Method and system for preparing iron phosphate through continuous feeding

Abstract

The invention relates to the field of iron phosphate production, and discloses a method and a system for preparing iron phosphate by continuous feeding, and the method is characterized in that reaction kettles are connected in series, and continuous feeding is performed at different points to realize continuous oxidation of iron-process iron phosphate. Firstly, a certain amount of ferrous liquid is supplemented into the first reaction kettle to serve as a reaction base solution, a PH buffer system is provided for the whole reaction, and the whole continuous feeding oxidation process is more controllable. By adjusting the parameters such as the feeding speed, the feeding proportion of each point, the temperature and the like in the oxidation process, the particle size-controllable iron phosphate dihydrate slurry in which coarse and fine particles are mixed can be obtained, so that the particle size distribution, the specific surface and Fe / P of an iron phosphate product are easy to regulate and control.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial production of iron phosphate, and particularly to a method and system for preparing iron phosphate by continuous feeding. BACKGROUND

[0002] Anhydrous iron phosphate is a mainstream precursor for producing lithium iron phosphate positive electrode materials, and the synthesis process is mainly divided into ferrous sulfate method process and pure iron method process. The ferrous sulfate method uses sulfate as raw material, in order to avoid the influence of a large amount of sulfate residues on the product, a large amount of washing water is often needed for producing one ton of iron phosphate, and the environmental protection pressure and production cost are relatively high.

[0003] With the intensification of market competition for iron phosphate products, low-cost high-quality iron phosphate has become the main target of technical iteration for major manufacturers. The pure iron method process is to react pure iron and phosphoric acid to generate ferrous phosphate solution (ferrous solution), then add hydrogen peroxide to the iron solution to oxidize the ferrous ions to obtain dihydrate iron phosphate slurry, and then filter, wash, dry, calcine, crush and other processes to obtain anhydrous iron phosphate production process. The iron phosphate synthesized by this process has high purity, and the process water can be recycled. With the market price of pure iron decreasing, the iron method process is favored by more and more manufacturers.

[0004] However, the oxidation reaction stage of ferrous phosphate solution is much more complex than the oxidation process of ferrous sulfate, which can lead to difficult control of the reaction process and poor batch stability of the product. In order to solve this problem, it is urgent to provide an iron method process for stably synthesizing iron phosphate.

[0005] In addition, the existing continuous oxidation process for preparing iron phosphate also wastes a long time in detecting and controlling pH during industrial production. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a method and system for preparing iron phosphate by continuous feeding. The following technical solutions are used to achieve this purpose: In a first aspect, the present application provides a method for preparing iron phosphate by continuous feeding, comprising the following steps: Step (1) placing pure iron in dilute phosphoric acid to carry out ironization reaction to obtain ferrous phosphate solution; Step (2) adjusting the Fe concentration of the ferrous phosphate solution, supplementing water and phosphoric acid to the ferrous solution according to the Fe and P contents of the original ferrous phosphate solution, adjusting the molar ratio of iron and phosphorus elements in the ferrous phosphate solution, then feeding the ferrous solution into a storage tank, and adding an antioxidant; Step (3) is carried out by using at least two reaction kettles for continuous oxidation, first pumping the ferrous solution of step (2) into the first reaction kettle as the reaction bottom solution, then adding hydrogen peroxide, and carrying out the oxidation reaction, whenever the solution in the previous stage reaction kettle reaches the control liquid level, the solution in the previous stage reaction kettle is pumped into the next stage reaction kettle, and hydrogen peroxide is added, and the oxidation reaction is continuously carried out in each stage reaction kettle in turn until the solution in the last stage reaction kettle reaches the control liquid level, and the oxidation slurry is obtained; Step (4) is to pump the oxidation slurry in the last stage reaction kettle into the aging kettle, supplement the metered hydrogen peroxide in the aging kettle, then adjust the aging temperature, and age the oxidation slurry to obtain the iron phosphate dihydrate slurry; Step (5) is to carry out pressure filtration and washing treatment on the iron phosphate dihydrate slurry of step (4) to separate the filter cake; Step (6) is to obtain the iron phosphate anhydrous product after drying and calcining the filter cake separated in step (5).

[0007] The method for producing iron phosphate iron of the application by continuous feeding can obtain the iron phosphate dihydrate slurry with mixed coarse and fine particles by adjusting the feeding and temperature parameters in the oxidation process, so that the particle size and specific surface area of the iron phosphate product can be easily controlled, and the consistency of the product is good under the fixed process conditions, and the production efficiency is high.

[0008] In the face of the problems of sudden change of PH value in the reaction kettle, serious agglomeration of slurry particle size and the like when the hydrogen peroxide and the iron solution are simultaneously fed in proportion, the application first supplements a certain amount of ferrous solution in the first reaction kettle as the reaction bottom solution to provide a PH buffer system for the whole reaction, and after adding the hydrogen peroxide, the originally existing ferrous solution plays a certain dispersion role, avoiding the agglomeration caused by the too fast crystal growth rate in the local area, which makes the whole continuous feeding oxidation process more controllable. There is no need to adjust the PH value by using alkali.

[0009] As a preferred scheme, in step (1), the concentration of dilute phosphoric acid is 20% to 28%, the iron solution reaction temperature is 80 to 95℃, and the iron solution reaction time is 6 to 14h. In order to be suitable for the treatment method of the application, the process parameters of the iron solution are also optimized to avoid the problems of serious agglomeration of slurry particle size and the like.

[0010] As a preferred scheme, in step (2), the Fe concentration in the ferrous phosphate solution is 40 to 65g / L, and the molar ratio of iron element to phosphorus element in the ferrous phosphate solution is adjusted to 1:2.4 to 3.2.

[0011] The application adjusts the Fe concentration of the ferrous phosphate solution before the continuous oxidation reaction, adjusts the P / Fe of the ferrous phosphate obtained by the iron reduction, and does not need to add alkali liquor to adjust the pH during the continuous oxidation by using the series reaction kettle, only needs to control the liquid level, material ratio, temperature and residence time in each reaction kettle, can avoid the introduction of new impurities, and can save process time.

[0012] As a preferred solution, in step (2), the antioxidant is added in an amount of 0.1‰-1‰ of the mass of the ferrous phosphate solution, and the antioxidant is one or more of ascorbic acid, oxalic acid, iron powder and citric acid.

[0013] The application adds a small amount of antioxidant to the ferrous phosphate obtained by the iron reduction, can effectively alleviate the auto-oxidation of the ferrous solution during the waiting reaction process, improves the stability of the divalent iron source solution, reduces the generation of the crystal seed in the ferrous solution, and is more conducive to the subsequent continuous feeding to produce stable iron phosphate products.

[0014] As a preferred solution, in step (3), the temperature of the reaction bottom solution is adjusted to 45-50℃, the amount of the reaction bottom solution is 20%-50% of the volume of the first reaction kettle, the first-stage hydrogen peroxide is fed, or the ferrous solution and the first-stage hydrogen peroxide are fed at the same time, the total amount of the hydrogen peroxide added in the oxidation stage is 0.45-0.55 times of the molar amount of iron in the simultaneously fed ferrous solution, the proportion of the hydrogen peroxide added in each stage is adjustable, and then, when the reaction solution in the upper-stage reaction kettle reaches 80%-90% of the volume of the reaction kettle, the upper-stage reaction slurry is started to discharge, and the lower-stage hydrogen peroxide is started to feed at the same time.

[0015] First, the hydrogen peroxide less than the actual required amount is fed into the continuous oxidation reaction stage to perform incomplete aging on the ferrous solution.

[0016] As a preferred solution, in step (3), the concentration of the hydrogen peroxide is 10%-30%, the residence time of the material in each reaction kettle is 5-60min, and the temperature is 50-80℃.

[0017] The whole continuous feeding oxidation process is more controllable, the application uses the series reaction kettle to perform the continuous oxidation, and it is more conducive to controlling the dispersibility of the reaction material and the residence time in each kettle by pumping, so that the particle size of the ferrous phosphate slurry can be adjusted to produce the iron-process iron phosphate products with stable parameters.

[0018] As a preferred solution, in step (4), the amount of the hydrogen peroxide supplemented in the aging kettle is 0.001-0.025 times of the mass of the oxidation slurry; the aging temperature is 70-90℃, and the aging time is 1-4h.

[0019] The application firstly uses hydrogen peroxide less than the actual required amount to input the continuous oxidation reaction stage, and then adds the remaining required hydrogen peroxide in the aging stage, so that the problem of too fast crystal growth in the early stage is avoided, the volatilization amount of hydrogen peroxide in the whole reaction process is reduced, the obtained slurry is more uniform, and the raw material consumption is reduced.

[0020] As a preferred solution, in step (6), the calcination temperature is 580-650 DEG C, and the calcination time is 3-5h.

[0021] The particle size distribution of the synthesized dihydrate iron phosphate slurry is controllable, the tap density and specific surface area of the corresponding product are simultaneously stabilized at a high level, and the n(Fe) / n(P) in the product meets the market requirements for battery-grade iron phosphate.

[0022] In the second aspect, the application provides a system for continuously feeding to prepare iron phosphate, comprising at least two reaction kettles, a hydrogen peroxide dropping assembly and an aging kettle. The upper end of the at least two reaction kettles is provided with the hydrogen peroxide dropping assembly, the reaction kettles are connected in series, the last reaction kettle is connected with the aging kettle, the slurry out of the aging kettle enters the next process, and the upper end of the aging kettle is also provided with the hydrogen peroxide dropping assembly. The prepared ferrous solution is pumped into the first reaction kettle as the reaction bottom liquid, then the hydrogen peroxide dropping assembly adds hydrogen peroxide, and the oxidation reaction is carried out, whenever the solution in the upper stage reaction kettle reaches the control liquid level, the solution in the upper stage reaction kettle is pumped into the next stage reaction kettle, and the hydrogen peroxide is added correspondingly, and the oxidation reaction is continuously carried out in the reaction kettles in turn until the solution in the last stage reaction kettle reaches the control liquid level, and the oxidation slurry is obtained. The oxidation slurry in the last stage reaction kettle is pumped into the aging kettle, the hydrogen peroxide dropping assembly supplements the metered hydrogen peroxide in the aging kettle, then the aging temperature is adjusted, and the oxidation slurry is aged to obtain the dihydrate iron phosphate slurry.

[0023] By setting the hydrogen peroxide dropping assembly, the multiple reaction kettles and the aging kettle, and setting multiple controllers, the reaction conditions can be accurately controlled, the continuous feeding and discharging of materials are realized, the production efficiency is significantly improved, and the automatic interlocking of the equipment ensures the stability and controllability of the reaction.

[0024] The production product quality is uniform and stable, the batch difference is reduced by continuous operation, the product consistency is ensured, the particle size of the continuously synthesized iron phosphate material is uniform, and the morphology is regular.

[0025] As a preferred solution, a single stirrer or a double stirrer is arranged in each reaction kettle, the stirring parts of the double stirrers are located in the middle and the bottom respectively, a temperature measuring element is arranged in each synthesis reaction kettle, the reaction kettles are connected through pumps, and the last reaction kettle is connected with the aging kettle through a pump. The hydrogen peroxide dropping assembly comprises at least one hydrogen peroxide storage tank, each hydrogen peroxide storage tank is arranged above each reaction kettle, a spraying pipe is connected below the hydrogen peroxide storage tank, and a controller for controlling the dropping speed of hydrogen peroxide is arranged between the spraying pipe and the hydrogen peroxide storage tank; the spraying pipe is annular or has another shape that can ensure that hydrogen peroxide enters the reaction kettle and the aging kettle from multiple points; the spraying pipe is arranged at the top of the reaction kettle and the aging kettle or at a certain distance from the top; and holes for receiving the spraying liquid are arranged on the reaction kettle and the aging kettle.

[0026] The rotation speed of the reaction kettle stirrer is controllable, the reaction can be further ensured to be sufficient, the synthesis reaction kettle combination can be precisely controlled in temperature, the crystal nucleation and crystal growth processes in the iron phosphate synthesis process can be precisely controlled, and the final crystal morphology and particle size are convenient to control. The double-layer stirrers arranged in the liquid storage tank can further eliminate the back mixing phenomenon caused in the continuous production process. The hydrogen peroxide spraying mode can reduce the local concentration when hydrogen peroxide contacts the ferrous liquid, and the reaction process is more controllable. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the system involved in one of the embodiments of the application; Figure 2 is a schematic diagram of the reaction kettle structure of one of the embodiments of the application; Figure 3 is a schematic diagram of the hydrogen peroxide dropping assembly structure of one of the embodiments of the application; Figure 4 is a schematic diagram of the spraying pipe structure connected with the pipeline of one of the embodiments of the application; Figure 5 is an SEM diagram of iron phosphate prepared in embodiment 2 of the application; Among them: 1-reaction kettle group, 11-first reaction kettle, 12-second reaction kettle, 13-third reaction kettle, 14-first pump, 15-second pump, 16-third pump, 17-first stirrer, 18-second stirrer, 19-third stirrer, 110-first temperature measuring element, 111-second temperature measuring element, 112-third temperature measuring element, 113-first conduit, 114-second conduit, 115-third conduit, 116-first variable frequency motor, 117-second variable frequency motor, 118-third variable frequency motor; 2-aging kettle; 3-hydrogen peroxide dropping assembly, 31-first hydrogen peroxide storage tank, 32-second hydrogen peroxide storage tank, 33-third hydrogen peroxide storage tank, 34-first spraying pipe, 35-second spraying pipe, 36-third spraying pipe, 37-first controller, 38-second controller, 39-third controller, 310-hydrogen peroxide conveying pipe. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Generally, the components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0029] It should be noted that the embodiments and features in the present application can be combined with each other without conflict.

[0030] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0031] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly understood by those skilled in the art, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0032] In the description of the present application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "arrange", "mount", "connect", "connect" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. If the specific techniques or conditions are not specified in the embodiments, they are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. If the reagents or instruments are not specified by the manufacturer, they are all conventional products that can be purchased.

[0034] Unless otherwise specified, the percentage herein represents the mass fraction. The ratio is the mass ratio, and the concentration is the mass concentration.

[0035] In the prior art, the oxidation reaction stage of the ferrous phosphate solution is much more complex than the oxidation process of ferrous sulfate, because phosphoric acid is a ternary acid, and there are multiple stages of ionization, so there are multiple intermediate states of coexistence of ferrous biphosphate, ferric biphosphate and ferric phosphate in the whole reaction process, which will lead to the difficulty in controlling the reaction process and the poor batch stability of the product. In order to solve this problem, it is urgent to provide an iron process for stably synthesizing ferric phosphate.

[0036] CN116534824A discloses a method for preparing ferric phosphate by a continuous oxidation process. The ferrous biphosphate solution is fed into a multi-cell oxidation tank, and the ferrous biphosphate solution is continuously overflowed in the multi-cell oxidation tank. When the ferrous biphosphate solution overflows into each cell tank of the multi-cell oxidation tank, the corresponding hydrogen peroxide pump is opened. In this method, the ferrous biphosphate solution is oxidized by multiple stages of overflow, and there is a problem of back mixing of the synthesized ferrous phosphate with increasingly coarse particle size, and the longer the continuous feeding time, the more serious the problem.

[0037] The reasons for back mixing may include the following points: 1. When continuous reaction is carried out by continuous overflow, the flow rate and residence time of the reaction material in the overflow tank will affect the dispersibility of the micro-particles in the solution, leading to the difficulty in controlling the growth rate of the ferric phosphate precipitate; 2. When oxidation reaction occurs, ferrous biphosphate and hydrogen peroxide are fed at the same time, and ferrous phosphate is rapidly generated by instantaneous collision, leading to too large supersaturation of ferrous phosphate in the solution, and too fast growth rate of the ferrous phosphate crystal, which leads to the difficulty in controlling the particle size; 3. The full amount of oxidizing agent is added into the oxidation tank according to the theoretical metering value in the continuous oxidation stage, which may also lead to too fast growth rate of the ferrous phosphate crystal, which is not conducive to controlling the particle size.

[0038] In addition, in the preparation of ferric phosphate by the existing continuous oxidation process, an alkali solution such as sodium hydroxide or ammonia solution is usually added to adjust the pH in the continuous oxidation reaction process to reduce the generation of impurities in the ferric phosphate slurry. However, the addition of the alkali solution not only may introduce new impurities, but also will waste a lot of time in the industrial production process to detect and control the pH.

[0039] Further, in a first aspect, the embodiments of the present application provide a method for preparing ferric phosphate by continuous feeding, comprising the following steps: Step (1) placing pure iron in dilute phosphoric acid to carry out ironization reaction to obtain a ferrous biphosphate solution; Step (2) adjusting the Fe concentration of the ferrous biphosphate solution, supplementing water and phosphoric acid to the ferrous biphosphate solution according to the Fe and P contents of the original ferrous biphosphate solution, adjusting the molar ratio of iron element to phosphorus element in the ferrous biphosphate solution, then feeding the ferrous biphosphate solution into a ferrous biphosphate solution storage tank, and adding an antioxidant; Step (3) is carried out in at least two reactors in series, first pumping the ferrous solution of step (2) into the first reactor as the reaction bottom solution, then adding hydrogen peroxide, and carrying out the oxidation reaction, whenever the solution in the previous reactor reaches the control liquid level, the solution in the previous reactor is pumped into the next reactor, and hydrogen peroxide is added, and the oxidation reaction is carried out in each reactor in turn, until the solution in the last reactor reaches the control liquid level, and the oxidation slurry is obtained; Step (4) pumps the oxidation slurry in the last reactor into the aging reactor, adds a metered amount of hydrogen peroxide in the aging reactor, then adjusts the aging temperature, and ages the oxidation slurry to obtain the iron phosphate dihydrate slurry; Step (5) carries out pressure filtration and washing treatment on the iron phosphate dihydrate slurry of step (4), and separates to obtain the filter cake; Step (6) dries and calcines the filter cake separated in step (5) to obtain the iron phosphate anhydrous product.

[0040] The method of continuous feeding is used to produce iron phosphate, by adjusting the feeding and temperature parameters in the oxidation process, the mixed iron phosphate dihydrate slurry of coarse and fine particles can be obtained, so that the particle size and specific surface area of the iron phosphate product can be easily controlled; and the consistency of the product is good under fixed process conditions, and the production efficiency is high.

[0041] In the face of iron phosphate hydrogen peroxide and iron solution, the pH value in the reactor is prone to sudden change, and the particle size of the slurry is prone to serious agglomeration, etc. The application first supplements a certain amount of ferrous solution in the first reactor as the reaction bottom solution to provide a PH buffer system for the whole reaction, then adds hydrogen peroxide, and the originally existing ferrous solution plays a certain dispersion role, avoiding the rapid growth rate of crystals in local areas and agglomeration, which makes the whole continuous feeding oxidation process more controllable. The pump selected can be a commercially available product, and the model can be selected according to needs. The aging reactor can be a conventional product.

[0042] As one of the embodiments, in step (1), the concentration of dilute phosphoric acid is 20%~28%; the iron reaction temperature is 80~95℃, and the iron reaction time is 6~14h. In order to be suitable for the treatment method of the application, the process parameters of iron are also optimized accordingly to avoid serious agglomeration of the particle size of the slurry, etc. The purity of pure iron is greater than 99.99% As one of the embodiments, in step (2), the Fe concentration in the ferrous phosphate solution is 40~65g / L, and the molar ratio of iron element to phosphorus element in the ferrous phosphate solution is adjusted to 1:2.4~3.2.

[0043] Before the continuous oxidation reaction, the P / Fe and Fe concentration of ferrous phosphate obtained by the iron reduction are adjusted, and after the subsequent continuous oxidation by using the series reaction kettle, the pH needs to be adjusted by adding alkali liquor again, and only the liquid level, material ratio, temperature and residence time in each reaction kettle need to be controlled, which not only can avoid the introduction of new impurities, but also can save the process time.

[0044] As one of the embodiments, in step (2), the antioxidant is added in an amount of 0.1‰-1‰ of the mass of the ferrous phosphate solution, and the antioxidant is one or more of ascorbic acid, oxalic acid, iron powder and citric acid.

[0045] Adding a small amount of antioxidant to the ferrous phosphate obtained by the iron reduction can effectively alleviate the self-oxidation of the ferrous solution during the waiting reaction process, improve the stability of the divalent iron source solution, reduce the generation of crystal seeds in the ferrous solution, and be more conducive to the subsequent continuous feeding to produce stable iron phosphate products.

[0046] As one of the embodiments, in step (3), the temperature of the reaction bottom solution is adjusted to 45-50℃, the amount of the reaction bottom solution is 20%-50% of the volume of the first reaction kettle, the first-stage hydrogen peroxide is fed, or the ferrous solution and the first-stage hydrogen peroxide are fed simultaneously, the total amount of hydrogen peroxide added in the oxidation stage is 0.45-0.55 times the molar amount of iron in the simultaneously fed ferrous solution, the ratio of hydrogen peroxide added in each stage can be adjusted, and thereafter, when the reaction solution in the upper-stage reaction kettle reaches 80%-90% of the volume of the reaction kettle, the upper-stage reaction slurry is started to be discharged, and the lower-stage hydrogen peroxide is started to be fed.

[0047] Here, the ferrous solution is first added to play a buffering role, the hydrogen peroxide less than the actual required amount is first fed into the continuous oxidation reaction stage to incompletely age the ferrous solution, so that the latter half of the reaction has a buffer system. When the amount of the reaction bottom solution is 20%-50% of the volume of the first reaction kettle, the hydrogen peroxide can be first fed to react, and after a certain time, the ferrous solution and the hydrogen peroxide are continuously fed until the reaction solution reaches 80%-90% of the volume of the reaction kettle. The ratio of each stage can be adjusted (such as the ratio of hydrogen peroxide added in two stages can be 5:5 or 1:9), and the residence time and the total amount of hydrogen peroxide added are ensured to meet the ratio.

[0048] As one of the embodiments, in step (3), the concentration of hydrogen peroxide is 10%-30%, and the residence time of the material in each reaction kettle is 5-60 min, and the temperature is 50-80℃.

[0049] The whole continuous feeding oxidation process is more controllable, and the series reaction kettle is used for continuous oxidation, and the dispersion of the reaction material and the residence time in each kettle are more conducive to being controlled by pumping, so that the particle size of the iron phosphate dihydrate slurry can be adjusted and controlled, and the iron phosphate product with stable parameters can be produced.

[0050] As one of the embodiments, in step (4), the amount of hydrogen peroxide supplemented in the aging kettle is 0.001-0.025 times the mass of the oxidation slurry; the aging temperature is 70-90℃, and the aging time is 1-4h.

[0051] First, hydrogen peroxide less than the actual required amount is put into the continuous oxidation reaction stage to incompletely age the ferrous liquid, and then the remaining required hydrogen peroxide is added in the aging stage, which not only avoids the problem of too fast growth of part of the crystals in the early stage, but also reduces the volatilization amount of hydrogen peroxide in the entire reaction process, so that the obtained slurry is more uniform, and the raw material consumption is reduced.

[0052] As one of the embodiments, in step (6), the calcination temperature is 580-650℃, and the calcination time is 3-5h.

[0053] The particle size distribution of the synthesized iron phosphate dihydrate slurry is controllable, the tap density and specific surface area of the corresponding product can be simultaneously stabilized at a high level, and the molar ratio of iron element to phosphorus element in the product, i.e., n(Fe) / n(P), meets the market requirements for battery-grade iron phosphate.

[0054] In a second aspect, an embodiment of the present application provides a system for continuously feeding to prepare iron phosphate, comprising at least two reaction kettles, a hydrogen peroxide dropping assembly and an aging kettle. The upper end of each of the at least two reaction kettles is provided with the hydrogen peroxide dropping assembly, the reaction kettles are connected in series, the last reaction kettle is connected with the aging kettle, the slurry from the aging kettle is fed to the next process, and the upper end of the aging kettle is also provided with the hydrogen peroxide dropping assembly. The prepared ferrous solution is pumped into the first reaction kettle as the reaction bottom liquid, and then the hydrogen peroxide dropping assembly adds hydrogen peroxide, and the oxidation reaction is carried out. When the solution in the upper stage reaction kettle reaches the control liquid level, the solution in the upper stage reaction kettle is pumped into the next stage reaction kettle, and the corresponding hydrogen peroxide is added. The oxidation reaction is continuously carried out in each stage reaction kettle in turn until the solution in the last stage reaction kettle reaches the control liquid level, and the oxidation slurry is obtained. The oxidation slurry in the last stage reaction kettle is pumped into the aging kettle, the hydrogen peroxide dropping assembly supplements the metered hydrogen peroxide in the aging kettle, and then the aging temperature is adjusted to age the oxidation slurry, and the iron phosphate dihydrate slurry is obtained.

[0055] By setting the hydrogen peroxide dropping assembly, multiple reaction kettles and the aging kettle, and setting multiple controllers, the reaction conditions can be accurately controlled, the continuous feeding and discharging of the material can be realized, the production efficiency is significantly improved, and the automatic interlocking of the equipment ensures the stability and controllability of the reaction. The product quality is uniform and stable, the batch difference is reduced by continuous operation, the product consistency is ensured, the particle size of the continuously synthesized iron phosphate material is uniform, and the morphology is regular.

[0056] As a preferred solution, a single stirrer or a double stirrer is arranged in each reaction kettle, the stirring parts of the double stirrer are arranged at the middle and the bottom respectively, a temperature measuring element is further arranged in each synthesis reaction kettle, the reaction kettles are connected through pumps, and the last reaction kettle is connected with the aging kettle through a pump; The hydrogen peroxide dropping assembly comprises at least one hydrogen peroxide storage tank, each hydrogen peroxide storage tank is arranged above each reaction kettle, a spraying pipe is connected below the hydrogen peroxide storage tank, and a controller for controlling the dropping speed of hydrogen peroxide is arranged between the spraying pipe and the hydrogen peroxide storage tank; the spraying pipe is annular or has another shape that can ensure that hydrogen peroxide enters the reaction kettle and the aging kettle from multiple points, and the spraying pipe is arranged at the top of the reaction kettle and the aging kettle or at a distance from the top; and holes for receiving the spraying liquid are arranged on the reaction kettle and the aging kettle.

[0057] The rotation speed of the reaction kettle stirrer is controllable, which can further ensure that the reaction is sufficient, and the synthesis reaction kettle combination can be precisely controlled in temperature, so as to precisely control the crystal nucleation and crystal growth process in the synthesis process of iron phosphate, facilitate the control of the final crystal morphology and particle size. The double-layer stirrers arranged in the liquid storage tank can eliminate the back mixing phenomenon caused in the continuous production process. The hydrogen peroxide spraying mode can reduce the local concentration when hydrogen peroxide contacts with ferrous liquid, and the reaction process is more controllable. The stirrers at the middle and the bottom can be stirring blades, which are traditional structures, and only one is arranged at the middle and the bottom. The motor of the stirrer is a commercially available product, which can be variable frequency. The temperature measuring element is a commercially available temperature sensor or thermometer or other temperature measuring product. The plurality of reaction kettles and the aging kettle can also be provided with an existing liquid level detection device, and when the liquid level reaches a certain level, feedback is given to the total controller, and the total controller controls the corresponding pump to operate and pump according to the instruction.

[0058] The spraying pipe is annular or has another shape that can ensure that hydrogen peroxide enters the synthesis reaction kettle from multiple points, and the spraying pipe is arranged at the top of the synthesis reaction kettle or at a distance from the top; and holes for receiving the spraying liquid are arranged on the synthesis reaction kettle. The controller can be an existing electromagnetic valve or other existing product for controlling flow. In order to make the reaction more sufficient, the spraying pipe can be an annular pipe or a pipe with other shapes, for example, an ellipse, a semicircle, a rectangle, a triangle, etc., as long as hydrogen peroxide can enter the reaction kettle from multiple points. The aging kettle can be provided with one or more than one according to the need, which can be an existing structure or the same as the synthesis kettle.

[0059] In order to further illustrate the present application, a continuous feeding method and system for preparing iron phosphate provided by the present application are described in detail below with reference to the embodiments.

[0060] As shown in Figure 1 Fig. 1, the embodiment of the present application provides a system for continuously feeding to prepare iron phosphate, which comprises a reaction kettle group 1, an aging kettle 2 and a hydrogen peroxide dropping assembly 3.

[0061] The upper end of the reaction kettle group 1 is provided with a hydrogen peroxide dropping assembly 3, the reaction kettles are connected in series, the last reaction kettle is connected with the aging kettle 2, the slurry discharged from the aging kettle enters the next process, and the upper end of the aging kettle 2 is also provided with a hydrogen peroxide dropping assembly 3.

[0062] As shown in Figure 2 The reaction kettle group 1 includes a first reaction kettle 11, a second reaction kettle 12 and a third reaction kettle 13. The bottom liquid outlet of the first reaction kettle 11 is connected with one end of a first pump 14, the other end of the first pump 14 is connected with the top liquid inlet of the second reaction kettle 12 through a first conduit 113, the bottom liquid outlet of the second reaction kettle 12 is connected with one end of a second pump 15, the other end of the second pump 15 is connected with the top liquid inlet of the third reaction kettle 13 through a second conduit 114, the bottom liquid outlet of the third reaction kettle 13 is connected with one end of a third pump 16, and the other end of the third pump 16 is connected with the aging kettle 2 through a third conduit 115.

[0063] The first reaction kettle 11, the second reaction kettle 12 and the third reaction kettle 13 are respectively provided with a first stirrer 17, a second stirrer 18 and a third stirrer 19, the stirrers used in the kettles are double stirrers, one pair of stirring blades is located at the bottom and one pair of stirring blades is located at the middle, the first stirrer 17, the second stirrer 18 and the third stirrer 19 are respectively controlled by a first variable frequency motor 116, a second variable frequency motor 117 and a third variable frequency motor 118. One side of the first reaction kettle 11, the second reaction kettle 12 and the third reaction kettle 13 is respectively provided with a first temperature measuring element 110, a second temperature measuring element 111 and a third temperature measuring element 112. In order to prevent back mixing, the rotating speed of the stirrer can be 240-250 r / min, and the stirrer can be started after feeding.

[0064] As shown in Figure 3 The hydrogen peroxide dropping assembly 3 includes a first hydrogen peroxide storage tank 31, a second hydrogen peroxide storage tank 32, a third hydrogen peroxide storage tank 33 and a fourth hydrogen peroxide storage tank, a first spray pipe 34, a second spray pipe 35, a third spray pipe 36 and a fourth spray pipe are sequentially arranged below the hydrogen peroxide storage tanks, the pipelines between the spray pipes and the hydrogen peroxide storage tanks are respectively provided with first, second, third and fourth controllers for controlling the dropping speed of the hydrogen peroxide, the inlets of the first, second, third and fourth hydrogen peroxide storage tanks are connected with a hydrogen peroxide conveying pipe 310, and a control valve can be arranged on the hydrogen peroxide conveying pipe 310. The fourth hydrogen peroxide storage tank is located above the aging kettle 2.

[0065] For example, the annular tube has a hole at the upper end connected to the pipeline and a plurality of spray holes at the bottom, and the reaction kettle group 1 and the aging kettle 2 have corresponding holes for receiving the sprayed liquid. The hole connected to the pipeline can have a larger diameter than the spray hole to ensure that hydrogen peroxide can be sprayed from at least part of the spray holes. Hydrogen peroxide is discharged from below the hydrogen peroxide storage tank, passes through the pipeline provided with a controller, and enters the spray pipe, as shown in FIG. 8. Figure 4 The agitator in the aging kettle 2 can also be provided as in the reaction kettle, and the slurry starts to enter at the same time as the agitator is started.

[0066] Example 1 The method for preparing iron phosphate by continuous feeding in this example uses the above-mentioned three-stage series reaction kettle for continuous oxidation reaction, which includes the following steps: Step (1) Iron is placed in dilute phosphoric acid for iron reduction reaction to prepare ferrous phosphate solution; the purity of pure iron is greater than 99.99%; the concentration of dilute phosphoric acid is 20%; the iron reduction reaction temperature is 85°C, and the iron reduction reaction time is 6h.

[0067] Step (2) After the iron reduction, the ferrous liquid iron concentration is adjusted to 58g / L, and the P / Fe molar ratio is 2.60, then the ferrous liquid storage tank is punched, and then 0.1wt‰ of iron powder is added to the ferrous liquid; Step (3) Adjust the temperature of the ferrous liquid in the ferrous liquid storage tank to 50°C, then pump it into the first reaction kettle 11, when the liquid level reaches 20% of the total volume of the first reaction kettle 11, start the first controller 37 to add hydrogen peroxide with a concentration of 15% to the first reaction kettle 11, and continue to add ferrous liquid, when the liquid level in the first reaction kettle 11 reaches 80% of the total volume, start the first pump 14 and the second controller 38 at the same time; when the liquid level reaches 80% of the total volume of the second reaction kettle, start the second pump 15 and the third controller 39 at the same time; when the liquid level reaches 80% of the total volume of the third reaction kettle 13, start the third pump 16 to pump the oxidation slurry into the aging kettle 2.

[0068] The ratio of hydrogen peroxide added to the three reaction kettles is 3:3:3, and the temperature of the three reaction kettles is controlled at 75°C.

[0069] The residence time of the material in each stage of the reaction kettle is 10min. In the oxidation stage, the total amount of hydrogen peroxide added is 0.45 times the molar amount of iron in the simultaneously fed ferrous liquid.

[0070] Step (4) When the liquid level of each aging kettle reaches 80% of the total volume of the kettle, open the fourth controller to supplement the amount of hydrogen peroxide, which is 0.015 times the mass of the slurry, and start the aging kettle temperature control system to adjust the aging temperature to 80°C for 2h to age the slurry to obtain iron phosphate dihydrate slurry.

[0071] Step (5) involves conventional pressure filtration and washing of the ferric phosphate dihydrate slurry to separate the filter cake. The process parameters are also conventional.

[0072] Step (6) The separated filter cake is dried and calcined to obtain anhydrous iron phosphate product TFL-FePO4-1. The calcination temperature is 600℃ and the calcination time is 3h.

[0073] Example 2 The method for preparing iron phosphate using continuous feeding in this embodiment employs the aforementioned three-stage series reactor for continuous oxidation reaction, and includes the following steps: Step (1) Pure iron is placed in dilute phosphoric acid to carry out the iron-dissolving reaction to prepare ferrous dihydrogen phosphate solution; the purity of pure iron is greater than 99.99%; the concentration of dilute phosphoric acid is 28%; the iron-dissolving reaction temperature is 95℃ and the iron-dissolving reaction time is 10h.

[0074] After step (2) ferrometallurgical treatment, the iron concentration of the ferrous liquid was adjusted to 45 g / L and the P / Fe molar ratio was 2.75. Then, it was poured into the ferrous liquid storage tank and ascorbic acid with a mass of 0.2 wt‰ of the ferrous liquid was added. Step (3) After adjusting the temperature of the ferrous liquid in the ferrous liquid storage tank to 45°C, pump it into the first reactor 11. When the liquid level reaches 30% of the total volume of the first reactor 11, start the first controller 37 to add 23% hydrogen peroxide into the first reactor 11, and continue to add ferrous liquid. When the liquid level in the first reactor 11 reaches 85% of the total volume, start the first pump 14 and the second controller 38 at the same time. When the liquid level reaches 85% of the total volume of the second reactor, start the second pump 15 and the third controller 39 at the same time. When the liquid level reaches 85% of the total volume of the third reactor 13, start the third pump 16 to pump the oxidized slurry into the aging reactor 2.

[0075] The ratio of hydrogen peroxide added to the three reactors is 2:3:5. The temperature of the three reactors is controlled at 80℃ during the process.

[0076] The residence time of materials in each stage reactor is 20 minutes. During the oxidation stage, the total amount of hydrogen peroxide added is 0.50 times the molar amount of iron in the simultaneously fed ferrous liquid.

[0077] Step (4) When the liquid level in each aging vessel reaches 80% of the total volume inside the vessel, turn on the fourth controller, add hydrogen peroxide to 0.001 times the mass of the slurry, start the temperature control system of the aging vessel, adjust the aging temperature to 85℃ and keep it at that temperature for 2 hours to age the slurry and obtain ferric phosphate dihydrate slurry.

[0078] Step (5) involves conventional pressure filtration and washing of the ferric phosphate dihydrate slurry to separate the filter cake. The process parameters are also conventional.

[0079] Step (6) The separated filter cake is dried and calcined to obtain anhydrous iron phosphate product TFL-FePO4-2. The calcination temperature is 620℃ and the calcination time is 4h.

[0080] Example 3 The method for preparing iron phosphate using continuous feeding in this embodiment employs the aforementioned three-stage series reactor for continuous oxidation reaction, and includes the following steps: Step (1) Pure iron is placed in dilute phosphoric acid to carry out the iron-dissolving reaction to prepare ferrous dihydrogen phosphate solution; the purity of pure iron is greater than 99.99%; the concentration of dilute phosphoric acid is 20%; the iron-dissolving reaction temperature is 95℃ and the iron-dissolving reaction time is 14h.

[0081] After step (2) molten iron, the iron concentration of the ferrous liquid was adjusted to 60 g / L and the P / Fe molar ratio was 2.85. Then, it was poured into the ferrous liquid storage tank and citric acid with a mass of 0.2 wt‰ of the ferrous liquid was added. Step (3) After adjusting the temperature of the ferrous liquid in the ferrous liquid storage tank to 45°C, pump it into the first reactor 11. When the liquid level reaches 50% of the total volume of the first reactor 11, start the first controller 37 to add 23% hydrogen peroxide into the first reactor 11, and continue to add ferrous liquid. When the liquid level in the first reactor 11 reaches 90% of the total volume, start the first pump 14 and the second controller 38 at the same time. When the liquid level reaches 90% of the total volume of the second reactor, start the second pump 15 and the third controller 39 at the same time. When the liquid level reaches 90% of the total volume of the third reactor 13, start the third pump 16 to pump the oxidized slurry into the aging reactor 2.

[0082] The ratio of hydrogen peroxide added to the three reactors is 2:4:4. The temperature of the three reactors is controlled at 80℃ during the process.

[0083] The residence time of materials in each stage reactor is 30 minutes. During the oxidation stage, the total amount of hydrogen peroxide added is 0.55 times the molar amount of iron in the simultaneously fed ferrous liquid.

[0084] Step (4) When the liquid level in each aging vessel reaches 90% of the total volume inside the vessel, turn on the fourth controller, add hydrogen peroxide to 0.02 times the mass of the slurry, start the temperature control system of the aging vessel, adjust the aging temperature to 90℃ and keep it at that temperature for 1 hour to age the slurry and obtain ferric phosphate dihydrate slurry.

[0085] Step (5) involves conventional pressure filtration and washing of the ferric phosphate dihydrate slurry to separate the filter cake. The process parameters are also conventional.

[0086] Step (6) The separated filter cake is dried and calcined to obtain anhydrous iron phosphate product TFL-FePO4-3. The calcination temperature is 650℃ and the calcination time is 3h.

[0087] Example 4 This embodiment describes a continuous feeding method for preparing iron phosphate, employing a five-stage series reactor for continuous oxidation. This involves adding two more reactors to the aforementioned system, and includes the following steps: Step (1) Pure iron is placed in dilute phosphoric acid to carry out the iron-dissolving reaction to prepare ferrous dihydrogen phosphate solution; the purity of pure iron is greater than 99.99%; the concentration of dilute phosphoric acid is 25%; the iron-dissolving reaction temperature is 90℃ and the iron-dissolving reaction time is 10h.

[0088] After step (2) ferrometallurgical treatment, the iron concentration of the ferrous liquid was adjusted to 50 g / L and the P / Fe molar ratio was 2.65. Then, it was poured into the ferrous liquid storage tank and ascorbic acid with a mass of 0.3 wt‰ of the ferrous liquid was added. Step (3): After adjusting the temperature of the ferrous liquid in the ferrous liquid storage tank to 40°C, pump it into the first reactor 11. When the liquid level reaches 50% of the total volume of the first reactor 11, start the first controller 37 to add 27% hydrogen peroxide to the first reactor 11 and react for a period of time. Then, continue to add ferrous liquid and hydrogen peroxide simultaneously. When the liquid level in the first reactor 11 reaches 90% of the total volume, start the first pump 14 and the second controller 38 simultaneously. When the liquid level reaches 85% of the total volume of the second reactor, start the second pump 15 and the third controller 39 simultaneously. Continue this process in sequence until the fifth reactor discharges. When the liquid level reaches 90% of the total volume of the fifth reactor, start the pump to pump the oxidized slurry into the aging reactor 2. The ratio of hydrogen peroxide added to the five reactors is 2:2:2:2:2. The temperature of the five reactors is controlled at 80°C during this process.

[0089] The residence time of materials in each stage reactor is 5 minutes. During the oxidation stage, the total amount of hydrogen peroxide added is 0.45 times the molar amount of iron in the simultaneously fed ferrous liquid.

[0090] Step (4) When the liquid level in each aging vessel reaches 85% of the total volume inside the vessel, turn on the fourth controller, add hydrogen peroxide at a rate of 0.002 times the mass of the slurry, start the temperature control system of the aging vessel, adjust the aging temperature to 85℃ and keep it at that temperature for 3 hours to age the slurry and obtain ferric phosphate dihydrate slurry.

[0091] Step (5) involves conventional pressure filtration and washing of the ferric phosphate dihydrate slurry to separate the filter cake. The process parameters are also conventional.

[0092] Step (6) The separated filter cake is dried and calcined to obtain anhydrous iron phosphate product TFL-FePO4-4. The calcination temperature is 650℃ and the calcination time is 3h.

[0093] Example 5 The method for preparing iron phosphate using continuous feeding in this embodiment employs the aforementioned three-stage series reactor for continuous oxidation reaction, and includes the following steps: Step (1) Pure iron is placed in dilute phosphoric acid to carry out the iron-dissolving reaction to prepare ferrous dihydrogen phosphate solution; the purity of pure iron is greater than 99.99%; the concentration of dilute phosphoric acid is 20%; the iron-dissolving reaction temperature is 85℃ and the iron-dissolving reaction time is 6h.

[0094] After step (2) ferrometallurgical treatment, the iron concentration of the ferrous liquid was adjusted to 45 g / L and the P / Fe molar ratio was 2.4. Then, it was poured into the ferrous liquid storage tank and ascorbic acid of 0.1 wt‰ of the ferrous liquid mass was added. Step (3) After adjusting the temperature of the ferrous liquid in the ferrous liquid storage tank to 45°C, pump it into the first reactor 11. When the liquid level reaches 20% of the total volume of the first reactor 11, start the first controller 37 to add 10% hydrogen peroxide into the first reactor 11, and continue to add ferrous liquid. When the liquid level in the first reactor 11 reaches 85% of the total volume, start the first pump 14 and the second controller 38 at the same time. When the liquid level reaches 85% of the total volume of the second reactor, start the second pump 15 and the third controller 39 at the same time. When the liquid level reaches 85% of the total volume of the third reactor 13, start the third pump 16 to pump the oxidized slurry into the aging reactor 2.

[0095] The ratio of hydrogen peroxide added to the three reactors is 2:3:5. The temperature of the three reactors is controlled at 75℃ during the process.

[0096] The residence time of materials in each stage reactor is 15 minutes. During the oxidation stage, the amount of hydrogen peroxide added is 0.50 times the molar amount of iron in the simultaneously fed ferrous liquid.

[0097] Step (4) When the liquid level in each aging vessel reaches 80% of the total volume inside the vessel, turn on the fourth controller, add hydrogen peroxide to 0.005 times the mass of the slurry, start the temperature control system of the aging vessel, adjust the aging temperature to 70℃ and keep it at that temperature for 2 hours to age the slurry and obtain ferric phosphate dihydrate slurry.

[0098] Step (5) involves conventional pressure filtration and washing of the ferric phosphate dihydrate slurry to separate the filter cake. The process parameters are also conventional.

[0099] Step (6) The separated filter cake is dried and calcined to obtain anhydrous iron phosphate product TFL-FePO4-5. The calcination temperature is 600℃ and the calcination time is 3h.

[0100] Example 6 This embodiment describes a continuous feeding method for preparing iron phosphate, employing a five-stage series reactor for continuous oxidation. This involves adding two more reactors to the aforementioned system, and includes the following steps: Step (1) Pure iron is placed in dilute phosphoric acid to carry out the iron-dissolving reaction to prepare ferrous dihydrogen phosphate solution; the purity of pure iron is greater than 99.99%; the concentration of dilute phosphoric acid is 28%; the iron-dissolving reaction temperature is 95℃ and the iron-dissolving reaction time is 14h.

[0101] After step (2) molten iron, the iron concentration of the ferrous liquid was adjusted to 65 g / L and the P / Fe molar ratio was 3.2. Then, it was poured into the ferrous liquid storage tank and iron powder with a mass of 1 wt‰ of the ferrous liquid was added. Step (3) After adjusting the temperature of the ferrous liquid in the ferrous liquid storage tank to 40°C, pump it into the first reactor 11. When the liquid level reaches 50% of the total volume of the first reactor 11, start the first controller 37 to add 30% hydrogen peroxide to the first reactor 11. React for a period of time, and then continue to add ferrous liquid and hydrogen peroxide simultaneously. When the liquid level in the first reactor 11 reaches 90% of the total volume, start the first pump 14 and the second controller 38 simultaneously. When the liquid level reaches 85% of the total volume of the second reactor 12, start the second pump 15 and the third controller 39 simultaneously. Continue to operate in sequence until the fifth reactor discharges. When the liquid level reaches 90% of the total volume of the fifth reactor, start the pump to pump the oxidized slurry into the aging reactor 2. The ratio of hydrogen peroxide added to the five reactors is 2:3:3:2:2. The temperature of the five reactors is controlled at 80°C during this process.

[0102] The residence time of materials in each stage reactor is 20 minutes. During the oxidation stage, the total amount of hydrogen peroxide added is 0.55 times the molar amount of iron in the simultaneously fed ferrous liquid.

[0103] Step (4) When the liquid level in each aging vessel reaches 85% of the total volume inside the vessel, turn on the fourth controller, add hydrogen peroxide to 0.002 times the mass of the slurry, start the temperature control system of the aging vessel, adjust the aging temperature to 90℃ and keep it at that temperature for 4 hours to age the slurry and obtain ferric phosphate dihydrate slurry.

[0104] Step (5) involves conventional pressure filtration and washing of the ferric phosphate dihydrate slurry to separate the filter cake. The process parameters are also conventional.

[0105] Step (6) The separated filter cake is dried and calcined to obtain anhydrous iron phosphate product TFL-FePO4-6. The calcination temperature is 650℃ and the calcination time is 5h.

[0106] Comparative Example 1 In Example 2, ferrous liquid was not used as the reaction base liquid. In step (3), the temperature of the ferrous liquid in the ferrous liquid storage tank was adjusted to 45°C, and hydrogen peroxide was added to the first reaction vessel 11 by starting the ferrochemical pump and the first controller 37.

[0107] Comparative Example 2 In Example 3, ferrous liquid was not used as the reaction base liquid. In step (3), the temperature of the ferrous liquid in the ferrous liquid storage tank was adjusted to 45°C, and hydrogen peroxide was added to the first reaction vessel 11 by starting the ferrochemical pump and the first controller 37.

[0108] Comparative Example 3 Example 3 uses a continuous three-compartment overflow tank for continuous oxidation reaction. In step (3), the ferrous liquid in the ferrous liquid storage tank is adjusted to 45°C and then continuously pumped into the first compartment of the three-compartment oxidation tank. When the liquid level reaches 80% of the compartment, the first-stage hydrogen peroxide pump is started to pump the metered hydrogen peroxide into the first compartment. When the reaction liquid overflows from the first compartment to the second compartment, the second-stage hydrogen peroxide pump is started to pump the metered hydrogen peroxide into the second compartment. When the reaction liquid overflows from the second compartment to the third compartment, the third-stage hydrogen peroxide pump is started to pump the metered hydrogen peroxide into the third compartment. The ratio of hydrogen peroxide added to the three compartments is 3:3:3. The temperature of the three reactors is controlled at 80°C during this process.

[0109] Comparative Example 4 Example 3 uses a continuous three-compartment overflow tank for continuous oxidation reaction, with ferrous liquid and hydrogen peroxide fed at the same time, and the hydrogen peroxide oxidation stage is fully fed according to theoretical values.

[0110] Step (3) After adjusting the temperature of the ferrous liquid in the ferrous liquid storage tank to 45°C, it is continuously pumped into the first square cell of the three-cell oxidation tank. At the same time, the first-stage hydrogen peroxide pump is started to pump the metered hydrogen peroxide into the first square cell. When the reaction liquid in the first square cell overflows into the second square cell, the second-stage hydrogen peroxide pump is started to pump the metered hydrogen peroxide into the second square cell. When the reaction liquid in the second square cell overflows into the third square cell, the third-stage hydrogen peroxide pump is started to pump the metered hydrogen peroxide into the third square cell. The ratio of hydrogen peroxide added to the three square cells is 3:3:3. During the continuous oxidation reaction, all hydrogen peroxide is added according to the theoretical metering value. The temperature of the three reaction vessels is controlled at 75°C during this process.

[0111] The particle size, anhydrous ferric phosphate compaction, and specific gravity of the ferric phosphate slurries prepared in Examples 1-4 and Comparative Examples 1-4 are shown in Table 1 below. The results of Examples 5-6 are also better than those of Comparative Examples 1-4. Only the results of Examples 1-4 are shown here.

[0112] Table 1. Results of particle size and anhydrous ferric phosphate slurry in different embodiments and comparative examples. Analysis of Table 1 shows that the particle size distribution of the iron phosphate dihydrate slurry synthesized under the conditions of Examples 1-4 is controllable. The tap and specific surface area of ​​the corresponding products are simultaneously stable at a high level, and the n(Fe) / n(P) ratio of the products meets the market requirements for battery-grade iron phosphate. However, in Comparative Examples 1-2, due to the absence of ferrous liquid as the reaction substrate, the particle size variation of the synthesized iron phosphate dihydrate slurry is relatively large and difficult to control. Although the tap of the corresponding products is greater than 1 g / cm3, the specific surface area is low and the n(Fe) / n(P) ratio is unstable, making it difficult to meet market requirements.

[0113] In addition, the results in Table 1 show that Comparative Examples 3 and 4 use an overflow series flow, which is different from bottom-controlled discharge. The overflow series flow causes severe backmixing, and some of the pre-aged crystals remain at the bottom of the reaction and continue to grow, resulting in a large particle distribution width and poor particle size uniformity.

[0114] In the embodiments of this application, when a series of reactors are used for continuous oxidation reaction, ferrous liquid is used as the base liquid in the first reactor. During the continuous oxidation reaction, the hydrogen peroxide is controlled to be incompletely oxidized, and the remaining hydrogen peroxide is added during the aging stage. The two interact with each other, which is more conducive to controlling the change in the particle size of ferric phosphate.

[0115] The particle size results of the aged slurry in Comparative Examples 4 and 5 were significantly unsatisfactory, as were the FePO4 results.

[0116] Figure 5 The image shows the SEM image of the iron phosphate prepared in Example 2. It shows that the iron phosphate synthesized by this process is a secondary agglomerate formed by the accumulation of primary lamellar particles, indicating that the secondary particles of iron phosphate prepared by continuous oxidation in multiple reactors are evenly distributed.

[0117] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ferric phosphate via continuous feeding, characterized in that, Includes the following steps: Step (1) Pure iron is placed in dilute phosphoric acid to carry out the iron-containing reaction, and ferrous dihydrogen phosphate solution is obtained; Step (2) Adjust the Fe concentration of the ferrous dihydrogen phosphate solution. Based on the Fe and P content of the original ferrous dihydrogen phosphate solution, add water and phosphoric acid to the ferrous solution to adjust the molar ratio of iron to phosphorus in the ferrous dihydrogen phosphate solution. Then, pour it into the ferrous solution storage tank and add antioxidants. Step (3) uses at least two reactors for continuous oxidation. First, the ferrous solution from step (2) is pumped into the first reactor as the reaction base liquid, and then hydrogen peroxide is added to carry out the oxidation reaction. Whenever the solution in the upper reactor reaches the control level, the upper reactor solution is pumped into the next reactor, and hydrogen peroxide is added at the same time. The oxidation reaction is carried out continuously in each reactor until the solution in the last reactor reaches the control level to obtain the oxidation slurry. Step (4) Pump the oxidized slurry in the last stage reactor into the aging reactor, add the metered hydrogen peroxide to the aging reactor, and then adjust the aging temperature to age the oxidized slurry to obtain ferric phosphate dihydrate slurry. Step (5) The ferric phosphate dihydrate slurry from step (4) is subjected to pressure filtration and washing to separate the filter cake. Step (6) The filter cake separated in step (5) is dried and calcined to obtain anhydrous ferric phosphate product.

2. The method according to claim 1, characterized in that: In step (1), the concentration of dilute phosphoric acid is 20%~28%; the iron melting reaction temperature is 80~95℃; and the iron melting reaction time is 6~14h.

3. The method according to claim 1, characterized in that: In step (2), the Fe concentration in the ferrous dihydrogen phosphate solution is 40~65g / L, and the molar ratio of iron to phosphorus in the ferrous dihydrogen phosphate solution is adjusted to 1:2.4~3.

2.

4. The method according to claim 1, characterized in that: In step (2), the amount of antioxidant added is 0.1‰ to 1‰ of the mass of the ferrous dihydrogen phosphate solution, and the antioxidant is one or more of ascorbic acid, oxalic acid, iron powder, and citric acid.

5. The method according to claim 1, characterized in that: In step (3), the temperature of the reaction base liquid is adjusted to 45~50℃. When the amount of the reaction base liquid is 20%~50% of the volume of the first reactor, the first-stage hydrogen peroxide is fed, or the ferrous solution and the first-stage hydrogen peroxide are fed at the same time. The total amount of hydrogen peroxide added during the oxidation stage is 0.45~0.55 times the molar amount of iron in the synchronously fed ferrous solution. The proportion of hydrogen peroxide added at each stage can be adjusted. After that, when the reaction solution in the previous reactor reaches 80%~90% of the reactor volume, the discharge of the previous reaction slurry is started, and the feeding of the next stage hydrogen peroxide is started at the same time.

6. The method according to claim 1, characterized in that: In step (3), the hydrogen peroxide concentration is 10%~30%, the residence time of the material in each stage reactor is 5~60 min, and the temperature is 50~80℃.

7. The method according to claim 1, characterized in that: In step (4), the amount of hydrogen peroxide added to the aging kettle is 0.001 to 0.025 times the mass of the oxidized slurry; the aging temperature is 70 to 90°C and the aging time is 1 to 4 hours.

8. The method according to claim 1, characterized in that: In step (6), the calcination temperature is 580~650℃ and the calcination time is 3~5h.

9. A system for continuous feeding to prepare ferric phosphate, characterized in that, Includes at least two reaction vessels, a hydrogen peroxide dripping assembly, and an aging vessel; At least two reactors are equipped with hydrogen peroxide dripping components at their upper ends. The reactors are connected in series, and the last reactor is connected to the aging reactor. The slurry coming out of the aging reactor enters the next process. The aging reactor is also equipped with a hydrogen peroxide dripping component at its upper end. The prepared ferrous solution is pumped into the first reactor as the reaction base liquid. Then, hydrogen peroxide is added by the hydrogen peroxide drop addition component to carry out the oxidation reaction. Whenever the solution in the previous reactor reaches the control level, the reaction solution of the previous reactor is pumped into the next reactor, and hydrogen peroxide is added accordingly. The oxidation reaction is carried out continuously in each reactor until the solution in the last reactor reaches the control level, and an oxidation slurry is obtained. The oxidized slurry in the last stage reactor is pumped into the aging reactor. The hydrogen peroxide dripping component adds metered hydrogen peroxide to the aging reactor. Then, the aging temperature is adjusted to age the oxidized slurry, resulting in ferric phosphate dihydrate slurry.

10. The system according to claim 9, characterized in that, Each reactor is equipped with a single or double stirrer, with the stirring elements of the double stirrer located in the middle and bottom respectively. Each synthesis reactor is also equipped with a temperature measuring element. The reactors are connected to each other by a pump, and the last reactor is connected to the aging reactor by a pump. The stirring speed is 240~250 r / min. The hydrogen peroxide dripping assembly includes at least one hydrogen peroxide storage tank, each hydrogen peroxide storage tank being positioned above each reactor. A spray pipe is connected below the hydrogen peroxide storage tank, and a controller for controlling the hydrogen peroxide dripping acceleration is provided between the spray pipe and the hydrogen peroxide storage tank. The spray pipe is annular or other shape that ensures that hydrogen peroxide enters the reactor and aging vessel from multiple points. The spray pipe is located at the top of the reactor and aging vessel or at a certain distance from the top. The reactor and aging vessel have corresponding holes for receiving the sprayed liquid.

Images