A method for regenerating battery-grade iron phosphate from waste lithium iron phosphate

Abstract

The present invention discloses a method for regenerating battery-grade iron phosphate from waste lithium iron phosphate, belonging to the technical field of waste battery recycling. The waste lithium iron phosphate is pretreated to obtain a positive electrode powder, the positive electrode powder is ball-milled with an ionic liquid to obtain an activated slurry, the activated slurry is acid-leached to obtain a lithium-containing filtrate and a phosphorus-iron filter residue, the lithium in the lithium-containing filtrate is precipitated to prepare lithium carbonate, the phosphorus-iron filter residue is dissolved with nitric acid, after impurity removal, it is co-precipitated with ammonia water, washed, and calcined to prepare battery-grade iron phosphate; the acid leaching of the activated slurry after ball milling with dilute sulfuric acid can increase the leaching rate of lithium and will not leach iron, thereby reducing the inclusion of lithium in the phosphorus-iron filter residue; in addition, this method also dissolves the phosphorus-iron filter residue with nitric acid, and after impurity removal, by adjusting the phosphorus-iron ratio and adjusting the pH with ammonia water to inhibit the formation of iron hydroxide, co-precipitation regenerates hydrated iron phosphate, and after high-temperature dehydration, battery-grade iron phosphate with higher purity can be obtained, which is beneficial to the recycling of lithium iron phosphate batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste battery recycling, and particularly relates to a method for regenerating battery-grade iron phosphate from waste lithium iron phosphate. Background Art

[0002] With the shortage of oil and gas resources, the transformation from fuel vehicles to new energy vehicles is an important trend in the development of the global automotive industry. The most important new energy vehicles are pure electric vehicles, that is, vehicles completely driven by electric motors, which do not produce vehicle exhaust emissions. The power batteries used in new energy vehicles generally include ternary lithium batteries, lithium iron phosphate batteries, and nickel-metal hydride batteries, etc.

[0003] Although the energy density of lithium iron phosphate batteries is relatively low, their safety performance is good and their service life is long, so they are still widely used in mid - to - high - end vehicles. If the service life of a lithium iron phosphate battery pack reaches its limit and it cannot be used for secondary utilization, it must be scrapped and recycled. Therefore, facing the situation of large - scale retirement of lithium iron phosphate batteries, recycling them can not only relieve the environmental pressure brought by battery waste, but also bring certain social and economic benefits, which is conducive to the green and sustainable development of the entire industry.

[0004] The recycling of waste lithium iron phosphate batteries generally requires discharging, disassembling, and then treating the positive electrode sheet with acid / alkali / organic solvents to recover the positive electrode powder, while the negative electrode sheet is treated at high temperature to recover the conductive agent. Existing methods for recycling waste lithium iron phosphate batteries generally require precipitating iron and phosphorus, and part of lithium will be entrained during the process, resulting in a decrease in the recovery rate of lithium and the purity of iron phosphate. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for regenerating battery - grade iron phosphate from waste lithium iron phosphate, so as to solve the problem of low recovery rate and purity of iron phosphate in the prior art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for regenerating battery - grade iron phosphate from waste lithium iron phosphate includes the following steps:

[0008] Step 1: Pretreat the waste lithium iron phosphate to obtain positive electrode powder;

[0009] Step 2: Stir and mix the positive electrode powder, a hydrogen peroxide solution with a mass fraction of 20 - 30%, a phosphorus - containing ionic liquid, and water, then transfer them to a ball - milling tank, and ball - mill for 1 - 2 h at a rotation speed of 200 - 500 r / min and a temperature of 50 - 60 °C to obtain an activated slurry; lithium ions exchange with the cations in the phosphorus - containing ionic liquid, realizing the selective extraction of lithium ions, which helps to improve the leaching rate of lithium.

[0010] Step 3: Transfer the activated slurry to an acid digestion tank and adjust the solid content to 20 - 30% with water. Add sulfuric acid with a molar concentration of 0.05 - 0.1 mol / L to the acid digestion tank to adjust the pH value of the activated slurry to 3 - 4. Stir at a temperature of 50 - 60 °C and a speed of 200 - 500 r / min for 0.5 - 1.5 h. During selective leaching, lithium ions in the phosphorus-containing ionic liquid combine with sulfate ions to form lithium sulfate, causing the lithium ions to transfer into the acid solution. Then filter to obtain a lithium-containing filtrate and a phosphorus-iron filter residue.

[0011] Step 4: After drying the phosphorus-iron filter residue, mix it with nitric acid with a molar concentration of 5 - 6 mol / L according to a mass ratio of 1:8 - 10. Stir at 80 - 90 °C and 200 - 500 r / min for 5 - 6 h. Filter to remove the solid waste residue, collect the iron-containing filtrate and the generated tail gas, and recycle the tail gas to prepare nitric acid.

[0012] Step 5: After removing impurities from the iron-containing filtrate, adjust the phosphorus-iron molar ratio to 1.03 - 1.05:1. Then use ammonia water with a mass fraction of 25 - 28% to adjust the pH value to 1.5 - 2.5. Stir at 80 - 90 °C and 200 - 500 r / min for 3 - 4 h, let it stand and filter to obtain a hydrated iron phosphate precipitate and an acid-containing waste liquid. Wash the hydrated iron phosphate precipitate with water at 50 - 60 °C until the pH value of the last washing liquid > 3.3. After drying, calcine it at 600 - 650 °C for 60 - 90 min to obtain battery-grade iron phosphate.

[0013] Step 6: Evaporate and concentrate the lithium-containing filtrate to 30 ± 5% of the original volume to obtain a concentrated solution. Under stirring conditions, add a sodium hydroxide solution with a mass fraction of 5 - 10% to the concentrated solution to adjust the pH value to 12 - 13. Let it stand for 10 - 30 min and then filter. After removing the precipitate, add a carbonate that is 2 - 3 times the theoretical amount to the remaining liquid. Stir and mix, then filter to collect the lithium carbonate precipitate and a salt-containing waste liquid.

[0014] Step 7: Mix the salt-containing waste liquid and the acid-containing waste liquid to obtain a mixed waste liquid and conduct waste liquid treatment. Recycle the tail gas generated during the waste liquid treatment process to prepare ammonia water.

[0015] Further, the specific method of pretreatment in Step 1 is: Discharge, disassemble, and crush the used lithium iron phosphate battery, then collect the cathode material. After pulverizing and drying the cathode material, transfer it to a muffle furnace and roast it at 450 - 500 °C for 1 - 2 h to decompose the binder in the cathode material. Then perform vibration screening to remove and collect the cathode powder on the surface of the aluminum foil.

[0016] Further, the dosage ratio of the cathode powder, hydrogen peroxide, ionic liquid, and water in Step 2 is 20 g:20 - 30 mL:0.6 - 1 g:20 - 30 mL.

[0017] Further, in Step 2, the phosphorus-containing ionic liquid is tributyl phosphate or trioctyl phosphate; the ionic liquid has high selectivity for lithium ions and has no leaching effect on iron at this concentration, and no iron ions are detected in the filtrate of the activated slurry.

[0018] Further, the medicaments used to adjust the phosphorus-iron molar ratio in Step 5 include, but are not limited to, phosphoric acid.

[0019] Further, the carbonate in Step 6 includes, but is not limited to, sodium carbonate.

[0020] Further, the method for removing impurities from the iron-containing filtrate is as follows: Add iron powder in an amount 1 - 1.15 times the theoretical amount of divalent copper to the iron-containing filtrate. After filtration, add an oxidant to the filtrate to control the Fe 3+ content to be 2 - 2.5 times the chloride ion content, and adjust the pH value of the system to 1.0 ± 0.15. After reacting and precipitating at 20 - 40 °C, filter the sediment to complete the impurity removal of the iron-containing filtrate.

[0021] Further, the oxidant includes, but is not limited to, hydrogen peroxide.

[0022] Further, the specific method for waste liquid treatment is as follows: Add barium hydroxide solution with a mass fraction of 5 - 8% in an amount 1.5 - 2 times the theoretical amount to the mixed waste liquid under stirring conditions. After standing for 10 - 30 min, filter. After removing the precipitate, add sulfuric acid with a molar concentration of 0.05 - 0.1 mol / L in an amount 1.5 times the theoretical amount to the remaining liquid. After filtering to remove barium sulfate precipitate, a nitric acid solution is obtained.

[0023] Advantages of the present invention:

[0024] The method for recycling waste lithium iron phosphate to battery-grade iron phosphate in the present invention activates the positive electrode powder by ball milling with a phosphorus-containing ionic liquid. The lithium ions in the positive electrode powder exchange with the cations in the phosphorus-containing ionic liquid to achieve selective extraction of lithium ions, which helps to increase the leaching rate of lithium. After adding dilute sulfuric acid to the activated slurry, through the adjustment of reaction parameters, lithium is further selectively leached without leaching iron, reducing the inclusion of lithium by the phosphorus-iron filter residue. At the same time, during the acid leaching process, the lithium ions in the phosphorus-containing ionic liquid combine with sulfate ions to form lithium sulfate, transferring the lithium ions to the acid solution, which helps to recover lithium carbonate by subsequent lithium precipitation. In addition, this method also dissolves the phosphorus-iron filter residue with nitric acid, removes impurities, adjusts the phosphorus-iron ratio, and adjusts the pH with ammonia water to inhibit the formation of iron hydroxide. The co-precipitation regenerates hydrated iron phosphate, and after high-temperature dehydration, battery-grade iron phosphate with higher purity can be obtained, which is beneficial to the recycling of lithium iron phosphate batteries.

[0025] Compared with the traditional method, the method of the present invention does not require a high temperature close to 1000 °C to completely remove the binder in the cathode material, so no tail gas carrying metal elements will be generated, which helps to reduce the difficulty of tail gas treatment. The excess impurities can be filtered out during the nitric acid solvent process; in addition, the nitrogen oxide tail gas generated from dissolving the phosphorus-iron filter residue can be recycled to prepare nitric acid and reused for dissolving the phosphorus-iron filter residue, and the ammonia gas generated during the waste liquid treatment process can be reused to prepare ammonia water for the coprecipitation of iron phosphate hydrate, realizing the recycling of resources. Detailed implementation mode

[0026] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0027] Example 1

[0028] This example provides a method for recycling waste lithium iron phosphate into battery-grade iron phosphate, which specifically includes the following implementation steps:

[0029] Step 1: Discharge, disassemble, and crush the waste lithium iron phosphate battery, collect the cathode material, crush and dry the cathode material, transfer it to a muffle furnace, and calcine it at 450 °C for 1 h to decompose the binder in the cathode material. Then, perform vibration screening to remove and collect the cathode powder on the surface of the aluminum foil.

[0030] Step 2: Stir and mix 200 kg of cathode powder, 200 L of hydrogen peroxide solution with a mass fraction of 20%, 6 kg of tributyl phosphate, and 200 L of water, then transfer it to a ball mill tank, and ball mill it at a rotation speed of 200 r / min and a temperature of 50 °C for 1 h to obtain an activated slurry.

[0031] Step 3: Transfer the activated slurry to an acidolysis tank and adjust the solid content to 20% with water. Add sulfuric acid with a molar concentration of 0.05 mol / L to the acidolysis tank to adjust the pH value of the activated slurry to 3, and stir it at a temperature of 50 °C and a speed of 200 r / min for 0.5 h. Then, perform selective leaching and filtration to obtain a lithium-containing filtrate and a phosphorus-iron filter residue.

[0032] Step 4: Dry the phosphorus-iron filter residue and mix it with nitric acid with a molar concentration of 5 mol / L according to a mass ratio of 1:8. Stir it at 80 °C and 200 r / min for 5 h, filter out the solid waste residue, collect the iron-containing filtrate and the generated tail gas, and recycle the tail gas to prepare nitric acid.

[0033] Step 5: Add iron powder in an amount 1 time the theoretical amount of divalent copper to the iron-containing filtrate. After filtration, add an oxidant to the filtrate to control the Fe content in the system to be 2 times the chloride content, and adjust the pH value of the system to 1.0 ± 0.15. After reacting and precipitating at 20 °C, filter the sediment. Then, adjust the phosphorus-iron molar ratio of the iron-containing filtrate to 1.03:1 with phosphoric acid, and then adjust the pH value to 1.5 with 25% ammonia water by mass fraction. Stir at 80 °C and 200 r / min for 3 h, let it stand and filter to obtain iron phosphate hydrate precipitate and acid-containing waste liquid. Wash the iron phosphate hydrate precipitate with water at 50 °C until the pH value of the last washing liquid > 3.3, dry it, and calcine it at 600 °C for 60 min to obtain battery-grade iron phosphate. 3+ Content is 2 times the chloride content, and adjust the pH value of the system to 1.0 ± 0.15. After reacting and precipitating at 20 °C, filter the sediment. Then, adjust the phosphorus-iron molar ratio of the iron-containing filtrate to 1.03:1 with phosphoric acid, and then adjust the pH value to 1.5 with 25% ammonia water by mass fraction. Stir at 80 °C and 200 r / min for 3 h, let it stand and filter to obtain iron phosphate hydrate precipitate and acid-containing waste liquid. Wash the iron phosphate hydrate precipitate with water at 50 °C until the pH value of the last washing liquid > 3.3, dry it, and calcine it at 600 °C for 60 min to obtain battery-grade iron phosphate.

[0034] Step 6: Evaporate and concentrate the lithium-containing filtrate to 30 ± 5% of the original volume to obtain a concentrated solution. Add a 5% sodium hydroxide solution by mass fraction to the concentrated solution under stirring conditions, adjust the pH value to 12, let it stand for 10 min and then filter. After removing the precipitate, add sodium carbonate in an amount 2 times the theoretical amount to the remaining liquid, stir and mix, and then filter to collect lithium carbonate precipitate and salt-containing waste liquid.

[0035] Step 7: Mix the salt-containing waste liquid and the acid-containing waste liquid to obtain a mixed waste liquid. Add a 5% barium hydroxide solution by mass fraction in an amount 1.5 times the theoretical amount to the mixed waste liquid under stirring conditions, let it stand for 10 min and then filter. After removing the precipitate, add sulfuric acid with a molar concentration of 0.05 mol / L in an amount 1.5 times the theoretical amount to the remaining liquid, filter to remove barium sulfate precipitate, and then obtain a nitric acid solution. Collect the tail gas recovered during the waste liquid treatment process to prepare ammonia water.

[0036] Through calculation and detection, the recovery rate of lithium in the positive electrode powder of this example is 98.35%, and the purity of the obtained lithium carbonate is 99.96%; the recovery rate of iron and phosphorus is 95.65%, and the purity of the obtained iron phosphate is 99.95%.

[0037] Example 2

[0038] This example provides a method for regenerating battery-grade iron phosphate from waste lithium iron phosphate batteries, specifically including the following implementation steps:

[0039] Step 1: Discharge, disassemble, and crush the waste lithium iron phosphate battery, and then collect the positive electrode material. Crush and dry the positive electrode material, transfer it to a muffle furnace, and calcine it at 480 °C for 1.5 h to decompose the binder in the positive electrode material. Vibrate and screen to remove and collect the positive electrode powder on the surface of the aluminum foil.

[0040] Step 2: Stir and mix 200 kg of cathode powder, 250 L of hydrogen peroxide solution with a mass fraction of 25%, 8 kg of tributyl phosphate, and 250 L of water, then transfer them to a ball mill tank and ball mill for 1.5 h under the conditions of a rotation speed of 350 r / min and a temperature of 55 °C to obtain an activated slurry.

[0041] Step 3: Transfer the activated slurry to an acid digestion tank and adjust the solid content to 25% with water. Add sulfuric acid with a molar concentration of 0.08 mol / L to the acid digestion tank to adjust the pH value of the activated slurry to 3.5, and stir for 1 h at a temperature of 55 °C and a speed of 350 r / min for selective leaching, then filter to obtain a lithium-containing filtrate and a phosphorus-iron filter residue.

[0042] Step 4: After drying the phosphorus-iron filter residue, mix it with nitric acid with a molar concentration of 5.5 mol / L according to a mass ratio of 1:9, stir for 5.5 h under the conditions of 85 °C and 350 r / min, filter to remove solid waste residues, collect the iron-containing filtrate and the generated tail gas, and recycle the tail gas to prepare nitric acid.

[0043] Step 5: Add iron powder with a quantity 1.1 times the theoretical amount of divalent copper to the iron-containing filtrate. After filtration, add an oxidant to the filtrate to control the Fe 3+ content to be 2.25 times the chloride ion content, and adjust the pH value of the system to 1.0 ± 0.15. After reacting and precipitating at 30 °C, filter the sediment. Then adjust the phosphorus-iron molar ratio of the iron-containing filtrate to 1.04:1 with phosphoric acid, and then adjust the pH value to 2 with ammonia water with a mass fraction of 26%. Stir for 3.5 h under the conditions of 85 °C and 350 r / min, let it stand and filter to obtain a hydrated iron phosphate precipitate and an acid-containing waste liquid. Wash the hydrated iron phosphate precipitate with water at 55 °C until the pH value of the last washing liquid > 3.3, dry it, and calcine it at 625 °C for 75 min to obtain battery-grade iron phosphate.

[0044] Step 6: Evaporate and concentrate the lithium-containing filtrate to 30 ± 5% of the original volume to obtain a concentrated solution. Add a sodium hydroxide solution with a mass fraction of 8% to the concentrated solution under stirring conditions to adjust the pH value to 12.5. Let it stand for 20 min and then filter to remove the precipitate. Then add sodium carbonate with a quantity 2.5 times the theoretical amount to the remaining liquid, stir and mix, and then filter to collect the lithium carbonate precipitate and a salt-containing waste liquid.

[0045] Step 7: Mix the salt-containing waste liquid and the acid-containing waste liquid to obtain a mixed waste liquid. Add a barium hydroxide solution with a mass fraction of 6% with a quantity 1.8 times the theoretical amount to the mixed waste liquid under stirring conditions. Let it stand for 20 min and then filter to remove the precipitate. Then add sulfuric acid with a molar concentration of 0.08 mol / L with a quantity 1.5 times the theoretical amount to the remaining liquid, filter to remove the barium sulfate precipitate, and obtain a nitric acid solution. Collect the tail gas recovered during the waste liquid treatment process to prepare ammonia water.

[0046] After calculation and detection, the recovery rate of lithium in the cathode powder of this example is 98.77%, and the purity of the obtained lithium carbonate is 99.97%; the recovery rate of iron and phosphorus is 95.83%, and the purity of the obtained iron phosphate is 99.96%.

[0047] Example 3

[0048] This example provides a method for regenerating battery-grade iron phosphate from waste lithium iron phosphate batteries, specifically including the following implementation steps:

[0049] Step 1: Discharge, disassemble, and crush the waste lithium iron phosphate battery, collect the cathode material, crush and dry the cathode material, then transfer it to a muffle furnace, calcine it at 500 °C for 2 h to decompose the binder in the cathode material, vibrate and screen to remove and collect the cathode powder on the surface of the aluminum foil.

[0050] Step 2: Stir and mix 200 kg of cathode powder, 300 L of hydrogen peroxide solution with a mass fraction of 30%, 10 kg of trioctyl phosphate, and 300 L of water, then transfer it to a ball mill tank, and ball mill it at a rotation speed of 500 r / min and a temperature of 60 °C for 2 h to obtain an activated slurry.

[0051] Step 3: Transfer the activated slurry to an acidolysis tank and adjust the solid content to 30% with water. Add sulfuric acid with a molar concentration of 0.1 mol / L to the acidolysis tank to adjust the pH value of the activated slurry to 4, stir at a temperature of 60 °C and a speed of 500 r / min for 1.5 h, perform selective leaching and filtration to obtain a lithium-containing filtrate and a phosphorus-iron filter residue.

[0052] Step 4: Dry the phosphorus-iron filter residue and mix it with nitric acid with a molar concentration of 6 mol / L according to a mass ratio of 1:10, stir at 90 °C and 500 r / min for 6 h, filter to remove solid waste residues, collect the iron-containing filtrate and the generated tail gas, and recycle the tail gas to prepare nitric acid.

[0053] Step 5: Add iron powder with a theoretical amount of 1.15 times that of divalent copper to the iron-containing filtrate. After filtration, add an oxidant to the filtrate to control the Fe 3+ content to 2.5 times the chloride ion content, and adjust the pH value of the system to 1.0 ± 0.15. After reacting and precipitating at 40 °C, filter the sediment. Then, adjust the phosphorus-iron molar ratio of the iron-containing filtrate to 1.05:1 with phosphoric acid, and then adjust the pH value to 2.5 with ammonia water with a mass fraction of 28%. Stir at 90 °C and 500 r / min for 4 h, let it stand and filter to obtain a hydrated iron phosphate precipitate and an acid-containing waste liquid. Wash the hydrated iron phosphate precipitate with water at 60 °C until the pH value of the last washing liquid > 3.3, dry it, and calcine it at 650 °C for 90 min to obtain battery-grade iron phosphate.

[0054] Step 6: Evaporate and concentrate the lithium-containing filtrate to 30±5% of the original volume to obtain a concentrated solution. Under stirring conditions, add a 10% sodium hydroxide solution to the concentrated solution, adjust the pH value to 13, let it stand for 30 min, then filter. After removing the precipitate, add sodium carbonate that is 3 times in excess of the theoretical amount to the remaining liquid, stir and mix, and then filter to collect lithium carbonate precipitate and salt-containing waste liquid.

[0055] Step 7: Mix the salt-containing waste liquid and the acid-containing waste liquid to obtain a mixed waste liquid. Under stirring conditions, add a 8% barium hydroxide solution that is 2 times in excess of the theoretical amount to the mixed waste liquid, let it stand for 30 min, then filter. After removing the precipitate, add sulfuric acid with a molar concentration of 0.1 mol / L that is 1.5 times in excess of the theoretical amount to the remaining liquid, filter to remove barium sulfate precipitate, and then obtain a nitric acid solution. Collect the tail gas recovered during the waste liquid treatment process to prepare ammonia water.

[0056] Through calculation and detection, the recovery rate of lithium in the cathode powder of this example is 98.69%, and the purity of the obtained lithium carbonate is 99.96%; the recovery rate of iron and phosphorus is 95.78%, and the purity of the obtained iron phosphate is 99.95%.

[0057] Comparative Example 1: On the basis of Example 3, without performing the operation of Step 2, directly adjust the cathode powder in Step 1 into a slurry with a solid content of 30% with water, and keep the subsequent steps unchanged to recover and prepare battery-grade iron phosphate and lithium carbonate.

[0058] Through calculation and detection, the recovery rate of lithium in the cathode powder of this comparative example is 97.24%, and the purity of the obtained lithium carbonate is 99.95%; the recovery rate of iron and phosphorus is 95.74%, and the purity of the obtained iron phosphate is 99.94%. It shows that the ball milling activation of phosphorus-containing ionic liquid helps to improve the recovery rate of lithium.

[0059] Comparative Example 2: On the basis of Example 3, mix the phosphorus-iron filter residue in Step 4 and hydrochloric acid with a molar concentration of 6 mol / L according to a mass ratio of 1:10, stir at 90°C and 500 r / min for 6 h, filter to remove solid waste residue, collect the iron-containing filtrate and add phosphoric acid to adjust the molar ratio of phosphorus to iron to 1.05:1, then adjust the pH value to 1.5 with 28% ammonia water, stir at 90°C and 500 r / min for 4 h, let it stand and filter to obtain a hydrated iron phosphate precipitate. Wash the hydrated iron phosphate precipitate with water at 60°C until the pH value of the last washing liquid > 3.3, dry it, and then calcine it at 650°C for 90 min to obtain battery-grade iron phosphate; keep the remaining steps unchanged to recover and prepare lithium carbonate.

[0060] After calculation and detection, the lithium recovery rate in the cathode powder of this comparative example is 98.65%, and the purity of the obtained lithium carbonate is 99.96%; the recovery rate of iron and phosphorus is 94.64%, and the purity of the obtained iron phosphate is 98.75%. It shows that the combination of nitric acid dissolution and ammonia co-precipitation helps to improve the purity of iron phosphate.

[0061] It can be seen from the examples and comparative examples that adding phosphorus-containing ionic liquid ball milling activation can increase the lithium recovery rate and the purity of iron phosphate, and using the method of nitric acid dissolving phosphorus-iron filter residue and ammonia co-precipitation can increase the purity of iron phosphate.

[0062] It should be noted that in this article, terms such as "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0063] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for recycling battery-grade iron phosphate from waste lithium iron phosphate, characterized in that, It includes the following steps: Step 1: Pretreat waste lithium iron phosphate to obtain positive electrode powder. Mix the positive electrode powder, 20 - 30wt% hydrogen peroxide solution, phosphorus-containing ionic liquid, and water by stirring, and transfer the mixture to a ball mill jar for ball milling to obtain an activated slurry. The phosphorus-containing ionic liquid is tributyl phosphate or trioctyl phosphate; Step 2: Transfer the activated slurry to an acidolysis tank and adjust the solid content to 20 - 30% with water. Adjust the pH value to 3 - 4 with sulfuric acid having a molar concentration of 0.05 - 0.1mol / L, stir at 50 - 60°C and 200 - 500r / min for 0.5 - 1.5h, and then filter to obtain a lithium-containing filtrate and a phosphorus-iron filter residue; Step 3: After drying the phosphorus-iron filter residue, mix it with nitric acid having a molar concentration of 5 - 6mol / L for reaction, filter to remove solid waste residues, collect the iron-containing filtrate and the generated tail gas, and recycle the tail gas to prepare nitric acid; Step 4: After impurity removal from the iron-containing filtrate, adjust the phosphorus-iron ratio, adjust the pH value to 1.5 - 2.5, precipitate iron phosphate, let it stand and filter to obtain a hydrated iron phosphate precipitate and an acid-containing waste liquid. The hydrated iron phosphate precipitate is washed, dried, and calcined to obtain battery-grade iron phosphate; Step 5: Evaporate and concentrate the lithium-containing filtrate to 30 ± 5% of the original volume to obtain a concentrated solution. Adjust the pH value to 12 - 13 with a 5 - 10wt% sodium hydroxide solution, let it stand for 10 - 30min and then filter. After removing the precipitate, add a carbonate that is 2 - 3 times in excess of the theoretical amount to the remaining liquid, stir and mix, and then filter to collect the lithium carbonate precipitate and a salt-containing waste liquid; Step 6: Mix the salt-containing waste liquid and the acid-containing waste liquid to obtain a mixed waste liquid and perform waste liquid treatment. Recycle the tail gas generated during the waste liquid treatment process to prepare ammonia water.

2. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The conditions for the ball milling in Step 1 are ball milling at 50 - 60°C and 200 - 500r / min for 1 - 2h.

3. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The specific method for the pretreatment in Step 1 is: Discharge, disassemble, and crush the waste lithium iron phosphate battery, collect the positive electrode material, crush and dry the positive electrode material, transfer it to a muffle furnace, calcine at 450 - 500°C for 1 - 2h, perform vibration screening, and collect the positive electrode powder.

4. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The dosage ratio of the positive electrode powder, hydrogen peroxide, ionic liquid, and water in Step 1 is 20g : 20 - 30mL : 0.6 - 1g : 20 - 30mL.

5. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The method for the waste liquid treatment in Step 6 is: Under stirring conditions, add a 5 - 8wt% barium hydroxide solution that is 1.5 - 2 times in excess of the theoretical amount to the mixed waste liquid, let it stand for 10 - 30min and then filter. After removing the precipitate, add sulfuric acid having a molar concentration of 0.05 - 0.1mol / L that is 1.5 times in excess of the theoretical amount to the remaining liquid, and filter to remove the barium sulfate precipitate to obtain a nitric acid solution.

6. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The mass ratio of the dried phosphorus-iron filter residue to nitric acid in Step 3 is 1 : 8 - 10.

7. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The phosphorus-iron molar ratio after adjusting the phosphorus-iron ratio in Step 4 is 1.03 - 1.05 :

1.

8. The method for recycling battery-grade iron phosphate from waste lithium iron phosphate according to claim 1, characterized in that, The control conditions for washing the hydrated iron phosphate precipitate in Step 4 are: Wash with water at 50 - 60°C until the pH value of the last washing liquid > 3.3.