Sourcing recovery method of scrapped lithium iron phosphate battery

Abstract

The invention discloses a source recovery method of a scrapped lithium iron phosphate battery. The source recovery method comprises the following steps: S1, scrapped battery treatment; S2, acid leaching treatment; S3, precipitation; according to the method, high-purity recovery of lithium is achieved, resource recovery of ferric sulfate of the scrapped lithium iron phosphate battery can be achieved, the recovered ferric sulfate is prepared into the fluorine removal agent, the problem that recycling is difficult in the lithium iron phosphate recovery process is solved, a large amount of fluorine-containing waste water generated by other production lines can be effectively treated, and green circulation is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery recycling, and in particular relates to a source recovery method for scrapped lithium iron phosphate batteries. Background Art

[0002] In recent years, with the rapid development of technology in the field of new energy in my country, lithium batteries have become increasingly irreplaceable in various electronic devices and power units. Among them, after more than 30 years of long-term development, lithium batteries that have been retired and scrapped for various reasons have begun to accumulate in large quantities since the beginning of the development of this technology, and have huge recycling potential. Among them, ternary lithium batteries have obvious recycling value due to a certain content of high-value metals. Recycling lithium and precious metals such as nickel, cobalt, and manganese in them through various methods has become an important way for some industries to pursue resource recycling profits. But at the same time, there is a considerable amount of inventory of discarded lithium batteries, which are also the mainstream of lithium batteries, at home and abroad, but it is difficult to completely recycle them, or they can only be simply disposed of. There are two main reasons for this:

[0003] 1. The overall cost of lithium iron phosphate batteries is low, and precious raw materials such as high-value precious metals are rarely used in the manufacturing process. Among them, the most valuable raw materials for recycling are various lithium-containing compounds, while the rest of the main iron phosphate has a low recycling value, and manufacturers often do not have enough willingness to process it deeply.

[0004] 2. The remaining part of the battery recycling, whose main component is iron phosphate, needs to be recovered and refined by acid leaching due to its poor water solubility. Many technical problems need to be solved in this process: such as impurity removal during the refining process, treatment of pollutants, and the removal of salts produced after multiple steps of purification after acid leaching; and the process used to solve these problems must strictly control the cost to ensure that the recovered iron phosphate products have a certain market competitiveness. However, the greater difficulty for the recovered iron phosphate is that it has fewer application fields in agriculture and industry. In addition to the manufacture of lithium iron phosphate batteries, it is only used in electronics, special cement building materials, and ceramic crafts. Battery-grade iron phosphate used for lithium iron phosphate batteries requires high purity, and it is necessary to thoroughly remove impurities from fluorine, copper, aluminum, calcium, magnesium and soluble organic matter in the scrapped lithium battery raw materials, which puts it in a relatively disadvantageous position in the competition with the originally lower-cost new iron phosphate. Summary of the invention

[0005] The purpose of the present invention is to provide a method for recycling scrapped lithium iron phosphate batteries to solve the technical problems raised in the above-mentioned background technology.

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

[0007] A method for recycling scrapped lithium iron phosphate batteries comprises the following steps:

[0008] S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of battery pole pieces in an anaerobic environment and cool to room temperature after pyrolysis;

[0009] S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor. After the mixing is completed, phosphoric acid is added according to the amount of lithium in the battery pole piece black powder, and then sulfuric acid is added to adjust the pH of the system solution to ≤ 0.9, and the solution is heated to 60-80°C, stirred for reaction, and the reaction is stopped when the pH is 1.25-1.75;

[0010] S3 precipitation: adding reduced iron powder to the system solution after the reaction is completed, heating to 75°C-85°C, concentrating the system solution, and adjusting the pH to 4-4.5;

[0011] S4 solution treatment: After the pH of the system solution is adjusted, filter it while hot to obtain an acid leaching solution and lithium phosphate precipitate;

[0012] S5 acid leaching solution treatment: after the Fe(II) ion concentration of the acid leaching solution is detected, aluminum sulfate is added to the acid leaching solution according to the detected Fe(II) ion concentration to obtain a mixed solution;

[0013] S6 Aeration and stirring: Add the mixed solution to the aeration equipment, heat it up, and aerate and stir it to react. When the solution forms a colloid and the pH value is 1<pH<2, the reaction is completed;

[0014] S7 preparation of defluorinating agent: filtering the obtained colloid to remove the precipitate to obtain a defluorinating agent;

[0015] Furthermore, in S1, the pyrolysis temperature is 475-525° C. and the time is 0.5-1 h.

[0016] Furthermore, in S2, the amount of phosphoric acid added is 2-2.5 times the amount of lithium substance.

[0017] Furthermore, in said S2, the solid-liquid ratio of this step is 1:2.5-5.

[0018] Furthermore, in S3, the system solution is concentrated to a phosphate concentration of 7-10 g / L.

[0019] Furthermore, in S5, the amount of aluminum phosphate added is 0.95-1.5 times the concentration of Fe(II) ions.

[0020] Furthermore, in S6, the temperature is raised to 50-80°C, the aeration flow rate is >30L / min·m3, and the reaction time is >12h.

[0021] Furthermore, in S7, the precipitate is filtered out to obtain a defluorination liquid, and a stabilizer is added to the defluorination liquid to obtain a defluorination agent.

[0022] Furthermore, the stabilizer is one or more of sodium nitrate and sodium sulfite.

[0023] Furthermore, the amount of the stabilizer added is 0.1%-0.5% of the total salt amount of the defluorination liquid.

[0024] The principle of the present invention is:

[0025] S1 Scrap battery processing: First, the scrapped lithium iron phosphate battery is disassembled and crushed to obtain the electrode black powder, which can increase the surface area of ​​the reactants and enable the subsequent chemical reactions to proceed more fully, thereby providing uniform raw materials for subsequent chemical treatment steps such as pyrolysis and acid leaching, ensuring that each particle can better contact with the pyrolysis environment or chemical reagents, thereby improving the efficiency and effectiveness of the entire recycling process.

[0026] The battery pole black powder is pyrolyzed in an anaerobic environment. Since the organic matter in the battery (such as the organic components in the binder and electrolyte, etc.) often has low thermal stability, it will decompose into small molecular volatile substances at high temperature and be removed. The volatile organic matter in the battery can be driven out first, thereby minimizing its interference with the quality of the products in the subsequent steps; at the same time, the anaerobic environment can prevent the oxidation of iron elements and protect Fe(II) in lithium iron phosphate from being oxidized, so that it will not precipitate with phosphate in the subsequent acid leaching process, which is conducive to the effective separation and recovery of lithium, iron and other elements.

[0027] S2 Acid leaching treatment: By detecting the amount of lithium substance and accurately controlling the amount of phosphoric acid added, it is ensured that lithium can enter the solution in a suitable chemical form during the acid leaching process. It also provides basic data for the subsequent lithium precipitation and recovery steps, which is beneficial to optimize the entire recovery process and improve the recovery rate of lithium. By adding phosphoric acid, an acid-base reaction occurs with lithium iron phosphate. Phosphoric acid provides sufficient hydrogen ions to separate lithium from the lattice structure of lithium iron phosphate to form lithium ions. At the same time, phosphate radicals also participate in the reaction balance. Deoxygenated water is used to avoid dissolved oxygen and other impurities in the water, such as chlorine in tap water, which undergoes oxidation or other chemical reactions with components in battery black powder. The addition of sulfuric acid can further provide hydrogen ions, while lowering the pH value of the system, enhancing the acidic environment, and facilitating the dissolution of other metal ions, thereby creating an environment that is beneficial to the main component of lithium iron phosphate (Li + , Fe 2+ PO4 3- ) in a strongly acidic environment to dissolve all the components, while ensuring that the reaction proceeds safely and stably.

[0028] S3 precipitation: After the reaction is completed, the pH is 1.5±0.25, and most of the iron is in the form of Fe 2+ It exists in the solution in the form of Li3PO4. Unlike FePO4, which is only soluble in solutions with a pH of less than 2.0, Fe3PO42 is soluble in solutions with a pH of less than 6.5. The precipitation of lithium phosphate is at a pH of more than 3.5. Therefore, the temperature is increased and the pH is adjusted to 4-5 to reduce the solubility of lithium phosphate, so that more than 95% of the lithium is precipitated in the form of Li3PO4, while the iron element is dissolved in the solution; concentrating the solution to a phosphate concentration of 7-10g / L can make the amount of lithium precipitation reach a platform, that is, at this concentration, the amount of lithium precipitation is relatively stable and high. Adding reducing iron powder can prevent Fe 2+ is oxidized because Fe 2+ After oxidation, iron hydroxide precipitate may be formed and mixed with lithium precipitate, which can reduce the difficulty of lithium purification in subsequent stages and prevent the flocs of iron precipitate from mixing lithium and impurities in a complex manner, causing lithium loss during separation.

[0029] S4 solution treatment: Ferrous phosphate and ferrous sulfate exist in the acid leaching solution, and by further purifying lithium phosphate precipitation, it can be used to recover battery-grade lithium phosphate or separate phosphate to prepare lithium carbonate, thereby realizing the recovery of lithium in scrapped lithium iron phosphate batteries.

[0030] S5 acid leaching treatment: Detecting the iron ion concentration is to accurately control the amount of aluminum sulfate added. Aluminum sulfate is added at 0.95-1.5 times the iron ion concentration to ensure that the iron ions and aluminum ions can react in a suitable ratio. If the amount of aluminum sulfate added is insufficient, all iron ions may not be able to effectively form a colloid with aluminum ions with a good defluorination effect; if too much is added, it will cause a waste of raw materials and may affect the performance and component stability of the defluoridation agent. At the same time, the performance of the defluoridation agent finally prepared is closely related to the iron ions and aluminum ions. The appropriate ratio can make the defluoridation agent form a stable colloidal structure to ensure the effect of the defluoridation agent.

[0031] S6 Aeration and stirring: After aluminum sulfate is added to the solution, under the conditions of heating and aeration, the oxygen in the air converts Fe 2+ Ions are oxidized to Fe 3+ ions, forming iron phosphate and iron sulfate. As the solution is gradually concentrated in this step, the aluminum ions produce a strong hydrolysis effect, which greatly reduces the pH, causing iron (III) to dissolve and eventually form a colloid with aluminum.

[0032] S7 Defluorination: After aeration and stirring, fluoride ions will react with other components in the solution, such as organic matter and metal ions, to form flocculants. The sediments that have formed flocculations with organic matter and fluorine in the solution are removed by filtration. A portion of phosphate that has not been completely removed with the precipitation of lithium is also removed with excess iron and aluminum precipitation at this time to obtain a bright red iron sulfate-aluminum solution, which is the defluorination liquid.

[0033] The preparation principle of the defluorination agent of this application is:

[0034] In the iron sulfate-aluminum solution obtained by the above-mentioned source recovery method of scrapped lithium iron phosphate batteries, the iron sulfate-aluminum solution is defluorinated based on ion exchange, complex reaction and precipitation. The polyhydroxy cations produced by the hydrolysis of aluminum ions in the solution can exchange ions with fluoride ions to generate precipitation, and the products of the hydrolysis of iron sulfate and aluminum ions can react with fluoride ions to form a stable complex; at the same time, iron ions and aluminum ions combine with fluoride ions to produce insoluble precipitates to achieve defluorination. In addition, since the iron sulfate-aluminum solution is made into a colloidal structure by the above method, the iron sulfate-aluminum colloid can form colloidal particles with positive charge in water, and the fluoride ion has a small radius and a strong electronegativity. Due to the electrostatic attraction, the colloidal particles will produce strong electrostatic adsorption on the fluoride ions, so that the fluoride ions are adsorbed to the surface of the colloid, thereby reducing the concentration of fluoride ions in the water; in addition, the colloid has a huge specific surface area and can provide a large number of adsorption sites. The fluoride ions can be attached to these sites on the surface of the colloid by physical adsorption, thereby improving the defluorination effect, and the colloid can maintain a relatively stable suspended state in the solution, so that the defluoridation agent can be evenly dispersed in the solution, ensuring that the defluoridation agent can fully contact with the fluoride-containing wastewater during the entire defluorination process, further improving the defluorination effect.

[0035] By adding a stabilizer, the defluorinating agent can remain a flowable solution at room temperature without stratification, thus ensuring the storage and use effect of the defluorinating agent.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The present invention not only realizes high-purity lithium recovery by recycling scrapped lithium iron phosphate batteries, but also can recycle the iron sulfate in scrapped lithium iron phosphate batteries, solving the open circuit of iron elements in lithium iron phosphate batteries, so that phosphorus and lithium, two relatively valuable elements, can be separated from iron through this process and effectively applied. It not only solves the problem of resource difficulty in the lithium iron phosphate recycling process, but also can effectively treat a large amount of fluorine-containing wastewater generated by other production lines.

[0038] 2. The present invention recovers iron sulfate from scrapped phosphoric acid to make a defluorinating agent, which can not only directly treat the fluorine in the acid leaching liquid during the lithium iron phosphate battery recycling process, but also can be further output in the form of a defluorinating agent, and can be used for deep defluorination in other types of other scrapped lithium battery recycling production lines or other industrial defluorination water treatment, to achieve the maximum added value application of each component in the lithium iron phosphate battery recycling process. The overall process does not conflict with the lithium iron phosphate valuable raw material recovery process, the lithium recovery rate is high, less reagents are added, and the investment cost is controllable. It can simultaneously solve the pollution treatment problem generated by part of the process and the problem that iron phosphate is difficult to recover as a high value-added product in the lithium iron phosphate recovery process, and has good benefits and operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are only for the purpose of enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0041] like Figure 1 As shown, a method for recycling scrapped lithium iron phosphate batteries comprises the following steps:

[0042] S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of the battery pole pieces in an anaerobic environment at a temperature of 475-525°C for 0.5-1h, and cool to room temperature after pyrolysis;

[0043] The anaerobic environment is constructed by using a semi-sealed electric furnace or a rotary kiln with positive pressure nitrogen;

[0044] S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor, wherein the deoxygenated water is deionized water that has been heated and then cooled; after the mixing is completed, phosphoric acid is added in an amount of 2-2.5 times the amount of lithium in the battery pole piece black powder, and sulfuric acid is added to adjust the system solution pH ≤ 0.9, and the solution is heated to 60-80°C, stirred for reaction, and the reaction is stopped when the system pH is 1.25-1.75; the solid-liquid ratio of this step is 1:2.5-5;

[0045] S3 precipitation: adding reduced iron powder to the system solution after the reaction is completed, heating to 75°C-85°C, concentrating the system solution to a phosphate concentration of 7-10g / L, and adjusting the pH to 4-4.5 with sodium carbonate or sodium hydroxide;

[0046] S4 solution treatment: after pH adjustment, filter while hot to obtain acid leaching solution and lithium phosphate precipitate; recover the lithium phosphate precipitate, and after further purification, it can be used to recover battery-grade lithium phosphate or separate phosphate to prepare lithium carbonate;

[0047] S5 acid leaching solution treatment: after the Fe(Ⅱ) ion concentration of the acid leaching solution is detected, aluminum sulfate with a concentration of 0.95-1.5 times the Fe(Ⅱ) ion concentration is added to the acid leaching solution according to the detected ion concentration to obtain a mixed solution;

[0048] S6 Aeration and stirring: Add the mixed solution to the aeration equipment, raise the temperature to 50-80℃ and flow rate>30L / min·m 3 The reaction is carried out by aeration and stirring at a flow rate of , and the reaction time is greater than 12h. When the solution forms a colloid and the pH value is 1<pH<2, the reaction is completed;

[0049] Preparation of S7 defluorinating agent: Filter the solution after the reaction, take the filtrate, obtain the defluorinated liquid, add a stabilizer, the defluorinated liquid has a total salt content of 0.1%-0.5%, and obtain a total salt content of 50.0-75.0g / L, PO4 3- Defluorination agent with concentration less than 0.5g / L.

[0050] The stabilizer is one or more of sodium nitrate and sodium sulfite.

[0051] The defluorinating agent can be maintained as an aqueous solution, or can be further evaporated to promote the precipitation of crystals to make it into a powder.

[0052] The method of using the defluoridator is as follows: for a type of fluoride-containing water sample, adjust its pH to 8-11, and add the defluoridator at 1%, heat the defluoridator to 45℃-60℃ and stir for 30 minutes; if the defluoridator is made into a powder, it should be pre-dissolved, prepared into a solution of about 20%-30%, and then heated and stirred; after stirring, add 1.2%-1.5% of 5% PAM solution to the defluoridator, stop stirring, at this time a large amount of flocs can be observed to settle, wait for ≥15 minutes, filter out the flocs, and the defluoridation operation can be completed.

[0053] After this step, the fluorine in the solution exceeding 3g / L can be removed to less than 50mg / L. It can be combined with other deep defluorination processes to further reduce the fluorine content in the wastewater to a concentration that meets local emission standards.

[0054] The following is described by more specific embodiments:

[0055] Example 1

[0056] A method for recycling scrapped lithium iron phosphate batteries comprises the following steps:

[0057] S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of the battery pole pieces in an anaerobic environment at a temperature of 500°C for 1 hour, and cool to room temperature after pyrolysis;

[0058] S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor, wherein the deoxygenated water is deionized water that has been heated and then cooled; after the mixing is completed, phosphoric acid is added in an amount twice the amount of lithium in the battery pole piece black powder, and sulfuric acid is added to adjust the pH of the system solution to ≤ 0.9, and the solution is heated to 60°C and stirred for reaction. The reaction is stopped when the pH of the system is 1.5; the solid-liquid ratio of this step is 1:5;

[0059] S3 precipitation: after the reaction is completed, reduced iron powder is added to the system solution, and the solution is heated to 75°C, the system solution is concentrated to a phosphate concentration of 10 g / L, and the pH is adjusted to 4 with sodium carbonate;

[0060] S4 solution treatment: after pH adjustment, filter while hot to obtain acid leaching solution and lithium phosphate precipitate;

[0061] S5 acid leaching solution treatment: after the Fe(Ⅱ) ion concentration of the acid leaching solution is detected, aluminum sulfate having a concentration of 1 times the Fe(Ⅱ) ion concentration is added to the acid leaching solution according to the detected ion concentration to obtain a mixed solution;

[0062] S6 Aeration and stirring: Add the mixed solution to the aeration equipment, raise the temperature to 55°C and flow at a flow rate of >30L / min·m 3 The reaction was carried out by aeration and stirring at a flow rate of , and the reaction time was > 12h. When the solution formed a colloid and the pH value was 1.2, the reaction was completed;

[0063] S7 Preparation of defluorinating agent: Filter the solution after the reaction is completed, take the filtrate to obtain a defluorinating liquid, add sodium nitrate with a total salt content of 0.2% of the defluorinating liquid to obtain a defluorinating agent.

[0064] Example 2

[0065] A method for recycling scrapped lithium iron phosphate batteries comprises the following steps:

[0066] S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of the battery pole pieces in an anaerobic environment at a temperature of 475°C for 0.8h, and cool to room temperature after pyrolysis;

[0067] S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor, wherein the deoxygenated water is deionized water that has been heated and then cooled; after the mixing is completed, phosphoric acid is added in an amount 2.2 times the amount of lithium in the battery pole piece black powder, and then sulfuric acid is added to adjust the pH of the system solution to ≤ 0.9, and the solution is heated to 70°C and stirred for reaction. The reaction is stopped when the pH of the system is 1.25; the solid-liquid ratio of this step is 1:4;

[0068] S3 precipitation: after the reaction is completed, reduced iron powder is added to the system solution, and the solution is heated to 80°C, the system solution is concentrated to a phosphate concentration of 7 g / L, and the pH is adjusted to 4.5 with sodium carbonate;

[0069] S4 solution treatment: after pH adjustment, filter while hot to obtain acid leaching solution and lithium phosphate precipitate;

[0070] S5 acid leaching solution treatment: after the Fe(Ⅱ) ion concentration of the acid leaching solution is detected, aluminum sulfate with a concentration of 0.95 times the Fe(Ⅱ) ion concentration is added to the acid leaching solution according to the detected ion concentration to obtain a mixed solution;

[0071] S6 Aeration and stirring: Add the mixed solution to the aeration equipment, raise the temperature to 60℃ and flow rate>30L / min·m 3 The reaction was carried out by aeration and stirring at a flow rate of , and the reaction time was > 12h. When the solution formed a colloid and the pH value was 1.8, the reaction was completed;

[0072] S7 Preparation of defluorinating agent: Filter the solution after the reaction is completed, take the filtrate to obtain a defluorinating liquid, add sodium nitrate with a total salt content of 0.5% of the defluorinating liquid to obtain a defluorinating agent.

[0073] Example 3

[0074] A method for recycling scrapped lithium iron phosphate batteries comprises the following steps:

[0075] S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of the battery pole pieces in an anaerobic environment at a temperature of 525°C for 0.5h, and cool to room temperature after pyrolysis;

[0076] S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor, wherein the deoxygenated water is deionized water that has been heated and then cooled; after the mixing is completed, phosphoric acid is added in an amount of 2-2.5 times the amount of lithium in the battery pole piece black powder, and sulfuric acid is added to adjust the pH of the system solution to ≤ 0.9, and the solution is heated to 80°C and stirred for reaction. The reaction is stopped when the pH of the system is 1.75; the solid-liquid ratio of this step is 1:2.5;

[0077] S3 precipitation: after the reaction is completed, reduced iron powder is added to the system solution, and the solution is heated to 85°C, the system solution is concentrated to a phosphate concentration of 9 g / L, and the pH is adjusted to 4.2 with sodium carbonate;

[0078] S4 solution treatment: after pH adjustment, filter while hot to obtain acid leaching solution and lithium phosphate precipitate;

[0079] S5 acid leaching solution treatment: after the Fe(Ⅱ) ion concentration of the acid leaching solution is detected, aluminum sulfate with a concentration of 1.5 times the Fe(Ⅱ) ion concentration is added to the acid leaching solution according to the detected ion concentration to obtain a mixed solution;

[0080] S6 Aeration and stirring: Add the mixed solution to the aeration equipment, raise the temperature to 80℃ and flow rate>30L / min·m 3 The reaction was carried out by aeration and stirring at a flow rate of , and the reaction time was > 12h. When the solution formed a colloid and the pH value was 1.6, the reaction was completed;

[0081] S7 Preparation of defluorinating agent: Filter the solution after the reaction is completed, take the filtrate to obtain a defluorinating liquid, add sodium sulfite with a total salt content of 0.1% of the defluorinating liquid to obtain a defluorinating agent.

[0082] Example 4

[0083] A method for recycling scrapped lithium iron phosphate batteries comprises the following steps:

[0084] S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of the battery pole pieces in an anaerobic environment at a temperature of 490°C for 1 hour, and cool to room temperature after pyrolysis;

[0085] S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor, wherein the deoxygenated water is deionized water that has been heated and then cooled; after the mixing is completed, phosphoric acid is added in an amount 2.1 times the amount of lithium in the battery pole piece black powder, and sulfuric acid is added to adjust the pH of the system solution to ≤0.9, and the solution is heated to 65°C and stirred for reaction. The reaction is stopped when the pH of the system is 1.25-1.75; the solid-liquid ratio of this step is 1:3;

[0086] S3 precipitation: after the reaction is completed, reduced iron powder is added to the system solution, and the solution is heated to 75°C, the system solution is concentrated to a phosphate concentration of 8 g / L, and the pH is adjusted to 4 using sodium hydroxide;

[0087] S4 solution treatment: after pH adjustment, filter while hot to obtain acid leaching solution and lithium phosphate precipitate;

[0088] S5 acid leaching solution treatment: after the Fe(Ⅱ) ion concentration of the acid leaching solution is detected, aluminum sulfate with a concentration of 1.2 times the Fe(Ⅱ) ion concentration is added to the acid leaching solution according to the detected ion concentration to obtain a mixed solution;

[0089] S6 Aeration and stirring: Add the mixed solution to the aeration equipment, raise the temperature to 50℃ and flow at a flow rate of >30L / min·m 3 The reaction was carried out by aeration and stirring at a flow rate of , and the reaction time was > 12h. When the solution formed a colloid and the pH value was 1.5, the reaction was completed;

[0090] S7 Preparation of defluorinating agent: Filter the solution after the reaction is completed, take the filtrate to obtain a defluorinating liquid, add sodium nitrate and sodium sulfite with a total salt content of 0.3% of the defluorinating liquid to obtain a defluorinating agent.

[0091] Experiment on wastewater treatment with defluoridation agent

[0092] 1. For the typical ternary lithium battery acid immersion liquid A water sample, take 100ml of A water sample as a fluorine-containing wastewater sample for treatment.

[0093] Fluoride content of original water sample: 2344 mg / L.

[0094] After the original water sample was simply decolorized, calcium hydroxide was added to adjust the pH to 9.5, and 15% of calcium sulfate was further added for crude defluorination. The mixture was mixed and stirred at room temperature for about 60 minutes. After the stirring was completed, the water sample was filtered to remove the precipitate, and a crude defluoridated water sample A1 was obtained.

[0095] Fluoride content of crude defluoridated water sample A1: 340.6 mg / L

[0096] According to the calculation of fluorine:aluminum+iron=1:15, 0.20 ml of the defluoridation agent solution (total salt content 59 g / L) prepared in Example 1 was added, and the pH value of the solution was adjusted to 6.5 using sodium hydroxide solution (0.1 mol / L) after the addition. The mixed solution was heated to 70°C, 0.1% PAM was added, and the heating was stopped after stirring for 30 minutes. The mixture was allowed to stand until the flocs were completely settled and then filtered to obtain the defluoridated water sample A2 and a dark green filter residue.

[0097] The fluoride concentration of defluoridated water sample A2 is 19 mg / L, which meets the deep defluoridation water inlet standard.

[0098] 2. For the electrolytic aluminum industry wastewater sample B, take 100 ml of sample B as a fluorine-containing wastewater sample for treatment.

[0099] Fluoride content of original water sample: 217 mg / L.

[0100] According to the calculation of fluorine:aluminum+iron=1:8, 0.7 ml of the defluoridation agent solution (total salt content 59 g / L) prepared by Example 1 of the present method was added, and after the addition, the pH value of the solution was adjusted to 6.5 using sodium hydroxide solution (0.1 mol / L). The mixed solution was heated to 70°C, 0.1% PAM was added, and the heating was stopped after stirring for 30 minutes. The mixture was allowed to stand until the flocs were completely settled and then filtered to obtain the defluoridated water sample B1 and white filter residue.

[0101] The fluoride concentration of defluoridated water sample B1 is 14.5 mg / L, which meets the deep defluoridation water inlet standard.

[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recycling scrapped lithium iron phosphate batteries, characterized in that: The following steps are involved: S1 Scrap battery treatment: Discharge, disassemble and crush the scrap lithium iron phosphate battery to obtain uniform black powder of lithium iron phosphate battery pole pieces; pyrolyze the black powder of battery pole pieces in an anaerobic environment and cool to room temperature after pyrolysis; S2 acid leaching treatment: the treated battery pole piece black powder is subjected to lithium content detection to obtain the amount of lithium in the battery pole piece black powder. After the detection, the battery pole piece black powder is mixed with deoxygenated water in a reactor. After the mixing is completed, phosphoric acid is added according to the amount of lithium in the battery pole piece black powder, and then sulfuric acid is added to adjust the pH of the system solution to ≤ 0.9, and the solution is heated to 60-80°C, stirred for reaction, and the reaction is stopped when the pH is 1.25-1.75; S3 precipitation: adding reduced iron powder to the system solution after the reaction is completed, heating to 75°C-85°C, concentrating the system solution, and adjusting the pH to 4-4.5; S4 solution treatment: After the pH of the system solution is adjusted, filter it while hot to obtain an acid leaching solution and lithium phosphate precipitate; S5 acid leaching solution treatment: after the Fe(II) ion concentration of the acid leaching solution is detected, aluminum sulfate is added to the acid leaching solution according to the detected Fe(II) ion concentration to obtain a mixed solution; S6 Aeration and stirring: Add the mixed solution to the aeration equipment, heat it up, and aerate and stir it to react. When the solution forms a colloid and the pH value is 1<pH<2, the reaction is completed; S7 Preparation of defluorinating agent: Filter the obtained colloid to remove the precipitate to obtain the defluorinating agent.

2. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In the S1, the pyrolysis temperature is 475-525°C and the time is 0.5-1h.

3. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In the S2, the amount of phosphoric acid added is 2-2.5 times the amount of lithium substance.

4. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In said S2, the solid-liquid ratio of this step is 1:2.5-5.

5. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In S3, the system solution is concentrated to a phosphate concentration of 7-10 g / L.

6. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In the S5, the amount of aluminum phosphate added is 0.95-1.5 times the concentration of Fe(II) ions.

7. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In S6, the temperature is raised to 50-80°C, and the aeration flow rate is >30L / min·m 3 , reaction time>12h.

8. The method for recycling scrapped lithium iron phosphate batteries according to claim 1, characterized in that: In S7, the precipitate is filtered out to obtain a defluorinated liquid, and a stabilizer is added to the defluorinated liquid to obtain a defluorinating agent.

9. The method for recycling scrapped lithium iron phosphate batteries according to claim 8, characterized in that: The stabilizer is one or more of sodium nitrate and sodium sulfite.

10. The method for recycling scrapped lithium iron phosphate batteries according to claim 8, characterized in that: The amount of the stabilizer added is 0.1%-0.5% of the total salt content of the defluorination liquid.

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