A continuous reaction and washing system for iron phosphate

Abstract

This invention relates to a continuous ferric phosphate reaction and washing system, comprising multi-stage ferric phosphate reaction and washing modules. Each stage of the ferric phosphate reaction and washing module includes a reaction device, an aging device, and a multi-stage membrane washing device connected sequentially along the feed direction. Between adjacent ferric phosphate reaction and washing modules, the multi-stage membrane washing device of the previous stage is connected to the reaction device of the next stage. This invention employs a specially designed reaction device to achieve uniform distribution and continuous reaction of the reaction raw materials, utilizes the aging device to achieve continuous aging of the slurry, and achieves continuous and efficient washing of ferric phosphate powder through the multi-stage membrane washing device. This eliminates the traditional pulping process, reduces washing energy and water consumption, achieves zero loss of phosphoric acid, and improves product quality and stability.

Description

Technical Field

[0001] This invention belongs to the field of iron phosphate preparation technology, and particularly relates to a continuous iron phosphate reaction and washing system. Background Technology

[0002] Iron phosphate is an important chemical raw material, and in recent years it has been widely used as a precursor for synthesizing lithium iron phosphate, the cathode material of lithium-ion batteries. Currently, iron phosphate is gradually replacing other precursors and becoming the core precursor for lithium iron phosphate. Most of the patents reported in China use batch methods to prepare iron phosphate, resulting in batch production, which cannot guarantee the stability and consistency of products between batches; furthermore, batch production equipment requires a large number of reaction vessels, occupies a large area, and has high labor costs.

[0003] Patent CN107337189A discloses a continuous production system and method for ferric phosphate. The system uses four reactors connected in series. The reactors are numerous and all are traditional paddle-type stirred tanks. In the first-stage precipitation reactor, liquid alkali is directly added to the raw solution at once through a metering pump to carry out the precipitation reaction. This can lead to problems such as excessively high local concentrations and uneven distribution, which affects the consistency and stability of the product morphology. In addition, the washing of the product in this system consists of a plate and frame filter press and a washing tank, which poses a risk of material loss. Furthermore, the amount of deionized water used for washing is 10 times the amount of product, resulting in high water consumption.

[0004] Patent CN106379877A discloses a continuous preparation apparatus for ferric phosphate. Ferric salt and phosphate are added separately to continuous tubular reactors via a screw feeder and dissolved in water to form solutions. The two solutions are then sequentially fed into continuous tubular reactors 1 and 2 for reaction. However, ferric sulfate is only slightly soluble in water and dissolves slowly, and it also undergoes slow hydrolysis to form ferric hydroxide colloid. Therefore, undissolved solids can easily clog the tubular reactors, leading to unstable feed, excessively high local concentrations, and an inability to obtain a stable product. Furthermore, for reactions that generate solid products, blockage of the tubular reactors may occur, disrupting continuous production. Summary of the Invention

[0005] To address the above technical problems, the present invention aims to provide a continuous reaction and washing system for ferric phosphate. This system employs a specially designed reaction apparatus to achieve uniform distribution and continuous reaction of the reaction raw materials, utilizes an aging device to achieve continuous aging of the slurry, and employs a multi-stage membrane washing device to achieve continuous and efficient washing of the ferric phosphate powder. This eliminates the traditional pulping process, reduces washing energy and water consumption, achieves zero loss of phosphoric acid, and improves product quality and stability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A continuous iron phosphate reaction and washing system includes multi-stage iron phosphate reaction and washing modules. Each stage of the iron phosphate reaction and washing module includes a reaction device, an aging device, and a multi-stage membrane washing device connected sequentially along the feed direction. Between two adjacent iron phosphate reaction and washing modules, the multi-stage membrane washing device of the previous stage iron phosphate reaction and washing module is connected to the reaction device of the next stage iron phosphate reaction and washing module.

[0008] In some technical solutions, the reaction device includes a built-in first feeding component, a second feeding component, and a stirring component. The first feeding component and the second feeding component are a hollow feeding tube and a dynamic disc membrane component, respectively, or both are hollow feeding tubes. The feeding port of the hollow feeding tube and the hollow membrane of the dynamic disc membrane component are adjacent to the stirring component.

[0009] In some technical solutions, the first feeding component is a hollow material distribution tube, which is connected to the first material input port of the reaction device and is used to continuously and evenly distribute material A into the reaction device.

[0010] The second feeding component is a dynamic disc membrane component, which includes a hollow rotating shaft and a plurality of hollow membranes spaced apart on the hollow rotating shaft. The hollow membranes are connected to the hollow rotating shaft, and the hollow rotating shaft is connected to the second material inlet of the reaction device, for continuously and evenly distributing material B into the reaction device from the inside to the outside through the hollow membranes.

[0011] The mixing assembly includes mixing wheels located on the upper and lower sides of the hollow membrane. Between adjacent mixing wheels, on the upper and lower sides of the hollow membrane, there are material outlets of the hollow material distribution tube. The hollow rotating shaft is connected to an external drive device to drive the hollow membrane and mixing wheels to rotate, thereby uniformly mixing material A and material B.

[0012] In some technical solutions, the dynamic disc membrane assembly also includes a metal sheet installed at the head and end of the hollow rotating shaft for flow pattern control within the reaction device to prevent material backmixing.

[0013] In some technical solutions, the first feeding component and the second feeding component are both hollow feeding tubes, the stirring component includes a stirring paddle, the stirring paddle is disposed between the two hollow feeding tubes, and the feeding port is provided at the end of the hollow feeding tube.

[0014] In some technical solutions, the aging device includes a built-in membrane aeration component to generate an air flotation effect and reduce the deposition of solid particles.

[0015] In some technical solutions, the membrane aeration assembly is located at the bottom of the aging device, including a compressed air inlet pipe and an aeration membrane connected thereto. A demister is also installed on the top inner side of the aging device to remove liquid droplets from the gas generated during aeration inside the device before discharging it; and / or,

[0016] The aging device is provided with a feed inlet on the upper side, and a perforated plate distributor is installed below the feed inlet to distribute the products in the reaction device evenly into the aging device.

[0017] In some technical solutions, the multi-stage membrane washing device includes a multi-stage membrane washing unit, a membrane separation unit, and a recovery unit.

[0018] Between two adjacent membrane washing units, the slurry outlet of the upper membrane washing unit is connected to the slurry inlet of the lower membrane washing unit, and the washing wastewater outlet of the lower membrane washing unit is connected to the water replenishment point of the upper membrane washing unit.

[0019] The wastewater outlet of the first-stage membrane washing unit is connected to the membrane separation unit, the concentrate outlet of the membrane separation unit is connected to the recovery unit, and the clear liquid outlet of the membrane separation unit is connected to the water replenishment point of the final-stage membrane washing unit.

[0020] Some technical solutions also include a membrane concentration unit connected in series to the pipeline between the aging device and the multi-stage membrane washing device, wherein the concentrated mother liquor outlet of the membrane concentration unit is connected to the recovery unit.

[0021] In some technical solutions, the multi-stage ferric phosphate reaction and washing module includes sequentially connected yellow material ferric phosphate reaction and washing modules and white material ferric phosphate reaction and washing modules.

[0022] The yellow material ferric phosphate reaction and washing module includes an oxidation kettle, a first aging kettle, a yellow material membrane concentration unit, and a yellow material multi-stage membrane washing device connected in sequence. The yellow material multi-stage membrane washing device includes a yellow material multi-stage membrane washing unit, a first membrane separation unit, and a by-product salt recovery unit.

[0023] The white ferric phosphate reaction and washing module includes a conversion kettle, a second aging kettle, a white material membrane concentration unit, and a white material multi-stage membrane washing device connected in sequence. The white material multi-stage membrane washing device includes a white material multi-stage membrane washing unit, a second membrane separation unit, and a dilute phosphoric acid recovery unit. The recovered dilute phosphoric acid solution is reused in the conversion kettle for conversion reaction or reused in the phosphorus source dissolution section.

[0024] The present invention, by employing the above technical solution, has at least the following beneficial effects:

[0025] 1. This application uses specially designed oxidation and conversion kettles to achieve uniform material distribution and continuous reaction, uses an aging kettle with built-in aeration membrane to achieve continuous aging of slurry, and uses membrane concentration and multi-stage membrane washing devices to achieve continuous washing of reaction slurry. The entire process involves continuous feeding and discharging, which can improve the level of automation and product stability, with high unit output value and low investment.

[0026] 2. This application divides the entire reaction process into an oxidation precipitation reaction and a conversion reaction, and adds a membrane concentration and membrane washing process between the oxidation precipitation reaction and the conversion reaction. After the precipitated slurry is washed and qualified, it is directly sent to the conversion kettle for conversion reaction, which can significantly reduce the content of impurity elements in the product and improve the quality of the product.

[0027] 3. This application utilizes membrane concentration and membrane washing technology to replace the traditional filter cake washing technology of pressure filter. It has a high solid particle retention rate, eliminates the pulping process, and the slurry flows from top to bottom in the co-current flow during the washing process, while the wash water flows from bottom to top in the counter-current flow, realizing continuous multi-stage membrane washing, reducing energy and water consumption, reducing the footprint, and operating in a fully enclosed manner with low pollution.

[0028] 4. The phosphoric acid used in the conversion reaction process of this application is recovered through membrane concentration mother liquor and membrane separation concentrate. The recovered dilute phosphoric acid solution with low impurity content is partially reused in the conversion reaction and partially reused for phosphorus source dissolution, basically achieving zero loss of phosphoric acid. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings and their markings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the continuous iron phosphate reaction and washing system described in an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the continuous reaction and washing process of iron phosphate as described in an embodiment of the present invention.

[0032] The meanings of the symbols in the diagram are as follows:

[0033] 1 - Oxidation reactor, 101 - Hollow rotating shaft, 102 - Hollow membrane, 103 - Drive device, 104 - Metal sheet, 105 - Stirring wheel, 106 - Hollow material distribution pipe, 107 - Nozzle;

[0034] 2 - First aging kettle, 201 - Perforated plate distributor, 202 - Aeration membrane, 203 - Demister;

[0035] 3 - Yellow material membrane concentration unit, 4 - Yellow material primary membrane washing unit, 5 - Yellow material secondary membrane washing unit, 6 - By-product salt recovery unit, 7 - First membrane separation unit, 8 - Water replenishment point;

[0036] 9 - Conversion vessel, 901 - First feed pipe, 902 - Second feed pipe, 903 - Stirring paddle, 10 - Second aging vessel, 11 - White material membrane concentration unit, 12 - White material primary membrane washing unit, 13 - White material secondary membrane washing unit, 14 - Dilute phosphoric acid recovery unit, 15 - Second membrane separation unit. Detailed Implementation

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0038] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0039] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0040] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0042] Example 1

[0043] Please see Figure 1This paper illustrates a continuous iron phosphate reaction and washing system, which includes multi-stage iron phosphate reaction and washing modules. Each stage of the iron phosphate reaction and washing module includes a reaction device, an aging device, and a multi-stage membrane washing device connected sequentially along the feed direction. Between two adjacent iron phosphate reaction and washing modules, the multi-stage membrane washing device of the previous stage iron phosphate reaction and washing module is connected to the reaction device of the next stage iron phosphate reaction and washing module.

[0044] This application enables a continuous process for the iron phosphate reaction steps, and by adding a multi-stage membrane washing process between adjacent reaction steps, the content of impurity elements in the products of each step can be significantly reduced, thereby improving product quality.

[0045] Example 2

[0046] Based on Example 1, this embodiment divides the entire reaction process for preparing ferric phosphate into an oxidation precipitation reaction process and a conversion reaction process, specifically including sequentially connected yellow ferric phosphate reaction and washing modules and white ferric phosphate reaction and washing modules.

[0047] The yellow material ferric phosphate reaction and washing module includes an oxidation kettle 1, a first aging kettle 2, and a yellow material multi-stage membrane washing device connected in sequence. The yellow material multi-stage membrane washing device includes a yellow material multi-stage membrane washing unit, a first membrane separation unit 7, and a by-product salt recovery unit 6.

[0048] The white ferric phosphate reaction and washing module includes a conversion kettle 9, a second aging kettle 10, and a white multi-stage membrane washing device connected in sequence. The white multi-stage membrane washing device includes a white multi-stage membrane washing unit, a second membrane separation unit 15, and a dilute phosphoric acid recovery unit 14. The recovered dilute phosphoric acid is reused in the conversion kettle 9 for conversion reaction, or reused in the phosphorus source dissolution section.

[0049] This application divides the iron phosphate synthesis reaction process into an oxidation precipitation reaction process and a conversion reaction process, and adds a multi-stage membrane washing process in between to purify the products of each stage and improve the product quality. In the oxidation precipitation reaction process, by-product salts in the product can be recovered. In the conversion reaction process, dilute phosphoric acid solution with low impurity content can be recovered. Part of it is reused in the conversion reaction and part of it is reused in phosphorus source dissolution, basically achieving zero loss of phosphoric acid.

[0050] Example 3

[0051] This embodiment improves upon Embodiment 2 by modifying the oxidation reactor 1 and the conversion reactor 9 to achieve uniform material distribution and continuous reaction. Specifically:

[0052] The oxidation reactor 1 includes a built-in hollow material distribution tube 106, a dynamic disc membrane assembly, and a first stirring assembly. The hollow material distribution tube 106 is connected to the first material inlet of the oxidation reactor 1 and is used to continuously and evenly distribute material A into the oxidation reactor 1. The dynamic disc membrane assembly includes a hollow rotating shaft 101 and a plurality of hollow membranes 102 spaced apart on the hollow rotating shaft 101. The hollow membranes 102 are connected to the hollow rotating shaft 101, and the hollow rotating shaft 101 is connected to the second material inlet of the reaction device. The first stirring assembly is used to continuously and evenly distribute material B from the inside of the hollow membrane 102 to the outside into the oxidation reactor 1. The first stirring assembly includes stirring wheels 105 located on the upper and lower sides of the hollow membrane 102. Between adjacent stirring wheels 105, there are material outlets, i.e. nozzles 107, of hollow material distribution pipes 106 located on the upper and lower sides of the hollow membrane 102. The hollow rotating shaft 101 is connected to an external driving device 103 to drive the hollow membrane 102 and stirring wheels 105 to rotate, thereby uniformly mixing material A and material B.

[0053] Specifically, material A is a ferrous purification solution, and material B is a mixture of phosphorus source purification solution and oxidant solution. The iron source of the ferrous purification solution can be selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous oxalate; the phosphorus source of the phosphorus source purification solution can be selected from at least one of phosphoric acid, monohydrogen phosphate, dihydrogen phosphate and neutral phosphate; and hydrogen peroxide can be selected as the oxidant.

[0054] In a preferred embodiment, the dynamic disc membrane assembly further includes a metal sheet 104 mounted at the beginning and end of the hollow rotating shaft 101 for flow pattern control within the oxidation reactor 1, increasing radial flow around the hollow membrane 102 and preventing material backmixing.

[0055] The conversion vessel 9 includes a built-in first distribution pipe 901, a second distribution pipe 902, and a second stirring assembly. The second stirring assembly includes a stirring paddle 903, which is located between the first distribution pipe 901 and the second distribution pipe 902. The ends of the first distribution pipe 901 and the second distribution pipe 902 are provided with several distribution ports facing the stirring paddle 903. The stirring paddle 903 rotates and stirs under power drive, so that the two materials input from the first distribution pipe 901 and the second distribution pipe 902 are uniformly mixed and undergo a conversion reaction.

[0056] The first feed pipe 901 is connected to the qualified yellow material outlet of the yellow material multi-stage membrane washing device to continuously input qualified iron phosphate yellow material; the second feed pipe 902 is connected to the phosphoric acid supply unit to continuously input phosphoric acid solution of appropriate concentration.

[0057] This application achieves uniform material distribution and continuous reaction through a specially designed oxidation reactor 1 and conversion reactor 9, which can significantly improve product quality and production efficiency.

[0058] It should be noted that the specific design of the oxidation vessel 1 and the conversion vessel 9 in this application can be based on the above improved structure in various combinations. That is, the oxidation vessel 1 and the conversion vessel 9 are collectively referred to as the reaction device. The reaction device is provided with a first feeding component and a second feeding component. The first feeding component and the second feeding component can be a hollow material distribution tube and a dynamic disc membrane component, respectively, or both can be hollow material distribution tubes.

[0059] Example 4

[0060] This embodiment improves upon Embodiment 2 by modifying the aging reactor to achieve continuous aging of the slurry. Specifically:

[0061] The bottoms of the first aging vessel 2 and the second aging vessel 10 are respectively equipped with membrane aeration components, each including a compressed air inlet pipe and an aeration membrane 202 connected thereto; demisters 203 are respectively installed on the top of the vessels. The oxidizing liquid is evenly distributed into the first aging vessel 2 for continuous aging, while the mixed slurry enters the second aging vessel 10 for continuous aging. Through the compressed air inlet pipe and the aeration membrane 202 at the bottom of the vessel, an air flotation effect is generated, reducing the deposition of solid particles; the gas generated by aeration is discharged after being de-dropped by the demister 203 at the top of the vessel. Specifically, the demister 203 is selected as a loose fiber bed demister.

[0062] In a preferred embodiment, the upper side of the first aging vessel 2 and the second aging vessel 10 is provided with a feed inlet, and a perforated plate distributor 201 is installed below the feed inlet to distribute the product in the reaction device evenly into the aging device.

[0063] Example 5

[0064] This embodiment, based on Embodiment 2, designs a multi-stage membrane washing device to achieve product washing and resource recycling, specifically as follows:

[0065] The multi-stage membrane washing device for yellow materials includes a multi-stage membrane washing unit for yellow materials, a first membrane separation unit 7, and a by-product salt recovery unit 6. Between two adjacent yellow material membrane washing units, the slurry outlet of the previous stage yellow material membrane washing unit is connected to the slurry inlet of the next stage yellow material membrane washing unit, and the washing wastewater outlet of the next stage yellow material membrane washing unit is connected to the water replenishment point 8 of the previous stage yellow material membrane washing unit. The washing wastewater outlet of the first stage yellow material membrane washing unit is connected to the first membrane separation unit 7, the concentrated liquid outlet of the first membrane separation unit 7 is connected to the by-product salt recovery unit 6, and the clarified liquid outlet of the first membrane separation unit 7 is connected to the water replenishment point 8 of the final stage yellow material membrane washing unit.

[0066] The white material multi-stage membrane washing device includes a white material multi-stage membrane washing unit, a second membrane separation unit 15, and a dilute phosphoric acid recovery unit 14. Between two adjacent white material membrane washing units, the slurry outlet of the previous white material membrane washing unit is connected to the slurry inlet of the next white material membrane washing unit, and the washing wastewater outlet of the next white material membrane washing unit is connected to the water replenishment point 8 of the previous white material membrane washing unit. The washing wastewater outlet of the first white material membrane washing unit is connected to the second membrane separation unit 15, the concentrated liquid outlet of the second membrane separation unit 15 is connected to the dilute phosphoric acid recovery unit 14, and the clarified liquid outlet of the second membrane separation unit 15 is connected to the water replenishment point 8 of the final white material membrane washing unit.

[0067] Preferably, the multi-stage membrane washing unit for yellow materials includes a primary membrane washing unit 4 and a secondary membrane washing unit 5. The washing wastewater outlet of the primary membrane washing unit 4 is connected to the first membrane separation unit 7. The concentrated liquid outlet of the first membrane separation unit 7 is connected to the by-product salt recovery unit 6. The clarified liquid outlet of the first membrane separation unit 7 is connected to the water replenishment point 8 of the secondary membrane washing unit 5. The washing wastewater outlet of the secondary membrane washing unit 5 is connected to the water replenishment point 8 of the primary membrane washing unit 4.

[0068] The white material multi-stage membrane washing unit includes a white material primary membrane washing unit 12 and a white material secondary membrane washing unit 13. The washing wastewater outlet of the white material primary membrane washing unit 12 is connected to the second membrane separation unit 15. The concentrated liquid outlet of the second membrane separation unit 15 is connected to the dilute phosphoric acid recovery unit 14. The clarified liquid outlet of the second membrane separation unit 15 is connected to the water replenishment point 8 of the white material secondary membrane washing unit 13. The washing wastewater outlet of the white material secondary membrane washing unit 13 is connected to the water replenishment point 8 of the white material primary membrane washing unit 12.

[0069] In some embodiments, the system also includes a yellow material membrane concentration unit 3 connected in series to the pipeline between the first aging reactor 2 and the yellow material primary membrane washing unit 4, with the concentrated mother liquor outlet of the yellow material membrane concentration unit 3 connected to the by-product salt recovery unit 6; and a white material membrane concentration unit 11 connected in series to the pipeline between the second aging reactor 10 and the white material primary membrane washing unit 12, with the concentrated mother liquor outlet of the white material membrane concentration unit 11 connected to the dilute phosphoric acid recovery unit 14.

[0070] In a preferred embodiment, it also includes a yellow material buffer tank connected in series to the pipeline between the first aging vessel 2 and the yellow material film concentration unit 3; and a white material buffer tank connected in series to the pipeline between the second aging vessel 10 and the white material film concentration unit 11.

[0071] This application adds membrane concentration and membrane washing processes between the oxidation precipitation reaction and the conversion reaction. After the precipitated slurry is washed and qualified, it is directly sent to the conversion reactor 9 for conversion reaction, which can significantly reduce the content of impurity elements in the product and improve the product quality.

[0072] By using membrane concentration and membrane washing technology to replace the traditional filter cake washing technology, the solid particle retention rate is high, the pulping process is eliminated, and the slurry flows downward from top to bottom during the washing process, while the wash water flows upward from bottom to top, realizing continuous multi-stage membrane washing, reducing energy and water consumption, reducing the footprint, and operating in a fully enclosed manner with low pollution.

[0073] In this application, the initial washing water for the primary membrane washing unit is fresh soft water, and subsequent washing water is recycled wastewater from the next stage of membrane washing. The number of membrane washing stages is determined based on the material and washing requirements.

[0074] It should be noted that any membrane concentration unit and membrane washing unit in this application include a built-in separation component. The separation component includes a rotating shaft and a plurality of hollow separation membranes spaced apart on the rotating shaft. The separation membranes are connected to the rotating shaft and allow liquid to penetrate the surface and enter the inner cavity. The rotating shaft is used to collect and discharge the separated mother liquor or washing wastewater.

[0075] Example 6

[0076] Please see Figure 2 This embodiment further provides a continuous reaction and washing process for iron phosphate, designed based on any one or a combination of the above embodiments. Specifically, it includes the following steps:

[0077] Yellow phosphate ferric phosphate reaction and washing steps: The mixture of phosphorus source purification solution and oxidant solution and ferrous phosphate purification solution are continuously and evenly distributed into oxidation reactor 1 to undergo oxidation reaction. The resulting oxidation solution enters the first aging reactor 2 for continuous aging. The generated yellow phosphate ferric phosphate is continuously washed by the yellow phosphate multi-stage membrane washing device and then transported.

[0078] The reaction and washing steps of the white material with iron phosphate: The iron phosphate yellow material and the phosphoric acid solution of appropriate concentration are continuously and evenly distributed into the conversion kettle 9 to undergo conversion reaction. The resulting mixed slurry enters the second aging kettle 10 for continuous aging. The generated iron phosphate white material is then continuously washed by the white material multi-stage membrane washing device to obtain qualified white material.

[0079] In a specific process, a mixture of phosphorus source purification solution and oxidant solution is continuously and uniformly distributed from the inside of hollow membrane 102 to the outside through hollow rotating shaft 101 into oxidation reactor 1; ferrous purification solution is continuously added into oxidation reactor 1 through the feeding port of hollow feeding pipe 106, i.e., nozzle 107; stirring wheel 105 rotates with hollow rotating shaft 101, stirring at a speed of 0-1000 r / min, so that the two raw material solutions are uniformly mixed for oxidation reaction; the temperature of the reaction solution in oxidation reactor 1 is maintained at 40-65℃ by a heating jacket set outside oxidation reactor 1; the molar concentration ranges of ferrous purification solution and phosphorus source purification solution are 1.6-2.8 mol / L and 1.1-3.0 mol / L, respectively; the feed rate ranges of ferrous purification solution, phosphorus source purification solution and oxidant solution mixture are 120-235 L / h and 157-300 L / h, respectively.

[0080] The oxidizing liquid is evenly distributed into the first aging tank 2 for continuous aging. Through the compressed air inlet pipe and aeration membrane 202 at the bottom of the tank, an air flotation effect is generated to reduce the deposition of solid particles. The inlet pressure of the compressed air inlet pipe is 0-5 bar. The gas generated by aeration is discharged after the liquid droplets are removed by the demister 203 at the top of the tank. The temperature of the liquid in the first aging tank 2 is maintained at 65-75℃ and the pH value is 2.5-3.0 to carry out precipitation and crystallization. The residence time of the oxidizing liquid in the first aging tank 2 is ensured to be 0.5-2.5 hours to obtain iron phosphate yellow material.

[0081] The pH value of the liquid in the first aging kettle 2 is adjusted by using one or more of the following: ammonia solution, sodium carbonate solution, sodium hydroxide solution, potassium hydroxide solution, or urea solution.

[0082] The generated iron phosphate yellow material sequentially enters the yellow material primary membrane washing unit 4 and the yellow material secondary membrane washing unit 5. The washing wastewater from the yellow material secondary membrane washing unit 5 is reused in the yellow material primary membrane washing unit 4. The washing wastewater from the yellow material primary membrane washing unit 4 enters the first membrane separation unit 7. The concentrated liquid from the first membrane separation unit 7 enters the by-product salt recovery unit 6, and the clear liquid enters the yellow material secondary membrane washing unit 5.

[0083] The washed and qualified iron phosphate yellow material and the 2-10% concentration phosphoric acid solution are continuously added to the near the agitator 903 in the conversion vessel 9 through the first distribution pipe 901 and the second distribution pipe 902, respectively. The agitator 903 rotates and stirs at a speed of 0-200 r / min to make the two materials uniformly mixed for conversion reaction. The solid content in the conversion vessel 9 is controlled at 5%-35%, and the temperature of the liquid in the conversion vessel 9 is maintained at 85-90℃ for conversion reaction.

[0084] The mixed slurry obtained after the conversion reaction is fed into the second aging reactor 10 for continuous aging. The temperature of the mixed slurry in the second aging reactor 10 is maintained at 95-98°C for aging. The residence time of the mixed slurry in the second aging reactor 10 is ensured to be 1.5-3.5 hours to obtain iron phosphate white material.

[0085] The generated iron phosphate white material sequentially enters the white material primary membrane washing unit 12 and the white material secondary membrane washing unit 13. The washing wastewater from the white material secondary membrane washing unit 13 is recycled back to the white material primary membrane washing unit 12. The washing wastewater from the white material primary membrane washing unit 12 enters the second membrane separation unit 15. The concentrated liquid from the second membrane separation unit 15 enters the dilute phosphoric acid recovery unit 14, and the clear liquid enters the white material secondary membrane washing unit 13. The recovered dilute phosphoric acid solution is recycled back to the conversion reactor 9 for conversion reaction, or recycled back to the phosphorus source dissolution section.

[0086] In a preferred process, it also includes:

[0087] The generated iron phosphate yellow material first enters the yellow material membrane concentration unit 3 for concentration and then enters the yellow material multi-stage membrane washing device. The concentrated mother liquor enters the by-product salt recovery unit 6.

[0088] The generated iron phosphate white material first enters the white material membrane concentration unit 11 for concentration and then enters the white material multi-stage membrane washing device. The concentrated mother liquor enters the dilute phosphoric acid recovery unit 14.

[0089] Another preferred process also includes:

[0090] The generated iron phosphate yellow material first enters the yellow material buffer tank, and then is fed into the yellow material membrane concentration unit 3 for concentration and recovery of by-product salt;

[0091] The generated iron phosphate white material first enters the white material buffer tank, and then is fed into the white material membrane concentration unit 11 for concentration and recovery of dilute phosphoric acid solution.

[0092] Example 7

[0093] This embodiment provides a specific example of Embodiment 6.

[0094] In this embodiment, ammonium dihydrogen phosphate is used as the phosphorus source, ferrous sulfate as the iron source, and hydrogen peroxide as the oxidant. Ammonia solution is used to adjust the pH value to synthesize battery-grade iron phosphate. The relevant process parameters and implementation procedures are as follows.

[0095] 1. Material preparation: Using the upstream purification section (not shown in the attached diagram), ferrous sulfate and ammonium dihydrogen phosphate solutions are purified to obtain a ferrous sulfate purified solution with a concentration of 1.64 mol / L (material A) and an ammonium dihydrogen phosphate purified solution with a concentration of 2.93 mol / L. 35% hydrogen peroxide is added to the ammonium dihydrogen phosphate solution and mixed evenly to obtain material B. The ratio of hydrogen peroxide added is 50 kg of 35% hydrogen peroxide to 100 kg of solid ammonium dihydrogen phosphate.

[0096] 2. Start-up and operation of the continuous unit:

[0097] 1) Confirm that oxidation reactor 1 and first aging reactor 2 are in the vented state, turn on drive device 103, and set the speed to 200 r / min. Close the bottom valve of oxidation reactor 1 and open the top exhaust valve of oxidation reactor 1.

[0098] 2) Pump approximately 100L of yellow material reaction mother liquor into the oxidation reactor 1 (if there is no mother liquor, hot water with pH 2.5 can be used to prepare it), ensuring that the liquid level exceeds the hollow membrane 102.

[0099] 3) Pump material B into the hollow membrane 102 of the oxidation vessel 1, and at the same time pump material A into the hollow distribution pipe 106 of the oxidation vessel 1 to start the oxidation reaction. Control the temperature of the oxidation vessel 1 to 50-55℃ and wait for the oxidation vessel 1 to be filled.

[0100] 4) Before the oxidation reactor 1 overflows, the compressed air inlet pipe at the bottom of the first aging reactor 2 is opened in advance, and the inlet pressure is about 2.5 bar. The gas is sprayed out from the aeration membrane 202.

[0101] 5) After the oxidation reactor 1 is filled, immediately open its top overflow valve and close the exhaust valve to allow the oxidation liquid material to continuously enter the first aging reactor 2 through the overflow pipe at the top of the oxidation reactor 1. At the same time, add ammonia solution to the first aging reactor 2 to adjust the pH value of the oxidation liquid to 2.8; control the temperature of the first aging reactor 2 to 65℃.

[0102] 6) Continue feeding until the first aging tank 2 is full. After filling to the specified liquid level, the slurry is discharged from the bottom drain port and drain pipe to the start-up temporary storage tank (not shown in the attached diagram). After the initial 100L of slurry has been discharged into the temporary storage tank, take a sample every 10 minutes from the drain pipe to test the iron content in the mother liquor. When the iron content reaches a stable level, switch the slurry from the temporary storage tank to the yellow film concentration unit 3.

[0103] 7) When the liquid levels in the yellow material membrane concentration unit 3, the yellow material primary membrane washing unit 4, and the yellow material secondary membrane washing unit 5 reach the specified values, the concentration and washing units are started one after another, and the outlet flow rate of each unit is adjusted to keep the liquid level constant.

[0104] 8) Qualified yellow material from the secondary membrane washing unit 5 is continuously fed into the conversion reactor 9. At the same time, 5% dilute phosphoric acid solution is added to the conversion reactor 9 at a certain speed ratio. The rotation speed is set to 100 r / min, the solid content in the reactor is controlled to be about 12%, and the reaction temperature is controlled to be 90℃ for conversion reaction.

[0105] 9) The slurry overflowing from the top of the conversion reactor 9 continuously enters the second aging reactor 10, and the temperature of the second aging reactor 10 is controlled at 95℃. The control and operation of the second aging reactor 10 and the subsequent white material membrane concentration unit 11, white material primary membrane washing unit 12, and white material secondary membrane washing unit 13 are similar to the yellow material treatment process. After the device is running stably, white slurry should flow from the bottom of the second aging reactor 10 into the white material membrane concentration unit 11.

[0106] 10) The qualified white material after washing flows out of the secondary membrane washing unit 13 and enters the subsequent concentration, pressure filtration, drying, dehydration and sintering units to finally obtain dehydrated ferric phosphate.

[0107] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

[0108] Those skilled in the art should understand that although the present invention has been described with reference to multiple embodiments, not every embodiment contains only one independent technical solution. This description is provided merely for clarity; those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of the present invention.

Claims

1. A continuous ferric phosphate reaction and washing system, characterized in that, It includes a multi-stage iron phosphate reaction and washing module. Each stage of the iron phosphate reaction and washing module includes a reaction device, an aging device and a multi-stage membrane washing device connected sequentially along the feed direction. Between two adjacent iron phosphate reaction and washing modules, the multi-stage membrane washing device of the upper stage iron phosphate reaction and washing module is connected to the reaction device of the lower stage iron phosphate reaction and washing module. The reaction apparatus is equipped with a first feeding assembly, a second feeding assembly, and a stirring assembly. The reaction apparatus includes an oxidation vessel. The first feeding component within the oxidation vessel is a hollow feed tube, which is connected to the first material inlet of the oxidation vessel for continuously and evenly distributing the ferrous purification solution into the oxidation vessel. The second feeding component within the oxidation vessel is a dynamic disc membrane assembly, which includes a hollow rotating shaft and multiple hollow membranes spaced apart on the shaft. The hollow membranes are connected to the hollow rotating shaft, which is connected to the second material inlet of the oxidation vessel for continuously and evenly distributing the mixture of phosphorus source purification solution and oxidant solution into the oxidation vessel from the inside to the outside via the hollow membranes. The stirring component within the oxidation vessel includes stirring wheels located on the upper and lower sides of the hollow membranes. Feeding ports of the hollow feed tube are located on the upper and lower sides of the hollow membranes between adjacent stirring wheels. The hollow rotating shaft is connected to an external drive device to drive the hollow membranes and stirring wheels to rotate, thereby uniformly mixing the ferrous purification solution and the mixture of the phosphorus source purification solution and oxidant solution. The aging device is provided with a feed inlet on the upper side, and a perforated plate distributor is installed below the feed inlet to distribute the product in the reaction device evenly into the aging device. The aging device includes a built-in membrane aeration component for producing an air flotation effect and reducing the deposition of solid particles; The inner top of the aging device is also equipped with a demister, which is used to remove liquid droplets from the gas generated by aeration inside the aging device and then discharge it.

2. The continuous ferric phosphate reaction and washing system according to claim 1, characterized in that, The dynamic disc membrane assembly also includes a metal plate installed at the head and end of the hollow rotating shaft for flow pattern control within the reaction device to prevent material backmixing.

3. The continuous iron phosphate reaction and washing system according to claim 1, characterized in that, The reaction apparatus also includes a conversion vessel, wherein the first feeding component and the second feeding component inside the conversion vessel are both hollow feeding tubes, and the stirring component inside the conversion vessel is a stirring paddle, which is located between the two hollow feeding tubes, and the feeding port is provided at the end of the hollow feeding tube.

4. The continuous ferric phosphate reaction and washing system according to claim 1, characterized in that, The membrane aeration assembly is located at the bottom of the aging device and includes a compressed air inlet pipe and an aeration membrane connected thereto.

5. The continuous ferric phosphate reaction and washing system according to claim 1, characterized in that, The multi-stage membrane washing device includes a multi-stage membrane washing unit, a membrane separation unit, and a recovery unit. Between two adjacent membrane washing units, the slurry outlet of the upper membrane washing unit is connected to the slurry inlet of the lower membrane washing unit, and the washing wastewater outlet of the lower membrane washing unit is connected to the water replenishment point of the upper membrane washing unit. The wastewater outlet of the first-stage membrane washing unit is connected to the membrane separation unit, the concentrate outlet of the membrane separation unit is connected to the recovery unit, and the clear liquid outlet of the membrane separation unit is connected to the water replenishment point of the final-stage membrane washing unit.

6. The continuous iron phosphate reaction and washing system according to claim 5, characterized in that, It also includes a membrane concentration unit connected in series to the pipeline between the aging unit and the multi-stage membrane washing unit, wherein the concentrated mother liquor outlet of the membrane concentration unit is connected to the recovery unit.

7. The continuous iron phosphate reaction and washing system according to any one of claims 1-6, characterized in that, The multi-stage ferric phosphate reaction and washing module includes sequentially connected yellow ferric phosphate reaction and washing modules and white ferric phosphate reaction and washing modules. The yellow material ferric phosphate reaction and washing module includes an oxidation kettle, a first aging kettle, a yellow material membrane concentration unit, and a yellow material multi-stage membrane washing device connected in sequence. The yellow material multi-stage membrane washing device includes a yellow material multi-stage membrane washing unit, a first membrane separation unit, and a by-product salt recovery unit. The white ferric phosphate reaction and washing module includes a conversion kettle, a second aging kettle, a white material membrane concentration unit, and a white material multi-stage membrane washing device connected in sequence. The white material multi-stage membrane washing device includes a white material multi-stage membrane washing unit, a second membrane separation unit, and a dilute phosphoric acid recovery unit. The recovered dilute phosphoric acid solution is reused in the conversion kettle for conversion reaction or reused in the phosphorus source dissolution section.

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