A method for recycling and utilizing zinc-containing wastewater

Abstract

This invention relates to the technical field of wastewater treatment and discloses a method for the resource recovery and utilization of zinc-containing wastewater, comprising the following steps: S1, pretreating the zinc-containing wastewater with activated carbon to obtain filtrate; S2, passing the filtrate through a primary desalination membrane to obtain primary desalinated water and primary concentrated water; S3, desalinating the primary desalinated water and then recycling it; concentrating the primary concentrated water through a secondary concentration membrane to obtain secondary concentrated concentrated water and secondary concentrated desalinated water, wherein the secondary concentration membrane is a polyethyleneimine-polyethersulfone composite nanofiltration membrane modified with a weakly positively charged surface and crown ether; conveying the secondary concentrated desalinated water to S2 for desalination treatment, and conveying the secondary concentrated concentrated water to an electrodeposition device to recover metallic zinc. This invention can efficiently recover the metal and water resources of high-concentration zinc-containing wastewater generated during the zinc resource recovery process from smelting flue dust, and has the advantages of simple process, high degree of automation, low operating cost, cleanliness, and high efficiency.

Description

Technical Field

[0001] This invention relates to the technical field of wastewater treatment, and in particular to a method for the resource recovery and utilization of zinc-containing wastewater. Background Technology

[0002] Smelting flue dust is a typical hazardous waste generated during non-ferrous metal production, primarily a solid waste produced during copper pyrometallurgical smelting. It is rich in heavy metals such as zinc, copper, cadmium, lead, and tin, and also contains large amounts of silicon, aluminum, arsenic, chlorine, fluorine, antimony, manganese, and nickel. Due to the toxicity to human health and environmental pollution caused by smelting flue dust, its disposal and the recovery of useful resources are of great significance. Currently, the main methods of recovering from smelting flue dust are the production of electrolytic zinc and electrolytic cathode copper. The production processes involve leaching, extraction and purification of copper (electrodeposition of copper), iron removal, cadmium removal, extraction and purification of zinc (electrodeposition of zinc), and purification of chlorine and fluorine. During the electrolytic process of stripping deposited metals and cleaning electrodes, a large amount of rinsing wastewater is generated, containing zinc, copper, sulfate, and chloride ions, as well as petroleum-based organic matter. The zinc ion concentration is particularly high, making the wastewater highly acidic. Direct discharge or mixing with other wastewater will result in the waste of metal resources and water pollution.

[0003] The large amount of washing wastewater generated during the recovery of zinc and copper resources from smelting flue dust is classified into zinc-containing wastewater and copper-containing wastewater based on its water quality characteristics. These two types of wastewater have pH values ​​as low as 1-2, and the zinc-containing wastewater contains Zn. 2+ Content approximately 5-10 g / L, Cl - Approximately 8-12 g / L, SO4 2- Approximately 1.5-2.5 g / L, petroleum-related wastewater approximately 10 mg / L; Cu in copper-containing wastewater 2+ The content is approximately 0.2 g / L, Cl - Approximately 1-2 g / L, SO4 2- Approximately 10-14 g / L for zinc-containing wastewater and approximately 10 mg / L for petroleum-containing wastewater. The zinc in this wastewater mainly exists in the form of zinc sulfate and zinc chloride, and the content is relatively high, making it valuable for recovery.

[0004] Currently, the main methods for recovering zinc-containing wastewater include ion exchange resin method, electrodialysis method, and electrodeposition method. Cation exchange resin is used to exchange zinc in wastewater, and zinc can be directly enriched on the resin. However, for high-concentration zinc-containing wastewater, the resin will quickly become saturated, and regeneration will generate a large amount of acidic wastewater, requiring further treatment. This method is only suitable for low-concentration zinc-containing wastewater. Electrodialysis is not effective for treating high-concentration metal wastewater, as concentration polarization is very severe, leading to increased membrane resistance and excessive power consumption. It is more suitable for medium concentrations, such as wastewater with metal ion concentrations in the range of 1-5 g / L, which can be concentrated to a concentration of about 15 g / L, and then combined with other processes to recover metal resources. High-concentration wastewater can be converted into metallic zinc through electrodeposition, with a conversion rate of over 90% and a purity of over 95% for elemental zinc. The recovery efficiency is high. For example, patent CN101921032B discloses a method for treating electrolytic zinc rinsing wastewater using an electrodeposition-membrane separation combination device. The wastewater passes through an inlet pipe (1) and an equalization tank (2), then enters the electrodeposition device (3) to deposit heavy metals. However, electrodeposition consumes a lot of energy and incurs high wastewater treatment costs. The higher the zinc concentration in the wastewater, the more economically viable the electrodeposition method becomes. Therefore, due to the high zinc content in the aforementioned zinc-containing wastewater, the method is less effective in reducing the risk of zinc leaching. 2+ The content is too low to be suitable for electrodeposition. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for the resource recycling of zinc-containing wastewater. This method utilizes multi-stage membrane integration technology to recycle zinc-containing wastewater, efficiently recovering both zinc and water resources. The recovered high-concentration zinc is returned to the production end for zinc electrodeposition, and the water is reused as clean water in the washing process during production, achieving closed-loop resource recycling and meeting the requirement of zero discharge.

[0006] The objective of this invention is achieved through the following technical solution: This invention provides a method for the resource recovery and utilization of zinc-containing wastewater, comprising the following steps: S1. Activated carbon is used to pretreat zinc-containing wastewater to obtain filtrate; S2. The filtrate is passed through a primary salt-separating membrane to separate salts, yielding primary fresh water and primary concentrated water. S3. The primary freshwater is desalinated and then recycled. The primary concentrate is concentrated through a secondary concentration membrane to obtain secondary concentrated concentrate and secondary concentrated freshwater. The secondary concentration membrane is a polyethyleneimine-polyethersulfone composite nanofiltration membrane modified with a weak positive charge and crown ether. The secondary concentrated freshwater is sent to S2 for salt separation treatment. The secondary concentrated concentrate is sent to an electrodeposition device to recover metallic zinc.

[0007] This invention first uses membrane technology to concentrate zinc-containing wastewater to obtain Zn. 2+After obtaining a concentrated solution with a high concentration, the solution is then subjected to electrodeposition to obtain metallic zinc for resource recovery and utilization. Compared with the direct use of electrodeposition for wastewater treatment, the method in this invention can greatly improve the electrodeposition mass transfer efficiency, save energy, and recover water resources while recovering heavy metal resources, thus achieving more efficient resource utilization.

[0008] Activated carbon is used to pretreat zinc-containing wastewater to remove petroleum-based organic matter, meeting the water quality requirements for the membrane system feed water. The filtrate is then passed through a primary desalination membrane to separate divalent and monovalent salts, yielding primary desalinated water and primary concentrated water. The primary desalinated water undergoes further desalination to obtain clean water suitable for washing, achieving water resource recycling. The primary concentrated water is then further concentrated using a secondary concentration membrane, which has a higher monovalent ion removal rate than the primary desalination membrane, resulting in a higher concentration of Zn in the final product. 2+ A concentration of 30 g / L or higher is required to meet the recovery concentration requirements.

[0009] Preferably, in S1, the zinc-containing wastewater contains Zn 2+ The concentration is 5-10 g / L.

[0010] Preferably, in S1, the amount of activated carbon added relative to the zinc-containing wastewater is 1-5 ppm; the pretreatment includes: adding activated carbon to the zinc-containing wastewater, stirring to adsorb and then precipitating, and then filtering to obtain the filtrate.

[0011] Preferably, in S2, the primary salt separation membrane is a three-layer composite nanofiltration membrane with a molecular weight cutoff of 150-300 Daltons; the operating pressure for salt separation is 1.8-2.2 MPa, and the Zn content of the primary desalinated water is... 2+ Zn concentration below 100 mg / L, in primary concentrate 2+ The concentration is 15-20 g / L.

[0012] Preferably, in step S3, the concentration operation pressure is 2.2-2.5 MPa, and the Zn in the secondary concentrate is... 2+ The concentration is not less than 30 g / L.

[0013] Preferably, in step S3, the method for preparing the secondary concentration membrane includes the following steps: (1) The support layer is immersed in casting solution I, which includes graphene oxide and polyethyleneimine. After being removed and dried, the base film is obtained. (2) Coat one side of the base film with casting solution II, which includes an ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and a photoinitiator, and dry it after photoinitiated polymerization. (3) Coat the other side of the base film with casting solution III containing polyethersulfone, and then dry it; (4) The resulting membrane is then immersed in a glutaraldehyde solution for crosslinking.

[0014] The secondary concentration membrane uses a polyethyleneimine membrane as the base membrane, which is also loaded with graphene oxide. The oxygen-containing groups in graphene oxide can enhance hydrophilicity and regulate surface charge. Graphene oxide can also provide a size sieving effect, retaining hydrated or complexed monovalent zinc ions. Furthermore, the active groups in graphene oxide can facilitate the modification of the base membrane by compounds in casting solution II, forming hydrogen bonds to improve binding. Dimethylaminoethyl methacrylate, after photoinitiated polymerization, can introduce a membrane layer with a positive charge (-N+(CH3)3), which enhances the retention of monovalent zinc ions through electrostatic repulsion, while the repulsion of divalent zinc ions is weaker, thereby improving the removal rate of monovalent ions. Simultaneously, the formation of polymeric molecular chains facilitates the fixation of 15-crown ether-5. The cavity diameter of 15-crown ether-5 matches that of monovalent zinc ions (such as Zn(OH)+ or ZnCl+), selectively complexing monovalent zinc ions through host-guest interactions to form a dynamic retention barrier. Divalent zinc ions, due to their large size, cannot enter the crown ether cavity, and their high charge density results in low affinity for the crown ether, allowing them to pass freely through the membrane pores. The added EDTA not only helps to adjust the charge density, achieving a separation effect of high removal of monovalent ions and low removal of divalent ions, but also improves the binding stability within and between membrane layers through hydrogen bonding and subsequent glutaraldehyde crosslinking. Therefore, through the synergistic effect of graphene oxide, weakly positively charged functionalization, and 15-crown ether-5, the removal rate of monovalent zinc ions by the composite nanofiltration membrane can be significantly improved, while allowing efficient passage of divalent zinc ions, and ensuring good mechanical properties, binding stability, and chemical resistance.

[0015] Preferably, in step (1), the support layer is a non-woven fabric layer or a PET layer; the concentration of graphene oxide in the casting solution I is 0.4-0.6 mg / mL, and the concentration of polyethyleneimine is 2-4 mg / mL; the soaking time is 20-30 min.

[0016] Preferably, in step (2), the casting solution II comprises an ethanol solution of dimethylaminoethyl methacrylate in a mass ratio of 100:1-2:3-6:0.05-0.2, EDTA, 15-crown ether-5, and a photoinitiator; the mass concentration of the ethanol solution of dimethylaminoethyl methacrylate is 1-2%; the photoinitiator is benzophenone; and the photoinitiated polymerization reaction is carried out under ultraviolet light irradiation for 20-30 minutes.

[0017] Preferably, in step (3), the casting solution III is an N-N dimethylformamide solution of polyethersulfone, and the mass concentration of polyethersulfone is 15-18%.

[0018] Polyethersulfone possesses excellent chemical resistance, high strength, and mechanical properties, which can enhance the overall performance of composite nanofiltration membranes.

[0019] Preferably, in step (4), the mass concentration of the glutaraldehyde solution is 0.5-1%; and the crosslinking is performed at room temperature for 1-2 hours.

[0020] Preferably, in S3, the primary freshwater is desalinated through a secondary desalination membrane to obtain secondary desalination concentrate and secondary desalination freshwater; the secondary desalination concentrate is sent to S2 for salt separation treatment, and the secondary desalination freshwater is discharged for recycling.

[0021] As a preferred method, the pH of the primary freshwater is first adjusted to 3-4, and then desalinated through a secondary desalination membrane.

[0022] Preferably, in S3, the secondary desalination membrane is a polyamide reverse osmosis membrane; the desalination operating pressure is 1.6-2.0 MPa, and the Cl of the secondary desalinated water is... - Concentration below 200 mg / L, Zn 2+ Concentration below 20 mg / L.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention can achieve a water resource recovery rate of over 80%, and the recycled water reaches Cl - Concentration ≤200mg / L, Zn 2+ Concentration ≤20mg / L, meeting the water quality requirements for reclaimed water; Concentrated Zn 2+ If the concentration is ≥30g / L, it is returned to the electrolytic zinc production section to produce zinc plates and recover metallic zinc; thus completing a closed-loop cycle, achieving zero emissions and realizing green environmental protection. (2) The method of the present invention can efficiently recycle the metal and water resources of the high-concentration zinc-containing wastewater generated during the zinc resource recovery process of smelting flue ash. It also has the advantages of simple process, high degree of automation, low operating cost, cleanliness and high efficiency. Detailed Implementation

[0024] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0025] The present invention provides a method for the resource recovery and utilization of zinc-containing wastewater, comprising the following steps: S1, Zn in zinc-containing wastewater 2+ Activated carbon with a concentration of 5-10 g / L was added to zinc-containing wastewater at a dosage of 1-5 ppm relative to the zinc-containing wastewater. The mixture was stirred and adsorbed for 1-2 hours, followed by sedimentation for 2-3 hours, resulting in obvious solid-liquid separation. The supernatant was filtered to obtain the filtrate, which was then collected in the primary raw water tank.

[0026] S2. The filtrate from the primary raw water tank is pressurized by a high-pressure pump and enters the primary membrane device. The membrane element used is a primary salt separation membrane (a three-layer composite nanofiltration membrane with a molecular weight cutoff of 150-300 Daltons) for salt separation; the Cl- of the filtrate... - Concentration of 7-11 g / L, Zn 2+ With a concentration of 4-10 g / L, an operating pressure of 1.8-2.2 MPa, and a water recovery rate controlled at 60±5%, primary desalinated water and primary concentrated water are obtained. The Cl content of the primary desalinated water is... - Concentration below 1.5 g / L, Zn 2+ The concentration of Cl in primary concentrate is below 100 mg / L. - Concentration of 18-22 g / L, Zn 2+ Concentration 15-20g / L.

[0027] S3. The primary concentrate is collected in the primary concentrate tank and pressurized by a booster pump before entering the secondary concentration membrane unit. A secondary concentration membrane element is used for concentration. The operating pressure is 2.2-2.5 MPa, and the water recovery rate is controlled at 50±5%. Secondary concentrated concentrate and secondary concentrated desalinated water are obtained. The secondary concentrated concentrate contains Zn. 2+ The concentration is not less than 30 g / L; the secondary concentrated desalinated water is sent to S2 for salt separation treatment, and the secondary concentrated concentrated water is sent to the electrodeposition unit to recover metallic zinc.

[0028] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine is added to graphene oxide dispersion (solvent is water) to obtain casting solution I. The concentration of graphene oxide in casting solution I is 0.4-0.6 mg / mL and the concentration of polyethyleneimine is 2-4 mg / mL. The support layer is immersed in casting solution I for 20-30 min, and then dried at 50-60℃ to obtain the base film. (2) Add EDTA, 15-crown ether-5 and photoinitiator (benzophenone) to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1-2%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and photoinitiator is 100:1-2:3-6:0.05-0.2 to obtain casting solution II. Coat one side of the substrate film with casting solution II and carry out photoinitiated polymerization reaction under ultraviolet light irradiation for 20-30 min, and then dry at 50-60℃. (3) Add polyethersulfone to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 15-18%; then coat the other side of the base film with casting solution III, and then dry at 50-60℃. (4) The obtained membrane is then immersed in a glutaraldehyde solution with a mass concentration of 0.5-1% and crosslinked at room temperature for 1-2 hours. After that, it is taken out and dried at 50-60℃ to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0029] S4. Collect the primary freshwater in the secondary raw water tank, add liquid alkali to adjust the pH to 3-4, and then pressurize it through a high-pressure pump before entering the secondary desalination membrane unit. The membrane element used is a secondary desalination membrane (fouling-resistant brackish water spiral wound polyamide reverse osmosis membrane element) for desalination. The operating pressure is 1.6-2.0 MPa, and the water recovery rate is controlled at 70±5%. Secondary desalination concentrate and secondary desalination dewater are obtained. The Cl- content of the secondary desalination dewater is... - Concentration below 200 mg / L, Zn 2+ The concentration is below 20 mg / L; the secondary desalination concentrate is sent to S2 for salt separation treatment, and the secondary desalination desalination freshwater is discharged for recycling.

[0030] In a specific embodiment of the present invention, the zinc-containing wastewater used is the zinc-containing wastewater generated during the recovery of zinc and copper resources from smelting flue ash, and the specific composition ratio is shown in Table 1.

[0031] Table 1 Example 1 S1, Zn in zinc-containing wastewater 2+ The concentration was 8.58 g / L. Activated carbon was added to zinc-containing wastewater at a dosage of 2 ppm relative to the zinc-containing wastewater. The mixture was stirred and adsorbed for 1 hour, followed by sedimentation for 2 hours, resulting in obvious solid-liquid separation. The supernatant (petroleum content less than 1 mg / L) was filtered to obtain the filtrate, which was collected in the primary raw water tank.

[0032] S2. The filtrate from the primary raw water tank is pressurized by a high-pressure pump and enters the primary membrane device. The membrane element used is a primary salt separation membrane (a three-layer composite nanofiltration membrane with a molecular weight cutoff of 150-300 Daltons) for salt separation; the Cl- of the filtrate... - Concentration of 10.65 g / L, Zn 2+ With a concentration of 8.43 g / L, an operating pressure of 2.1 MPa, and a water recovery rate of 60%, primary desalinated water and primary concentrated water were obtained. The Cl- content of the primary desalinated water was... - Concentration below 1.5 g / L, Zn 2+ The concentration of Cl in primary concentrate is below 100 mg / L. - The concentration was 20.51 g / L, Zn 2+ Concentration 17.26 g / L.

[0033] S3. The primary concentrate is collected in the primary concentrate tank and pressurized by a booster pump before entering the secondary concentration membrane unit. A secondary concentration membrane element is used for concentration. The operating pressure is 2.3 MPa, and the water recovery rate is controlled at 50%. Secondary concentrated concentrate and secondary concentrated desalinate are obtained. The secondary concentrated concentrate contains Zn. 2+ The concentration is not less than 30 g / L; the secondary concentrated desalinated water is sent to S2 for salt separation treatment, and the secondary concentrated concentrated water is sent to the electrodeposition unit to recover metallic zinc.

[0034] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine was added to the graphene oxide dispersion to obtain casting solution I. The concentration of graphene oxide in casting solution I was 0.4 mg / mL and the concentration of polyethyleneimine was 4 mg / mL. The support layer was immersed in casting solution I for 20 min, and then dried at 60 °C to obtain the base film. (2) EDTA, 15-crown ether-5 and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and photoinitiator was 100:1:3:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film and photoinitiated polymerization was carried out under ultraviolet light irradiation for 20 min. Then it was dried at 60 °C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 18%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 0.5% glutaraldehyde solution and crosslinked at room temperature for 2 hours. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0035] S4. Collect the primary freshwater in the secondary raw water tank, add liquid alkali to adjust the pH to 3-4, and then pressurize it through a high-pressure pump before entering the secondary desalination membrane unit. The membrane element used is a secondary desalination membrane (fouling-resistant brackish water spiral wound polyamide reverse osmosis membrane element) for desalination. The operating pressure is 1.8 MPa, and the water recovery rate is controlled at 70%. Secondary desalination concentrate and secondary desalination dewater are obtained. The Cl- content of the secondary desalination dewater is... - Concentration below 200 mg / L, Zn 2+ The concentration is below 20 mg / L; the secondary desalination concentrate is sent to S2 for salt separation treatment, and the secondary desalination desalination freshwater is discharged for recycling.

[0036] Example 2 Regarding the primary concentrate obtained in Example 1 (the Cl of the primary concentrate) - The concentration was 20.51 g / L, Zn 2+The concentration was 17.26 g / L, and the difference from Example 1 was that a different secondary concentration membrane was used.

[0037] The primary concentrate is collected in the primary concentrate tank, and then pressurized by a booster pump before entering the secondary concentration membrane unit. The membrane element used is a secondary concentration membrane for concentration. The operating pressure is 2.3 MPa, and the water recovery rate is controlled at 50%, resulting in secondary concentrated concentrate and secondary concentrated desalinated water.

[0038] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine was added to the graphene oxide dispersion to obtain casting solution I. The concentration of graphene oxide in casting solution I was 0.5 mg / mL and the concentration of polyethyleneimine was 3 mg / mL. The support layer was immersed in casting solution I for 30 min, and then dried at 60 °C to obtain the base film. (2) EDTA, 15-crown ether-5 and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1.5%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and photoinitiator was 100:2:5:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film and photoinitiated polymerization was carried out under ultraviolet light irradiation for 30 min, and then dried at 60 °C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 15.5%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 0.5% glutaraldehyde solution and crosslinked at room temperature for 2 hours. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0039] Example 3 Regarding the primary concentrate obtained in Example 1 (the Cl of the primary concentrate) - The concentration was 20.51 g / L, Zn 2+ The concentration was 17.26 g / L, and the difference from Example 1 was that a different secondary concentration membrane was used.

[0040] The primary concentrate is collected in the primary concentrate tank, and then pressurized by a booster pump before entering the secondary concentration membrane unit. The membrane element used is a secondary concentration membrane for concentration. The operating pressure is 2.3 MPa, and the water recovery rate is controlled at 50%, resulting in secondary concentrated concentrate and secondary concentrated desalinated water.

[0041] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine was added to the graphene oxide dispersion to obtain casting solution I. The concentration of graphene oxide in casting solution I was 0.6 mg / mL and the concentration of polyethyleneimine was 3 mg / mL. The support layer was immersed in casting solution I for 30 min, and then dried at 60 °C to obtain the base film. (2) EDTA, 15-crown ether-5 and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and photoinitiator was 100:1:5:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film and photoinitiated polymerization was carried out under ultraviolet light irradiation for 30 min. Then it was dried at 60 °C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 16%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 1% glutaraldehyde solution and crosslinked at room temperature for 1 hour. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0042] Comparative Example 1 Regarding the primary concentrate obtained in Example 1 (the Cl of the primary concentrate) - The concentration was 20.51 g / L, Zn 2+ The concentration was 17.26 g / L. The difference from Example 1 is that no graphene oxide was added during the preparation of the secondary concentration membrane.

[0043] The preparation method of the secondary concentration membrane includes the following steps: (1) Add polyethyleneimine to water to obtain casting solution I, the concentration of polyethyleneimine in casting solution I is 4 mg / mL; immerse the support layer in casting solution I for 20 min, take it out and dry it at 60℃ to obtain the base membrane; (2) EDTA, 15-crown ether-5 and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and photoinitiator was 100:1:3:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film and photoinitiated polymerization was carried out under ultraviolet light irradiation for 20 min. Then it was dried at 60 °C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 18%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 0.5% glutaraldehyde solution and crosslinked at room temperature for 2 hours. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0044] Comparative Example 2 Regarding the primary concentrate obtained in Example 1 (the Cl of the primary concentrate) - The concentration was 20.51 g / L, Zn 2+ The concentration was 17.26 g / L. The difference from Example 1 is that 15-crown ether-5 was not added during the preparation of the secondary concentration membrane.

[0045] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine was added to the graphene oxide dispersion to obtain casting solution I. The concentration of graphene oxide in casting solution I was 0.4 mg / mL and the concentration of polyethyleneimine was 4 mg / mL. The support layer was immersed in casting solution I for 20 min, and then dried at 60 °C to obtain the base film. (2) EDTA and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA and photoinitiator was 100:1:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film and photoinitiated polymerization was carried out under ultraviolet light irradiation for 20 min. Then it was dried at 60°C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 18%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 0.5% glutaraldehyde solution and crosslinked at room temperature for 2 hours. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0046] Comparative Example 3 Regarding the primary concentrate obtained in Example 1 (the Cl of the primary concentrate) - The concentration was 20.51 g / L, Zn 2+ The concentration was 17.26 g / L. The difference from Example 1 is that EDTA was not added during the preparation of the secondary concentration membrane.

[0047] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine was added to the graphene oxide dispersion to obtain casting solution I. The concentration of graphene oxide in casting solution I was 0.4 mg / mL and the concentration of polyethyleneimine was 4 mg / mL. The support layer was immersed in casting solution I for 20 min, and then dried at 60 °C to obtain the base film. (2) 15-crown ether-5 and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 1%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, 15-crown ether-5 and photoinitiator was 100:3:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film and photoinitiated polymerization was carried out under ultraviolet light irradiation for 20 min. Then it was dried at 60 °C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 18%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 0.5% glutaraldehyde solution and crosslinked at room temperature for 2 hours. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0048] Comparative Example 4 Regarding the primary concentrate obtained in Example 1 (the Cl of the primary concentrate) - The concentration was 20.51 g / L, Zn 2+ The concentration was 17.26 g / L. The difference from Example 1 is that the proportion of dimethylaminoethyl methacrylate added during the preparation of the secondary concentration membrane is different.

[0049] The preparation method of the secondary concentration membrane includes the following steps: (1) Polyethyleneimine was added to the graphene oxide dispersion to obtain casting solution I. The concentration of graphene oxide in casting solution I was 0.4 mg / mL and the concentration of polyethyleneimine was 4 mg / mL. The support layer was immersed in casting solution I for 20 min, and then dried at 60 °C to obtain the base film. (2) EDTA, 15-crown ether-5 and photoinitiator (benzophenone) were added to an ethanol solution of dimethylaminoethyl methacrylate with a mass concentration of 0.5%. The mass ratio of the ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and photoinitiator was 100:1:3:0.1 to obtain casting solution II. Casting solution II was coated on one side of the substrate film, and photoinitiated polymerization was carried out under ultraviolet light irradiation for 10 min, and then dried at 60°C. (3) Polyethersulfone was added to NN dimethylformamide to obtain casting solution III with a polyethersulfone mass concentration of 18%; casting solution III was then coated on the other side of the base film and dried at 60°C. (4) The obtained membrane is then immersed in a 0.5% glutaraldehyde solution and crosslinked at room temperature for 2 hours. After that, it is taken out and dried at 60°C to obtain a composite nanofiltration membrane (i.e., a secondary concentration membrane).

[0050] Table 2 As shown in Table 2, the method of this invention can be used to treat zinc-containing wastewater and obtain Zn. 2+ Secondary concentrate with a concentration ≥30 g / L is used in the electrolytic zinc production process to produce zinc plates and recover metallic zinc, achieving efficient recycling of zinc resources. The secondary concentrate membrane achieves high removal of monovalent ions and low removal of divalent ions from the primary concentrate, resulting in excellent concentration and the production of high-concentration Zn. 2+ The secondary concentrate was obtained. However, due to changes in components and parameters during the preparation of the secondary concentrate membrane in Comparative Examples 1-4, it was not conducive to obtaining a composite nanofiltration membrane with high removal efficiency of monovalent zinc ions. Specifically, in Comparative Examples 1-3, the absence of graphene oxide, 15-crown ether-5, and EDTA significantly affected the surface charge control effect, size sieving effect, hydrophilicity, and binding properties. In Comparative Example 4, the low amount of dimethylaminoethyl methacrylate resulted in a decrease in the surface positive charge density, which also affected the binding stability of the composite membrane, thus leading to a decrease in the amount of Zn in the secondary concentrate. 2+ The concentration has decreased, making it impossible to meet the recycling and treatment standards.

[0051] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for the resource recovery and utilization of zinc-containing wastewater, characterized in that, Includes the following steps: S1. Activated carbon is used to pretreat zinc-containing wastewater to obtain filtrate; S2. The filtrate is passed through a primary salt-separating membrane to separate salts, yielding primary fresh water and primary concentrated water. S3. The primary freshwater is desalinated and then recycled; the primary concentrate is concentrated through a secondary concentration membrane to obtain secondary concentrated concentrate and secondary concentrated freshwater. The secondary concentrated desalinated water is sent to S2 for salt separation treatment, and the secondary concentrated concentrated water is sent to the electrodeposition unit to recover metallic zinc. The preparation of the secondary concentration membrane includes: (1) The support layer is immersed in casting solution I, which includes graphene oxide and polyethyleneimine. After being removed and dried, the base film is obtained. (2) Coat one side of the base membrane with casting solution II, which includes an ethanol solution of dimethylaminoethyl methacrylate, EDTA, 15-crown ether-5 and a photoinitiator. The mass concentration of the ethanol solution of dimethylaminoethyl methacrylate is 1-2%. Under ultraviolet light irradiation, react for 20-30 min and then dry. (3) Coat the other side of the base film with casting solution III containing polyethersulfone, and then dry it; (4) The resulting membrane is then immersed in a glutaraldehyde solution for crosslinking.

2. The method for resource recovery and utilization of zinc-containing wastewater according to claim 1, characterized in that, In S1, the zinc-containing wastewater contains Zn 2+ The concentration is 5-10 g / L.

3. The method for resource recovery and utilization of zinc-containing wastewater according to claim 1, characterized in that, In S1, the amount of activated carbon added relative to the zinc-containing wastewater is 1-5 ppm; the pretreatment includes: adding activated carbon to the zinc-containing wastewater, stirring to adsorb and then precipitating, and then filtering to obtain the filtrate.

4. The method for resource recovery and utilization of zinc-containing wastewater according to any one of claims 1-3, characterized in that, In S2, the primary salt separation membrane is a three-layer composite nanofiltration membrane with a molecular weight cutoff of 150-300 Daltons; the operating pressure for salt separation is 1.8-2.2 MPa, and the Zn content of the primary freshwater is... 2+ Concentration below 100 mg / L.

5. The method for resource recovery and utilization of zinc-containing wastewater according to claim 1, characterized in that, In S3, the concentration operation pressure is 2.2-2.5 MPa, and the Zn in the secondary concentrate is... 2+ Zn concentration not less than 30 g / L, primary concentrate 2+ The concentration is 15-20 g / L.

6. The method for resource recovery and utilization of zinc-containing wastewater according to claim 1, characterized in that, The casting solution I contains graphene oxide at a concentration of 0.4-0.6 mg / mL and polyethyleneimine at a concentration of 2-4 mg / mL; the casting solution II comprises an ethanol solution of dimethylaminoethyl methacrylate in a mass ratio of 100:1-2:3-6:0.05-0.2, EDTA, 15-crown ether-5, and a photoinitiator; the casting solution III is an N,N-dimethylformamide solution of polyethersulfone, with a polyethersulfone mass concentration of 15-18%.

7. The method for resource recovery and utilization of zinc-containing wastewater according to claim 1, characterized in that, In S3, the primary freshwater is desalinated through a secondary desalination membrane to obtain secondary desalination concentrate and secondary desalination freshwater. The secondary desalination concentrate is then sent to S2 for salt separation, and the secondary desalination freshwater is discharged for recycling.

8. The method for resource recovery and utilization of zinc-containing wastewater according to claim 7, characterized in that, The primary freshwater is first adjusted to a pH of 3-4, and then desalinated through a secondary desalination membrane.

9. The method for resource recovery and utilization of zinc-containing wastewater according to claim 7 or 8, characterized in that, In S3, the secondary desalination membrane is a polyamide reverse osmosis membrane; the desalination operating pressure is 1.6-2.0 MPa, and the Cl of the secondary desalinated water is... - Concentrations below 200 mg / L, Zn 2+ Concentration below 20 mg / L.

Images