Battery-grade iron phosphate and method for preparing iron phosphate by recycling waste battery ferrophosphorus slag

Abstract

The invention discloses battery-grade iron phosphate and a method for preparing iron phosphate by recycling waste battery ferrophosphorus slag. The method comprises the following steps: mixing ferrophosphorus slag and oxalate, ball-milling, and calcining to obtain a mixture B containing an iron compound and phosphate; the mixture B is subjected to water leaching and separation, and an aluminum-containing phosphate solution A and an iron mixture are obtained; removing impurities to obtain a purified phosphate solution B; dissolving the iron mixture into a ferrous solution by using acid, and extracting to remove Ti < 4 + > ions and impurities; oxidizing ferrous iron into an iron solution by adopting hydrogen peroxide, and then extracting Fe < 3 + > to obtain a ferric iron solution B; and mixing the purified phosphate solution B with the ferric iron solution B to obtain an iron-phosphorus mixed solution, and carrying out precipitation, filtration and calcination to obtain battery-grade iron phosphate. According to the method, oxalate is adopted as a reducing agent and an auxiliary agent at the same time, phosphorus and iron in the ferrophosphorus slag are separated into an iron compound and phosphate, impurity metal is removed through multi-step extraction, finally, iron phosphate is prepared, and the ferrophosphorus slag with complex impurity components is effectively prepared into high-purity iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate battery cathode material recycling technology, and more specifically, it relates to a battery-grade iron phosphate and a method for removing impurities from the iron phosphate residue remaining after lithium extraction from waste lithium iron phosphate and for preparing iron phosphate. Background Technology

[0002] Lithium iron phosphate (LFP) offers advantages such as high safety, high cycle stability, and high economic efficiency as a cathode material for lithium-ion batteries, leading to its widespread application in automotive power, communication base stations, and industrial energy storage. However, with the increasing number of end-of-life LFP batteries, the inability to effectively recycle them will result in resource waste and environmental pollution. Because lithium iron phosphate itself has limited economic value and low content of high-value elements, current recycling efforts primarily focus on the selective extraction of lithium, leading to the accumulation of large amounts of waste material as phosphoric acid residue. This not only causes secondary waste of valuable resources such as phosphorus and iron but also poses potential environmental pollution risks.

[0003] Waste lithium iron phosphate contains a large number of impurity metal elements. After selective extraction of lithium, most of the impurity metals are mixed in the lithium iron phosphate slag, making its reuse difficult. Patents CN 118183651A and CN120717426A disclose similar methods for recycling lithium iron phosphate slag, namely acid dissolution of lithium iron phosphate slag-alkali precipitation of ferric phosphate dihydrate-sintering to prepare ferric phosphate. This method usually ignores the problem that phosphate ions will co-precipitate with iron and impurity metal ions, and colloidal ferric phosphate dihydrate will also adsorb impurity metals.

[0004] Therefore, separating phosphorus and iron from ferrophosphate slag through stepwise purification and preparation of ferric phosphate shows promise as an alternative method for recycling ferrophosphate slag. Patents CN 114229812A and CN 115385314A disclose similar methods for separating phosphorus and iron through calcination using additives and reducing agents. However, these methods require the use of large amounts of graphite as a reducing agent, leading to significant resource waste, and the stepwise purification of phosphorus and iron has not been thoroughly investigated.

[0005] Therefore, in order to achieve resource recycling and promote the sustainable development of the industry, how to fully recover waste lithium iron phosphate, especially the recovery of iron phosphate slag, has become an urgent technical problem to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing battery-grade iron phosphate and the recycling of iron phosphate slag from waste batteries. Oxalate is used as both a reducing agent and an auxiliary agent. A reducing atmosphere is created by the high-temperature decomposition of oxalate, separating phosphorus and iron in the iron phosphate slag into an iron complex and phosphate. This involves using oxalate to assist in the calcination and transformation of the iron phosphate slag. The iron complex and phosphate are then separated by water leaching. Alkali precipitation is used to remove impurity metals from the phosphate solution. The iron mixture is dissolved with acid, and impurity metals are removed through a multi-step extraction method. Finally, the purified iron solution is mixed with phosphate to prepare iron phosphate. This invention can effectively prepare high-purity iron phosphate from iron phosphate slag with complex impurity components.

[0007] To achieve the above objectives, the present invention provides a method for preparing iron phosphate from waste battery ferric phosphate slag, comprising the following steps: S1, Phosphorus-Iron Slag Separation: Phosphorus-iron slag is mixed with oxalate, ball-milled, and then calcined at high temperature. The reducing atmosphere field is constructed by the high-temperature decomposition of oxalate to separate phosphorus and iron in the phosphorus-iron slag into a mixture B containing iron mixture and phosphate. S2, Phosphate purification: Mixture B is soaked in water to separate phosphorus and iron and dissolve aluminum foil, resulting in aluminum phosphate solution A and an iron mixture; aluminum phosphate solution A is purified to obtain purified phosphate solution B; S3, Iron mixture purification: The iron mixture is dissolved in acid to form a ferrous solution, followed by removal of Ti from the ferrous solution using a phosphate ester extractant. 4+ The ions were used to remove impurities from the iron mixture; then, the ferrous iron was oxidized to an iron solution using hydrogen peroxide, followed by extraction of Fe with a tertiary amine extractant. 3+ The resulting back-extracted ferric iron solution B was obtained. S4, Preparation of iron phosphate: The purified phosphate solution B is mixed with the trivalent iron solution B to obtain an iron-phosphorus mixture, which is then precipitated, filtered, and calcined to obtain battery-grade iron phosphate.

[0008] In one embodiment of the present invention, step S1 includes: Oxalate and ferrophosphate slag are mixed and weighed according to a molar ratio of ferrophosphate slag: oxalate = 4:1 to 1:4. The mixture is then ball-milled to obtain mixture A. Mixture A is placed in a vacuum environment and calcined at 400~800℃ for 4~12 hours to obtain mixture B.

[0009] Preferably, the oxalate comprises one or more of sodium oxalate, potassium oxalate, and potassium oxalate monohydrate.

[0010] Preferably, the molar ratio of the ferrophosphate slag to oxalate is 1:1 to 1:2.

[0011] Preferably, the calcination temperature is 500~700℃ and the calcination time is 6~8 hours.

[0012] In one embodiment of the present invention, step S2 includes: Mixture B and water at a mass ratio of 1:5 to 1:20, immerse in water at 40 to 100°C for 20 to 100 minutes, filter, and separate to obtain aluminum phosphate solution A and iron mixture. Add a type I acid to the aluminum phosphate solution A, adjust the pH of the solution to 9-5, preferably 7.5-6.5, stir, filter, and obtain purified phosphate solution B.

[0013] In one embodiment of the present invention, the method further includes adding an alkali to an aluminum phosphate solution A to remove impurity metal elements from the phosphate solution by precipitation.

[0014] In one embodiment of the present invention, the first type of acid is selected from one or more combinations of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, citric acid, acetic acid, and oxalic acid.

[0015] In one embodiment of the present invention, the mixture B and water are mixed at a mass ratio of 1:8 to 1:12, the water immersion temperature is 60 to 80°C, and the water immersion time is 40 to 60 minutes.

[0016] In one embodiment of the present invention, the step of removing impurities from the iron mixture in step S3 includes: S31, weigh according to the molar ratio of ferric acid to acid of 1:1 to 1:5, preferably 1:2 to 1:3, and weigh according to the mass ratio of ferric acid to water of 1:10, dissolve and filter to obtain ferrous solution A; S32, based on Ti in ferrous solution A 4+ The content of Ti, according to the molar ratio 4+ Extractant 1 is prepared in a ratio of 1:2 to 1:8. Sulfonated kerosene is added with an A / O ratio of 1. The extraction to remove titanium is carried out at a temperature of 25 to 55°C and an oscillation frequency of 50 to 100 rpm for 10 to 30 minutes. After A / O separation, ferrous solution B is obtained. S33, hydrogen peroxide is added to the ferrous solution B for oxidation to obtain a ferric solution A; wherein Fe 2+ The molar ratio with hydrogen peroxide is 1:1; S34, based on Fe in iron solution 3+ The content, according to the molar ratio Fe 3+Extractant 2 is prepared in a ratio of 1:1 to 1:6. Sulfonated kerosene is added with an A / O ratio of 1. Iron extraction is performed at a temperature of 25 to 55°C and an oscillation frequency of 50 to 200 rpm for 10 to 60 minutes. After A / O separation, iron-loaded extractant 3 is obtained. S35 is prepared according to the molar ratio of extractant 3 : second type acid = 3:1~1:3. Water is added with an A / O ratio of 1. Iron back-extraction is performed at a temperature of 25~55℃ and an oscillation frequency of 200~500 rpm for 1~4 h. After A / O separation, trivalent iron solution B is obtained.

[0017] In one embodiment of the present invention, in step S32, the extractant 1 is selected from one or more of 2-ethylhexyl phosphate mono-2-ethylhexyl ester, isoalkylphosphonate (1-methylheptyl) ester, di(2-ethylhexyl) phosphate, tributyl phosphate, triheptyl phosphate, trioctyl phosphate, dibutyl butylphosphonate, dimethylheptyl methylphosphonate, diisooctyl isopropylphosphonate, and dibutylphosphonate.

[0018] In one embodiment of the present invention, the Ti 4+ The molar ratio with extractant 1 is 1:3 to 1:5.

[0019] Preferably, the extraction temperature is 30~40℃, the oscillation frequency is 60~80rpm, and the extraction time is 15~20 min; In one embodiment of the present invention, in step S34, the extractant 2 is selected from one or more combinations of trioctylamine, trilauridine, trioctylamine, triisooctylamine and triheptylamine.

[0020] Preferably, the Fe 3+ The molar ratio of extractant 2 to extractant 2 is 1:2 to 1:4; Preferably, the extraction temperature is 30~40℃, the oscillation frequency is 100~150rpm, and the extraction time is 30~50min.

[0021] In one embodiment of the present invention, in step S35, the second type of acid is selected from one or more combinations of sulfuric acid, hydrochloric acid and nitric acid; The molar ratio of the extractant 3 to the acid is 3:2 to 2:3; the extraction temperature is 30 to 40°C; the oscillation frequency is 300 to 400 rpm; and the extraction time is 2 to 3 h.

[0022] In one embodiment of the present invention, step S4 includes: S41, according to the molar ratio Fe 3+ :PO4 3+ =1.1:1~1:1.1 Mix the iron solution B and phosphate solution B to obtain an iron-phosphorus mixture; S42, add alkali to the iron-phosphorus mixture to adjust the pH of the iron-phosphorus mixture to 1.5~2.0, age, filter, wash, and dry to obtain ferric phosphate dihydrate; calcine the ferric phosphate dihydrate at a certain temperature to obtain battery-grade ferric phosphate.

[0023] In one embodiment of the present invention, the Fe 3+ and PO4 3+ The molar ratio is 1:1.

[0024] Preferably, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; Preferably, the pH value is adjusted to 1.8, and the aging time is 30 minutes; Preferably, the ferric phosphate dihydrate is calcined at a certain temperature to obtain battery-grade ferric phosphate; Preferably, the calcination temperature is 600℃ and the calcination time is 3 hours.

[0025] The present invention also provides a battery-grade iron phosphate, which is prepared by the above-mentioned method for recycling and utilizing waste battery iron phosphate slag.

[0026] The beneficial effects of this invention are: This invention separates phosphate slag into iron complex and phosphate by constructing a reducing atmosphere field through high-temperature decomposition of oxalate. The separation of iron complex and phosphate is achieved by water immersion, and aluminum in iron complex is dissolved by alkaline phosphate solution. Impurity metal elements in phosphate solution are further removed by alkaline precipitation.

[0027] The iron mixture was dissolved in acid to form a ferrous solution, and then the Ti in the ferrous solution was removed using a phosphate ester extractant. 4+ The ions were oxidized to ferric solution using hydrogen peroxide, and then the Fe was extracted with a tertiary amine extractant. 3+ Ultimately, the Fe after back-extraction 3 + Battery-grade iron phosphate was prepared by mixing it with phosphate. XRD characterization and ICP impurity content analysis of the iron phosphate prepared in the examples and comparative examples demonstrate that the preparation process of this invention, which separates and removes impurities from the iron phosphate slag, is beneficial for preparing battery-grade iron phosphate. Attached Figure Description

[0028] Figure 1 This is a process flow diagram for preparing ferric phosphate according to the present invention; Figure 2 These are XRD characterization diagrams of the iron phosphate prepared in Examples 1-2 and Comparative Examples 1-2. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0030] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0031] Example 1 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Phosphorus iron slag and sodium oxalate were ball-milled thoroughly at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B was then soaked in water at a mass ratio of 1:8 at 60℃ for 40 minutes, filtered, and separated to obtain an iron mixture and a sodium aluminum phosphate solution A.

[0032] Reaction equation: (Fractional 1) (Fractional 2) (General Formula) 2) Purification of aluminum phosphate solution: The pH of aluminum sodium phosphate solution A was adjusted to 7.5 with sulfuric acid, stirred for 30 min, and then filtered to remove metal impurities such as aluminum phosphate, resulting in purified sodium phosphate solution B.

[0033] 3) Removal of impurities from iron mixtures: The iron mixture was dissolved in a ferrous solution A by dissolving it in a ferrous sulfate solution in a ferrous sulfate molar ratio of 1:2 and a ferrous sulfate mass ratio of 1:10. According to Ti in ferrous solution A 4+ The molar ratio of 2-ethylhexyl phosphate mono-2-ethylhexyl ester was 1:3, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The titanium removal operation was carried out at 30°C and oscillation frequency of 60 rpm for 15 min. After A / O separation, ferrous solution B was obtained. According to Fe in ferrous solution B 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. According to Fe in iron solution A 3+The iron was extracted with trioctylamine at a molar ratio of 1:2, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The iron was extracted at 30°C and an oscillation frequency of 100 rpm for 30 min. After A / O separation, the iron-loaded extractant 3 was obtained.

[0034] According to the molar ratio of iron-carrying extractant 3 to sulfuric acid 3:2, an appropriate amount of water was added to make the A / O ratio 1. The ferric iron back-extraction operation was carried out at 30°C and 300 rpm for 2 h. After A / O separation, a purified ferric iron solution B was obtained. 4) Preparation of ferric phosphate: According to the Fe content of ferric phosphate solution B and sodium phosphate solution B... 3+ With PO4 3+ The iron and phosphorus mixture was mixed in a 1:1 molar ratio to obtain an iron-phosphorus mixture; sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8, and after aging for 30 min, it was filtered, washed, and dried to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain battery-grade ferric phosphate.

[0035] Example 2 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Phosphorus iron slag and potassium oxalate were ball-milled thoroughly at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B and water were then leached at 60℃ for 40 minutes at a mass ratio of 1:8. The mixture was then filtered to separate the iron mixture and a sodium aluminum phosphate solution A.

[0036] 2) Purification of aluminum phosphate solution: The pH of aluminum potassium phosphate solution A was adjusted to 7.5 with sulfuric acid, stirred for 30 min, and then filtered to remove metal impurities such as aluminum phosphate, resulting in purified potassium phosphate solution B.

[0037] 3) Removal of impurities from iron mixture: Dissolve the iron mixture in a 1:2 molar ratio of iron to sulfuric acid and a 1:10 mass ratio of iron to water, and filter to obtain ferrous solution A; According to Ti in ferrous solution A 4+ The molar ratio of 2-ethylhexyl phosphate mono-2-ethylhexyl ester was 1:3, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The titanium removal operation was carried out at 30°C and oscillation frequency of 60 rpm for 15 min. After A / O separation, ferrous solution B was obtained. According to Fe in ferrous solution B 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. According to Fe in iron solution A 3+The iron was extracted with trioctylamine at a molar ratio of 1:2, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The iron was extracted at 30°C and an oscillation frequency of 100 rpm for 30 min. After A / O separation, the iron-loaded extractant 3 was obtained.

[0038] With the iron-carrying extractant 3 and sulfuric acid in a molar ratio of 3:2, and an appropriate amount of water added to make the A / O ratio 1, the ferric iron back-extraction operation was carried out at 30°C and an oscillation frequency of 300 rpm for 2 h. After A / O separation, a purified ferric iron solution B was obtained.

[0039] 4) Preparation of ferric phosphate: According to the Fe content of ferric solution B and sodium phosphate solution B... 3+ With PO4 3+ The iron and phosphorus mixture was mixed in a 1:1 molar ratio to obtain an iron-phosphorus mixture; sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8, and after aging for 30 min, it was filtered, washed, and dried to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain battery-grade ferric phosphate.

[0040] Example 3 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Ferrophosphate slag and sodium oxalate were ball-milled thoroughly at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B and water were then subjected to a water leaching process at 80℃ for 60 minutes at a mass ratio of 1:8. The mixture was then filtered to separate the iron mixture and a sodium aluminum phosphate solution A.

[0041] 2) Purification of aluminum phosphate solution: The pH of aluminum sodium phosphate solution A was adjusted to 6.8 with sulfuric acid, stirred for 30 min, and then filtered to remove metal impurities such as aluminum phosphate, resulting in purified sodium phosphate solution B.

[0042] 3) Removal of impurities from iron mixtures: The iron mixture was dissolved in a ferrous solution A by dissolving the iron in a 1:2 molar ratio of iron to sulfuric acid and a 1:10 mass ratio of iron to water, and the solution was filtered. According to Ti in ferrous solution A 4+ The molar ratio of 1-methylheptyl phosphonate to isoalkylphosphonic acid (1-methylheptyl) ester was 1:3. At the same time, an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The titanium removal operation was carried out at 30°C and oscillation frequency of 60 rpm for 15 min. After A / O separation, ferrous solution B was obtained. According to Fe in ferrous solution B 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. According to Fe in iron solution A3+ The iron was extracted with trioctylamine at a molar ratio of 1:2, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The iron was extracted at 30°C and an oscillation frequency of 100 rpm for 30 min. After A / O separation, the iron-loaded extractant 3 was obtained.

[0043] According to the molar ratio of iron-carrying extractant 3 to sulfuric acid 3:2, an appropriate amount of water was added to make the A / O ratio 1. The ferric iron back-extraction operation was carried out at 30°C and 300 rpm for 2 h. After A / O separation, a purified ferric iron solution B was obtained. 4) Preparation of ferric phosphate: According to the Fe content of ferric solution B and sodium phosphate solution B... 3+ With PO4 3+ The iron and phosphorus mixture was mixed in a 1:1 molar ratio to obtain an iron-phosphorus mixture; sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8, and after aging for 30 min, it was filtered, washed, and dried to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain battery-grade ferric phosphate.

[0044] Example 4 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Phosphorus iron slag and sodium oxalate were thoroughly ball-milled at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B and water were then subjected to a water leaching process at 60℃ for 40 minutes at a mass ratio of 1:8. The mixture was then filtered to separate the iron mixture and a sodium aluminum phosphate solution A.

[0045] 2) Purification of aluminum phosphate solution: The pH of aluminum sodium phosphate solution A was adjusted to 7.5 with sulfuric acid, stirred for 30 min, and then filtered to remove metal impurities such as aluminum phosphate, resulting in purified sodium phosphate solution B.

[0046] 3) Removal of impurities from iron mixtures: The iron mixture was dissolved in a ferrous solution A by dissolving the iron in a 1:2 molar ratio of iron to sulfuric acid and a 1:10 mass ratio of iron to water, and the solution was filtered. According to Ti in ferrous solution A 4+ The molar ratio of isoalkylphosphonic acid (1-methylheptyl) ester was 1:3, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The titanium removal operation was carried out at 30°C and oscillation frequency of 60 rpm for 15 min. After A / O separation, ferrous solution B was obtained. According to Fe in ferrous solution B 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. According to Fe in iron solution A3+ The iron was extracted with trioctylamine at a molar ratio of 1:2, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The iron was extracted at 30°C and an oscillation frequency of 100 rpm for 30 min. After A / O separation, the iron-loaded extractant 3 was obtained.

[0047] With the iron-carrying extractant 3 and sulfuric acid in a molar ratio of 3:2, and an appropriate amount of water added to make the A / O ratio 1, the ferric iron back-extraction operation was carried out at 30°C and an oscillation frequency of 300 rpm for 2 h. After A / O separation, a purified ferric iron solution B was obtained.

[0048] 4) Preparation of ferric phosphate: According to the Fe content of ferric solution B and sodium phosphate solution B... 3+ With PO4 3+ The iron and phosphorus mixtures were mixed at a molar ratio of 1:1 to obtain an iron-phosphorus mixture. Sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8. After aging for 30 min, the mixture was filtered, washed, and dried to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain battery-grade ferric phosphate.

[0049] Example 5 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Phosphorus iron slag and sodium oxalate were thoroughly ball-milled at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B and water were then subjected to a water leaching process at 60℃ for 60 minutes at a mass ratio of 1:8. The mixture was then filtered to separate the iron mixture and a sodium aluminum phosphate solution A.

[0050] 2) Purification of aluminum phosphate solution: The pH of aluminum sodium phosphate solution A was adjusted to 6.8 with sulfuric acid, stirred for 30 min, and then filtered to remove metal impurities such as aluminum phosphate, resulting in purified sodium phosphate solution B.

[0051] 3) Removal of impurities from iron mixtures: The iron mixture was dissolved in a ferrous solution A by dissolving it in a ferrous sulfate solution in a ferrous sulfate molar ratio of 1:2 and a ferrous sulfate mass ratio of 1:10. According to Ti in ferrous solution A 4+ The molar ratio of 2-ethylhexyl phosphate mono-2-ethylhexyl ester was 1:3, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The titanium removal operation was carried out at 30°C and oscillation frequency of 60 rpm for 15 min. After A / O separation, ferrous solution B was obtained. According to Fe in ferrous solution B 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. According to Fe in iron solution A 3+ The iron was extracted with trioctylamine at a molar ratio of 1:2, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The iron was extracted at 30°C and an oscillation frequency of 100 rpm for 30 min. After A / O separation, the iron-loaded extractant 3 was obtained.

[0052] According to the molar ratio of iron-carrying extractant 3 to sulfuric acid 3:2, an appropriate amount of water was added to make the A / O ratio 1. The ferric iron back-extraction operation was carried out at 30°C and 300 rpm for 2 h. After A / O separation, a purified ferric iron solution B was obtained. 4) Preparation of ferric phosphate: According to the Fe content of ferric solution B and sodium phosphate solution B... 3+ With PO4 3+ The iron and phosphorus mixture was mixed in a 1:1 molar ratio to obtain an iron-phosphorus mixture; sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8, and after aging for 30 min, it was filtered, washed, and dried to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain battery-grade ferric phosphate.

[0053] Comparative Example 1 1) Dissolve ferric phosphate slag with sulfuric acid at a molar ratio of 1:3, filter to obtain a mixture of ferric sulfate and phosphoric acid, adjust the pH of the mixture to 1.8 with sodium hydroxide, age for 30 min, filter, wash and dry to obtain ferric phosphate dihydrate; place ferric phosphate dihydrate in a muffle furnace and calcine at 600℃ for 3 h to obtain ferric phosphate.

[0054] Comparative Example 2 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Phosphorus iron slag and sodium oxalate were thoroughly ball-milled at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B was then soaked in water at 60℃ for 40 minutes at a mass ratio of 1:8, followed by filtration to separate the iron mixture and a sodium aluminum phosphate solution A.

[0055] 2) Method for removing impurities from aluminum phosphate solution: The pH of aluminum sodium phosphate solution A was adjusted to 7.5 with sulfuric acid, stirred for 30 min, and then filtered to remove metal impurities such as aluminum phosphate, resulting in purified sodium phosphate solution B.

[0056] 3) Removal of impurities from the iron mixture: Dissolve the iron mixture in sulfuric acid at a molar ratio of 1:2 and a water mass ratio of 1:10, and filter to obtain ferrous solution A; according to the Fe content in ferrous solution B... 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. 4) Preparation of ferric phosphate: According to the Fe content of ferric phosphate solution A and sodium phosphate solution B... 3+ With PO4 3+ The iron and phosphorus mixture was mixed at a molar ratio of 1:1 to obtain an iron-phosphorus mixture. Sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8. After aging for 30 min, the mixture was filtered, washed, and dried to obtain ferric phosphate dihydrate. Ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain ferric phosphate.

[0057] from Figure 2 As can be seen from the comparison of the ferric phosphate prepared by Examples 1-2 and Comparative Examples 1-2, their XRD characterization shows that the XRD spectra of Examples 1-2 are in complete agreement with the XRD standard card (PDF#77-0094 FePO4), indicating that the ferric phosphate prepared after separation and impurity removal from the ferric phosphate slag has a good crystal structure and purity. The XRD spectra of Comparative Examples 1-2 show a bump near 20°, indicating that the ferric phosphate prepared by Comparative Examples 1-2 has a changed crystal structure due to the presence of other impurities; in particular, compared with Comparative Example 2, the XRD spectrum of Comparative Example 1 has a significant impurity peak at 28°, which is most likely caused by aluminum phosphate produced by the impurity aluminum element.

[0058] Comparative Example 3 1) Oxalate-assisted calcination and transformation of phosphate-iron slag, followed by water leaching to separate the iron mixture from the phosphate and dissolve the aluminum foil: Ferrophosphate slag and sodium oxalate were ball-milled thoroughly at a molar ratio of 3:2 to obtain mixture A. Mixture A was then heated for 6 hours under vacuum at a controlled calcination temperature of 500℃ to obtain mixture B. Mixture B was then leached with water at a mass ratio of 1:8 at 60℃ for 40 minutes. The mixture was then filtered to separate the iron mixture and a sodium aluminum phosphate solution A.

[0059] 2) Removal of impurities from iron mixture: The iron mixture was dissolved and filtered at a molar ratio of iron to sulfuric acid of 1:2 and a mass ratio of iron to water of 1:10 to obtain ferrous solution A. According to Ti in ferrous solution A 4+ The molar ratio of 2-ethylhexyl phosphate mono-2-ethylhexyl ester was 1:3, and an appropriate amount of sulfonated kerosene was added to make the A / O ratio 1. The titanium removal operation was carried out at 30°C and oscillation frequency of 60 rpm for 15 min. After A / O separation, ferrous solution B was obtained. According to Fe in ferrous solution B 2+ Adding hydrogen peroxide to ferrous solution B in a 1:1 molar ratio with hydrogen peroxide yields ferric solution A. According to Fe in iron solution A 3+With a molar ratio of 1:2 to trilauramine, and with the addition of an appropriate amount of sulfonated kerosene to make the A / O ratio 1, the ferric iron was extracted at 30°C and an oscillation frequency of 100 rpm for 30 min. After A / O separation, the iron-loaded extractant 3 was obtained.

[0060] With the iron-carrying extractant 3 and sulfuric acid in a molar ratio of 3:2, and an appropriate amount of water added to make the A / O ratio 1, the ferric iron back-extraction operation was carried out at 30°C and an oscillation frequency of 300 rpm for 2 h. After A / O separation, a purified ferric iron solution B was obtained.

[0061] 3) Preparation of ferric phosphate: According to the ferric phosphate solution B and the phosphorus-containing sodium phosphate solution A, the Fe... 3+ With PO4 3+ The iron and phosphorus mixture was mixed in a 1:1 molar ratio to obtain an iron-phosphorus mixture; sodium hydroxide was added to adjust the pH of the iron-phosphorus mixture to 1.8, and after aging for 30 min, it was filtered, washed, and dried to obtain ferric phosphate dihydrate; ferric phosphate dihydrate was placed in a muffle furnace and calcined at 600℃ for 3 h to obtain ferric phosphate.

[0062] Table 1. Impurity content of phosphorus-iron slag waste used in Examples 1-5 and Comparative Examples 1-3

[0063] Table 2. Impurity content of ferric phosphate prepared in Examples 1-5 and Comparative Examples 1-3

[0064] As can be seen from the ICP impurity content analysis in Table 2, the contents of impurities Al, Ca, Mg, Cu, Zn, Na, K, Ni, and Mn in the examples are low, and even the presence of Cr, As, Pb, Cd, and Ti is undetectable, indicating that the impurity content standard for battery-grade iron phosphate has been met.

[0065] Specifically, the Al and Ti contents in Comparative Example 1 are very high, the Ti content in Comparative Example 2 is extremely high, and the Al content in Comparative Example 3 is extremely high. This indicates that simple calcination of ferrophosphate slag cannot produce high-purity ferric phosphate. It also shows that Ti and Fe co-precipitate with phosphate ions simultaneously and cannot be separated by simple water washing, thus requiring impurity removal from the iron mixture; similarly, Ti and Al co-precipitate with phosphate ions simultaneously and cannot be separated by simple water washing, thus requiring impurity removal from the aluminum phosphate solution. Therefore, it demonstrates that using the preparation process of this invention to separate and independently remove ferrophosphate from the ferrophosphate slag is beneficial for preparing battery-grade ferric phosphate.

[0066] In summary, the technical solution of this application separates phosphate-iron slag into iron complexes and phosphates by constructing a reducing atmosphere through high-temperature decomposition of oxalate. Water leaching is used to separate the iron complexes and phosphates. An alkaline phosphate solution is used to dissolve aluminum in the iron complexes, and further alkaline precipitation removes impurity metal elements from the phosphate solution. An acid is used to dissolve the iron mixture into a ferrous solution, followed by the removal of Ti from the ferrous solution using a phosphate ester extractant. 4+ The ions were oxidized to ferric solution using hydrogen peroxide, and then the Fe was extracted with a tertiary amine extractant. 3+ Ultimately, the Fe after back-extraction 3+ When mixed with phosphate, battery-grade iron phosphate was prepared.

[0067] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing iron phosphate from waste battery phosphate slag, characterized in that, Includes the following steps: S1, Phosphorus-Iron Slag Separation: Phosphorus-iron slag is mixed with oxalate, ball-milled, and then calcined at high temperature. The reducing atmosphere field is constructed by the high-temperature decomposition of oxalate to separate phosphorus and iron in the phosphorus-iron slag into a mixture B containing iron mixture and phosphate. S2, Phosphate purification: Mixture B is soaked in water to separate phosphorus and iron and dissolve aluminum foil, resulting in aluminum phosphate solution A and an iron mixture; aluminum phosphate solution A is purified to obtain purified phosphate solution B; S3, Iron mixture purification: The iron mixture is dissolved in acid to form a ferrous solution, followed by removal of Ti from the ferrous solution using a phosphate ester extractant. 4+ The ions were used to remove impurities from the iron mixture; then, the ferrous iron was oxidized to an iron solution using hydrogen peroxide, followed by extraction of Fe with a tertiary amine extractant. 3+ The resulting back-extracted ferric solution B was obtained. S4, Preparation of iron phosphate: The purified phosphate solution B is mixed with the trivalent iron solution B to obtain an iron-phosphorus mixture, which is then precipitated, filtered, and calcined to obtain battery-grade iron phosphate.

2. The method according to claim 1, characterized in that, Step S1 includes: Oxalate and ferrophosphate slag are mixed and weighed according to a molar ratio of ferrophosphate slag: oxalate = 4:1 to 1:

4. The mixture is then ball-milled to obtain mixture A. Mixture A was placed in a vacuum environment and calcined at 400-800℃ for 4-12 hours to obtain mixture B; Preferably, the oxalate comprises one or more combinations of sodium oxalate, potassium oxalate, and potassium oxalate monohydrate; Preferably, the molar ratio of ferrophosphate slag to oxalate is 1:1 to 1:2; Preferably, the calcination temperature is 500~700℃ and the calcination time is 6~8 hours.

3. The method according to claim 1, characterized in that, Step S2 includes: Mixture B and water at a mass ratio of 1:5 to 1:20, immerse in water at 40 to 100°C for 20 to 100 minutes, filter, and separate to obtain aluminum phosphate solution A and iron mixture. Add a type I acid to the aluminum phosphate solution A, adjust the pH of the solution to 9-5, preferably 7.5-6.5, stir, filter, and obtain purified phosphate solution B; Preferably, the method further includes the step of adding an alkali to the aluminum phosphate solution A to remove impurity metal elements from the phosphate solution by precipitation.

4. The method according to claim 3, characterized in that, The first type of acid is selected from one or more combinations of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, citric acid, acetic acid, and oxalic acid; Preferably, the mixture B and water are mixed at a mass ratio of 1:8 to 1:12, the water immersion temperature is 60 to 80°C, and the water immersion time is 40 to 60 minutes.

5. The method according to claim 1, characterized in that, The step of removing impurities from the iron mixture in step S3 includes: S31, weigh according to the molar ratio of iron to acid = 1:1 to 1:5, preferably the molar ratio of iron to acid = 1:2 to 1:3, and weigh according to the mass ratio of iron to water = 1:10, dissolve and filter to obtain ferrous solution A; S32, based on Ti in ferrous solution A 4+ The content of Ti, according to the molar ratio 4+ Extractant 1 was prepared in a ratio of 1:2 to 1:

8. Sulfonated kerosene was added with an A / O ratio of 1. The extraction process to remove titanium was carried out at a temperature of 25 to 55°C and an oscillation frequency of 50 to 100 rpm for 10 to 30 minutes. After A / O separation, ferrous solution B was obtained. S33, hydrogen peroxide is added to the ferrous solution B for oxidation to obtain a ferric solution A; wherein Fe 2+ The molar ratio with hydrogen peroxide is 1:1; S34, based on Fe in iron solution 3+ The content, according to the molar ratio Fe 3+ Extractant 2 is prepared in a ratio of 1:1 to 1:

6. Sulfonated kerosene is added with an A / O ratio of 1. Iron extraction is performed at a temperature of 25 to 55°C and an oscillation frequency of 50 to 200 rpm for 10 to 60 minutes. After A / O separation, iron-loaded extractant 3 is obtained. S35 is prepared according to the molar ratio of extractant 3 : second type acid = 3:1~1:

3. Water is added with an A / O ratio of 1. Iron back-extraction is performed at a temperature of 25~55℃ and an oscillation frequency of 200~500 rpm for 1~4 h. After A / O separation, trivalent iron solution B is obtained.

6. The method according to claim 5, characterized in that, In step S32 The extractant 1 is selected from one or more of the following: 2-ethylhexyl phosphate mono-2-ethylhexyl ester, isoalkylphosphonate (1-methylheptyl) ester, di(2-ethylhexyl) phosphate, tributyl phosphate, triheptyl phosphate, trioctyl phosphate, dibutyl butylphosphonate, dimethylheptyl methylphosphonate, diisooctyl isopropylphosphonate, and dibutylphosphonate octyl. Preferably, the Ti 4+ The molar ratio with extractant 1 is 1:3 to 1:5; Preferably, the extraction temperature is 30~40℃, the oscillation frequency is 60~80rpm, and the extraction time is 15~20min.

7. The method according to claim 5, characterized in that, In step S34 The extractant 2 is selected from one or more combinations of trioctylamine, trilauridine, trioctylamine, triisooctylamine, and triheptylamine; Preferably, the Fe 3+ The molar ratio of extractant 2 to extractant 2 is 1:2 to 1:4; Preferably, the extraction temperature is 30~40℃, the oscillation frequency is 100~150rpm, and the extraction time is 30~50min.

8. The method according to claim 5, characterized in that, In step S35 The second type of acid is selected from one or more combinations of sulfuric acid, hydrochloric acid, and nitric acid; The molar ratio of the extractant 3 to the acid is 3:2 to 2:3; the extraction temperature is 30 to 40°C; the oscillation frequency is 300 to 400 rpm; and the extraction time is 2 to 3 h.

9. The method according to claim 1, characterized in that, Step S4 includes: S41, according to the molar ratio Fe 3+ :PO4 3+ =1.1:1~1:1.1 Mix the iron solution B and phosphate solution B to obtain an iron-phosphorus mixture; S42, add alkali to the iron-phosphorus mixture to adjust the pH of the iron-phosphorus mixture to 1.5~2.0, age, filter, wash, and dry to obtain ferric phosphate dihydrate; calcine the ferric phosphate dihydrate at a certain temperature to obtain battery-grade ferric phosphate; Preferably, the Fe 3+ and PO4 3+ The molar ratio is 1:1; Preferably, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; Preferably, the pH value is adjusted to 1.8, and the aging time is 30 minutes; Preferably, the ferric phosphate dihydrate is calcined at a certain temperature to obtain battery-grade ferric phosphate; Preferably, the calcination temperature is 600℃ and the calcination time is 3 hours.

10. A battery-grade iron phosphate, characterized in that, It is obtained by recycling and preparing iron phosphate from waste battery slag as described in any one of claims 1 to 9.

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