Method for recovering and preparing battery-grade ferric phosphate from ferric phosphate waste

Abstract

The application belongs to the field of resource recycling, and discloses a method for recycling iron phosphate waste to prepare battery-grade iron phosphate, which comprises the following steps: phosphoric acid leaching of iron phosphate waste, adjustment of pH of mixed powder of iron powder and iron-containing compound, removal of aluminum by fluorine, oxidation precipitation and the like. The obtained iron phosphate dihydrate precipitate is calcined to obtain battery-grade iron phosphate. The obtained mother liquor can be reused as a leaching agent after supplement of phosphoric acid. The above-mentioned recycling method avoids the introduction of impurity ions, the solution system can be recycled, the impurity removal process is simple and effective, the reagent cost and wastewater treatment cost are reduced, and the method has good industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the field of resource recovery and relates to a method for preparing battery-grade iron phosphate by recycling iron phosphate waste. Background Art

[0002] Lithium iron phosphate (LIFP) has become a highly promising cathode material for lithium-ion batteries due to its high theoretical capacity, low cost, non-toxicity, excellent charge-discharge reversibility, and high-temperature stability. LFP batteries hold a significant share of the lithium battery market, driven by the emerging new energy vehicle and energy storage industries. However, with the retirement of LFP batteries, the amount of spent LFP batteries has surged, making recycling LFP materials extremely important from both a resource and environmental perspective.

[0003] Lithium is the most valuable element in retired lithium iron phosphate batteries, and its recovery is crucial for improving the economic benefits of recycling these batteries. Existing technologies typically use oxidative leaching to selectively recover lithium from battery waste containing lithium iron phosphate. This process is mature and has been industrialized. However, the iron-phosphorus slag left after lithium extraction is currently difficult to process economically and can only be used as a building material supplement, resulting in a waste of resources.

[0004] Patent CN112520718A discloses a method for selectively recovering battery-grade iron phosphate from lithium-extraction residue acid leaching. This method involves leaching the waste lithium-extraction residue with an inorganic acid and then adding an alkaline precipitant to selectively precipitate the iron phosphate to obtain the target product. However, this method requires the consumption of acid and alkaline reagents in both the leaching and precipitation stages, and produces large amounts of saline wastewater, which is difficult to dispose of.

[0005] Patent CN114394582A discloses a method for regenerating ferric phosphate from ferrophosphorus slag after lithium extraction. This method involves alkaline aluminum removal, reduction roasting, and acid leaching, followed by co-precipitation to produce ferric phosphate. While this method reduces acid usage, the alkaline leaching and reduction roasting processes still require significant reagent and energy consumption, increasing costs.

[0006] Patent CN115196609A discloses a method for recovering iron phosphate from lithium iron phosphate extraction slag and its application. The method introduces sulfur or sulfide as a reducing agent, which improves the leaching rate of phosphorus and iron elements and inhibits the leaching of other impurity metals in the lithium iron phosphate extraction slag. However, the application does not mention the sulfur content in the iron phosphate product, and sulfur may also have adverse effects on the electrochemical properties of the lithium iron phosphate positive electrode material.

[0007] In summary, most of the existing technologies for recycling ferric phosphate waste to prepare ferric phosphate have problems such as large consumption of reagents such as acids and alkalis, and large discharge of washing water and salt-containing wastewater. Summary of the Invention

[0008] In view of the defects and shortcomings of the existing technology, the present invention provides a method for recycling iron phosphate waste to prepare battery-grade iron phosphate.

[0009] To achieve the above objectives, the present invention provides the following technical solutions.

[0010] In a first aspect, the present invention provides a method for recycling waste iron phosphate to prepare battery-grade iron phosphate, comprising the following steps:

[0011] (1) Leaching the iron phosphate waste with phosphoric acid and filtering to obtain solution A;

[0012] (2) adding iron powder and a mixed powder of an iron-containing compound to solution A to adjust the pH of the leachate, reacting, and filtering to obtain solution B;

[0013] (3) Add sodium fluoride to solution B, react, and filter to obtain solution C;

[0014] (4) adding hydrogen peroxide to solution C, reacting, filtering, and obtaining a dihydrated ferric phosphate precipitate and a mother liquor. The dihydrated ferric phosphate precipitate is calcined to obtain battery-grade ferric phosphate;

[0015] (5) The mother liquor is supplemented with phosphoric acid and returned to step (1) for recycling as a leaching agent.

[0016] Preferably, in step (1), the concentration of the phosphoric acid is 2-6 mol / L.

[0017] Preferably, in step (1), the liquid-to-solid ratio of the phosphoric acid and the ferric phosphate waste is 2-10 mL / g.

[0018] Preferably, in step (1), the leaching temperature is 25-75° C., and the leaching time is 30-180 min.

[0019] Preferably, in step (2), the pH value of solution A is adjusted to 1.5-1.8.

[0020] Preferably, in step (2), the mass ratio of the iron powder to the iron-containing compound powder in the mixed powder of the iron powder and the iron-containing compound is 1:0.5-2.

[0021] Preferably, in step (2), the iron-containing compound is one or more of ferric oxide, ferric hydroxide, ferrosoferric oxide, ferrous oxide, and ferrous hydroxide.

[0022] Preferably, in step (2), the mixed powder of the iron powder and the iron-containing compound is added to the solution A at a rate of 0.5-1 g / min·L.

[0023] Preferably, in step (3), the molar ratio of aluminum in the solution B to sodium in the sodium fluoride is 1:6-15.

[0024] More preferably, in step (3), the reaction temperature of the sodium fluoride and the solution B is 50-80° C.; and the reaction time is 30-60 min.

[0025] Preferably, in step (4), the molar ratio of oxygen in the hydrogen peroxide to divalent iron in the solution C is 1-2:1.

[0026] Preferably, in step (4), when hydrogen peroxide is added, the reaction temperature is 60°C and the reaction time is 15-60 min; then the temperature is raised to 90°C and the reaction time is 60-240 min.

[0027] Compared with the prior art, the present invention has the following obvious beneficial effects:

[0028] (1) Phosphoric acid is used as a leaching agent, and a mixed powder of iron powder and an iron-containing compound is used as a pH regulator. On the one hand, neither the leaching agent nor the pH regulator introduces any impurity ions, and the amount of washing water used in the product is greatly reduced; on the other hand, the presence of iron powder can deeply remove copper while adjusting the pH of the solution, and the iron-containing compound can adjust the pH of the solution without causing an oxidation-reduction reaction. The synergistic treatment of the two substances on the leachate can effectively improve the adaptability of the present invention to raw materials of different types and compositions;

[0029] (2) The precipitation mother liquor can be recycled, and the reagent cost and the cost of treating saline wastewater are greatly reduced. DETAILED DESCRIPTION

[0030] The present invention provides the following specific technical solutions.

[0031] In a first aspect, the present invention provides a method for recycling waste iron phosphate to prepare battery-grade iron phosphate, comprising the following steps:

[0032] (1) Leaching the iron phosphate waste with phosphoric acid and filtering to obtain solution A;

[0033] (2) adding iron powder and a mixed powder of an iron-containing compound to solution A to adjust the pH of the leachate, reacting, and filtering to obtain solution B;

[0034] (3) Add sodium fluoride to solution B, react, and filter to obtain solution C;

[0035] (4) adding hydrogen peroxide to solution C, reacting, filtering, and obtaining a dihydrated ferric phosphate precipitate and a mother liquor. The dihydrated ferric phosphate precipitate is calcined to obtain battery-grade ferric phosphate;

[0036] (5) The mother liquor is supplemented with phosphoric acid and returned to step (1) for recycling as a leaching agent.

[0037] The inventors have found that the prior art usually uses sodium hydroxide solution as a pH regulator to adjust the pH value of solution A, while the present application uses a mixed powder of iron powder and iron-containing compound as a pH regulator to adjust the pH value of solution A. In the first aspect, no impurity ions are introduced, the purity of the product is improved, and the amount of washing water is greatly reduced. In the second aspect, impurities such as copper can be removed by iron powder replacement. In the third aspect, the mother liquor can be recycled, and almost no salt-containing wastewater is discharged.

[0038] In the specific embodiment of the present application, in step (1), the concentration of the phosphoric acid is 2-6 mol / L.

[0039] In practical applications, the concentration of the phosphoric acid can be adjusted according to actual needs. In the specific embodiment of the present application, the concentration of the phosphoric acid can be 2 mol / L, 4 mol / L, or 6 mol / L.

[0040] In the specific embodiment of the present application, in step (1), the liquid-solid ratio of the phosphoric acid and the iron phosphate waste is 2-10 mL / g.

[0041] In practical applications, the solid-liquid ratio of the phosphoric acid and the iron phosphate waste can be adjusted according to actual needs. The liquid-solid ratio of the phosphoric acid and the iron phosphate waste can be 2 mL / g, 6 mL / g, or 10 mL / g.

[0042] Further preferably, in step (1), the leaching temperature is 25-75℃, and the leaching time is 30-180 min.

[0043] In practical applications, the leaching temperature and the leaching time can be adjusted according to actual needs. In the specific embodiment of the present application, the leaching temperature can be 25℃, 50℃, or 75℃; and the leaching time can be 30 min, 105 min, or 180 min.

[0044] In the specific embodiment of the present application, in step (2), the pH value is 1.5-1.8.

[0045] In practical applications, the pH in step (2) can be adjusted according to actual conditions. In the specific embodiment of the present application, the pH can be 1.5, 1.6, or 1.8.

[0046] In the specific embodiment of the present application, in step (2), the mass ratio of the iron powder in the mixed powder of iron powder and iron-containing compound to the iron-containing compound powder is 1:0.5-2.

[0047] In practical application, the mass ratio of the iron powder and the iron-containing compound can be adjusted according to actual conditions. The inventors have found through research that when the mass ratio of the iron powder and the iron-containing compound in the mixed powder of the iron powder and the iron-containing compound is 1:0.5-2, good pH adjustment effect and impurity removal effect are achieved in the treatment of leaching solutions of different types of raw materials.

[0048] In the specific embodiments of the present application, in step (2), the iron-containing compound is one or two or more of iron oxide, iron hydroxide, ferroferric oxide, ferrous oxide and ferrous hydroxide.

[0049] In the specific embodiments of the present application, the rate of adding the mixed powder of the iron powder and the iron-containing compound to the solution A is 0.5-1 g / min·L.

[0050] In practical application, in step (2), the rate of adding the mixed powder of the iron powder and the iron-containing compound can be adjusted according to actual conditions. In the specific embodiments of the present application, the rate of adding the mixed powder of the iron powder and the iron-containing compound to the solution A can be 0.5 g / min·L, 0.8 g / min·L or 1 g / min·L.

[0051] In the specific embodiments of the present application, in step (3), the molar ratio of aluminum in the solution B to sodium in the sodium fluoride is 1:6-15.

[0052] In practical application, the molar ratio of aluminum in the solution B to sodium in the sodium fluoride can be adjusted according to actual requirements. In order to sufficiently remove aluminum in the solution B, the molar ratio of aluminum in the solution B to sodium in the sodium fluoride is preferably 1:6-18. In the specific embodiments of the present application, the molar ratio of aluminum in the solution B to sodium in the sodium fluoride can be 1:6, 1:12 or 1:15.

[0053] Further preferably, in step (3), the reaction temperature of the sodium fluoride and the solution B is 50-80℃, and the reaction time is 30-60 min.

[0054] In practical application, the reaction temperature and the reaction time of the sodium fluoride and the solution B can be adjusted according to actual conditions. In the specific embodiments of the present application, the reaction temperature can be 50℃, 65℃ or 80℃.

[0055] In the specific embodiments of the present application, in step (4), the molar ratio of oxygen in the hydrogen peroxide to divalent iron in the solution C is 1-2:1.

[0056] In actual application, the molar ratio of oxygen in hydrogen peroxide to the divalent iron in solution C can be adjusted according to actual needs. The inventors have found through research that when the molar ratio of oxygen in hydrogen peroxide to the divalent iron in solution C is 1-2:1, the divalent iron in solution C can be fully oxidized and the utilization rate of hydrogen peroxide is high.

[0057] In a specific embodiment of the present invention, in step (4), when hydrogen peroxide is added, the reaction temperature is 60°C and the reaction time is 15-60 min; then the temperature is raised to 90°C and the reaction time is 60-240 min.

[0058] In practical applications, the reaction temperature and reaction time in step (4) can be adjusted according to actual conditions. In a specific embodiment of the present invention, the reaction temperature can be 80°C, 90°C, or 100°C; and the reaction time can be 90 min, 120 min, or 150 min.

[0059] In order to make the technical problems, technical solutions and technical advantages to be solved by the present invention clearer, they will be described in detail below with reference to specific examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0060] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0061] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0062] Example 1:

[0063] A method for recycling iron phosphate waste to prepare battery-grade iron phosphate comprises the following steps:

[0064] (1) 100 g of ferric phosphate waste was leached with 600 ml of 4 mol / L phosphoric acid at 50 °C for 105 min and filtered to obtain solution A. The composition of the ferric phosphate waste was 55.56% C, 15.92% Fe, 8.81% P, 0.59% Al, and 0.35% Cu. The leaching rate of Al in solution A was approximately 83%.

[0065] (2) Mix 4.5 g of iron powder and 4.5 g of iron oxide powder, add the mixed powder of iron powder and iron-containing compound to solution A at a rate of 0.8 g / min·L, adjust the pH value of the leachate to 1.6, filter, and obtain solution B;

[0066] (3) adding 8.4 g of sodium fluoride into solution B, and reacting at 65℃ for 45 min, and filtering to obtain solution C;

[0067] (4) adding 16.7 ml of 30% hydrogen peroxide into solution C dropwise, and reacting at 60℃ for 30 min, and then increasing the temperature to 90℃ for 120 min, and filtering to obtain iron phosphate dihydrate precipitate and mother liquor, and the mother liquor is returned to step (1) after being supplemented with phosphoric acid as leaching agent for recycling, and the iron phosphate dihydrate is calcined to obtain battery-grade iron phosphate, and the composition of the battery-grade iron phosphate is: 36.3% Fe, 20.4% P, 0.01% Al, and 0.001% Cu.

[0068] Example 2:

[0069] A method for recycling and preparing battery-grade iron phosphate from iron phosphate waste, comprising the following steps:

[0070] (1) 100 g of iron phosphate waste is leached with 200 ml of 2 mol / L phosphoric acid, and the leaching is carried out at 25℃ for 30 min, and filtering to obtain solution A. The composition of the iron phosphate waste is: 6.25% C, 31.9% Fe, 18.4% P, 0.1% Al, and 0.12% Cu, and the leaching rate of Al in solution A is about 30%.

[0071] (2) mixing 3.9 g of iron powder and 1.95 g of iron hydroxide powder, and adding the mixed powder of iron powder and iron-containing compound into solution A at a rate of 0.5 g / min·L, and adjusting the pH value of the leaching solution to 1.5, and filtering to obtain solution B;

[0072] (3) adding 0.28 g of sodium fluoride into solution B, and reacting at 50℃ for 30 min, and filtering to obtain solution C;

[0073] (4) adding 9.6 ml of 30% hydrogen peroxide into solution C dropwise, and reacting at 60℃ for 15 min, and then increasing the temperature to 90℃ for 60 min, and filtering to obtain iron phosphate dihydrate precipitate and mother liquor, and the mother liquor is returned to step (1) after being supplemented with phosphoric acid as leaching agent for recycling, and the iron phosphate dihydrate is calcined to obtain battery-grade iron phosphate, and the composition of the battery-grade iron phosphate is: 36.0% Fe, 20.5% P, 0.02% Al, and 0.002% Cu.

[0074] Example 3:

[0075] A method for recycling and preparing battery-grade iron phosphate from iron phosphate waste, comprising the following steps:

[0076] (1) 100 g of ferric phosphate waste was leached with 1000 ml of 6 mol / L phosphoric acid at 75°C for 180 min and filtered to obtain solution A. The composition of the ferric phosphate waste was 55.56% C, 15.92% Fe, 8.81% P, 0.59% Al, and 0.35% Cu. The leaching rate of Al in solution A was approximately 92%.

[0077] (2) Mix 6.4 g of iron powder and 12.8 g of ferroferric oxide powder to obtain a mixed powder of iron powder and an iron-containing compound, add the mixed powder of iron powder and an iron-containing compound to solution A at a rate of 1 g / min·L, adjust the pH value of the leaching solution to 1.5, filter, and obtain solution B;

[0078] (3) Add 12.6 g of sodium fluoride to solution B, react at 80°C for 60 min, and filter to obtain solution C;

[0079] (4) 31.6 ml of 30% by mass hydrogen peroxide was added dropwise to solution C. The mixture was reacted at 60°C for 60 min, then heated to 90°C for 240 min. The mixture was filtered to obtain a precipitate of ferric phosphate dihydrate and a mother liquor. The mother liquor was supplemented with phosphoric acid and returned to step (1) for recycling as a leaching agent. After calcining the ferric phosphate dihydrate, battery-grade ferric phosphate was obtained. The composition of the ferric phosphate dihydrate was 36.2% Fe and 20.7% P. Al and Cu elements were not detected.

[0080] In Examples 1 to 3, the method for determining the divalent iron in solution C is titration. The content of divalent iron in Example 1 is 20.25 g / L; the content of divalent iron in Example 2 is 52.65 g / L; and the content of divalent iron in Example 3 is 17.28 g / L.

[0081] Comparing the iron phosphate waste used in Examples 1 to 3 and the components of the battery-grade iron phosphate obtained, it can be seen that the recovery method proposed in the present invention can deeply remove copper.

[0082] The embodiments described above are only preferred specific implementation methods of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solutions and concepts of the present invention within the technical scope of the present invention, and they should be covered by the scope of protection of the present invention.

Claims

1. A method for recovering waste iron phosphate to prepare battery-grade iron phosphate, characterized in that: The following steps are involved: (1) using phosphoric acid to leach the iron phosphate waste, filtering, and obtaining a solution A; the concentration of the phosphoric acid is 2 to 6 mol / L; the liquid-to-solid ratio of the phosphoric acid to the iron phosphate waste is 2 to 10 mL / g; the leaching temperature is 25 to 75° C., and the leaching time is 30 to 180 min; (2) adding a mixed powder of iron powder and an iron-containing compound to solution A to adjust the pH of the leachate, reacting, filtering, and obtaining solution B; in step (2), adjusting the pH value of solution A to 1.5-1.8; the mass ratio of iron powder to iron-containing compound powder in the mixed powder of iron powder and iron-containing compound is 1:0.5-2; the iron-containing compound is one or more of iron oxide, iron hydroxide, ferrosoferric oxide, ferrous oxide, and ferrous hydroxide; and the rate of adding the mixed powder of iron powder and iron-containing compound to solution A is 0.5-1 g / min·L; (3) adding sodium fluoride to solution B, reacting, and filtering to obtain solution C; (4) adding hydrogen peroxide to solution C, reacting, filtering, and obtaining a dihydrated ferric phosphate precipitate and a mother liquor. The dihydrated ferric phosphate precipitate is calcined to obtain battery-grade ferric phosphate; (5) The mother liquor is returned to step (1) after being supplemented with phosphoric acid and recycled as a leaching agent.

2. The method for preparing battery-grade iron phosphate from iron phosphate waste according to claim 1, wherein: In step (3), the molar ratio of the aluminum in the solution B to the sodium in the sodium fluoride is 1:6-15.

3. The method for preparing battery-grade iron phosphate from iron phosphate waste according to claim 1, wherein: In step (3), the reaction temperature of the sodium fluoride and the solution B is 50-80° C.; and the reaction time is 30-60 min.

4. The method for recovering waste iron phosphate to prepare battery-grade iron phosphate according to claim 1, wherein: In step (4), the molar ratio of oxygen in the hydrogen peroxide solution to the divalent iron ions in the solution C is 1 to 2:1.