Treatment method of hot galvanizing wastewater

Abstract

The invention discloses a hot galvanizing wastewater treatment method, which comprises: S1, mixing hot galvanizing pickling wastewater with alkali washing wastewater, adjusting the pH value, and introducing air to obtain a mixed wastewater liquid; s2, adding a composite additive A into the mixed wastewater liquid in the step S1, stirring to react, introducing CO2 gas after the reaction is completed, controlling the pH value of the wastewater to be 6-7, and then standing, settling and filtering to obtain supernate; and S3, adding a composite additive B into the supernatant in the step S2, carrying out a constant-temperature reaction, controlling the pH value to 8-9, and after the reaction is completed, carrying out microfiltration membrane treatment. According to the treatment method, all the steps are mutually linked in function positioning, multi-stage synergistic removal of heavy metal and ammonia nitrogen in the hot galvanizing wastewater is jointly achieved, and the effluent quality meets the corresponding emission standard requirement.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for treating hot-dip galvanizing wastewater. Background Technology

[0002] Hot-dip galvanizing is one of the most widely used steel corrosion protection methods in industrial production. Its production process involves multiple steps, including pickling and rust removal, flux treatment, and hot-dip galvanizing, each of which generates a certain amount of wastewater. The wastewater from hot-dip galvanizing exhibits significant complexity: the wastewater from the pickling process has a pH as low as 1-3 and contains a large amount of Fe. 2+ Fe 3+ and Cl - The fluxes used in the plating process typically consist mainly of zinc chloride and ammonium chloride, and their residual solutions and rinsing water contain high concentrations of Zn. 2+ and NH4 + Alkaline washing wastewater has a high pH and contains suspended solids and a certain amount of organic matter. If the above wastewater is discharged directly without effective treatment, it will cause serious pollution to the receiving water body.

[0003] Zn in hot-dip galvanizing wastewater 2+ The form in which Zn exists is the core issue limiting its treatment effectiveness. In actual industrial wastewater, Zn... 2+ Not all Zn exists in a free state; a considerable proportion of it is ionized. 2+ It exists in wastewater in a complexed form. On the one hand, NH4 in the flux... + Under weakly alkaline conditions, it can be partially converted into free NH3, which then reacts with Zn. 2+ On the one hand, stable zinc-ammonia complexes are formed; on the other hand, residues of organic corrosion inhibitors, surfactants, and other additives used in the production process contain various coordinating groups such as hydroxyl, carboxyl, and amino groups, which can react with Zn. 2+ Formation of stable organic complexes. Complexed Zn 2+ Thermodynamically, compared to free Zn 2+ More stable, its conditional stability constant is significantly higher than the reciprocal of the solubility product of precipitates such as Zn(OH)2 and ZnCO3, resulting in more complexed Zn within the pH range of conventional alkaline precipitation treatment (pH 8-10). 2+ It cannot be effectively converted into precipitate and removed, making it difficult to consistently meet the standard for total zinc concentration in the effluent.

[0004] Currently, industrial treatment of Zn in hot-dip galvanizing wastewater... 2+ The mainstream method is chemical precipitation, which involves adding alkaline reagents such as lime, NaOH, or Na₂CO₃ to precipitate Zn. 2+ After conversion to Zn(OH)₂ or ZnCO₃ precipitate, solid-liquid separation is performed. This method is effective for free Zn. 2+It exhibits good removal efficiency, with mature technology, simple operation, and low treatment cost, and is widely used in practical engineering. However, for complexed Zn in wastewater... 2+ The removal effect of direct alkaline precipitation is very limited. Studies have shown that when complexed Zn in wastewater... 2+ When the zinc content exceeds 20% of the total zinc, the total zinc concentration in the effluent from the alkaline precipitation method often exceeds the discharge standards, requiring enhanced treatment using other methods. Furthermore, Zn(OH)₂ is an amphoteric hydroxide; when the wastewater pH exceeds 9, Zn(OH)₂ will revert to [Zn(OH)₄] due to amphoteric dissolution. 2- The back dissolution causes the zinc concentration in the effluent to rise, which places stricter requirements on the dosage of alkaline reagents and pH control.

[0005] To address the treatment of complexed heavy metals, researchers have proposed several enhanced methods for breaking down these complexes. The stripping-oxidation method uses aeration or heating to release free NH3 from wastewater, thereby disrupting the equilibrium of zinc-ammonia complexes. However, this method is only effective for ammonia-complexed wastewater, and not for organically ligand-complexed Zn. 2+ This method is ineffective, and the ammonia-containing exhaust gas generated by stripping requires secondary treatment, increasing processing costs. Chemical oxidation methods (such as Fenton oxidation and ozone oxidation) can oxidize and degrade organic complexed ligands, thereby releasing complexed Zn. 2+ However, these methods consume large amounts of reagents, have limited applicability to different wastewater qualities, and high operating costs, making them uneconomical for treating large volumes of industrial wastewater. Ion exchange and membrane separation methods are effective for treating Zn... 2+ While both methods have good deep removal capabilities, the former suffers from frequent resin regeneration and insufficient selectivity, while the latter is prone to membrane fouling in hot-dip galvanizing wastewater containing high concentrations of suspended solids and organic matter, and its operational stability needs to be improved.

[0006] In summary, hot-dip galvanizing wastewater is characterized by complex water quality and high Zn content. 2+ NH4 exists in various forms + With Zn 2+ There is mutual interference between them, resulting in significant shortcomings in existing treatment processes in terms of stable effluent compliance, cost control, and ease of operation. Therefore, it is necessary to develop a method that can effectively address the interference between complexed Zn and other pollutants. 2+ The comprehensive treatment method meets the needs of practical engineering. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for treating hot-dip galvanizing wastewater.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH, and then introduce air to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1, stir and react. After the reaction is complete, introduce CO2 gas to control the pH of the wastewater at 6-7. Then allow it to settle and filter to obtain the supernatant. S3. Add composite additive B to the supernatant from step S2, carry out a constant temperature reaction, control the pH to 8-9, and after the reaction is complete, perform microfiltration membrane treatment.

[0009] Preferably, in step S1, the pH is 4-6, the aeration rate of the air is 1-1.5 L / (L·min), and the aeration time is 20-40 min.

[0010] Preferably, the composite additive A is prepared by the following method: (1) Add mesoporous silica to an aqueous ethanol solution, then add γ-glycidyl etheroxypropyltrimethoxysilane, and carry out a constant temperature reaction. After the reaction is completed, filter, wash and dry to obtain pretreated mesoporous silica. Add the pretreated mesoporous silica to DMF, then add tris(2-aminoethyl)amine, and carry out a heating reaction. After the reaction is completed, filter, wash and dry to obtain organosilica. (2) Add 4-carboxyphenylboronic acid to MES buffer, then add EDC and NHS, stir to activate, then add organo-modified silica, stir to react, filter, wash and dry after the reaction is complete to obtain solid product; add deionized water to solid product, adjust pH to 11-12, then add sodium chloroacetate, heat to react, adjust pH to 7 after the reaction is complete, filter, wash and dry to obtain modified silica; (3) Mix the modified silica, polyaluminum chloride and polyethylene glycol evenly to obtain the final product.

[0011] Preferably, in step (1), the mass ratio of mesoporous silica to γ-glycidoxypropyltrimethoxysilane is 100:8-12, the temperature of the isothermal reaction is 60-70℃, and the time is 3-4h; the mass ratio of pretreated mesoporous silica to tris(2-aminoethyl)amine is 100:15-25, the temperature of the heating reaction is 75-85℃, and the time is 4-5h.

[0012] Preferably, in step (2), the mass ratio of 4-carboxyphenylboronic acid, EDC, NHS, and organosilica is 8-12:20-30:15-20:100, the stirring reaction temperature is 20-25℃, and the time is 2-4h; the mass ratio of the solid product and sodium chloroacetate is 100:20-30, and the heating reaction temperature is 60-70℃, and the time is 8-10h.

[0013] In this invention, Zn in hot-dip galvanizing wastewater 2+ Typically, silica exists as a stable complex with organic complexing agents such as EDTA and citric acid, making it difficult to effectively remove by direct addition of precipitants. This invention prepares modified silica with solid-phase complex-breaking and adsorption functions using a specific method: First, mesoporous silica is used as a carrier, and its surface is silanized with γ-glycidyl etheroxypropyltrimethoxysilane to introduce epoxy groups. Then, a ring-opening addition reaction is performed with tris(2-aminoethyl)amine to covalently graft the polyamine structure onto the carrier surface. Subsequently, 4-carboxyphenylboronic acid is linked to a primary amine site of tris(2-aminoethyl)amine via EDC / NHS coupling, introducing phenylboronic acid functional groups. Finally, the remaining primary amine is N-alkylated with sodium chloroacetate to introduce carboxymethyl coordinating groups, resulting in modified silica with both phenylboronic acid groups and carboxymethyl polyamine chelating groups on its surface. The mesoporous silica carrier has a high specific surface area and regular pore structure, which helps to fully expose the functional groups and improve the complexation with Zn in wastewater. 2+ The contact efficiency is high; coupled with the synergistic effect of polyaluminum chloride flocculation, it can adsorb Zn 2+ The modified silica particles are efficiently sedimented and separated, thereby significantly improving the removal rate of total zinc in wastewater.

[0014] Preferably, the mass ratio of modified silica, polyaluminum chloride and polyethylene glycol in step (3) is 15-25:30-50:5-10.

[0015] Preferably, in step S2, the amount of the composite additive A added is 0.1-0.3% of the mass of the mixed wastewater, the temperature of the stirring reaction is 40-50℃, and the time is 30-60 min; the gas flow rate of CO2 is 0.3-0.5 L / (L·min), and the settling time is 1-2 h.

[0016] Preferably, the preparation method of the composite additive B in step S3 is as follows: By weight, mix 35-50 parts sodium bicarbonate, 15-25 parts modified molecular sieve, 3-8 parts cationic polyacrylamide, 8-15 parts sodium carbonate, and 20-30 parts diatomaceous earth evenly to obtain the final product.

[0017] Preferably, the modified molecular sieve is prepared as follows: 4A type molecular sieve is added to an NH4Cl solution with a concentration of 1-2 mol / L, stirred at 80-90℃ for 4-5 h, and then calcined at 350-450℃ for 2-3 h to obtain the product.

[0018] The H-type 4A molecular sieve prepared by ion exchange with NH4Cl solution followed by calcination in this invention has a framework acidic site (H). + ) for NH4 + It has ion exchange adsorption capacity and can be used in wastewater systems through NH4+. + Replacement skeleton H + Selective adsorption is achieved; simultaneously, in step S3, under isothermal reaction conditions of 55-65℃, the pH of the wastewater rises to 8.0-9.0, and NH4+... + The NH3 equilibrium shifts towards NH3, and the solubility of NH3 decreases with increasing temperature, prompting NH3 to transfer from the liquid phase to the gas phase, thus reducing the NH3-N concentration in the effluent.

[0019] Preferably, in step S3, the amount of the composite additive B added is 0.4-0.6% of the mass of the supernatant, the temperature of the isothermal reaction is 55-65℃, the time is 1.5-2.5h, the pore size of the microfiltration membrane is 0.1-0.45μm, the operating pressure is 0.05-0.15MPa, and the operating temperature is 50-60℃.

[0020] In this invention, cationic polyacrylamide is introduced into composite additive B. ZnCO3 particles have a negative charge on their surface when the pH of the reaction system is 8-9. The cationic polyacrylamide aggregates the nano-ZnCO3 particles into flocs through a dual mechanism of charge neutralization and polymer bridging, and the flocs are effectively retained by the microfiltration membrane. Diatomaceous earth is used as a filter aid to form a pre-coating on the membrane surface, which reduces the direct clogging of the membrane pores by ZnCO3 nanoparticles, extends the effective operating cycle of the microfiltration membrane, and ensures stable membrane flux.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The hot-dip galvanizing wastewater treatment method provided by the present invention addresses the challenges of significant differences in composition between pickling wastewater and alkaline pickling wastewater during hot-dip galvanizing production, complex heavy metal complexation morphology, and interference of treatment efficiency by the coexistence of ammonia nitrogen. A specific series treatment process is designed; in step S1, the two wastewater streams are combined and neutralized, and the natural pH complementarity of the acid and alkaline wastewater is used to achieve cost-controllable preliminary neutralization. At the same time, Fe is removed through aeration oxidation. 2+ Converted to Fe 3+ This creates conditions for subsequent flocculation and sedimentation; in step S2, the modified mesoporous silica in composite additive A, with its surface-loaded phenylboronic acid groups and multiple amino / carboxyl coordination groups working synergistically, directly competes with organic complexes to chelate Zn.2+ Complexed Zn is adsorbed by solid phase adsorption. 2+ The Zn is removed along with the solids, and combined with polyaluminum chloride flocculation and precise pH control using CO2, most of the Zn is removed. 2+ And efficient sedimentation removal of suspended solids; step S3 uses a sodium bicarbonate / sodium carbonate composite carbon source system at 55-65℃ to remove residual free Zn in the supernatant. 2+ The solution is deeply precipitated as ZnCO3, while NH4 is adsorbed by ion exchange using H-type modified molecular sieves. + After being enlarged by cationic polyacrylamide flocculation, the ZnCO3 particles are then retained by a microfiltration membrane, achieving the desired Zn concentration in the effluent. 2+ The process involves the deep removal of suspended solids; each step is functionally interconnected to achieve multi-stage synergistic removal of heavy metals and ammonia nitrogen from hot-dip galvanizing wastewater, ensuring that the effluent quality meets the corresponding discharge standards.

[0022] (2) The hot-dip galvanizing wastewater treatment method provided by the present invention uses composite additive A as a carrier. Epoxy groups are introduced onto the surface of the silica via γ-glycidyl etheroxypropyltrimethoxysilane silanization, followed by ring-opening grafting with tris(2-aminoethyl)amine to construct a multi-arm amino skeleton. Subsequently, 4-carboxyphenylboronic acid is coupled and immobilized at some amino sites via EDC / NHS to introduce phenylboronic acid coordinating groups. The remaining amino groups are alkylated with sodium chloroacetate to introduce carboxymethyl groups. Finally, a highly efficient chelating system containing phenylboronic acid groups and multiple carboxyl coordinating groups is introduced onto the surface of the mesoporous silica. This modified mesoporous silica is effective for complexing Zn. 2+ It has strong competitive coordination ability and can complex Zn 2+ By fixing it in solid form, the problem of complexed Zn is fundamentally solved. 2+ The technical challenge of removing Zn from wastewater using traditional precipitation methods is overcome; simultaneously, the mesoporous structure provides the material with a large specific surface area, which is beneficial for removing Zn from wastewater. 2+ Mass transfer and diffusion to adsorption sites enhance adsorption kinetics efficiency. The composite additive A simultaneously introduces polyaluminum chloride and polyethylene glycol. The former exerts flocculation and sedimentation efficiency within the optimal pH window of 6-7 regulated by CO2, while the latter acts as a dispersant to prevent the agglomeration of modified silica particles and ensure their effective contact area. The synergistic effect of these three additives significantly improves the adsorption efficiency of Zn in step S2. 2+ The combined removal efficiency with suspended solids.

[0023] (3) The hot-dip galvanizing wastewater treatment method provided by the present invention uses composite additive B, with sodium bicarbonate as the main carbon source and sodium carbonate as the auxiliary alkali source, to automatically stabilize the reaction pH in the range of 8.0-9.0: a small amount of sodium carbonate provides the initial OH- - Raising the pH to above 8.5 triggers the nucleation of ZnCO3 precipitation; a large amount of sodium bicarbonate continuously replenishes HCO3. + HCO3- / CO3 2- The buffer suppresses pH overshoot, ensuring the entire precipitation process occurs within the Zn group. 2+ The process was continued within the pH range where Zn(OH)2 had the lowest solubility, effectively preventing the amphoteric dissolution and re-dissolution of Zn(OH)2 and improving Zn's solubility. 2+ The removal rate of NH4 in wastewater was improved; meanwhile, H-type modified molecular sieve was prepared by NH4Cl ion exchange and high-temperature calcination of type 4A molecular sieve, which improved the removal rate of NH4 in wastewater in a weakly alkaline system with pH 8-9. + It has a high efficiency of ion exchange adsorption capacity to achieve deep removal of ammonia nitrogen; diatomaceous earth also serves as a filter aid and adsorption carrier, and works in synergy with cationic polyacrylamide to flocculate fine precipitates such as ZnCO3 into larger particles, which are then efficiently intercepted by the microfiltration membrane to ensure that the concentration of suspended solids and heavy metals in the effluent meets the discharge standards. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0026] The mesoporous silica has a particle size of 20-50 μm and a pore size of 4-15 nm; the 4A type molecular sieve has a particle size of 5-15 μm, and the diatomaceous earth has a particle size of 5-20 μm. Example 1

[0027] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 5, and then introduce air at an aeration rate of 1.3 L / (L·min) for 30 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.2% of the mass of the mixed wastewater. Stir and react at 45°C for 50 min. After the reaction is completed, CO2 gas is introduced at a rate of 0.4 L / (L·min). The pH of the wastewater is controlled at 6.5. Then, the mixture is allowed to stand and settle for 1.5 h. After filtration, the supernatant is obtained. S3. Add composite additive B to the supernatant from step S2. The amount of composite additive B added is 0.5% of the mass of the supernatant. React at a constant temperature of 60°C for 2 hours, and control the pH to 8.5. After the reaction is completed, perform microfiltration membrane treatment. The pore size of the microfiltration membrane is 0.45 μm, the operating pressure is 0.1 MPa, and the operating temperature is 55°C.

[0028] In step S2, the preparation method of the composite additive A is as follows: (1) 100g of mesoporous silica was added to 1L of ethanol aqueous solution (the volume ratio of ethanol to water was 9:1), followed by the addition of 10g of γ-glycidoxypropyltrimethoxysilane. The reaction was carried out at 65℃ for 3.5h. After the reaction was completed, the silica was filtered, washed, and dried to obtain pretreated mesoporous silica. 100g of pretreated mesoporous silica was added to 1L of DMF, followed by the addition of 20g of tris(2-aminoethyl)amine. The reaction was carried out at 80℃ under a nitrogen atmosphere for 4.5h. After the reaction was completed, the silica was filtered, washed, and dried to obtain organo-silica. (2) 10g of 4-carboxyphenylboronic acid was added to 1L of MES buffer, followed by 25g of EDC and 18g of NHS. The mixture was stirred and activated at 25°C for 20min. Then, 100g of organosilica was added and stirred at 25°C for 3h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. 100g of the solid product was added to 1L of deionized water and the pH was adjusted to 11. Then, 25g of sodium chloroacetate was added and the mixture was reacted at 65°C for 9h. After the reaction was completed, the pH was adjusted to 7. The mixture was then filtered, washed, and dried to obtain modified silica. (3) Mix 20g of modified silica, 40g of polyaluminum chloride and 8g of polyethylene glycol evenly to obtain the final product.

[0029] The preparation method of the composite additive B in step S3 is as follows: By weight, 45 parts sodium bicarbonate, 20 parts modified molecular sieve, 5 parts cationic polyacrylamide, 11 parts sodium carbonate, and 25 parts diatomaceous earth are mixed evenly to obtain the modified molecular sieve. The modified molecular sieve is prepared as follows: 4A type molecular sieve is added to a 1.5 mol / L NH4Cl solution, stirred at 85℃ for 4.5 h, and then calcined at 400℃ for 2.5 h to obtain the modified molecular sieve. Example 2

[0030] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 6, and then introduce air at an aeration rate of 1 L / (L·min) for 40 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.3% of the mass of the mixed wastewater. Stir and react at 40°C for 60 min. After the reaction is completed, CO2 gas is introduced at a rate of 0.3 L / (L·min). The pH of the wastewater is controlled at 6. Then, the mixture is allowed to stand and settle for 1 h. After filtration, the supernatant is obtained. S3. Add composite additive B to the supernatant from step S2. The amount of composite additive B added is 0.4% of the mass of the supernatant. React at a constant temperature of 55°C for 2.5 hours, and control the pH to 8. After the reaction is completed, perform microfiltration membrane treatment. The pore size of the microfiltration membrane is 0.45 μm, the operating pressure is 0.05 MPa, and the operating temperature is 50°C.

[0031] In step S2, the preparation method of the composite additive A is as follows: (1) 100g of mesoporous silica was added to 1L of ethanol aqueous solution (ethanol to water volume ratio of 9:1), followed by 8g of γ-glycidoxypropyltrimethoxysilane. The mixture was reacted at 60℃ for 4h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated mesoporous silica. 100g of pretreated mesoporous silica was added to 1L of DMF, followed by 15g of tris(2-aminoethyl)amine. The mixture was reacted at 75℃ under a nitrogen atmosphere for 5h. After the reaction was completed, the mixture was filtered, washed and dried to obtain organo-silica. (2) Add 8g of 4-carboxyphenylboronic acid to 1L of MES buffer, then add 20g of EDC and 15g of NHS, stir and activate at 25℃ for 20min, then add 100g of organosilica, stir and react at 20℃ for 4h, after the reaction is completed, filter, wash and dry to obtain solid product; add 100g of solid product to 1L of deionized water, adjust pH to 11, then add 20g of sodium chloroacetate, react at 60℃ for 10h, after the reaction is completed, adjust pH to 7, filter, wash and dry to obtain modified silica; (3) Mix 15g of modified silica, 30g of polyaluminum chloride and 5g of polyethylene glycol evenly to obtain the final product.

[0032] The preparation method of the composite additive B in step S3 is as follows: By weight, 35 parts sodium bicarbonate, 15 parts modified molecular sieve, 3 parts cationic polyacrylamide, 8 parts sodium carbonate, and 20 parts diatomaceous earth are mixed evenly to obtain the modified molecular sieve. The modified molecular sieve is prepared as follows: 4A type molecular sieve is added to a 1 mol / L NH4Cl solution, stirred at 80℃ for 5 hours, and then calcined at 350℃ for 3 hours to obtain the modified molecular sieve. Example 3

[0033] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 4, and then introduce air at an aeration rate of 1.5 L / (L·min) for 20 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.3% of the mass of the mixed wastewater. Stir and react at 50°C for 30 min. After the reaction is completed, CO2 gas is introduced at a rate of 0.5 L / (L·min). The pH of the wastewater is controlled at 7. Then, the mixture is allowed to stand and settle for 2 h. After filtration, the supernatant is obtained. S3. Add composite additive B to the supernatant from step S2. The amount of composite additive B added is 0.6% of the mass of the supernatant. React at a constant temperature of 65°C for 1.5 hours, and control the pH to 9. After the reaction is completed, perform microfiltration membrane treatment. The pore size of the microfiltration membrane is 0.45 μm, the operating pressure is 0.15 MPa, and the operating temperature is 60°C.

[0034] In step S2, the preparation method of the composite additive A is as follows: (1) 100g of mesoporous silica was added to 1L of ethanol aqueous solution (the volume ratio of ethanol to water was 9:1), followed by the addition of 12g of γ-glycidoxypropyltrimethoxysilane. The reaction was carried out at 70℃ for 3h. After the reaction was completed, the silica was filtered, washed, and dried to obtain pretreated mesoporous silica. 100g of pretreated mesoporous silica was added to 1L of DMF, followed by the addition of 25g of tris(2-aminoethyl)amine. The reaction was carried out at 85℃ under a nitrogen atmosphere for 4h. After the reaction was completed, the silica was filtered, washed, and dried to obtain organo-silica. (2) 12g of 4-carboxyphenylboronic acid was added to 1L of MES buffer, followed by 30g of EDC and 20g of NHS. The mixture was stirred and activated at 25°C for 20min. Then 100g of organosilica was added and stirred at 25°C for 2h. After the reaction was completed, the mixture was filtered, washed and dried to obtain a solid product. 100g of the solid product was added to 1L of deionized water and the pH was adjusted to 12. Then 0g of sodium chloroacetate was added and the mixture was reacted at 70°C for 8h. After the reaction was completed, the pH was adjusted to 7. The mixture was then filtered, washed and dried to obtain modified silica. (3) Mix 25g of modified silica, 50g of polyaluminum chloride and 10g of polyethylene glycol evenly to obtain the final product.

[0035] The preparation method of the composite additive B in step S3 is as follows: By weight, 50 parts sodium bicarbonate, 25 parts modified molecular sieve, 8 parts cationic polyacrylamide, 15 parts sodium carbonate, and 30 parts diatomaceous earth are mixed evenly to obtain the modified molecular sieve. The modified molecular sieve is prepared as follows: 4A type molecular sieve is added to a 2 mol / L NH4Cl solution, stirred at 90℃ for 4 hours, and then calcined at 450℃ for 2 hours to obtain the modified molecular sieve. Comparative Example 1

[0036] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 5, and then introduce air at an aeration rate of 1.3 L / (L·min) for 30 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.2% of the mass of the mixed wastewater. Stir and react at 45°C for 50 min. After the reaction is completed, CO2 gas is introduced at a rate of 0.4 L / (L·min). The pH of the wastewater is controlled at 6.5. Then, the mixture is allowed to stand and settle for 1.5 h. After filtration, the supernatant is obtained. S3. Add composite additive B to the supernatant from step S2. The amount of composite additive B added is 0.5% of the mass of the supernatant. React at a constant temperature of 60°C for 2 hours, and control the pH to 8.5. After the reaction is completed, perform microfiltration membrane treatment. The pore size of the microfiltration membrane is 0.45 μm, the operating pressure is 0.1 MPa, and the operating temperature is 55°C.

[0037] In step S2, the preparation method of the composite additive A is as follows: (1) 100g of mesoporous silica was added to 1L of ethanol aqueous solution (ethanol to water volume ratio of 9:1), followed by 8g of γ-glycidoxypropyltrimethoxysilane. The reaction was carried out at 60℃ for 4h. After the reaction was completed, the silica was filtered, washed and dried to obtain pretreated mesoporous silica. 100g of pretreated mesoporous silica was added to 1L of DMF, followed by 15g of tris(2-aminoethyl)amine. The reaction was carried out at 75℃ under nitrogen atmosphere for 5h. After the reaction was completed, the silica was filtered, washed and dried to obtain modified silica. (2) Mix 15g of modified silica, 30g of polyaluminum chloride and 5g of polyethylene glycol evenly to obtain the final product.

[0038] The preparation method of the composite additive B in step S3 is as follows: By weight, 45 parts sodium bicarbonate, 20 parts modified molecular sieve, 5 parts cationic polyacrylamide, 11 parts sodium carbonate, and 25 parts diatomaceous earth are mixed evenly to obtain the modified molecular sieve. The modified molecular sieve is prepared as follows: 4A type molecular sieve is added to a 1.5 mol / L NH4Cl solution, stirred at 85℃ for 4.5 h, and then calcined at 400℃ for 2.5 h to obtain the modified molecular sieve.

[0039] Compared to Example 1, 4-carboxyphenylboronic acid was not introduced into the composite additive A of this comparative example. Comparative Example 2

[0040] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 5, and then introduce air at an aeration rate of 1.3 L / (L·min) for 30 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.2% of the mass of the mixed wastewater. Stir and react at 45°C for 50 min. After the reaction is completed, CO2 gas is introduced at a rate of 0.4 L / (L·min). The pH of the wastewater is controlled at 6.5. Then, the mixture is allowed to stand and settle for 1.5 h. After filtration, the supernatant is obtained. S3. Add composite additive B to the supernatant from step S2. The amount of composite additive B added is 0.5% of the mass of the supernatant. React at a constant temperature of 60°C for 2 hours, and control the pH to 8.5. After the reaction is completed, perform microfiltration membrane treatment. The pore size of the microfiltration membrane is 0.45 μm, the operating pressure is 0.1 MPa, and the operating temperature is 55°C.

[0041] In step S2, the preparation method of the composite additive A is as follows: (1) Mix 100g of mesoporous silica, 15g of tris(2-aminoethyl)amine and 8g of 4-carboxyphenylborone evenly to obtain modified silica; (3) Mix 15g of modified silica, 30g of polyaluminum chloride and 5g of polyethylene glycol evenly to obtain the final product.

[0042] The preparation method of the composite additive B in step S3 is as follows: By weight, 45 parts sodium bicarbonate, 20 parts modified molecular sieve, 5 parts cationic polyacrylamide, 11 parts sodium carbonate, and 25 parts diatomaceous earth are mixed evenly to obtain the modified molecular sieve. The modified molecular sieve is prepared as follows: 4A type molecular sieve is added to a 1.5 mol / L NH4Cl solution, stirred at 85℃ for 4.5 h, and then calcined at 400℃ for 2.5 h to obtain the modified molecular sieve.

[0043] Compared with Example 1, the modified silica in the composite additive of this comparative example was prepared by physical blending of mesoporous silica with 4-carboxyphenylboronic acid and tris(2-aminoethyl)amine. Comparative Example 3

[0044] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 5, and then introduce air at an aeration rate of 1.3 L / (L·min) for 30 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.2% of the mass of the mixed wastewater. Stir and react at 45°C for 50 min. After the reaction is completed, CO2 gas is introduced at a rate of 0.4 L / (L·min). The pH of the wastewater is controlled at 6.5. Then, the mixture is allowed to stand and settle for 1.5 h. After filtration, the supernatant is obtained. S3. Add composite additive B to the supernatant from step S2. The amount of composite additive B added is 0.5% of the mass of the supernatant. React at a constant temperature of 60°C for 2 hours, and control the pH to 8.5. After the reaction is completed, perform microfiltration membrane treatment. The pore size of the microfiltration membrane is 0.45 μm, the operating pressure is 0.1 MPa, and the operating temperature is 55°C.

[0045] In step S2, the preparation method of the composite additive A is as follows: (1) 100g of mesoporous silica was added to 1L of ethanol aqueous solution (ethanol to water volume ratio of 9:1), followed by 8g of γ-glycidoxypropyltrimethoxysilane. The mixture was reacted at 60℃ for 4h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated mesoporous silica. 100g of pretreated mesoporous silica was added to 1L of DMF, followed by 15g of tris(2-aminoethyl)amine. The mixture was reacted at 75℃ under a nitrogen atmosphere for 5h. After the reaction was completed, the mixture was filtered, washed and dried to obtain organo-silica. (2) Add 8g of 4-carboxyphenylboronic acid to 1L of MES buffer, then add 20g of EDC and 15g of NHS, stir and activate at 25℃ for 20min, then add 100g of organosilica, stir and react at 20℃ for 4h, after the reaction is completed, filter, wash and dry to obtain solid product; add 100g of solid product to 1L of deionized water, adjust pH to 11, then add 20g of sodium chloroacetate, react at 60℃ for 10h, after the reaction is completed, adjust pH to 7, filter, wash and dry to obtain modified silica; (3) Mix 15g of modified silica, 30g of polyaluminum chloride and 5g of polyethylene glycol evenly to obtain the final product.

[0046] The preparation method of the composite additive B in step S3 is as follows: By weight, mix 45 parts sodium bicarbonate, 5 parts cationic polyacrylamide, 11 parts sodium carbonate, and 25 parts diatomaceous earth evenly to obtain the final product.

[0047] Compared with Example 1, no modified molecular sieve was added to the composite additive B in this comparative example. Comparative Example 4

[0048] A method for treating hot-dip galvanizing wastewater includes the following steps: S1. Mix the hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH to 5, and then introduce air at an aeration rate of 1.3 L / (L·min) for 30 min to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1. The amount of composite additive A added is 0.2% of the mass of the mixed wastewater. Stir and react at 45°C for 50 min. After the reaction is completed, introduce CO2 gas at a rate of 0.4 L / (L·min) to control the pH of the wastewater at 6.5. Then allow it to settle for 1.5 h and filter.

[0049] In step S2, the preparation method of the composite additive A is as follows: (1) 100g of mesoporous silica was added to 1L of ethanol aqueous solution (ethanol to water volume ratio of 9:1), followed by 8g of γ-glycidoxypropyltrimethoxysilane. The mixture was reacted at 60℃ for 4h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated mesoporous silica. 100g of pretreated mesoporous silica was added to 1L of DMF, followed by 15g of tris(2-aminoethyl)amine. The mixture was reacted at 75℃ under a nitrogen atmosphere for 5h. After the reaction was completed, the mixture was filtered, washed and dried to obtain organo-silica. (2) Add 8g of 4-carboxyphenylboronic acid to 1L of MES buffer, then add 20g of EDC and 15g of NHS, stir and activate at 25℃ for 20min, then add 100g of organosilica, stir and react at 20℃ for 4h, after the reaction is completed, filter, wash and dry to obtain solid product; add 100g of solid product to 1L of deionized water, adjust pH to 11, then add 20g of sodium chloroacetate, react at 60℃ for 10h, after the reaction is completed, adjust pH to 7, filter, wash and dry to obtain modified silica; (3) Mix 15g of modified silica, 30g of polyaluminum chloride and 5g of polyethylene glycol evenly to obtain the final product.

[0050] Compared with Example 1, step S3 was not performed in this comparative example.

[0051] The wastewater treated in Examples 1-3 and Comparative Examples 1-4 was tested for water quality. Before treatment, the concentration of total zinc in the hot-dip galvanizing wastewater was 130 mg / L, the concentration of NH3-N was 300 mg / L, the concentration of SS was 200 mg / L, and the concentration of total iron was 110 mg / L. The test results are shown in Table 1 below.

[0052] Table 1

[0053] As can be seen from Table 1 above, the hot-dip galvanizing wastewater treatment method provided by the present invention can significantly reduce the total zinc content and suspended solids removal rate in the wastewater, achieve multi-stage synergistic removal of heavy metals and ammonia nitrogen in hot-dip galvanizing wastewater, and ensure that the effluent quality meets the corresponding discharge standards.

[0054] The above description is a further detailed explanation of the present invention in conjunction with specific implementation examples. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.

[0055] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for treating hot-dip galvanizing wastewater, characterized in that, Includes the following steps: S1. Mix hot-dip galvanizing pickling wastewater and alkaline washing wastewater, adjust the pH, and then introduce air to obtain a mixed wastewater solution. S2. Add composite additive A to the mixed wastewater in step S1, stir and react. After the reaction is complete, introduce CO2 gas to control the pH of the wastewater at 6-7. Then allow it to settle and filter to obtain the supernatant. S3. Add composite additive B to the supernatant from step S2, carry out a constant temperature reaction, control the pH to 8-9, and after the reaction is complete, perform microfiltration membrane treatment.

2. The method for treating hot-dip galvanizing wastewater according to claim 1, characterized in that, In step S1, the pH is 4-6, the air aeration rate is 1-1.5 L / (L·min), and the aeration time is 20-40 min.

3. The method for treating hot-dip galvanizing wastewater according to claim 1, characterized in that, In step S2, the preparation method of the composite additive A is as follows: (1) Add mesoporous silica to an aqueous ethanol solution, then add γ-glycidyl etheroxypropyltrimethoxysilane, and carry out a constant temperature reaction. After the reaction is completed, filter, wash and dry to obtain pretreated mesoporous silica. Add the pretreated mesoporous silica to DMF, then add tris(2-aminoethyl)amine, and carry out a heating reaction. After the reaction is completed, filter, wash and dry to obtain organosilica. (2) Add 4-carboxyphenylboronic acid to MES buffer, then add EDC and NHS, stir to activate, then add organosilica, stir to react, filter, wash and dry after the reaction is complete to obtain solid product; The solid product was added to deionized water, and the pH was adjusted to 11-12. Then sodium chloroacetate was added, and the reaction was carried out by heating. After the reaction was completed, the pH was adjusted to 7, and the product was filtered, washed, and dried to obtain modified silica. (3) Mix the modified silica, polyaluminum chloride and polyethylene glycol evenly to obtain the final product.

4. The method for treating hot-dip galvanizing wastewater according to claim 3, characterized in that, In step (1), the mass ratio of mesoporous silica to γ-glycidoxypropyltrimethoxysilane is 100:8-12, the temperature of the isothermal reaction is 60-70℃, and the time is 3-4h; the mass ratio of pretreated mesoporous silica to tris(2-aminoethyl)amine is 100:15-25, the temperature of the heating reaction is 75-85℃, and the time is 4-5h.

5. The method for treating hot-dip galvanizing wastewater according to claim 3, characterized in that, In step (2), the mass ratio of 4-carboxyphenylboronic acid, EDC, NHS, and organosilica is 8-12:20-30:15-20:100, the stirring reaction temperature is 20-25℃, and the time is 2-4h; the mass ratio of the solid product and sodium chloroacetate is 100:20-30, the heating reaction temperature is 60-70℃, and the time is 8-10h.

6. The method for treating hot-dip galvanizing wastewater according to claim 3, characterized in that, The mass ratio of modified silica, polyaluminum chloride, and polyethylene glycol in step (3) is 15-25:30-50:5-10.

7. The method for treating hot-dip galvanizing wastewater according to claim 1, characterized in that, In step S2, the amount of the composite additive A added is 0.1-0.3% of the mass of the mixed wastewater, the temperature of the stirring reaction is 40-50℃, and the time is 30-60 min; the CO2 aeration rate is 0.3-0.5 L / (L·min), and the settling time is 1-2 h.

8. The method for treating hot-dip galvanizing wastewater according to claim 1, characterized in that, The preparation method of the composite additive B in step S3 is as follows: By weight, mix 35-50 parts sodium bicarbonate, 15-25 parts modified molecular sieve, 3-8 parts cationic polyacrylamide, 8-15 parts sodium carbonate, and 20-30 parts diatomaceous earth evenly to obtain the final product.

9. The method for treating hot-dip galvanizing wastewater according to claim 8, characterized in that, The modified molecular sieve is prepared as follows: 4A type molecular sieve is added to an NH4Cl solution with a concentration of 1-2 mol / L, stirred at 80-90℃ for 4-5 h, and then calcined at 350-450℃ for 2-3 h to obtain the product.

10. The method for treating hot-dip galvanizing wastewater according to claim 1, characterized in that, In step S3, the amount of the composite additive B added is 0.4-0.6% of the mass of the supernatant, the temperature of the isothermal reaction is 55-65℃, the time is 1.5-2.5h, the pore size of the microfiltration membrane is 0.1-0.45μm, the operating pressure is 0.05-0.15MPa, and the operating temperature is 50-60℃.

Images