A method for preparing low-impurity ferric phosphate using a hetero-iron-containing source, low-impurity ferric phosphate and applications

Abstract

This invention belongs to the field of battery cathode material preparation technology, and discloses a method for preparing low-impurity iron phosphate using an iron source containing impurities, the low-impurity iron phosphate, and its application. The method includes the following steps: dissolving an iron source in a mixture of sulfuric acid and phosphoric acid, heating, and filtering to obtain solution A; using solution A as the base liquid in a reaction vessel, adding an oxidant, and then adjusting the pH of the solution with sulfuric acid to obtain solution B; adding iron phosphate dihydrate seed crystals to solution B, heating, and obtaining a white slurry; solid-liquid separation, washing, drying, and calcination to obtain the final product. In the reaction process of this invention, by adjusting the pH of the system, controlling the composition of the complexes in the solution, and introducing iron phosphate seed crystals to induce precipitation, the effective separation of iron phosphate from impurities such as aluminum, magnesium, and manganese is achieved, and the final iron phosphate product meets the impurity content standards. This method utilizes a low-cost iron source to produce iron phosphate with properties comparable to conventional iron sources, significantly reducing raw material costs.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material preparation technology, and in particular to a method for preparing low-impurity iron phosphate using a mixed iron source, the low-impurity iron phosphate, and its application. Background Technology

[0002] Currently, the main methods for preparing lithium iron phosphate include the ammonium method, the sodium method, and the iron method. Among them, the iron method has attracted much attention due to its lower by-products and less environmental impact. In recent years, the price of ferrous sulfate, a key raw material used in the ammonium / sodium method, has risen sharply due to insufficient titanium dioxide production, significantly increasing the production cost of lithium iron phosphate. Therefore, the cost advantage of the iron method has gradually become more prominent. The traditional iron method uses high-purity iron sources such as pure iron powder and iron blocks as raw materials, which react with phosphoric acid to produce a ferrous dihydrogen phosphate solution, followed by oxidation and precipitation to obtain lithium iron phosphate. With the rapid expansion of the lithium iron phosphate market, in order to cope with increasingly fierce market competition, the industry has begun to try to replace pure iron powder with cheaper iron sources such as iron oxide scale, iron black, ferric phosphate slag, and siderite. However, these cheaper iron sources usually contain high levels of impurities such as aluminum, magnesium, manganese, and titanium, which enter the lithium iron phosphate mixture during dissolution and are difficult to remove effectively later, resulting in excessive impurities in the lithium iron phosphate product, failing to meet battery-grade requirements.

[0003] In existing technologies, removing impurities from ferric phosphate solutions typically requires complex impurity removal processes at the raw material end, such as adding alkali to adjust pH for precipitation and adding complexing agents. For example, Chinese patent publication CN119794053A provides a method for removing impurities from ferric phosphate slag, obtaining high-purity ferric phosphate solution through steps such as high-temperature calcination with chlorination, leaching, sodium fluoride treatment, and iron powder reduction; Chinese patent publication CN120246954A uses a stepwise acid leaching combined with a two-step synthesis method of ferric phosphate to prepare low-aluminum titanium ferric phosphate; and Chinese patent publication CN107863531B uses siderite as raw material, dissolving it with low-concentration phosphoric acid and oxidizing it with hydrogen peroxide to obtain a precursor of ferric phosphate dihydrate. Among these methods, the first two have long process flows, introduce additional ions such as ammonium and fluorine, increase the difficulty of reusing phosphorus-containing mother liquor, and have high impurity removal costs; while the latter method, although simple in process, does not consider the problem of impurity removal, and the resulting ferric phosphate product has difficulty meeting the standards for impurities such as aluminum, magnesium, and manganese.

[0004] Therefore, how to use inexpensive iron sources as raw materials, simplify the process, and efficiently remove impurities such as aluminum, magnesium, and manganese from iron-phosphorus mixtures to prepare iron phosphate that meets battery-grade requirements has become a pressing technical challenge in this field. To address this, this invention proposes a synergistic seed-induced precipitation method combining pH control and complex morphology control. This method directly achieves efficient separation of impurities such as aluminum, magnesium, and manganese in the one-step synthesis stage of iron phosphate, while simplifying the dissolution and impurity removal process and the two-step synthesis process of iron phosphate, thus achieving extreme cost reduction. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing low-impurity iron phosphate using a mixed iron source, as well as the application of low-impurity iron phosphate.

[0006] The technical solution adopted by this invention to solve its technical problem is: A method for preparing low-impurity iron phosphate using a mixed iron source includes the following steps: S1. Dissolution: Iron is dissolved in a mixture of sulfuric acid and phosphoric acid, heated to 90-95℃ and kept at that temperature, and then filtered to obtain solution A. S2, Pre-oxidation: Using solution A as the base liquid in the reactor, an oxidant is added to oxidize Fe. 2+ Oxidized to Fe 3+ Then, adjust the pH of the solution to 0.1–0.8 with sulfuric acid to obtain solution B; S3, Seed-induced precipitation: Add ferric phosphate dihydrate seed crystals to solution B, heat to 90-98℃ and keep at that temperature for 0.5-3 h to obtain a white slurry; S4. The white slurry is subjected to solid-liquid separation and washing to obtain a white filter cake, which is then dried and calcined to obtain the low-impurity ferric phosphate.

[0007] Furthermore, in step S1, the iron source is prepared by any one or a combination of two or more of pure iron powder, iron oxide scale, iron black, siderite, and phosphate slag.

[0008] Further, in step S1, the heat preservation time is 2 to 6 hours; in step S1, the pH of the solution A is 0.4 to 1.5; in step S1, the molar ratio of iron:sulfuric acid:phosphoric acid in the iron source is 1:(0.5 to 1):(1 to 3).

[0009] Furthermore, in step S2, the oxidant is any one or a combination of two or more of air, oxygen, and hydrogen peroxide.

[0010] Furthermore, in step S3, the amount of ferric phosphate dihydrate seed crystals added is greater than 5% of the molar amount of iron in solution B; the heating time to 90-98℃ is 30-120 min.

[0011] Further, in step S4, the washing is performed until the conductivity of the wash water is ≤1000 μS / cm; the drying temperature is 100~150℃ and the drying time is 2h; the calcination temperature is 550~650℃ and the calcination time is 4h.

[0012] The low-impurity iron phosphate was prepared by the method described above.

[0013] The application of low-impurity iron phosphate in battery manufacturing, as described above.

[0014] The method described above is used to efficiently remove aluminum, magnesium, and manganese impurities from iron phosphate mixtures and prepare iron phosphate that meets battery-grade requirements.

[0015] The advantages and positive effects of this invention are as follows: 1. This invention uses a mixed acid composed of phosphoric acid and sulfuric acid as the phosphorus source. After dissolving the iron source containing impurities, a high-impurity mixed solution containing ferrous dihydrogen phosphate and ferrous sulfate is obtained. Ferric phosphate is then prepared using this solution as a raw material. During the reaction, by adjusting the pH of the system, controlling the composition of the complexes in the solution, and introducing ferric phosphate seeds to induce precipitation, the effective separation of ferric phosphate from impurities such as aluminum, magnesium, and manganese is achieved. The final ferric phosphate product meets the impurity content standards. This invention's method can produce ferric phosphate with comparable performance to conventional iron sources using a low-cost iron source, significantly reducing raw material costs.

[0016] 2. This invention can use inexpensive iron sources such as siderite and ferrophosphate slag as raw materials to replace expensive pure iron powder, which significantly reduces the production cost of iron phosphate.

[0017] 3. This invention directly uses the dissolved high-impurity ferrous dihydrogen phosphate solution, eliminating the need for complex impurity removal processes at the raw material end (such as adding alkali to adjust pH, adding complexing agents, etc.). The system does not introduce additional ions such as ammonium ions and fluorine, which simplifies the process and saves costs while ensuring the reuse of subsequent phosphorus-containing mother liquor.

[0018] 4. This invention achieves efficient separation of iron from impurities such as aluminum, magnesium, and manganese through the synergistic effect of pH control and seed crystal-induced precipitation. Under strongly acidic conditions (pH = 0.1–0.8), impurity ions such as aluminum, magnesium, and manganese are difficult to precipitate, while iron and phosphorus ions are selectively precipitated under the induction of iron phosphate seed crystals. The final product's impurity content can meet the battery-grade iron phosphate standard.

[0019] 5. This invention, through a pre-oxidation process, ensures that the ions in the solution are transformed into FeH2PO4 before seed-induced precipitation. 2+ and Fe(H2PO4)2 + Fe 3+ With H2PO4 - The stability constant of the complex (lg K = 5~6) is much higher than that of Al. 3+ (lg K=2~3) and Mg 2+ Mn 2+ (lg K = 1~2). After adding seed crystals, FeH2PO4 2+ and Fe(H2PO4)2 + The ions are rapidly induced to precipitate, while other ions remain in the mother liquor.

[0020] 6. This invention uses pH control, pre-oxidation, and seed crystal method to distribute impurities such as aluminum, magnesium, and manganese into dilute sulfuric acid-phosphoric acid mother liquor. Combined with commercially available nanofiltration separation technology, it can effectively remove metal ions from the acid solution. The purified acid solution can be reused in the iron source dissolution process, achieving efficient recycling of resources.

[0021] 7. In this invention, the system has a low pH and no precipitation occurs during the oxidation process. Based on this characteristic, the pre-oxidation stage can be separated from the main process and used as a raw material preparation step. Excess or by-product oxygen, which is inexpensive, can be used for large-scale oxidation and storage, thereby reducing production costs.

[0022] 8. Currently, whether using traditional iron-based processes or emerging processes that use inexpensive iron sources such as iron oxide scale, iron black, ferrophosphate slag, and siderite to replace iron powder, all require dissolving iron-containing materials to form a ferrophosphate mixture before use in ferric phosphate preparation. However, inexpensive iron sources typically contain high levels of impurities such as aluminum, manganese, magnesium, and titanium. These impurities enter the ferrophosphate mixture during dissolution and are difficult to remove to battery-grade requirements. Therefore, how to prepare low-impurity ferric phosphate from a high-impurity ferrophosphate mixture has become a pressing problem for the industry. This invention provides a method for preparing low-impurity ferric phosphate from a high-impurity ferrophosphate mixture at low cost. By controlling pH and complexation morphology in synergistic seed-induced precipitation, a low-cost, low-impurity ferric phosphate is prepared, solving the aforementioned problem. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the method of the present invention; Figure 2 This is a graph showing the impurity content of ferric phosphate in each embodiment and comparative example of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0025] The various experimental operations involved in the specific embodiments are all conventional techniques in the art. For parts not specifically annotated herein, those skilled in the art can refer to various commonly used reference books, scientific and technological literature, or related instructions and manuals prior to the filing date of this invention for implementation. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art, and the raw materials used are all commercially available products.

[0026] A method for preparing low-impurity ferric phosphate using a mixed iron source, low-impurity ferric phosphate, and its application, comprising the following steps: S1. Dissolution: Iron is dissolved in a mixture of sulfuric acid and phosphoric acid, heated to 90-95℃ and kept at that temperature, and then filtered to obtain solution A. S2, Pre-oxidation: Using solution A as the base liquid in the reactor, an oxidant is added to oxidize Fe. 2+ Oxidized to Fe 3+ Then, adjust the pH of the solution to 0.1–0.8 with sulfuric acid to obtain solution B; S3, Seed-induced precipitation: Add ferric phosphate dihydrate seed crystals to solution B, heat to 90-98℃ and keep at that temperature for 0.5-3 h to obtain a white slurry; S4. The white slurry is subjected to solid-liquid separation and washing to obtain a white filter cake, which is then dried and calcined to obtain the low-impurity ferric phosphate.

[0027] Furthermore, in step S1, the iron source is prepared by any one or a combination of two or more of pure iron powder, iron oxide scale, iron black, siderite, and phosphate slag.

[0028] Further, in step S1, the heat preservation time is 2 to 6 hours; in step S1, the pH of the solution A is 0.4 to 1.5; in step S1, the molar ratio of iron:sulfuric acid:phosphoric acid in the iron source is 1:(0.5 to 1):(1 to 3).

[0029] Furthermore, in step S2, the oxidant is any one or a combination of two or more of air, oxygen, and hydrogen peroxide.

[0030] Furthermore, in step S3, the amount of ferric phosphate dihydrate seed crystals added is greater than 5% of the molar amount of iron in solution B; the heating time to 90-98℃ is 30-120 min.

[0031] Further, in step S4, the washing is performed until the conductivity of the wash water is ≤1000 μS / cm; the drying temperature is 100~150℃ and the drying time is 2h; the calcination temperature is 550~650℃ and the calcination time is 4h.

[0032] The low-impurity iron phosphate was prepared by the method described above.

[0033] The application of low-impurity iron phosphate in battery manufacturing, as described above.

[0034] The method described above is used to efficiently remove aluminum, magnesium, and manganese impurities from iron phosphate mixtures and prepare iron phosphate that meets battery-grade requirements.

[0035] Specifically, the relevant preparation and testing methods are as follows: In the specific embodiments below, the iron source used is siderite flotation concentrate powder (hereinafter referred to as siderite concentrate). The component analysis results of the dried siderite concentrate are shown in Table 1: Table 1. Analysis of major components of siderite concentrate (mass percentage)

[0036] Example 1 A method for preparing low-impurity iron phosphate using a mixed iron source can be as follows: Figure 1 As shown, its preparation process is as follows: 1) Dissolution: Add 6 L of water to a 10 L reactor, then add 1.3 kg of phosphoric acid (85 wt%) and 1 kg of concentrated sulfuric acid. Mix thoroughly and heat to 90 ℃. Weigh 1.5 kg of siderite concentrate powder and slowly add it. Keep at 90 ℃ for 4 h, and filter to obtain solution A. The pH of the obtained solution A is 0.88, and the molar ratio of iron, sulfuric acid and phosphoric acid is 1 : 0.8 : 1.1.

[0037] 2) Pre-oxidation: Using 2 L of solution A as the base liquid, place it in the reaction vessel, and add 200 g of hydrogen peroxide solution (27.5 wt%, mass concentration) at a uniform rate over 30 min. Then, add Fe... 2+ All oxidized to Fe 3+ Solution B was obtained.

[0038] 3) Seed-induced precipitation: 100 g of iron phosphate dihydrate seed slurry (iron content 150 g / L) was added to solution B, heated to 98 ℃ for 60 min, and kept at that temperature for 2 h to obtain a white slurry.

[0039] 4) The white slurry was filtered and washed until the conductivity of the wash water was <1000 μS / cm to obtain a white filter cake. The filter cake was dried at 120 ℃ for 2 h to obtain ferric phosphate dihydrate, and then calcined at 600 ℃ for 4 h to obtain anhydrous ferric phosphate material, i.e., low-impurity ferric phosphate.

[0040] Example 2 The process parameters in this embodiment are consistent with those in Embodiment 1. The difference is that in step 2), sulfuric acid is added to lower the pH of the bottom solution to 0.5, as detailed below: 1) Dissolution: Add 6 L of water to a 10 L reactor, then add 1.3 kg of phosphoric acid (85 wt%) and 1 kg of concentrated sulfuric acid. Mix thoroughly and heat to 90 ℃. Weigh 1.5 kg of siderite concentrate powder and slowly add it. Keep at 90 ℃ for 4 h, and filter to obtain solution A. The pH of the obtained solution A is 0.88, and the molar ratio of iron, sulfuric acid and phosphoric acid is 1 : 0.8 : 1.1.

[0041] 2) Pre-oxidation: Using 2 L of solution A as the base solution, place it in a reaction vessel, add 40 g of concentrated sulfuric acid to lower the pH of the base solution to 0.5, and then uniformly add 200 g of hydrogen peroxide solution (27.5 wt%, mass concentration) over 30 min. This will allow the Fe... 2+ All oxidized to Fe 3+ Solution B was obtained.

[0042] 3) Seed-induced precipitation: 100 g of iron phosphate dihydrate seed slurry (iron content 150 g / L) was added to solution B, heated to 98 ℃ for 60 min, and kept at that temperature for 2 h to obtain a white slurry.

[0043] 4) The white slurry was filtered and washed until the conductivity of the wash water was <1000 μS / cm to obtain a white filter cake. The filter cake was dried at 120 ℃ for 2 h to obtain ferric phosphate dihydrate, and then calcined at 600 ℃ for 4 h to obtain anhydrous ferric phosphate material, i.e., low-impurity ferric phosphate.

[0044] Example 3 The process parameters in this embodiment are the same as in Embodiment 1. The difference is that in step 3), the heating time is reduced from 60 minutes to 30 minutes, as detailed below: 1) Dissolution: Add 6 L of water to a 10 L reactor, then add 1.3 kg of phosphoric acid (85 wt%) and 1 kg of concentrated sulfuric acid. Mix thoroughly and heat to 90 ℃. Weigh 1.5 kg of siderite concentrate powder and slowly add it. Keep at 90 ℃ for 4 h, and filter to obtain solution A. The pH of the obtained solution A is 0.88, and the molar ratio of iron, sulfuric acid and phosphoric acid is 1 : 0.8 : 1.1.

[0045] 2) Pre-oxidation: Using 2 L of solution A as the base liquid, place it in the reaction vessel, and add 200 g of hydrogen peroxide solution (27.5 wt%, mass concentration) at a uniform rate over 30 min. Then, add Fe... 2+ All oxidized to Fe 3+ Solution B was obtained.

[0046] 3) Seed-induced precipitation: 100 g of iron phosphate dihydrate seed slurry (iron content 150 g / L) was added to solution B, heated to 98 ℃ for 30 min, and kept at that temperature for 2 h to obtain a white slurry.

[0047] 4) The white slurry was filtered and washed until the conductivity of the wash water was <1000 μS / cm to obtain a white filter cake. The filter cake was dried at 120 ℃ for 2 h to obtain ferric phosphate dihydrate, and then calcined at 600 ℃ for 4 h to obtain anhydrous ferric phosphate material, i.e., low-impurity ferric phosphate.

[0048] Comparative Example 1 This comparative example uses the traditional iron-based method for preparing iron phosphate, as detailed below: 1) Dissolution: The siderite concentrate was placed in a reaction vessel containing a dilute phosphoric acid solution (mass concentration of 7%) and stirred to dissolve. The molar ratio of phosphorus to (iron + magnesium + manganese) was controlled at 2.5:1. The temperature was raised to 90℃ and kept at the temperature for 4 h. The solution was then filtered to obtain the dissolved solution. 2) Synthesis oxidation: Using 2L of solution as the base liquid, control the temperature of the base liquid at 55℃, add 200g of hydrogen peroxide solution (27.5wt%, mass concentration) to the reactor at a uniform rate over 50 min. After the addition is completed, raise the temperature to 90℃ for 30 min and keep it at that temperature for 2 h. 3) Washing, drying and calcining: Filter and wash until the conductivity of the wash water is ≤800 μS / cm to obtain a white filter cake. Dry at 120℃ for 2 h and calcinate at 580℃ for 4 h to obtain the iron phosphate material.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that the pre-oxidation step was not performed; all other operations remain the same, as follows: 1) Dissolution: Add 6 L of water to a 10 L reactor, then add 1.3 kg of phosphoric acid (85 wt%) and 1 kg of concentrated sulfuric acid. Mix thoroughly and heat to 90 ℃. Weigh 1.5 kg of siderite concentrate powder and slowly add it. Keep at 90 ℃ for 4 h, and filter to obtain solution A. The pH of the obtained solution A is 0.88, and the molar ratio of iron, sulfuric acid and phosphoric acid is 1 : 0.8 : 1.1.

[0050] 2) Induced precipitation and oxidation: Using 2 L of solution A as the base solution in a reactor, 100 g of ferric phosphate dihydrate seed slurry (iron content 150 g / L) was added to solution A. Then, 200 g of hydrogen peroxide solution (27.5 wt%, mass concentration) was added uniformly over 30 min to induce precipitation and oxidation. 2+ All oxidized to Fe 3+ Then, the temperature is raised to 98 °C for 60 minutes and kept at that temperature for 2 hours to obtain a white slurry.

[0051] 3) The white slurry was filtered and washed until the conductivity of the wash water was <1000 μS / cm to obtain a white filter cake. The filter cake was dried at 120 ℃ for 2 h to obtain ferric phosphate dihydrate, and then calcined at 600 ℃ for 4 h to obtain anhydrous ferric phosphate material.

[0052] Comparative Example 3 The main difference between this comparative example and Example 1 is that the pH of the solution was not lowered, as detailed below: 1) Dissolution: Add 6 L of water to a 10 L reactor, then add 1.3 kg of phosphoric acid (85 wt%) and 0.5 kg of concentrated sulfuric acid. Mix thoroughly and heat to 95 ℃. Weigh 1.5 kg of siderite concentrate powder and slowly add it. Keep at 95 ℃ for 4 h, and filter to obtain solution A. The pH of the obtained solution A is 1.23, and the molar ratio of iron, sulfuric acid and phosphoric acid is 1:0.4:1.1.

[0053] 2) Pre-oxidation: Using 2 L of solution A as the base liquid, place it in the reaction vessel, and add 200 g of hydrogen peroxide solution (27.5 wt%, mass concentration) at a uniform rate over 30 min. Then, add Fe... 2+ All oxidized to Fe 3+ Slurry B is obtained.

[0054] 3) Seed-induced precipitation: 100 g of iron phosphate dihydrate seed slurry (iron content 150 g / L) was added to slurry B, and the temperature was raised to 98 ℃ after 60 min and kept at that temperature for 2 h to obtain a white slurry.

[0055] 4) The white slurry was filtered and washed until the conductivity of the wash water was <1000 μS / cm to obtain a white filter cake. The filter cake was dried at 120 ℃ for 2 h to obtain ferric phosphate dihydrate, and then calcined at 600 ℃ for 4 h to obtain anhydrous ferric phosphate material.

[0056] Experimental Section Impurities were detected in the ferric phosphate samples prepared in Examples 1-3 and Comparative Examples 1-3, and the results are shown in Table 1. For further analysis, the data in Table 1 were plotted, and the results are as follows: Figure 2 As shown.

[0057] Table 1 Comparison and analysis of impurities in each sample

[0058] As shown in Table 1 and Figure 2 The data show that Examples 1-3 all successfully prepared low-impurity iron phosphate materials. Compared with Comparative Example 1 (conventional iron method), the contents of impurities such as Al, Mg, Mn, and Ca in Examples 1-3 were significantly reduced. Specifically, the Al content decreased by approximately 66%-71%, the Mg content decreased by over 90%, and the Mn content decreased by approximately 74%-86%. This indicates that the "pH-controlled synergistic seed-induced precipitation" process can achieve efficient separation of iron from impurities such as aluminum, magnesium, and manganese.

[0059] In Comparative Example 2 (without pre-oxidation, seed crystals added before oxidation), the Al content was 202 ppm, close to that of Comparative Example 1 (207 ppm), but significantly higher than that of Example 1 (65 ppm), demonstrating the importance of the pre-oxidation process. Pre-oxidation converts iron into Fe... 3+ It exists in the form of H2PO4.- Strong complexes are formed, which preferentially precipitate under seed induction, thus avoiding Al. 3+ with Fe 3+ Co-precipitation significantly reduces the aluminum content in the product.

[0060] The Al content in Comparative Example 3 (solution pH 1.23, without additional acid to lower it) was 184 ppm, significantly higher than that in Example 1 (65 ppm). This is because precipitation begins during the pre-oxidation stage under higher pH conditions, resulting in severe co-precipitation of aluminum and iron.

[0061] Meanwhile, by comparing Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that in step 1) of the method of the present invention, "6 L of water is added to a 10 L reactor, followed by 1.3 kg of phosphoric acid (85 wt%, mass concentration) and 1 kg of concentrated sulfuric acid. After mixing evenly, the mixture is heated to 90 °C. 1.5 kg of siderite concentrate powder is weighed and slowly added, and the mixture is kept at 90 °C for 4 h. The solution A is obtained by filtration. The pH of the obtained solution A is 0.88, and the molar ratio of iron, sulfuric acid, and phosphoric acid is 1:0.8:1.1." and in step 2), "2 L of solution A is placed in a reactor as the base liquid, and 200 g of hydrogen peroxide solution (27.5 wt%, mass concentration) is added at a uniform rate over 30 min, and Fe..." 2+ All oxidized to Fe 3+ The two steps have a synergistic effect, which can synergistically reduce the content of impurities such as Al, Mg, Mn, and Ca in the prepared anhydrous ferric phosphate material, i.e., low-impurity ferric phosphate. In particular, it can significantly synergistically reduce the content of Al impurities in the prepared anhydrous ferric phosphate material, i.e., low-impurity ferric phosphate.

[0062] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing low-impurity iron phosphate using a source containing mixed iron, characterized in that: Includes the following steps: S1. Dissolution: Iron is dissolved in a mixture of sulfuric acid and phosphoric acid, heated to 90-95℃ and kept at that temperature, and then filtered to obtain solution A. S2, Pre-oxidation: Using solution A as the base liquid in the reactor, an oxidant is added to oxidize Fe. 2+ Oxidized to Fe 3+ Then, adjust the pH of the solution to 0.1–0.8 with sulfuric acid to obtain solution B; S3, Seed-induced precipitation: Add ferric phosphate dihydrate seed crystals to solution B, heat to 90-98℃ and keep at that temperature for 0.5-3 h to obtain a white slurry; S4. The white slurry is subjected to solid-liquid separation and washing to obtain a white filter cake, which is then dried and calcined to obtain the low-impurity ferric phosphate.

2. The method according to claim 1, characterized in that: In step S1, the iron source is prepared by any one or a combination of two or more of pure iron powder, iron oxide scale, iron black, siderite, and phosphate slag.

3. The method according to claim 1, characterized in that: In step S1, the heat preservation time is 2 to 6 hours; in step S1, the pH of the solution A is 0.4 to 1.5; in step S1, the molar ratio of iron:sulfuric acid:phosphoric acid in the iron source is 1:(0.5 to 1):(1 to 3).

4. The method according to claim 1, characterized in that: In step S2, the oxidant is any one or a combination of two or more of air, oxygen, and hydrogen peroxide.

5. The method according to claim 1, characterized in that: In step S3, the amount of ferric phosphate dihydrate seed crystals added is greater than 5% of the molar amount of iron in solution B; the heating time to 90-98℃ is 30-120 min.

6. The method according to claim 1, characterized in that: In step S4, the washing is performed until the conductivity of the wash water is ≤1000 μS / cm; the drying temperature is 100~150℃ and the drying time is 2h; the calcination temperature is 550~650℃ and the calcination time is 4h.

7. Low-impurity iron phosphate prepared by the method according to any one of claims 1 to 6.

8. The application of low-impurity iron phosphate as described in claim 7 in battery preparation.

9. The application of the method according to any one of claims 1 to 6 in the efficient removal of aluminum, magnesium, and manganese impurities from a phosphorus-iron mixture and the preparation of phosphorus-iron phosphate that meets battery-grade requirements.

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