Lithium iron phosphate production wastewater recycling method and device

Abstract

The application provides a lithium iron phosphate production wastewater recycling method and device, and belongs to the technical field of wastewater treatment, wherein the lithium iron phosphate production wastewater recycling method comprises the following steps: adjusting the pH of lithium iron phosphate production wastewater to 2.5-6.0 by using inorganic acid, or adjusting the conductivity of lithium iron phosphate production wastewater by using electrolyte, obtaining a first solution and precipitate after solid-liquid separation; performing dewatering treatment on the precipitate to obtain a second solution and mud cake; and mixing the first solution and the second solution to prepare lithium iron phosphate. The application adjusts the pH or conductivity of lithium iron phosphate production wastewater to cause the aggregation and precipitation of suspended solids in the wastewater, thereby removing impurities in the wastewater, obtaining recycled water containing lithium carbonate and iron phosphate, and realizing the resource utilization of water resources and valuable metal elements in lithium iron phosphate production wastewater.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, specifically to a method and apparatus for recycling wastewater from lithium iron phosphate production. Background Technology

[0002] With the rapid development of new energy technologies, lithium-ion batteries have been widely used due to their advantages such as energy storage, rapid charging and discharging, long cycle life, and environmental friendliness. Lithium iron phosphate, as the mainstream cathode material for lithium-ion batteries, is experiencing a growing market demand.

[0003] Currently, the treatment of wastewater generated during lithium iron phosphate production is becoming increasingly prominent. Traditional wastewater treatment methods not only consume large amounts of reagents and energy, but also require the construction of massive biological treatment systems, and the treatment effect is unstable, easily leading to substandard effluent. In addition, traditional methods also waste water resources and the precious metal lithium.

[0004] Therefore, it is particularly important to develop an efficient, environmentally friendly, and resource-efficient method for recycling wastewater from the production of lithium iron phosphate cathode materials. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a method and apparatus for recycling wastewater from lithium iron phosphate production, aiming to solve the technical problems of complex treatment processes, serious environmental pollution, and inability to achieve efficient resource utilization of traditional lithium iron phosphate production wastewater.

[0006] In a first aspect, embodiments of this application provide a method for recycling wastewater from lithium iron phosphate production, comprising the following steps: The pH of lithium iron phosphate production wastewater is adjusted to 2.5-6.0 using inorganic acids, or the conductivity of lithium iron phosphate production wastewater is adjusted using electrolytes. After solid-liquid separation, a first solution and precipitate are obtained. The precipitate was dehydrated to obtain a second solution and a mud cake; The first and second solutions were mixed and used in the preparation of lithium iron phosphate.

[0007] In the technical solution of this application embodiment, the suspended solids in the wastewater are aggregated by adjusting the pH or conductivity of the lithium iron phosphate production wastewater, thereby removing the impurities (such as magnetic impurities) attached to the wastewater and obtaining recycled water containing only lithium carbonate and iron phosphate. This avoids the impurities in the wastewater from affecting the quality of lithium iron phosphate products. Not only is the process short and the reagent consumption low, but it also realizes the resource utilization of water resources and precious metal elements in the lithium iron phosphate production wastewater.

[0008] In some embodiments, in the step of adjusting the pH of lithium iron phosphate production wastewater using inorganic acids, if the lithium iron phosphate production wastewater is milky white or pale yellow, the pH of the lithium iron phosphate production wastewater is adjusted to 2.5-4; if the lithium iron phosphate production wastewater is black, the pH of the lithium iron phosphate production wastewater is adjusted to 5-6.

[0009] In this embodiment, when the lithium iron phosphate production wastewater is fresh, the pH is adjusted to 2.5-4; when the lithium iron phosphate production wastewater is fermented and blackened wastewater that has been discharged for a long time, the pH is adjusted to 5-6. Different pH ranges are adjusted according to the different characteristics of the lithium iron phosphate production wastewater to fully remove suspended solids and ensure the cleanliness of the recycled water.

[0010] In some embodiments, the inorganic acid is at least one of phosphoric acid, sulfuric acid, and hydrochloric acid; the electrolyte is an ammonium salt.

[0011] In this embodiment, only conventional inorganic acids or ammonium salt electrolytes are needed to achieve the coagulation of suspended solids in wastewater. The consumption of reagents is low, there are no sewage discharge fees or waste residue treatment fees, the production cost is extremely low, and it has good economic benefits.

[0012] In some embodiments, the molar ratio of iron ions to lithium ions in the first solution is (0.08~0.32):(52.1~69).

[0013] In this embodiment, by controlling the sedimentation process, the lithium carbonate and iron phosphate in the first solution are kept within a suitable ratio range so that they can be directly pulped and reused with the raw materials for producing lithium iron phosphate, thereby ensuring the elemental ratio in the lithium iron phosphate product and not affecting the quality of lithium iron phosphate.

[0014] In some embodiments, the pH of the lithium iron phosphate production wastewater is adjusted using inorganic acids, and after solid-liquid separation, the pH of the first solution is 3.0 to 6.0.

[0015] In this embodiment, by controlling the pH of the first solution to 3.0~6.0, the dissolution of calcium and magnesium in the suspended matter is avoided due to excessive acidity of the solution, while the precipitation of iron and other elements is avoided due to excessive alkalinity of the solution, thus preventing the resource utilization of elements in the wastewater.

[0016] In some embodiments, the solid-liquid separation step includes allowing the reaction mixture to settle and detecting the liquid level L of the first solution. 液 and sediment mud level L 泥 ; If L 液 / L 泥 ≥5, the first solution and precipitate are discharged separately; If 3 < L 液 / L 泥 <5, continue to stand until L液 / L 泥 ≥5, then the first solution and precipitate are discharged separately; If L 液 / L 泥 If the pH is ≤3, continue adjusting the pH or conductivity until L is reached. 液 / L 泥 ≥5, then the first solution and precipitate are discharged separately.

[0017] In this embodiment, the completeness of sedimentation is determined by detecting the liquid level and sludge level, thus avoiding the presence of excessive impurities in the first solution discharged due to incomplete sedimentation. When L 液 / L 泥 ≥5 indicates that sedimentation is complete and mud-water separation can proceed; when 3 < L 液 / L 泥 <5 indicates that the sedimentation effect is good and sedimentation is still ongoing. Discharge should only proceed after sedimentation is complete; when L 液 / L 泥 If the value is ≤3, it indicates poor precipitation. In this case, continue to adjust the pH or conductivity to ensure sufficient precipitation.

[0018] In some embodiments, after dehydration, the moisture content of the sludge cake is less than 5%, and the lithium content is 2-4%.

[0019] In this embodiment, by controlling the moisture content and lithium content of the sludge cake after dehydration, not only can the dehydrated water be reused, but the sludge cake can also be recycled as cathode material waste, and can be sold or used as raw material for resource utilization to extract lithium carbonate and iron phosphate.

[0020] In some embodiments, the content of solid suspended matter in the second solution is 5~20 mg / L.

[0021] In this embodiment, by controlling the content of solid suspended matter in the second solution, the reuse effect is avoided due to excessive suspended matter containing impurities.

[0022] Secondly, this application provides a lithium iron phosphate production wastewater recycling device for performing the lithium iron phosphate production wastewater recycling method as described in the first aspect, including a wastewater collection device, a sedimentation device, and a recycled water collection device connected in sequence; the sludge outlet of the sedimentation device is connected to a dewatering device, and the clean water outlet of the dewatering device is connected to the recycled water collection device. Wastewater collection device for collecting wastewater from lithium iron phosphate production; Sedimentation devices are used to adjust the pH or conductivity of wastewater and to carry out sedimentation reactions. A dehydration device is used to dehydrate precipitates. Reclaimed water collection device, used to collect reclaimed water.

[0023] In the technical solution of this application embodiment, wastewater from lithium iron phosphate production is collected by a wastewater collection device, and then the wastewater is transported to a sedimentation device. In the sedimentation device, the acidity or conductivity of the solution is adjusted so that the solids in the wastewater form a precipitate, and then mud-water separation is carried out to obtain recycled water. The precipitate is dehydrated by a dewatering device to obtain mud cake and recycled water, thus realizing the collection and reuse of recycled water.

[0024] In some embodiments, the sedimentation device includes a cylindrical body with a cavity, a mud level gauge, a liquid level gauge and a detector installed in the cylindrical body, and a stirring assembly disposed in the cylindrical body; the top of the cylindrical body is provided with a feed inlet and the bottom is provided with a mud outlet and a liquid outlet; wherein, the detector includes a pH detector and / or a conductivity detector.

[0025] In this embodiment, a mud level gauge is used to detect the mud level of the precipitate, and a liquid level gauge is used to detect the liquid level of the first solution, so as to determine whether the precipitation reaction is complete; a detector is used to detect the pH value or conductivity of the wastewater to ensure the amount of inorganic acid and electrolyte; and a stirring assembly is used to stir the mixture to ensure that the reaction proceeds fully.

[0026] The beneficial effects of this application are as follows: This application adjusts the pH or conductivity of lithium iron phosphate production wastewater to cause suspended solids in the wastewater to precipitate, thereby removing impurities (such as magnetic impurities) attached to the wastewater. This not only recovers water resources but also recovers some iron phosphate and lithium carbonate. The resulting sludge cake can be used as a product or raw material to extract lithium carbonate and iron phosphate. There is no wastewater or waste residue discharge, which is beneficial to environmental protection. Furthermore, both the recycled water and the sludge cake achieve resource utilization.

[0027] This application treats wastewater from lithium iron phosphate production with a short process, low energy consumption, low reagent consumption, and no sewage discharge fees or waste residue treatment fees. Therefore, the production cost is extremely low, resulting in good economic benefits.

[0028] 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, the following are specific embodiments of this application. Attached Figure Description

[0029] 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.

[0030] Figure 1This is a schematic diagram of the method for recycling wastewater from lithium iron phosphate production in the embodiments of this application; Figure 2 This is a schematic diagram of the lithium iron phosphate production wastewater recycling device in the embodiments of this application; Figure 3 This is a schematic diagram of the precipitation device in the embodiments of this application; Explanation of reference numerals in the attached drawings: 1. Wastewater collection device; 2. Sedimentation device; 21. Cylinder; 22. Sludge level gauge; 23. Liquid level gauge; 24. Detector; 241. pH meter; 242. Conductivity meter; 25. Agitator assembly; 26. Feed inlet; 27. Sludge outlet; 28. Liquid outlet; 3. Reclaimed water collection device; 4. Dewatering device. Detailed Implementation

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0038] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0039] Existing wastewater treatment methods for lithium iron phosphate production involve lengthy processes, high reagent consumption, the generation of large amounts of waste residue, high treatment costs, and require sewage discharge, causing a certain impact on the environment. Furthermore, traditional methods also result in the waste of water resources and precious metal elements.

[0040] To address the technical challenges of complex processes, severe environmental pollution, and inability to utilize resources in traditional lithium iron phosphate (LFP) production wastewater, this application provides a method and apparatus for recycling LFP production wastewater. The method utilizes acid precipitation or electrolyte methods to control the flocculation and sedimentation of suspended solids in the wastewater, effectively removing impurities such as magnetic substances. This yields recycled water containing large amounts of lithium carbonate and iron phosphate for LFP production, simultaneously achieving the reuse of water and precious metal resources. Furthermore, the process is short, requires few reagents, has low energy consumption and cost, and generates no wastewater or waste residue, making it environmentally friendly.

[0041] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for recycling wastewater from lithium iron phosphate production, comprising the following steps: The pH of lithium iron phosphate production wastewater is adjusted to 2.5-6.0 using inorganic acids, or the conductivity of lithium iron phosphate production wastewater is adjusted using electrolytes. After solid-liquid separation, a first solution and precipitate are obtained. The precipitate was dehydrated to obtain a second solution and a mud cake; The first and second solutions were mixed and used in the preparation of lithium iron phosphate.

[0042] In the technical solution of this application embodiment, the suspended solids in the lithium iron phosphate production wastewater are aggregated by adjusting the pH or conductivity, thereby removing impurities (such as magnetic impurities) from the wastewater and obtaining recycled water containing lithium carbonate and iron phosphate. This avoids the impact of impurities in the wastewater on product quality, resulting in a shorter process flow, lower reagent consumption, and resource utilization of water resources and precious metal elements in the lithium iron phosphate production wastewater. By controlling the pH to 2.5~6.0, not only is the aggregation of suspended solids in the wastewater more complete, but the lithium carbonate content in the solution can also be effectively controlled. If the pH is too high, the aggregation effect of suspended solids is poor, making it difficult to achieve mud-water separation, or even preventing the aggregation reaction from occurring at all; while if the pH is too low, the ionic strength in the solution is too high, and lithium carbonate will completely dissolve, making it impossible to control the appropriate iron-lithium ratio in the solution. This also leads to high acid consumption, increased dissolution of calcium, magnesium, and iron, resulting in a decline in the quality of the produced lithium iron phosphate product, making it unsuitable for direct reuse in production. Specifically, the pH can be 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, or any value within the above range.

[0043] Furthermore, in some embodiments, the conductivity of the lithium iron phosphate production wastewater is adjusted to 13,000-16,000 μS / cm using an electrolyte.

[0044] In the technical solutions of this application embodiment, the conductivity can be 13000 μS / cm, 14000 μS / cm, 15000 μS / cm, 16000 μS / cm, or any value within the above range. By controlling the conductivity to be 13000~16000 μS / cm, the suspended impurities in the wastewater can be more fully flocculated, thereby improving the quality of the recycled water.

[0045] Furthermore, in some embodiments, in the step of adjusting the pH of lithium iron phosphate production wastewater using inorganic acids, if the lithium iron phosphate production wastewater is milky white or pale yellow, the pH of the lithium iron phosphate production wastewater is adjusted to 2.5-4; if the lithium iron phosphate production wastewater is black, the pH of the lithium iron phosphate production wastewater is adjusted to 5-6.

[0046] Lithium iron phosphate (LFP) production wastewater generally falls into two categories: fresh washing wastewater, which is milky white or pale yellow and generally weakly alkaline; and fermented, blackened wastewater, which is black and has a fishy odor and is generally near neutral. In fresh wastewater, the organic components have not yet fermented into organic acids, resulting in weak ionic strength. More acid is needed to strengthen the ionic strength, causing suspended solids to precipitate. In contrast, in blackened wastewater, the organic matter has been converted into organic acids, increasing the ionic strength, requiring only a small amount of acid to induce precipitation. Therefore, in the technical solution of this application embodiment, when the LFP production wastewater is fresh, the pH is adjusted to 2.5-4; when the LFP production wastewater is fermented, blackened wastewater that has been discharged for a longer period, the pH is adjusted to 5-6. Adjusting the pH range according to the different characteristics of the LFP production wastewater not only reduces the amount of acid used but also effectively removes suspended solids, ensuring the cleanliness of the recycled water.

[0047] Furthermore, in some embodiments, the inorganic acid is at least one of phosphoric acid, sulfuric acid, and hydrochloric acid; and the electrolyte is an ammonium salt.

[0048] In the technical solution of this application embodiment, only conventional inorganic acids are needed to achieve the coagulation of suspended solids in wastewater. This results in low reagent consumption, no sewage discharge fees or waste residue treatment fees, and extremely low production costs, leading to good economic benefits. Ammonium salts are selected as the electrolyte. Compared to sodium and potassium salts, ammonium salts are completely converted into essential elements of lithium iron phosphate during the high-temperature calcination process in lithium iron phosphate preparation, without introducing new cationic impurities such as sodium and potassium. Furthermore, monoammonium phosphate and diammonium phosphate may convert into polyphosphates and metapolyphosphates at high temperatures; therefore, the ammonium salt is further preferably one or more of ammonium bicarbonate, ammonium sulfate, and ammonium chloride.

[0049] Furthermore, in some embodiments, the molar ratio of iron ions to lithium ions in the first solution is (0.08~0.32):(52.1~69).

[0050] In the technical solution of this application embodiment, by controlling the sedimentation process, the lithium carbonate and iron phosphate in the first solution are kept within a suitable ratio range so that they can be directly pulped and reused with the raw material for producing lithium iron phosphate, thereby ensuring a suitable element ratio in the lithium iron phosphate product and not affecting the quality of lithium iron phosphate.

[0051] Furthermore, in some embodiments, the pH of the lithium iron phosphate production wastewater is adjusted using inorganic acids, and after solid-liquid separation, the pH of the first solution is 3.0~6.05.

[0052] In the technical solution of this application embodiment, by controlling the pH of the first solution to 3.0~6.05, the dissolution of calcium and magnesium in the suspended matter is avoided due to excessive acidity of the solution, and the precipitation of iron and other elements is avoided due to excessive alkalinity of the solution, which would prevent the resource utilization of elements such as iron and lithium in the wastewater. Furthermore, in some embodiments, the solid-liquid separation step includes allowing the reaction mixture to settle and detecting the liquid level L of the first solution. 液 and sediment mud level L 泥 ; If L 液 / L 泥 ≥5, the first solution and precipitate are discharged separately; If 3 < L 液 / L 泥 <5, continue to stand until L 液 / L 泥 ≥5, then the first solution and precipitate are discharged separately; If L 液 / L 泥 If the pH is ≤3, continue adjusting the pH or conductivity until L is reached. 液 / L 泥 ≥5, then the first solution and precipitate are discharged separately.

[0053] In the technical solution of this application embodiment, the completeness of sedimentation is determined by detecting the liquid level and sludge level, thus avoiding the presence of excessive impurities in the first solution discharged due to incomplete sedimentation. When L 液 / L 泥 ≥5 indicates that sedimentation is complete and mud-water separation can proceed; when 3 < L 液 / L 泥 <5 indicates that the sedimentation effect is good and sedimentation is still ongoing. Discharge should only proceed after sedimentation is complete; when L 液 / L 泥 If the value is ≤3, it indicates poor precipitation. In this case, continue to adjust the pH or conductivity to ensure sufficient precipitation.

[0054] Furthermore, in some embodiments, after dehydration, the moisture content of the sludge cake is less than 5%, and the lithium content is 2-4%.

[0055] In the technical solution of this application embodiment, by controlling the moisture content and lithium content of the sludge cake after dehydration treatment, not only can the dehydrated water be reused, but the sludge cake can also be recycled as cathode material waste, and can be sold or used as raw material for resource utilization to extract lithium carbonate and iron phosphate.

[0056] Furthermore, in some embodiments, the content of solid suspended matter in the second solution is 5~20 mg / L.

[0057] In the technical solution of this application embodiment, by controlling the content of solid suspended matter in the second solution, the reuse effect is avoided due to excessive suspended matter containing impurities.

[0058] Secondly, please refer to Figure 2 This application provides an apparatus for recycling wastewater from lithium iron phosphate production, comprising a wastewater collection device 1, a sedimentation device 2, and a recycled water collection device 3 connected in sequence; the sludge outlet of the sedimentation device 2 is connected to a dewatering device 4, and the clean water outlet of the dewatering device 4 is connected to the recycled water collection device 3. Specifically, the wastewater collection device 1 is used to collect wastewater from lithium iron phosphate production; the sedimentation device 2 is used to adjust the pH or conductivity of the wastewater and to perform a sedimentation reaction; the dewatering device 4 is used to dewater the precipitate; and the recycled water collection device 3 is used to collect recycled water.

[0059] Furthermore, in some embodiments, such as Figure 3 As shown, the sedimentation device 2 includes a cylindrical body 21 with a cavity, a mud level gauge 22, a liquid level gauge 23 and a detector 24 installed in the cylindrical body 21, and a stirring assembly 25 disposed inside the cylindrical body 21; the top of the cylindrical body 21 is provided with a feed inlet 26, and the bottom is provided with a mud outlet 27 and a liquid outlet 28.

[0060] Furthermore, in some embodiments, the bottom of the cylinder 21 is conical, and the detector 24 includes a pH meter 241 and a conductivity meter 242. The stirring assembly 25 is a mixer, and the dewatering device 4 is a belt filter press or a centrifuge, preferably a horizontal screw sedimentation centrifuge. In other embodiments, devices with similar functions can be selected according to actual needs, and are not limited here.

[0061] Furthermore, in some embodiments, the method for recycling lithium iron phosphate production wastewater of this application is implemented based on the above-mentioned apparatus, and specifically includes the following steps: 1) The lithium iron phosphate wastewater in the wastewater collection device 1 enters the cylinder 21 from the feed port 26 of the sedimentation device 2 via the slurry pump, and the stirring component 25 is turned on.

[0062] 2) Add inorganic acid into cylinder 21 through feed inlet 26. The acid pump is interlocked with pH meter 241 to adjust the pH of the wastewater to 2.5~6.0. Alternatively, add electrolyte into cylinder 21. The electrolyte pump is interlocked with conductivity meter 242 to adjust the conductivity of lithium iron phosphate production wastewater to 13000~16000μS / cm.

[0063] 3) After stirring the mixture in the cylinder 21 until it is evenly mixed, turn off the stirring component 25 and let it stand; after standing for a certain period of time, read the reading L of the mud level gauge 22. 泥 The reading L of level gauge 23 液 .

[0064] 4) Based on L 液 / L 泥 Adjusting the discharge steps after solid-liquid separation: If L 液 / L 泥 ≥5 indicates sedimentation is complete. Open sludge outlet 27 to discharge sludge. After sludge discharge is complete, close sludge outlet 27 and open liquid outlet 28 to discharge the first solution. The first solution enters the recycled water collection device 3 through a pipe. If 3 < L 液 / L 泥 <5 indicates good precipitation, but not complete precipitation. Continue to let it stand, and continuously monitor L during this period. 液 / L 泥 Until L 液 / L 泥 ≥5, then the sludge and the first solution are discharged separately; if L 液 / L 泥 ≤3 indicates poor precipitation; continue adjusting the pH or conductivity until L 液 / L 泥 ≥5, then the sludge and the first solution are discharged separately.

[0065] 5) The sludge discharged from sludge outlet 27 is fed into dewatering device 4 for dewatering treatment to obtain a second solution and sludge cake; the second solution is fed into recycled water collection device 3 through a pipeline. The mixture of the first solution and the second solution in recycled water collection device 3 is used for the preparation of lithium iron phosphate.

[0066] 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.

[0067] Example 1 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 1.

[0068] Table 1

[0069] (2) Add sulfuric acid to cylinder 21 to adjust the pH of the wastewater to 6. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L泥 ; measured L 液 / L 泥 <3, sedimentation effect is not good; continue to add sulfuric acid to cylinder 21 to adjust the pH of wastewater to 5, stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21 respectively. 液 and sediment mud level L 泥 ; measured L 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 2.

[0070] Table 2

[0071] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 6 mg / L; the water content of the mud cake was 4.8%, and the lithium content was 3.2%. The mud cake was sold as lithium-containing waste.

[0072] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed to obtain a mixture with a turbidity of 10 NTU and a solid suspended matter content of 9 mg / L. The mixture is then reused for the preparation of lithium iron phosphate to obtain a qualified lithium iron phosphate product.

[0073] As can be seen from Tables 1 and 2, for the fermented and blackened lithium iron phosphate production wastewater, by adjusting the pH to 5-6, the clear liquid obtained after solid-liquid separation has a high content of phosphorus, iron and lithium. This indicates that acid precipitation not only achieves the coagulation and removal of suspended solids in the wastewater, but also dissolves some lithium carbonate, thereby realizing the direct reuse of water resources and precious metal resources.

[0074] Example 2 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 3.

[0075] Table 3

[0076] (2) Add sulfuric acid to cylinder 21 to adjust the pH of the wastewater to 3.5. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 The measurement showed that 3 < L液 / L 泥 <5, continue to stand for 20 minutes and then measure L. 液 / L 泥 >5, then the supernatant and precipitate are discharged separately; the composition of the supernatant is shown in Table 4.

[0077] Table 4

[0078] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 10 mg / L; the water content of the mud cake was 4%, and the lithium content was 3%. The mud cake was sold as lithium-containing waste.

[0079] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0080] Example 3 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 5.

[0081] Table 5

[0082] (2) Add sulfuric acid to cylinder 21 to adjust the pH of the wastewater to 4. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 <3 indicates poor precipitation effect. Continue to adjust the pH to 3.0, stir for 15 minutes, let stand for 30 minutes, and measure L. 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 6.

[0083] Table 6

[0084] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 5 mg / L; the water content of the mud cake was 3.0%, and the lithium content was 2.5%. The mud cake was sold as lithium-containing waste.

[0085] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0086] As can be seen from Examples 2 and 3, for fresh washing wastewater, adjusting the pH to 2.5-4 results in a clear liquid with high phosphorus, iron, and lithium content after solid-liquid separation. Comparing Example 3 and Example 2, it can be seen that with increasing acid dosage, phosphorus and lithium in the suspended solids dissolve significantly, while calcium also dissolves in large quantities. Therefore, for fresh wastewater, a pH of 3.5 is preferred.

[0087] Example 4 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 7.

[0088] Table 7

[0089] (2) Add phosphoric acid to cylinder 21 to adjust the pH of the wastewater to 6. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 <3 indicates poor precipitation. Continue adding phosphoric acid to cylinder 21 to adjust the pH to 5, stir for 15 minutes, let stand for 30 minutes, and measure L. 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 8.

[0090] Table 8

[0091] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 6 mg / L; the water content of the mud cake was 4.8%, and the lithium content was 4.0%. The mud cake was sold as lithium-containing waste.

[0092] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate.

[0093] Compared with Example 1, Example 4 shows that when phosphoric acid is used to adjust the pH, the concentrations of iron and lithium in the supernatant decrease. This is because phosphoric acid converts the iron and lithium dissolved in the water into iron phosphate and lithium phosphate precipitates, but does not introduce sulfate ions into the solution. When the wastewater is reused to produce lithium iron phosphate, no sulfur oxides are generated.

[0094] Example 5 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 9.

[0095] Table 9

[0096] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 6. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 10.

[0097] Table 10

[0098] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 6 mg / L; the water content of the mud cake was 4.8%, and the lithium content was 3.2%. The mud cake was sold as lithium-containing waste.

[0099] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed to obtain a mixture with a turbidity of 10 NTU and a solid suspended matter content of 9 mg / L. This mixture is reused in the preparation of lithium iron phosphate to obtain a qualified lithium iron phosphate product.

[0100] Example 6 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 11.

[0101] Table 11

[0102] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 5. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 12.

[0103] Table 12

[0104] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 6 mg / L; the water content of the mud cake was 4.8%, and the lithium content was 3.2%. The mud cake was sold as lithium-containing waste.

[0105] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0106] Example 7 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 13.

[0107] Table 13

[0108] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 7. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 <3, sedimentation effect is not good; continue to add hydrochloric acid to cylinder 21 to adjust the pH of wastewater to 5, stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21 respectively. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 14.

[0109] Table 14

[0110] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 8 mg / L; the water content of the mud cake was 4.8%, and the lithium content was 3.2%. The mud cake was sold as lithium-containing waste.

[0111] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0112] Example 8 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 15.

[0113] Table 15

[0114] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 6. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 The measurement showed that 3 < L 液 / L 泥 <5; Continue adding hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 5, stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21 respectively. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 16.

[0115] Table 16

[0116] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 7 mg / L; the water content of the mud cake was 4.8%, and the lithium content was 3.2%. The mud cake was sold as lithium-containing waste.

[0117] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0118] Example 9 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 17.

[0119] Table 17

[0120] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 4. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L 液 / L 泥 >5, then the supernatant and precipitate are discharged separately; the composition of the supernatant is shown in Table 18.

[0121] Table 18

[0122] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 10 mg / L; the water content of the mud cake was 4%, and the lithium content was 3%. The mud cake was sold as lithium-containing waste.

[0123] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0124] Example 10 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 19.

[0125] Table 19

[0126] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 5. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21.液 and sediment mud level L 泥 The measurement showed that 3 < L 液 / L 泥 <5, then continue adding hydrochloric acid to adjust the pH of the wastewater to 3, stir for 15 minutes, let stand for 20 minutes, and then measure L. 液 / L 泥 >5, then the supernatant and precipitate are discharged separately; the composition of the supernatant is shown in Table 20.

[0127] Table 20

[0128] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 10 mg / L; the water content of the mud cake was 4%, and the lithium content was 3%. The mud cake was sold as lithium-containing waste.

[0129] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0130] Example 11 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh washing wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 21.

[0131] Table 21

[0132] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 3. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5, then the supernatant and precipitate are discharged separately; the composition of the supernatant is shown in Table 22.

[0133] Table 22

[0134] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 8 mg / L; the water content of the mud cake was 4%, and the lithium content was 3%. The mud cake was sold as lithium-containing waste.

[0135] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0136] Example 12 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 23.

[0137] Table 23

[0138] (2) Add ammonium bicarbonate to cylinder 21 to adjust the conductivity of the wastewater to 13000 μS / cm. Stir for 15 min using stirring assembly 25, let stand for 30 min, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 <3 indicates poor precipitation. The conductivity was further adjusted to 16000 μS / cm, stirred for 15 min, and allowed to stand for 30 min. The L value was then measured. 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 24.

[0139] Table 24

[0140] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 5 mg / L; the water content of the mud cake was 4%, and the lithium content was 2%. The mud cake was sold as lithium-containing waste.

[0141] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0142] Example 13 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 25.

[0143] Table 25

[0144] (2) Add ammonium bicarbonate to cylinder 21 to adjust the conductivity of the wastewater to 16000 μS / cm. Stir for 15 min using stirring assembly 25, let stand for 30 min, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 26.

[0145] Table 26

[0146] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 5 mg / L; the water content of the mud cake was 4%, and the lithium content was 2%. The mud cake was sold as lithium-containing waste.

[0147] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0148] Example 14 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 27.

[0149] Table 27

[0150] (2) Add ammonium bicarbonate to cylinder 21 to adjust the conductivity of the wastewater to 13000 μS / cm. Stir for 15 min using stirring assembly 25, let stand for 30 min, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 28.

[0151] Table 28

[0152] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be 5 mg / L; the water content of the mud cake was 4%, and the lithium content was 2%. The mud cake was sold as lithium-containing waste.

[0153] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0154] Example 15 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 29.

[0155] Table 29

[0156] (2) Add ammonium bicarbonate to cylinder 21 to adjust the conductivity of the wastewater to 8000 μS / cm. Stir for 15 min using stirring assembly 25, let stand for 30 min, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 <3, sedimentation effect is not good; continue to add ammonium bicarbonate to cylinder 21 to adjust the conductivity of wastewater to 16000 μS / cm, stir with stirring component 25 for 15 min, let stand for 30 min, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L in cylinder 21 respectively. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 30.

[0157] Table 30

[0158] (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be approximately 5 mg / L; the water content of the mud cake was 4%, and the lithium content was 2%. The mud cake was sold as lithium-containing waste.

[0159] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0160] Example 16 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in Table 31.

[0161] Table 31

[0162] (2) Add ammonium bicarbonate to cylinder 21 to adjust the conductivity of the wastewater to 15000 μS / cm. Stir for 15 min using stirring assembly 25, let stand for 30 min, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5 indicates that precipitation is complete. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in Table 32.

[0163] Table 32

[0164] Note that "-" in the table indicates that this indicator was not detected. (3) The precipitate was centrifuged using dehydration device 4 to obtain centrifuged liquid and mud cake. The content of suspended solids in the centrifuged liquid was measured to be approximately 5 mg / L; the water content of the mud cake was 4%, and the lithium content was 2%. The mud cake was sold as lithium-containing waste.

[0165] (4) The supernatant obtained in step (2) and the centrifuged liquid obtained in step (3) are mixed and reused for the preparation of lithium iron phosphate to obtain qualified lithium iron phosphate products.

[0166] Comparative Example 1 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fermented black wastewater with a fishy smell) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in the table below.

[0167]

[0168] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 2. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥L was measured 液 / L 泥 <3, no sedimentation occurs, and recycled water cannot be obtained.

[0169] Comparative Example 2 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in the table below.

[0170]

[0171] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 1. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21 respectively. 液 and sediment mud level L 泥 L was measured 液 / L 泥 <3, no sedimentation occurs, and recycled water cannot be obtained.

[0172] Comparative Example 3 A method for recycling wastewater from lithium iron phosphate production includes the following steps: (1) The lithium iron phosphate wastewater (fresh cleaning wastewater, milky white) in the wastewater collection device 1 is transported to the cylinder 21 of the sedimentation device 2 by a slurry pump. The composition of the lithium iron phosphate wastewater is shown in the table below.

[0173]

[0174] (2) Add hydrochloric acid to cylinder 21 to adjust the pH of the wastewater to 2. Stir for 15 minutes using stirring component 25, let stand for 30 minutes, and then use mud level gauge 22 and liquid level gauge 23 to detect the liquid level L of the solution in cylinder 21. 液 and sediment mud level L 泥 L was measured 液 / L 泥 >5. Discharge the supernatant and precipitate separately. The composition of the supernatant is shown in the table below. It can be seen that a low pH will lead to a large amount of acid consumption, and at the same time, the dissolution of calcium and magnesium will increase, making it impossible to directly reuse in production.

[0175]

[0176] As can be seen from Examples 1 to 16, the method for recycling lithium iron phosphate production wastewater provided by the present invention not only has a short process flow and low reagent consumption, but also realizes the resource utilization of water resources and precious metal elements in lithium iron phosphate production wastewater. The recycled water obtained after treatment can be directly used for the preparation of lithium iron phosphate and obtain qualified lithium iron phosphate products.

[0177] Compared with the comparative examples, it can be seen that when pH < 2.5, the ionic strength in the solution is too high, lithium carbonate will completely dissolve, making it impossible to control the appropriate lithium iron phosphate ratio in the solution. This also leads to high acid consumption and increased dissolution of calcium, magnesium, and iron, resulting in a decline in the quality of the produced lithium iron phosphate product. It cannot be directly reused in production, and even if flocculation does not occur, recycled water cannot be obtained. Specifically, for fermentation blackening wastewater, at pH 2.0, the wastewater remains a stable system without flocculation, and recycled water cannot be obtained. For fresh washing wastewater, at pH 1.0, the wastewater remains a stable system without flocculation, and recycled water cannot be obtained; while at pH 2.0, although flocculation can occur to obtain recycled water, the recycled water contains a large amount of calcium and magnesium ions, which is not conducive to preparing qualified lithium iron phosphate products.

[0178] 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 recycling wastewater from lithium iron phosphate production, characterized in that, Includes the following steps: The pH of the lithium iron phosphate production wastewater is adjusted to 2.5-6.0 using inorganic acids, or the conductivity of the lithium iron phosphate production wastewater is adjusted to 13000-16000 μS / cm using electrolytes. After solid-liquid separation, the first solution and precipitate are obtained. The precipitate is dehydrated to obtain a second solution and a sludge cake; The first solution and the second solution are mixed and used for the preparation of lithium iron phosphate; In the step of adjusting the pH of lithium iron phosphate production wastewater using inorganic acids, if the lithium iron phosphate production wastewater is milky white or light yellow, the pH of the lithium iron phosphate production wastewater is adjusted to 2.5-4; if the lithium iron phosphate production wastewater is black, the pH of the lithium iron phosphate production wastewater is adjusted to 5-6.

2. The method for recycling lithium iron phosphate production wastewater according to claim 1, characterized in that, The inorganic acid is at least one of phosphoric acid, sulfuric acid, and hydrochloric acid; the electrolyte is an ammonium salt.

3. The method for recycling lithium iron phosphate production wastewater according to claim 1, characterized in that, The molar ratio of iron ions to lithium ions in the first solution is (0.08~0.32):(52.1~69).

4. The method for recycling lithium iron phosphate production wastewater according to claim 1, characterized in that, The pH of the lithium iron phosphate production wastewater was adjusted using an inorganic acid, and after solid-liquid separation, the pH of the first solution was 3.0~6.

0.

5. The method for recycling lithium iron phosphate production wastewater according to claim 1, characterized in that, The solid-liquid separation step includes allowing the reaction mixture to settle and detecting the liquid level L of the first solution. 液 and the sludge level L of the sediment 泥 ; If L 液 / L 泥 ≥5, the first solution and the precipitate are discharged separately; If 3 < L 液 / L 泥 <5, continue to stand until L 液 / L 泥 ≥5, then the first solution and the precipitate are discharged separately; If L 液 / L 泥 If the pH is ≤3, continue adjusting the pH or conductivity until L is reached. 液 / L 泥 ≥5, then the first solution and the precipitate are discharged separately.

6. The method for recycling lithium iron phosphate production wastewater according to claim 1, characterized in that, After the dehydration treatment, the moisture content of the mud cake is less than 5%, and the lithium content is 2-4%.

7. The method for recycling lithium iron phosphate production wastewater according to claim 1, characterized in that, The content of suspended solids in the second solution is 5~20 mg / L.

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