A method for producing iron phosphate

Abstract

The application discloses a preparation method of iron phosphate, and belongs to the technical field of inorganic materials. In the method, an iron source containing metallic iron, a phosphorus source and an aqueous nitric acid solution are reacted to directly synthesize iron phosphate dihydrate suspension in one step, and then the magnetic substance is removed, the obtained product is filtered and washed, dried, and dehydrated to obtain anhydrous iron phosphate finished product. The specific surface area of the product is not less than 10 m 2 / g, and the particle size DN50 of the finished product is 1-100 μm. In the method, no crystallization promoter needs to be added in the synthesis process, the purity of the iron phosphate product is high, the particle size and particle size distribution are controllable, and the specific surface area of the iron phosphate product is large. The method is simple in process and low in production cost, the prepared iron phosphate product is high in purity and large in specific surface area, and is more suitable for producing lithium iron phosphate which is excellent in electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic materials, and particularly relates to a preparation method of iron phosphate. BACKGROUND

[0002] Iron phosphate is currently mainly used as a raw material for preparing positive electrode material lithium iron phosphate of a battery, and is also used in the fields of ceramics, food additives, etc. Lithium iron phosphate is an important positive electrode material of a battery. At present, the synthesis route of lithium iron phosphate can be divided into three routes according to different iron sources, i.e. iron red method, ferrous oxalate method and iron phosphate method. The preparation of lithium iron phosphate from iron phosphate as a precursor has the advantages of simple production process, high purity of product lithium iron phosphate, high specific capacity, stable performance and low production cost, and has become the mainstream production process of lithium iron phosphate. The microstructure of lithium iron phosphate prepared by the iron phosphate route depends on the microstructure of synthesized iron phosphate. The microstructure of iron phosphate particles, such as particle morphology, specific surface area, particle size and particle size distribution, and the purity of iron phosphate have a significant influence on the tap density, electrochemical performance of lithium iron phosphate, especially the high-rate performance and low-temperature performance of lithium iron phosphate batteries. The charging and discharging process of lithium iron phosphate batteries involves lithium ion deintercalation and migration. The greater the specific surface area of lithium iron phosphate is, the more the contact area between the positive electrode material lithium iron phosphate and the electrolyte is, and the shorter the migration distance of lithium ions in the charging and discharging process of the battery is, which is beneficial to improve the rate performance and low-temperature performance of lithium iron phosphate batteries. In order to improve the specific surface area of lithium iron phosphate, technical personnel in the industry often use ultra-fine grinding means with high energy consumption.

[0003] At present, there are three main preparation methods of iron phosphate: 1) trivalent iron salt such as ferric chloride or ferric nitrate is used as an iron source, and phosphoric acid, dihydrogen phosphate, monohydrogen phosphate or phosphate is used as a phosphoric acid reaction to prepare iron phosphate. This method has high cost of high-iron salt, resulting in high cost of synthesized iron phosphate; 2) copperas ferrous sulfate is used as an iron source, and phosphoric acid, dihydrogen phosphate, monohydrogen phosphate or phosphate is used as a phosphoric acid reaction to prepare iron phosphate, which is oxidized by hydrogen peroxide and neutralized by alkali to prepare iron phosphate. This method has the disadvantages of complex process, large amount of wastewater, high sulfur content in iron phosphate products, which reduces the performance of lithium iron phosphate batteries, etc.; 3) metal iron is used as an iron source, and is reacted with phosphoric acid to first prepare a ferrous dihydrogen phosphate solution, which is then oxidized by hydrogen peroxide and a crystallization promoter is added to synthesize dihydrate iron phosphate at high temperature. The iron phosphate product synthesized by this method has high purity, and the process is environmentally friendly, but the specific surface area of the iron phosphate product is small, and the preparation of ferrous dihydrogen phosphate produces flammable and explosive hydrogen gas, which has safety hazards.

[0004] The existing patent "A preparation method for changing the pore of iron phosphate to improve the rate of lithium iron phosphate" adds organic carbon sources polyvinyl alcohol fiber and polyethylene glycol in the process of synthesizing iron phosphate from copperas, phosphoric acid and hydrogen peroxide as raw materials. The specific surface area of the iron phosphate product after doping is 9.5 m 2 / g, and the specific surface area of the iron phosphate product without doping is 6.9 m2 / g, the specific surface area is increased by 30%. SUMMARY

[0005] The first object of the present application is to provide a preparation method of iron phosphate, which directly synthesizes iron phosphate dihydrate suspension by reacting iron source containing metallic iron, phosphorus source and aqueous nitric acid solution in one step, removes magnetic substances, filters and washes, dries, and removes crystallization water to obtain anhydrous iron phosphate product. The product has a specific surface area of not less than 10 m 2 / g, and a product particle size DN50 of 1-100 μm. In the method, no crystallization promoter is added during the synthesis process, the iron phosphate product has high purity, controllable particle size and particle size distribution, and large specific surface area. The technical problems of adding various raw materials or auxiliary preparations for complex process treatment, small specific surface area of the product, and low product particle size in the prior art are solved.

[0006] The second object of the present application is to provide a preparation method of iron phosphate, which has simple process and low production cost, and the prepared iron phosphate product has high purity and large specific surface area, and is more suitable for producing lithium iron phosphate with excellent electrochemical performance.

[0007] The present application is achieved by the following technical solutions:

[0008] A preparation method of iron phosphate, comprising:

[0009] S1, preparing iron phosphate dihydrate suspension:

[0010] mixing iron source containing metallic iron, water and phosphorus source, heating to the starting temperature, and then adding aqueous nitric acid solution to react, to obtain iron phosphate dihydrate suspension;

[0011] or mixing iron source containing metallic iron and water, heating to the starting temperature, and then adding a mixed solution of phosphorus source and aqueous nitric acid solution to react, to obtain iron phosphate dihydrate suspension;

[0012] S2, removing impurities and filtering and washing: removing unreacted metallic iron in the iron phosphate dihydrate suspension, filtering and washing to obtain iron phosphate dihydrate filter cake;

[0013] S3, product: drying the iron phosphate dihydrate filter cake and removing crystallization water to obtain anhydrous iron phosphate product.

[0014] Preferably, the molar ratio of the iron source containing metallic iron to the phosphorus source is 0.8-2:1;

[0015] The molar ratio of the nitric acid solution to the phosphorus source is 0.3-3:1;

[0016] The concentration of nitric acid in the nitric acid solution is 1wt%-68wt%.

[0017] The initial temperature refers to the temperature of the liquid in the reaction kettle when the aqueous nitric acid solution is added or the phosphorus source and the aqueous nitric acid solution are added.

[0018] Preferably, the mass ratio of the iron source containing metallic iron to water is 1:3-30; preferably 1:5-20.

[0019] Preferably, in S1, the initial temperature is 20-120℃.

[0020] Preferably, in S1, the highest temperature reached by the reaction liquid is 50-180℃; preferably 80-160℃.

[0021] Preferably, in S1, the reaction time is 0.2-16h.

[0022] Preferably, the specific surface area of the anhydrous iron phosphate product is not less than 10m 2 / g.

[0023] In S2, the unreacted metallic iron is removed by screening and / or magnetic separation. However, it is not limited to the above two methods, but any method that can remove iron impurities can be used.

[0024] Preferably, the iron source containing metallic iron includes metallic iron or a combination of metallic iron and ferrous salt.

[0025] The metallic iron includes one or more of iron powder, iron block, iron pellet, iron sheet, iron wire, iron nail and iron filings.

[0026] Preferably, the phosphorus source includes one or more of phosphoric acid, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium monohydrogen phosphate, sodium phosphate and ammonium phosphate.

[0027] Compared with the prior art, the present application has at least the following technical effects:

[0028] The present application provides a preparation method of iron phosphate. The method reacts an iron source containing metallic iron, a phosphorus source and an aqueous nitric acid solution to directly synthesize a suspension of dihydrate iron phosphate in one step, removes magnetic substances, filters and washes, dries, and removes crystallization water to obtain an anhydrous iron phosphate product. The specific surface area of the product is not less than 10m 2 / g, and the particle size of the finished product is 1-100μm. The method does not need to add a crystallization promoter during synthesis, the purity of the iron phosphate product is high, the particle size and particle size distribution are controllable, and the specific surface area of the iron phosphate product is large.

[0029] The method has simple process and low production cost, and the prepared iron phosphate product has high purity and large specific surface area, and is more suitable for producing lithium iron phosphate with excellent electrochemical performance. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application, and should not be regarded as limiting the scope of the present application, the specific conditions not noted in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the reagents or instruments not noted the manufacturer are all the conventional products that can be purchased in the market.

[0031] Example 1:

[0032] 103g iron sheet with a thickness of 1.2mm was placed in a reaction kettle, and a water solution prepared by using 280g sodium dihydrogen phosphate and 1600g deionized water was added. When the solution temperature was heated to the initial temperature of 82℃, 605g dilute nitric acid solution with a concentration of 43% was started to be added, and the dilute nitric acid solution was added within 20min. The reaction temperature reached 108℃. After the dilute nitric acid solution was added, the reaction was continued for 4 hours. After the reaction was completed, the filter cake was obtained by filtration and washing with deionized water, and the white iron phosphate dihydrate filter cake was obtained.

[0033] The filter cake was dried in an oven at 120℃ for 2 hours to obtain iron phosphate dihydrate, and then the iron phosphate dihydrate was calcined in an oven at 500℃ for 4 hours to obtain the iron phosphate anhydride product.

[0034] The particle size DN50 of the iron phosphate anhydride was 36 microns, and the specific surface area of the iron phosphate anhydride product was 14.8m 2 / g.

[0035] Example 2:

[0036] 102g iron sheet with a thickness of 1.6mm was placed in a reaction kettle, and a water solution prepared by using 262g sodium dihydrogen phosphate and 1800g deionized water was added. When the solution temperature was heated to the initial temperature of 86℃, 350g dilute nitric acid solution with a concentration of 43% was started to be added, and the dilute nitric acid solution was added within 20min. The reaction temperature reached 104℃. After the dilute nitric acid solution was added, the reaction was continued for 4 hours. After the reaction was completed, the filter cake was obtained by filtration and washing with deionized water, and the white iron phosphate dihydrate filter cake was obtained.

[0037] The filter cake was dried in an oven at 120℃ for 2 hours to obtain iron phosphate dihydrate, and then the iron phosphate dihydrate was calcined in an oven at 500℃ for 4 hours to obtain the iron phosphate anhydride product.

[0038] The particle size DN50 of the iron phosphate anhydride was 36 microns, and the specific surface area of the iron phosphate anhydride product was 15.3m 2 / g.

[0039] Example 3:

[0040] Put 106 g iron sheet with thickness of 1.2 mm and 1000 g deionized water into a reactor, start to add an aqueous solution prepared from 250 g phosphoric acid with concentration of 85%, 148 g nitric acid with concentration of 68% and 800 g deionized water when the solution is heated to initial temperature of 86 ℃, add the solution completely within 30 min, the reaction temperature reaches 103 ℃, continue to react for 4 hours after the addition of the dilute nitric acid solution, the reaction is finished, filter and wash with deionized water to obtain white iron phosphate dihydrate filter cake.

[0041] Dry the filter cake in an oven at 120 ℃ for 2 hours to obtain iron phosphate dihydrate, then put the iron phosphate dihydrate into an oven at 500 ℃ for calcination for 4 hours to obtain iron phosphate anhydride product.

[0042] The particle size DN50 of the iron phosphate anhydride is 28 microns, and the specific surface area of the iron phosphate anhydride product is 16.4 m 2 / g.

[0043] Example 4:

[0044] Put 76 g iron sheet with thickness of 1.2 mm and 800 g deionized water into a reactor, start to add an aqueous solution prepared from 600 g deionized water, 225 g phosphoric acid with concentration of 85% and 96 g ferrous nitrate when the solution is heated to initial temperature of 92 ℃, add the solution completely within 30 min, the reaction temperature reaches 110 ℃, continue to react for 3 hours after the addition of the dilute nitric acid solution, the reaction is finished, filter and wash with deionized water to obtain white iron phosphate dihydrate filter cake.

[0045] Dry the filter cake in an oven at 120 ℃ for 2 hours to obtain iron phosphate dihydrate, then put the iron phosphate dihydrate into an oven at 500 ℃ for calcination for 4 hours to obtain iron phosphate anhydride product.

[0046] The particle size DN50 of the iron phosphate anhydride is 28 microns, and the specific surface area of the iron phosphate anhydride product is 13.7 m 2 / g.

[0047] Example 5:

[0048] Put 106 g iron wire with diameter of 2 mm into a reactor, add an aqueous solution prepared from 268 g ammonium dihydrogen phosphate and 1500 g deionized water, start to add 360 g dilute nitric acid solution with concentration of 42% when the solution is heated to initial temperature of 86 ℃, add the dilute nitric acid solution completely within 20 min, the reaction temperature reaches 108 ℃, continue to react for 3 hours after the addition of the dilute nitric acid solution, the reaction is finished, filter and wash with deionized water to obtain white iron phosphate dihydrate filter cake.

[0049] Dry the filter cake in an oven at 120 ℃ for 2 hours to obtain iron phosphate dihydrate, then put the iron phosphate dihydrate into an oven at 500 ℃ for calcination for 4 hours to obtain iron phosphate anhydride product.

[0050] The particle size DN50 of the anhydrous ferric phosphate is 24 microns, and the specific surface area of the anhydrous ferric phosphate product is 15.6 m 2 / g.

[0051] Example 6

[0052] 98g iron nails with a thickness of 1.6mm were placed in a reaction kettle, and a water solution prepared by using 256g ammonium dihydrogen phosphate and 1200g deionized water was added. When the solution was heated to a starting temperature of 95℃, 380g of a dilute nitric acid solution with a concentration of 43% was added, and the addition was completed within 20min. The reaction temperature reached 116℃. After the addition of the dilute nitric acid solution was completed, the reaction was continued for 4 hours. After the reaction was completed, the filter cake was washed with deionized water, and white ferric phosphate dihydrate filter cake was obtained.

[0053] The filter cake was dried in an oven at 120℃ for 2 hours to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then placed in an oven at 500℃ for calcination for 4 hours to obtain an anhydrous ferric phosphate product.

[0054] The particle size DN50 of the anhydrous ferric phosphate is 56 microns, and the specific surface area of the anhydrous ferric phosphate product is 13.4 m 2 / g.

[0055] Example 7

[0056] 103g iron sheets with a thickness of 1.2mm were placed in a reaction kettle, and a water solution prepared by using 280g sodium dihydrogen phosphate, 1600g deionized water and 12g sodium dodecyl benzene sulfonate was added. When the solution was heated to a starting temperature of 82℃, 605g of a dilute nitric acid solution with a concentration of 43% was added, and the addition was completed within 20min. The reaction temperature reached 108℃. After the addition of the dilute nitric acid solution was completed, the reaction was continued for 4 hours. After the reaction was completed, the filter cake was washed with deionized water, and white ferric phosphate dihydrate filter cake was obtained.

[0057] The filter cake was dried in an oven at 120℃ for 2 hours to obtain ferric phosphate dihydrate powder. The ferric phosphate dihydrate powder was then placed in an oven at 500℃ for calcination for 4 hours to obtain an anhydrous ferric phosphate product.

[0058] The particle size DN50 of the anhydrous ferric phosphate is 6 microns, and the specific surface area of the anhydrous ferric phosphate product is 18.7 m 2 / g.

[0059] From the above examples, it can be seen that for the nitric acid concentration set range of 1wt%-68wt%, the concentration and addition speed of the nitric acid aqueous solution (which can be controlled by the solution addition time) have a significant effect on the reaction temperature.

[0060] At the same time, the higher the concentration of the nitric acid and the faster the addition speed, the higher the reaction temperature.

[0061] The performance parameters of the iron phosphate product, such as particle size and particle size distribution, can be adjusted and controlled by the difference between the initial reaction temperature and the temperature of the obtained iron phosphate dihydrate suspension. Under the same other reaction conditions, the lower the reaction temperature, the smaller the particle size of the synthesized iron phosphate product, and the higher the reaction temperature, the coarser the particle size of the synthesized iron phosphate product; under the same reaction temperature, the addition of a dispersing agent in the reaction solution can obtain an iron phosphate product with finer particles. If the same reaction temperature is controlled, the faster the addition speed of the aqueous nitric acid solution, the finer the particle size of the product iron phosphate.

[0062] The anhydrous iron phosphate product synthesized by the method of the present application has a specific surface area of up to 13.4 m 2 / g even if the particle size DN50 is as high as 56 microns.

[0063] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing ferric phosphate, characterized in that, include: S1. Preparation of ferric phosphate dihydrate suspension: Iron source containing metallic iron, water and phosphorus source are mixed and heated to an initial temperature of 20-120℃. Then, nitric acid aqueous solution with a concentration of 1wt%-68wt% is added to carry out the reaction. The highest temperature reached by the reaction solution is 50-180℃ and the reaction time is 0.2-16h to obtain ferric phosphate dihydrate suspension. Alternatively, a mixture of an iron source containing metallic iron and water can be heated to an initial temperature of 20-120℃, and then a mixture of a phosphorus source and a nitric acid aqueous solution with a concentration of 1wt%-68wt% can be added to react. The reaction solution reaches a maximum temperature of 50-180℃ and the reaction time is 0.2-16h to obtain a ferric phosphate dihydrate suspension. The molar ratio of the iron source containing metallic iron to the phosphorus source is 0.8-2:1; The molar ratio of the nitric acid aqueous solution to the phosphorus source is 0.3-3:1; S2. Removal of impurities and filtration and washing: After removing unreacted metallic iron from the ferric phosphate dihydrate suspension, filter and wash to obtain ferric phosphate dihydrate filter cake. S3. Finished product: After drying and removing the water of crystallization from the ferric phosphate dihydrate filter cake, anhydrous ferric phosphate is obtained. The specific surface area of ​​the anhydrous ferric phosphate product is not less than 10 m². 2 / g.

2. The method for preparing ferric phosphate according to claim 1, characterized in that, The mass ratio of the iron source containing metallic iron to water is 1:3-30.

3. The method for preparing ferric phosphate according to claim 2, characterized in that, The mass ratio of the iron source containing metallic iron to water is 1:5-20.

4. The method for preparing ferric phosphate according to claim 1, characterized in that, The iron source containing metallic iron includes metallic iron or a combination of metallic iron and ferrous salt. The metallic iron includes one or more of the following: iron powder, iron blocks, iron shot, iron sheet, iron wire, iron nails, and iron filings.

5. The method for preparing ferric phosphate according to claim 1, characterized in that, The phosphorus source includes one or more of phosphoric acid, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium monohydrogen phosphate, sodium phosphate, and ammonium phosphate.