Photocatalytic oxidation and zero emission method for electroplating nickel flushing wastewater

Abstract

The invention discloses a photocatalytic oxidation and zero discharge method for nickel electroplating flushing wastewater. The method comprises the following steps: mixing and staying the nickel electroplating flushing wastewater to be treated and H2O2 in a pipeline mixer I; the catalytic reactor I is filled with a composite molecular sieve catalyst and a plurality of ultraviolet lamp tubes; effluent of the photocatalytic reactor I enters a microfiltration filter I, and the catalyst and water are separated in the microfiltration filter I; outlet water of the microfiltration filter I is heated, steam on the heated nickel-containing flushing wastewater side penetrates through a membrane of a membrane distillation system and then enters a steam side, and the steam penetrating through the membrane is pumped into a condenser by a vacuum pump on the steam side; the concentrated solution and H2O2 are mixed in a pipeline mixer II, and then enter a photocatalytic reactor II; effluent enters a microfiltration filter II, and the catalyst and the water are separated in the microfiltration filter II. According to the method, multiple components can be recycled, no waste is generated, and the economic and environment-friendly dual effects are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for photocatalytic oxidation and zero-discharge of nickel electroplating flushing wastewater. Background Art

[0002] Nickel electroplating is a method of depositing a layer of nickel on the surface of ferrous or non-ferrous metal parts by electrochemical action. It can be used as a surface coating, but it is mainly used for chrome plating to prevent corrosion, increase wear resistance, gloss and beauty. It is widely used in the manufacturing industry of machinery, instruments, meters, medical equipment, household appliances, etc. The workpiece is used as the cathode and the pure nickel plate is used as the anode. It is hung in an electrolyte composed of nickel sulfate, sodium chloride and boric acid for electroplating.

[0003] After electroplating, the surface of the plated parts will carry a small amount of electroplating solution. Therefore, the plated parts need to be rinsed after electroplating. During the rinsing process, rinsing wastewater will be generated. The main pollutants in the rinsing wastewater are the diluted electroplating solution. The main components of the commonly used Watt electroplating solution include nickel chloride, nickel sulfate, boric acid and a small amount of organic additives. Among them, inorganic components such as nickel chloride, nickel sulfate and boric acid will basically not change during the electroplating process, while organic additives will undergo oxidation, decomposition and other reactions as the electroplating time increases. Therefore, the main pollutants in the rinsing wastewater include nickel, boron, organic matter, etc.

[0004] If the organic matter in the flushing wastewater is removed and the flushing wastewater is concentrated, and a small amount of organic additives are added after the concentrate reaches the concentration of the electroplating solution, the nickel-containing flushing wastewater can be recycled. In order to ensure the purity of the electroplating solution, no new substances can be introduced during the removal of organic matter.

[0005] The invention of CN201210368797.1 discloses a zero-discharge online circulation treatment system for electroplating nickel-containing wastewater, which comprises: an early stage pretreatment system, a filtration and permeation system and an evaporation and concentration system; the early stage pretreatment system comprises a raw water pool (1), a booster pump (2), an MBR membrane treatment device (3), a bag filter (4), an oil removal filter (5), and a security filter (6); the filtration and permeation system comprises: an ultrafiltration device (7), a first high-pressure pump (8), a first-stage reverse osmosis unit (9), a first-stage intermediate water tank (10), a second high-pressure pump (11), a second-stage reverse osmosis unit (12) and a high-concentration nickel water collection tank (13); the evaporation and concentration system comprises a solar water heater (14), an electric heater (15), a hot water storage tank (16), a circulation pump (17), a ring ladder multi-effect evaporation tower (18), and an ultra-high concentration nickel water collection tank (19). The device has good equipment completeness and high degree of automation. The nickel recovery rate can reach 99.98%, the water reuse rate can reach 100%, there is no secondary pollution, and it can achieve zero discharge of nickel plating wastewater more thoroughly, which is of great significance to the sustainable development of the electroplating industry.

[0006] N201310345579.0 discloses a device and method for recovering nickel from nickel-containing wastewater using a microbial electrolytic cell, the device comprising a microbial electrolytic cell, a data acquisition system and a recording unit; the microbial electrolytic cell is a double-chamber microbial electrolytic cell; the microbial electrolytic cell uses a conductive inert material as an anode electrode and a conductive inert material as a cathode electrode, and the anode electrode and the cathode electrode are connected by a titanium wire, a constant potential instrument and a resistor; the data acquisition system is connected in parallel with the resistor, and the recording unit is connected to the data acquisition system. The present invention provides a feasibility analysis and a specific operation method for recovering nickel from nickel-containing wastewater using a microbial electrolytic cell, and realizes the recovery of nickel from nickel-containing wastewater using a microbial electrolytic cell. Compared with the traditional method of recovering nickel from water by electrolysis, this method greatly reduces energy consumption, reduces the use of chemical reagents, reduces costs, and avoids environmental pollution.

[0007] CN201410301526.3 discloses a method for treating nickel-containing wastewater in the electroplating industry. The method for treating nickel-containing wastewater comprises the following steps: (1) adding an oxidant to the nickel-containing wastewater under acidic conditions to carry out an oxidation reaction; (2) adding alkali to the nickel-containing wastewater after the oxidation reaction in step (1) to make the nickel-containing wastewater alkaline, then standing and settling, and taking out the supernatant; (3) adding a precipitant and a flocculant to the supernatant in step (2) in sequence to carry out co-precipitation, and the resulting final supernatant is the treated dischargeable wastewater. The treatment method of the present invention is simple to operate, has a stable effect, and the reagents used will not cause secondary pollution to the environment; the treatment method of the present invention utilizes the co-precipitation effect of the flocculant and the precipitate on the basis of secondary precipitation, which can ensure that the total nickel concentration of the treated effluent from the nickel-containing wastewater can meet the discharge standard.

[0008] CN201410473920.5 discloses a nickel-containing wastewater treatment device, including a nickel-containing wastewater storage and input device, a nickel-containing wastewater pH adjustment tank, a pump system, an electrolysis device and a control device, and also includes a sewage circulation treatment device. The present invention also discloses a treatment method corresponding to the nickel-containing wastewater treatment device. The present invention adds chemical nickel waste liquid and nickel-containing sewage concentrate into a nickel-containing wastewater pH adjustment tank for mixing, and adjusts the pH value to 6-7; the wastewater with the adjusted pH value is passed into an electrolytic tank for electrolysis at 65-75°C to recover elemental nickel, and the nickel discharge concentration of the wastewater after electrolysis is below 0.02g / L, and the recovery rate is above 97%; the wastewater after electrolysis is then subjected to reverse osmosis resin exchange treatment, and the treated wastewater can be directly discharged or recycled.

[0009] CN201510136498.9 discloses a method and system for treating nickel-containing wastewater, which can ensure the stability of effluent water quality. The method of the embodiment of the present invention comprises: discharging the nickel-containing waste liquid into a decomposition reaction tank, adding bleaching water, discharging the effluent into a first pH adjustment tank, adding NaOH, adjusting the pH value, discharging the effluent into a calcium salt reaction tank, adding CaO and DTC, discharging the effluent into a coagulation sedimentation tank, adding polyaluminium chloride and polyacrylamide, standing and settling, filtering to obtain a supernatant, discharging the supernatant into a second pH adjustment tank, adding H2SO4 solution, discharging the effluent into a Fenton reaction tank after the reaction, adding H2O2 and FeSO4, discharging the effluent into a third pH adjustment tank, adding NaOH, and then discharging into a Fenton sedimentation tank, adding polyaluminium chloride and polyacrylamide, and then discharging the effluent into an ammonia nitrogen reaction tank. Summary of the invention

[0010] Therefore, the technical problem to be solved by the present invention is to provide a zero-discharge method for nickel electroplating flushing wastewater.

[0011] The technical solution of the present invention is a method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater, comprising the following steps:

[0012] (1) The nickel electroplating washing wastewater to be treated is mixed with H2O2 in a pipeline mixer I, and the amount of H2O2 added is 2:1 to 3:1 according to H2O2:COD; after mixing, it enters a photocatalytic reactor I, and the hydraulic retention time of the nickel electroplating washing wastewater in the photocatalytic reactor I is 1 to 3 hours; the photocatalytic reactor I is filled with a high-efficiency composite molecular sieve catalyst, and a plurality of ultraviolet lamps are set; the high-efficiency composite molecular sieve catalyst is a molecular sieve loaded with a composite catalyst of manganese nitrate, iron nitrate and titanium dioxide;

[0013] (2) The effluent from the photocatalytic reactor I enters the microfiltration filter I, where the catalyst and water are separated; the microfiltration membrane uses a tubular microfiltration membrane, and the produced water after microfiltration enters the membrane distillation reactor for concentration. The concentrated liquid mainly contains the catalyst, which is returned to the photocatalytic reactor I for recycling;

[0014] (3) A two-stage membrane distillation concentration process is used to heat the effluent from the microfiltration flushing wastewater filter I to 50-80° C. The water vapor from the heated nickel-containing flushing wastewater side passes through the membrane of the membrane distillation system and enters the steam side. On the steam side, the water vapor that passes through the membrane is pumped into a condenser using a vacuum pump. The concentrated liquid after membrane concentration is circulated to the inlet of the membrane distillation component for further concentration until the nickel content in the concentrated liquid reaches the requirement of the electroplating solution, and part of the concentrated liquid is discharged, and the concentrated liquid enters the subsequent treatment system for further treatment;

[0015] (4) After concentration by membrane distillation, the concentrate is mixed with H2O2 in a pipeline mixer II, the dosage of H2O2 is 4.:1 to 6:1 according to H2O2:COD, and after mixing, it enters the photocatalytic reactor II, and the hydraulic retention time of the concentrate in the photocatalytic reactor II is 36 to 48 hours; the photocatalytic reactor II is filled with a high-efficiency composite molecular sieve catalyst and is also provided with a number of ultraviolet lamps; the organic matter in the concentrate is continuously decomposed in the photocatalytic reactor to further reduce the concentration of the organic matter;

[0016] (5) The effluent from the photocatalytic reactor II enters the microfiltration filter II, where the catalyst and water are separated. The organic matter is removed from the water produced by the microfiltration filter II, and the concentrated nickel is recycled as a plating solution. The concentrated solution mainly contains the catalyst, which is returned to the photocatalytic reactor II for recycling.

[0017] In step (1), in the photocatalytic reactor I, H2O2 is used as an oxidant, and under the combined action of the catalyst and the ultraviolet lamp, the organic pollutants in the flushing wastewater are oxidized and decomposed into harmless substances such as carbon dioxide and water. H2O2 is decomposed into H2O and O2, and no new substances are added; the catalyst itself, as a catalyst for the oxidation reaction, does not participate in the reaction and does not change. It is recycled after the reaction and does not affect the use of the concentrated and recycled electroplating solution.

[0018] In step (2), the microfiltration flushing wastewater filter I can remove the catalyst and suspended matter in the water, which is beneficial to the stable operation of the membrane distillation system.

[0019] In step (3), a vacuum pump is used on the water vapor side to pump the water vapor that has passed through the membrane into the condenser, thereby ensuring the steam pressure difference on both sides of the membrane. The water vapor is condensed into condensed water in the condenser, and the condensed water is returned to the production process for use. In order to ensure the quality of the produced water, a multi-stage series concentration can be used, and the water produced by the following stages is used as the inlet water for the first stage. The membrane of the membrane distillation system is a hydrophobic membrane that only allows water vapor to pass through. The conductivity of the water produced by the first-stage membrane distillation process is 3-10μs / cm, Ni 2+ <0.05mg / L; Ni in the concentrate of the secondary membrane distillation process 2+ 150~200g / L. The primary membrane distillation is to control the quality of the produced water to ensure that the produced water can be reused, but does not control the concentrated water; the secondary membrane distillation is to control the nickel ions in the concentrated water to meet the requirements of the plating solution, but does not control the quality of the produced water.

[0020] After concentration by membrane distillation, the organic matter content in the concentrated solution is also concentrated. In order to ensure the purity of the plating solution, the organic matter needs to be further removed.

[0021] In step (5), the main components of the water produced by the microfiltration filter II are nickel chloride, nickel sulfate and boric acid. Organic matter is removed from the produced water, and nickel is concentrated to meet the requirements of the new plating solution. For example, a small amount of organic additives can be added to recycle it as a plating solution; the concentrated solution mainly contains catalysts, which are returned to the photocatalytic reactor II for recycling.

[0022] According to the method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater of the present invention, preferably, the spacing between the ultraviolet lamp tubes in step (1) is 5 to 15 cm.

[0023] According to the method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater of the present invention, preferably, the preparation process of the high-efficiency composite molecular sieve catalyst described in step (1) comprises:

[0024] a. Select Y-type molecular sieve with a particle size of 50-200 mesh, rinse the molecular sieve with deionized water, and dry it;

[0025] b. The dried molecular sieve is immersed in a nitric acid solution, and manganese nitrate (Mn(NO3)2) and iron nitrate (Fe(NO3)3) are added, wherein the molar ratio of manganese nitrate to iron nitrate is 1:1 to 3:1; the solution is heated to 80 to 85°C and reacted at a constant temperature for 3 to 5 hours;

[0026] c. After the reaction is completed, the water is filtered out by vacuum filtration, and the mixture is placed in a drying oven at 100-110°C and dried to constant weight, and manganese nitrate and iron nitrate are loaded on the surface of the molecular sieve;

[0027] d. Tetrabutyl titanate (CH3CH2O)4Ti) is added to polyethylene glycol, the ratio of polyethylene glycol to tetrabutyl titanate is 4:1 to 6:1, and then anhydrous ethanol is added, the amount of anhydrous ethanol added is 4 to 6 times that of tetrabutyl titanate, and the tetrabutyl titanate is fully dissolved by stirring to form a colorless transparent sol; the molecular sieve loaded with manganese nitrate and iron nitrate is mixed evenly with the transparent sol, and placed in a hydrothermal reactor, and the hydrothermal reactor is placed in a heating device at a temperature of 140 to 160°C, maintained for 6 to 8 hours, and then cooled to room temperature;

[0028] e. Wash with distilled water and anhydrous ethanol respectively until neutral, and dry at 70-95°C to constant weight; obtain a molecular sieve loaded with a composite catalyst of manganese nitrate, iron nitrate and titanium dioxide.

[0029] Step d is to load the molecular sieve with titanium dioxide, so that the loaded titanium dioxide is more uniform and not easy to fall off.

[0030] Furthermore, in the preparation process of the high-efficiency composite molecular sieve catalyst, the Y-type molecular sieve in step a is a Y-type molecular sieve with relatively large pore size; the drying temperature in step a is 100-110° C. The pore size of the Y-type molecular sieve is 0.7-0.9 nm.

[0031] Furthermore, in the preparation process of the high-efficiency composite molecular sieve catalyst, the mass concentration of the nitric acid solution in step b is 10-30%.

[0032] Furthermore, in the preparation process of the high-efficiency composite molecular sieve catalyst, the drying temperature in step e is 75-90°C.

[0033] According to the method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater of the present invention, preferably, the filtration in step (2) adopts cross-flow filtration; the circulation volume of the microfiltration system is 5 to 20 times the water production volume, the microfiltration membrane filtration accuracy is 1 μm to 10 μm, and the flux is 200 to 600 L / m 2 ·h, operating pressure 0.3~1.0MPa. Cross-flow filtration can reduce membrane fouling.

[0034] According to the method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater of the present invention, preferably, the heating in step (3) can be steam heating, electric heating or waste flue gas heating.

[0035] According to the method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater described in the present invention, preferably, in step (4), the structure of photocatalytic reactor II is the same as that of photocatalytic reactor I; in step (5), microfiltration filter II is the same as that of microfiltration filter I, and has the same operating parameters.

[0036] According to the method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater of the present invention, preferably, the water quality of the nickel electroplating rinsing wastewater is as follows: Ni 2+ 300~1000mg / L, Cl - 80~300mg / L, SO4 2- 250~800mg / L, B 20~70mg / L, COD 80~400mg / L.

[0037] Beneficial effects:

[0038] The present invention provides a method for photocatalytic oxidation and zero emission of electroplating nickel-containing rinsing wastewater, wherein the rinsing wastewater is treated by primary hydrogen peroxide high-efficiency photocatalytic oxidation, membrane distillation concentration, and secondary hydrogen peroxide high-efficiency photocatalytic oxidation. The water produced by membrane distillation is recycled as rinsing water, and the membrane distillation concentrated liquid is treated by secondary hydrogen peroxide high-efficiency photocatalytic oxidation and a small amount of organic additives are added to the concentrated liquid, which can be recycled as a plating solution. After the treatment of the invention, the water in the electroplating rinsing wastewater and the effective plating solution components such as nickel chloride, nickel sulfate, and boric acid can be recycled respectively, and the process does not generate waste. The invention has both economic and environmental protection effects, and has good social and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a process flow chart of the method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater provided by the present invention.

[0040] Figure 2 Schematic diagram of the structure of the photocatalytic reactor.

[0041] In the figure, 1. water inlet, 2. water outlet, 3. aeration device, 4. UV lamp, 5. nickel-containing wastewater mixed with catalyst. DETAILED DESCRIPTION

[0042] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0043] Example 1

[0044] Water quality of nickel electroplating rinsing wastewater: Ni 2+ 650mg / L, Cl-165mg / L, SO4 2- 523mg / L, B45mg / L, COD230mg / L.

[0045] H2O2 is mixed with nickel electroplating rinsing wastewater, H2O2:COD is 2.5:1, and then enters the photocatalytic reactor I. The hydraulic retention time of nickel electroplating rinsing wastewater in the photocatalytic reactor I is 2h. The spacing between the ultraviolet lamps in the photocatalytic reactor I is 10cm.

[0046] Preparation process of high-efficiency composite molecular sieve catalyst: Y-type molecular sieve particle size 100 mesh, rinse the molecular sieve with deionized water, and dry it at 105℃. Soak the dried molecular sieve in 20% nitric acid, add manganese nitrate (Mn(NO3)2) and iron nitrate (Fe(NO3)3), where the molar ratio of manganese nitrate to iron nitrate is 2:1, heat the solution to 80℃, and react at constant temperature for 4h; after the reaction, vacuum filter to dry the water, place it in a drying oven at 105℃ and dry it to constant weight. Tetrabutyl titanate (CH3CH2O )4Ti) is added to polyethylene glycol, the ratio of polyethylene glycol to tetrabutyl titanate is 5:1, and then anhydrous ethanol is added, the amount of anhydrous ethanol added is 5 times that of tetrabutyl titanate, and the tetrabutyl titanate is fully dissolved by stirring to form a colorless transparent sol. The molecular sieve loaded with manganese nitrate and ferric nitrate is mixed evenly with the transparent sol, placed in a hydrothermal reactor, and the hydrothermal reactor is placed in an oven. The temperature of the oven is maintained at 150°C for 7 hours, and then cooled to room temperature. Wash with distilled water and anhydrous ethanol respectively until neutral, and dry at 85°C to constant weight. A molecular sieve loaded with manganese nitrate, ferric nitrate and titanium dioxide composite catalyst is obtained.

[0047] The effluent from the photocatalytic reactor I enters the microfiltration filter I, where the catalyst and water are separated. The microfiltration membrane uses a tubular microfiltration membrane. In order to reduce membrane fouling, cross-flow filtration is used. The circulation volume of the microfiltration system is 10 times the water production volume. The microfiltration membrane has a filtration accuracy of 5μm and a flux of 385L / m 2 ·h, operating pressure 0.75MPa. COD in microfiltration water is 35mg / L. The water produced after microfiltration enters the membrane distillation reactor for concentration. The concentrate mainly contains catalyst, which returns to the photocatalytic reactor I for recycling.

[0048] The two-stage membrane distillation concentration process was used to heat the effluent from the microfiltration wastewater filter I to 70°C. The conductivity of the water produced by the first-stage membrane distillation process was 5.3μs / cm, and Ni 2+ 0.01mg / L, Ni in concentrate 2+ 11.8g / L, COD659mg / L; conductivity of water produced by two-stage membrane distillation process is 56.2μs / cm, Ni 2+ 2.1mg / L, Ni in concentrate 2+ 154g / L, COD7230mg / L. The membrane of the membrane distillation system is a hydrophobic membrane that only allows water vapor to pass through. The water vapor on the side of the heated nickel-containing flushing wastewater passes through the membrane and enters the steam side. On the water vapor side, a vacuum pump is used to pump the water vapor that passes through the membrane into the condenser, thereby ensuring the vapor pressure difference on both sides of the membrane. The water vapor is condensed into condensed water in the condenser, and the condensed water is returned to the production process for use. In order to ensure the quality of the produced water, two-stage series concentration is used here, and the water produced by the following stages is used as the inlet water of the first stage. The concentrated liquid after membrane concentration is circulated to the inlet of the membrane distillation component for further concentration until the nickel content in the concentrated liquid meets the requirements of the electroplating solution, and part of the concentrated liquid begins to be discharged, and the concentrated liquid enters the subsequent treatment system for further treatment.

[0049] In the pipeline mixer II, H2O2 is added to the membrane distillation concentrate, and the dosage of H2O2 is 5:1 according to H2O2:COD. The hydraulic retention time of the concentrate in the photocatalytic reactor II is 42h. The structure of the photocatalytic reactor II is the same as that of the photocatalytic reactor I. The organic matter in the concentrate is further decomposed in the photocatalytic reactor to further reduce the concentration of organic matter. After filtering through the microfiltration filter II, the COD in the produced water is reduced to 321mg / L.

[0050] The effluent from the photocatalytic reactor II enters the microfiltration filter II, where the catalyst and water are separated. The microfiltration filter II has the same structure and operating parameters as the microfiltration filter I. The main components of the water produced by the microfiltration filter II are nickel chloride, nickel sulfate and boric acid. Organic matter is removed from the water, nickel is concentrated to meet the requirements of the new plating solution, and it is recycled as the plating solution; the concentrated solution mainly contains the catalyst, which is returned to the photocatalytic reactor II for recycling.

[0051] Example 2

[0052] Water quality of nickel electroplating rinsing wastewater: Ni 2+ 320mg / L, Cl - 90mg / L, SO4 2- 295mg / L, B23mg / L, COD102mg / L.

[0053] H2O2 is mixed with nickel electroplating rinsing wastewater, H2O2:COD is 2:1, and then enters the photocatalytic reactor I. The hydraulic retention time of nickel electroplating rinsing wastewater in the photocatalytic reactor I is 1h. The spacing between the ultraviolet lamps in the photocatalytic reactor I is 15cm.

[0054] Preparation process of high-efficiency composite molecular sieve catalyst: Y-type molecular sieve particle size 200 mesh, rinse the molecular sieve with deionized water, and dry it at 105℃. Soak the dried molecular sieve in 10% nitric acid, add manganese nitrate (Mn(NO3)2) and iron nitrate (Fe(NO3)3), where the molar ratio of manganese nitrate to iron nitrate is 1:1, heat the solution to 85℃, and react at constant temperature for 3h; after the reaction, vacuum filter to dry the water, place it in a drying oven at 105℃ and dry it to constant weight. Tetrabutyl titanate (CH3CH2O )4Ti) is added to polyethylene glycol, the ratio of polyethylene glycol to tetrabutyl titanate is 6:1, and then anhydrous ethanol is added, the amount of anhydrous ethanol added is 4 times that of tetrabutyl titanate, and the tetrabutyl titanate is fully dissolved by stirring to form a colorless transparent sol. The molecular sieve loaded with manganese nitrate and ferric nitrate is mixed evenly with the transparent sol, placed in a hydrothermal reactor, and the hydrothermal reactor is placed in an oven. The temperature of the oven is maintained at 140°C for 8 hours, and then cooled to room temperature. Wash with distilled water and anhydrous ethanol respectively until neutral, and dry at 85°C to constant weight. A molecular sieve loaded with manganese nitrate, ferric nitrate and titanium dioxide composite catalyst is obtained.

[0055] The effluent from the photocatalytic reactor I enters the microfiltration filter I, where the catalyst and water are separated. The microfiltration membrane uses a tubular microfiltration membrane. In order to reduce membrane fouling, cross-flow filtration is used. The circulation volume of the microfiltration system is 5 times the water production volume. The microfiltration membrane has a filtration accuracy of 10μm and a flux of 550L / m 2 ·h, operating pressure 1.0MPa. COD in microfiltration water is 26mg / L. The water produced after microfiltration enters the membrane distillation reactor for concentration. The concentrate mainly contains catalyst, which returns to the photocatalytic reactor I for recycling.

[0056] The two-stage membrane distillation concentration process was used to heat the effluent from the microfiltration wastewater filter I to 50°C. The conductivity of the water produced by the first-stage membrane distillation process was 3.6μs / cm. 2+ 0.01mg / L, Ni in concentrate 2+ 10.5g / L, COD635mg / L; conductivity of water produced by two-stage membrane distillation process is 62.3μs / cm, Ni 2+ 2.2mg / L, Ni in concentrate 2+ 135g / L, COD5320mg / L. The membrane of the membrane distillation system is a hydrophobic membrane that only allows water vapor to pass through. The water vapor on the side of the heated nickel-containing flushing wastewater passes through the membrane and enters the steam side. On the water vapor side, a vacuum pump is used to pump the water vapor that passes through the membrane into the condenser, thereby ensuring the vapor pressure difference on both sides of the membrane. The water vapor is condensed into condensed water in the condenser, and the condensed water is returned to the production process for use. In order to ensure the quality of the produced water, two-stage series concentration is used here, and the water produced by the following stages is used as the inlet water of the first stage. The concentrated liquid after membrane concentration is circulated to the inlet of the membrane distillation component for further concentration until the nickel content in the concentrated liquid reaches the requirements of the electroplating solution, and part of the concentrated liquid begins to be discharged, and the concentrated liquid enters the subsequent treatment system for further treatment.

[0057] In the pipeline mixer II, H2O2 is added to the membrane distillation concentrate, and the dosage of H2O2 is 4:1 according to H2O2:COD. The hydraulic retention time of the concentrate in the photocatalytic reactor II is 36h. The structure of the photocatalytic reactor II is the same as that of the photocatalytic reactor I. The organic matter in the concentrate is further decomposed in the photocatalytic reactor to further reduce the concentration of organic matter. After filtering through the microfiltration filter II, the COD in the produced water is reduced to 356mg / L.

[0058] The effluent from the photocatalytic reactor II enters the microfiltration filter II, where the catalyst and water are separated. The microfiltration filter II has the same structure and operating parameters as the microfiltration filter I. The main components of the water produced by the microfiltration filter II are nickel chloride, nickel sulfate and boric acid. Organic matter is removed from the water, nickel is concentrated to meet the requirements of the new plating solution, and it is recycled as the plating solution; the concentrated solution mainly contains the catalyst, which is returned to the photocatalytic reactor II for recycling.

[0059] Example 3

[0060] Water quality of nickel electroplating rinsing wastewater: Ni 2+ 930mg / L, Cl - 290mg / L, SO4 2- 740mg / L, B63mg / L, COD352mg / L.

[0061] H2O2 is mixed with nickel electroplating rinsing wastewater, H2O2:COD is 3:1, and then enters the photocatalytic reactor I. The hydraulic retention time of nickel electroplating rinsing wastewater in the photocatalytic reactor I is 3h. The spacing between the ultraviolet lamps in the photocatalytic reactor I is 5cm.

[0062] Preparation process of high-efficiency composite molecular sieve catalyst: Y-type molecular sieve particle size 50 mesh, rinse the molecular sieve with deionized water, and dry it at 105℃. Soak the dried molecular sieve in 30% nitric acid, add manganese nitrate (Mn(NO3)2) and iron nitrate (Fe(NO3)3), where the molar ratio of manganese nitrate to iron nitrate is 3:1, heat the solution to 80℃, and react at constant temperature for 5h; after the reaction, vacuum filter to dry the water, place it in a drying oven at 105℃ and dry it to constant weight. Tetrabutyl titanate (CH3CH2O )4Ti) is added to polyethylene glycol in a ratio of 4:1, and then anhydrous ethanol is added. The amount of anhydrous ethanol added is 6 times that of tetrabutyl titanate. Stir thoroughly to dissolve tetrabutyl titanate and form a colorless transparent sol. The molecular sieve loaded with manganese nitrate and ferric nitrate is mixed evenly with the transparent sol and placed in a hydrothermal reactor. The hydrothermal reactor is placed in an oven. The temperature of the oven is maintained at 160°C for 6 hours and then cooled to room temperature. Wash with distilled water and anhydrous ethanol respectively until neutral, and dry at 85°C to constant weight. A molecular sieve loaded with manganese nitrate, ferric nitrate and titanium dioxide composite catalyst is obtained.

[0063] The effluent from the photocatalytic reactor I enters the microfiltration filter I, where the catalyst and water are separated. The microfiltration membrane uses a tubular microfiltration membrane. In order to reduce membrane fouling, cross-flow filtration is used. The circulation volume of the microfiltration system is 20 times the water production volume. The microfiltration membrane has a filtration accuracy of 1μm and a flux of 220L / m 2 h, operating pressure 0.4MPa. COD in microfiltration water is 43mg / L. The water produced after microfiltration enters the membrane distillation reactor for concentration. The concentrate mainly contains catalyst, which returns to the photocatalytic reactor I for recycling.

[0064] The two-stage membrane distillation concentration process was used to heat the effluent from the microfiltration wastewater filter I to 80°C. The conductivity of the water produced by the first-stage membrane distillation process was 6.5μs / cm. 2+ 0.02mg / L, Ni in concentrate 2+ 13.1g / L, COD725mg / L; conductivity of water produced by two-stage membrane distillation process is 93.7μs / cm, Ni 2+ 4.31mg / L, Ni in concentrate 2+ 186g / L, COD8620mg / L. The membrane of the membrane distillation system is a hydrophobic membrane that only allows water vapor to pass through. The water vapor on the side of the heated nickel-containing flushing wastewater passes through the membrane and enters the steam side. On the water vapor side, a vacuum pump is used to pump the water vapor that passes through the membrane into the condenser, thereby ensuring the vapor pressure difference on both sides of the membrane. The water vapor is condensed into condensed water in the condenser, and the condensed water is returned to the production process for use. In order to ensure the quality of the produced water, two-stage series concentration is used here, and the water produced by the following stages is used as the inlet water of the first stage. The concentrated liquid after membrane concentration is circulated to the inlet of the membrane distillation component for further concentration until the nickel content in the concentrated liquid reaches the requirements of the electroplating solution, and part of the concentrated liquid begins to be discharged, and the concentrated liquid enters the subsequent treatment system for further treatment.

[0065] In the pipeline mixer II, H2O2 is added to the membrane distillation concentrate, and the dosage of H2O2 is 6:1 according to H2O2:COD. The hydraulic retention time of the concentrate in the photocatalytic reactor II is 48h. The structure of the photocatalytic reactor II is the same as that of the photocatalytic reactor I. The organic matter in the concentrate is further decomposed in the photocatalytic reactor to further reduce the concentration of organic matter. After filtering through the microfiltration filter II, the COD in the produced water is reduced to 352mg / L.

[0066] The effluent from the photocatalytic reactor II enters the microfiltration filter II, where the catalyst and water are separated. The microfiltration filter II has the same structure and operating parameters as the microfiltration filter I. The main components of the water produced by the microfiltration filter II are nickel chloride, nickel sulfate and boric acid. Organic matter is removed from the water, nickel is concentrated to meet the requirements of the new plating solution, and it is recycled as the plating solution; the concentrated solution mainly contains the catalyst, which is returned to the photocatalytic reactor II for recycling.

Claims

1. A method for photocatalytic oxidation and zero emission of nickel electroplating flushing wastewater, characterized in that: The steps include: (1) The nickel electroplating washing wastewater to be treated is mixed with H2O2 in a pipeline mixer I, and the amount of H2O2 added is 2:1 to 3:1 according to H2O2:COD; after mixing, it enters a photocatalytic reactor I, and the hydraulic retention time of the nickel electroplating washing wastewater in the photocatalytic reactor I is 1 to 3 hours; the photocatalytic reactor I is filled with a high-efficiency composite molecular sieve catalyst, and a plurality of ultraviolet lamps are set; the high-efficiency composite molecular sieve catalyst is a molecular sieve loaded with a composite catalyst of manganese nitrate, iron nitrate and titanium dioxide; (2) The effluent from the photocatalytic reactor I enters the microfiltration filter I, where the catalyst and water are separated; the microfiltration membrane uses a tubular microfiltration membrane, and the produced water after microfiltration enters the membrane distillation reactor for concentration. The concentrated liquid mainly contains the catalyst, which is returned to the photocatalytic reactor I for recycling; (3) A two-stage membrane distillation concentration process is used to heat the effluent from the microfiltration flushing wastewater filter I to 50-80° C. The water vapor from the heated nickel-containing flushing wastewater side passes through the membrane of the membrane distillation system and enters the steam side. On the steam side, the water vapor that passes through the membrane is pumped into a condenser using a vacuum pump. The concentrated liquid after membrane concentration is circulated to the inlet of the membrane distillation component for further concentration until the nickel content in the concentrated liquid reaches the requirement of the electroplating solution, and part of the concentrated liquid is discharged, and the concentrated liquid enters the subsequent treatment system for further treatment; (4) After concentration by membrane distillation, the concentrate is mixed with H2O2 in a pipeline mixer II, the dosage of H2O2 is 4.:1 to 6:1 according to H2O2:COD, and after mixing, it enters the photocatalytic reactor II, and the hydraulic retention time of the concentrate in the photocatalytic reactor II is 36 to 48 hours; the photocatalytic reactor II is filled with a high-efficiency composite molecular sieve catalyst and is also provided with a number of ultraviolet lamps; the organic matter in the concentrate is continuously decomposed in the photocatalytic reactor to further reduce the concentration of the organic matter; (5) The effluent from the photocatalytic reactor II enters the microfiltration filter II, where the catalyst and water are separated. The organic matter is removed from the water produced by the microfiltration filter II, and the concentrated nickel is recycled as a plating solution. The concentrated solution mainly contains the catalyst, which is returned to the photocatalytic reactor II for recycling.

2. The method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater according to claim 1, characterized in that: The spacing between the ultraviolet lamp tubes described in step (1) is 5 to 15 cm.

3. The method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater according to claim 1, characterized in that: The preparation process of the high-efficiency composite molecular sieve catalyst described in step (1) comprises: a. Select Y-type molecular sieve with a particle size of 50-200 mesh, rinse the molecular sieve with deionized water, and dry it; b. The dried molecular sieve is immersed in a nitric acid solution, and manganese nitrate (Mn(NO3)2) and iron nitrate (Fe(NO3)3) are added, wherein the molar ratio of manganese nitrate to iron nitrate is 1:1 to 3:1; the solution is heated to 80 to 85°C and reacted at a constant temperature for 3 to 5 hours; c. After the reaction is completed, the water is filtered out by vacuum filtration, and the mixture is placed in a drying oven at 100-110°C and dried to constant weight, and manganese nitrate and iron nitrate are loaded on the surface of the molecular sieve; d. Tetrabutyl titanate (CH3CH2O)4Ti) is added to polyethylene glycol, the ratio of polyethylene glycol to tetrabutyl titanate is 4:1 to 6:1, and then anhydrous ethanol is added, the amount of anhydrous ethanol added is 4 to 6 times that of tetrabutyl titanate, and the tetrabutyl titanate is fully dissolved by stirring to form a colorless transparent sol; the molecular sieve loaded with manganese nitrate and iron nitrate is mixed evenly with the transparent sol, and placed in a hydrothermal reactor, and the hydrothermal reactor is placed in a heating device at a temperature of 140 to 160°C, maintained for 6 to 8 hours, and then cooled to room temperature; e. Wash with distilled water and anhydrous ethanol respectively until neutral, and dry at 70-95°C to constant weight; obtain a molecular sieve loaded with a composite catalyst of manganese nitrate, iron nitrate and titanium dioxide.

4. The method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater according to claim 3, characterized in that: The Y-type molecular sieve described in step a is a Y-type molecular sieve with relatively large pore diameter; the drying temperature in step a is 100-110°C.

5. The method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater according to claim 3, characterized in that: The mass concentration of the nitric acid solution in step b is 10-30%.

6. The method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater according to claim 3, characterized in that: The drying temperature in step e is 75-90°C.

7. The method for photocatalytic oxidation and zero emission of nickel electroplating rinsing wastewater according to claim 1, characterized in that: The filtration in step (2) is cross-flow filtration; the circulation volume of the microfiltration system is 5 to 20 times the water production volume, the microfiltration membrane filtration accuracy is 1 μm to 10 μm, and the flux is 200 to 600 L / m 2 ·h, operating pressure 0.3~1.0MPa.

8. The method for photocatalytic oxidation and zero discharge of nickel electroplating rinsing wastewater according to claim 1, characterized in that: The heating in step (3) can be performed by steam heating, electric heating or waste flue gas heating.

9. The method for photocatalytic oxidation and zero discharge of nickel electroplating rinsing wastewater according to claim 1, characterized in that: In step (4), the structure of the photocatalytic reactor II is the same as that of the photocatalytic reactor I; in step (5), the structure of the microfiltration filter II is the same as that of the microfiltration filter I, and the operating parameters are the same.

10. The method for photocatalytic oxidation and zero discharge of nickel electroplating rinsing wastewater according to claim 1, characterized in that: The water quality of the nickel electroplating rinsing wastewater before treatment in step (1) is as follows: Ni 2+ 300~1000mg / L, Cl - 80~300mg / L, SO4 2- 250~800mg / L, B 20~70mg / L, COD 80~400mg / L.

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