Method and system for treating and recycling phosphorus resources from iron phosphate wastewater evaporation tail liquid

Abstract

The application provides a method and system for treating iron phosphate wastewater evaporation tail liquid and recycling phosphorus resources, and belongs to the field of wastewater treatment. The method comprises the following steps: adding alkali liquor to the evaporation tail liquid for pretreatment, and then performing solid-liquid separation to obtain first clear liquid; adjusting the pH value of the first clear liquid to 7.5-8, adding aluminum salt solution, controlling the reaction pH value to 5.5-6.5, and then performing solid-liquid separation to obtain aluminum mud and second clear liquid; adjusting the pH value of the iron phosphate wastewater to 8.5-9, and then performing solid-liquid separation to obtain third clear liquid; adjusting the pH value of the third clear liquid to 9-10, adding aluminum mud, and then performing solid-liquid separation to obtain fourth clear liquid; adjusting the pH value of the fourth clear liquid to 6-7, and then performing solid-liquid separation to obtain fifth clear liquid; and finally, the fifth clear liquid enters a subsequent water treatment process. The application effectively removes pollutants and recycles phosphorus through multiple steps of pH adjustment and sedimentation separation, the aluminum mud is recycled to reduce costs and reduce secondary pollution, the phosphorus recycling improves the metal removal rate, and the fouling and pollution blocking problems of subsequent membrane treatment and evaporation processes are alleviated, thereby improving the evaporation efficiency.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method and system for treating the tail liquid of ferric phosphate wastewater evaporation and for the recycling of phosphorus resources. Background Technology

[0002] With the continuous expansion of lithium iron phosphate (LFP) production, a key material for new energy batteries, the production scale of its precursor, iron phosphate, is also increasing, leading to a corresponding increase in the total amount of wastewater generated. Currently, the common method for treating wastewater from iron phosphate production is to use reverse osmosis (RO) combined with an MVR evaporation system for wastewater purification and by-product salt recovery. Since the wastewater is rich in sulfate, phosphate, ammonium, and metal ions such as calcium, magnesium, manganese, and iron, and RO equipment has strict requirements for influent water quality, chemical precipitation is usually used in the pretreatment stage to reduce the content of metal elements and protect the RO membrane.

[0003] In the production of ferric phosphate using the ammonia process, the synthesis mother liquor and the aged mother liquor are often reused in stages to recover phosphate from the wastewater. However, this reuse process leads to a significant reduction in phosphate content, resulting in insufficient phosphate at the front end and a reduced metal ion removal rate. This causes scaling and fouling during the membrane concentration process at the back end. In addition, under conditions of high alkalinity and the presence of magnesium, manganese, calcium, and iron ions in the sedimentation tank, scaling is likely to occur in the pipelines and transfer pumps.

[0004] In a zero-emission treatment system using RO+MVR, the small amount of residual phosphate after pretreatment is concentrated dozens of times and recovered using a cooling crystallization method. However, the treatment effect on the generated tailings is not ideal: one method is to use a drum scraper dryer to evaporate it to obtain mixed salts, but this method is energy-intensive and the added value of the mixed salts is low, resulting in poor economic efficiency; another method is to directly recirculate the tailings to the system pretreatment recirculation, but the tailings contain high total dissolved solids (TDS), and recirculation will increase the TDS concentration of the influent to the pretreatment unit, thereby increasing the treatment load of the reverse osmosis equipment; or the tailings can be directly recirculated to the evaporation system for re-evaporation treatment, but this will cause impurities to continuously accumulate in the system, ultimately affecting the quality of the by-product ammonium salt product. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a method and system for treating the evaporation tail liquid of ferric phosphate wastewater and recycling phosphorus resources, aiming to solve the technical problems of high impurity element content, high treatment cost, and insufficient phosphorus source in wastewater pretreatment causing membrane equipment fouling and scaling of conveying pipelines and pumps during the concentration process.

[0006] In a first aspect, embodiments of this application provide a method for treating the tail liquid from the evaporation of ferric phosphate wastewater and for recycling phosphorus resources, comprising the following steps: Alkali solution was added to the evaporation tail liquid for pretreatment, and then the first clear liquid was obtained by solid-liquid separation. The pH of the first clear liquid was adjusted to 7.5-8, and an aluminum salt solution was added to control the reaction pH to 5.5-6.5. After solid-liquid separation, aluminum mud and a second clear liquid were obtained. The pH of the ferric phosphate wastewater was adjusted to 8.5-9, and after solid-liquid separation, a third clear liquid was obtained. The pH of the third clear liquid is adjusted to 9-10, and the aluminum mud is added. After solid-liquid separation, the fourth clear liquid is obtained. The pH of the fourth clear liquid was adjusted to 6-7, and the fifth clear liquid was obtained by solid-liquid separation; The fifth clear liquid enters the downstream water treatment process.

[0007] In the technical solution of this application embodiment, multiple pollutants in wastewater can be effectively removed and phosphorus can be recovered through multi-step pH adjustment and precipitation separation. The generated aluminum sludge is used as a precipitant for phosphorus recovery, realizing the resource utilization of aluminum sludge, avoiding secondary pollution, and reducing treatment costs. The extraction and reuse of phosphate ions supplements the pretreatment problem of insufficient phosphate content in the incoming water. At the same time, phosphorus reuse increases the precipitation removal rate of metal ions, alleviating the problems of fouling in the membrane equipment concentration process and scaling in pipelines and transfer pumps. The treatment of evaporation tail liquid reduces the content of impurity elements and phosphate in the tail liquid. The decrease in phosphate content leads to a decrease in the viscosity of the tail liquid, indirectly improving the evaporation efficiency of the tail liquid. Compared with directly reusing untreated evaporation tail liquid to wastewater pretreatment, this application avoids the increase in the treatment load of the membrane equipment caused by a large amount of TDS entrained in the tail liquid, ensuring that the TDS of the pretreated wastewater does not rise abnormally during the phosphorus reuse process, and ensuring the stable operation of the entire water treatment system.

[0008] In some embodiments, the alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide, and the pH value of the evaporation tail liquid is adjusted to 8.5-9.

[0009] In this embodiment, adjusting the pH value can ensure the full progress of the subsequent precipitation reaction and improve the solid-liquid separation effect. Under the condition of pH value of 8.5~9, the solubility of hydroxides of many metal ions is significantly reduced, and precipitation begins to form. At the same time, the treatment cost and operation convenience are optimized by selecting the type of alkali solution.

[0010] In some embodiments, the pH value of the aluminum salt solution is 2 to 3; and / or, the aluminum ion concentration in the aluminum salt solution is 2 to 4%.

[0011] In this embodiment, the aluminum salt can be completely dissolved under acidic conditions to form a homogeneous solution; the aluminum ion concentration range provides a sufficient amount of aluminum ions required for subsequent reactions, ensuring that sufficient aluminum phosphate precipitate can be generated with the first supernatant to effectively remove the target pollutant.

[0012] In some embodiments, the Al in the aluminum salt solution 3+ With the PO4 in the first clear liquid 3- The molar ratio is (2~3):1.

[0013] In this embodiment, an excess of Al is provided. 3+ This can ensure PO4 3- It can be fully and completely precipitated, maximizing phosphorus recovery and reducing phosphorus resource loss to subsequent processing steps.

[0014] In some embodiments, the aluminum salt in the aluminum salt solution is one or more of aluminum sulfate and aluminum chloride.

[0015] In this embodiment, aluminum sulfate or aluminum chloride can be selected as aluminum salts, which have the advantages of low cost, wide availability, good solubility, mature and reliable flocculation and sedimentation effect, and can generate aluminum mud products suitable for subsequent use.

[0016] In some embodiments, the molar ratio of phosphorus in the aluminum sludge to the total amount of magnesium and manganese in the third clear liquid is (2.2~3):1.

[0017] In this embodiment, aluminum ions in the aluminum sludge hydrolyze into AlO2 under alkaline conditions. - Or Al(OH)4 - The dissolution of aluminum sludge produces a large amount of hydrogen phosphate, which reacts with the remaining magnesium, manganese and other metal ions in the wastewater to form precipitates and be removed.

[0018] In some embodiments, the sludge obtained by solid-liquid separation of the fourth clear liquid is an aluminum salt precipitate, and the aluminum salt precipitate is used to prepare an aluminum salt solution for recycling through an aluminum salt compounding process.

[0019] In this embodiment, the recycling of aluminum salts helps reduce costs, decrease solid waste emissions, and improve overall treatment efficiency and economy.

[0020] Secondly, embodiments of this application provide a system for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources. The system uses the method described in the first aspect for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources to treat the ferric phosphate wastewater evaporation tail liquid. The system is characterized by comprising a tail liquid pretreatment device, a tail liquid phosphorus recovery device, a ferric phosphate wastewater pretreatment device, a neutralization tank, and a zero-discharge water treatment system connected in sequence.

[0021] In the technical solution of this application embodiment, each processing unit is connected in an orderly manner to form a continuous and automated processing flow. By optimizing the processing path, the material transfer and potential loss in the intermediate links are reduced, the overall processing efficiency and stability are improved, and the efficient recovery of phosphorus resources is realized. Furthermore, through collaborative processing and zero-emission design, the efficiency, economy and environmental friendliness of the entire wastewater treatment system are improved.

[0022] In some embodiments, the zero-discharge water treatment system includes a UF device, an NF device, an RO device, and an MVR device.

[0023] In this embodiment, efficient water purification and water resource recovery are achieved through multi-stage membrane treatment. The energy-saving advantages of MVR are utilized to treat the concentrate, ultimately maximizing the reuse of water resources and solidifying pollutants, achieving the goal of zero emissions with high efficiency, energy saving, and stable operation.

[0024] In some embodiments, the ferric phosphate wastewater pretreatment device includes a primary sedimentation tank and a secondary sedimentation tank.

[0025] In this embodiment, the synergistic effect of two-stage precipitation combined with aluminum sludge can more thoroughly remove phosphorus and various metal ions from wastewater, ensuring the pretreatment effect. Through staged treatment, the solid-liquid separation effect can be significantly improved, the concentration of suspended solids in the effluent can be reduced, providing favorable conditions for subsequent deep treatment and improving the stability and treatment efficiency of the entire wastewater treatment and resource recovery system.

[0026] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0028] Figure 1 This is a process flow diagram of the treatment of ferric phosphate wastewater evaporation tail liquid and phosphorus resource recycling in the embodiments of this application; Figure 2 This is a schematic diagram of aluminum salt compounding and recycling in the embodiments of this application. Detailed Implementation

[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0035] Existing technologies for treating ferric phosphate wastewater suffer from several drawbacks. Phosphate recycling leads to a decrease in pretreatment metal removal rates, easily causing scaling and fouling in subsequent membrane equipment and pipeline pumps. Furthermore, the evaporation tail liquid generated by RO+MVR zero-discharge systems is difficult to treat. Using a drum scraper dryer to evaporate it and obtain mixed salts is energy-intensive and yields low-value-added mixed salts, resulting in poor economic efficiency. Directly recirculating the tail liquid to the pretreatment system for recycling increases the TDS concentration in the pretreatment unit's feed water due to its high total dissolved solids (TDS), thus increasing the processing load on the reverse osmosis equipment. Alternatively, directly recirculating the tail liquid to the evaporation system for further evaporation leads to the continuous accumulation of impurities in the system, ultimately affecting the quality of the byproduct ammonium salt.

[0036] To address the technical problems of high impurity content, high treatment costs, and insufficient phosphorus source in the evaporation tail liquid of ferric phosphate wastewater, which leads to membrane equipment fouling and scaling in the conveying pipelines and pumps during the concentration process, this application provides a method and system for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources. Through multi-step pH adjustment and precipitation separation, pollutants are effectively removed and phosphorus is recovered. Aluminum sludge recycling reduces costs and secondary pollution. Phosphorus recovery improves metal removal rate, alleviates scaling and fouling problems in subsequent membrane treatment and evaporation processes, and improves evaporation efficiency.

[0037] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for treating the tail liquid from the evaporation of ferric phosphate wastewater and for recycling phosphorus resources, comprising the following steps: Alkali solution was added to the evaporation tail liquid for pretreatment, and then the first clear liquid was obtained by solid-liquid separation. Adjust the pH of the first clear liquid to 7.5-8, add aluminum salt solution, control the reaction pH to 5.5-6.5, and obtain aluminum mud and second clear liquid through solid-liquid separation; The pH of the ferric phosphate wastewater was adjusted to 8.5-9, and after solid-liquid separation, a third clear liquid was obtained. Adjust the pH of the third clear liquid to 9-10, add aluminum mud, and then separate the solid and liquid to obtain the fourth clear liquid; Adjust the pH of the fourth clear liquid to 6-7, and then perform solid-liquid separation to obtain the fifth clear liquid; The fifth clear liquid enters the downstream water treatment process.

[0038] In the technical solution of this application embodiment, the main characteristics of the ferric phosphate wastewater evaporation tail liquid are: pH value of 1.2~1.8, TDS content of 20~25%, phosphorus content of 2~5%, magnesium content of 1200~2000ppm, manganese content of 500~1500ppm, calcium content of 400~800ppm, sodium content of 2~3.5%, and other components are mainly ammonium sulfate. The pretreatment process increases the pH value of the evaporation tail liquid by adding alkali, promoting the precipitation of metal ions. Solid-liquid separation yields a first sludge and a first clear liquid. The first sludge is used as a citrate-soluble phosphate fertilizer, and the first clear liquid enters the next stage for phosphorus recovery.

[0039] Further, acid is added to adjust the pH of the first clear liquid to 7.5-8, and an aluminum salt solution is added for reaction. The preferred acid is dilute sulfuric acid, and phosphoric acid can be selected. The reaction pH is controlled within the acidic range of 5.5-6.5 to ensure that phosphate ions react with excess aluminum salt to produce aluminum phosphate at the optimal reaction pH. Since the pH is lower than that after pretreatment, no other metal elements precipitate and affect the reaction process. The slurry after reaction is separated into solid and liquid by plate and frame filter press to obtain aluminum mud and a second clear liquid. The second clear liquid has a lower metal element content and is directly refluxed into the evaporation system for circulating evaporation to produce salt. The removal of metal impurities reduces the impact on the purity of the by-salt separated by evaporation.

[0040] Furthermore, a two-stage sedimentation method was adopted to treat the ferric phosphate wastewater. The pH of the first-stage sedimentation was adjusted to 8.5-9, utilizing phosphate ions in the raw water to precipitate some calcium, magnesium, iron, and manganese ions, while preventing the iron ion precipitate from re-dissolving and forming ferrates at excessively high pH. At this point, the iron ions from the first-stage sedimentation were essentially completely removed. Solid-liquid separation yielded a second sludge and a third clear liquid. The second sludge was used as a citrate-soluble phosphate fertilizer, while the third clear liquid entered the second-stage sedimentation, where the pH was adjusted to 9-10. Simultaneously, aluminum sludge was added; under alkaline conditions, the aluminum ions in the aluminum sludge hydrolyzed into AlO2. - Or Al(OH)4 - The solution dissolves and produces a large amount of hydrogen phosphate, which replenishes the phosphorus element in the wastewater. It reacts with the remaining magnesium, manganese and other metal ions in the wastewater to form precipitates, increasing the removal rate of calcium, magnesium and manganese ions in the wastewater. After solid-liquid separation, the third sludge and the fourth clear liquid are obtained. The third sludge is put into the untreated evaporation tail liquid. After the tail liquid is pretreated, it forms a soluble phosphate fertilizer for sale, so as to save some of the alkali consumption generated by the tail liquid alkali adjustment pretreatment.

[0041] The fourth clear liquid, with a pH of 9-10, enters the neutralization tank, where sulfuric acid is used to adjust the pH to 6-7. The AlO2 produced by hydrolysis... - Or Al(OH)4 - Aluminum hydroxide precipitate is reformed, causing a large amount of aluminum salt in the fourth clear liquid to precipitate. The aluminum salt precipitate and the fifth clear liquid are obtained by solid-liquid separation through plate and frame filtration. The aluminum salt precipitate is transferred to the aluminum salt compounding process for acid dissolution to prepare an aluminum salt solution, forming aluminum salt for phosphorus extraction and recycling.

[0042] The fifth clear liquid enters the downstream treatment process, which includes a zero-discharge water treatment system using a combination of processes such as UF (ultrafiltration), NF (nanofiltration), RO (reverse osmosis), and MVR (mechanical vapor recompression) for further purification or reuse.

[0043] Furthermore, in some embodiments, the alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide, and the pH value of the evaporation tail liquid is adjusted to 8.5-9.

[0044] In the technical solution of this application embodiment, alkali is added to adjust the pH to 8.5-9. Under conditions rich in phosphorus and ammonium, metal elements are precipitated. The alkaline conditions promote the formation of hydroxide precipitates from metal ions in the evaporation tail liquid. Simultaneously, utilizing the phosphorus already present in the tail liquid and the formed alkaline substances, the precipitate can be used as citrate-soluble phosphate fertilizer, achieving preliminary resource utilization. Through solid-liquid separation, most metal impurities are removed, and the phosphorus-rich first clear liquid is sent to the next stage for phosphorus recovery, reducing the load on subsequent processing and creating conditions for further processing.

[0045] Furthermore, in some embodiments, the pH value of the aluminum salt solution is 2 to 3; and / or, the aluminum ion concentration in the aluminum salt solution is 2 to 4%.

[0046] In the technical solution of this application embodiment, by dissolving aluminum salt and adjusting the pH value of the aluminum salt solution to 2-3 with acid to maintain the stability of the aluminum salt solution, an aluminum salt solution with an aluminum ion concentration of 2-4% is prepared. In the subsequent phosphorus recovery step, the aluminum salt acts as a precipitant and reacts with phosphate to generate insoluble aluminum phosphate precipitate. The appropriate concentration of aluminum salt solution ensures the effective progress of the phosphorus precipitation reaction.

[0047] Furthermore, in some embodiments, the Al in the aluminum salt solution 3+ With PO4 in the first clear liquid 3- The molar ratio is (2~3):1.

[0048] In the technical solution of this application embodiment, the addition of excess aluminum salt ensures complete phosphorus precipitation reaction, overcomes the limitation of precipitation solubility, and improves the sedimentation and filtration performance of the precipitate.

[0049] Furthermore, in some embodiments, the aluminum salt in the aluminum salt solution is one or more of aluminum sulfate and aluminum chloride.

[0050] In the technical solution of this application embodiment, aluminum sulfate or aluminum chloride has high solubility in water and can quickly and completely dissolve to form a uniform aluminum ion solution, which facilitates subsequent reaction with phosphate. Aluminum sulfate is preferred. Aluminum chloride has requirements for the evaporation material system when used, and titanium or Hastelloy-type materials resistant to chloride ion corrosion need to be used.

[0051] Furthermore, in some embodiments, the molar ratio of phosphorus in the aluminum sludge to the total amount of magnesium and manganese in the third clear liquid is (2.2~3):1.

[0052] In the technical solution of this application embodiment, excess phosphorus can ensure that almost all magnesium and manganese ions can react with phosphate to form precipitates, thereby improving precipitation efficiency and recovery rate.

[0053] Furthermore, in some embodiments, the sludge obtained by solid-liquid separation of the fourth supernatant is an aluminum salt precipitate, which is then used to prepare an aluminum salt solution for recycling through an aluminum salt compounding process.

[0054] In the technical solution of this application embodiment, aluminum salt precipitate is dissolved and prepared to be transformed into a reusable aluminum salt solution, realizing the internal circulation of aluminum resources, reducing the procurement cost of new aluminum salt, and reducing wastewater discharge.

[0055] Secondly, embodiments of this application provide a system for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources. The system employs the method described in the first aspect for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources. It includes a tail liquid pretreatment device, a tail liquid phosphorus recovery device, a ferric phosphate wastewater pretreatment device, a neutralization tank, and a zero-discharge water treatment system connected in sequence. By removing impurities stepwise, recovering valuable phosphorus resources, and ultimately using advanced treatment technology to separate water and salt for reuse, a complete solution for phosphorus resource recycling and zero wastewater discharge is constructed.

[0056] Specifically, the tailings pretreatment device includes a tailings storage tank, a booster pump, a vertical flow sedimentation tank, a plate and frame filter press, and a dosing device. The vertical flow sedimentation tank has a built-in stirring device and a hydraulic retention time of 2-4 hours. Solid-liquid separation is achieved through full filtration using a plate and frame filter press. The tailings phosphorus recovery device includes a phosphorus-containing clear liquid storage tank, a booster pump, a vertical flow sedimentation tank, and a clear liquid tank. The sedimentation tank has a built-in stirring device to prevent crystallization and sedimentation. The hydraulic retention time is 2-3 hours. Solid-liquid separation is achieved through full filtration using a plate and frame filter press. The neutralization tank uses mechanical stirring for clarification. The hydraulic retention time is 3-5 hours. The clear liquid is fully filtered. The sludge is concentrated and collected, and then subjected to full filtration using a plate and frame filter press to achieve solid-liquid separation.

[0057] Furthermore, in some embodiments, the zero-discharge water treatment system includes a UF device, an NF device, an RO device, and an MVR device.

[0058] In the technical solution of this application embodiment, impurities of different particle sizes and properties are gradually removed through step-by-step purification, thereby improving the salt removal rate. MVR technology greatly reduces energy consumption by recovering and reusing the water vapor generated by evaporation. The zero-discharge water treatment system can reuse most of the treated water for production, realizing the recycling of water resources. It can also concentrate difficult-to-treat salts and convert them into solid salt mud, avoiding environmental pollution from high-salt wastewater.

[0059] Furthermore, in some embodiments, the ferric phosphate wastewater pretreatment device includes a primary sedimentation tank and a secondary sedimentation tank.

[0060] In the technical solution of this application embodiment, the primary sedimentation tank utilizes phosphorus and metal ions in the raw ferric phosphate wastewater to directly precipitate and form citrate-soluble phosphate fertilizer, while removing some metal ions; the secondary sedimentation tank utilizes aluminum sludge produced in the phosphorus recovery process, and through the dissolution and hydrolysis of the aluminum sludge, further releases phosphorus and promotes the precipitation of remaining metal ions (mainly Mg). 2+ Mn 2+ The sedimentation process involves two stages: a two-stage sedimentation system and a vertical flow sedimentation tank. These two stages work together to efficiently remove metal ions from the wastewater, recover phosphorus resources, and reduce the burden on subsequent treatment processes. Specifically, an inclined plate sedimentation tank and a vertical flow sedimentation tank are used, both with a hydraulic retention time of 2-4 hours. The clear liquid overflows, and the sludge is concentrated and collected before undergoing full plate and frame filtration to achieve solid-liquid separation.

[0061] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1 This embodiment provides a method for treating the tail liquid from the evaporation of ferric phosphate wastewater and for recycling phosphorus resources, such as... Figure 1 As shown, it includes the following steps: S1. Add ammonia to the evaporation tail liquid to adjust the pH value to 8.5. Under the conditions of rich phosphorus and ammonium, metal elements are precipitated. Solid-liquid separation is carried out by plate and frame filter press to obtain the first sludge and the first clear liquid. The first sludge is used as citrate-soluble phosphate fertilizer. S2. Adjust the pH of the first supernatant to 7.5, add aluminum sulfate solution to initiate the reaction. The aluminum sulfate solution has a pH of 2 and an aluminum ion concentration of 2%. Control the reaction pH to 5.5. 3+ With PO4 in the first clear liquid 3- The molar ratio was 2:1. After the reaction was completed, the mixture was filtered by plate and frame filter press to obtain aluminum mud and a second clear liquid. S3. A two-stage sedimentation method is used to treat ferric phosphate wastewater. The first stage sedimentation adjusts the pH value of the ferric phosphate wastewater to 8.5, and uses the phosphate in the raw water to precipitate some metal ions. The resulting second sludge is used as citrate-soluble phosphate fertilizer, and the third clear liquid enters the second stage sedimentation tank. S4. Adjust the pH of the third clear liquid to 9 and add aluminum mud. The molar ratio of phosphorus in the aluminum mud to the total amount of magnesium and manganese in the third clear liquid is 2.2:1. After the reaction, solid-liquid separation is performed to obtain the third sludge and the fourth clear liquid. The third sludge is put into the untreated evaporation tail water. After the tail water is pretreated, it forms citrate-soluble phosphate fertilizer for sale, so as to save some of the alkali consumption generated by the tail water alkali adjustment pretreatment. S5. The fourth clarified liquid enters the neutralization tank, where the pH is adjusted to 6, causing a large amount of aluminum salts in the clarified liquid to precipitate and be removed from the wastewater. Solid-liquid separation is then performed using a plate and frame filter press to obtain the fourth sludge and the fifth clarified liquid. The fourth sludge is an aluminum salt precipitate, such as... Figure 2 As shown, the aluminum salt precipitate is transferred to the aluminum salt compounding process for acid dissolution to prepare an aluminum salt solution, forming aluminum salt for phosphorus extraction and recycling; S6. The fifth clear liquid enters the downstream water treatment process, which includes a zero-discharge water treatment system consisting of a combination of UF unit, NF unit, RO unit, MVR unit and other processes.

[0063] Example 2 This embodiment provides a method for treating the tail liquid from the evaporation of ferric phosphate wastewater and for recycling phosphorus resources, including the following steps: S1. Add sodium hydroxide to the evaporation tail liquid to adjust the pH value to 9, and precipitate metal elements under the conditions of rich phosphorus and ammonium. Separate solid and liquid by plate and frame filter press to obtain the first sludge and the first clear liquid. The first sludge is used as citrate-soluble phosphate fertilizer. S2. Adjust the pH of the first supernatant to 8, add aluminum sulfate solution to initiate the reaction. The aluminum sulfate solution has a pH of 3 and an aluminum ion concentration of 4%. Control the reaction pH to 6.5. 3+ With PO4 in the first clear liquid 3- The molar ratio was 3:1. After the reaction was completed, the mixture was filtered by plate and frame filter press to obtain aluminum mud and a second clear liquid. S3. A two-stage sedimentation method is used to treat ferric phosphate wastewater. The first stage sedimentation adjusts the pH value of the ferric phosphate wastewater to 9, and uses the phosphate in the raw water to precipitate some metal ions. The resulting second sludge is used as citrate-soluble phosphate fertilizer, and the third clear liquid enters the second stage sedimentation tank. S4. Adjust the pH of the third clear liquid to 10 and add aluminum mud. The molar ratio of phosphorus in the aluminum mud to the total amount of magnesium and manganese in the third clear liquid is 3:1. After the reaction, solid-liquid separation is performed to obtain the third sludge and the fourth clear liquid. The third sludge is put into the untreated evaporation tail water. After the tail water is pretreated, it forms citrate-soluble phosphate fertilizer for sale to save some of the alkali consumption generated by the tail water alkali adjustment pretreatment. S5. The fourth clear liquid enters the neutralization tank, and the pH value is adjusted to 7, so that a large amount of aluminum salt in the clear liquid forms a precipitate and is removed from the wastewater. The fourth sludge and the fifth clear liquid are obtained by solid-liquid separation through plate and frame filter press. The fourth sludge is aluminum salt precipitate. The aluminum salt precipitate is transferred to the aluminum salt compounding process for acid dissolution to prepare aluminum salt solution, forming aluminum salt for phosphorus extraction and recycling. S6. The fifth clear liquid enters the downstream water treatment process, which includes a zero-discharge water treatment system consisting of a combination of UF unit, NF unit, RO unit, MVR unit and other processes.

[0064] Example 3 The only difference between Example 3 and Example 1 is that: In step S1, ammonia is added to the evaporation tail liquid to adjust the pH value to 6.0; In step S2, the pH of the first supernatant is adjusted to 6.0, and the reaction pH is controlled at 5.0; In step S3, the pH of the ferric phosphate wastewater is adjusted to 8 by primary precipitation; In step S4, the pH of the third supernatant is adjusted to 7.5; In step S5, the fourth clear liquid enters the neutralization tank, and the pH value is adjusted to 6.

[0065] Comparative Example 1 Compared with the examples, in Comparative Example 1, the evaporation tail liquid was not treated and was directly recycled into the ferric phosphate wastewater for recycling. The ferric phosphate wastewater treatment also adopted a two-stage precipitation method for pretreatment. The first-stage precipitation treatment adjusted the pH value to 8-9. The clear liquid after solid-liquid separation was mixed with the evaporation tail liquid for the second-stage precipitation treatment, and the pH value was adjusted to 8-9. The clear liquid after solid-liquid separation entered the zero-discharge water treatment system of the subsequent UF unit, NF unit, RO unit, MVR unit and other combined processes for water and salt separation.

[0066] Specifically, the relevant indicators of the evaporation tail liquid of the ferric phosphate wastewater to be treated are shown in Table 1. Table 1. Indicators of the tail liquid from the evaporation of ferric phosphate wastewater The clarified liquid after pretreatment of the evaporation tail liquid in each embodiment and comparative example was tested to determine the content of each element. The results are shown in Table 2. Table 2 Indicators of the First Clear Liquid According to the corresponding indicators in Table 2, the metal ion removal rate of the evaporation tail liquid is significantly reduced after pretreatment, effectively lowering the content of metal impurity elements in the reflux MVR.

[0067] The second clear liquid in each embodiment and comparative example was tested to determine the content of each element. The results are shown in Table 3. Table 3 Indicators of the Second Clear Liquid According to the corresponding indicators in Tables 2 and 3, if the pH of the precipitation and phosphorus recovery reaction of the evaporation tail liquid cannot meet the requirements, the phosphorus and impurity elements in the evaporation tail liquid cannot be effectively recovered and removed. The second clear liquid will be returned to the evaporation system, carrying a large amount of phosphate and impurity elements, which will affect the purity of the ammonium sulfate by-product of salt separation.

[0068] Specifically, the relevant indicators of the ferric phosphate wastewater to be treated are shown in Table 4. Table 4. Indicators of the ferric phosphate wastewater to be treated The fifth clear liquid in each embodiment and comparative example was tested to determine the content of each element. The results are shown in Table 5. Table 5. Indicators of the fifth clear liquid According to the corresponding indicators in Tables 4 and 5, even if aluminum sludge is added within the range required by the process, if the pH of the third clear liquid reaction does not meet the requirements, the added aluminum sludge hydrolyzes very little or almost no phosphorus release, and does not effectively improve the precipitation effect of the pretreatment. In contrast, after adding aluminum sludge, the reaction conditions are within the process requirements, and the aluminum sludge effectively releases phosphorus and improves the removal rate of metal elements.

[0069] The ammonium sulfate products in each embodiment and comparative example were tested to determine the content of each element. The results are shown in Table 6. Table 6. Detection Indicators for Ammonium Sulfate Products According to the corresponding indicators in Table 6, in Example 3, the third clear liquid reflux introduced phosphate and impurity elements, changing the initial material composition ratio during evaporation. This caused the composition of the material during salt separation after evaporation and concentration to deviate from the optimal salt separation range for ammonium sulfate, resulting in a small amount of mixed salts being carried into the ammonium sulfate product. Consequently, the ammonium sulfate product failed to meet the quality requirements (national standard fertilizer-grade ammonium sulfate). Although Comparative Example 1 improved the wastewater treatment effect through pretreatment, the evaporation tail liquid reflux also introduced phosphate. Furthermore, the high TDS of the tail liquid caused an increase in the TDS of the influent to the upstream UF / NF / RO equipment, indirectly increasing the osmotic pressure required by the membrane equipment and creating an operational burden.

[0070] In summary, this application addresses the pretreatment problem of insufficient phosphate content in incoming water by extracting and reusing phosphate ions; phosphorus recycling increases the precipitation and removal rate of metal ions, alleviating fouling during the membrane equipment concentration process and scaling problems in pipelines and transfer pumps; the treatment of evaporation tailwater reduces the content of impurity elements and phosphate in the tailwater, and the decrease in phosphate content leads to a decrease in tailwater viscosity, indirectly improving the evaporation efficiency of the tailwater; compared with direct tailwater reuse pretreatment, it avoids the increased processing load on the membrane equipment caused by a large amount of TDS entrainment, ensuring that the TDS of the pretreated wastewater does not rise abnormally during the phosphorus recycling process.

[0071] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for treating the tail liquid from the evaporation of ferric phosphate wastewater and for recycling phosphorus resources, characterized in that, Includes the following steps: Alkali solution was added to the evaporation tail liquid for pretreatment, and then the first clear liquid was obtained by solid-liquid separation. The pH of the first clear liquid was adjusted to 7.5-8, and an aluminum salt solution was added to control the reaction pH to 5.5-6.

5. After solid-liquid separation, aluminum mud and a second clear liquid were obtained. The pH of the ferric phosphate wastewater was adjusted to 8.5-9, and after solid-liquid separation, a third clear liquid was obtained. The pH of the third clear liquid is adjusted to 9-10, and the aluminum mud is added. After solid-liquid separation, the fourth clear liquid is obtained. The pH of the fourth clear liquid was adjusted to 6-7, and the fifth clear liquid was obtained by solid-liquid separation; The fifth clear liquid enters the downstream water treatment process; the downstream water treatment process includes the MVR process, and the evaporation tail liquid is the evaporation tail liquid generated by the MVR process.

2. The method for treating the tail liquid from the evaporation of ferric phosphate wastewater and recycling phosphorus resources according to claim 1, characterized in that, The alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide, and the pH value of the evaporation tail liquid is adjusted to 8.5-9.

3. The method for treating the tail liquid from the evaporation of ferric phosphate wastewater and recycling phosphorus resources according to claim 1, characterized in that, The pH value of the aluminum salt solution is 2-3; and / or The aluminum ion concentration in the aluminum salt solution is 2-4%.

4. The method for treating the tail liquid of ferric phosphate wastewater evaporation and recycling phosphorus resources according to claim 3, characterized in that, Al in aluminum salt solution 3+ With the PO4 in the first clear liquid 3- The molar ratio is (2~3):

1.

5. The method for treating the tail liquid of ferric phosphate wastewater evaporation and recycling phosphorus resources according to claim 4, characterized in that, The aluminum salt in the aluminum salt solution is one or more of aluminum sulfate and aluminum chloride.

6. The method for treating the tail liquid of ferric phosphate wastewater evaporation and recycling phosphorus resources according to claim 1, characterized in that, The molar ratio of phosphorus in the aluminum sludge to the total amount of magnesium and manganese in the third clear liquid is (2.2~3):

1.

7. The method for treating the tail liquid of ferric phosphate wastewater evaporation and recycling phosphorus resources according to claim 1, characterized in that, The sludge obtained by solid-liquid separation of the fourth clear liquid is aluminum salt precipitate, which is then used to prepare an aluminum salt solution for recycling through an aluminum salt compounding process.

8. A system for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources, comprising treating the ferric phosphate wastewater evaporation tail liquid using the method for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources as described in any one of claims 1 to 7, characterized in that, It includes a tail liquid pretreatment device, a tail liquid phosphorus recovery device, an iron phosphate wastewater pretreatment device, a neutralization tank, and a zero-discharge water treatment system connected in sequence. The tail liquid pretreatment device is used to add alkaline solution to the evaporation tail liquid for pretreatment, and after solid-liquid separation, a first clear liquid is obtained; The tail liquid phosphorus recovery device is used to adjust the pH value of the first clear liquid to 7.5~8, and add aluminum salt solution to control the reaction pH value to 5.5~6.

5. After solid-liquid separation, aluminum mud and second clear liquid are obtained. The ferric phosphate wastewater pretreatment device includes a primary sedimentation tank and a secondary sedimentation tank; the tailings phosphorus recovery device is connected to the secondary sedimentation tank; The primary sedimentation tank is used to adjust the pH value of the ferric phosphate wastewater to 8.5-9, and after solid-liquid separation, a third clear liquid is obtained; the secondary sedimentation tank is used to adjust the pH value of the third clear liquid to 9-10, and the aluminum sludge is added, and after solid-liquid separation, a fourth clear liquid is obtained. The neutralization tank is used to adjust the pH value of the fourth clear liquid to 6-7, and after solid-liquid separation, the fifth clear liquid is obtained; The zero-discharge water treatment system is used to enable the fifth clear liquid to undergo downstream water treatment processes.

9. The system for treating ferric phosphate wastewater evaporation tail liquid and recycling phosphorus resources according to claim 8, characterized in that, The zero-discharge water treatment system includes a UF device, an NF device, an RO device, and an MVR device.

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