Method for full-chain integrated recycling of lithium-extracted ferrophosphorus slag from waste batteries

Abstract

Disclosed is a method for full-chain integrated recycling of post-lithium-extractraction ferrophosphorus slag from waste batteries. The method comprises the following steps: (1) carrying out primary acid leaching on post-lithium-extractraction ferrophosphorus slag, and adding an iron ion precipitant for reaction to obtain impurity-removed ferrophosphorus slag; (2) carrying out secondary acid leaching on the impurity-removed ferrophosphorus slag to obtain a ferrophosphorus solution; and (3) mixing the ferrophosphorus solution with a buffer solution, carrying out a precipitation reaction, and carrying out heat treatment on obtained precipitates upon completion of reaction to obtain iron phosphate. According to the present application, firstly, impurities in ferrophosphorus slag are removed by means of primary acid leaching, and an iron ion precipitant is added such that iron ions dissolved in the acid leaching form precipitates, avoiding iron loss; and then secondary acid leaching is carried out such that all Fe and P are leached out, effectively increasing the recovery rate of iron in the ferrophosphorus slag. In addition, the iron phosphate precipitation process is carried out in a buffer solution, so that the purity of iron phosphate can be increased, and the uniform consistency of iron phosphate particles can be improved, thereby obtaining high-quality iron phosphate.

Description

A full-chain integrated method for recycling waste batteries to extract lithium-phosphorus-iron slag Technical Field

[0001] The embodiments of the present application relate to the field of recycling of waste lithium iron phosphate batteries, for example, a method for recycling waste batteries into lithium-phosphorus iron slag in an integrated whole-chain manner. Background Art

[0002] New energy vehicles have experienced rapid growth in recent years. Lithium-ion batteries, with their significant advantages such as high specific capacity, stable performance, and long service life, have become the primary power source for these vehicles. Lithium iron phosphate batteries, in particular, are one of the mainstream lithium battery products on the market due to their low production cost and high safety performance. However, as their use increases, the amount of used lithium iron phosphate batteries is also rapidly increasing. If not promptly processed and recycled, they can cause serious environmental pollution.

[0003] In spent lithium iron phosphate batteries, lithium iron phosphate accounts for 30-35% of the battery's mass, while copper and aluminum foil contribute approximately 10%. The concentrations of the valuable metal elements Li, Fe, Cu, and Al far exceed their natural mineral content, making the recycling of spent lithium iron phosphate batteries extremely important. Al, Cu, and Fe have similar properties and are difficult to separate. The presence of these impurities can hinder the recovery of battery-grade iron phosphate from this ferrophosphorus slag, affecting the electrochemical performance of the cathode material used in lithium iron phosphate batteries.

[0004] Currently, methods for removing aluminum and copper impurities include using acidic solutions to leach them. For example, CN115583643A discloses using a low-acid solution to pre-remove impurities from ferrophosphorus slag to leach out impurity metal ions such as aluminum and copper, thereby reducing the impurity content in the ferrophosphorus slag. However, during pre-removal, iron ions in the ferrophosphorus slag 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 recovery process and improve the recovery rate of iron in ferrophosphorus slag is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The embodiment of the present application provides a method for recycling lithium ferrophosphorus slag from waste batteries through a full chain integration. The present application first removes metal ion impurities such as Al and Cu in the ferrophosphorus slag by a single acid leaching, and adds an iron ion precipitant to form a precipitate of the iron ions dissolved in the acid leaching, thereby avoiding the loss of iron during the acid leaching impurity removal process, and then performs a secondary acid leaching to leach all Fe and P. This can effectively avoid the loss of iron ions during the acid leaching process and significantly improve the recovery rate of iron in the ferrophosphorus slag. In addition, the iron phosphate precipitation process is carried out in a buffer solution, which can not only improve the purity of the iron phosphate, but also improve the uniformity of the iron phosphate particles to obtain high-quality iron phosphate.

[0009] In a first aspect, the present invention provides a method for recycling waste batteries to extract lithium-phosphorus-iron slag in an integrated manner, the method comprising the following steps:

[0010] (1) acid leaching the ferrophosphorus slag after lithium extraction, and adding an iron ion precipitant to react to obtain impurity-removed ferrophosphorus slag;

[0011] (2) subjecting the impurity-removed ferrophosphorus slag to secondary acid leaching to obtain a ferrophosphorus solution;

[0012] (3) mixing the ferrophosphorus solution and a buffer solution to carry out a precipitation reaction, and after the reaction is completed, heat-treating the obtained precipitate to obtain ferric phosphate.

[0013] The present application first removes metal ion impurities such as Al and Cu in ferrophosphorus slag by a single acid leaching, and adds an iron ion precipitant to form a precipitate of the iron ions dissolved in the acid leaching, thereby avoiding the loss of iron during the acid leaching and impurity removal process. A secondary acid leaching is then performed to leach all of Fe and P, which can effectively avoid the loss of iron ions during the acid leaching process and significantly improve the recovery rate of iron in ferrophosphorus slag. In addition, the iron phosphate precipitation process is carried out in a buffer solution, which can keep the pH value of the solution system stable during the precipitation process and prevent the pH value of the reaction system from changing too drastically, resulting in the formation of iron hydroxide precipitation, further improving the purity of iron phosphate, and controlling the rate of iron phosphate precipitation, thereby preventing iron phosphate from agglomerating, regulating the nucleation size of iron phosphate, improving the uniformity of iron phosphate particles, and obtaining high-quality iron phosphate.

[0014] It should be noted that the ferrophosphorus slag after lithium extraction refers to the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate, and its main components are FePO4 and C, including a small amount of impurities such as Al and Cu.

[0015] As a preferred technical solution of the present application, during the acid leaching process in step (1), the acidic solution used includes any one of sulfuric acid solution, hydrochloric acid solution or phosphoric acid solution, or a combination of at least two of them.

[0016] Preferably, 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.

[0017] As a preferred technical solution of the present application, the temperature of the acid leaching in step (1) is 85-95°C, for example, it can be 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C.

[0018] Preferably, the time for the single acid leaching in step (1) is 1-2 h, for example, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h or 2 h.

[0019] As a preferred technical solution of the present application, the iron ion precipitant in step (1) includes sodium sulfate.

[0020] In the present application, sodium sulfate reacts with the iron ions dissolved in the first acid leaching to generate natantialuminum precipitate, thereby avoiding the loss of iron during the acid leaching and impurity removal process.

[0021] Preferably, the amount of the iron ion precipitant added in step (1) is 2-20% of the mass of the ferrophosphorus slag, for example, 2%, 5%, 10%, 15% or 20%.

[0022] In the present application, if the amount of the iron ion precipitant added is too little, the iron ions dissolved in the solution will be lost after solid-liquid separation during the acid leaching process; if the amount of the iron ion precipitant added is too much, too many impurity ions will be introduced.

[0023] Preferably, the reaction time of step (1) is 0.5-1.5 h, for example, 0.5 h, 0.7 h, 0.9 h, 1.1 h, 1.3 h or 1.5 h.

[0024] As a preferred technical solution of the present application, during the process of adding the iron ion precipitant to react in step (1), a pH regulator is also added to make the pH value of the reaction system 1.5-1.7, for example, it can be 1.5, 1.6 or 1.7.

[0025] In the present application, the pH value of the reaction system is 1.5-1.7, which can cause the precipitation of natantolacite.

[0026] Preferably, the pH adjuster comprises aqueous ammonia.

[0027] As a preferred technical solution of the present application, before the dephosphorus-iron slag is subjected to secondary acid leaching in step (2), the dephosphorus-iron slag is first mixed with water to dissolve the iron ions.

[0028] Preferably, the solid-liquid ratio of the impurity-removed ferrophosphorus 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.

[0029] Preferably, the time for mixing the impurity-removed ferrophosphorus slag and water is 30-60 minutes, for example, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0030] As a preferred technical solution of the present application, during the secondary acid leaching process in step (2), the concentrated acid used includes any one of concentrated sulfuric acid, concentrated hydrochloric acid or concentrated phosphoric acid, or a combination of at least two of them.

[0031] In the present application, concentrated acid is added in the secondary acid leaching to allow all Fe and P to be leached out.

[0032] Preferably, 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.

[0033] As a preferred technical solution of the present application, the buffer solution in step (3) includes any one of citric acid-sodium dihydrogen phosphate buffer solution, phthalic acid-hydrochloric acid buffer solution or citric acid-sodium citrate buffer solution or a combination of at least two thereof, preferably citric acid-sodium dihydrogen phosphate buffer solution.

[0034] In the present application, a citric acid-sodium dihydrogen phosphate buffer solution is mixed with the ferric phosphate solution. Citric acid can complex iron ions, control the rate of ferric phosphate precipitation, prevent ferric phosphate agglomeration, regulate the size of ferric phosphate nuclei, and improve the uniformity of ferric phosphate particles.

[0035] Preferably, the concentration of citric acid in the citric acid-sodium dihydrogen phosphate buffer 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.

[0036] 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 selection range of citric acid "2-4" can be, for example, 2, 2.5, 3, 3.5 or 4, and the selection 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, etc.

[0037] In the present application, if the volume ratio of citric acid and sodium dihydrogen phosphate is too small, that is, the content of sodium dihydrogen phosphate is too high, the pH value of the buffer solution is too high; if the volume ratio of citric acid and sodium dihydrogen phosphate is too large, that is, the content of sodium dihydrogen phosphate is too low, the pH value of the buffer solution is too low, both situations are not conducive to the precipitation reaction.

[0038] Preferably, the volume ratio of the ferrophosphorus solution to 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.

[0039] In the present application, if the volume ratio of the ferrophosphorus solution and the buffer solution is too small, that is, the amount of the buffer solution is too much, the concentration of the reactive ions in the solution is too low, which will reduce the reaction efficiency; if the volume ratio of the ferrophosphorus solution and the buffer solution is too large, that is, the amount of the buffer solution is too little, the pH value of the precipitate will be unstable.

[0040] Preferably, the pH value of the reaction system after the ferrophosphorus solution and the buffer solution are mixed in step (3) is 1.8-2.2, for example, it can be 1.8, 1.9, 2, 2.1 or 2.2.

[0041] Preferably, the precipitation reaction time in step (3) is 1-2 h, for example, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h or 2 h.

[0042] As a preferred technical solution of the present application, the temperature of the heat treatment in step (3) is 500-600°C, for example, it can be 500°C, 520°C, 550°C, 570°C, 580°C or 600°C, etc., preferably 500-550°C.

[0043] In the present application, heat treatment is performed within the preferred range of 500-550° C., which can effectively remove the crystal water in the precipitated ferric phosphate dihydrate, and is beneficial for the subsequent preparation of lithium iron phosphate by mixed sintering with a lithium source as a precursor.

[0044] 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.

[0045] As a preferred technical solution of the present application, the method comprises the following steps:

[0046] (1) Place the ferrophosphorus slag after lithium extraction in H + The product is acid-leached in an acid solution with a concentration of 0.2-0.5 mol / L at a temperature of 85-95°C for 1-2 hours, and then sodium sulfate and ammonia water are added to control the pH to 1.5-1.7 and stirred for 0.5-1.5 hours. After solid-liquid separation, impurity-removed ferrophosphorus slag is obtained;

[0047] Wherein, the amount of sodium sulfate added is 2-20% of the mass of the ferrophosphorus slag;

[0048] (II) The impurity-removed ferrophosphorus slag was placed in water and mixed for 30-60 min, and then H + The concentrated acid with a concentration of 1-1.5 mol / L is used for secondary acid leaching, and a ferrophosphorus solution is obtained after solid-liquid separation;

[0049] The solid-liquid ratio of the impure phosphorus-free ferro-slag to water is 1 g: (2-4) mL;

[0050] (III) supplementing the ferrophosphorus solution with a phosphorus source or an iron source to control the phosphorus to iron ratio in the solution to be (1-1.05):1;

[0051] (IV) adding the ferrophosphorus solution to a citric acid-sodium dihydrogen phosphate buffer solution at a flow rate of 30-70 mL / min, controlling the pH value to 1.8-2.2, and performing a precipitation reaction for 1-2 hours. After the reaction, heat-treating the obtained precipitate at 500-600° C. for 1-3 hours to remove crystal water to obtain ferric phosphate;

[0052] The volume ratio of the ferrophosphide solution to the citric acid-sodium dihydrogen phosphate buffer solution is 1:(20-60).

[0053] In the present 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.

[0054] 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 limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0055] Compared with the related art, the embodiments of the present application have the following beneficial effects:

[0056] The embodiment of the present application first removes metal ion impurities such as Al and Cu in the ferrophosphorus slag by a single acid leaching, and adds an iron ion precipitant to form a precipitate of the iron ions dissolved in the acid leaching, thereby avoiding the loss of iron during the acid leaching and impurity removal process. A secondary acid leaching is then performed to leach all of Fe and P, which can effectively avoid the loss of iron ions during the acid leaching process and significantly improve the recovery rate of iron in the ferrophosphorus slag. In addition, the iron phosphate precipitation process is carried out in a buffer solution, which can keep the pH value of the solution system stable during the precipitation process, prevent the pH value of the reaction system from changing too drastically, resulting in the formation of iron hydroxide precipitation, further improve the purity of the iron phosphate, and control the rate of iron phosphate precipitation, prevent iron phosphate from agglomerating, regulate the size of iron phosphate nucleation, improve the uniformity of the iron phosphate particles, and obtain high-quality iron phosphate.

[0057] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation to the technical solution of this article.

[0059] FIG1 is a SEM image of the iron phosphate recovered in Example 1 of the present application.

[0060] FIG2 is a SEM image of the iron phosphate recovered in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0061] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0062] Example 1

[0063] This embodiment provides a method for recycling waste batteries to extract lithium-phosphorus-iron slag in an integrated manner, the method comprising the following steps:

[0064] (1) Place the ferrophosphorus slag after lithium extraction in H + The product is acid-leached in a 0.3 mol / L sulfuric acid solution at 90°C for 1.5 hours, and then sodium sulfate and ammonia water are added to control the pH of the reaction system to 1.6 and stirred for 1 hour. After the reaction, the solid and liquid are separated to obtain impurity-removed ferrophosphorus slag;

[0065] Wherein, the amount of sodium sulfate added is 10% of the mass of the ferrophosphorus slag;

[0066] (2) The impurity-removed ferrophosphorus slag was placed in water and mixed for 40 min, and then H + The concentrated sulfuric acid with a concentration of 1.2 mol / L is used for secondary acid leaching, and a ferrophosphorus solution is obtained after solid-liquid separation;

[0067] Among them, the solid-liquid ratio of the impure phosphorus-iron slag and water is 1g:3mL;

[0068] (3) supplementing the ferrophosphorus solution with ammonium dihydrogen phosphate or ferric sulfate, thereby controlling the phosphorus to iron ratio of the ferrophosphorus solution to be 1.02:1;

[0069] (4) adding the ferrophosphorus solution to a citric acid-sodium dihydrogen phosphate buffer solution (comprising 174 L 0.1 mol / L citric acid and 6 L 0.2 mol / L disodium hydrogen phosphate, with a volume ratio of 3:0.1) at a flow rate of 50 mL / min, mixing, controlling the pH value to 2.1, and performing a precipitation reaction for 1.5 h. After the reaction, heat-treating the obtained precipitate at 550° C. for 2 h to remove crystal water to obtain ferric phosphate;

[0070] The volume ratio of the ferrophosphide solution to the citric acid-sodium dihydrogen phosphate buffer solution is 1:30.

[0071] Example 2

[0072] This embodiment provides a method for recycling waste batteries to extract lithium-phosphorus-iron slag in an integrated manner, the method comprising the following steps:

[0073] (1) Place the ferrophosphorus slag after lithium extraction in H + The slag was acid-leached in a 0.2 mol / L sulfuric acid solution at 85°C for 2 hours, and then sodium sulfate and ammonia water were added to control the pH of the reaction system to 1.7, and stirred for 1 hour. After the reaction, the solid and liquid were separated to obtain impurity-removed ferrophosphorus slag.

[0074] Wherein, the amount of sodium sulfate added is 2% of the mass of the ferrophosphorus slag;

[0075] (2) The impurity-removed ferrophosphorus slag was placed in water and mixed for 30 min, and then H + The concentrated sulfuric acid with a concentration of 1 mol / L is used for secondary acid leaching, and a ferrophosphorus solution is obtained after solid-liquid separation;

[0076] Among them, the solid-liquid ratio of the impure phosphorus-iron slag and water is 1g:2mL;

[0077] (3) supplementing the ferrophosphorus solution with ammonium dihydrogen phosphate or ferric sulfate, thereby controlling the phosphorus to iron ratio of the ferrophosphorus solution to be 1:1;

[0078] (4) adding the ferrophosphorus solution to a citric acid-sodium dihydrogen phosphate buffer solution (comprising 210 L of 0.1 mol / L citric acid and 5.3 L of 0.2 mol / L disodium hydrogen phosphate, with a volume ratio of 4:0.1) at a flow rate of 30 mL / min, mixing, controlling the pH value to 1.8, and performing a precipitation reaction for 2 h. After the reaction, heat-treating the obtained precipitate at 500° C. for 3 h to remove crystal water to obtain ferric phosphate;

[0079] The volume ratio of the ferrophosphide solution to the citric acid-sodium dihydrogen phosphate buffer solution is 1:20.

[0080] Example 3

[0081] This embodiment provides a method for recycling waste batteries to extract lithium-phosphorus-iron slag in an integrated manner, the method comprising the following steps:

[0082] (1) Place the ferrophosphorus slag after lithium extraction in H + The product is acid-leached in a 0.5 mol / L sulfuric acid solution at 95°C for 1 hour, and then sodium sulfate and ammonia water are added to control the pH of the reaction system to 1.5 and stirred for 0.5 hour. After the reaction is completed, the solid and liquid are separated to obtain impurity-removed ferrophosphorus slag;

[0083] Wherein, the amount of sodium sulfate added is 2% of the mass of the ferrophosphorus slag;

[0084] (2) The impurity-removed ferrophosphorus slag was placed in water and mixed for 60 min, and then H + The concentrated sulfuric acid with a concentration of 1.5 mol / L is used for secondary acid leaching, and a ferrophosphorus solution is obtained after solid-liquid separation;

[0085] Among them, the solid-liquid ratio of the impure phosphorus-iron slag and water is 1g:4mL;

[0086] (3) supplementing the ferrophosphorus solution with ammonium dihydrogen phosphate or ferric sulfate, thereby controlling the phosphorus to iron ratio of the ferrophosphorus solution to be 1.05:1;

[0087] (4) adding the ferrophosphorus solution to a citric acid-sodium dihydrogen phosphate buffer solution (comprising 77 L of 0.1 mol / L citric acid and 3 L of 0.2 mol / L disodium hydrogen phosphate, with a volume ratio of 3:0.12) at a flow rate of 70 mL / min, mixing, controlling the pH value to 2.2, and performing a precipitation reaction for 1 h. After the reaction is completed, the obtained precipitate is heat-treated at 500° C. for 3 h to remove crystal water, thereby obtaining ferric phosphate;

[0088] The volume ratio of the ferrophosphide solution to the citric acid-sodium dihydrogen phosphate buffer solution is 1:40.

[0089] Example 4

[0090] The difference between this embodiment and embodiment 1 is that the amount of sodium sulfate added is 1% of the mass of the ferrophosphorus slag.

[0091] The remaining methods and parameters remained the same as in Example 1.

[0092] Example 5

[0093] The difference between this embodiment and embodiment 1 is that the amount of sodium sulfate added is 25% of the mass of the ferrophosphorus slag.

[0094] The remaining methods and parameters remained the same as in Example 1.

[0095] Example 6

[0096] The difference between this embodiment and embodiment 1 is that no ammonia water is added in step (1) to control the pH of the reaction system.

[0097] The remaining methods and parameters remained the same as in Example 1.

[0098] Example 7

[0099] The difference between this embodiment and embodiment 1 is that the volume ratio of the ferrophosphorus solution to the citric acid-sodium dihydrogen phosphate buffer in step (4) is 1:10.

[0100] The remaining methods and parameters remained the same as in Example 1.

[0101] Example 8

[0102] The difference between this embodiment and embodiment 1 is that the volume ratio of the ferrophosphorus solution to the citric acid-sodium dihydrogen phosphate buffer in step (4) is 1:70.

[0103] The remaining methods and parameters remained the same as in Example 1.

[0104] Example 9

[0105] The difference between this embodiment and embodiment 1 is that the volume ratio of citric acid to sodium dihydrogen phosphate in step (4) is 5:0.05.

[0106] The remaining methods and parameters remained the same as in Example 1.

[0107] Example 10

[0108] The difference between this embodiment and embodiment 1 is that the volume ratio of citric acid to sodium dihydrogen phosphate in step (4) is 1:0.2.

[0109] The remaining methods and parameters remained the same as in Example 1.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 1 is that the iron ion precipitant sodium sulfate is not added in step (1).

[0112] The remaining methods and parameters remained the same as in Example 1.

[0113] Comparative Example 2

[0114] This comparative example provides a method for recovering ferrophosphorus slag after lithium extraction from waste lithium iron phosphate, the method comprising the following steps:

[0115] (1) Place the ferrophosphorus slag after lithium extraction in H +The product is acid-leached in a 0.3 mol / L sulfuric acid solution at 90°C for 1.5 hours, and then sodium sulfate and ammonia water are added to control the pH of the reaction system to 1.6 and stirred for 1 hour. After the reaction, the solid and liquid are separated to obtain impurity-removed ferrophosphorus slag;

[0116] Wherein, the amount of sodium sulfate added is 10% of the mass of the ferrophosphorus slag;

[0117] (2) The impurity-removed ferrophosphorus slag was placed in water and mixed for 40 min, and then H + The concentrated sulfuric acid with a concentration of 1.2 mol / L is used for secondary acid leaching, and a ferrophosphorus solution is obtained after solid-liquid separation;

[0118] Among them, the solid-liquid ratio of the impure phosphorus-iron slag and water is 1g:3mL;

[0119] (3) supplementing the ferrophosphorus solution with ammonium dihydrogen phosphate or ferric sulfate to control the phosphorus-iron ratio of the ferrophosphorus solution to 1.02:1, adding ammonia water to control the pH value of the solution to 2.1, and reacting for 1.5 hours to obtain ferric phosphate dihydrate;

[0120] (4) The ferric phosphate dihydrate is heat-treated at 550° C. for 2 h to remove crystal water and obtain ferric phosphate.

[0121] Figures 1 and 2 show SEM images of the iron phosphate recovered in Example 1 and Comparative Example 2, respectively. It can be seen from the figures that the iron phosphate particles obtained in Example 1 are relatively uniform, while the iron phosphate obtained in Comparative Example 2 is severely agglomerated. This shows that using a buffer solution for iron phosphate precipitation can avoid the formation of iron hydroxide and make the generated particles more uniform.

[0122] Performance Testing

[0123] The ferric phosphate obtained after recovery from the above examples and comparative examples was tested for component content and recovery rate.

[0124] The recovery rate is calculated as follows: recovery rate = iron content in the ferrophosphorus solution obtained by leaching ferrophosphorus slag (g) / iron content in the ferrophosphorus slag (g) × 100%.

[0125] The above detection and test results are shown in Table 1.

[0126] Table 1

[0127] analyze:

[0128] As can be seen from the table above, this application uses a single acid leaching, adds an iron ion precipitant, and then performs a secondary acid leaching, and the iron phosphate precipitation process is carried out in a buffer solution. The above method can effectively avoid the loss of iron ions and significantly improve the recovery rate of iron in ferrophosphorus slag.

[0129] It can be seen from the data results of Example 1 and Examples 4-5 that if the amount of iron ion precipitant added is too little, the iron ions lost by acid leaching cannot be completely precipitated, resulting in the loss of iron ions and reducing the iron recovery rate; if the amount of iron ion precipitant added is too much, the impurity ion content is too high, thereby affecting the purity of ferric phosphate.

[0130] From the data results of Example 1 and Example 6, it can be seen that if ammonia water is not added in step (1) to control the pH of the reaction system, the pH of the solution after acid leaching is too low, thereby affecting the formation of natantronite precipitation and reducing the iron recovery rate.

[0131] It can be seen from the data results of Example 1 and Examples 7-8 that if the volume ratio of the ferrophosphorus solution and the buffer solution is too large, that is, the amount of the buffer solution is too small, the pH value of the precipitation reaction is unstable, which makes it easy for side reactions to occur, resulting in a decrease in the purity of the generated ferric phosphate; if the volume ratio of the ferrophosphorus solution and the buffer solution is too small, that is, the amount of the buffer solution is too large, the concentration of the metal ions reacting in the solution is too low, resulting in a decrease in the reaction rate of the ferric phosphate precipitation reaction and a high incidence of side reactions.

[0132] From the data results of Examples 1 and 9-10, it can be seen that if the volume ratio of citric acid to sodium dihydrogen phosphate is too small, that is, the content of sodium dihydrogen phosphate is too high, the pH of the buffer solution is too high, thereby reducing the quality of the precipitated ferric phosphate; if the volume ratio of citric acid to sodium dihydrogen phosphate is too large, that is, the content of sodium dihydrogen phosphate is too low, the pH of the buffer solution is too low, and the requirements for ferric phosphate precipitation cannot be met.

[0133] It can be seen from the data results of Example 1 and Comparative Example 1 that the addition of sodium sulfate during the acid leaching and impurity removal process can effectively avoid the loss of iron ions and significantly improve the recovery rate of iron in the recovery of ferrophosphorus slag.

[0134] From the data results of Example 1 and Comparative Example 2, it can be seen that the phosphorus content in the iron phosphate obtained in Comparative Example 2 is relatively low, indicating that the purity of the iron phosphate obtained in Comparative Example 2 without using a buffer solution for precipitation is relatively low.

[0135] The applicant declares that while the above-mentioned embodiments are used to illustrate the process of the present application, the present application is not limited to the above-mentioned process steps, which does not mean that the present application must rely on the above-mentioned process steps in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials used in the present application, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A method for recycling lithium-phosphorus-iron slag from waste batteries in an integrated whole-chain manner, comprising the following steps: (1) acid leaching the ferrophosphorus slag after lithium extraction, and adding an iron ion precipitant to react to obtain impurity-removed ferrophosphorus slag; (2) subjecting the impurity-removed ferrophosphorus slag to secondary acid leaching to obtain a ferrophosphorus solution; (3) mixing the ferrophosphorus solution and a buffer solution to perform a precipitation reaction, and after the reaction is completed, heat-treating the obtained precipitate to obtain ferric phosphate.

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

3. The method according to claim 2, wherein: The acidic solution contains H + The concentration is 0.2-0.5mol / L.

4. The method according to any one of claims 1 to 3, wherein: The temperature of the first acid leaching in step (1) is 85-95°C.

5. The method according to any one of claims 1 to 4, wherein: The time of the acid leaching in step (1) is 1-2 hours.

6. The method according to any one of claims 1 to 5, wherein: The iron ion precipitant in step (1) comprises sodium sulfate; Preferably, the amount of the iron ion precipitant added in step (1) is 2-20% of the mass of the ferrophosphorus slag; Preferably, the reaction time in step (1) is 0.5-1.5 h.

7. The method according to any one of claims 1 to 6, wherein: During the reaction of adding the iron ion precipitant in step (1), a pH adjuster is also added to adjust the pH value of the reaction system to 1.5-1.7; Preferably, the pH adjuster comprises aqueous ammonia.

8. The method according to any one of claims 1 to 7, wherein: Before the impurity-removed ferrophosphorus slag is subjected to secondary acid leaching in step (2), the impurity-removed ferrophosphorus slag is first mixed with water to dissolve the iron ions; Preferably, the solid-to-liquid ratio of the impurity-removed ferrophosphorus slag and water is 1 g: (2-4) mL; Preferably, the time for mixing the impurity-removed ferrophosphorus slag and water is 30-60 minutes.

9. The method according to any one of claims 1 to 8, wherein: In the secondary acid leaching process of step (2), the concentrated acid used includes any one of concentrated sulfuric acid, concentrated hydrochloric acid or concentrated phosphoric acid, or a combination of at least two thereof; Preferably, the concentrated acid contains H + The concentration is 1-1.5mol / L.

10. The method according to any one of claims 1 to 9, wherein: The buffer in step (3) comprises any one of citric acid-sodium dihydrogen phosphate buffer, phthalic acid-hydrochloric acid buffer or citric acid-sodium citrate buffer or a combination of at least two thereof, preferably citric acid-sodium dihydrogen phosphate buffer.

11. The method according to any one of claims 1 to 10, wherein: The volume ratio of the ferrophosphide solution to the buffer solution in step (3) is 1:(20-60).

12. The method according to claim 10, wherein: 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).

13. The method according to any one of claims 1 to 12, wherein: The pH value of the reaction system after the ferrophosphorus solution and the buffer solution are mixed in step (3) is 1.8-2.2; Preferably, the precipitation reaction time in step (3) is 1-2 h.

14. The method according to any one of claims 1 to 13, wherein: The temperature of the heat treatment in step (3) is 500-600°C; Preferably, the heat treatment time in step (3) is 1-3 hours.

15. The method according to any one of claims 1 to 14, comprising the following steps: (I) Placing the ferrophosphorus slag after lithium extraction in H + Acid leaching is performed once in an acid solution with a concentration of 0.2-0.5 mol / L at a temperature of 85-95°C for 1-2 hours, and then sodium sulfate and ammonia water are added to control the pH to 1.5-1.7 for stirring reaction for 0.5-1.5 hours, and after solid-liquid separation, impurity-removed ferrophosphorus slag is obtained; Wherein, the amount of sodium sulfate added is 2-20% of the mass of the ferrophosphorus slag; (II) The impurity-removed ferrophosphorus slag is placed in water and mixed for 30-60 min, and then H + A secondary acid leaching is performed with concentrated acid having a concentration of 1-1.5 mol / L, and a ferrophosphorus solution is obtained after solid-liquid separation; The solid-liquid ratio of the impure phosphorus-iron slag and water is 1g:(2-4)mL; (III) supplementing the ferrophosphorus solution with a phosphorus source or an iron source to control the phosphorus to iron ratio in the solution to be (1-1.05):1; (IV) adding the ferrophosphorus solution to a citric acid-sodium dihydrogen phosphate buffer solution at a flow rate of 30-70 mL / min, mixing, controlling the pH value to 1.8-2.2, performing a precipitation reaction for 1-2 hours, and after the reaction, heat treating the obtained precipitate at 500-600° C. for 1-3 hours to remove crystal water to obtain ferric phosphate; Wherein, the volume ratio of the ferrophosphide solution to the citric acid-sodium dihydrogen phosphate buffer solution is 1:(20-60).

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