Iron phosphate and preparation method thereof

Abstract

The invention provides iron phosphate and a preparation method thereof, and belongs to the field of preparation of lithium iron phosphate positive electrode material precursors, and the preparation method of the iron phosphate comprises the following steps: carrying out acid leaching treatment on pyrite cinder to obtain a first solution; adding an oxidizing agent into the first solution to obtain a second solution; mixing the second solution with phosphorite crude acid and a pH regulator, and reacting to obtain a mixture containing ferric hydroxide colloid and amorphous iron phosphate; carrying out pulpifying treatment on the mixture to obtain mixed slurry; and carrying out aging crystal transformation treatment on the mixed slurry, and then drying and calcining to obtain the iron phosphate. According to the method, iron in the pyrite cinder is leached out and oxidized, then the iron reacts with phosphorite crude acid, the pH is controlled, ferric hydroxide colloid and amorphous phosphoric acid can be generated synchronously, the particle size and morphology of iron phosphate can be adjusted and controlled, introduction of impurities is reduced, and the yield of iron phosphate is increased. Therefore, iron phosphate with regular morphology, small particle size, narrow particle size distribution, large specific surface area and many holes is obtained.

Description

Technical Field

[0001] This invention relates to the field of preparation technology of iron phosphate, a precursor for lithium iron phosphate cathode materials, and specifically to an iron phosphate and its preparation method. Background Technology

[0002] LiFePO4 (lithium iron phosphate) batteries possess excellent thermal stability and ultra-long cycle life, leading to their widespread application in the new energy vehicle sector. Iron phosphate (FePO4) is the precursor for synthesizing LiFePO4 cathode materials, and its physicochemical properties (specific surface area, iron-to-phosphorus ratio, morphology, particle size, etc.) significantly influence the performance of the prepared LiFePO4 cathode material. For example, a larger specific surface area increases the number of electrochemical reaction sites, while smaller, more uniform particle size shortens the lithium-ion diffusion path and improves interfacial ion transport efficiency. However, current techniques typically involve adding phosphate salts to ferrous iron to obtain amorphous iron phosphate, followed by aging and crystallization treatment to prepare FePO4. This method is detrimental to crystal transformation and regular particle growth, resulting in FePO4 with irregular morphology, wide particle size distribution, and small specific surface area. Summary of the Invention

[0003] In view of the technical problems existing in the background art, this application provides ferric phosphate and its preparation method, aiming to solve the technical problems that the ferric phosphate prepared by the traditional preparation method has an irregular morphology, a wide particle size distribution, and a small specific surface area.

[0004] In a first aspect, embodiments of this application provide a method for preparing ferric phosphate, comprising the following steps: The pyrite cinder was subjected to acid leaching to obtain the first solution; An oxidizing agent is added to the first solution to obtain a second solution; The second solution was mixed with crude acid from phosphate rock and a pH adjuster, and the mixture was reacted to obtain a mixture containing ferric hydroxide colloid and amorphous ferric phosphate. A mixture containing ferric hydroxide colloid and amorphous ferric phosphate is subjected to pulping treatment to obtain a mixed slurry; The mixed slurry was aged and crystallized, and then dried and calcined to obtain ferric phosphate.

[0005] In the technical solution of this application embodiment, acid leaching is beneficial for leaching iron from pyrite slag. Further treatment with an oxidant oxidizes ferrous ions in the first solution to ferric ions. Subsequently, a second solution containing ferric ions is reacted with crude acid from phosphate rock to obtain a mixture containing ferric hydroxide colloid and amorphous ferric phosphate. The ferric hydroxide colloid helps to control the particle size and morphology of the ferric phosphate. Afterwards, slurrying and aging / crystallization treatments facilitate complete reaction and crystallization to obtain ferric phosphate with smaller, more uniform particle size and more pores.

[0006] In some embodiments, during the mixing of the second solution with crude phosphate rock acid and pH adjuster, the molar ratio of iron to phosphorus in the mixed system is controlled to be (1.9~2.1):1, and the pH value is 3~3.3; and / or, the pH adjuster is at least one of ammonia water and sodium hydroxide; and / or, the reaction temperature is 50~60℃, and the reaction time is 50~70min.

[0007] In this embodiment, by mixing the second solution with crude phosphate rock acid and a pH adjuster, and controlling the molar ratio of iron to phosphorus, it is beneficial to allow some of the ferric sulfate in the second solution to react with the phosphoric acid in the crude phosphate rock acid to form amorphous ferric phosphate, while the other part of the ferric sulfate reacts with the pH adjuster to form ferric hydroxide colloid. Because the ferric hydroxide colloid and amorphous ferric phosphate are formed simultaneously, the ferric hydroxide colloid has the effect of limiting the particle size of amorphous ferric phosphate, which helps to control the particle size of amorphous ferric phosphate, thereby resulting in a small and uniform particle size of the prepared amorphous ferric phosphate.

[0008] Specifically, FePO4 can be selectively precipitated by controlling the reaction pH to reduce the introduction of impurity ions (e.g., aluminum, copper, potassium, magnesium, lead, zinc, etc.). Preferably, the pH adjuster is at least one of ammonia or sodium hydroxide, which facilitates the conversion of ferric ions into ferric hydroxide colloid while simultaneously adjusting the pH. Furthermore, by controlling the reaction temperature and time, it is beneficial to fully convert ferric ions into ferric hydroxide colloid and amorphous ferric phosphate, resulting in a mixture containing ferric hydroxide colloid and amorphous ferric phosphate.

[0009] In some embodiments, the molar ratio of ferric hydroxide colloid to amorphous ferric phosphate in the mixture is 1:(0.9~1.1).

[0010] In this embodiment, by controlling the molar ratio of the ferric hydroxide colloid generated by the reaction to the amorphous ferric phosphate, it is beneficial to ensure that the ferric hydroxide colloid fully restricts the particle size and particle size distribution of the amorphous ferric phosphate.

[0011] In some embodiments, sulfuric acid solution is used to leach pyrite cinder, wherein the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite cinder is 1:(0.75~1.2); and / or, the concentration of sulfuric acid solution is 30%~40%; and / or, the pH value of the first solution is 0.15~0.5; and / or, the temperature of acid leaching treatment is 90~100℃, and the time of acid leaching treatment is 3~5h.

[0012] In this embodiment, acid leaching with sulfuric acid facilitates the conversion of iron in pyrite cinders into ferric sulfate for subsequent reactions. Controlling the molar ratio of sulfuric acid to iron and the concentration of the sulfuric acid solution improves the reaction rate and iron leaching rate, while also reducing sulfuric acid usage and lowering processing costs. Controlling the pH of the first solution provides a favorable reaction environment for subsequent oxidation. Controlling the temperature and time of the acid leaching treatment ensures the iron is fully and efficiently leached into its ionic state.

[0013] In some embodiments, the step of adding an oxidant to the first solution includes: diluting the first solution to an iron content of 5.5-6%, and then adding an oxidant to the diluted first solution.

[0014] In this embodiment, diluting the first solution helps to improve the efficiency and conversion rate of the oxidation reaction. The oxidation process oxidizes the relatively small amount of ferrous ions in the first solution into ferric ions, which helps to reduce the amount of oxidant used and lower the preparation cost.

[0015] In some embodiments, the molar ratio of the oxidant to the ferrous ions in the first solution is (0.75~0.85):1; and / or, the oxidant includes at least one of hydrogen peroxide, ozone, and ammonium persulfate.

[0016] In this embodiment, controlling the molar ratio of the oxidant to the ferrous ions in the first solution facilitates a full and efficient reaction, while reducing the amount of oxidant used and lowering preparation costs. Furthermore, optimizing the type of oxidant helps improve reaction efficiency and reduce the introduction of impurity elements.

[0017] In some embodiments, the aging and crystallization treatment includes: mixing the mixed slurry with phosphoric acid, aging it at 80~90°C, and keeping it at that temperature for 2~2.5h after the mixed slurry turns pinkish-white; wherein, in the system of mixing the mixed slurry with phosphoric acid, the molar ratio of phosphorus to iron is (1.05~1.15):1.

[0018] In this embodiment, by controlling the temperature and time of aging and crystallization, as well as the molar ratio of phosphorus to iron, it is beneficial to convert the remaining ferric hydroxide colloid in the mixed slurry into amorphous ferric phosphate, and at the same time, to crystallize the amorphous ferric phosphate to obtain ordered ferric phosphate crystal particles.

[0019] In some embodiments, prior to pulping, the mixture is further subjected to rinsing until the conductivity of the rinsing solution is less than 5 mS / cm.

[0020] In this embodiment, rinsing helps to fully remove free soluble salts, resulting in a purer product. This avoids the salting-out effect from affecting subsequent pulping, drying, and calcination steps, and reduces the agglomeration of ferric phosphate.

[0021] Secondly, this application provides an iron phosphate, prepared according to any of the iron phosphate preparation methods described in the foregoing technical solutions.

[0022] In some embodiments, the median particle size of ferric phosphate is 3.75–4.65 μm; the particle size distribution of ferric phosphate is 1.63–1.85 μm; and the specific surface area of ​​ferric phosphate is 9.96–10.18 m². 2 / g; Ferric phosphate has an Al content ≤25.3ppm, Cu content ≤8.66ppm, K content ≤6.2ppm, Mg content ≤5.6, Pb content ≤13.2ppm, and Zn content ≤10.53ppm.

[0023] In this embodiment, by controlling the morphology, particle size, specific surface area, and purity of ferric phosphate, ferric phosphate with low impurity content, regular morphology, small particle size, narrow particle size distribution, large specific surface area, and many pores was obtained, which effectively improved the electrochemical performance of ferric phosphate.

[0024] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0026] Figure 1 This is a SEM image of the iron phosphate prepared in Example 1 of this application; Figure 2 SEM image of the iron phosphate prepared in Comparative Example 3 of this application; Figure 3 This is a SEM image of the iron phosphate prepared in Comparative Example 5 of this application. Detailed Implementation

[0027] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0029] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0033] To address the technical problems of irregular morphology, wide particle size distribution, and small specific surface area of ​​ferric phosphate prepared by traditional methods, this application provides ferric phosphate and its preparation method. In the preparation method of ferric phosphate, ferric hydroxide colloid and amorphous phosphoric acid are generated simultaneously. The ferric hydroxide colloid is used to regulate the particle size and morphology of ferric phosphate, so that the prepared ferric phosphate has a regular morphology, narrow particle size distribution, and large specific surface area.

[0034] In a first aspect, embodiments of this application provide a method for preparing ferric phosphate, comprising the following steps: S1. The pyrite cinder is subjected to acid leaching to obtain the first solution; S2. Add an oxidizing agent to the first solution to obtain the second solution; S3. The second solution is mixed with crude acid from phosphate rock and a pH adjuster, and the mixture is reacted to obtain a mixture containing ferric hydroxide colloid and amorphous ferric phosphate. S4. The mixture containing ferric hydroxide colloid and amorphous ferric phosphate is subjected to pulping treatment to obtain a mixed slurry; S5. The mixed slurry is aged and crystallized, and then dried and calcined to obtain iron phosphate.

[0035] In this application, iron is leached from pyrite slag through acid leaching to obtain a first solution containing both ferrous and ferric ions. Then, an oxidizing agent is used to oxidize the ferrous ions in the first solution to ferric ions, yielding a second solution, namely, ferric sulfate solution. Subsequently, the ferric sulfate solution, crude acid from phosphate rock, and a pH adjuster are mixed and reacted to obtain a mixture of ferric hydroxide colloid and amorphous ferric phosphate. By uniformly mixing the ferric hydroxide colloid and amorphous ferric phosphate, the ferric hydroxide colloid can limit the particle size of the amorphous ferric phosphate particles and regulate their morphology. Further, a mixed slurry is obtained through pulping. During the pulping process, phosphoric acid can be added to the mixed slurry as needed to allow the ferric hydroxide colloid to continue reacting with phosphoric acid to obtain amorphous ferric phosphate. Through aging and crystallization treatment, the amorphous ferric phosphate is transformed from a disordered state into an ordered crystalline structure, thus obtaining ferric phosphate.

[0036] The preparation method provided in this application helps to reduce the introduction of impurities and prepare iron phosphate with regular morphology, small particle size, narrow particle size distribution, large specific surface area and many pores, thereby improving the electrochemical performance of iron phosphate.

[0037] Furthermore, in some embodiments, during the mixing of the second solution with the crude acid from phosphate rock and the pH adjuster, the molar ratio of iron to phosphorus in the mixed system is controlled to be (1.9~2.1):1, and the pH value is 3~3.3; and / or, the pH adjuster is at least one of ammonia water and sodium hydroxide; and / or, the reaction temperature is 50~60℃, and the reaction time is 50~70min.

[0038] In this application, by controlling the molar ratio of iron to phosphorus in the mixed system to (1.9~2.1):1 and the pH value to 3~3.3, the specific surface area of ​​ferric phosphate particles can be increased, the introduction of impurities can be reduced, and it is beneficial to prepare ferric phosphate with small and uniform particle size, thereby improving the electrochemical performance of ferric phosphate. Understandably, during the reaction of ferric sulfate solution with crude acid from phosphate rock, a portion of the ferric sulfate fully precipitates as ferric hydroxide colloid at a pH of 3~3.3, while other impurity metal ions remain in the solution. Simultaneously, another portion of the ferric sulfate reacts with phosphoric acid in the crude acid from the phosphate rock to generate amorphous ferric phosphate. This allows the smaller ferric hydroxide colloid particles and the amorphous ferric phosphate to be uniformly mixed in the reaction system. The ferric hydroxide colloid plays a role in limiting the particle size, thereby preparing nano-sized ferric phosphate with uniform particle size. By precisely controlling the pH within the range of 3~3.3, this application allows most FePO4 to selectively precipitate, while impurity ions (aluminum, copper, potassium, magnesium, lead, zinc) do not reach the precipitation pH and therefore will not be co-precipitated or adsorbed.

[0039] Specifically, the molar ratio of iron to phosphorus in the mixed system can be any value within the range of 1.9:1, 1.91:1, 1.92:1, 1.93:1, 1.94:1, 1.95:1, 1.96:1, 1.97:1, 1.98:1, 1.99:1, 2.0:1, 2.01:1, 2.02:1, 2.03:1, 2.04:1, 2.05:1, 2.06:1, 2.07:1, 2.08:1, 2.09:1, 2.1:1, or (1.9~2.1):1); the pH value in the mixed system can be any value within the range of 3, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, or 3~3.3.

[0040] In this application, by preferably using at least one of ammonia and sodium hydroxide as the pH adjuster, it is beneficial to smoothly convert ferric ions into ferric hydroxide colloid while adjusting the pH. Simultaneously, by controlling the reaction temperature and reaction time, it is beneficial to fully convert ferric ions into ferric hydroxide colloid and amorphous ferric phosphate, thus smoothly obtaining a mixture.

[0041] Furthermore, in some embodiments, the second solution is mixed with the crude acid from the phosphate rock and a pH adjuster by simultaneous dropwise addition, and the molar ratio of iron to phosphorus in the mixture is controlled to be 2:1, so as to simultaneously generate ferric hydroxide colloid and amorphous ferric phosphate in the same molar ratio. In this application, the generated ferric hydroxide colloid and amorphous ferric phosphate are uniformly mixed, which is beneficial for preparing nanoscale ferric phosphate with uniform particle distribution.

[0042] Furthermore, in some embodiments, the molar ratio of ferric hydroxide colloid to amorphous ferric phosphate in the mixture is 1:(0.9~1.1).

[0043] In this application, the pH value and the molar ratio of iron to phosphorus in the mixed system jointly affect the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate. By controlling the molar ratio of the ferric hydroxide colloid to amorphous ferric phosphate generated in the reaction, it is beneficial to achieve uniform doping of ferric hydroxide colloid and amorphous ferric phosphate. Sufficient ferric hydroxide colloid can effectively limit the excessive growth of amorphous ferric phosphate grains, resulting in ferric phosphate with small particle size and narrow particle size distribution. At the same time, the limiting effect of ferric hydroxide colloid helps to reduce the agglomeration of amorphous ferric phosphate, thereby increasing the specific surface area of ​​ferric phosphate.

[0044] Specifically, in the mixture, the molar ratio of ferric hydroxide colloid to amorphous ferric phosphate can be any value within the range of 1:0.9, 1:0.92, 1:0.94, 1:0.96, 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.1, or 1:(0.9~1.1).

[0045] Furthermore, in some embodiments, sulfuric acid solution is used to perform acid leaching treatment on pyrite cinder, wherein the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite cinder is 1:(0.75~1.2); and / or, the concentration of sulfuric acid solution is 30%~40%; and / or, the pH value of the first solution is 0.15~0.5; and / or, the acid leaching treatment temperature is 90~100℃, and the acid leaching treatment time is 3~5h.

[0046] In this application, acid leaching helps dissolve the iron in the pyrite cinder into an ionic state, facilitating subsequent efficient reactions and allowing for control over the particle size and morphology of the product. Using sulfuric acid for leaching helps reduce the introduction of impurities and facilitates rapid reaction with phosphoric acid to form amorphous iron phosphate. The molar ratio of sulfuric acid to iron in the sulfuric acid solution significantly affects the pH of the first solution. By adjusting the molar ratio of sulfuric acid to iron, with a slight excess of iron, the contact area between iron and sulfuric acid is increased, improving the iron leaching rate. Furthermore, the pH of the solution is high after the reaction, eliminating the need for large amounts of alkali to adjust the pH, and the unreacted sulfuric acid residue can be recycled.

[0047] Specifically, the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag can be any value within the range of 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2, or 1:(0.75~1.2).

[0048] In this application, by controlling the concentration of the sulfuric acid solution, a first solution containing a large amount of iron ions is obtained through efficient reaction, facilitating subsequent processing. If the sulfuric acid concentration is too low, the pH of the reaction system will be too high, resulting in a low reaction rate and hindering iron leaching. Conversely, if the sulfuric acid concentration is too high, the liquid-to-solid ratio will be too small, making stirring difficult and causing slag to settle. This also reduces the contact area between the slag and the sulfuric acid, affecting the reaction rate. Furthermore, the molar ratio of sulfuric acid to iron and the concentration of the sulfuric acid solution jointly determine the pH of the first solution, providing a favorable reaction environment for oxidizing to obtain a second solution with ferric sulfate as the main component. Specifically, the pH of the first solution can be 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any value within the range of 0.15 to 0.5.

[0049] In this application, by controlling the temperature and time of the acid leaching treatment, it is beneficial to fully and efficiently leach iron into an ionic state.

[0050] Furthermore, in some embodiments, the step of adding an oxidant to the first solution includes: diluting the first solution to a content of 5.5-6% iron, and then adding an oxidant to the diluted first solution.

[0051] In this application, controlling the concentration of iron in the diluted first solution is beneficial to improving reaction efficiency and conversion rate. Adding an oxidant to the diluted first solution facilitates the thorough and efficient oxidization of ferrous ions to ferric ions, enabling the subsequent direct preparation of ferric phosphate using ferric ions. Since the content of ferric ions in the first solution is higher than that of ferrous ions, less reagent is needed to convert ferrous ions to ferric ions, thus reducing preparation costs.

[0052] Furthermore, in some embodiments, the molar ratio of the oxidant to the ferrous ions in the first solution is (0.75~0.85):1; and / or, the oxidant includes at least one of hydrogen peroxide, ozone, and ammonium persulfate.

[0053] In this application, by controlling the molar ratio of the oxidant to the ferrous ions in the first solution, it is beneficial to efficiently oxidize the ferrous ions in the first solution to ferric ions while saving the amount of oxidant used and reducing the preparation cost. Furthermore, by optimizing the type of oxidant, it is beneficial to improve the reaction efficiency and reduce the introduction of impurity elements.

[0054] Furthermore, in some embodiments, the aging and crystallization treatment includes: mixing the mixed slurry with phosphoric acid, aging it at 80~90°C, and keeping it at that temperature for 2~2.5h after the mixed slurry turns pinkish-white; wherein, in the system of mixing the mixed slurry with phosphoric acid, the molar ratio of phosphorus to iron is (1.05~1.15):1.

[0055] In this application, by controlling the temperature and time of aging and crystallization, as well as the molar ratio of phosphorus to iron, it is beneficial to allow ferric hydroxide colloid to continue reacting with phosphoric acid to obtain amorphous ferric phosphate. At the same time, the relatively excessive phosphoric acid is also beneficial to the transformation of amorphous ferric phosphate crystals and the regular growth of particles. Within a suitable temperature and time range, amorphous ferric phosphate is transformed from a disordered state into an ordered crystal structure, thus obtaining ferric phosphate.

[0056] Specifically, the molar ratio of phosphorus to iron can be 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.1:1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, 1.15:1, or any value within the range of (1.05~1.15):1. Phosphoric acid can be produced by wet processing or thermal processing.

[0057] Furthermore, in some embodiments, the mixture is further subjected to rinsing before pulping until the conductivity of the rinsing solution is less than 5 mS / cm.

[0058] In this application, rinsing the mixture helps to remove free SO4. 2- Cl- Na + Fe 2+ Fe 3 + Soluble salts should be thoroughly washed away to avoid affecting subsequent pulping, drying, and calcination steps, as well as the electrochemical properties of the product. For example, soluble salts can easily cause salting-out, leading to agglomeration of primary iron phosphate particles and a decrease in specific surface area.

[0059] Furthermore, in some embodiments, the solids content of the mixed slurry is 10-14%.

[0060] In this application, by controlling the solid content of the mixed slurry, it is beneficial to regulate the supersaturation of micro-regions and the collision frequency of particles, thereby regulating the crystallization rate and crystal size distribution during the aging and crystallization process.

[0061] Secondly, embodiments of this application provide an iron phosphate, prepared according to any of the iron phosphate preparation methods described in the foregoing technical solutions.

[0062] Furthermore, in some embodiments, the median particle size of iron phosphate is 3.75~4.65 μm; The radial distance of iron phosphate is 1.63~1.85; The specific surface area of ​​iron phosphate is 9.96~10.18 m². 2 / g; The iron phosphate has an Al content ≤25.3ppm, a Cu content ≤8.66ppm, a K content ≤6.2ppm, a Mg content ≤5.6ppm, a Pb content ≤13.2ppm, and a Zn content ≤10.53ppm.

[0063] In this application, by limiting the proportions and reaction conditions in the acid leaching treatment, the proportions and reaction conditions in the oxidation reaction, the proportions and reaction conditions in the mixing of the second solution with the crude acid of phosphate rock and the pH adjuster, and the proportions and reaction conditions in the aging and crystallization treatment, especially the molar ratio of iron in the second solution to phosphorus in the crude acid of phosphate rock and the pH value of the reaction between the second solution and the crude acid of phosphate rock, the morphology, particle size, specific surface area and purity of ferric phosphate are controlled, resulting in ferric phosphate with low impurity content, regular morphology, small particle size, narrow particle size distribution, large specific surface area and many pores, thereby effectively improving the electrochemical performance of ferric phosphate.

[0064] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0065] I. Preparation Method The components of the pyrite cinder and phosphate rock crude acid used in the embodiments and comparative examples of this application are shown in Tables 1 and 2.

[0066] Table 1. Composition of pyrite cinder Table 2 Components of crude acid from phosphate rock Example 1 This embodiment provides a method for preparing ferric phosphate, including the following steps: S1. 830.17g of 70% sulfuric acid and 857.14g of deionized water were added to the first reaction vessel and stirred until homogeneous to obtain a 34.44% sulfuric acid solution. Next, 490.44g of pyrite cinder was added to the first reaction vessel and stirred until homogeneous, so that the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite cinder was 1:0.9. The internal temperature of the first reaction vessel was then raised to 96℃ and maintained for 4 hours before filtration to obtain the first solution. The molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite cinder significantly affects the pH value of the first solution. In this embodiment, the pH value of the first solution is 0.35.

[0067] S2. Mix 567.69g of the first solution with 70.52g of deionized water and stir until homogeneous, so that the iron content in the first solution is diluted to 5.8%. Then, add 98.98g of hydrogen peroxide dropwise to the diluted first solution, so that the molar ratio of hydrogen peroxide to ferrous ions in the first solution is 0.8:1. The hydrogen peroxide is added over a period of 10 minutes to obtain the second solution, which is a ferric sulfate solution.

[0068] S3. The second solution, crude phosphate rock acid, and ammonia water are simultaneously added dropwise to the second reaction vessel over a period of 30 minutes. During the addition, the molar ratio of iron to phosphorus in the mixture within the second reaction vessel is 2, and the ammonia water adjusts the pH of the mixture to 3.158. After the addition is complete, the mixture is kept at 55°C for 60 minutes to obtain a mixture containing ferric hydroxide colloid and amorphous ferric phosphate. The pH value and the molar ratio of iron to phosphorus in the mixture significantly affect the molar ratio of ferric hydroxide colloid to amorphous ferric phosphate. In this embodiment, the molar ratio of ferric hydroxide colloid to amorphous ferric phosphate is 1:1.

[0069] S4. Rinse the mixture until the conductivity of the rinsing solution is less than 5 mS / cm, then add deionized water and pulp to prepare a mixed slurry with a solid content of 12%.

[0070] S5. Add 66.94g of wet-process phosphoric acid to the mixed slurry to make the molar ratio of phosphorus to iron in the system 1.12:1. Then heat to 85℃ for aging. After the slurry turns pinkish-white, continue to keep it at the temperature for 2 hours. After that, dry and calcine to obtain iron phosphate.

[0071] Example 2 This embodiment provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the molar ratio of sulfuric acid to iron in pyrite slag in step S1, and the temperature of the acid leaching treatment. In this embodiment, 857.14g of 70% sulfuric acid and 642.89g of deionized water are added to the first reaction vessel and stirred until homogeneous to obtain a 40% sulfuric acid solution. Next, 650.73g of pyrite slag is added to the first reaction vessel and stirred until homogeneous, so that the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag is 1:1.2. Then, the internal temperature of the first reaction vessel is raised to 100°C, and after holding at this temperature for 4 hours, the solution is filtered to obtain the first solution. The remaining steps are the same as in Example 1 and will not be repeated here. In this embodiment, the pH value of the first solution is 0.483.

[0072] Example 3 This embodiment provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the molar ratio of sulfuric acid to iron in pyrite slag in step S1, and the temperature of the acid leaching treatment. In this embodiment, 643.07g of 70% sulfuric acid and 857.24g of deionized water are added to the first reaction vessel and stirred until homogeneous to obtain a 30% sulfuric acid solution. Next, 408.55g of pyrite slag is added to the first reaction vessel and stirred until homogeneous, so that the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag is 1:0.75. Then, the internal temperature of the first reaction vessel is raised to 90°C, and after holding at this temperature for 4 hours, the solution is filtered to obtain the first solution. The remaining steps are the same as in Example 1 and will not be repeated here. In this embodiment, the pH value of the first solution is 0.181.

[0073] Example 4 This embodiment provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the pH value of the mixing system in step S3. In this embodiment, the pH value of the mixing system adjusted with ammonia is 3.3. The remaining steps are the same as in Example 1 and will not be repeated here. In this embodiment, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 1:1.

[0074] Example 5 This embodiment provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the pH value of the mixing system in step S3. In this embodiment, the pH value of the mixing system adjusted with ammonia is 3.0. The remaining steps are the same as in Example 1 and will not be repeated here. In this embodiment, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 1:1.

[0075] Example 6 This embodiment provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the molar ratio of iron to phosphorus in the mixed system in step S3. In this embodiment, the molar ratio of iron to phosphorus in the mixed system in the second reactor is 1.9:1. The remaining steps are the same as in Example 1 and will not be repeated here. In this embodiment, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 1:0.9.

[0076] Example 7 This embodiment provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the molar ratio of iron to phosphorus in the mixed system in step S3. In this embodiment, the molar ratio of iron to phosphorus in the mixed system in the second reactor is 2.1:1. The remaining steps are the same as in Example 1 and will not be repeated here. In this embodiment, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 1.1:1.

[0077] Example 8 This embodiment provides a method for preparing iron phosphate. Compared with Example 1, the only difference is the change in the molar ratio of phosphorus to iron in step S5. In this embodiment, 57.6g of wet-process phosphoric acid is added to the mixed slurry to make the molar ratio of phosphorus to iron in the system 1.05:1, and then the temperature is raised to 88°C for aging. The remaining steps are the same as in Example 1 and will not be repeated here.

[0078] Example 9 This embodiment provides a method for preparing iron phosphate. Compared with Example 1, the only difference is the change in the molar ratio of phosphorus to iron in step S5. In this embodiment, 63.1g of wet-process phosphoric acid is added to the mixed slurry to make the molar ratio of phosphorus to iron in the system 1.15:1, and then the temperature is raised to 88°C for aging. The remaining steps are the same as in Example 1 and will not be repeated here.

[0079] Comparative Example 1 This comparative example provides a method for preparing iron phosphate. Compared with Example 1, the only difference is the change in the molar ratio of sulfuric acid to iron in pyrite slag in step S1, and the temperature of the acid leaching treatment. In this comparative example, 535.71g of 70% sulfuric acid and 964.29g of deionized water were added to the first reaction vessel and stirred until homogeneous to obtain a 25% sulfuric acid solution. Next, 306.38g of pyrite slag was added to the first reaction vessel and stirred until homogeneous, so that the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag was 1:0.66. Then, the internal temperature of the first reaction vessel was raised to 90°C, and after holding at this temperature for 4 hours, the solution was filtered to obtain the first solution. The remaining steps are the same as in Example 1 and will not be repeated here. In this comparative example, the pH value of the first solution is -0.368.

[0080] Comparative Example 2 This comparative example provides a method for preparing iron phosphate. Compared with Example 1, the only difference is the change in the molar ratio of sulfuric acid to iron in pyrite slag in step S1, and the temperature of the acid leaching treatment. In this comparative example, 535.71g of 70% sulfuric acid and 401.78g of deionized water were added to the first reaction vessel and stirred until homogeneous to obtain a 45% sulfuric acid solution. Next, 612.76g of pyrite slag was added to the first reaction vessel and stirred until homogeneous, so that the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag was 1:1.32. Then, the internal temperature of the first reaction vessel was raised to 90°C, and after holding at this temperature for 4 hours, the solution was filtered to obtain the first solution. The remaining steps are the same as in Example 1 and will not be repeated here. In this comparative example, the pH value of the first solution is 0.63.

[0081] Comparative Example 3 This comparative example provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the pH value of the mixing system in step S3. In this example, the pH value of the mixing system adjusted with ammonia is 4.225. The remaining steps are the same as in Example 1 and will not be repeated here. In this comparative example, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 1:1.

[0082] Comparative Example 4 This comparative example provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the pH value of the mixed system in step S3. In this example, the pH value of the mixed system adjusted with ammonia is 2.25. The remaining steps are the same as in Example 1 and will not be repeated here. In this comparative example, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is less than 1:1. This is because the pH of the mixed system is low, which inhibits the formation of ferric hydroxide. This allows the iron element, which should have been converted into ferric hydroxide, to exist in ionic form in the mixture containing ferric hydroxide colloid and amorphous ferric phosphate, while the formation of amorphous ferric phosphate is unaffected.

[0083] Comparative Example 5 This comparative example provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the molar ratio of iron to phosphorus in the mixing system of step S3. In this comparative example, during the dropwise addition process, the molar ratio of iron to phosphorus in the mixing system in the second reaction vessel is 1.8:1. The remaining steps are the same as in Example 1 and will not be repeated here. In this comparative example, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 0.8:1.

[0084] Comparative Example 6 This comparative example provides a method for preparing ferric phosphate. Compared with Example 1, the only difference is the change in the molar ratio of iron to phosphorus in the mixing system during step S3. In this comparative example, during the dropwise addition process in step S3, the molar ratio of iron to phosphorus in the mixing system in the second reaction vessel is 2.2:1. The remaining steps are consistent with Example 1 and will not be repeated here. In this comparative example, the molar ratio of ferric hydroxide colloid and amorphous ferric phosphate is 1.2:1.

[0085] II. Testing Methods 1. SEM testing The iron phosphate prepared in each example and comparative example was detected by scanning electron microscopy, and the particle sizes of D10, D50 and D90 were measured, and the particle size distribution ((D90~D10) / D50) was calculated.

[0086] 2. Elemental Analysis The iron phosphate prepared in each example and comparative example was tested using an elemental analyzer, and the contents of impurities such as aluminum, copper, potassium, magnesium, lead, and zinc were recorded.

[0087] 3. Specific surface area test The specific surface area of ​​the iron phosphate prepared in each example and comparative example was determined by gas adsorption BET method, with reference to standard GB / T 19587~2017.

[0088] III. Analysis of Test Results for Each Embodiment and Comparative Example Figure 1 The SEM image of the iron phosphate prepared in Example 1 shows that the iron phosphate has a regular morphology, narrow particle size distribution, and contains numerous pores. The regular morphology indicates a stable crystal structure of the iron phosphate prepared in this application, which is beneficial for improving battery cycle stability and reducing local polarization; the narrow particle size distribution is beneficial for improving battery cycle life; and the porous structure is beneficial for increasing specific surface area, improving lithium-ion transport efficiency, and thus improving the battery's rate performance. Therefore, the morphological characteristics of the iron phosphate prepared in Example 1 of this application give it good electrochemical performance.

[0089] Figure 2, Figure 3 The SEM images of the iron phosphate prepared in Comparative Examples 3 and 5 are shown respectively. It can be seen that the iron phosphate has an irregular morphology, severe agglomeration, highly uneven particle size distribution, and no obvious pores. These morphological characteristics result in the electrochemical performance of the iron phosphate prepared in Comparative Examples 3 and 5 being far inferior to that of the iron phosphate prepared in Example 1.

[0090] Table 3. Components of ferric phosphate prepared in each example and comparative example. Table 4. Particle size and specific surface area of ​​ferric phosphate prepared in each example and comparative example. As shown in Table 3, the impurity content of the ferric phosphate prepared in Examples 1-9 is much lower than that in Comparative Examples 3 and 5, especially for impurities such as aluminum and potassium. This indicates that this application effectively reduces the introduction of metallic impurities by controlling the pH value and the molar ratio of iron to phosphorus in the mixed system, resulting in higher purity ferric phosphate. This is because controlling the pH value of the mixed system at 3.3 or below allows most FePO4 to selectively precipitate, while impurity ions (aluminum, copper, potassium, magnesium, lead, zinc) do not reach the precipitation pH and therefore will not be co-precipitated or adsorbed. However, when the pH value is greater than 3.3, impurity ions are more likely to co-precipitate, and Fe... 3+ Under these pH conditions, the product is easily hydrolyzed, resulting in a significant decrease in product purity.

[0091] Table 4 shows that although the iron phosphate prepared in Comparative Examples 1-2, 4, and 6 had lower impurity content, their large diameter and small specific surface area significantly affected their electrochemical performance. The iron phosphate prepared in Examples 1-9 had a diameter between 1.63 and 1.85 μm and a specific surface area between 9.96 and 10.24 μm. 2 The ratio of ferric phosphate to phosphorus in the mixture is between 1 / g, indicating that this application effectively improves the particle size uniformity of ferric phosphate and increases its specific surface area by controlling the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag, the pH value of the mixture, and the molar ratio of iron to phosphorus in the mixture. Specifically, the pH value of the mixture and the molar ratio of iron to phosphorus in the mixture significantly affect the molar ratio of ferric hydroxide colloid to amorphous ferric phosphate. The ferric hydroxide colloid has a limiting effect on the particle size and morphology of amorphous ferric phosphate, thereby preparing nanoscale ferric phosphate with small and uniform particle size and high specific surface area.

[0092] Furthermore, comparing Example 1 and Comparative Examples 1-2, it can be seen that controlling the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite slag is also beneficial to improving the yield of iron phosphate.

[0093] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing ferric phosphate, characterized in that, Includes the following steps: The pyrite cinder was subjected to acid leaching to obtain the first solution; An oxidizing agent is added to the first solution to obtain a second solution; The second solution is mixed with crude acid from phosphate rock and a pH adjuster, and the mixture is reacted to obtain a mixture containing ferric hydroxide colloid and amorphous ferric phosphate. The mixture containing ferric hydroxide colloid and amorphous ferric phosphate is subjected to slurry treatment to obtain a mixed slurry; The mixed slurry was subjected to aging and crystallization treatment, and then dried and calcined to obtain iron phosphate.

2. The method for preparing ferric phosphate according to claim 1, characterized in that, During the mixing of the second solution with the crude phosphate rock acid and the pH adjuster, the molar ratio of iron to phosphorus in the mixture is controlled to be (1.9~2.1):1, and the pH value is 3~3.3; and / or, The pH adjuster is at least one of ammonia water and sodium hydroxide; and / or, The reaction temperature is 50~60℃, and the reaction time is 50~70min.

3. The method for preparing ferric phosphate according to claim 1, characterized in that, In the mixture, the molar ratio of the ferric hydroxide colloid to the amorphous ferric phosphate is 1:(0.9~1.1).

4. The method for preparing ferric phosphate according to claim 1, characterized in that, The pyrite cinder is subjected to acid leaching treatment with a sulfuric acid solution, wherein the molar ratio of sulfuric acid in the sulfuric acid solution to iron in the pyrite cinder is 1:(0.75~1.2); and / or, The concentration of the sulfuric acid solution is 30%~40%; and / or, The pH value of the first solution is 0.15~0.5; and / or, The acid leaching treatment is performed at a temperature of 90~100℃ for 3~5 hours.

5. The method for preparing ferric phosphate according to claim 1, characterized in that, The step of adding the oxidant to the first solution includes: diluting the first solution to an iron content of 5.5-6%, and then adding the oxidant to the diluted first solution.

6. The method for preparing ferric phosphate according to claim 1, characterized in that, The molar ratio of the oxidant to the ferrous ions in the first solution is (0.75~0.85):1; and / or, The oxidant includes at least one of hydrogen peroxide, ozone, and ammonium persulfate.

7. The method for preparing ferric phosphate according to claim 1, characterized in that, The aging and crystallization treatment includes: mixing the mixed slurry with phosphoric acid, aging it at 80-90°C, and maintaining the temperature for 2-2.5 hours after the mixed slurry turns pinkish-white; wherein, In the system of the mixed slurry and the phosphoric acid, the molar ratio of phosphorus to iron is (1.05~1.15):

1.

8. The method for preparing ferric phosphate according to claim 1, characterized in that, Prior to the pulping process, the mixture is further subjected to rinsing until the conductivity of the rinsing solution is less than 5 mS / cm.

9. A type of iron phosphate, characterized in that, The ferric phosphate is prepared according to any one of claims 1 to 8.

10. The ferric phosphate according to claim 9, characterized in that, The average particle size of the iron phosphate is 3.75~4.65μm; The radial distance of the iron phosphate is 1.63~1.85; The specific surface area of ​​the iron phosphate is 9.96~10.18 m². 2 / g; The iron phosphate has an Al content ≤25.3ppm, a Cu content ≤8.66ppm, a K content ≤6.2ppm, a Mg content ≤5.6ppm, a Pb content ≤13.2ppm, and a Zn content ≤10.53ppm.

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