Process for recycling zinc-nickel alloy wastewater

Abstract

This invention relates to a process for recycling wastewater from zinc-nickel alloy plating. The process includes: (1) separating wastewater generated from each step of the zinc-nickel alloy plating process into oily wastewater, zinc-nickel waste liquid, and combined wastewater; (2) passing the oily wastewater through an automatic fine filter; (3) adjusting the pH of the oily wastewater and adding a coagulant aid for coagulation and sedimentation; (4) filtering the supernatant from the coagulation and sedimentation of the oily wastewater using sand filtration; (5) adjusting the pH of the combined wastewater with acid and then adding a reducing agent for reaction; (6) adjusting the pH of the combined wastewater after the reduction reaction with alkali, adding a gravity trap for reaction, and then sequentially adding PAC and PAM flocculants. (7) Flocculation and sedimentation; (8) Sand filtration of the supernatant after flocculation and sedimentation of the comprehensive wastewater; (9) Membrane separation of the supernatant after sand filtration; (10) Plate and frame filter press of the bottom mud; (11) Changing the overflow water wash of the first washing tank of zinc and zinc-nickel plating to a water-stop wash; (12) Using low-temperature evaporation equipment to evaporate and concentrate zinc-nickel waste liquid; (13) Outsourcing the disposal of the concentrated liquid, using condensate and membrane separation product water for post-treatment and reuse, and using the membrane concentrated liquid and sand filtration supernatant for waste gas tower reuse and pre-treatment reuse, respectively.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, and specifically relates to a process for recycling zinc-nickel alloy wastewater. Background Technology

[0002] The zinc-nickel plating process includes alkaline degreasing, acidic derusting, electrolytic degreasing, zinc plating, zinc-nickel plating, surface passivation, and hot water washing. Alkaline degreasing, acidic derusting, and electrolytic degreasing are pretreatment processes; zinc plating, zinc-nickel plating, surface passivation, and hot water washing are post-treatment processes. The wastewater generated by alkaline degreasing and electrolytic degreasing is alkaline, while the wastewater generated by acidic derusting is acidic and has high conductivity. Surface passivation uses oxidants such as potassium permanganate and hexavalent chromium, producing passivation wastewater containing heavy metals such as nickel and chromium.

[0003] Zinc-nickel alloy wastewater generated during zinc-nickel alloy electroplating contains zinc ions, nickel ions, and complexing agents. According to the national standard (Table 3), zinc ions need to be treated to a concentration of 1 mg / L, and nickel ions to 0.1 mg / L. Because nickel ions combine with complexing agents to form stable complexes, the presence of these complexes makes it difficult for nickel ions to precipitate during alkali treatment, resulting in failure to meet discharge standards. Currently, the treatment of zinc-nickel alloy wastewater remains a challenge for enterprises, and the treatment cost is also very high, reaching 200-300 yuan per ton of water. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a process for recycling zinc-nickel alloy wastewater. This treatment process enables the recycling of zinc-nickel alloy wastewater, effectively saves water consumption, and reduces the cost of outsourced wastewater treatment. It has advantages such as low cost, low equipment investment, and strong adaptability. The overflow water washing is changed to a stop-flow washing, which increases the concentration of zinc-nickel wastewater. Combined with low-temperature evaporation equipment, the zinc-nickel waste liquid is evaporated and concentrated, so that nickel is enriched in the concentrated liquid for outsourced disposal. The condensate is reused, which solves the problem of nickel failing to meet discharge standards in the zinc-nickel wastewater treatment process.

[0005] The technical solution of the present invention is the zinc-nickel alloy wastewater recycling process, which is characterized by including the following steps:

[0006] (1) Classification: Wastewater generated from each process of zinc-nickel alloy plating is classified into oily wastewater, zinc-nickel waste liquid, and mixed wastewater;

[0007] (2) Oil removal: Pass the oily wastewater through an automatic fine filter;

[0008] (3) Coagulation and sedimentation: After adjusting the pH of the oily wastewater from step (2), add a coagulant aid for coagulation and sedimentation;

[0009] (4) Sand filtration: The supernatant of oily wastewater after coagulation and sedimentation is filtered through sand.

[0010] (5) Reduction reaction: After adjusting the pH of the combined wastewater with acid, a reducing agent is added to react;

[0011] (6) Flocculation and sedimentation: After adjusting the pH of the combined wastewater after the reduction reaction with alkali and adding a gravity precipitant, PAC and PAM are added in sequence for flocculation and sedimentation.

[0012] (7) Sand filtration: The supernatant after flocculation and sedimentation of the combined wastewater is filtered through sand.

[0013] (8) Membrane separation: The supernatant after sand filtration in step (7) is subjected to membrane separation;

[0014] (9) Plate and frame filter press: The bottom sediment produced in steps (3) and (6) is subjected to plate and frame filter press.

[0015] (10) Concentration: Change the overflow water rinse of the first washing tank of zinc and nickel plating to a water-stopping rinse to increase the concentration of zinc and nickel wastewater;

[0016] (11) Zinc-nickel separation: Low-temperature evaporation equipment is used to evaporate and concentrate the zinc-nickel waste liquid;

[0017] ⑿ The concentrate produced in step ⑾ is disposed of by an external contractor. The condensate and the membrane separation product water from step ⑻ are treated together for reuse. The membrane concentrate produced in step ⑻ and the supernatant after sand filtration in step ⑷ are respectively used for waste gas tower reuse and pretreatment reuse.

[0018] Preferably, the oily wastewater in step (1) includes wastewater generated from degreasing, rust removal, and electrolytic degreasing processes; the zinc-nickel waste liquid includes scrap tank liquid and concentrated wash water generated from zinc plating and zinc-nickel plating processes; and the combined wastewater includes wastewater generated from surface passivation and cleaning processes.

[0019] Preferably, the main material of the automatic fine filter in step (2) is a ceramic membrane with a membrane size of 40-500 nanometers, and a filter bag with a pore size of 10-40 micrometers is provided in front of the automatic fine filter.

[0020] Preferably, the pH range in step (3) is 10-13, and the coagulant is composed of the following components by weight: 3-5 parts iron salt, 1-2 parts aluminum salt, 2-3 parts calcium salt, and 1-2 parts carbon powder; the iron salt is any one of ferric sulfate, ferrous sulfate, polyferric sulfate, ferric chloride, ferrous chloride, and polyferric chloride; the aluminum salt is any one of aluminum sulfate, aluminum chloride, polyaluminum sulfate, and polyaluminum chloride; the calcium salt is any one of calcium chloride, calcium sulfate, quicklime, and hydrated lime; and the carbon powder is powdered coal-based activated carbon with a particle size <45 μm and an iodine value range of 600-800 mg / g.

[0021] Preferably, the reducing agent in step (5) is any one of sodium sulfite, sodium bisulfite, sodium metabisulfite, and ferrous sulfate; the reduction reaction further includes:

[0022] (5.1) Adjust the pH of the combined wastewater to 2-3 using acid;

[0023] (5.2) Add reducing agent at 1 to 3 times the theoretical amount of metal ions, and stir the reaction for 10 to 30 minutes.

[0024] Preferably, in step (6), the pH range is 9–12, and the dosage of the precipitant is 50–300 mg / L; the flocculation and precipitation further includes:

[0025] (6.1) Adjust the pH to 9-12 using alkali;

[0026] (6.2) Add the precipitant and stir for 10-30 minutes;

[0027] (6.3) After the reaction is complete, add PAC and PAM in sequence to flocculate and precipitate.

[0028] Preferably, the membrane in step (8) is a polysulfone separation membrane material, and the conductivity of the water produced after membrane separation is <150 μS / cm, and the water recovery rate is 50-70%.

[0029] Preferably, the concentration in step (10) further includes:

[0030] (10.1) When the zinc and nickel content in the water-stopping tank reaches the specified concentration, pump the water into the zinc and nickel waste liquid collection tank;

[0031] (10.2) Pump the second overflow wash water into the water stop tank, and at the same time add tap water to the second wash tank.

[0032] Preferably, the evaporation and concentration in step (11) further includes:

[0033] (11.1) Add 100-500 mg / L of defoamer to the zinc-nickel waste liquid collection tank and stir well;

[0034] (11.2) Using negative pressure, the zinc-nickel waste liquid is pumped from the zinc-nickel waste liquid collection tank to the evaporation kettle through a pipeline;

[0035] (11.3) Low-temperature evaporation is carried out at 30–40℃;

[0036] (11.4) Based on the concentration ratio of zinc-nickel waste liquid, set the number of feeding times and discharge time of zinc-nickel waste liquid.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The present invention provides a zinc-nickel alloy wastewater recycling process, which can realize the recycling of zinc-nickel alloy wastewater, effectively save water consumption, and reduce the cost of outsourced wastewater treatment. It has the advantages of low cost, low equipment investment, and strong adaptability, and has high market potential.

[0039] (2) This invention modifies the zinc-nickel plating process by changing the overflow water wash to a stop-water wash, increasing the concentration of zinc-nickel wastewater, and combining it with a low-temperature evaporation device to evaporate and concentrate the zinc-nickel waste liquid, so that nickel is enriched in the concentrate and disposed of externally, and the condensate is reused, thus solving the problem that nickel is difficult to meet the discharge standards in the zinc-nickel wastewater treatment process. Attached Figure Description

[0040] Figure 1 This is a process flow diagram of the zinc-nickel alloy wastewater recycling process of the present invention. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings:

[0042] Please see Figure 1 As shown, the zinc-nickel alloy wastewater recycling process includes the following steps:

[0043] (1) Classification: Wastewater generated from each process of zinc-nickel alloy plating is classified into oily wastewater, zinc-nickel waste liquid, and comprehensive wastewater; wherein: the oily wastewater includes wastewater generated from degreasing, derusting, and electrolytic degreasing processes; the zinc-nickel waste liquid includes scrap tank liquid and concentrated wash water generated from zinc plating and zinc-nickel plating processes; the comprehensive wastewater includes wastewater generated from surface passivation and cleaning processes;

[0044] This invention, based on the characteristics of zinc-nickel alloy wastewater, divides the wastewater into three streams: oily wastewater, mixed wastewater, and zinc-nickel waste liquid. Oily wastewater includes cleaning wastewater from alkaline degreasing, acidic rust removal, and electrolytic degreasing processes; mixed wastewater is overflow cleaning wastewater from galvanizing, zinc-nickel plating, surface passivation, and hot water washing processes; zinc-nickel waste liquid consists of scrapped galvanizing and zinc-nickel plating tank solutions and concentrated cleaning water. Oily wastewater mainly contains oil and color; after degreasing and decolorization, it can be reused or recycled in the exhaust gas treatment tower. Mixed wastewater mainly has excessive heavy metals and high salt content; after removing heavy metals, the salt content can be reduced through membrane separation, allowing it to be reused in subsequent treatment processes. Zinc-nickel waste liquid contains a large amount of complexes and heavy metals; the difficulty in treating heavy metals to meet standards is the main reason for the difficulty in treating zinc-nickel waste liquid. It can be treated by low-temperature evaporation and concentration, with the concentrated liquid disposed of externally and the condensate recycled.

[0045] (2) Oil removal: The oily wastewater is passed through an automatic fine filter; the main material of the automatic fine filter is a ceramic membrane with a membrane size of 40-500 nanometers, and a filter bag with a pore size of 10-40 micrometers is provided in front of the automatic fine filter;

[0046] (3) Coagulation and sedimentation: After adjusting the pH of the oily wastewater from step (2), add a coagulant aid for coagulation and sedimentation; the pH range is 10-13; the coagulant aid consists of 3-5 parts iron salt, 1-2 parts aluminum salt, 2-3 parts calcium salt, and 1-2 parts carbon powder; the iron salt is any one of ferric sulfate, ferrous sulfate, polyferric sulfate, ferric chloride, ferrous chloride, and polyferric chloride; the aluminum salt is any one of aluminum sulfate, aluminum chloride, polyaluminum sulfate, and polyaluminum chloride; the calcium salt is any one of calcium chloride, calcium sulfate, quicklime, and hydrated lime; the carbon powder is powdered coal-based activated carbon with a particle size <45μm and an iodine value range of 600-800mg / g;

[0047] (4) Sand filtration: The supernatant of oily wastewater after coagulation and sedimentation is filtered through sand.

[0048] (5) Reduction reaction: After adjusting the pH of the combined wastewater with acid, a reducing agent is added to react; the reducing agent is any one of sodium sulfite, sodium bisulfite, sodium metabisulfite, and ferrous sulfate; the reduction reaction further includes:

[0049] (5.1) Adjust the pH of the combined wastewater to 2-3 using acid;

[0050] (5.2) Add reducing agent at 1 to 3 times the theoretical amount of metal ions, and stir the reaction for 10 to 30 minutes;

[0051] (6) Flocculation and sedimentation: Adjust the pH of the combined wastewater after the reduction reaction to 9-12 with alkali, add a heavy precipitant and stir for 10-30 minutes. After the reaction is completed, add PAC and PAM in sequence for flocculation and sedimentation. The pH range is 9-12 and the dosage of heavy precipitant is 50-300 mg / L.

[0052] (7) Sand filtration: The supernatant after flocculation and sedimentation of the combined wastewater is filtered through sand.

[0053] (8) Membrane separation: The supernatant after sand filtration in step (7) is subjected to membrane separation; the membrane is a polysulfone separation membrane material, and the conductivity of the water produced after membrane separation is <150 μS / cm, and the water recovery rate is 50-70%.

[0054] (9) Plate and frame filter press: The bottom sediment produced in steps (3) and (6) is subjected to plate and frame filter press.

[0055] (10) Concentration: The overflow rinse of the first washing tank in zinc and zinc-nickel plating is changed to a stop-flow rinse to increase the concentration of zinc-nickel wastewater; the concentration further includes:

[0056] (10.1) When the zinc and nickel content in the water-stopping tank reaches the specified concentration, pump the water into the zinc and nickel waste liquid collection tank;

[0057] (10.2) Pump the second overflow wash water into the water stop tank, and at the same time add tap water to the second wash tank;

[0058] (11) Zinc-nickel separation: The zinc-nickel waste liquid is concentrated by evaporation using a low-temperature evaporation device; the evaporation and concentration further includes;

[0059] (11.1) Add 100-500 mg / L of defoamer to the zinc-nickel waste liquid collection tank and stir well;

[0060] (11.2) Using negative pressure, the zinc-nickel waste liquid is pumped from the zinc-nickel waste liquid collection tank to the evaporation kettle through a pipeline;

[0061] (11.3) Low-temperature evaporation is carried out at 30–40℃;

[0062] (11.4) Based on the concentration ratio of zinc-nickel waste liquid, set the number of feeding times and discharge time of zinc-nickel waste liquid;

[0063] ⑿ The concentrate produced in step ⑾ is disposed of by an external contractor. The condensate and the membrane separation product water from step ⑻ are treated together for reuse. The membrane concentrate produced in step ⑻ and the supernatant after sand filtration in step ⑷ are respectively used for waste gas tower reuse and pretreatment reuse.

[0064] Example 1: A process for recycling zinc-nickel alloy wastewater

[0065] The composition of zinc-nickel alloy wastewater is shown in Table 1: the wastewater and waste liquid treatment volume is 34m³. 3 / d.

[0066] Table 1 Composition of Zinc-Nickel Alloy Wastewater

[0067]

[0068] The process for recycling zinc-nickel alloy wastewater includes the following steps:

[0069] (1) Classification: Oily wastewater A1, A2, A3, B1, rust removal wastewater B2, and electrolytic degreasing wastewater B3 are collected as oily wastewater; zinc-nickel raw solution A, zinc-nickel raw solution B, zinc-nickel wastewater A1, nickel-containing wastewater B1, nickel-containing wastewater A1, and nickel-containing wastewater are collected as zinc-nickel waste liquid; dyeing wastewater A1, A2, B1, B2, and cleaning wastewater A1, A2, A3 are collected as comprehensive wastewater.

[0070] (2) Oil removal: The oily wastewater is passed through an automatic fine filter. The main material of the automatic fine filter is a ceramic membrane with a membrane size of 100 nanometers. A filter bag with a pore size of 20 micrometers is installed in front of the automatic fine filter.

[0071] (3) Coagulation and sedimentation: After adjusting the pH of the oily wastewater in step (2) to 12, add a coagulant aid for coagulation and sedimentation. The coagulant aid consists of 5 parts ferrous sulfate, 2 parts aluminum sulfate, 2 parts quicklime, and 1 part powdered coal-based activated carbon with a particle size <45um and an iodine value of 800mg / g.

[0072] (4) Sand filtration: The supernatant of oily wastewater after coagulation and sedimentation is filtered through sand.

[0073] (5) Reduction reaction: After adjusting the pH of the combined wastewater to 2.5 with acid, add sodium sulfite at 1 times the theoretical amount of heavy metals and stir for 30 minutes.

[0074] (6) Flocculation and sedimentation: Adjust the pH of the combined wastewater after the reduction reaction to 10.5 with alkali, add heavy precipitant at a dosage of 50 mg / L, stir and react for 30 minutes, and add PAC and PAM in sequence after the reaction is completed to flocculate and precipitate.

[0075] (7) Sand filtration: The supernatant after flocculation and sedimentation of the combined wastewater is filtered through sand.

[0076] (8) Membrane separation: The supernatant after sand filtration in step (7) is subjected to membrane separation. The membrane is a polysulfone separation membrane material. The conductivity of the water produced after membrane separation is <150 μS / cm, and the water recovery rate is 60%.

[0077] (9) Plate and frame filter press: The bottom sediment produced in steps (3) and (6) is subjected to plate and frame filter press.

[0078] (10) Concentration: Change the overflow water rinse of the first rinsing tank for galvanizing and zinc-nickel plating to a water-stopping rinse; when the zinc-nickel content in the water-stopping tank reaches the specified concentration, pump the water to the zinc-nickel waste liquid collection tank; pump the overflow water of the second rinsing tank to the water-stopping tank, and at the same time add tap water to the second rinsing tank.

[0079] 11. Zinc-nickel separation: Add 100 mg / L of defoamer to the zinc-nickel waste liquid collection tank and stir evenly; use negative pressure to pump the zinc-nickel waste liquid from the collection tank through the pipeline into the evaporator; carry out low-temperature evaporation at 37°C; set the number of feeding times and discharge time of the zinc-nickel waste liquid according to the concentration ratio of the zinc-nickel waste liquid.

[0080] ⑿ The concentrate produced in step ⑾ is disposed of by an external contractor. The condensate and the membrane separation product water from step ⑻ are treated together for reuse. The membrane concentrate produced in step ⑻ and the supernatant after sand filtration in step ⑷ are respectively used for waste gas tower reuse and pretreatment reuse.

[0081] Table 2. Analysis of solution composition before and after coagulation and sedimentation of oily wastewater.

[0082] category Electrical conductivity (ms / cm) pH Oily wastewater 128.4 13.3 Supernatant 40 12.7

[0083] Table 3 Evaporation data of zinc and nickel waste liquid

[0084] water sample pH Electrical conductivity (ms / cm) COD (mg / L) Volume (mL) raw water 12.5 38.2 11210 100 Concentrate - - - 15 Condensate 9.3 0.0788 24.08 85

[0085] Table 4. Data on heavy metal removal from comprehensive wastewater

[0086] water sample ORP(mv) pH Electrical conductivity (ms / cm) COD (mg / L) Ni (mg / L) Cr (mg / L) Combined wastewater 440 3.4 3.01 522 28.5 65 After processing 210 8.4 3.72 350.6 ＜0.5 ＜1

[0087] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims

1. A process for recycling zinc-nickel alloy wastewater, characterized in that, Includes the following steps: (1) Classification: Wastewater generated from each process of zinc-nickel alloy plating is classified into oily wastewater, zinc-nickel waste liquid, and comprehensive wastewater; the oily wastewater includes wastewater generated from degreasing, derusting, and electrolytic degreasing processes; the zinc-nickel waste liquid includes scrap tank liquid and concentrated wash water generated from zinc plating and zinc-nickel plating processes; the comprehensive wastewater includes wastewater generated from surface passivation and cleaning processes. (2) Oil removal: Pass the oily wastewater through an automatic fine filter; (3) Coagulation and sedimentation: After adjusting the pH of the oily wastewater from step (2), a coagulant aid is added for coagulation and sedimentation; the pH range is 10-13; the coagulant aid is composed of the following components by weight: 3-5 parts iron salt, 1-2 parts aluminum salt, 2-3 parts quicklime or hydrated lime, and 1-2 parts carbon powder; the iron salt is any one of ferric sulfate, ferrous sulfate, polyferric sulfate, ferric chloride, ferrous chloride, and polyferric chloride; the aluminum salt is any one of aluminum sulfate, aluminum chloride, polyaluminum sulfate, and polyaluminum chloride; the carbon powder is powdered coal-based activated carbon with a particle size <45μm and an iodine value range of 600-800mg / g. (4) Sand filtration: The supernatant of oily wastewater after coagulation and sedimentation is filtered through sand. (5) Reduction reaction: After adjusting the pH of the combined wastewater with acid, a reducing agent is added to react; (6) Flocculation and sedimentation: After adjusting the pH of the combined wastewater after the reduction reaction with alkali and adding a gravity precipitant, PAC and PAM are added in sequence for flocculation and sedimentation. (7) Sand filtration: The supernatant after flocculation and sedimentation of the combined wastewater is filtered through sand. (8) Membrane separation: The supernatant after sand filtration in step (7) is subjected to membrane separation; (9) Plate and frame filter press: The bottom sediment produced in steps (3) and (6) is subjected to plate and frame filter press. (10) Concentration: Change the overflow water rinse of the first washing tank of zinc plating and zinc-nickel plating to a water-stopping rinse to increase the concentration of zinc-nickel waste liquid; (11) Zinc-nickel separation: The zinc-nickel waste liquid is concentrated by evaporation using a low-temperature evaporation device; the evaporation and concentration further includes: (11.1) Add 100-500 mg / L of defoamer to the zinc-nickel waste liquid collection tank and stir well; (11.2) Using negative pressure, the zinc-nickel waste liquid is pumped from the zinc-nickel waste liquid collection tank to the evaporation kettle through a pipeline; (11.3) Low-temperature evaporation is carried out at 30–40℃; (11.4) Based on the concentration ratio of zinc-nickel waste liquid, set the number of feeding times and discharge time of zinc-nickel waste liquid; ⑿ The concentrate produced in step ⑾ is disposed of by an external contractor. The condensate and the membrane separation product water from step ⑻ are treated together for reuse. The membrane concentrate produced in step ⑻ and the supernatant after sand filtration in step ⑷ are respectively used for waste gas tower reuse and pretreatment reuse.

2. The zinc-nickel alloy wastewater recycling process according to claim 1, characterized in that, The main material of the automatic fine filter in step (2) is a ceramic membrane with a membrane size of 40-500 nanometers. The automatic fine filter is equipped with a filter bag with a pore size of 10-40 micrometers.

3. The zinc-nickel alloy wastewater recycling process according to claim 1, characterized in that, The reducing agent in step (5) is any one of sodium sulfite, sodium bisulfite, sodium metabisulfite, and ferrous sulfate; the reduction reaction further includes: (5.1) Adjust the pH of the combined wastewater to 2-3 using acid; (5.2) Add reducing agent at 1 to 3 times the theoretical amount of metal ions, and stir the reaction for 10 to 30 minutes.

4. The zinc-nickel alloy wastewater recycling process according to claim 1, characterized in that, The pH range in step (6) is 9–12, and the dosage of the precipitant is 50–300 mg / L; the flocculation and precipitation further includes: (6.1) Adjust the pH to 9-12 using alkali; (6.2) Add the precipitant and stir for 10-30 minutes; (6.3) After the reaction is complete, add PAC and PAM in sequence to flocculate and precipitate.

5. The zinc-nickel alloy wastewater recycling process according to claim 1, characterized in that, The membrane in step (8) is a polysulfone separation membrane material. After membrane separation, the conductivity of the produced water is <150 μS / cm and the water recovery rate is 50-70%.

6. The zinc-nickel alloy wastewater recycling process according to claim 1, characterized in that, The concentration in step (10) further includes: (10.1) When the zinc and nickel content in the water-stopping tank reaches the specified concentration, pump the water into the zinc and nickel waste liquid collection tank; (10.2) Pump the second overflow wash water into the water stop tank, and at the same time add tap water to the second wash tank.

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