Method for preferentially extracting lithium from positive electrode material of waste lithium iron phosphate battery through salt leaching

Abstract

The invention belongs to the field of secondary resource recycling, and discloses a method for preferentially extracting lithium from a waste lithium iron phosphate battery positive electrode material through salt leaching, the waste lithium iron phosphate battery positive electrode material is leached by adopting a soluble chloride and metal sulfate mixed solution, and a lithium-containing leaching solution and ferrophosphorus slag are obtained, the soluble chloride solution is selected from at least one of a potassium chloride solution, an ammonium chloride solution or a sodium chloride solution, and the metal sulfate comprises at least one of ferric sulfate, copper sulfate and high-valence manganese sulfate. According to the method, the valuable metal is recycled from the waste lithium iron phosphate battery powder by adopting a novel salt leaching process, the use of a large amount of acid and alkali reagents in a conventional wet process is avoided, the whole recycling process is green, environment-friendly and low in cost, and the lithium-extracted liquid is recycled after being blended, so that the input cost of a production reagent is reduced, and the efficient utilization of the reagent is realized; no waste water is generated, and cleaning and environment-friendly effects are achieved.

Description

Technical Field

[0001] The invention belongs to the field of recycling of secondary resources, and in particular relates to a method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials. Background Art

[0002] Lithium-ion batteries are widely used in the electric vehicle industry due to their high energy density and good cycle performance. As the electric vehicle industry continues to expand, the production of lithium-ion batteries has increased rapidly, and their service life is 5-8 years. As a result, the number of waste lithium-ion batteries has shown explosive growth. Among them, lithium iron phosphate batteries have the characteristics of high safety and low production cost, and their share in electric vehicle installations is as high as 70%. Waste lithium iron phosphate batteries contain rich valuable metal resources. Recycling them can achieve comprehensive resource recycling and reduce environmental pollution.

[0003] At present, there are two main methods for the disposal of waste lithium iron phosphate batteries, one is to recover the valuable metals therein, and the other is to regenerate the lithium iron phosphate positive electrode material. The most commonly used method for recovering the valuable metals therein is a wet recovery process, which is a process in which valuable metals are dissolved by chemical reagents such as inorganic acids (HCl, H2SO4, HNO3, H3PO4), organic acids (citric acid, oxalic acid, ascorbic acid) and other solutions to achieve metal enrichment, separation and extraction. The patent document with publication number CN112331949A discloses a method for recovering phosphorus, iron and lithium from waste lithium iron phosphate batteries, specifically disclosing the waste lithium iron phosphate powder after alkali leaching and aluminum removal with a mixed solution of sulfuric acid and hydrogen peroxide, and obtaining crude iron phosphate by adjusting the pH of the leachate; obtaining battery-grade iron phosphate after acid dissolution, precipitation and calcination; and obtaining lithium carbonate precipitate by evaporating and concentrating the lithium-containing filtrate and adding an alkali solution to obtain battery-grade lithium carbonate. The process flow of this method is short and the reaction system is simple, but the amount of slag is large, the lithium loss rate is high, the acid and alkali consumption is large, and a large amount of wastewater is generated during the leaching process, which puts a certain pressure on the environment. A patent document with the publication number CN114512737A discloses a new oxidation leaching method for waste lithium iron phosphate, which specifically discloses dissolving and stirring lithium iron phosphate powder with sulfuric acid, separating and obtaining a lithium-containing filtrate to achieve lithium leaching; then adding an oxidant hydroxyl manganese oxide to oxidize the divalent iron in the filtrate into trivalent iron, filtering out excess oxidant, adding sodium hydroxide to the filtrate to adjust the pH and precipitate and recover iron phosphate; continuing to add sodium hydroxide to the secondary filtrate to adjust the pH and aerate and oxidize to obtain hydroxyl manganese oxide for reuse; adding sodium carbonate to the tertiary filtrate after separating the hydroxyl manganese oxide, evaporating and concentrating, and precipitating and recovering lithium carbonate. The invention realizes the recycling of the oxidant, but the process of recovering iron phosphate and circulating the oxidant is complicated, and both require pH adjustment, and the consumption of alkali solution is large. The patent document with the publication number CN114655969A discloses a method for recycling high-impurity lithium iron phosphate cathode waste to prepare lithium carbonate and iron phosphate, which specifically discloses the use of copper iron chloride salt to leach Li and impurity Al through air water; the iron and phosphorus in the iron phosphorus slag after lithium extraction are leached out with an acid solution, and the leachate is deeply impurized by sulfide precipitation. The purified liquid is evaporated and crystallized at 100 ° C to obtain dihydrate iron phosphate, and the gas generated by evaporation and crystallization is condensed and mixed with the crystallization mother liquor for recycling. This method realizes the high-value recovery of lithium iron phosphate cathode waste containing high aluminum and high copper impurities, but the leaching process is ventilated with air, which increases energy consumption, and at the same time, the pH is adjusted from acidic to alkaline, resulting in reagent waste. Patent document with publication number CN115044780A discloses a method for recovering lithium from positive electrode materials of lithium iron phosphate batteries. Specifically, the positive electrode materials of lithium iron phosphate batteries are leached with persulfate, and an alkaline precipitant is added to the leached solution for precipitation and filtration. The obtained lithium-containing solution is concentrated and then a phosphorus-based precipitant is added to obtain lithium phosphate.The invention does not need to use strong acids such as hydrochloric acid or sulfuric acid as leaching agents, which reduces production costs, but the persulfate solution after the reaction is difficult to recycle, which increases the cost of wastewater treatment. Therefore, it is necessary to develop a green and environmentally friendly method for recycling waste lithium iron phosphate battery positive electrode materials, which has recyclable reagents, high metal recovery rate and simple process. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching, wherein a mixed solution of soluble chloride and metal sulfate is used to leach the waste lithium iron phosphate battery positive electrode materials to obtain a lithium-containing leachate and ferrophosphorus slag, wherein the soluble chloride solution is selected from at least one of potassium chloride solution, ammonium chloride solution or sodium chloride solution, and the metal sulfate includes at least one of iron sulfate, copper sulfate and high-valent manganese sulfate.

[0006] In the above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the high-valent manganese sulfate includes manganese sulfate yl MnOSO4.

[0007] The above-mentioned method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching, preferably, Cl in the mixed solution of soluble chloride and metal sulfate - The concentration is 100-400g / L. - The concentration needs to be controlled within the preferred range of the present invention. - If the concentration is not high enough, the olivine structure of lithium iron phosphate will not be completely destroyed, making it difficult to fully leach lithium. - If the concentration is too high, it will result in a waste of reagents.

[0008] In the above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the molar ratio of the waste lithium iron phosphate battery positive electrode material to the metal sulfate is 1:(0.5-1.5). The molar ratio of the waste lithium iron phosphate battery positive electrode material to the metal sulfate needs to be controlled within the preferred range of the present invention. If the amount is too much, the reagent cost will increase; if the amount is too little, the reaction will be incomplete, thereby affecting the lithium leaching rate.

[0009] The above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the liquid-to-solid ratio of the leaching process is 3:1-20:1, and the ratio unit is mL / g. The liquid-to-solid ratio needs to be controlled within the preferred range of the present invention. If the liquid-to-solid ratio is too large, the amount of water in the leaching process will increase, which will affect the leaching effect on the one hand, and on the other hand, the concentration of the leached liquid is low and it is not easy to recover valuable metals; if the liquid-to-solid ratio is small, the solution viscosity will increase, limiting the exchange between ions and reducing the recovery rate.

[0010] In the above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the temperature during the leaching process is 30-90 ° C, and the leaching time is 1-5 h. The leaching temperature needs to be controlled within the preferred range of the present invention. If the temperature is too low, the molecular motion is reduced, the contact between the raw materials is insufficient, and the lithium leaching rate decreases; if the temperature is too high, the energy consumption of the leaching process and the evaporation of the solution will be increased. The leaching time within this range can ensure complete reaction. If the leaching time is too short, the reaction will be incomplete. If the leaching time is too long, the energy consumption will increase.

[0011] In the above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the main components of the waste lithium iron phosphate battery positive electrode materials include Li 3-4.4 wt%, Fe 29-35 wt%, Al 3-5 wt%, and P 15-19 wt%.

[0012] The above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the waste lithium iron phosphate battery positive electrode materials are cyclically leached with the lithium-containing leaching solution, and the lithium-rich leaching solution obtained by the cyclic leaching is dealuminized and then sodium carbonate is added to obtain a lithium carbonate product.

[0013] In the above-mentioned method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials, preferably, the ferrophosphorus slag is acid-dissolved and purified to prepare iron phosphate.

[0014] The leaching mechanism of the present invention is to dissolve soluble chloride and metal sulfate in an aqueous solution to form a mixed solution with a certain oxidizing property, and the divalent iron in the waste lithium iron phosphate positive electrode material is oxidized into trivalent iron ions by the variable-valent metal ions in the mixed solution and dissolved, and then combined with the phosphate ions in the solution to form iron phosphate precipitates, and the olivine structure of the lithium iron phosphate is destroyed to achieve lithium leaching; at the same time, the impurity aluminum in the waste lithium iron phosphate positive electrode material is oxidized and enters the solution to achieve leaching.

[0015] The main reaction equations occurring during the leaching process include: LiFePO4+ Me2 (2n / m)+ = Li + + FePO4↓ + Me2 [(2n / m)-1]+ Al + 3Me2(2n / m)+ = Al 3+ + 3Me2 [(2n / m)-1]+ (Me2 is a high-valent metal ion of Fe, Cu or Mn; n = 1, 2, 3; m = 1, 2) Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a novel salt leaching process to recover valuable metals from waste lithium iron phosphate battery powder, avoiding the large-scale use of acid and alkali reagents in conventional wet processes. The entire recovery process is green, environmentally friendly and low in cost. The lithium-extracted liquid is recycled after being prepared, reducing the investment cost of production reagents, achieving efficient use of reagents, and generating no wastewater, which is cleaner and more environmentally friendly.

[0016] (2) The present invention uses a mixed solution of soluble chloride and metal sulfate to leach waste lithium iron phosphate battery positive electrode materials, with a high leaching rate of valuable metals. The operation process is simple and easy to control, and can be applied to large-scale industrial production. It overcomes the problems of strong corrosion to equipment and insufficient selectivity in traditional wet process recovery.

[0017] (3) The present invention improves the effective utilization rate of the leaching reagent through the cyclic leaching process, and at the same time increases the concentration of lithium and aluminum in the leachate, which is beneficial to the removal of aluminum and the recovery of lithium in the subsequent enrichment solution.

[0018] In summary, the method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials of the present invention has the advantages of being green and environmentally friendly, recyclable reagents, high metal recovery rate and simple process, and solves the problems of large-scale use of acid and alkali reagents, strong corrosion to equipment, and insufficient selectivity in traditional wet processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a process flow chart for leaching waste lithium iron phosphate positive electrode materials for preferential lithium extraction in an embodiment of the present invention.

[0021] Figure 2 This is the XRD diagram of the lithium carbonate product obtained in Example 2 of the present invention.

[0022] Figure 3 This is the XRD diagram of the iron phosphate product obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] The main components of the waste lithium iron phosphate battery positive electrode material treated in the following embodiments include Li 4.35 wt%, Fe 33.28 wt%, Al 3.29 wt%, and P 17.34 wt%.

[0027] Embodiment 1: A method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching of the present invention specifically comprises the following steps: (1) Accurately weigh 30 g of KCl at room temperature and dissolve it in 100 mL of deionized water to prepare a KCl solution; (2) Accurately weigh 35.75 g of Fe2(SO4)3, dissolve it in the KCl solution obtained in step (1), and stir evenly until it is completely dissolved to obtain a mixed solution; (3) According to the molar ratio of the waste lithium iron phosphate battery positive electrode material to Fe2(SO4)3 being 1:1.5, 10 g of the waste lithium iron phosphate positive electrode material was weighed and poured into the beaker containing the mixed solution prepared in step (2); (4) Place the beaker in a water bath for leaching reaction, control the reaction temperature to 60 °C, and the reaction time to 2 h. After the reaction is completed, filter and separate to obtain a primary leachate and a leaching residue (phosphorus iron slag). The primary leachate is used for cyclic leaching of waste lithium iron phosphate positive electrode materials. After the lithium concentration reaches the target, impurities are removed and aluminum is removed, and sodium carbonate precipitation is used to recover lithium. The leaching residue (phosphorus iron slag) is acid-dissolved and purified to prepare iron phosphate. After testing, the leaching rates of lithium and aluminum after salt leaching of lithium are 97.17% and 95.12%, respectively, and the conversion rate of iron in waste lithium iron phosphate positive electrode materials is 98.11%.

[0028] Comparative Example 1: The method for extracting lithium from waste lithium iron phosphate battery positive electrode material salt in this comparative example specifically comprises the following steps: (1) Accurately weigh 8 g of KCl at room temperature and dissolve it in 100 mL of deionized water to prepare a KCl solution; (2) Accurately weigh 35.75 g of Fe2(SO4)3, dissolve it in the KCl solution obtained in step (1), and stir evenly until it is completely dissolved to obtain a mixed solution; (3) According to the molar ratio of waste lithium iron phosphate battery positive electrode material to Fe2(SO4)3 being 1:1.5, weigh 10 g of waste lithium iron phosphate positive electrode material and pour it into the beaker containing the mixed solution; (4) Place the beaker in a water bath for leaching reaction, control the reaction temperature to 60 °C, and the reaction time to 2 h. After the reaction is completed, filter and separate to obtain the primary leachate and leaching residue (phosphorus iron slag). The primary leachate is used for cyclic leaching of waste lithium iron phosphate positive electrode materials. After the lithium concentration reaches the target, impurities are removed by dealuminization and sodium carbonate precipitation is used to recover lithium. The leaching residue (phosphorus iron slag) is acid-dissolved and purified to prepare iron phosphate.

[0029] After testing, the leaching rates of lithium and aluminum after salt extraction were 21.51% and 23.17% respectively, and the conversion rate of iron in waste lithium iron phosphate positive electrode materials was 22.73%.

[0030] It can be seen from Example 1 and Comparative Example 1 that when Cl - When the concentration is not enough, the olivine structure of lithium iron phosphate is not completely destroyed, making it difficult to fully leach lithium.

[0031] Embodiment 2: A method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching, the process flow chart of which is as follows: Figure 1 As shown, the specific steps include: (1) Accurately weigh 35 g of NaCl at room temperature and dissolve it in 100 mL of deionized water to prepare a NaCl solution; (2) Accurately weigh 24.32 g of CuSO4•5H2O, dissolve it in the NaCl solution obtained in step (1), and stir evenly until it is completely dissolved to obtain a mixed solution; (3) According to the molar ratio of waste lithium iron phosphate battery positive electrode material to CuSO4•5H2O being 1:1.25, 10 g of waste lithium iron phosphate positive electrode material was weighed and poured into a beaker containing the mixed solution prepared in step (2); (4) Place the beaker in a water bath for leaching reaction, control the reaction temperature to 60 °C, and the reaction time to 2 h. After the reaction is completed, filter and separate to obtain the primary leaching solution and leaching residue (phosphorus iron residue). The primary leaching solution is used for the cyclic leaching of waste lithium iron phosphate positive electrode materials. After the lithium concentration reaches the target, the impurities are removed by dealumination and sodium carbonate precipitation is used to recover lithium. The XRD pattern of the recovered lithium carbonate product is shown in the figure below. Figure 2 As shown; the leached slag (phosphorus iron slag) is acid dissolved and purified to prepare iron phosphate, and its XRD diagram is as shown Figure 3 shown.

[0032] After salt leaching of lithium, the leaching rates of lithium and aluminum were 99.25% and 98.89% respectively, and the conversion rate of iron in waste lithium iron phosphate positive electrode materials was 99.76%.

[0033] Comparative Example 2: The method for extracting lithium from salt of waste lithium iron phosphate battery positive electrode materials in this comparative example comprises the following steps: (1) Accurately weigh 35 g of NaCl at room temperature and dissolve it in 100 mL of deionized water to prepare a NaCl solution; (2) Accurately weigh 7.78 g of CuSO4•5H2O, dissolve it in the NaCl solution prepared in step (1), and stir until it is completely dissolved to obtain a mixed solution; (3) According to the molar ratio of waste lithium iron phosphate battery positive electrode material to CuSO4•5H2O being 1:0.4, 10 g of waste lithium iron phosphate positive electrode material was weighed and poured into the beaker containing the mixed solution prepared in step (2); (4) Place the beaker in a water bath for leaching reaction at a temperature of 60 °C for 2 h. After the reaction is completed, filter and separate to obtain a primary leachate and leaching residue (phosphorus iron slag). The primary leachate is used for cyclic leaching of waste lithium iron phosphate positive electrode materials. After the lithium concentration reaches the target, impurities are removed by dealuminization and sodium carbonate precipitation is used to recover lithium. The leaching residue (phosphorus iron slag) is acid-dissolved and purified to prepare iron phosphate.

[0034] After salt leaching of lithium, the leaching rates of lithium and aluminum were 34.32% and 31.85%, and the conversion rate of iron in waste lithium iron phosphate positive electrode materials was 32.69%.

[0035] It can be seen from Example 2 and Comparative Example 2 that when the concentration of variable-valence metal ions in the leachate is low, it is difficult for the divalent iron in the lithium iron phosphate to be effectively leached through ion valence transformation, and the leaching of lithium is insufficient.

[0036] Comparative Example 3: The method for extracting lithium from waste lithium iron phosphate battery positive electrode material salt in this comparative example specifically comprises the following steps: (1) Accurately weigh 35.75 g of Fe2(SO4)3, dissolve it in 100 mL of deionized water, and stir until it is completely dissolved; (2) According to the molar ratio of waste lithium iron phosphate battery positive electrode material to Fe2(SO4)3 being 1:1.5, weigh 10 g of waste lithium iron phosphate positive electrode material and pour it into the beaker containing the mixed solution; (3) Place the beaker in a water bath for leaching reaction, control the reaction temperature to 60 °C, and the reaction time to 2 h. After the reaction is completed, filter and separate to obtain a primary leaching solution and leaching residue (phosphorus iron residue). After testing, the leaching rates of lithium and aluminum after leaching and lithium extraction are 78.62% and 53.49% respectively, and the conversion rate of iron in waste lithium iron phosphate positive electrode materials is 75.73%.

[0037] It can be seen from Example 1 and Comparative Example 3 that Cl - The introduction of helps to destroy the olivine structure of lithium iron phosphate and promotes the full leaching of valuable metals.

Claims

1. A method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching, characterized in that: A mixed solution of soluble chloride and metal sulfate is used to leach the positive electrode material of waste lithium iron phosphate batteries to obtain a lithium-containing leachate and ferrophosphorus slag, wherein the soluble chloride solution is selected from at least one of potassium chloride solution, ammonium chloride solution or sodium chloride solution, and the metal sulfate includes at least one of iron sulfate, copper sulfate and high-valent manganese sulfate.

2. The method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching as claimed in claim 1, characterized in that: The Cl in the mixed solution of soluble chloride and metal sulfate - The concentration is 100-400g / L.

3. The method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching as claimed in claim 1, characterized in that: The molar ratio of the waste lithium iron phosphate battery positive electrode material to the metal sulfate is 1:(0.5-1.5).

4. The method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching as claimed in claim 1, characterized in that: The liquid-to-solid ratio of the leaching process is 3:1-20:1, and the ratio unit is mL / g.

5. The method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials as claimed in claim 1, characterized in that: The temperature during the leaching process is 30-90°C, and the leaching time is 1-5 hours.

6. The method for preferentially extracting lithium by salt leaching of waste lithium iron phosphate battery positive electrode materials as claimed in claim 1, characterized in that: The main components of the waste lithium iron phosphate battery positive electrode material include Li 3-4.4 wt%, Fe 29-35 wt%, Al 3-5 wt%, and P 15-19 wt%.

7. The method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching according to any one of claims 1 to 6, characterized in that: The lithium-containing leaching solution is used to cyclically leach waste lithium iron phosphate battery positive electrode materials, and the lithium-rich leaching solution obtained by the cyclic leaching is dealuminized and then added with sodium carbonate to obtain a lithium carbonate product.

8. The method for preferentially extracting lithium from waste lithium iron phosphate battery positive electrode materials by salt leaching according to any one of claims 1 to 6, characterized in that: The ferrophosphorus slag is acid-dissolved and purified to prepare ferrophosphate.

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