Process for the preparation of spherical iron phosphate

Abstract

The application discloses a preparation method of spherical iron phosphate, and comprises the following steps: S1, preparing a ferrous salt solution; S2, preparing a trivalent iron salt mixed solution; S3, preparing a phosphorus salt solution; S4, mixing the trivalent iron salt mixed solution and the phosphorus salt solution in a reaction kettle, and heating and keeping warm for 2-3 hours to obtain a crystal seed A; S5, repeatedly adding the ferrous salt solution prepared in the step S1 and the phosphorus salt solution prepared in the step S3 into the crystal seed A, and keeping warm for 2-3 hours after heating to 80-100 DEG C to obtain white iron phosphate slurry B; and S6, filtering, washing, drying and calcining the slurry B to prepare the spherical iron phosphate. The application does not need to add a surfactant and does not need to customize a special reaction equipment, avoids technical problems such as high-temperature and high-pressure reaction, addition of a surfactant and requirement of a reaction equipment, and is suitable for industrial application.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a preparation method of spherical iron phosphate. BACKGROUND

[0002] The spherical iron phosphate prepared by the prior art has the following problems:

[0003] ①The reaction condition is harsh and complex. Most of the prior art needs to prepare the spherical iron phosphate by a hydrothermal method, and the reaction condition requires high temperature and high pressure and needs to maintain constant high temperature, and the equipment performance is required to be high. However, the sphericity of the prepared iron phosphate is not high under such harsh conditions, and the specific reason is that the dispersibility between particles is poor in the conventional hydrothermal method, and the growth rates of various crystal faces are not consistent in the crystal growth process, so that the sphericity of the prepared spherical iron phosphate is not high. For example, the patent document with the publication number CN102139869 discloses a method for preparing spherical iron phosphate by combining a precipitation method and a hydrothermal method. First, the iron salt and phosphorus salt solution are pumped into the reaction kettle at a certain rate under the condition of 90 DEG C, and then the ammonia water is pumped in to maintain the pH of the reaction system stable. Then, the temperature is raised to 200 DEG C and reacted for 8h. The reaction condition is harsh, and the iron phosphate prepared by this method is an olive ball, and the sphericity is not high.

[0004] ②Additional chemicals need to be added. In order to prepare the iron phosphate with high sphericity and good dispersibility, a surfactant needs to be added to the reaction system in the prior art, which increases the difficulty of wastewater treatment. For example, the patent document with the publication number CN110010890 A discloses a method for preparing spherical nano iron phosphate at room temperature, and 1kg of citric acid and 0.1kg of dodecyltrimethylammonium chloride need to be added to 100kg of 0.1mol / kg Fe(NO3)3 aqueous solution. The amount of the additive (molar amount) is more than half of the iron source (Fe:T=1:0.558), and the amount is very large, which causes the problem of difficult wastewater treatment.

[0005] ③High requirements for equipment. In addition to changing the process conditions, a few special reaction kettles are also used to prepare the spherical iron phosphate in the prior art. For example, the patent document with the publication number CN102849702 A discloses a method for preparing nano spherical iron phosphate, and a constant-temperature homogenizing variable-speed emulsification reaction kettle is used. The features need two independent motors to provide homogenizing stirring and emulsifying stirring, the homogenizing stirring speed is adjusted by frequency conversion, the temperature in the reaction kettle is uniform, the emulsifying stirring speed is adjusted by frequency conversion, and the product morphology is spherical and the particle size is normally distributed. However, the equipment has high manufacturing requirements. SUMMARY

[0006] To solve the above technical problems, the application provides a method for preparing spherical iron phosphate with mild reaction conditions, without adding any additive and simple operation, so as to solve the defects of harsh reaction conditions, complex operation, the need of adding surfactant and high requirement for equipment in the existing preparation technology of spherical iron phosphate, and specifically as follows.

[0007] A method for preparing spherical iron phosphate, comprising the following steps:

[0008] Step S1, configuring a ferrous salt raw solution by adding an acidic substance to form a ferrous salt solution;

[0009] Step S2, taking an iron source and adding phosphoric acid to prepare a trivalent iron salt mixed solution;

[0010] Step S3, configuring a phosphorus salt raw solution by adding an oxidizing agent to form a phosphorus salt solution;

[0011] Step S4, under the condition of 40-60 DEG C and continuous stirring, the trivalent iron salt mixed solution prepared in step S2 and the phosphorus salt solution prepared in step S3 are put into a reaction kettle for mixing, and after being heated to 80-100 DEG C, heat preservation is carried out for 2-3 h to obtain highly dispersed nanocrystals A; a multi-frequency ultrasonic generator is installed on the outer side of the reaction kettle wall;

[0012] Step S5, under the condition of 40-60 DEG C and continuous stirring, the ferrous salt solution prepared in step S1 and the phosphorus salt solution prepared in step S3 are put into the above-mentioned nanocrystals A, and after being heated to 80-100 DEG C, heat preservation is carried out for 2-3 h to obtain white iron phosphate slurry B;

[0013] Step S6, after the slurry B is filtered, washed, dried and calcined, the spherical iron phosphate is prepared.

[0014] Moreover, in step S1, the concentration of iron element in the ferrous salt raw solution is 0.5-1.5 mol / L; the ferrous salt raw solution is configured by ferrous sulfate, ferrous nitrate, iron powder and iron scale; the acidic substance is inorganic acid; the inorganic acid is phosphoric acid, sulfuric acid or nitric acid.

[0015] Moreover, in step S2, the iron source is iron single element;

[0016] The preparation process of the trivalent iron salt mixed solution is that the iron single element is dissolved in sulfuric acid to form an iron salt solution, and then phosphoric acid is added to form a trivalent iron salt mixed solution.

[0017] Moreover, in step S2, the iron source is ferrous salt;

[0018] The preparation process of the trivalent iron salt mixed solution is that the ferrous salt is dissolved in water, then an excess of oxidizing agent is added to oxidize the ferrous salt into trivalent iron salt, and then phosphoric acid is added to form a trivalent iron salt mixed solution.

[0019] Moreover, in the step S3, the concentration of phosphorus element in the phosphorus salt raw material solution is 0.5-1.5 mol / L; the phosphorus salt raw material solution is configured by monohydrogen ammonium phosphate, dihydrogen ammonium phosphate, phosphoric acid, monohydrogen sodium phosphate and dihydrogen sodium phosphate; and the oxidant is one or more of sodium persulfate, hydrogen peroxide and perchloric acid.

[0020] Moreover, the stirring rate in the steps S3 and S4 is 200-800 rpm.

[0021] Moreover, the reaction in the steps S4 and S5 is divided into two stages, the first stage is a feeding stage, the reaction is carried out at 40-60 ℃ for 30-60 min; and the second stage is a feeding end temperature rising stage, the reaction is carried out at 80-100 ℃ for 2-3 h.

[0022] Moreover, the frequency of the multi-frequency ultrasonic generator in the step S4 is 20 KHZ-28 KHZ; the multi-frequency ultrasonic generator is turned on in the step S4 seed preparation process and is turned off in the step S5 control crystallization process.

[0023] Moreover, in the step S5, the ferrous salt solution prepared in the step S1 and the phosphorus salt solution prepared in the step S3 are fed into the nanocrystalline seed A for 4-8 times.

[0024] Moreover, the spherical phosphoric acid iron prepared in the step S6 has a sphericity of 0.90 or above.

[0025] The principle of preparing the spherical phosphoric acid iron in the application is as follows: ① under the action of ultrasonic energy, highly dispersed fine phosphoric acid iron seeds are prepared by directly mixing ferric iron salt and phosphorus salt; ② in the process of feeding the seeds with ferrous salt and phosphorus salt, the newly generated phosphoric acid iron particles are adsorbed on the surface of the seeds under the action of surface energy between the particles, and the seeds grow; ③ the highly dispersed fine seeds are beneficial to the mutual dispersion of the growing spherical particles and the agglomeration does not occur; ④ under the mild reaction condition (40-60 ℃), the ammonium phosphate iron material precursor absorbs on the seeds in all directions, the seeds grow into spherical shape, and then the ammonium phosphate iron material is converted into phosphoric acid iron under the subsequent temperature rising, and the spherical phosphoric acid iron is obtained.

[0026] Compared with the prior art, the application has the following beneficial effects:

[0027] 1. The application can prepare the spherical phosphoric acid iron material by using the ultrasonic-control crystallization method under the mild reaction temperature (40-100 ℃), adding a simple ultrasonic device, and without adding additional surfactant and without customizing special reaction equipment.

[0028] 2. Compared with conventional iron phosphate preparation technology, this invention adds ultrasonic energy to the seed preparation process, directly preparing highly dispersed seed crystals by mixing trivalent iron salt and phosphate salt. By controlling the reaction temperature, the iron phosphate seed crystals grow uniformly, producing iron phosphate with high sphericity and good dispersibility.

[0029] 3. Compared with the spherical iron phosphate preparation technology, this invention is the first to prepare seed crystals by mixing ultrasonic energy, trivalent iron salt and phosphate salt at a mild reaction temperature (40~100℃), and prepares the ideal precursor of lithium iron phosphate battery cathode material - spherical iron phosphate by controlled crystallization method.

[0030] 4. This invention requires no additional surfactants or customized special reaction equipment, avoiding the harsh reaction conditions such as high temperature and high pressure of hydrothermal methods; it avoids the addition of surfactants to the reaction system, reducing the pressure on wastewater treatment; it avoids special reaction equipment; this invention is simple to operate, reduces production costs, and is suitable for industrial applications.

[0031] 5. This invention uses ultrasonic energy to prepare highly dispersed and uniform seed crystals. By controlling the temperature and number of crystallization cycles during the crystallization process, the seed crystals grow uniformly, ultimately yielding D50 particles with a size of 3μm~5μm and a specific surface area of ​​7~9g / cm³. 2 Sphericity > 0.90 spherical iron phosphate. Attached Figure Description

[0032] Figure 1 (a) shows the microstructure of seed crystal A prepared in Example 1; Figure 1 (b) shows the microstructure of the iron phosphate prepared in Example 1;

[0033] Figure 2 The microstructure of the iron phosphate prepared in Example 2 is shown.

[0034] Figure 3 The microstructure of the iron phosphate prepared in Example 3 is shown.

[0035] Figure 4 The microstructure of the iron phosphate prepared in Comparative Example 1 is shown.

[0036] Figure 5 The microstructure of the iron phosphate prepared in Comparative Example 2 is shown.

[0037] Figure 6 The microstructure of the iron phosphate prepared in Comparative Example 3 is shown.

[0038] Figure 7 The microstructure of the iron phosphate seed crystals prepared in Comparative Example 4 is shown.

[0039] Figure 8 The microstructure of the iron phosphate prepared in Comparative Example 4 is shown.

[0040] Figure 9 Micro-morphology of iron phosphate prepared for Comparative Example 5;

[0041] Figure 10 Micro-morphology of iron phosphate prepared for Comparative Example 6;

[0042] Figure 11 Schematic diagram of a reaction kettle for preparing seed A. DETAILED DESCRIPTION

[0043] Example 1

[0044] (1) 6670 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 415 g of 85wt% phosphoric acid was added thereto, and the volume was made up to 20 L to obtain a ferrous sulfate solution, and the concentration of iron element was 1.2 mol / L;

[0045] (2) 2760 g of monoammonium phosphate was weighed and dissolved in deionized water, 1600 g of 30wt% hydrogen peroxide was added, and the volume was made up to 4 L to obtain a phosphorus salt solution, and the molar concentration of phosphorus element was 1.2 mol / L;

[0046] (3) 1334 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 83 g of 85wt% phosphoric acid was added thereto, and 320 g of 30wt% hydrogen peroxide was added to convert all divalent iron ions into trivalent iron ions, and the volume was made up to 4 L to obtain a trivalent iron salt solution;

[0047] (4) Under the conditions of a reaction temperature of 45°C and a 20KHZ ultrasonic power, and continuous stirring, 4 L of the trivalent iron salt solution and 4 L of the phosphorus salt solution were mixed, and then the temperature was raised to 90°C and maintained for 2 h to obtain seed A; the primary particles of seed A were small, dispersed, and round, and the seed morphology is shown in FIG. 1, and the reaction kettle is shown in FIG. 2; Figure 1 (a) shown in FIG. 1, and the reaction kettle is shown in FIG. 2; Figure 11

[0048] (5) Under the conditions of a reaction temperature of 45°C and a stirring rate of 300 rpm, 4 L of the ferrous sulfate solution and 4 L of the phosphorus salt solution were put into seed A, the feeding time was 2 h, and then the temperature was raised to 90°C and maintained for 2 h;

[0049] (6) The process of step (5) was repeated 5 times to obtain phosphorus iron slurry B, and spherical phosphorus iron was obtained after drying; (7) After filtration, washing, and drying, spherical phosphorus iron was obtained.

[0050] Example 2

[0051] (1) 6670 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 415 g of 85wt% phosphoric acid was added thereto, and the volume was made up to 20 L to obtain a ferrous sulfate solution, and the concentration of iron element was 1.2 mol / L; ​

[0052] (2) 2760 g of monoammonium phosphate was weighed and dissolved in deionized water, 1600 g of 30 wt% hydrogen peroxide was added, and the volume was made up to 4 L to obtain a phosphorus salt solution with a phosphorus element molar concentration of 1.2 mol / L;

[0053] (3) 1334 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 83 g of 85 wt% phosphoric acid was added, 320 g of 30 wt% hydrogen peroxide was added to convert all divalent iron ions to trivalent iron ions, and the volume was made up to 4 L to obtain a trivalent iron salt solution;

[0054] (4) Under the conditions of a reaction temperature of 55°C and continuous stirring, 4 L of the trivalent iron salt solution and 4 L of the phosphorus salt solution were mixed, then heated to 90°C and kept for 2 h to obtain crystal seed A;

[0055] (5) Under the conditions of a reaction temperature of 55°C and a stirring rate of 300 rpm, 4 L of the ferrous sulfate solution and 4 L of the phosphorus salt solution were added to the crystal seed A, the feeding time was 2 h, then heated to 90°C and kept for 2 h;

[0056] (6) The process of step (5) was repeated 5 times to obtain phosphoric acid iron slurry B;

[0057] (7) After filtration, washing and drying, spherical phosphoric acid iron was obtained.

[0058] Example 3

[0059] 1) 6670 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 415 g of 85 wt% phosphoric acid was added, and the volume was made up to 20 L to obtain a ferrous sulfate solution with an iron element concentration of 1.2 mol / L;

[0060] (2) 2760 g of monoammonium phosphate was weighed and dissolved in deionized water, 1600 g of 30 wt% hydrogen peroxide was added, and the volume was made up to 4 L to obtain a phosphorus salt solution with a phosphorus element molar concentration of 1.2 mol / L;

[0061] (3) 1334 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 83 g of 85 wt% phosphoric acid was added, 320 g of 30 wt% hydrogen peroxide was added to convert all divalent iron ions to trivalent iron ions, and the volume was made up to 4 L to obtain a trivalent iron salt solution;

[0062] (4) Under the conditions of a reaction temperature of 55°C and continuous stirring, 4 L of the trivalent iron salt solution and 4 L of the phosphorus salt solution were mixed, then heated to 90°C and kept for 2 h to obtain crystal seed A;

[0063] (5) 4 L of the ferrous sulfate solution and 4 L of the phosphorus salt solution were added into the seed A under the conditions of a reaction temperature of 55°C and a stirring speed of 300 rpm, the feeding time was 2 h, then the temperature was increased to 90°C and kept for 2 h;

[0064] (6) The process of step (5) was repeated 5 times to obtain the iron phosphate slurry B;

[0065] (7) After the iron phosphate slurry B was filtered, washed and dried, the spherical iron phosphate was obtained.

[0066] Comparative Example 1

[0067] The present comparative example was the same as Example 1 except that the reaction temperature in steps (4) and (5) was 65°C.

[0068] Comparative Example 2

[0069] The present comparative example was the same as Example 1 except that the reaction temperature in steps (4) and (5) was 35°C.

[0070] Comparative Example 3

[0071] The present comparative example was different from Example 2 in that the seed A was prepared by mixing the ferrous salt and the phosphorus salt, and the specific method was as follows:

[0072] (1) 6670 g of ferrous sulfate heptahydrate was weighed and dissolved in deionized water, 415 g of 85wt% phosphoric acid was added, the volume was made up to 20 L to obtain a ferrous sulfate solution, and the concentration of iron element was 1.2 mol / L;

[0073] (2) 2760 g of monoammonium phosphate was weighed and dissolved in deionized water, 1600 g of 30wt% hydrogen peroxide was added, the volume was made up to 4 L to obtain a phosphorus salt solution, and the molar concentration of phosphorus element was 1.2 mol / L;

[0074] (3) 4 L of the ferrous sulfate solution, 4 L of the phosphorus salt solution and excess hydrogen peroxide were mixed under the conditions of a reaction temperature of 55°C and continuous stirring at a speed of 300 rpm, then the temperature was increased to 90°C and kept for 2 h to obtain the seed A;

[0075] (4) 4 L of the ferrous sulfate solution and 4 L of the phosphorus salt solution were added into the seed A under the conditions of a reaction temperature of 55°C, a 28 KHZ ultrasonic power and a stirring speed of 300 rpm, the feeding time was 2 h, then the temperature was increased to 90°C and kept for 2 h;

[0076] (5) The process of step (4) was repeated 5 times to obtain the iron phosphate slurry B;

[0077] (6) After the iron phosphate slurry B was filtered, washed and dried, the spherical iron phosphate was obtained.

[0078] Comparative Example 4

[0079] The present comparative example is the same as Example 3 except that the multi-frequency ultrasonic generator is not turned on during the seed crystal preparation process.

[0080] Comparative Example 5

[0081] The present comparative example is the same as Example 3 except that the ferrous salt solution prepared in step S1 and the phosphorus salt solution prepared in step S3 are added to the nanoseed A twice.

[0082] Comparative Example 6

[0083] The present comparative example is the same as Example 3 except that the ferrous salt solution prepared in step S1 and the phosphorus salt solution prepared in step S3 are added to the nanoseed A nine times.

[0084] Experimental Section

[0085] Experiment 1

[0086] The particle size of the seed crystal A obtained in Examples 1-3 and Comparative Example 4 was tested, and the results are shown in Table 1; the sphericity, particle size, and specific surface area of the iron phosphate obtained in Examples 1-3 and Comparative Examples 1-6 were tested, and the results are shown in Table 2.

[0087] Table 1 Particle size range of different seed crystals

[0088]

[0089] As can be seen from Table 1, the D10, D50, D90, D99, and D100 of the seed crystal A of Examples 1-3 are smaller than those of Comparative Example 4, and the particle size is more uniform.

[0090] Table 2 Sphericity of iron phosphate obtained in test examples and comparative examples

[0091]

[0092] As can be seen from Table 2, the sphericity of the iron phosphate prepared in Examples 1-3 is greater than 0.9, while the sphericity of the iron phosphate prepared in Comparative Examples 1-6 is 0.523, 0.656, 0.529, 0.765, 0.457, and 0.634, respectively. The sphericity of the iron phosphate prepared in the present application is close to a perfect circle, and the specific surface area is 7-9 g / cm 2, D50 is 3~5 μm, while the iron phosphate of the comparative example is irregular shape, which can prove that: 1. highly dispersed, uniform and small primary particles of the seed are the basis for preparing spherical iron phosphate, and the method of ultrasonic energy combined with direct mixing of ferric salt and ammonium salt is an important means to achieve the preparation of the seed under the above conditions; 2. Reasonable reaction temperature controls the growth rate and direction of the seed, so that the seed grows uniformly; 3. Suitable crystallization growth times make the seed growth size grow to an appropriate level, while filling the area with large surface energy of the sphere surface and increasing the sphericity of the particles.

[0093] Experiment 2

[0094] The iron phosphate seed prepared in Example 1 was microscopically characterized, and the results are shown in Figure 1 (a); the iron phosphate prepared in Example 1 was microscopically characterized, and the results are shown in Figure 1 (b);

[0095] The iron phosphate prepared in Example 2 was microscopically characterized, and the results are shown in Figure 2 ;

[0096] The iron phosphate prepared in Example 3 was microscopically characterized, and the results are shown in Figure 3 ;

[0097] The iron phosphate prepared in Comparative Example 1 was microscopically characterized, and the results are shown in Figure 4 ;

[0098] The iron phosphate prepared in Comparative Example 2 was microscopically characterized, and the results are shown in Figure 5 ;

[0099] The iron phosphate prepared in Comparative Example 3 was microscopically characterized, and the results are shown in Figure 6 , Figure 7 ;

[0100] The iron phosphate prepared in Comparative Example 4 was microscopically characterized, and the results are shown in Figure 8 ;

[0101] The iron phosphate prepared in Comparative Example 5 was microscopically characterized, and the results are shown in Figure 9 ;

[0102] The iron phosphate prepared in Comparative Example 6 was microscopically characterized, and the results are shown in Figure 10 ;

[0103] From Figure 1(b) It can be seen that the spherical iron phosphate prepared in Example 1 has a spherical morphology, the spherical particles are dispersed without agglomeration, and the particle size is 3-5 μm. It is shown that under the reaction temperature of 45℃, the seed crystal preparation process assisted by ultrasonic energy can obtain a seed crystal with D50 of 1.52 μm, uniform primary particles, and high overall dispersion, and the control of the crystallization number is 5 times, which can prepare spherical iron phosphate with suitable particle size, moderate specific surface area, and spherical degree >0.90.

[0104] From Figure 2 It can be seen that the spherical iron phosphate prepared in Example 2 is similar to Example 1, which shows that under the suitable reaction temperature of 40-60℃, the seed crystal grows uniformly from all directions under the suitable supersaturation and reaction rate, and the control of the crystallization number is 5 times, which can prepare spherical iron phosphate with suitable particle size, moderate specific surface area, and spherical degree >0.90.

[0105] From Figure 3 It can be seen that the spherical iron phosphate prepared in Example 3 is similar to Example 1, which shows that the seed crystal prepared based on the ultrasonic frequency of 20KHZ under the suitable supersaturation and reaction rate can prepare spherical iron phosphate with suitable particle size, moderate specific surface area, and spherical degree >0.90. Since the ultrasonic energy is lower than that of Example 1 and Example 2, the spherical degree is slightly lower than that of Example 1 and Example 2.

[0106] From Figure 4 It can be seen that the spherical iron phosphate prepared in Comparative Example 1 is very different from that prepared in Examples 1-3 in morphology, and the secondary particles are stacked by blocky primary particles. The reason for this morphology is that the high reaction temperature promotes the formation of irregular blocky primary particles with high crystallinity. These blocky primary particles have sharp corners and flat surfaces with lower surface free energy. In order to maintain the stability of the secondary particles, the blocky primary particles spontaneously expose the flat surface to the outside, forming flat secondary block particles, and cannot form spherical iron phosphate.

[0107] From Figure 5 It can be seen that the spherical iron phosphate prepared in Comparative Example 2 has a morphology that is quite different from that of Example 1, and the spherical particles are of different sizes, and the spherical particles between them have serious agglomeration, resulting in low overall sphericity. The reason for the low sphericity is that the reaction is carried out at low temperature, the supersaturation of the system is low, and the reaction rate is reduced, so the spherical particles between them have agglomeration, and the spherical particles are of different sizes.

[0108] From Figure 6 It can be seen that the spherical iron phosphate prepared in Comparative Example 3 has a morphology that is quite different from that of Example 1, and the spherical particles between them have serious agglomeration and the secondary particles are of different sizes. This result shows that using a mixture of ferrous salt and phosphorus salt to prepare seed crystals cannot form uniform spherical iron phosphate with good dispersion in the subsequent control of the crystallization process. The reason is that Fe 2+ The radius is greater than Fe 3Therefore, the seed particles prepared by mixing ferrous sulfate and phosphorus salt are larger, stacked with each other, and form flaky secondary particles, as shown in Figure 7 As shown, compared with fine seed particles, it is difficult for iron phosphate to grow into a spherical shape on flaky seed particles.

[0109] As shown in Figure 8 It can be seen that the iron phosphate prepared in Comparative Example 4 has a similar morphology to that of Comparative Example 2, and the spherical particles are severely agglomerated and the size of the secondary particles is uneven, indicating that the seed particles are agglomerated and have poor dispersibility because the seed preparation process is not provided with ultrasonic energy, and the subsequent control of the crystallization process cannot form iron phosphate with good dispersibility and uniform spherical morphology.

[0110] As shown in Figure 9 It can be seen that the spherical degree of the iron phosphate prepared in Comparative Example 5 is very poor, indicating that the number of crystallization times is insufficient, the number of crystal grains is insufficient, and the seed particles cannot grow uniformly in all directions to form spherical iron phosphate with a size of 3-5 μm. Therefore, the number of crystallization times is a key parameter for controlling the size and spherical degree of spherical iron phosphate.

[0111] As shown in Figure 10 It can be seen that the spherical degree D50 of the iron phosphate prepared in Comparative Example 6 is as high as 10 μm, indicating that too many crystallization times will cause the seed particles to grow too large, resulting in a decrease in the spherical degree, and too many crystallization times will increase the viscosity of the system, causing the spherical particles to be severely agglomerated. Therefore, the number of crystallization times needs to be controlled within an appropriate range.

Claims

1. A method for producing spherical iron phosphate, characterized by, The method comprises the following steps: Step S1, configuring a ferrous salt raw solution, adding an acidic substance to configure a ferrous salt solution; Step S2, taking an iron source, adding phosphoric acid to prepare a ferric salt mixed solution; Step S3, configuring a phosphorus salt raw solution, adding an oxidizing agent to configure a phosphorus salt solution; Step S4, under the condition of 40-60℃ and continuous stirring, the ferric salt mixed solution prepared in step S2 and the phosphorus salt solution prepared in step S3 are put into a reaction kettle for mixing, and after being heated to 80-100℃, the temperature is kept for 2-3h to obtain highly dispersed nanocrystalline seeds A; The outer side of the wall of the reaction kettle is provided with a multi-frequency ultrasonic generator; the frequency of the multi-frequency ultrasonic generator is 20KHZ-28KHZ; Step S5, under the condition of 40-60℃ and continuous stirring, the ferrous salt solution prepared in step S1 and the phosphorus salt solution prepared in step S3 are put into the above-mentioned nanocrystalline seeds A in 4-8 times, and after being heated to 80-100℃, the temperature is kept for 2-3h to obtain white iron phosphate slurry B; The multi-frequency ultrasonic generator is turned on during step S4 and turned off during step S5; Step S6, the slurry B is filtered, washed, dried and calcined to prepare spherical iron phosphate.

2. The method for preparing spherical iron phosphate according to claim 1, characterized in that, In step S1, the concentration of iron element in the ferrous salt raw solution is 0.5-1.5mol / L; the ferrous salt raw solution is configured by ferrous sulfate, ferrous nitrate, iron powder and iron scale; the acidic substance is an inorganic acid; the inorganic acid is any one of phosphoric acid, sulfuric acid and nitric acid.

3. The method of claim 1, wherein the spherical iron phosphate is prepared by the steps of: In step S2, the iron source is iron single substance; the preparation process of the ferric salt mixed solution is that the iron single substance is dissolved in sulfuric acid to prepare an iron salt solution, and then phosphoric acid is added to prepare a ferric salt mixed solution. ​ 4. The method for preparing spherical iron phosphate according to claim 1, characterized in that, In step S2, the iron source is ferrous salt; the preparation process of the ferric salt mixed solution is that the ferrous salt is dissolved in water, then an excess of oxidizing agent is added to oxidize the ferrous salt into ferric salt, and then phosphoric acid is added to prepare a ferric salt mixed solution.

5. The method for preparing spherical iron phosphate according to claim 1, characterized in that, In step S3, the concentration of phosphorus element in the phosphorus salt raw solution is 0.5-1.5mol / L; the phosphorus salt raw solution is configured by ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, sodium monohydrogen phosphate and sodium dihydrogen phosphate; the oxidizing agent is one or more of sodium persulfate, hydrogen peroxide and perchloric acid.

6. The method for preparing spherical iron phosphate according to claim 1, characterized in that, The stirring rate in steps S3 and S4 is 200-800rpm.

7. The method for preparing spherical iron phosphate according to claim 1, characterized in that, The reaction in steps S4 and S5 is divided into two stages, the first stage is a feeding stage, and the reaction is carried out at 40-60℃ for 30-60min; the second stage is a heating stage after the feeding is completed, and the reaction is carried out at 80-100℃ for 2-3h.

8. The method of claim 1, wherein the spherical iron phosphate is prepared by the steps of: The spherical iron phosphate prepared in step S6 has a sphericity of 0.90 or more. ​

Images