Preparation method of iron phosphate

Abstract

The invention provides a preparation method of iron phosphate, which comprises the following step: carrying out crystal transformation reaction on a mixed system containing basic iron phosphate and a crystal modifier under a high-pressure microwave condition to obtain the iron phosphate. According to the preparation method of the iron phosphate provided by the invention, under the high-pressure microwave condition, the mixed system comprising the basic iron phosphate and the crystal modifier is subjected to the crystal transformation reaction, the binding capacity of the iron phosphate in the high-pressure microwave environment is stronger, impurity ions are not easy to enter crystal lattices, and the activity degree of the ions can be improved under the high-temperature microwave condition; impurities can be more easily removed from a solid phase; and the high-pressure microwave condition is beneficial to formation of a relatively compact crystal structure. Therefore, the prepared iron phosphate is relatively high in purity, relatively low in impurity content and relatively high in tap density.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a method for preparing iron phosphate. Background Art

[0002] As the world's attention to renewable energy and environmentally friendly technologies continues to increase, lithium iron phosphate batteries have become one of the mainstream choices for electric vehicles and other energy storage applications due to their cost advantages, safety and good cycle performance. However, with the widespread use of these batteries, how to effectively recycle and dispose of spent lithium iron phosphate batteries has become an urgent environmental and economic issue.

[0003] The main components of lithium iron phosphate batteries include lithium, iron, phosphorus and other materials such as carbon, aluminum, copper, etc. Although lithium iron phosphate batteries are considered a green energy source, they may still have a negative impact on the environment if their waste is not properly handled. Elements such as lithium, iron and phosphorus contained in waste batteries are valuable resources. Reasonable recycling of these elements can not only slow down the consumption of mineral resources, but also generate significant economic benefits.

[0004] At present, the recycling of waste lithium iron phosphate batteries still faces the problems of low purity, high impurity content and low tap density of the recycled iron phosphate. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for preparing ferric phosphate. The ferric phosphate prepared by the preparation method has high purity, low impurity content and high tap density.

[0006] The present invention provides a method for preparing ferric phosphate, comprising the following steps:

[0007] A mixed system including basic ferric phosphate and a crystal-transforming agent is subjected to a crystal-transforming reaction under high-pressure microwave conditions to obtain the ferric phosphate.

[0008] In the preparation method as described above, the high-pressure microwave conditions are: pressure of 0.1 MPa-10 MPa, and microwave output power of 0.1 kW-10 kW.

[0009] In the preparation method as described above, the crystal-changing agent comprises dilute phosphoric acid, ammonium bicarbonate solution and ethanol;

[0010] The mass ratio of the dilute phosphoric acid, ammonium bicarbonate solution and ethanol is 1:(0.1-10):(0.1-10);

[0011] The mass concentration of the dilute phosphoric acid is 1%-10%, and the mass concentration of the ammonium bicarbonate solution is 1%-30%.

[0012] In the preparation method described above, the mass percentage of phosphoric acid in the crystal conversion agent with respect to the mass of iron basic phosphate is 0.1% - 10%.

[0013] In the preparation method described above, the time of the crystal conversion reaction is 0.1 h - 48 h.

[0014] In the preparation method described above, the iron basic phosphate is prepared by a method including the following process:

[0015] An acid leaching reaction is carried out on a first system including phosphoferric slag after lithium extraction and an inorganic acid to obtain an iron-containing solution;

[0016] A pH regulator is added to the iron-containing solution to obtain the iron basic phosphate.

[0017] In the preparation method described above, the molar ratio of iron element to inorganic acid in the phosphoferric slag after lithium extraction is (0.1 - 10) : 1.

[0018] In the preparation method described above, the solid-liquid ratio of the first system is 0.1 g / ml - 10 g / ml.

[0019] In the preparation method described above, the time of the acid leaching reaction is 0.5 h - 8 h.

[0020] In the preparation method described above, adding a pH regulator to the iron-containing solution to obtain the iron basic phosphate includes:

[0021] At 25°C - 95°C, the pH value of the iron-containing solution is adjusted to 1 - 4 using a pH regulator, and after stabilizing for 0.1 h - 12 h, solid-liquid separation is carried out to obtain the iron basic phosphate;

[0022] And / or, the pH regulator includes at least one of ammonium carbonate, ammonium bicarbonate, and ammonia water.

[0023] In the preparation method of iron phosphate provided by the present invention, under high-pressure microwave conditions, a crystal conversion reaction is carried out on a mixed system including iron basic phosphate and a crystal conversion agent. The binding ability of iron phosphate is stronger in a high-pressure microwave environment, and impurity ions are not easily incorporated into the crystal lattice. Moreover, the high-temperature microwave conditions can increase the activity of ions, making it easier to remove impurities from the solid phase; and the high-pressure microwave conditions are conducive to forming a relatively dense crystal structure. Therefore, the prepared iron phosphate has a high purity, a low impurity content, and a high tapped density. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the related art, the following briefly introduces the drawings required for the description of the embodiments of the present invention or the related art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 XRD pattern of Example 1 of the present invention. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0027] Lithium iron phosphate batteries have been widely used in electric vehicles, energy storage systems and other portable electronic devices in recent years due to their excellent performance and environmental friendliness. Compared with other types of lithium-ion batteries, lithium iron phosphate batteries have higher safety, longer service life and lower cost. However, with the increase in their usage, the problems of recycling and treating waste batteries have become increasingly prominent.

[0028] Waste lithium iron phosphate batteries contain various valuable metal elements such as lithium, iron, and phosphorus. The recycling of these elements can not only reduce the dependence on primary mineral resources but also lower the production cost. However, existing recycling technologies often face technical and economic challenges when extracting and purifying these elements. For example, traditional hydrometallurgical and pyrometallurgical processes usually require complex chemical treatment steps and may generate a large amount of chemical waste. In addition, when separating and purifying iron phosphate, it is often difficult to achieve high purity, resulting in a high impurity content and affecting the quality and application value of the recycled materials.

[0029] To solve these problems, the inventors of the present application have found through research that under high-pressure microwave reaction conditions, the crystal structure of iron phosphate can be effectively induced and promoted to recombine by the crystal conversion agent, thereby improving the purity and tap density of the final product.

[0030] Based on this, the present invention provides a method for preparing iron phosphate, comprising the following steps:

[0031] Subject a mixed system comprising basic iron phosphate and a crystal conversion agent to a crystal conversion reaction under high-pressure microwave conditions to obtain iron phosphate.

[0032] In the present invention, basic iron phosphate can be mixed with deionized water, and the solid-liquid ratio is controlled to be 0.1 g / mL - 10 g / mL. Under the conditions of high-pressure microwave reaction, a crystal conversion agent is added for crystal conversion reaction. After the reaction ends, solid-liquid separation is carried out to obtain iron phosphate. This iron phosphate contains crystal water, and the iron phosphate can also be sintered at a certain temperature to obtain iron phosphate without crystal water, that is, anhydrous iron phosphate. The sintering temperature can be 500°C - 700°C, and the sintering time can be 3 h - 6 h.

[0033] The preparation method of iron phosphate provided by the present invention can obtain iron phosphate with relatively high purity and low impurity content. This is because basic iron phosphate contains iron hydroxide and iron phosphate. The iron hydroxide in basic iron phosphate can be converted into iron phosphate through a crystal conversion agent. Since the binding ability of phosphate ions and iron ions is stronger in a high-pressure microwave environment, impurity ions are not easily incorporated into the crystal lattice, so impurity ions can be removed from the solid. In addition, impurity ions are interspersed in basic iron phosphate. During the crystal conversion process, the crystal lattice is transformed. The high-temperature microwave conditions can increase the activity of ions, making it easier to remove impurities from the solid phase. Specifically, in the high-pressure microwave reaction conditions, the high-pressure effect is to lower the energy barrier required for ion movement, reduce the intermolecular distance, enhance the influence of the interaction, increase the intermolecular collision frequency, and increase the molecular movement rate through microwave, so that the reaction rate is enhanced from both the molecular self-movement rate and the intermolecular exchange frequency, thereby improving the exchange efficiency of elements. On the other hand, under high-pressure conditions, it is beneficial to increase the solubility and diffusion rate of reactants, promote the densification and homogenization of crystals, and make it easier for crystals to expel internal voids and defects, forming a more dense structure; and under microwave conditions, it can significantly accelerate the chemical reaction rate, which is beneficial to the formation of a relatively dense crystal structure, thereby increasing the tapped density of iron phosphate.

[0034] Therefore, the preparation method of iron phosphate provided by the present invention can achieve the crystal conversion of basic iron phosphate and the removal of impurity ions during the crystal conversion process under high-pressure microwave conditions, and is beneficial to the formation of a relatively dense crystal structure. Therefore, the prepared iron phosphate has relatively high purity, low impurity content, and high tapped density.

[0035] In some embodiments of the present invention, the high-pressure microwave conditions are as follows: the pressure is 0.1 MPa - 10 MPa. For example, it can be 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa or any range composed of any two of them; the microwave output power is 0.1 kW - 10 kW. For example, it can be 0.1 kW, 1 kW, 2 kW, 3 kW, 4 kW, 5 kW, 6 kW, 7 kW, 8 kW, 9 kW, 10 kW or any range composed of any two of them.

[0036] Under the high-pressure microwave conditions of the present invention, when the pressure and microwave output power are within the above ranges, the binding ability of iron phosphate can be further improved, making it difficult for impurity ions to enter the crystal lattice, and the impurity ions can be removed from the solid. Moreover, under these conditions, the activity of the ions can be increased, and it is easier to remove the impurity ions from the solid phase. As a result, the iron phosphate finally prepared has a higher purity and a lower impurity content.

[0037] If the pressure is too high or the microwave output power is too large, the safety risk increases, the requirements for the equipment are relatively high, and more energy needs to be consumed, which affects the service life of the equipment.

[0038] In some embodiments of the present invention, the crystal conversion agent includes dilute phosphoric acid, ammonium bicarbonate solution and ethanol; wherein, the mass ratio of dilute phosphoric acid, ammonium bicarbonate solution and ethanol is 1:(0.1 - 10):(0.1 - 10). For example, it can be 1:0.1:0.1, 1:1:1, 1:1:5, 1:5:5, 1:7:7, 1:8:8, 1:9:9, 1:10:10 or the range composed of any two of them; the mass concentration of dilute phosphoric acid is 1% - 10%. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of them; the mass concentration of ammonium bicarbonate solution is 1% - 30%. For example, it can be 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30% or the range composed of any two of them.

[0039] In the crystal conversion agent of the present invention, the function of dilute phosphoric acid is crystal conversion, that is, converting iron hydroxide into iron phosphate. The function of ethanol is impurity removal, which can elute the impurity ions, and ethanol can be used as a dispersant to disperse the impurity ions more evenly, making it easier for the impurity ions to be removed from the solid phase, and enabling iron hydroxide to react better with phosphoric acid. The ammonium bicarbonate solution is used to stabilize the pH value. Since the addition of dilute phosphoric acid will cause the pH value of the system to decrease, the addition of ammonium bicarbonate solution can stabilize the pH value and prevent the pH value of the system from fluctuating too much. In addition, controlling the mass ratio of dilute phosphoric acid, ammonium bicarbonate solution and ethanol, as well as the mass concentration of dilute phosphoric acid and the mass concentration of ammonium bicarbonate solution within the above ranges, can further improve the purity of the finally prepared iron phosphate and reduce the impurity content.

[0040] It should be noted that the three reagents in the crystal conversion agent are added to the solution separately.

[0041] In some embodiments of the present invention, the mass percentage of phosphoric acid in the crystal conversion agent in the mass of basic iron phosphate is 0.1% - 10%. For example, it can be 0.1%, 0.5%, 1%, 2%, 2.5%, 5%, 7%, 8%, 10% or the range composed of any two of them.

[0042] In the present invention, when the mass percentage of phosphoric acid in the crystal conversion agent with respect to the mass of iron oxyhydroxide phosphate is within the above range, the iron hydroxide in the iron oxyhydroxide phosphate can be fully converted into iron phosphate, and excessive impurity ions will not be introduced into the system, thereby being beneficial to the purity of the finally prepared iron phosphate and reducing the content of impurities.

[0043] In some embodiments of the present invention, the time of the crystal conversion reaction is 0.1 h - 48 h. For example, it can be 0.1 h, 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 20 h, 30 h, 40 h, 48 h or the range composed of any two of them.

[0044] In the present invention, when the time of the crystal conversion reaction is within the above range, there is sufficient time for the iron oxyhydroxide phosphate to combine with the dilute phosphoric acid in the crystal conversion agent, that is, to carry out a sufficient crystal conversion reaction, which can improve the yield and purity of iron phosphate and reduce the impurity content.

[0045] In some embodiments of the present invention, the iron oxyhydroxide phosphate is prepared by a method including the following process:

[0046] An leaching reaction is carried out on a first system including phosphoferric slag after lithium extraction and an inorganic acid to obtain an iron-containing solution; a pH regulator is added to the iron-containing solution to obtain iron oxyhydroxide phosphate.

[0047] It can be understood that the phosphoferric slag after lithium extraction is a phosphoferric slag substantially free of lithium formed after lithium extraction from waste lithium iron phosphate. Conventional methods in the art can be used to extract lithium from waste lithium iron phosphate to obtain the phosphoferric slag after lithium extraction. For example, sulfuric acid and hydrogen peroxide are added to the waste lithium iron phosphate to preferentially extract lithium elements, and solid-liquid separation is carried out. The obtained solution contains lithium elements, and the solid phase is the phosphoferric slag after lithium extraction.

[0048] In the present invention, a wet leaching reaction is carried out on a first system including phosphoferric slag after lithium extraction and an inorganic acid. After the reaction is completed, solid-liquid separation is carried out to obtain an iron-containing solution and a residue. Among them, the inorganic acid can be at least one of hydrochloric acid, nitric acid, phosphoric acid and sulfuric acid. A pH regulator is added to the iron-containing solution, and the pH regulator can be a basic reagent. Since the iron-containing solution contains not only iron elements but also sodium, sulfur, fluorine impurities and phosphate ions, iron hydroxide and iron phosphate, that is, iron oxyhydroxide phosphate, can be generated. Among them, the iron oxyhydroxide phosphate contains sodium, sulfur, fluorine impurities.

[0049] The present invention uses the phosphoferric slag after lithium extraction as a raw material, effectively realizes the resource utilization of waste, reduces the discharge of solid waste, conforms to the concept of circular economy and sustainable development, and can reduce production costs and environmental pollution.

[0050] In some embodiments of the present invention, the molar ratio of iron element to inorganic acid in the phosphoferric slag after lithium extraction is (0.1 - 10):1. For example, it can be 0.1:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or the range composed of any two of them.

[0051] In the present invention, when the molar ratio of iron element to inorganic acid in the phosphoferric slag after lithium extraction is within the above range, the iron element in the phosphoferric slag after lithium extraction can be effectively dissolved, that is, the iron element can be effectively recycled. At the same time, controlling an appropriate molar ratio can reduce the use of excessive acid, thereby reducing the generation of by-products, reducing the dissolution of impurities, improving the purity of the final iron basic phosphate, and thus improving the purity of iron phosphate and reducing the content of impurities.

[0052] In some embodiments of the present invention, the solid-liquid ratio of the first system is 0.1 g / ml - 10 g / ml. For example, it can be 0.1 g / ml, 1 g / ml, 2 g / ml, 3 g / ml, 4 g / ml, 5 g / ml, 6 g / ml, 7 g / ml, 8 g / ml, 9 g / ml, 10 g / ml or the range composed of any two of them.

[0053] By adjusting the solid-liquid ratio of the first system in the present invention, the efficiency of the leaching reaction can be optimized, the leaching of impurities can be effectively controlled, the purity of iron basic phosphate can be improved, and thus the purity of the final iron phosphate can be improved and the impurity content can be reduced.

[0054] In some embodiments of the present invention, the time of the leaching reaction is 0.5 h - 8 h. For example, it can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or the range composed of any two of them.

[0055] In the present invention, when the time of the leaching reaction is within the above range, while ensuring the full leaching of iron element, unnecessary time waste can be avoided and resource utilization can be optimized. An appropriate leaching reaction time can reduce overreaction and the generation of by-products, and improve the purity and quality of the product.

[0056] In some embodiments of the present invention, adding a pH regulator to the iron-containing solution to obtain iron basic phosphate includes:

[0057] At 25°C - 95°C, use a pH regulator to adjust the pH value of the iron-containing solution to 1 - 4, and after stabilizing for 0.1 h - 12 h, perform solid-liquid separation to obtain iron basic phosphate.

[0058] Exemplarily, the temperature can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 95°C, or a range composed of any two of them; the pH value can be 1, 1.5, 2, 2.5, 3, 3.5, 4, or a range composed of any two of them; the stabilization time can be 0.1 h, 0.2 h, 0.5 h, 0.8 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 10 h, 12 h, or a range composed of any two of them.

[0059] In the present invention, at an appropriate temperature, a pH regulator is added to an iron-containing solution to adjust the pH value of the system to 1-4, which is beneficial to controlling the precipitation behavior of iron, reducing co-precipitation of impurities, and improving the purity and quality of iron basic phosphate. By stabilizing for an appropriate time, the reaction can proceed fully, enabling the iron element to be fully precipitated. After solid-liquid separation, high-purity iron basic phosphate can be obtained.

[0060] In some embodiments, the pH regulator includes at least one of ammonium carbonate, ammonium bicarbonate, and ammonia water.

[0061] The types of pH regulators in the present invention are relatively mild basic substances, which can effectively adjust the pH value of the solution, reduce the damage to the reaction system, and do not introduce metal ions, reducing the impact on the product purity. After the reaction, they can volatilize into gases, reducing the generation of residues, thereby improving the purity of iron basic phosphate, and further improving the purity of iron phosphate and reducing the content of impurities.

[0062] Hereinafter, the technical solution of the present invention will be further described in conjunction with specific embodiments.

[0063] Example 1

[0064] The preparation method of iron phosphate in this example includes the following steps:

[0065] 1) Mix the lithium-extracted phosphorus-iron slag after recycling lithium from waste lithium iron phosphate with sulfuric acid to obtain a first system. Among them, the molar ratio of iron element to sulfuric acid in the lithium-extracted phosphorus-iron slag is 2:1, and the solid-liquid ratio of the first system is 1 g / 1 ml. Perform a wet leaching reaction. After reacting for 3 h, perform solid-liquid separation to obtain a ferric sulfate solution and residues.

[0066] 2) At 60°C, add ammonium bicarbonate as a pH regulator to the ferric sulfate solution to control the pH = 2 in the mixed solution, stabilize for 3 h, and perform solid-liquid separation to obtain iron basic phosphate.

[0067] 3) Mix ferric iron basic phosphate with deionized water at a solid-liquid ratio of 1 g / mL, and add a crystal conversion agent for crystal conversion reaction under the conditions of high-pressure microwave reaction. Among them, the conditions of high-pressure microwave reaction are: the pressure is 1.5 MPa, and the microwave output power is 1 kW; the crystal conversion agent includes dilute phosphoric acid, ammonium bicarbonate solution and ethanol with a mass ratio of 1:1:1. The mass concentration of dilute phosphoric acid is 1%, and the mass concentration of ammonium bicarbonate solution is 15%. The mass percentage of phosphoric acid in the crystal conversion agent accounting for the mass of ferric iron basic phosphate is 1%. After the crystal conversion reaction is carried out for 12 h, solid-liquid separation is carried out, and sintering is carried out at 600 °C for 4 h to obtain iron phosphate, and this iron phosphate is anhydrous iron phosphate.

[0068] Example 2

[0069] The preparation method of iron phosphate in Example 2 is basically the same as that in Example 1, except that the conditions of high-pressure microwave reaction are: the pressure is 1.0 MPa, and the microwave output power is 1.2 kW.

[0070] Example 3

[0071] The preparation method of iron phosphate in Example 3 is basically the same as that in Example 1, except that the crystal conversion agent includes dilute phosphoric acid, ammonium bicarbonate solution and ethanol with a mass ratio of 1:0.5:0.5.

[0072] Example 4

[0073] The preparation method of iron phosphate in Example 4 is basically the same as that in Example 1, except that the conditions of high-pressure microwave reaction are: the pressure is 0.1 MPa, and the microwave output power is 10 kW.

[0074] Example 5

[0075] The preparation method of iron phosphate in Example 5 is basically the same as that in Example 1, except that the conditions of high-pressure microwave reaction are: the pressure is 10 MPa, and the microwave output power is 0.1 kW.

[0076] Example 6

[0077] The preparation method of iron phosphate in Example 6 is basically the same as that in Example 1, except that the mass concentration of ammonium bicarbonate solution in the crystal conversion agent is 1%, and the mass percentage of phosphoric acid in the crystal conversion agent accounting for the mass of ferric iron basic phosphate is 0.1%.

[0078] Example 7

[0079] The preparation method of iron phosphate in Example 7 is basically the same as that in Example 1, except that the mass concentration of dilute phosphoric acid in the crystal conversion agent is 10%, the mass concentration of ammonium bicarbonate solution is 30%, and the mass percentage of phosphoric acid in the crystal conversion agent accounting for the mass of ferric iron basic phosphate is 10%.

[0080] Example 8

[0081] The preparation method of iron phosphate in Example 8 is basically the same as that in Example 1, except that the time of the conversion reaction is 0.1 h.

[0082] Example 9

[0083] The preparation method of iron phosphate in Example 9 is basically the same as that in Example 1, except that the time of the conversion reaction is 48 h.

[0084] Example 10

[0085] The preparation method of iron phosphate in Example 10 is basically the same as that in Example 1, except that in step 1), after lithium extraction from waste lithium iron phosphate, the phosphorus-iron slag and hydrochloric acid are mixed at a molar ratio of 0.1:1 to obtain a first system. The solid-liquid ratio of the first system is 0.1 g / 1 ml, and the time of the leaching reaction is 0.5 h to obtain a ferric chloride solution and residues.

[0086] Example 11

[0087] The preparation method of iron phosphate in Example 11 is basically the same as that in Example 1, except that in step 1), the molar ratio of iron element and sulfuric acid in the phosphorus-iron slag after lithium extraction is 10:1, the solid-liquid ratio of the first system is 10 g / 1 ml, and the time of the leaching reaction is 8 h to obtain a ferric nitrate solution and residues.

[0088] Example 12

[0089] The preparation method of iron phosphate in Example 12 is basically the same as that in Example 1, except that in step 2), at 25 °C, ammonium carbonate as a pH regulator is added to the ferric sulfate solution to control the pH of the mixed solution to be 1, and it is stabilized for 0.1 h, followed by solid-liquid separation to obtain basic iron phosphate.

[0090] Example 13

[0091] The preparation method of iron phosphate in Example 13 is basically the same as that in Example 1, except that in step 2), at 95 °C, ammonia water as a pH regulator is added to the ferric sulfate solution to control the pH of the mixed solution to be 4, and it is stabilized for 12 h, followed by solid-liquid separation to obtain basic iron phosphate.

[0092] Example 14

[0093] The preparation method of iron phosphate in Example 14 is basically the same as that in Example 1, except that the high-pressure microwave reaction conditions are: the pressure is 0.01 MPa and the microwave output power is 1 kW.

[0094] Example 15

[0095] The preparation method of iron phosphate in Example 15 is basically the same as that in Example 1, except that the high-pressure microwave reaction conditions are as follows: the pressure is 1.5 MPa, and the microwave output power is 0.01 kW.

[0096] Comparative Example 1

[0097] The preparation method of iron phosphate in Comparative Example 1 is basically the same as that in Example 1, except that the crystal transformation reaction is carried out at 25 °C and 101 kPa.

[0098] Comparative Example 2

[0099] The preparation method of iron phosphate in Comparative Example 2 is basically the same as that in Example 1, except that step 2) is omitted, basic iron phosphate is not obtained, and the ferric sulfate solution is directly involved in the crystal transformation reaction.

[0100] Comparative Example 3

[0101] The preparation method of iron phosphate in Comparative Example 3 is basically the same as that in Example 1, except that the conditions of the crystal transformation reaction are as follows: heating at 600 °C for 4 h.

[0102] Comparative Example 4

[0103] The preparation method of iron phosphate in Comparative Example 4 is basically the same as that in Example 1, except that the crystal transformation agent is not added.

[0104] Test Example:

[0105] 1. Purity of iron phosphate: The iron phosphate in Example 1 was tested by XRD. As Figure 1 shown, the qualitatively judged substance is high-purity phase iron phosphate. The iron content in the iron phosphate of the examples and comparative examples was tested by ICP, the actual content of iron phosphate was calculated, and the purity of iron phosphate was the actual content of iron phosphate / the mass of iron phosphate.

[0106] 2. Appearance: Under natural light, the appearance was judged visually on a surface dish or a white porcelain plate with a white substrate.

[0107] 3. Tap density: It was measured according to the method specified in HGT 6262-2024.

[0108] 4. Particle size (D50): It was tested using a laser particle size analyzer.

[0109] 5. Specific surface area: It was measured according to the method specified in HGT 6262-2024. The adsorbed gas was nitrogen; the degassing conditions were: 180 °C, 1 h.

[0110] 6. Determination of moisture content, iron content, phosphorus content, iron-to-phosphorus ratio, magnetic substance content, and impurity content: Refer to the national standard HGT 6262-2024.

[0111] Table 1

[0112]

[0113] Table 2

[0114]

[0115] As can be seen from Tables 1-2, for the preparation method of iron phosphate provided by the present invention, under high-pressure microwave conditions, a conversion reaction is carried out on a mixed system including basic iron phosphate and a crystal conversion agent. Iron phosphate has a stronger binding ability in a high-pressure microwave environment, and impurity ions are not easily incorporated into the crystal lattice. Moreover, the high-temperature microwave conditions can increase the activity of ions, making it easier to remove impurities from the solid phase. Therefore, the prepared iron phosphate has a high purity, a low impurity content, and a high tapped density.

[0116] Finally, it should be noted that: After considering the specification and practicing the invention disclosed herein, those skilled in the art will readily think of other embodiments of the present invention. The present invention is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include common general knowledge or conventional technical means in the technical field not disclosed in the present invention. It is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A method for preparing ferric phosphate, characterized in that: The following steps are involved: A mixed system including basic ferric phosphate and a crystal-transforming agent is subjected to a crystal-transforming reaction under high-pressure microwave conditions to obtain the ferric phosphate.

2. The preparation method according to claim 1, characterized in that: The high-pressure microwave conditions are: pressure of 0.1MPa-10MPa, and microwave output power of 0.1kW-10kW.

3. The preparation method according to claim 1 or 2, characterized in that: The crystal-changing agent includes dilute phosphoric acid, ammonium bicarbonate solution and ethanol; The mass ratio of the dilute phosphoric acid, ammonium bicarbonate solution and ethanol is 1:(0.1-10):(0.1-10); The mass concentration of the dilute phosphoric acid is 1%-10%, and the mass concentration of the ammonium bicarbonate solution is 1%-30%.

4. The preparation method according to any one of claims 1 to 3, characterized in that The mass percentage of phosphoric acid in the crystal-changing agent to the mass percentage of basic iron phosphate is 0.1%-10%.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The time of the crystal transformation reaction is 0.1h-48h.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The basic ferric phosphate is prepared by a method comprising the following steps: Performing a leaching reaction on the first system including the ferrophosphorus slag after lithium extraction and the inorganic acid to obtain an iron-containing solution; A pH regulator is added to the iron-containing solution to obtain the basic ferric phosphate.

7. The preparation method according to claim 6, characterized in that: The molar ratio of iron element to inorganic acid in the ferrophosphorus slag after lithium extraction is (0.1-10):

1.

8. The preparation method according to claim 6 or 7, characterized in that: The solid-to-liquid ratio of the first system is 0.1 g / ml-10 g / ml.

9. The preparation method according to any one of claims 6 to 8, characterized in that: The leaching reaction time is 0.5h-8h.

10. The preparation method according to any one of claims 6 to 9, characterized in that: The step of adding a pH regulator to the iron-containing solution to obtain the basic ferric phosphate comprises: At 25° C.-95° C., using a pH regulator to adjust the pH value of the iron-containing solution to 1-4, stabilizing for 0.1 h-12 h, and then performing solid-liquid separation to obtain the basic ferric phosphate; And / or, the pH adjuster includes at least one of ammonium carbonate, ammonium bicarbonate, and ammonia water.

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