Method for preparing iron phosphate from phosphorus iron slag

Abstract

This invention discloses a method for preparing ferric phosphate from ferrophosphate slag. The method includes the following steps: S1, mixing and heating a phosphoric acid solution and waste ferrophosphate slag to react, and filtering to obtain a leachate; S2, heating the leachate, then adding ammonia to adjust the pH to ≤2.5; separating the solid and liquid to obtain hydrated iron-phosphorus oxide; S3, mixing the hydrated iron-phosphorus oxide and phosphoric acid to form a slurry, holding at 90-95℃, and separating the solid and liquid to obtain the ferric phosphate precursor; S4, sintering the ferric phosphate precursor to obtain ferric phosphate. This invention first leaches waste ferrophosphate slag with phosphoric acid, then adjusts the pH with ammonia to remove impurities, and then holds at 90-95℃ for solid-liquid separation to remove impurities before sintering to obtain ferric phosphate. This method deeply removes various impurities such as titanium, aluminum, magnesium, and manganese, ensuring the high purity of the final product.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate preparation technology, and in particular to a method for preparing ferric phosphate from ferric phosphate slag. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in electric vehicles, energy storage devices, and other electronic products due to their high safety and long cycle life. Consequently, a large number of LFP batteries are nearing the end of their service life and will be scrapped. Therefore, how to efficiently and environmentally recycle their valuable resources (such as lithium, iron, and phosphorus) has become an urgent issue.

[0003] In the recycling process of lithium iron phosphate batteries, lithium, the most valuable element, is usually recovered first. The remaining solid waste is called iron phosphate slag. Iron phosphate slag is rich in iron and phosphorus, but also contains various impurities such as titanium, aluminum, magnesium, manganese, and copper. If it cannot be effectively recycled, it not only wastes resources, but its heavy metals and other components may also pose a potential threat to the environment.

[0004] Currently, the industry primarily uses sulfuric acid leaching to recycle ferrophosphate slag. This involves dissolving the slag in sulfuric acid, then adding ammonia to the leachate to adjust the pH, causing ferrophosphate to precipitate. However, this traditional method has significant drawbacks: the resulting ferrophosphate product contains unstable impurities such as titanium and aluminum, making effective removal difficult; furthermore, the product has large particles and low purity, resulting in poor performance and failing to meet the requirements for high-performance lithium-ion battery cathode material precursors.

[0005] Therefore, developing a new process for the economical and efficient preparation of high-purity iron phosphate from iron phosphate slag is of great practical significance and economic value. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention relates to a method for preparing ferric phosphate from ferric phosphate slag, wherein the ferric phosphate prepared by this method has high purity.

[0007] According to a first aspect of the present invention, a method for preparing ferric phosphate from ferric phosphate slag is provided, comprising the following steps: S1. Mix phosphoric acid solution and waste phosphorus iron slag, heat to react, and filter to obtain leachate; S2. Heat the leachate; then add ammonia to adjust the pH to ≤2.5; separate the solid and liquid to obtain hydrated iron-phosphorus oxide; S3. Mix the hydrated iron-phosphorus oxide and phosphoric acid into a slurry, keep it at 90~95℃, and separate the solid and liquid to obtain the iron phosphate precursor. S4. The iron phosphate precursor is sintered to obtain iron phosphate.

[0008] According to a preferred embodiment of the present invention, in step S2, ammonia is added to adjust the pH to 1.60~1.70.

[0009] According to a preferred embodiment of the present invention, in step S3, the heat preservation time is 2-3 hours.

[0010] According to a preferred embodiment of the present invention, in step S2, the mass concentration of the ammonia water is 20-25%.

[0011] According to a preferred embodiment of the present invention, in step S4, the sintering temperature is 550°C to 600°C.

[0012] According to a preferred embodiment of the present invention, in step S4, the sintering time is 2h to 6h.

[0013] According to a preferred embodiment of the present invention, in step S2, the heating temperature is 60°C to 70°C.

[0014] According to a preferred embodiment of the present invention, in step S1, the concentration of the phosphoric acid solution is 1~2 mol / L.

[0015] According to a preferred embodiment of the present invention, in step S2, the solid-liquid separation step includes filtration and washing.

[0016] According to a preferred embodiment of the present invention, in step S3, the solid-liquid separation step includes filtration and washing.

[0017] According to a preferred embodiment of the present invention, the waste phosphorus iron slag refers to the product remaining after the dismantling, crushing and lithium extraction of waste lithium batteries. Its main components include iron and phosphorus, and its main impurities include carbon, aluminum, titanium, manganese, sulfur, magnesium and copper.

[0018] The method for preparing ferric phosphate from ferric phosphate slag according to embodiments of the present invention has at least the following beneficial effects: This invention first leaches waste ferric phosphate slag with phosphoric acid, then adjusts the pH value with ammonia water to remove impurities, and then holds it at 90-95℃ for solid-liquid separation to remove impurities before sintering to obtain ferric phosphate. This process deeply removes various impurities such as titanium, aluminum, magnesium, manganese, and sulfur, ensuring the high purity of the final product.

[0019] Furthermore, during subsequent high-temperature recrystallization, the nanoscale hydrated iron-phosphorus oxide exhibits denser crystal growth and smaller secondary agglomeration particle size, resulting in nanoscale iron phosphate. This prevents surface over-burning and incomplete sintering of the central portion during high-temperature sintering.

[0020] Furthermore, by introducing step S3, a high-temperature recrystallization step is used to convert amorphous or poorly crystallized hydrated oxides into well-crystallized iron phosphate, thereby improving the stability and consistency of the product.

[0021] Furthermore, this invention uses industrial waste phosphorus-iron slag as raw material, realizing the resource utilization of solid waste and reducing raw material costs; at the same time, the entire process is relatively simple, easy to scale up industrially, and meets the requirements of green circular economy.

[0022] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0023] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0024] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0025] In some embodiments of the present invention, a method for preparing ferric phosphate from ferric phosphate slag is provided, comprising the following steps: S1. Mix phosphoric acid solution and waste phosphorus iron slag, heat to react, and filter to obtain leachate; S2. Heat the leachate; then add ammonia to adjust the pH to ≤2.5; separate the solid and liquid to obtain hydrated iron-phosphorus oxide; S3. Mix the hydrated iron-phosphorus oxide and phosphoric acid into a slurry, keep it at 90~95℃, and separate the solid and liquid to obtain the iron phosphate precursor. S4. The iron phosphate precursor is sintered to obtain iron phosphate.

[0026] Understandably, this invention first leaches waste ferric phosphate slag with phosphoric acid, then adjusts the pH value with ammonia water to remove impurities, and then holds it at 90-95℃ for solid-liquid separation to remove impurities before sintering to obtain ferric phosphate. This process deeply removes various impurities such as titanium, aluminum, magnesium, and manganese, ensuring the high purity of the final product.

[0027] Furthermore, during subsequent high-temperature recrystallization, the nanoscale hydrated iron-phosphorus oxide exhibits denser crystal growth and smaller secondary agglomeration particle size, resulting in nanoscale iron phosphate. This prevents surface over-burning and incomplete sintering of the central portion during high-temperature sintering.

[0028] Furthermore, by introducing step S3, a high-temperature recrystallization step is used to convert amorphous or poorly crystallized hydrated oxides into well-crystallized iron phosphate, thereby improving the stability and consistency of the product.

[0029] Furthermore, this invention uses industrial waste phosphorus-iron slag as raw material, realizing the resource utilization of solid waste and reducing raw material costs; at the same time, the entire process is relatively simple, easy to scale up industrially, and meets the requirements of green circular economy.

[0030] In some embodiments of the present invention, in step S2, ammonia is added to adjust the pH to 1.60-1.70. For example, this includes adjusting the pH value to 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, or any sub-range consisting of two of the above values.

[0031] It is understandable that ammonia is added to adjust the pH to 1.60~1.70, so that the iron and phosphorus in the leachate can be precipitated. Too low a pH will reduce the iron and phosphorus yield in the solution, while too high a pH will increase costs and affect aluminum removal.

[0032] In some embodiments of the present invention, the heat preservation time in step S3 is 2-3 hours. For example, it includes 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, 3 hours, or any sub-range of two of the above values. This allows the iron phosphate crystals and crystal form to be more stable, preventing damage to the crystals during subsequent high-pressure filtration and washing processes.

[0033] In some embodiments of the present invention, in step S2, the mass concentration of the ammonia water is 20-25%.

[0034] In some embodiments of the present invention, in step S4, the sintering temperature is 550°C to 600°C. For example, it includes 550°C, 555°C, 560°C, 565°C, 570°C, 575°C, 580°C, 585°C, 590°C, 595°C, 600°C, or any sub-range of any two of the above values. Therefore, In some embodiments of the present invention, the sintering time in step S4 is 2h to 6h. For example, it includes 2h, 2.5h, 3h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6h, or any sub-range consisting of two of the above values. This more effectively removes free water from the material, resulting in a more stable material crystal structure.

[0035] In some embodiments of the present invention, in step S2, the heating temperature is 60°C to 70°C. For example, it includes 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, or any sub-range of two of the above values. Further, 60°C to 65°C is preferred, as this results in a higher ferrophosphorus dissolution rate. Lower temperatures reduce the ferrophosphorus dissolution rate, while higher temperatures do not significantly increase the actual ferrophosphorus dissolution rate and instead increase the energy consumption for dissolution.

[0036] In some embodiments of the present invention, in step S1, the concentration of the phosphoric acid solution is 1~2 mol / L.

[0037] In some embodiments of the present invention, in step S1, the molar ratio of iron in the waste phosphoric acid slag to phosphoric acid in the phosphoric acid solution is 1:2.5~2.6.

[0038] In some embodiments of the present invention, step S2, the solid-liquid separation step includes filtration and washing.

[0039] In some embodiments of the present invention, step S3 includes filtration and washing.

[0040] In some embodiments of the present invention, in step S3, the washing refers to washing with pure water until the conductivity of the wash water is less than 500 μS / cm.

[0041] In some embodiments of the present invention, the waste phosphorus iron slag refers to the product remaining after the dismantling, crushing and lithium extraction of waste lithium batteries. Its main components include iron and phosphorus, and its main impurities include carbon, aluminum, titanium, manganese, sulfur, magnesium and copper.

[0042] Furthermore, the waste phosphorus iron slag is the waste phosphorus iron slag after lithium extraction from waste lithium iron phosphate cathode material. For ease of comparison, the following examples and comparative examples all use the same batch of waste phosphorus iron slag, and its composition detection results (ICP test) are shown in Table 1 below: Table 1

[0043] Example 1 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 1.7. At this point, a large amount of hydrated iron-phosphorus oxides will precipitate. Then filter and wash the filter cake repeatedly with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0044] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is heated to 95°C and kept at this temperature for 2 hours. After the reaction is complete, the mixture is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0045] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0046] Example 2 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 1.6. At this point, a large amount of hydrated iron-phosphorus oxide precipitates. Then filter and repeatedly wash the filter cake with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0047] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is heated to 95°C and kept at this temperature for 2 hours. After the reaction is complete, the mixture is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0048] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0049] Example 3 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 2.5. At this point, a large amount of hydrated iron-phosphorus oxide precipitates. Then filter and repeatedly wash the filter cake with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0050] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is heated to 95°C and kept at this temperature for 2 hours. After the reaction is complete, the mixture is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0051] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0052] Example 4 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While continuously stirring, rapidly add 25% ammonia solution to adjust the pH of the solution to 2.0. At this point, a large amount of hydrated iron-phosphorus oxides will precipitate. Then filter and repeatedly wash the filter cake with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0053] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is heated to 95°C and kept at this temperature for 2 hours. After the reaction is complete, the mixture is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0054] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0055] Example 5 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 1.7. At this point, a large amount of hydrated iron-phosphorus oxides will precipitate. Then filter and wash the filter cake repeatedly with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0056] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is heated to 90°C and kept at this temperature for 2 hours. After the reaction is complete, the mixture is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0057] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0058] Comparative Example 1 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 3. At this point, a large amount of hydrated iron-phosphorus oxides will precipitate. Then filter and wash the filter cake repeatedly with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0059] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is heated to 95°C and maintained at this temperature for 2 hours. After the reaction is complete, the mixture is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm, yielding a high-purity iron phosphate precursor filter cake.

[0060] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0061] Comparative Example 2 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 1.7. At this point, a large amount of hydrated iron-phosphorus oxides will precipitate. Then filter and wash the filter cake repeatedly with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0062] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is kept at room temperature for 2 hours. After the reaction is complete, it is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0063] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0064] Comparative Example 3 This example provides a method for preparing ferric phosphate from ferric phosphate slag, including the following steps: S1. Take 85% concentrated phosphoric acid, dilute it with pure water, and prepare 1 liter of phosphoric acid solution with a concentration of 1 mol / L. Pour this acid solution into a reaction vessel equipped with stirring and circulating heating, heat it to 40℃ and maintain a constant temperature. Weigh a certain amount of waste phosphorus iron slag (ensuring that the molar ratio of iron to phosphoric acid in step 1 is 1:2.5), slowly add it to the reaction vessel, keep stirring, and react for 2.5 hours. After the reaction is completed, filter while hot, separate the residue, and obtain the leachate; S2. Transfer the leachate to another clean reactor and heat to 70°C. While stirring continuously, rapidly add 25% ammonia solution to adjust the pH of the solution to 1.7. At this point, a large amount of hydrated iron-phosphorus oxides will precipitate. Then filter and wash the filter cake repeatedly with pure water until the conductivity of the outflowing wash water drops to 450 μS / cm.

[0065] S3. The washed hydrated iron-phosphorus oxide filter cake is returned to the reactor, and pure water and phosphoric acid are added for slurry preparation. The iron-phosphorus molar ratio in the slurry is 1.05:1. The slurry is kept at 80°C for 2 hours. After the reaction is complete, it is filtered again and washed with pure water until the conductivity of the wash water is below 500 μS / cm to obtain a high-purity iron phosphate precursor filter cake.

[0066] S4. Place the filter cake in a porcelain crucible, put it in a muffle furnace, and sinter at 580℃ for 4 hours. After natural cooling, remove and grind to obtain ferric phosphate.

[0067] Performance testing The iron phosphate prepared in Example 1 of this invention was tested by scanning electron microscopy (SEM), which showed that the primary particle size distribution was 80~150 nm, and the secondary particle size after agglomeration was in the range of 300~500 nm.

[0068] Furthermore, the impurity content of the ferric phosphate prepared in Examples 1-5 and Comparative Examples 1-3 of this invention was tested using ICP. The results are shown in Table 2: Table 2

[0069] As shown in Table 2, the ferric phosphate produced in Examples 1-5 of this invention has higher purity and lower impurity content. This is because this invention first leaches the waste ferric phosphate slag with phosphoric acid, then adjusts the pH value with ammonia water to remove impurities, and then holds it at 90-95℃ for solid-liquid separation to remove impurities before sintering to obtain the ferric phosphate. This process deeply removes various impurities such as titanium, aluminum, magnesium, manganese, and sulfur, ensuring the high purity of the final product.

[0070] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing ferric phosphate from ferric phosphate slag, characterized in that, Includes the following steps: S1. Mix phosphoric acid solution and waste phosphorus iron slag, heat to react, and filter to obtain leachate; S2. Heat the leachate; then add ammonia to adjust the pH to ≤2.5; separate the solid and liquid to obtain hydrated iron-phosphorus oxide; S3. Mix the hydrated iron-phosphorus oxide and phosphoric acid into a slurry, keep it at 90~95℃, and separate the solid and liquid to obtain the iron phosphate precursor. S4. The iron phosphate precursor is sintered to obtain iron phosphate.

2. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S2, ammonia is added to adjust the pH to 1.60~1.

70.

3. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S3, the heat preservation time is 2-3 hours.

4. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S2, the mass concentration of the ammonia water is 20-25%.

5. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S4, the sintering temperature is 550℃~600℃.

6. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S4, the sintering time is 2h to 6h.

7. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S2, the heating temperature is 60℃~70℃.

8. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S1, the concentration of the phosphoric acid solution is 1~2 mol / L.

9. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S2, the solid-liquid separation step includes filtration and washing.

10. The method for preparing ferric phosphate from ferric phosphate slag according to claim 1, characterized in that, In step S3, the solid-liquid separation step includes filtration and washing.

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