A method for preparing iron phosphate dihydrate using wet-process phosphoric acid

Abstract

The present disclosure belongs to the technical field of battery materials, and particularly relates to a method for preparing iron phosphate dihydrate by using wet-process phosphoric acid, comprising the following steps: (1) mixing a wet-process phosphoric acid solution with an aluminum shielding agent to obtain a mixed solution, and then adding a pH regulator and standing; the aluminum shielding agent is at least one of malonate, succinate and phthalate; (2) performing water bath on the mixed solution obtained in step (1) under stirring, adding iron sulfate to the mixed solution, and then adding iron phosphate dihydrate seeds, and then performing solid-liquid separation after reaction to obtain a solid, and then washing to obtain iron phosphate dihydrate.

Description

Technical Field

[0001] This disclosure belongs to the field of battery materials technology, and specifically relates to a method for preparing iron phosphate dihydrate using wet phosphoric acid. Background Technology

[0002] Since their invention, lithium-ion batteries have attracted widespread attention due to their advantages such as high specific energy, long lifespan, and low pollution. Among them, lithium iron phosphate batteries have become an important branch of lithium batteries due to their high safety, low manufacturing cost, and good electrochemical performance. As a precursor material for the preparation of lithium iron phosphate, the low-cost, high-quality synthesis and production process of iron phosphate is receiving increasing attention. One important method for preparing iron phosphate is the synthesis of iron phosphate dihydrate from phosphoric acid and iron salts, followed by further calcination to remove crystallization water.

[0003] Currently, there are two main methods for producing phosphoric acid: pyrometallurgical and wet processes. Pyrometallurgical phosphoric acid has high purity, but its production cost remains high; wet process phosphoric acid has lower cost, but it contains more impurities. As one of the more abundant impurities in wet process phosphoric acid, aluminum ions, like iron ions, can form insoluble precipitates with phosphate ions. Furthermore, aluminum phosphate and iron phosphate have similar solubility products, making them easily mixed into the product during synthesis and difficult to separate. Industrially, extraction and ammoniation methods are commonly used to remove impurities from wet process phosphoric acid, but these methods suffer from significant phosphorus loss and low utilization value of byproducts.

[0004] Ferric phosphate dihydrate is a precursor to ferric phosphate, and its impurity content significantly affects the quality of the ferric phosphate obtained from calcination, thereby impacting the performance of lithium iron phosphate. Therefore, controlling its impurity content is of paramount importance. Summary of the Invention

[0005] This disclosure aims to at least address one of the technical problems existing in the related art. To this end, this disclosure proposes a method for preparing ferric phosphate dihydrate using a wet-process phosphoric acid method, which can effectively reduce the impurity content in the prepared ferric phosphate dihydrate, especially the aluminum impurity content.

[0006] The above-mentioned technical objective of this disclosure is achieved through the following technical solution:

[0007] A method for preparing ferric phosphate dihydrate using wet phosphoric acid includes the following steps: (1) mixing wet phosphoric acid solution with an aluminum shielding agent to form a mixture, adding a pH adjuster and allowing it to stand, wherein the aluminum shielding agent is at least one of malonate, succinate and phthalate; (2) subjecting the mixture obtained in step (1) to a water bath under stirring, adding ferric sulfate to the mixture, then adding ferric phosphate dihydrate seed crystals, and after the reaction, separating the solid and liquid to obtain a solid, which is then washed to obtain the ferric phosphate dihydrate.

[0008] In one embodiment, in step (1), the concentration of P in the wet-process phosphoric acid solution is 0.2-2.5 mol / L.

[0009] In one embodiment, in step (1), the concentration of P in the wet-process phosphoric acid solution is 0.5-2.0 mol / L.

[0010] In one embodiment, in step (1), the concentration of the aluminum shielding agent is 0.05-2.5 mol / L.

[0011] In one embodiment, in step (1), the concentration of the aluminum shielding agent is 0.1-2 mol / L.

[0012] In one embodiment, in step (1), the wet phosphoric acid solution is mixed with the aluminum shielding agent by adding the aluminum shielding agent into the wet phosphoric acid solution.

[0013] In one embodiment, the amount of aluminum shielding agent added is 120%-500% of the theoretical amount, wherein the theoretical amount refers to the total molar amount of shielding agent added being equal to the molar amount of Al in one equivalent of phosphoric acid solution.

[0014] In one embodiment, in step (1), the pH adjuster is ammonia water, and after adding the pH adjuster, the pH of the mixture is 1.0-2.5.

[0015] In one embodiment, the mass concentration of the ammonia solution is 5%-15%.

[0016] In one embodiment, in step (1), the settling time is 0.5-4 hours.

[0017] In one embodiment, in step (2), the temperature of the water bath is 70-98°C.

[0018] In one embodiment, in step (2), the stirring speed is 300-600 rpm.

[0019] In one embodiment, in step (2), the molar amount of ferric sulfate added is 0.4-0.6 times the molar amount of phosphoric acid in the wet phosphoric acid solution.

[0020] In one embodiment, in step (2), after the added ferric sulfate has dissolved, the ferric phosphate seed crystals dihydrate are added.

[0021] In one embodiment, in step (2), the ratio of the mass of the added iron phosphate dihydrate seed crystals to the theoretical mass of the product is 1:(5-50), where the theoretical mass refers to the mass of the synthesized product calculated based on a 100% yield.

[0022] In one embodiment, in step (2), after adding iron phosphate dihydrate seed crystals, the mixture is heated in a water bath and reacted under stirring for 4-8 hours before solid-liquid separation.

[0023] In one embodiment, the present disclosure discloses a method for preparing ferric phosphate dihydrate using wet-process phosphoric acid, comprising the following steps:

[0024] (1) Preparation of aluminum shielding agent: Take one or more of the mononuclear bidentate carboxylic acid complexes such as malonate, succinate, and phthalate to prepare an aluminum shielding agent for later use. The concentration of the aluminum shielding agent is 0.1-2 mol / L.

[0025] (2) Prepare dilute phosphoric acid solution: Take a certain volume of wet phosphoric acid, dilute it to a P concentration of 0.5-2.0 mol / L, and transfer it to a beaker;

[0026] (3) At room temperature, slowly add aluminum shielding agent to dilute phosphoric acid solution to form a mixture. The amount of aluminum shielding agent added is 120-500% of the theoretical amount. After stirring thoroughly, adjust the pH of the solution to between 1.0 and 2.5 with ammonia water with a mass concentration of 5%-15%. Let it stand at room temperature for 0.5-4 hours to allow the generated aluminum complex to be fully stabilized.

[0027] (4) Transfer the beaker containing the mixture to a water bath, set the water bath temperature between 70-98℃, adjust the stirring speed to 300-600rpm, stir continuously, and add the pre-weighed ferric sulfate to the system. The amount of ferric sulfate added is 0.7-1.1 times the amount of phosphate.

[0028] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate product. The ratio of the mass of the added seed crystals to the theoretical mass of the product is between 1:(5-50).

[0029] (6) React under water bath heating and stirring for 4-8 hours, filter, wash the precipitate with deionized water to prepare ferric phosphate dihydrate product.

[0030] The beneficial effects of this disclosure are:

[0031] (1) The preparation method disclosed herein uses a specific aluminum shielding agent that does not complex with iron ions to mask aluminum ions in the mixture. This allows aluminum ions to remain in the solution as complexes and not participate in precipitation. At the same time, the aluminum ions exist in the solution as complexes and do not enter the iron dihydrate product. This also avoids the situation where the shielding agent complexes with iron, resulting in low iron utilization. This greatly reduces the aluminum content of impurities in the iron dihydrate product, achieves efficient separation of the product and impurities, and improves product quality.

[0032] (2) The aluminum shielding method used in the preparation method disclosed herein is less restricted by the system and can be used in other non-oxidizing acidic systems, thus having a wide range of applications. Therefore, it has practical significance for improving the wet process of phosphoric acid to iron phosphate synthesis.

[0033] (3) This disclosure provides a simple preparation method to obtain a ferric phosphate dihydrate product with qualified aluminum content, without the need for aluminum removal by precipitation and filtration, thus reducing phosphorus loss during the impurity removal process. Attached Figure Description

[0034] Figure 1 This is a SEM image of ferric phosphate dihydrate prepared in Example 1 of this disclosure. Detailed Implementation

[0035] The present disclosure will be further described below with reference to specific embodiments.

[0036] Example 1:

[0037] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0038] (1) Preparation of aluminum shielding agent: Weigh a certain amount of disodium malonate and dissolve it in water to prepare an aluminum shielding agent with a concentration of 1 mol / L;

[0039] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0040] (3) At room temperature, aluminum shielding agent is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of aluminum shielding agent added is 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with ammonia water with a mass concentration of 15%. The solution is left to stand at room temperature for 4 hours to allow the generated aluminum complex to stabilize fully.

[0041] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0042] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0043] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water to obtain ferric phosphate dihydrate product. The SEM image of the prepared ferric phosphate dihydrate is shown below. Figure 1 As shown, by Figure 1 It can be seen that the prepared ferric phosphate dihydrate is an aggregate composed of plate-like primary particles, with adhesion between the aggregates, and the particle size is about 10 μm. The plate-like structure of the primary particles increases its specific surface area to some extent.

[0044] Example 2: (The only difference from Example 1 is the amount of aluminum shielding agent added.)

[0045] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0046] (1) Preparation of aluminum shielding agent: Weigh a certain amount of disodium malonate and dissolve it in water to prepare an aluminum shielding agent with a concentration of 1 mol / L;

[0047] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0048] (3) At room temperature, aluminum shielding agent is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of aluminum shielding agent added is 200% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with ammonia water with a mass concentration of 15%. The solution is left to stand at room temperature for 4 hours to allow the generated aluminum complex to stabilize fully.

[0049] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0050] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0051] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0052] Example 3: (The only difference from Example 1 is the aging time)

[0053] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0054] (1) Preparation of aluminum shielding agent: Weigh a certain amount of disodium malonate and dissolve it in water to prepare an aluminum shielding agent with a concentration of 1 mol / L;

[0055] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0056] (3) At room temperature, aluminum shielding agent is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of aluminum shielding agent added is 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with ammonia water with a mass concentration of 15%. The solution is left to stand at room temperature for 0.5 hours to allow the generated aluminum complex to stabilize fully.

[0057] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0058] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0059] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0060] Example 4: (The only difference from Example 1 is the concentration of phosphoric acid after dilution)

[0061] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0062] (1) Preparation of aluminum shielding agent: Weigh a certain amount of disodium malonate and dissolve it in water to prepare an aluminum shielding agent with a concentration of 1 mol / L;

[0063] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 2.0 mol / L, and transfer it to a beaker;

[0064] (3) At room temperature, aluminum shielding agent is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of aluminum shielding agent added is 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with ammonia water with a mass concentration of 15%. The solution is left to stand at room temperature for 4 hours to allow the generated aluminum complex to stabilize fully.

[0065] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0066] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0067] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0068] Example 5: (The only difference from Example 1 is that the aluminum shielding agent used is disodium succinate)

[0069] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0070] (1) Preparation of aluminum shielding agent: Weigh a certain amount of disodium succinate and dissolve it in water to prepare an aluminum shielding agent with a concentration of 1 mol / L;

[0071] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0072] (3) At room temperature, aluminum shielding agent is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of aluminum shielding agent added is 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with ammonia water with a mass concentration of 15%. The solution is left to stand at room temperature for 4 hours to allow the generated aluminum complex to stabilize fully.

[0073] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0074] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0075] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0076] Example 6: (The only difference from Example 1 is that the aluminum shielding agent used is sodium hydrogen phthalate)

[0077] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0078] (1) Preparation of aluminum shielding agent: Weigh a certain amount of sodium hydrogen phthalate and dissolve it in water to prepare an aluminum shielding agent with a concentration of 1 mol / L;

[0079] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0080] (3) At room temperature, aluminum shielding agent is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of aluminum shielding agent added is 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with ammonia water with a mass concentration of 15%. The solution is left to stand at room temperature for 4 hours to allow the generated aluminum complex to stabilize fully.

[0081] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0082] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0083] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0084] Comparative Example 1: (Producing ferric phosphate dihydrate using the ammoniation method)

[0085] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0086] (1) Using wet-process phosphoric acid as raw material, the wet-process phosphoric acid is diluted to a dilute phosphoric acid solution with a P concentration of 1.3 mol / L, transferred into a beaker, and heated in a constant temperature water bath;

[0087] (2) Add concentrated ammonia water to the mixture under heating and stirring at 90℃, adjust the pH to 4.0, react for 2 hours, filter and wash the precipitate, mix the mother liquor and washing liquid, transfer to a beaker, and test the phosphorus concentration in the purified liquid.

[0088] (3) Add ferric sulfate to a beaker containing dilute phosphoric acid purification solution at a 1:1 iron-phosphorus molar ratio under a 95℃ water bath heating. After dissolving, add ferric phosphate dihydrate seed crystals to carry out the ferric phosphate dihydrate synthesis reaction. After 8 hours, filter, wash the precipitate, dry, and obtain ferric phosphate dihydrate. Detect the aluminum content in the product and calculate the phosphorus loss rate.

[0089] Comparative Example 2: (The only difference from Example 1 is that sodium citrate was used instead of aluminum shielding agent)

[0090] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0091] (1) Preparation of sodium citrate solution: Weigh a certain amount of sodium citrate and dissolve it in water to prepare a sodium citrate solution with a concentration of 1 mol / L;

[0092] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0093] (3) At room temperature, sodium citrate solution was slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of sodium citrate added was 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution was adjusted to 1.8 with 15% ammonia water and left to stand at room temperature for 4 hours.

[0094] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0095] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0096] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0097] Comparative Example 3: (The only difference from Example 1 is that sodium tartrate was used instead of aluminum shielding agent)

[0098] A method for preparing ferric phosphate dihydrate using wet-process phosphoric acid includes the following specific steps:

[0099] (1) Preparation of sodium tartrate solution: Weigh a certain amount of sodium tartrate and dissolve it in water to prepare a sodium tartrate solution with a concentration of 1 mol / L.

[0100] (2) Prepare dilute phosphoric acid solution: Take 60 mL of wet phosphoric acid, dilute it to prepare a dilute phosphoric acid solution with a P concentration of 1.1 mol / L, and transfer it to a beaker;

[0101] (3) At room temperature, sodium tartrate solution is slowly added to dilute phosphoric acid solution to form a mixed solution. The amount of sodium tartrate added is 300% of the theoretical amount. After stirring thoroughly, the pH of the mixed solution is adjusted to 1.8 with 15% ammonia water and left to stand at room temperature for 4 hours.

[0102] (4) Transfer the beaker containing the mixed solution to a water bath, set the water bath temperature to 95°C, adjust the speed of the stirring paddle to 500 rpm, stir continuously, and at the same time, add the pre-weighed ferric sulfate to the system according to the iron-phosphorus molar ratio of 1:1.

[0103] (5) After the ferric sulfate is dissolved, ferric phosphate dihydrate seed crystals are added to the system to promote the precipitation of ferric phosphate dihydrate. The ratio of the mass of the added seed crystals to the theoretical mass of the product is 1:10.

[0104] (6) React for 8 hours under water bath heating and stirring, filter, wash the precipitate with deionized water, and the ferric phosphate dihydrate product can be obtained.

[0105] Experimental example:

[0106] 1. Finished product quality test: The impurity content in the ferric phosphate dihydrate prepared in Examples 1-6 and Comparative Examples 1-3 was tested using an ICP-AES instrument. The test results are shown in Table 1.

[0107] Table 1: Impurity content in ferric phosphate dihydrate

[0108]

[0109]

[0110] As shown in Table 1, the Al content in the ferric phosphate dihydrate prepared by the method of this disclosure is less than 0.0244%, the Ca content is less than 0.0044%, the Mg content is less than 0.0041%, and the Na content is less than 0.0072%. The Al content in the ferric phosphate dihydrate prepared by the method of this disclosure is significantly lower than that in the ferric phosphate dihydrate prepared by the ammoniation method. In addition, comparing Example 1 with Comparative Example 2 and Comparative Example 3, it can be seen that when the aluminum shielding agent is replaced with sodium citrate or sodium tartrate, the Al content in the obtained ferric phosphate dihydrate increases significantly.

[0111] 2. Phosphorus and iron utilization rate test:

[0112] (1) Phosphorus and iron loss caused by impurity removal

[0113] Table 2 shows the phosphorus loss caused by the pretreatment before the synthesis reaction in Examples 1-6 and Comparative Examples 1-3. As can be seen from Table 2, the shielding method eliminates the need for filtration separation when pretreating the wet-process phosphoric acid solution, thus avoiding additional phosphorus loss. Compared to the ammoniation method, it achieves a higher phosphorus utilization rate.

[0114] Table 2: Phosphorus loss due to impurity removal (%)

[0115]

[0116] (2) Concentration test of residual ferric phosphorus in the synthesis mother liquor

[0117] Table 3 shows the residual iron-phosphorus concentration in the mother liquor after the synthesis reaction of Examples 1-6 and Comparative Examples 1-3. As can be seen from Table 3, when the shielding agent was replaced with the reagent in Comparative Examples 2-3 that had a good complexing effect on both iron and aluminum, the excess shielding agent reacted with some iron ions, resulting in a larger residual amount of iron-phosphorus.

[0118] Table 3: Phosphorus iron concentration in the mother liquor (g / L)

[0119]

Claims

1. A process for the preparation of iron phosphate dihydrate from wet-process phosphoric acid, characterized in that: The method comprises the following steps: (1) mixing a wet phosphoric acid solution with an aluminum shielding agent to form a mixed solution, the aluminum shielding agent being at least one of malonate, succinate and phthalate, and adding a pH regulator and then standing; (2) performing water bath on the mixed solution obtained in step (1) under stirring, adding ferric sulfate into the mixed solution, adding ferric phosphate dihydrate seed crystal, and then performing solid-liquid separation after reaction to obtain a solid product, and then washing to obtain the ferric phosphate dihydrate; in step (1), the concentration of the aluminum shielding agent is 0.1-2 mol / L, the mixing manner of the wet phosphoric acid solution and the aluminum shielding agent is adding the aluminum shielding agent into the wet phosphoric acid solution, and the addition amount of the aluminum shielding agent is 120%-500% of the theoretical amount.

2. The method for preparing iron phosphate dihydrate using wet-process phosphoric acid according to claim 1, characterized by: In step (1), the P concentration in the wet phosphoric acid solution is 0.2-2.5 mol / L.

3. The method for preparing iron phosphate dihydrate using wet-process phosphoric acid according to claim 1, characterized by: In step (1), the pH regulator is ammonia water, and the pH of the mixed solution after adding the pH regulator is 1.0-2.

5.

4. The method for preparing iron phosphate dihydrate using wet-process phosphoric acid according to claim 1, characterized by: In step (2), the temperature of the water bath is 70-98℃.

5. The method of claim 1, wherein the method is characterized by: In step (2), the molar amount of the added ferric sulfate is 0.4-0.6 times the molar amount of phosphoric acid in the wet phosphoric acid solution.

6. The method for preparing iron phosphate dihydrate using wet-process phosphoric acid according to claim 1, characterized by: In step (2), the ratio of the mass of the added ferric phosphate dihydrate seed crystal to the theoretical mass of the product is 1: (5-50).

7. The method of claim 1, wherein the method is characterized by: In step (2), after adding the ferric phosphate dihydrate seed crystal, water bath heating is continued and the reaction is performed under stirring for 4-8 h, and then solid-liquid separation is performed.

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