Method for preparing iron phosphate from lithium extraction residue of lithium iron phosphate, iron phosphate and waste lithium ion battery recycling method

Abstract

The application discloses a method for preparing iron phosphate from lithium extraction residue of lithium iron phosphate, the iron phosphate and a waste lithium ion battery recycling method. The method comprises the following steps: mixing lithium extraction residue of lithium iron phosphate with first acid liquor to obtain leaching liquor containing phosphorus elements and iron elements; adjusting the pH value of the leaching liquor to make the phosphorus elements and the iron elements undergo a precipitation reaction to obtain phosphorus-iron leaching residue; mixing the phosphorus-iron leaching residue with second acid liquor to obtain a mixture; and adjusting the pH value of the mixture to make the phosphorus elements and the iron elements undergo a precipitation reaction to obtain iron phosphate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of recycling waste lithium batteries, and particularly relates to a method for preparing iron phosphate from lithium iron phosphate lithium extraction residue, iron phosphate and a method for recycling waste lithium ion batteries. BACKGROUND

[0002] Many competitive companies and research institutions have iron phosphate recovery technology, which recovers phosphorus and iron elements from iron phosphate residue to prepare iron phosphate. The average recovery rate of phosphorus and iron elements in the industry is between 85% and 90%. At present, the iron phosphate recovery technology mainly adopts wet recovery. For example, phosphorus iron residue is obtained by acid leaching, iron powder is added to remove impurities such as copper, resin is used to remove impurities such as aluminum, hydrogen peroxide and ammonia water are added to adjust the pH value so that the iron phosphate precursor precipitates, and the precursor is calcined to obtain battery-grade iron phosphate product. In the prior art, there is also a two-stage acid leaching method for recovering iron phosphate. In the first stage, low-concentration acid leaching is used to remove impurities such as aluminum, copper and lithium, and in the second stage, high-concentration acid leaching is used to leach phosphorus and iron elements, filter to remove graphite, add hydroxide to precipitate iron phosphate, and finally calcine to obtain finished product iron phosphate. However, the above technologies have the following problems: (1) the recovery process requires oxidation of divalent iron, consumes a large amount of hydrogen peroxide, and the high cost of resin leads to high overall cost of the process; (2) the recovery rate of iron and phosphorus elements in the whole process is below 90%; (3) the selectivity of ion exchange resin for aluminum ions is poor, which leads to the adsorption of iron and phosphorus elements, making it difficult to enter the next process; (4) only copper and aluminum are targeted for impurity removal, and other impurities remain in the finished product iron phosphate, affecting the electrical performance; (5) single sulfuric acid or hydrochloric acid is used for acid leaching, which leads to a high aluminum leaching rate, increasing the difficulty of impurity removal. SUMMARY

[0003] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the purpose of the present application is to propose a method for preparing iron phosphate from lithium iron phosphate lithium extraction residue, iron phosphate and a method for recycling waste lithium ion batteries. The present application effectively solves the problem of low recovery rate of iron and phosphorus elements in the recovery of iron phosphate, improves the purity of iron phosphate and the recovery rate of iron and phosphorus elements, and at the same time, the process flow of the present application is short, avoiding the use of expensive chemicals and medicines such as hydrogen peroxide and ion exchange resin, and achieving efficient recovery of iron phosphate from lithium extraction residue at low cost.

[0004] In one aspect of the present application, the present application proposes a method for preparing iron phosphate from lithium iron phosphate lithium extraction residue. According to embodiments of the present application, the method comprises:

[0005] mixing lithium iron phosphate lithium extraction residue with a first acid solution to obtain a leaching solution containing phosphorus elements and iron elements;

[0006] adjusting the pH value of the leaching solution to cause a precipitation reaction of the phosphorus elements and the iron elements to obtain a phosphorus-iron leaching residue;

[0007] mixing the ferrophosphorus leaching residue with a second acid solution to obtain a mixture;

[0008] The pH value of the mixture is adjusted to cause a precipitation reaction between phosphorus and iron to obtain iron phosphate.

[0009] According to the method of the embodiment of the present application, the present application is based on the intrinsic differences between impurity metals and the main element of ferrophosphorus, and utilizes their different precipitation products to separate impurities and ferrophosphorus elements in lithium iron phosphate extraction slag. Through two-stage deep impurity removal, the ferrophosphate in the lithium extraction slag can be efficiently recovered to ensure the high purity of the ferrophosphate.

[0010] In addition, the method according to the above embodiment of the present application may also have the following additional technical features:

[0011] In some embodiments of the present application, the pH value of the leachate is adjusted to 1.2-2.0.

[0012] In some embodiments of the present application, the first acid solution includes at least one of sulfuric acid, hydrochloric acid, and nitric acid; and / or the concentration of the first acid solution is 1.2 mol / L-2.0 mol / L; and / or the mass ratio of the volume of the first acid solution to the lithium iron phosphate lithium extraction slag is (4-10) L:1 Kg.

[0013] In some embodiments of the present application, the second acid solution includes at least one of sulfuric acid, hydrochloric acid, and nitric acid; and / or the concentration of the second acid solution is 0.6 mol / L-1.2 mol / L; and / or the mass ratio of the volume of the second acid solution to the ferrophosphorus leaching residue is (4-10) L:1 Kg; and / or the pH value of the mixture is adjusted to 1.2-2.0.

[0014] In some embodiments of the present application, the step of obtaining a leachate containing phosphorus and iron includes:

[0015] The lithium iron phosphate lithium extraction slag is mixed with the first acid solution and subjected to a first heat treatment to obtain a leachate containing phosphorus and iron elements; and / or the temperature of the first heat treatment is 40° C.-100° C. and the time is 2 h-6 h.

[0016] In some embodiments of the present application, the step of obtaining ferrophosphorus leaching slag comprises:

[0017] The pH value of the leachate is adjusted to cause a precipitation reaction between phosphorus and iron, and a second heat treatment is performed to obtain phosphorus-iron leaching residue; and / or the temperature of the second heat treatment is 40° C.-100° C. and the time is 1 hour-4 hours.

[0018] In some embodiments of the present application, the step of obtaining the mixture comprises:

[0019] mixing the phosphorus iron leaching residue with a second acid liquor, and performing a third heat treatment to obtain a mixture; and / or, the third heat treatment is performed at a temperature of 40-100°C for 1-4 hours.

[0020] In some embodiments of the application, the step of obtaining the mixture comprises:

[0021] mixing the phosphorus iron leaching residue with a second acid liquor, and performing a third heat treatment to obtain a mixture; and / or, the third heat treatment is performed at a temperature of 40-100°C for 1-4 hours.

[0022] In some embodiments of the application, the phosphorus iron ratio adjusting agent comprises at least one of phosphoric acid, sodium phosphate, and ammonium dihydrogen phosphate.

[0023] In some embodiments of the application, the step of obtaining the mixture comprises:

[0024] mixing the phosphorus iron leaching residue with a second acid liquor, a phosphorus iron ratio adjusting agent, and a surfactant to obtain a mixture; and / or, the surfactant comprises γ-aminopropyl triethoxysilane.

[0025] In some embodiments of the application, the mass ratio of the surfactant to the estimated mass of iron phosphate in the phosphorus iron leaching residue is (0.5-2):100.

[0026] In some embodiments of the application, the step of obtaining the iron phosphate comprises:

[0027] adjusting the pH value of the obtained mixture to cause a precipitation reaction of phosphorus and iron elements to obtain an iron phosphate precursor, and performing a fourth heat treatment on the iron phosphate precursor to obtain the iron phosphate; and / or, the fourth heat treatment is performed at a temperature of 500-800°C for 2-8 hours.

[0028] In a second aspect of the application, the application provides an iron phosphate. According to embodiments of the application, the iron phosphate is prepared by the method of the above embodiments.

[0029] In a third aspect of the application, the application provides a method for recycling waste lithium ion batteries. According to embodiments of the application, the method for recycling waste lithium ion batteries comprises the method of the above embodiments. Thus, the method for recycling waste lithium ion batteries has all the advantages of the method for preparing iron phosphate from lithium phosphate lithium extraction residue, which are not described herein again.

[0030] Additional aspects and advantages of the application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0031] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings of which:

[0032] Figure 1 A flowchart of a process for preparing iron phosphate from lithium iron phosphate lithium extraction residue according to an embodiment of the present application;

[0033] Figure 2 An XRD pattern of iron phosphate prepared in Example 2 of the present application;

[0034] Figure 3 An SEM image (20 pm) of iron phosphate prepared in Example 2 of the present application;

[0035] Figure 4 An SEM image (1 pm) of iron phosphate prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0036] Embodiments of the present application are described in detail below with reference to examples illustrated in the accompanying drawings, in which the same or like reference numerals in the drawings represent the same or like elements or elements having the same or similar functions throughout. The embodiments described below through reference to the drawings are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0037] In one aspect of the present application, a method for preparing iron phosphate from lithium iron phosphate lithium extraction residue is provided, as shown in Figure 1 According to an embodiment of the present application, the method comprises:

[0038] S100: mixing lithium iron phosphate lithium extraction residue with a first acid solution to obtain a leaching solution containing phosphorus elements and iron elements

[0039] In this step, the lithium iron phosphate lithium extraction residue is mixed with the first acid solution. The iron phosphate in the lithium iron phosphate lithium extraction residue reacts with hydrogen ions in the first acid solution to generate iron ions and phosphate radicals. The impurity metal oxides in the lithium iron phosphate lithium extraction residue also react with hydrogen ions to generate impurity metal ions and water. The insoluble leaching residue in the first acid solution and the leaching solution containing phosphorus elements and iron elements are obtained by subsequent solid-liquid separation.

[0040] As some specific examples, the lithium iron phosphate lithium extraction residue used in the present application can be derived from waste lithium iron phosphate batteries, but is not limited to this source. The positive electrode black powder can be obtained by disassembling and crushing the waste lithium iron phosphate batteries. The solid filter residue produced after the positive electrode black powder is subjected to lithium extraction by acid leaching is the lithium iron phosphate lithium extraction residue. The lithium iron phosphate lithium extraction residue contains valuable metal elements such as iron and phosphorus, and also contains other impurity elements such as carbon, aluminum, copper, sodium, sulfur, and manganese.

[0041] In the embodiments of the present application, the mixing method of the lithium extraction residue of lithium iron phosphate and the first acid liquid does not affect the acid leaching result. That is, the required first acid liquid (such as sulfuric acid) can be prepared in advance, and then mixed with the lithium extraction residue of lithium iron phosphate for acid leaching treatment; or the lithium extraction residue of lithium iron phosphate is mixed with deionized water to make a slurry, and then concentrated sulfuric acid is added for acid leaching treatment. The above two methods do not affect the result of this step.

[0042] In the embodiments of the present application, the selected first acid liquid can provide an acidic environment for the leaching reaction of the lithium extraction residue of lithium iron phosphate. The concentration of the first acid liquid determines the pH value of the reaction system, and the pH value in turn affects the leaching of phosphorus, iron elements and impurities in the lithium extraction residue of lithium iron phosphate through precipitation, so that the impurities and phosphorus and iron elements can be preliminarily and effectively separated by controlling the concentration of the first acid liquid.

[0043] In the embodiments of the present application, the specific type of the first acid liquid is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the first acid liquid can include but is not limited to sulfuric acid, hydrochloric acid, nitric acid.

[0044] In some embodiments of the present application, the concentration of the first acid liquid is 1.2 mol / L-2.0 mol / L, for example, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, etc., thereby achieving the preliminary and effective separation of impurities and phosphorus and iron elements.

[0045] In some embodiments of the present application, the volume ratio of the first acid liquid to the mass of the lithium extraction residue of lithium iron phosphate is (4-10) L:1 Kg, for example, 4 L:1 Kg, 5 L:1 Kg, 6 L:1 Kg, 7 L:1 Kg, 8 L:1 Kg, 9 L:1 Kg, 10 L:1 Kg, etc., thereby making this step have better leaching effect.

[0046] In some embodiments of the present application, the lithium extraction residue of lithium iron phosphate is mixed with the first acid liquid, and a first heat treatment is performed to obtain a leaching liquid containing phosphorus and iron elements. The method of the first heat treatment is not particularly limited, and those skilled in the art can select according to actual needs, and the leaching reaction of this step is not affected.

[0047] In some embodiments of the present application, the temperature of the first heat treatment is 40℃-100℃, for example, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc., and the time is 2h-6h, for example, 2h, 3h, 4h, 5h, 6h, etc. The obtained reaction product is subjected to solid-liquid separation, and the leaching liquid containing phosphorus and iron elements is retained.

[0048] S200: adjust the pH value of the leaching solution to make the phosphorus element and the iron element precipitate, to obtain a phosphorus-iron leaching residue

[0049] In this step, by adjusting the pH value of the leaching solution, the different solubility products of different metal elements are used to make the phosphorus element and the iron element in the leaching solution precipitate, while the impurities such as copper and aluminum remain in the leaching solution.

[0050] In the embodiments of the present application, the pH value of the reaction system can be adjusted by adding an alkaline substance to the above-mentioned leaching solution. The specific type of the above-mentioned alkaline substance is not particularly limited, and those skilled in the art can select according to the actual needs. As some specific examples, the alkaline substance can include but is not limited to sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia.

[0051] In the embodiments of the present application, the pH value of the leaching solution can be adjusted to 1.2-2.0, for example, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc. In this way, the precipitation reaction of the phosphorus element and the iron element in the leaching solution is accurately controlled, while the impurities such as copper and aluminum remain in the leaching solution.

[0052] In some embodiments of the present application, the pH value of the leaching solution is adjusted to make the phosphorus element and the iron element precipitate, and a second heat treatment is performed to obtain a phosphorus-iron leaching residue. The mode of the second heat treatment is not particularly limited, and those skilled in the art can select according to the actual needs, which does not affect the precipitation reaction of this step.

[0053] In some embodiments of the present application, the temperature of the second heat treatment can be 40℃-100℃, for example, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc., and the time can be 1h-4h, for example, 1h, 2h, 3h, 4h, etc. The obtained reaction product is subjected to solid-liquid separation to obtain a phosphorus-iron leaching residue.

[0054] S300: mixing the phosphorus-iron leaching residue with a second acid solution to obtain a mixture

[0055] In this step, the phosphorus-iron leaching residue is mixed with the second acid solution, and then subjected to solid-liquid separation to obtain a leaching residue that is insoluble in the second acid solution and a leaching solution containing phosphorus and iron elements.

[0056] In the embodiments of the present application, the mixing mode of the phosphorus-iron leaching residue and the second acid solution does not affect the acid leaching result, and a second acid solution (such as sulfuric acid) that meets the requirements can be prepared in advance, and then mixed with the phosphorus-iron leaching residue for acid leaching treatment; or the phosphorus-iron leaching residue is mixed with deionized water to prepare a slurry, and then concentrated sulfuric acid is added for acid leaching treatment. Both methods do not affect the result of this step.

[0057] In the embodiments of the present application, the selected second acid liquor can provide an acidic environment for the leaching reaction of the phosphorus-iron leaching residue, the concentration of the second acid liquor determines the pH value of the reaction system, and the pH value can affect the leaching of phosphorus, acid elements and impurities in the phosphorus-iron leaching residue through precipitation, so that the impurities and phosphorus-iron elements can be effectively separated again by controlling the concentration of the second acid liquor.

[0058] In the embodiments of the present application, the specific type of the second acid liquor is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the second acid liquor can include but is not limited to sulfuric acid, hydrochloric acid, nitric acid.

[0059] In some embodiments of the present application, the concentration of the second acid liquor is 0.6 mol / L-1.2 mol / L, for example, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, etc., thereby realizing the secondary effective separation of impurities and phosphorus-iron elements.

[0060] In some embodiments of the present application, the volume-to-mass ratio of the second acid liquor to the phosphorus-iron leaching residue is (4-10) L:1 Kg, for example, 4 L:1 Kg, 5 L:1 Kg, 6 L:1 Kg, 7 L:1 Kg, 8 L:1 Kg, 9 L:1 Kg, 10 L:1 Kg, etc., thereby making this step have better leaching effect.

[0061] According to some specific embodiments of the present application, the above step S300 can include:

[0062] S310: mixing the phosphorus-iron leaching residue with a second acid liquor and a phosphorus-iron ratio adjusting agent to obtain a mixture

[0063] In this step, the phosphorus-iron ratio adjusting agent is used to adjust the molar ratio of phosphorus to iron in the leaching liquor to 1:1 or close to 1:1, and the specific type thereof is not particularly limited. Those skilled in the art can select according to actual needs. As some specific examples, the phosphorus-iron ratio adjusting agent can include but is not limited to phosphoric acid, sodium phosphate, and ammonium dihydrogen phosphate.

[0064] S320: mixing the phosphorus-iron leaching residue with a second acid liquor and a surfactant to obtain a mixture

[0065] In this step, the surfactant provides coordination electrons, which are adsorbed on the surface of the generated iron phosphate crystal grains. The steric curling of the long-chain molecules in the structure produces a steric hindrance effect, preventing the aggregation and growth between the crystal grains, so as to generate smaller particle size iron phosphate, thereby realizing the particle size control of the iron phosphate product.

[0066] In the embodiments of the present application, the specific type of the above-mentioned surfactant is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some specific examples, the surfactant can include but is not limited to γ-aminopropyl triethoxysilane.

[0067] According to some specific embodiments of the present application, the mass ratio of the surfactant to the estimated mass of the iron phosphate in the phosphorus-iron leaching residue is (0.5-2):100. When the surfactant is added too much, it is difficult to remove in the subsequent calcination process, i.e., impurities are introduced into the system; when the surfactant is added too little, the particle size of the prepared iron phosphate product is large, which directly affects the particle size of the prepared lithium iron phosphate when it is used as a lithium iron phosphate precursor, and ultimately affects the electrical performance of the entire battery. At the same time, the above-mentioned estimated mass of the iron phosphate refers to the maximum mass of the iron phosphate that can be theoretically prepared by testing the phosphorus and iron contents in the phosphorus-iron leaching residue and calculating the theoretical mass of the iron phosphate according to the phosphorus and iron contents.

[0068] S330: mixing the phosphorus-iron leaching residue with the second acid liquor, performing a third heat treatment to obtain a mixture

[0069] In the embodiments of the present application, the temperature and treatment time of the above-mentioned heat treatment are not particularly limited, and can be selected by those skilled in the art according to actual needs. As some specific examples, the temperature of the third heat treatment is 40-100°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc., and the time is 1-4h, for example, 1h, 2h, 3h, 4h, etc.

[0070] In addition, the above-mentioned steps S310, S320 and S330 are three steps parallel to each other, but they can also be combined according to actual preparation needs. For example, steps S310 and S320 can be combined, i.e., the phosphorus-iron leaching residue is mixed with the second acid liquor, the phosphorus-iron ratio adjusting agent and the surfactant to obtain a mixture; steps S310 and S330 can be combined, i.e., the phosphorus-iron leaching residue is mixed with the second acid liquor and the phosphorus-iron ratio adjusting agent, and a third heat treatment is performed to obtain a mixture; steps S320 and S330 can be combined, i.e., the phosphorus-iron leaching residue is mixed with the second acid liquor and the surfactant, and a third heat treatment is performed to obtain a mixture; steps S310, S320 and S330 can be combined, i.e., the phosphorus-iron leaching residue is mixed with the second acid liquor, the phosphorus-iron ratio adjusting agent and the surfactant, and a third heat treatment is performed to obtain a mixture. The combination of the three steps includes but is not limited to the above-mentioned combination.

[0071] S400: adjusting the pH value of the mixture to make the phosphorus element and the iron element undergo a precipitation reaction to obtain iron phosphate

[0072] In this step, the impurities in the mixture are removed by adjusting the pH value of the mixture so that the phosphorus and iron in the solution are precipitated in the form of iron phosphate, and other metal impurities remain in the leaching solution.

[0073] In the embodiments of the present application, a basic substance can be added to the above mixture to adjust the pH value of the reaction system. The specific type of the above basic substance is not particularly limited, and those skilled in the art can select according to the actual needs. As some specific examples, the basic substance can include but is not limited to sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia.

[0074] In the embodiments of the present application, the pH value of the mixture can be 1.2-2.0, for example, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc. In this way, the precipitation reaction of phosphorus and iron elements in the mixture is controlled, while the impurities such as copper and aluminum remain in the leaching solution. After the reaction is completed, a high-purity filter residue and an impurity-containing filtrate can be obtained by solid-liquid separation. The filter residue can be dried to remove free water to obtain an iron phosphate precursor.

[0075] In the embodiments of the present application, this step can further specifically include: adjusting the pH value of the obtained mixture to make the phosphorus and iron elements precipitate to obtain an iron phosphate precursor; and performing a fourth heat treatment on the iron phosphate precursor to obtain an iron phosphate

[0076] According to the specific embodiments of the present application, the above iron phosphate precursor can be subjected to high-temperature calcination treatment (i.e., the fourth heat treatment) in an air atmosphere, and can be subjected to crushing and grinding treatment according to the preparation needs to obtain a finished iron phosphate powder.

[0077] In some embodiments of the present application, the temperature and time of the above high-temperature calcination treatment are not particularly limited, and those skilled in the art can select according to the actual needs. As some specific examples, the temperature of the high-temperature calcination treatment is 500-800°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, etc. The calcination time can be 2-8h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0078] In a second aspect of the present application, an iron phosphate is provided. According to the embodiments of the present application, the iron phosphate is prepared by the method of the above embodiments. In this way, a battery-grade iron phosphate is obtained.

[0079] In a third aspect of the present application, a treatment method for recycling waste lithium ion batteries is provided. According to the embodiments of the present application, the recycling of waste lithium ion batteries includes the method of the above embodiments.

[0080] The embodiments of the present application are described in detail below, it should be noted that the embodiments described below are exemplary, only for explaining the present application, and can not be understood as limiting the present application. Among them, the concentrated sulfuric acid used below is a mass fraction of 98% concentrated sulfuric acid chemicals. In addition, if not specified, all reagents used in the following examples are commercially available or can be synthesized according to the method described herein or known to those skilled in the art, and the reaction conditions not listed are also readily available to those skilled in the art.

[0081] Example 1

[0082] The present embodiment provides a method for preparing iron phosphate from lithium extraction residue of lithium iron phosphate, comprising:

[0083] (1) 1 kg of lithium extraction residue is added to 5.5 L of deionized water to mix and prepare slurry, 490 mL of concentrated sulfuric acid is added to make the final concentration of sulfuric acid 1.5 mol / L, heated to 60℃, and after stirring for 4 h, solid-liquid separation is carried out by a filter press to obtain a filtrate;

[0084] (2) The pH value of the filtrate is adjusted to 1.5 with ammonia water, heated to 60℃, and after stirring for 2 h, solid-liquid separation is carried out by a filter press to obtain a filter residue;

[0085] (3) The filter residue is added to 5.74 L of deionized water to mix and prepare slurry, 260 mL of concentrated sulfuric acid is added to make the final concentration of sulfuric acid 0.8 mol / L, heated to 60℃, 14.3 g of sodium phosphate is added, the pH value of the mixed slurry is adjusted to 1.5 with ammonia water, stirred for 2 h, and then solid-liquid separation is carried out by a filter press to obtain a filter residue, which is dried in an oven at 80℃ for 8 h;

[0086] (4) The dried filter residue is placed in a tube furnace, air is introduced, and calcination is carried out at 600℃ for 4 h, and finally the solid is taken out and ground into a powder to obtain the finished product of iron phosphate.

[0087] Example 2

[0088] The difference between Example 2 and Example 1 is only that:

[0089] In step (3), 14.3 g of sodium phosphate is added at the same time as 9 g of γ-aminopropyl triethoxysilane.

[0090] The other contents are the same as those of Example 1. Figure 2 The XRD pattern of the prepared iron phosphate shows that the measured powder diffraction peak is consistent with PDF #29-0715 (quartz phase iron phosphate standard card), which indicates that the finished product of iron phosphate prepared has a quartz crystal phase. Figures 3-4For the SEM image of the prepared iron phosphate, the results show that the particle size of the finished iron phosphate is small, so the particle size of the lithium iron phosphate obtained as an iron phosphate lithium precursor is also small, the migration path of lithium ions in the prepared lithium ion battery is shortened, and the electrical performance of the battery is improved.

[0091] Example 3

[0092] The difference between Example 3 and Example 1 is only that:

[0093] In step (1), the deionized water is 5.6 L, the amount of concentrated sulfuric acid added is 390 mL, and the final concentration of sulfuric acid is 1.2 mol / L.

[0094] The other contents are the same as those in Example 1.

[0095] Example 4

[0096] The difference between Example 4 and Example 1 is only that:

[0097] In step (1), the deionized water is 5.35 L, the amount of concentrated sulfuric acid added is 650 mL, and the final concentration of sulfuric acid is 2.0 mol / L.

[0098] The other contents are the same as those in Example 1.

[0099] Example 5

[0100] The difference between Example 5 and Example 1 is only that:

[0101] In step (2), the pH value of the filtrate is adjusted to 1.2.

[0102] The other contents are the same as those in Example 1.

[0103] Example 6

[0104] The difference between Example 6 and Example 1 is only that:

[0105] In step (2), the pH value of the filtrate is adjusted to 2.0.

[0106] The other contents are the same as those in Example 1.

[0107] Example 7

[0108] The difference between Example 7 and Example 1 is only that:

[0109] In step (3), the deionized water is 5.8 L, the amount of concentrated sulfuric acid added is 200 mL, and the final concentration of sulfuric acid is 0.6 mol / L.

[0110] The other contents are the same as those in Example 1.

[0111] Example 8

[0112] Example 8 differs from Example 1 only in that:

[0113] In step (3), the deionized water was 5.68 L, the concentrated sulfuric acid was added in an amount of 320 mL, and the final concentration of sulfuric acid was 1.0 mol / L.

[0114] The other contents were the same as in Example 1.

[0115] Example 9

[0116] Example 9 differs from Example 1 only in that:

[0117] In step (3), the deionized water was 5.61 L, the concentrated sulfuric acid was added in an amount of 390 mL, and the final concentration of sulfuric acid was 1.2 mol / L. The other contents were the same as in Example 1.

[0118] Example 10

[0119] Example 10 differs from Example 1 only in that:

[0120] In step (3), the pH value of the mixed slurry was adjusted to 1.2.

[0121] The other contents were the same as in Example 1.

[0122] Example 11

[0123] Example 11 differs from Example 1 only in that:

[0124] In step (3), the pH value of the mixed slurry was adjusted to 2.0.

[0125] The other contents were the same as in Example 1.

[0126] Example 12

[0127] Example 12 differs from Example 2 only in that:

[0128] In step (3), 4.5 g of γ-aminopropyltriethoxysilane was added.

[0129] The other contents were the same as in Example 2.

[0130] Example 13

[0131] Example 13 differs from Example 2 only in that:

[0132] In step (3), 13.5 g of γ-aminopropyltriethoxysilane was added.

[0133] The other contents were the same as in Example 2.

[0134] Example 14

[0135] Example 14 differs from Example 2 only in that:

[0136] In step (3), 18 g of γ-aminopropyltriethoxysilane was added.

[0137] The other contents were the same as in Example 2.

[0138] Comparative Example 1

[0139] Comparative Example 1 differs from Example 1 only in that:

[0140] In step (1), the deionized water was 5.74 L, the concentrated sulfuric acid was added in an amount of 260 mL, and the final concentration of sulfuric acid was about 0.8 mol / L. The other contents were the same as in Example 1.

[0141] Comparative Example 2

[0142] Comparative Example 2 differs from Example 1 only in that:

[0143] In step (3), the deionized water was 5.87 L, the concentrated sulfuric acid was added in an amount of 130 mL, and the final concentration of sulfuric acid was about 0.4 mol / L. The other contents were the same as in Example 1.

[0144] Comparative Example 3

[0145] Comparative Example 3 differs from Example 2 only in that:

[0146] In step (3), 1 g of γ-aminopropyltriethoxysilane was added.

[0147] The other contents were the same as in Example 2.

[0148] Comparative Example 4

[0149] This comparative example used one-time acid leaching to prepare iron phosphate:

[0150] (1) 1 kg of lithium extraction residue was added to 5.7 L of deionized water to mix and prepare a slurry, 320 mL of concentrated sulfuric acid was added, heated to 60°C, and stirred for 4 h before solid-liquid separation by a filter press to obtain a filtrate;

[0151] (2) The pH value of the filtrate was adjusted to 1.5 using ammonia water, heated to 60°C, and stirred for 2 h before solid-liquid separation by a filter press to obtain a filter residue;

[0152] (3) The dried filter residue was placed in a tube furnace, air was introduced, and calcination was carried out at 600°C for 4 h. Finally, the solid was taken out, crushed and ground into a powder to obtain the finished product iron phosphate.

[0153] The recovery rates of phosphorus and iron elements in Examples 1-14 and Comparative Example 1-2 were tested to obtain Table 1. The impurity content in the finished ferric phosphate obtained in Examples 1-14 and Comparative Example 4 was tested to obtain Table 2. The particle size of the ferric phosphate products obtained in Examples 1-2, 12-14 and Comparative Example 3 was tested to obtain Table 3. The iron recovery rate was calculated as the iron content in the product ferric phosphate / the iron content in the lithium extraction slag*100%, and the same was true for the phosphorus recovery rate. The impurity content was obtained by inductively coupled plasma chromatograph testing. The particle size data was obtained by Malvern particle size analyzer testing.

[0154] Table 1

[0155]

[0156]

[0157] Table 2

[0158] Ca / ppm Al / ppm Mn / ppm Cu / ppm Lithium extraction residue 436.22 1683.02 702.36 1138.96 Example 1 43.21 57.61 3.25 1.92 Example 2 37.83 35.63 2.09 0.56 Example 3 42.21 75.83 2.33 2.66 Example 4 47.99 65.49 4.97 0.75 Example 5 26.72 74.32 3.57 0.47 Example 6 36.55 69.31 2.08 2.22 Example 7 21.79 56.84 3.01 0.85 Example 8 43.95 40.67 2.44 1.25 Example 9 36.13 54.73 3.87 6.30 Example 10 42.88 63.80 4.26 1.57 Example 11 34.27 75.92 4.97 3.36 Example 12 38.61 70.01 2.86 0.78 Example 13 45.11 65.49 5.76 1.12 Example 14 30.42 57.66 4.43 0.94 Comparative Example 4 214.76 443.90 176.53 323.54

[0159] Table 3

[0160] D10 / pm D50 / pm D99 / pm Example 1 0.943 6.755 82.331 Example 2 0.702 3.043 18.299 Example 12 0.711 3.089 24.717 Example 13 0.698 2.830 17.224 Example 14 0.696 2.766 16.002 Comparative Example 3 0.873 5.688 52.701

[0161] From Table 1 we can see that:

[0162] (1) The ferrophosphorus recovery rates of Examples 1-14 were all higher than 98%, while the ferrophosphorus recovery rates of Comparative Examples 1-2 were all lower than 80%, with the ferrophosphorus recovery rate of Comparative Example 2 being lower than 50%, indicating that the method provided by the present invention has a higher ferrophosphorus recovery rate;

[0163] (2) The only difference between Example 2 and Example 1 is that a surfactant, γ-aminopropyltriethoxysilane, is added in step (3). The results show that the recovery rates of ferrophosphorus in both Example 1 and Example 2 are higher than 99%, indicating that the addition of the surfactant does not affect the recovery rate of ferrophosphorus.

[0164] (3) The only difference between Examples 3-4 and Example 1 is that the final concentration of sulfuric acid in step (1) is different (their sulfuric acid concentrations are mol / L, mol / L, and mol / L, respectively), all of which are within the range defined by the present invention (1.2 mol / L-2.0 mol / L). The results show that the ferrophosphorus recovery rates of Examples 1, 3, and 4 are generally higher than 99%, indicating that a higher ferrophosphorus recovery rate can be achieved within the concentration range defined by the present invention;

[0165] (4) The difference between Comparative Example 1 and Example 1 is only in the concentration of sulfuric acid in step (1), the concentration of sulfuric acid in Comparative Example 1 is 0.8 mol / L, which is less than the concentration range defined in the application, and the recovery rate of phosphorus iron is about 72%, which shows that the decrease of the concentration of sulfuric acid will affect the leaching of phosphorus iron elements in the lithium extraction residue of lithium iron phosphate, and further lead to the loss of phosphorus iron elements;

[0166] (5) The difference between Example 5-6 and Example 1 is only in the pH value of the filtrate in step (2) (the pH value of the filtrate is 1.2, 2.0, 1.5 respectively), which is within the range defined in the application (1.2-2.0), and the results show that the recovery rate of phosphorus iron in Example 1, Example 5 and Example 6 is about 99%, which shows that a higher recovery rate of phosphorus iron can be achieved within the pH value range defined in the application;

[0167] (6) The difference between Example 7-9 and Example 1 is only in the concentration of sulfuric acid in step (3) (the concentration of sulfuric acid is 0.6 mol / L, 1.0 mol / L, 1.2 mol / L, 0.8 mol / L respectively), which is within the range defined in the application (0.6 mol / L-1.2 mol / L), and the results show that the recovery rate of phosphorus iron in Example 1 and Example 7-9 is about 99%, which shows that a higher recovery rate of phosphorus iron can be achieved within the concentration range defined in the application;

[0168] (7) The difference between Comparative Example 2 and Example 1 is only in the concentration of sulfuric acid in step (3), the concentration of sulfuric acid in Comparative Example 2 is 0.4 mol / L, which is less than the concentration range defined in the application, and the recovery rate of phosphorus iron is about 72%, which shows that the decrease of the concentration of sulfuric acid will affect the leaching of phosphorus iron elements in the filter residue (i.e. phosphorus iron leaching residue), and further lead to the loss of phosphorus iron elements;

[0169] (8) The difference between Example 10-11 and Example 1 is only in the pH value of the mixed slurry in step (3) (the pH value of the mixed slurry is 1.2, 2.0, 1.5 respectively), which is within the range defined in the application (1.2-2.0), and the results show that the recovery rate of phosphorus iron in Example 1, Example 10-11 is about 99%, which shows that a higher recovery rate of phosphorus iron can be achieved within the pH value range defined in the application;

[0170] (9) The difference between Example 12-14 and Example 2 is only in the amount of γ-aminopropyl triethoxysilane added in step (3) (the mass ratio of γ-aminopropyl triethoxysilane to the estimated mass of iron phosphate in the filter residue is 0.5:100, 1.5:100, 2:100 respectively), which is within the range defined in the application ((0.5-2):100), which shows that a higher recovery rate of phosphorus iron can be achieved within the ratio range defined in the application.

[0171] From Table 2, it can be seen that:

[0172] (1) The impurity (Ca, Al, Mn, Cu) contents of the finished product iron phosphate prepared in Examples 1-14 are far lower than the impurity contents in the lithium extraction residue, indicating that good impurity removal effect can be achieved within the scope defined by the application, and the high purity of the prepared iron phosphate is ensured.

[0173] (2) Compared with Examples 1-14, the finished product iron phosphate prepared by only one acid leaching treatment in Comparative Example 4 still contains a large amount of metal impurities. For example, the Al content in the finished product iron phosphate is 443.90 ppm, which is far higher than the reference standard value (100 ppm), while the Al content in the finished product iron phosphate prepared in Examples 1-14 is all lower than 100 ppm, also indicating that the method provided by the application has superiority in the purity of the finished product iron phosphate.

[0174] From Table 3, it can be seen that:

[0175] (1) The difference between Example 2 and Example 1 is only that a surfactant γ-aminopropyl triethoxysilane is added in step (3), and the results show that the particle size of the finished product iron phosphate prepared in Example 2 is smaller than that in Example 1, indicating that the addition of the surfactant in the acid leaching treatment in step (3) can control the particle size distribution of the finished product iron phosphate.

[0176] (2) Examples 12-14 all add the surfactant γ-aminopropyl triethoxysilane within the scope defined by the application, and the results show that the particle size of the finished product iron phosphate prepared is smaller and the distribution is narrower. In Comparative Example 3, the addition amount of γ-aminopropyl triethoxysilane is less (the mass ratio of γ-aminopropyl triethoxysilane to the estimated mass of iron phosphate in the filter residue is 0.11:100), and compared with Example 2, the particle size of the finished product iron phosphate prepared is larger and the distribution is wider, also indicating that when the addition amount of the surfactant is within the scope defined by the application, the particle size of the finished product iron phosphate prepared can be ensured to be smaller and the distribution can be ensured to be narrower.

[0177] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0178] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A method for preparing iron phosphate from lithium iron phosphate slag, characterized in that: include: Mixing the lithium iron phosphate lithium extraction slag with the first acid solution to obtain a leaching solution containing phosphorus and iron elements; Adjusting the pH value of the leachate to cause a precipitation reaction between phosphorus and iron to obtain phosphorus-iron leaching residue; mixing the ferrophosphorus leaching residue with a second acid solution to obtain a mixture; Adjusting the pH value of the mixture to cause a precipitation reaction between phosphorus and iron to obtain iron phosphate; Adjusting the pH value of the leachate to 1.2-2.0; The concentration of the first acid solution is 1.2 mol / L-2.0 mol / L; the mass ratio of the volume of the first acid solution to the lithium iron phosphate lithium extraction slag is (4-10) L:1 kg; The concentration of the second acid solution is 0.6 mol / L-1.2 mol / L; the mass ratio of the volume of the second acid solution to the ferrophosphorus leaching residue is (4-10) L:1 kg; The pH of the mixture was adjusted to 1.2-2.

0.

2. The method according to claim 1, characterized in that The first acid solution includes at least one of sulfuric acid, hydrochloric acid, and nitric acid.

3. The method according to claim 1, characterized in that The second acid solution includes at least one of sulfuric acid, hydrochloric acid, and nitric acid.

4. The method according to claim 1, wherein The step of obtaining the leachate containing phosphorus and iron comprises: Mixing the lithium iron phosphate lithium extraction slag with the first acid solution and performing a first heat treatment to obtain a leachate containing phosphorus and iron elements; The temperature of the first heat treatment is 40° C.-100° C., and the time is 2 h-6 h.

5. The method according to claim 1, wherein The step of obtaining ferrophosphorus leaching slag comprises: Adjusting the pH value of the leachate to cause a precipitation reaction between phosphorus and iron, and performing a second heat treatment to obtain phosphorus-iron leaching residue; The temperature of the second heat treatment is 40° C.-100° C., and the time is 1 hour-4 hours.

6. The method according to claim 1, characterized in that The step of obtaining the mixture comprises: mixing the ferrophosphorus leaching residue with the second acid solution and performing a third heat treatment to obtain a mixture; The temperature of the third heat treatment is 40° C.-100° C., and the time is 1 hour-4 hours.

7. The method according to claim 1, characterized in that The step of obtaining the mixture comprises: mixing the ferrophosphorus leaching residue with a second acid solution and a ferrophosphorus ratio regulator to obtain a mixture; The phosphorus-iron ratio regulator includes at least one of phosphoric acid, sodium phosphate, and ammonium dihydrogen phosphate.

8. The method according to claim 7, characterized in that The step of obtaining the mixture comprises: mixing the ferrophosphorus leaching residue with a second acid solution, a ferrophosphorus ratio regulator, and a surfactant to obtain a mixture; The surfactant includes gamma-aminopropyltriethoxysilane.

9. The method according to claim 8, characterized in that The mass ratio of the surfactant to the mass ratio of the ferric phosphate in the ferrophosphorus leaching residue is (0.5-2):

100.

10. The method according to claim 1, characterized in that The step of obtaining ferric phosphate comprises: adjusting the pH value of the obtained mixture to cause a precipitation reaction between phosphorus and iron to obtain an iron phosphate precursor, and subjecting the iron phosphate precursor to a fourth heat treatment to obtain iron phosphate; The temperature of the fourth heat treatment is 500° C.-800° C., and the time is 2 h-8 h.

11. A method for recycling waste lithium-ion batteries, characterized in that: The method for recycling waste lithium-ion batteries comprises the method according to any one of claims 1 to 10.

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