Iron phosphate continuous reaction process

Abstract

The invention relates to the technical field of phosphorus chemical industry, and particularly discloses an iron phosphate continuous reaction process. Comprising the following steps: step 1, preparing a solution: adding ammonia water into phosphoric acid and mixing with the phosphoric acid to obtain an ammonium phosphate solution; mixing the ammonium phosphate solution and the ferrous sulfate solution to prepare a premixed solution; the oxidation reaction is divided into three-stage reaction, hydrogen peroxide and ammonia water are added in the first-stage reaction, hydrogen peroxide and ammonia water are added in the second-stage reaction, and only ammonia water is added in the third-stage reaction; and 4, drying and packaging: carrying out centrifugal separation on the aged reaction crystallization slurry, and drying and calcining to obtain an iron phosphate product. The technical problems that after hydrogen peroxide is added into an iron source and a phosphorus source in a mixed mode in an existing continuous production technology of iron phosphate, crystallization is prone to being separated out due to reaction heat release, and then pipelines, valves, plate exchange and the like of a continuous production system are prone to scaling and blocking are solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of phosphorus chemical industry, and particularly discloses a continuous reaction process of iron phosphate. BACKGROUND

[0002] Iron phosphate (FePO4) is a core precursor of lithium iron phosphate as a positive material of a lithium ion battery, and the optimization of a technical route and the control of impurities in the production process of the iron phosphate directly determine the energy density, cycle life and safety performance of the battery. In recent years, with the rapid development of new energy vehicles and energy storage industries, the preparation process of iron phosphate is continuously iterated and innovated in multiple dimensions such as cost, environmental protection and product uniformity, and gradually forms an industrialized route mainly based on ammonium method and sodium method.

[0003] The synthesis process of the iron phosphate produced by the ammonium method and the sodium method needs to go through multiple process steps such as oxidation, precipitation and aging. The oxidation and aging reaction time is long (the oxidation time is 1-2 hours, and the aging time is 2-4 hours), and the reaction environment needs to be maintained stable. If the reaction environment fluctuates frequently, problems such as uneven reaction, crystal structure defects and poor particle size uniformity will be caused. Therefore, in order to ensure the product quality, the industry mostly adopts a batch process for production. The batch process uses different reaction containers for reaction in different sections, and after the reaction is completed, the reaction crystallization slurry is pumped into the next section as a whole. Therefore, the different sections (oxidation and aging processes) can be independently controlled, and after the control, the reaction crystallization slurry does not flow and can be kept stable for a long time. The adaptability to the requirement that the oxidation and aging processes need to maintain the reaction environment stable for a long time is high, and thus the batch process has gradually become the mainstream in the iron phosphate production industry. Although the batch production has a long history in the iron phosphate industry, the batch production still has some shortcomings, for example, due to the batch production, there are differences in the reaction materials in each tank, and the consistency of different batches of products is poor. In order to overcome this problem, some continuous production processes have appeared in the industry, for example, a patent with the application number CN202311368605.1 discloses a method for continuous production of battery-grade iron phosphate. The method uses the advantages of a microreactor to continuously produce the iron phosphate and improves the production efficiency. For another example, a patent with the application number CN202410640986.2 discloses a method for continuous production of large-scale battery-grade iron phosphate. The method uses a continuous production process for the whole preparation process from iron source and phosphorus source raw materials to iron phosphate finished products, and the whole reaction can be connected to prepare the iron phosphate.

[0004] Although the above patent technology can complete the continuous production of iron phosphate, it is found that when the iron source and phosphorus source are mixed and added with hydrogen peroxide, the reaction releases heat, causing crystallization to precipitate, resulting in easy scaling and plugging of the pipelines, valves, plate exchangers, etc. of the continuous production system. The plugged pipelines, valves, etc. can affect the flow changes of the reaction crystallization slurry and materials in the system, thereby causing a gap between the designed proportion of reaction raw materials and the actual production proportion, resulting in large fluctuations in the quality of the produced product, and easy occurrence of poor quality iron phosphate products. If the plugging is severe, it can also cause shutdown for cleaning, and the cleaning is difficult. SUMMARY

[0005] The purpose of the present application is to provide a continuous reaction process for iron phosphate, which solves the technical problem that the above-mentioned existing continuous production technology for iron phosphate easily causes crystallization to precipitate due to reaction heat release after the iron source and phosphorus source are mixed and added with hydrogen peroxide, thereby causing easy scaling and plugging of the pipelines, valves, plate exchangers, etc. of the continuous production system.

[0006] In order to solve the above problems, the technical scheme adopted by the present application is as follows: a continuous reaction process for iron phosphate, comprising the following steps: Step 1, liquid preparation: adding ammonia water into phosphoric acid and mixing, controlling the pH to be 2.45-2.55 to prepare a phosphorus ammonium solution; then mixing the phosphorus ammonium solution and ferrous sulfate solution, adjusting the iron-phosphorus ratio to 0.945-0.960, and controlling the pH to be 1.8-2.0 to prepare a premix solution; Step 2, oxidation reaction: delivering the premix solution in step 1 to a reaction kettle to add hydrogen peroxide and ammonia water for oxidation reaction to obtain a reaction crystallization slurry, The oxidation reaction is divided into three stages. Hydrogen peroxide and ammonia water are added in the first stage, the flow ratio of the premix solution to hydrogen peroxide is controlled to be 14-17:1, the flow ratio of ammonia water to hydrogen peroxide is 1:1, the flow ratio of the first-stage crystallization slurry to ammonia water is controlled to be 8.5-10:1, and the flow of hydrogen peroxide is between 0.85-0.1% of the flow of the first-stage crystallization slurry. In the third stage, only ammonia water is added, and the ammonia water is added according to the residual iron content and the divalent iron content in the second-stage crystallization slurry. The flow of the added ammonia water is 1-1.5‰ m3 / h of the content of the residual iron and the divalent iron in ppm. The concentration of the ammonia water is 6.10-6.20%; Step 3, aging: delivering the reaction crystallization slurry after the oxidation reaction in step 2 to an aging reaction kettle, heating to 75-95℃, and performing aging reaction; Step 4, drying and packaging: centrifuging the reaction crystallization slurry after aging, drying, and calcining to obtain an iron phosphate product.

[0007] The beneficial effects of the present embodiment are as follows: 1. In the application of continuous production of ferric phosphate in the existing technology, it has been found that when hydrogen peroxide is added to the mixed iron and phosphorus sources of the reaction, the reaction is exothermic and crystallization occurs, which leads to scaling and blockage of the pipes, valves, heat exchangers, etc. of the continuous production system. The blocked pipes and valves will affect the flow rate of the reaction crystallization slurry and materials in the system, which in turn leads to the difference between the designed ratio of reaction raw materials and the actual production ratio. The quality of the produced product fluctuates greatly, and poor-quality ferric phosphate products are easy to be produced. To address scaling issues and ensure stable production, this application employs a premixing of phosphoric acid and ammonia during the solution preparation stage. The pH of the premixed solution is controlled between 2.45 and 2.55, ensuring that the temperature after solution preparation does not exceed 40°C. Ferrous solution is then added and mixed, resulting in a pH of approximately 1.8. Ferrous and ammonium phosphate solutions do not crystallize or precipitate when mixed at a pH below 1.85. Furthermore, the temperature after solution preparation is controlled at a low level (below 40°C), making it less likely for hydrogen peroxide to crystallize due to exothermic reaction. By adding ammonia in advance and controlling its pH value, the scaling problem during the solution preparation stage can be effectively solved.

[0008] 2. This application divides the oxidation reaction into three stages. A premixed solution, after being properly prepared, is transported to the primary reaction vessel. Hydrogen peroxide is added during transport to facilitate oxidation before the solution enters the primary reaction vessel. Simultaneously, ammonia is added to the primary reaction vessel. Once the pH of the primary reaction vessel is within acceptable limits, the material is transported to the secondary reaction vessel. Based on the analysis results from the secondary reaction vessel, appropriate amounts of hydrogen peroxide and ammonia are added. After the levels of ferrous iron and residual iron in the secondary reaction vessel are within acceptable limits, a third-stage pump is activated to transport the material to the tertiary reaction vessel. Samples are taken for analysis of residual iron, ferrous iron, particle size, and pH. Ammonia is added based on the analysis results. The reaction is complete once the parameters and liquid level in the tertiary reaction vessel stabilize. Because the reaction is carried out in stages, with hydrogen peroxide and ammonia added sequentially, the exothermic reaction time is slowed down, allowing time for heat dissipation and preventing localized overheating that could lead to the precipitation of large amounts of crystals, which could then trap impurities and clog the pipes.

[0009] Furthermore, in step 1, when mixing the ammonium phosphate solution and the ferrous sulfate solution, the ferrous sulfate solution is first pumped into the mixing tank as the base liquid, and then the ammonium phosphate solution is added to the ferrous sulfate solution.

[0010] Furthermore, the ferrous sulfate solution in step 1 is prepared with ferrous sulfate heptahydrate and purified by a purification process.

[0011] Furthermore, in step 2, the pH value of the first-order reaction is controlled at 1.1-1.2, and the pH value of the second-order and third-order reactions is controlled at 1.65-1.85.

[0012] Furthermore, in step 3, the reaction crystallization slurry needs to be washed before aging.

[0013] Furthermore, the washing process includes three stages: the reaction crystallization slurry is introduced into a primary plate and frame filter press for filtration, and the filter cake is re-slurried in a primary re-slurry tank, with a solid content of 6-7% after primary re-slurry; after primary re-slurry, it is fed into a secondary plate and frame filter press for filtration, and the wet filter cake separated by the secondary plate and frame filter press is re-slurried in a secondary re-slurry tank, with a solid content of 15-20% after secondary re-slurry; after secondary re-slurry, it is fed into a tertiary plate and frame filter press for filtration, and the wet filter cake is fed into a tertiary re-slurry tank for re-slurry, with the amount of water added in the tertiary re-slurry required to ensure that the solid content of the re-slurry is 22-25%, and the re-slurry then enters the aging reaction.

[0014] Furthermore, after washing, phosphoric acid is added to adjust the pH of the slurry to 1.8-1.85 for aging. This synergistic effect with the oxidation reaction shortens the time required for the aged crystals to whiten.

[0015] Furthermore, after the aging reaction is completed, water is added to the slurry to adjust the solid content of the slurry to 9-11%.

[0016] Furthermore, in step 4, the drying process specifically involves first pumping the aged slurry to a horizontal spiral sedimentation centrifuge for solid-liquid separation, then re-slurrying the crystalline filter media, and finally re-entering the horizontal spiral sedimentation centrifuge for separation. The separated crystalline slurry then enters the flash drying section.

[0017] Attached image description.

[0018] Fig. 1 This is a process flow diagram of the oxidation reaction of the present invention. Fig. 2 This is a graph showing the quality index data of the product of this invention. Fig. 3 This is a graph showing the quality index data of the comparative products.

[0019] Detailed implementation method.

[0020] The following detailed description illustrates the specific implementation method: Implementation, for example, attached Figs. 1-3 As shown: Methodology Overview: A continuous reaction process for iron phosphate includes the following steps: Step 1, Solution preparation: Add ammonia to phosphoric acid and mix, controlling the pH to 2.45-2.55 to prepare ammonium phosphate solution; then mix ammonium phosphate solution and ferrous sulfate solution, adjusting the iron-to-phosphorus ratio to 0.945-0.960, and adjust the pH to 1.8-2.0 to prepare premixed solution; Step 2, Oxidation Reaction: The premixed solution from Step 1 is transferred to a reaction vessel, where hydrogen peroxide and ammonia are added to carry out an oxidation reaction to obtain a reaction crystallization slurry. The oxidation reaction is divided into three stages. In the first stage, hydrogen peroxide and ammonia are added, with the flow ratio of the premixed solution to hydrogen peroxide controlled at 14-17:1, and the flow ratio of ammonia to hydrogen peroxide at 1:1. In the second stage, hydrogen peroxide and ammonia are added, with the flow ratio of the first-stage crystallization slurry to ammonia controlled at 8.5-10:1, and the hydrogen peroxide flow rate at 0.85-0.1% of the first-stage crystallization slurry flow rate. In the third stage, only ammonia is added, supplemented according to the residual iron and ferrous iron content in the second-stage crystallization slurry. The supplemented ammonia flow rate is 1-1.5‰ of the residual iron and ferrous iron content (ppm) in the second-stage crystallization slurry. 3 / h; the ammonia concentration is 6.10-6.20%; Step 3, Aging: The reaction crystallization slurry after the oxidation reaction in Step 2 is transported to the aging reactor and heated to 75-95℃ for aging reaction; Step 4, Drying and Packaging: The aged reaction crystallization slurry is centrifuged, dried, and calcined to obtain the iron phosphate product.

[0021] Example 1 Step 1, Solution preparation: Ferrous sulfate heptahydrate, a byproduct of titanium dioxide production, was added to a dissolving tank to prepare a 5% concentration solution. The ferrous sulfate solution could be prepared using either clean water or recycled water. After complete dissolution, the solution was pumped into a purification tank, where a purification agent was added. The agent used was 85% concentrated phosphoric acid and 0.1% polyacrylamide flocculant. After adding the purification agent, the mixture was stirred for 10 minutes and then pumped out. The solution was then filtered using a filter plate and frame to obtain a pure ferrous sulfate solution, which was then pumped into a ferrous sulfate storage tank.

[0022] Phosphoric acid (85% concentration) and ammonia (7.24% concentration) were added to the ammonium phosphate preparation vessel and mixed together. The amount of ammonia added was such that the pH of the ammonium phosphate solution was 2.45-2.50 90 minutes after the ammonia was added. The temperature was controlled at 38℃ by a heat exchanger to prepare the ammonium phosphate solution.

[0023] A ferrous solution is pumped from the ferrous storage tank into a premixing tank as a base solution, and then an ammonium phosphate solution is pumped in and mixed. The mixing ratio is adjusted to an iron-to-phosphorus ratio of 0.945-0.960, which is 0.966 in this example. After the solution is prepared, the temperature of the premixed solution is controlled at 26-29℃, and the pH should be controlled at 1.8-2.0, which is 1.8 in this example. After the solution is qualified, it is transferred to an iron-to-ammonium phosphate mixing tank for later use.

[0024] Step 2, Oxidation reaction The premixed solution was pumped from the iron-ammonium phosphate mixing tank to the primary reactor at an initial temperature of 28°C and a flow rate of 18 m³ / h. 3 At the same time, hydrogen peroxide is pumped in at a flow rate of 1.0-1.2 m³ / h. 3 / h, which is 1.075m in this embodiment. 3 / h. The premixed solution and hydrogen peroxide are added entirely from the bottom of the primary reactor, with the flow ratio of premixed solution to hydrogen peroxide controlled at 16-17:1. The ammonia water added to the primary reactor is at a flow rate of 1m³ / h. 3 / h, the flow ratio of ammonia water and hydrogen peroxide is controlled to be approximately 1:1; the reaction is carried out by the built-in agitator and the external emulsifying pump B2 for circulation shearing, and the primary crystallized slurry is obtained after the reaction. The temperature of the primary crystallized slurry is measured to be 54-58℃ and the pH is 1.1-1.2.

[0025] The primary crystallization slurry in the primary reactor is pumped to the secondary reactor, where hydrogen peroxide and ammonia are added. The flow rate of the primary crystallization slurry is approximately 22.15 m³ / s. 3 / h; the ammonia water addition flow rate is 2-3m³ / h. 3 / h, in this embodiment it is approximately 2.55m 3 / h; the flow rate of hydrogen peroxide is 0.16-0.2m³ / h. 3 The flow rate was controlled within the following range: the flow ratio of primary crystallizing slurry to ammonia was approximately 8.5:1; the hydrogen peroxide flow rate was 0.85-0.1% of the primary crystallizing slurry flow rate. After the reaction, the temperature of the secondary crystallizing slurry was measured to be 63-65℃, and the pH was controlled to be 1.6-1.8.

[0026] The secondary crystallization slurry is pumped to the tertiary reactor via a transfer pump. The flow rate of the secondary crystallization slurry is 20 m³ / s. 3 At approximately [per hour], only ammonia water is added to the tertiary reactor. The amount of ammonia water added is based on the residual iron and ferrous iron content in the secondary crystallization slurry. The ammonia water flow rate is 1-1.5‰m³ of the residual iron and ferrous iron content (ppm) in the secondary crystallization slurry. 3 / h, for example: the residual iron and ferrous iron content in the secondary crystallization slurry is 1000ppm, and the flow rate of the secondary crystallization slurry is 20m³ / h. 3 / h; the flow rate of the added ammonia water is 1000 multiplied by 1.5‰ 1-1.5m 3 The temperature of the tertiary reaction crystallization slurry was measured to be 63-65℃, and the pH was controlled at 1.6-1.8. The tertiary reaction crystallization slurry flowed by gravity into the reaction material storage tank through the valve at the bottom of the reactor to complete the oxidation reaction.

[0027] Step 3, Aging Before aging, the reaction slurry needs to undergo three stages of washing, as follows: The slurry from the reaction, which has undergone oxidation in the reaction tank, is introduced into a primary plate and frame filter press for filtration. The wet filter cake separated in the primary plate and frame filter press is then re-slurried in a primary re-slurry tank. After re-slurrying, it is fed into a secondary plate and frame filter press for filtration. The wet filter cake separated in the secondary plate and frame filter press is then re-slurried in a secondary re-slurry tank. After re-slurrying, it is fed into a tertiary plate and frame filter press for filtration. The wet filter cake after filtration is then fed into a tertiary re-slurry tank for further re-slurrying. Water is added to the tertiary re-slurry tank at 20% of its volume, resulting in a solid content of 22-25% in the re-slurry.

[0028] After the three-stage washing is completed, the slurry is pumped from the three-stage reslurry tank into the aging kettle. Phosphoric acid is added to the aging kettle to adjust the pH value to about 1.8 before the aging reaction is carried out. The aging temperature is 95℃ and the reaction time is about 6 hours. After the aging is completed, water is added until the solid content is 9-10%.

[0029] Step 4: Drying After aging, the slurry needs to be washed once. Specifically, the aged slurry is pumped to a first-stage horizontal spiral sedimentation centrifuge for solid-liquid separation. The horizontal spiral sedimentation centrifuge uses the principle of centrifugal sedimentation, which generates centrifugal force through the high-speed rotation of the drum, causing the solid crystals in the slurry to settle. The separated crystals are then discharged by a spiral pusher, thus achieving solid-liquid separation. After separation, the crystals discharged from the horizontal spiral sedimentation centrifuge are re-slurried in a fourth-stage re-slurry tank. After re-slurrying, the slurry is pumped into a second-stage horizontal spiral sedimentation centrifuge for solid-liquid separation. The separated slurry is then sent to an arch-breaking feed tank.

[0030] The iron phosphate crystals in the arch-breaking feeding bucket are flash-dried, calcined in a rotary kiln, ground, and then packaged as finished iron phosphate products.

[0031] Example 2 Step 1, Solution preparation: Ferrous sulfate heptahydrate, a byproduct of titanium dioxide production, is added to a dissolving tank to prepare a 30% concentration solution. The solution is heated to 50–60°C and stirred until completely dissolved. Clean water or recycled water can be used to prepare the ferrous sulfate solution. After complete dissolution, the solution is pumped into a purification tank, where a purification agent is added. The agent used is 10–30% dilute phosphoric acid and 0.1% polyacrylamide flocculant. After adding the purification agent, the solution is stirred for 10 minutes, then pumped out and filtered through a filter plate and frame to obtain a pure ferrous sulfate solution, which is then pumped into a ferrous sulfate storage tank.

[0032] Add phosphoric acid (85% concentration) and ammonia water (7.24% concentration) to the ammonium phosphate preparation vessel and mix them together. The amount of ammonia water added is to control the pH to 2.50-2.55. Prepare an ammonium phosphate solution. After preparation, measure the temperature of the ammonium phosphate solution to be 38℃.

[0033] Ferrous solution was pumped from the ferrous storage tank into the premixing tank as a base solution, and then ammonium phosphate solution was pumped in to mix. The mixing ratio was adjusted to an iron-to-phosphorus ratio of 0.945-0.960, which was 0.947 in this example. After the solution was prepared, the temperature of the premixed solution was 26-29℃, and the pH was 1.8-2.0, which was 1.97 in this example. After the solution was qualified, it was transferred to the iron-to-ammonium phosphate mixing tank for later use.

[0034] Step 2, Oxidation reaction The premixed solution was pumped from the iron-ammonium phosphate mixing tank to the primary reactor at an initial temperature of 28°C and a flow rate of 17.5 m³ / s. 3 At the same time, hydrogen peroxide is pumped in at a flow rate of 1.0-1.2 m³ / h. 3 / h, which is 1.175m in this embodiment. 3 / h. The premixed solution and hydrogen peroxide are added entirely from the bottom of the primary reactor, with the flow ratio of premixed solution to hydrogen peroxide controlled at 14-15:1. The ammonia water added to the primary reactor is at a flow rate of 1m³ / h. 3 / h, control the flow ratio of ammonia water and hydrogen peroxide to approximately 1:1; emulsifying pump B2 performs cyclic shearing, and after the reaction, a primary crystallized slurry is obtained. The temperature of the primary crystallized slurry is measured to be 54-58℃, and the pH is controlled to be 1.1-1.2.

[0035] The primary crystallization slurry in the primary reactor is pumped to the secondary reactor. Hydrogen peroxide and ammonia are added to the secondary reactor. The flow rate of the primary crystallization slurry is approximately 23.05 m³ / s. 3 / h; the ammonia water addition flow rate is 2-3m³ / h. 3 / h, in this embodiment it is approximately 2.10m 3 / h; the flow rate of hydrogen peroxide is 0.2-0.25m³ / h. 3 The flow rate was controlled within the following range: the flow ratio of primary crystallizing slurry to ammonia was approximately 10:1; the hydrogen peroxide flow rate was 0.85-0.1% of the primary crystallizing slurry flow rate. After the reaction, the temperature of the secondary crystallizing slurry was measured to be 63-65℃, and the pH was 1.6-1.7.

[0036] The secondary crystallization slurry is pumped to the tertiary reactor via a transfer pump. The flow rate of the secondary crystallization slurry is 24 m³ / s. 3 At approximately [time], only ammonia water is added to the tertiary reactor. The amount of ammonia water added is based on the residual iron and ferrous iron content in the secondary crystallization slurry. After the tertiary reaction is completed, the temperature of the reaction crystallization slurry that has completed the entire oxidation reaction is measured to be 63-65℃, and the pH is 1.6-1.8. The reaction crystallization slurry flows by gravity into the reaction material storage tank through the valve at the bottom of the reactor, thus completing the oxidation reaction.

[0037] Step 3, Aging Before aging, the reaction crystallization slurry needs to undergo three stages of washing, as follows: The slurry from the reaction, after oxidation in the reaction tank, is introduced into a primary plate and frame filter press for filtration. The wet filter cake separated in the primary plate and frame filter press is then re-slurried in a primary re-slurry tank. The amount of water added during re-slurrying in the primary re-slurry tank must ensure that the solid content of the slurry after re-slurrying is 6-7%. After re-slurrying, the slurry is passed through a secondary plate and frame filter press for filtration. The wet filter cake separated in the secondary plate and frame filter press is then re-slurried in a secondary re-slurry tank. The amount of water added during re-slurrying in the secondary re-slurry tank must ensure that the solid content of the slurry after re-slurrying is 15-20%. After re-slurrying, the slurry is passed through a tertiary plate and frame filter press for filtration. The wet filter cake after filtration is then passed through a tertiary re-slurry tank for re-slurrying. The amount of water added during tertiary re-slurrying must ensure that the solid content of the slurry after re-slurrying is 22-25%.

[0038] After the three-stage washing is completed, the slurry is pumped from the three-stage reslurry tank into the aging kettle. Phosphoric acid is added to the aging kettle to adjust the pH value to about 1.8 before the aging reaction is carried out. The aging temperature is 75℃ and the reaction time is about 4 hours. After the aging is completed, water is added until the solid content is 10-11%.

[0039] Step 4: Drying After aging, the slurry needs to be washed once. Specifically, the aged slurry is pumped to a first-stage horizontal spiral sedimentation centrifuge for solid-liquid separation. The horizontal spiral sedimentation centrifuge uses the principle of centrifugal sedimentation, which generates centrifugal force through the high-speed rotation of the drum, causing the solid crystals in the slurry to settle. The separated crystals are then discharged by a spiral pusher, thus achieving solid-liquid separation. After separation, the crystals discharged from the horizontal spiral sedimentation centrifuge are re-slurried in a fourth-stage re-slurry tank. After re-slurrying, the slurry is pumped into a second-stage horizontal spiral sedimentation centrifuge for solid-liquid separation. The separated slurry is then sent to an arch-breaking feed tank.

[0040] The iron phosphate crystals in the arch-breaking feeding bucket are flash-dried, calcined in a rotary kiln, ground, and then packaged as finished iron phosphate products.

[0041] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is as follows: In step 1, when preparing the solution, the pH value of the phosphoric acid solution after adding ammonia was 2.8-3.0. After the solution preparation was completed, the temperature of the ammonium phosphate solution was measured to be 75℃. In step 2, the oxidation reaction was a one-step reaction in which hydrogen peroxide and ammonia were added at once. Specifically, the premixed solution was first pumped to the reactor at an initial temperature of 28℃. Hydrogen peroxide was added to the reactor at a rate of 2t / h for oxidation, which took 30-40 minutes to complete at a temperature of 53℃ and a pH of 1.1-1.2. Then, ammonia was added for the reaction, which took 30-40 minutes. After the reaction was completed, the temperature was 63℃ and the pH was 1.6-1.8. Everything else was completely the same.

[0042] In the experiments of Examples 1, 2, and Comparative Example 1, multiple test samples were taken for each process segment to obtain multiple sets of data. Partial data from the test samples of Examples 1, 2, and Comparative Example 1 are as follows: The solution preparation data are shown in Tables 1, 2, 3, and 4 below. It is worth noting that the same ammonium phosphate solution was used in Examples 1 and 2.

[0043] Table 1: Solution preparation control table for ammonium phosphate solution in the examples

[0044] Table 2: Control Table for Preparing Phosphate Ammonium Solution in Comparative Example 1 In the comparative example, the phosphoric acid concentration was 85% and the ammonia concentration was 6.7%. During the preparation of the ammonium phosphate solution, the temperature increased dramatically, from 35°C to 76°C, and the ratio of phosphoric acid to ammonia was approximately 1:2, with a pH of 2.65-2.72. In the example, the phosphoric acid concentration was 85% and the ammonia concentration was 7.24%. During the preparation of the ammonium phosphate solution, the temperature did not exceed 45°C after heat exchange with circulating water. The ratio of phosphoric acid to ammonia was approximately 1:1.76, the pH was 2.45, and the solution was clear.

[0045]

[0046] Table 3: Parameters of each index after the premixed solution is prepared in the example

[0047] Table 4: Parameters of each indicator after the comparative premixed solution is prepared Two groups of solutions were prepared for Comparative Example 1. For Group I, ammonium phosphate solution was added first as a base solution, followed by ferrous phosphate solution. After addition, the temperature was 36°C. Samples taken after mixing showed a slightly turbid solution with some precipitate upon standing. For Group II, ferrous phosphate solution was added first as a base solution, followed by ammonium phosphate solution. After addition, the temperature was 38°C. Samples taken after mixing showed a slightly turbid solution with some precipitate upon standing. The precipitation in Group I was due to the ammonium phosphate solution having a pH of 2.75. When ferrous phosphate was first added, the pH of the solution was too high, and the ferrous phosphate was partially oxidized, forming ferric phosphate precipitate. Precipitation also occurred in Group II, but it was significantly reduced. Table 4 above only shows the qualified solutions used in the subsequent processes of the comparative examples.

[0048] In the example, three groups of solutions were prepared. The average iron concentration, phosphorus concentration, and iron-to-phosphorus ratio were 3.87%, 2.23%, and 0.963, respectively. The iron concentration was about 0.13% lower than the original process, and the iron-to-phosphorus ratio was about 0.3 higher. After the first and second batches of solution preparation, the pH was 1.8 and 1.97, respectively, and the ammonia nitrogen was 0.88 and 0.89, respectively. No precipitation occurred after 16 hours. After the third batch of solution preparation, the pH was 2.01 and the ammonia nitrogen was 0.92. After 16 hours, a greenish precipitate appeared, and after 48 hours, the precipitate turned white. The high pH and ammonia nitrogen were due to the high pH of the raw material. To stabilize the pH of the solution, it is necessary to ensure that the pH of the ferrous solution is stable. The pH of the solution should be controlled below 1.95 to prevent precipitation and ensure the uniformity of the solution. Table 3 above only shows the qualified solutions used in the subsequent processes of the example.

[0049] Compared with the comparative example, the embodiment of this application does not produce precipitation. When the comparative example is prepared, the solution is turbid. However, the qualified solution of this application (pH value controlled below 1.9) does not show precipitation after standing for 16 hours. Therefore, the method of preparing the premixed solution by adding ammonium phosphate to ferrous solution as the base liquid is not easy to cause scaling and blockage in the pipelines, valves, heat exchangers, etc. of the production system.

[0050] The data for the oxidation reaction process are shown in Tables 5, 6, 7, and 8 below:

[0051] Table 5: First-order reaction data for oxidation reactions in the examples

[0052] Table 6: Second-order reaction data for oxidation reactions in the examples

[0053] Table 7: Data Table of Third-Order Oxidation Reactions in Examples

[0054] Table 8: Comparative Oxidation Reaction Data Table The data above shows that the residual iron content in the filtrate after the three-stage reaction is lower, indicating a more complete reaction. Furthermore, the pH value of the first-stage reaction in this application remains consistently around 1.1-1.2, rises to around 1.6 after the second-stage reaction, and only slowly approaches 1.8 after the third-stage reaction. Compared to the comparative example where the pH value after a single reaction is around 1.8, this method is less prone to ferrous precipitation and blockage of the reaction system's pipes, valves, and other structures due to localized pH increases in the early stages of the reaction.

[0055] The data for its three-stage washing process are shown in Tables 9 and 10 below:

[0056] Table 9: Washing Data Table of Examples

[0057] Table 10: Comparative Washing Data Table The data above shows that the moisture content of the filter cake after washing in this embodiment is lower than that in the comparative example, which reduces energy consumption and saves drying time in subsequent drying. Furthermore, compared to the wash water before aging in the comparative example, the Fe and P content in the wash water of this embodiment is significantly reduced, indicating that this application reduces Fe and P losses in the aged materials.

[0058] Its aging data are shown in Tables 11 and 12 below:

[0059] Table 11: Aging Reaction Data of Examples

[0060] Table 12: Comparative Aging Reaction Data Table The average whitening time for traditional aging is 85 minutes, the average whitening time for comparative aging is 49.5 minutes, while the average whitening time for aging in this application is 24.25 minutes. Therefore, this application greatly shortens the aging time.

[0061] The final product data is as follows: Fig. 2 , Fig. 3 As shown in the final product data, the continuous production product of this application has several advantages in quality compared with the intermediate production product of the comparative example. Moreover, in actual operation, the continuous production of this application does not have scaling or blockage in pipes, valves, heat exchangers, etc.

[0062] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A continuous reaction process for iron phosphate, characterized in that: Includes the following steps: Step 1, Solution preparation: Add ammonia water to phosphoric acid and mix it to control the pH at 2.45-2.55 to prepare an ammonium phosphate solution; Then mix the ammonium phosphate solution and ferrous sulfate solution, adjust the iron-to-phosphorus ratio to 0.945-0.960, and set the pH to 1.8-2.0 to prepare a premixed solution; Step 2, Oxidation Reaction: The premixed solution from Step 1 is transferred to a reaction vessel, where hydrogen peroxide and ammonia are added to carry out an oxidation reaction to obtain a reaction crystallization slurry. The oxidation reaction is divided into three stages. In the first stage, hydrogen peroxide and ammonia are added, with the flow ratio of the premixed solution to hydrogen peroxide controlled at 14-17:1, and the flow ratio of ammonia to hydrogen peroxide at 1:

1. In the second stage, hydrogen peroxide and ammonia are added, with the flow ratio of the first-stage crystallization slurry to ammonia controlled at 8.5-10:1, and the hydrogen peroxide flow rate at 0.85-0.1% of the first-stage crystallization slurry flow rate. In the third stage, only ammonia is added, supplemented according to the residual iron and ferrous iron content in the second-stage crystallization slurry. The supplemented ammonia flow rate is 1-1.5‰ of the residual iron and ferrous iron content (ppm) in the second-stage crystallization slurry. 3 / h; the ammonia concentration is 6.10-6.20%; Step 3, Aging: The reaction crystallization slurry after the oxidation reaction in Step 2 is transported to the aging reactor and heated to 75-95℃ for aging reaction; Step 4, Drying and Packaging: The aged reaction crystallization slurry is centrifuged, dried, and calcined to obtain the iron phosphate product.

2. The continuous reaction process for iron phosphate according to claim 1, characterized in that: In step 1, when mixing the ammonium phosphate solution and the ferrous sulfate solution, the ferrous sulfate solution is first pumped into the mixing tank as the base liquid, and then the ammonium phosphate solution is added to the ferrous sulfate solution.

3. The continuous reaction process for iron phosphate according to claim 1, characterized in that: The ferrous sulfate solution in step 1 is prepared as ferrous sulfate heptahydrate and purified through a purification process.

4. The continuous reaction process for iron phosphate according to claim 1, characterized in that: In step 2, the pH value of the primary reaction is controlled at 1.1-1.2, and the pH value of the secondary and tertiary reactions is controlled at 1.65-1.

85.

5. The continuous reaction process for iron phosphate according to claim 1, characterized in that: Before aging the reaction crystallization slurry in step 3, the reaction crystallization slurry needs to be washed.

6. The continuous reaction process for iron phosphate according to claim 5, characterized in that: The washing process includes three stages: The reaction crystallization slurry is fed into a primary plate and frame filter press for filtration. The filter cake is then re-slurried in a primary re-slurry tank. The solid content of the slurry after primary re-slurrying is 6-7%. After primary reslurrying, the material is fed into a secondary plate and frame filter press for filtration. The wet filter cake separated by the secondary plate and frame filter press is then re-slurryed in a secondary reslurry tank. The solid content of the slurry after secondary reslurrying is 15-20%. After secondary resizing, the filter cake is fed into a tertiary plate and frame filter press for filtration. The wet filter cake after filtration is then fed into a tertiary resizing tank for resizing. The amount of water added during tertiary resizing should be such that the solid content of the slurry after resizing is 22-25%. The slurry after resizing then enters the aging reaction.

7. The continuous reaction process for iron phosphate according to claim 6, characterized in that: After washing, phosphoric acid is added to adjust the pH of the slurry to 1.8-1.85 before aging.

8. The continuous reaction process for iron phosphate according to claim 1, characterized in that: After the aging reaction is completed, water is added to the slurry to adjust the solid content of the slurry to 9-11%.

9. The continuous reaction process for iron phosphate according to claim 1, characterized in that: In step 4, the drying process specifically involves pumping the aged slurry to a horizontal spiral sedimentation centrifuge for solid-liquid separation. After separation, the crystal filter material is re-slurried and then re-entered into the horizontal spiral sedimentation centrifuge for further separation. The separated crystal slurry then enters the flash drying section.

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