CN117263153A

CN117263153A - Porous spherical ferric phosphate, preparation method thereof and metal phosphate

Info

Publication number: CN117263153A
Application number: CN202311321194.0A
Authority: CN
Inventors: 李玉云; 何绪锋; 木宗云; 赵鹏; 曾旭; 曾永详; 张海艳; 胡志兵; 胡海诗
Original assignee: Hunan Changyuan Lico Co Ltd; Jinchi Energy Materials Co Ltd
Current assignee: Hunan Changyuan Lico Co Ltd; Jinchi Energy Materials Co Ltd
Priority date: 2023-10-12
Filing date: 2023-10-12
Publication date: 2023-12-22

Abstract

The invention provides porous spherical ferric phosphate which is spherical or spheroidic secondary particles formed by the aggregation of primary particles, and the secondary particles are loose and porous and have higher specific surface area and tap density. Also provides a preparation method of the porous spherical ferric phosphate. When the ferric phosphate is used as a precursor to prepare the lithium metal phosphate positive electrode material, the porous and spherical morphology is beneficial to maintaining the qualified specific surface area and improving the tap density of the product, and the obtained positive electrode material has higher compaction density and tap density and good multiplying power performance and capacity.

Description

Porous spherical ferric phosphate, preparation method thereof and metal phosphate

Technical Field

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to porous spherical ferric phosphate, a preparation method thereof and metal phosphate.

Background

In recent years, battery manufacturers put higher and higher requirements on the compacted density of lithium iron phosphate batteries, and the compacted density needs to reach 2.6g/cm while meeting the capacity requirement ³ The compaction of the positive electrode material is influenced by the tap density of the precursor, and the tap density of the iron phosphate in the current market is mostly 0.7-1.0 g/cm ³ Between to achieve compaction of the positive electrode material of 2.6g/cm ³ The above has difficulty, and thus, it is required to increase the tap density of iron phosphate.

The patent application CN202210549125. X mentions a porous ferric phosphate and a preparation method thereof, the invention carries out parallel flow precipitation by an acid solution of the ferric phosphate and an aluminum alkali solution to generate a mixed precipitate of ferric phosphate, ferric hydroxide and aluminum hydroxide, then the phosphine generated by decomposing sodium hypophosphite reacts with the ferric hydroxide to generate ferric phosphide, finally aluminum is removed by dissolution under weak acid, and the porous ferric phosphate material is obtained after calcination. The process is complex, highly toxic phosphine gas participates in the reaction, industrial production is completely impossible, and the porous material is similar to spherical particles, and the spherical secondary particles have obvious differences.

Patent application CN201710387290.3 mentions a method for synthesizing a spheroid porous ferric phosphate precursor and a lithium iron phosphate positive electrode material, which comprises the steps of preparing micron-sized ferric phosphate precursor particles; continuously stirring, continuously growing a mixture of ferric phosphate and ferric hydroxide on the original micron-sized ferric phosphate precursor particles by controlling the pH value and the feeding rate of the reaction solution, and then dissolving the ferric hydroxide by reducing the pH value to generate the ferric phosphate precursor with a spheroid-like porous structure. The method adopts the scheme that micron-sized ferric phosphate precursor particles are prepared firstly in the synthesis stage, then particle growth is induced, and then the pH value is reduced, so that ferric hydroxide is dissolved out, and holes are formed. However, the process cannot ensure that all ferric hydroxide is dissolved, iron phosphate material iron-phosphorus ratio disorder is caused by the ferric hydroxide contained in particles, and in addition, phosphoric acid is added into mother liquor to dissolve ferric hydroxide, so that the ferric phosphate is synthesized by a one-step method, the impurity content of the synthesized ferric phosphate is high, the sphericity of the prepared ferric phosphate is poor, and the Tap Density (TD) is difficult to improve correspondingly.

Disclosure of Invention

Aiming at the technical problems, the invention provides a method for preparing high-tap-density core uniform porous spherical core-shell structure ferric phosphate by seed crystal induction.

To achieve the above object, the present invention proposes the following solution:

the invention provides a porous spherical ferric phosphate, which is spherical or spheroidic secondary particles formed by the aggregation of primary particles, wherein the secondary particles are loose and porous, the particle diameter D50 of the secondary particles is 1-30 mu m, and the specific surface area is 4-20 m ² Per gram, the tap density is 0.8-1.6 g/cm ³ 。

Preferably, the secondary particles comprise an inner core and an outer shell part positioned on the inner core, the inner core is a single-generation, twin-generation or multi-generation core, the inner core is composed of primary particles, and the outer shell part comprises the primary particles which are radially arranged on the inner core.

Preferably, the total diameter of the inner core accounts for 10% -90% of the total diameter of the secondary particles; the particle diameter D50 of the inner core is 0.1-15 mu m.

The present invention also provides a method for preparing porous spherical iron phosphate, comprising:

(1) Preparing clarified ferric phosphate seed crystal induction liquid by taking an iron source, a phosphorus source and an oxidant as raw materials, and heating and stirring the ferric phosphate seed crystal induction liquid for reaction to obtain seed crystal induction slurry;

(2) Adding ferric phosphate slurry into seed crystal induction slurry, performing crystal transformation reaction to obtain a reaction product I, and performing solid-liquid separation, washing, drying, calcination, water removal and screening on the reaction product I to obtain the porous spherical ferric phosphate material.

Preferably, in the step (1), the pH of the iron phosphate seed crystal inducing solution is 0.05 to 3; the pH value of the ferric phosphate seed crystal induction liquid is regulated and controlled by adding acid.

Preferably, the acid for regulating the pH value is one or more selected from the group consisting of permanganate, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and phosphoric acid.

Preferably, in the step (1), the concentration of iron ions in the iron phosphate seed crystal inducing solution is 0.5 to 3.0mol/L; mixing a phosphorus source and an iron source according to the mole ratio of phosphorus to iron of 1-5:1; and the oxidant and the iron source are mixed according to the molar ratio of 0-10:1.

Preferably, the iron source is one or more of ferrous sulfate, ferrous chloride, ferrous oxalate, iron oxide red, iron powder, ferric phosphate dihydrate and basic ferric phosphate.

Preferably, the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, monoammonium phosphate and ammonium phosphate.

Preferably, the oxidant is one or more of hydrogen peroxide, peracetic acid, oxygen and air.

Preferably, in the step (1), the preparation method of the iron phosphate seed crystal inducing solution comprises: adding an iron source and a phosphorus source into water, regulating the pH value to be 0.05-3, carrying out full mixing reaction to obtain seed crystal induction pre-liquid, and then introducing an oxidant into the seed crystal induction pre-liquid for oxidation to prepare the seed crystal induction liquid.

Preferably, in the step (2), the temperature of the crystal transformation reaction is 70-95 ℃;

preferably, in the process of the crystal transformation reaction, controlling the solid content in the reaction kettle to be 50-400 g/L;

preferably, the adding time of the ferric phosphate slurry is 20-200 min;

preferably, the mass ratio of the theoretical iron phosphate amount in the seed crystal induction slurry to the iron phosphate in the iron phosphate slurry is 1:0.5-4.

Preferably, in the step (1), the reaction temperature of the heating and stirring reaction is 70-95 ℃; the stirring speed of the heating stirring reaction is 300-1000 r/min.

Preferably, in the step (1), the morphology of the seed particles in the seed crystal induction slurry is spherical or spheroidic; the grain diameter D50 of the seed crystal is 0.1-15 mu m.

Preferably, in step (2), the iron phosphate slurry is prepared by a method comprising the steps of: and (3) putting the ferric phosphate into a pulping device containing water for pulping to obtain uniformly dispersed ferric phosphate slurry.

Preferably, the temperature in the pulping equipment is 40-95 ℃, the solid content of the pulp is 50-500 g/L, and the pulping time is 1-6 h.

The present invention also provides a metal phosphate prepared by using the porous spherical ferric phosphate or the porous spherical ferric phosphate prepared by the preparation method as a raw material.

Compared with the prior art, the invention has the following beneficial effects:

1. the ferric phosphate provided by the invention is loose and porous, the tap density is higher, the specific surface area is higher, the secondary particles are spherical, when the ferric phosphate is used as a precursor to prepare the lithium metal phosphate positive electrode material, the porous and spherical morphology is beneficial to maintaining the qualified Specific Surface Area (SSA) and improving the Tap Density (TD) of the product at the same time, and the obtained positive electrode material has higher compaction density and tap density and good multiplying power performance and capacity.

2. The iron phosphate secondary particle comprises an inner core and an outer shell part positioned on the inner core, wherein the inner core is a single-generation, twin-generation or multi-generation core, the inner core is composed of primary particles, and the outer shell part comprises the primary particles which are radially arranged on the inner core; the secondary particles have one or more radial centers. The ferric phosphate with the structure is favorable for grinding and carbon coating of the positive electrode, and the prepared positive electrode product has high primary particle sphericity and compaction density, and further has better electrochemical performance.

3. According to the invention, the seed crystal induction slurry is prepared firstly, then the ferric phosphate slurry is introduced into the seed crystal slurry, the seed crystal induction process is adopted to prepare the ferric phosphate, the prepared ferric phosphate secondary particles are higher in agglomeration degree and agglomerate into a sphere, the inner core is solid and porous, the spherical morphology particles are generally piled up to have higher tap density, the spherical secondary particles have strong plasticity, and the porosity is favorable for lithium ion transmission and full immersion of electrolyte, so that the activation degree of the material is improved, and the compaction, rate capability and capacity are all improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 shows the morphology of iron phosphate prepared at various stages in example 1, wherein (a) is amorphous iron phosphate morphology; (b) the morphology of the ferric phosphate dihydrate obtained by crystal transformation; (c) calcining the de-crystallization water to obtain the appearance of the ferric phosphate; (d) the cross-sectional morphology of the iron phosphate obtained by calcining the de-crystallization water; and (e) the section morphology of the iron phosphate obtained after the particles are crushed.

FIG. 2 shows the morphology of iron phosphate and the resulting morphology of lithium iron phosphate prepared at various stages in example 2, wherein (a) is an amorphous morphology of iron phosphate; (b) the morphology of the ferric phosphate dihydrate obtained by crystal transformation; (c) calcining the de-crystallization water to obtain the appearance of the ferric phosphate; (d) the cross-sectional morphology of the iron phosphate obtained by calcining the de-crystallization water; and (e) the morphology of the obtained lithium iron phosphate.

FIG. 3 shows the morphology of iron phosphate prepared at various stages in example 3, wherein (a) is amorphous iron phosphate morphology; (b) the morphology of the ferric phosphate dihydrate obtained by crystal transformation; and (c) calcining the water for decrystallization to obtain the appearance of the ferric phosphate.

FIG. 4 shows the morphology of iron phosphate prepared at various stages in example 4, wherein (a) is amorphous iron phosphate morphology; (b) the morphology of the ferric phosphate dihydrate obtained by crystal transformation; and (c) calcining the water for decrystallization to obtain the appearance of the ferric phosphate.

FIG. 5 shows the morphology of iron phosphate prepared at various stages in example 5, wherein (a) is amorphous iron phosphate morphology; (b) the morphology of the ferric phosphate dihydrate obtained by crystal transformation; (c) calcining the de-crystallization water to obtain the appearance of the ferric phosphate; and (d) the section morphology of the ferric phosphate obtained by calcining the decrystallization water.

FIG. 6 shows the morphology of iron phosphate prepared at various stages in comparative example 1, wherein (a) is the morphology of amorphous iron phosphate; (b) the morphology of the ferric phosphate dihydrate obtained by crystal transformation; and (c) calcining the water for decrystallization to obtain the appearance of the ferric phosphate.

Detailed Description

The applicant finds that through a great deal of research, spherical or spheroidal crystal seed induction slurry is prepared firstly, then the iron phosphate slurry is introduced into the crystal seed induction slurry, crystal seed induced crystal transformation is carried out to prepare spherical or spheroidal iron phosphate, the introduced slurry is dissolved and recrystallized under the crystal seed induction slurry, and preferentially recrystallized on the surface of the crystal seed, the particles gradually grow into spherical or spheroidal, but not recrystallized on the surface of the iron phosphate in the introduced iron phosphate slurry, so that the recrystallized secondary particles cannot break and become hollow due to the dissolution of the particles, and loose porous iron phosphate with higher specific surface area and high tap density and the spherical or spheroidal secondary particles is obtained.

The present invention provides a porous spherical iron phosphate which is spherical or spheroid secondary particles agglomerated from primary particles, the secondary particles being porous and having a particle diameter D50 of 1 to 30 μm, more preferably 5 to 30 μm, for example 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, etc., and a specific surface area of 4 to 20 μm ² /g, e.g. 5m ² /g、6m ² /g、7m ² /g、8m ² /g、9m ² /g、10m ² /g、11m ² /g、12m ² /g、13m ² /g、14m ² /g、15m ² /g、16m ² /g、17m ² /g、18m ² /g、19m ² Per gram, etc., the tap density is 0.8-1.6 g/cm ³ For example 0.9g/cm ³ 、1g/cm ³ 、1.1m ² /g、1.2m ² /g、1.3m ² /g、1.4m ² /g、1.5m ² /g, etc.

In some preferred embodiments, the porous spherical iron phosphate comprises a secondary particle comprising an inner core and an outer shell portion on the inner core, the inner core being a mono-, twin-or multi-core, the inner core being composed of primary particles, the outer shell portion comprising primary particles radially arranged on the inner core, the secondary particles having one, two or more radial centers.

In some preferred embodiments, the total diameter of the inner core is 10% -90% of the total diameter of the secondary particles, the proportion of the core-shell is adjustable, preferably the proportion is 20% -80%, more preferably 30% -60%, such as 35%, 40%, 45%, 50%, 55%, 58%, etc., when the core is too small, the tap of the product is low, when the core is too large, the full immersion of the electrolyte is not favored, the cracks inside the particles are favored for the immersion of the electrolyte, and the particles are more easily broken when the breaking process is added. "diameter of the core" refers to the length between the two endpoints of the surface of the core furthest apart, and "total diameter of the core" refers to the sum of the diameters of the individual cores. The inner core is preferably a spherical or spheroid core.

The particle diameter D50 of the inner core is 0.1 to 15. Mu.m, for example, 1. Mu.m, 2. Mu.m, 3. Mu.m, 4. Mu.m, 5. Mu.m, 6. Mu.m, 7. Mu.m, 8. Mu.m, 9. Mu.m, 10. Mu.m, 11. Mu.m, 12. Mu.m, 13. Mu.m, 14. Mu.m, etc.

The primary particles of the inner core can be flaky or plate-shaped, loose and dense according to different conditions, and the corresponding shells can also be punctiform, flaky, plate-shaped and the like according to the conditions of the induced liquid. The porosity of the core may be less than or greater than the shell portion, or may be equal to the shell portion.

The invention also provides a preparation method of the porous spherical ferric phosphate, which comprises the following steps:

(1) Preparing ferric phosphate and water into uniformly dispersed ferric phosphate slurry;

(2) Taking an iron source, a phosphorus source and an oxidant as raw materials to prepare a clarified ferric phosphate seed crystal induction solution;

(3) Heating and stirring the ferric phosphate seed crystal induction liquid in a reaction kettle to react, and preparing seed crystals to obtain seed crystal induction slurry; by heating in the reaction vessel, the solubility of the iron phosphate containing hydrogen ions gradually decreases (e.g., fe (H) ₂ PO ₄ ) ²⁺ 、FeH ₃ (PO ₄ ) ₂ 、FeH ₅ (PO ₄ ) ₂ ²⁺ 、 Fe(H ₂ PO ₄ ) ₃ 、FeH ₇ (PO ₄ ) ³⁺ ) Gradually losing hydrogen ions, and generating homogeneous precipitation, wherein the precipitation rate is relatively slow and is easy to form a sphere;

(4) Introducing the ferric phosphate slurry into seed crystal induction slurry to perform a crystal transformation reaction; the ferric phosphate in the ferric phosphate slurry is dissolved and then recrystallized on the surface of the seed crystal, and the crystallization reaction is to dissolve particles and then recrystallize, wherein the recrystallization preferentially occurs on the surface of a stable phase;

(5) After the crystal transformation reaction is finished, solid-liquid separation, washing, drying, calcination, crystallization water removal and screening are carried out, so that the high-tap-density core uniform porous spherical ferric phosphate material is obtained.

The seed crystal inducing liquid has the functions of inducing crystallization, promoting the formation of spherical or spheroidic ferric phosphate particles and improving the appearance and physical and chemical indexes of the product. The crystal form of the calcined product is ferric orthophosphate, and the crystal form of the crystal transformation product is ferric phosphate dihydrate.

In some preferred embodiments, in the step (2), the pH of the iron phosphate seed induction solution is 0.05 to 3, more preferably 0.05 to 2.0, still more preferably 0.1 to 2, such as 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, etc., and in the seeding reaction, as the seed induction solution is added to adjust the pH to between 0 and 3.0, an acid is generated, which results in a slow decrease in pH, and the lower pH is favorable for generating iron phosphate dihydrate crystals with a higher specific surface area, that is, the iron phosphate is dissolved by seeding and then recrystallized to form iron phosphate dihydrate crystals.

In some embodiments, in the step (2), the pH of the ferric phosphate seed crystal inducing solution may be controlled in a higher range, and when the pH is higher, the basic ferric phosphate with a smaller specific surface area than ferric phosphate dihydrate crystals is more advantageously produced during the crystal transformation reaction. The invention can be prepared into crystalline ferric phosphate dihydrate by regulating and controlling the pH, for example, by adding phosphoric acid. The present invention is more desirable to produce crystalline ferric phosphate dihydrate than crystalline basic ferric phosphate because of the higher specific surface area (Specific Surface Area, SSA) of the ferric phosphate dihydrate. It should be noted that, in some pH ranges, basic ferric phosphate may be formed, or ferric phosphate dihydrate and basic ferric phosphate coexist, but this does not affect the implementation of the present invention, but is more advantageous to increase the specific surface area when the crystal form after the crystal transformation is pure crystalline ferric phosphate dihydrate or crystalline ferric phosphate dihydrate with a higher ratio.

The pH value of the ferric phosphate seed crystal induction liquid is regulated by adding acid; the acid for adjusting the pH value is one or more of permanganate, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and phosphoric acid, and more preferably is phosphoric acid or a mixed acid of phosphoric acid and one or more selected from the group consisting of permanganate, hydrochloric acid, sulfuric acid, nitric acid and perchloric acid.

In a preferred embodiment, the concentration of iron ions in the seed crystal inducing solution is 0.5 to 3.0mol/L.

In some preferred embodiments, the phosphorus source and the iron source are dosed at a phosphorus to iron molar ratio of 1 to 5:1, e.g., 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc.

In some preferred embodiments, the molar ratio of the oxidizing agent to the iron source is 0 to 10:1, more preferably 0 to 3:1, a step of; when the iron source is ferrous iron, it is more preferably 1 to 3:1, for example 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, etc.

In some embodiments, the iron source is one or more of ferrous sulfate, ferrous chloride, ferrous oxalate, iron oxide red, iron powder, ferric phosphate dihydrate, and basic ferric phosphate;

the phosphorus source is one or more than two of phosphoric acid, diammonium hydrogen phosphate, monoammonium hydrogen phosphate and ammonium phosphate;

The oxidant is one or more than two of hydrogen peroxide, peracetic acid, oxygen and air.

In a part of preferred embodiments, in the step (2), the preparation method of the iron phosphate seed crystal inducing solution includes: adding an iron source and a phosphorus source into water, regulating the pH value to be 0.05-3, carrying out full mixing reaction to obtain seed crystal induction pre-liquid, and then introducing an oxidant into the seed crystal induction pre-liquid for oxidation to prepare the seed crystal induction liquid. The seed crystal induction liquid is a clear solution, and after oxidation, the iron element in the induction liquid is ferric iron. In some embodiments, the thorough mixing reaction may be carried out at a temperature of 20 to 55 ℃.

In a part of preferred embodiments, in the step (4), the temperature of the seeding reaction is 70 to 95 ℃, and the seeding reaction time is not particularly limited, as long as the seeding of the iron phosphate in the iron phosphate slurry can be completed.

In some preferred embodiments, in step (4), the solid content in the reaction vessel is controlled to be 50-400 g/L, for example, 100g/L, 150g/L, 200g/L, 250g/L, 300g/L, 350g/L, 400g/L, etc. during the crystal transformation reaction. The yield is low when the solid content is too low, and the seed crystal is easy to adsorb and agglomerate, so that the granularity of the prepared product is too large, and the tap density can reach 1.6g/cm ³ Above, but the specific surface area SSA will be lower, the solid content is too high, the slurry is more viscous, the rate of recrystallization on the surface of the recrystal seed is reduced, and the recrystalization on the surface of the novel crystal nucleus is favorable for forming novel crystal nucleus, and the particles formed by the recrystalization on the surface of the novel crystal nucleus are non-spherical, in the shape of flakes or flakes, and have poor sphericity.

In a part of preferred embodiments, in the step (4), the iron phosphate slurry is added for 20 to 200 minutes.

In some preferred embodiments, in step (4), the mass ratio of the theoretical iron phosphate in the seed induced slurry to the iron phosphate in the iron phosphate slurry is 1:0.5-4, such as 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc., wherein the theoretical iron phosphate in the seed induced slurry refers to the amount of iron phosphate that can be formed by complete reaction of the material in the seed induced slurry.

In a part of preferred embodiments, in the step (3), in the heating and stirring reaction, the temperature of the heat preservation is 70-95 ℃, such as 75 ℃, 80 ℃, 85 ℃, 90 ℃ and the like, and the reaction time is the same as that of the seed crystal with the target particle size; the stirring speed is 300 to 1000r/min, preferably 300 to 800r/min, for example 350r/min, 400r/min, 450r/min, 500r/min, 550r/min, 600r/min, 650r/min, 700r/min, 750r/min, etc. When the stirring speed is too low, the sphericity of the product is reduced, and too high the requirement on equipment is high and the running cost is high.

In some embodiments, in the step (3), the seed crystal inducing solution is used in an amount of 1/10 to 1/2 of the volume of the reaction vessel.

In a partially preferred embodiment, in step (3), the morphology of the particles of the seed crystal obtained is spherical or spheroidal; the grain diameter D50 of the seed crystal is 0.1-15 mu m.

In a partially preferred embodiment, in step (1), the iron phosphate slurry is prepared by a process comprising the steps of: throwing ferric phosphate into a pulping device containing water for pulping to obtain uniformly dispersed ferric phosphate slurry;

the temperature in the beating equipment is 40-95 ℃, such as 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃ and the like, the solid content of the slurry is 50-500 g/L, such as 100g/L, 150g/L, 200g/L, 250g/L, 300g/L, 350g/L, 400g/L, 450g/L and the like, and the beating time is 1-6 h, such as 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h and the like.

Preferred water includes deionized water, purified water, etc., in order to reduce the introduced impurities.

The specific operation methods and equipment of the solid-liquid separation, washing, drying and calcining to remove crystallization water and sieving are not particularly limited, and can be performed by methods and equipment known in the art, and the solid-liquid separation can be performed by a mother liquor treatment system in the iron phosphate production process disclosed in CN 216614296U, the washing can be performed by a method disclosed in CN109761208a, and the drying and calcining to remove crystallization water can be performed by a method disclosed in CN 111232945A.

In a part of preferred embodiments, in step (1), the iron phosphate is obtained by a continuous process, comprising:

(a) Preparing a soluble ferric salt solution A, a soluble phosphorus salt solution B or a soluble ferric salt and phosphorus salt mixed solution C; preparing a reaction kettle bottom solution;

(b) And (2) introducing the ferric salt solution A, the phosphorus salt solution B, pH regulator and the oxidant into the bottom solution of the reaction kettle, or introducing the mixed solution C, pH regulator and the oxidant into the bottom solution of the reaction kettle, controlling the pH value of the system to be 1-7, carrying out reaction, feeding the solution, discharging slurry, continuously carrying out the reaction, carrying out continuous production while feeding and discharging, and having no reaction time limit, stabilizing the particle size D50 of the slurry of the reaction system to be 1-20 mu m, collecting the slurry, and carrying out solid-liquid separation and washing to obtain the ferric phosphate.

The spherical or spheroidal amorphous ferric phosphate is synthesized by adopting a continuous method, the crystal transformation reaction of the amorphous ferric phosphate is quick, the productivity is improved, the cost is reduced, and the morphology is spherical amorphous ferric phosphate. It is worth noting that the present invention can also be used to prepare spherical or spheroidal amorphous iron phosphate by batch process, which does not affect the practice of the present invention, but is more efficient, higher productivity and lower cost by continuous process.

In some preferred embodiments, the iron phosphate is amorphous iron phosphate; the amorphous ferric phosphate is ferric phosphate dihydrate and/or basic ferric phosphate (NH) ₄ (Fe ₂ (PO ₄ ) ₂ OH.H ₂ O).H ₂ O), the morphology of amorphous ferric phosphate dihydrate or basic ferric phosphate does not substantially affect the morphology of crystalline ferric phosphate prepared by a seed crystal induction process, because the amorphous ferric phosphate is recrystallized after dissolution, and because the material contains higher sulfate radical, magnesium and other impuritiesAfter aging and dissolution, the content of recrystallized crystallized precipitated impurities can be further reduced.

In a part of preferred embodiments, in the step (b), the pH value of the bottom solution of the reaction kettle is 1.5-4.5; the temperature of the reaction kettle is controlled between 30 and 65 ℃.

In a part of preferred embodiments, in the step (b), the pH value of the system is controlled to be 1-7, and when the pH value is too high, the content of impurity ferric hydroxide is increased, and ferric hydroxide is precipitated. When the pH is too low, the iron ions are not easy to completely settle, resulting in loss. The pH of the continuous process must not be too low; the pH value directly affects the prepared ferric phosphate crystal form, and for example, amorphous ferric phosphate dihydrate or basic ferric phosphate; further preferably, the pH is 1.5 to 4.5, more preferably 1.8 to 3.5, for example 1.9, 2.0, 2.3, 2.5, 2.7, 3, 3.3, 3.5, etc.

In a part of preferred embodiments, in the step (a), preparing a soluble Fe salt solution A or an iron source of a mixed solution C of soluble Fe salt and phosphorus salt, wherein the iron source is one or more than two of ferrous sulfate, ferrous chloride, ferrous oxalate, ferric oxide red, iron powder, ferric phosphate dihydrate and basic ferric phosphate; in the Fe salt solution A or the mixed solution C, the concentration of Fe salt is 0.5-1.5 mol/L.

Preparing a soluble phosphorus salt solution B and a soluble Fe salt and phosphorus salt mixed solution C, wherein the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, monoammonium phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, calcium hydrogen phosphate, potassium dihydrogen phosphate and phosphorus slag; in the phosphorus salt solution B or the mixed solution C, the concentration of phosphate radical in the phosphorus salt solution is 0.5-3.0 mol/L.

When preparing the mixed solution C, the mixed solution C is preferably prepared according to the molar ratio of iron to phosphorus of 1:0.8-4.5;

the oxidant is one or more than two of hydrogen peroxide, peracetic acid, oxygen and air;

the pH regulator is one or more than two of ammonia water solution, alkali solution, urea solution, diammonium hydrogen phosphate solution, monoammonium phosphate solution, ammonium phosphate solution, disodium hydrogen phosphate solution, sodium dihydrogen phosphate solution and trisodium phosphate solution; the alkali is NaOH or KOH.

In a part of preferred embodiments, when a 100L reaction kettle is used as a reaction kettle for preparing the ferric phosphate slurry by a continuous method, if the Fe salt solution A, the phosphorus salt solution B, pH regulator and the oxidant are added into the 100L reaction kettle together in parallel, controlling the flow rate of the Fe salt solution to be 100-1500 ml/min, controlling the flow rate of the phosphorus salt solution according to a mode that the molar ratio of iron to phosphorus is 1:0.8-1.5 in unit time, controlling the pH in the feeding process to be 1.5-4.5, and controlling the molar number of the oxidant to be 1-2.4 times that of the Fe salt in unit time.

In a part of preferred embodiments, when a 100L reaction kettle is used as a reaction kettle for continuously preparing the ferric phosphate slurry, if a mixed solution C of Fe salt and phosphorus salt, a pH regulator and an oxidant are added into the 100L reaction kettle in parallel, the flow rate of the mixed solution of the ferric source and the phosphorus source is controlled to be 100-1500 ml/min, the pH in the feeding process is controlled to be 1.5-4.5, and when the ferric ions in the mixed solution C are divalent, the mole number of the oxidant fed into the reaction kettle in unit time is 1-2.4 times the mole number of the ferric ions. When the iron ions in the mixed solution C are ferric iron after oxidation treatment, the mole number of the oxidant fed into the reaction kettle in unit time is 0-1 times of the mole number of the iron ions.

In some embodiments, when preparing the ferric phosphate slurry, the reaction kettle is added with a reaction kettle bottom solution, the pH of the reaction kettle bottom solution is regulated to be 1.5-4.5, and the dosage of the reaction kettle bottom solution can be the dosage of the conventional ferric phosphate preparation process in the field.

In some embodiments, in the step (b), the slurry particle size D50 of the reaction system is stabilized at 1-20 μm, and the slurry is collected, subjected to solid-liquid separation and washing to obtain ferric phosphate; the ferric phosphate comprises amorphous ferric phosphate dihydrate or basic ferric phosphate filter cake;

and (3) stabilizing the granularity of the slurry of the reaction system at 1-20 mu m, collecting the slurry overflowed from an overflow port of the reaction kettle in a slurry tank, separating the material with qualified particle size from the material with unqualified particle size which is just fed in the slurry tank, taking the material with unqualified particle size as a waste pump for emptying, then receiving the material again, carrying out solid-liquid separation, and washing to obtain the amorphous ferric phosphate dihydrate or basic ferric phosphate filter cake.

In some embodiments, the porous spherical iron phosphate obtained may be subjected to a crushing treatment after calcining the de-crystallization water, and then sieved to crush the spherical particles into a smaller sized polyhedral iron phosphate material.

The solid-liquid separation can be carried out by adopting a filter press, mother liquor is collected and is recycled after standing for preparing phosphorus source solution. The intermittent washing method can be adopted for washing in three times, the washing process can be circulation washing, the loss of small particles is prevented, and the yield is increased.

The calcination temperature is preferably 450-650 ℃, the calcination temperature is too low, the generated phase is not ferric orthophosphate phase but phosphorus quartz phase, and when the calcination temperature is too high, the materials are difficult to grind, and SSA is lower.

The invention also provides a metal phosphate which is prepared by adopting the porous spherical ferric phosphate or the porous spherical ferric phosphate prepared by adopting the preparation method as a raw material, wherein the metal phosphate can be lithium metal phosphate, sodium metal phosphate and the like, for example, when only lithium iron phosphate/sodium is prepared, the porous spherical ferric phosphate is adopted to be mixed and roasted with a lithium/sodium source to obtain lithium iron phosphate/sodium, and when lithium manganese iron phosphate/sodium iron phosphate is prepared, the porous spherical ferric phosphate is adopted to be mixed and roasted with a manganese source and a lithium/sodium source to obtain the lithium iron phosphate/sodium iron phosphate; when the porous spherical ferric phosphate is used for preparing doped lithium iron phosphate/sodium or lithium manganese iron phosphate/sodium, the porous spherical ferric phosphate is obtained by mixing and roasting the porous spherical ferric phosphate with doping elements (including doping metal elements, non-metal cation elements, non-metal anion elements such as halogen and the like) and lithium/sodium sources (optionally adding manganese sources).

The invention will be described more fully hereinafter with reference to the accompanying drawings and preferred embodiments in order to facilitate an understanding of the invention, but the scope of the invention is not limited to the following specific embodiments.

In the examples described below, SSA represents the specific surface area; TD represents tap density.

SSA is detected by a specific surface tester, the model is BSD-BET400, and the manufacturer is Bei Shide instrument technology (Beijing) limited company;

the tap density is detected by a tap density meter, the model is BT-313, and the manufacturer is Dandong Baite instruments.

The uniformity of the pore distribution is judged by means of the profile shape cut by a three-ion beam cutting instrument, and the model of the three-ion beam cutting instrument manufacturer Leica is EM TIC 3X.

Example 1

(1) Preparing a 1mol/L ferrous sulfate solution A and a 2mol/L monoammonium phosphate solution B separately, adding the prepared ferrous sulfate solution A, monoammonium phosphate solution B, hydrogen peroxide and ammonia water into a 100L reaction kettle with a certain initial pH of 2.7 in parallel flow, controlling the pH of the feeding process to be 2.7, controlling the mole number of hydrogen peroxide fed into the reaction kettle in unit time to be 1.5 times that of ferrous sulfate, controlling the temperature of the reaction kettle to be 50 ℃, controlling the flow of the solution A to be 800ml/min, controlling the flow of the solution B to be 412ml/min, stirring and reacting to generate amorphous ferric phosphate, stabilizing the granularity D50 of slurry to 5 mu m, taking the material connected with a slurry tank as a good material, and carrying out solid-liquid separation and washing after the slurry tank is full of slurry to obtain an amorphous ferric phosphate filter cake.

(2) And (3) putting the amorphous ferric phosphate filter cake into a pulping kettle containing deionized water, wherein the internal temperature of the pulping kettle is 50 ℃, the solid content of the slurry is 300g/L, the pulping time is 2h, and uniformly dispersed slurry is obtained after pulping is finished for later use.

(3) Preparing an iron phosphate seed crystal induction solution at 50 ℃, wherein an iron source is ferric phosphate dihydrate, a phosphorus source is phosphoric acid, the seed crystal induction solution is a clear solution, the molar ratio of iron ions to phosphate ions in the seed crystal induction solution is 1:2, the concentration of iron ions in the seed crystal induction solution is 1.7mol/L, and the pH value of the seed crystal induction solution is adjusted to be 1.5 by utilizing hydrochloric acid;

adding the seed crystal induction liquid into an aging reaction kettle, controlling the rotating speed to be 500r/min, heating to 90 ℃, generating seed crystals, and reacting for a period of time until the granularity of the seed crystals is increased to 7 mu m.

(4) In order to control the granularity of the product to be between 20 and 25 mu m, pumping evenly dispersed slurry obtained by pulping into an ageing kettle containing seed crystals within 60min, wherein the mass ratio of the iron phosphate which can be theoretically generated by the seed crystal induction liquid to the iron phosphate in the slurry is 1:2, the solid content of the mixed seed crystals and slurry is 250g/L, and preserving the heat for 80min at 90 ℃ after the pumping is finished, so as to carry out crystal transformation reaction.

(5) Then discharging from the bottom of the aging kettle to a slurry tank, and then performing filter pressing, washing, drying, calcination and decrystallization water (the calcination temperature is 600 ℃ and the time is 4 hours) and screening treatment to obtain the high-tap-density core uniform porous spherical ferric phosphate material. Wherein. The amorphous ferric phosphate morphology does not substantially affect the morphology of the crystalline ferric phosphate prepared by the seed induction process.

Wherein, 5000 times SEM of amorphous iron phosphate prepared in example 1 is shown in FIG. 1 (a), 1000 times SEM of crystalline obtained iron phosphate dihydrate is shown in FIG. 1 (b), secondary particles are spherical or spheroidic, 5000 times SEM of iron phosphate after calcining and removing crystallization water is shown in FIG. 1 (c), porous spherical iron phosphate is obtained, spherical secondary particles formed by agglomerating primary particles are obtained, 4000 times cross-section SEM of calcined iron phosphate is shown in FIG. 1 (d), primary particles radially grow from the center of the secondary particles to the surface, porous spherical iron phosphate comprises an inner core and an outer shell part positioned on the inner core, the porosity of the inner core is smaller than that of the outer shell part, the particle size of the inner core is 7.0 μm, and 30000 times cross-section SEM of the crushed particles is shown in FIG. 1 (e). The main physical and chemical indexes of the product D50=21.1 μm, and TD=1.20 g/cm ³ ，SSA=11.9m ² And/g, the core accounts for 33.17% of the diameter. Main physical and chemical index d50=1.98 μm, td=1.25 g/cm of iron phosphate after particle crushing ³ ，SSA=12.3m ² And/g, the tap density of the product is higher, and the tap density and the specific surface area of the crushed particles are further improved.

Example 2

(1) Preparing 1mol/L ferrous sulfate solution A and 2mol/L monoammonium phosphate solution B separately, adding the prepared ferrous sulfate solution A, monoammonium phosphate solution B, hydrogen peroxide and ammonia water into a 100L reaction kettle with a certain initial pH value of 2.7 in parallel, wherein the mole number of the hydrogen peroxide fed into the reaction kettle in unit time is 1.5 times of the mole number of the ferrous sulfate, the temperature of the reaction kettle is controlled at 50 ℃, the flow rate of the solution A is 800mL/min, the flow rate of the solution B is 412mL/min, stirring and reacting, the pH value of a reaction system is controlled at 2.7 in the reaction process, amorphous ferric phosphate is generated, the granularity D50 of slurry is stabilized to 5 mu m, the material connected with a slurry tank is used as a good material, and after the slurry tank is full of slurry, solid-liquid separation and washing are carried out to obtain an amorphous ferric phosphate filter cake.

(2) And (3) putting the amorphous ferric phosphate filter cake into a pulping kettle containing deionized water, wherein the internal temperature of the pulping kettle is 50 ℃, the solid content of the slurry is 500g/L, the pulping time is 2h, and uniformly dispersed slurry is obtained after pulping is finished for later use.

(3) Preparing an iron phosphate seed crystal induction liquid at 50 ℃, wherein an iron source is ferrous sulfate, a phosphorus source is phosphoric acid, firstly preparing a ferrous sulfate solution, then mixing the ferrous sulfate with the phosphoric acid, adding hydrogen peroxide, wherein the molar addition amount of the hydrogen peroxide is 3 times of the molar number of ferrous ions, so as to obtain the iron phosphate seed crystal induction liquid, the seed crystal induction liquid is a clear solution, the molar ratio of iron ions to phosphate ions in the seed crystal induction liquid is 1:5, the concentration of the iron ions in the seed crystal induction liquid is 1.7mol/L, and the pH value of the seed crystal induction liquid is adjusted to be 1.0 by utilizing sulfuric acid;

adding the seed crystal induction liquid into an aging reaction kettle, controlling the rotating speed to be 800r/min, heating to 90 ℃, generating seed crystals, and reacting for a period of time until the granularity of the seed crystals is increased to 7 mu m.

(4) In order to control the granularity of the product to be between 15 and 20 mu m, pumping evenly dispersed slurry obtained by pulping into an ageing kettle containing seed crystals within 60min, wherein the mass ratio of the iron phosphate which can be theoretically generated by the seed crystal induction liquid to the iron phosphate in the slurry is 1:4, the solid content of the mixed seed crystals and slurry is 400g/L, and preserving the heat for 80min at 90 ℃ after the pumping is finished, so as to carry out crystal transformation reaction.

(5) Then discharging from the bottom of the aging kettle to a slurry tank, and then performing filter pressing, washing, drying, calcination and decrystallization water (the calcination temperature is 600 ℃ and the time is 4 hours) and screening treatment to obtain the high-tap-density core uniform porous spherical ferric phosphate material. Wherein, the amorphous ferric phosphate morphology does not substantially affect the morphology of the crystalline ferric phosphate prepared by the seed crystal induction process.

Iron phosphate, glucose (the dosage is 7% of the mass of the iron phosphate), lithium carbonate (the dosage is 0.52 times of the molar quantity of the iron phosphate) and additive nano titanium dioxide (the dosage is 1% of the molar quantity of the iron phosphate) are dispersed in water to form aqueous solution, grinding, spray drying and sintering (the sintering temperature is 790 ℃, the sintering time is 6h, and the sintering atmosphere is nitrogen), and the air current is crushed to prepare the lithium iron phosphate anode material.

The 5000-fold SEM of amorphous iron phosphate prepared in example 2 is shown in fig. 2 (a), the 1000-fold SEM of the post-crystal-conversion iron phosphate dihydrate prepared by aging is shown in fig. 2 (b), the secondary particles are spherical or spheroidic, the 5000-fold SEM of the iron phosphate after calcination and decrystallization water is shown in fig. 2 (c), it can be seen that porous spherical iron phosphate is obtained and is spherical secondary particles formed by aggregation of primary particles, the 5000-fold cross-section SEM of the calcined iron phosphate is shown in fig. 2 (d), the porous spherical iron phosphate is a twin sphere composed of two particle aggregates, a single particle aggregate comprises an inner core and an outer shell part located on the inner core, the porosity of the inner core is smaller than that of the outer shell part, the outer shell part comprises the primary particles radially arranged on the inner core, and the secondary particles have two radial centers; the individual core particle size was 6.7 μm. The main physical and chemical index D50 of the product is 16.32 mu m, and the TD is 1.13g/cm ³ SSA of 9.76m ² And/g. The total diameter of the two inner cores accounts for 62.5% of the total particle size, and the 50000 times SEM of the lithium iron phosphate prepared by the precursor is shown in FIG. 2 (e), and the primary particles of the positive electrode material also have higher sphericity.

Example 3

(1) Preparing 1mol/L ferrous sulfate solution A and 2mol/L monoammonium phosphate solution B separately, adding the prepared ferrous sulfate solution A, monoammonium phosphate solution B, hydrogen peroxide and ammonia water into a 100L reaction kettle with a certain initial pH value of 2.7 in parallel, wherein the mole number of the hydrogen peroxide fed into the reaction kettle in unit time is 1.5 times of the mole number of the ferrous sulfate, the temperature of the reaction kettle is controlled at 50 ℃, the flow rate of the solution A is 800ml/min, the flow rate of the solution B is 412ml/min, stirring and reacting, the pH value of a reaction system is controlled at 2.7 in the reaction process, amorphous ferric phosphate is generated, the granularity D50 of slurry is stabilized to 5 mu m, the material connected with a slurry tank is used as a good material, and after the slurry tank is full of slurry, solid-liquid separation and washing are carried out, so as to obtain an amorphous ferric phosphate filter cake.

(2) And (3) putting the amorphous ferric phosphate filter cake into a pulping kettle containing deionized water, wherein the internal temperature of the pulping kettle is 50 ℃, the solid content of the slurry is 100g/L, the pulping time is 2h, and uniformly dispersed slurry is obtained after pulping is finished for later use.

(3) Preparing an iron phosphate seed crystal induction solution at 50 ℃, wherein an iron source is ferric phosphate dihydrate, a phosphorus source is phosphoric acid, the seed crystal induction solution is a clear solution, the molar ratio of iron ions to phosphate ions in the seed crystal induction solution is 1:1.5, the concentration of iron ions in the seed crystal induction solution is 1.7mol/L, and the pH value of the seed crystal induction solution is adjusted to be 1.5 by utilizing hydrochloric acid;

adding the seed crystal induction liquid into an aging reaction kettle, controlling the rotating speed to be 300r/min, heating to 90 ℃, generating seed crystals, and reacting for a period of time until the granularity of the seed crystals is increased to 3 mu m.

(4) In order to control the granularity of the product to be between 5 and 10 mu m, pumping evenly dispersed slurry obtained by pulping into an ageing kettle containing seed crystals within 60min, wherein the mass ratio of the iron phosphate which can be theoretically generated by the seed crystal induction liquid to the iron phosphate in the slurry is 1:0.5, the solid content of the mixed seed crystals and slurry is 100g/L, and after the pumping is finished, preserving the temperature for 80min at 90 ℃ to carry out crystal transformation reaction.

The 5000-fold SEM of amorphous iron phosphate prepared in example 3 is shown in FIG. 3 (a), the 1000-fold SEM of crystalline iron phosphate dihydrate prepared by aging is shown in FIG. 3 (b), the secondary particles are spheroidic, and the 5000-fold SEM of iron phosphate after calcination of the de-crystallized water is shown in FIG. 3 (c). The main physical and chemical index D50 of the product is 6.96 mu m, and the TD is 1.51g/cm ³ SSA of 4.30m ² /g。

Example 4

This example differs from example 1 only in that step (1) is different, and the preparation of the iron phosphate filter cake by the discontinuous method specifically includes: (1) Preparing a 1mol/L ferrous sulfate solution A and a 2mol/L monoammonium phosphate solution B, pumping the prepared ferrous sulfate solution A into a 100L reaction kettle, wherein the volume of the solution A is 1/2 of that of the reaction kettle, the monoammonium phosphate solution B and hydrogen peroxide are added into the reaction kettle with the ferrous sulfate solution A in a parallel flow mode within 1 hour, the flow rate of the solution B is 428ml/min, the flow rate of the hydrogen peroxide is 112ml/min, the mole number of the hydrogen peroxide is 2.4 times that of the ferrous sulfate, the pH is not controlled in the whole process, the temperature of the reaction kettle is controlled at 50 ℃, the monoammonium phosphate solution B and the hydrogen peroxide are continuously stirred and kept for 1h after the parallel flow of the feed is finished, and then slurry in the reaction kettle is put into a slurry tank, pumped into a centrifugal machine for solid-liquid separation and washing, so that an amorphous ferric phosphate filter cake is obtained. Other steps were consistent with example 1.

adding the seed crystal induction liquid into an aging reaction kettle, controlling the rotating speed to be 500r/min, heating to 90 ℃, generating seed crystals, and reacting for a period of time until the granularity of the seed crystals is increased to 2 mu m.

(4) In order to control the granularity of the product to be between 5 and 10 mu m, pumping evenly dispersed slurry obtained by pulping into an ageing kettle containing seed crystals within 60min, wherein the mass ratio of the iron phosphate which can be theoretically generated by the seed crystal induction liquid to the iron phosphate in the slurry is 1:2, the solid content of the mixed seed crystals and slurry is 250g/L, and preserving the heat for 80min at 90 ℃ after the pumping is finished, so as to carry out crystal transformation reaction.

(5) Then discharging from the bottom of the aging kettle to a slurry tank, and then performing filter pressing, washing, drying, calcination and decrystallization water (the calcination temperature is 600 ℃ and the time is 4 hours) and screening treatment to obtain the high-tap-density core uniform porous sphere-like ferric phosphate material. Wherein, the amorphous ferric phosphate morphology does not substantially affect the morphology of the crystalline ferric phosphate prepared by the seed crystal induction process.

The 5000-fold SEM of amorphous iron phosphate prepared in example 4 is shown in FIG. 4 (a), the 1000-fold SEM of crystalline iron phosphate dihydrate prepared by aging is shown in FIG. 4 (b), the secondary particles are spheroidic, and the 5000-fold SEM of iron phosphate after calcination to remove the crystal water is shown in FIG. 4 (c). The main physical and chemical index D50 of the product is 8.32 mu m, and the TD is 1.33g/cm ³ SSA of 4.70m ² /g。

Example 5

The difference between this embodiment and embodiment 2 is that step (1) is different, specifically including: preparing 1mol/L ferrous sulfate solution A and 2mol/L monoammonium phosphate solution B separately, adding the prepared ferrous sulfate solution A, monoammonium phosphate solution B, hydrogen peroxide and ammonia water together in a 100L reaction kettle with a certain base solution with initial pH of 6.0 (the base solution is prepared by ammonia water, water and phosphoric acid), wherein the mole number of the hydrogen peroxide fed into the reaction kettle in unit time is 2 times of that of the ferrous sulfate, the temperature of the reaction kettle is controlled at 50 ℃, the flow rate of the solution A is 800ml/min, the flow rate of the solution B is 412ml/min, stirring and reacting, the pH of a reaction system is controlled at 2.7 in the reaction process, amorphous basic ferric phosphate is generated, the slurry granularity D50 is stabilized to 4 mu m, the material connected with a slurry tank is used as a good material, and after the slurry tank is connected with slurry, solid-liquid separation and washing are carried out, so as to obtain an amorphous ferric phosphate filter cake. Other steps were consistent with example 2.

The amorphous basic ferric phosphate prepared in example 5 was 5000 times SEM as shown in FIG. 5 (a), the crystalline ferric phosphate dihydrate prepared by aging was 1000 times SEM as shown in FIG. 5 (b), the secondary particles were spherical, and the amorphous basic ferric phosphate obtained by calcining and removing the crystalline water was 5000 times SEM as shown in FIG. 5 (c), and it was found that porous spherical ferric phosphate was obtained, as a result of growthThe morphology of the primary particles is different from that of example 2, the primary particles are spherical secondary particles formed by agglomeration, and as shown in an SEM (cross section) of 4000 times of calcined iron phosphate, as shown in FIG. 5 (d), the primary particles are radially grown from the center to the surface of the secondary particles, and the porous spherical iron phosphate comprises an inner core and an outer shell part positioned on the inner core, wherein the porosity of the inner core is smaller than that of the outer shell part, and the particle size of the inner core is 6.8 mu m. The main physical and chemical index D50 of the product is 21.3 mu m, and the TD is 1.32g/cm ³ SSA of 8.4m ² /g, core fraction 31.92%.

Comparative example 1

And (3) independently preparing a 1.2mol/L ferrous sulfate solution A and a 2mol/L monoammonium phosphate solution B, adding the prepared ferrous sulfate solution A, monoammonium phosphate solution B, ammonia water and hydrogen peroxide into a reaction kettle with a certain base solution in parallel, wherein the initial pH value is 4.0, and the mole number of the hydrogen peroxide fed into the reaction kettle per unit time is 1.5 times that of the ferrous sulfate. The temperature of the reaction kettle is controlled at 50 ℃, the flow rate of the solution A is 700ml/min, the flow rate of the solution B is 360ml/min, the reaction is carried out, the pH value of a reaction system is controlled to be 2.7 in the reaction process, amorphous ferric phosphate is generated, and the amorphous ferric phosphate filter cake is obtained through solid-liquid separation and washing.

And (3) putting the amorphous ferric phosphate dihydrate filter cake into a pulping kettle containing deionized water, wherein the internal temperature of the pulping kettle is 50 ℃, the solid content of the slurry is 350g/L, the pulping time is 2h, and uniformly dispersed slurry is obtained after pulping is finished for later use.

Pumping the slurry which is uniformly dispersed after pulping is finished into an aging reaction kettle, adding water and phosphoric acid, adjusting the solid content to 250g/L, adjusting the pH to 1.5, starting heating, controlling the rotating speed to 500r/min, heating to 95 ℃, preserving heat at the temperature of 95 ℃ for 90min, discharging the bottom of the aging kettle into a slurry tank, and then performing filter pressing, washing, drying, calcining and de-crystallizing water (the calcining temperature is 600 ℃ for 4 h) and screening treatment to obtain the iron phosphate material of which the secondary particles cannot be agglomerated into spheres or spheroids.

Comparative example 1 amorphous ferric phosphate dihydrate 5000 times SEM as shown in FIG. 6 (a), and ferric phosphate dihydrate 1000 times SEM after crystal transformation as shown in FIG. 6 (b), from the figureThe secondary particles of the resulting ferric phosphate dihydrate are seen to be broken open. The SEM of 5000 times of iron phosphate after calcination of the decrystallized water is shown in FIG. 6 (c). The main physical and chemical index d50=9.1 μm, and td=0.72 g/cm ³ ，SSA=4.5m ² And/g. The tap density of the product is lower.

The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims

1. A porous spherical ferric phosphate is characterized in that the porous spherical ferric phosphate is spherical or spheroidic secondary particles formed by the aggregation of primary particles, the secondary particles are loose and porous, the particle size D50 of the secondary particles is 1-30 mu m, and the specific surface area is 4-20 m ² Per gram, the tap density is 0.8-1.6 g/cm ³ 。

2. The porous spherical iron phosphate of claim 1, wherein the secondary particles comprise an inner core and an outer shell portion on the inner core, the inner core being a mono-, twinned-, or multi-core, the inner core being comprised of primary particles, the outer shell portion comprising primary particles radially arranged on the inner core;

preferably, the total diameter of the inner core accounts for 10% -90% of the total diameter of the secondary particles;

preferably, the particle diameter D50 of the inner core is 0.1-15 μm.

3. A method for preparing porous spherical ferric phosphate, which is characterized by comprising the following steps:

4. The method for producing porous spherical iron phosphate according to claim 3, wherein in the step (1), the pH of the iron phosphate seed crystal inducing solution is 0.05 to 3; the pH value of the ferric phosphate seed crystal induction liquid is regulated and controlled by adding acid;

preferably, the acid for regulating the pH value is one or more selected from the group consisting of permanganate, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and phosphoric acid;

preferably, in the step (1), the concentration of iron ions in the iron phosphate seed crystal induction solution is 0.5-3.0 mol/L; mixing a phosphorus source and an iron source according to the mole ratio of phosphorus to iron of 1-5:1; the oxidant and the iron source are mixed according to the mol ratio of 0-10:1;

preferably, the iron source is one or more than two of ferrous sulfate, ferrous chloride, ferrous oxalate, iron oxide red, iron powder, ferric phosphate dihydrate and basic ferric phosphate;

preferably, the phosphorus source is one or more than two of phosphoric acid, diammonium hydrogen phosphate, monoammonium phosphate and ammonium phosphate;

preferably, the oxidant is one or more than two of hydrogen peroxide, peracetic acid, oxygen and air.

5. The method of preparing porous spherical ferric phosphate according to claim 3 or 4, wherein in the step (1), the method of preparing the ferric phosphate seed crystal inducing solution comprises: adding an iron source and a phosphorus source into water, regulating the pH value to be 0.05-3, carrying out full mixing reaction to obtain seed crystal induction pre-liquid, and then introducing an oxidant into the seed crystal induction pre-liquid for oxidation to prepare the seed crystal induction liquid.

6. The method for preparing porous spherical ferric phosphate according to any one of claims 3 to 5, wherein in the step (2), the temperature of the crystal transformation reaction is 70 to 95 ℃;

preferably, the adding time of the ferric phosphate slurry is 20-200 min;

preferably, the mass ratio of the theoretical iron phosphate amount in the seed crystal induced slurry to the iron phosphate in the iron phosphate slurry is 1:0.5-4.

7. The method for producing porous spherical iron phosphate according to any one of claims 3 to 6, wherein in the step (1), the reaction temperature of the heating and stirring reaction is 70 to 95 ℃; the stirring speed of the heating stirring reaction is 300-1000 r/min.

8. The method for producing porous spherical iron phosphate according to any one of claims 3 to 6, wherein in step (1), the morphology of the seed particles in the seed crystal-induced slurry is spherical or spheroidal; the grain diameter D50 of the seed crystal is 0.1-15 mu m.

9. The method of producing porous spherical iron phosphate according to any one of claims 3 to 7, wherein in step (2), the iron phosphate slurry is produced by a method comprising the steps of: throwing ferric phosphate into a pulping device containing water for pulping to obtain uniformly dispersed ferric phosphate slurry;

10. A metal phosphate prepared by using the porous spherical iron phosphate according to claim 1 or 2 or the porous spherical iron phosphate prepared by the preparation method according to any one of claims 3 to 9 as a raw material.