CN115043383B - High-tap-density battery-grade iron phosphate and preparation method thereof - Google Patents

High-tap-density battery-grade iron phosphate and preparation method thereof Download PDF

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CN115043383B
CN115043383B CN202210977755.1A CN202210977755A CN115043383B CN 115043383 B CN115043383 B CN 115043383B CN 202210977755 A CN202210977755 A CN 202210977755A CN 115043383 B CN115043383 B CN 115043383B
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iron
acid
oxidant
ferric phosphate
phosphate
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CN115043383A (en
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孙留根
杨玮娇
张正阳
杨永强
韦其晋
程俊武
张胜梅
张逸飞
马鑫铭
张义
彭煜华
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BGRIMM Technology Group Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C01B25/375—Phosphates of heavy metals of iron
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/54—Reclaiming serviceable parts of waste accumulators
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/11—Powder tap density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/84—Recycling of batteries or fuel cells

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Abstract

The invention belongs to the technical field of waste battery recovery, and particularly relates to high-tap density battery grade iron phosphate and a preparation method thereof, wherein the method comprises the following steps: (1) mixing the raw material with an acid solution to carry out primary acid full-leaching; (2) purifying and removing impurities from the obtained primary full immersion liquid; (3) Carrying out acid dissolution on a first iron source and a first phosphorus source, adding a first oxidant, and controlling Fe2+Carrying out a first precipitation reaction to obtain dihydrate ferric phosphate seed crystals; (4) Adding a second phosphorus source and/or a second iron source into the purified liquid; adding ferric phosphate dihydrate seed crystals to obtain a mixed solution; (5) Adding a second oxidant into the mixed solution to control Fe2+Carrying out a second precipitation reaction at the oxidation speed and the stirring angular speed of the iron phosphate to obtain crude iron phosphate; (6) washing and aging; and (7) calcining. The method can realize the high-efficiency recovery of the waste lithium iron phosphate battery and simultaneously obtain the iron phosphate with high tap density.

Description

High-tap-density battery-grade iron phosphate and preparation method thereof
Technical Field
The invention belongs to the technical field of waste battery recovery, and particularly relates to high-tap-density battery-grade iron phosphate and a preparation method thereof.
Background
The advantages of long service life, high charge-discharge efficiency, low manufacturing cost, good safety and the like are achieved, so that LiFePO in the energy storage equipment4The demand for (LFP) type batteries has increased significantly. Lithium iron phosphate batteries are large in scale and can have negative environmental impact due to improper handling, which raises concerns about proper disposal after decommissioning. Therefore, recycling of waste LFP batteries is receiving much attention.
CN112573496A discloses a preparation method of a high tap density ferric phosphate material, comprising the following steps: s1, reacting a high-concentration iron source solution with a high-concentration phosphorus source solution to obtain iron phosphate seed crystals; and S2, slowly and uniformly adding the low-concentration iron source solution and the phosphorus source solution to realize the growth of iron phosphate crystals, thereby obtaining the iron phosphate material with high tap density. The method effectively separates the crystal seed reaction and the crystallization reaction of the ferric phosphate, and successfully prepares the spheroidal micron-sized ferric phosphate particles. The primary particles of the spheroidal large-particle ferric phosphate are tightly agglomerated, and the secondary particles show extremely high tap density (> 1.05 g/cm)3). However, in the method, high-concentration seed crystals are added into a low-concentration (0.1-1.0 mol/L) iron phosphorus solution, and in the recovery process of waste LFP batteries, because the recovery rate of lithium iron phosphorus needs to be improved as much as possible, the iron phosphorus solution needs to exceed 1mol/L, and the tap density of the iron phosphate prepared by the method is less than 0.7 g/cm3Therefore, the above patent technology has limitations in the waste battery recycling technology.
In summary, the technical difficulty in the art is how to recover iron and phosphorus at a higher iron and phosphorus concentration to obtain a high tap density iron phosphate product when recovering waste lithium iron phosphate batteries.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide the high-tap-density battery-grade iron phosphate and the preparation method thereof.
The research of the inventor of the invention finds that the prior related art synthesis of iron phosphate often has the following defects: because the crystal nucleus formation and growth process can not be effectively controlled, the prepared iron phosphate primary particles are more loose in agglomeration, and the secondary particles are in a random soft polymer body and show lower tap density (0.5-0.8 g/cm)3). Based on the above, the present invention is further provided.
In order to achieve the purpose, the invention provides a method for preparing iron phosphate from waste lithium iron phosphate batteries, which comprises the following steps of:
(1) Mixing the raw materials with an acid solution, performing primary acid full leaching, and filtering to obtain a primary full leaching solution and primary leaching residues; the raw materials comprise battery black powder;
(2) Purifying and removing impurities from the primary full immersion liquid, and filtering to obtain purified liquid and purified slag;
(3) Carrying out acid dissolution on a first iron source and a first phosphorus source, and then adding a first oxidant to control Fe2+The oxidation speed is 0.1-0.6mol/min, the stirring angular speed is 1800-4300rad/s during the period, after the first oxidant is added, a first precipitation reaction is carried out, and ferric phosphate dihydrate seed crystals are obtained;
(4) Adding a second phosphorus source and/or a second iron source into the purified liquid, wherein the molar concentrations of Fe and P in the purified liquid are 1-2mol/L respectively; then adding the ferric phosphate dihydrate seed crystal and mixing to obtain a mixed solution; wherein the addition amount of the ferric phosphate dihydrate seed crystals is 5-15% of the mass of the ferric phosphate dihydrate theoretically produced after the iron and phosphorus amount of the purified liquid is adjusted;
(5) Adding a second oxidant into the mixed solution to control Fe2+The oxidation speed of the reactor is 0.01-0.06mol/min, the stirring angular speed is 600-1500rad/s, after the second oxidant is added, a second precipitation reaction is carried out, and primary precipitation mother liquor and crude ferric phosphate are obtained by filtration;
(6) Washing and aging the crude ferric phosphate, filtering to obtain ferric phosphate dihydrate, and optionally using the obtained ferric phosphate dihydrate as a seed crystal in the step (3);
(7) And (4) calcining the ferric phosphate dihydrate obtained in the step (6) to obtain anhydrous ferric phosphate.
In some preferred embodiments, in step (1), the amount of the acid in the acid solution is 60-70% of the mass of the raw material, and the liquid-solid ratio is 2-4 mL/g.
In some preferred embodiments, the acid is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid.
In some preferred embodiments, the conditions of the primary acid full leach include: the temperature is 20-40 ℃, and the time is 1-3h.
In some preferred embodiments, in step (3), the acid-soluble conditions include: in the presence of sulfuric acid, adjusting the molar concentrations of Fe and P in the solution to be 1-1.5mol/L respectively by a first iron source and a first phosphorus source, and adjusting the molar ratio of Fe/P to be 1-1.05; and/or, the acid dissolution is carried out in a water bath, and the temperature of the water bath is 60-80 ℃.
In some preferred embodiments, the first oxidant in step (3) is added in an amount of 1 to 2 times the theoretical molar amount required for oxidizing ferrous iron in the solution after acid dissolution.
In some preferred embodiments, step (3) further comprises: during the addition of the first oxidant, the base is added to maintain the pH of the system at 1.6-2.0.
In some preferred embodiments, step (3) further comprises: and after the first precipitation reaction, washing, aging and filtering to obtain the ferric phosphate dihydrate seed crystal.
In some preferred embodiments, in the step (4), the second phosphorus source and/or the second iron source is added so that the molar ratio of Fe/P in the purification solution is adjusted to 1.
In some preferred embodiments, in the step (4), the iron phosphate dihydrate seed crystal is added in an amount which is 10-15% of the theoretical mass of the iron phosphate dihydrate produced after the iron and phosphorus amount of the purified liquid is adjusted.
In some preferred embodiments, in step (4), the time for mixing is 0 to 15min.
In some preferred embodiments, step (5) further comprises: during the addition of the second oxidant, a base is added to maintain the pH of the system at 1.6-2.0.
In some preferred embodiments, the amount of the second oxidant added in step (5) is 1 to 2 times the theoretical molar amount of the divalent iron oxide in the mixed solution.
In some preferred embodiments, the first and second iron sources each independently comprise at least one of ferrous sulfate, ferrous chloride, ferric sulfate, and ferric chloride, and the first and second phosphorus sources each independently comprise at least one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.
In some preferred embodiments, the first and second oxidizing agents are each independently hydrogen peroxide, SO2And O2Mixed gas of (3), SO2And air, and each independently satisfies: the dripping speed is 0.5-25mL/min when it is liquid, and 1-20m when it is gas3/h。
In some preferred embodiments, the conditions of the first and second precipitation reactions each independently comprise: the reaction temperature is 40-70 ℃, and the precipitation reaction time is 1-3h.
In a second aspect, the invention provides high tap density battery grade iron phosphate prepared by the method of the first aspect, wherein the tap density of the battery grade iron phosphate is more than or equal to 0.9g/cm3The specific surface area is 8-20m2/g。
According to the technical scheme, the iron phosphate with high tap density can be obtained by matching the specific ferric phosphate dihydrate seed crystal under the condition of the ferrophosphorus recovery liquid (namely the solution after the iron phosphorus is adjusted by the purification liquid) with high concentration of iron phosphorus (more than or equal to 1 mol/L). In particular, fe in the system, especially when preparing and synthesizing the product iron phosphate by controlling the seed crystal2+The oxidation speed and the appropriate seed crystal adding amount are controlled, the morphology of the seed crystal and the morphology of the final iron phosphate product can be cooperatively controlled, a product with high tap density is obtained, and the quality is improved. Wherein, inIn the preparation of the seed crystal, the oxidation speed of ferrous ions is emphatically controlled, the oxidation speed can effectively regulate and control the crystal nucleus formation and growth speed, and the iron phosphate crystal nucleus with uniform dispersion and fine crystal grains is obtained in an excellent mass transfer system. Adding seed crystals into the purified liquid, mixing, and then adding a second oxidant, so that the seed crystals are mixed and pre-oxidized for a certain time, and firstly, the seed crystals are dispersed more uniformly; secondly, under the oxidation action of air, iron phosphate begins to be formed at a slow speed, which plays an important role in inducing the crystal equilibrium to develop towards the growth direction of crystal nucleus; the shape and the tap density of the iron phosphate product are closely related to the number of crystal grains in unit volume, particularly the high-concentration iron-phosphorus solution, the appropriate number of crystal grains in unit volume in the initial solution is controlled, and spherical high-tap-density iron phosphate is obtained in the high-concentration iron-phosphorus solution by matching with the subsequent slower oxidation rate of ferrous ions and the stirring angular speed, so that the production efficiency is improved. The method can also directly use the spherical high-tap-density iron phosphate generated by induction as the seed crystal in the next cycle step without additional preparation.
The method can realize the efficient recovery of the waste lithium iron phosphate batteries, and has stable product quality indexes and strong practicability. The high-tap density iron phosphate product can be used for preparing a high-specific-capacity lithium iron phosphate battery, and has higher economic value.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a process flow diagram of the process of the present invention.
FIG. 2 (a) is a topographical electron micrograph of the product of example 1 of the present invention at 5000 times magnification;
FIG. 2 (b) is a topographical electron micrograph of the product of example 1 of the present invention at 10000 times magnification.
FIG. 3 (a) is a topographical electron micrograph of a product of example 2 of the present invention magnified 2000 times;
FIG. 3 (b) is a morphology electron micrograph of the product of example 2 of the present invention magnified 5000 times.
FIG. 4 (a) is a topographical electron micrograph of a product of example 3 of the present invention magnified 2000 times;
FIG. 4 (b) is a morphological electron micrograph of the product of example 3 of the present invention magnified 10000 times.
FIG. 5 (a) is an electron micrograph of comparative example 1 product of the present invention magnified 2000 times;
FIG. 5 (b) is an electron micrograph of the morphology of the comparative example 1 product of the present invention magnified 10000 times.
FIG. 6 (a) is a schematic SEM image of a product of comparative example 2 of the present invention at 2000 times magnification;
FIG. 6 (b) is an electron micrograph of the inventive comparative example 2 at 10000 times magnification.
FIG. 7 (a) is a schematic electron micrograph of a comparative example 3 of the present invention enlarged 5000 times;
FIG. 7 (b) is an electron micrograph of the inventive comparative example 3 at 20000 times magnification.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to give one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.
The invention provides a method for preparing iron phosphate by using waste lithium iron phosphate batteries, which comprises the following steps:
(1) Mixing the raw material and an acid solution, performing primary acid full immersion, and filtering to obtain primary full immersion liquid and primary leaching residues; the raw materials comprise battery black powder;
(2) Purifying and impurity removing are carried out on the primary full immersion liquid, and purified liquid and purified slag are obtained through filtering;
(3) Carrying out acid dissolution on a first iron source and a first phosphorus source, and then adding a first oxidant to control Fe2+The oxidation speed is 0.1-0.6mol/min, the stirring angular speed is 1800-4300rad/s in the period, after the first oxidant is added, the first precipitation reaction is carried out to obtain ferric phosphate dihydrate seed crystals;
(4) Adding a second phosphorus source and/or a second iron source into the purified liquid, wherein the molar concentrations of Fe and P in the purified liquid are respectively 1-2mol/L, preferably more than 1mol/L; then adding the ferric phosphate dihydrate seed crystal and mixing to obtain a mixed solution; wherein the addition amount of the ferric phosphate dihydrate seed crystals is 5-15% of the mass of the theoretically produced ferric phosphate dihydrate after the iron and phosphorus amount of the purified liquid is adjusted;
(5) Adding a second oxidant into the mixed solution to control Fe2+The oxidation speed of the reactor is 0.01-0.06mol/min, the stirring angular speed is 600-1500rad/s, after the second oxidant is added, a second precipitation reaction is carried out, and primary precipitation mother liquor and crude ferric phosphate are obtained by filtration;
(6) Washing and aging the crude ferric phosphate, filtering to obtain ferric phosphate dihydrate, and optionally using the obtained ferric phosphate dihydrate as a seed crystal in the step (3);
(7) And (4) calcining the ferric phosphate dihydrate obtained in the step (6) to obtain anhydrous ferric phosphate.
The raw material is battery black powder which can be obtained by sorting and pretreating waste lithium iron phosphate battery materials, and the sorting and pretreatment are not described herein again. The waste lithium iron phosphate battery material can be any one of a positive electrode material, a negative electrode material or a mixture of the positive electrode material, the negative electrode material and electrolyte, and can be used in the invention.
In some preferred embodiments, in step (1), the amount of the acid in the acid solution is 60 to 70% of the mass of the raw material, and the liquid-solid ratio is 2 to 4 mL/g.
In some preferred embodiments, the acid is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid.
In some preferred embodiments, the conditions of the primary acid full leach include: the temperature is 20-40 ℃ and the time is 1-3h.
The purification and impurity removal in the step (2) of the invention is used for removing impurities such as copper, aluminum, titanium and the like. The purification and impurity removal process preferably comprises the following steps: adding iron powder, the molar amount of which is 1.5-3 times of the molar amount of copper in the primary full immersion liquid, and adding alkali liquor to adjust the pH value of the system to 3-3.5.
In some preferred embodiments, in step (3), the acid-soluble conditions include: in the presence of sulfuric acid, the molar concentrations of Fe and P in the solution are respectively adjusted to be 1-1.5mol/L by a first iron source and a first phosphorus source, and the molar ratio of Fe/P is adjusted to be 1-1.05.
In some preferred embodiments, in step (3), the acid-soluble conditions further include: the acid dissolution is carried out in a water bath at a temperature of 60-80 ℃.
In the step (3), the first oxidant is added to control Fe2+The oxidation rate is 0.1 to 0.6mol/min, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6mol/min, etc., preferably 0.2 to 0.4mol/min; while the stirring angular velocity is 1800 to 4300rad/s, for example, 1800, 1900, 2000, 2200, 2400, 2600, 2800, 3000, 3300, 3500, 3700, 4000, 4200, 4300rad/s and the like can be used.
In the step (3), the addition amount of the first oxidant is 1-2 times of the theoretical molar amount of the ferrous oxide in the solution after the acid dissolution.
In some preferred embodiments, step (3) further comprises: during the addition of the first oxidizing agent, a base is added to maintain the pH of the system at 1.6-2.0.
Preferably, the base may be selected from at least one of sodium hydroxide, potassium hydroxide and ammonia, more preferably sodium hydroxide. The base may be introduced in the form of a base compound or an alkaline solution having a concentration of 2 to 5mol/L.
In some preferred embodiments, step (3) further comprises: and after the first precipitation reaction, washing, aging and filtering to obtain the ferric phosphate dihydrate seed crystal.
The person skilled in the art can select the above-mentioned washing and aging methods in the prior art according to the requirements. Preferably, the washing process comprises: washing with pure water, wherein the mass ratio of the pure water to the crude iron phosphate is 3-10. Preferably, the aging process comprises: adding phosphoric acid, wherein the adding amount of the phosphoric acid is 5-15% of the theoretical mass yield of the ferric phosphate dihydrate, the aging temperature is 70-90 ℃, and the aging time is 2-10h.
The dihydrate ferric phosphate seed crystal in the step (3) of the invention is directly used as the seed crystal in the step (4) without being dried.
In some preferred embodiments, in the step (4), the second phosphorus source and/or the second iron source is/are added so that the molar ratio of Fe/P in the purification solution is adjusted to 1 to 1.05.
In the step (4), after the second phosphorus source and/or the second iron source are/is added, the molar concentrations of Fe and P in the purified liquid are 1-2mol/L, preferably 1-1.5mol/L respectively. The method can obtain a solution with a proper iron-phosphorus ratio, and avoids the defect that the traditional process controls the molar concentration of Fe and P not to exceed 1mol/L, such as the tap density of the prepared iron phosphate is less than 0.7, and the shape of the prepared iron phosphate is irregular rod-shaped, sheet-shaped and the like.
In the step (4), ferric phosphate dihydrate seed crystals are added into the solution with a proper iron-phosphorus ratio obtained after the second phosphorus source and/or the second iron source are added, so that the battery-grade ferric phosphate with high tap density can be obtained. The addition amount of the ferric phosphate dihydrate seed crystals is 5-15% of the theoretical yield of the ferric phosphate dihydrate after the iron and phosphorus amount of the purified liquid is adjusted, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15% and the like, preferably 10-15%.
In some preferred embodiments, in step (4), the mixing time is 0 to 15min.
Adding a second oxidant into the mixed solution in the step (5) of the invention to control Fe2+The oxidation rate of (b) is 0.01 to 0.06mol/min, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06mol/min, etc., preferably 0.01 to 0.03mol/min, while the stirring angular velocity is controlled to 600 to 1500rad/s, for example, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500rad/s, preferably 600 to 1000 rad/s; not only creates favorable crystal nucleus growth environment, but also is favorable forDiffusion mass transfer between crystal grains and uniform particle size distribution.
In some preferred embodiments, step (5) further comprises: during the addition of the second oxidant, a base is added to maintain the pH of the system at 1.6-2.0.
In some preferred embodiments, the amount of the second oxidant added in step (5) is 1 to 2 times the theoretical molar amount of iron (ii) oxide in the mixed liquor.
In some preferred embodiments, the first and second iron sources each independently comprise at least one of ferrous sulfate, ferrous chloride, ferric sulfate, and ferric chloride, and the first and second phosphorus sources each independently comprise at least one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.
In some preferred embodiments, the first and second oxidizing agents are each independently hydrogen peroxide, SO2And O2Mixed gas of (3), SO2And air, and each independently satisfies: the dripping speed is 0.5-25mL/min when it is liquid, and 1-20m when it is gas3/h。
According to a preferred embodiment of the present invention, the dropping rate of the first oxidizing agent is 10 to 25mL/min when it is a liquid, and 10 to 20m when it is a gas3H; the dripping speed of the second oxidant is 0.5-10mL/min when the second oxidant is liquid, and the dripping speed of the second oxidant is 1-10m when the second oxidant is gas3/h。
In some preferred embodiments, the conditions of the first and second precipitation reactions each independently comprise: the reaction temperature (preferably the water bath temperature) is 40-70 ℃, and the precipitation reaction time is 1-3h.
The method of washing and aging described in step (6) can be selected by those skilled in the art according to the needs in the art. Preferably, the washing process comprises: washing with pure water, wherein the mass ratio of the pure water to the crude iron phosphate is 3-10. Preferably, the aging process comprises: adding phosphoric acid, wherein the adding amount of the phosphoric acid is 5-15% of the theoretical yield of the ferric phosphate dihydrate by mass, the aging temperature is 70-90 ℃, and the aging time is 2-10h. The ferric phosphate dihydrate obtained in the step (6) is spherical ferric phosphate dihydrate, and can be used as the seed crystal in the step (3) to induce and form the high-tap-density ferric phosphate.
The conditions for the calcination in step (7) can be selected by those skilled in the art according to requirements, for example, the calcination conditions may include: the temperature is 500-600 ℃, and the time is 2-5h.
In a second aspect, the invention provides high tap density battery grade iron phosphate prepared by the method of the first aspect, wherein the tap density of the battery grade iron phosphate is more than or equal to 0.9g/cm3The specific surface area is 8-20m2/g。
In a preferred embodiment of the present invention, the quality of the high tap density battery grade iron phosphate product of the present invention can meet the criteria as shown in table 1 below.
TABLE 1 quality parameters of battery grade anhydrous iron phosphate products
Item Unit of Standard of merit
Fe % 36.0-36.6
P % 20.5-21.1
Fe/P / 0.96-0.98
Ca % ≤ 0.0030
Mg % ≤ 0.0030
Na % ≤ 0.0030
Ni % ≤ 0.0020
Zn % ≤ 0.0020
Cu % ≤ 0.0010
Mn % ≤ 0.0090
Pb % ≤ 0.0030
Cr % ≤ 0.0040
Co % ≤ 0.0020
K % ≤ 0.0020
Al % ≤ 0.0060
Ti % ≤ 0.00 50
Mo % ≤ 0.0020
Cd % ≤ 0.0030
Magnetic foreign matter ppm ≤ 1000
S % ≤ 0.0400
Tap density g/cm 3 ≥ 1 .0
Specific surface area m 2 /g 8- 20
The present invention is further illustrated in detail below with reference to specific examples.
Example 1
A method for preparing high-tap-density battery-grade iron phosphate from mixed black powder of waste lithium iron phosphate batteries is shown in figure 1 and specifically comprises the following steps:
(1) Sorting and pretreating the mixture of the waste lithium iron phosphate anode material, the waste lithium iron phosphate cathode material and the electrolyte to obtain battery black powder, wherein the battery black powder is used as a subsequent leaching raw material;
fully leaching the battery black powder with sulfuric acid for the first time, wherein the addition of the sulfuric acid is 65% of the mass of the battery black powder, the liquid-solid ratio of a sulfuric acid solution to the battery black powder is 3 mL/g, the temperature is 25 ℃, and the time is 2.5 hours, so as to obtain a primary full-leaching solution and primary leaching residues;
adding iron powder and alkali liquor into the primary full immersion liquid, mixing and purifying for 6h, and removing impurities of copper, aluminum and titanium to obtain purified liquid; wherein the molar amount of the iron powder is 1.8 times of that of copper in the primary full immersion liquid, and alkali liquor is added to adjust the pH value of the system to 3.1.
(2) Preparing iron phosphate seed crystal: preparing iron-phosphorus solution in sulfuric acid system, where the iron source is ferrous sulfate and the phosphorus source is phosphoric acid. Dissolving an iron source and a phosphorus source in a sulfuric acid system by acid, adjusting the molar concentrations of Fe and P in the solution to be 1mol/L and 1mol/L respectively, adjusting the Fe/P molar ratio to be 1, the water bath temperature to be 60 ℃, the stirring angular velocity to be 2000rad/s, adding hydrogen peroxide (the mass concentration to be 30 percent), wherein the adding amount of the hydrogen peroxide in the hydrogen peroxide is 1.2 times of the theoretical molar amount of the ferrous oxide in the solution after acid dissolution, controlling the dropping speed to be 20mL/min, and controlling the Fe dropping speed to be 20mL/min2+The oxidation speed is 0.42mol/min, sodium hydroxide is added to keep the pH value at 1.8, and the precipitation time is 1h. Filtering to obtain crude iron phosphate; washing the crude ferric phosphate with pure water, wherein the mass ratio of the washing water to the crude ferric phosphate is 10; and adding phosphoric acid into the washed crude ferric phosphate for aging, wherein the adding amount of the phosphoric acid is 10 percent of the theoretical mass yield of the dihydrate ferric phosphate, the aging time is 6 hours, the aging temperature is 90 ℃, and the filtering is carried out to obtain dihydrate ferric phosphate seed crystals which can be directly used as the seed crystals without being dried.
(3) Adjusting the iron-phosphorus ratio of the purification liquid, and adding phosphoric acid according to the mixture ratio of Fe/P = 1.02 (molar ratio), wherein the concentration of Fe is 1.2 mol/L; and (3) then mixing the crystal seeds prepared in the step (2), wherein the adding amount of the crystal seeds is 5% of the mass of the dihydrate ferric phosphate theoretically produced after the iron and phosphorus amount of the purified liquid is adjusted, mixing for 15min to obtain a mixed liquid, and beginning to precipitate the ferric phosphate.
(4) The precipitation temperature is 60 ℃, and Fe oxide is slowly added2+Hydrogen peroxide with 1.2 times of the theoretical molar dosage is needed, the dropping speed is controlled to be 1.5mL/min, and Fe is strictly controlled2+The oxidation speed of the reactor is 0.02mol/min, the stirring angular speed is controlled at 800rad/s, 3mol/L sodium hydroxide solution is added to maintain the pH value at 2.0, and after the oxidant is added, the precipitation time is 2 hours. And filtering to obtain primary precipitation mother liquor and crude iron phosphate.
(5) Washing and aging the crude ferric phosphate, wherein the aging conditions are as follows: the adding mass of the phosphoric acid is 7 percent of the theoretical mass yield of the ferric phosphate dihydrate, the aging temperature is 85 ℃, and the aging time is 8 hours. Filtering to obtain the iron phosphate dihydrate, wherein a part of the induced spherical iron phosphate dihydrate can be reserved to be used as the seed crystal of the next circulation step (3).
(6) Calcining the dihydrate ferric phosphate in the step (5) at 550 ℃ for 3h to obtain the anhydrous battery grade ferric phosphate. The tap density of the powder is 0.92 g/cm3The morphology is as shown in FIG. 2 (a) and FIG. 2 (b), the specific surface area is 15.28m2/g。
Example 2
The procedure was carried out in accordance with example 1, except that in the step (2), the acceleration of the hydrogen peroxide droplets was controlled to 15mL/min, and Fe was controlled2+The oxidation rate was 0.25mol/min.
The tap density of the obtained anhydrous battery grade iron phosphate is 0.95 g/cm3The morphology is as shown in FIG. 3 (a) and FIG. 3 (b), and the specific surface area is 13.36m2/g。
Example 3
The method is carried out according to the method in the example 2, except that in the step (3), the seed crystal is added in an amount which is 10% of the mass of the dihydrate ferric phosphate after the iron and phosphorus amount of the purified liquid is adjusted.
The tap density of the obtained anhydrous battery grade iron phosphate is 1.06 g/cm3The morphology is as shown in FIG. 4 (a) and FIG. 4 (b), and the specific surface area is 12.77m2In terms of/g, which meets the quality parameter requirements indicated in Table 1 above.
Comparative example 1
The process of example 1 was followed, except that the step (2) was not performed, and no seed crystal was added in the step (3).
The tap density of the obtained anhydrous iron phosphate is 0.41 g/cm3The morphology is as shown in FIG. 5 (a) and FIG. 5 (b), and the specific surface area is 12.22m2/g。
Comparative example 2
The process of example 2 was followed, except that in step (3), the amount of seed crystals added was 3% of the theoretical mass of ferric phosphate dihydrate produced after adjusting the amount of iron and phosphorus in the purified solution.
The tap density of the obtained anhydrous iron phosphate is 0.60 g/cm3The morphology is as shown in FIGS. 6 (a) and 6 (b), and the specific surface area is 12.16m2/g。
Comparative example 3
The process was carried out by referring to example 2, except that in the step (4), hydrogen peroxide was added to control Fe2+The oxidation rate of (2) is 0.1mol/min, and the stirring angular velocity is controlled at 4000rad/s.
The tap density of the obtained anhydrous iron phosphate is 0.58 g/cm3The morphology is as shown in FIGS. 7 (a) and 7 (b), and the specific surface area is 11.54m2/g。
According to the embodiment and the comparative example, the proper oxidation speed and stirring angular speed are respectively controlled in the processes of preparing the seed crystal and precipitating the iron phosphate, and the proper addition amount of the seed crystal is matched with the step of mixing and inducing the seed crystal before the precipitation of the purified liquid, so that the high-efficiency recovery of the waste lithium iron phosphate battery can be cooperatively realized, and the iron phosphate with high tap density can be obtained. In the scheme of the comparative example, crystal seeds are not added or the addition amount of the crystal seeds is not appropriate, or the iron oxidation speed is not appropriate, so that the crystal growth process is not facilitated, and the tap density of the obtained product is in a lower level, the appearance is poor and irregular, and the requirements cannot be met.
Further, as can be seen from examples 1 and 2 to 3, the preferable seed crystal addition amount scheme or the preferable iron oxidation rate scheme of the present invention is more advantageous for promoting the generation of iron phosphate with high tap density.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including various technical features being combined in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (10)

1. A method for preparing iron phosphate from waste lithium iron phosphate batteries is characterized by comprising the following steps:
(1) Mixing the raw materials with an acid solution, performing primary acid full leaching, and filtering to obtain a primary full leaching solution and primary leaching residues; the raw material comprises battery black powder;
(2) Purifying and impurity removing are carried out on the primary full immersion liquid, and purified liquid and purified slag are obtained through filtering;
(3) Carrying out acid dissolution on a first iron source and a first phosphorus source, and then adding a first oxidant to control Fe2+The oxidation speed is 0.1-0.6mol/min, the stirring angular speed is 1800-4300rad/s during the period, after the first oxidant is added, a first precipitation reaction is carried out, and ferric phosphate dihydrate seed crystals are obtained;
(4) Adding a second phosphorus source and/or a second iron source into the purified liquid, wherein the molar concentrations of Fe and P in the purified liquid are 1-2mol/L respectively; then adding the ferric phosphate dihydrate seed crystal and mixing to obtain a mixed solution; wherein the addition amount of the ferric phosphate dihydrate seed crystals is 5-15% of the mass of the theoretically produced ferric phosphate dihydrate after the iron and phosphorus amount of the purified liquid is adjusted;
(5) Adding a second oxidant into the mixed solution to control Fe2+The oxidation speed of (2) is 0.01-0.06mol/min, the stirring angular speed is 600-1500rad/s, after the second oxidant is addedCarrying out a second precipitation reaction, and filtering to obtain primary precipitation mother liquor and crude ferric phosphate;
(6) Washing and aging the crude ferric phosphate, filtering to obtain ferric phosphate dihydrate, and optionally using the obtained ferric phosphate dihydrate as a seed crystal in the step (3);
(7) And (5) calcining the ferric phosphate dihydrate obtained in the step (6) to obtain anhydrous ferric phosphate.
2. The method according to claim 1, wherein in the step (1), the amount of the acid in the acid solution is 60-70% of the mass of the raw material, and the liquid-solid ratio is 2-4 mL/g;
and/or the acid is at least one selected from sulfuric acid, hydrochloric acid and phosphoric acid.
3. The method as claimed in claim 1, wherein the conditions of the primary acid full leaching include: the temperature is 20-40 ℃, and the time is 1-3h.
4. The method of claim 1,
in the step (3), the acid-soluble condition comprises: in the presence of sulfuric acid, adjusting the molar concentrations of Fe and P in the solution to be 1-1.5mol/L respectively by a first iron source and a first phosphorus source, and adjusting the molar ratio of Fe/P to be 1-1.05; and/or, the acid dissolution is carried out in a water bath, and the temperature of the water bath is 60-80 ℃.
5. The method of claim 1,
the step (3) further comprises: during the addition of the first oxidant, adding alkali to maintain the pH value of the system at 1.6-2.0;
and/or the addition amount of the first oxidant is 1-2 times of the theoretical molar amount of the ferrous oxide in the solution after the acid dissolution;
and/or, the step (3) further comprises: and after the first precipitation reaction, washing, aging and filtering to obtain the ferric phosphate dihydrate seed crystal.
6. The method of claim 1,
in the step (4), adding a second phosphorus source and/or a second iron source to adjust the molar ratio of Fe/P in the purified liquid to 1-1.05;
and/or in the step (4), the addition amount of the ferric phosphate dihydrate seed crystals is 10-15% of the mass of the theoretically produced ferric phosphate dihydrate after the iron and phosphorus amount of the purified liquid is adjusted;
and/or in the step (4), the mixing time is 0-15min.
7. The method of claim 1,
the step (5) further comprises: during the period of adding the second oxidant, adding alkali to maintain the pH value of the system at 1.6-2.0;
and/or the addition amount of the second oxidant in the step (5) is 1-2 times of the theoretical molar amount of the ferrous oxide in the mixed solution.
8. The method according to any one of claims 1 to 7,
the first iron source and the second iron source each independently comprise at least one of ferrous sulfate, ferrous chloride, ferric sulfate, and ferric chloride, and the first phosphorus source and the second phosphorus source each independently comprise at least one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate;
and/or the first oxidant and the second oxidant are respectively and independently hydrogen peroxide and SO2And O2Mixed gas of (3), SO2And air, and each independently satisfies: the dripping speed is 0.5-25mL/min when it is liquid, and 1-20m when it is gas3/h。
9. The method according to any one of claims 1 to 7, wherein the conditions of the first and second precipitation reactions each independently comprise: the reaction temperature is 40-70 ℃, and the precipitation reaction time is 1-3h.
10. High tap density battery grade iron phosphate, characterized in that it is prepared by a method according to any one of claims 1 to 9, said battery grade iron phosphate having a tap density of not less than 0.9g/cm3The specific surface area is 8-20m2/g。
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