Method for preparing iron phosphate product by recycling waste lithium iron phosphate battery

Abstract

The invention discloses a method for preparing an iron phosphate product by recycling waste lithium iron phosphate batteries and the prepared iron phosphate product. The method comprises the following steps: acidolysis of waste lithium iron phosphate battery powder, filtration and separation of a lithium solution, alkaline leaching of acid leaching residues, separation of phosphorus and iron, respective extraction, impurity removal and synthesis of the iron phosphate product. The invention aims to efficiently recycle the waste lithium iron phosphate battery, the process can realize closed-loop efficient recycling of all elements of the lithium iron phosphate battery, the obtained iron phosphate product is battery-grade iron phosphate and can be used for preparing a lithium iron phosphate battery material, the economic benefit is remarkable, and the industrial prospect is good.

Description

Technical Field

[0001] The invention relates to the technical field of recycling waste lithium iron phosphate batteries, and in particular to a method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products. Background Art

[0002] Lithium iron phosphate battery refers to a lithium-ion battery that uses lithium iron phosphate as the positive electrode material. It has the advantages of low-cost and easy-to-obtain raw materials, high theoretical capacity, good thermal stability and cycle stability. Therefore, it is widely used in lithium-ion battery positive electrode materials. Together with lithium cobalt oxide, lithium manganese oxide, and ternary materials, it constitutes the current main lithium-ion positive electrode materials. From January to May 2023, the cumulative installed capacity of lithium iron phosphate batteries was 17.1GWh, a year-on-year increase of 456.6%. Based on its unique advantages, the application and proportion of lithium iron phosphate power batteries in the field of electric vehicles will continue to grow in the future. The volume of retired lithium iron phosphate batteries in the future is huge. If they cannot be handled in time, not only will valuable resources be unable to be recycled and wasted, but large-scale stockpiling will also cause great harm to the environment and public safety.

[0003] At present, lithium-ion batteries are mainly used for cascade utilization and recycling after retirement. Among them, cascade utilization faces the defects of large investment, high cost and potential safety hazards. Therefore, recycling is the main way to deal with waste lithium-ion batteries. Lithium cobalt oxide, lithium manganese oxide and ternary materials have significant recycling economic benefits due to the recycling of metals such as nickel, cobalt and manganese. Many institutions and enterprises have actively invested in research and development experiments. At present, the recycling technology for lithium cobalt oxide, lithium manganese oxide and ternary materials has become increasingly mature and industrialized. The recovery rate of nickel, cobalt and manganese can reach more than 99%, and the recycled materials are fully recycled. However, due to the high recycling cost and low economic efficiency of lithium iron phosphate recycling technology, although there are relevant literature records, the feasibility of industrialization is low. At present, there is no economic recycling of waste lithium iron phosphate batteries. Therefore, how to control the recycling cost of waste lithium iron phosphate batteries and improve their economic benefits is an urgent problem facing the lithium battery recycling industry.

[0004] In view of this problem, simplifying the recovery process, improving the comprehensive recovery rate of valuable elements, and improving product purity and added value are the research directions of many institutions. In the prior art, CN112441572 discloses a method for recovering waste lithium iron phosphate positive electrode materials, in which the residue after acid leaching for lithium extraction is aluminum-removed by alkaline leaching, and the alkaline leaching residue is acid-dissolved to extract iron and phosphorus, and then alkali is added to adjust the pH to prepare basic iron phosphate, and finally phosphoric acid is added to obtain iron phosphate. In the leaching and lithium extraction stage, weakly acidic oxidizing or alkaline oxidizing leaching agent A and acidic oxidizing leaching agent B need to be added respectively. The leaching process is complicated, and the repeated use of acid and alkali reagents leads to large reagent loss and wastewater treatment. In addition, the alkali leaching process removes aluminum alone, which is easy to cause phosphorus loss, and phosphorus recovery is difficult to guarantee. CN112310500 and CN116002646 remove aluminum by adding a fluorinating agent to the aluminum-containing acid leaching solution of lithium iron phosphate to react with the aluminum in the solution to generate a fluoroaluminate complex precipitate. The introduction of the fluorinating agent not only has a significant impact on the performance of the iron phosphate product, but also requires subsequent washing with hot phosphoric acid to increase the process and cost. The introduction of fluoride ions in the solution greatly increases the difficulty of wastewater treatment, and the corresponding fluoroaluminate complex precipitate has little reuse value, which also causes the generation of waste residue, facing dual challenges in environmental protection and economy. CN106910889 removes aluminum by adjusting the content of Li + , Fe 2+ 、Al 3+ ,PO 4 3+ The pH value of the solution is adjusted to 3-5 to achieve the purpose of aluminum removal, but when the pH value is 3-5, a large amount of ferrous phosphate and ferrous hydroxide precipitation is produced, and a large amount of iron ions and phosphate ions are lost, affecting the recovery rate of iron ions and phosphate ions. In CN 114195112, phosphorus is extracted from acid-leached lithium slag by alkali leaching to obtain phosphorus-rich leaching solution and iron-rich slag. The iron-rich slag is calcined at medium temperature to obtain industrial iron red for sale. The phosphorus-rich leaching solution is evaporated and crystallized to obtain hydrated sodium phosphate or purified and impurities are removed before adding hydrogen peroxide and ferrous ions to synthesize ferric phosphate. In this process, the iron-rich slag is calcined at medium temperature to open a circuit in the form of iron red with low added value. In the preparation process of ferric phosphate, a high-purity ferrous solution is additionally used, and the iron element cannot form a closed cycle, which undoubtedly greatly increases the recovery cost and reduces the economic efficiency of the process. When the phosphorus-rich leaching solution is directly evaporated and crystallized to prepare hydrated sodium phosphate, the product purity and added value are low. When the phosphorus-rich leaching solution is removed by the current process, there are also defects such as serious iron and phosphorus losses or high impurity removal costs. In the process of ferric phosphate synthesis, the iron source almost entirely depends on the added fresh iron source, the process cost is high, and the feasibility of industrialization is low. Summary of the invention

[0005] In view of the defects of iron phosphate prepared by recycling lithium iron phosphate battery powder in the prior art, the purpose of the present invention is to provide a method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products with low recycling cost and high economic benefit, so as to solve the problems raised in the above background technology.

[0006] The present invention solves the technical problem by adopting the following technical solution:

[0007] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, characterized in that it comprises the following steps:

[0008] Step 1, adding water to waste lithium iron phosphate battery powder and stirring to make slurry, adding acid and oxidant to the slurry separately or simultaneously after stirring evenly, filtering to obtain lithium-containing solution and insoluble matter after reaction, and obtaining lithium carbonate by purifying and precipitating the lithium-containing solution; the acid is sulfuric acid or hydrochloric acid, preferably sulfuric acid, and the amount of addition is n(H + ):n(PO 4 3+ )=1:1-1:1.2;Control the leaching solid-liquid ratio to be 1:2-1:10g / mL, the reaction time to be 20-180min, and the reaction temperature to be 20-100℃;Preferably, when adding acid and oxidant to the slurry, both are added at the same time, or either acid and oxidant are added first, stirred evenly and then the other is added, or acid and one oxidant are added at the same time, and then the other oxidant is added. The oxidant is one or more of hydrogen peroxide, chlorate, hypochlorite, persulfate, oxygen or air, preferably a combination of any one of air, oxygen or hydrogen peroxide and any one of chlorate, hypochlorite or persulfate, and the oxidation end point is that the concentration of divalent iron ions in the solution is less than 0.1g / L.

[0009] The main sources of waste lithium iron phosphate battery powder are lithium iron phosphate powder scrapped by battery manufacturers, lithium iron phosphate powder obtained after battery disassembly and sorting, and lithium iron phosphate powder obtained from lithium iron phosphate electrode processing.

[0010] Step 2, add water to the insoluble matter obtained in step 1, stir and make pulp, add alkaline substance to the pulp, preferably add reducing agent, the pH of the leaching solution system is ≥10.5, filter to obtain phosphate solution and iron-containing precipitate, wash the iron-containing precipitate with alkali solution, control the aluminum content in the iron-containing precipitate to be below 0.1%, and return the alkali washing solution to make pulp; the alkaline substance in step 3 is at least one of sodium sulfide, potassium sulfide, sodium hydroxide, and potassium hydroxide, and the amount added is based on the phosphorus element fully entering the solution; preferably, the reducing agent is at least one of sodium sulfide, potassium sulfide, sulfite, and reduced iron powder, so that iron exists in the form of ferrous ions. The alkali washing solution is an alkali solution of 0.1-0.5 mol / L, preferably an alkali solution of the same type as the alkali leaching in this step, and the number of washings is more than 3 times.

[0011] Step 3, adding an acidic substance to the phosphate solution in step 2 to adjust the pH value, filtering to remove aluminum impurities, and obtaining a pure phosphate solution; the acidic substance is hydrochloric acid, sulfuric acid, phosphoric acid or carbon dioxide gas, and the pH is adjusted to 4-10.

[0012] Step 4, add water to the iron-containing precipitate described in step 2 to make a pulp, then add sulfuric acid with a concentration of 2-8 mol / L, the amount of sulfuric acid used is 1-1.4 times the theoretical amount, the solid-liquid ratio is 1:2-1:8 g / L, the reaction temperature is 20-60°C, and after the reaction, filter to obtain an iron salt solution and insoluble matter; preferably, iron powder is added to the obtained iron salt solution, and the amount of iron powder added is 1.01-1.2 times the amount of trivalent iron substance in the solution, and solid-liquid separation is performed after the reaction.

[0013] Step 5: Mix the pure phosphate solution obtained in step 3 and the (iron) salt solution obtained in step 4 to prepare ferric phosphate, preferably the phosphorus-iron molar ratio is 0.96-1.0, more preferably, an oxidant is added to the mixed solution, preferably one or more of hydrogen peroxide, oxygen or air.

[0014] The iron phosphate product is prepared by the above method and its application in lithium iron phosphate battery materials.

[0015] Beneficial effects of the present invention:

[0016] The present invention optimizes the process steps and controls the element trend of lithium iron phosphate, and can realize the full element recovery and reuse of lithium iron phosphate batteries through a simple and easy-to-implement process. The obtained product has high purity and high added value. The impurity elements can be fully removed by controlling the trend of the impurity elements, while avoiding the introduction of difficult-to-treat anions and the entrainment loss of ferrophosphorus. The iron phosphate prepared by the present invention has high purity, good morphology and crystal shape, and can be used to prepare lithium iron phosphate battery materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the XRD diagram of the product of the present invention;

[0018] Figure 2 It is the SEM picture of the product of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example

[0021] Embodiment 1:

[0022] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, comprising the following steps:

[0023] Step 1: Slurry the waste lithium iron phosphate battery powder and water, mix them evenly and add n(H+ ):n(PO 4 3+ )=1:1 add sulfuric acid to the slurry, mix well and then add hydrogen peroxide, take the divalent iron ion concentration of 0.05g / L as the oxidation end point, the solid-liquid ratio of the leaching system is 1:3g / mL, react at 20°C for 180min and then filter to obtain a lithium-containing solution and insoluble matter, and purify and precipitate the lithium-containing solution to obtain lithium carbonate;

[0024] Step 2: The insoluble matter obtained in step 1 is slurried with water, sodium sulfide is added to the slurry, the pH of the system after leaching is 10.5, and the phosphate solution and the iron-containing precipitate are filtered out, and the iron-containing precipitate is washed with a 0.2 mol / L sodium hydroxide solution for 5 times, and the aluminum content is controlled to be below 0.1%, and the washing liquid is collected and returned to the slurry;

[0025] Step 3, adding sulfuric acid to the phosphate solution in step 2, adjusting the pH value to 8, filtering to remove aluminum impurities, and obtaining a pure phosphate solution;

[0026] Step 4, after slurrying the iron-containing precipitate and insoluble matter in step 2 with water, adding 2 mol / L sulfuric acid, the amount of sulfuric acid is 1 times the theoretical amount, the solid-liquid ratio is 1:3, reacting at 60° C., filtering to obtain the iron salt solution and insoluble matter;

[0027] Step 5: Mix the pure phosphate obtained in step 3 and the iron salt solution obtained in step 4, control the phosphorus-iron molar ratio to be 0.96, and react to obtain a battery-grade iron phosphate product, which can be used to prepare lithium iron phosphate materials. The recovery rates of lithium, iron, and phosphorus in this embodiment are 97.1%, 94.2%, and 96.2%, respectively.

[0028] Embodiment 2:

[0029] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, comprising the following steps:

[0030] Step 1: Slurry the waste lithium iron phosphate battery powder with water and introduce oxygen, mix well and then add n(H + ):n(PO 4 3 + )=1:1.1 add sulfuric acid to the slurry, take the divalent iron ion concentration in the solution as 0.1g / L as the oxidation end point, the solid-liquid ratio of the leaching system is 1:5g / mL, react at 30°C for 180min, filter to obtain the lithium-containing solution and insoluble matter, and purify and precipitate the lithium-containing solution to obtain lithium carbonate;

[0031] Step 2: The insoluble matter obtained in step 1 is slurried with water, sodium hydroxide is added to the slurry, the pH of the system after leaching is 13.5, and the phosphate solution and the iron-containing precipitate are filtered out, and the iron-containing precipitate is washed with 0.3 mol / L sodium hydroxide solution for 6 times, and the aluminum content is controlled to be below 0.1%, and the washing liquid is collected and returned to the slurry;

[0032] Step 3, adding sulfuric acid to the phosphate solution in step 2, adjusting the pH value to 5.5, filtering to remove aluminum impurities, and obtaining a pure phosphate solution;

[0033] Step 4, after slurrying the iron-containing precipitate and insoluble matter in step 2 with water, add 3 mol / L sulfuric acid, the amount of sulfuric acid is 1.05 times the theoretical amount, the solid-liquid ratio is 1:4, and after reacting at 50° C., add iron powder, the amount of iron powder added is 1.05 times the amount of trivalent iron in the solution, and filter to obtain a ferrous salt solution and insoluble matter;

[0034] Step 5: Mix the pure phosphoric acid obtained in step 3 and the ferrous salt solution obtained in step 4, control the phosphorus-iron molar ratio to be 0.97, and react under oxidizing conditions to obtain a battery-grade iron phosphate product, which can be used to prepare lithium iron phosphate materials. The recovery rates of lithium, iron, and phosphorus in this embodiment are 97.3%, 92.5%, and 96.3%, respectively.

[0035] Embodiment 3:

[0036] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, comprising the following steps:

[0037] Step 1: Slurry the waste lithium iron phosphate battery powder and water, mix them evenly and add n(H + ):n(PO 4 3+ )=1:1.05, hydrochloric acid and potassium chlorate are added to the slurry, and the oxidation end point is 0.03g / L of the divalent iron ion concentration in the solution, the solid-liquid ratio of the leaching system is 1:6g / mL, and the reaction is carried out at 45°C for 90min, and then the lithium-containing solution and insoluble matter are obtained by filtering, and the lithium-containing solution is purified and precipitated to obtain lithium carbonate;

[0038] Step 2: The insoluble matter obtained in step 1 is slurried with water, potassium hydroxide and potassium sulfite are added to the slurry to make the iron exist in the form of ferrous iron. The pH of the system after leaching is 14. The phosphate solution and the iron-containing precipitate are filtered out. The iron-containing precipitate is washed with a 0.4 mol / L potassium hydroxide solution for 4 times to control the aluminum content below 0.1%. The washing liquid is collected and returned to the slurry;

[0039] Step 3, adding hydrochloric acid to the phosphate solution in step 2, adjusting the pH value to 7, filtering to remove aluminum impurities, and obtaining a pure phosphate solution;

[0040] Step 4, after slurrying the iron-containing precipitate and insoluble matter in step 2 with water, add 5 mol / L sulfuric acid, the amount of sulfuric acid is 1.1 times the theoretical amount, the solid-liquid ratio is 1:5, and after reacting at 45°C, add iron powder, the amount of iron powder added is 1.1 times the amount of trivalent iron in the solution, and filter to obtain a ferrous salt solution and insoluble matter;

[0041] Step 5: Mix the pure phosphoric acid obtained in step 3 and the ferrous salt solution obtained in step 4, control the phosphorus-iron molar ratio to be 1, and react under oxidizing conditions to obtain a battery-grade iron phosphate product, which can be used to prepare lithium iron phosphate materials. The recovery rates of lithium, iron, and phosphorus in this embodiment are 97.6%, 95.7%, and 96.9%, respectively.

[0042] Embodiment 4:

[0043] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, comprising the following steps:

[0044] Step 1: Slurry the waste lithium iron phosphate battery powder and water, mix them evenly and add n(H + ):n(PO 4 3+ )=1:1.2 add sulfuric acid to the slurry, mix well and then add sodium persulfate to the slurry obtained in step 1, take the divalent iron ion concentration in the solution as 0.06g / L as the oxidation end point, the solid-liquid ratio of the leaching system is 1:5g / mL, react at 60°C for 60min, filter to obtain a lithium-containing solution and insoluble matter, and purify and precipitate the lithium-containing solution to obtain lithium carbonate;

[0045] Step 2: The insoluble matter obtained in step 1 is slurried with water, sodium hydroxide and sodium sulfite are added to the slurry to make the iron exist in the form of ferrous iron, the pH of the system after leaching is 13.9, and the phosphate solution and the iron-containing precipitate are filtered out, and the iron-containing precipitate is washed with a 0.35 mol / L potassium hydroxide solution for 3 times, and the aluminum content is controlled to be below 0.1%, and the washing liquid is collected and returned to the slurry;

[0046] Step 3, adding phosphoric acid to the phosphate solution in step 2, adjusting the pH value to 4, filtering to remove aluminum impurities, and obtaining a pure phosphate solution;

[0047] Step 4, after slurrying the iron-containing precipitate and insoluble matter in step 2 with water, add 6 mol / L sulfuric acid, the amount of sulfuric acid is 1.2 times the theoretical amount, the solid-liquid ratio is 1:6, and after reacting at 35°C, add iron powder, the amount of iron powder added is 1.2 times the amount of trivalent iron in the solution, and filter to obtain a ferrous salt solution and insoluble matter;

[0048] Step 5: Mix the pure phosphoric acid obtained in step 3 and the ferrous salt solution obtained in step 4, control the phosphorus-iron molar ratio to be 0.99, and react under oxidizing conditions to obtain a battery-grade iron phosphate product, which can be used to prepare lithium iron phosphate materials. The recovery rates of lithium, iron, and phosphorus in this embodiment are 98.3%, 96.3%, and 97.2%, respectively.

[0049] Embodiment 5:

[0050] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, comprising the following steps:

[0051] Step 1: Slurry the waste lithium iron phosphate battery powder and water, mix them evenly and add n(H + ):n(PO 4 3+ )=1:1.15 add sulfuric acid to the slurry and introduce oxygen at the same time, mix well, add sodium persulfate to the slurry obtained in step 1, take the divalent iron ion concentration in the solution as 0.01g / L as the oxidation end point, the solid-liquid ratio of the leaching system is 1:10g / mL, react at 95°C for 20min, filter to obtain a lithium-containing solution and insoluble matter, and purify and precipitate the lithium-containing solution to obtain lithium carbonate;

[0052] Step 2: The insoluble matter obtained in step 1 is slurried with water, sodium hydroxide and sodium sulfide are added to the slurry to make the iron exist in the form of ferrous iron, the pH of the system after leaching is 14, and the phosphate solution and the iron-containing precipitate are filtered out, and the iron-containing precipitate is washed with a 0.5 mol / L sodium sulfide solution for 4 times, and the aluminum content is controlled to be below 0.1%, and the washing liquid is collected and returned to the slurry;

[0053] Step 3, introducing carbon dioxide gas into the phosphate solution in step 2, adjusting the pH value to 9, filtering to remove aluminum impurities, and obtaining a pure phosphate solution;

[0054] Step 4, after slurrying the iron-containing precipitate and insoluble matter in step 2 with water, add 8 mol / L sulfuric acid, the amount of sulfuric acid is 1 times the theoretical amount, the solid-liquid ratio is 1:8, and after reacting at 30°C, add iron powder, the amount of iron powder added is 1.15 times the amount of trivalent iron in the solution, and filter to obtain a ferrous salt solution and insoluble matter;

[0055] Step 5: Mix the pure phosphoric acid obtained in step 3 and the ferrous salt solution obtained in step 4, control the phosphorus-iron molar ratio to be 1, and react under oxidizing conditions to obtain a battery-grade iron phosphate product, which can be used to prepare lithium iron phosphate materials. The recovery rates of lithium, iron, and phosphorus in this embodiment are 98.5%, 95.1%, and 96.5%, respectively.

[0056] Embodiment 6:

[0057] A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, comprising the following steps:

[0058] Step 1: Prepare a slurry of waste lithium iron phosphate battery powder and water, mix well, add sodium hypochlorite to the slurry, and then + ):n(PO 4 3+ )=1:1.1 add hydrochloric acid to the slurry, take the divalent iron ion concentration in the solution as 0.02g / L as the oxidation end point, the solid-liquid ratio of the leaching system is 1:2g / mL, react at 75°C for 75min, filter to obtain a lithium-containing solution and insoluble matter, and purify and precipitate the lithium-containing solution to obtain lithium carbonate;

[0059] Step 2: The insoluble matter obtained in step 1 is slurried with water, sodium hydroxide is added to the slurry, the pH of the system after leaching is 13.8, and the phosphate solution and the iron-containing precipitate are filtered out, and the iron-containing precipitate is washed with 0.1 mol / L sodium hydroxide solution for 8 times, and the aluminum content is controlled to be below 0.1%, and the washing liquid is collected and returned to the slurry;

[0060] Step 3, adding phosphoric acid to the phosphate solution in step 2, adjusting the pH value to 10, filtering to remove aluminum impurities, and obtaining a pure phosphate solution;

[0061] Step 4, after slurrying the iron-containing precipitate and insoluble matter in step 2 with water, adding 4 mol / L sulfuric acid, the amount of sulfuric acid is 1.4 times the theoretical amount, the solid-liquid ratio is 1:2, reacting at 25°C and filtering to obtain an iron solution and insoluble matter;

[0062] Step 5: Mix the pure phosphoric acid obtained in step 3 and the iron solution obtained in step 4, control the phosphorus-iron molar ratio to be 1, and react to obtain a battery-grade iron phosphate product, which can be used to prepare lithium iron phosphate materials. The recovery rates of lithium, iron, and phosphorus in this embodiment are 97.9%, 92.9%, and 96.4%, respectively.

[0063] Iron phosphate composition index of Example 4

[0064]

[0065]

[0066] It can be seen from the above embodiments that the present application scheme can achieve high lithium, phosphorus and iron recovery rates when treating waste lithium iron phosphate batteries, and can prepare high-purity iron phosphate products. The overall process steps are simple, the process is easy to implement and control, and it has significant industrial economic benefits.

[0067] It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, so it is intended to describe the embodiments in the claims according to the embodiments, but not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products, It is characterized in that The following steps are involved: Step 1, adding water to waste lithium iron phosphate battery powder to prepare slurry, stirring evenly, adding acid and oxidant to the slurry, filtering to obtain lithium-containing solution and insoluble matter after reaction, and obtaining lithium carbonate by purifying and precipitating the lithium-containing solution; Step 2, adding water to the insoluble matter obtained in step 1, stirring and slurrying, adding alkaline substances to the slurry, preferably also adding reducing agents, filtering to obtain phosphate solution and iron-containing precipitates, washing the iron-containing precipitates with alkaline solution, controlling the aluminum content in the iron-containing precipitates to be below 0.1%, and returning the alkaline washing solution to slurrying; Step 3, adding an acidic substance to the phosphate solution in step 2 to adjust the pH value, filtering to remove aluminum impurities, and obtaining a pure phosphate solution; Step 4, add water to the iron-containing precipitate in step 2 to make a slurry, then add sulfuric acid with a concentration of 2-8 mol / L, and the amount of sulfuric acid is 1-1.4 times the theoretical amount; the reaction temperature is 20-60°C, and after the reaction, the iron salt solution and insoluble matter are filtered; Step 5: Mix the pure phosphate solution obtained in step 3 and the iron salt solution obtained in step 4 to prepare iron phosphate.

2. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to claim 1, It is characterized in that The acid in step 1 is sulfuric acid or hydrochloric acid, preferably sulfuric acid, and the amount of addition is n(H + ):n(PO 4 3+ )=1:1-1:1.2; control the leaching solid-liquid ratio to be 1:2-1:10g / mL, the reaction time to be 20-180min, and the reaction temperature to be 20-100°C; preferably, when adding the acid and the oxidant to the slurry, the two are added simultaneously, or either the acid and the oxidant are added first, stirred evenly and then the other is added, or the acid and one oxidant are added simultaneously, and then the other oxidant is added.

3. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to any one of claims 1 or 2, It is characterized in that The oxidant in step 1 is one or more of hydrogen peroxide, chlorate, hypochlorite, persulfate, oxygen or air, preferably a combination of any one of air, oxygen or hydrogen peroxide and any one of chlorate, hypochlorite or persulfate, and the oxidation endpoint is that the concentration of divalent iron ions in the solution is less than 0.1 g / L.

4. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to any one of claims 1 to 3, It is characterized in that The alkaline substance in step 2 is at least one of sodium sulfide, potassium sulfide, sodium hydroxide, and potassium hydroxide, and the pH of the leaching solution system is ≥10.5; preferably, the reducing agent is at least one of sodium sulfide, potassium sulfide, sulfite, and reduced iron powder, so that the iron exists in the form of ferrous iron.

5. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to any one of claims 1 to 4, It is characterized in that The alkaline washing solution in step 2 is an alkaline solution of 0.1-0.5 mol / L, preferably an alkaline solution of the same type as that of the alkaline leaching in this step, and the washing times are more than 3 times.

6. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to any one of claims 1 to 5, It is characterized in that The acidic substance in step 3 is hydrochloric acid, sulfuric acid, phosphoric acid or acidic gas, and the pH is adjusted to 4-10.

7. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to any one of claims 1 to 6, It is characterized in that Step 4: The solid-liquid ratio is 1:2-1:8 g / L. Preferably, iron powder is added to the obtained iron salt solution, and the amount of iron powder added is 1.01-1.2 times the amount of trivalent iron in the solution. After the reaction, the solid and liquid are separated.

8. A method for recycling waste lithium iron phosphate batteries to prepare iron phosphate products according to any one of claims 1 to 7, It is characterized in that The molar ratio of phosphorus to iron in step 5 is 0.96-1.0; preferably, an oxidant is added to the mixed solution in step 5, preferably one or more of hydrogen peroxide, oxygen or air.

9. An iron phosphate product, It is characterized in that Prepared by the method according to any one of claims 1 to 9.

10. Use of the iron phosphate product as claimed in claim 9 in lithium iron phosphate battery materials.

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