Method for recycling lithium manganese iron phosphate waste

Abstract

This invention provides a method for recycling lithium manganese iron phosphate waste. The recycling method includes the following steps: (1) mixing lithium manganese iron phosphate waste with a first acid solution, introducing sulfur dioxide and oxygen, and performing oxidative leaching to obtain a leaching slurry; (2) subjecting the leaching slurry to copper removal treatment to obtain leaching residue and leaching solution; (3) mixing the leaching residue from step (2) with a second acid solution, adjusting the pH value to perform a first precipitation reaction to obtain manganese iron phosphate; and subjecting the leaching solution from step (2) to lithium extraction treatment to obtain purified lithium salt. The recycling method provided by this invention has a better oxidation effect, does not introduce a large amount of cationic impurities, can realize the full-component recovery of lithium manganese iron phosphate battery cathode materials, and can obtain battery-grade purified lithium salt materials and the precursor manganese iron phosphate products required for battery-grade lithium manganese iron phosphate cathode materials; and the process cost is low, which improves the added value of the products and better meets the actual production needs.

Description

Technical Field

[0001] This invention belongs to the field of battery recycling technology and relates to a method for recycling lithium manganese iron phosphate waste. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are the preferred power source for new energy vehicles, boasting advantages such as high cycle performance and superior safety. LFP battery recycling has mature technology. Similar to LFP, lithium manganese iron phosphate (LFP) batteries, due to their high energy density, even higher safety performance, and relatively lower price, hold promise as a potential next-generation high-energy-density power battery cathode material. To achieve the recycling of LFP, the recovery of LFP waste has become a research hotspot.

[0003] Currently, the recovery of lithium manganese iron phosphate mainly involves wet selective recovery of lithium, impurity removal, and distribution precipitation to obtain precipitates such as iron phosphate, manganese phosphate, or manganese iron phosphate.

[0004] For example, CN115632185A discloses a method for the full-component recycling and treatment of waste lithium manganese iron phosphate battery cathode materials. A lithium leaching solution and a manganese iron phosphorus leaching solution are prepared to sequentially leach the corresponding lithium and phosphorus from the cathode powder of the waste lithium manganese iron phosphate battery, obtaining a lithium leaching solution and a solution containing manganese iron phosphorus. The leached lithium leaching solution is purified to obtain high-purity lithium carbonate. The iron ions in the leached manganese iron phosphorus solution are reduced to ferrous ions, neutralized with alkali, and filtered to obtain crude manganese iron phosphate. The crude manganese iron phosphate is dissolved in phosphoric acid solution, and the dissolved manganese iron phosphate solution is injected into a reactor at a certain flow rate to prepare a manganese iron phosphate precursor. Simultaneously, an alkali solution is injected into the reactor at a certain proportion and flow rate. After filtration, the filter residue is dried to obtain the manganese iron phosphate precursor. Although the technical solution in this literature achieves the complete recovery of lithium manganese iron phosphate and obtains battery-grade lithium carbonate and manganese iron phosphate precursors, its selective lithium leaching agent is prepared from hydrogen peroxide, acid, and persulfate. The oxidizing power of hydrogen peroxide is insufficient to oxidize Mn in the leaching solution. 2+ Selective leaching of lithium manganese iron phosphate requires the use of persulfate in conjunction with hydrogen peroxide. Using persulfate as the leaching agent introduces more cationic impurities, and the high cost of persulfate increases the process cost.

[0005] For example, CN108736090A, CN115535987A, and CN115448335A disclose a method for selectively extracting lithium from waste lithium manganese iron phosphate batteries (or their cathode waste powder). These documents use strong oxidants such as ammonium persulfate, hydrogen peroxide, ozone, and sodium persulfate to directly selectively oxidize and leach the waste lithium manganese iron phosphate batteries (or their cathode waste powder). Compared to the aforementioned method of full-element leaching-precipitation separation and lithium recovery, this method allows for selective lithium leaching and is relatively simpler. However, while this selective lithium extraction method achieves excellent selective leaching results, the high iron and manganese content in lithium manganese iron phosphate consumes a large amount of oxidant. These strong oxidants are generally very expensive, and storing excessive amounts of strong oxidants also poses significant safety risks.

[0006] Therefore, how to effectively recycle lithium manganese iron phosphate waste while reducing process costs is an urgent technical problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for recycling lithium manganese iron phosphate waste. The recycling method provided by this invention offers better oxidation performance, avoids introducing large amounts of cationic impurities, achieves full-component recovery of lithium manganese iron phosphate battery cathode materials, and yields battery-grade purified lithium salt materials as well as the precursor iron manganese phosphate product required for battery-grade lithium manganese iron phosphate cathode materials. Furthermore, it features low process costs, increases product added value, and better meets actual production needs.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for recycling lithium manganese iron phosphate waste, the recycling method comprising the following steps:

[0010] (1) Mix the waste manganese iron lithium phosphate with the first acid solution, and pass in sulfur dioxide and oxygen to carry out oxidative leaching to obtain leaching slurry;

[0011] (2) The leaching slurry is subjected to copper removal treatment to obtain leaching residue and leaching solution;

[0012] (3) Mix the leaching residue from step (2) with the second acid solution, adjust the pH value to carry out the first precipitation reaction, and obtain manganese iron phosphate; perform lithium extraction treatment on the leaching solution from step (2) to obtain purified lithium salt.

[0013] It should be noted that the lithium manganese iron phosphate waste in this invention refers to the waste positive electrode waste of waste lithium manganese iron phosphate batteries. The specific recycling methods are all conventional technical solutions, and all technical solutions that can be reasonably known by those skilled in the art are applicable to this invention.

[0014] For example, the present invention provides a method for processing waste manganese iron lithium phosphate, the method comprising:

[0015] Waste lithium iron phosphate batteries are sequentially discharged, disassembled, crushed, and screened to separate waste lithium iron phosphate powder.

[0016] The recycling method provided by this invention utilizes the interaction between sulfur dioxide and oxygen in a mixed system of lithium iron phosphate waste and a first acid solution to generate highly oxidizing free radical ions with high redox potentials. These free radical ions can remove Fe from the lithium iron phosphate waste. 2+ and Mn 2+ Oxidation is performed with excellent results, not only increasing the valence state of manganese in lithium iron phosphate, causing manganese to precipitate in the leaching residue, but also enabling selective extraction of lithium from lithium iron phosphate. This avoids the problem of introducing a large amount of cationic impurities that can occur when using strong oxidants such as persulfate. The leaching slurry after oxidation undergoes deep copper removal treatment, reducing the copper and aluminum impurity content in the resulting leaching residue, thus obtaining high-purity leaching residue and leachate. The leaching residue is then mixed with a second acid solution, and the pH is adjusted to carry out the first precipitation reaction, yielding the precursor iron manganese phosphate product required for battery-grade lithium iron phosphate cathode materials. After lithium extraction treatment of the leachate, battery-grade purified lithium salt materials can be obtained.

[0017] In this invention, sulfur dioxide and oxygen react in a mixed system of lithium manganese iron phosphate waste and a first acid solution to generate strong oxidizing free radical ions, which oxidize the divalent iron and divalent manganese in the solution. The strong oxidizing free radical ions can act as an oxidant to selectively oxidize and leach lithium. However, if sulfur dioxide and oxygen are introduced into a non-solution system, such as at a high temperature (700-900°C) for solid-phase lithium extraction, strong oxidizing free radical ions cannot be obtained.

[0018] In this invention, after introducing sulfur dioxide and oxygen into a mixed system of lithium manganese iron phosphate waste and a first acid solution, the reaction process in the system is as follows:

[0019] SO2 + H2O → H2SO3 (1)

[0020] H2SO3 → HSO3 - + H + (2)

[0021] Fe 2+ + HSO3 - → FeHSO3 + (3)

[0022] 4FeHSO3 + + O2 → 4FeSO3 ++ 2H2O (4)

[0023] FeSO3 + + → Fe 2+ + SO3 .- (5)

[0024] SO3 .- + O2 → SO5 .- (6)

[0025] SO5 .- + HSO3 - → SO4 2- + SO4 .- + H + (7)

[0026] SO5 .- + Mn 2+ + H + → HSO5 - + Mn 3+ (8).

[0027] In this invention, sulfur dioxide and oxygen are simultaneously introduced into a mixed system of lithium manganese iron phosphate waste and a first acid solution to obtain sulfite radical ions, persulfate radical ions, and sulfate radical ions with strong oxidizing power. These radical ions have high redox potentials, which are beneficial to the oxidation of manganese and iron ions in the lithium manganese iron phosphate waste, causing manganese and iron to precipitate in the leaching residue, thereby obtaining a lithium-containing leachate with high purity and few impurities.

[0028] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0029] Preferably, the concentration of the first acid solution in step (1) is 1 to 5 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L.

[0030] Preferably, in step (1), the molar amount of acid added to the first acid solution is 1 to 2 times the theoretical amount, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 times.

[0031] In this invention, the specific type of the first acid solution is a conventional technical solution, that is, an acid solution used for acid leaching of lithium manganese iron phosphate. This invention is applicable to all such solutions. For example, the acid in the first acid solution includes, but is not limited to, at least one of sulfuric acid, hydrochloric acid, or nitric acid. It should be noted that the theoretical amount of the first acid solution added in this invention refers to the molar amount.

[0032] Specifically:

[0033] When the acid in the first acid solution is sulfuric acid, the theoretical molar amount of sulfuric acid added is 0.5 times the total molar amount of lithium in the mixed system of lithium manganese iron phosphate waste and the first acid solution, that is, n(H2SO4):n(Li)=1:2.

[0034] When the acid in the first acid solution is hydrochloric acid, the theoretical molar amount of hydrochloric acid added is 1 times the total molar amount of lithium in the mixed system of lithium manganese iron phosphate waste and the first acid solution, that is, n(HCl):n(Li)=1:1.

[0035] When the acid in the first acid solution is nitric acid, the theoretical molar amount of nitric acid added is 1 times the total molar amount of lithium in the mixed system of lithium manganese iron phosphate waste and the first acid solution, that is, n(HNO3):n(Li)=1:1.

[0036] Preferably, the flow rate of the sulfur dioxide is 20 to 50 L / h, such as 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h or 50 L / h.

[0037] Preferably, the oxygen flow rate is 10-30 L / h, such as 10 L / h, 13 L / h, 15 L / h, 18 L / h, 20 L / h, 23 L / h, 25 L / h, 28 L / h or 30 L / h.

[0038] In this invention, by controlling the flow rate of sulfur dioxide to 20-50 L / h and / or the flow rate of oxygen to 10-30 L / h, it is more conducive to the formation of a sufficient number of highly oxidizing free radical ions.

[0039] Preferably, the copper removal agent used in the copper removal process in step (2) includes a compound containing thiomolybdate ions, and the compound containing thiomolybdate ions includes ammonium tetrathiomolybdate.

[0040] In this invention, a compound containing thiomolybdate ions is selected as the copper removal agent because this ion can form a complex with copper ions in the leaching slurry without changing the morphology of the leaching residue, thus achieving copper removal from the leaching residue. Furthermore, ammonium tetrathiomolybdate is selected as the copper removal agent, where the ammonium ions can also form a copper-ammonia complex with copper ions. These two complexes can remove copper ions from the leaching residue. The thiomolybdate ions and ammonium ions work synergistically to reduce the copper content in the leaching residue, achieving deep copper removal from the leaching residue. In contrast, conventional copper removal agents, such as sodium sulfate, iron sulfide, ammonium sulfide, or iron powder, are commonly used to remove copper impurities from the leaching solution but cannot achieve the deep copper removal treatment of the leaching residue described in this invention.

[0041] Preferably, in the copper removal process described in step (2), the amount of copper removal agent used is 1 to 2 times the mass of copper in the leaching slurry, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 times.

[0042] Preferably, the leaching residue after copper removal treatment in step (2) is subjected to acid washing and water washing in sequence.

[0043] In this invention, the leaching residue after copper removal treatment in step (2) is subjected to acid washing and water washing in sequence, which can further reduce the aluminum content in the leaching residue, thereby obtaining leaching residue with higher purity.

[0044] Specifically, the pickling is performed using dilute acid, such as 0.1–0.4 mol / L dilute sulfuric acid, 0.1–0.4 mol / L dilute hydrochloric acid, or 0.1–0.4 mol / L dilute nitric acid.

[0045] Preferably, the concentration of the second acid solution in step (3) is 1 to 5 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L.

[0046] Preferably, in step (3), after mixing the leaching residue from step (2) with the second acid solution, manganese ferric phosphate solution and acid-soluble residue are obtained.

[0047] In this invention, the leaching residue is first mixed with a second acid solution for acid dissolution, so as to dissolve the leaching residue containing iron phosphate and manganese phosphate in step (2) in the second acid solution to obtain manganese iron phosphate liquid. The acid-dissolved residue that is insoluble in the second acid solution and is not iron phosphate or manganese phosphate will be further removed.

[0048] Furthermore:

[0049] In step (3), the mixing temperature of the leaching residue and the second acid solution can be 40 to 60°C, such as 40°C, 45°C, 50°C, 55°C or 60°C, and the mixing time can be 1 to 10 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0050] Step (3) The acid in the second acid solution includes, but is not limited to, at least one of sulfuric acid, hydrochloric acid or nitric acid.

[0051] In step (3), the amount of the second acid solution used is 1 to 2 times the total mass of iron and manganese in the leaching residue, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 times.

[0052] Preferably, the pH adjustment in step (3) is to adjust the pH value of the manganese ferric phosphate solution.

[0053] Preferably, after adjusting the pH value in step (3), the pH value in the system is maintained at 4 to 5, such as 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.

[0054] Preferably, the reaction temperature for adjusting the pH value to carry out the first precipitation reaction in step (3) is 30 to 80°C, such as 30°C, 40°C, 50°C, 60°C, 70°C or 80°C, and the reaction time for the first precipitation reaction is 5 to 10 hours, such as 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0055] In this invention, the pH value of the mixed system of leaching residue and second acid solution can be adjusted by adding a precipitant solution. This invention does not impose any special limitations on the type of precipitant. Any type of substance that can adjust the pH value without affecting the precipitation of manganese ferric phosphate product is applicable to this invention. For example, the precipitant can be liquid alkali and / or ammonia water, and the liquid alkali includes sodium hydroxide or potassium hydroxide, etc.

[0056] Preferably, the lithium extraction process in step (3) includes:

[0057] Remove impurities from the leachate obtained in step (2) to obtain a lithium-rich solution. Then, subject the lithium-rich solution to a second precipitation reaction to obtain purified lithium salt.

[0058] In this invention, the leachate obtained in step (2) is a lithium-containing leachate. By removing impurities from it, a high-purity lithium-rich solution is obtained. The high-purity lithium-rich solution is reacted with a precipitant to obtain battery-grade lithium salt.

[0059] It should be noted that this invention does not specifically limit the method for removing impurities from the leachate. Conventional methods for removing impurities from lithium-containing leachates in this invention are applicable to all such methods, such as the process of adding liquid alkali to adjust the pH value for impurity removal. The liquid alkali includes at least one of sodium hydroxide, magnesium hydroxide, or calcium hydroxide.

[0060] Preferably, the pH value of the impurity removal process is 5 to 6, such as 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.

[0061] In this invention, the types of precipitants used in the second precipitation reaction are all selected using conventional techniques. The selection and adjustment can be made according to the type of lithium salt obtained. For example, the precipitant can be sodium carbonate or sodium phosphate. The amount of precipitant added is also selected using conventional techniques, and the mass amount of precipitant added is also selected using conventional techniques. The mass amount added is 1.1 to 2 times the theoretical mass amount required to obtain the corresponding lithium salt. That is, excessive addition can make the reaction more complete.

[0062] As a preferred technical solution, the recycling method includes the following steps:

[0063] (1) Mix the lithium iron phosphate manganese phosphate waste with the first acid solution, and introduce sulfur dioxide with a flow rate of 20-50 L / h and oxygen with a flow rate of 10-30 L / h to carry out oxidative leaching to obtain leaching slurry;

[0064] (2) The leaching slurry is treated with ammonium tetrathiomolybdate to remove copper, and the copper-removed leaching residue and leaching liquid are obtained. The copper-removed leaching residue is acid-washed and water-washed to obtain water-washed leaching residue.

[0065] (3) Mix the leaching residue after water washing in step (2) with the second acid solution to obtain manganese ferric phosphate solution and acid-soluble residue. Adjust the pH of the manganese ferric phosphate solution to 4-5 and maintain the pH of the system at 4-5 to carry out the first precipitation reaction to obtain manganese ferric phosphate.

[0066] The leachate from step (2) is purified under a pH of 5 to 6 to obtain a lithium-rich solution. The lithium-rich solution is then subjected to a second precipitation reaction to obtain purified lithium salt.

[0067] It should be noted that, due to space limitations and to avoid redundancy, this invention does not exhaustively list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] The recycling method provided by this invention utilizes the reaction of sulfur dioxide and oxygen in a mixed system of lithium iron phosphate waste and a first acid solution to generate highly oxidizing free radical ions with high redox potentials, which can remove Fe from the lithium iron phosphate waste. 2+ and Mn 2+ Oxidation is performed with excellent results, not only increasing the valence state of manganese in lithium iron phosphate, causing manganese to precipitate in the leaching residue, but also enabling selective extraction of lithium from lithium iron phosphate. This avoids the problem of introducing a large amount of cationic impurities that can occur when using strong oxidants such as persulfate. The leaching slurry after oxidation undergoes deep copper removal treatment, reducing the copper and aluminum impurity content in the resulting leaching residue, thus obtaining high-purity leaching residue and leachate. The leaching residue is then mixed with a second acid solution, and the pH is adjusted to carry out the first precipitation reaction, yielding the precursor iron manganese phosphate product required for battery-grade lithium iron phosphate cathode materials. After lithium extraction treatment of the leachate, battery-grade purified lithium salt materials can be obtained. Attached Figure Description

[0070] Figure 1 This is a schematic flowchart of the recycling method for lithium manganese iron phosphate waste provided in Example 1. Detailed Implementation

[0071] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0072] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0073] In the description of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0074] In one specific embodiment, the present invention provides a method for processing waste manganese iron lithium phosphate, the method comprising:

[0075] Waste lithium iron phosphate batteries are sequentially discharged, disassembled, crushed, and screened to separate waste lithium iron phosphate powder.

[0076] The following examples and comparative examples all use the above-described treatment method to obtain lithium iron phosphate waste powder, and are all of the same type of battery.

[0077] Example 1

[0078] This embodiment provides a method for recycling lithium iron phosphate waste, such as... Figure 1 As shown, the recycling method is as follows:

[0079] (1) 100g of lithium manganese iron phosphate waste was mixed with sulfuric acid solution (first acid solution) with a molar concentration of 1mol / L to prepare a slurry. The amount of sulfuric acid added was 1.5 times the theoretical amount (the theoretical amount is 0.5 times the total molar amount of lithium in the prepared slurry). Sulfur dioxide and oxygen were introduced and oxidative leaching was carried out at 50℃ for 4h. The flow rate of sulfur dioxide was 25L / h and the flow rate of oxygen was 15L / h to obtain the leaching slurry.

[0080] (2) Add ammonium tetrathiomolybdate copper removal agent to the leaching slurry in step (1). The amount of copper removal agent is 1 times the mass of copper in the leaching slurry. The copper-removed leaching residue and leaching liquid are obtained. The copper-removed leaching residue is acid-washed with 0.2 mol / L dilute sulfuric acid and then washed with water to obtain the water-washed leaching residue.

[0081] (3) The leaching residue after water washing in step (2) is subjected to acid dissolution treatment with a 1.2 mol / L sulfuric acid solution (second acid solution). The amount of sulfuric acid solution used is 1.5 times the total mass of iron and manganese in the leaching residue. The acid dissolution temperature is 60℃ and the acid dissolution time is 4h, resulting in manganese ferric phosphate solution and acid-dissolved residue.

[0082] The obtained manganese ferric phosphate solution and sodium hydroxide solution were slowly fed into the reaction vessel at a flow rate of 3 mL / min. The pH of the system was maintained at 4–4.5 by pH meter. The first precipitation reaction was carried out at 50 °C for 6 h to obtain the manganese ferric phosphate product.

[0083] The leachate obtained in step (2) was adjusted to pH 6 by adding liquid sodium hydroxide to obtain a lithium-rich solution after impurity removal. Sodium carbonate was added as a precipitant (the amount of sodium carbonate added was 1.5 times the theoretical mass of lithium salt required in the lithium-rich solution) and a second precipitation reaction was carried out at 90°C for 3 hours to obtain lithium carbonate.

[0084] Example 2

[0085] This embodiment provides a method for recycling lithium iron phosphate waste, the recycling method is as follows:

[0086] (1) 100g of lithium manganese iron phosphate waste was mixed with a nitric acid solution (first acid solution) with a molar concentration of 2mol / L to prepare a slurry. The molar amount of nitric acid added was 1 times the theoretical amount (the theoretical amount of nitric acid added was 1 times the total molar amount of lithium in the prepared slurry). Sulfur dioxide and oxygen were introduced, and oxidative leaching was carried out at 50℃ for 4h. The flow rate of sulfur dioxide was 25L / h, and the flow rate of oxygen was 15L / h to obtain the leaching slurry.

[0087] (2) Add ammonium tetrathiomolybdate copper removal agent to the leaching slurry in step (1). The amount of copper removal agent is 1.5 times the mass of copper in the leaching slurry. The copper-removed leaching residue and leaching liquid are obtained. The copper-removed leaching residue is acid-washed with 0.4 mol / L dilute nitric acid and washed with water to obtain the water-washed leaching residue.

[0088] (3) The leaching residue after water washing in step (2) is subjected to acid dissolution treatment with a 1.2 mol / L sulfuric acid solution (second acid solution). The amount of sulfuric acid solution used is 1 times the total mass of iron and manganese in the leaching residue. The acid dissolution temperature is 60℃ and the acid dissolution time is 4h, resulting in manganese ferric phosphate solution and acid-dissolved residue.

[0089] The obtained manganese ferric phosphate solution and sodium hydroxide solution were slowly fed into the reaction vessel at a flow rate of 3 mL / min. The pH of the system was maintained at 4–4.5 by pH meter. The reaction was carried out at 50 °C for 6 h to obtain the manganese ferric phosphate product.

[0090] The leachate obtained in step (2) was adjusted to pH 6 by adding liquid sodium hydroxide to obtain a lithium-rich solution after impurity removal. Sodium dodecahydrate phosphate was added as a precipitant (the amount of sodium dodecahydrate phosphate added was 1.1 times the theoretical mass of lithium salt required in the lithium-rich solution) and the precipitation reaction was carried out at 90°C for 3 hours to obtain lithium salt lithium phosphate.

[0091] Example 3

[0092] This embodiment provides a method for recycling lithium iron phosphate waste, the recycling method is as follows:

[0093] (1) 1000g of lithium manganese iron phosphate waste was mixed with sulfuric acid solution (first acid solution) with a molar concentration of 2mol / L to prepare a slurry. The amount of sulfuric acid added was twice the theoretical amount (the theoretical amount is 0.5 times the total molar amount of lithium in the prepared slurry). Sulfur dioxide and oxygen were introduced and oxidative leaching was carried out at 50℃ for 4h. The flow rate of sulfur dioxide was 25L / h and the flow rate of oxygen was 15L / h to obtain the leaching slurry.

[0094] (2) Add ammonium tetrathiomolybdate copper removal agent to the leaching slurry in step (1). The amount of copper removal agent is 1 times the mass of copper in the leaching slurry. The copper-removed leaching residue and leaching liquid are obtained. The copper-removed leaching residue is acid-washed with 0.2 mol / L dilute sulfuric acid and then washed with water to obtain the water-washed leaching residue.

[0095] (3) The leaching residue after water washing in step (2) is subjected to acid dissolution treatment with a 1.2 mol / L sulfuric acid solution (second acid solution). The amount of sulfuric acid solution used is twice the total mass of iron and manganese in the leaching residue. The acid dissolution temperature is 60℃ and the acid dissolution time is 4h, resulting in manganese ferric phosphate solution and acid-dissolved residue.

[0096] The obtained manganese ferric phosphate solution and sodium hydroxide solution were slowly fed into the reaction vessel at a flow rate of 3 mL / min. The pH of the system was maintained at 4–4.5 by pH meter. The first precipitation reaction was carried out at 50 °C for 6 h to obtain the manganese ferric phosphate product.

[0097] The leachate obtained in step (2) was adjusted to pH 6 by adding liquid sodium hydroxide to obtain a lithium-rich solution after impurity removal. Sodium carbonate (the amount of sodium carbonate added was twice the theoretical mass of lithium salt required in the lithium-rich solution) was added as a precipitant and a second precipitation reaction was carried out at 90°C for 3 hours to obtain lithium carbonate.

[0098] Example 4

[0099] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the flow rate of sulfur dioxide is 20L / h and the flow rate of oxygen is 10L / min.

[0100] The remaining recovery methods and parameters are consistent with those in Example 1.

[0101] Example 5

[0102] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the flow rate of sulfur dioxide is 50L / h and the flow rate of oxygen is 30L / min.

[0103] The remaining recovery methods and parameters are consistent with those in Example 1.

[0104] Example 6

[0105] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the flow rate of sulfur dioxide is 15L / h.

[0106] The remaining recovery methods and parameters are consistent with those in Example 1.

[0107] Example 7

[0108] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the flow rate of sulfur dioxide is 55L / h.

[0109] The remaining recovery methods and parameters are consistent with those in Example 1.

[0110] Example 8

[0111] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the oxygen flow rate is 5L / min.

[0112] The remaining recovery methods and parameters are consistent with those in Example 1.

[0113] Example 9

[0114] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the oxygen flow rate is 35L / min.

[0115] The remaining recovery methods and parameters are consistent with those in Example 1.

[0116] Comparative Example 1

[0117] (1) 100g of lithium manganese iron phosphate waste was mixed with sulfuric acid solution (first acid solution) with a molar concentration of 1mol / L to prepare slurry. The amount of sulfuric acid added was 1.5 times the theoretical amount (the theoretical amount is 0.5 times the total molar amount of lithium in the prepared slurry). Then hydrogen peroxide was pumped in as an oxidant to obtain leachate slurry.

[0118] (2) Add ammonium tetrathiomolybdate copper removal agent to the leaching slurry in step (1). The amount of copper removal agent is 1 times the mass of copper in the leaching slurry. The copper-removed leaching residue and leaching liquid are obtained. The copper-removed leaching residue is acid-washed with 0.2 mol / L dilute sulfuric acid and then washed with water to obtain the water-washed leaching residue.

[0119] (3) The leaching residue after water washing in step (2) is subjected to acid dissolution treatment with a 1.2 mol / L sulfuric acid solution (second acid solution). The amount of sulfuric acid solution used is 1.5 times the total mass of iron and manganese in the leaching residue. The acid dissolution temperature is 60℃ and the acid dissolution time is 4h, resulting in manganese ferric phosphate solution and acid-dissolved residue.

[0120] The obtained manganese ferric phosphate solution and sodium hydroxide solution were slowly fed into the reaction vessel at a flow rate of 3 mL / min. The pH of the system was maintained at 4–4.5 by pH meter. The first precipitation reaction was carried out at 50 °C for 6 h to obtain the manganese ferric phosphate product.

[0121] The leachate obtained in step (2) was adjusted to pH 6 by adding liquid sodium hydroxide to obtain a lithium-rich solution after impurity removal. Sodium carbonate was added as a precipitant (the amount of sodium carbonate added was 1.5 times the theoretical mass of lithium salt required in the lithium-rich solution) and a second precipitation reaction was carried out at 90°C for 3 hours to obtain lithium carbonate.

[0122] Comparative Example 2

[0123] (1) 100g of lithium manganese iron phosphate waste was mixed with sulfuric acid solution (first acid solution) with a molar concentration of 1mol / L to prepare a slurry. The amount of sulfuric acid added was 1.5 times the theoretical amount (the theoretical amount is 0.5 times the total molar amount of lithium in the prepared slurry). Sulfur dioxide and oxygen were introduced and oxidative leaching was carried out at 50℃ for 4h. The flow rate of sulfur dioxide was 25L / h and the flow rate of oxygen was 15L / h to obtain the leaching slurry.

[0124] (2) Filter the leachate from step (1) to obtain leachate and leachate residue;

[0125] (3) The leaching residue after water washing in step (2) is subjected to acid dissolution treatment with a 1.2 mol / L sulfuric acid solution (second acid solution). The amount of sulfuric acid solution used is 1.5 times the total mass of iron and manganese in the leaching residue. The acid dissolution temperature is 60℃ and the acid dissolution time is 4h, resulting in manganese ferric phosphate solution and acid-dissolved residue.

[0126] The obtained manganese ferric phosphate solution and sodium hydroxide solution were slowly fed into the reaction vessel at a flow rate of 3 mL / min. The pH of the system was maintained at 4–4.5 by pH meter. The first precipitation reaction was carried out at 50 °C for 6 h to obtain the manganese ferric phosphate product.

[0127] The leachate obtained in step (2) was adjusted to pH 6 by adding liquid sodium hydroxide to obtain a lithium-rich solution after impurity removal. Sodium carbonate was added as a precipitant (the amount of sodium carbonate added was 1.5 times the theoretical mass of lithium salt required in the lithium-rich solution) and a second precipitation reaction was carried out at 90°C for 3 hours to obtain lithium carbonate.

[0128] Comparative Example 3

[0129] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, sulfur dioxide gas is not introduced, only oxygen is introduced.

[0130] The remaining recovery methods and parameters are consistent with those in Example 1.

[0131] Comparative Example 4

[0132] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, oxygen is not introduced, but only sulfur dioxide gas is introduced.

[0133] The remaining recovery methods and parameters are consistent with those in Example 1.

[0134] Comparative Example 5

[0135] The difference between this comparative example and Example 1 is that an equal amount of iron powder is added as a copper removal agent in step (2) of this comparative example.

[0136] The remaining preparation methods and parameters are consistent with those in Example 1.

[0137] The purity and impurity content of the lithium salts recovered from Examples 1-9 and Comparative Examples 1-5 were tested, and the test results are shown in Table 1.

[0138] Table 1

[0139]

[0140] The composition of manganese iron phosphate recovered from Examples 1-9 and Comparative Examples 1-5 was analyzed, and the results are shown in Table 2.

[0141] Table 2

[0142]

[0143]

[0144]

[0145]

[0146] The recycling method provided by this invention utilizes the reaction of sulfur dioxide and oxygen in a mixed system of lithium iron phosphate waste and a first acid solution to generate highly oxidizing free radical ions with high redox potentials, which can remove Fe from the lithium iron phosphate waste. 2+ and Mn 2+ Oxidation is performed with excellent results, not only increasing the valence state of manganese in lithium iron phosphate, causing manganese to precipitate in the leaching residue, but also enabling selective extraction of lithium from lithium iron phosphate. This avoids the problem of introducing a large amount of cationic impurities that can occur when using strong oxidants such as persulfate. The leaching slurry after oxidation undergoes deep copper removal treatment, reducing the copper and aluminum impurity content in the resulting leaching residue, thus obtaining high-purity leaching residue and leachate. The leaching residue is then mixed with a second acid solution, and the pH is adjusted to carry out the first precipitation reaction, yielding the precursor iron manganese phosphate product required for battery-grade lithium iron phosphate cathode materials. After lithium extraction treatment of the leachate, battery-grade purified lithium salt materials can be obtained.

[0147] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for recovering a lithium iron manganese phosphate waste material, characterized in that, The recycling method includes the following steps: (1) Mix the waste manganese iron lithium phosphate with the first acid solution, and pass in sulfur dioxide and oxygen to carry out oxidative leaching to obtain leaching slurry; (2) The leaching slurry is subjected to copper removal treatment to obtain leaching residue and leaching solution; (3) Mix the leaching residue from step (2) with the second acid solution, adjust the pH value to carry out the first precipitation reaction, and obtain manganese iron phosphate; perform lithium extraction treatment on the leaching solution from step (2) to obtain purified lithium salt; The flow rate of sulfur dioxide introduced is 20~50 L / h; The oxygen flow rate is 10~30L / h; The copper removal agent used in step (2) of the copper removal process includes ammonium tetrathiomolybdate.

2. The recycling method according to claim 1, characterized in that, Step (1) The concentration of the first acid solution is 1~5 mol / L.

3. The recycling method according to claim 1, characterized in that, Step (1) The amount of acid added to the first acid solution is 1 to 2 times the theoretical amount.

4. The recycling method of claim 1, wherein, In step (2), the amount of copper removal agent used in the copper removal process is 1 to 2 times the mass of copper in the leaching slurry.

5. The recycling method of claim 1, wherein, The leaching residue after copper removal treatment in step (2) is then subjected to acid washing and water washing in sequence.

6. The recycling method of claim 1, wherein, In step (3), the concentration of the second acid solution is 1~5 mol / L.

7. The recycling method of claim 1, wherein, In step (3), after mixing the leaching residue from step (2) with the second acid solution, manganese ferric phosphate solution and acid-soluble residue are obtained.

8. The recycling method of claim 1, wherein, The pH adjustment in step (3) is to adjust the pH value of the manganese ferric phosphate solution.

9. The recycling method of claim 1, wherein, After adjusting the pH value as described in step (3), maintain the pH value of the system at 4~5.

10. The recycling method of claim 1, wherein, The lithium extraction process in step (3) includes: Remove impurities from the leachate obtained in step (2) to obtain a lithium-rich solution. Then, subject the lithium-rich solution to a second precipitation reaction to obtain purified lithium salt.

11. The recycling method of claim 10, wherein, The pH value of the impurity removal process is 5-6.

12. The recycling method of claim 1, wherein, The recycling method includes the following steps: (1) Mix the waste manganese iron lithium phosphate with the first acid solution, and introduce sulfur dioxide with a flow rate of 20~50L / h and oxygen with a flow rate of 10~30L / h to carry out oxidative leaching to obtain leaching slurry; (2) The leaching slurry is treated with ammonium tetrathiomolybdate to remove copper, and copper-removed leaching residue and leaching liquid are obtained. The copper-removed leaching residue is acid-washed and water-washed to obtain water-washed leaching residue. (3) Mix the leaching residue after water washing in step (2) with the second acid solution to obtain manganese ferric phosphate solution and acid-soluble residue. Adjust the pH value of the manganese ferric phosphate solution to 4~5 and maintain the pH value of the system at 4~5 to carry out the first precipitation reaction to obtain manganese ferric phosphate. The leachate from step (2) is purified under a pH of 5-6 to obtain a lithium-rich solution. The lithium-rich solution is then subjected to a second precipitation reaction to obtain purified lithium salt.

Images