Treatment methods for mixed wastewater from alkaline zinc-nickel alloy electroplating and passivation

Abstract

This invention provides a method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater. The method involves adjusting the pH of the wastewater to 4-6 by adding acid, adding ferrous chloride, and then adjusting the pH to 10-12 with lime slurry. Ferrous and calcium ions work synergistically to precipitate a carboxylic acid complexing agent, reducing hexavalent chromium to trivalent chromium by ferrous ions. Some zinc and trivalent chromium ions form hydroxide precipitates, which are then separated by filtration. The pH of the wastewater is then adjusted to 4.5-5.5 by adding acid, and sodium dimethyldithiocarbamate or sodium diethyldithiocarbamate is added to precipitate nickel and zinc ions, followed by filtration. Sodium hydroxide solution is added to adjust the pH to 6-8, and a biochemical method is used to reduce the COD of the wastewater. The treatment results meet the requirements of my country's electroplating pollutant emission standards and have good market prospects.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, and specifically relates to a method for treating mixed wastewater from alkaline zinc-nickel alloy electroplating and passivation. Background Technology

[0002] Alkaline zinc-nickel alloy electroplating wastewater contains aliphatic polyamine ligands, such as diethylenetriamine, which has extremely strong antioxidant capabilities, posing a significant challenge to wastewater treatment. The wastewater also contains hydroxylamine ligands and their oxidized forms, which are amine-containing carboxylic acid ligands. The impact of these ligands on wastewater treatment outcomes has not yet been studied in the industry.

[0003] Chinese invention patent with authorization announcement number "CN 104961273 B" entitled "A method for treating alkaline zinc-nickel alloy electroplating wastewater" discloses a technical solution: using hydrogen peroxide to oxidize the complexing agent, and precipitating zinc ions and nickel ions with sodium dimethyl dithiocarbamate under pH=4.5~5.5 conditions, so that the nickel ion content in the treated wastewater meets the requirements of Table 2 of GB21900-2008 "Electroplating Pollutant Discharge Standard".

[0004] Chinese invention patent application number "CN 107857389 A" entitled "Method for Treating Alkaline Zinc-Nickel Alloy Electroplating Wastewater" discloses a technical solution: zinc and nickel ions are precipitated using sodium diethyldithiocarbamate under pH conditions of 4.5–5.5. When the concentrations of zinc and nickel in the wastewater are less than or equal to 1% of the zinc and nickel concentrations in the plating solution, the nickel content in the treated wastewater meets the requirements of Table 3 of GB 21900-2008 "Electroplating Pollutant Discharge Standard". However, experiments have shown that this method can achieve the same result for wastewater from newly started alkaline zinc-nickel alloy plating tanks. However, for alkaline zinc-nickel alloy plating tanks that have been used for a long time, hydroxylamine is oxidized into a carboxylic acid ligand with strong coordinating ability, resulting in the wastewater treatment result failing to meet the requirements of Table 3 of GB 21900-2008. In many electroplating plants, alkaline zinc-nickel alloy electroplating wastewater and passivation wastewater are mixed together and discharged into the wastewater equalization tank. This method is not suitable for treating such mixed wastewater, and there are still some difficulties in treating this mixed wastewater. Summary of the Invention

[0005] Therefore, it is necessary to provide a new method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater, so that zinc, nickel, chromium, cobalt, coordinating agents and additives in the treated alkaline zinc-nickel alloy electroplating and passivation mixed wastewater can be effectively treated.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for treating mixed wastewater from alkaline zinc-nickel alloy electroplating and passivation includes the following steps:

[0008] (1) Under mechanical stirring, dilute hydrochloric acid was added to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater to adjust the pH to 4-6, and ferrous chloride solution was added;

[0009] (2) Under mechanical stirring, lime slurry is added to the wastewater treated in step (1) to adjust the pH to 10-12, precipitating the carboxylic acid complexing agent containing amine groups in the alkaline zinc-nickel alloy electroplating wastewater and the carboxylic acid complexing agent in the passivation wastewater, and some heavy metal ions in the wastewater are precipitated.

[0010] (3) Add flocculant to the wastewater after step (2) to cause the precipitate to aggregate into large particles and then settle.

[0011] (4) Filter to remove the precipitate after step (3);

[0012] (5) Under mechanical stirring, acid is added to adjust the pH of the wastewater treated in step (4) to 4.5-5.5, and a chelating agent is added to form precipitates of heavy metal ions;

[0013] (6) Add flocculant to the wastewater after step (5) to cause the precipitate to aggregate into large particles and then settle.

[0014] (7) Filter to remove the precipitate after step (6);

[0015] (8) Under mechanical stirring, add alkaline solution to the wastewater treated in step (7) to adjust the pH to 6-8, and reduce COD by biochemical method;

[0016] In step (2), within the pH range of 10 to 12, ferrous ions are used to reduce hexavalent chromium to trivalent chromium and generate chromium hydroxide precipitate.

[0017] The chelating agent mentioned in step (5) is sodium dimethyl dithiocarbamate solution with a mass concentration of (80-120) g / L;

[0018] The chelating agent mentioned in step (5) is sodium diethyldithiocarbamate trihydrate solution with a mass concentration of (80-120) g / L;

[0019] The flocculant mentioned in steps (3) and (6) is an aqueous solution of polyacrylamide with a mass concentration of 5 g / L.

[0020] In some embodiments, the ferrous chloride solution in step (1) contains ferrous chloride tetrahydrate at a mass concentration of (150-250) g / L; the volume ratio of the added ferrous chloride solution to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater is (0.3-2):100.

[0021] In some embodiments, the lime slurry in step (2) contains a calcium oxide concentration of (50-100) g / L.

[0022] In some embodiments, the chelating agent in step (5) is a sodium dimethyl dithiocarbamate solution with a mass concentration of 100 g / L.

[0023] In some embodiments, the volume ratio of sodium dimethyl dithiocarbamate solution added in step (5) to the treated wastewater is (0.5-5):100.

[0024] In some embodiments, the chelating agent in step (5) is a sodium diethyldithiocarbamate trihydrate solution with a mass concentration of 100 g / L.

[0025] In some embodiments, the volume ratio of sodium diethyldithiocarbamate trihydrate solution added in step (5) to the treated wastewater is (0.8-8):100.

[0026] In some embodiments, the flocculant in steps (3) and (6) is an aqueous solution of polyacrylamide with a mass concentration of 3 to 8 / L.

[0027] In some embodiments, dilute hydrochloric acid is used to adjust the pH in steps (1) and (5), wherein the dilute hydrochloric acid is hydrochloric acid with a mass fraction of 5% to 10%; and the alkaline solution in step (8) is a sodium hydroxide solution with a mass concentration of (20 to 80) g / L.

[0028] In some embodiments, the biochemical method described in step (8) employs a conventional biochemical degradation method.

[0029] The mixed wastewater from alkaline zinc-nickel alloy electroplating and passivation includes alkaline zinc-nickel alloy electroplating rinsing water and passivation rinsing water. The wastewater contains zinc, nickel, trivalent chromium, hexavalent chromium, cobalt, aliphatic polyamine ligands, hydroxylamine ligands, carboxylic acid ligands, and electroplating additives.

[0030] Within a pH range of 10–12, the synergistic effect of ferrous and calcium ions can precipitate and remove carboxylic acid complexing agents from wastewater. Ferrous ions can reduce hexavalent chromium to trivalent chromium. Aliphatic polyamines have strong coordination abilities for nickel, cobalt, and zinc ions, but no coordination effect on trivalent ions. After removing carboxylic acid complexing agents under pH conditions of 10–12, trivalent ions precipitate as chromium hydroxide.

[0031] Under pH conditions of 4.5–5.5, sodium dimethyl dithiocarbamate or sodium diethyl dithiocarbamate can precipitate and remove zinc, nickel, and cobalt ions, and can further precipitate residual trivalent chromium ions.

[0032] The aliphatic polyamine ligands in alkaline zinc-nickel alloy electroplating wastewater have extremely strong antioxidant properties, and oxidation methods are basically ineffective. Therefore, biochemical degradation methods are required to reduce the COD (chemical oxygen demand) of the wastewater.

[0033] In the treatment of electroplating wastewater, there are two methods: mechanical stirring and air stirring. This invention uses mechanical stirring because it can prevent ferrous ions from being oxidized by air and losing their function.

[0034] Based on the above technical solution, the present invention has the following beneficial effects:

[0035] 1. Utilizing the synergistic effect of ferrous ions and calcium ions, the carboxylic acid complexing agent containing amine groups in alkaline zinc-nickel alloy electroplating wastewater is precipitated, and the carboxylic acid complexing agent in the passivation mixed wastewater is also precipitated. At the same time, trivalent ions and some zinc ions are precipitated as hydroxides. The treatment cost is low, and it overcomes the technical defect of traditional oxidation methods that cannot effectively destroy carboxylic acid complexing agents such as citric acid.

[0036] 2. Sodium dimethyl dithiocarbamate or sodium diethyl dithiocarbamate can be used to precipitate zinc ions, nickel ions, cobalt ions and residual trivalent chromium ions, so that these metal ions can be completely precipitated.

[0037] 3. The treatment method for the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater of the present invention can achieve the requirements of Table 3 of GB21900-2008 "Electroplating Pollutant Discharge Standard". Detailed Implementation

[0038] To facilitate understanding of the present invention, a more complete description will be given below with reference to embodiments, of which preferred embodiments are provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided so that a thorough and complete understanding of the disclosure of the present invention will be achieved.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] The alkaline zinc-nickel alloy electroplating and passivation mixed wastewater of the present invention includes alkaline zinc-nickel alloy electroplating rinsing water, trivalent chromium passivation rinsing water, trivalent passivation waste liquid, and hexavalent chromium passivation rinsing water.

[0041] The equipment used in the following embodiments of the present invention is conventional equipment, and the main equipment and chemical reagents are as follows:

[0042] The system includes: an alkaline zinc-nickel alloy electroplating and passivation mixed wastewater equalization tank, a ferrous feed tank, a sedimentation tank A, a flocculation tank A, an inclined tube sedimentation tank A, a sedimentation tank B, a flocculation tank B, an inclined tube sedimentation tank B, a neutralization reaction tank, a biochemical reaction tank, and a plate and frame filter press.

[0043] Ferrous chloride solution: A ferrous chloride tetrahydrate aqueous solution with a mass concentration of 200 g / L.

[0044] Lime slurry: The mass concentration of calcium oxide is 80 g / L.

[0045] Flocculant: A 5 g / L aqueous solution of polyacrylamide.

[0046] Sodium dimethyl dithiocarbamate aqueous solution: mass concentration of 100 g / L.

[0047] Sodium diethyldithiocarbamate trihydrate aqueous solution: mass concentration of 100 g / L.

[0048] Sodium hydroxide solution: mass concentration of 100 g / L.

[0049] Dilute hydrochloric acid: Hydrochloric acid with a mass fraction of 8%.

[0050] Example 1: Treatment of mixed wastewater from alkaline zinc-nickel alloy electroplating and trivalent chromium passivation

[0051] This embodiment provides a method for treating alkaline zinc-nickel alloy electroplating and passivation wastewater containing 20 mg / L nickel ions, 100 mg / L zinc ions, and 20 mg / L trivalent chromium ions. The method includes the following steps:

[0052] Step 1: Precipitate the carboxylic acid complexing agent

[0053] Wastewater is transported from the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater conditioning tank to the ferrous chloride feeding tank. Under mechanical stirring, dilute hydrochloric acid is added to adjust the pH to 4-5, and 5L of ferrous chloride solution is added to each ton of wastewater.

[0054] Wastewater flows from the ferrous feed tank into sedimentation tank A. Under mechanical stirring, lime slurry is added until the pH is 10-12. Ferrous ions and calcium ions react with carboxylic acid complexing agents to form precipitates, while trivalent chromium ions, some zinc ions, and ferrous ions form hydroxide precipitates.

[0055] Step 2: Precipitation Separation

[0056] Wastewater flows from sedimentation tank A into flocculation tank A. Flocculant is added under mechanical stirring to cause sedimentation and flocculation, and the sediment aggregates into large particles.

[0057] Wastewater flows from flocculation tank A into inclined tube settling tank A, where sediment settles to the bottom. A sludge pump then pumps the sediment into a plate and frame filter press for filtration. The filtrate flows back to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater equalization tank. Filter residue is disposed of by a qualified professional manufacturer.

[0058] Step 3: Precipitate heavy metal ions

[0059] The supernatant in inclined tube sedimentation tank A flows into sedimentation tank B. Under mechanical stirring, dilute hydrochloric acid is added to adjust the pH of the wastewater to 4.5-5.5. 20 liters of sodium dimethyl dithiocarbamate solution is added to each ton of wastewater, and nickel ions, cobalt ions and zinc ions are precipitated.

[0060] Step 4: Precipitation Separation

[0061] Wastewater flows from sedimentation tank B into flocculation tank B. Flocculant is added under mechanical stirring to cause sedimentation and flocculation, and the sediment aggregates into large particles.

[0062] Wastewater flows from flocculation tank B into inclined tube settling tank B, where sediment settles to the bottom. A sludge pump then pumps the sediment into a plate and frame filter press for filtration. The filtrate flows back to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater equalization tank. Filter residue is disposed of by a qualified professional manufacturer.

[0063] Step 5: Neutralization treatment

[0064] The supernatant in inclined tube sedimentation tank B flows into the neutralization reaction tank, the tank liquid is stirred, and sodium hydroxide solution is added to adjust the pH to 6-8.

[0065] Step Six: Reduce COD in Wastewater

[0066] Wastewater flows from the neutralization reaction tank into the biochemical reaction tank, and reacts for 8–24 hours after the addition of bacteria.

[0067] Step 7: Wastewater Discharge

[0068] The treated alkaline zinc-nickel alloy electroplating and passivation mixed wastewater is discharged from the equipment outlet.

[0069] Example 2: Treatment of mixed wastewater from alkaline zinc-nickel alloy electroplating and low-chromium hexavalent chromium passivation

[0070] This embodiment provides a method for treating alkaline zinc-nickel alloy electroplating and passivation wastewater containing 20 mg / L nickel ions, 100 mg / L zinc ions, 50 mg / L hexavalent chromium ions, and 20 mg / L trivalent chromium ions. The method includes the following steps:

[0071] Step 1: Precipitate the carboxylic acid complexing agent

[0072] Wastewater is transported from the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater conditioning tank to the ferrous chloride feeding tank. Under mechanical stirring, dilute hydrochloric acid is added to adjust the pH to 4-5, and 8L of ferrous chloride solution is added per ton of wastewater.

[0073] Wastewater flows from the ferrous feed tank into sedimentation tank A. Under mechanical stirring, lime slurry is added until the pH is 10-12. Ferrous ions and calcium ions react with carboxylic acid complexing agents to form precipitates, while trivalent chromium ions, some zinc ions, and ferrous ions form hydroxide precipitates.

[0074] Step 2: Precipitation Separation

[0075] Wastewater flows from sedimentation tank A into flocculation tank A. Flocculant is added under mechanical stirring to cause sedimentation and flocculation, and the sediment aggregates into large particles.

[0076] Wastewater flows from flocculation tank A into inclined tube settling tank A, where sediment settles to the bottom. A sludge pump then pumps the sediment into a plate and frame filter press for filtration. The filtrate flows back to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater equalization tank. Filter residue is disposed of by a qualified professional manufacturer.

[0077] Step 3: Precipitate heavy metal ions

[0078] The supernatant in inclined tube sedimentation tank A flows into sedimentation tank B. Under mechanical stirring, dilute hydrochloric acid is added to adjust the pH of the wastewater to 4.5-5.5. 30 liters of sodium trihydrate diethyldithiocarbamate solution is added to each ton of wastewater, and nickel ions, cobalt ions and zinc ions are precipitated.

[0079] Step 4: Precipitation Separation

[0080] Wastewater flows from sedimentation tank B into flocculation tank B. Flocculant is added under mechanical stirring to cause sedimentation and flocculation, and the sediment aggregates into large particles.

[0081] Wastewater flows from flocculation tank B into inclined tube settling tank B, where sediment settles to the bottom. A sludge pump then pumps the sediment into a plate and frame filter press for filtration. The filtrate flows back to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater equalization tank. Filter residue is disposed of by a qualified professional manufacturer.

[0082] Step 5: Neutralization treatment

[0083] The supernatant in inclined tube sedimentation tank B flows into the neutralization reaction tank, the tank liquid is stirred, and sodium hydroxide solution is added to adjust the pH to 6-8.

[0084] Step Six: Reduce COD in Wastewater

[0085] Wastewater flows from the neutralization reaction tank into the biochemical reaction tank, and reacts for 8–24 hours after the addition of bacteria.

[0086] Step 7: Wastewater Discharge

[0087] The treated alkaline zinc-nickel alloy electroplating and passivation mixed wastewater is discharged from the equipment outlet.

[0088] Experimental Example 1: Reduction of hexavalent chromium with ferrous chloride under alkaline conditions

[0089] Prepare 1L of chromium trioxide solution with a concentration of 200mg / L, containing 104mg / L of chromium.

[0090] 20 mL of ferrous chloride solution was added to the chromium trioxide solution, and the pH was adjusted to 11 with lime slurry. Ferrous ions reduced hexavalent chromium to trivalent chromium, forming chromium hydroxide precipitate. The remaining ferrous chloride precipitated as ferrous hydroxide precipitate. After 60 min, the solution was filtered through quantitative filter paper to obtain the filtrate. The hexavalent chromium content in the filtrate was determined by diphenylformylhydrazine spectrophotometry, yielding a concentration of 0.032 mg / L and a removal rate of 99.97%. The experiment shows that the treatment method for alkaline zinc-nickel alloy electroplating and passivation mixed wastewater of this invention can effectively remove hexavalent chromium, meeting the requirements of Table 3 in GB 21900-2008 standard.

[0091] Experimental Example 2: Treatment of alkaline zinc-nickel alloy electroplating wastewater by chelating agents alone

[0092] Preparation of test solution: Take 10 mL of alkaline zinc-nickel alloy electroplating solution from the electroplating plant and dilute it with water to 1 L.

[0093] 30 mL of sodium diethyldithiocarbamate trihydrate solution was added to the test solution, and the pH was adjusted to 5 with dilute hydrochloric acid. The mixture was stirred thoroughly, and filtered after 30 min to obtain the filtrate. The filtrate was analyzed by atomic absorption spectrometry, revealing a nickel concentration of 0.23 mg / L and a zinc concentration of 1.75 mg / L. The treated test solution did not meet the requirements of Table 3 in GB 21900-2008 standard.

[0094] Experimental Example 3: Results of the present invention in treating mixed wastewater from alkaline zinc-nickel alloy electroplating and passivation

[0095] Preparation of test solution: Take 10 mL of alkaline zinc-nickel alloy electroplating solution from the electroplating plant and 10 mL of trivalent chromium passivation solution, then dilute with water to 1 L.

[0096] The pH of the test solution was adjusted to 5 with dilute hydrochloric acid, followed by 5 mL of ferrous chloride solution and lime slurry to adjust the pH to 11. After 30 minutes, the solution was filtered. Then, 20 mL of sodium dimethyl dithiocarbamate solution was added to the filtrate, and the pH was adjusted to 5 with dilute hydrochloric acid. The mixture was stirred thoroughly and filtered again after 30 minutes. The filtrate was analyzed by atomic absorption spectrometry, yielding a nickel concentration of 0.08 mg / L, a zinc concentration of 0.43 mg / L, a chromium concentration of 0.24 mg / L, and a cobalt concentration of 0.12 mg / L. The nickel, zinc, and chromium concentrations in the treated test solution met the requirements of Table 3 in GB 21900-2008 standard.

[0097] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0098] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for treating mixed wastewater from alkaline zinc-nickel alloy electroplating and passivation, characterized in that, Includes the following steps: (1) Under mechanical stirring, dilute hydrochloric acid was added to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater to adjust the pH to 4-6, and ferrous chloride solution was added; (2) Under mechanical stirring, lime slurry is added to the wastewater treated in step (1) to adjust the pH to 10-12, precipitating the carboxylic acid complexing agent containing amine groups in the alkaline zinc-nickel alloy electroplating wastewater and the carboxylic acid complexing agent in the passivation wastewater, and some heavy metal ions in the wastewater are precipitated. (3) Add flocculant to the wastewater after step (2) to cause the precipitate to aggregate into large particles and then settle. (4) Filter to remove the precipitate after step (3); (5) Under mechanical stirring, acid is added to adjust the pH of the wastewater treated in step (4) to 4.5-5.5, and a chelating agent is added to form precipitates of heavy metal ions; (6) Add flocculant to the wastewater after step (5) to cause the precipitate to aggregate into large particles and then settle. (7) Filter to remove the precipitate after step (6); (8) Under mechanical stirring, add alkaline solution to the wastewater treated in step (7) to adjust the pH to 6-8, and reduce COD by biochemical method; In step (2), within the pH range of 10 to 12, ferrous ions are used to reduce hexavalent chromium to trivalent chromium and generate chromium hydroxide precipitate. The chelating agent mentioned in step (5) is sodium dimethyl dithiocarbamate solution with a mass concentration of (80-120) g / L; The chelating agent mentioned in step (5) is sodium diethyldithiocarbamate trihydrate solution with a mass concentration of (80-120) g / L; The flocculant mentioned in steps (3) and (6) is an aqueous solution of polyacrylamide with a mass concentration of (3-8) g / L.

2. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, The ferrous chloride solution in step (1) contains ferrous chloride tetrahydrate with a mass concentration of (150-250) g / L; the volume ratio of the added ferrous chloride solution to the alkaline zinc-nickel alloy electroplating and passivation mixed wastewater is (0.3-2):

100.

3. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, The lime slurry in step (2) contains a calcium oxide concentration of (50-100) g / L.

4. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, The chelating agent mentioned in step (5) is sodium dimethyl dithiocarbamate solution with a mass concentration of 100 g / L.

5. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 4, characterized in that, The volume ratio of sodium dimethyl dithiocarbamate solution added in step (5) to the wastewater being treated is (0.5-5):

100.

6. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, The chelating agent mentioned in step (5) is sodium diethyldithiocarbamate trihydrate solution with a mass concentration of 100 g / L.

7. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 6, characterized in that, The volume ratio of sodium trihydrate diethyldithiocarbamate solution added in step (5) to the wastewater being treated is (0.8-8):

100.

8. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, The flocculant mentioned in steps (3) and (6) is an aqueous solution of polyacrylamide with a mass concentration of 5 g / L.

9. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, In steps (1) and (5), dilute hydrochloric acid is used to adjust the pH. The dilute hydrochloric acid is hydrochloric acid with a mass fraction of 5% to 10%. In step (8), the alkaline solution is a sodium hydroxide solution with a mass concentration of (20 to 80) g / L.

10. The method for treating alkaline zinc-nickel alloy electroplating and passivation mixed wastewater according to claim 1, characterized in that, The biochemical method described in step (8) adopts the current biochemical degradation method.