Recycling device for phosphoric acid recrystallization filtrate of iron phosphate dihydrate

Abstract

The utility model discloses a recycling device for phosphoric acid recrystallization filtrate of iron phosphate dihydrate. The recycling device comprises a separating device, a clear liquid adjusting tank, a heat exchange device, a filtering device, a recycling tank and a dissolving tank which are connected in sequence. According to the device, the filtrate in the recrystallization process is subjected to solid-liquid separation, filtration, cooling and performance parameter adjustment and then is put into the recrystallization process again, so that the consumption of phosphoric acid is reduced while the performance index of iron phosphate dihydrate is not influenced, and the production cost is reduced; the accumulation of impurity phosphoric acid in a wastewater system is reduced, and the difficulty and cost of later wastewater treatment are reduced; the device is simple in structure, low in cost, easy to operate and good in flexibility.

Description

Technical Field

[0001] This utility model relates to a device for recovering phosphoric acid waste liquid, and more particularly to a device for recovering and reusing filtrate from the recrystallization of ferric phosphate dihydrate. Background Technology

[0002] With the rapid growth of global demand for clean energy, lithium-ion batteries, as mainstream energy storage devices, are widely used in electric vehicles, energy storage power stations, and other fields. Lithium iron phosphate (LFP), as the cathode material for lithium-ion batteries, has become a key factor influencing new energy batteries, and its preparation process has become a focus of research and production. The performance of the iron phosphate precursor is a crucial factor affecting the LFP cathode material. In the preparation of iron phosphate, recrystallization is the process of separating crystals from a mixed solution. Common methods include solvothermal or hydrothermal methods to react the raw materials to generate iron phosphate crystals, which are then separated from the solution. Generally, filtration, centrifugation, or cooling crystallization are used to extract the crystals from the solution, followed by drying to finally obtain the target product, iron phosphate crystals. The recrystallization process, acting as crystallinity reforming, crystal shape reforming, impurity removal, or purification processes, is crucial for controlling the specific surface area and particle size of iron phosphate, reducing impurities, and ensuring phase purity. In the production of ferric phosphate, the one-step ammonia process consumes relatively more phosphoric acid compared to the two-step process. Phosphoric acid plays an indispensable role in the recrystallization process. On the one hand, supplementing phosphoric acid during recrystallization can create micro-dissolved ion channels on the surface of ferric phosphate, which is beneficial for the release of impurities such as metals and sulfur, thereby improving the purity of ferric phosphate. On the other hand, in order to improve the crystallinity of dihydrate ferric phosphate, the conversion reaction usually requires the addition of a high amount of phosphoric acid for crystal transformation. Phosphoric acid mainly acts as a conversion medium to adjust the pH value of the system, further resulting in a large consumption of phosphoric acid and increasing production costs. Furthermore, in this process, only a very small portion of phosphoric acid participates in the physicochemical reactions of ferric phosphate, and the recrystallized phosphoric acid mother liquor has a high temperature and turbidity, making it unusable for direct reuse. Most of the phosphoric acid accumulates in the wastewater treatment system, increasing the difficulty and cost of wastewater treatment. Utility Model Content

[0003] Purpose of the utility model: The purpose of this utility model is to reduce the accumulation of phosphoric acid in the wastewater system, which increases the difficulty and cost of wastewater treatment, while reducing phosphoric acid consumption and production costs, and to provide a device for the recovery and reuse of filtrate from the recrystallization of dihydrate phosphate and phosphoric acid.

[0004] Technical solution: The device for recycling and reusing filtrate of ferric phosphate dihydrate recrystallization filtrate according to this utility model includes a separation device, a clear liquid conditioning tank, a heat exchange device, a filtration device, a recovery tank and a dissolving tank connected in sequence.

[0005] Furthermore, the separation device is a plate and frame filter press, which also includes a turbidimeter for controlling the turbidity of the separated liquid and a turbid liquid pipeline for sending the turbid mother liquor to the wastewater treatment system. The turbidity threshold of the turbidimeter is 5 NTU. After filtration, the recrystallized filtrate is controlled by the turbidimeter to ensure that the impurity content in the clarified liquid meets the turbidity requirements before flowing into the subsequent recovery device.

[0006] Furthermore, the capacity of the clear liquid conditioning tank is 100-300 m³. 3 The filter press has a built-in stirring device. Since the amount and quality of the mother liquor recovered by the plate and frame filter press in a single batch are subject to certain fluctuations, the amount of water in the clear liquid adjustment tank is adjusted to stabilize the P content in the clear liquid adjustment tank. The turbidity of the clear liquid in the clear liquid adjustment tank is <5 NTU and the P content is 900±150 ppm.

[0007] Furthermore, the heat exchange device is a plate heat exchange device, and the temperature of the clear liquid is controlled at 50±5℃. After cooling treatment, it can meet the requirements of the recrystallization process. At the same time, the heat energy of the clear liquid can be further reused through the heat exchange device, reducing the energy consumption of the production line.

[0008] Furthermore, the filtration device is a polypropylene bag filter with a filtration accuracy of 0.5 μm. After filtration, the turbidity of the clear liquid is <1.50 NTU. The recovered dilute phosphoric acid solution is mixed with the original phosphorus source material in a certain proportion and added to the dissolving tank. The solution is then adjusted to meet the pH requirements before being put into production. Performance tests such as the iron-phosphorus ratio and specific surface area of ​​ferric phosphate dihydrate are tested under different input ratios. The results show that the performance of ferric phosphate dihydrate is not significantly different after different proportions of the recovered phosphorus source are added to production, and the iron-phosphorus ratio and specific surface area all meet the process requirements.

[0009] Beneficial effects: Compared with the prior art, the present invention has the following advantages: 1. After solid-liquid separation, filtration, cooling and performance parameter adjustment of the filtrate in the recrystallization process, it is put back into the recrystallization process, which reduces the consumption of phosphoric acid and lowers the production cost without affecting the performance index of ferric phosphate dihydrate; 2. It reduces the accumulation of impurity phosphoric acid in the wastewater system, which reduces the difficulty and cost of subsequent wastewater treatment; 3. The device has a simple structure, low cost, easy operation and good flexibility. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the device process of this utility model. Detailed Implementation

[0011] The technical solution of this utility model will be further described below with reference to the accompanying drawings.

[0012] like Figure 1The device shown is for the recovery and reuse of recrystallized filtrate from ferric phosphate dihydrate, comprising a separation unit 1, a clarified liquid conditioning tank 3, a heat exchange unit 4, a filtration unit 5, a recovery tank 6, and a dissolving tank 7 connected in sequence. The separation unit 1 is a plate and frame filter press, equipped with a turbidity meter 2 with a threshold of 5 NTU for online monitoring of the turbidity of the separated liquid, and also includes a turbidity pipeline 9 for sending the turbid mother liquor to a wastewater treatment system. The clarified liquid conditioning tank 3 has a capacity of 100–300 m³. 3 The recovered clarified liquid is temporarily stored in a clarified liquid conditioning tank 3 in a certain amount. An internal stirring device mixes the accumulated clarified liquid, ensuring that the turbidity of the clarified liquid in the conditioning tank 3 is <5 NTU and the phosphorus content is 900±150 ppm. The heat exchange device 4 is a plate heat exchange device, and the temperature of the clarified liquid is controlled at 50±5℃. The heat energy of the clarified liquid can be further reused through the heat exchange device, reducing the energy consumption of the production line. The filtration device 5 is a polypropylene bag filter with a filtration accuracy of 0.5 μm. After filtration by the filtration device 5, the turbidity of the clarified liquid is <1.50 NTU. The recovered phosphoric acid clarified liquid is then sent to a dissolving tank 7 for indexing and adjustment of the solution to meet the process requirements before being put into production.

[0013] Because the volume and quality of the mother liquor recovered by the plate and frame filter press in a single batch fluctuate, the phosphoric acid content in the real-time recovered phosphoric acid solution is unstable, affecting the process adjustment for subsequent recovery and reuse. To avoid this problem, a certain amount of clear liquid is accumulated in the clear liquid conditioning tank 3 for mixing before being put into the subsequent recovery and reuse system. The effect of different accumulation volumes in the clear liquid conditioning tank 3 on the phosphoric acid content and turbidity stability of the clear liquid was tested. Ten batches were tested, and the results are detailed in Table 1.

[0014] Table 1. P content and turbidity of different accumulation capacities in the clear liquid conditioning tank.

[0015]

[0016] As can be seen from Table 1, when the accumulation in the clear liquid conditioning tank 3 is 300m³, 3 At that time, the P content range of each batch of clear liquid was the smallest, indicating that after 300m 3 After adjustment, the P content and turbidity of the recovered clarified liquid fluctuated slightly, meeting the stability requirements of the current process. Ten batches of clarified liquid at this accumulation level were transported to the subsequent heat exchanger 4, filter 5, and recovery tank 6. The P content and turbidity in the recovery tank 6 were tested, as detailed in Table 2.

[0017] As can be seen from Table 2, the difference in P content and turbidity of the phosphoric acid solution in recovery tank 6 is very small, indicating that the P content and turbidity of the phosphoric acid solution recovered from different batches are relatively close and the performance is stable.

[0018] Table 2. Test results of P content and turbidity in the recovery tank.

[0019]

[0020] The recovered phosphoric acid solution and the original phosphorus source material in the recovery tank 6 were added to the dissolving tank 7 in different proportions through the flow meter 8. The P solubility and pH value of the solution were adjusted. Ten batches were tested with different recovery ratios. The results are shown in Table 3.

[0021] Table 3. P solubility and pH value of the solution in the dissolving tank.

[0022]

[0023] As shown in Table 3, when recycled phosphoric acid with different proportions is mixed with the original phosphorus source, the P content and pH value in the dissolved phosphoric acid solution are not significantly different, indicating stable solution performance. Theoretically, the larger the accumulation in the clarified solution conditioning tank 3, the smaller the fluctuations in P content and turbidity. However, considering the production line's capacity and the stability of the recycled phosphoric acid solution over a long period, a storage capacity of 300 m³ is a more rational approach. This allows for minimizing fluctuations in P content and turbidity in the recycled solution, preventing different batches of recycled solution from affecting the recrystallization effect of ferric phosphate dihydrate, and simultaneously meeting production capacity requirements.

[0024] The dissolved phosphoric acid solution was added to the recrystallization process of ferric phosphate dihydrate, and the iron-to-phosphorus ratio and specific surface area of ​​10 batches of recovered ferric phosphate dihydrate were tested. The test results are detailed in Table 4.

[0025] Table 4. Results of iron-to-phosphorus ratio and specific surface area tests for recrystallized ferric phosphate dihydrate.

[0026]

[0027] As can be seen from Table 4, after the phosphoric acid solution with different proportions was put into the recrystallization process of ferric phosphate dihydrate, the iron-phosphorus ratio and specific surface area of ​​the ferric phosphate met the process production requirements and did not change much. This indicates that the performance of the produced ferric phosphate is very stable, and thus shows that the recovery and reuse of phosphoric acid meets the production requirements.

Claims

1. An apparatus for recovering and reusing a dihydrate iron phosphate phosphoric acid recrystallization filtrate, characterized by, The separation device (1), the clear liquid adjusting tank (3), the heat exchange device (4), the filtering device (5), the recovery tank (6) and the dissolving tank (7) are sequentially connected.

2. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 1, characterized in that, The separation device (1) is a plate-and-frame filter press, further comprising a turbidity meter (2) for controlling the turbidity of the separated liquid and a turbid liquid pipeline (9) for sending the turbid mother liquor to a wastewater treatment system.

3. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 2, characterized in that, The turbidity threshold of the turbidity meter (2) is 5 NTU.

4. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 1, characterized in that, The capacity of the clear liquor conditioning tank (3) is 100-300 m 3 with built-in stirring device.

5. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 4, characterized in that, The turbidity of the clear liquid in the clear liquid adjusting tank (3) is less than 5 NTU, and the P content is 900±150 ppm.

6. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 1, characterized in that, The heat exchange device (4) is a plate heat exchanger, and the temperature of the clear liquid is controlled at 50±5℃.

7. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 1, characterized in that, The filtering device (5) is a polypropylene bag filter, and the filtering precision is 0.5 um.

8. The apparatus for recovering and reusing the dihydrate iron phosphate phosphoric acid recrystallization filtrate according to claim 7, characterized in that, The turbidity of the clear liquid filtered by the filtering device (5) is less than 1.50 NTU.

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