A treatment process for complexing heavy metals in zinc-nickel electroplating wastewater

Abstract

This application relates to the technical field of industrial wastewater treatment, specifically disclosing a treatment process for complexed heavy metals in zinc-nickel electroplating wastewater. The process involves collecting wastewater in an equalization tank for water quality equilibration, monitored online by ORP; after primary pH adjustment to 10-12, the wastewater is sent to an ultraviolet catalytic oxidation reactor for staged oxidation and complex breaking under ultraviolet light irradiation; after secondary pH adjustment to 4.5-5.5, reduction is performed; a composite heavy metal chelating agent is added in stages for chelation and precipitation; after coagulation, flocculation, and primary sedimentation, the supernatant enters a deep adsorption unit, where a fly ash-modified sludge-based adsorbent is added for deep treatment, followed by secondary sedimentation before discharge meeting standards; the underflow from the sediment is partially recycled back to the oxidation reactor as an adsorption medium after pressure filtration, and partially used to prepare the adsorbent. This application can improve the treatment effect of zinc-nickel electroplating wastewater containing complexed heavy metals.

Description

Technical Field

[0001] This invention relates to the technical field of industrial wastewater treatment, and in particular to a treatment process for complexed heavy metals in zinc-nickel electroplating wastewater. Background Technology

[0002] Zinc-nickel alloy electroplating is widely used in the automotive, aerospace, and electronics industries due to its excellent corrosion resistance. However, the wastewater generated during zinc-nickel electroplating contains high concentrations of zinc and nickel ions, and these heavy metal ions typically form stable complexes with complexing agents added to the electroplating solution. Common complexing agents include EDTA, citric acid, hydroxycarboxylic acids, and aliphatic polyamines. The complexes formed by these complexing agents and heavy metal ions are extremely stable and difficult to remove effectively using traditional chemical precipitation methods.

[0003] In related technologies, the treatment methods for electroplating wastewater containing complexed heavy metals mainly include complex-breaking-chemical precipitation, advanced oxidation, membrane separation, and ion exchange. Among these, complex-breaking-chemical precipitation is the most commonly used process. It involves adding a complex-breaking agent to disrupt the complex structure, releasing free heavy metal ions, which are then removed by a chelating precipitant. Chinese patent CN111675369A proposes a method for treating electroplating wastewater containing complexed heavy metals using electroplating sludge as an adsorbent, realizing the concept of treating waste with waste.

[0004] However, this patented technology is mainly aimed at chemical nickel plating wastewater and copper pyrophosphate wastewater, and its effect on zinc-nickel electroplating wastewater, which has more complex complexing agents and higher complexing stability, is limited. Summary of the Invention

[0005] To improve the treatment effect of complexed heavy metal wastewater from zinc-nickel electroplating, this application provides a process for treating complexed heavy metals in zinc-nickel electroplating wastewater.

[0006] This application provides a treatment process for complexed heavy metals in zinc-nickel electroplating wastewater, which adopts the following technical solution: A process for treating complexed heavy metals in zinc-nickel electroplating wastewater includes the following steps: S1. Collect the zinc-nickel electroplating complex heavy metal wastewater into the equalization tank. After water quality equalization treatment, send it to the primary pH equalization tank. Add lime milk to adjust the pH of the wastewater to 10-12. Then send it to the ultraviolet catalytic oxidation reaction tank. Under ultraviolet light irradiation, add oxidant and perform staged oxidation to break the complex, and obtain the complex-broken wastewater. S2. The wastewater after complex breaking is sent to the secondary pH adjustment tank, where dilute hydrochloric acid or dilute sulfuric acid is added to adjust the pH of the wastewater to 4.5-5.5. Then it is sent to the reduction reaction tank, where a reducing agent is added. After the reaction is completed, it is sent to the chelation precipitation reaction tank, where composite heavy metal capture agents are added in stages. After the reaction is completed, it is sent to the coagulation and flocculation tank, where coagulants and flocculants are added. After coagulation and flocculation are completed, it is sent to the primary sedimentation tank for solid-liquid separation to obtain the first supernatant and the first underflow. S3. The first supernatant is sent to the deep adsorption unit, where adsorbent is added for adsorption treatment. It is then sent to the secondary sedimentation tank for solid-liquid separation to obtain the second supernatant and the second underflow. The second supernatant is discharged or reused after meeting the standards. S4. The first underflow and the second underflow are sent to a filter press for filtration to obtain electroplating sludge. Part of the electroplating sludge is recycled to the ultraviolet catalytic oxidation reaction tank in step S1 as an adsorption medium, and the other part of the electroplating sludge is used to prepare the adsorbent.

[0007] In one specific implementation, the composite heavy metal scavenger comprises the following components in parts by weight: 25-35 parts sodium dimethyl dithiocarbamate, 15-25 parts trisodium trimercaptotriazine, 5-15 parts sodium metatitanate, and 5-15 parts sodium alginate.

[0008] In one specific implementation scheme, the step S2 of adding the composite heavy metal scavenging agent in stages is as follows: Sodium dimethyl dithiocarbamate and trithiomercaptotriazine trisodium salt are mixed beforehand to obtain a mixed agent. The mixed agent is divided into a first part and a second part in a ratio of (3-4):(1-2). The first part of the mixed agent is added within 5 minutes of the wastewater entering the chelation precipitation reaction tank. Sodium metatitanate is added within 5-10 minutes of the wastewater entering the chelation precipitation reaction tank. Sodium alginate powder is added within 10-15 minutes of the wastewater entering the chelation precipitation reaction tank. The second part of the mixed agent is added within 15-20 minutes of the wastewater entering the chelation precipitation reaction tank, thus completing the staged addition.

[0009] In one specific implementation scheme, the equalization tank in step S1 is equipped with an online ORP monitor for real-time monitoring of the oxidation-reduction potential of the wastewater.

[0010] In one specific implementation scheme, the step S1 step of graded oxidation and complex breaking treatment is performed as follows: hydrogen peroxide is added at a dosage of 3-8 mL / L under pH 10-12 conditions, and the reaction is carried out under 254 nm ultraviolet light irradiation for 60 minutes; sodium hypochlorite is added at a dosage of 2-5 g / L, and the reaction is carried out under ultraviolet light irradiation for another 30 minutes; ferrous sulfate is added at a dosage of 0.3-1.0 g / L, and the reaction is carried out for another 30 minutes to complete the graded oxidation and complex breaking treatment.

[0011] In one specific implementation scheme, the reducing agent in step S2 is sodium metabisulfite, the amount of sodium metabisulfite added is 0.8-1.0 times the amount of hydrogen peroxide added in step S1, and the reaction time is 15-30 minutes.

[0012] In one specific implementation scheme, the coagulant in step S2 is polyaluminum chloride, with a dosage of 80-200 mg / L; the flocculant is anionic polyacrylamide, with a dosage of 1-3 mg / L, and the stirring reaction time is 10-15 minutes.

[0013] In one specific implementation scheme, the adsorbent in step S3 is a fly ash modified sludge-based adsorbent, the dosage of the adsorbent is 1-2 g / L, and the reaction time of the adsorption treatment is 20-40 minutes.

[0014] In one specific implementation scheme, the adsorbent is prepared by mixing electroplating sludge and fly ash at a mass ratio of (3.5-4.5):3, followed by pyrolysis treatment to obtain the adsorbent.

[0015] In summary, this application has the following beneficial effects: 1. This application sets up an ultraviolet catalytic oxidation reaction tank and adopts a staged oxidation and complex-breaking method under ultraviolet photocatalysis. The process involves three stages: alkaline oxidation with hydrogen peroxide, oxidation with sodium hypochlorite, and Fenton oxidation with ferrous sulfate. This method can selectively break down various types of complexing agents such as EDTA, citric acid, hydroxycarboxylic acids, and aliphatic polyamines, which helps to significantly improve the complex-breaking efficiency.

[0016] 2. This application uses a four-component composite heavy metal scavenger containing sodium dimethyl dithiocarbamate, trithiodimethyltriazine trisodium salt, sodium metatitanate and sodium alginate, which can realize a triple adsorption mechanism of chemical chelation, physical adsorption of nanomaterials and polymer coordination adsorption, which helps to improve adsorption capacity and selectivity.

[0017] 3. The process described in this application employs a staged dosing method, allowing different components to function sequentially under their respective optimal reaction conditions. This avoids interference between different reagents, improves reagent utilization efficiency, and reduces reagent waste. A deep adsorption unit is added after the primary sedimentation tank, using fly ash-modified sludge-based adsorbents to perform bottom-line adsorption of residual trace heavy metals, ensuring stable effluent discharge that meets standards regardless of water quality fluctuations. All heavy metal-containing sludge generated during the treatment process is reused: part is directly reused in the UV catalytic oxidation reactor as an adsorption medium, achieving waste-to-waste treatment; the rest is mixed with fly ash to prepare modified adsorbents, enabling closed-loop resource recycling of sludge and reducing the discharge of hazardous waste. An online ORP monitor is installed in the equalization tank to monitor the wastewater's oxidation-reduction status in real time, providing real-time feedback for oxidant dosage, facilitating precise control, and further improving treatment stability. Detailed Implementation

[0018] Unless otherwise specified, all raw materials used in this application were commercially available. Hydrogen peroxide, AR grade. Sodium hypochlorite, AR grade. Ferrous sulfate, AR grade. Sodium metabisulfite, AR grade. Polyaluminum chloride, CAS No. 1327-41-9, standard GB / T 22627-2022, purchased from Wuhan Jiyesheng Chemical Co., Ltd. Anionic polyacrylamide, model JC-1. Sodium dimethyl dithiocarbamate, CAS No. 128-04-1, active ingredient content 95%. Trithiomercaptotriazine trisodium salt, model KNX20241127. Sodium metatitanate, CAS No. 12034-36-5, AR grade. Sodium alginate, CAS No. 9005-38-3, active ingredient content 99%.

[0019] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0020] Example Example 1

[0021] The zinc-nickel electroplating complex wastewater from a Jiangsu electroplating company was used as the wastewater to be treated. The initial water quality of the wastewater was as follows: total nickel concentration 85.6 mg / L, total zinc concentration 62.3 mg / L, total copper concentration 15.2 mg / L, EDTA concentration 120 mg / L, citric acid concentration 80 mg / L, and pH 11.5.

[0022] This embodiment provides a treatment process for complexed heavy metals in zinc-nickel electroplating wastewater, including the following steps: S1. The wastewater to be treated is collected in an equalization tank equipped with an online ORP monitor for real-time monitoring of the wastewater's oxidation-reduction potential (ORP), with an ORP reading of -120mV. After equalization treatment, the wastewater is sent to a primary pH equalization tank, where lime slurry is added to adjust the pH to 11. Then, it is sent to an ultraviolet catalytic oxidation reactor. Hydrogen peroxide is added at a dosage of 5 mL / L under pH 11 conditions, and the reaction is carried out for 60 minutes under 254 nm ultraviolet light irradiation. Next, sodium hypochlorite is added at a dosage of 3.5 g / L, and the reaction continues under ultraviolet light irradiation for 30 minutes. Finally, ferrous sulfate is added at a dosage of 0.6 g / L, and the reaction is carried out for 30 minutes, completing the staged oxidation and complex-breaking treatment, yielding the complex-broken wastewater.

[0023] S2. The wastewater after complex breaking is sent to the secondary pH adjustment tank. Dilute hydrochloric acid is added to adjust the pH of the wastewater to 5. Then it is sent to the reduction reaction tank, where sodium metabisulfite is added. The dosage of sodium metabisulfite is 0.9 times that of hydrogen peroxide in step S1. After reacting for 22 minutes, the reaction is stopped, and the wastewater is sent to the chelation precipitation reaction tank. A composite heavy metal scavenging agent is added in stages. After the reaction is completed, the wastewater is sent to the coagulation and flocculation tank, where polyaluminum chloride and anionic polyacrylamide are added. The dosage of polyaluminum chloride is 140 mg / L, and the dosage of anionic polyacrylamide is 2 mg / L. The mixture is stirred and reacted for 12 minutes to complete the coagulation and flocculation. Then, the wastewater is sent to the primary sedimentation tank for solid-liquid separation to obtain the first supernatant and the first slurry. The composite heavy metal scavenging agent includes the following components: 30 kg of sodium dimethyl dithiocarbamate, 20 kg of trisodium trimercaptotriazine, 10 kg of sodium metatitanate, and 10 kg of sodium alginate. The procedure for staged addition of the composite heavy metal scavenging agent is as follows: Sodium dimethyl dithiocarbamate and trisodium trimercaptotriazine are mixed beforehand to obtain a mixed agent. This mixed agent is then divided into two portions at a ratio of 3.5:1.5. The first portion of the mixed agent is added within 5 minutes of the wastewater entering the chelation sedimentation tank; sodium metatitanate is added within 5-10 minutes; sodium alginate powder is added within 10-15 minutes; and the second portion of the mixed agent is added within 15-20 minutes, completing the staged addition.

[0024] S3. The first supernatant is sent to the deep adsorption unit, where fly ash modified sludge-based adsorbent is added at a dosage of 1.5 g / L for adsorption treatment. The adsorption treatment reaction time is 30 minutes. Then, it is sent to the secondary sedimentation tank for solid-liquid separation to obtain the second supernatant and the second underflow. The second supernatant is discharged or reused after meeting the standards.

[0025] S4. The first and second underflows are sent to a filter press for filtration to obtain electroplating sludge. A portion of this sludge is recycled back to the UV catalytic oxidation reactor in step S1 as an adsorption medium, while the other portion is used to prepare a fly ash-modified sludge-based adsorbent. The adsorbent is prepared by mixing the electroplating sludge and fly ash at a mass ratio of 4:3, pyrolyzing the mixture at 750-850℃ for 60 minutes, and then naturally cooling it to room temperature to obtain the adsorbent.

[0026] Example 2

[0027] The only difference between this embodiment and Example 1 is that the composite heavy metal scavenger includes the following components: 25 kg of sodium dimethyl dithiocarbamate, 15 kg of trithiodimethyltriazine trisodium salt, 5 kg of sodium metatitanate, and 5 kg of sodium alginate.

[0028] Example 3

[0029] The only difference between this embodiment and Example 1 is that the composite heavy metal scavenger includes the following components: 35 kg of sodium dimethyl dithiocarbamate, 25 kg of trithiodimethyltriazine trisodium salt, 15 kg of sodium metatitanate, and 15 kg of sodium alginate.

[0030] Example 4

[0031] The only difference between this embodiment and Embodiment 1 is that, in the process of adding the composite heavy metal scavenging agent in stages, the mixed agent is divided into a first mixed agent and a second mixed agent in a 3:2 ratio.

[0032] Example 5

[0033] The only difference between this embodiment and Example 1 is that in step S1, hydrogen peroxide is added at a dosage of 3 mL / L under pH 10 conditions, and the reaction is carried out for 60 minutes under 254 nm ultraviolet light irradiation. Then, sodium hypochlorite is added at a dosage of 2 g / L, and the reaction is continued under ultraviolet light irradiation for 30 minutes. Finally, ferrous sulfate is added at a dosage of 0.3 g / L, and the reaction is carried out for 30 minutes to complete the staged oxidation and complex-breaking treatment.

[0034] Example 6

[0035] The only difference between this embodiment and Example 1 is that in step S1, hydrogen peroxide is added at a dosage of 8 mL / L under pH 10 conditions, and the reaction is carried out for 60 minutes under 254 nm ultraviolet light irradiation. Then, sodium hypochlorite is added at a dosage of 5 g / L, and the reaction is continued under ultraviolet light irradiation for 30 minutes. Finally, ferrous sulfate is added at a dosage of 1.0 g / L, and the reaction is carried out for 30 minutes to complete the staged oxidation and complex-breaking treatment.

[0036] Example 7

[0037] The only difference between this embodiment and Embodiment 1 is that in step S2, the amount of sodium metabisulfite added is 0.8 times the amount of hydrogen peroxide added in step S1, and the reaction is terminated after 15 minutes.

[0038] Example 8

[0039] The only difference between this embodiment and Embodiment 1 is that in step S2, the amount of sodium metabisulfite added is 1.0 times the amount of hydrogen peroxide added in step S1, and the reaction is terminated after 30 minutes.

[0040] Example 9

[0041] The only difference between this embodiment and Example 1 is that in step S2, the dosage of polyaluminum chloride is 80 mg / L, the dosage of anionic polyacrylamide is 1 mg / L, and the reaction is stirred for 10 minutes to complete the coagulation and flocculation.

[0042] Example 10

[0043] The only difference between this embodiment and Example 1 is that in step S2, the dosage of polyaluminum chloride is 200 mg / L, the dosage of anionic polyacrylamide is 3 mg / L, and the reaction is stirred for 15 minutes to complete the coagulation and flocculation.

[0044] Example 11

[0045] The only difference between this embodiment and Embodiment 1 is that, in step S3, fly ash modified sludge-based adsorbent is added at a dosage of 1 g / L for adsorption treatment, and the reaction time for adsorption treatment is 20 minutes.

[0046] Example 12

[0047] The only difference between this embodiment and Embodiment 1 is that, in step S3, fly ash modified sludge-based adsorbent is added at a dosage of 2 g / L for adsorption treatment, and the reaction time for adsorption treatment is 40 minutes.

[0048] Example 13

[0049] The only difference between this embodiment and Embodiment 1 is that the adsorbent is prepared by mixing electroplating sludge and fly ash at a mass ratio of 3.5:3, pyrolyzing them at a temperature range of 750-850℃ for 60 minutes, and then naturally cooling them to room temperature to obtain the adsorbent.

[0050] Example 14

[0051] The only difference between this embodiment and Embodiment 1 is that the adsorbent is prepared by mixing electroplating sludge and fly ash at a mass ratio of 4.5:3, pyrolyzing the mixture at a temperature range of 750-850℃ for 60 minutes, and then naturally cooling it to room temperature to obtain the adsorbent.

[0052] Example 15

[0053] The difference between this embodiment and Embodiment 1 lies only in the following steps: In step S1 of the treatment process for complexed heavy metals in zinc-nickel electroplating wastewater, after water quality equalization treatment, the wastewater is sent to a primary pH adjustment tank where lime slurry is added to adjust the wastewater pH to 10. In step S2, the wastewater after complex breaking is sent to a secondary pH adjustment tank where dilute hydrochloric acid is added to adjust the wastewater pH to 4.5.

[0054] Example 16

[0055] The difference between this embodiment and Embodiment 1 lies only in the following: In step S1 of the treatment process for complexed heavy metals in zinc-nickel electroplating wastewater, after water quality equalization treatment, the wastewater is sent to a primary pH adjustment tank where lime slurry is added to adjust the wastewater pH to 12. In step S2, the wastewater after complex breaking is sent to a secondary pH adjustment tank where dilute hydrochloric acid is added to adjust the wastewater pH to 5.5.

[0056] Comparative Example Comparative Example 1 The only difference between this comparative example and Example 1 is that step S1 is as follows: The wastewater to be treated is collected in an equalization tank equipped with an online ORP monitor for real-time monitoring of the wastewater's oxidation-reduction potential (ORP), which displays a value of -120mV. After water quality equalization, it is sent to a primary pH equalization tank, where lime slurry is added to adjust the pH to 11. Then, it is sent to an ultraviolet catalytic oxidation reaction tank, where hydrogen peroxide is added at a dosage of 5 mL / L under pH 11 conditions, and the reaction is stirred for 60 minutes. Next, sodium hypochlorite is added at a dosage of 3.5 g / L, and the reaction continues for another 30 minutes. Finally, ferrous sulfate is added at a dosage of 0.6 g / L, and the reaction is carried out for 30 minutes, completing the staged oxidation and complex-breaking treatment, yielding the complex-broken wastewater.

[0057] Comparative Example 2 The only difference between this comparative example and Example 1 is that step S1 is as follows: The wastewater to be treated is collected in an equalization tank equipped with an online ORP monitor for real-time monitoring of the wastewater's oxidation-reduction potential (ORP), which displays a value of -120mV. After water quality equalization, it is sent to a primary pH equalization tank, where lime slurry is added to adjust the pH to 11. Then, it is sent to an ultraviolet catalytic oxidation reaction tank and reacted for 60 minutes under 254nm ultraviolet light irradiation at pH 11. Next, sodium hypochlorite is added at a dosage of 3.5 g / L, and the reaction continues for 30 minutes under ultraviolet light irradiation. Finally, ferrous sulfate is added at a dosage of 0.6 g / L, and the reaction continues for 30 minutes, completing the staged oxidation and complex-breaking treatment, yielding the complex-broken wastewater.

[0058] Comparative Example 3 The only difference between this comparative example and Example 1 is that step S1 is as follows: The wastewater to be treated is collected in an equalization tank, which is equipped with an online ORP monitor for real-time monitoring of the wastewater's oxidation-reduction potential. The ORP reading is -120mV. After water quality equalization treatment, it is sent to a primary pH equalization tank, where lime slurry is added to adjust the pH of the wastewater to 11. Then, it is sent to an ultraviolet catalytic oxidation reaction tank, where hydrogen peroxide is added at a dosage of 5 mL / L under pH 11 conditions. The reaction is carried out under 254 nm ultraviolet light irradiation for 60 minutes to complete the staged oxidation and complex-breaking treatment, obtaining the complex-broken wastewater.

[0059] Comparative Example 4 The only difference between this comparative example and Example 1 is that, in step S2, an equal amount of sodium dimethyl dithiocarbamate is used to replace the composite heavy metal scavenger.

[0060] Comparative Example 5 The only difference between this comparative example and Example 1 is that, in step S2, an equal amount of trithiotriazine trisodium salt is used to replace the composite heavy metal scavenger.

[0061] Comparative Example 6 The only difference between this comparative example and Example 1 is that, in step S2, an equal amount of sodium alginate is used to replace the composite heavy metal scavenging agent.

[0062] Comparative Example 7 The only difference between this comparative example and Example 1 is that step S2 is as follows: The wastewater after complex breaking is sent to a secondary pH adjustment tank, where dilute hydrochloric acid is added to adjust the pH to 5. It is then sent to a reduction reaction tank, where sodium metabisulfite is added. The dosage of sodium metabisulfite is 0.9 times the amount of hydrogen peroxide added in step S1. The reaction is stopped after 22 minutes, and the wastewater is then sent to a chelation precipitation reaction tank. A composite heavy metal scavenging agent is added. After the reaction is complete, the wastewater is sent to a coagulation and flocculation tank, where polyaluminum chloride and anionic polyacrylamide are added. The dosage of polyaluminum chloride is 140 mg / L, and the dosage of anionic polyacrylamide is 2 mg / L. The mixture is stirred for 12 minutes to complete coagulation and flocculation. Then, the wastewater is sent to a primary sedimentation tank for solid-liquid separation, yielding the first supernatant and the first slurry. The composite heavy metal scavenging agent comprises the following components: 30 kg of sodium dimethyl dithiocarbamate, 20 kg of trithiodimethyltriazine trisodium salt, 10 kg of sodium metatitanate, and 10 kg of sodium alginate. The procedure for adding the composite heavy metal scavenging agent is as follows: Sodium dimethyl dithiocarbamate, trisodium trimercaptotriazine, sodium metatitanate, and sodium alginate are mixed beforehand to obtain the composite heavy metal scavenging agent. All of the composite heavy metal scavenging agent is added within 5 minutes of the wastewater entering the chelation precipitation reaction tank to complete the addition.

[0063] Comparative Example 8 The only difference between this comparative example and Example 1 is that an equal amount of fly ash is used to replace the fly ash-modified sludge-based adsorbent.

[0064] Comparative Example 9 The only difference between this comparative example and Example 1 is that chemical nickel wastewater was used as the wastewater to be treated. The initial water quality of the chemical nickel wastewater was: nickel 100 mg / L, total zinc 0.5 mg / L, COD 1500 mg / L, total phosphorus 500 mg / L, pH 9.0.

[0065] Performance testing The following performance tests were conducted on Examples 1-16 and Comparative Examples 1-9: The total nickel, total zinc, and COD in the effluent were measured according to Table 3 of the "Electroplating Pollutant Discharge Standard" (GB 21900-2008) – Special Discharge Limits for Water Pollutants. The values ​​were calculated using the following formula: The test results are shown in Table 1.

[0066] Table 1

[0067] As can be seen from Example 1 and Comparative Examples 1-9, and in conjunction with Table 1, compared to Example 1, the total nickel, total zinc, and COD in the effluent of Comparative Examples 1-9 are all significantly higher. This indicates that the treatment process using the steps and conditions of Example 1 can improve the treatment effect of zinc-nickel electroplating complexed heavy metal wastewater.

[0068] This may be because, in Comparative Example 1, the absence of ultraviolet light significantly reduced the efficiency of H2O2 decomposition to generate ·OH, resulting in insufficient EDTA complex breaking. Consequently, the effluent from Comparative Example 1 showed severe exceedances of standards. In Comparative Example 2, the lack of H2O2 led to a severe shortage of ·OH free radical sources in the system. The combined effects of ultraviolet light and FeSO4 were limited, and aminocarboxylic acid complexing agents such as EDTA were not effectively destroyed. Therefore, nickel mainly remained in the water as an EDTA-Ni complex. In Comparative Example 3, the single oxidation stage only destroyed part of the complexing agent; therefore, both citric acid and EDTA remained. In Comparative Example 4, DTC had limited ability to capture EDTA-complexed heavy metals; therefore, the total nickel in the effluent significantly exceeded standards, while COD was less affected. In Comparative Example 5, TMT had limited ability to capture Ni... 2+ The selectivity of sodium alginate is lower than that of DTC, and its removal effect on complexed nickel is even worse. In Comparative Example 6, sodium alginate has a weaker chelating ability than DTC / TMT and is mainly used as a flocculation aid. In Comparative Example 7, the surface of sodium metatitanate is occupied by organic chelating agents, and sodium alginate competes with DTC for the reaction, resulting in an imbalance in the distribution ratio of each component. In Comparative Example 8, the adsorption capacity of ordinary fly ash is much lower than that of the modified adsorbent, and the effect of the deep adsorption unit is significantly weakened. In Comparative Example 9, the total nickel in the effluent is high. The nickel in the chemical nickel wastewater is mainly composed of hydroxycarboxylic acid complexes such as nickel citrate and nickel lactate. The stability constant of Ni-EDTA complexes in EDTA-type wastewater is much higher than that of nickel citrate. EDTA complexes are more easily attacked by ·OH free radicals in the staged oxidation and complex-breaking system of this process, while nickel citrate and nickel lactate are relatively insensitive to the oxidative attack of ·OH free radicals, requiring stronger oxidation conditions or longer reaction times.

[0069] Zinc-nickel electroplating wastewater contains various complexing agents, including EDTA, citric acid, and aliphatic polyamines. Different types of complexing agents respond differently to oxidation conditions. Example 1 utilizes a UV-catalyzed oxidation reactor and a staged oxidation process under 254nm UV photocatalysis. The process involves three stages: alkaline oxidation with hydrogen peroxide, oxidation with sodium hypochlorite, and Fenton oxidation with ferrous sulfate. This selectively breaks down complexes of various types, including EDTA, citric acid, hydroxycarboxylic acids, and aliphatic polyamines, significantly improving the complex-breaking efficiency. Example 1 also employs a four-component composite heavy metal scavenger comprising sodium dimethyl dithiocarbamate, trisodium trithiotriazine, sodium metatitanate, and sodium alginate. This achieves a triple adsorption mechanism of chemical chelation, physical adsorption by nanomaterials, and polymeric coordination adsorption, significantly enhancing adsorption capacity and selectivity. Sodium metatitanate and sodium alginate work synergistically with Zn... 2+ Ni 2+Strong coordination bonds are formed, increasing the adsorption capacity for nickel ions. Example 1 employs a staged dosing method, allowing different components to function sequentially under their optimal reaction conditions. This helps avoid interference between different reagents, improving reagent utilization efficiency and reducing waste. Example 1 adds a deep adsorption unit after the primary sedimentation tank, using fly ash-modified sludge-based adsorbent for bottom-line adsorption of residual trace heavy metals, ensuring stable discharge compliance regardless of water quality fluctuations. All heavy metal-containing sludge generated during the treatment process is reused: part is directly reused in the UV catalytic oxidation reactor as an adsorption medium, achieving waste-to-waste treatment; the rest is mixed with fly ash to prepare modified adsorbents, realizing closed-loop resource recycling of sludge and significantly reducing hazardous waste discharge. By installing an online ORP monitor in the equalization tank, the oxidation-reduction state of the wastewater is monitored in real time, providing real-time feedback for oxidant dosage, achieving precise control and further improving treatment stability.

[0070] As can be seen from Examples 1-16 and Table 1, the total nickel, total zinc, and COD in the effluent from Examples 1-16 are all relatively low. This indicates that the treatment processes within the process conditions of Examples 1-16 can all improve the treatment effect of zinc-nickel electroplating complexed heavy metal wastewater.

[0071] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for treating complexed heavy metals in zinc-nickel electroplating wastewater, characterized in that, Includes the following steps: S1. Collect the zinc-nickel electroplating complex heavy metal wastewater into the equalization tank. After water quality equalization treatment, send it to the primary pH equalization tank. Add lime milk to adjust the pH of the wastewater to 10-12. Then send it to the ultraviolet catalytic oxidation reaction tank. Under ultraviolet light irradiation, add oxidant and perform staged oxidation to break the complex, and obtain the complex-broken wastewater. S2. The wastewater after complex breaking is sent to the secondary pH adjustment tank, where dilute hydrochloric acid or dilute sulfuric acid is added to adjust the pH of the wastewater to 4.5-5.

5. Then it is sent to the reduction reaction tank, where a reducing agent is added. After the reaction is completed, it is sent to the chelation precipitation reaction tank, where composite heavy metal capture agents are added in stages. After the reaction is completed, it is sent to the coagulation and flocculation tank, where coagulants and flocculants are added. After coagulation and flocculation are completed, it is sent to the primary sedimentation tank for solid-liquid separation to obtain the first supernatant and the first underflow. S3. The first supernatant is sent to the deep adsorption unit, where adsorbent is added for adsorption treatment. It is then sent to the secondary sedimentation tank for solid-liquid separation to obtain the second supernatant and the second underflow. The second supernatant is discharged or reused after meeting the standards. S4. The first underflow and the second underflow are sent to a filter press for filtration to obtain electroplating sludge. Part of the electroplating sludge is recycled to the ultraviolet catalytic oxidation reaction tank in step S1 as an adsorption medium, and the other part of the electroplating sludge is used to prepare the adsorbent.

2. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 1, characterized in that, The composite heavy metal scavenger comprises the following components in parts by weight: 25-35 parts sodium dimethyl dithiocarbamate, 15-25 parts trisodium trimercaptotriazine, 5-15 parts sodium metatitanate, and 5-15 parts sodium alginate.

3. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 2, characterized in that, The operation of adding the composite heavy metal scavenging agent in step S2 is as follows: Sodium dimethyl dithiocarbamate and trithiomercaptotriazine trisodium salt are mixed in advance to obtain a mixed agent. The mixed agent is divided into a first mixed agent and a second mixed agent in a ratio of (3-4):(1-2). The first mixed agent is added within 5 minutes when the wastewater enters the chelation precipitation reaction tank. Sodium metatitanate is added within 5-10 minutes when the wastewater enters the chelation precipitation reaction tank. Sodium alginate powder is added within 10-15 minutes after the wastewater enters the chelation sedimentation reaction tank. The second mixed agent is added within 15-20 minutes after the wastewater enters the chelation sedimentation reaction tank, thus completing the staged addition.

4. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 1, characterized in that, In step S1, the equalization tank is equipped with an online ORP monitor for real-time monitoring of the oxidation-reduction potential of the wastewater.

5. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 1, characterized in that, The step S1 step of graded oxidation and complex breaking treatment is performed as follows: hydrogen peroxide is added at a dosage of 3-8 mL / L under pH 10-12 conditions, and the reaction is carried out under 254 nm ultraviolet light for 60 minutes; sodium hypochlorite is added at a dosage of 2-5 g / L, and the reaction is carried out under ultraviolet light for another 30 minutes; ferrous sulfate is added at a dosage of 0.3-1.0 g / L, and the reaction is carried out for another 30 minutes to complete the graded oxidation and complex breaking treatment.

6. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 1, characterized in that, In step S2, the reducing agent is sodium metabisulfite, and the amount of sodium metabisulfite added is 0.8-1.0 times that of hydrogen peroxide added in step S1. The reaction time is 15-30 minutes.

7. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 6, characterized in that, In step S2, the coagulant is polyaluminum chloride, with a dosage of 80-200 mg / L; the flocculant is anionic polyacrylamide, with a dosage of 1-3 mg / L, and the stirring reaction time is 10-15 minutes.

8. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 1, characterized in that, In step S3, the adsorbent is a fly ash modified sludge-based adsorbent, the dosage of the adsorbent is 1-2 g / L, and the reaction time of the adsorption treatment is 20-40 minutes.

9. The treatment process for complexed heavy metals in zinc-nickel electroplating wastewater according to claim 8, characterized in that, The adsorbent is prepared by mixing electroplating sludge and fly ash at a mass ratio of (3.5-4.5):3, followed by pyrolysis treatment to obtain the adsorbent.

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