Treatment method of waste lithium iron phosphate black powder

Abstract

The invention discloses a waste lithium iron phosphate black powder treatment method, which comprises: 1) carrying out acid leaching on lithium iron phosphate black powder to obtain a leaching solution; (2) Cu and Al are removed from the leachate, and impurity-removed liquid is obtained; (3) carrying out electrolytic reaction by taking the impurity removal liquid as cathode liquid to obtain crude electrolytic iron at a cathode; (4) adding a first precipitator into the electrolyzed barren solution to adjust the pH value, and carrying out solid-liquid separation after reaction to obtain a lithium-precipitated solution and lithium phosphate; (5) adding a second precipitant into the lithium-precipitated liquid, and carrying out solid-liquid separation after reaction to obtain phosphate slag; and 6) reacting acid with the phosphate slag, and carrying out solid-liquid separation to obtain phosphoric acid. According to the method disclosed by the invention, iron, lithium and phosphorus in the waste lithium iron phosphate positive electrode black powder are respectively recovered and prepared into iron powder, lithium phosphate and phosphoric acid, so that the recovery direction and the product type are expanded. Moreover, all-element recovery and resource treatment of the waste lithium iron phosphate positive electrode black powder are realized, and the environmental protection pressure is effectively relieved.

Description

Technical Field

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

[0002] Lithium iron phosphate is a commonly used positive electrode material in batteries. It is widely used in batteries because of its advantages such as environmental protection, good safety, and high discharge platform. A large amount of waste lithium iron phosphate positive electrode black powder is generated in the battery preparation process and after use, which contains a large amount of lithium, iron and phosphorus. The comprehensive recycling of waste lithium iron phosphate positive electrode black powder has attracted more and more attention.

[0003] The current treatment method is usually to use full leaching or selective leaching to recover the lithium as lithium carbonate or lithium hydroxide, and to recover the iron and phosphorus to prepare iron phosphate or directly discard them into landfill.

[0004] CN114421042A discloses a method for recovering metallic aluminum, lithium carbonate and sodium nitrate from waste lithium iron phosphate materials and its application. The method comprises: S1: separating aluminum foil and lithium iron phosphate powder from lithium iron phosphate positive electrode materials; S2: adding acid and hydrogen peroxide to the lithium iron phosphate powder, and separating to obtain iron phosphate precipitate and primary leachate after reaction; S3: adding saturated sodium carbonate solution to the primary leachate, and separating to obtain lithium carbonate and secondary leachate after reaction; S4: evaporating and crystallizing the secondary leachate to recover sodium nitrate.

[0005] CN116768248A discloses a method for recycling lithium iron phosphate battery waste to produce battery-grade lithium carbonate, comprising the following steps: providing lithium iron phosphate waste, adding the lithium iron phosphate waste powder into a lithium sulfate solution, stirring to obtain a slurry, then adding an acid solution, an auxiliary agent and an oxidant into the slurry for oxidative leaching, filtering the obtained leaching solution once, adding an alkaline regulator to the obtained primary filtrate, filtering twice, then adding sodium carbonate to the secondary filtrate, filtering three times, drying the obtained solid, crushing it, adding it to water, and obtaining the final product after carbonization reaction and two purifications.

[0006] CN117602607A discloses a method for recycling and utilizing waste lithium iron phosphate batteries to prepare lithium iron phosphate, comprising the following steps: disassembling waste lithium iron phosphate batteries to obtain lithium iron phosphate positive electrode powder; adding to an acid aqueous solution to obtain an aqueous solution containing iron salt and lithium salt; adjusting pH, adding an auxiliary agent A, reacting; standing, filtering, obtaining a filtrate, and measuring Fe in the filtrate. 2+ Molar concentration and Li + Molar concentration; adjust Fe 2+concentration, adding a phosphorus source and hexadecyltrimethylammonium bromide, adding an oxidant to react, and obtaining iron phosphate; combining the filtrate and the water washing solution, concentrating, adding a carbonate, reacting, and obtaining lithium carbonate; mixing the lithium carbonate with acetic acid, stirring, and evaporating and crystallizing to obtain lithium acetate; preparing a lithium acetate solution, adding a reducing agent and iron phosphate, and reacting to obtain a lithium iron phosphate precursor; mixing evenly with a carbon source, and calcining in the absence of oxygen, and obtaining lithium iron phosphate.

[0007] However, among the recycled products, lithium products are mainly lithium carbonate or lithium hydroxide, and phosphorus and iron products are mainly iron phosphate, which is too single. In addition, considering that a large number of companies have invested in iron phosphate production lines in recent years, the market supply of iron phosphate is oversupply and the market is sluggish. In order to alleviate this situation, it is urgent to develop new process products to deal with the current treatment status of lithium iron phosphate positive electrode black powder. Summary of the invention

[0008] In view of the above technical problems existing in the prior art, the purpose of the present invention is to provide a method for treating waste lithium iron phosphate black powder. The present invention provides a new recycling idea for waste lithium iron phosphate black powder, and the three elements of iron, lithium and phosphorus in the waste lithium iron phosphate positive electrode black powder are recycled and prepared into iron powder, lithium phosphate and phosphoric acid, respectively, expanding the recycling direction and product types. Moreover, the present invention realizes the full element recycling and resource disposal of waste lithium iron phosphate positive electrode black powder, effectively alleviating the environmental pressure.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for treating waste lithium iron phosphate black powder, the method comprising the following steps:

[0011] (1) acid leaching the lithium iron phosphate black powder to obtain a leachate;

[0012] (2) removing impurities from the leaching solution to remove Cu and Al, thereby obtaining a de-impurity solution;

[0013] (3) using the impurity removal liquid as cathode liquid to carry out electrolytic reaction to obtain crude electrolytic iron at the cathode;

[0014] (4) adding a first precipitant to the electrolytic lean solution after electrolysis to adjust the pH, and performing solid-liquid separation after the reaction to obtain a lithium precipitated solution and lithium phosphate;

[0015] (5) adding a second precipitant to the lithium precipitated liquid, and performing solid-liquid separation after the reaction to obtain phosphate slag;

[0016] (6) Using an acid to react with the phosphate slag, and obtaining phosphoric acid after solid-liquid separation.

[0017] The present invention provides a new recycling idea for waste lithium iron phosphate black powder, which recycles the three elements of iron, lithium and phosphorus in waste lithium iron phosphate positive electrode black powder into iron powder, lithium phosphate and phosphoric acid, respectively, expanding the recycling direction and product types. Moreover, the present invention realizes the full element recycling and resource disposal of waste lithium iron phosphate positive electrode black powder, effectively alleviating environmental pressure.

[0018] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0019] Preferably, the acid used for the acid leaching in step (1) comprises any one of sulfuric acid or hydrochloric acid, or a combination of the two.

[0020] Preferably, in the acid leaching step of step (1), the amount of acid used is 1.05-1.2 times the theoretical total leaching requirement of iron and lithium elements, for example, it can be 1.05 times, 1.08 times, 1.1 times, 1.12 times, 1.15 times, 1.17 times, 1.18 times or 1.2 times, etc.

[0021] Preferably, the impurity remover used in step (2) comprises impurity remover A and impurity remover B, wherein the impurity remover A comprises any one of sodium sulfide or iron powder or a combination of the two, and the impurity remover B comprises sodium fluoride.

[0022] Preferably, the dosage of the impurity remover is 2-5 times of the theoretical amount required to remove the impurities Cu and Al, for example, it can be 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times or 5 times.

[0023] Preferably, the electrolysis reaction in step (3) is carried out in an electrolytic cell, using a diaphragm electrolysis method, the anode is any one of a lead-silver alloy, a titanium-based inert metal coating plate, a titanium-based lead dioxide or a manganese dioxide coating plate, and the cathode is a stainless steel plate. The stainless steel plate can be a highly polished stainless steel plate.

[0024] Preferably, during the electrolysis reaction in step (3), the pH of the cathode liquid is maintained in the range of 3.0-5.0, and the pH may be, for example, 3.0, 3.2, 3.5, 3.7, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8 or 5.0.

[0025] Preferably, the current density of the electrolysis reaction in step (3) is 500-5000A / m 2 , for example, it can be 500A / m 2 、550A / m 2 、600A / m 2 , 700A / m 2、800A / m 2 , 900A / m 2 , 1000A / m 2 , 1200A / m 2 、1300A / m 2 、1400A / m 2 、1500A / m 2 、1600A / m 2 、1800A / m 2 、2000A / m 2 、2200A / m 2 、2300A / m 2 、2500A / m 2 、2600A / m 2 、2700A / m 2 、2800A / m 2 、3000A / m 2 、3250A / m 2 、3500A / m 2 、3650A / m 2 、3800A / m 2 、4000A / m 2 、4100A / m 2 、4300A / m 2 、4400A / m 2 、4500A / m 2 、4650A / m 2 、4800A / m 2 or 5000A / m 2 Etc., preferably 500-2000A / m 2 .

[0026] Preferably, the method further comprises washing, crushing, screening and drying the crude electrolytic iron to obtain treated crude electrolytic iron.

[0027] As a preferred technical solution of the method of the present invention, the method also includes a step of reducing the treated crude electrolytic iron, and the reduction step includes: heating the crude electrolytic iron under the action of a reducing gas to obtain high-purity electrolytic iron.

[0028] Preferably, the reducing gas comprises hydrogen.

[0029] Preferably, the temperature of the heat treatment is 750-1000°C, for example, it can be 750°C, 760°C, 770°C, 780°C, 800°C, 850°C, 880°C, 900°C, 925°C, 950°C, 975°C or 1000°C.

[0030] As a preferred technical solution of the method of the present invention, the method further comprises, after step (3) and before step (4), removing impurities from the electrolytic barren solution and using the impurity-removed solution in step (4), wherein the impurity-removing step comprises:

[0031] An oxidant is added to the electrolytic lean solution, and then an alkali is added to adjust the pH to 2.5-3.5. After reacting at a certain temperature, solid-liquid separation is performed to obtain a solution after impurities are removed.

[0032] In this preferred technical solution, the pH can be, for example, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4 or 3.5.

[0033] Preferably, the oxidant includes any one of hydrogen peroxide, sodium chlorate, sodium hypochlorite, sodium persulfate or oxygen, or a combination of two or more thereof.

[0034] Preferably, the amount of the oxidant is the residual Fe 2+ All oxidized to Fe 3+ 1.1-1.2 times of the theoretical demand, for example, it can be 1.1 times, 1.12 times, 1.14 times, 1.16 times, 1.18 times, or 1.2 times.

[0035] Preferably, the base comprises sodium hydroxide.

[0036] Preferably, the certain temperature is 40-90°C, for example, it may be 40°C, 50°C, 60°C, 70°C, 80°C, or 90°C.

[0037] As a preferred technical solution of the method of the present invention, in step (4), the first precipitant includes any one of sodium hydroxide or sodium phosphate, or a combination of the two.

[0038] Preferably, in step (4), the pH is adjusted to 10-13, for example, 10, 10.2, 10.3, 10.5, 10.6, 10.7, 10.8, 11, 11.2, 11.3, 11.4, 11.6, 11.8, 12, 12.3, 12.5, 12.6, 12.7, 12.8 or 13, etc.

[0039] Preferably, in step (5), the second precipitant comprises any one of calcium oxide or calcium hydroxide, or a mixture of the two.

[0040] Preferably, the method further comprises the step of washing the phosphate slag with water.

[0041] Preferably, the acid in step (6) comprises sulfuric acid.

[0042] Preferably, in step (6), the amount of the acid added is 0.95-1.0 times the theoretical amount required to generate phosphoric acid, for example, 0.95, 0.96, 0.97, 0.98, 0.99 or 1.0, etc.

[0043] 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.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention provides a new recycling idea for waste lithium iron phosphate black powder, which recycles the three elements of iron, lithium and phosphorus in waste lithium iron phosphate positive electrode black powder into iron powder, lithium phosphate and phosphoric acid, respectively, expanding the recycling direction and product types. Moreover, the present invention realizes the full element recycling and resource disposal of waste lithium iron phosphate positive electrode black powder, effectively alleviating environmental pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a process flow chart of the method for treating waste lithium iron phosphate positive electrode black powder in Example 1. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0048] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0049] Example 1

[0050] This embodiment provides a method for treating waste lithium iron phosphate positive electrode black powder, and its process flow chart is shown in Figure 1 , including the following steps:

[0051] (1) Leaching: waste lithium iron phosphate positive electrode black powder is mixed with water to prepare a slurry, and then acid is added to carry out a leaching reaction. After the reaction, the solid and liquid are separated to obtain a leachate; wherein the acid is sulfuric acid, and the amount of the acid used is 1.1 times the theoretical amount required for the total leaching of iron and lithium.

[0052] (2) primary impurity removal: adding impurity remover A and impurity remover B to the leachate of step (1), and performing solid-liquid separation after reaction to obtain impurity-removing liquid A; wherein the impurity remover A is sodium sulfide, the impurity remover B is sodium fluoride, and the amount of the impurity remover A and the impurity remover B is 3.5 times the theoretical amount required to remove the impurities Cu and Al.

[0053] (3) Electrolysis: The pH of the impurity removal solution A obtained in step (2) is adjusted to 4.0 and added to the electrolytic cell as the cathode liquid for electrolysis. During the electrolysis reaction, the pH of the cathode liquid is maintained in the range of 3.0-5.0. The current density of the electrolysis reaction is 500 A / m 2 , crude electrolytic iron is obtained at the cathode.

[0054] (4) Reduction and purification: The crude electrolytic iron obtained in step (3) is stripped from the cathode, washed with pure water, crushed, sieved and vacuum dried, and the product is further deeply reduced with hydrogen at 800°C to obtain high-purity electrolytic iron powder.

[0055] (5) Secondary impurity removal: adding an oxidant to the electrolytic lean solution obtained in step (3), and then adding sodium hydroxide to adjust the pH to 2.7, reacting at 70° C. and separating the solid and liquid to obtain impurity removal solution B; wherein the oxidant is hydrogen peroxide, and the amount of the oxidant added is to reduce the residual Fe in the electrolytic lean solution to 2.7. 2+ All oxidized to Fe 3+ 1.1 times the theoretical demand.

[0056] (6) lithium precipitation: adding precipitant A to the impurity removal solution B in step (5) to adjust the pH to 10, and performing solid-liquid separation after the reaction to obtain a lithium precipitation solution and a lithium phosphate product; wherein the precipitant A is sodium hydroxide.

[0057] (7) Phosphorus precipitation: adding a precipitant B to the solution after lithium precipitation in step (6), separating the solid and the liquid after the reaction, and washing the solid residue with water to obtain calcium phosphate residue; wherein the precipitant B is calcium oxide.

[0058] (8) Phosphorus extraction: adding sulfuric acid to the calcium phosphate residue obtained in step (7) to react, and obtaining phosphoric acid after solid-liquid separation; wherein the amount of sulfuric acid added is 0.95 times the theoretical amount required to generate phosphoric acid.

[0059] Example 2

[0060] This embodiment provides a method for treating waste lithium iron phosphate positive electrode black powder, and its process flow chart is shown in Figure 1 , including the following steps:

[0061] (1) Leaching: waste lithium iron phosphate positive electrode black powder is mixed with water to prepare a slurry, and then acid is added to carry out a leaching reaction. After the reaction, the solid and liquid are separated to obtain a leachate; wherein the acid is sulfuric acid, and the amount of the acid used is 1.05 times the theoretical amount required for the total leaching of iron and lithium.

[0062] (2) primary impurity removal: adding impurity remover A and impurity remover B to the leachate of step (1), and performing solid-liquid separation after reaction to obtain impurity-removing liquid A; wherein the impurity remover A is sodium sulfide, the impurity remover B is sodium fluoride, and the amount of the impurity remover A and the impurity remover B is 2.5 times the theoretical amount required to remove the impurities Cu and Al.

[0063] (3) Electrolysis: The pH of the impurity removal solution A obtained in step (2) is adjusted to 4.5 and added to the electrolytic cell as the cathode liquid for electrolysis. During the electrolysis reaction, the pH of the cathode liquid is maintained in the range of 3.0-5.0. The current density of the electrolysis reaction is 2000 A / m 2 , crude electrolytic iron is obtained at the cathode.

[0064] (4) Reduction and purification: The crude electrolytic iron obtained in step (3) is stripped from the cathode, washed with pure water, crushed, sieved and vacuum dried, and the product is further deeply reduced with hydrogen at 750°C to obtain high-purity electrolytic iron powder.

[0065] (5) Secondary impurity removal: adding an oxidant to the electrolytic lean solution obtained in step (3), and then adding sodium hydroxide to adjust the pH to 3.3, reacting at 40° C. and separating the solid and liquid to obtain impurity removal solution B; wherein the oxidant is hydrogen peroxide, and the amount of the oxidant added is to reduce the residual Fe in the electrolytic lean solution to 2+ All oxidized to Fe 3+ 1.16 times the theoretical demand.

[0066] (6) lithium precipitation: adding precipitant A to the impurity removal solution B in step (5) to adjust the pH to 10.5, and performing solid-liquid separation after the reaction to obtain a lithium precipitation solution and a lithium phosphate product; wherein the precipitant A is sodium hydroxide.

[0067] (7) Phosphorus precipitation: adding a precipitant B to the solution after lithium precipitation in step (6), separating the solid and the liquid after the reaction, and washing the solid residue with water to obtain calcium phosphate residue; wherein the precipitant B is calcium oxide.

[0068] (8) Phosphorus extraction: adding sulfuric acid to the calcium phosphate residue obtained in step (7) to react, and obtaining phosphoric acid after solid-liquid separation; wherein the amount of sulfuric acid added is 0.95 times the theoretical amount required to generate phosphoric acid.

[0069] Example 3

[0070] This embodiment provides a method for treating waste lithium iron phosphate positive electrode black powder, and its process flow chart is shown in Figure 1 , including the following steps:

[0071] (1) Leaching: waste lithium iron phosphate positive electrode black powder is mixed with water to prepare a slurry, and then acid is added to carry out a leaching reaction. After the reaction, the solid and liquid are separated to obtain a leachate; wherein the acid is sulfuric acid, and the amount of the acid used is 1.2 times the theoretical amount required for the total leaching of iron and lithium.

[0072] (2) primary impurity removal: adding impurity remover A and impurity remover B to the leachate of step (1), and performing solid-liquid separation after reaction to obtain impurity-removing liquid A; wherein the impurity remover A is sodium sulfide, the impurity remover B is sodium fluoride, and the amount of the impurity remover A and the impurity remover B is twice the theoretical amount required to remove the impurities Cu and Al.

[0073] (3) Electrolysis: The pH of the impurity removal solution A obtained in step (2) is adjusted to 3.5 and added to the electrolytic cell as the cathode liquid for electrolysis. During the electrolysis reaction, the pH of the cathode liquid is maintained in the range of 3.0-5.0. The current density of the electrolysis reaction is 1500 A / m 2 , crude electrolytic iron is obtained at the cathode.

[0074] (4) Reduction and purification: The crude electrolytic iron obtained in step (3) is stripped from the cathode, washed with pure water, crushed, sieved and vacuum dried, and the product is further deeply reduced with hydrogen at 900°C to obtain high-purity electrolytic iron powder.

[0075] (5) Secondary impurity removal: adding an oxidant to the electrolytic lean solution obtained in step (3), and then adding sodium hydroxide to adjust the pH to 2.8, reacting at 90° C. and then separating the solid and liquid to obtain an impurity removal solution B; wherein the oxidant is hydrogen peroxide, and the amount of the oxidant added is to reduce the residual Fe in the electrolytic lean solution to 2+ All oxidized to Fe 3+ 1.2 times the theoretical demand.

[0076] (6) lithium precipitation: adding precipitant A to the impurity removal solution B in step (5) to adjust the pH to 11, and performing solid-liquid separation after the reaction to obtain a lithium precipitation solution and a lithium phosphate product; wherein the precipitant A is sodium hydroxide.

[0077] (7) Phosphorus precipitation: adding a precipitant B to the solution after lithium precipitation in step (6), separating the solid and the liquid after the reaction, and washing the solid residue with water to obtain calcium phosphate residue; wherein the precipitant B is calcium oxide.

[0078] (8) Phosphorus extraction: adding sulfuric acid to the calcium phosphate slag obtained in step (7) to react, and obtaining phosphoric acid after solid-liquid separation; wherein the amount of sulfuric acid added is 1.0 times the theoretical amount required to generate phosphoric acid.

[0079] Example 4

[0080] This embodiment provides a method for treating waste lithium iron phosphate positive electrode black powder, and its process flow chart is shown in Figure 1 , including the following steps:

[0081] (1) Leaching: waste lithium iron phosphate positive electrode black powder is mixed with water to prepare a slurry, and then acid is added to carry out a leaching reaction. After the reaction, the solid and liquid are separated to obtain a leachate; wherein the acid is sulfuric acid, and the amount of the acid used is 1.08 times the theoretical amount required for the total leaching of iron and lithium.

[0082] (2) primary impurity removal: adding impurity remover A and impurity remover B to the leaching solution of step (1), and performing solid-liquid separation after reaction to obtain impurity-removing liquid A; wherein the impurity remover A is sodium sulfide, the impurity remover B is sodium fluoride, and the amount of the impurity remover A and the impurity remover B is 5 times the theoretical amount required to remove the impurities Cu and Al.

[0083] (3) Electrolysis: The pH of the impurity removal solution A obtained in step (2) is adjusted to 5.0 and added to the electrolytic cell as the cathode liquid for electrolysis. During the electrolysis reaction, the pH of the cathode liquid is maintained in the range of 3.0-5.0. The current density of the electrolysis reaction is 1000 A / m 2 , crude electrolytic iron is obtained at the cathode.

[0084] (4) Reduction and purification: The crude electrolytic iron obtained in step (3) is stripped from the cathode, washed with pure water, crushed, sieved and vacuum dried, and the product is further deeply reduced with hydrogen at 1000°C to obtain high-purity electrolytic iron powder.

[0085] (5) Secondary impurity removal: adding an oxidant to the electrolytic lean solution obtained in step (3), and then adding sodium hydroxide to adjust the pH to 2.5, reacting at 50° C. and separating the solid and liquid to obtain impurity removal solution B; wherein the oxidant is hydrogen peroxide, and the amount of the oxidant added is to reduce the residual Fe in the electrolytic lean solution to 2+ All oxidized to Fe 3+ 1.12 times the theoretical demand.

[0086] (6) lithium precipitation: adding precipitant A to the impurity removal solution B in step (5) to adjust the pH to 13, and performing solid-liquid separation after the reaction to obtain a lithium precipitation solution and a lithium phosphate product; wherein the precipitant A is sodium hydroxide.

[0087] (7) Phosphorus precipitation: adding a precipitant B to the solution after lithium precipitation in step (6), separating the solid and the liquid after the reaction, and washing the solid residue with water to obtain calcium phosphate residue; wherein the precipitant B is calcium oxide.

[0088] (8) Phosphorus extraction: adding sulfuric acid to the calcium phosphate residue obtained in step (7) to react, and obtaining phosphoric acid after solid-liquid separation; wherein the amount of sulfuric acid added is 0.96 times the theoretical amount required to generate phosphoric acid.

[0089] Example 5

[0090] This embodiment provides a method for treating waste lithium iron phosphate positive electrode black powder, and its process flow chart is shown in Figure 1 , including the following steps:

[0091] (1) Leaching: waste lithium iron phosphate positive electrode black powder is mixed with water to prepare a slurry, and then acid is added to carry out a leaching reaction. After the reaction, the solid and liquid are separated to obtain a leachate; wherein the acid is sulfuric acid, and the amount of the acid used is 1.15 times the theoretical amount required for the total leaching of iron and lithium.

[0092] (2) primary impurity removal: adding impurity remover A and impurity remover B to the leaching solution of step (1), and performing solid-liquid separation after reaction to obtain impurity-removing liquid A; wherein the impurity remover A is sodium sulfide, the impurity remover B is sodium fluoride, and the amount of the impurity remover A and the impurity remover B is 4 times the theoretical amount required to remove the impurities Cu and Al.

[0093] (3) Electrolysis: The pH of the impurity removal solution A obtained in step (2) is adjusted to 3.0 and added to the electrolytic cell as the cathode liquid for electrolysis. During the electrolysis reaction, the pH of the cathode liquid is maintained in the range of 3.0-5.0. The current density of the electrolysis reaction is 800 A / m 2 , crude electrolytic iron is obtained at the cathode.

[0094] (4) Reduction and purification: The crude electrolytic iron obtained in step (3) is stripped from the cathode, washed with pure water, crushed, sieved and vacuum dried, and the product is further deeply reduced with hydrogen at 950°C to obtain high-purity electrolytic iron powder.

[0095] (5) Secondary impurity removal: adding an oxidant to the electrolytic lean solution obtained in step (3), and then adding sodium hydroxide to adjust the pH to 3.5, reacting at 60° C. and then separating the solid and liquid to obtain an impurity removal solution B; wherein the oxidant is hydrogen peroxide, and the amount of the oxidant added is to reduce the residual Fe in the electrolytic lean solution to 2+ All oxidized to Fe 3+ 1.14 times the theoretical demand.

[0096] (6) lithium precipitation: adding precipitant A to the impurity removal solution B in step (5) to adjust the pH to 12.5, and performing solid-liquid separation after the reaction to obtain a lithium precipitation solution and a lithium phosphate product; wherein the precipitant A is sodium hydroxide.

[0097] (7) Phosphorus precipitation: adding a precipitant B to the solution after lithium precipitation in step (6), separating the solid and the liquid after the reaction, and washing the solid residue with water to obtain calcium phosphate residue; wherein the precipitant B is calcium oxide.

[0098] (8) Phosphorus extraction: adding sulfuric acid to the calcium phosphate residue obtained in step (7) to react, and obtaining phosphoric acid after solid-liquid separation; wherein the amount of sulfuric acid added is 0.98 times the theoretical amount required to generate phosphoric acid.

[0099] Example 6

[0100] This embodiment provides a method for treating waste lithium iron phosphate positive electrode black powder, and its process flow chart is shown in Figure 1 , including the following steps:

[0101] (1) Leaching: waste lithium iron phosphate positive electrode black powder is mixed with water to prepare a slurry, and then acid is added to carry out a leaching reaction. After the reaction, the solid and liquid are separated to obtain a leachate; wherein the acid is sulfuric acid, and the amount of the acid used is 1.1 times the theoretical amount required for the total leaching of iron and lithium.

[0102] (2) primary impurity removal: adding impurity remover A and impurity remover B to the leachate of step (1), and performing solid-liquid separation after reaction to obtain impurity-removing liquid A; wherein the impurity remover A is sodium sulfide, the impurity remover B is sodium fluoride, and the amount of the impurity remover A and the impurity remover B is 3 times the theoretical amount required to remove the impurities Cu and Al.

[0103] (3) Electrolysis: The pH of the impurity removal solution A obtained in step (2) is adjusted to 5.0 and added to the electrolytic cell as the cathode liquid for electrolysis. During the electrolysis reaction, the pH of the cathode liquid is maintained in the range of 3.0-5.0. The current density of the electrolysis reaction is 1200 A / m 2 , crude electrolytic iron is obtained at the cathode.

[0104] (4) Reduction and purification: The crude electrolytic iron obtained in step (3) is stripped from the cathode, washed with pure water, crushed, sieved and vacuum dried, and the product is further deeply reduced with hydrogen at 850°C to obtain high-purity electrolytic iron powder.

[0105] (5) Secondary impurity removal: adding an oxidant to the electrolytic lean solution obtained in step (3), and then adding sodium hydroxide to adjust the pH to 3.0, reacting at 80° C. and separating the solid and liquid to obtain impurity removal solution B; wherein the oxidant is hydrogen peroxide, and the amount of the oxidant added is to reduce the residual Fe in the electrolytic lean solution to 0. 2+ All oxidized to Fe 3+ 1.16 times the theoretical demand.

[0106] (6) lithium precipitation: adding precipitant A to the impurity removal solution B in step (5) to adjust the pH to 12, and performing solid-liquid separation after the reaction to obtain a lithium precipitation solution and a lithium phosphate product; wherein the precipitant A is sodium hydroxide.

[0107] (7) Phosphorus precipitation: adding a precipitant B to the solution after lithium precipitation in step (6), separating the solid and the liquid after the reaction, and washing the solid residue with water to obtain calcium phosphate residue; wherein the precipitant B is calcium oxide.

[0108] (8) Phosphorus extraction: adding sulfuric acid to the calcium phosphate residue obtained in step (7) to react, and obtaining phosphoric acid after solid-liquid separation; wherein the amount of sulfuric acid added is 0.95 times the theoretical amount required to generate phosphoric acid.

[0109] It can be seen from Examples 1-6 that the method of the present invention can recover the three elements of iron, lithium and phosphorus in the waste lithium iron phosphate positive electrode black powder and prepare them into iron powder, lithium phosphate and phosphoric acid, respectively, expanding the recycling direction and product types. Moreover, the present invention realizes the full element recovery and resource disposal of waste lithium iron phosphate positive electrode black powder, effectively alleviating the environmental pressure.

[0110] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of 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 treating waste lithium iron phosphate black powder, characterized in that: The method comprises the following steps: (1) acid leaching the lithium iron phosphate black powder to obtain a leachate; (2) removing impurities from the leaching solution to remove Cu and Al, thereby obtaining a de-impurity solution; (3) using the impurity removal liquid as cathode liquid to carry out electrolytic reaction to obtain crude electrolytic iron at the cathode; (4) adding a first precipitant to the electrolytic lean solution after electrolysis to adjust the pH, and performing solid-liquid separation after the reaction to obtain a lithium precipitated solution and lithium phosphate; (5) adding a second precipitant to the lithium precipitated liquid, and performing solid-liquid separation after the reaction to obtain phosphate slag; (6) Using an acid to react with the phosphate slag, and obtaining phosphoric acid after solid-liquid separation.

2. The method for treating waste lithium iron phosphate black powder according to claim 1, characterized in that: The acid used in the acid leaching in step (1) includes any one of sulfuric acid and hydrochloric acid or a combination of the two; Preferably, in the acid leaching step of step (1), the amount of acid used is 1.05-1.2 times the theoretical total leaching amount of iron and lithium elements.

3. The method for treating waste lithium iron phosphate black powder according to claim 1 or 2, characterized in that: The impurity remover used in step (2) comprises an impurity remover A and an impurity remover B, wherein the impurity remover A comprises any one of sodium sulfide or iron powder or a combination of the two, and the impurity remover B comprises sodium fluoride; Preferably, the dosage of the impurity remover is 2-5 times the theoretical amount required to remove the impurities Cu and Al.

4. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 3, characterized in that: The electrolysis reaction in step (3) is carried out in an electrolytic cell using diaphragm electrolysis. The anode is any one of a lead-silver alloy, a titanium-based inert metal coating plate, a titanium-based lead dioxide or a manganese dioxide coating plate, and the cathode is a stainless steel plate.

5. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 4, characterized in that: During the electrolysis reaction in step (3), the pH of the cathode liquid is maintained in the range of 3.0-5.0; Preferably, the current density of the electrolysis reaction in step (3) is 500-5000A / m 2 , preferably 500-2000A / m 2 ; Preferably, the method further comprises washing, crushing, screening and drying the crude electrolytic iron to obtain treated crude electrolytic iron.

6. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 5, characterized in that: The method further comprises the step of reducing the treated crude electrolytic iron, wherein the reducing step comprises: heating the crude electrolytic iron under the action of a reducing gas to obtain high-purity electrolytic iron; Preferably, the reducing gas comprises hydrogen; Preferably, the temperature of the heating treatment is 750-1000°C.

7. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 6, characterized in that: The method further comprises, after step (3) and before step (4), removing impurities from the electrolytic barren solution and using the removed impurity solution in step (4), wherein the step of removing impurities comprises: Adding an oxidant to the electrolytic lean solution, then adding alkali to adjust the pH to 2.5-3.5, reacting at a certain temperature, performing solid-liquid separation, and obtaining a solution after impurities are removed; Preferably, the oxidant includes any one of hydrogen peroxide, sodium chlorate, sodium hypochlorite, sodium persulfate or oxygen, or a combination of two or more thereof; Preferably, the amount of the oxidant is the residual Fe 2+ All oxidized to Fe 3+ 1.1-1.2 times of the theoretical demand; Preferably, the base comprises sodium hydroxide; Preferably, the certain temperature is 40-90°C.

8. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 7, characterized in that: Step (4) the first precipitating agent comprises any one of sodium hydroxide or sodium phosphate or a combination of the two; Preferably, in step (4), the pH is adjusted to 10-13.

9. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 8, characterized in that: Step (5) the second precipitant comprises any one of calcium oxide or calcium hydroxide or a mixture of the two; Preferably, the method further comprises the step of washing the phosphate slag with water.

10. The method for treating waste lithium iron phosphate black powder according to any one of claims 1 to 9, characterized in that: The acid in step (6) comprises sulfuric acid; Preferably, in step (6), the amount of the acid added is 0.95-1.0 times the theoretical amount required to generate phosphoric acid.

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