A treatment system and method for treating wastewater with strongly complexed heavy metals in the electroplating industry

Abstract

The application discloses a treatment system for treating strongly complexed heavy metal wastewater in an electroplating industry, comprising an oxidation reaction tank, a Fenton-like reaction tank, a homogenizing adjusting tank, a chemical mixing tank, a No. I flocculation tank, a No. I sedimentation tank, a heavy metal adsorption tank, a No. II flocculation tank, a No. II sedimentation tank and a clean water tank which are connected in sequence; wherein, the bottom of the No. II sedimentation tank is provided with two sludge discharge ports, one of which is connected with the heavy metal adsorption tank through a sludge backflow pipeline, and the other is connected with a regeneration system. The application also discloses a method for treating strongly complexed heavy metal wastewater in the electroplating industry based on the treatment system. The method adopts the process of first oxidizing and breaking the complex, then adding alkali to precipitate, and finally modifying zeolite to adsorb, so that the electroplating strongly complexed heavy metal wastewater can be treated, the concentration of heavy metal ions in the effluent can be stably reduced to below 0.1 mg / L, and the discharge standard can be reached.

Description

Technical Field

[0001] This invention relates to a treatment system for wastewater containing strongly complexed heavy metals from the electroplating industry, and also to a method for treating such wastewater based on the aforementioned treatment system. Background Technology

[0002] In the electroplating process of metal parts such as electronic component brackets and contacts, complexing agents are added to the plating solution to make the coating finer and more stable. As a result, the electroplating industry generates a large amount of wastewater containing strongly complexed heavy metals. Compared with traditional wastewater, electroplating complexed wastewater is characterized by large volume, high proportion of complexed heavy metals, low conductivity, and high ammonia nitrogen concentration.

[0003] Traditional methods for treating electroplating complex wastewater, such as coagulation sedimentation, ion exchange, and adsorption, cannot effectively break the stable cyclic structure of EDTA complexes. Existing advanced oxidation methods, such as Fenton oxidation, electrocatalytic oxidation, UV oxidation, and O3 oxidation, suffer from problems such as large dosage of chemicals, high sludge production, difficulty in achieving effluent standards, and high subsequent treatment costs.

[0004] In addition, heavy metal precipitators are commonly used to treat heavy metal wastewater. These precipitators utilize DTC-like salts, modified with additives to enhance their binding capacity with low-concentration heavy metal ions, thereby achieving stable removal of heavy metals. However, heavy metal precipitators are only effective at removing free heavy metal ions from wastewater. They cannot reduce the target heavy metal ions below the standard level for those that strongly complex with EDTA, citric acid, etc. Furthermore, heavy metal precipitators are mainly composed of organic sulfur compounds, and residual organic sulfur compounds have high biotoxicity. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a treatment system for strongly complexed heavy metal wastewater from the electroplating industry. Another purpose of this invention is to provide a method for treating strongly complexed heavy metal wastewater from the electroplating industry based on the above treatment system. This method can effectively destroy the stable ring structure of the complex and effectively remove the free heavy metal ions after the complex is destroyed, thereby reducing the target heavy metal ions to below the standard.

[0006] Technical solution: The electroplating industry wastewater treatment system for highly complexed heavy metals described in this invention includes an oxidation reaction tank, a Fenton-like reaction tank, a homogenization and conditioning tank, a chemical mixing tank, a No. I flocculation tank, a No. I sedimentation tank, a heavy metal adsorption tank, a No. II flocculation tank, a No. II sedimentation tank, and a clear water tank connected in sequence. The No. II sedimentation tank has two sludge discharge ports at the bottom. One sludge discharge port returns the sludge to the heavy metal adsorption tank through a sludge return pipe, and the other sludge discharge port is connected to the regeneration system.

[0007] The method for treating strongly complexed heavy metal wastewater from the electroplating industry based on the above system includes the following steps:

[0008] (1) Add ferrate to the oxidation reaction tank containing electroplating complex wastewater until its molar ratio with heavy metal ions is n[Fe(VI)]:n(R) m+ The ratio of 2 to 5:1 was used to adjust the pH of the wastewater to 2 to 3. The mixture was stirred rapidly and reacted for 20 to 30 minutes.

[0009] (2) Send the effluent from the oxidation reaction tank to the Fenton-like reaction tank, add ferrous acid salt until the molar ratio of ferrous acid salt to ferrate salt is n[Fe(II)]:n[Fe(VI)]=5~10:1, adjust the pH of the wastewater to 2~3, stir rapidly, and react for 40~60min;

[0010] (3) Send the effluent from the Fenton-like reaction tank to the homogenization and equalization tank, adjust the pH of the wastewater to 9.5-10.0 (after adjusting the pH to alkaline, the free heavy metals will precipitate first in the form of hydroxides, reducing the amount of heavy metal adsorbent added later), stir quickly, and react for 15-20 minutes.

[0011] (4) Send the effluent from the homogenization equalization tank to the mixing tank, add coagulant to the mixing tank, stir quickly, and react for 10-15 minutes.

[0012] (5) Send the effluent from the mixing tank to the No. 1 flocculation tank, add flocculant to the flocculation tank, stir slowly, and react for 3 to 5 minutes.

[0013] (6) Send the effluent from flocculation tank I to sedimentation tank I. After sedimentation, send the supernatant to heavy metal adsorption tank. Add heavy metal adsorbent to the heavy metal adsorption tank to a concentration of 500-1500 mg / L, adjust the pH of the wastewater to neutral, stir quickly, and adsorb for 40-60 minutes.

[0014] (7) Send the effluent from the heavy metal adsorption tank to the No. II flocculation tank, add flocculant to it, stir slowly, and react for 3 to 5 minutes.

[0015] (8) The effluent from flocculation tank II is sent to sedimentation tank II. After sedimentation, the supernatant is sent to clear water tank. A portion of the sludge at the bottom of sedimentation tank is returned to heavy metal adsorption tank through sludge return pipe. The sludge is recycled in the adsorption tank. The remaining sludge is discharged to the regeneration system.

[0016] In step (1), the ferrate is potassium ferrate or sodium ferrate.

[0017] In step (1), the initial concentration of heavy metal ions in the wastewater is 5 mg / L to 10 mg / L.

[0018] In step (2), the ferrous salt is ferrous sulfate or ferrous chloride.

[0019] In steps (1) to (3) and step (6), the reagents for adjusting pH are HCl, H2SO4 and NaOH.

[0020] In step (4), the coagulant is polyaluminum chloride (PAC); the concentration of the coagulant added to the wastewater is 500-1000 mg / L.

[0021] In steps (5) and (7), the flocculant is polyacrylamide (PAM); the concentration of the flocculant added to the wastewater is 3-5 mg / L.

[0022] In steps (1) to (7), the speed of rapid stirring is 300 r / min; the speed of slow stirring is 150 r / min.

[0023] In step (8), 15wt% to 20wt% of the sludge is returned to the heavy metal adsorption tank, that is, the sludge return flow rate is 15wt% to 20wt%.

[0024] To improve the adsorption performance and increase the adsorption capacity of the adsorbent for heavy metal ions, the heavy metal adsorbent of this invention is prepared by the following method, the specific steps of which are as follows:

[0025] (1) Wash natural zeolite with deionized water 3 to 5 times to remove impurities on the surface of zeolite, and then soak it in deionized water for more than 24 hours.

[0026] (2) Place the rinsed zeolite in a muffle furnace, set the temperature to 400-500℃, and calcine for 2 hours;

[0027] (3) Grind the thermally modified zeolite into 100-200 mesh powder;

[0028] (4) Dissolve 5-10g of chitosan in 800-1000mL of acetic acid and stir thoroughly to obtain a chitosan-acetic acid solution; add 10-20g of zeolite powder from step (3) to 100mL of chitosan-acetic acid solution, heat in a water bath at 60℃-70℃, and stir for 8-12 hours to ensure that the chitosan is fully loaded onto the surface of the activated zeolite.

[0029] (5) Cool the solution after the reaction in step (4) to room temperature, wash and filter it several times, and place the solid product obtained in an oven to dry at 105°C.

[0030] (6) Immerse 5-10g of the dried zeolite powder from step (5) in 150-200mL of DTPA aqueous solution (concentration of 5mg / mL), heat in a water bath at 60-70℃, and stir for 30-40min.

[0031] (7) Centrifuge the solution after the reaction in step (6), and wash the precipitate with deionized water multiple times until there is no DTPA (detected by LC-MS, the precipitate is clean if there is no residual DTPA in the washing water). Dry and age at 40-50℃ for 24 hours to obtain the heavy metal adsorbent.

[0032] The natural zeolite has a particle size of 40-60 mesh, the chitosan has a degree of deacetylation of 80%-95%, and the acetic acid has a mass fraction of 2%-5%.

[0033] Ferrate's strong oxidizing properties can oxidize organic matter that strongly chelates with heavy metals, breaking the complexation form between them and heavy metals, allowing metal ions to exist in a free state again. Subsequently, by adjusting the pH and using heavy metal adsorbents to specifically adsorb and remove recalcitrant heavy metal ions, the concentration of heavy metal ions in wastewater can be stably reduced to below 0.1 mg / L, improving the problems of low oxidation efficiency, large dosage, and large sludge production caused by the traditional Fenton process.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0035] (1) This invention uses ferrate to oxidize and break down the complexes in wastewater containing strongly complexed heavy metals; simultaneously, H2O2, an active oxidizing agent, is generated during the ferrate oxidation reaction, and Fe is added to the wastewater. 2+ It reacts with H2O2 to form the Fenton system, thus making the entire reaction process a synergistic oxidation system of high-valent iron and Fenton. Compared with the Fenton system alone, the complex is broken, and the oxidation efficiency is increased by 15% to 20%.

[0036] (2) This invention uses a high-temperature-organic loading method to modify zeolite in combination. Thermal modification can remove moisture and organic impurities from the zeolite channels, widen the zeolite channels, thereby increasing the specific surface area and thus increasing its adsorption and ion exchange capacity, especially increasing the loading of subsequent organic matter. Chitosan with high degree of deacetylation has a strong metal coordination ability. Loading chitosan onto the surface of thermally modified zeolite can increase the zeolite's adsorption and chelation capacity for heavy metals. Compared with zeolite with single thermal modification, its adsorption capacity can be increased by more than 10%. Furthermore, DTPA (diethyltriaminepentaacetic acid) is used to modify the organically loaded zeolite. Since the stability constant of DTPA with metal is greater than that of the commonly used complexing agent EDTA, it can adsorb the chelated heavy metals, that is, it has a strong chelating effect on heavy metals. The modified zeolite after DTPA modification can stably bind with heavy metal ions in wastewater, further reducing the concentration of complexed heavy metals in electroplating wastewater. Attached Figure Description

[0037] Figure 1This is a system schematic diagram of the processing system of the present invention. Detailed Implementation

[0038] Example 1

[0039] The heavy metal adsorbent of the present invention uses thermally modified zeolite as a framework and loads chitosan on the framework to provide active sites that can form chelates with heavy metals. The stability of the coordination compound can be further enhanced by modifying the organically loaded zeolite with DTPA.

[0040] The above-mentioned heavy metal adsorbent was prepared by the following method, the specific steps of which are as follows:

[0041] (1) Wash the natural zeolite with deionized water 3 to 5 times to remove impurities on the surface of the zeolite, and then soak it in deionized water for more than 24 hours; the particle size of the natural zeolite is 40 to 60 mesh.

[0042] (2) Place the rinsed zeolite in a muffle furnace, set the temperature to 400℃, and calcine for 2 hours;

[0043] (3) Grind the thermally modified zeolite into 100-mesh powder;

[0044] (4) Dissolve 10g of chitosan in 1000mL of acetic acid and stir thoroughly to obtain a chitosan-acetic acid solution; add 20g of zeolite powder from step (3) to 100mL of chitosan-acetic acid solution, heat in a water bath at 60℃ and stir for 8 hours to ensure that the chitosan is fully loaded on the surface of the activated zeolite; wherein, the degree of deacetylation of chitosan is 95% and the mass fraction of acetic acid is 10%;

[0045] (5) Cool the solution after the reaction in step (4) to room temperature, soak and wash it with deionized water several times, filter it and place the solid product obtained in an oven to dry at 105°C.

[0046] (6) Immerse 10g of the organically loaded zeolite powder dried in step (5) in 200mL of DTPA aqueous solution (the concentration of DTPA aqueous solution is 5mg / mL), heat in a water bath at 60°C and stir for 30min.

[0047] (7) Centrifuge the solution after the reaction in step (6), wash the precipitate several times until DTPA is removed, and dry and age it at 40-50℃ for 24 hours to obtain the heavy metal adsorbent.

[0048] Example 2

[0049] This embodiment is basically the same as Example 1, except that the mass ratio of each component has been adjusted.

[0050] (1) Wash the natural zeolite with deionized water 3 to 5 times to remove impurities on the surface of the zeolite, and then soak it in deionized water for more than 24 hours; the particle size of the natural zeolite is 40 to 60 mesh.

[0051] (2) Place the rinsed zeolite in a muffle furnace, set the temperature to 400℃, and calcine for 2 hours;

[0052] (3) Grind the thermally modified zeolite into 100-mesh powder;

[0053] (4) Dissolve 5g of chitosan in 800mL of acetic acid and stir thoroughly to obtain a chitosan-acetic acid solution; add 10g of zeolite powder from step (3) to 100mL of chitosan-acetic acid solution, heat in a water bath at 60℃ and stir for 8 hours to ensure that the chitosan is fully loaded onto the surface of the activated zeolite; wherein, the degree of deacetylation of chitosan is 95% and the mass fraction of acetic acid is 10%;

[0054] (5) Cool the solution after the reaction in step (4) to room temperature, soak and wash it with deionized water several times, filter it and place the solid product obtained in an oven to dry at 105°C.

[0055] (6) Immerse 5g of the organically loaded zeolite powder dried in step (5) in 150mL of DTPA aqueous solution (concentration of 5mg / mL), heat in a water bath at 60°C and stir for 30min.

[0056] (7) Centrifuge the solution after the reaction in step (6), wash the precipitate several times until DTPA is removed, and dry and age it at 40-50℃ for 24 hours to obtain the heavy metal adsorbent.

[0057] Example 3

[0058] The present invention relates to a treatment system for strongly complexing heavy metal wastewater in the electroplating industry, comprising an oxidation reaction tank 1, a Fenton-like reaction tank 2, a homogenization and conditioning tank 3, a chemical mixing tank 4, a No. I flocculation tank 5, a No. I sedimentation tank 6, a heavy metal adsorption tank 7, a No. II flocculation tank 8, a No. II sedimentation tank 9, and a clear water tank 10 connected in sequence. The No. II sedimentation tank 9 is provided with two sludge discharge ports at the bottom. One sludge discharge port returns the sludge to the heavy metal adsorption tank 7 through a sludge return pipe 11, and the other sludge discharge port is connected to a regeneration system.

[0059] Using the heavy metal adsorbent of Example 1, the above system was used to treat strongly complexed heavy metal wastewater from the electroplating industry (Ni in electroplating complexed wastewater). 2+ The method (initial concentration 5.0 mg / L, COD = 120 mg / L) includes the following steps:

[0060] (1) The electroplating complex wastewater is sent to oxidation reaction tank 1, and potassium ferrate is added to it until its concentration is 100 mg / L. The pH of the wastewater is adjusted to about 2.5 with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred quickly and reacted for 30 min. At this pH, potassium ferrate is conducive to the production of H2O2 active oxidizing substances during the oxidation reaction.

[0061] (2) Send the effluent from oxidation reaction tank 1 to Fenton-like reaction tank 2, add ferrous sulfate to it until its concentration is 350 mg / L, adjust the pH of the wastewater to about 2.5 with 50% wt H2SO4 and 30 wt NaOH, stir quickly, and react for 60 min.

[0062] (3) Send the effluent from Fenton-like reaction tank 2 to homogenization equalization tank 3, adjust the pH of the wastewater to about 10.0 with 50wt% H2SO4 and 30wt% NaOH, stir quickly, and react for 20 minutes;

[0063] (4) Send the effluent from the equalization tank 3 to the mixing tank 4, add PAC to the mixing tank 4 to make its concentration 500 mg / L, stir quickly, and react for 10 min.

[0064] (5) Send the effluent from the mixing tank 4 to the No. I flocculation tank 5, add PAM to it to a concentration of 3 mg / L, stir slowly, and react for 3 min.

[0065] (6) The effluent from flocculation tank I is sent to sedimentation tank I 6. After sedimentation, the supernatant is sent to heavy metal adsorption tank 7. The heavy metal adsorbent prepared in Example 1 is added to heavy metal adsorption tank 7 to a concentration of 1000 mg / L. The pH of the wastewater is adjusted to neutral with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred rapidly and adsorbed for 60 min.

[0066] (7) Send the effluent from the heavy metal adsorption tank 7 to the No. II flocculation tank 8, add PAM to it to a concentration of 5 mg / L, stir slowly, and react for 5 min.

[0067] (8) The effluent from flocculation tank II is sent to sedimentation tank II 9. After sedimentation, the supernatant is sent to clear water tank 10. In the clear water tank, c(Ni) 2+ =0.076mg / L; 20wt% of the sludge at the bottom of the sedimentation tank is returned to the heavy metal adsorption tank 7 through the sludge return pipe 11, and the sludge is recycled in the adsorption tank. The remaining sludge is discharged to the regeneration system.

[0068] Example 4

[0069] This embodiment is basically the same as Embodiment 3, except that the heavy metal adsorbent used is the one prepared in Embodiment 2, wherein the electroplating complex wastewater Ni 2+The initial concentration was 5.0 mg / L, and the COD was 120 mg / L. The implementation steps are as follows:

[0070] (1) The electroplating complex wastewater is sent to oxidation reaction tank 1, and potassium ferrate is added to it until its concentration is 100 mg / L. The pH of the wastewater is adjusted to about 2.5 with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred quickly and reacted for 30 min. At this pH, potassium ferrate is conducive to the production of H2O2 active oxidizing substances during the oxidation reaction.

[0071] (2) Send the effluent from oxidation reaction tank 1 to Fenton-like reaction tank 2, add ferrous sulfate to it until its concentration is 350 mg / L, adjust the pH of the wastewater to about 2.5 with 50% wt H2SO4 and 30 wt NaOH, stir quickly, and react for 60 min.

[0072] (3) Send the effluent from Fenton-like reaction tank 2 to homogenization equalization tank 3, adjust the pH of the wastewater to about 10.0 with 50wt% H2SO4 and 30wt% NaOH, stir quickly, and react for 20 minutes;

[0073] (4) Send the effluent from the equalization tank 3 to the mixing tank 4, add PAC to the mixing tank 4 to make its concentration 500 mg / L, stir quickly, and react for 10 min.

[0074] (5) Send the effluent from the mixing tank 4 to the No. I flocculation tank 5, add PAM to it to a concentration of 3 mg / L, stir slowly, and react for 3 min.

[0075] (6) The effluent from flocculation tank I is sent to sedimentation tank I 6. After sedimentation, the supernatant is sent to heavy metal adsorption tank 7. The heavy metal adsorbent prepared in Example 2 is added to heavy metal adsorption tank 7 to a concentration of 1500 mg / L. The pH of the wastewater is adjusted to neutral with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred rapidly and adsorbed for 60 min.

[0076] (7) Send the effluent from the heavy metal adsorption tank 7 to the No. II flocculation tank 8, add PAM to it to a concentration of 5 mg / L, stir slowly, and react for 5 min.

[0077] (8) The effluent from flocculation tank II is sent to sedimentation tank II 9. After sedimentation, the supernatant is sent to clear water tank 10. In the clear water tank, c(Ni) 2+ =0.094mg / L; 20wt% of the sludge at the bottom of the sedimentation tank is returned to the heavy metal adsorption tank 7 through the sludge return pipe 11, and the sludge is recycled in the adsorption tank. The remaining sludge is discharged to the regeneration system.

[0078] Comparative Example 1

[0079] Comparative Example 1 and Example 3 treated wastewater (electroplated complex wastewater Ni) in exactly the same way. 2+ With an initial concentration of 5.0 mg / L and COD of 120 mg / L, heavy metal degradation was carried out using an existing Fenton oxidation system combined with the heavy metal adsorbent prepared in Example 1 of this invention. Specifically:

[0080] (1) The electroplating complex wastewater is sent to oxidation reaction tank 1, and 30wt% H2O2 and Fe are added to it. 2+ The mass ratio of COD to H2O2 in the water is 0.5, and Fe... 2+ The mass ratio of H2O2 to NaOH is 0.1; the pH of the wastewater is adjusted to about 2.5 with 50wt% H2SO4 and 30wt% NaOH, and the mixture is stirred rapidly for 120 min.

[0081] (2) Send the effluent from oxidation reaction tank 1 to homogenization equalization tank 3, adjust the pH of the wastewater to about 10.0 with 50wt% H2SO4 and 30wt% NaOH, stir quickly, and react for 20 minutes;

[0082] (3) Send the effluent from the homogenization equalization tank 3 to the mixing tank 4, add PAC to the mixing tank 4 to make its concentration 500mg / L, stir quickly, and react for 10min.

[0083] (4) Send the effluent from the mixing tank 4 to the No. I flocculation tank 5, add PAM to it to a concentration of 3 mg / L, stir slowly, and react for 3 min.

[0084] (6) The effluent from flocculation tank I is sent to sedimentation tank I 6. After sedimentation, the supernatant is sent to heavy metal adsorption tank 7. The heavy metal adsorbent prepared in Example 1 is added to heavy metal adsorption tank 7 until its concentration is 1000 mg / L. The pH of the wastewater is adjusted to neutral with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred rapidly and adsorbed for 60 min.

[0085] (7) Send the effluent from the heavy metal adsorption tank 7 to the No. II flocculation tank 8, add PAM to it to a concentration of 5 mg / L, stir slowly, and react for 5 min.

[0086] (8) The effluent from flocculation tank II is sent to sedimentation tank II 9. After sedimentation, the supernatant is sent to clear water tank 10. In the clear water tank, c(Ni) 2+ = 0.128 mg / L.

[0087] As can be seen from Comparative Example 1, the traditional Fenton oxidation complexation of heavy metals has low oxidation efficiency (effluent heavy metal ions > 0.1 mg / L), requires a large amount of reagent and generates a large amount of sludge.

[0088] Comparative Example 2

[0089] A heavy metal adsorbent is prepared by the following method, the specific steps of which are as follows:

[0090] (1) Wash the natural zeolite with deionized water 3 to 5 times to remove impurities on the surface of the zeolite, and then soak it in deionized water for more than 24 hours; the particle size of the natural zeolite is 40 to 60 mesh.

[0091] (2) Place the rinsed zeolite in a muffle furnace, set the temperature to 400℃, and calcine for 2 hours;

[0092] (3) Grind the thermally modified zeolite into 100-mesh powder;

[0093] (4) Dissolve 10g of chitosan in 1000mL of acetic acid and stir thoroughly to obtain a chitosan-acetic acid solution; add 20g of zeolite powder from step (3) to 100mL of chitosan-acetic acid solution, heat in a water bath at 60℃ and stir for 8 hours to ensure that the chitosan is fully loaded on the surface of the activated zeolite; wherein, the degree of deacetylation of chitosan is 95% and the mass fraction of acetic acid is 10%;

[0094] (5) Cool the solution after the reaction in step (4) to room temperature, soak and wash it with deionized water several times, filter it and place the solid product in an oven to dry at 105°C.

[0095] Comparative Example 3

[0096] This embodiment is basically the same as Example 3, except that the heavy metal adsorbent used is the one prepared in Comparative Example 2, wherein the electroplating complex wastewater Ni 2+ The initial concentration was 5.0 mg / L, and the COD was 120 mg / L. The implementation steps are as follows:

[0097] (1) The electroplating complex wastewater is sent to oxidation reaction tank 1, and potassium ferrate is added to it until its concentration is 100 mg / L. The pH of the wastewater is adjusted to about 2.5 with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred quickly and reacted for 30 min. At this pH, potassium ferrate is conducive to the production of H2O2 active oxidizing substances during the oxidation reaction.

[0098] (2) Send the effluent from oxidation reaction tank 1 to Fenton-like reaction tank 2, add ferrous sulfate to it until its concentration is 350 mg / L, adjust the pH of the wastewater to about 2.5 with 50% wt H2SO4 and 30 wt NaOH, stir quickly, and react for 60 min.

[0099] (3) Send the effluent from Fenton-like reaction tank 2 to homogenization equalization tank 3, adjust the pH of the wastewater to about 10.0 with 50wt% H2SO4 and 30wt% NaOH, stir quickly, and react for 20 minutes;

[0100] (4) Send the effluent from the equalization tank 3 to the mixing tank 4, add PAC to the mixing tank 4 to make its concentration 500 mg / L, stir quickly, and react for 10 min.

[0101] (5) Send the effluent from the mixing tank 4 to the No. I flocculation tank 5, add PAM to it to a concentration of 3 mg / L, stir slowly, and react for 3 min.

[0102] (6) The effluent from flocculation tank I is sent to sedimentation tank I 6. After sedimentation, the supernatant is sent to heavy metal adsorption tank 7. The heavy metal adsorbent prepared in Comparative Example 2 is added to heavy metal adsorption tank 7 to a concentration of 1500 mg / L. The pH of the wastewater is adjusted to neutral with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred rapidly and adsorbed for 60 min.

[0103] (7) Send the effluent from the heavy metal adsorption tank 7 to the No. II flocculation tank 8, add PAM to it to a concentration of 5 mg / L, stir slowly, and react for 5 min.

[0104] (8) The effluent from flocculation tank II is sent to sedimentation tank II 9. After sedimentation, the supernatant is sent to clear water tank 10. In the clear water tank, c(Ni) 2+ = 0.185 mg / L.

[0105] Comparative Example 4

[0106] This embodiment is basically the same as embodiment 3, except that in step (3), the wastewater was not alkali-precipitated in the homogenization and equalization tank 3, wherein the electroplating complex wastewater Ni 2+ The initial concentration was 5.0 mg / L, and the COD was 120 mg / L. The implementation steps are as follows:

[0107] (1) The electroplating complex wastewater is sent to oxidation reaction tank 1, and potassium ferrate is added to it until its concentration is 100 mg / L. The pH of the wastewater is adjusted to about 2.5 with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred quickly and reacted for 30 min. At this pH, potassium ferrate is conducive to the production of H2O2 active oxidizing substances during the oxidation reaction.

[0108] (2) Send the effluent from oxidation reaction tank 1 to Fenton-like reaction tank 2, add ferrous sulfate to it until its concentration is 350 mg / L, adjust the pH of the wastewater to about 2.5 with 50% wt H2SO4 and 30 wt NaOH, stir quickly, and react for 60 min.

[0109] (3) The effluent from the Fenton-like reaction tank 2 is sent to the homogenization and equalization tank 3. After the wastewater is homogenized in the homogenization and equalization tank 3, the effluent enters the chemical mixing tank 4. PAC is added to the chemical mixing tank 4 to make its concentration 500mg / L, and the mixture is stirred quickly for 10min.

[0110] (4) Send the effluent from the mixing tank 4 to the No. I flocculation tank 5, add PAM to it to a concentration of 3 mg / L, stir slowly, and react for 3 min.

[0111] (5) The effluent from flocculation tank I is sent to sedimentation tank I 6. After sedimentation, the supernatant is sent to heavy metal adsorption tank 7. The heavy metal adsorbent prepared in Example 1 is added to heavy metal adsorption tank 7 to a concentration of 1500 mg / L. The pH of the wastewater is adjusted to neutral with 50 wt% H2SO4 and 30 wt% NaOH. The mixture is stirred rapidly and adsorbed for 60 min.

[0112] (6) Send the effluent from the heavy metal adsorption tank 7 to the No. II flocculation tank 8, add PAM to it to a concentration of 5 mg / L, stir slowly, and react for 5 min.

[0113] (7) The effluent from flocculation tank II is sent to sedimentation tank II 9. After sedimentation, the supernatant is sent to clear water tank 10. In the clear water tank, c(Ni) 2+ = 0.112 mg / L.

[0114] The method of this invention uses a process of first oxidizing and breaking the complex, then adding alkali for precipitation, and finally modifying zeolite for adsorption to treat electroplating wastewater with strong complexed heavy metals. This method can ensure that the concentration of heavy metal ions in the effluent is stably reduced to below 0.1 mg / L, meeting the discharge standards.

Claims

1. A method for treating wastewater containing strongly complexed heavy metals from the electroplating industry, characterized in that, Includes the following steps: (1) Add ferrate to the oxidation reaction tank containing electroplating complex wastewater until its molar ratio with heavy metal ions is n[Fe(VI)]:n(R) m+ The ratio of 2 to 5:1 was used to adjust the pH of the wastewater to 2 to 3. The mixture was stirred rapidly and reacted for 20 to 30 minutes. (2) Send the effluent from the oxidation reaction tank to the Fenton-like reaction tank, add ferrous acid salt until the molar ratio of ferrous acid salt to ferrate salt is n[Fe(II)]:n[Fe(VI)]=5~10:1, adjust the pH of the wastewater to 2~3, stir rapidly, and react for 40~60 min; (3) Send the effluent from the Fenton-like reaction tank to the homogenization and equalization tank, adjust the pH of the wastewater to 9.5~10.0, stir rapidly, and react for 15~20 minutes; (4) Send the effluent from the homogenization equalization tank to the mixing tank, add coagulant to the mixing tank, stir quickly, and react for 10-15 minutes; (5) Send the effluent from the mixing tank to the No. 1 flocculation tank, add flocculant to the flocculation tank, stir slowly, and react for 3~5 minutes; (6) Send the effluent from flocculation tank I to sedimentation tank I. After sedimentation, send the supernatant to heavy metal adsorption tank. Add heavy metal adsorbent to the heavy metal adsorption tank to a concentration of 500~1500 mg / L, adjust the pH of the wastewater to neutral, stir quickly, and adsorb for 40~60 min. (7) Send the effluent from the heavy metal adsorption tank to the No. II flocculation tank, add flocculant to it, stir slowly, and react for 3~5 minutes; (8) The effluent from the No. II flocculation tank is sent to the No. II sedimentation tank. After sedimentation, the supernatant is sent to the clear water tank. A portion of the sludge at the bottom of the sedimentation tank is returned to the heavy metal adsorption tank through the sludge return pipe. The sludge is recycled in the adsorption tank. The remaining sludge is discharged to the regeneration system. The above treatment method is based on the following system, which includes an oxidation reaction tank, a Fenton-like reaction tank, a homogenization and conditioning tank, a chemical mixing tank, a No. I flocculation tank, a No. I sedimentation tank, a heavy metal adsorption tank, a No. II flocculation tank, a No. II sedimentation tank, and a clear water tank connected in sequence. The No. II sedimentation tank has two sludge discharge ports at the bottom. One sludge discharge port returns the sludge to the heavy metal adsorption tank through a sludge return pipe, and the other sludge discharge port is connected to the regeneration system. The above-mentioned heavy metal adsorbent was prepared by the following method, the specific steps of which are as follows: (1.1) Wash the natural zeolite 3 to 5 times with deionized water to remove impurities on the surface of the zeolite, and then soak it in deionized water for more than 24 hours; wherein the particle size of the natural zeolite is 40 to 60 mesh. (1.2) Place the rinsed zeolite in a muffle furnace, set the temperature to 400℃, and calcine for 2 hours; (1.3) Grind the heat-modified zeolite into 100-mesh powder; (1.4) Dissolve 10g of chitosan in 1000mL of acetic acid and stir thoroughly to obtain a chitosan-acetic acid solution; add 20g of zeolite powder from step (1.3) to 100mL of chitosan-acetic acid solution, heat in a water bath at 60℃, and stir for 8 hours to ensure that the chitosan is fully loaded onto the surface of the activated zeolite; wherein, the degree of deacetylation of chitosan is 95% and the mass fraction of acetic acid is 10%; (1.5) Cool the solution after the reaction in step (1.4) to room temperature, wash it repeatedly with deionized water, filter it and place the solid product in an oven to dry at 105°C. (1.6) Immerse 10g of the organically loaded zeolite powder dried in step (1.5) in 200mL of DTPA aqueous solution, heat in a water bath at 60℃ and stir for 30min; the concentration of DTPA aqueous solution is 5mg / mL; (1.7) Centrifuge the solution after the reaction in step (1.6), wash the precipitate several times until DTPA is removed, and dry and age it at 40~50℃ for 24h to obtain the heavy metal adsorbent.

2. The processing method according to claim 1, characterized in that: In step (1), the ferrate is potassium ferrate or sodium ferrate.

3. The processing method according to claim 1, characterized in that: In step (1), the initial concentration of heavy metal ions in the wastewater is 5 mg / L to 10 mg / L.

4. The processing method according to claim 1, characterized in that: In step (2), the ferrous salt is ferrous sulfate or ferrous chloride.

5. The processing method according to claim 1, characterized in that: In steps (1) to (3) and step (6), the reagents for adjusting pH are HCl, H2SO4 and NaOH.

6. The processing method according to claim 1, characterized in that: In step (4), the coagulant is polyaluminum chloride; in the wastewater, the concentration of the coagulant added is 500~1000 mg / L.

7. The processing method according to claim 1, characterized in that: In steps (5) and (7), the flocculant is polyacrylamide; in the wastewater, the concentration of the flocculant added is 3~5 mg / L.

8. The processing method according to claim 1, characterized in that: In steps (1) to (7), the speed of rapid stirring is 300 to 350 r / min; the speed of slow stirring is 130 to 150 r / min.

9. The processing method according to claim 1, characterized in that: In step (8), 15wt%~20wt% of the sludge is returned to the heavy metal adsorption tank.

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