Method for recovering and preparing battery-grade iron phosphate from lithium-extracted ferrophosphorus slag

Abstract

The present application relates to a kind of methods for preparing battery-grade iron phosphate from lithium-extracted phosphorous iron slag, comprising the following steps: mixing lithium-extracted phosphorous iron slag with first leaching bottom solution for leaching reaction, and obtaining primary leaching solution by separation; removing copper impurities by iron powder reduction and solid-liquid separation of primary leaching solution, obtaining copper-removed solution; first leaching bottom solution includes mixture of acid solution and pure water or iron phosphate mother liquor; adding first iron phosphate seed to copper-removed solution for aluminum removal treatment, obtaining aluminum-removed solution; obtaining iron phosphate dihydrate by oxidation precipitation reaction of aluminum-removed solution; obtaining battery-grade iron phosphate by washing, flashing and sintering of iron phosphate dihydrate in sequence. The present application does not need to introduce fluorine element impurities in the whole process of copper and aluminum removal, and the consumption of acid-base reagents for copper and aluminum removal is low. The Fe / P ratio of obtained iron phosphate is 0.962-0.976, and Al≤100ppm, which meets the battery-grade standard.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology for waste lithium-ion batteries, specifically relating to a method for recovering lithium-phosphate slag to prepare battery-grade iron phosphate. Background Technology

[0002] With the rapid development of new energy vehicles, the installed capacity of lithium batteries has gradually increased. Among them, lithium iron phosphate batteries have occupied a mainstream position in power lithium batteries due to their cost advantages, strong safety, and long cycle life. However, the treatment of phosphorus iron slag from waste lithium iron phosphate batteries has always been a difficult problem to solve. Traditional methods either treat it as waste or use it to make low-value phosphate fertilizer and iron oxide, resulting in resource waste. In addition, traditional methods use high-purity phosphoric acid or phosphates to react with iron salts to prepare battery-grade iron phosphate, which is costly. How to efficiently and cost-effectively treat phosphorus iron slag from waste lithium iron phosphate batteries, especially how to improve the lithium extraction leaching rate and prepare high-purity low-aluminum iron phosphate, is a technical problem that urgently needs to be solved. Regarding the problem of low leaching rate of lithium extraction phosphorus iron slag, some invention patents have been issued. For example: CN117602604A discloses a method for recovering and preparing battery-grade iron phosphate from lithium-extracted iron phosphate slag. The method first involves adding iron powder to the lithium-extracted iron phosphate slag for reducing acid leaching, obtaining a leachate and leaching residue. Then, by adjusting the pH and using an aluminum remover, a purified iron-phosphorus solution is obtained. This solution is supplemented with a phosphorus source to adjust the iron-phosphorus ratio, followed by an oxidation precipitation reaction to obtain iron phosphate dihydrate. Finally, battery-grade iron phosphate is prepared by high-temperature calcination. This method achieves efficient recovery and regeneration of both iron and phosphorus elements from the high-impurity lithium-extracted iron phosphate slag. However, this method requires removing aluminum impurities at a relatively high pH (1.8–2.5), and the introduction of fluorine poses a risk of equipment corrosion.

[0003] CN119218951A discloses a method for regenerating battery-grade iron phosphate from lithium-extraction iron phosphate slag. This method involves wet reduction leaching of the iron phosphate slag, followed by calcination of the leachate after impurity removal to prepare battery-grade iron phosphate. This method enhances the leaching reaction of the iron phosphate slag without introducing impurity elements, achieving a phosphorus and iron leaching rate of up to 99%. The purified solution prepared through impurity removal achieves an impurity removal rate as high as 99.93%, with a phosphorus and iron loss rate as low as 2.44%. However, this method, which also uses fluorine-containing substances as aluminum impurity removal agents, also faces the risk of fluoride formation.

[0004] Therefore, developing a low-cost, impurity-free method for recycling lithium-ion phosphate slag to prepare battery-grade iron phosphate is of great significance for realizing the resource recycling of waste lithium batteries and reducing environmental pollution. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method for recovering lithium-phosphate iron slag to prepare battery-grade iron phosphate, solving the technical problems of high consumption of acid and alkali reagents and introduction of impurity fluorine elements during the recovery of lithium-phosphate iron slag in the prior art.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for preparing battery-grade iron phosphate from lithium-extracting iron phosphate slag, comprising the following steps: S1, mixing lithium-extracting iron phosphate slag with a first leaching base solution for leaching reaction, and separating to obtain a primary leaching solution; removing copper impurities from the primary leaching solution by iron powder reduction and solid-liquid separation to obtain a copper-removed solution; the first leaching base solution comprises a mixture of acid solution and pure water or iron phosphate mother liquor; S2, adding a first iron phosphate seed crystal to the copper-removed solution for aluminum removal treatment to obtain an aluminum-removed solution; S3, subjecting the aluminum-removed solution to an oxidation precipitation reaction to obtain iron phosphate dihydrate; S4, sequentially washing, flash evaporating, and sintering the iron phosphate dihydrate to obtain battery-grade iron phosphate.

[0007] Compared with the prior art, the beneficial effects of the present invention include: This invention first mixes lithium-phosphate slag with a first leaching solution for leaching reaction, separating the resulting primary leaching solution. This primary leaching solution is then subjected to iron powder reduction for efficient copper removal. First-stage iron phosphate seed crystals are added to the copper-removed solution to promote the precipitation of residual aluminum ions as hydrated aluminum phosphate, without introducing other metallic impurities, achieving gentle and efficient aluminum removal. The aluminum-removed solution undergoes an oxidation precipitation reaction to generate iron phosphate dihydrate, which is finally sintered to obtain battery-grade iron phosphate. This invention eliminates the need to introduce fluorine impurities throughout the copper and aluminum removal process, consumes low levels of acid and alkali reagents for copper and aluminum removal, and yields iron phosphate with an Fe / P ratio of 0.962-0.976 and Al ≤ 100 ppm, meeting battery-grade standards. Attached Figure Description

[0008] Figure 1 This is a flowchart illustrating the method of the present invention; Figure 2 This is a SEM image of ferric phosphate from Example 1 of the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0010] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0011] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0012] To address the shortcomings of current lithium-phosphate slag recycling methods, such as high consumption of acid and alkali reagents for copper and aluminum removal, and the introduction of fluorine impurities, this invention provides a method for preparing battery-grade iron phosphate from lithium-phosphate slag. This method achieves efficient copper / aluminum removal, resource recycling, and low-cost preparation of battery-grade iron phosphate.

[0013] Firstly, see [the following] Figure 1 This invention provides a method for recovering lithium iron phosphate slag to prepare battery-grade iron phosphate, comprising the following steps: S1. The lithium-phosphate iron slag is mixed with the first leaching base solution for leaching reaction, and the first leaching solution is obtained by separation. The copper impurities in the first leaching solution are removed by iron powder reduction and solid-liquid separation to obtain copper-removed solution. The first leaching base solution includes a mixture of acid solution and pure water or iron phosphate mother liquor. S2. Add the first iron phosphate seed crystal to the copper-removed solution to remove aluminum, and obtain the aluminum-removed solution. S3. The aluminum-removed liquid is subjected to an oxidation precipitation reaction to obtain ferric phosphate dihydrate. S4. The iron phosphate dihydrate is washed, flash-evaporated, and sintered sequentially to obtain battery-grade iron phosphate.

[0014] This invention first mixes lithium-ion ferrophosphate slag with a first leaching solution for leaching reaction, separating the primary leaching solution and the insoluble carbon slag (derived from the conductive carbon powder contained in the ferrophosphate slag itself) after acid leaching. The carbon slag, after removing metallic impurities, can be used as a graphite raw material. The primary leaching solution undergoes efficient copper removal through iron powder reduction, resulting in a copper-removed liquid and sponge copper through solid-liquid separation. The sponge copper is sold directly. Ferric phosphate seed crystals are added to the copper-removed liquid, promoting the precipitation of residual aluminum ions in the solution as aluminum phosphate without introducing other metallic impurities, achieving gentle and efficient aluminum removal. The aluminum-removed liquid undergoes an oxidation precipitation reaction to generate ferric phosphate dihydrate, which is finally sintered to obtain battery-grade ferric phosphate. This invention requires no introduction of fluorine impurities throughout the process and consumes low levels of acid and alkali reagents for copper and aluminum removal.

[0015] In some embodiments, in step S1, the mass ratio of lithium-phosphorus iron slag to iron powder is (6-8):1.

[0016] In some embodiments, in step S1, the mass ratio of lithium-phosphorus iron slag to the first leaching solution is (15-20):80.

[0017] In some embodiments, in step S1, the mass ratio of acid solution to pure water or ferric phosphate mother liquor in the first leaching solution is 1:(6-8); the acid solution includes sulfuric acid with a mass fraction of 98%.

[0018] In some embodiments, in step S1, the leaching reaction is carried out at 45–75°C for 2.5–3.5 h.

[0019] In some embodiments, in step S2, the mass ratio of the first iron phosphate seed crystal to the lithium extraction iron phosphate slag is (0.20~0.35):1. Insufficient iron phosphate seed crystals will result in poor aluminum removal efficiency, while excessive amounts will reduce production efficiency.

[0020] In some embodiments, in step S2, the aluminum removal treatment is carried out at 80-90°C for 1-4 hours.

[0021] In some embodiments, step S3 involves subjecting the aluminum-removed liquid to an oxidation precipitation reaction, specifically including: sequentially adding phosphoric acid, second iron phosphate seed crystals, and an oxidant to the aluminum-removed liquid to carry out an oxidation precipitation reaction.

[0022] Further, phosphoric acid is added sequentially to the aluminum-removed liquid to adjust the iron-phosphorus ratio to 1:(0.95-1.05); the phosphoric acid mass concentration is 80-90%.

[0023] Furthermore, the amount of the second iron phosphate seed crystal is 0.4 to 0.6% of the total mass of the aluminum-removed liquid and phosphoric acid.

[0024] Furthermore, the oxidant includes at least one of hydrogen peroxide and air; even further, the oxidant includes hydrogen peroxide with a mass concentration of 20-30%, and the amount used is 0.8-1.2% of the total mass of the aluminum-removed solution and phosphoric acid.

[0025] In some embodiments, the conditions for the oxidation precipitation reaction in step S3 include: a stirring speed of 150–300 r / min, a reaction temperature of 85–95 °C, and a reaction time of 1–3 h.

[0026] In the oxidation precipitation reaction of this invention, by adding phosphoric acid, second ferric phosphate seed crystals and oxidant, and controlling the reaction conditions, ferric phosphate dihydrate can be generated in one step; the traditional two-step conversion process of first preparing amorphous ferric phosphate and then secondary crystallization is not required.

[0027] In some embodiments, after the oxidation precipitation reaction is completed in step S3, iron phosphate dihydrate and iron phosphate mother liquor are obtained by solid-liquid separation, and 80-100 wt% of the iron phosphate mother liquor is returned to step S1 to prepare the first leaching solution.

[0028] In some embodiments, in step S4, the washing process uses pure water, and the wash water is purified through water treatment or partially reused.

[0029] In some embodiments, in step S4, flash evaporation is performed at 350–550°C for flash dehydration.

[0030] In some embodiments, in step S4, sintering is performed at 550–650°C for 1–3 hours.

[0031] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0032] The lithium-phosphate iron slag comes from the lithium carbonate manufacturers in the market after extracting lithium from lithium iron phosphate black powder. The iron content is between 20 and 25%, and the phosphorus content is between 10 and 15%.

[0033] Example 1 A method for recovering lithium iron phosphate slag to prepare battery-grade iron phosphate includes the following steps: S1. Mix the iron phosphate mother liquor and acid solution as the first leaching base liquid, wherein the iron phosphate mother liquor is 70 kg and the acid solution is 10 kg of sulfuric acid (98%). Add 17.5 kg of lithium-iron phosphate slag in sequence and control the temperature at 60℃ for 3 h. Then, separate the solid and liquid to obtain the first leaching solution. Add 2.5 kg of iron powder to the first leaching solution and keep it at 60℃ for 0.5 h. Filter it a second time to obtain the copper-removed solution.

[0034] S2. Add 5 kg of iron phosphate seed crystals to the copper-removed liquid and react at 85°C for 1 hour to obtain the aluminum-removed liquid through solid-liquid separation.

[0035] S3. Add 85% phosphoric acid to the aluminum-removed solution to control the iron-phosphorus ratio at 1:1.05. Then add 0.5wt% of iron phosphate seed crystals and 1wt% hydrogen peroxide (content 27%) as oxidants to carry out the oxidation precipitation reaction. The reaction temperature is 90℃, the time is 2h, and the reaction speed is 200r / min. After the reaction is completed, the solid and liquid are separated to obtain iron phosphate dihydrate and iron phosphate mother liquor. 80% of the iron phosphate mother liquor is recycled to step S1 to prepare the first leaching solution.

[0036] S4. The ferric phosphate dihydrate was washed with pure water; the washed ferric phosphate dihydrate was flash-evaporated at 450°C to remove moisture; and finally, it was sintered at 600°C for 2 hours to obtain battery-grade ferric phosphate.

[0037] Example 2 (Adjusting the iron-phosphorus ratio) A method for recovering lithium iron phosphate slag to prepare battery-grade iron phosphate includes the following steps: S1. Mix the iron phosphate mother liquor and acid solution as the first leaching base liquid, wherein the iron phosphate mother liquor is 70 kg and the acid solution is 10 kg of sulfuric acid (98%). Add 17.5 kg of lithium-iron phosphate slag in sequence and control the temperature at 60℃ for 3 h. Then, separate the solid and liquid to obtain the first leaching solution. Add 2.5 kg of iron powder to the first leaching solution and keep it at 60℃ for 0.5 h. Filter it a second time to obtain the copper-removed solution.

[0038] S2. Add 5 kg of iron phosphate seed crystals to the copper-removed liquid and react at 85°C for 1 hour to obtain the aluminum-removed liquid through solid-liquid separation.

[0039] S3. Add 85% phosphoric acid to the aluminum-removed liquid to control the iron-phosphorus ratio at 1:1. Then add 0.5wt% iron phosphate seed crystals and 1wt% hydrogen peroxide (content 27%) as oxidants to carry out the oxidation precipitation reaction. The reaction temperature is 90℃, the time is 2h, and the reaction speed is 200r / min. After the reaction is completed, solid-liquid separation is performed to obtain iron phosphate dihydrate and iron phosphate mother liquor. 80% of the iron phosphate mother liquor is recycled to step S1 to prepare the first leaching solution.

[0040] S4. The ferric phosphate dihydrate is washed with pure water, and the washing water is reused at a rate of 15%. The washed ferric phosphate dihydrate is then flash-evaporated at 450°C to remove moisture. Finally, it is sintered at 600°C for 2 hours to obtain battery-grade ferric phosphate.

[0041] Example 3 (Adjusting the iron-phosphorus ratio) A method for recovering lithium iron phosphate slag to prepare battery-grade iron phosphate includes the following steps: S1. Mix the iron phosphate mother liquor and acid solution as the first leaching base liquid, wherein the iron phosphate mother liquor is 70 kg and the acid solution is 10 kg of sulfuric acid (98%). Add 17.5 kg of lithium-iron phosphate slag in sequence and control the temperature at 60℃ for 3 h. Then, separate the solid and liquid to obtain the first leaching solution. Add 2.5 kg of iron powder to the first leaching solution and keep it at 60℃ for 0.5 h. Filter it a second time to obtain the copper-removed solution.

[0042] S2. Add 5 kg of iron phosphate seed crystals to the copper-removed liquid and react at 85°C for 1 hour to obtain the aluminum-removed liquid through solid-liquid separation.

[0043] S3. Add 85% phosphate to the aluminum-removed solution to control the iron-phosphorus ratio at 1:0.95. Then add 0.5wt% ferric phosphate seed crystals and 1wt% hydrogen peroxide (content 27%) to carry out the oxidation precipitation reaction. The reaction temperature is 90℃, the time is 2h, and the reaction speed is 200r / min. After the reaction is completed, ferric phosphate dihydrate and ferric phosphate mother liquor are obtained by solid-liquid separation. 80% of the ferric phosphate mother liquor is recycled to step S1 to prepare the first leaching solution.

[0044] S4. The ferric phosphate dihydrate is washed with pure water, and the washing water is reused at a rate of 15%. The washed ferric phosphate dihydrate is then flash-evaporated at 450°C to remove moisture. Finally, it is sintered at 600°C for 2 hours to obtain battery-grade ferric phosphate.

[0045] Comparative Example 1 Compared with Example 1, the only difference is that the mass ratio of lithium-phosphorus iron slag to iron powder is adjusted to 9:1; all other steps and conditions are the same as in Example 1. Specifically, the following steps are included: S1. Mix the iron phosphate mother liquor and acid solution as the first leaching base liquid, wherein the iron phosphate mother liquor is 70 kg and the acid solution is 10 kg of sulfuric acid (98%). Add 18 kg of lithium-iron phosphate slag in sequence and control the temperature at 60℃ for 3 h. Then, separate the solid and liquid to obtain the first leaching solution. Add 2 kg of iron powder to the first leaching solution and keep it at 60℃ for 0.5 h. Filter it a second time to obtain the copper-removed solution.

[0046] S2. Add 5 kg of iron phosphate seed crystals to the copper-removed liquid and react at 85°C for 1 hour to obtain the aluminum-removed liquid through solid-liquid separation.

[0047] S3. Add 85% phosphate to the aluminum-removed solution to control the iron-phosphorus ratio at 1:1.05. Then add 0.5wt% ferric phosphate seed crystals and 1wt% hydrogen peroxide (content 27%) as oxidants to carry out the oxidation precipitation reaction. The reaction temperature is 90℃, the time is 2h, and the reaction speed is 200r / min. After the reaction is completed, ferric phosphate dihydrate and ferric phosphate mother liquor are obtained by solid-liquid separation. 80% of the ferric phosphate mother liquor is recycled to step S1 to prepare the first leaching solution.

[0048] S4. The ferric phosphate dihydrate was washed with pure water, and the washing water reuse ratio was 15%. The washed ferric phosphate dihydrate was then flash-evaporated at 450℃ to remove moisture. Finally, it was sintered at 600℃ for 2 hours to obtain ferric phosphate.

[0049] Comparative Example 2 Compared with Example 1, the only difference is that the amount of iron phosphate seed crystals added to the copper-removed solution in step S2 is adjusted to 3 kg; the other steps and conditions are the same as in Example 1.

[0050] S1. Mix the iron phosphate mother liquor and acid solution as the first leaching base liquid, wherein the iron phosphate mother liquor is 70 kg and the acid solution is 10 kg of sulfuric acid (98%). Add 17.5 kg of lithium-iron phosphate slag in sequence and control the temperature at 60℃ for 3 h. Then, separate the solid and liquid to obtain the first leaching solution. Add 2.5 kg of iron powder to the first leaching solution and keep it at 60℃ for 0.5 h. Filter it a second time to obtain the copper-removed solution.

[0051] S2. Add 3 kg of iron phosphate seed crystals to the copper-removed liquid and react at 85°C for 1 hour to obtain the aluminum-removed liquid through solid-liquid separation.

[0052] S3. Add 85% phosphoric acid to the aluminum-removed solution to control the iron-phosphorus ratio at 1:1.05. Then add 0.5wt% iron phosphate seed crystals and 1wt% hydrogen peroxide (content 27%) as oxidants to carry out the oxidation precipitation reaction. The reaction temperature is 90℃, the time is 2h, and the reaction speed is 200r / min. After the reaction is completed, solid-liquid separation is performed to obtain iron phosphate dihydrate and iron phosphate mother liquor. 80% of the iron phosphate mother liquor is recycled to step S1 to prepare the first leaching solution. S4. The ferric phosphate dihydrate was washed with pure water, and the washing water reuse ratio was 15%. The washed ferric phosphate dihydrate was then flash-evaporated at 450℃ to remove moisture. Finally, it was sintered at 600℃ for 2 hours to obtain ferric phosphate.

[0053] Comparative Example 3 Compared with Example 1, the only difference is that no seed crystals are added in step S2; the other steps and conditions are the same as in Example 1.

[0054] S1. Mix the iron phosphate mother liquor and acid solution as the first leaching base liquid, wherein the iron phosphate mother liquor is 70 kg and the acid solution is 10 kg of sulfuric acid (98%). Add 17.5 kg of lithium-iron phosphate slag in sequence and control the temperature at 60℃ for 3 h. Then, separate the solid and liquid to obtain the first leaching solution. Add 2.5 kg of iron powder to the first leaching solution and keep it at 60℃ for 0.5 h. Filter it a second time to obtain the copper-removed solution.

[0055] S2. The copper-removed liquid is reacted at 85°C for 1 hour and then filtered through a pressure filter to obtain the unremoved aluminum liquid.

[0056] S3. Add 85% phosphate to the untreated solution to control the iron-phosphorus ratio at 1:1.05. Then add 0.5wt% ferric phosphate seed crystals and 1wt% hydrogen peroxide (content 27%) as oxidants to carry out the oxidation precipitation reaction. The reaction temperature is 90℃, the time is 2h, and the reaction speed is 200r / min. After the reaction is completed, ferric phosphate dihydrate and ferric phosphate mother liquor are obtained by solid-liquid separation. 80% of the ferric phosphate mother liquor is recycled to step S1 to prepare the first leaching solution.

[0057] S4. The ferric phosphate dihydrate was washed with pure water, and the washing water reuse ratio was 15%. The washed ferric phosphate dihydrate was then flash-evaporated at 450℃ to remove moisture. Finally, it was sintered at 600℃ for 2 hours to obtain ferric phosphate.

[0058] Performance testing (1) Electron microscopy was performed on the iron phosphate obtained in Example 1, and the results are as follows: Figure 2 As shown.

[0059] from Figure 2 As can be seen from the above, the iron phosphate obtained by this invention maintains a regular and uniform sheet-like structure after sintering, with good crystal growth, which meets the requirements of battery-grade iron phosphate.

[0060] (2) The main elements of the aluminum-removed liquids of Examples 1-3 and Comparative Examples 1-3 were detected by ICP, and the results are shown in Table 1.

[0061] Table 1. Statistical table of main element contents in the aluminum-removed liquid

[0062] As shown in Table 1, the present invention can effectively remove copper and aluminum impurities without introducing new impurities. In Comparative Example 1, the mass ratio of lithium phosphate slag to iron powder was too high and the iron powder was insufficient, resulting in a poorer copper removal effect. In Comparative Example 2, the amount of first iron phosphate seed crystals added was insufficient, and in Comparative Example 3, no first iron phosphate seed crystals were added, resulting in a poorer aluminum removal effect.

[0063] (3) The main indicators of the iron phosphate obtained in Examples 1-3 and Comparative Examples 1-3 were tested. The iron content was obtained by potassium dichromate potentiometric titration, the phosphorus content was obtained by quinomolybdate precipitation, and the impurity content was obtained by ICP test. The results are shown in Table 2 below.

[0064] Table 2. Statistics of main indicators of ferric phosphate obtained in Examples 1-3 and Comparative Examples 1-3

[0065] As can be seen from Table 2, in the embodiments of the present invention, the finished product indicators remain stable even when the parameters are changed within a certain range. The first iron phosphate seed crystal can significantly remove aluminum impurities in the iron phosphate liquid, and the finished product can meet the requirements of battery-grade iron phosphate, showing a wide range of synthesis and promising large-scale industrial application.

[0066] In summary, this invention provides a method for recovering lithium iron phosphate slag to prepare battery-grade iron phosphate. First, a first iron phosphate seed crystal is used to promote the precipitation of aluminum impurities, eliminating the need for external aluminum removal agents and preventing the introduction of new impurities. By reusing a high proportion of mother liquor and wash water (80-100% mother liquor reuse, 0-25% wash water reuse), acid and alkali consumption and wastewater discharge are significantly reduced. The process parameter window is wide, and the resulting iron phosphate has an Fe / P ratio of 0.962-0.976 and Al ≤ 100 ppm, meeting battery-grade standards. This invention achieves high-value, green, and low-cost regeneration of lithium iron phosphate slag from waste lithium iron phosphate batteries.

[0067] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering lithium-phosphate slag to prepare battery-grade iron phosphate, characterized in that, Includes the following steps: S1. The lithium-phosphate iron slag is mixed with the first leaching base solution for leaching reaction, and the first leaching solution is obtained by separation. The copper impurities in the first leaching solution are removed by iron powder reduction and solid-liquid separation to obtain copper-removed solution. The first leaching base solution includes a mixture of acid solution and pure water or iron phosphate mother liquor. S2. Add the first iron phosphate seed crystal to the copper-removed solution to perform aluminum removal treatment, and obtain the aluminum-removed solution; S3. The aluminum-removed liquid is subjected to an oxidation precipitation reaction to obtain ferric phosphate dihydrate. S4. The ferric phosphate dihydrate is washed, flash-evaporated, and sintered sequentially to obtain battery-grade ferric phosphate.

2. The method for recovering lithium-phosphate slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S1, the mass ratio of the lithium-phosphorus iron slag to iron powder is (6-8):

1.

3. The method for recovering lithium-phosphate ferric slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S1, the mass ratio of the lithium-phosphorus iron slag to the first leaching solution is (15-20):80; In the first leaching solution, the mass ratio of the acid solution to the pure water or ferric phosphate mother liquor is 1:(6-8); the acid solution includes sulfuric acid with a mass fraction of 98%.

4. The method for recovering lithium-phosphate ferric slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S1, the leaching reaction is carried out at 45–75°C for 2.5–3.5 hours.

5. The method for recovering lithium-phosphate ferric slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S2, the mass ratio of the first iron phosphate seed crystal to the lithium-iron phosphate slag is (0.20~0.35):

1.

6. The method for recovering lithium-phosphate slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S2, the aluminum removal process is carried out at 80-90°C for 1-4 hours.

7. The method for recovering lithium-phosphate slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S3, the oxidation precipitation reaction of the aluminum-removed liquid specifically includes: adding phosphoric acid, second iron phosphate seed crystals and oxidant to the aluminum-removed liquid in sequence to carry out the oxidation precipitation reaction.

8. The method for recovering lithium-phosphate slag and preparing battery-grade iron phosphate according to claim 7, characterized in that, Phosphoric acid is added sequentially to the aluminum-removed solution to adjust the iron-to-phosphorus ratio to 1:(0.95–1.05); the mass concentration of the phosphoric acid is 80–90%. The amount of the second iron phosphate seed crystal is 0.4-0.6% of the total mass of the aluminum-removed solution and phosphoric acid; The oxidant includes at least one of hydrogen peroxide and air.

9. The method for recovering lithium-phosphate slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S3, the conditions for the oxidation precipitation reaction include: a stirring speed of 150-300 r / min, a reaction temperature of 85-95℃, and a reaction time of 1-3 h; After the oxidation precipitation reaction is completed, ferric phosphate dihydrate and ferric phosphate mother liquor are obtained by solid-liquid separation. 80-100% of the ferric phosphate mother liquor is returned to step S1 for the preparation of the first leaching solution.

10. The method for recovering lithium-phosphate ferric slag and preparing battery-grade iron phosphate according to claim 1, characterized in that, In step S4, the washing process uses pure water. The flash evaporation is a process of dehydration at 350–550°C. The sintering is carried out at 550-650℃ for 1-3 hours.

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