Method for preparing ferric phosphate using low-purity sodium phosphate

Abstract

This application provides a method for preparing ferric phosphate using low-purity sodium phosphate, comprising: mixing low-purity sodium phosphate with sulfuric acid solution to form a mixture, wherein the pH value of the mixture is 4.5-7; filtering the mixture after a first reaction to obtain a first filtrate; filtering the first filtrate after freezing to obtain a second filtrate; mixing the second filtrate with an iron salt solution, and / or mixing the second filtrate with a ferrous salt solution and an oxidant, followed by a second reaction and filtration to obtain a filter; and aging, washing, and calcining the filter to obtain ferric phosphate. This preparation method is simple, convenient to operate, and can produce battery-grade ferric phosphate, thus improving resource utilization.

Description

Technical Field

[0001] This application relates to the field of materials preparation technology, and in particular to a method for preparing iron phosphate using low-purity sodium phosphate. Background Technology

[0002] Iron phosphate is one of the core raw materials for lithium iron phosphate batteries, and its performance has a significant impact on the energy density, safety, and cycle life of lithium batteries. Related technologies often use raw materials such as phosphoric acid and ammonium dihydrogen phosphate to prepare iron phosphate. However, the rapid increase in the price of these raw materials has raised the production cost of iron phosphate, thus limiting the development of lithium batteries. Summary of the Invention

[0003] In view of this, this application provides a method for preparing ferric phosphate using low-purity sodium phosphate. Using low-cost, low-purity sodium phosphate as a raw material to prepare ferric phosphate can reduce the preparation cost. At the same time, the preparation process is simple to operate, has a short operation process, low energy consumption, and is more green and environmentally friendly.

[0004] This application provides a method for preparing ferric phosphate using low-purity sodium phosphate, comprising: mixing low-purity sodium phosphate with sulfuric acid solution to form a mixture, wherein the pH value of the mixture is 4.5-7; filtering the mixture after a first reaction to obtain a first filtrate; filtering the first filtrate after freezing to obtain a second filtrate; mixing the second filtrate with an iron salt solution, and / or mixing the second filtrate with a ferrous salt solution and an oxidant, and filtering after a second reaction to obtain a filter; and aging, washing, and calcining the filter to obtain ferric phosphate.

[0005] Optionally, the concentration of the sulfuric acid solution is greater than or equal to 50%.

[0006] Optionally, the freezing process includes holding at 5℃ to 30℃ for 0.5h to 1h, and then holding at -10℃ to 0℃ for 2h to 5h.

[0007] Optionally, the first reaction includes reacting at 15°C to 40°C for 15 min to 60 min.

[0008] Optionally, the second reaction includes reacting at 55℃ to 90℃ for 0.5h to 2h.

[0009] Optionally, the aging process includes adding water to the filter material to form a slurry; and adding a phosphoric acid solution to the slurry to carry out a third reaction.

[0010] Furthermore, the solid content of the slurry is 5% to 30%.

[0011] Furthermore, the concentration of the phosphoric acid solution is 5 g / L to 25 g / L.

[0012] Furthermore, the third reaction includes reacting at 70℃ to 95℃ for 0.5h to 4h.

[0013] Optionally, the calcination includes treatment at 500℃ to 800℃ for 1 to 5 hours.

[0014] Optionally, the phosphorus concentration in the mixture is 25 g / L to 40 g / L.

[0015] Optionally, the phosphorus concentration in the second filtrate is 25 g / L to 35 g / L.

[0016] Optionally, the pH of the second filtrate is 6 to 7.

[0017] Optionally, the cleaning includes treatment at 30℃ to 80℃ for 15 min to 120 min.

[0018] Optionally, the purity of the low-purity sodium phosphate is less than or equal to 90%.

[0019] Optionally, the particle size D50 of the iron phosphate is 2 μm to 5 μm.

[0020] Optionally, the specific surface area of ​​the iron phosphate is 8 m². 2 / g~14m 2 / g.

[0021] Optionally, the iron content in the iron phosphate is 35.5% to 36.5%, the phosphate content is 63.0% to 64.5%, and the molar ratio of iron to phosphorus is 0.955 to 0.980.

[0022] This application uses low-cost, low-purity sodium phosphate as a raw material to prepare iron phosphate. The preparation process is simple, has a short operation time, low energy consumption, and low preparation cost. It can produce battery-grade iron phosphate, which is beneficial for its use in batteries. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0024] Figure 1 A flowchart illustrating a method for preparing ferric phosphate using low-purity sodium phosphate, provided as an embodiment of this application. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] Please see Figure 1 The flowchart of a method for preparing ferric phosphate using low-purity sodium phosphate according to an embodiment of this application includes:

[0027] S101: Low-purity sodium phosphate is mixed with sulfuric acid solution to form a mixture with a pH of 4.5 to 7.

[0028] S102: The mixture is filtered after the first reaction to obtain the first filtrate.

[0029] S103: The first filtrate is frozen and then filtered to obtain the second filtrate.

[0030] S104: The second filtrate is mixed with the iron salt solution, and / or the second filtrate is mixed with the ferrous salt solution and the oxidant, and then filtered through the second reaction to obtain the filtrate.

[0031] S105: The filtered material is aged, washed and calcined to obtain ferric phosphate.

[0032] In related technologies, phosphoric acid and ammonium dihydrogen phosphate are used as phosphorus sources to prepare ferric phosphate. However, the price of the phosphorus sources currently used is relatively high, which is not conducive to the large-scale preparation and application of ferric phosphate. This application uses low-cost, low-purity sodium phosphate as a raw material to prepare ferric phosphate. This not only improves the utilization rate of low-purity sodium phosphate, but also obtains high-purity ferric phosphate with excellent performance. Furthermore, this preparation method is simple to operate, avoids the synthesis of intermediate products, has low energy consumption, and low preparation cost, which is beneficial to the production and use of ferric phosphate.

[0033] In S101 and S102, low-purity sodium phosphate is mixed with sulfuric acid solution, which dissolves the low-purity sodium phosphate in the sulfuric acid solution and reacts with the sulfuric acid solution, thus ensuring the acquisition of phosphorus and the removal of impurities.

[0034] In this application, by using low-purity sodium phosphate, the preparation cost can be reduced, while resource utilization can be improved and resource waste can be avoided. Low-purity sodium phosphate can be purchased or obtained by dissolving and crystallizing lithium-extracted battery waste with alkali, making it more environmentally friendly. In one embodiment of this application, phosphate aluminum slag can be extracted with an alkaline solution (sodium hydroxide, sodium carbonate, etc.), filtered to obtain a filtrate, and then subjected to freeze crystallization and centrifugation to obtain low-purity sodium phosphate. The filtrate contains sodium phosphate and sodium aluminate. During the freeze crystallization process, the difference in solubility of sodium phosphate and sodium aluminate with temperature is utilized, and centrifugation yields low-purity sodium phosphate crystals. In one embodiment of this application, the purity of the low-purity sodium phosphate is less than or equal to 90%. Specifically, the purity of the low-purity sodium phosphate can be, but is not limited to, less than or equal to 90%, less than or equal to 88%, less than or equal to 85%, less than or equal to 82%, less than or equal to 80%, less than or equal to 75%, less than or equal to 65%, etc. In one embodiment, the purity of the low-purity sodium phosphate can be 80% to 90%. In one embodiment of this application, the aluminum content of the low-purity sodium phosphate is 0.2% to 1.5%. Specifically, the aluminum content of the low-purity sodium phosphate can be, but is not limited to, less than or equal to 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, or 1.5%.

[0035] Low-purity sodium phosphate contains sodium phosphate and impurities, including aluminum and, more specifically, iron. During the reaction of low-purity sodium phosphate with sulfuric acid solution at a pH of 4.5–7, aluminum and iron in the low-purity sodium phosphate form hydroxide precipitates, which can be removed by filtration, thus improving the purity and performance of ferric phosphate. Therefore, maintaining a pH of 4.5–7 in the mixed solution during preparation ensures the removal of impurities such as aluminum from the low-purity sodium phosphate; a pH that is too low or too high hinders the formation of aluminum hydroxides, thereby impeding the removal of impurities.

[0036] In one embodiment of this application, the concentration of the sulfuric acid solution is greater than or equal to 50%, which is beneficial for adjusting the pH value of the mixture to between 4.5 and 7; at the same time, it ensures that the phosphorus concentration in the mixture is suitable, which is beneficial for improving the production capacity of iron phosphate. In one embodiment of this application, the concentration of the sulfuric acid solution can be 50% to 98%. Specifically, the concentration of the sulfuric acid solution can be, but is not limited to, 50%, 55%, 60%, 68%, 70%, 73%, 80%, 85%, 90%, or 96%. In one embodiment, the concentration of the sulfuric acid solution can be 50% to 68%. In another embodiment, the concentration of the sulfuric acid solution can be 70% to 98%. The above-mentioned concentrations of sulfuric acid solution ensure sufficient dissolution of low-purity sodium phosphate and sufficient reaction with low-purity sodium phosphate, ensuring the acquisition of phosphorus.

[0037] In one embodiment of this application, the phosphorus concentration in the mixture is 25 g / L to 40 g / L, which ensures the amount of ferric phosphate obtained and improves the preparation efficiency. Specifically, the phosphorus concentration in the mixture can be, but is not limited to, 25 g / L, 38 g / L, 30 g / L, 32 g / L, 35 g / L, 36 g / L, 39 g / L, or 40 g / L. In one embodiment, the phosphorus concentration in the mixture can be 25 g / L to 35 g / L. In another embodiment, the phosphorus concentration in the mixture can be 30 g / L to 40 g / L.

[0038] In one embodiment of this application, the first reaction includes reacting at 15°C to 40°C for 15 to 60 minutes. These first reaction conditions facilitate the complete reaction of low-purity sodium phosphate with sulfuric acid solution, while further enhancing the complete reaction of impurity elements in the low-purity sodium phosphate, removing impurity elements such as aluminum and iron as much as possible, and further improving the purity and performance of the obtained ferric phosphate. Specifically, the temperature of the first reaction can be, but is not limited to, 15°C, 17°C, 20°C, 22°C, 25°C, 29°C, 30°C, 33°C, 35°C, 36°C, or 40°C; the time of the first reaction can be, but is not limited to, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 40 minutes, 45 minutes, or 55 minutes. The time of the first reaction is the reaction time after the low-purity sodium phosphate and sulfuric acid solution are mixed and the pH value is adjusted. In one embodiment, the first reaction includes reacting at 15°C to 30°C for 30 to 60 minutes. In another embodiment, the first reaction includes reacting at 25°C to 40°C for 15 min to 45 min.

[0039] In this application, after the mixture undergoes a first reaction, it is filtered to obtain a first filtrate and a first precipitate, the first precipitate including but not limited to aluminum hydroxide, iron hydroxide, etc.

[0040] In S103, sodium sulfate (sodium sulfate) is produced by mixing and reacting low-purity sodium phosphate with sulfuric acid solution. That is, the first filtrate contains sodium sulfate. Freezing treatment is used to achieve denitrification, thereby removing sodium sulfate impurities from the first filtrate.

[0041] In this application, sodium sulfate is precipitated from the first filtrate through freezing treatment, thereby allowing it to be removed by filtration. In one embodiment of this application, the freezing treatment includes holding at 5℃ to 30℃ (e.g., 8℃, 10℃, 13℃, 15℃, 17℃, 20℃, 23℃, 25℃, or 30℃, etc.) for 0.5h to 1h (e.g., 0.5h, 0.6h, 0.7h, 0.8h, or 0.9h, etc.), and then holding at -10℃ to 0℃ (e.g., -9℃, -8℃, -7℃, -6℃, -5℃, -4℃, -3℃, -2℃, or -1℃, etc.) for 2h to 5h (e.g., 2.5h, 3h, 3.5h, 4h, or 4.5h, etc.). This segmented cooling freezing treatment helps to increase the particle size of the precipitated sodium sulfate, thereby reducing the moisture content of the sodium sulfate particles, which in turn reduces the loss of phosphorus and also simplifies filtration. Understandably, the temperature of the first reaction is higher than 5℃ to 30℃, thereby achieving the first stage of cooling treatment. In one embodiment, the freezing treatment includes holding at 5℃ to 15℃ for 0.6h to 1h, and then holding at -8℃ to -2℃ for 2h to 4h. In one embodiment, the freezing treatment includes holding at 10℃ to 25℃ for 0.6h to 0.8h, and then holding at -10℃ to -4℃ for 2h to 5h. In one embodiment, the freezing treatment includes holding at 20℃ to 30℃ for 0.5h to 0.7h, and then holding at -9℃ to -3℃ for 3h to 5h. In one embodiment of this application, the sodium sulfate obtained by the above freezing treatment has a particle size D50 of 150μm to 200μm. This sodium sulfate particle size is suitable, easy to filter, and has a low water content, avoiding the loss of phosphorus. Specifically, the particle size D50 of sodium sulfate can be, but is not limited to, 150μm, 160μm, 170μm, 175μm, 180μm, 190μm or 200μm.

[0042] In one embodiment of this application, when the sodium concentration in the first filtrate after freezing treatment is 20 g / L to 25 g / L, filtration can be performed to remove sodium sulfate. In this application, one or more freezing treatments can be performed to improve the removal rate of sodium sulfate.

[0043] In one embodiment of this application, the phosphorus concentration in the first filtrate after freezing is 35 g / L to 50 g / L. This ensures that sodium phosphate is removed without increasing the phosphorus loss rate, which is beneficial for improving the yield of ferric phosphate. Specifically, the phosphorus concentration in the first filtrate after freezing can be, but is not limited to, 35 g / L, 36 g / L, 40 g / L, 43 g / L, 45 g / L, 49 g / L, or 50 g / L. In one embodiment, the phosphorus concentration in the first filtrate after freezing is 35 g / L to 45 g / L. In another embodiment, the phosphorus concentration in the first filtrate after freezing is 40 g / L to 50 g / L.

[0044] In one embodiment of this application, the first filtrate is subjected to freezing treatment and then filtered to obtain a second filtrate and sodium sulfate, wherein the water content of the sodium sulfate is 2% to 5%. The method of this application can also produce sodium sulfate, further improving resource utilization.

[0045] In S104, the second filtrate is mixed with the iron salt solution, and / or the second filtrate is mixed with the ferrous salt solution and the oxidant to react and obtain crude iron phosphate (ferric phosphate dihydrate). Both the iron salt solution and the ferrous salt solution are iron sources.

[0046] In one embodiment of this application, the phosphorus concentration in the second filtrate is 25 g / L to 35 g / L. When the phosphorus concentration is too low, the yield of ferric phosphate is low, affecting the preparation efficiency; when the phosphorus concentration is too high, the second filtrate is relatively viscous, which is not conducive to sufficient mixing and reaction between the second filtrate and the iron source. Therefore, a phosphorus concentration of 25 g / L to 35 g / L in the second filtrate is beneficial for further improving the yield of ferric phosphate. Specifically, the phosphorus concentration in the second filtrate can be, but is not limited to, 25 g / L, 26 g / L, 29 g / L, 30 g / L, 33 g / L, 34 g / L, or 35 g / L. In this application, the phosphorus concentration can be adjusted by adding water to the second filtrate, but is not limited to this method.

[0047] In one embodiment of this application, the pH value of the second filtrate is 6-7, which is conducive to the second reaction. Specifically, the pH value of the second filtrate can be adjusted by using an alkaline solution (such as ammonia, sodium hydroxide solution, etc.).

[0048] It is understood that the ferric salt solution is a solution containing ferric ions (Fe3+) and the ferrous salt solution is a solution containing ferrous ions (Fe2+). In this application, the second filtrate can be mixed and reacted with the ferric salt solution, the second filtrate can also be mixed and reacted with the ferrous salt solution and the oxidizing agent, and the second filtrate can also be mixed and reacted with the ferric salt solution, the ferrous salt solution, and the oxidizing agent. In one embodiment, the ferric salt solution may include, but is not limited to, at least one of ferric sulfate solution, ferric nitrate solution, and ferric chloride solution. In one embodiment, the ferrous salt solution may include, but is not limited to, at least one of ferrous sulfate solution, ferrous nitrate solution, and ferrous chloride solution.

[0049] In one embodiment of this application, the molar concentration ratio of phosphorus in the second filtrate to iron in the iron source is (1.02 to 1.1):1. This is beneficial because the content and ratio of phosphorus and iron in the obtained ferric phosphate meet the requirements for battery-grade ferric phosphate. Specifically, the molar concentration ratio of phosphorus in the second filtrate to iron in the iron source can be, but is not limited to, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, or 1.1:1, etc. Understandably, when the iron source is an iron salt solution, the molar concentration ratio of phosphorus in the second filtrate to iron in the iron source refers to the molar concentration ratio of phosphorus in the second filtrate to iron in the iron salt solution; when the iron source is a ferrous salt solution, the molar concentration ratio of phosphorus in the second filtrate to iron in the iron source refers to the molar concentration ratio of phosphorus in the second filtrate to iron in the ferrous salt solution; when the iron source is both an iron salt solution and a ferrous salt solution, the molar concentration ratio of phosphorus in the second filtrate to iron in the iron source refers to the ratio of the molar concentration of phosphorus in the second filtrate to the sum of the molar concentrations of iron in the iron salt solution and the ferrous salt solution.

[0050] In one embodiment of this application, the oxidant may include, but is not limited to, hydrogen peroxide. Using hydrogen peroxide as the oxidant can avoid the introduction of impurity elements and improve the purity of the obtained ferric phosphate. In one embodiment of this application, the concentration of hydrogen peroxide can be 15% to 30%. In this application, the reaction process of ferrous ions with hydrogen peroxide is 2Fe 2+ +H₂O₂ + 2H₂ + =2Fe 3+ +2H₂O. In one embodiment of this application, the amount of hydrogen peroxide added can be the theoretical amount calculated according to the above reaction equation multiplied by a coefficient, where the coefficient can be 1.1 to 1.4, thereby ensuring that the reaction proceeds fully. Specifically, the coefficient can be, but is not limited to, 1.1, 1.2, 1.3, or 1.4, etc.

[0051] In one embodiment of this application, the mixing time is 0.5h to 2h (e.g., 0.5h, 0.8h, 1h, 1.2h, 1.5h, or 1.7h). In this application, the second filtrate can be added to the iron source, or the iron source can be added to the second filtrate. In one embodiment, the second filtrate and hydrogen peroxide can be added to the ferrous salt solution in a parallel flow for 0.5h to 2h; in this case, the addition time is the mixing time.

[0052] In one embodiment of this application, the second reaction includes reacting at 55°C to 90°C for 0.5 to 2 hours. These second reaction conditions facilitate a thorough reaction between the second filtrate and the iron source to generate crude iron phosphate. Specifically, the temperature of the second reaction can be, but is not limited to, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, or 90°C; the reaction time can be, but is not limited to, 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 1.9 hours, or 2 hours. The reaction time refers to the time it takes for the second filtrate to react with the iron salt solution, ferrous salt solution, and oxidant. In one embodiment, the second reaction includes reacting at 55°C to 75°C for 1 to 2 hours. In another embodiment, the second reaction includes reacting at 65°C to 90°C for 0.5 to 1.5 hours. During the mixing and reaction process, stirring can be performed to ensure uniform mixing and thorough reaction of the reactants.

[0053] In S105, the crystal structure of the filter material can be adjusted by aging, impurities in the filter material can be further removed by washing, and high-purity, high-performance iron phosphate can be obtained by calcination.

[0054] In one embodiment of this application, aging includes adding water to the filter material to form a slurry; then adding a phosphoric acid solution to the slurry to carry out a third reaction. This can adjust the crystal structure of ferric phosphate and improve its performance. In one embodiment of this application, the solid content of the slurry is 5% to 30% (e.g., 5%, 10%, 15%, 20%, 25%, or 28%), the concentration of the phosphoric acid solution is 5 g / L to 25 g / L (e.g., 8 g / L, 12 g / L, 15 g / L, 19 g / L, or 20 g / L), and the third reaction includes reacting at 70°C to 95°C (e.g., 70°C, 75°C, 80°C, 85°C, or 90°C) for 0.5 h to 4 h (e.g., 0.5 h, 1 h, 2 h, 3 h, or 4 h). In one embodiment, a phosphoric acid solution is added to the slurry to carry out the third reaction, and the filter material is filtered after turning white.

[0055] In one embodiment of this application, cleaning includes treatment at 30℃ to 80℃ for 15 to 120 minutes. Specifically, the cleaning temperature can be, but is not limited to, 30℃, 40℃, 50℃, 60℃, 70℃, or 80℃, and the cleaning time can be, but is not limited to, 15 minutes, 30 minutes, 45 minutes, 60 minutes, 75 minutes, 90 minutes, or 110 minutes. In one embodiment of this application, a two-step countercurrent water washing process can be used for cleaning. That is, the water from the second washing is reused in the first washing, pure water is used for the second washing, and the filtrate from the second washing is used for the first washing. In one embodiment, the filter material is dispersed in water with a solid content of 5% to 15%, and then cleaned using a two-step countercurrent water washing process. In this application, filtration is performed after cleaning.

[0056] In one embodiment of this application, calcination includes treatment at 500℃ to 800℃ for 1 to 5 hours. Specifically, the calcination temperature can be, but is not limited to, 500℃, 550℃, 585℃, 600℃, 625℃, 650℃, 700℃, 750℃, 780℃, or 800℃, and the calcination time can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours. In one embodiment, calcination can be performed at 500℃ to 700℃ for 2 to 5 hours. In another embodiment, calcination can be performed at 600℃ to 800℃ for 1 to 4 hours. In one embodiment of this application, the moisture content of the calcined filter material is less than or equal to 2%. Specifically, the above moisture content can be obtained by drying.

[0057] In this application, after calcination, demagnetization and air jet milling can be performed. Specifically, demagnetization can be performed using a demagnetizer, and ferric phosphate can be pulverized using air jet milling to obtain ferric sulfate of the desired particle size.

[0058] In one embodiment of this application, the particle size D50 of ferric phosphate is 2 μm to 5 μm. Specifically, the particle size D50 of ferric phosphate can be, but is not limited to, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or 5 μm. In one embodiment of this application, the specific surface area of ​​ferric phosphate is 8 m². 2 / g~14m 2 / g. Specifically, the specific surface area of ​​ferric phosphate can be, but is not limited to, 8m². 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g or 14m 2 / g etc. In one embodiment of this application, the iron content in ferric phosphate is 35.5% to 36.5%, the phosphate content is 63.0% to 64.5%, and the molar ratio of iron to phosphorus is 0.955 to 0.980, which meets the requirements of battery-grade ferric phosphate and is beneficial to the use of ferric phosphate.

[0059] This application utilizes low-cost, low-purity sodium phosphate as a raw material to prepare iron phosphate. The preparation process is simple, has a short operation time, low energy consumption, and low preparation cost. It can produce battery-grade iron phosphate, which is beneficial for its use in batteries.

[0060] The effects of the technical solution provided in this application will be further illustrated by specific embodiments below.

[0061] Example 1

[0062] The aluminum phosphate slag was placed in a sodium hydroxide solution, reacted, and then filtered. The filtrate was frozen to crystallize, and then centrifuged to obtain low-purity sodium phosphate, which had a purity of about 85%.

[0063] At room temperature (25℃), low-purity sodium phosphate was mixed with sulfuric acid solution (concentration of 50%). The pH value was adjusted to about 4.5 by controlling the amount of sulfuric acid added to form a mixture with a phosphorus concentration of 25 g / L. After pH adjustment, the reaction was continued for 15 min, and the first filtrate was obtained by filtration.

[0064] The first filtrate was cooled to 5°C and held for 0.5 hours, then cooled to -10°C and held for 2 hours to complete the freezing treatment (freezing denitrification process). When the sodium ion concentration in the first filtrate was 20 g / L and the phosphorus concentration was 35 g / L, the first filtrate was centrifuged to obtain the second filtrate and wet sodium sulfate with a water content of approximately 2%.

[0065] The phosphorus concentration of the second filtrate was adjusted to 25 g / L with pure water, and the pH of the second filtrate was adjusted to 6 with alkali solution. A ferrous sulfate solution was prepared based on a phosphorus to iron molar ratio of 1.1:1 in the second filtrate, and a 15% hydrogen peroxide solution was prepared based on an excess coefficient of 1.1. The phosphorus solution and hydrogen peroxide were added concurrently to the ferrous sulfate solution over a period of 0.5 h. After addition, the temperature was raised to 55 °C and maintained for 0.5 h. The resulting product (wet ferric phosphate dihydrate I) was obtained through filtration.

[0066] The filtered material (wet ferric phosphate dihydrate I) was slurried with pure water to form a slurry with a solid content of 5%. A phosphoric acid solution (concentration 5 g / L) was added to the slurry, and the mixture was reacted at 70℃ for 4 hours. After the color of the ferric phosphate dihydrate slurry changed from light yellow to white, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate II). The filtered material (wet ferric phosphate dihydrate II) was washed to remove impurities, and after washing, it was filtered again to obtain the filtered material (wet ferric phosphate dihydrate III). The washing process employed a two-step countercurrent stirring process, with a solid content of 15%, a stirring temperature of 30℃, and a stirring time of 15 minutes. The filtered material (wet ferric phosphate dihydrate III) was dried until the moisture content was below 2% and then placed in a calcination furnace and calcined at 600℃ for 2 hours. After calcination, it underwent demagnetization and airflow crushing to obtain ferric phosphate.

[0067] Example 2

[0068] The aluminum phosphate slag was placed in a sodium hydroxide solution, reacted, and then filtered. The filtrate was frozen to crystallize, and then centrifuged to obtain low-purity sodium phosphate, which had a purity of about 80%.

[0069] At room temperature (25℃), low-purity sodium phosphate was mixed with sulfuric acid solution (concentration of 60%). The pH value was adjusted to about 5 by controlling the amount of sulfuric acid added to form a mixture with a phosphorus concentration of 28 g / L. After pH adjustment, the reaction was continued for 20 min, and the first filtrate was obtained by filtration.

[0070] The first filtrate was cooled to 10°C and held for 0.6 hours, then cooled to 0°C and held for 5 hours to complete the freezing treatment (freezing denitrification process). When the sodium ion concentration in the first filtrate was 21 g / L and the phosphorus concentration was 38 g / L, the first filtrate was centrifuged to obtain the second filtrate and wet sodium sulfate with a water content of approximately 2.5%.

[0071] The phosphorus concentration of the second filtrate was adjusted to 28 g / L with pure water, and the pH of the second filtrate was adjusted to 6.1 with alkali solution. A ferrous sulfate solution was prepared based on a phosphorus to iron molar ratio of 1.08:1 in the second filtrate, and an 18% hydrogen peroxide solution was prepared based on an excess coefficient of 1.15. The phosphorus solution and hydrogen peroxide were added concurrently to the ferrous sulfate solution over a period of 0.7 h. After addition, the temperature was raised to 65 °C and maintained for 0.7 h. The resulting product (wet ferric phosphate dihydrate I) was obtained through filtration.

[0072] The filtered material (wet ferric phosphate dihydrate I) was slurried with pure water to form a slurry with a solid content of 8%. A phosphoric acid solution (concentration 8 g / L) was added to the slurry, and the reaction was carried out at 75℃ for 3.5 h. After the color of the ferric phosphate dihydrate slurry changed from light yellow to white, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate II). The filtered material (wet ferric phosphate dihydrate II) was washed to remove impurities, and after washing, it was filtered again to obtain the filtered material (wet ferric phosphate dihydrate III). The washing process employed a two-step countercurrent stirring process, with a solid content of 13%, a stirring temperature of 40℃, and a stirring time of 30 min. The filtered material (wet ferric phosphate dihydrate III) was dried until the moisture content was below 2% and then placed in a calcination furnace and calcined at 650℃ for 2.5 h. After calcination, it underwent demagnetization and airflow crushing to obtain ferric phosphate.

[0073] Example 3

[0074] The aluminum phosphate slag was placed in a sodium hydroxide solution, reacted, and then filtered. The filtrate was frozen to crystallize, and then centrifuged to obtain low-purity sodium phosphate, which had a purity of approximately 83%.

[0075] At room temperature (25℃), low-purity sodium phosphate was mixed with sulfuric acid solution (70% concentration). The pH value was adjusted to approximately 5.5 by controlling the amount of sulfuric acid added, forming a mixed solution with a phosphorus concentration of 30 g / L. After pH adjustment, the reaction was continued for 30 min, and the first filtrate was obtained by filtration.

[0076] The first filtrate was cooled to 15°C and held for 0.7 hours, then cooled to -2°C and held for 4.5 hours to complete the freezing treatment (freezing denitrification process). When the sodium ion concentration in the first filtrate was 22 g / L and the phosphorus concentration was 42 g / L, the first filtrate was centrifuged to obtain the second filtrate and wet sodium sulfate with a water content of approximately 3%.

[0077] The phosphorus concentration of the second filtrate was adjusted to 30 g / L with pure water, and the pH of the second filtrate was adjusted to 6.2 with alkali solution. A ferrous sulfate solution was prepared based on a phosphorus to iron molar ratio of 1.07:1 in the second filtrate, and a 20% hydrogen peroxide solution was prepared based on an excess coefficient of 1.2. The phosphorus solution and hydrogen peroxide were added concurrently to the ferrous sulfate solution over a period of 1 hour. After addition, the temperature was raised to 75°C and maintained for 1 hour. The filtrate (wet ferric phosphate dihydrate I) was obtained after filtration.

[0078] The filtered material (wet ferric phosphate dihydrate I) was slurried with pure water to form a slurry with a solid content of 12%. A phosphoric acid solution (concentration 12 g / L) was added to the slurry, and the mixture was reacted at 80℃ for 3 hours. After the color of the ferric phosphate dihydrate slurry changed from light yellow to white, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate II). The filtered material (wet ferric phosphate dihydrate II) was washed to remove impurities, and after washing, it was filtered again to obtain the filtered material (wet ferric phosphate dihydrate III). The washing process employed a two-step countercurrent stirring process, with a solid content of 10%, a stirring temperature of 50℃, and a stirring time of 45 minutes. The filtered material (wet ferric phosphate dihydrate III) was dried until the moisture content was below 2% and then placed in a calcination furnace and calcined at 500℃ for 3 hours. After calcination, it underwent demagnetization and airflow crushing to obtain ferric phosphate.

[0079] Example 4

[0080] The aluminum phosphate slag was placed in a sodium hydroxide solution, reacted, and then filtered. The filtrate was frozen to crystallize, and then centrifuged to obtain low-purity sodium phosphate, which had a purity of about 90%.

[0081] At room temperature (25℃), low-purity sodium phosphate was mixed with sulfuric acid solution (concentration of 80%). The pH value was adjusted to about 6 by controlling the amount of sulfuric acid added to form a mixture with a phosphorus concentration of 33 g / L. After pH adjustment, the reaction was continued for 40 min, and the first filtrate was obtained by filtration.

[0082] The first filtrate was cooled to 20°C and held for 0.8 hours, then cooled to -4°C and held for 4 hours to complete the freezing treatment (freezing denitrification process). When the sodium ion concentration in the first filtrate was 23 g / L and the phosphorus concentration was 44 g / L, the first filtrate was centrifuged to obtain the second filtrate and wet sodium sulfate with a water content of approximately 3%.

[0083] The phosphorus concentration of the second filtrate was adjusted to 31 g / L with pure water, and the pH of the second filtrate was adjusted to 6.3 with alkali solution. A ferrous sulfate solution was prepared based on a phosphorus to iron molar ratio of 1.06:1, and a 30% hydrogen peroxide solution was prepared based on an excess coefficient of 1.25. The phosphorus solution and hydrogen peroxide were added concurrently to the ferrous sulfate solution over a period of 1 hour. After addition, the temperature was raised to 80°C and maintained for 1.2 hours. The resulting product (wet ferric phosphate dihydrate I) was obtained through filtration.

[0084] The filtered material (wet ferric phosphate dihydrate I) was slurried with pure water to form a slurry with a solid content of 16%. A phosphoric acid solution (concentration 15 g / L) was added to the slurry, and the mixture was reacted at 83℃ for 3 hours. After the color of the ferric phosphate dihydrate slurry changed from light yellow to white, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate II). The filtered material (wet ferric phosphate dihydrate II) was washed to remove impurities, and after washing, it was filtered again to obtain the filtered material (wet ferric phosphate dihydrate III). The washing process employed a two-step countercurrent stirring process, with a solid content of 9%, a stirring temperature of 55℃, and a stirring time of 65 minutes. The filtered material (wet ferric phosphate dihydrate III) was dried until the moisture content was below 2% and then placed in a calcination furnace and calcined at 700℃ for 1 hour. After calcination, it underwent demagnetization and airflow crushing to obtain ferric phosphate.

[0085] Example 5

[0086] The aluminum phosphate slag was placed in a sodium carbonate solution, reacted, filtered, and the filtrate was frozen to crystallize. After centrifugation, low-purity sodium phosphate was obtained, with a purity of approximately 87%.

[0087] At room temperature (25℃), low-purity sodium phosphate was mixed with sulfuric acid solution (concentration of 85%). The pH value was adjusted to approximately 6.5 by controlling the amount of sulfuric acid added, forming a mixed solution with a phosphorus concentration of 36 g / L. After pH adjustment, the reaction was continued for 50 min, and the first filtrate was obtained by filtration.

[0088] The first filtrate was cooled to 25°C and held for 0.9 hours, then cooled to -8°C and held for 2.5 hours to complete the freezing treatment (freezing denitrification process). When the sodium ion concentration in the first filtrate was 24 g / L and the phosphorus concentration was 47 g / L, the first filtrate was centrifuged to obtain the second filtrate and wet sodium sulfate with a water content of approximately 4%.

[0089] The phosphorus concentration of the second filtrate was adjusted to 33 g / L with pure water, and the pH of the second filtrate was adjusted to 6.5 with alkali solution. A ferrous sulfate solution was prepared based on a phosphorus to iron molar ratio of 1.07:1 in the second filtrate, and a 25% hydrogen peroxide solution was prepared based on an excess coefficient of 1.3. The phosphorus solution and hydrogen peroxide were added concurrently to the ferrous sulfate solution over a period of 1.5 hours. After addition, the temperature was raised to 85°C and maintained for 1.4 hours. The resulting product (wet ferric phosphate dihydrate I) was obtained through filtration.

[0090] The filtered material (wet ferric phosphate dihydrate I) was slurried with pure water to form a slurry with a solid content of 20%. A phosphoric acid solution (concentration 20 g / L) was added to the slurry, and the reaction was carried out at 90℃ for 1.5 h. After the color of the ferric phosphate dihydrate slurry changed from light yellow to white, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate II). The filtered material (wet ferric phosphate dihydrate II) was washed to remove impurities, and after washing, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate III). The washing process employed a two-step countercurrent stirring process, with a solid content of 12%, a stirring temperature of 60℃, and a stirring time of 80 min. The filtered material (wet ferric phosphate dihydrate III) was dried until the moisture content was below 2% and then placed in a calcination furnace and calcined at 700℃ for 1.1 h. After calcination, it was demagnetized and subjected to airflow crushing to obtain ferric phosphate.

[0091] Example 6

[0092] The aluminum phosphate slag was placed in a sodium hydroxide solution, reacted, and then filtered. The filtrate was frozen to crystallize, and then centrifuged to obtain low-purity sodium phosphate, which had a purity of about 85%.

[0093] At room temperature (25℃), low-purity sodium phosphate was mixed with sulfuric acid solution (concentration of 98%). The pH value was adjusted to about 7 by controlling the amount of sulfuric acid added to form a mixture with a phosphorus concentration of 40 g / L. After pH adjustment, the reaction was continued for 60 min, and the first filtrate was obtained by filtration.

[0094] The first filtrate was cooled to 30°C and held for 1 hour, then cooled to -6°C and held for 5 hours to complete the freezing treatment (freezing denitrification process). When the sodium ion concentration in the first filtrate was 25 g / L and the phosphorus concentration was 50 g / L, the first filtrate was centrifuged to obtain the second filtrate and wet sodium sulfate with a water content of approximately 4.5%.

[0095] The phosphorus concentration of the second filtrate was adjusted to 35 g / L with pure water, and the pH of the second filtrate was adjusted to 7 with alkali solution. A ferrous sulfate solution was prepared based on a phosphorus to iron molar ratio of 1.1:1 in the second filtrate, and a 25% hydrogen peroxide solution was prepared based on an excess coefficient of 1.4. The phosphorus solution and hydrogen peroxide were added concurrently to the ferrous sulfate solution over a period of 2 hours. After addition, the temperature was raised to 90°C and maintained for 1.5 hours. The resulting product (wet ferric phosphate dihydrate I) was obtained through filtration.

[0096] The filtered material (wet ferric phosphate dihydrate I) was slurried with pure water to form a slurry with a solid content of 25%. A phosphoric acid solution (concentration 25 g / L) was added to the slurry, and the mixture was reacted at 95°C for 3 hours. After the color of the ferric phosphate dihydrate slurry changed from light yellow to white, it was filtered to obtain the filtered material (wet ferric phosphate dihydrate II). The filtered material (wet ferric phosphate dihydrate II) was washed to remove impurities, and after washing, it was filtered again to obtain the filtered material (wet ferric phosphate dihydrate III). The washing process employed a two-step countercurrent stirring process, with a solid content of 15%, a stirring temperature of 70°C, and a stirring time of 90 minutes. The filtered material (wet ferric phosphate dihydrate III) was dried until the moisture content was below 2% and then placed in a calcination furnace and calcined at 800°C for 3 hours. After calcination, it underwent demagnetization and airflow crushing to obtain ferric phosphate.

[0097] Example 7

[0098] It is largely the same as Example 1, except that the concentration of the sulfuric acid solution is 35%.

[0099] Comparative Example 1

[0100] Similar to Example 1, except that at room temperature (25°C), low-purity sodium phosphate was mixed with a sulfuric acid solution (concentration of 50%), and the pH value was adjusted to approximately 3.5 by controlling the amount of sulfuric acid added.

[0101] Comparative Example 2

[0102] Similar to Example 1, except that at room temperature (25°C), low-purity sodium phosphate was mixed with a sulfuric acid solution (concentration of 50%), and the pH value was adjusted to approximately 8 by controlling the amount of sulfuric acid added.

[0103] Performance testing

[0104] The ferric phosphate prepared in the above examples was tested, and the results are shown in Table 1. Moisture content was determined using the 150℃ weight loss method; iron (Fe) content was determined by redox titration; phosphorus (P) content and phosphate (PO4) content were determined by gravimetric analysis. 3-The sulfur content (S) was measured using a carbon-sulfur analyzer. The sodium (Na), nickel (Ni), chromium (Cr), zinc (Zn), copper (Cu), aluminum (Al), and calcium (Ca) content were analyzed using ICP-OES. The particle size was measured using a particle size analyzer. The specific surface area was measured using a specific surface area analyzer. X-ray diffraction (XRD) was performed to obtain the intensity of XRD impurity peaks. In Table 1, " / " indicates that the corresponding element was not detected.

[0105] Table 1 Test Results

[0106]

[0107] Table 1 lists the technical standards for battery-grade iron phosphate. It can be seen that the iron phosphate prepared in Examples 1-7 meets the performance requirements for battery-grade iron phosphate. However, the iron phosphate prepared in Comparative Examples 1-2 has an excessively high aluminum content, failing to meet the performance requirements for battery-grade iron phosphate. This means that excessively low or high pH during the impurity removal process leads to a high aluminum impurity content in the final synthesized iron phosphate, thus failing to meet the performance requirements for battery-grade iron phosphate. Furthermore, compared to Example 7, Example 1 yields a greater amount of iron phosphate, resulting in higher production capacity. Therefore, the iron phosphate preparation method provided in this application can produce iron phosphate that meets the performance requirements for battery-grade iron phosphate, which is beneficial for its application in batteries. Simultaneously, this application utilizes low-cost, low-purity sodium phosphate to prepare high-purity, high-performance iron phosphate, significantly reducing preparation costs. The preparation process is relatively simple and can be industrialized, which is beneficial for the preparation and application of iron phosphate.

[0108] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing ferric phosphate using low-purity sodium phosphate, characterized in that, include: The aluminum phosphate slag was placed in a sodium hydroxide solution, reacted, filtered, and the filtrate was frozen to crystallize. After centrifugation, low-purity sodium phosphate was obtained. The low-purity sodium phosphate is mixed with sulfuric acid solution to form a mixture, wherein the concentration of sulfuric acid solution is greater than or equal to 50%, the pH value of the mixture is 4.5~7, and the low-purity sodium phosphate contains impurities, wherein the impurities contain aluminum. The mixture is filtered after the first reaction to obtain the first filtrate; The first filtrate is filtered after freezing treatment to obtain the second filtrate. The freezing treatment includes holding at 5℃~30℃ for 0.5h~1h, and then holding at -10℃~0℃ for 2h~5h. The second filtrate is mixed with an iron salt solution, and / or the second filtrate is mixed with a ferrous salt solution and an oxidant, and then filtered through a second reaction to obtain the filtrate. The filtered material is aged, washed and calcined to obtain ferric phosphate. The aging process includes adding water to the filtered material to form a slurry. A third reaction is carried out by adding phosphoric acid solution to the slurry, wherein the solid content of the slurry is 5% to 30% and the concentration of the phosphoric acid solution is 5 g / L to 25 g / L, and the third reaction includes reacting at 70℃ to 95℃ for 0.5 h to 4 h.

2. The method as described in claim 1, characterized in that, The first reaction includes reacting at 15℃~40℃ for 15min~60min; The second reaction includes reacting at 55℃~90℃ for 0.5h~2h.

3. The method as described in claim 1, characterized in that, The calcination includes treatment at 500℃~800℃ for 1h~5h.

4. The method as described in claim 1, characterized in that, The phosphorus concentration in the mixture is 25 g / L to 40 g / L; The phosphorus concentration in the second filtrate is 25 g / L to 35 g / L, and the pH value of the second filtrate is 6 to 7.

5. The method as described in claim 1, characterized in that, The cleaning process includes treatment at 30℃~80℃ for 15min~120min.

6. The method as described in claim 1, characterized in that, The purity of the low-purity sodium phosphate is less than or equal to 90%.

7. The method as described in claim 1, characterized in that, The ferric phosphate has a particle size D50 of 2μm to 5μm and a specific surface area of ​​8m². 2 / g~14m 2 / g.

8. The method as described in claim 1, characterized in that, The iron phosphate contains 35.5% to 36.5% iron and 63.0% to 64.5% phosphate, with a molar ratio of iron to phosphorus of 0.955 to 0.980.

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