume ratio of the top solution to water is 1:1-2; In S4, the molar ratio of aluminum in the bottom raffinate to the complexing agent is 1:1-2, and the stirring reaction time is 1-2h; The complexing agent includes one or a combination of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, and dipotassium ethylenediaminetetraacetate.

[0008] A system for removing impurities and decolorizing waste acid for surface treatment, characterized in that it comprises an extraction reaction tank, a complex reaction tank and a stripping reaction tank; the feed port of the extraction reaction tank is connected to waste liquid through a self-cleaning filter, the feed port of the extraction reaction tank is also connected to tributyl phosphate, the extraction lower layer liquid outlet of the extraction reaction tank is connected to the first inlet of the complex reaction tank, and the extraction upper layer liquid outlet of the extraction reaction tank is connected to the first inlet of the stripping reaction tank; the second inlet of the complex reaction tank is connected to a complexing agent, the third inlet is connected to a stripping liquid tank, the lower layer liquid outlet of the complex reaction tank is connected to the inlet of a filter press through a diaphragm pump, and the outlet of the filter press is connected to a mixed acid temporary storage tank; the lower layer liquid outlet of the stripping reaction tank is connected to the liquid inlet of the stripping liquid tank, the upper layer liquid outlet of the stripping reaction tank is connected to the inlet of an extractant tank, the second inlet of the stripping reaction tank is connected to the liquid outlet of the stripping liquid tank, and the liquid outlet of the extractant tank is connected to the extraction reaction tank.

[0009] It is further characterized by: The upper and lower liquid outlets of the extraction reaction tank, the upper and lower liquid outlets of the stripping reaction tank, the liquid outlet of the stripping liquid tank and the liquid outlet of the extractant tank are all provided with centrifugal pumps; The feed inlet and upper liquid outlet of the extraction reaction tank, the first inlet, the second inlet and the upper liquid outlet of the stripping reaction tank, and the first inlet and the lower liquid outlet of the complexing reaction tank are all provided with ball valves, the upper liquid outlet and the lower liquid outlet of the extraction reaction tank are connected by the ball valve, and the upper liquid outlet and the lower liquid outlet of the stripping reaction tank are connected by the ball valve; The extraction reaction tank and the stripping reaction tank are provided with a hydrometer, and the lower liquid outlets of the extraction reaction tank and the stripping reaction tank are both provided with a cut-off valve and a pipeline sight glass, the hydrometer of the extraction reaction tank is control-connected with the cut-off valve, and the hydrometer of the stripping reaction tank is control-connected with the cut-off valve; The self-cleaning filter includes a main bin, a scraper is arranged inside the main bin, a waste liquid feed port is arranged at the top of the main bin, a backwash liquid inlet and a filtrate outlet are arranged in the middle of the main bin, a solid and impurity discharge port is arranged at the bottom of the main bin, and the waste liquid feed port, the backwash liquid inlet, the filtrate outlet and the solid and impurity discharge port are all provided with cut-off valves.

[0010] After adopting the present invention, the treatment of the residual acid adopts a circulating extraction method to increase the concentration of the stripping solution, reduce the amount of water used, and reduce the production cost. The complexing effect of the complexing agent on the metal is used to deeply remove the metal salt in the waste acid, and the metal ions therein are complexed to form solid impurities and then filtered and removed, so that they can be reused for surface treatment, thereby improving the waste acid recovery efficiency. During filtration, the filtrate is used to backwash the stock solution, and the mud cake is washed and scraped off without affecting the concentration of the stock solution. After discharging, the next wave of filtration can be entered, reducing the frequency of replacing the filter screen, thereby improving the filtration efficiency and further improving the waste acid recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The present invention is a process flow chart of a method for removing impurities and decolorizing waste acid by surface treatment; Figure 2 This is a schematic structural diagram of a system for removing impurities and decolorizing waste acid for surface treatment of the present invention; Figure 3 It is a structural schematic diagram of the extraction tank of the present invention; Figure 4 It is a schematic structural diagram of the self-cleaning filter of the present invention. DETAILED DESCRIPTION

[0012] See Figures 2 to 4 , a system for removing impurities and decolorizing waste acid for surface treatment, comprising an extraction reaction tank 2, a complexation reaction tank 4 and a stripping reaction tank 8; the feed port of the extraction reaction tank 2 is connected to the waste liquid through a self-cleaning filter 1, the feed port 1-1 of the extraction reaction tank 2 is also connected to tributyl phosphate, the extraction lower layer liquid outlet 1-4 of the extraction reaction tank 2 is connected to the first inlet 4-1 of the complexation reaction tank 4, the extraction upper layer liquid outlet 1-5 of the extraction reaction tank 2 is connected to the first inlet 8-1 of the stripping reaction tank 8; the first inlet 8-1 of the complexation reaction tank 4 is connected to the first inlet 8-2 of the stripping reaction tank 8; the first inlet 8-2 of the stripping reaction tank 8 is connected to the first inlet 8-3 of the stripping reaction tank 8; the first inlet 8-4 of the stripping reaction tank 8 is connected to the first inlet 8-4 of the stripping reaction tank 8; the first inlet 8-1 of the stripping reaction tank 8 is connected to the first inlet 8-2 ...1 of the stripping reaction tank 8; the first inlet 8-1 of the stripping reaction tank 8 is connected to the first inlet 8-1 of the stripping reaction tank 8; the first inlet 8-1 of the stripping reaction tank 8 is connected to the The second inlet 4-2 is connected to the complexing agent, the third inlet 4-3 is connected to the stripping liquid tank 9, the lower liquid outlet of the complexing reaction tank 4 is connected to the inlet of the filter press 6 through the diaphragm pump 5, and the outlet of the filter press 6 is connected to the mixed acid temporary storage tank 7; the lower liquid outlet of the stripping reaction tank 8 is connected to the liquid inlet of the stripping liquid tank 9, the upper liquid outlet of the stripping reaction tank 8 is connected to the inlet of the extractant tank 10, the second inlet 8-2 of the stripping reaction tank 8 is connected to the liquid outlet of the stripping liquid tank 9, and the liquid outlet of the extractant tank 10 is connected to the extraction reaction tank 2.

[0013] The upper liquid outlet 1-5 and the lower liquid outlet 1-4 of the extraction reaction tank 2, the upper liquid outlet 8-4 and the lower liquid outlet 8-3 of the stripping reaction tank 8, the liquid outlet of the stripping liquid tank 9 and the liquid outlet of the extractant tank 10 are all provided with a centrifugal pump 3.

[0014] The feed port 1-1 and the upper liquid outlet 1-5 of the extraction reaction tank 2, the first inlet 8-1, the second inlet 8-2 and the upper liquid outlet 8-4 of the stripping reaction tank 8, and the first inlet 4-1 and the lower liquid outlet 4-4 of the complexing reaction tank 4 are all provided with a ball valve 1-2, the upper liquid outlet 1-5 and the lower liquid outlet 1-4 of the extraction reaction tank 2 are connected by the ball valve 1-2, and the upper liquid outlet 8-4 and the lower liquid outlet 8-3 of the stripping reaction tank 8 are connected by the ball valve 1-2.

[0015] The extraction reaction tank 2 and the stripping reaction tank 8 are provided with a hydrometer 12, and the lower liquid outlets of the extraction reaction tank 2 and the stripping reaction tank 8 are provided with a cut-off valve 11 and a pipeline sight glass 13. The hydrometer 12 of the extraction reaction tank 2 is control-connected to the cut-off valve 11, and the hydrometer 12 of the stripping reaction tank 8 is control-connected to the cut-off valve 11.

[0016] The self-cleaning filter 1 includes a main bin 2-8, a scraper is arranged inside the main bin 2-8, the scraper is connected to a motor, a waste liquid feed port is arranged at the top of the main bin 2-8, a backwash liquid inlet 2-4 and a filtrate outlet 2-6 are arranged in the middle of the main bin 2-8, a solid and impurity discharge port 2-7 is arranged at the bottom of the main bin 2-8, and a shut-off valve 11 is arranged at the waste liquid feed port, the backwash liquid inlet, the filtrate outlet and the solid and impurity discharge port.

[0017] Figure 3 In the middle, 1-3 are stirring blades.

[0018] See Figure 1 , a method for removing impurities and decolorizing surface-treated waste acid, comprising the following steps: S1: Filtration; the waste liquid passes through the self-cleaning filter 1 to remove suspended impurities in the waste liquid to form a filtrate; the suspended impurities in the self-cleaning filter 1 are enriched on the inner wall of the self-cleaning filter 1 to form a mud cake layer, which is dispersed by backwashing liquid and scraped off with the assistance of a scraper. The backwashing liquid is preferably the filtrate; During filtration, the self-cleaning filter 1 closes the backwash liquid inlet 2-4 and the solid impurity outlet 2-7. The waste liquid enters the main bin from the waste liquid inlet 2-1, the scraper is turned on for stirring, and the filtrate is discharged from the filtrate outlet 2-6. If the solid content in the self-cleaning filter 1 is too high and filtration is difficult, close the feed inlet 2-1 and the filtrate outlet 2-6. Open the 2-4 backwash liquid feed inlet, and after the backwash liquid enters the main filtration bin, it cooperates with the scraper to flush the mud cake down, and is discharged from the solid impurity outlet 2-7, and then collected and filtered separately. Reduce the number of filter screen changes in production and improve efficiency.

[0019] S2: Extraction; tributyl phosphate is added to the filtrate at a volume ratio of 1:0.5-1, mixed evenly for 15-30 minutes, and then allowed to stand and separate into a bottom solution and a top solution. The bottom solution includes the decolorized mixed acid solution, and the top solution includes the solution after tributyl phosphate absorption and a phosphoric acid solution.

[0020] The extraction tank is connected to the cut-off valve 11 by a hydrometer 12. The feed inlet valve 1-2 is opened. During extraction, the extractant and waste acid are added from the feed inlet 1-1. The stirrer 1-3 is opened to stir and mix well, and then closed and left to stand. After standing, the bottom 1-4 discharge pipe discharges the bottom solution after stratification. The hydrometer 121-6 is installed at the bottom of the extraction tank and is interlocked with the cut-off valve 111-8. When the hydrometer 12 contacts the top solution and the specific gravity result drops significantly, the bottom discharge cut-off valve 111-8 is interlocked and closed. After closing, the remaining upper liquid is discharged from the upper liquid outlet 1-5. If the hydrometer 121-6 fails, the stratified discharge situation can be judged through the sight glass 1-7.

[0021] S3: stripping; adding water to the top solution, the volume ratio of the top solution to water is 1:1-2; after uniform mixing, standing and stratifying into an upper solution and a lower solution, the lower solution includes the stripping solution of stripping phosphoric acid, the upper solution includes the tributyl phosphate solution after stripping, and the pigment is deposited on the top; the tributyl phosphate after stripping is used as an extractant for extraction and decolorization until too much pigment is deposited and there is no decolorization effect, then it is discharged into activated carbon for adsorption decolorization and reused; the lower solution is used for repeated stripping until the mixed acid concentration reaches the requirement to obtain the bottom residual acid.

[0022] S4: complexation: add a complexing agent to the bottom residual acid after stripping at a molar ratio of aluminum to complexing agent of 1:1-2, and stir to react for 1-2 hours to form a solid mixed solution. The complexing agent includes one or a combination of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, and dipotassium ethylenediaminetetraacetate.

[0023] S5: re-filtration; The solid-containing mixed solution is filtered to obtain a mixed acid solution after impurities are removed, and the mixed acid after impurities are used for aluminum plate surface treatment. The filtered solid is metal salt mud, which needs to be outsourced for treatment.

[0024] The present invention is further described below in conjunction with application examples and accompanying drawings: Embodiment 1: The filtrate generated after the polishing waste liquid is filtered through the self-cleaning filter 1 is added with tributyl phosphate at a volume ratio of 1:1, mixed evenly for 15 minutes and then allowed to stand for stratification. The bottom solution is the decolorized mixed acid solution, and the top solution is discharged into the stripping reaction tank 8.

[0025] The top solution is added with water in a volume ratio of 1:1 according to the liquid level, mixed evenly, and then allowed to stand for stratification. The lower solution is the stripping solution for stripping phosphoric acid, and the phosphoric acid concentration is about 15%. The stripping solution is stored in the stripping solution tank 9 for the second stripping, and stripping is performed 7 times until the phosphoric acid concentration reaches about 54%, and the bottom residual acid is obtained and discharged into the complex reaction tank 4. The upper solution is the tributyl phosphate solution after stripping, which is repeatedly used for decolorization until there is no decolorization effect and discharged, and enters the activated carbon for adsorption decolorization, and the decolorized tributyl phosphate is reused as an extractant.

[0026] Add the complexing agent to the bottom residual acid after stripping at a molar ratio of aluminum to complexing agent of 1:1, stir and react for 1 hour, and then filter to obtain a mixed acid solution after impurity removal. The mixed acid solution after impurity removal is temporarily stored in the mixed acid temporary storage tank 7. The test results after decolorization and impurity removal are as follows: Index before impurity removal Index after impurity removal Phosphoric acid content / % 55.46 54.21 Sulfuric acid content / % 10 9.87 Aluminum content / % 0.256 0.035 sodium / % 0.045 0.041 calcium / % 0.082 0.001 titanium / % 0.012 0.001 Potassium / % 0.024 0.012 Embodiment 2: The filtrate generated after the polishing waste liquid is filtered through the self-cleaning filter 1 is added with tributyl phosphate at a volume ratio of 1:1.5, mixed evenly for 30 minutes and then allowed to stand for stratification. The bottom solution is the decolorized mixed acid solution, and the top solution is discharged into the stripping reaction tank 8.

[0027] The top solution is added with water at a volume ratio of 1:1.5 according to the liquid level, mixed evenly, and then allowed to stand for stratification. The lower solution is the stripping solution for stripping phosphoric acid, with a phosphoric acid concentration of about 15%. The stripping solution is stored in the stripping solution tank 9 for the second stripping, and stripping is performed 13 times until the phosphoric acid concentration reaches about 53%, and the bottom residual acid is obtained and discharged into the complex reaction tank 4. The upper solution is the tributyl phosphate solution after stripping, which is repeatedly used for decolorization until there is no decolorization effect and discharged, and enters the activated carbon for adsorption decolorization. The decolorized tributyl phosphate is reused as an extractant.

[0028] Add the complexing agent to the bottom residual acid after stripping at a molar ratio of aluminum to complexing agent of 1:1.5, stir and react for 1.5 hours, and then filter to obtain a mixed acid solution after impurity removal. The mixed acid solution after impurity removal is temporarily stored in the mixed acid temporary storage tank 7. The test results after decolorization and impurity removal are as follows: Index before impurity removal Index after impurity removal Phosphoric acid content / % 55.46 54.51 Sulfuric acid content / % 10 9.65 Aluminum content / % 0.256 0.025 sodium / % 0.045 0.033 calcium / % 0.082 0.0008 titanium / % 0.012 0.0002 Potassium / % 0.024 0.019 Embodiment 3: The filtrate generated after the polishing waste liquid is filtered through the self-cleaning filter 1 is added with tributyl phosphate at a volume ratio of 1:2, and the mixture is evenly mixed for 30 minutes and then allowed to stand for stratification. The bottom solution is the mixed acid solution after decolorization, and the top solution is discharged into the stripping reaction tank 8.

[0029] The top solution is added with water at a volume ratio of 1:2 according to the liquid level, mixed evenly, and then allowed to stand for stratification. The lower solution is the stripping solution for stripping phosphoric acid, and the phosphoric acid concentration is about 15%. The stripping solution is stored in the stripping solution tank 9 for the second stripping, and stripping is performed 16 times until the phosphoric acid concentration reaches about 52%, and the bottom residual acid is obtained and discharged into the complex reaction tank 4. The upper solution is the tributyl phosphate solution after stripping, which is repeatedly used for decolorization until there is no decolorization effect and discharged, and enters the activated carbon for adsorption decolorization, and the decolorized tributyl phosphate is reused as an extractant.

[0030] Add the complexing agent to the bottom residual acid after stripping at a molar ratio of aluminum to complexing agent of 1:2, stir and react for 2 hours, and then filter to obtain a mixed acid solution after impurity removal. The mixed acid solution after impurity removal is temporarily stored in the mixed acid temporary storage tank 7. The test results after decolorization and impurity removal are as follows: Index before impurity removal Index after impurity removal Phosphoric acid content / % 55.46 53.51 Sulfuric acid content / % 10 9.81 Aluminum content / % 0.256 0.015 sodium / % 0.045 0.033 calcium / % 0.082 0.0004 titanium / % 0.012 0.0003 Potassium / % 0.024 0.018 It can be seen from Examples 1, 2 and 3 that after adopting the present invention, the phosphoric acid content and sulfuric acid content of the mixed acid after impurity removal are stable, the metal ion content is greatly reduced, and the recovery efficiency of the waste acid is greatly improved.

Claims

1. A method for removing impurities and decolorizing surface-treated waste acid, characterized in that: It includes the following steps: S1: Filtration: The waste acid passes through a self-cleaning filter to remove suspended impurities in the waste liquid to form a filtrate; S2: extraction; adding tributyl phosphate to the filtrate, mixing evenly and then standing to separate into a bottom solution and a top solution, wherein the bottom solution includes a decolorized mixed acid solution, and the top solution includes a solution after tributyl phosphate absorption and a phosphoric acid solution; S3: stripping; adding water to the top solution, mixing evenly, standing and stratifying into an upper solution and a lower solution, wherein the lower solution comprises a stripping solution of stripping phosphoric acid, and the upper solution comprises a stripping tributyl phosphate solution, and the pigment is deposited on the top; the stripped tributyl phosphate is used as an extractant for extraction and decolorization until too much pigment is deposited and there is no decolorization effect, and then discharged into activated carbon for adsorption and decolorization and reuse; the lower solution is used for repeated stripping until the mixed acid concentration reaches the requirement to obtain the bottom residual acid; S4: complexation; adding a complexing agent to the bottom residual acid after stripping, stirring and reacting to form a solid-containing mixed solution; S5: re-filtration; The solid-containing mixed solution is filtered to obtain a mixed acid solution after impurities are removed, and the mixed acid after impurities are removed is used for surface treatment of aluminum plates.

2. The method for removing impurities and decolorizing surface treated waste acid according to claim 1, characterized in that: In S1, the suspended impurities in the self-cleaning filter are enriched on the inner wall of the self-cleaning filter to form a mud cake layer, which is dispersed by backwashing liquid and scraped off with the assistance of a scraper. The backwashing liquid includes the filtered mixed acid.

3. The method for removing impurities and decolorizing surface treated waste acid according to claim 1, characterized in that: In S2, the volume ratio of the mixed acid to tributyl phosphate is 1:0.5-1. After mixing evenly, let it stand for 15-30 minutes to separate into layers.

4. The method for removing impurities and decolorizing surface treated waste acid according to claim 1, characterized in that: In S3, the volume ratio of the top solution to water is 1:1-2.

5. The method for removing impurities and decolorizing surface treated waste acid according to claim 1, characterized in that: In S4, the molar ratio of aluminum in the bottom raffinate to the complexing agent is 1:1-2, and the stirring reaction time is 1-2h.

6. The method for removing impurities and decolorizing surface treated waste acid according to claim 5, characterized in that: The complexing agent includes one or a combination of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, and dipotassium ethylenediaminetetraacetate.

7. A system for removing impurities and decolorizing waste acid from surface treatment, comprising an extraction reaction tank, a complex reaction tank and a stripping reaction tank; the feed port of the extraction reaction tank is connected to the waste liquid through a self-cleaning filter, the feed port of the extraction reaction tank is also connected to tributyl phosphate, the extraction lower layer liquid outlet of the extraction reaction tank is connected to the first inlet of the complex reaction tank, and the extraction upper layer liquid outlet of the extraction reaction tank is connected to the first inlet of the stripping reaction tank; the second inlet of the complex reaction tank is connected to the complexing agent, the third inlet is connected to the stripping liquid tank, the lower layer liquid outlet of the complex reaction tank is connected to the inlet of the filter press through a diaphragm pump, and the outlet of the filter press is connected to the mixed acid temporary storage tank; the lower layer liquid outlet of the stripping reaction tank is connected to the liquid inlet of the stripping liquid tank, the upper layer liquid outlet of the stripping reaction tank is connected to the inlet of the extractant tank, the second inlet of the stripping reaction tank is connected to the liquid outlet of the stripping liquid tank, and the liquid outlet of the extractant tank is connected to the extraction reaction tank.

8. The impurity removal and decolorization system for surface treatment waste acid according to claim 7, characterized in that: The upper layer liquid outlet and the lower layer liquid outlet of the extraction reaction tank, the upper layer liquid outlet and the lower layer liquid outlet of the stripping reaction tank, the liquid outlet of the stripping liquid tank and the liquid outlet of the extractant tank are all provided with centrifugal pumps, the feed port and the upper layer liquid outlet of the extraction reaction tank, the first inlet, the second inlet and the upper layer liquid outlet of the stripping reaction tank, the first inlet and the lower layer liquid outlet of the complexing reaction tank are all provided with ball valves, the upper layer liquid outlet and the lower layer liquid outlet of the extraction reaction tank are connected by a ball valve, and the upper layer liquid outlet and the lower layer liquid outlet of the stripping reaction tank are connected by a ball valve.

9. The impurity removal and decolorization system for waste acid from surface treatment according to claim 8, characterized in that: The extraction reaction tank and the stripping reaction tank are provided with a hydrometer, and the lower liquid outlets of the extraction reaction tank and the stripping reaction tank are both provided with a cut-off valve and a pipeline sight glass, the hydrometer of the extraction reaction tank is control-connected to the cut-off valve, and the hydrometer of the stripping reaction tank is control-connected to the cut-off valve.

10. The impurity removal and decolorization system for waste acid from surface treatment according to claim 7, characterized in that: The self-cleaning filter includes a main bin, a scraper is arranged inside the main bin, the scraper is connected to a motor, a waste liquid feed port is arranged at the top of the main bin, a backwash liquid inlet and a filtrate outlet are arranged in the middle of the main bin, a solid and impurity discharge port is arranged at the bottom of the main bin, and the waste liquid feed port, the backwash liquid inlet, the filtrate outlet and the solid and impurity discharge port are all provided with cut-off valves.

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