A method for resourceful treatment of iron phosphate acid mother liquor wastewater

Abstract

This invention discloses a resource-based treatment method for acidic mother liquor wastewater from ferric phosphate, relating to the field of wastewater treatment technology. The specific process is as follows: the wastewater is pretreated with a ceramic membrane and then cooled using a heat exchanger; subsequently, it enters a primary acid membrane system for concentration under acidic conditions, with the concentrated water used to produce ammonium sulfate and ammonium phosphate; the primary permeate enters a secondary acid membrane system for deep purification, with the permeate reused and the concentrated water recycled. In this invention, the primary acid membrane is a polysulfonamide composite nanofiltration membrane prepared by interfacial polymerization, and the secondary acid membrane is a polyurea nanofiltration membrane prepared by interfacial polymerization with the addition of surfactants and catalysts. This method does not require pH adjustment and operates directly under strongly acidic conditions, achieving efficient separation, concentration, and resource recovery of sulfate and phosphate ions in the wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a method for the resource-based treatment of acidic mother liquor wastewater containing iron phosphate. Background Technology

[0002] Currently, with the rapid development of the new energy vehicle industry, lithium iron phosphate batteries have become one of the mainstream choices in the power battery field due to their advantages such as high safety, long cycle life, and relatively low cost. As a key cathode material for lithium iron phosphate batteries, the production process generates a large amount of acidic mother liquor wastewater. This wastewater is characterized by strong acidity, high sulfate and phosphate content, a variety of heavy metal ions, and complex pollutant composition. If discharged directly without proper treatment, it will cause serious pollution to water bodies and soil, and also result in resource waste.

[0003] Currently, some technologies have been explored for the treatment of ferric phosphate mother liquor wastewater. For example, some existing technologies use chemical precipitation combined with multi-stage filtration processes, adjusting the pH value by adding neutralizing agents, and then removing pollutants through sedimentation and filtration. However, these methods require large amounts of reagents, have high operating costs, and generate a large amount of chemical sludge, increasing the difficulty of subsequent disposal and environmental impact. Another technology uses a combination of ultrafiltration and reverse osmosis, but due to the high acidity and salt content of the mother liquor, the reverse osmosis membrane is prone to fouling and corrosion, resulting in poor system stability, and the effluent quality is difficult to meet reuse requirements, limiting resource recovery efficiency.

[0004] To address the aforementioned problems, this invention provides a method for the resource-based treatment of acidic mother liquor wastewater containing ferric phosphate. Summary of the Invention

[0005] The purpose of this invention is to provide a resource-based treatment method for acidic mother liquor wastewater of iron phosphate, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for resource-based treatment of acidic mother liquor wastewater containing ferric phosphate includes the following steps: Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger, control the outlet water temperature, and obtain the heat exchanger outlet water; Step 3: Introduce the heat exchanger effluent into the primary acid membrane system, select a polysulfonamide composite nanofiltration membrane as the primary acid membrane, and separate and concentrate it under acidic conditions to obtain the primary acid membrane permeate and the primary acid membrane concentrate; neutralize the primary acid membrane concentrate with ammonia water and then introduce it into the evaporation system; Step 4: Introduce the primary acid membrane permeate into the secondary acid membrane system, select a polyurea nanofiltration membrane as the secondary acid membrane, and perform secondary purification under acidic conditions to obtain secondary acid membrane concentrate; the secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to obtain secondary acid membrane permeate.

[0007] Furthermore, in step three, the preparation process of the primary acid membrane is as follows: using a polysulfone ultrafiltration membrane as the base membrane, immerse the base membrane in a polyethyleneimine aqueous solution for 2-4 minutes, then discard and dry it. Add a hexane solution of 1,3-benzenedisulfonyl chloride to the membrane surface, react for 20-30 seconds, then discard and dry it. Add a hexane solution of terephthalic acid to the membrane surface, continue the reaction for 20-30 seconds, discard the solution, and then dry and heat-treat at 60-80℃ for 2-5 minutes to obtain a polysulfonamide composite nanofiltration membrane as the primary acid membrane.

[0008] Furthermore, in step four, the preparation process of the secondary acid membrane is as follows: using a polysulfone ultrafiltration membrane as the base membrane, the base membrane is fixed, pretreated with sodium dodecylbenzenesulfonate aqueous solution for 2-4 min, then discarded, soaked in polyethyleneimine and polyvinylpyrrolidone aqueous solution for 2-4 min, then discarded and dried; a hexane solution of terephthalic diisocyanate and catalyst is added dropwise to the membrane surface, reacted for 50-60 s, then discarded, and dried and heat-treated at 60-80℃ for 5-10 min to obtain a polyurea nanofiltration membrane as the secondary acid membrane.

[0009] Furthermore, in step two, the outlet water temperature ranges from 45 to 50°C.

[0010] Furthermore, in step three, the acidic conditions are specifically pH = 1.2-1.5.

[0011] Furthermore, the concentration of the polyethyleneimine aqueous solution is 1wt%-2wt%, the concentration of the n-hexane solution of 1,3-benzene disulfonyl chloride is 0.05wt%-0.075wt%, and the concentration of the n-hexane solution of terephthalic acid is 0.05wt%-0.075wt%.

[0012] Furthermore, the concentration of the sodium dodecylbenzenesulfonate aqueous solution is 0.1wt%-0.15wt%.

[0013] Furthermore, the aqueous solution of polyethyleneimine and polyvinylpyrrolidone comprises the following components, by mass percentage: 0.3wt%-0.4wt% polyethyleneimine, 0.1wt%-0.5wt% polyvinylpyrrolidone, and the balance being deionized water.

[0014] Furthermore, the hexane solution of terephthalic diisocyanate and catalyst comprises the following components: 0.1wt%-0.2wt% terephthalic diisocyanate, 0.1wt%-0.2wt% catalyst, and the balance being hexane.

[0015] Furthermore, the thickness of the polysulfone ultrafiltration membrane is 0.01-0.03 mm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a resource-based treatment scheme for ferric phosphate mother liquor wastewater. The scheme employs a ceramic membrane for pretreatment and utilizes an acid-resistant membrane system for wastewater concentration and separation. The entire process requires no chemical additives, significantly reducing operating costs. The system's permeate can be directly reused in the ferric phosphate synthesis process, achieving water resource recycling; simultaneously, the primary concentrate, through neutralization with ammonia water and evaporation, can be crystallized to recover economically valuable ammonium sulfate and ammonium phosphate solid products. This invention offers significant economic and environmental benefits, providing an effective pathway for the zero-discharge resource-based treatment of ferric phosphate mother liquor wastewater.

[0017] 2. By introducing terephthalic acid copolymerization into the primary acid membrane, a highly cross-linked and dense separation layer is constructed, improving concentration efficiency and pressure resistance. A polysulfonamide composite membrane is used in the primary unit, which undergoes interfacial polymerization with 1,3-benzenedisulfonyl chloride and terephthalic acid sequentially. The highly reactive terephthalic acid, as a comonomer, can form a polymer network with a higher degree of cross-linking with polyethyleneimine. This dense structure increases the membrane's rejection rate of divalent salts such as magnesium sulfate, ensuring the high efficiency of primary concentration.

[0018] 3. A polyurea membrane is used in the secondary acid membrane, which is prepared by interfacial polymerization of terephthalic diisocyanate and polyethyleneimine. The urea bonds (-NH-CO-NH-) generated by the reaction of terephthalic diisocyanate and polyethyleneimine can form extensive intermolecular hydrogen bonds, forming a dense physical cross-linked network. This solves the core problem of performance degradation of traditional polyamide membranes due to amide bond hydrolysis in strong acid environments, and ensures the long-term stability of the system's produced water quality.

[0019] 4. Simultaneously, by synergistically adding sodium dodecylbenzenesulfonate and pyridine in the secondary membrane preparation, the morphology and hydrophilicity of the separation layer were optimized, achieving high throughput and low energy consumption. In the polyurea membrane preparation process, the anionic surfactant sodium dodecylbenzenesulfonate was added during the bottom membrane pretreatment stage, and the catalyst pyridine was added to the organic phase. Sodium dodecylbenzenesulfonate reduced interfacial tension, promoting the uniform diffusion of the aqueous monomer polyethyleneimine to the reaction interface; pyridine catalyzed the reaction between isocyanate and amine, improving polymerization efficiency and crosslinking degree. This resulted in a thinner, more complete, and more hydrophilic separation layer. Furthermore, the addition of polyvinylpyrrolidone further optimized the hydrophilicity, also helping to reduce membrane fouling and further facilitating separation. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, and all described quantities are by weight. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The sources and types of substances involved in this invention are not specifically limited. Exemplary examples include the following raw materials: Polyethyleneimine: PEI-600, molecular weight: 600, available from Shanghai Aladdin Biochemical Technology Co., Ltd.; Catalyst: Pyridine: Product No.: P816288, purity: 99.5%, available from Shanghai Maclean Biochemical Technology Co., Ltd.; Polysulfone ultrafiltration membrane: Base membrane: thickness: 0.01mm, model: SFP2660, available from Shenzhen Shengda Environmental Protection Equipment Co., Ltd.; Ceramic membrane: Model: CRM-UF ceramic ultrafiltration membrane, thickness: 50nm, available from Nanjing Titanium Clean Fluid Technology Co., Ltd.

[0022] Example 1:

[0023] Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger and control the outlet water temperature at 45℃ to obtain the heat exchanger outlet water; Step 3: The heat exchanger outlet water is fed into the primary acid membrane system for separation and concentration under acidic conditions with a pH of 1.2 to obtain primary acid membrane permeate and primary acid membrane concentrate; the primary acid membrane concentrate is neutralized with ammonia water and then fed into the evaporation system for further use in production. Step 4: The permeate from the primary acid membrane is fed into the secondary acid membrane system for secondary purification under acidic conditions (pH 1.2) to obtain secondary acid membrane concentrate. This secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to further avoid wasting sulfate ions, yielding secondary acid membrane permeate. The preparation of the primary and secondary acid membranes is as follows: Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and soaked in a 1 wt% aqueous solution of polyethyleneimine for 2 min, then the solution was discarded and dried. Subsequently, a 0.05 wt% hexane solution of 1,3-benzenedisulfonyl chloride was added dropwise to the membrane surface, and the reaction was carried out for 20 s, then the solution was discarded and dried. A 0.05 wt% hexane solution of terephthalic acid was added dropwise to the membrane surface, and the reaction was continued for 20 s, then the solution was dried. After discarding the organic phase, the membrane was placed in a 60℃ forced-air drying oven for 2 min for heat treatment to obtain a polysulfonamide composite nanofiltration membrane as a primary acid membrane. Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame. It was first pretreated with a 0.1 wt% sodium dodecylbenzenesulfonate aqueous solution for 2 min. After discarding the pretreatment solution, it was soaked in a 3 wt% polyethyleneimine and 0.1 wt% polyvinylpyrrolidone aqueous solution for 2 min, then discarded and dried. Subsequently, a hexane solution containing 0.1 wt% terephthalic diisocyanate and 0.1 wt% pyridine catalyst was added dropwise to the membrane surface. The reaction was carried out for 50 s, then discarded. The membrane was then heat-treated in a 60℃ forced-air drying oven for 5 min to obtain a polyurea nanofiltration membrane as a secondary acid membrane.

[0024] Example 2:

[0025] Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger and control the outlet water temperature at 48℃ to obtain the heat exchanger outlet water; Step 3: The heat exchanger outlet water is fed into the primary acid membrane system and separated and concentrated under acidic conditions with a pH of 1.4 to obtain the primary acid membrane permeate and the primary acid membrane concentrate; the primary acid membrane concentrate is neutralized with ammonia water and then fed into the evaporation system for further use in production. Step 4: The permeate from the primary acid membrane is fed into the secondary acid membrane system for secondary purification under acidic conditions (pH 1.4) to obtain secondary acid membrane concentrate. This secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to further avoid wasting sulfate ions, yielding secondary acid membrane permeate. The preparation of the primary and secondary acid membranes is as follows: Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and soaked in a 1.5 wt% polyethyleneimine aqueous solution for 3 min, then the solution was discarded and dried. Subsequently, a 0.06 wt% hexane solution of 1,3-benzenedisulfonyl chloride was added dropwise to the membrane surface, and the solution was discarded after reacting for 25 s. The solution was then dried, and a 0.06 wt% hexane solution of terephthalic acid was added dropwise to the membrane surface. The reaction was continued for 25 s, and the solution was dried. After discarding the organic phase, the membrane was placed in a 70℃ forced-air drying oven for 3 min to obtain a polysulfonamide composite nanofiltration membrane as a primary acid membrane. Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and pretreated with a 0.12 wt% sodium dodecylbenzenesulfonate aqueous solution for 3 min. After discarding the pretreatment solution, an aqueous solution of 0.35 wt% polyethyleneimine and 0.3 wt% polyvinylpyrrolidone was added to the membrane surface and soaked for 3 min. The solution was then discarded and the membrane was dried. Subsequently, a hexane solution containing 0.15 wt% terephthalic diisocyanate and 0.15 wt% pyridine catalyst was added to the membrane surface and reacted for 55 s. The solution was then discarded, and the membrane was heat-treated in a 70℃ forced-air drying oven for 8 min to obtain a polyurea nanofiltration membrane as a secondary acid membrane.

[0026] Example 3:

[0027] Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger and control the outlet water temperature at 50℃ to obtain the heat exchanger outlet water; Step 3: The heat exchanger outlet water is fed into the primary acid membrane system and separated and concentrated under acidic conditions with a pH of 1.5 to obtain the primary acid membrane permeate and the primary acid membrane concentrate; the primary acid membrane concentrate is neutralized with ammonia water and then fed into the evaporation system for further use in production. Step 4: The permeate from the primary acid membrane is fed into the secondary acid membrane system for secondary purification under acidic conditions (pH 1.5) to obtain secondary acid membrane concentrate. This secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to further avoid wasting sulfate ions, yielding secondary acid membrane permeate. The preparation of the primary and secondary acid membranes is as follows: Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and soaked in a 2 wt% aqueous solution of polyethyleneimine for 4 min, then the solution was discarded and dried. Subsequently, a 0.075 wt% hexane solution of 1,3-benzenedisulfonyl chloride was added dropwise to the membrane surface, and the reaction was carried out for 30 s, then the solution was discarded and dried. A 0.075 wt% hexane solution of terephthalic acid was added dropwise to the membrane surface, and the reaction was continued for 30 s, then the solution was dried. After discarding the organic phase, the membrane was placed in an 80℃ forced-air drying oven for 5 min for heat treatment to obtain a polysulfonamide composite nanofiltration membrane as a primary acid membrane. Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and pretreated with a 0.15 wt% sodium dodecylbenzenesulfonate aqueous solution for 4 min. After discarding the pretreatment solution, an aqueous solution of 0.4 wt% polyethyleneimine and 0.5 wt% polyvinylpyrrolidone was added to the membrane surface and soaked for 4 min. The solution was then discarded and the membrane was dried. Subsequently, a hexane solution containing 0.2 wt% terephthalic diisocyanate and 0.2 wt% pyridine catalyst was added to the membrane surface and reacted for 60 s. The solution was then discarded, and the membrane was heat-treated in an 80℃ forced-air drying oven for 10 min to obtain a polyurea nanofiltration membrane as a secondary acid membrane.

[0028] Comparative Example 1: No polyvinylpyrrolidone was added to the secondary acid membrane; all other aspects were the same as in Example 1. Specifically: Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger and control the outlet water temperature at 45℃ to obtain the heat exchanger outlet water; Step 3: The heat exchanger outlet water is fed into the primary acid membrane system for separation and concentration under acidic conditions with a pH of 1.2 to obtain primary acid membrane permeate and primary acid membrane concentrate; the primary acid membrane concentrate is neutralized with ammonia water and then fed into the evaporation system for further use in production. Step 4: The permeate from the primary acid membrane is fed into the secondary acid membrane system for secondary purification under acidic conditions (pH 1.2) to obtain secondary acid membrane concentrate. This secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to further avoid wasting sulfate ions, yielding secondary acid membrane permeate. The preparation of the primary and secondary acid membranes is as follows: Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and soaked in a 1 wt% aqueous solution of polyethyleneimine for 2 min, then the solution was discarded and dried. Subsequently, a 0.05 wt% hexane solution of 1,3-benzenedisulfonyl chloride was added dropwise to the membrane surface, and the reaction was carried out for 20 s, then the solution was discarded and dried. A 0.05 wt% hexane solution of terephthalic acid was added dropwise to the membrane surface, and the reaction was continued for 20 s, then the solution was dried. After discarding the organic phase, the membrane was placed in a 60℃ forced-air drying oven for 2 min for heat treatment to obtain a polysulfonamide composite nanofiltration membrane as a primary acid membrane. Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame. It was first pretreated with a 0.1 wt% sodium dodecylbenzenesulfonate aqueous solution for 2 min. After discarding the pretreatment solution, a 0.3 wt% polyethyleneimine aqueous solution was added to the membrane surface and soaked for 2 min. The solution was then discarded and dried. Subsequently, a hexane solution containing 0.1 wt% terephthalic diisocyanate and 0.1 wt% pyridine catalyst was added to the membrane surface and reacted for 50 s. The solution was then discarded, and the membrane was heat-treated in a 60℃ forced-air drying oven for 5 min to obtain a polyurea nanofiltration membrane as a secondary acid membrane.

[0029] Comparative Example 2: Pyridine catalyst was not added to the secondary acid membrane; otherwise, it was the same as in Example 1. Specifically: Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger and control the outlet water temperature at 45℃ to obtain the heat exchanger outlet water; Step 3: The heat exchanger outlet water is fed into the primary acid membrane system for separation and concentration under acidic conditions with a pH of 1.2 to obtain primary acid membrane permeate and primary acid membrane concentrate; the primary acid membrane concentrate is neutralized with ammonia water and then fed into the evaporation system for further use in production. Step 4: The permeate from the primary acid membrane is fed into the secondary acid membrane system for secondary purification under acidic conditions (pH 1.2) to obtain secondary acid membrane concentrate. This secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to further avoid wasting sulfate ions, yielding secondary acid membrane permeate. The preparation of the primary and secondary acid membranes is as follows: Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame and soaked in a 1 wt% aqueous solution of polyethyleneimine for 2 min, then the solution was discarded and dried. Subsequently, a 0.05 wt% hexane solution of 1,3-benzenedisulfonyl chloride was added dropwise to the membrane surface, and the reaction was carried out for 20 s, then the solution was discarded and dried. A 0.05 wt% hexane solution of terephthalic acid was added dropwise to the membrane surface, and the reaction was continued for 20 s, then the solution was dried. After discarding the organic phase, the membrane was placed in a 60℃ forced-air drying oven for 2 min for heat treatment to obtain a polysulfonamide composite nanofiltration membrane as a primary acid membrane. Using a polysulfone ultrafiltration membrane as the substrate, the substrate membrane was fixed in a plate frame. It was first pretreated with a 0.1 wt% sodium dodecylbenzenesulfonate aqueous solution for 2 min. After discarding the pretreatment solution, it was soaked in a 3 wt% polyethyleneimine and 0.1 wt% polyvinylpyrrolidone aqueous solution for 2 min, then discarded and dried. Subsequently, a hexane solution containing 0.1 wt% terephthalic diisocyanate was added dropwise to the membrane surface, reacted for 50 s, discarded, and the membrane was placed in a 60℃ forced-air drying oven for 5 min for heat treatment to obtain a polyurea nanofiltration membrane as a secondary acid membrane.

[0030] Comparative Example 3: The polysulfone ultrafiltration membrane at the bottom was not modified; it was directly used for the primary and secondary acid membranes, and the rest was the same as in Example 1; specifically: Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger and control the outlet water temperature at 45℃ to obtain the heat exchanger outlet water; Step 3: The heat exchanger outlet water is fed into the primary acid membrane system for separation and concentration under acidic conditions with a pH of 1.2 to obtain primary acid membrane permeate and primary acid membrane concentrate; the primary acid membrane concentrate is neutralized with ammonia water and then fed into the evaporation system for further use in production. Step 4: The permeate from the primary acid membrane is fed into the secondary acid membrane system for secondary purification under acidic conditions with a pH of 1.2 to obtain secondary acid membrane concentrate. The secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to further avoid the waste of sulfate ions and obtain secondary acid membrane permeate. Polysulfone ultrafiltration membranes are used for both the primary and secondary acid membranes.

[0031] Experiment: The heat exchanger effluent, primary acid membrane concentrate, and secondary acid membrane permeate obtained from Examples 1-3 and Comparative Examples 1-3 were tested for their performance indicators; the data obtained are shown in Table 1 below:

[0032] Conclusion: The data above show that the resource-based treatment method for ferric phosphate mother liquor wastewater provided by this invention can achieve a sulfate concentration of more than 5 times through the primary acid membrane, with a concentrated water concentration exceeding 90,000 mg / L, which can be used for recycling; the sulfate concentration in the secondary acid membrane product water is less than 150 mg / L. In summary, this invention successfully achieves efficient concentration, deep purification, and resource recycling of ferric phosphate mother liquor wastewater under extremely acidic conditions.

[0033] Comparative Example 1 did not add polyvinylpyrrolidone to the secondary acid membrane. This membrane lacked the enhanced hydrophilicity and optimized pore structure provided by polyvinylpyrrolidone. Compared to Example 1, the permeation flux of the secondary acid membrane was significantly reduced, indicating that the addition of polyvinylpyrrolidone can significantly improve the hydrophilicity and permeation efficiency of the polyurea nanofiltration membrane. Comparative Example 2 did not add pyridine catalyst during the preparation of the secondary acid membrane. Under these conditions, a complete and dense polyurea separation layer could not be formed. Compared to Example 1, the absorption rate of sulfate, phosphate, and ferrous ions by the secondary acid membrane decreased sharply, resulting in severely substandard product water quality. This indicates that pyridine catalyst plays a crucial role in ensuring the degree of interfacial polymerization. Comparative Example 3 did not construct an acid-resistant nanofiltration separation layer but directly used a polysulfone ultrafiltration membrane. This membrane lacked ion-level sieving capability, and compared to Example 1, the system's primary concentration and secondary purification functions were poor.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for the resource-based treatment of acidic mother liquor wastewater containing ferric phosphate, characterized in that: Includes the following steps: Step 1: Take the ferric phosphate mother liquor wastewater to be treated and put it into the ceramic membrane system for pretreatment by ceramic membrane filtration to obtain ceramic membrane effluent; Step 2: Introduce the ceramic membrane outlet water into the plate heat exchanger, control the outlet water temperature, and obtain the heat exchanger outlet water; Step 3: Introduce the heat exchanger effluent into the primary acid membrane system, select a polysulfonamide composite nanofiltration membrane as the primary acid membrane, and separate and concentrate it under acidic conditions to obtain the primary acid membrane permeate and the primary acid membrane concentrate; neutralize the primary acid membrane concentrate with ammonia water and then introduce it into the evaporation system; Step 4: Introduce the primary acid membrane permeate into the secondary acid membrane system, select a polyurea nanofiltration membrane as the secondary acid membrane, and perform secondary purification under acidic conditions to obtain secondary acid membrane concentrate; the secondary acid membrane concentrate is then fed back into the primary acid membrane inlet to obtain secondary acid membrane permeate.

2. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 1, characterized in that: In step three, the preparation process of the primary acid membrane is as follows: using a polysulfone ultrafiltration membrane as the base membrane, the base membrane is soaked in a polyethyleneimine aqueous solution for 2-4 minutes, then discarded and dried. A hexane solution of 1,3-benzenedisulfonyl chloride is added dropwise to the membrane surface, and after reacting for 20-30 seconds, it is discarded and dried. A hexane solution of terephthalic acid is added dropwise to the membrane surface, and the reaction continues for 20-30 seconds. After discarding, the membrane is dried and heat-treated at 60-80℃ for 2-5 minutes to obtain a polysulfonamide composite nanofiltration membrane as the primary acid membrane.

3. The resource-based treatment method for acidic mother liquor wastewater of ferric phosphate according to claim 1, characterized in that: In step four, the preparation process of the secondary acid membrane is as follows: using a polysulfone ultrafiltration membrane as the base membrane, the base membrane is fixed, pretreated with sodium dodecylbenzenesulfonate aqueous solution for 2-4 min, then discarded, soaked in polyethyleneimine and polyvinylpyrrolidone aqueous solution for 2-4 min, then discarded and dried; a hexane solution of terephthalic diisocyanate and catalyst is added dropwise to the membrane surface, reacted for 50-60 s, then discarded, and dried and heat-treated at 60-80℃ for 5-10 min to obtain a polyurea nanofiltration membrane as the secondary acid membrane.

4. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 1, characterized in that: In step two, the outlet water temperature ranges from 45 to 50°C.

5. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 1, characterized in that: In step three, the acidic conditions are specifically pH = 1.2-1.

5.

6. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 2, characterized in that: The concentration of the polyethyleneimine aqueous solution is 1wt%-2wt%, the concentration of the 1,3-benzenesulfonyl chloride n-hexane solution is 0.05wt%-0.075wt%, and the concentration of the terephthalic acid n-hexane solution is 0.05wt%-0.075wt%.

7. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 3, characterized in that: The concentration of the sodium dodecylbenzenesulfonate aqueous solution is 0.1wt%-0.15wt%.

8. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 3, characterized in that: The aqueous solution of polyethyleneimine and polyvinylpyrrolidone comprises the following components, by mass percentage: 0.3wt%-0.4wt% polyethyleneimine, 0.1wt%-0.5wt% polyvinylpyrrolidone, and the balance being deionized water.

9. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 3, characterized in that: The n-hexane solution of terephthalic diisocyanate and catalyst comprises the following components: 0.1wt%-0.2wt% terephthalic diisocyanate, 0.1wt%-0.2wt% catalyst, and the balance being n-hexane.

10. The method for resource-based treatment of acidic mother liquor wastewater of ferric phosphate according to claim 3, characterized in that: The thickness of the polysulfone ultrafiltration membrane is 0.01-0.03 mm.

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