Recycling method of lithium iron phosphate black powder

Abstract

The invention provides a recycling method of lithium iron phosphate black powder. The recycling method comprises the following steps that lithium iron phosphate black powder and a nitric acid solution are mixed and subjected to self-pyrolysis oxidation, acidolysis recovery gas and an acidolysis solution are obtained, and the acidolysis recovery gas contains carbon dioxide and nitric oxide; carrying out first-stage impurity removal leaching and oxidation leaching on the acidolysis solution, and carrying out solid-liquid separation to obtain an oxidation leaching solution and a filter cake; calcining the filter cake to obtain an iron phosphate product; carrying out second-stage impurity removal leaching on the oxidation leaching solution to obtain a second-stage impurity removal leaching solution; an acidolysis recovery gas is introduced into the second-stage impurity removal leaching solution, third-stage impurity removal leaching is carried out, and a third-stage impurity removal leaching solution and a lithium carbonate product are obtained after solid-liquid separation; and concentrating and crystallizing the third-stage impurity-removed leachate to obtain nitric acid products and carbonic acid products. The lithium iron phosphate black powder is comprehensively utilized by adopting the nitric acid solution, comprehensive recovery of carbon, lithium, phosphorus and nitrogen elements is achieved, the lithium recovery rate is larger than 95%, and the phosphorus recovery rate is larger than 98%.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery recycling, and specifically relates to a method for recycling lithium iron phosphate black powder. Background Art

[0002] In recent years, the new energy industry has been booming under this situation. In the field of electric vehicles, lithium iron phosphate batteries have received widespread attention due to their excellent stability and excellent safety. With the widespread application of lithium iron phosphate batteries, a large number of scrapped lithium iron phosphate batteries have appeared. If they are not handled in a timely and good manner, they will not only cause serious harm to the environment and human health, but also cause a huge waste of resources. From the perspective of resource reuse, waste lithium iron phosphate batteries have significant resource value. The metal elements such as Li in them are of high value, and efficient recycling 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 protecting the ecological environment and human health. Therefore, the recycling of waste lithium iron phosphate batteries is imperative.

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

[0004] Therefore, there is an urgent need to provide a method for recycling lithium iron phosphate black powder with a high recovery rate, so as to comprehensively recover the carbon element, lithium element and phosphorus element in the lithium iron phosphate black powder and realize the recycling of resources. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for recycling lithium iron phosphate black powder. The present invention uses nitric acid solution to comprehensively utilize lithium iron phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are produced by self-pyrolysis oxidation. Carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, and nitrogen oxides generate nitric acid products, which are crystallized and sold out to achieve comprehensive resource utilization; on the other hand, multi-step recycling treatment is carried out through acid hydrolysis solution, which effectively realizes the comprehensive recovery of carbon, lithium, phosphorus and nitrogen. In the recycling method provided by the present invention, the lithium recovery rate is greater than 95%, the phosphorus recovery rate is greater than 98%, and the recovery rate is high.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for recycling lithium iron phosphate black powder, the recycling method comprising the following steps:

[0008] The lithium iron phosphate black powder and the nitric acid solution are mixed and subjected to self-thermal oxidation to obtain an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides.

[0009] The acid hydrolysis solution is subjected to a stage of impurity removal leaching and 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 an iron phosphate product; the oxidation leaching solution is subjected to two-stage impurity removal leaching to obtain a two-stage impurity removal leaching solution.

[0011] The acid hydrolysis recovery gas is introduced into the second-stage impurity removal leaching solution to carry out the third-stage impurity removal leaching, and the third-stage impurity removal leaching solution and the lithium carbonate product are obtained after solid-liquid separation; the third-stage impurity removal leaching solution is concentrated and crystallized to obtain nitric acid products and carbonic acid products.

[0012] The present invention uses nitric acid solution to comprehensively utilize lithium iron phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are produced by self-pyrolysis oxidation. Carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, and nitrogen oxides generate nitric acid products, which are crystallized and sold out to achieve comprehensive resource utilization. On the other hand, multi-step recycling treatment is carried out by acid hydrolysis solution, which effectively realizes the comprehensive recovery of carbon, lithium, phosphorus and nitrogen. In the recycling method provided by the present invention, 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.

[0014] In the present invention, a nitric acid solution with an appropriate concentration helps to improve the dissolution rate of black powder while reducing the dissolution cost and the back-end evaporation and crystallization cost.

[0015] Preferably, the molar ratio of the lithium iron phosphate black powder to 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.

[0016] In the present invention, the lithium iron phosphate black powder and the nitric acid solution with a suitable molar ratio (molar ratio refers to the ratio of the molar amount of black powder calculated based on lithium iron phosphate to nitric acid) are helpful to fully improve the dissolution rate of the black powder.

[0017] Preferably, the one-stage impurity removal and leaching method comprises:

[0018] The pH value of the acid hydrolysis solution is adjusted to 1.5-2.5 (for example, it can be 1.5, 2 or 2.5, etc.), and then a copper replacement agent is added to carry out a copper replacement reaction to obtain a first-stage impurity-removing leaching solution.

[0019] The purpose of the one-stage impurity removal leaching in the present invention is to remove copper impurities.

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

[0021] Preferably, the molar ratio of the displacing agent to the copper ions in the acid hydrolysis solution is (1-3):1, for example, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1.

[0022] The present invention adopts the above molar ratio, which is helpful for completely removing copper impurities.

[0023] Preferably, the oxidative leaching method comprises:

[0024] A first stage impurity removal leaching solution and an oxidant are mixed, and the pH value is adjusted to 3-5, for example, 3, 4 or 5.

[0025] In the present invention, the purpose of adding an oxidant and adjusting the pH value to 3-5 is to make the Fe 2+ Convert to Fe 3+ .

[0026] Preferably, the oxidant comprises H2O2.

[0027] Preferably, the oxidant and the Fe 2+ The molar ratio is 1:(1-2), for example, it can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8 or 1:2, etc.

[0028] In the present invention, the above molar ratio helps to make the Fe in the first stage impurity removal leachate 2+ Completely converted to Fe 3+ .

[0029] Preferably, the calcination temperature is 550-700°C, for example, 550°C, 600°C, 650°C or 700°C.

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

[0031] Preferably, the calcination time is 0.5-3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h.

[0032] Preferably, the two-stage impurity removal and leaching method comprises:

[0033] The oxidation leaching solution and the phosphorus replacement agent are mixed, the pH value is adjusted to 5-7 (for example, 5, 6 or 7, etc.), and filtered.

[0034] In the present invention, the purpose of adding a phosphorus replacement agent and adjusting the pH value to 5-7 is to remove phosphorus in the oxidation leaching solution.

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

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

[0037] In the present invention, the type of iron salt will affect the purity of the final by-product. Ferric sulfate or ferric chloride will introduce other anions and increase impurities, so ferric nitrate is preferred.

[0038] Preferably, in the mixed solution obtained by mixing the oxidizing leaching solution and the iron salt, the molar ratio of iron element to phosphorus element 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.

[0039] Preferably, during the process of introducing the acid hydrolysis recovery gas into the second-stage impurity removal leaching solution, ammonia water is added to adjust the pH to 5-7, for example, 5, 6 or 7.

[0040] In the present invention, 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) Adding lithium iron phosphate black powder to a nitric acid solution with a concentration of 2-8 mol / L, and performing self-thermal oxidation to obtain an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides.

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

[0044] (2) filtering the acid hydrolysis solution, and adding ammonia water to adjust the pH value of the acid hydrolysis solution to 1.5-2.5; then adding iron powder to carry out copper replacement reaction, and filtering to obtain a section of impurity-removed leaching solution.

[0045] Wherein, the molar ratio of the iron powder to the copper ions in the acid hydrolysis solution is (1-3):1.

[0046] (3) adding H2O2 to the first stage impurity removal leaching solution, adjusting the pH value to 3-5, and filtering to obtain an oxidized leaching solution and a filter cake.

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

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

[0049] Add ferric nitrate to the oxidizing leaching solution, adjust the pH value to 5-7, filter, and obtain a second-stage impurity-removed leaching solution and an iron phosphate product.

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

[0051] (5) introducing the acid hydrolysis recovery gas into the second-stage impurity-removed leaching solution, and adding ammonia water to adjust the pH value to 5-7, filtering, and obtaining the third-stage impurity-removed leaching solution and filter cake.

[0052] The filter cake is washed until the conductivity is ≤100 μS / cm (for example, 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] The three-stage impurity-removed leaching solution is concentrated and crystallized to obtain ammonium nitrate product and ammonium carbonate product.

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

[0055] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

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

[0057] (1) The present invention uses nitric acid solution to comprehensively utilize lithium iron phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are produced through self-thermal oxidation. The carbon dioxide is used as a carbon source for the preparation and carbonization of lithium carbonate, and the nitrogen oxides are used to generate nitric acid products, which are crystallized and sold out to achieve comprehensive resource utilization. On the other hand, the acid hydrolysis solution is used for multi-step recovery treatment, thereby effectively achieving comprehensive recovery of carbon, lithium, phosphorus and nitrogen.

[0058] (2) In the recycling method provided by the present invention, the lithium recovery rate is greater than 95%, and the phosphorus recovery rate is greater than 98%, and the recovery rate is high.

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

[0060] Figure 1 This is a process flow chart of the recycling method provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0061] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

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

[0063] Table 1

[0064]

[0065] Example 1

[0066] This embodiment provides a method for recycling lithium iron phosphate black powder, and its process flow chart is as follows: Figure 1 As shown, the recycling method comprises the following steps:

[0067] (1) adding lithium iron phosphate black powder to a nitric acid solution with a concentration of 5 mol / L to perform autothermal oxidation to obtain an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides;

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

[0069] (2) filtering the acid hydrolysis solution and adding ammonia water to adjust the pH value of the acid hydrolysis solution to 2; then adding iron powder to carry out copper replacement reaction, and filtering to obtain a section of impurity-removed leaching solution;

[0070] Wherein, the molar ratio of iron powder to copper ions in the acid solution is 2:1;

[0071] (3) adding H2O2 to the first stage impurity-removing leachate, adjusting the pH value to 4, and filtering to obtain an oxidized leachate and a filter cake;

[0072] Among them, H2O2 and Fe in the first stage impurity removal leaching solution 2+ The molar ratio is 1:1.5;

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

[0074] Adding ferric nitrate to the oxidizing leaching solution, adjusting the pH value to 6, filtering, and obtaining a second-stage impurity-removed leaching solution and an iron phosphate product;

[0075] Wherein, in the mixed solution obtained by mixing the oxidation leaching solution and ferric nitrate, the molar ratio of iron element to phosphorus element is 1.5:1;

[0076] (5) introducing the acid hydrolysis recovery gas into the second-stage impurity-removed leachate, adding ammonia water to adjust the pH value to 6, and filtering to obtain a third-stage impurity-removed leachate and a filter cake;

[0077] The filter cake is washed until the conductivity is ≤100 μS / cm to obtain a lithium carbonate product with a purity of 99.9%;

[0078] The three-stage impurity-removed leaching solution is concentrated and crystallized to obtain ammonium nitrate product and ammonium carbonate product.

[0079] Example 2

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

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

[0082] Wherein, the molar ratio of lithium iron phosphate black powder to nitric acid solution is 1:4;

[0083] (2) filtering the acid hydrolysis solution and adding ammonia water to adjust the pH value of the acid hydrolysis solution to 2.5; then adding iron powder to carry out copper replacement reaction, and filtering to obtain a section of impurity-removed leaching solution;

[0084] The molar ratio of the iron powder to the copper ions in the acid solution is 3:1;

[0085] (3) adding H2O2 to the first stage impurity-removing leachate, adjusting the pH value to 3, and filtering to obtain an oxidized leachate and a filter cake;

[0086] Among them, H2O2 and Fe in the first stage impurity removal leaching solution 2+ The molar ratio is 1:1;

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

[0088] Adding ferric nitrate to the oxidizing leaching solution, adjusting the pH value to 5, filtering, and obtaining a second-stage impurity-removed leaching solution and an iron phosphate product;

[0089] Wherein, in the mixed solution obtained by mixing the oxidation leaching solution and ferric nitrate, the molar ratio of iron element to phosphorus element is 1:1;

[0090] (5) introducing the acid hydrolysis recovery gas into the second-stage impurity-removed leachate, adding ammonia water to adjust the pH value to 5, and filtering to obtain a third-stage impurity-removed leachate and a filter cake;

[0091] The filter cake is washed until the conductivity is ≤100 μS / cm to obtain a lithium carbonate product with a purity of 99.8%;

[0092] The three-stage impurity-removed leaching solution is concentrated and crystallized to obtain ammonium nitrate product and ammonium carbonate product.

[0093] Example 3

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

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

[0096] Wherein, the molar ratio of lithium iron phosphate black powder to nitric acid solution is 1:2.5;

[0097] (2) filtering the acid hydrolysis solution and adding ammonia water to adjust the pH value of the acid hydrolysis solution to 1.5; then adding iron powder to carry out copper replacement reaction, and filtering to obtain a section of impurity-removed leaching solution;

[0098] Wherein, the molar ratio of the iron powder to the copper ions in the acid hydrolysis solution is 1:1;

[0099] (3) adding H2O2 to the first stage impurity-removing leachate, adjusting the pH value to 5, and filtering to obtain an oxidized leachate and a filter cake;

[0100] Among them, H2O2 and Fe in the first stage impurity removal leaching solution 2+ The molar ratio is 1:2;

[0101] (4) washing the filter cake until the conductivity is ≤100 μS / cm, then drying at 130° C. until the free water content is ≤2%, and then calcining at 700° C. for 0.5 h to obtain an iron phosphate product;

[0102] Adding ferric nitrate to the oxidizing leaching solution, adjusting the pH value to 7, filtering, and obtaining a second-stage impurity-removed leaching solution and an iron phosphate product;

[0103] Wherein, in the mixed solution obtained by mixing the oxidation leaching solution and ferric nitrate, the molar ratio of iron element to phosphorus element is 2:1;

[0104] (5) introducing the acid hydrolysis recovery gas into the second-stage impurity-removed leachate, adding ammonia water to adjust the pH value to 7, and filtering to obtain a third-stage impurity-removed leachate and a filter cake;

[0105] The filter cake is washed until the conductivity is ≤100 μS / cm to obtain a lithium carbonate product with a purity of 99.7%;

[0106] The three-stage impurity-removed leaching solution is concentrated and crystallized to obtain ammonium nitrate product and ammonium carbonate product.

[0107] Example 4

[0108] The difference between this embodiment and embodiment 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 remain the same as in Example 1.

[0110] Example 5

[0111] The difference between this embodiment and embodiment 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 remain the same as in Example 1.

[0113] Example 6

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

[0115] The rest of the recycling method and parameters remain the same as in Example 1.

[0116] Example 7

[0117] The difference between this embodiment and embodiment 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 remain the same as in Example 1.

[0119] Example 8

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

[0121] The rest of the recycling method and parameters remain the same as in Example 1.

[0122] Example 9

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

[0124] The rest of the recycling method and parameters remain the same as in Example 1.

[0125] Example 10

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

[0127] The rest of the recycling method and parameters remain the same as in 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 sulfuric acid solution.

[0130] The rest of the recycling method and parameters remain the same as in Example 1.

[0131] Comparative Example 2

[0132] The difference between this comparative example and Example 1 is that in step (5), the acid hydrolysis recovery gas is not introduced into the second-stage impurity removal leachate.

[0133] The rest of the recycling method and parameters remain the same as in Example 1.

[0134] Performance Testing

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

[0136] The detection method is: recovery rate = n1 / n×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 test results are shown in Table 1.

[0138] Table 1

[0139]

[0140] analyze:

[0141] As can be seen from the above table, the present invention uses nitric acid solution to comprehensively utilize lithium iron phosphate black powder. On the one hand, carbon dioxide and nitrogen oxides are produced through self-pyrolysis oxidation. Carbon dioxide is used as a carbon source for lithium carbonate preparation and carbonization, and nitrogen oxides generate nitric acid products, which are crystallized and sold out to achieve comprehensive resource utilization; on the other hand, multi-step recycling treatment is carried out through acid hydrolysis solution, which effectively realizes the comprehensive recovery of carbon, lithium, phosphorus and nitrogen. The lithium recovery rate is greater than 95%, and the phosphorus recovery rate is greater than 98%, with high recovery rates.

[0142] By comparing Example 1 with Examples 4-5, it can be seen that if the concentration of the nitric acid solution is too low, the amount of liquid is too large, resulting in too high energy consumption and cost of evaporation at the back 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 increases, and even the nitrogen oxide waste gas cannot be collected in time, affecting the environment and safety.

[0143] By comparing Example 1 with Examples 6-7, it can be seen that if the molar ratio of lithium iron phosphate black powder and nitric acid solution is too small, the reaction will be too fast, the gas will evaporate too quickly, and the risk of the reaction will increase; if the molar ratio of lithium iron phosphate black powder and nitric acid solution is too large, it will be unfavorable for the dissolution of black powder and the reaction of carbon powder.

[0144] By comparing Example 1 with Examples 8-9, it can be seen that if the calcination temperature is too low, it is not conducive to the removal of moisture in the ferric phosphate and the particle size is too fine; if the calcination temperature is too high, the particles agglomerate, which is not conducive to rear-end dispersion.

[0145] By comparing Example 1 with Example 10, it can be seen that if no ammonia water is added in step (5), the precipitation rate of lithium carbonate is low or even no precipitation occurs.

[0146] By comparing Example 1 with Comparative Example 1, it can be seen that 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 residue, and an additional carbonate precipitant needs to be added to produce lithium carbonate precipitation.

[0147] By comparing Example 1 with Comparative Example 2, it can be seen that if the acid hydrolysis recovery gas is not introduced into the second-stage impurity removal leachate in step (5), lithium ions cannot be precipitated and an external carbonate precipitant is required.

[0148] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recycling lithium iron phosphate black powder, characterized in that: The recycling method comprises the following steps: The lithium iron phosphate black powder and the nitric acid solution are mixed and subjected to autothermal oxidation to obtain an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides; The acid hydrolysis solution is subjected to a stage of impurity removal leaching and oxidation leaching, and solid-liquid separation is performed to obtain an oxidation leaching solution and a filter cake; The filter cake is calcined to obtain an iron phosphate product; the oxidation leaching solution is subjected to a two-stage impurity removal leaching to obtain a two-stage impurity removal leaching solution; The acid hydrolysis recovery gas is introduced into the second-stage impurity removal leaching solution to carry out the third-stage impurity removal leaching, and the third-stage impurity removal leaching solution and the lithium carbonate product are obtained after solid-liquid separation; the third-stage impurity removal leaching solution is concentrated and crystallized to obtain nitric acid products and carbonic acid products.

2. The recycling method according to claim 1, characterized in that: The concentration of the nitric acid solution is 2-8 mol / L; Preferably, 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 or 2, characterized in that: The one-stage impurity removal and leaching method comprises: The pH value of the acid hydrolysis solution is adjusted to 1.5-2.5, and then a copper replacement agent is added to carry out a copper replacement reaction to obtain a first-stage impurity-removing leaching solution.

4. The recycling method according to claim 3, characterized in that: The displacing agent includes iron powder; Preferably, the molar ratio of the displacing agent to the copper ions in the acidolysis solution is (1-3):

1.

5. The recycling method according to claim 3 or 4, characterized in that: The oxidation leaching method comprises: Mix the first stage impurity removal leaching solution and the oxidant, and adjust the pH value to 3-5; Preferably, the oxidant comprises H2O2; Preferably, the oxidant and the Fe 2+ The molar ratio is 1:(1-2).

6. The recycling method according to any one of claims 1 to 5, characterized in that: The calcination temperature is 550-700°C; Preferably, the calcination time is 0.5-3h.

7. The recycling method according to any one of claims 1 to 6, characterized in that: The two-stage impurity removal and leaching method comprises: The oxidation leaching solution and the phosphorus replacement agent are mixed, the pH value is adjusted to 5-7, and filtered.

8. The recycling method according to claim 7, characterized in that: The phosphorus replacement agent includes an iron salt; Preferably, the iron salt comprises any one of ferric nitrate, ferric sulfate or ferric chloride or a combination of at least two thereof, preferably ferric nitrate; Preferably, in the mixed solution obtained by mixing the oxidizing leaching solution and the iron salt, the molar ratio of iron element to phosphorus element is (1-2):

1.

9. The recycling method according to any one of claims 1 to 8, characterized in that: The acid decomposition recovery gas is introduced into the second-stage impurity removal leaching solution, and ammonia water is added to adjust the pH to 5-7.

10. The recycling method according to any one of claims 1 to 9, characterized in that: The recycling method comprises the following steps: (1) adding lithium iron phosphate black powder to a nitric acid solution with a concentration of 2-8 mol / L, and performing autothermal oxidation to obtain an acidolysis recovery gas and an acidolysis solution, wherein the acidolysis recovery gas contains carbon dioxide and nitrogen oxides; Wherein, the molar ratio of lithium iron phosphate black powder to nitric acid solution is 1:(2.5-4); (2) filtering the acid hydrolysis solution and adding ammonia water to adjust the pH value of the acid hydrolysis solution to 1.5-2.5; then adding iron powder to carry out copper replacement reaction, and filtering to obtain a section of impurity-removed leaching solution; Wherein, the molar ratio of the iron powder to the copper ions in the acid hydrolysis solution is (1-3):1; (3) adding H2O2 to the first stage impurity-removing leachate, adjusting the pH value to 3-5, and filtering to obtain an oxidized leachate and a filter cake; Among them, H2O2 and Fe in the first stage impurity removal leaching solution 2+ The molar ratio is 1:(1-2); (4) washing the filter cake until the conductivity is ≤100 μS / cm, then drying at 90-130° C. until the free water content is ≤2%, and then calcining at 550-700° C. for 0.5-3 h to obtain an iron phosphate product; Adding ferric nitrate to the oxidizing leaching solution, adjusting the pH value to 5-7, filtering, and obtaining a second-stage impurity-removed leaching solution and an iron phosphate product; Wherein, in the mixed solution obtained by mixing the oxidation leaching solution and ferric nitrate, the molar ratio of iron element to phosphorus element is (1-2):1; (5) introducing the acid hydrolysis recovery gas into the second-stage impurity-removed leachate, adding ammonia water to adjust the pH value to 5-7, and filtering to obtain a third-stage impurity-removed leachate and a filter cake; Washing the filter cake until the conductivity is ≤100 μS / cm to obtain a lithium carbonate product; The three-stage impurity-removed leaching solution is concentrated and crystallized to obtain ammonium nitrate product and ammonium carbonate product.

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