Method and system for treating wastewater by magnetic polymerization condensation process

Abstract

The invention provides a method and system for treating wastewater through a magnetic polymerization condensation process, and belongs to the field of ferric phosphate wastewater treatment.The method comprises the steps that composite alkali liquor is added into ferric phosphate wastewater, the pH value of the wastewater is adjusted to be within a preset range, and pretreated wastewater is obtained; adding polycondensation magnetic particles into the pretreated wastewater, and carrying out magnetic polycondensation treatment; carrying out solid-liquid separation on the wastewater subjected to magnetic coagulation treatment to obtain clear water and a coagulation body; carrying out recovery treatment on the polycondensation magnetic particles in the polycondensation body; performing membrane concentration treatment on the clear water to obtain fresh water and concentrated water, recycling the fresh water, and performing evaporation concentration on the concentrated water to obtain an ammonium sulfate byproduct. The iron phosphate wastewater treatment effect is improved, the treatment speed is increased, the wastewater treatment efficiency is improved, and it is ensured that the effluent quality reaches the environmental protection standard. And through recycling of the magnetic particles condensed by magnetic polymerization and recycling of by-products, the overall treatment cost is reduced, waste discharge and environmental pollution are reduced, and the requirements of large-scale industrial production are met.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly to a method and system for treating wastewater by a magnetic coagulation and condensation process. Background Art

[0002] With the rapid development of the new energy vehicle market, the demand for lithium iron phosphate batteries has increased sharply. Correspondingly, the problem of treating lithium iron phosphate wastewater has become increasingly prominent. In the field of treating lithium iron phosphate wastewater, the traditional solid-liquid separation and precipitation process in the pretreatment stage is mainly the gravity precipitation method. This method relies on the density difference between solute particles and the solvent to make the particles with a large density sink to achieve separation, and is commonly used for the treatment of larger particles or suspended solids, with the characteristic of simple operation. However, for lithium iron phosphate wastewater with a high COD content, the traditional gravity precipitation process has many disadvantages: 1. The solid-liquid separation effect is poor, resulting in low removal efficiency of metal ions, affecting the operation of the subsequent membrane system and the purity of by-products; 2. The treatment speed is slow, the floor area is large, and it is difficult to meet the treatment requirements of high-concentration organic wastewater; 3. A large amount of chemicals are required for pretreatment, the treatment cost is high, and the cost of treating the generated sludge is high, causing pressure on the environment; 4. It is difficult to effectively remove fine particles and organic matter, and the effluent quality cannot meet the requirements of high-standard reuse; 5. The maintenance of the solid-liquid separation equipment is complex, the operation cost is high, and it is easily affected by the fluctuation of the wastewater composition, with poor stability. In view of these problems, it is necessary to explore and develop more efficient and stable wastewater treatment technologies to meet the development needs of the new energy vehicle industry. Summary of the Invention

[0003] In view of the technical problems existing in the background art, the present application provides a method for treating wastewater by a magnetic coagulation and condensation process, aiming to solve the technical problems of poor solid-liquid separation effect, slow treatment speed, large chemical consumption, and high cost existing in the traditional treatment process.

[0004] In a first aspect, an embodiment of the present application provides a method for treating wastewater by a magnetic coagulation and condensation process, including the following steps:

[0005] Adding a composite alkali solution to the lithium iron phosphate wastewater to adjust the pH value of the wastewater to a predetermined range to obtain pretreated wastewater;

[0006] Adding coagulation and condensation magnetic particles to the pretreated wastewater for magnetic coagulation and condensation treatment;

[0007] Performing solid-liquid separation on the wastewater after magnetic coagulation and condensation treatment to obtain clear water and a coagulation and condensation body;

[0008] Recycling the coagulation and condensation magnetic particles in the coagulation and condensation body;

[0009] Performing membrane concentration treatment on the clear water to obtain fresh water and concentrated water, recycling the fresh water, and performing evaporation concentration on the concentrated water to obtain ammonium sulfate by-products.

[0010] In the technical solution of the embodiment of the present application, by adding a composite alkali solution to adjust the pH value, the suspended solids and metal ions in the wastewater are more likely to combine with the coagulating magnetic particles, which helps to achieve efficient solid-liquid separation during the magnetic coagulation process. The magnetic coagulation process can effectively remove fine particles and organic matter in the wastewater and improve the effluent quality. By recycling the coagulating magnetic particles, not only the generation of waste is reduced, but also the economy of the treatment process is improved, and the magnetic particles can be recycled. Through membrane concentration treatment, fresh water and concentrated water can be further obtained from the clear water. The fresh water can be recycled, and ammonium sulfate by-products can be obtained by evaporation and concentration of the concentrated water, realizing the effective recovery of resources. The entire process reduces the dosage of chemical agents, reduces the potential impact on the environment during the treatment process, and also reduces the environmental burden of sludge.

[0011] In some embodiments, the composite alkali solution is composed of ammonia water and polyepichlorohydrin-dimethylamine; and / or the concentration of the ammonia water is 20-22%, and the concentration of the polyepichlorohydrin-dimethylamine is 98-99%; and / or the volume ratio of the ammonia water to the polyepichlorohydrin-dimethylamine is 25:1-30:1; and / or the predetermined range of the pH value is 8-9.

[0012] In this embodiment, the combined use of ammonia water and polyepichlorohydrin-dimethylamine can effectively neutralize the acidic components in the wastewater, increase the pH value of the wastewater, thereby optimizing the effect of the flocculant and making it easier for suspended solids and metal ions to form flocs. By controlling the concentration and volume ratio of ammonia water and polyepichlorohydrin-dimethylamine, the stability of the wastewater treatment process can be ensured. Using an appropriate amount of ammonia water and polyepichlorohydrin-dimethylamine can reduce the chemical agent cost while ensuring the treatment effect. In the range of pH value from 8 to 9, metal ions can form insoluble precipitates, improving the removal efficiency of metal ions.

[0013] In some embodiments, the coagulating magnetic particles have a core-shell structure, with the inner core being magnetite and the shell layer being silica or iron oxide.

[0014] In this embodiment, magnetite has a high magnetic permeability, making the magnetic particles easy to manipulate and separate under the action of an external magnetic field. The shell layer can protect the magnetite inner core from the influence of the external environment and improve the chemical stability and corrosion resistance of the magnetic particles.

[0015] In some embodiments, functionalized functional groups are grafted on the surface of the shell layer, and the functionalized functional groups are one or more of quaternary ammonium salt groups, crown ether molecules, sulfonic acid groups, and carboxylic acid groups.

[0016] In this embodiment, grafting functional groups on the surface of the shell layer can significantly improve the adsorption and removal ability of the magnetic particles for pollutants. Specifically, positively charged quaternary ammonium salt groups and crown ether molecules with selective adsorption functions are grafted onto the surface of the shell layer through silane coupling agents. This unique structure enables the coagulation magnetic particles to not only have strong magnetism and high adsorption performance but also selectively adsorb specific metal ion precipitates; sulfonic acid groups can adsorb cationic pollutants in wastewater through ion exchange, thereby improving the adsorption efficiency of the magnetic particles; carboxylic acid groups can adsorb heavy metal ions in wastewater through chelation, thereby achieving precise removal of target pollutants.

[0017] In some embodiments, the solid-liquid separation includes superconducting magnetic separation and ultrafiltration membrane filtration.

[0018] In this embodiment, superconducting magnetic separation uses the strong magnetic field of a superconducting magnet to separate the magnetized coagulation aggregates, while ultrafiltration membrane filtration can effectively intercept macromolecular substances and suspended particles in the solution to achieve antibacterial and antifouling fine filtration. The combination of the two can achieve efficient solid-liquid separation.

[0019] In some embodiments, the surface of the ultrafiltration membrane is coated with a polydopamine-silver nanoparticle composite coating or a polydopamine-zinc oxide composite coating; and / or the ultrafiltration membrane has a hollow fiber-flat composite structure.

[0020] In this embodiment, the polydopamine-silver nanoparticle composite coating can increase the hydrophilicity of the membrane surface, helping to improve the adsorption and filtration efficiency of the membrane for pollutants in the solution. Due to the antibacterial properties of the coating, biological fouling can be slowed down, thereby extending the service life of the ultrafiltration membrane. The polydopamine-zinc oxide composite coating can effectively adsorb and decompose pollutants on the membrane surface, thereby reducing the accumulation of pollutants and membrane fouling. The hollow fiber-flat composite structure improves the filtration efficiency of the membrane and enhances its durability.

[0021] In some embodiments, a multi-stage gradient magnetic field screening technique is used to recover the coagulation magnetic particles.

[0022] In this embodiment, the multi-stage gradient magnetic field can provide a strong magnetic field intensity and a uniform magnetic field distribution, effectively attracting and separating the coagulation magnetic particles and improving the recovery efficiency. By adjusting the magnetic field intensity and gradient, the separation process of the coagulation magnetic particles can be precisely controlled to ensure that only the target magnetic particles are recovered and the mixing of non-target substances is reduced.

[0023] In some embodiments, the membrane material for the membrane concentration treatment is one of a polyimide-graphene composite membrane, a polysulfone-graphene composite membrane, and a polyimide-carbon nanotube composite membrane.

[0024] In this embodiment, the membrane material has a high water flux and strong anti-fouling performance, further improving the concentration effect.

[0025] In a second aspect, an embodiment of the present application provides a system for treating wastewater by a magnetic coagulation and condensation process. The method for treating iron phosphate wastewater by using the magnetic coagulation and condensation process described in the first aspect is adopted, and it includes a wastewater pretreatment device, a magnetic coagulation and condensation device, a superconducting magnetic separation-ultrafiltration coupling device, a membrane concentration device, and an evaporation device connected in sequence; the magnetic coagulation and condensation device includes a magnetic field generating device, and the magnetic field is an alternating rotating magnetic field or a pulsed magnetic field; and / or the membrane concentration device includes a reverse flow membrane module or a forward flow membrane module; and / or the evaporation device includes a falling film evaporator and a forced circulation evaporator.

[0026] In the technical solution of the embodiment of the present application, through the pretreatment device, the magnetic coagulation and condensation device, the superconducting magnetic separation-ultrafiltration coupling device, the membrane concentration device, and the evaporation device connected in sequence, the system can continuously and efficiently treat iron phosphate wastewater, ensuring the treatment efficiency and the compliance of the effluent quality. The alternating rotating magnetic field generating device in the magnetic coagulation and condensation device can generate a changing magnetic field, improving the formation speed and quality of the coagulation and condensation bodies. The strong magnetic field generated by the pulsed magnetic field interacts with the current in the substance, causing the magnetic particles to move directionally in the magnetic field, thereby accelerating the formation of the coagulation and condensation bodies and forming an ordered coagulation structure. The reverse flow membrane module in the membrane concentration device can reduce membrane fouling and blockage, extend the service life of the membrane, and improve the concentration efficiency at the same time. The forward flow membrane module helps to reduce energy consumption and simplify the operation, and is suitable for the separation of macromolecular substances. The falling film evaporator and the forced circulation evaporator in the evaporation device can effectively concentrate the wastewater to the required degree, while reducing energy consumption and operating costs.

[0027] In some embodiments, it further includes a coagulation and condensation magnetic particle recovery device connected to the superconducting magnetic separation-ultrafiltration coupling device; and / or the system further includes an on-line cleaning system connected to the membrane concentration device.

[0028] In this embodiment, the coagulation and condensation magnetic particle recovery device can gradually screen and purify the coagulation and condensation magnetic particles in the coagulation and condensation bodies, and the recovered coagulation and condensation magnetic particles are re-injected into the front-end coagulation and condensation reaction system, thereby reducing the treatment cost. The on-line cleaning system can avoid the aging or damage of the membrane module due to long-term fouling by timely removing pollutants. The integrated design of the on-line cleaning system and the membrane concentration device simplifies the operation process, reduces system failures caused by untimely cleaning, improves the stability and reliability of the system, and ensures the continuity and efficiency of the wastewater treatment process.

[0029] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of the present application more obvious and understandable, the specific embodiments of the present application are hereinafter specifically exemplified. Description of the Drawings

[0030] To more clearly illustrate the technical solution of this application, the attached drawings used in this application will be briefly introduced below. Obviously, the attached drawings described below are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other attached drawings can be obtained based on these attached drawings.

[0031] Figure 1 It is a flowchart of the method for treating wastewater by the magnetic coagulation and condensation process in the embodiments of this application. Specific embodiments

[0032] The embodiments of the technical solution of this application will be described in detail below with reference to the attached drawings. The following embodiments are only used to more clearly illustrate the technical solution of this application, so they are only examples and cannot be used to limit the protection scope of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above attached drawing descriptions are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise clearly and specifically defined.

[0035] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments of this application, the term "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0037] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0038] In the process of treating iron phosphate wastewater, the traditional gravity sedimentation method has problems such as poor solid-liquid separation effect, low metal ion removal efficiency, slow speed, large chemical consumption, high cost, and the effluent quality cannot meet the requirements of high-standard reuse when treating high-COD iron phosphate wastewater, which seriously hinders the improvement of treatment effect and efficiency.

[0039] In order to solve the technical problems of poor effect, slow speed, high cost, and unqualified effluent quality existing in the traditional method for treating iron phosphate wastewater, the present application provides a method and system for treating wastewater by a magnetic coagulation and flocculation process. Among them, by integrating magnetic coagulation and flocculation technology, superconducting magnetic separation-ultrafiltration coupling technology, and a magnetic particle recovery system, the technical effects of efficiently removing metal ions, quickly treating, reducing costs, and improving the effluent quality can be achieved.

[0040] Please refer to Figure 1 , in the first aspect, the embodiments of the present application provide a method for treating wastewater by a magnetic coagulation and flocculation process, including the following steps:

[0041] Add a composite alkali solution to the iron phosphate wastewater to adjust the pH value of the wastewater to a predetermined range to obtain pretreated wastewater;

[0042] Add coagulation and flocculation magnetic particles to the pretreated wastewater for magnetic coagulation and flocculation treatment;

[0043] Perform solid-liquid separation on the wastewater after magnetic coagulation and flocculation treatment to obtain clear water and flocculates;

[0044] Recover the coagulation and flocculation magnetic particles in the flocculates;

[0045] Perform membrane concentration treatment on the clear water to obtain fresh water and concentrated water. The fresh water is recycled, and the concentrated water is subjected to evaporation concentration to obtain ammonium sulfate by-products.

[0046] In the technical solution of the embodiment of the present application, by adding a composite alkali solution to adjust the pH value, the existing form of metal ions in the wastewater can be changed, making it easier to react with the coagulation magnetic particles. Through solid-liquid separation of the wastewater after magnetic coagulation treatment, the magnetic flocs are separated from the wastewater by using a magnetic field, obtaining relatively clean clear water and a coagulation body containing coagulation magnetic particles. The coagulation magnetic particles are recycled for reuse. The clear water is concentrated using a membrane concentration technology to separate fresh water and concentrated water. The fresh water can be recycled, while the concentrated water contains a high concentration of sulfates and other valuable substances. The water in the concentrated water is evaporated by an evaporator, and finally by-products such as ammonium sulfate are obtained to achieve resource utilization.

[0047] Further, in some embodiments, the composite alkali solution is composed of ammonia water and polyepichlorohydrin-dimethylamine; and / or the concentration of ammonia water is 20-22%, and the concentration of polyepichlorohydrin-dimethylamine is 98-99%; and / or the volume ratio of ammonia water to polyepichlorohydrin-dimethylamine is 25:1-30:1; and / or the predetermined range of the pH value is 8-9.

[0048] In the technical solution of the embodiment of the present application, the composite alkali solution is composed of ammonia water and a novel alkaline polymer (polyepichlorohydrin-dimethylamine, PEI), and is mixed through an ultrasonic emulsification process to form a stable emulsion with a nanoscale microstructure. A high mass percentage concentration of PEI can provide more amino groups, enhancing its complexation ability with metal ions, thereby improving the coagulation effect. The pH of the wastewater is adjusted to 8-9. During this process, phosphate in the water first reacts with metal ions such as Mg, Mn, and Fe to form metal precipitates. Polyepichlorohydrin-dimethylamine can chelate with the metal ion precipitates to form large-particle-size chelate precipitates, and at the same time enhance the stability of the reaction between phosphate and metal ions to form precipitates.

[0049] Further, in some embodiments, the coagulation magnetic particles have a core-shell structure, with the inner core being magnetite and the shell layer being silica or iron oxide.

[0050] In the technical solution of the embodiment of the present application, the core-shell structure separates the magnetic core from the functional shell layer, enabling the magnetic particles to have both the convenience of magnetic separation and the functionality of the shell layer material. The presence of the shell layer can prevent the aggregation of magnetic particles and improve their dispersibility in water. By introducing specific functional groups on the shell layer, targeted adsorption of specific pollutants by the magnetic particles can be achieved. Magnetite (Fe3O4) is a material with strong magnetism that can rapidly aggregate and separate under the action of an external magnetic field. As the "core" material, it can effectively adsorb and remove metal ions and other pollutants in wastewater. Silicon dioxide (SiO2) is a material with stable chemical properties, non-toxicity, and good biocompatibility. As the "shell" material, SiO2 can protect the Fe3O4 core from unnecessary chemical reactions with other components in the wastewater, improving the stability and service life of the magnetic powder. The SiO2 shell layer helps to improve the dispersibility of the Fe3O4 magnetic powder in wastewater, prevent the magnetic powder from aggregating, and thus improve the coagulation efficiency. Fe2O3 has high catalytic activity, which helps to enhance the removal effect of pollutants. The Fe2O3 shell layer can improve the corrosion resistance of the magnetic particles and extend their service life.

[0051] Further, in some embodiments, functionalized functional groups are grafted on the surface of the shell layer, and the functionalized functional groups are one or more of quaternary ammonium salt groups, crown ether molecules, sulfonic acid groups, and carboxylic acid groups.

[0052] In the technical solution of the embodiment of the present application, functionalized functional groups are grafted on the surface of the shell layer through a silane coupling agent. The quaternary ammonium salt group has cationic characteristics and can adsorb negatively charged pollutants; the crown ether molecule has a specific cavity structure and can form coordination bonds with metal ions to achieve selective adsorption of specific metal ions; the sulfonic acid group and the carboxylic acid group have acidity and can form complexes with metal ions to enhance the adsorption ability of metal ions. The coagulation and separation magnetic particles with a core-shell structure not only have strong magnetism and high adsorption performance but also can selectively adsorb specific metal ion precipitates.

[0053] Specifically, an alternating rotating magnetic field generating device is used for magnetic coagulation and separation treatment, and the generated magnetic field intensity and direction change according to a specific periodic law. The alternating rotating magnetic field generating device is a device that can generate a rotating magnetic field and make it change alternately at a certain frequency. By adjusting the direction and frequency of the current through the control unit, the electromagnetic coil can be rotated around the central axis, so that the magnetic field changes in a rotating manner in space, and this rotation can be unidirectional or alternately changing. In the initial stage of the reaction, the magnetic field intensity rapidly increases and rotates, prompting the coagulation and separation magnetic particles to quickly disperse and combine with suspended particles and organic matter to form an initial coagulation and separation body; subsequently, the magnetic field intensity and rotation speed gradually decrease, enabling the coagulation and separation body to further grow and densify in a relatively mild magnetic field environment. Through this dynamic magnetic field regulation method, the formation speed and quality of the coagulation and separation body are improved.

[0054] Furthermore, in some embodiments, solid-liquid separation includes superconducting magnetic separation and ultrafiltration membrane filtration.

[0055] In the technical solution of the embodiment of the present application, the ultra-strong magnetic field generated by the superconducting magnetic separation-ultrafiltration coupling device is used to quickly adsorb the magnetized aggregate to the surface of the magnet to achieve preliminary solid-liquid separation. Afterwards, the liquid after the preliminary separation is filtered for the second time through the ultrafiltration membrane, and the separated clean water enters the membrane concentration system.

[0056] Furthermore, in some embodiments, the surface of the ultrafiltration membrane is coated with a polydopamine-silver nanoparticle composite coating or a polydopamine-zinc oxide composite coating; and / or the ultrafiltration membrane is a hollow fiber-flat plate composite structure.

[0057] In the technical solution of the present application's embodiments, the ultrafiltration membrane is coated with a polydopamine-silver nanoparticle composite coating with antibacterial and anti-fouling properties, effectively preventing membrane fouling and improving filtration flux and stability. The polydopamine-zinc oxide composite coating exhibits photocatalytic properties, capable of decomposing organic pollutants under illumination, enhancing the membrane's purification capacity. The hollow fiber-flat plate composite structure possesses a high specific surface area and mechanical strength, enhancing its durability and anti-fouling capabilities.

[0058] Furthermore, in some embodiments, a multi-stage gradient magnetic field screening technology is used to recover the aggregated magnetic particles.

[0059] In the technical solution of the embodiment of the present application, the polycondensate magnetic particles in the polycondensate are gradually screened and purified by setting up multiple regions with different magnetic field strengths and gradients. Specifically, multiple magnetic field regions are designed in series, each region has a different magnetic field strength and gradient, and a permanent magnet or an electromagnet is used to generate the required magnetic field. Initial separation stage: the polycondensate is passed through the first-level magnetic field to separate particles or impurities with weaker magnetism; intermediate separation stage: the mixture after the initial separation is passed through the second-level magnetic field to further separate the magnetic particles; final recovery stage: the mixture after the intermediate separation is passed through the third-level magnetic field to recover high-purity magnetic particles. In the first magnetic field region, the weaker magnetic field strength allows the non-magnetic impurities mixed in the polycondensate to be separated first; in the subsequent magnetic field regions, as the magnetic field strength and gradient gradually increase, the high-purity polycondensate magnetic particles are recovered in sequence, and the recovery rate can reach more than 99%.

[0060] Furthermore, in some embodiments, the membrane material for the membrane concentration process is one of a polyimide-graphene composite membrane, a polysulfone-graphene composite membrane, and a polyimide-carbon nanotube composite membrane.

[0061] In the technical solution of the embodiment of the present application, the membrane material is a new polyimide-graphene composite membrane, which has high chemical stability, mechanical strength, anti-pollution ability and separation efficiency, enabling it to maintain long-term stable operation under harsh conditions and efficiently concentrate pollutants in wastewater.

[0062] In a second aspect, the embodiment of the present application provides a system for treating wastewater by a magnetic coagulation and condensation process, which uses the method for treating wastewater by the magnetic coagulation and condensation process described in the first aspect to treat iron phosphate wastewater, and includes a wastewater pretreatment device, a magnetic coagulation and condensation device, a superconducting magnetic separation-ultrafiltration coupling device, a membrane concentration device and an evaporation device connected in sequence; the magnetic coagulation and condensation device includes a magnetic field generating device, and the magnetic field is an alternating rotating magnetic field or a pulsed magnetic field; and / or the membrane concentration device includes a reverse flow membrane module or a forward flow membrane module; and / or the evaporation device includes a falling film evaporator and a forced circulation evaporator.

[0063] Among them, in the membrane concentration device, the reverse flow membrane module uses the reverse osmosis principle to efficiently separate small molecule substances or ions; the forward flow membrane module uses the forward filtration principle and is suitable for the separation of macromolecular substances, with advantages such as reduced energy consumption and simplified operation. The reverse flow membrane module enables the concentrated water and the draw solution to perform mass exchange in a reverse flow manner on both sides of the membrane through a cleverly designed flow channel structure, effectively reducing the concentration polarization phenomenon and improving the membrane concentration efficiency. The evaporation device adopts a multi-stage evaporation structure combining a high-efficiency falling film evaporator and a forced circulation evaporator. In the falling film evaporator, the liquid flows down along the heating tube wall in a film shape under the action of gravity for rapid evaporation; the forced circulation evaporator further concentrates the remaining liquid after falling film evaporation to improve the evaporation efficiency and reduce energy consumption. The purity of the final formed ammonium sulfate by-product can reach more than 99.2%, meeting the requirements for high-quality external sales.

[0064] Furthermore, in some embodiments, it further includes a coagulation and condensation magnetic particle recovery device connected to the superconducting magnetic separation-ultrafiltration coupling device; and / or the system further includes an on-line cleaning system connected to the membrane concentration device.

[0065] In the technical solution of the embodiment of the present application, for the coagulation and condensation body obtained by solid-liquid separation through the superconducting magnetic separation-ultrafiltration coupling device, a multi-stage gradient magnetic field screening technology is used to recover the coagulation and condensation magnetic particles in the coagulation and condensation body, and the recovered coagulation and condensation magnetic particles can be returned to the magnetic coagulation and condensation device for reuse. The pollutants on the membrane surface are removed in an automated manner, thereby maintaining the stable operation of the membrane module.

[0066] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0067] Example 1

[0068] This embodiment provides a method for treating wastewater using a magnetic coagulation process, comprising the following steps:

[0069] S1. A 20% ammonia solution and a 98% polyepichlorohydrin-dimethylamine solution were mixed in a volume ratio of 25:1 by ultrasonic emulsification to form a stable emulsion with a nanoscale microstructure, which was added to the iron phosphate wastewater and the pH value of the wastewater was adjusted to 8.5 to obtain pretreated wastewater;

[0070] S2. Adding core-shell structured and surface-functionalized coagulant magnetic particles to the pretreated wastewater for magnetic coagulant treatment; the coagulant magnetic particles have a core of ferroferric oxide and an outer layer of silica, the silica surface of which is grafted with positively charged quaternary ammonium groups and crown ether molecules with selective adsorption capabilities via a silane coupling agent; an alternating rotating magnetic field generator is used to power the coagulant formation and accelerate the binding process; the alternating magnetic field rotation speed is 60 rpm, and the coagulant formation time is 5 min;

[0071] S3. The wastewater after magnetic coagulation treatment is subjected to solid-liquid separation. The ultrastrong magnetic field generated by the superconducting magnetic separation-ultrafiltration coupling device is used to rapidly adsorb the magnetized coagulation product to the magnet surface, achieving initial solid-liquid separation. The liquid after the initial separation is then subjected to a secondary filtration through an ultrafiltration membrane. The surface of the ultrafiltration membrane is coated with a polydopamine-silver nanoparticle composite coating with antibacterial and anti-fouling properties to effectively prevent membrane fouling, improve filtration flux and stability, and separate the coagulation product into clean water. The clean water enters the membrane concentration device for treatment;

[0072] S4. The polymerized condensate magnetic particles in the polymerized condensate are recovered and processed using a multi-stage gradient magnetic field screening technology. The polymerized condensate magnetic particles in the polymerized condensate are gradually screened and purified by a four-stage gradient magnetic field (0.2T→0.5T→0.8T→1.0T). The remaining sludge enters the sludge transfer tank for treatment to obtain phosphate fertilizer.

[0073] S5. Perform membrane concentration treatment on the fresh water. Use a reverse flow membrane module and a polyimide-graphene composite membrane for treatment to obtain fresh water and concentrated water. The fresh water is recycled to the production workshop, and the concentrated water enters the MVR evaporation device. Use a multi-stage evaporation structure combining a high-efficiency falling film evaporator and a forced circulation evaporator for treatment. The purity of the ammonium sulfate by-product finally formed reaches 99.5%.

[0074] In this embodiment, through the selective adsorption of the core-shell structured coagulation magnetic particles and the high-efficiency filtration of the reverse flow membrane module, fine particles and organic matters are effectively removed. The effluent COD is reduced to below 50 mg / L, meeting the strict recycling standard, and the pretreatment time is shortened to 13 min. The alternating rotating magnetic field provides power for the formation of coagulation aggregates, accelerating the combination process, and solving the problems of poor solid-liquid separation effect and low efficiency in the traditional gravity sedimentation process. By using the composite alkali solution and accurately controlling the dosage of the coagulation magnetic particles, the dosage of the medicament is reduced by more than 50%. The multi-stage gradient magnetic field screening technology improves the recovery rate of the coagulation magnetic particles, making the magnetic particle recovery rate reach more than 99%, reducing the loss cost; at the same time, the high-efficiency evaporation structure reduces the MVR evaporation energy consumption by more than 30%, and the comprehensive treatment cost is significantly reduced. Through the superconducting magnetic separation-ultrafiltration coupling device and the efficient reaction equipment design, the floor area of the entire treatment system is reduced by 40% - 60% compared with the traditional process, and it is suitable for sewage treatment occasions under various space conditions. Through the intelligent algorithm to control the dosage of the coagulation magnetic particles, the magnetic field parameters and the equipment operation, automatic operation is realized. The system processes the data from various sensors through real-time monitoring and data analysis to monitor water quality parameters such as pH value, temperature, turbidity, etc., and automatically adjusts the treatment parameters according to the real-time data, so as to optimize the treatment efficiency and reduce the overall cost. At the same time, the system has strong adaptability to the fluctuation of the wastewater composition, and the operation stability is increased by more than 80%, reducing the manual intervention and maintenance cost. In the traditional coagulation sedimentation technology, the flocculation reaction time is relatively long, while the magnetic coagulation technology of this application can shorten the reaction time to 10 - 15 min, which is much lower than the treatment time of the traditional process.

[0075] Example 2

[0076] This embodiment provides a method for treating wastewater by a magnetic coagulation process, including the following steps:

[0077] S1. Mix ammonia water with a concentration of 22% and polyepichlorohydrin-dimethylamine with a concentration of 99% at a volume ratio of 30:1, form a stable emulsion through ultrasonic emulsification, add it to the phosphoric acid iron wastewater, and adjust the pH value of the wastewater to 8.5 to obtain pretreated wastewater;

[0078] S2. Add core-shell structured coagulation magnetic particles (Fe3O4 core, SiO2 shell surface grafted with sulfonic acid groups) to the pretreated wastewater, and use a pulsed magnetic field (frequency 40 Hz, intensity 0.5 T) to accelerate the formation of coagulation aggregates;

[0079] S3. Use a superconducting magnetic separation - hollow fiber ultrafiltration coupling device to perform solid - liquid separation on the wastewater after magnetic coagulation - flocculation treatment. The membrane pore size is 0.05 μm, and the operating pressure is 0.3 MPa; clear water and coagulation - flocculation bodies are separated;

[0080] S4. Recover the coagulation - flocculation magnetic particles in the coagulation - flocculation bodies through a four - stage gradient magnetic field (0.2 T → 0.5 T → 0.8 T → 1.0 T), and the recovery rate is 98.5%;

[0081] S5. Perform membrane concentration treatment on the clear water. Use a reverse - flow membrane module and a polysulfone - graphene composite membrane. The reverse flow rate ratio is 1:1.2. The concentrated water is treated by a single - stage falling - film evaporator to obtain ammonium sulfate with a purity of 99.2%.

[0082] The treatment effect of this example is: the COD is reduced to 55 mg / L, the pretreatment time is shortened to 14 min, the chemical agent cost is reduced by 45%, and the system energy consumption is reduced by 28% compared with the traditional process.

[0083] Example 3

[0084] This example provides a method for treating wastewater by a magnetic coagulation - flocculation process, including the following steps:

[0085] S1. Mix ammonia water with a concentration of 20% and polyepichlorohydrin - dimethylamine with a concentration of 98% in a volume ratio of 28:1 through an ultrasonic emulsification process to form a stable emulsion with a nanoscale microstructure, add it to the phosphoric acid iron wastewater, and adjust the pH value of the wastewater to 8.6 to obtain pretreated wastewater;

[0086] S2. Add coagulation - flocculation magnetic particles to the pretreated wastewater for magnetic coagulation - flocculation treatment; the coagulation - flocculation magnetic particles have a core of magnetite and a shell of Fe2O3, with carboxylic acid groups grafted on the surface, and the alternating magnetic field rotation speed is 60 rpm;

[0087] S3. Use a superconducting magnetic separation - ultrafiltration coupling device to perform solid - liquid separation on the wastewater after magnetic coagulation - flocculation treatment. The ultrafiltration membrane is coated with a polydopamine - zinc oxide coating, and the anti - fouling performance is improved by 30%. Clear water and coagulation - flocculation bodies are separated;

[0088] S4. Recover the coagulation - flocculation magnetic particles in the coagulation - flocculation bodies. Adopt a multi - stage gradient magnetic field screening technology. Through a four - stage gradient magnetic field (0.2 T → 0.5 T → 0.8 T → 1.0 T), gradually screen and purify the coagulation - flocculation magnetic particles in the coagulation - flocculation bodies; the remaining sludge enters the sludge transfer tank for treatment to obtain phosphate fertilizer;

[0089] S5. The clean water is concentrated through membrane treatment using a forward-flow membrane module and a polyimide-carbon nanotube composite membrane. This increases the flux by 20%, resulting in fresh water and concentrated water. The fresh water is reused in the production workshop, while the concentrated water enters an evaporation unit. The evaporation unit combines multiple-effect evaporation (MEE) with MVR, reducing energy consumption by 35%. The resulting ammonium sulfate byproduct has a purity of 99.6%.

[0090] The treatment effects of this embodiment are: COD is reduced to 48 mg / L, pretreatment time is shortened to 12 minutes, metal ion removal rate is increased to 99.8%, and system operation stability reaches 85%.

[0091] Example 4

[0092] This embodiment provides a method for treating wastewater using a magnetic coagulation process, comprising the following steps:

[0093] S1. A 20% ammonia solution and a 98% polyepichlorohydrin-dimethylamine solution were mixed in a volume ratio of 27:1 by ultrasonic emulsification to form a stable emulsion with a nanoscale microstructure, which was added to the iron phosphate wastewater and the pH value of the wastewater was adjusted to 8.7 to obtain pretreated wastewater;

[0094] S2. Polymerized magnetic particles were added to the pretreated wastewater for magnetic condensation treatment; the core of the polymerized magnetic particles was ferroferric oxide, the outer layer was coated with silica, and the silica surface was grafted with a bifunctional crown ether molecule by a silane coupling agent to enhance selectivity. The alternating magnetic field rotation speed was 60 rpm.

[0095] S3. The wastewater after magnetic coagulation treatment is subjected to solid-liquid separation. The ultrastrong magnetic field generated by the superconducting magnetic separation-ultrafiltration coupling device is used to rapidly adsorb the magnetized coagulation product to the magnet surface, achieving initial solid-liquid separation. The liquid after the initial separation is then subjected to a secondary filtration through an ultrafiltration membrane. The ultrafiltration membrane adopts a hollow fiber-flat plate composite structure and is coated with a polydopamine-silver nanoparticle composite coating with a compressive strength increased to 0.5 MPa. The resulting purified water and coagulation product are separated.

[0096] S4. The polymerized condensate magnetic particles in the polymerized condensate are recovered and processed using a multi-stage gradient magnetic field screening technology. The polymerized condensate magnetic particles in the polymerized condensate are gradually screened and purified by a four-stage gradient magnetic field (0.3T→0.6T→0.9T→1.2T); the remaining sludge enters the sludge transfer tank for treatment to obtain phosphate fertilizer;

[0097] S5 membrane-concentrates fresh water. The membrane concentration module integrates an in-line cleaning system, extending the cycle to 72 hours; fresh water and concentrated water are obtained. The fresh water is recycled to the production workshop, and the concentrated water enters the MVR evaporation device, which is processed using a multi-stage evaporation structure combining a high-efficiency falling-film evaporator and a forced-circulation evaporator. The concentrated water reflux rate is reduced by 15%, and the ammonium sulfate purity reaches 99.7%.

[0098] The treatment effect of this example is as follows: the COD is reduced to 51 mg / L, the pretreatment time is shortened to 13 minutes, the fresh water recovery rate is 95%, and the comprehensive cost is reduced by 40%.

[0099] Comparative Example 1

[0100] This comparative example provides a traditional method for treating iron phosphate wastewater, including the following steps:

[0101] S1. Alkaline solution adjustment: Only 20% ammonia water is used to adjust the pH value of the wastewater to 9.0, and no PEI is added;

[0102] S2. Precipitation treatment: The traditional gravity precipitation method is used, and a flocculant is added for flocculation precipitation, with a reaction time of 40 minutes.

[0103] Treatment effect: The COD of the effluent is 120 mg / L, the metal ion removal rate is less than 70%, and the sludge production increases by 30%.

[0104] Conclusion: The lack of a composite alkaline solution results in insufficient complexing ability, exceeding the COD standard. The dosage of the flocculant needs to be increased by 2 times compared with the traditional method to achieve the flocculation effect of Example 1, and the treatment efficiency is low.

[0105] Comparative Example 2

[0106] This comparative example provides a method for treating iron phosphate wastewater using non-core-shell-structured magnetic particles. Compared with Example 1, the only difference is that pure Fe3O4 magnetic particles are used without SiO2 coating, and the magnetic field strength is 1.0 T.

[0107] Treatment effect: The magnetic particles agglomerate severely, the recovery rate is only 75%, and the turbidity of the effluent exceeds the standard (>10 NTU).

[0108] Conclusion: The lack of shell protection leads to poor stability of the magnetic particles and a significant decrease in separation efficiency.

[0109] Comparative Example 3

[0110] This comparative example provides a method for treating iron phosphate wastewater using a static magnetic field. Compared with Example 1, the only difference is that a static magnetic field (0.8 T) is used to replace the alternating rotating magnetic field, and the formation time of the coagulation aggregate is extended to 1 hour.

[0111] Treatment effect: The ultrafiltration membrane flux decreases by 40%, and the system energy consumption increases by 25%.

[0112] Conclusion: Dynamic magnetic field regulation is crucial for accelerating flocculation, while the static field is inefficient.

[0113] The purity of ammonium sulfate prepared in each of the above examples and comparative examples was detected respectively, and the results are shown in Table 1; the removal effects of metal ions and COD in the iron phosphate wastewater are shown in Table 2.

[0114] Table 1 Purity of Ammonium Sulfate

[0115] Group Purity Example 1 99.5％ Example 2 99.2％ Example 3 99.6％ Example 4 99.7％ Comparative Example 1 97.5％ Comparative Example 2 97.8％ Comparative Example 3 98.2％

[0116] Table 2 Treatment Effect of Iron Phosphate Wastewater

[0117]

[0118]

[0119] It can be seen from Table 1 to Table 2 that the method and system for treating wastewater by the magnetic coagulation and separation process provided in this application can efficiently remove metal ions and various pollutants in wastewater by integrating magnetic coagulation and separation technology, superconducting magnetic separation-ultrafiltration coupling technology, and magnetic particle recovery system. In Example 1, the effluent COD was reduced to less than 50 mg / L, meeting the strict reuse standard; in Example 3, the metal ion removal rate was increased to 99.8%, indicating that the magnetic coagulation and separation process has significant advantages in removing COD and metal ions, far higher than the effects of traditional treatment methods. In the traditional coagulation and sedimentation technology, the flocculation reaction time is relatively long. In this application, through the alternating rotating magnetic field and superconducting magnetic separation-ultrafiltration coupling technology, the treatment time is significantly shortened and the treatment efficiency is improved.

[0120] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same effect as the technical idea within the technical solution scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various deformations that those skilled in the art can think of for the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for treating wastewater by a magnetic coagulation process, characterized in that, It includes the following steps: Adding a composite alkali solution to the iron phosphate wastewater to adjust the pH value of the wastewater to a predetermined range to obtain pretreated wastewater; Adding coagulation magnetic particles to the pretreated wastewater for magnetic coagulation treatment; Performing solid-liquid separation on the wastewater after magnetic coagulation treatment to obtain clear water and coagulation bodies; Recycling the coagulation magnetic particles in the coagulation bodies; Performing membrane concentration treatment on the clear water to obtain fresh water and concentrated water, recycling the fresh water, and performing evaporation concentration on the concentrated water to obtain ammonium sulfate by-products.

2. The method for treating wastewater by the magnetic coagulation separation process according to claim 1, characterized in that The composite alkali solution is composed of ammonia water and polyepichlorohydrin-dimethylamine; and / or The concentration of the ammonia water is 20-22%, and the concentration of the polyepichlorohydrin-dimethylamine is 98-99%; and / or The volume ratio of the ammonia water to the polyepichlorohydrin-dimethylamine is 25:1-30:1; and / or The predetermined range of the pH value is 8-9.

3. The method for treating wastewater by the magnetic coagulation process according to claim 1, characterized in that, The coagulation magnetic particles have a core-shell structure, with the inner core being magnetite and the shell layer being silica or iron oxide.

4. The method for treating wastewater by the magnetic coagulation and condensation process according to claim 3, characterized in that, The surface of the shell layer is grafted with functionalized functional groups, and the functionalized functional groups are one or more of quaternary ammonium salt groups, crown ether molecules, sulfonic acid groups, and carboxylic acid groups.

5. The method for treating wastewater by the magnetic coagulation separation process according to claim 1, wherein The solid-liquid separation includes superconducting magnetic separation and ultrafiltration membrane filtration.

6. The method for treating wastewater by the magnetic coagulation and condensation process according to claim 5, characterized in that, The surface of the ultrafiltration membrane is coated with a polydopamine-silver nanoparticle composite coating or a polydopamine-zinc oxide composite coating; and / or The ultrafiltration membrane has a hollow fiber-flat composite structure.

7. The method for treating wastewater by the magnetic coagulation and condensation process according to claim 1, characterized in that, Recycling the coagulation magnetic particles by using a multi-stage gradient magnetic field screening technique.

8. The method for treating wastewater by the magnetic coagulation process according to claim 1, characterized in that, The membrane material for the membrane concentration treatment is one of a polyimide-graphene composite membrane, a polysulfone-graphene composite membrane, and a polyimide-carbon nanotube composite membrane.

9. A system for treating wastewater by a magnetic coagulation and condensation process, which uses the method for treating iron phosphate wastewater by the magnetic coagulation and condensation process described in any one of claims 1 to 8 above, is characterized in that, It includes a wastewater pretreatment device, a magnetic coagulation device, a superconducting magnetic separation-ultrafiltration coupling device, a membrane concentration device, and an evaporation device connected in sequence; The magnetic coagulation device includes a magnetic field generating device, and the magnetic field is an alternating rotating magnetic field or a pulsed magnetic field; and / or The membrane concentration device includes a reverse flow membrane module or a forward flow membrane module; and / or The evaporation device includes a falling film evaporator and a forced circulation evaporator.

10. The system for treating wastewater by the magnetic coagulation process according to claim 9, characterized in that, It further includes a coagulation magnetic particle recycling device connected to the superconducting magnetic separation-ultrafiltration coupling device; and / or The system further includes an on-line cleaning system connected to the membrane concentration device.

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