Method for recycling lithium iron phosphate black powder

Abstract

The application provides a recycling method of lithium iron phosphate black powder. The recycling method comprises the following steps: mixing the lithium iron phosphate black powder and a nitric acid solution, performing self-thermal oxidation to obtain an acidolysis recovery gas and an acidolysis solution, the acidolysis recovery gas containing carbon dioxide and nitrogen oxides; performing one-stage impurity removal leaching and oxidative leaching on the acidolysis solution, and performing solid-liquid separation to obtain an oxidative leaching solution and a filter cake; calcining the filter cake to obtain a ferric phosphate product; performing two-stage impurity removal leaching on the oxidative leaching solution to obtain a two-stage impurity removal leaching solution; introducing the acidolysis recovery gas into the two-stage impurity removal leaching solution to perform three-stage impurity removal leaching, and performing solid-liquid separation to obtain a three-stage impurity removal leaching solution and a lithium carbonate product; and concentrating and crystallizing the three-stage impurity removal leaching solution to obtain a nitric acid product and a carbonic acid product. The lithium iron phosphate black powder is comprehensively utilized by using the nitric acid solution, the comprehensive recovery of carbon, lithium, phosphorus and nitrogen elements is realized, the lithium recovery rate is greater than 95%, and the phosphorus recovery rate is greater than 98%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery recycling, and particularly relates to a recycling method of lithium iron phosphate black powder. BACKGROUND

[0002] In recent years, the new energy industry has developed more vigorously under this condition. In the field of electric vehicles, lithium iron phosphate batteries have attracted widespread attention due to their excellent stability and excellent safety. With the wide application of lithium iron phosphate batteries, a large number of scrap lithium iron phosphate batteries appear, which not only seriously harm the environment and human health, but also cause great waste of resources if not properly treated. From the perspective of resource recycling, waste lithium iron phosphate batteries have significant resource value, and the metal elements such as Li therein are of high value, and efficient recovery can greatly alleviate the consumption of mineral resources. From the perspective of environmental protection, the recycling of waste lithium iron phosphate batteries is conducive to the protection of the ecological environment and human health. Therefore, the recycling and utilization of waste lithium iron phosphate batteries is imperative.

[0003] At present, the recycling of lithium iron phosphate black powder mainly uses hydrochloric acid or sulfuric acid to dissolve and recover lithium carbonate. However, the recovery of iron phosphate and the treatment of carbon residue are less, and the recovery rate is low.

[0004] Therefore, it is urgent to provide a recycling method of lithium iron phosphate black powder with high recovery rate to comprehensively recover carbon elements, lithium elements and phosphorus elements in lithium iron phosphate black powder and realize resource recycling. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a recycling method of lithium iron phosphate black powder. The present application uses nitric acid solution to comprehensively utilize lithium iron phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are generated by self-thermal oxidation, carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, nitrogen oxides generate nitric acid products, and crystallization is sold, realizing resource comprehensive utilization. On the other hand, through acid hydrolysis solution, multi-process recovery treatment is effectively realized to comprehensively recover carbon elements, lithium elements, phosphorus elements and nitrogen elements. In the recycling method provided by the present application, the lithium recovery rate is greater than 95%, the phosphorus recovery rate is greater than 98%, and the recovery rate is high.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a recycling method of lithium iron phosphate black powder, which comprises the following steps:

[0008] Mixing lithium iron phosphate black powder and nitric acid solution for self-thermal oxidation to obtain acid hydrolysis recovery gas and acid hydrolysis solution, the acid hydrolysis recovery gas containing carbon dioxide and nitrogen oxides.

[0009] The acidolysis solution is subjected to a first impurity removal leaching and an oxidation leaching, and solid-liquid separation is performed to obtain an oxidation leaching solution and a filter cake.

[0010] The filter cake is calcined to obtain a ferric phosphate product, and the oxidation leaching solution is subjected to a second impurity removal leaching to obtain a second impurity removal leaching solution.

[0011] The second impurity removal leaching solution is subjected to a third impurity removal leaching by introducing the acidolysis recovery gas, and solid-liquid separation is performed to obtain a third impurity removal leaching solution and a lithium carbonate product; the third impurity removal leaching solution is concentrated and crystallized to obtain a nitric acid product and a carbonic acid product.

[0012] The present application uses a nitric acid solution to comprehensively utilize the lithium ferric phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are generated by self-thermal oxidation, carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, nitrogen oxides generate a nitric acid product, and crystallization is sold externally, realizing comprehensive utilization of resources; on the other hand, the acidolysis solution is subjected to multi-process recovery treatment, effectively realizing the comprehensive recovery of carbon elements, lithium elements, phosphorus elements and nitrogen elements. In the recycling method provided by the present application, the lithium recovery rate is greater than 95%, the phosphorus recovery rate is greater than 98%, and the recovery rate is high.

[0013] Preferably, the concentration of the nitric acid solution is 2-8 mol / L, for example, it can be 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L or 8 mol / L, etc.

[0014] In the present application, a suitable concentration of nitric acid solution helps to improve the dissolution rate of black powder while reducing the dissolution cost and the evaporation and crystallization cost at the back end.

[0015] Preferably, the molar ratio of the lithium ferric phosphate black powder and the nitric acid solution is 1:(2.5-4), for example, it can be 1:2.5, 1:3, 1:3.5 or 1:4, etc.

[0016] In the present application, a suitable molar ratio (molar ratio refers to the ratio of the molar amount of black powder calculated according to lithium ferric phosphate and nitric acid) of lithium ferric phosphate black powder and nitric acid solution helps to fully improve the dissolution rate of black powder.

[0017] Preferably, the method of the first impurity removal leaching comprises:

[0018] The pH value of the acidolysis solution is adjusted to 1.5-2.5 (for example, it can be 1.5, 2 or 2.5, etc.), then a copper displacement agent is added, and a copper displacement reaction is performed to obtain a first impurity removal leaching solution.

[0019] The purpose of the first impurity removal leaching in the present application is to remove copper impurities.

[0020] Preferably, the displacement agent comprises iron powder.

[0021] Preferably, the molar ratio of the displacement agent to copper ions in the acidolysis solution is (1-3):1, such as 1:1, 1.5:1, 2:1, 2.5:1, or 3:1, etc.

[0022] The present application employs the above-mentioned molar ratio, which helps to completely remove copper impurities.

[0023] Preferably, the method of the oxidative leaching comprises:

[0024] The first impurity-removing leaching solution is mixed with an oxidizing agent, and the pH value is adjusted to 3-5, such as 3, 4, or 5, etc.

[0025] In the present application, the purpose of adding the oxidizing agent and adjusting the pH value to 3-5 is to convert Fe 2+ in the first impurity-removing leaching solution into Fe 3+ .

[0026] Preferably, the oxidizing agent comprises H2O2.

[0027] Preferably, the molar ratio of the oxidizing agent to Fe 2+ in the first impurity-removing leaching solution is 1:(1-2), such as 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2, etc.

[0028] In the present application, the above-mentioned molar ratio helps to completely convert Fe 2+ in the first impurity-removing leaching solution into Fe 3+ .

[0029] Preferably, the calcination temperature is 550-700℃, such as 550℃, 600℃, 650℃, or 700℃, etc.

[0030] In the present application, the calcination at a suitable temperature helps to improve the purity and compaction density performance of the product.

[0031] Preferably, the calcination time is 0.5-3h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, or 3h, etc.

[0032] Preferably, the method of the second impurity-removing leaching comprises:

[0033] The oxidative leaching solution is mixed with a phosphorus displacement agent, the pH value is adjusted to 5-7 (such as 5, 6, or 7, etc.), and then filtered.

[0034] In the present application, the purpose of adding the phosphorus displacement agent and adjusting the pH value to 5-7 is to remove phosphorus elements in the oxidative leaching solution.

[0035] Preferably, the phosphorus displacement agent comprises an iron salt.

[0036] Preferably, the iron salt comprises any one or a combination of at least two of ferric nitrate, ferric sulfate or ferric chloride, preferably ferric nitrate.

[0037] In the present application, the type of iron salt affects the purity of the final by-product, and ferric sulfate or ferric chloride introduces other anions, increasing impurities, so ferric nitrate is preferred.

[0038] Preferably, the molar ratio of iron to phosphorus in the mixed solution obtained by mixing the oxidized leaching solution and the iron salt is (1-2):1, for example, it can be 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1 or 2:1, etc.

[0039] Preferably, in the process of passing the acidolysis recovery gas into the second-stage impurity removal leaching solution, ammonia water is added to adjust the pH to 5-7, for example, it can be 5, 6 or 7, etc.

[0040] In the present application, the purpose of adding ammonia water to adjust the pH to 5-7 is to react with nitrogen oxides to generate ammonium nitrate.

[0041] Preferably, the recycling method comprises the following steps:

[0042] (1) The lithium iron phosphate black powder is added to a nitric acid solution with a concentration of 2-8 mol / L for self-thermal oxidation to obtain acidolysis recovery gas and an acidolysis solution, and the acidolysis recovery gas contains carbon dioxide and nitrogen oxides.

[0043] The molar ratio of the lithium iron phosphate black powder to the nitric acid solution is 1:(2.5-4).

[0044] (2) The acidolysis solution is filtered, and ammonia water is added to adjust the pH of the acidolysis solution to 1.5-2.5; then iron powder is added to perform a copper displacement reaction, and after filtration, a first-stage impurity removal leaching solution is obtained.

[0045] The molar ratio of the iron powder to the copper ions in the acidolysis solution is (1-3):1.

[0046] (3) H2O2 is added to the first-stage impurity removal leaching solution to adjust the pH to 3-5, and after filtration, an oxidized leaching solution and a filter cake are obtained.

[0047] The molar ratio of H2O2 to Fe 2+ in the first-stage impurity removal leaching solution is 1:(1-2).

[0048] (4) washing the filter cake to a conductivity of ≤100 μS / cm (for example, it can be 100 μS / cm, 90 μS / cm, 80 μS / cm, 70 μS / cm, 60 μS / cm or 50 μS / cm, etc.), and then drying at 90-130 ℃ (for example, it can be 90 ℃, 100 ℃, 110 ℃, 120 ℃ or 130 ℃, etc.) to free water ≤2% (for example, it can be 2%, 1% or 0.5%, etc.), and then calcining at 550-700 ℃ for 0.5-3 h to obtain the iron phosphate product.

[0049] Adding ferric nitrate to the oxidized leaching solution, adjusting the pH value to 5-7, and filtering to obtain a second impurity removal leaching solution and an iron phosphate product.

[0050] The molar ratio of iron element to phosphorus element in the mixed solution obtained by mixing the oxidized leaching solution and the ferric nitrate is (1-2):1.

[0051] (5) passing the acidolysis recovery gas into the second impurity removal leaching solution, and adding ammonia water to adjust the pH value to 5-7, and filtering to obtain a third impurity removal leaching solution and a filter cake.

[0052] Washing the filter cake to a conductivity of ≤100 μS / cm (for example, it can be 100 μS / cm, 90 μS / cm, 80 μS / cm, 70 μS / cm, 60 μS / cm or 50 μS / cm, etc.) to obtain a lithium carbonate product.

[0053] Concentrating and crystallizing the third impurity removal leaching solution to obtain an ammonium nitrate product and an ammonium carbonate product.

[0054] Preferably, the purity of the lithium carbonate product is greater than 99.6%, for example, it can be 99.7%, 99.8% or 99.9%, etc.

[0055] The numerical ranges described in the present application include not only the point values listed above, but also any point values between the above-listed numerical values, which are not listed due to the limitation of the length and for the sake of simplicity, and the present application does not exhaustively list the specific point values included in the range.

[0056] Compared with the prior art, the present application has the following beneficial effects:

[0057] (1) The present application uses nitric acid solution to comprehensively utilize the lithium iron phosphate black powder, on the one hand, carbon dioxide and nitrogen oxides are generated by self-thermal oxidation, carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, nitrogen oxides generate nitric acid products, and crystallization is sold, realizing resource comprehensive utilization; on the other hand, through multi-process recovery treatment of the acidolysis solution, the comprehensive recovery of carbon element, lithium element, phosphorus element and nitrogen element is effectively realized.

[0058] (2) The recycling method provided by the application has a lithium recovery rate of greater than 95% and a phosphorus recovery rate of greater than 98%, and has high recovery rates.

[0059] (3) The lithium carbonate product and the iron phosphate product obtained by the recycling method provided by the application both meet the preparation requirements of battery-grade lithium iron phosphate materials. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 A process flowchart of the recycling method provided by Example 1 in the application is shown in the figure. DETAILED DESCRIPTION

[0061] The technical solutions of the application will be further described through specific embodiments. It should be understood by those skilled in the art that the embodiments are only used to help understand the application and should not be regarded as specific limitations on the application.

[0062] It should be noted that the component content of the lithium iron phosphate black powder used in the following embodiments is shown in Table 1.

[0063] Table 1

[0064]

[0065] Example 1

[0066] This embodiment provides a recycling method for lithium iron phosphate black powder, and a process flowchart thereof is shown in the figure. Figure 1 The recycling method comprises the following steps:

[0067] (1) The lithium iron phosphate black powder is added to a nitric acid solution with a concentration of 5 mol / L to perform self-thermal decomposition oxidation, to obtain an acidolysis recovery gas and an acidolysis solution, and the acidolysis recovery gas contains carbon dioxide and nitrogen oxides;

[0068] The molar ratio of the lithium iron phosphate black powder to the nitric acid solution is 1:3;

[0069] (2) The acidolysis solution is filtered, and ammonia water is added to adjust the pH value of the acidolysis solution to 2; then iron powder is added to perform copper displacement reaction, and a first impurity removal leaching solution is obtained after filtration;

[0070] The molar ratio of the iron powder to the copper ions in the acidolysis solution is 2:1;

[0071] (3) H2O2 is added to the first impurity removal leaching solution to adjust the pH value to 4, and an oxidation leaching solution and a filter cake are obtained after filtration;

[0072] The molar ratio of H2O2 to Fe 2+ in the first impurity removal leaching solution is 1:1.5;

[0073] (4) washing the filter cake until the conductivity is less than or equal to 100 μS / cm, then drying at 110°C until the free water is less than or equal to 2%, and then calcining at 600°C for 1.5 h to obtain the iron phosphate product;

[0074] adding iron nitrate to the oxidized leaching solution, adjusting the pH value to 6, and filtering to obtain a second impurity removal leaching solution and an iron phosphate product;

[0075] In the mixture obtained by mixing the oxidized leaching solution and the iron nitrate, the molar ratio of iron to phosphorus is 1.5:1.

[0076] (5) passing the acidolysis recovery gas into the second impurity removal leaching solution while adding ammonia water to adjust the pH value to 6, and filtering to obtain a third impurity removal leaching solution and a filter cake;

[0077] washing the filter cake until the conductivity is less than or equal to 100 μS / cm to obtain a lithium carbonate product with a purity of 99.9%;

[0078] concentrating and crystallizing the third impurity removal leaching solution to obtain an ammonium nitrate product and an ammonium carbonate product.

[0079] Example 2

[0080] The present embodiment provides a recycling method for lithium iron phosphate black powder, which comprises the following steps:

[0081] (1) adding lithium iron phosphate black powder into a nitric acid solution with a concentration of 2 mol / L to perform self-thermal oxidation, thereby obtaining an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides;

[0082] In the present embodiment, the molar ratio of lithium iron phosphate black powder to the nitric acid solution is 1:4.

[0083] (2) filtering the acidolysis solution, adding ammonia water to adjust the pH value of the acidolysis solution to 2.5, and then adding iron powder to perform a copper displacement reaction, thereby obtaining a first impurity removal leaching solution after filtration;

[0084] In the present embodiment, the molar ratio of iron powder to copper ions in the acidolysis solution is 3:1.

[0085] (3) adding H2O2 to the first impurity removal leaching solution to adjust the pH value to 3, and filtering to obtain an oxidized leaching solution and a filter cake;

[0086] In the present embodiment, the molar ratio of H2O2 to Fe 2+ in the first impurity removal leaching solution is 1:1.

[0087] (4) washing the filter cake until the conductivity is less than or equal to 100 μS / cm, and then drying at 90°C until the free water is less than or equal to 2%, and then calcining at 550°C for 3h to obtain the iron phosphate product;

[0088] adding iron nitrate to the oxidized leaching solution, adjusting the pH value to 5, and filtering to obtain a second impurity removal leaching solution and an iron phosphate product;

[0089] In the mixture obtained by mixing the oxidized leaching solution and the iron nitrate, the molar ratio of iron to phosphorus is 1:1.

[0090] (5) passing the acidolysis recovery gas into the second impurity removal leaching solution, and adjusting the pH value to 5 by adding ammonia water, and filtering to obtain a third impurity removal leaching solution and a filter cake;

[0091] washing the filter cake until the conductivity is less than or equal to 100 μS / cm to obtain a lithium carbonate product with a purity of 99.8%;

[0092] concentrating and crystallizing the third impurity removal leaching solution to obtain an ammonium nitrate product and an ammonium carbonate product.

[0093] Example 3

[0094] The present embodiment provides a recycling method for lithium iron phosphate black powder, which comprises the following steps:

[0095] (1) adding lithium iron phosphate black powder into a nitric acid solution with a concentration of 8 mol / L to perform self-thermal oxidation, and obtaining an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides;

[0096] In the present embodiment, the molar ratio of lithium iron phosphate black powder to nitric acid solution is 1:2.5.

[0097] (2) filtering the acidolysis solution, and adjusting the pH value of the acidolysis solution to 1.5 by adding ammonia water; and then adding iron powder to perform a copper displacement reaction, and filtering to obtain a first impurity removal leaching solution;

[0098] In the present embodiment, the molar ratio of iron powder to copper ions in the acidolysis solution is 1:1.

[0099] (3) adding H2O2 to the first impurity removal leaching solution, adjusting the pH value to 5, and filtering to obtain an oxidized leaching solution and a filter cake;

[0100] In the present embodiment, the molar ratio of H2O2 to Fe 2+ in the first impurity removal leaching solution is 1:2.

[0101] (4) washing the filter cake to a conductivity of <100 μS / cm, then drying at 130°C to free water <2%, then calcining at 700°C for 0.5 h to obtain the iron phosphate product;

[0102] adding ferric nitrate to the oxidized leach liquor, adjusting the pH to 7, and filtering to obtain a second impurity removal leach liquor and an iron phosphate product;

[0103] wherein the molar ratio of iron to phosphorus in the mixture obtained by mixing the oxidized leach liquor and the ferric nitrate is 2:1;

[0104] (5) passing the acid decomposition recovery gas into the second impurity removal leach liquor while adding ammonia to adjust the pH to 7, and filtering to obtain a third impurity removal leach liquor and a filter cake;

[0105] washing the filter cake to a conductivity of <100 μS / cm to obtain a lithium carbonate product with a purity of 99.7%;

[0106] concentrating and crystallizing the third impurity removal leach liquor to obtain an ammonium nitrate product and an ammonium carbonate product.

[0107] Example 4

[0108] The difference between this example and Example 1 is that the concentration of the nitric acid solution in step (1) is 1 mol / L.

[0109] The rest of the recycling method and parameters are consistent with Example 1.

[0110] Example 5

[0111] The difference between this example and Example 1 is that the concentration of the nitric acid solution in step (1) is 9 mol / L.

[0112] The rest of the recycling method and parameters are consistent with Example 1.

[0113] Example 6

[0114] The difference between this example and Example 1 is that the molar ratio of the lithium iron phosphate black powder to the nitric acid solution in step (1) is 1:2.

[0115] The rest of the recycling method and parameters are consistent with Example 1.

[0116] Example 7

[0117] The difference between this example and Example 1 is that the molar ratio of the lithium iron phosphate black powder to the nitric acid solution in step (1) is 1:4.5.

[0118] The rest of the recycling method and parameters are consistent with Example 1.

[0119] Example 8

[0120] The difference between this example and Example 1 is that the calcination temperature in step (4) is 500°C.

[0121] The rest of the recycling method and parameters remain consistent with Example 1.

[0122] Example 9

[0123] The difference between this example and Example 1 is that the calcination temperature in step (4) is 750°C.

[0124] The rest of the recycling method and parameters remain consistent with Example 1.

[0125] Example 10

[0126] The difference between this example and Example 1 is that no ammonia water is added in step (5).

[0127] The rest of the recycling method and parameters remain consistent with Example 1.

[0128] Comparative Example 1

[0129] The difference between this comparative example and Example 1 is that the nitric acid solution in step (1) is replaced by a sulfuric acid solution.

[0130] The rest of the recycling method and parameters remain consistent with Example 1.

[0131] Comparative Example 2

[0132] The difference between this comparative example and Example 1 is that no acidolysis recovery gas is passed into the two-stage impurity removal leaching solution in step (5).

[0133] The rest of the recycling method and parameters remain consistent with Example 1.

[0134] Performance Test

[0135] The recovery rates of carbon, lithium, phosphorus, and nitrogen elements were detected for the recycling methods provided in the above examples and comparative examples.

[0136] The detection method is: recovery rate = n1 / n x 100%, where n1 is the molar amount of the product element, and n is the molar amount of the corresponding element in the lithium iron phosphate black powder.

[0137] The detection results are shown in Table 1.

[0138] Table 1

[0139]

[0140] Analysis:

[0141] From the above table, the present application uses nitric acid solution to comprehensively utilize the lithium iron phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are generated by self-thermal decomposition and oxidation, carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, nitrogen oxides generate nitric acid products, and crystallization is sold, realizing resource comprehensive utilization; on the other hand, through acidolysis solution multi-process recovery treatment, the comprehensive recovery of carbon elements, lithium elements, phosphorus elements and nitrogen elements is effectively realized. The lithium recovery rate is greater than 95%, the phosphorus recovery rate is greater than 98%, and the recovery rate is high.

[0142] From the comparison of Example 1 and Examples 4-5, if the concentration of the nitric acid solution is too low, the liquid volume is too large, resulting in high energy consumption and cost of evaporation in the rear end, and more evaporation wastewater is generated; if the concentration of the nitric acid solution is too high, the reaction is too fast, the control difficulty is increased, and even the nitrogen oxide waste gas is not collected in time, affecting the environment and safety.

[0143] From the comparison of Example 1 and Examples 6-7, if the molar ratio of lithium iron phosphate black powder and nitric acid solution is too small, the reaction is too fast, the gas volatilization is too fast, and the reaction risk is increased; if the molar ratio of lithium iron phosphate black powder and nitric acid solution is too large, it is not conducive to the dissolution of the black powder and the reaction of the carbon powder.

[0144] From the comparison of Example 1 and Examples 8-9, if the calcination temperature is too low, it is not conducive to the removal of water in the iron phosphate, and the particle size is too fine; if the calcination temperature is too high, the particles are aggregated and verified, which is not conducive to the dispersion in the rear end.

[0145] From the comparison of Example 1 and Example 10, if no ammonia water is added in step (5), the precipitation rate of lithium carbonate is low, and even no precipitation is generated.

[0146] From the comparison of Example 1 and Comparative Example 1, if the nitric acid solution in step (1) is replaced by a sulfuric acid solution, the carbon powder can only be discharged in the form of waste slag, and an additional carbon salt precipitant is required to generate lithium carbonate precipitation.

[0147] From the comparison of Example 1 and Comparative Example 2, if the acidolysis recovery gas is not introduced into the two-stage impurity removal leaching liquid in step (5), lithium ions cannot be precipitated, and an additional carbon salt precipitant is required

[0148] The applicant declares that the process method of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, i.e. it does not mean that the present application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement on the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the present application.

Claims

1. A method for recycling lithium iron phosphate black powder, characterized in that, The recycling method comprises the following steps: Mixing lithium iron phosphate black powder and nitric acid solution, and performing self-thermal decomposition oxidation to obtain acidolysis recovery gas and acidolysis solution, the acidolysis recovery gas containing carbon dioxide and nitrogen oxides; the concentration of the nitric acid solution is 3-8 mol / L; Performing one-stage impurity removal leaching and oxidative leaching on the acidolysis solution, and performing solid-liquid separation to obtain oxidative leaching solution and filter cake; Performing calcination on the filter cake to obtain a phosphoric iron product; and performing two-stage impurity removal leaching on the oxidative leaching solution to obtain two-stage impurity removal leaching solution; Passing the acidolysis recovery gas into the two-stage impurity removal leaching solution to perform three-stage impurity removal leaching, and performing solid-liquid separation to obtain three-stage impurity removal leaching solution and lithium carbonate product; concentrating and crystallizing the three-stage impurity removal leaching solution to obtain nitric acid product and carbonic acid product; and adding ammonia water to adjust the pH value to 5-7 during the process of passing the acidolysis recovery gas into the two-stage impurity removal leaching solution.

2. The recycling method according to claim 1, characterized in that, The molar ratio of the lithium iron phosphate black powder to the nitric acid solution is 1:(2.5-4).

3. The recycling method according to claim 1, characterized in that, The one-stage impurity removal leaching method comprises the following steps: Adjusting the pH value of the acidolysis solution to 1.5-2.5, and then adding a copper displacement agent to perform copper displacement reaction to obtain one-stage impurity removal leaching solution.

4. The recycling method according to claim 3, characterized in that, The displacement agent comprises iron powder.

5. The recycling method according to claim 3, characterized in that, The molar ratio of the displacement agent to copper ions in the acidolysis solution is (1-3):

1.

6. The recycling method according to claim 3, characterized in that, The oxidative leaching method comprises the following steps: Mixing the one-stage impurity removal leaching solution and an oxidizing agent, and adjusting the pH value to 3-5.

7. The recycling method according to claim 6, characterized in that, The oxidizing agent comprises H2O2.

8. The recycling method according to claim 6, characterized in that, The oxidant and Fe in the first stage of impurity removal leachate 2+ The molar ratio is 1:(1-2).

9. The recycling method of claim 1, wherein, The calcination temperature is 550-700℃.

10. The recycling method of claim 1, wherein, The calcination time is 0.5-3h.

11. The recycling method of claim 1, wherein, The two-stage impurity removal leaching method comprises the following steps: Mixing the oxidative leaching solution and a phosphorus displacement agent, adjusting the pH value to 5-7, and filtering.

12. The recycling method of claim 11, wherein, The phosphorus displacement agent comprises an iron salt.

13. The recycling method of claim 12, wherein, The iron salt comprises any one or a combination of at least two of iron nitrate, iron sulfate or iron chloride.

14. The recycling method according to claim 13, characterized in that, The iron salt is iron nitrate.

15. The recycling method of claim 12, wherein, The molar ratio of iron element to phosphorus element in the mixed solution obtained by mixing the oxidative leaching solution and the iron salt is (1-2):

1.

16. The recycling method of claim 1, wherein, The recycling method comprises the following steps: (1) adding lithium iron phosphate black powder into a nitric acid solution with a concentration of 3-8 mol / L to perform self-thermal decomposition oxidation, to obtain acidolysis recovery gas and acidolysis solution, the acidolysis recovery gas containing carbon dioxide and nitrogen oxides; wherein the molar ratio of the lithium iron phosphate black powder to the nitric acid solution is 1:(2.5-4); (2) filtering the acidolysis solution, and adding ammonia water to adjust the pH value of the acidolysis solution to 1.5-2.5; then adding iron powder to perform copper displacement reaction, and filtering to obtain one-stage impurity removal leaching solution; wherein the molar ratio of the iron powder to copper ions in the acidolysis solution is (1-3):1; (3) adding H2O2 into the one-stage impurity removal leaching solution, adjusting the pH value to 3-5, and filtering to obtain oxidative leaching solution and filter cake; Among them, H2O2 and Fe in a first-stage impurity removal leachate 2+ The molar ratio is 1:(1-2); (4) washing the filter cake to a conductivity of ≤100 μS / cm, then drying at 90-130℃ to a free water content of ≤2%, and then calcining at 550-700℃ for 0.5-3h to obtain a phosphoric iron product; The iron nitrate is added to the oxidizing leaching solution, the pH value is adjusted to 5-7, and filtration is performed to obtain a second impurity removal leaching solution and an iron phosphate product; In the mixed solution obtained by mixing the oxidizing leaching solution and the iron nitrate, the molar ratio of iron elements to phosphorus elements is (1-2):1; (5) The acidolysis recovery gas is introduced into the second impurity removal leaching solution, ammonia water is added to adjust the pH value to 5-7, and filtration is performed to obtain a third impurity removal leaching solution and a filter cake; The filter cake is washed until the conductivity is less than or equal to 100 μS / cm to obtain a lithium carbonate product; The third impurity removal leaching solution is concentrated and crystallized to obtain an ammonium nitrate product and an ammonium carbonate product.

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