A treatment method for recycling iron phosphate and iron phosphate

Abstract

The application relates to the technical field of iron phosphate waste regeneration, in particular to a treatment method for iron phosphate regeneration and utilization and iron phosphate. The treatment method comprises the following steps: step one, mixing a phosphoric acid solution and a hydrochloric acid solution to obtain mixed acid solution, putting iron phosphate waste into the mixed acid solution to obtain a first mixed solution, and removing impurities from the first mixed solution to obtain a first filtrate; step two, adding hydroxyl iron oxide slurry to the first filtrate, mixing and slushing to obtain a second mixed solution, the pH of the second mixed solution is 1-2, and the second mixed solution is filtered to obtain a second filtrate; step three, stirring the second filtrate and heating to 75-90 DEG C, precipitating a solid-liquid mixture containing iron phosphate dihydrate solid, filtering the solid-liquid mixture, separating the iron phosphate dihydrate solid and a third filtrate, washing and drying the iron phosphate dihydrate solid to obtain battery-grade iron phosphate, and recycling the third filtrate. The treatment method for iron phosphate regeneration and utilization can regenerate iron phosphate waste at low cost and high efficiency, and the obtained battery-grade iron phosphate has the advantages of high purity.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate waste recycling technology, specifically to a treatment method for the recycling of ferric phosphate and ferric phosphate itself. Background Technology

[0002] Iron phosphate (FePO4) is an important precursor for lithium iron phosphate (LFP) cathode materials. Its parameters, such as the iron-to-phosphorus ratio, particle size, specific surface area, and structural morphology, significantly influence the physicochemical and electrochemical performance of LFP batteries. Battery-grade FePO4 is particularly important when prepared by recycling waste FePO4.

[0003] During the preparation of lithium iron phosphate, factors such as personnel, machinery, materials, methods, environment, and testing can lead to the production of substandard lithium iron phosphate, known as lithium iron phosphate waste. This waste is characterized by abnormalities in impurity content, iron-to-phosphorus ratio, magnetic properties, morphology, and purity, making it unsuitable for lithium iron phosphate production. If this waste is disposed of as solid waste or landfill, it will be considered waste.

[0004] This leads to resource waste and loss. Therefore, the resource recycling and utilization of iron phosphate waste is of great significance for the healthy development of the industry and for improving ecological and economic benefits.

[0005] Chinese patent CN116002643 A discloses a method for regenerating ferric phosphate waste. The method involves mixing ferric phosphate waste with a phosphoric acid solution of 16-20% (mass concentration), reacting, filtering, and obtaining a filtrate. The filtrate is then mixed with water to obtain a mixed solution, which is reacted at 70-90°C, aged, and filtered again. The filtered material is then calcined to obtain regenerated ferric phosphate. This method uses a low-concentration phosphoric acid to dissolve the ferric phosphate waste, and then dilutes the solution with water to a pH of 1.0-1.2 and an iron content of 1.35-1.45%. This requires a large amount of water for dilution, generating a large amount of dilute acidic water that is difficult to treat. Furthermore, dissolving the ferric phosphate waste with phosphoric acid requires a sand mill, placing high demands on the equipment.

[0006] Chinese patent CN118702080 A discloses a method for recovering and preparing battery-grade iron phosphate from iron phosphate waste. The method includes processes such as leaching the iron phosphate waste with phosphoric acid, adjusting the pH of a mixture of iron powder and iron-containing compounds, removing aluminum with sodium fluoride, and oxidation precipitation. The resulting dihydrate iron phosphate precipitate, after calcination, yields battery-grade iron phosphate. The resulting mother liquor can be reused as a leaching agent after replenishment with phosphoric acid. However, this method suffers from a long process flow and introduces numerous impurity ions, making post-treatment of the washing water difficult.

[0007] Therefore, it is necessary to develop a treatment method for recycling ferric phosphate waste that is simple in process, low in cost, high in capacity, and produces high-purity and high-performance recycled ferric phosphate. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for recycling iron phosphate. This method can regenerate iron phosphate waste at low cost and high efficiency, and the resulting battery-grade iron phosphate has the advantage of high purity.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for recycling iron phosphate is provided, comprising the following steps:

[0011] Step 1: Mix phosphoric acid solution and hydrochloric acid solution to obtain mixed acid solution. Add ferric phosphate waste into the mixed acid solution to obtain a first mixed solution. Remove impurities from the first mixed solution to obtain a first filtrate.

[0012] Step 2: Add ferric hydroxide slurry to the first filtrate, mix and beat to obtain a second mixed solution with a pH of 1-2. Filter the second mixed solution to obtain a second filtrate.

[0013] Step 3: Stir the second filtrate and heat it to 75-90°C to precipitate a solid-liquid mixture containing ferric phosphate dihydrate. Filter the solid-liquid mixture to separate the ferric phosphate dihydrate solid and the third filtrate. The ferric phosphate dihydrate solid is washed and dried to obtain battery-grade ferric phosphate. The third filtrate is recycled.

[0014] In some embodiments, the phosphoric acid solution has a concentration of 60% to 85%, the hydrochloric acid solution has a concentration of 5% to 15%, and the mass ratio of the phosphoric acid solution to the hydrochloric acid solution is 2 to 5:1.

[0015] In some embodiments, the mixing and stirring speed of the iron phosphate waste and the mixed acid solution is 50 r / min to 300 r / min.

[0016] In some embodiments, the reaction time of the ferric phosphate waste and the mixed acid solution is 1 to 2 hours, and the reaction temperature is 70 to 90°C.

[0017] In some embodiments, the mass ratio of the mixed acid solution to the iron phosphate waste is 3 to 5:1.

[0018] In some embodiments, the ferric hydroxide slurry is obtained by mixing ferric hydroxide with water or dilute acid water, and the solids content of the ferric hydroxide slurry is 10% to 15%.

[0019] In some embodiments, the molar ratio of the added ferric hydroxide slurry to the ferric phosphorus in the first filtrate is 1.2 to 1.4:1.

[0020] In some embodiments, the reaction temperature of the ferric hydroxide slurry with the first filtrate is 50-70°C, the reaction stirring time is 0.5-2 h, and the Fe mass fraction of the second mixed solution is 4.5%-6.5%.

[0021] The time for the second filtrate to precipitate solid ferric phosphate dihydrate is 1 to 3 hours.

[0022] In some embodiments, the third filtrate is returned to the ferric hydroxide slurry of step two for pulping reaction or returned to the ferric phosphate waste dissolution reaction of step one.

[0023] The beneficial effects of the present invention's method for recycling iron phosphate are as follows:

[0024] (1) The method for recycling iron phosphate of the present invention first uses a mixed acid solution obtained by mixing phosphoric acid and hydrochloric acid to dissolve iron phosphate. The phosphoric acid in the mixed acid solution helps to improve the dissolution efficiency of iron phosphate. Since the solubility of iron phosphate in hydrochloric acid is higher than that of phosphoric acid, adding hydrochloric acid to phosphoric acid to dissolve iron phosphate effectively improves the dissolution efficiency, overcomes the problem of low efficiency when using phosphoric acid alone, and the hydrochloric acid in the mixed acid can be recycled in the future without the need to replenish the hydrochloric acid solution, without high cost and can be recycled. After the mixed acid solution fully dissolves the iron phosphate waste, an iron phosphate salt solution is obtained, which is filtered to remove its insoluble impurities and avoids reintroducing them into the regeneration process.

[0025] (2) The treatment method for the recycling of iron phosphate of the present invention uses mixed acid solution to dissolve waste iron phosphate. The first filtrate obtained is a highly acidic iron phosphate salt solution. The present invention uses iron hydroxyl oxide for neutralization reaction, which avoids the problem of needing a large amount of water to adjust the pH with water, and also avoids the problem of introducing a large amount of salt by using alkaline solution or ammonia water to neutralize the acidity. It effectively avoids the introduction of other impurity ions, and the impurities of the raw materials used are effectively controlled. In addition, the use of iron hydroxyl oxide for neutralization can quickly adjust the pH by simply adjusting the molar ratio of the raw materials, thereby improving production efficiency. Furthermore, the neutralization with iron hydroxyl oxide produces less salt and less impurity ions, resulting in less washing water, reducing the wastewater treatment load, saving energy and costs, and having good environmental benefits.

[0026] (3) The method for recycling iron phosphate of the present invention gradually precipitates solid iron phosphate dihydrate by controlling the temperature, which can better control the morphology and obtain a product with stable morphology, controllable particles and high tap density. After washing and drying, the iron phosphate solid is suitable for preparing high-voltage solid lithium iron phosphate batteries and has good electrical performance.

[0027] (4) The method for recycling iron phosphate of the present invention, compared with the traditional method for preparing iron phosphate, does not require the process of removing aluminum with sodium fluoride, oxidation precipitation or aging, which effectively shortens the production process, is highly efficient and suitable for large-scale production and application.

[0028] (5) The method for recycling iron phosphate of the present invention allows the mother liquor generated from the recycling of iron phosphate waste to be reused in the recycling production line for ferric hydroxide pulping; or for iron phosphate synthesis production line. It does not require separate processing steps and equipment, and has the advantages of being environmentally friendly and low-cost.

[0029] (6) The method for recycling iron phosphate of the present invention can be operated without expensive equipment, has low energy consumption cost, is easy to realize industrial production, and the recycled iron phosphate meets battery grade requirements and has good performance.

[0030] Also provided is ferric phosphate, obtained by the above-described method for the recycling of ferric phosphate. (See attached figures)

[0031] Figure 1 This is the XRD pattern of the regenerated anhydrous ferric phosphate obtained in Experiment Example 3.

[0032] Figure 2 This is a SEM image of the regenerated anhydrous ferric phosphate obtained in Experiment Example 3. Detailed Implementation

[0033] Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0034] Example

[0035] The method for recycling iron phosphate disclosed in this embodiment includes the following steps:

[0036] Step 1: Mix phosphoric acid and hydrochloric acid to obtain a mixed acid solution. Add the iron phosphate waste to the mixed acid solution to obtain a first mixed solution. Remove impurities from the first mixed solution to obtain a first filtrate.

[0037] Step 2: Add ferric hydroxide slurry to the first filtrate, mix and beat to obtain a second mixed solution with a pH of 1-2. Filter the second mixed solution to obtain a second filtrate.

[0038] Step 3: Stir the second filtrate and heat it to 75-90°C to precipitate a solid-liquid mixture containing ferric phosphate dihydrate. Filter the solid-liquid mixture to separate the ferric phosphate dihydrate solid and the third filtrate. The ferric phosphate dihydrate solid is washed and dried to obtain battery-grade ferric phosphate. The third filtrate is recycled.

[0039] The aforementioned method for recycling ferric phosphate involves dissolving it using a mixed acid solution of phosphoric acid and hydrochloric acid. The high concentration of phosphoric acid helps improve the dissolution efficiency of ferric phosphate, and the mixed acid method is more efficient than using phosphoric acid alone. Furthermore, ferric phosphate has a higher solubility in hydrochloric acid than in phosphoric acid. In other words, the ferric phosphate waste is initially dissolved using a mixed acid solution with a small amount of hydrochloric acid added; subsequent recycling does not require replenishing the hydrochloric acid solution.

[0040] After the mixed acid solution fully dissolves the ferric phosphate waste, a ferric phosphate salt solution is obtained. This solution is then filtered to remove insoluble impurities and prevent them from being reintroduced into the regeneration process.

[0041] The resulting ferric phosphate solution is highly acidic. If the pH is adjusted with water, a large amount of water is needed to reduce the acidity. If alkaline solution or ammonia is used, neutralizing the acidity will introduce a large amount of salt. Using ferric hydroxyl oxide avoids the introduction of other impurity ions. Ferric hydroxyl oxide has already controlled metallic impurities during the production process, and the impurities in the raw materials used in the process are effectively controlled.

[0042] The ferric hydroxide is first pulped to disperse the lumps of material coming out of the filter press. Then it is neutralized with a high-acidity ferric phosphate solution to generate ferric phosphate. The dispersed ferric hydroxide is more likely to react with the high-acidity ferric phosphate solution, thus increasing the reaction rate. Under the process conditions, ferric phosphate is first formed in solution, and the mass fraction of iron in the solution is relatively high (4.5%-6.5%).

[0043] Under the aforementioned conditions, iron phosphate dihydrate solid is gradually precipitated from solution under these conditions. The morphology can be well controlled, resulting in a product with stable morphology, controllable particle size, and high tap density. After washing and drying, the obtained solid iron phosphate is suitable for preparing high-voltage lithium iron phosphate batteries and exhibits good electrical performance. This step differs from conventional processes by eliminating the need for an aging process, thus improving efficiency.

[0044] This method uses ferric hydroxide to participate in the neutralization reaction, without using alkaline materials to adjust the pH. It produces less salt and fewer impurity ions, resulting in less wash water, reducing the wastewater treatment load, saving energy and costs, and having good environmental benefits.

[0045] The mother liquor generated from the recycling of ferric phosphate waste can be reused in the recycling production line for ferric hydroxide pulping; or used in the ferric phosphate synthesis production line, without the need for separate processes and equipment.

[0046] The process involves simple equipment, low energy consumption, and is easy to industrialize. The recycled iron phosphate produced meets battery-grade requirements and exhibits excellent performance.

[0047] In this embodiment, the concentration of the phosphoric acid solution in the mixed acid is 60% to 85%, preferably 70%, the concentration of the hydrochloric acid solution is 5% to 15%, preferably 10%, and the mass ratio of the phosphoric acid solution to the hydrochloric acid solution is 2 to 5:1, preferably 4:1.

[0048] The amount of hydrochloric acid used should not be too large to avoid excessive introduction of chloride ions.

[0049] In this embodiment, the mixing and stirring speed of the iron phosphate waste and the mixed acid solution is 50 r / min to 300 r / min, preferably 200 r / min.

[0050] In this embodiment, the mixing reaction time of the iron phosphate waste and the mixed acid solution is 1-2 hours, preferably 1.5 hours, and the reaction temperature is 70-90°C, preferably 80°C.

[0051] In this embodiment, the mass ratio of the mixed acid solution to the iron phosphate waste is 3 to 5:1, preferably 4:1.

[0052] In this embodiment, the ferric hydroxide slurry is obtained by mixing ferric hydroxide with water or dilute acid water, and the solid content of the ferric hydroxide slurry is 10% to 15%, preferably 12%.

[0053] A certain solids content results in good mixing and agitation; too high a content leads to viscous materials, poor flowability, and difficulty in material transfer. Too low a solids content reduces production capacity and lowers efficiency.

[0054] In this embodiment, the molar ratio of the amount of ferric hydroxide slurry added to the phosphorus iron in the first filtrate is 1.2 to 1.4:1, preferably 1.3:1.

[0055] In this embodiment, the reaction temperature of the ferric hydroxide slurry and the first filtrate is 50-70°C, preferably 60°C, the reaction stirring time is 1 hour, and the Fe mass fraction of the second mixed solution is 4.5%-6.5%, preferably 5%.

[0056] The time for the second filtrate to precipitate solid ferric phosphate dihydrate is 1 to 3 hours, preferably 2 hours.

[0057] In this embodiment, the third filtrate is returned to the ferric hydroxide slurry in step two for pulping reaction or returned to the ferric phosphate waste in step one.

[0058] Experimental Example 1

[0059] 200 kg of ferric phosphate waste was dissolved in a mixed acid solution of 730 kg of phosphoric acid (600 kg, 85%) and hydrochloric acid (130 kg, 5%) in a stirred tank. The reaction conditions were: stirring speed 50 r / min, reaction temperature 70℃, and reaction time 1 h. After the ferric phosphate waste was completely dissolved, impurities and insoluble matter were removed by filtration using a filter press to obtain the filtrate. 480 kg of ferric hydroxide was pulped and mixed with 2800 kg of water (solid content 14.63%), and then mixed with the ferric phosphate waste filtrate. The amount of ferric hydroxide slurry added was based on a phosphorus-to-ferric ratio (molar ratio) of 1.37:1. The reaction temperature was 50℃, and the stirring time was 0.5 h. After the reaction, the Fe mass fraction in the solution was 6.27%. The temperature was raised to 83℃, and the stirring time was 1 h. After filtration, washing, and drying, 710 kg of anhydrous ferric phosphate solid was obtained. The mother liquor obtained from filtration was returned for ferric hydroxide pulping.

[0060] Experimental Example 2

[0061] 150 kg of ferric phosphate waste was dissolved in a mixed acid solution of 740 kg of phosphoric acid (500 kg, 60%) and hydrochloric acid (240 kg, 15%) in a stirred tank. The reaction conditions were: stirring speed 300 r / min, reaction temperature 90℃, and reaction time 1.5 h. After the ferric phosphate waste was completely dissolved, impurities and insoluble matter were removed by filtration using a filter press to obtain the filtrate. 330 kg of ferric hydroxide was mixed with 2800 kg of water to form a slurry (solid content 10.54%), which was then mixed with the ferric phosphate waste filtrate. The amount of ferric hydroxide slurry added was based on a phosphorus-to-ferric ratio (molar ratio) of 1.21:1. The reaction temperature was 60℃, and the stirring time was 1 h. After the reaction, the Fe mass fraction in the solution was 4.63%. The temperature was raised to 90℃, and the stirring time was 2 h. After filtration, washing, and drying, 498 kg of anhydrous ferric phosphate solid was obtained. The mother liquor obtained from filtration was returned for ferric hydroxide slurry production.

[0062] Experimental Example 3

[0063] 170 kg of ferric phosphate waste was dissolved in a stirred tank with a mixed acid solution of 667 kg of phosphoric acid (520 kg, 70%) and hydrochloric acid (147 kg, 10%). The reaction conditions were: stirring speed 200 r / min, reaction temperature 80℃, and reaction time 2 h. After the ferric phosphate waste was completely dissolved, it was filtered using a filter press to remove impurities and insoluble matter, obtaining a filtrate. 355 kg of ferric hydroxide and 2650 kg of dilute acid recycled water were mixed into a slurry (solid content 11.81%), and then mixed with the ferric phosphate waste filtrate. The amount of ferric hydroxide slurry added was based on a phosphorus-to-ferric ratio (molar ratio) of 1.32:1. The reaction temperature was 70℃, and the stirring time was 2 h. After the reaction, the Fe mass fraction in the solution was 5.29%. The temperature was raised to 75℃, and the stirring time was 3 h. After filtration, washing, and drying, 532 kg of anhydrous ferric phosphate solid was obtained. The mother liquor obtained from filtration was returned to the ferric phosphate synthesis production line.

[0064] The test results for regenerated anhydrous ferric phosphate are as follows:

[0065] project Manufacturer's required value Experimental Example 1 Experimental Example 2 Experimental Example 3 Fe / % 35.7-36.7 36.33 36.41 36.28 P / ％ 20.0-21.1 20.90 20.89 20.85 Fe / P 0.96-0.97 0.964 0.966 0.965 Ca / ppm ≤50 10.2 18.1 20.5 Mg / ppm ≤50 8.7 9.3 7.2 Na / ppm ≤50 29.1 20.8 24.3 K / ppm ≤50 1.7 2.3 3.2 Cu / ppm ≤1 0.1 0.2 0.1 Zn / ppm ≤30 2.3 5.2 3.9 Mn / ppm ≤100 2.9 3.8 4.8 Al / ppm ≤80 3.5 8.1 6.9 Ti / ppm ≤100 8.8 7.9 9.1 Co / ppm ≤20 2.3 3.1 4.2 Pb / ppm ≤20 4.6 2.5 5.3 Cr / ppm ≤30 10.2 9.8 7.1 S / ppm ≤100 20.1 23.5 30.5 Magnetic substances / ppm ≤0.5 0.15 0.12 0.18 Moisture / % ≤0.5 0.20 0.33 0.25 <![CDATA[Tap density g / cm 3 > ≥0.6 0.91 0.93 0.90 Particle size D50 / um ≤6 2.7 2.4 3.1 <![CDATA[Specific surface area m 2 / g]]> 7-10 9.3 9.1 8.7

[0066] Parameters for preparing lithium iron phosphate from regenerated iron phosphate in the examples:

[0067] project compaction 0.1C charging 0.1C discharge 1C charging 1C discharge Experimental Example 1: Lithium Iron Phosphate 2.59 157.5 157.2 153.1 130.4 Experimental Example 2: Lithium Iron Phosphate 2.57 159.1 158.6 155.5 131.9 Experimental Example 3: Lithium Iron Phosphate 2.63 156.4 156.1 151.6 128.9

[0068] according to Figures 1-2 It can be seen that the present invention can produce high-purity iron phosphate.

[0069] The test results of the regenerated anhydrous iron phosphate in the table above show that all indicators of the regenerated iron phosphate prepared in this way meet the standards for iron phosphate battery grade, with high purity and good crystallinity; it is suitable for preparing high-pressure iron phosphate; and it has good performance in preparing lithium iron phosphate batteries.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recycling iron phosphate, characterized in that, Includes the following steps: Step 1: Mix phosphoric acid solution and hydrochloric acid solution to obtain mixed acid solution. Add ferric phosphate waste into the mixed acid solution to obtain a first mixed solution. Remove impurities from the first mixed solution to obtain a first filtrate. Step 2: Add ferric hydroxide slurry to the first filtrate, mix and beat to obtain a second mixed solution with a pH of 1-2. Filter the second mixed solution to obtain a second filtrate. Step 3: Stir the second filtrate and heat it to 75-90°C to precipitate a solid-liquid mixture containing ferric phosphate dihydrate. Filter the solid-liquid mixture to separate the ferric phosphate dihydrate solid and the third filtrate. Wash and dry the ferric phosphate dihydrate solid to obtain battery-grade ferric phosphate. Recycle the third filtrate. The reaction temperature of the ferric hydroxide slurry with the first filtrate is 50-70°C, the reaction stirring time is 0.5-2 hours, and the Fe mass fraction of the second mixed solution is 4.5%-6.5%. The second filtrate precipitates solid ferric phosphate dihydrate in 1-3 hours; The mass ratio of the mixed acid solution to the iron phosphate waste is 3~5:1; The reaction time for mixing the iron phosphate waste with the mixed acid solution is 1-2 hours, and the reaction temperature is 70-90℃. The ferric hydroxide slurry is obtained by mixing ferric hydroxide with water or dilute acid water, and the solid content of the ferric hydroxide slurry is 10%~15%. The molar ratio of the added ferric hydroxide slurry to the phosphorus and iron in the first filtrate is 1.2~1.4:1; In the mixed acid, the concentration of the phosphoric acid solution is 60%~85%, the concentration of the hydrochloric acid solution is 5%-15%, and the mass ratio of the phosphoric acid solution to the hydrochloric acid solution is 2~5:

1.

2. The method for recycling iron phosphate according to claim 1, characterized in that, The mixing and stirring speed of the iron phosphate waste and the mixed acid solution is 50 r / min to 300 r / min.

3. The method for recycling iron phosphate according to claim 1, characterized in that, The third filtrate is returned to the ferric hydroxide slurry in step two for pulping reaction or returned to the ferric phosphate waste dissolution reaction in step one.

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