A method for recycling waste batteries and extracting lithium, phosphorus, and iron slag through a complete, integrated chain.

Abstract

This paper discloses a method for the integrated recycling of lithium-extracting iron phosphate slag from waste batteries. The method includes the following steps: (1) acid leaching the lithium-extracting iron phosphate slag and adding an iron ion precipitant to react and obtain impurity-removed iron phosphate slag; (2) acid leaching the impurity-removed iron phosphate slag a second time to obtain an iron phosphate solution; (3) mixing the iron phosphate solution with a buffer solution to carry out a precipitation reaction. After the reaction, the precipitate is heat-treated to obtain iron phosphate. This application first removes impurities from the iron phosphate slag through a first acid leaching and adds an iron ion precipitant to precipitate the iron ions dissolved in the acid leaching, avoiding iron loss. Then, a second acid leaching is carried out to leach out all Fe and P, effectively improving the iron recovery rate in the iron phosphate slag. In addition, the iron phosphate precipitation process is carried out in a buffer solution, which can improve the purity of iron phosphate and the uniformity of iron phosphate particles, resulting in high-quality iron phosphate.

Description

Technical Field

[0001] This application relates to the field of waste lithium iron phosphate battery recycling, such as a method for recycling waste batteries and extracting lithium iron phosphate slag through a complete chain integration. Background Technology

[0002] In recent years, the new energy vehicle industry has developed rapidly. Among them, lithium-ion batteries have become the power batteries for new energy vehicles due to their significant advantages such as high specific capacity, stable performance, and long service life. In particular, lithium iron phosphate batteries are one of the mainstream lithium battery products on the market due to their low manufacturing cost and high safety performance. With the increase in their usage, the number of waste lithium iron phosphate batteries has also increased rapidly. If they are not processed and recycled in a timely manner, they will cause serious environmental pollution.

[0003] In spent lithium iron phosphate batteries, lithium iron phosphate accounts for 30-35% of the mass, while copper and aluminum foil account for about 10%. The content of valuable metal elements such as Li, Fe, Cu, and Al is far higher than their content in natural minerals. Therefore, the recycling and treatment of spent lithium iron phosphate batteries is very important. Al, Cu, and Fe have similar properties and are difficult to separate. The presence of these impurities will affect the recycling of this type of lithium iron phosphate slag for the preparation of battery-grade iron phosphate, thus affecting the electrochemical performance of the positive electrode material of lithium iron phosphate batteries.

[0004] Currently, methods for removing aluminum and copper impurities include using acidic solutions to leach the impurities. For example, CN115583643A discloses the use of low-acid solutions to pre-remove impurities such as aluminum and copper from iron phosphate slag, thereby reducing the impurity content in the iron phosphate slag. However, during pre-remove impurities, iron ions in the iron phosphate slag will enter the leachate along with the impurity metal ions, resulting in a large loss of iron and low recovery efficiency.

[0005] Therefore, how to effectively avoid the loss of iron ions during the recycling process and improve the iron recovery rate in phosphate slag is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] This application provides a method for the integrated recycling of lithium-phosphate ferric slag from waste batteries. First, an acid leaching process removes metal ion impurities such as Al and Cu from the ferric phosphate slag. An iron ion precipitant is added to precipitate the iron ions dissolved during acid leaching, preventing iron loss during the impurity removal process. A second acid leaching process then extracts all Fe and P, effectively preventing iron ion loss and significantly improving the iron recovery rate from the ferric phosphate slag. Furthermore, the iron phosphate precipitation process is carried out in a buffer solution, which improves both the purity and the uniformity of the iron phosphate particles, resulting in high-quality iron phosphate.

[0008] In a first aspect, embodiments of this application provide a method for the integrated recycling of waste batteries to extract lithium, phosphorus, and iron slag across the entire supply chain, the method comprising the following steps:

[0009] (1) The phosphorus iron slag after lithium extraction is subjected to acid leaching once, and iron ion precipitant is added to react to obtain impurity-removed phosphorus iron slag;

[0010] (2) The impurity-removed phosphorus-iron slag is subjected to a second acid leaching to obtain a phosphorus-iron solution;

[0011] (3) The ferric phosphate solution and the buffer solution are mixed to carry out a precipitation reaction. After the reaction is completed, the precipitate is heat-treated to obtain ferric phosphate.

[0012] This application first removes metal ion impurities such as Al and Cu from the ferrophosphate slag through a single acid leaching process. An iron ion precipitant is added to precipitate the iron ions dissolved during acid leaching, preventing iron loss during the impurity removal process. A second acid leaching is then performed to leach out all Fe and P, effectively preventing iron ion loss and significantly improving the iron recovery rate from the ferrophosphate slag. Furthermore, the ferrophosphate precipitation process is carried out in a buffer solution, which not only maintains a stable pH in the precipitation solution, preventing drastic pH changes that could lead to the formation of ferric hydroxide precipitate and further improving the purity of the ferrophosphate, but also controls the rate of ferrophosphate precipitation, prevents agglomeration, regulates the nucleation size, and improves the uniformity of ferrophosphate particles, resulting in high-quality ferrophosphate.

[0013] It should be noted that the phosphorus iron slag after lithium extraction refers to the phosphorus iron slag after lithium extraction from waste lithium iron phosphate. Its main components are FePO4 and C, including a small amount of impurities such as Al and Cu.

[0014] As a preferred technical solution of this application, in the first acid leaching process of step (1), the acidic solution used includes any one or a combination of at least two of sulfuric acid solution, hydrochloric acid solution or phosphoric acid solution.

[0015] Preferably, the acidic solution contains H + The concentration is 0.2-0.5 mol / L, for example, it can be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc.

[0016] As a preferred technical solution of this application, the temperature of the first acid leaching in step (1) is 85-95℃, for example, it can be 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃ or 95℃, etc.

[0017] Preferably, the acid leaching time in step (1) is 1-2 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours.

[0018] As a preferred technical solution of this application, the iron ion precipitant in step (1) includes sodium sulfate.

[0019] In this application, sodium sulfate reacts with the iron ions dissolved during the first acid leaching to form a yellow sodium iron alum precipitate, thus avoiding the loss of iron during the acid leaching process for removing impurities.

[0020] Preferably, the amount of iron ion precipitant added in step (1) is 2-20% of the mass of the phosphorus iron slag, for example, it can be 2%, 5%, 10%, 15% or 20%, etc.

[0021] In this application, if the amount of iron ion precipitant added is too small, the iron ions dissolved in the solution will be lost after solid-liquid separation during the acid leaching process; if the amount of iron ion precipitant added is too large, it will lead to the introduction of too many impurity ions.

[0022] Preferably, the reaction time in step (1) is 0.5-1.5h, for example, it can be 0.5h, 0.7h, 0.9h, 1.1h, 1.3h or 1.5h.

[0023] As a preferred technical solution of this application, in the process of adding iron ion precipitant in step (1) to carry out the reaction, a pH adjuster is also added so that the pH value of the reaction system is 1.5-1.7, for example, it can be 1.5, 1.6 or 1.7.

[0024] In this application, the pH value of the reaction system is 1.5-1.7, which can cause sodium ferric sulfate to precipitate.

[0025] Preferably, the pH adjuster includes ammonia.

[0026] As a preferred technical solution of this application, before the phosphorus-removed iron slag in step (2) undergoes secondary acid leaching, the phosphorus-removed iron slag is first mixed with water to dissolve iron ions.

[0027] Preferably, the solid-liquid ratio of the phosphorus-removed iron slag and water is 1g:(2-4)mL, for example, it can be 1g:2mL, 1g:2.5mL, 1g:3mL, 1g:3.5mL or 1g:4mL, etc.

[0028] Preferably, the mixing time of the phosphorus-iron slag and water is 30-60 minutes, for example, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0029] As a preferred technical solution of this application, in the secondary acid leaching process described in step (2), the concentrated acid used includes any one or a combination of at least two of concentrated sulfuric acid, concentrated hydrochloric acid, or concentrated phosphoric acid.

[0030] In this application, the addition of concentrated acid during the secondary acid leaching process allows all Fe and P to be leached out.

[0031] Preferably, the concentrated acid contains H + The concentration is 1-1.5 mol / L, for example, it can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, etc.

[0032] As a preferred technical solution of this application, the buffer solution in step (3) includes any one or a combination of at least two of citrate-sodium dihydrogen phosphate buffer, phthalic acid-hydrogen phosphate buffer or citrate-sodium citrate buffer, preferably citrate-sodium dihydrogen phosphate buffer.

[0033] In this application, a citric acid-sodium dihydrogen phosphate buffer solution is mixed with an iron phosphate solution. Citric acid can complex iron ions, control the precipitation rate of iron phosphate, prevent iron phosphate agglomeration, regulate the nucleation size of iron phosphate, and improve the uniformity of iron phosphate particles.

[0034] Preferably, the concentration of citric acid in the citrate-sodium dihydrogen phosphate buffer solution is 0.05-0.15 mol / L, for example, 0.05 mol / L, 0.1 mol / L, or 0.15 mol / L, and the concentration of sodium dihydrogen phosphate is 0.15-0.25 mol / L, for example, 0.15 mol / L, 0.2 mol / L, or 0.25 mol / L.

[0035] Preferably, the volume ratio of citric acid to sodium dihydrogen phosphate in the citric acid-sodium dihydrogen phosphate buffer is (2-4):(0.1-0.15), wherein the range of citric acid "2-4" can be, for example, 2, 2.5, 3, 3.5 or 4, and the range of sodium dihydrogen phosphate "0.1-0.015" can be, for example, 0.1, 0.11, 0.12, 0.13, 0.14 or 0.15.

[0036] In this application, if the volume ratio of citric acid to sodium dihydrogen phosphate is too small, i.e., the content of sodium dihydrogen phosphate is too high, the pH value of the buffer solution will be too high; if the volume ratio of citric acid to sodium dihydrogen phosphate is too large, i.e., the content of sodium dihydrogen phosphate is too low, the pH value of the buffer solution will be too low. Both situations are not conducive to the precipitation reaction.

[0037] Preferably, the volume ratio of the phosphorus iron solution and the buffer solution in step (3) is 1:(20-60), for example, it can be 1:20, 1:30, 1:40, 1:50 or 1:60, etc.

[0038] In this application, if the volume ratio of the ferric phosphorus solution to the buffer solution is too small, i.e., the amount of buffer solution used is too large, the concentration of the reacting ions in the solution will be too small, which will reduce the reaction efficiency; if the volume ratio of the ferric phosphorus solution to the buffer solution is too large, i.e., the amount of buffer solution used is too small, the pH value of the precipitation will be unstable.

[0039] Preferably, the pH value of the reaction system after mixing the ferric phosphorus solution and the buffer solution in step (3) is 1.8-2.2, for example, it can be 1.8, 1.9, 2, 2.1 or 2.2, etc.

[0040] Preferably, the precipitation reaction time in step (3) is 1-2 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours.

[0041] As a preferred technical solution of this application, the heat treatment temperature in step (3) is 500-600℃, for example, it can be 500℃, 520℃, 550℃, 570℃, 580℃ or 600℃, etc., preferably 500-550℃.

[0042] In this application, heat treatment within the preferred range of 500-550℃ can effectively remove the water of crystallization from the precipitated iron phosphate dihydrate, which is beneficial for subsequent preparation of lithium iron phosphate by mixing and sintering with lithium source as a precursor.

[0043] Preferably, the heat treatment time in step (3) is 1-3 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0044] As a preferred technical solution of this application, the method includes the following steps:

[0045] (I) Place the lithium-extracted ferrophosphate slag in H + The solution is first acid-leached in an acidic solution with a concentration of 0.2-0.5 mol / L at a temperature of 85-95℃ for 1-2 hours. Then, sodium sulfate and ammonia are added to control the pH at 1.5-1.7 and the mixture is stirred for 0.5-1.5 hours. After solid-liquid separation, the impurity-removed phosphorus-iron slag is obtained.

[0046] The amount of sodium sulfate added is 2-20% of the mass of the phosphorus-iron slag;

[0047] (II) Place the impurity-removed phosphorus and iron slag in water and mix for 30-60 minutes, then add H + A second acid leaching was performed with concentrated acid at a concentration of 1-1.5 mol / L, and a phosphorus-iron solution was obtained after solid-liquid separation.

[0048] The solid-liquid ratio of the phosphorus-containing iron slag and water is 1g:(2-4)mL.

[0049] (III) Supplement the phosphorus-iron solution with a phosphorus source or an iron source to control the phosphorus-iron ratio in the solution to be (1-1.05):1;

[0050] (IV) The ferric phosphate solution is added to the citrate-sodium dihydrogen phosphate buffer solution at a flow rate of 30-70 mL / min and mixed. The pH value is controlled at 1.8-2.2. The precipitation reaction is carried out for 1-2 h. After the reaction is completed, the precipitate is heat-treated at 500-600℃ for 1-3 h to remove the water of crystallization and obtain ferric phosphate.

[0051] The volume ratio of the ferric phosphorus solution to the citrate-sodium dihydrogen phosphate buffer solution is 1:(20-60).

[0052] In this application, the phosphorus-to-iron ratio in the solution is (1-1.05):1, for example, it can be 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1 or 1.05:1, etc.

[0053] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0054] Compared with related technologies, the embodiments of this application have the following beneficial effects:

[0055] This application first removes metal ion impurities such as Al and Cu from the ferrophosphate slag through a single acid leaching process. An iron ion precipitant is added to precipitate the iron ions dissolved during acid leaching, preventing iron loss during the impurity removal process. A second acid leaching is then performed to leach out all Fe and P, effectively preventing iron ion loss and significantly improving the iron recovery rate from the ferrophosphate slag. Furthermore, the ferrophosphate precipitation process is carried out in a buffer solution. This maintains a stable pH in the precipitation solution, preventing drastic pH changes that could lead to ferric hydroxide precipitation, further improving the purity of the ferrophosphate. It also allows for control of the ferrophosphate precipitation rate, preventing agglomeration, regulating the nucleation size, and improving the uniformity of ferrophosphate particles, resulting in high-quality ferrophosphate.

[0056] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0057] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0058] Figure 1 This is a SEM image of the iron phosphate recovered in Example 1 of this application.

[0059] Figure 2 This is a SEM image of the iron phosphate recovered in Comparative Example 2 of this application. Detailed Implementation

[0060] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0061] Example 1

[0062] This embodiment provides a method for the integrated recycling of waste batteries to extract lithium, phosphorus, and iron slag, comprising the following steps:

[0063] (1) Place the lithium-extracted ferrophosphate slag in H + The solution was leached once in a 0.3 mol / L sulfuric acid solution at 90°C for 1.5 h. Then, sodium sulfate and ammonia were added to control the pH of the reaction system to 1.6 and the mixture was stirred for 1 h. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-removed iron slag.

[0064] The amount of sodium sulfate added is 10% of the mass of the phosphorus-iron slag;

[0065] (2) The impurity-removed phosphorus and iron slag is placed in water and mixed for 40 minutes, then H is added. + A second acid leaching was performed with concentrated sulfuric acid at a concentration of 1.2 mol / L, and a phosphorus-iron solution was obtained after solid-liquid separation.

[0066] The solid-liquid ratio of the phosphorus-containing iron slag and water is 1g:3mL.

[0067] (3) Add ammonium dihydrogen phosphate or ferric sulfate to the phosphorus iron solution to control the phosphorus iron ratio of the phosphorus iron solution to 1.02:1;

[0068] (4) The ferric phosphate solution was added to a citrate-sodium dihydrogen phosphate buffer (containing 174 L of 0.1 mol / L citric acid and 6 L of 0.2 mol / L disodium hydrogen phosphate in a volume ratio of 3:0.1) at a flow rate of 50 mL / min. The pH was controlled at 2.1 and a precipitation reaction was carried out for 1.5 h. After the reaction was completed, the precipitate was heat-treated at 550 °C for 2 h to remove the water of crystallization and obtain ferric phosphate.

[0069] The volume ratio of the ferric phosphorus solution to the citrate-sodium dihydrogen phosphate buffer solution is 1:30.

[0070] Example 2

[0071] This embodiment provides a method for the integrated recycling of waste batteries to extract lithium, phosphorus, and iron slag, comprising the following steps:

[0072] (1) Place the lithium-extracted ferrophosphate slag in H + The solution was leached once in a 0.2 mol / L sulfuric acid solution at 85°C for 2 hours. Then, sodium sulfate and ammonia were added to control the pH of the reaction system to 1.7 and the mixture was stirred for 1 hour. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-removed iron slag.

[0073] The amount of sodium sulfate added is 2% of the mass of the phosphorus-iron slag;

[0074] (2) Mix the impurity-removed phosphorus and iron slag in water for 30 minutes, then add H + A second acid leaching was performed with concentrated sulfuric acid at a concentration of 1 mol / L, and a phosphorus-iron solution was obtained after solid-liquid separation.

[0075] The solid-liquid ratio of the phosphorus-containing iron slag and water is 1g:2mL.

[0076] (3) Add ammonium dihydrogen phosphate or ferric sulfate to the phosphorus iron solution to control the phosphorus iron ratio of the phosphorus iron solution to 1:1;

[0077] (4) The ferric phosphate solution was added to a citrate-sodium dihydrogen phosphate buffer (containing 210 L of 0.1 mol / L citric acid and 5.3 L of 0.2 mol / L disodium hydrogen phosphate in a volume ratio of 4:0.1) at a flow rate of 30 mL / min. The pH was controlled at 1.8 and a precipitation reaction was carried out for 2 h. After the reaction was completed, the precipitate was heat-treated at 500 °C for 3 h to remove the water of crystallization and obtain ferric phosphate.

[0078] The volume ratio of the ferric phosphorus solution to the citrate-sodium dihydrogen phosphate buffer solution is 1:20.

[0079] Example 3

[0080] This embodiment provides a method for the integrated recycling of waste batteries to extract lithium, phosphorus, and iron slag, comprising the following steps:

[0081] (1) Place the lithium-extracted ferrophosphate slag in H +The solution was leached once in a 0.5 mol / L sulfuric acid solution at 95°C for 1 hour. Then, sodium sulfate and ammonia were added to control the pH of the reaction system to 1.5 and the mixture was stirred for 0.5 hours. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-removed iron slag.

[0082] The amount of sodium sulfate added is 2% of the mass of the phosphorus-iron slag;

[0083] (2) The impurity-removed phosphorus and iron slag is placed in water and mixed for 60 minutes, then H is added. + A second acid leaching was performed with concentrated sulfuric acid at a concentration of 1.5 mol / L, and a phosphorus-iron solution was obtained after solid-liquid separation.

[0084] The solid-liquid ratio of the phosphorus-containing iron slag and water is 1g:4mL.

[0085] (3) Add ammonium dihydrogen phosphate or ferric sulfate to the phosphorus iron solution to control the phosphorus iron ratio of the phosphorus iron solution to 1.05:1;

[0086] (4) The ferric phosphate solution was added to a citrate-sodium dihydrogen phosphate buffer (containing 77 L of 0.1 mol / L citric acid and 3 L of 0.2 mol / L disodium hydrogen phosphate in a volume ratio of 3:0.12) at a flow rate of 70 mL / min. The pH was controlled at 2.2, and a precipitation reaction was carried out for 1 h. After the reaction was completed, the precipitate was heat-treated at 500 °C for 3 h to remove the water of crystallization and obtain ferric phosphate.

[0087] The volume ratio of the ferric phosphorus solution to the citrate-sodium dihydrogen phosphate buffer solution is 1:40.

[0088] Example 4

[0089] The difference between this embodiment and Embodiment 1 is that the amount of sodium sulfate added is 1% of the mass of the ferrophosphate slag.

[0090] The remaining methods and parameters are consistent with those in Example 1.

[0091] Example 5

[0092] The difference between this embodiment and Embodiment 1 is that the amount of sodium sulfate added is 25% of the mass of the ferrophosphate slag.

[0093] The remaining methods and parameters are consistent with those in Example 1.

[0094] Example 6

[0095] The difference between this embodiment and embodiment 1 is that ammonia is not added in step (1) to control the pH of the reaction system.

[0096] The remaining methods and parameters are consistent with those in Example 1.

[0097] Example 7

[0098] The difference between this embodiment and embodiment 1 is that the volume ratio of ferric phosphorus solution and citrate-sodium dihydrogen phosphate buffer in step (4) is 1:10.

[0099] The remaining methods and parameters are consistent with those in Example 1.

[0100] Example 8

[0101] The difference between this embodiment and embodiment 1 is that the volume ratio of ferric phosphorus solution and citrate-sodium dihydrogen phosphate buffer in step (4) is 1:70.

[0102] The remaining methods and parameters are consistent with those in Example 1.

[0103] Example 9

[0104] The difference between this embodiment and embodiment 1 is that the volume ratio of citric acid and sodium dihydrogen phosphate in step (4) is 5:0.05.

[0105] The remaining methods and parameters are consistent with those in Example 1.

[0106] Example 10

[0107] The difference between this embodiment and embodiment 1 is that the volume ratio of citric acid and sodium dihydrogen phosphate in step (4) is 1:0.2.

[0108] The remaining methods and parameters are consistent with those in Example 1.

[0109] Comparative Example 1

[0110] The difference between this comparative example and Example 1 is that sodium sulfate, an iron ion precipitant, is not added in step (1).

[0111] The remaining methods and parameters are consistent with those in Example 1.

[0112] Comparative Example 2

[0113] This comparative example provides a method for recycling phosphorus slag after lithium extraction from waste lithium iron phosphate, the method comprising the following steps:

[0114] (1) Place the lithium-extracted ferrophosphate slag in H + The solution was leached once in a 0.3 mol / L sulfuric acid solution at 90°C for 1.5 h. Then, sodium sulfate and ammonia were added to control the pH of the reaction system to 1.6 and the mixture was stirred for 1 h. After the reaction was completed, the solid and liquid were separated to obtain phosphorus-removed iron slag.

[0115] The amount of sodium sulfate added is 10% of the mass of the phosphorus-iron slag;

[0116] (2) The impurity-removed phosphorus and iron slag is placed in water and mixed for 40 minutes, then H is added. + A second acid leaching was performed with concentrated sulfuric acid at a concentration of 1.2 mol / L, and a phosphorus-iron solution was obtained after solid-liquid separation.

[0117] The solid-liquid ratio of the phosphorus-containing iron slag and water is 1g:3mL.

[0118] (3) Add ammonium dihydrogen phosphate or ferric sulfate to the ferric phosphorus solution to control the phosphorus-iron ratio of the ferric phosphorus solution to 1.02:1, add ammonia water to control the pH value of the solution to 2.1, and react for 1.5 h to obtain ferric phosphorus dihydrate;

[0119] (4) The ferric phosphate dihydrate was heat-treated at 550°C for 2 hours to remove the water of crystallization and obtain ferric phosphate.

[0120] Figure 1 and Figure 2 SEM images of the recovered ferric phosphate from Example 1 and Comparative Example 2 are shown respectively. As can be seen from the images, the ferric phosphate particles obtained from Example 1 are more uniform, while the ferric phosphate particles obtained from Comparative Example 2 are more severely agglomerated. Therefore, it can be concluded that using a buffer solution for ferric phosphate precipitation can avoid the formation of ferric hydroxide and make the generated particles more uniform.

[0121] Performance testing

[0122] The ferric phosphate obtained after recovery from the above embodiments and comparative examples was subjected to component content detection and recovery rate testing.

[0123] The formula for calculating the recovery rate is: Recovery rate = Iron content (g) in the ferrophosphate leaching solution obtained from ferrophosphate slag / Iron content (g) in ferrophosphate slag × 100%.

[0124] The above test results are shown in Table 1.

[0125] Table 1

[0126]

[0127]

[0128] analyze:

[0129] As shown in the table above, this application employs a first acid leaching process, followed by the addition of an iron ion precipitant, and then a second acid leaching. Furthermore, the iron phosphate precipitation process is carried out in a buffer solution. This method effectively avoids iron ion loss and significantly improves the iron recovery rate from the iron phosphate slag.

[0130] The data results from Examples 1 and 4-5 show that if the amount of iron ion precipitant added is too small, the iron ions lost by acid leaching cannot completely form a precipitate, resulting in the loss of iron ions and reducing the iron recovery rate; if the amount of iron ion precipitant added is too large, the content of impurity ions will be too large, thus affecting the purity of iron phosphate.

[0131] The data results from Examples 1 and 6 show that if ammonia is not added in step (1) to control the pH of the reaction system, the pH of the solution after acid leaching will be too low, which will affect the formation of sodium ferric sulfate precipitate and reduce the iron recovery rate.

[0132] The data from Examples 1 and 7-8 show that if the volume ratio of the ferric phosphate solution to the buffer solution is too large, i.e., the amount of buffer solution is too small, the pH value of the precipitation reaction will be unstable, which will easily lead to side reactions and reduce the purity of the ferric phosphate produced. If the volume ratio of the ferric phosphate solution to the buffer solution is too small, i.e., the amount of buffer solution is too large, the concentration of metal ions in the solution will be too small, which will reduce the rate of ferric phosphate precipitation and easily lead to side reactions.

[0133] The data from Examples 1 and 9-10 show that if the volume ratio of citric acid to sodium dihydrogen phosphate is too small, i.e., the content of sodium dihydrogen phosphate is too high, the pH of the buffer solution is too high, thereby reducing the mass of ferric phosphate precipitate; if the volume ratio of citric acid to sodium dihydrogen phosphate is too large, i.e., the content of sodium dihydrogen phosphate is too low, the pH of the buffer solution is too low, thereby failing to meet the requirements for ferric phosphate precipitation.

[0134] The data from Example 1 and Comparative Example 1 show that adding sodium sulfate during the acid leaching process can effectively prevent the loss of iron ions and significantly improve the iron recovery rate in the recovery of phosphate slag.

[0135] The data from Example 1 and Comparative Example 2 show that the phosphorus content in the ferric phosphate obtained in Comparative Example 2 is lower, indicating that the ferric phosphate obtained in Comparative Example 2 without using a buffer solution for precipitation has lower purity.

[0136] The applicant declares that this application illustrates the process method through the above embodiments, but this application is not limited to the above process steps, that is, it does not mean that this application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used in this application, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A method for recovering lithium from waste batteries by full-chain integrated recycling, comprising the following steps: (1) performing a first acid leaching on the lithium-extracted phosphorus-iron residue and adding an iron ion precipitant to react, to obtain a phosphorus-iron residue with impurities removed; (2) performing a second acid leaching on the phosphorus-iron residue with impurities removed, to obtain a phosphorus-iron solution; (3) mixing the phosphorus-iron solution with a buffer solution, controlling the pH value to be 1.8-2.2, performing a precipitation reaction, and performing a heat treatment on the obtained precipitate after the reaction is completed, to obtain iron phosphate; the buffer solution is a citric acid-sodium dihydrogen phosphate buffer solution.

2. The method of claim 1, wherein, In the process of the first acid leaching in step (1), the acid solution used includes any one or a combination of at least two of a sulfuric acid solution, a hydrochloric acid solution or a phosphoric acid solution.

3. The method of claim 2, wherein, The concentration of H + in the acidic solution is 0.2-0.5 mol / L.

4. The method of claim 1, wherein, The temperature of the first acid leaching in step (1) is 85-95℃.

5. The method of claim 1, wherein, The time of the first acid leaching in step (1) is 1-2h.

6. The method of claim 1, wherein, The iron ion precipitant in step (1) includes sodium sulfate.

7. The method of claim 1, wherein, The amount of the iron ion precipitant added in step (1) is 2-20% of the mass of the phosphorus-iron residue.

8. The method of claim 1, wherein, The reaction time in step (1) is 0.5-1.5h.

9. The method of claim 1, wherein, In the process of adding the iron ion precipitant to react in step (1), a pH regulator is also added, so that the pH value of the reaction system is 1.5-1.

7.

10. The method of claim 9, wherein, The pH regulator includes ammonia water.

11. The method of claim 1, wherein, Before the second acid leaching of the phosphorus-iron residue with impurities removed in step (2), the phosphorus-iron residue with impurities removed is mixed with water, so that the iron ions are dissolved out.

12. The method of claim 11, wherein, The solid-liquid ratio of the phosphorus-iron residue with impurities removed and water is 1g:(2-4)mL.

13. The method of claim 11, wherein, The mixing time of the phosphorus-iron residue with impurities removed and water is 30-60min.

14. The method of claim 1, wherein, In the process of the second acid leaching in step (2), the concentrated acid used includes any one or a combination of at least two of concentrated sulfuric acid, concentrated hydrochloric acid or concentrated phosphoric acid.

15. The method of claim 14, wherein, The concentration of H + in the concentrated acid is 1-1.5 mol / L.

16. The method of claim 1, wherein, The volume ratio of the phosphorus-iron solution to the buffer solution in step (3) is 1:(20-60).

17. The method of claim 1, wherein, The volume ratio of citric acid to sodium dihydrogen phosphate in the citric acid-sodium dihydrogen phosphate buffer solution is (2-4):(0.1-0.15).

18. The method of claim 1, wherein, The precipitation reaction time in step (3) is 1-2h.

19. The method of claim 1, wherein, The heat treatment temperature in step (3) is 500-600℃.

20. The method of claim 1, wherein, The heat treatment time in step (3) is 1-3h. 21.The method of claim 1, comprising the following steps: (I) Place the lithium-extracted ferrophosphate slag in H + The solution is first acid-leached in an acidic solution with a concentration of 0.2-0.5 mol / L at a temperature of 85-95℃ for 1-2 hours. Then, sodium sulfate and ammonia are added to control the pH at 1.5-1.7 and the mixture is stirred for 0.5-1.5 hours. After solid-liquid separation, the impurity-removed phosphorus-iron slag is obtained. wherein the amount of sodium sulfate added is 2-20% of the mass of the phosphorus-iron residue; (II) the impurity-removed phosphorous iron slag is mixed in water for 30-60 min, then H + secondary acid leaching with concentrated acid with a concentration of 1-1.5 mol / L, and solid-liquid separation to obtain a phosphorous iron solution; wherein the solid-liquid ratio of the phosphorus-iron residue with impurities removed and water is 1g:(2-4)mL; (Ⅲ) supplementing the phosphorus-iron solution with a phosphorus source or an iron source to control the phosphorus-iron ratio in the solution to be (1-1.05):1; (Ⅳ) mixing the phosphorus-iron solution with a citric acid-sodium dihydrogen phosphate buffer solution at a flow rate of 30-70mL / min, controlling the pH value to be 1.8-2.2, performing a precipitation reaction for 1-2h, performing a heat treatment on the obtained precipitate at 500-600℃ for 1-3h after the reaction is completed, and removing the crystal water to obtain iron phosphate; wherein the volume ratio of the phosphorus-iron solution to the citric acid-sodium dihydrogen phosphate buffer solution is 1:(20-60).

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