Method for extracting lithium from positive electrode material of waste lithium iron phosphate battery

Abstract

The invention relates to the technical field of recycling of waste lithium iron phosphate batteries, in particular to a method for extracting lithium from a positive electrode material of a waste lithium iron phosphate battery. The method comprises the following steps: (1) crushing the waste lithium iron phosphate battery, and sorting positive electrode powder; (2) two-stage leaching: adding a sulfuric acid solution into the lithium iron phosphate positive electrode powder to control the leaching pH value, and carrying out selective leaching; (3) two-stage impurity removal: controlling the impurity removal pH value to remove impurities, and adopting ultrasonic to enhance the impurity removal effect; and (4) precipitating lithium carbonate. According to the method, two-stage leaching is adopted for the positive electrode material of the waste lithium iron phosphate battery, so that the leaching effect of lithium is guaranteed, the leaching rate of lithium is 99.5% or above, the impurity removal effect of the lithium leachate is enhanced through ultrasonic waves, impurity removal precipitates are uniform, the slag type is good, the filtering performance is good, the entrained valuable metal lithium is less, the impurity content in the lithium solution is reduced, and the quality of a lithium carbonate product is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling waste lithium iron phosphate batteries, and in particular to a method for extracting lithium from positive electrode materials of waste lithium iron phosphate batteries. Background Art

[0002] Due to its high energy density, good cycle performance, low price, good safety performance and fast charging speed, lithium iron phosphate batteries have been adopted and installed by major domestic electric vehicle companies in recent years, and the installed capacity has increased year by year. Data from Gaogong Industry Research Institute (GGII) shows that since the end of November 2021, the installation of lithium iron phosphate batteries has exceeded ternary batteries, and has maintained a strong development momentum since then. In 2021, 2022 and 2023, the shipment share of lithium iron phosphate batteries was 47.9%, 61% and 64% respectively, showing an increasing trend year by year. Domestic waste lithium-ion battery recycling companies are also developing rapidly. The recycling method of waste lithium iron phosphate power batteries is mainly based on wet process. The pretreated waste lithium iron phosphate active material can be dissolved by acid leaching to recover lithium in the leachate. For example, Chinese patent CN118374698A discloses a method for recovering lithium from waste lithium iron phosphate batteries, which includes the following steps: crushing and pretreating the waste lithium iron phosphate batteries to obtain black powder, slurry leaching to obtain leachate and leach residue, decontaminating the leachate to obtain a decontamination mixture, defluoridating to obtain a defluoridated leachate, decalcifying to obtain a purified liquid, concentrating to obtain a concentrated liquid, and precipitating lithium to obtain lithium carbonate. This method yields high-purity lithium carbonate, but the copper, iron, and aluminum in the impurity removal residue are mixed and cannot be further utilized. Furthermore, the use of calcium oxide as an impurity remover adds additional cost and introduces impurities, necessitating an additional calcium removal process. Alternatively, a lithium-first extraction process can be employed, where the iron phosphate precipitates into the leached residue during leaching. For example, Chinese patent CN106981699A discloses a method for recovering lithium from spent lithium iron phosphate batteries. The spent lithium iron phosphate batteries are disassembled and shelled, and the resulting battery cores are crushed and mechanically separated to obtain a powder. The powder is then calcined in air to remove carbon. An alkaline solution is added for a chemical reaction, and the product is filtered to obtain an aluminum hydroxide precipitate and a filter mud. Water is added to the filter mud and stirred, followed by a strong acid reaction, which is then filtered to obtain a lithium solution. The pH of the lithium solution is adjusted, and a small amount of iron in the lithium solution is extracted with an extractant, retaining the extracted aqueous phase. The pH of the aqueous phase is adjusted, and solid sodium phosphate is added to obtain a lithium phosphate precipitate. This process requires the use of a large amount of acid.

[0003] In general, the wet recycling process of waste lithium iron phosphate batteries has problems such as long process, many control points, long time for impurity removal, precipitation and filtration, complex slag washing process, high cost, high impurity content of the solution after impurity removal, and poor economic benefits, which need to be solved urgently. Summary of the Invention

[0004] In order to solve the problems of the prior art, the present invention provides a method for preparing battery-grade lithium carbonate from waste lithium iron phosphate battery positive electrode materials with a short lithium sulfate solution impurity removal process and time and a high lithium recovery rate, comprising the following steps:

[0005] Step 1: crush, roast, crush and separate the used lithium iron phosphate batteries to obtain the positive electrode materials;

[0006] Step 2: Add water to the positive electrode material to form a slurry, then add 98% concentrated sulfuric acid solution for acid leaching at a temperature of 55-65°C. Then, add 30% hydrogen peroxide (0.04-0.06% by mass of the positive electrode material) to the system. After the reaction is completed, solid-liquid separation is performed to obtain a leachate and a leach residue.

[0007] Step 3: The first-stage leaching residue is slurried with water, and then a 98% concentrated sulfuric acid solution accounting for 3.0-6.0% of the mass of the positive electrode material is added for second-stage leaching. After the reaction is completed, solid-liquid separation is performed to obtain a second-stage leachate and a second-stage leaching residue. The second-stage leachate is returned to the acid leaching process of step 2 to replace water for slurrying;

[0008] Step 4: adding sodium hydroxide solution to the first stage leachate, and performing ultrasonic-assisted impurity removal, adjusting the pH to 4.5-7.0, and performing solid-liquid separation to obtain a first stage impurity-removed liquid and a first stage impurity-removed residue;

[0009] Step 5: adding sodium hydroxide solution to the first stage impurity removal liquid and adding sodium carbonate accounting for 0.3-0.4% of the mass of the positive electrode material, and performing ultrasonic assisted impurity removal, adjusting the pH to 12.0-13.0 during the process, and then finely filtering to obtain the second stage impurity removal residue and the second stage impurity removal liquid;

[0010] Step 6: Heat the second-stage impurity removal liquid, add sodium carbonate solution for precipitation, separate the solid and liquid to obtain solid lithium carbonate and mother liquor, wash the solid lithium carbonate until the pH of the washing water is 6.5-7.5, and dry to obtain the lithium carbonate product.

[0011] Furthermore, in step 1, the waste lithium iron phosphate battery material is crushed to less than 1 mm, and aluminum, copper and carbon powder in the waste lithium iron phosphate battery are removed by sorting.

[0012] Furthermore, in step 2, the solid-liquid mass ratio of the positive electrode material to the concentrated sulfuric acid solution is 2.5-3.5:1, the leaching time is 1-3 hours, the reaction time after adding hydrogen peroxide is 1-3 hours, and the pH value at the reaction endpoint is controlled to be 3.0-3.5.

[0013] Furthermore, the second-stage leaching temperature in step 3 is 55-65° C., and the second-stage leaching time is 1-3 hours.

[0014] Furthermore, in step 4 and / or step 5, the ultrasonic frequency is 80-100 kHz, the ultrasonic power is 500-1500 W, the reaction time is 1-3 h, and the reaction temperature is 60-70° C.

[0015] Furthermore, in step 6, the heating temperature is 90-100° C., the concentration of the sodium carbonate solution is 340-370 g / L, and the precipitation time is 50-80 min.

[0016] The beneficial effects of the present invention are:

[0017] (1) This method adopts a two-stage acid leaching method. In the first stage of leaching, acid leaching is first performed to dissolve most of the lithium and iron therein, and then hydrogen peroxide is added to oxidize the leached iron to trivalent iron and precipitate it as ferric phosphate. The acidity of the leaching process is controlled to ensure that the trivalent iron is completely precipitated, the amount of hydrogen peroxide used is reduced, and the leaching efficiency is improved. The ferric phosphate slag produced by leaching has a good shape, is relatively uniform, has good looseness, carries less lithium, and has good slag filtration performance.

[0018] (2) Impurities can be removed in two stages. The first stage of impurity removal adjusts the pH value to 4.5-7.0 to remove impurities such as iron and aluminum in the leachate. The second stage of impurity removal adjusts the pH value of the system to 12.0-13.0 and adds a small amount of sodium carbonate to remove impurities such as manganese, calcium, magnesium, and copper while ensuring that Li does not precipitate. Fine impurity particles are removed through precise filtration. The impurity removal efficiency is high.

[0019] (3) The impurity removal process of this scheme adopts ultrasonic enhanced impurity removal, which can shorten the impurity removal time, improve the impurity removal accuracy, enhance the effect of precipitation impurity removal, improve the slag shape of the precipitation, reduce the inclusion of lithium in the impurity removal slag, improve the lithium recovery rate, and ensure the impurity content of the lithium solution. Battery-grade lithium carbonate can be directly prepared without using the carbonization method.

[0020] This method simply and efficiently solves the problems of low leaching efficiency, long impurity removal time, and insufficient impurity removal depth by precipitation method in the recycling process of waste lithium iron phosphate batteries, and improves the lithium recovery rate to more than 90%, achieving the purpose of efficiently recycling the positive electrode materials in waste lithium iron phosphate batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0022] Figure 1 The process flow chart of this method is shown. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] Step 1: The waste lithium iron phosphate batteries are coarsely crushed, roasted, finely pulverized, and the positive electrode materials are sorted out; the waste lithium iron phosphate battery materials are crushed to less than 1 mm, and the aluminum, copper and carbon powder in the waste lithium iron phosphate batteries are removed by sorting.

[0025] Step 2: Add water to the positive electrode material to slurry, and then add 98% concentrated sulfuric acid solution for acid leaching, the solid-liquid mass ratio of the positive electrode material to the concentrated sulfuric acid solution is 2.5-3.5:1, the acid leaching temperature is 55-65 ° C, the reaction time is 1-3h, and then 0.04-0.06% of the mass of the positive electrode material is added to the system. 30% hydrogen peroxide solution, the reaction time is 1-3h, and the pH value of the reaction endpoint is controlled to be 3.0-3.5. After the reaction is completed, solid-liquid separation is performed to obtain a leachate and a leach residue;

[0026] Step 3: The first stage leaching residue is slurried with water, and then a 98% concentrated sulfuric acid solution accounting for 3.0-6.0% of the mass of the positive electrode material is added to carry out the second stage leaching. The second stage leaching temperature is 55-65°C, and the second stage leaching time is 1-3h. After the reaction is completed, solid-liquid separation is carried out to obtain the second stage leaching liquid and the second stage leaching residue. The second stage leaching liquid is returned to the acid leaching process of step 2 to replace water for slurrying; the leaching reaction equation is as shown in chemical formula (1):

[0027] 2LiFePO4+H2SO4+H2O2→Li2SO4+2FePO4+2H2O (1)

[0028] Step 4: adding sodium hydroxide solution to the first-stage leachate and performing ultrasonic-assisted impurity removal, with an ultrasonic frequency of 80-100 kHz and an ultrasonic power of 500-1500 W. During the reaction, the pH is controlled at 4.5-7.0, the reaction time is 1-3 hours, and the reaction temperature is 60-70° C. Solid-liquid separation is performed to obtain a first-stage impurity removal liquid and a first-stage impurity removal residue. The main chemical equations are as follows:

[0029] Al2(SO4)3+6NaOH→3Na2SO4+2Al(OH)3↓ (2)

[0030] Fe2(SO4)3+6NaOH→3Na2SO4+2Fe(OH)3↓ (3)

[0031] Fe2(SO4)3+6NaOH→3Na2SO4+2FeO(OH)↓+2H2O (4)

[0032] Step 5: Add sodium hydroxide solution to the first impurity removal liquid and add sodium carbonate accounting for 0.3-0.4% of the mass of the positive electrode material, and perform ultrasonic-assisted impurity removal. The pH is adjusted to 12.0-13.0 during the process. After precise filtration, the second-stage impurity removal residue and the second-stage impurity removal liquid are obtained. The ultrasonic frequency is 80-100kHz, the ultrasonic power is 500-1500W, the reaction time is 1-3h, and the reaction temperature is 60-70°C. The main chemical equations are as follows:

[0033] Mn 2+ +2NaOH→2Na + +Mn(OH)2↓ (5)

[0034] Ca 2+ +2NaOH→2Na + +Ca(OH)2↓ (6)

[0035] Ca 2+ +Na2CO3→Ca2CO3↓+2Na +

[0036] 2CuSO4+Na2CO3+2NaOH=CuCO3·Cu(OH)2↓+2Na2SO4 (7)

[0037] CuSO4+2NaOH=Cu(OH)2↓+Na2SO4 (8)

[0038] Step 6: heating the second-stage impurity removal liquid to 90-100° C., adding 340-370 g / L sodium carbonate solution and carrying out precipitation for 50-80 minutes, solid-liquid separation to obtain solid lithium carbonate and mother liquor, washing the solid lithium carbonate until the pH of the washing water is 6.5-7.5, drying to obtain lithium carbonate product, and evaporating, concentrating the mother liquor and cooling and crystallizing to obtain sodium sulfate crystals.

[0039] Li2SO4+ Na2CO3→Li2CO3↓+ 2Na2SO4 (9)

[0040] The specific embodiments are as follows:

[0041] A certain amount of waste lithium iron phosphate batteries were collected, crushed, roasted, sorted, and crushed to less than 1 mm. The positive electrode material was sorted out as the raw material of the embodiment, and 350 g / L sodium carbonate solution, 200 g / L sodium hydroxide solution and 98% concentrated sulfuric acid solution were prepared for use.

[0042] Example 1

[0043] 500kg of sorted lithium iron phosphate positive electrode powder plus 1.5m 3The second-stage leachate was stirred at 30 Hz and heated to 40°C. 85 L of 98% sulfuric acid solution was added for leaching. The leaching temperature was about 55°C. After 1 hour of leaching, 250 mL of 30% hydrogen peroxide was added. The temperature was maintained at 55°C for 1 hour. The end point pH was 3.0. After leaching, solid-liquid separation was performed to obtain a first-stage leachate and a first-stage leach residue. The first-stage leach residue was slurried with wash water and 10 L of sulfuric acid solution was added for second-stage leaching. The pH was about 1.85. The temperature was controlled at 55°C for 1 hour. After leaching, solid-liquid separation was performed to obtain a second-stage leachate and a second-stage leach residue. The second-stage leachate was returned to the first-stage leaching. The lithium concentration in the first-stage leachate was 16.37 g / L, the lithium leaching rate was 99.85%, the iron leaching rate was 0.018%, the aluminum concentration was 0.055 g / L, and the calcium concentration was 0.020 g / L.

[0044] The first-stage leachate is subjected to impurity removal. An ultrasonic generator with a power of 500W is inserted into the first-stage impurity removal reactor. The pH value is adjusted to 5.0 with a sodium hydroxide solution. The reaction time is 1 hour. After filtration, a first-stage impurity removal liquid and a first-stage impurity removal residue are obtained. An ultrasonic generator with a power of 500W is inserted into the second-stage impurity removal reactor. The pH value is adjusted to 12.5 by continuously adding sodium hydroxide solution to the second-stage impurity removal reactor. At the same time, 2kg of sodium carbonate is added. The reaction time is 1 hour. The impurity removal process temperature is 60-70°C. Solid-liquid separation is performed to obtain a second-stage impurity removal liquid.

[0045] The second-stage impurity removal liquid was heated to 90° C., 350 g / L sodium carbonate was added, the reaction (precipitation) time was 1 hour, and solid lithium carbonate and mother liquor were obtained by centrifugation. The solid lithium carbonate was washed until the pH of the washing water was 6.5-7.5, and dried to obtain a lithium carbonate product (purity 99.58%). The mother liquor was evaporated, concentrated, cooled and crystallized to obtain sodium sulfate crystals.

[0046] Example 2

[0047] 1 ton of waste lithium iron phosphate positive electrode powder plus 2.5m of second-stage leaching solution 3 The slurry was preheated with a stirring speed of 40 Hz. 160 L of 98% sulfuric acid was added for leaching at a leaching temperature of approximately 60°C. After leaching for 2 hours, 410 mL of 30% hydrogen peroxide was added. The temperature was maintained at 60°C and the reaction time was 2 hours. The endpoint pH value was 3.2. After leaching, solid-liquid separation was performed to obtain a first-stage leachate and a first-stage leach residue. The first-stage leach residue was slurried with wash water and 20 L of concentrated sulfuric acid was added to control the pH value to approximately 1.70 for a second-stage leaching. The temperature was controlled at 60°C and the leaching time was 2 hours. After leaching, solid-liquid separation was performed to obtain a second-stage leachate and a second-stage leach residue. The second-stage leachate was returned to the first-stage leaching process for use as slurry water. The lithium sulfate concentration in the first-stage leachate was 19.67 g / L, the recovery rate was 99.75%, the iron leaching rate was 0.016%, the aluminum concentration was 0.050 g / L, and the calcium concentration was 0.021 g / L.

[0048] The first-stage leachate is subjected to impurity removal. An ultrasonic generator with a power of 1000W is installed in the first-stage impurity removal reactor. A sodium hydroxide solution is added to adjust the pH value to 6.0. The reaction time is 2h. After filtration, a first-stage impurity removal liquid and a first-stage impurity removal residue are obtained. An ultrasonic generator with a power of 1000W is installed in the second-stage impurity removal reactor. A sodium hydroxide solution is added to adjust the pH value to 13.0. 3kg of sodium carbonate is added at the same time. The reaction time is 2h. The temperature of the two-stage impurity removal process is 60-70°C. The solid-liquid separation is performed to obtain the second-stage impurity removal liquid.

[0049] The second-stage impurity removal liquid was heated to 98° C., 350 g / L sodium carbonate was added, the reaction (precipitation) time was 50 min, and solid lithium carbonate and mother liquor were obtained by centrifugation. The solid lithium carbonate was washed until the pH of the washing water was 6.5-7.5, and dried to obtain a lithium carbonate product (purity 99.64%). The mother liquor was evaporated, concentrated, cooled and crystallized to obtain sodium sulfate crystals.

[0050] Example 3

[0051] 3t of waste lithium iron phosphate positive electrode powder plus 10m of second-stage leaching solution 3 , 480L of 98% sulfuric acid was used for leaching, the stirring speed was 50Hz, the leaching temperature was 65℃, and 1.2m 3 30% hydrogen peroxide, maintained at 65°C for 3 hours, with an endpoint pH of 3.4. After leaching, solid-liquid separation was performed to obtain a first-stage leachate and a first-stage leach residue. The first-stage leach residue was then added with 90L of concentrated sulfuric acid solution for a second-stage leaching, with the pH controlled at approximately 1.50 and the temperature maintained at 65°C for 3 hours. After leaching, solid-liquid separation was performed to obtain a second-stage leachate and a second-stage leach residue. The second-stage leachate was then returned to the first-stage leaching process. The lithium sulfate concentration in the first-stage leachate was 11.71g / L, with a recovery rate of 99.78%, an iron leaching rate of 0.015%, an aluminum concentration of 0.048g / L, and a calcium concentration of 0.020g / L.

[0052] The first-stage leachate is subjected to impurity removal. An ultrasonic generator with a power of 1500W is installed in the first-stage impurity removal reactor. Sodium hydroxide solution is added to adjust the pH value to 7.0. The reaction time is 3 hours. After filtration, a first-stage impurity removal liquid and a first-stage impurity removal residue are obtained. An ultrasonic generator with a power of 1500W is installed in the second-stage impurity removal reactor. Sodium hydroxide solution is continued to be added to adjust the pH value to 12.0. 10 kg of sodium carbonate is weighed, dissolved in water and added to the reactor. The reaction time is 3 hours. The temperature of the two-stage impurity removal processes is 60-70°C. The solid-liquid separation is performed to obtain the second-stage impurity removal liquid.

[0053] The second-stage impurity removal liquid is heated to 100° C., 350 g / L sodium carbonate is added, the reaction (precipitation) time is 80 min, and solid lithium carbonate and mother liquor are obtained by centrifugation. The solid lithium carbonate is washed until the pH of the washing water is 6.5-7.5, and dried to obtain a lithium carbonate product (purity 99.60%). The mother liquor is evaporated, concentrated, cooled and crystallized to obtain sodium sulfate crystals.

[0054] Comparative Example 1

[0055] 500kg of sorted lithium iron phosphate positive electrode powder plus 1.5m 3 The water was washed with stirring at 30 Hz. When heated to 40°C, 80 L of 98% sulfuric acid solution was added for leaching. The leaching temperature was about 55°C. After leaching for 1 hour, 250 mL of 30% hydrogen peroxide was added. The temperature was maintained at 55°C for 1 hour. The end point pH value was 3.0. After leaching, solid-liquid separation was performed to obtain a first-stage leachate and a first-stage leach residue. 10 L of concentrated sulfuric acid was added to the first-stage leach residue. The pH value was about 1.85 for a second-stage leaching. The temperature was controlled at 55°C for 1 hour. After leaching, solid-liquid separation was performed to obtain a second-stage leachate and a second-stage leach residue. The second-stage leachate returned to the first-stage leaching. The lithium concentration in the first-stage leachate was 16.40 g / L, the lithium leaching rate was 99.84%, the iron leaching rate was 0.015%, the aluminum concentration was 0.048 g / L, and the calcium concentration was 0.019 g / L.

[0056] The first stage leachate is subjected to impurity removal, and sodium hydroxide solution is added to the first stage impurity removal reactor to adjust the pH value to 12.5, and 2 kg of sodium carbonate is added at the same time. The reaction time is 3 hours, the impurity removal process temperature is 60-70 ° C, and the solid-liquid separation is performed to obtain the second stage impurity removal solution.

[0057] The impurity-removed liquid was heated to 90°C, 350 g / L sodium carbonate was added and precipitated for 1 hour, centrifuged and washed with pure water and dried to obtain a lithium carbonate product with a purity of 96%.

[0058] Some exemplary embodiments of the present invention are described above. It will be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. The features in these embodiments can be recombined in an appropriate manner, and the solutions obtained thereby are still within the scope of protection claimed by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for extracting lithium from waste lithium iron phosphate battery cathode materials, characterized in that: The following steps are involved: Step 1: crush, roast, crush and separate the used lithium iron phosphate batteries to obtain the positive electrode materials; Step 2: Add water to the positive electrode material to form a slurry, then add 98% concentrated sulfuric acid solution for acid leaching at a temperature of 55-65°C. Then, add 30% hydrogen peroxide (0.04-0.06% by mass of the positive electrode material) to the system. After the reaction is completed, solid-liquid separation is performed to obtain a leachate and a leach residue. Step 3: The first-stage leaching residue is slurried with water, and then a 98% concentrated sulfuric acid solution accounting for 3.0-6.0% of the mass of the positive electrode material is added for second-stage leaching. After the reaction is completed, solid-liquid separation is performed to obtain a second-stage leachate and a second-stage leaching residue. The second-stage leachate is returned to the acid leaching process of step 2 to replace water for slurrying; Step 4: adding sodium hydroxide solution to the first stage leachate, and performing ultrasonic-assisted impurity removal, adjusting the pH to 4.5-7.0, and performing solid-liquid separation to obtain a first stage impurity-removed liquid and a first stage impurity-removed residue; Step 5: adding sodium hydroxide solution to the first stage impurity removal liquid and adding sodium carbonate accounting for 0.3-0.4% of the mass of the positive electrode material, and performing ultrasonic assisted impurity removal, adjusting the pH to 12.0-13.0 during the process, and then finely filtering to obtain the second stage impurity removal residue and the second stage impurity removal liquid; Step 6: Heat the second-stage impurity removal liquid, add sodium carbonate solution for precipitation, separate the solid and liquid to obtain solid lithium carbonate and mother liquor, wash the solid lithium carbonate until the pH of the washing water is 6.5-7.5, and dry to obtain the lithium carbonate product.

2. The method for extracting lithium from waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step 1, the waste lithium iron phosphate battery material is crushed to less than 1 mm, and the aluminum, copper and carbon powder in the waste lithium iron phosphate battery are removed by sorting.

3. The method for extracting lithium from a waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step 2, the solid-liquid mass ratio of the positive electrode material to the concentrated sulfuric acid solution is 2.5-3.5:1, the leaching time is 1-3 hours, the reaction time after adding hydrogen peroxide is 1-3 hours, and the pH value at the reaction endpoint is controlled to be 3.0-3.

5.

4. The method for extracting lithium from waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: The second-stage leaching temperature in step 3 is 55-65° C., and the second-stage leaching time is 1-3 hours.

5. The method for extracting lithium from waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step 4 and / or step 5, the ultrasonic frequency is 80-100 kHz, the ultrasonic power is 500-1500 W, the reaction time is 1-3 h, and the reaction temperature is 60-70° C.

6. The method for extracting lithium from waste lithium iron phosphate battery cathode material according to claim 1, characterized in that: In step 6, the heating temperature is 90-100° C., the concentration of the sodium carbonate solution is 340-370 g / L, and the precipitation time is 50-80 min.

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