A method and system for processing lithium iron phosphate battery powder

Abstract

The application discloses a method and system for processing lithium iron phosphate battery powder, and belongs to the technical field of lithium iron phosphate recovery processing. The method comprises the following steps: after the lithium iron phosphate battery powder containing impurity metals is made into a first slurry, the first slurry is subjected to first oxidation treatment by electrolytic oxidation until the lithium iron phosphate is completely changed into iron phosphate, and a second slurry is obtained; the pH value of the second slurry is reduced and the second slurry is subjected to second oxidation treatment so that the impurity metals in the second slurry are dissolved; solid-liquid separation is performed to obtain iron phosphate slag and a solution containing impurity metals; wherein the impurity metals include at least one of aluminum and copper; the second oxidation treatment includes electrolytic oxidation or chemical oxidation. The method is simple in operation, mild in conditions, and can realize efficient separation of iron phosphate in the lithium iron phosphate battery powder and impurity metals, and can produce iron phosphate by-products with low aluminum and / or copper content and high yield. The corresponding processing system is simple in structure, low in cost and convenient to operate.

Description

Technical Field

[0001] This invention relates to the field of lithium iron phosphate recycling and processing technology, and more specifically, to a method and system for processing lithium iron phosphate battery powder. Background Technology

[0002] Currently, the mixture of carbon powder and lithium iron phosphate powder recovered from industrial production contains a large amount of copper and aluminum powder. Lithium and most of the copper and / or aluminum can be recovered from the leachate through simple oxidation and acid dissolution. However, if the goal is to recover iron phosphate, it is necessary to produce iron phosphate slag with as low a copper and aluminum content as possible. Otherwise, it will increase the difficulty of subsequent iron phosphate dissolution and impurity removal, resulting in iron phosphate slag products with excessive aluminum and copper content that fail to meet usability standards.

[0003] However, there is currently no effective method to produce high-yield iron phosphate byproducts with low aluminum and / or copper content from lithium iron phosphate battery powder.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for processing lithium iron phosphate battery powder, so as to solve or improve the above-mentioned technical problems.

[0006] This invention can be implemented as follows:

[0007] In a first aspect, the present invention provides a method for processing lithium iron phosphate battery powder, comprising the following steps: preparing lithium iron phosphate battery powder containing impurity metals into a first slurry, performing a first oxidation treatment by electrolytic oxidation until lithium iron phosphate is completely converted into iron phosphate, thereby obtaining a second slurry; lowering the pH value of the second slurry and performing a second oxidation treatment to dissolve the impurity metals in the second slurry; and performing solid-liquid separation to obtain iron phosphate slag and a solution containing impurity metals.

[0008] The impurity metals include at least one of aluminum and copper; the second oxidation treatment can be carried out by electrolytic oxidation or chemical oxidation.

[0009] In an optional embodiment, during the first oxidation treatment, the pH value of the first slurry is 3 to 10.

[0010] In an optional embodiment, during the first electrolytic oxidation process, a first acidic solution is added to maintain the pH value of the first slurry at 3 to 10.

[0011] In an optional embodiment, the first acidic solution includes at least one of sulfuric acid and hydrochloric acid.

[0012] In an optional embodiment, the first slurry further includes at least one of the following features:

[0013] Feature 1: The solid content of the first slurry is 5% to 40%;

[0014] Feature 2: The first slurry also contains conductive reagents.

[0015] In an optional embodiment, the conductive agent includes an electrolyte, preferably, the electrolyte includes at least one of sulfate and chloride.

[0016] In an optional embodiment, the conductive reagent content in the first slurry is 5 g / L to 10 g / L.

[0017] In an optional embodiment, the anolyte current density for the first oxidation treatment is 100 A / m. 2 ~500A / m 2 ;

[0018] And / or, the electrolytic endpoint of the first oxidation treatment is: the potential of the first slurry relative to the standard hydrogen electrode is ≥0.6V.

[0019] In an optional embodiment, the second oxidation treatment further includes at least one of the following features:

[0020] Feature 3: During the second oxidation process, the pH value of the second slurry is <2.0, preferably 1.0 to 1.5;

[0021] Feature 4: During the second oxidation process, the potential of the second slurry is ≥0.6V relative to the standard hydrogen electrode;

[0022] Feature 5: The temperature of the second oxidation treatment is ≥45℃;

[0023] Feature 6: The endpoint of the second oxidation treatment is that the content of Cu and Al in the ferric phosphate slag does not exceed 0.1%.

[0024] In an optional implementation, the pH value of the second slurry is reduced by adding a second acidic solution to the second slurry.

[0025] In an optional embodiment, the second acidic solution includes at least one of sulfuric acid and hydrochloric acid.

[0026] In an optional embodiment, a potential buffer is also added to the second slurry during the second electrolytic oxidation process.

[0027] In an optional embodiment, the potential buffer comprises a material containing ferric iron.

[0028] In an optional embodiment, the material containing ferric iron includes at least one of ferric sulfate and ferric chloride.

[0029] In an optional embodiment, the concentration of the material containing ferric iron in the second slurry is ≥1.5 g / L.

[0030] In an optional embodiment, when the second oxidation is performed by chemical oxidation, the method further includes: adding an oxidant to the second slurry to maintain the potential of the second slurry ≥0.6V relative to the standard hydrogen electrode.

[0031] In an optional embodiment, the oxidant includes at least one of hydrogen peroxide, persulfate, chlorine, hypochlorite, and chlorate.

[0032] In a second aspect, the present invention provides a system for processing lithium iron phosphate battery powder, the system being used to perform the operations in any of the methods described in the foregoing embodiments;

[0033] The system includes a reaction vessel and a cyclone electrolysis unit;

[0034] The material inlet of the cyclone electrolysis device is connected to the material outlet of the reaction vessel, and the material outlet of the cyclone electrolysis device is connected to the material inlet of the reaction vessel, so that the material forms a circulation path between the cyclone electrolysis device and the reaction vessel.

[0035] The reaction vessel is used at least for material mixing and the second oxidation process by chemical oxidation; the cyclone electrolysis device is used for the first oxidation process and the second oxidation process by electrolytic oxidation.

[0036] In an optional embodiment, the cyclone electrolysis device includes an electrolytic cell, an anode, and a cathode. The electrolytic cell has an electrolysis chamber. The anode is disposed on the inner wall of the electrolytic cell, and the cathode is disposed in the electrolysis chamber and its surface is covered with an insulating cloth.

[0037] In an alternative embodiment, the anode includes a graphite anode, a lead-containing anode, or a titanium-containing anode.

[0038] In an optional embodiment, the insulating fabric includes at least one of polyester fabric and polypropylene fabric.

[0039] In an optional implementation, the system further includes a pH monitoring device for monitoring the pH value of the reaction process, an automatic acid addition device for adding acidic solutions, and a circulation pump and circulation pipeline for conveying materials between the cyclone electrolysis unit and the mixing container.

[0040] The beneficial effects of this invention include:

[0041] This invention employs electrolytic oxidation to perform a first oxidation treatment on lithium iron phosphate battery powder. During electrolysis, the strong oxidizing effect at the anode oxidizes the lithium iron phosphate, yielding iron phosphate and releasing lithium. A second oxidation treatment is then performed by lowering the pH value, dissolving copper and aluminum impurities in the lithium iron phosphate battery powder. This facilitates the separation of the iron phosphate residue and the solution containing dissolved impurities through solid-liquid separation, resulting in iron phosphate residue with a low impurity metal content.

[0042] This method is simple to operate and operates under mild conditions, enabling efficient separation of iron phosphate from impurity metals in lithium iron phosphate battery powder. It can produce iron phosphate byproducts with low aluminum and / or copper content and high yield. The corresponding processing system is simple in structure, low in cost, and easy to operate. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 A schematic flowchart of the method for processing lithium iron phosphate battery powder provided by the present invention;

[0045] Figure 2 A schematic diagram of the system for processing lithium iron phosphate battery powder provided by the present invention;

[0046] Figure 3 This is a SEM image of the lithium iron phosphate battery dry powder used in Example 1 of the present invention;

[0047] Figure 4 This is a SEM image of the iron phosphate byproduct obtained in Example 1 of the present invention.

[0048] Icons: 10-Reaction vessel; 11-Stirrer; 20-Swirl electrolysis device; 21-Electrolytic cell; 211-Electrolysis chamber; 22-Anode; 23-Cathode; 24-Isolation cloth; 30-pH monitoring equipment; 40-Automatic acid addition equipment; 51-Circulation pump; 52-Circulation pipeline. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0050] The method and system for processing lithium iron phosphate battery powder provided by the present invention will be described in detail below.

[0051] This invention provides a method for processing lithium iron phosphate battery powder, please refer to... Figure 1 The process includes the following steps: preparing lithium iron phosphate battery powder containing impurity metals into a first slurry, and then performing a first oxidation treatment by electrolytic oxidation until lithium iron phosphate is completely converted into iron phosphate to obtain a second slurry; lowering the pH value of the second slurry and performing a second oxidation treatment to dissolve the impurity metals in the second slurry; and performing solid-liquid separation to obtain iron phosphate slag and a solution containing impurity metals.

[0052] The impurity metals include at least one of aluminum and copper; the second oxidation treatment can be carried out by electrolytic oxidation or chemical oxidation.

[0053] The first oxidation treatment described above employs electrolytic oxidation, where the strong oxidizing effect of anode 22 during electrolysis oxidizes lithium iron phosphate, thereby obtaining iron phosphate and extracting lithium. The second oxidation treatment is carried out under conditions of reduced pH, primarily to dissolve impurity metals in the second slurry. This facilitates the separation of the iron phosphate slag and the solution containing dissolved impurity metals (which also retains lithium extracted in the first oxidation treatment) through solid-liquid separation, resulting in iron phosphate slag with a low impurity metal content.

[0054] In some embodiments, during the first oxidation treatment, the pH value of the first slurry is 3 to 10, such as 3, 4, 5, 6, 7, 8, 9 or 10, or other values ​​within the range of 3 to 10.

[0055] In practice, the pH of the first slurry can be maintained between 3 and 10 by adding a first acidic solution. The first acidic solution may, by way of example but not limitation, include at least one of sulfuric acid and hydrochloric acid.

[0056] In some embodiments, the solid content of the first slurry can be 5% to 40%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%, or other values ​​within the range of 5% to 40%.

[0057] If the solid content of the first slurry is less than 5%, it will result in low equipment utilization and small single-batch processing volume; if the solid content of the first slurry is higher than 40%, it will result in poor material flowability and reduced processing effect.

[0058] In some embodiments, the first slurry also contains a conductive agent. For example, the conductive agent may include an electrolyte, such as at least one of sulfate and chloride.

[0059] The content of the conductive reagent in the first slurry can be 5 g / L to 10 g / L, such as 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, or other values ​​within the range of 5 g / L to 10 g / L.

[0060] By adding a conductive reagent to make the first slurry conductive, electrolytic oxidation can proceed smoothly, resulting in a better electrolysis effect.

[0061] In some embodiments, the anolyte current density for the first oxidation treatment can be 100 A / m. 2 ~500A / m 2 such as 100A / m 2 150A / m 2 200A / m 2 250A / m 2 300A / m 2 350A / m 2 400A / m 2 450A / m 2 Or 500A / m 2 etc., can also be 100A / m 2 ~500A / m 2 Other values ​​within the range.

[0062] If the anolyte current density is too low in the first oxidation process, the throughput will be low; if the anolyte current density is too high in the first oxidation process, the voltage and energy consumption will increase.

[0063] In some embodiments, the electrolytic endpoint of the first oxidation treatment is: the potential of the first slurry is ≥0.6V relative to the standard hydrogen electrode.

[0064] It should be noted that conventional near-neutral oxidation methods for slurries typically require the use of strong oxidants. However, among commonly used oxidants, some (such as hydrogen peroxide) have insufficient oxidizing power, some (such as chlorine, ozone, and chlorine dioxide) are toxic, and some (such as sodium persulfate) are expensive. This invention utilizes electrolytic oxidation for the first oxidation treatment, which can be achieved through electrode contact oxidation, electric field oxidation, or catalytic oxidation using other anolyte products (hypochlorite, hydroxyl radicals, sulfate radicals). This first oxidation treatment process can achieve a strong oxidizing effect without the use of chemical oxidants, while also avoiding the introduction of other impurity ions.

[0065] In this invention, the pH value of the second slurry in the second oxidation process is less than the pH value of the first slurry in the first oxidation process.

[0066] In some embodiments, the pH value of the second slurry during the second oxidation process is <2.0, such as 1.8, 1.6, 1.4, 1.2, 1.0, 0.8, 0.6, or 0.4. In some specific embodiments, the pH value of the second slurry during the second oxidation process can be 1.0 to 1.5, such as 1.0, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5.

[0067] In some embodiments, lowering the pH of the second slurry can be achieved by adding a second acidic solution to the second slurry. For example, the second acidic solution may include at least one of sulfuric acid and hydrochloric acid.

[0068] In some embodiments, a potential buffer is also added to the second slurry. For example, the potential buffer may include a material containing ferric iron, such as at least one of ferric sulfate and ferric chloride.

[0069] The concentration of the above-mentioned ferric iron-containing material in the second slurry can be ≥1.5 g / L, such as 1.5 g / L, 1.8 g / L, 2 g / L or 2.5 g / L, etc.

[0070] Since the second oxidation process takes place under high acid conditions, it is mainly used to dissolve aluminum and copper. By adding a potential buffer (ferric ions) to the second slurry, it is beneficial to stabilize the potential value of the second slurry and avoid or reduce the reduction and dissolution of ferric phosphate by copper and aluminum.

[0071] In some embodiments, when a second oxidation is performed using chemical oxidation, an oxidant is further added to the second slurry to maintain the potential of the second slurry ≥0.6V relative to the standard hydrogen electrode. Exemplarily, the oxidant may include at least one of hydrogen peroxide, persulfate, chlorine, hypochlorite, and chlorate. The addition of the oxidant also helps stabilize the potential value of the second slurry, preventing or reducing the dissolution of ferric phosphate by the reduction of copper and aluminum.

[0072] In this invention, during the second oxidation process, the potential of the second slurry is ≥0.6V relative to the standard hydrogen electrode. The temperature of the second oxidation process is ≥45℃, such as 45℃, 50℃, 55℃, or 60℃, etc. This temperature range is beneficial for increasing the reaction rate and shortening the reaction time. Furthermore, the second oxidation process can also be carried out at room temperature or other suitable temperatures.

[0073] The endpoint of the second oxidation treatment can be controlled according to actual needs. In some embodiments, the content of Cu and Al in the ferric phosphate slag can both be no more than 0.1% as the endpoint of the second oxidation treatment.

[0074] As mentioned above, the first oxidation treatment mainly involves electrolytically oxidizing lithium iron phosphate into iron phosphate and dissolving lithium under relatively high pH conditions (near neutral conditions). The second oxidation treatment mainly involves dissolving copper and aluminum under relatively low pH conditions (high acid conditions). By combining the first and second oxidation treatments, lithium, aluminum, and copper are gradually leached out, preventing the leached aluminum from being co-precipitated during the ferrous phosphate oxidation process.

[0075] Accordingly, the present invention also provides a system for processing lithium iron phosphate battery powder, which is used to perform the operations in the above-described method for processing lithium iron phosphate battery powder.

[0076] Please refer to Figure 2 The system includes a reaction vessel 10 and a cyclone electrolysis device 20. The material inlet of the cyclone electrolysis device 20 is connected to the material outlet of the reaction vessel 10, and the material outlet of the cyclone electrolysis device 20 is connected to the material inlet of the reaction vessel 10, so that the material forms a circulation path between the cyclone electrolysis device 20 and the reaction vessel 10.

[0077] The aforementioned reaction vessel 10 can be used for material mixing and a second oxidation process via chemical oxidation. For example, the first slurry can be prepared by mixing lithium iron phosphate battery powder containing impurity metals with water within the reaction vessel 10. Furthermore, the addition of conductive reagents, potential buffers, and oxidants can all be carried out within the reaction vessel 10. As an example, the aforementioned reaction vessel 10 can be a stirred tank equipped with a stirrer 11.

[0078] The aforementioned cyclone electrolysis device 20 can be used for both the first oxidation process and the second oxidation process via electrolytic oxidation.

[0079] In some embodiments, the cyclone electrolysis device 20 includes an electrolytic cell 21, an anode 22 and a cathode 23. The electrolytic cell 21 has an electrolysis chamber 211. The anode 22 is disposed on the inner wall of the electrolytic cell 21, and the cathode 23 is disposed in the electrolysis chamber 211 and the surface of the cathode 23 is covered with an insulating cloth 24.

[0080] The shell of the electrolytic cell 21 can be made of plastic and can be cylindrical.

[0081] Anode 22 may, by way of example but not limitation, include graphite anode 22, lead-containing anode 22 or titanium-containing anode 22.

[0082] The cathode 23 only needs to be insoluble in weak acids (pH 1-4), conductive, and have suitable strength; for example, it can be made of graphite, metal, or alloy materials. In some specific embodiments, the cathode 23 is located in the middle of the electrolysis chamber 211, and the cathode 23 can be in the form of a rod.

[0083] The isolation cloth 24 may, by way of example but not limitation, include at least one of polyester cloth and polypropylene cloth so that the slurry does not come into direct contact with the cathode 23.

[0084] This invention, through the use of a cyclone electrolysis device 20, enables stable circulation of the slurry within the electrolysis equipment, preventing clogging or sedimentation. Furthermore, due to the centrifugal force of the cyclone, lithium iron phosphate can be oxidized more effectively by losing electrons through direct contact with the anode 22. In addition, by placing the anode 22 on the inner wall of the electrolysis cell 21 and the cathode rod in the middle of the electrolysis chamber 211, a larger effective electrode area is achieved, which is more conducive to saving electrolysis energy consumption and increasing production capacity. By wrapping the surface of the cathode 23 with a separating cloth 24, a selective ion membrane is unnecessary, simplifying and simplifying equipment manufacturing.

[0085] In addition, the system also includes a pH monitoring device 30 for monitoring the pH value of the reaction process, an automatic acid addition device 40 for adding acidic solutions, and a circulation pump 51 and circulation pipeline 52 for conveying materials between the cyclone electrolysis unit 20 and the mixing container.

[0086] Continuing from the above, in the context of the system, the processing method provided by this invention may include the following steps:

[0087] Lithium iron phosphate battery powder and water are mixed in a reaction vessel 10 to form a first slurry. This first slurry is pumped into a cyclone electrolysis device 20 at a certain circulation rate via a circulation pump 51 and a circulation pipe 52 for a first oxidation treatment (electrolytic oxidation). Simultaneously, the electrolyzed slurry is returned to the reaction vessel 10 through the circulation pipe 52. Based on the pH value of the slurry returning to the reaction vessel 10, a first acidic solution is added as needed to stabilize the pH value of the slurry continuously pumped into the cyclone electrolysis device 20 for further circulation within a preset range. After the first oxidation treatment (electrolytic oxidation) is performed for a period of time, the lithium iron phosphate in the lithium iron phosphate battery powder is oxidized by electrode contact, other anolyte products (such as hypochlorite, hydroxyl radicals, and sulfate radicals), and electric field oxidation to become iron phosphate, releasing lithium ions. After the lithium iron phosphate is fully oxidized, a second slurry is obtained. A potential buffer is added to the second slurry, and a second acidic solution is added to slowly adjust the acidity of the second slurry, lowering its pH to a preset value for a second oxidation treatment (electrolytic oxidation or chemical oxidation), allowing copper and aluminum to dissolve in the acid. The potential buffer protects the generated iron phosphate from being reduced and dissolved by copper and aluminum in the battery powder, preventing repeated reduction and oxidation of iron phosphate and lithium iron phosphate, which would cause aluminum ions in the solution to co-precipitate with ferric ions and enter the iron phosphate slag (in subsequent aluminum removal from the iron phosphate slag, a large amount of phosphorus and iron will co-precipitate, and these precipitates will carry away a large amount of phosphorus, resulting in a reduction in the high-value phosphorus yield). Finally, after solid-liquid separation, an acidic solution containing lithium, copper, aluminum, and iron ions and iron phosphate slag with a lower aluminum content are obtained, achieving efficient separation of iron phosphate from other metal components in lithium iron phosphate battery powder.

[0088] This invention is the first to apply the cyclone electrolysis device 20 to the recovery of iron phosphate from lithium iron phosphate battery powder. The reaction process has uniform mass transfer and mild reaction conditions, which enables the preparation of iron phosphate slag products with low copper and aluminum content and high yield under mild conditions.

[0089] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0090] Example 1

[0091] This embodiment provides a system for processing lithium iron phosphate battery powder, which includes a reaction vessel 10, a cyclone electrolysis device 20, a pH monitoring device 30 for monitoring the pH value of the reaction process, an automatic acid addition device 40 for adding acidic solution, and a circulation pump 51 and circulation pipeline 52 for conveying materials between the cyclone electrolysis device 20 and the mixing container.

[0092] The reaction vessel 10 is a stirred tank with a stirrer 11 (specifically a stirring paddle), and the probe or sensor of the pH monitoring device 30 extends into the reaction vessel 10.

[0093] The cyclone electrolysis device 20 includes an electrolytic cell 21, an anode 22, and a cathode 23. The electrolytic cell 21 includes a plastic cylindrical shell, and an electrolysis chamber 211 is formed inside the shell. The anode 22 (graphite anode) is disposed on the inner wall of the electrolytic cell 21, and the cathode 23 (graphite) is rod-shaped and disposed in the middle of the electrolysis chamber 211, with the surface of the cathode 23 covered with a separating cloth 24 (polyester cloth).

[0094] The material inlet of the cyclone electrolysis device 20 (located at the lower part of the electrolytic cell 21) is connected to the material outlet of the reaction vessel 10 (located at the lower part of the reaction vessel 10) through the circulation pipe 52. The material outlet of the cyclone electrolysis device 20 (located at the upper part of the electrolytic cell 21) is connected to the material inlet of the reaction vessel 10 through the circulation pipe 52. The circulation pump 51 is installed on the pipe connecting the material outlet of the cyclone electrolysis device 20 and the material inlet of the reaction vessel 10.

[0095] Example 2

[0096] This embodiment provides a method for processing lithium iron phosphate battery powder, and the processing system used in this method is the lithium iron phosphate battery powder processing system provided in Embodiment 1.

[0097] The method includes the following steps:

[0098] Step (1): The lithium iron phosphate battery dry powder and water are stirred in a mixing tank equipped with a stirrer to form a stable first slurry with a solid content of 20%. A small amount (7.5 g / L) of supporting electrolyte NaCl is added to the first slurry as a conductive agent to improve the conductivity of the slurry.

[0099] The main chemical composition of the lithium iron phosphate battery dry powder is shown in Table 1, and the SEM images are shown below. Figure 3 As shown.

[0100] Table 1. Composition of main chemical components (%)

[0101] content 3.2673 27.2457 2.1707 1.9203

[0102] Step (2): Turn on the circulation pump 51 to start the first slurry circulating between the reaction vessel 10 and the cyclone electrolysis device 20.

[0103] Step (3): At an anode current density of 200 A / m 2 Under conditions of pH 4 to 9, the first oxidation treatment is carried out by electrolytic oxidation. During the first oxidation treatment, the pH value of the slurry in the mixing tank is monitored by pH monitoring device 30, and the first acid solution (hydrochloric acid) is added to the slurry in the mixing tank by an automatic acid addition system to maintain the pH value of the slurry undergoing the first oxidation treatment stable.

[0104] Step (4): After the charge reaches 0.18 Ah / g battery powder, the slurry potential is >0.4V (0.2415V relative to saturated KCl calomel electrode, pH value is 4.0, temperature is 30℃), and this slurry is used as the initial second slurry;

[0105] Step (5): Add ferric sulfate as a potential buffer to the second slurry in the mixing tank at a concentration of 2.5 g / L, and maintain the temperature of the second slurry at this time >45℃.

[0106] Step (6): Using an automatic acid-adding device 40, a second acidic solution (hydrochloric acid) is slowly added to the second slurry to adjust the pH of the second slurry to about 1.5. At the same time, hydrogen peroxide is added as an oxidant to maintain the potential of the second slurry >0.4V (0.2415V relative to the saturated KCl calomel electrode). After stirring for 4 hours, the Al content in the slurry at this time (defined as the final slurry) is 0.07%, and the Cu content is 0.04%.

[0107] Step (7): The final slurry is subjected to solid-liquid separation and filter cake washing to obtain iron phosphate by-product and a mixed solution containing lithium, copper, aluminum, iron and phosphate ions.

[0108] The main chemical compositions of the above mixed solution and the ferric phosphate byproducts are shown in Tables 2 and 3, respectively. SEM images of the ferric phosphate byproducts are shown below. Figure 4 As shown.

[0109] Table 2. Main chemical composition (g / L)

[0110] content 6.41 0.63 4.15 3.60 0.35

[0111] Table 3. Composition of main chemical components (%)

[0112] content 0.05 27.4 0.04 0.07 14.0

[0113] As can be seen from Tables 1, 2 and 3, the loss of Fe and P by dissolution is relatively small, and the impurities of Al and Cu in the iron phosphate byproducts have been reduced to a low level.

[0114] Depend on Figure 3 and Figure 4 It can be seen that the main materials are carbon and iron phosphate.

[0115] Example 3

[0116] This embodiment provides a method for processing lithium iron phosphate battery powder, and the processing system used in this method is the lithium iron phosphate battery powder processing system provided in Embodiment 1.

[0117] The method includes the following steps:

[0118] Step (1): The lithium iron phosphate battery dry powder and water are stirred in a mixing tank equipped with a stirring paddle to form a stable first slurry with a solid content of 5%. A small amount (5 g / L) of supporting electrolyte Na2SO4 is added to the first slurry as a conductive agent to make the first slurry conductive.

[0119] The lithium iron phosphate battery dry powder described above is the same as the lithium iron phosphate battery dry powder used in Example 2.

[0120] Step (2): Turn on the circulation pump 51 to start the first slurry circulating between the reaction vessel 10 and the cyclone electrolysis device 20.

[0121] Step (3): At an anode current density of 100 A / m 2 Under conditions of pH 4 to 10, the first oxidation treatment is carried out by electrolytic oxidation. During the first oxidation treatment, the pH value of the slurry in the mixing tank is monitored by pH monitoring device 30, and the first acid solution (sulfuric acid) is added to the slurry in the mixing tank by an automatic acid addition system to maintain the pH value of the slurry undergoing the first oxidation treatment stable.

[0122] Step (4): After the charge reaches 0.20 Ah / g battery powder, the slurry potential is >0.6V relative to the standard hydrogen electrode, the pH value is 4.5, and the temperature is 43℃. This slurry is used as the initial second slurry.

[0123] Step (5): Add ferric chloride as a potential buffer to the second slurry in the mixing tank at a concentration of 2.0 g / L, and maintain the temperature of the second slurry at this time >45℃.

[0124] Step (6): Using an automatic acid addition device 40, a second acidic solution (sulfuric acid) is slowly added to the second slurry to adjust the pH of the second slurry to about 1.25. At the same time, sodium persulfate is added as an oxidant to maintain the potential of the second slurry relative to the standard hydrogen electrode > 0.6V. After stirring for 5 hours, the Al content in the slurry at this time (defined as the final slurry) is 0.09% and the Cu content is 0.08%.

[0125] Step (7): The final slurry is subjected to solid-liquid separation and filter cake washing to obtain iron phosphate by-product and a mixed solution containing lithium, copper, aluminum, iron and phosphate ions.

[0126] The main chemical compositions of the above mixed solution and the iron phosphate byproduct are shown in Tables 4 and 5, respectively.

[0127] Table 4. Main chemical composition (g / L)

[0128] content 1.15 0.52 0.81 0.73 0.25

[0129] Table 5. Composition of main chemical components (%)

[0130] content 0.08 27.9 0.08 0.09 14.2

[0131] Comparative Example 1

[0132] The difference between this comparative example and Example 2 is that the pH value of the second slurry was 2.2 during the second oxidation process.

[0133] The comparative example yielded iron phosphate byproducts with copper and aluminum contents exceeding 0.1%. Specifically, the iron phosphate byproducts contained 0.12% Li, 28.20% Fe, 0.11% Cu, 0.16% Al, and 14.10% P.

[0134] Comparative Example 2

[0135] The difference between this comparative example and Example 2 is that no potential buffer was added to the second slurry.

[0136] This comparative example makes it difficult to control and stabilize the potential during the addition of acid, resulting in large fluctuations in the slurry potential value and making it difficult to efficiently separate iron phosphate from impurity metals in lithium iron phosphate battery powder.

[0137] Comparative Example 3

[0138] The difference between this comparative example and Example 2 is that no oxidant was added to the second slurry.

[0139] The concentrations of Fe and P in the final mixed solution obtained in this comparative example will increase significantly. Specifically, in this mixed solution, the concentrations are: Li 6.41 g / L, Fe 8.10 g / L, Cu 4.15 g / L, Al 3.60 g / L, and P 5.20 g / L.

[0140] In summary, the method for processing lithium iron phosphate battery powder provided by this invention is simple to operate, operates under mild conditions, and can achieve efficient separation of iron phosphate and impurity metals in lithium iron phosphate battery powder, producing iron phosphate byproducts with low aluminum and / or copper content and high yield. The corresponding processing system has a simple structure, low cost, and is easy to operate.

[0141] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for processing lithium iron phosphate battery powder, characterized in that, The process includes the following steps: first, the lithium iron phosphate battery powder containing impurity metals is made into a first slurry, and then subjected to a first oxidation treatment by electrolytic oxidation until the lithium iron phosphate is completely converted into iron phosphate to obtain a second slurry; the pH value of the second slurry is reduced and a second oxidation treatment is performed to dissolve the impurity metals in the second slurry; solid-liquid separation is performed to obtain iron phosphate slag and a solution containing impurity metals. The impurity metal includes at least one of aluminum and copper; the second oxidation treatment includes electrolytic oxidation or chemical oxidation. During the second oxidation process, the pH value of the second slurry is <2.0; a potential buffer is also added to the second slurry; when the second oxidation is carried out by chemical oxidation, it also includes: adding an oxidant to the second slurry to maintain the potential of the second slurry ≥0.6V relative to the standard hydrogen electrode; In the first electrolytic oxidation process, a first acidic solution is added to maintain the pH value of the first slurry at 3-10.

2. The method according to claim 1, characterized in that, The first acidic solution includes at least one of sulfuric acid and hydrochloric acid.

3. The method according to claim 1 or 2, characterized in that, The first slurry further includes at least one of the following features: Feature 1: The solid content of the first slurry is 5%~40%; Feature 2: The first slurry also contains conductive reagents.

4. The method according to claim 3, characterized in that, The conductive reagent includes an electrolyte.

5. The method according to claim 4, characterized in that, The electrolyte includes at least one of sulfate and chloride.

6. The method according to claim 3, characterized in that, The conductive reagent is present in the first slurry at a concentration of 5 g / L to 10 g / L.

7. The method according to claim 1, characterized in that, The anolyte current density for the first oxidation treatment is 100 A / m 2 ~500A / m 2 ; And / or, the electrolytic endpoint of the first oxidation treatment is: the potential of the first slurry relative to the standard hydrogen electrode is ≥0.6V.

8. The method according to claim 1, characterized in that, The second oxidation treatment also includes at least one of the following features: Feature 3: During the second oxidation process, the pH value of the second slurry is 1.0~1.5; Feature 4: The temperature of the second oxidation treatment is ≥45℃; Feature 5: The endpoint of the second oxidation treatment is that the content of Cu and Al in the ferric phosphate slag does not exceed 0.1%.

9. The method according to claim 1, characterized in that, The method to lower the pH value of the second slurry is to add a second acidic solution to the second slurry.

10. The method according to claim 9, characterized in that, The second acidic solution includes at least one of sulfuric acid and hydrochloric acid.

11. The method according to claim 1, characterized in that, The potential buffer includes materials containing ferric iron.

12. The method according to claim 11, characterized in that, The material containing ferric iron includes at least one of ferric sulfate and ferric chloride.

13. The method according to claim 11, characterized in that, The concentration of the material containing ferric iron in the second slurry is ≥1.5 g / L.

14. The method according to claim 1, characterized in that, The oxidant includes at least one of hydrogen peroxide, persulfate, chlorine, hypochlorite, and chlorate.

15. A system for processing lithium iron phosphate battery powder, characterized in that, The system is used to perform the operations described in any one of claims 1 to 14; The system includes a reaction vessel and a cyclone electrolysis device; The material inlet of the cyclone electrolysis device is connected to the material outlet of the reaction vessel, and the material outlet of the cyclone electrolysis device is connected to the material inlet of the reaction vessel, so that the material forms a circulation path between the cyclone electrolysis device and the reaction vessel; The reaction vessel is used for at least the material mixing and the second oxidation process by chemical oxidation; the cyclone electrolysis device is used for the first oxidation process and the second oxidation process by electrolytic oxidation. The system also includes a pH monitoring device for monitoring the pH value of the reaction process, an automatic acid addition device for adding acidic solutions, and a circulation pump and circulation pipeline for conveying materials between the cyclone electrolysis unit and the mixing container.

16. The system according to claim 15, characterized in that, The cyclone electrolysis device includes an electrolytic cell, an anode, and a cathode. The electrolytic cell has an electrolysis chamber. The anode is disposed on the inner wall of the electrolytic cell, and the cathode is disposed in the electrolysis chamber, with the surface of the cathode covered with an insulating cloth.

17. The system according to claim 16, characterized in that, The anode includes a graphite anode, a lead-containing anode, or a titanium-containing anode.

18. The system according to claim 16, characterized in that, The insulating fabric includes at least one of polyester fabric and polypropylene fabric.

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