Method for preparing battery-grade iron phosphate and lithium carbonate from waste positive electrode material

Abstract

The present application belongs to the technical field of waste battery recycling, and particularly relates to a method for preparing battery-grade iron phosphate and lithium carbonate from waste positive electrode materials. The method comprises the following steps: (1) acid leaching; (2) copper removal by extraction; (3) aluminum removal by ammonium sulfate; (4) adjusting the iron-phosphorus ratio, oxidation, and iron phosphate synthesis; (5) aging, phosphoric acid washing, and pure water washing; (6) iron phosphate drying and calcination to prepare battery-grade iron phosphate; (7) impurity removal and ammonia removal by lime; (8) lithium extraction by evaporation and concentration, lithium precipitation by sodium carbonate, and washing; (9) carbonization, calcium and magnesium removal by resin, pyrolysis, and drying to prepare battery-grade lithium carbonate. The method can realize comprehensive recovery of valuable elements such as iron, phosphorus, lithium, aluminum, and copper in waste lithium iron phosphate positive electrode materials, can realize ammonia water recycling, and can realize zero wastewater discharge through evaporation and concentration and solution recycling. The method has a high valuable metal recovery rate, and the comprehensive recovery rates of lithium and iron are both greater than 95%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling of waste lithium ion batteries, and in particular to a method for preparing battery-grade iron phosphate and lithium carbonate from waste positive electrode materials. BACKGROUND

[0002] With the rapid development of the new energy vehicle industry, the use of lithium iron phosphate batteries has increased significantly. Recycling lithium iron phosphate can effectively reduce the demand for primary resources and reduce the environmental damage caused by resource extraction. For example, lithium resources are unevenly distributed globally, and recycling can improve resource self-sufficiency and reduce dependence on imports. Environmental protection: Waste lithium iron phosphate batteries contain harmful substances such as heavy metals, which can cause serious pollution to soil, water, and other resources if discarded or improperly disposed of. Effective recycling of waste lithium iron phosphate batteries can prevent these potential environmental hazards. Economic benefits: With technological advancements and market expansion, efficient recycling of lithium carbonate and iron phosphate from lithium iron phosphate batteries through appropriate recycling methods can generate significant economic value. Additionally, reducing resource waste has economic significance in itself.

[0003] There are currently two main methods for recycling waste lithium iron phosphate batteries: wet recovery and physical recovery. Wet recovery is a common technique used by domestic power battery recycling companies for lithium iron phosphate batteries. This method uses chemical reactions to dissolve valuable metal elements from waste lithium iron phosphate batteries into a solution, which is then separated and purified to recover lithium, iron, and other elements. The advantage of this method is that it has a high recovery efficiency and a relatively mature process, but it may generate wastewater, waste residue, and other byproducts that need to be treated. Physical recovery mainly involves mechanical crushing, screening, and other physical methods to process waste lithium iron phosphate batteries, separating different material components such as metal casings and electrode materials. Physical recovery has relatively low costs, but the purity and efficiency of the recovered materials may not be as high as wet recovery.

[0004] Wet recovery mainly includes selective recovery (preferential lithium extraction) and full recovery processes. Current wet recovery techniques for waste lithium iron phosphate batteries have the following difficulties in actual production: (1) In the selective recovery process, a large amount of acid is consumed to dissolve the crude iron phosphate, and a large amount of base is also consumed during the subsequent preparation of iron phosphate solution and iron phosphate precipitation, as well as a large amount of phosphoric acid conversion; (2) The full recovery process has a high pressure for impurity removal, and the quality of the obtained lithium carbonate and iron phosphate will be affected by the impurity removal effect; it is difficult to achieve a high recovery rate of valuable metals; the entire full recovery process requires a large amount of solution, and the solution's destination during production and wastewater treatment need to be considered.

[0005] In view of the various problems existing in the recovery process of waste lithium iron phosphate positive electrode material in the prior art, there is an urgent need to develop a method for fully recovering iron phosphate and lithium carbonate from waste lithium iron phosphate positive electrode material with high practical application value and low processing cost. SUMMARY

[0006] In view of the problems of large impurity removal pressure, low valuable metal recovery rate and large process solution volume existing in the full recovery process of waste lithium iron phosphate positive electrode material, the present application provides a method for preparing battery-grade iron phosphate and battery-grade lithium carbonate from waste lithium iron phosphate positive electrode material, which comprises the following steps: (1) acid leaching; (2) copper extraction; (3) ammonium sulfate aluminum removal; (4) adjusting iron-phosphorus ratio, oxidation, and iron phosphate synthesis; (5) aging, phosphoric acid washing, and pure water washing; (6) iron phosphate drying and calcination to prepare battery-grade iron phosphate; (7) lime impurity removal and ammonia removal; (8) evaporation and concentration to extract lithium, sodium carbonate lithium precipitation, and washing; (9) carbonization, resin calcium and magnesium removal, pyrolysis, and drying to prepare battery-grade lithium carbonate. This method uses a wet full recovery process to treat waste lithium iron phosphate positive electrode material, which can realize the comprehensive recovery of valuable elements such as iron, phosphorus, lithium, copper, etc. in waste lithium iron phosphate positive electrode material, can realize the recycling of ammonia water, and can realize zero wastewater discharge through evaporation and concentration and solution recycling. This method has high valuable metal recovery rate, and the comprehensive recovery rate of lithium and iron is greater than 95%. This method is simple and easy to operate, has good impurity removal effect, can obtain battery-grade iron phosphate and battery-grade lithium carbonate products with good performance and high quality, and the purity of battery-grade iron phosphate and battery-grade lithium carbonate is more than 99.6%, which is suitable for industrial application.

[0007] The present application can be realized by the following technical solutions:

[0008] The present application discloses a method for preparing battery-grade iron phosphate and lithium carbonate from waste positive electrode material, which comprises the following steps:

[0009] (1) Alkali leaching to remove aluminum: crushing the waste lithium iron phosphate positive electrode material to obtain lithium iron phosphate positive electrode powder; adding sulfuric acid solution to the lithium iron phosphate positive electrode powder for acid leaching, and then pressure filtering after acid leaching to obtain acid leaching liquid and graphite residue;

[0010] (2) Copper extraction: using ZJ980 copper extractant to extract copper from the acid leaching liquid obtained in step (1) to obtain copper-removed liquid and high-purity copper sulfate solution, and the high-purity copper sulfate solution can be used to produce cathode copper;

[0011] (3) Ammonium sulfate aluminum removal: adding ammonium sulfate to the copper-removed liquid obtained in step (2) to remove aluminum, and obtaining aluminum-removed liquid and aluminum-removed residue;

[0012] (4) Adjusting iron-phosphorus ratio, oxidation, synthesizing iron phosphate: ammonium dihydrogen phosphate is added into the solution after aluminum removal to adjust the iron-phosphorus molar ratio of the solution to 1:1-1.05, then hydrogen peroxide is added for oxidation, and then ammonia solution is added to synthesize iron phosphate precipitate by controlling the PH of the solution, and the iron phosphate slurry is obtained after the reaction is completed;

[0013] (5) Aging, phosphoric acid washing, and pure water washing: the iron phosphate slurry obtained in step (4) is aged at high temperature, and the slurry after aging is filtered to obtain the solution after aging and iron phosphate residue after aging; the iron phosphate residue after aging is washed with phosphoric acid and pure water respectively, and the iron phosphate after washing is obtained by filtering.

[0014] (6) Iron phosphate drying and calcination to prepare battery-grade iron phosphate: the iron phosphate obtained in step (5) is dried and calcined to obtain the battery-grade iron phosphate product.

[0015] (7) Lime impurity removal and ammonia removal: lime milk is added into the solution after impurity removal obtained in step (5) to remove iron, phosphorus, silicon and other impurities in the solution, and to remove ammonium ions in the solution to avoid the reaction of ammonium ions and sodium carbonate in the process of lithium precipitation.

[0016] (8) Evaporation concentration for lithium extraction, sodium carbonate lithium precipitation, and washing: the solution after impurity removal obtained in step (7) is evaporated and concentrated to deeply remove ammonia and calcium, and a lithium-rich solution with a lithium concentration of 15-20 g / L is obtained; sodium carbonate solution is added into the lithium-rich solution to synthesize crude lithium carbonate, and the crude lithium carbonate is washed with pure water.

[0017] (9) Carbonization, resin calcium and magnesium removal, pyrolysis, and drying: the crude lithium carbonate obtained in step (8) is slurried by adding water at a certain liquid-solid ratio, and then carbon dioxide is introduced for carbonization, and the solution after carbonization and calcium carbonate residue are obtained by filtering; the solution after carbonization deeply removes calcium and magnesium by calcium and magnesium removal resin; the solution after calcium and magnesium removal is pyrolyzed at high temperature to obtain battery-grade lithium carbonate.

[0018] Preferably, the concentration of the sulfuric acid solution in step (1) is 2-5 mol / L, the liquid-solid ratio is 3-6 mL / g, the acid leaching temperature is 25℃, and the acid leaching time is 2-6 h.

[0019] Preferably, the concentration of the ammonium sulfate in step (3) is 10-15%, the reaction temperature is 30-60℃, the reaction PH is controlled to be 0.5-1.0, and the reaction time is 0.5-1 h.

[0020] Preferably, the amount of hydrogen peroxide in step (4) is 1.5-3 times the theoretical amount based on the molar amount of iron, the oxidation time is 1-3 h; the concentration of the ammonia solution is 5-15%, the PH for synthesizing iron phosphate is controlled to be 1-3, the reaction time is 1-4 h, and the reaction temperature is 25℃.

[0021] Preferably, the phosphoric acid iron slurry in step (5) is aged at a temperature of 60-100 DEG C for 8-16 hours; the phosphoric acid iron residue is slurried with pure water at a liquid-solid ratio of 5-10 mL / g after aging; the phosphoric acid washing temperature is 50-80 DEG C, and the washing time is 1-3 hours; the phosphoric acid iron residue is slurried with pure water at a liquid-solid ratio of 5-10 mL / g after phosphoric acid washing; the pure water washing times are 2-5 times, the temperature of each pure water washing is 50-80 DEG C, and the time of each pure water washing is 1-4 hours.

[0022] Preferably, the phosphoric acid iron in step (6) is dried at a temperature of 70-100 DEG C for 8-16 hours; the calcination temperature of the phosphoric acid iron is 500-700 DEG C, and the calcination time is 1-4 hours.

[0023] Preferably, the lime milk concentration in step (7) is 20-30%, the impurity removal and deamination PH is 10-14, the impurity removal and deamination temperature is 70-100 DEG C, the impurity removal and deamination time is 1-4 hours, the ammonia gas after deamination is absorbed by an absorption tower, and the absorbed ammonia water can be recycled to the phosphoric acid iron synthesis process.

[0024] Preferably, the lithium extraction temperature of the impurity-removed liquid in step (8) is 70-100 DEG C; the sodium carbonate addition amount is 1-2 times the theoretical amount based on the lithium molar amount, the sodium carbonate solution concentration is 200-400 g / L, the lithium precipitation temperature is 70-100 DEG C, and the lithium precipitation time is 1-4 hours; the crude lithium carbonate washing times are 2-5 times, and the washing temperature is 70-100 DEG C.

[0025] Preferably, the crude lithium carbonate in step (9) is slurried with pure water at a liquid-solid ratio of 15-30 mL / g and then carbonized; the pyrolysis temperature of the calcium and magnesium removal liquid is 70-100 DEG C, and the pyrolysis time is 1-4 hours; the lithium carbonate drying temperature is 70-100 DEG C, and the drying time is 1-4 hours.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] (1) The present application efficiently separates and recycles aluminum and copper and other useful metal elements in waste lithium iron phosphate positive electrode materials through acid leaching, copper removal by extraction, aluminum removal by ammonium sulfate, etc., and the generated graphite residue can be recycled to produce conductive graphite; the processes of oxidation, synthesis of phosphoric acid iron, aging, phosphoric acid washing, pure water washing, drying, calcination, etc. are adopted to avoid the introduction of sodium ions, reduce the generation of iron hydroxide and basic iron sulfate, and gradually remove the residual ammonium ions in the synthesized phosphoric acid iron residue through washing and calcination, so as to achieve the purpose of deep impurity removal of the phosphoric acid iron and obtain a high-value battery-grade phosphoric acid iron product.

[0028] (2) The technical scheme of the present application adopts lime impurity removal and deamination, evaporation concentration lithium extraction, lithium precipitation with sodium carbonate, carbonization, resin calcium and magnesium removal, pyrolysis, drying and other processes to deeply remove phosphorus, iron, silicon, ammonium, calcium, magnesium and other elements in the lithium-containing aged liquid, thereby realizing deep impurity removal and concentration of the lithium-containing aged liquid, achieving zero discharge of wastewater, and obtaining high-value battery-grade lithium carbonate products.

[0029] (3) The ammonia water produced by the lime impurity removal and deamination process of the technical scheme of the present application can be recycled to the iron phosphate synthesis process, thereby greatly reducing the consumption of ammonia water and effectively reducing the production cost of waste lithium iron phosphate battery recycling.

[0030] (4) The solution of the technical scheme of the present application realizes recycling and has a high valuable element recovery rate. In terms of valuable metals in the waste lithium iron phosphate positive material, the comprehensive recovery rate of lithium and iron is greater than 95%.

[0031] (5) The technical scheme of the present application has a simple process flow, easy operation, good impurity removal effect, high product purity and good performance, the purity of battery-grade lithium phosphate and battery-grade lithium carbonate is more than 99.6%, it is suitable for large-scale production, and has obvious economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0032] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings, in which:

[0033] Figure 1 is a process flow diagram of the present application;

[0034] Figure 2 is the SEM morphology of the battery-grade lithium phosphate described in Example 1 of the present application;

[0035] Figure 3 is the SEM morphology of the battery-grade lithium phosphate described in Example 2 of the present application. DETAILED DESCRIPTION

[0036] The present application provides a method for preparing battery-grade lithium phosphate and battery-grade lithium carbonate from waste lithium iron phosphate positive material, comprising the following steps:

[0037] (1) Acid leaching: crushing the waste lithium iron phosphate positive material to obtain lithium iron phosphate positive powder; adding sulfuric acid solution to the lithium iron phosphate positive powder for acid leaching, and after acid leaching is completed, pressure filtration to obtain acid leaching liquid and graphite residue;

[0038] (2) Copper extraction: the acid leaching liquid obtained in step (1) is extracted with ZJ980 copper extractant to obtain copper-removed liquid and copper sulfate solution.

[0039] (3) Ammonium sulfate de-aluminum: ammonium sulfate is added to the copper-removed solution obtained in step (2) to remove aluminum, to obtain a de-aluminum solution and de-aluminum residue.

[0040] (4) Adjusting iron-phosphorus ratio, oxidation, and synthesizing iron phosphate: ammonium dihydrogen phosphate is added to the de-aluminum solution to adjust the iron-phosphorus molar ratio of the solution to 1:1-1.05, then hydrogen peroxide is added for oxidation, and then ammonia solution is added to synthesize iron phosphate precipitate by controlling the PH of the solution. After the reaction is completed, an iron phosphate slurry is obtained.

[0041] (5) Aging, phosphoric acid washing, and pure water washing: the iron phosphate slurry obtained in step (4) is aged at high temperature, the aged slurry is filtered, to obtain an aged solution and an aged iron phosphate residue; the aged iron phosphate residue is washed with phosphoric acid, washed with pure water multiple times, and filtered, to obtain washed iron phosphate.

[0042] (6) Iron phosphate drying and calcination to prepare battery-grade iron phosphate: the iron phosphate obtained in step (5) is dried and calcined, to obtain a battery-grade iron phosphate product.

[0043] (7) Lime impurity removal and ammonia removal: lime milk is added to the aged solution obtained in step 5) to remove impurities such as iron, phosphorus, and silicon in the solution, and to remove ammonium ions in the solution, to avoid the reaction of ammonium ions with sodium carbonate in the lithium precipitation process and the consumption of a large amount of sodium carbonate.

[0044] (8) Evaporation concentration for lithium extraction, sodium carbonate lithium precipitation, and washing: the impurity-removed solution obtained in step (7) is evaporated and concentrated to deeply remove ammonia and calcium, to obtain a lithium-rich solution with a lithium concentration of 15-20 g / L; sodium carbonate solution is added to the lithium-rich solution to synthesize crude lithium carbonate, and the crude lithium carbonate is washed with pure water.

[0045] (9) Crude lithium carbonate carbonization, resin calcium and magnesium removal, pyrolysis, and drying: the crude lithium carbonate obtained in step (8) is slurried by adding water at a certain liquid-solid ratio, then carbon dioxide is introduced for carbonization, and filtration is performed to obtain a carbonized solution and calcium carbonate residue; the carbonized solution is deeply removed of calcium and magnesium by calcium and magnesium removal resin; the calcium and magnesium-removed solution is pyrolyzed at high temperature and dried to obtain battery-grade lithium carbonate.

[0046] The following examples will illustrate the present application in detail.

[0047] Example 1:

[0048] The waste old lithium iron phosphate positive material is crushed to obtain lithium iron phosphate positive powder, and the main element content is as follows: Li 3.89%, Fe 29.68%, Al 1.12%, P 16.42%, and Cu 1.05%.

[0049] (1) Acid leaching:

[0050] The lithium iron phosphate positive electrode powder is added into a 2.5 mol / L sulfuric acid solution according to a liquid-solid ratio of 5 mL / g for acid leaching, the acid leaching temperature is 25°C, and the acid leaching time is 3 h. After the acid leaching is completed, the acid leaching residue and graphite residue are obtained by pressure filtration.

[0051] The acid leaching solution is sampled and detected, and the main element contents in the acid leaching solution are as follows: Li 6.26 g / L, Fe 48.28 g / L, Al 2.02 g / L, P 26.74 g / L, and Cu 1.6 g / L. The leaching rates of lithium, iron, and phosphorus in the acid leaching process are 99.4%, 99.3%, and 99.1%, respectively.

[0052] (2) Copper removal by extraction:

[0053] The acid leaching solution is subjected to copper removal by extraction with a ZJ980 copper extractant, and a copper-removed solution and a high-purity copper sulfate solution are obtained. The copper concentration in the copper-removed solution is 0.01 g / L, and the high-purity copper sulfate solution can be used for producing cathode copper. The main element contents in the copper-removed solution are as follows: Li 6.13 g / L, Fe 48.12 g / L, Al 1.93 g / L, P 25.85 g / L, and Cu 0.01 g / L.

[0054] (3) Ammonium sulfate removal of aluminum:

[0055] The copper-removed solution is added with a 12% ammonium sulfate solution, the reaction PH is controlled to be 1.0, the reaction temperature is controlled to be 30°C, and the reaction time is controlled to be 1 h. The aluminum-removed solution and aluminum-removed residue are obtained by pressure filtration after aluminum removal. The main element contents in the aluminum-removed solution are as follows: Li 6.07 g / L, Fe 48.01 g / L, Al 0.001 g / L, P 25.74 g / L, and Cu 0.01 g / L.

[0056] (4) Adjustment of iron-phosphorus ratio, oxidation, and synthesis of iron phosphate:

[0057] The ammonium dihydrogen phosphate is added into the aluminum-removed solution to adjust the iron-phosphorus molar ratio of the solution to 1:1, then the theoretical amount of 30% hydrogen peroxide is added according to 2 times the iron molar amount, the oxidation time is 1 h, and the reaction temperature is 25°C; the reaction temperature is controlled to be 25°C, the 5% ammonia water solution is slowly added into the oxidized solution, the iron phosphate synthesis PH is controlled to be 1.5, and the iron phosphate slurry is obtained after the reaction is completed.

[0058] (5) Aging, phosphoric acid washing, and pure water washing:

[0059] The iron phosphate slurry is aged at high temperature, the aging temperature is 80℃, and the aging time is 10h; the aged slurry is pressure filtered to obtain an aged liquid and an aged iron phosphate residue; the aged iron phosphate residue is slurried by adding pure water at a liquid-solid ratio of 5mL / g, and then washed with phosphoric acid, the temperature of the phosphoric acid washing is 80℃, and the washing time is 1h; the phosphoric acid washed iron phosphate residue is washed with pure water three times at a liquid-solid ratio of 5mL / g, the temperature of each pure water washing is 80℃, and the time of each pure water washing is 1h. The slurry after pure water washing is pressure filtered to obtain washed wet iron phosphate.

[0060] Table 1 Comparison of element content before and after washing of the aged iron phosphate residue

[0061]

[0062] (6) Iron phosphate drying and calcination to prepare battery-grade iron phosphate:

[0063] The wet iron phosphate is dried, the drying temperature is 100℃, and the drying time is 8h; the dried iron phosphate is calcined at high temperature, the calcination temperature is 600℃, and the calcination time is 2h, and the battery-grade iron phosphate product is obtained after calcination.

[0064] (7) Lime removal and ammonia removal:

[0065] 25% lime milk is added to the aged liquid for removal and ammonia removal, the removal and ammonia removal PH is controlled at 12, the removal and ammonia removal temperature is 80℃, and the removal and ammonia removal time is 2h. The ammonia gas generated during the ammonia removal process is absorbed by an absorption tower, and the absorbed ammonia water can be returned to the iron phosphate synthesis process for recycling, and the lime removal and ammonia removal liquid and removal residue are obtained by pressure filtration after the reaction is completed.

[0066] Table 2 Element content of the lime removal and ammonia removal liquid

[0067]

[0068]

[0069] (8) Evaporation concentration to extract lithium, sodium carbonate lithium precipitation, and washing:

[0070] The lime impurity removal and deamination liquid is evaporated and concentrated, and deep deamination and decalcification are carried out. The evaporation and concentration lithium extraction temperature is 100°C. After the reaction is completed, pressure filtration is performed to obtain calcium removal residue and lithium-rich liquid with a lithium concentration of 18g / L. Then, 1.2 times the theoretical amount of sodium carbonate solution based on the molar amount of lithium is added to the lithium-rich liquid to precipitate lithium. The sodium carbonate solution concentration is 300g / L, the lithium precipitation temperature is 90°C, and the lithium precipitation time is 1h. After the reaction is completed, pressure filtration is performed to obtain crude lithium carbonate and lithium precipitation mother liquor. The crude lithium carbonate is washed with pure water three times at a liquid-solid ratio of 5mL / g. The pure water washing temperature is 80°C, and the pure water washing time is 1h each time. After pure water washing, pressure filtration is performed to obtain water-washed crude lithium carbonate and washing water.

[0071] (9) Crude lithium carbonate carbonization, resin calcium and magnesium removal, pyrolysis, and drying:

[0072] The water-washed crude lithium carbonate is slurried with pure water at a liquid-solid ratio of 25mL / g, and then carbon dioxide is introduced for carbonization. The carbonization time is 2h. After carbonization is completed, pressure filtration is performed to obtain carbonized liquid and calcium carbonate residue. The carbonized liquid is subjected to deep removal of calcium and magnesium in the solution by calcium and magnesium removal resin to obtain calcium and magnesium removal liquid. The calcium and magnesium removal liquid is subjected to high-temperature pyrolysis, with the pyrolysis temperature controlled at 100°C and the pyrolysis time controlled at 2h. After pyrolysis is completed, pyrolysis lithium carbonate and pyrolysis liquid are obtained. The pyrolysis lithium carbonate is dried, with the drying temperature controlled at 100°C and the drying time controlled at 8h. After drying is completed, battery-grade lithium carbonate product is obtained.

[0073] Table 3 Element content in battery-grade iron phosphate product

[0074]

[0075]

[0076] Table 4 Element content in battery-grade lithium carbonate product

[0077] Analysis item Result Li2CO3 content, (%) 99.75 Na, (%) 0.01 Mg, (%) 0.001 Ca, (%) 0.001 K，(％) 0.0006 Fe, (%) 0.0007 Zn, (%) 0.0002 Cu, (%) 0.0002 Pb, (%) 0.0001 Si, (%) 0.001 Al，(％) 0.001 Mn, (%) 0.0002 Ni, (%) 0.0008 SO4 2- , (%)]] 0.007 Cl - , (%)]] 0.001

[0078] Example 2:

[0079] The waste lithium iron phosphate positive material is crushed to obtain lithium iron phosphate positive powder, and the main element content is as follows: Li 3.11%, Fe 29.32%, Al 1.36%, P 16.23%, and Cu 1.28%.

[0080] (1) Acid leaching

[0081] The lithium iron phosphate positive powder is added to a 3mol / L sulfuric acid solution at a liquid-solid ratio of 5mL / g for acid leaching. The acid leaching temperature is 25°C, and the acid leaching time is 4h. After acid leaching is completed, pressure filtration is performed to obtain acid leaching residue and graphite residue.

[0082] The acid leaching solution was sampled and detected, and the main element contents in the acid leaching solution were as follows: Li 5.08 g / L, Fe 47.96 g / L, Al 2.58 g / L, P 26.21 g / L, and Cu 1.92 g / L. The leaching rates of lithium, iron, and phosphorus in the acid leaching process were 99.5%, 99.2%, and 99%, respectively.

[0083] (2) Copper removal by extraction:

[0084] The acid leaching solution was subjected to copper removal by extraction with a ZJ980 copper extractant, and a copper-removed solution and a high-purity copper sulfate solution were obtained. The copper concentration in the copper-removed solution was 0.01 g / L, and the high-purity copper sulfate solution could be used for producing cathode copper. The main element contents in the copper-removed solution were as follows: Li 4.91 g / L, Fe 47.82 g / L, Al 2.39 g / L, P 25.65 g / L, and Cu 0.01 g / L.

[0085] (3) Aluminum removal by ammonium sulfate:

[0086] The copper-removed solution was added with a 15% ammonium sulfate solution, the reaction PH was controlled at 0.8, the reaction temperature was 30°C, and the reaction time was 1 h. After pressure filtration, an aluminum-removed solution and an aluminum-removed residue were obtained. The main element contents in the aluminum-removed solution were as follows: Li 4.84 g / L, Fe 47.73 g / L, Al 0.001 g / L, P 25.52 g / L, and Cu 0.01 g / L.

[0087] (4) Adjustment of iron-phosphorus ratio, oxidation, and synthesis of iron phosphate:

[0088] The aluminum-removed solution was added with ammonium dihydrogen phosphate to adjust the iron-phosphorus molar ratio of the solution to 1:1, then 30% hydrogen peroxide was added at 1.6 times the theoretical amount based on the iron molar amount, the oxidation time was 1 h, and the reaction temperature was 25°C; the reaction temperature was controlled at 25°C, and 8% ammonia water solution was slowly added to the oxidized solution, the iron phosphate synthesis PH was controlled at 2.0, and the iron phosphate slurry was obtained after the reaction was completed.

[0089] (5) Iron phosphate aging, phosphoric acid washing, and pure water washing:

[0090] The iron phosphate slurry was subjected to high-temperature aging, the aging temperature was 80°C, and the aging time was 10 h; the aged slurry was subjected to pressure filtration, and an aged liquid and an aged iron phosphate residue were obtained; the aged iron phosphate residue was slurried with pure water at a liquid-solid ratio of 5 mL / g, and then washed with phosphoric acid, the phosphoric acid washing temperature was 80°C, and the washing time was 1 h; the phosphoric acid washed iron phosphate residue was washed with pure water three times at a liquid-solid ratio of 5 mL / g, the temperature of each pure water washing was 80°C, and the time of each pure water washing was 1 h. The slurry after pure water washing was subjected to pressure filtration, and the washed wet iron phosphate was obtained.

[0091] Table 5 Comparison of element content before and after washing of aged iron phosphate slag

[0092]

[0093] (6) Iron phosphate drying and calcination to prepare battery-grade iron phosphate:

[0094] The wet iron phosphate is dried at a drying temperature of 100°C for 8h. The dried iron phosphate is calcined at a calcination temperature of 600°C for 2h. The battery-grade iron phosphate product is obtained after calcination.

[0095] (7) Lime removal and ammonia removal:

[0096] 25% lime milk is added to the aged liquid for removal and ammonia removal, the removal and ammonia removal PH is controlled at 11, the removal and ammonia removal temperature is 80°C, the removal and ammonia removal time is 2h, the ammonia gas generated during the ammonia removal process is absorbed by the absorption tower, the absorbed ammonia water can be returned to the iron phosphate synthesis process for recycling, and the lime removal and ammonia removal liquid and removal residue are obtained after pressure filtration.

[0097] Table 6 Element content of lime removal and ammonia removal liquid

[0098]

[0099] (8) Evaporation concentration to extract lithium, sodium carbonate lithium precipitation, and washing:

[0100] The lime removal and ammonia removal liquid is evaporated and concentrated for deep ammonia removal and calcium removal. The evaporation concentration temperature for lithium extraction is 100°C. The calcium removal residue and lithium-rich liquid with a lithium concentration of 20g / L are obtained after pressure filtration. Then, 1.4 times the theoretical amount of sodium carbonate solution is added to the lithium-rich liquid for lithium precipitation. The sodium carbonate solution concentration is 260g / L, the precipitation temperature is 90°C, and the precipitation time is 1h. The crude lithium carbonate and lithium precipitation mother liquor are obtained after pressure filtration. The crude lithium carbonate is washed with pure water at a liquid-solid ratio of 5mL / g for three times. The pure water washing temperature is 80°C, and the pure water washing time is 1h. The washed crude lithium carbonate and washing water are obtained after pressure filtration.

[0101] (9) Crude lithium carbonate carbonization, resin calcium and magnesium removal, pyrolysis, and drying:

[0102] The crude lithium carbonate after water washing is slurried by adding pure water at a liquid-solid ratio of 23 mL / g, and then carbonization is performed by passing carbon dioxide, with a carbonization time of 2 h. After carbonization, carbonized liquid and calcium carbonate residue are obtained by pressure filtration. The carbonized liquid is subjected to deep removal of calcium and magnesium in the solution by calcium and magnesium removal resin to obtain calcium and magnesium removed liquid. The calcium and magnesium removed liquid is subjected to high temperature pyrolysis, with a pyrolysis temperature of 100 ℃ and a pyrolysis time of 2 h. After pyrolysis, pyrolysis lithium carbonate is obtained. The pyrolysis lithium carbonate is subjected to drying, with a drying temperature of 100 ℃ and a drying time of 8 h. After drying, battery grade lithium carbonate product is obtained.

[0103] Table 7 is the element content in the battery grade iron phosphate product

[0104] Analysis item Result Iron (Fe), % 36.32 Phosphorus (P), % 20.14 Iron phosphorus ratio (Fe:P) 0.998 Calcium (Ca), % 0.004 Magnesium (Mg), % 0.0006 Sodium (Na), % 0.008 Potassium (K), % ≤0.001 Copper (Cu), % ≤0.001 Zinc (Cu), % ≤0.001 Manganese (Mn), % ≤0.001 Aluminum (Al), % 0.006 Sulfur (S), % 0.005 Moisture, % 0.12 Tap density, (g / cm 3 )]]> 0.72 Magnetic foreign matter, % 0.00023 Particle size (D 50 ), μm]]> 4.87 Specific surface area, m 2 / g]] 5.2 Product appearance Yellowish white powder, no caking, no agglomerates, no foreign matter

[0105] Table 8 is the element content in the battery grade lithium carbonate product

[0106] Analysis item Result Li2CO3 content, (%) 99.69 Na, (%) 0.008 Mg, (%) 0.001 Ca, (%) 0.001 K，(％) 0.0005 Fe, (%) 0.0007 Zn, (%) 0.0001 Cu, (%) 0.0002 Pb, (%) 0.0001 Si, (%) 0.001 Al，(％) 0.001 Mn, (%) 0.0002 Ni, (%) 0.0008 SO4 2- , (%)]] 0.008 Cl - , (%)]] 0.001

[0107] The above only describes the preferred embodiments of the present application. It should be noted that for those skilled in the art, various changes, modifications, replacements and variations can be made to the embodiments without departing from the technical principles of the present application. These changes, modifications, replacements and variations should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing battery grade iron phosphate and lithium carbonate from spent cathode material, the method comprising: Comprise the following steps: ​ (1) acid dipping: the waste lithium iron phosphate positive material is crushed to obtain lithium iron phosphate positive powder; sulfuric acid solution is added to the lithium iron phosphate positive powder for acid dipping, and after acid dipping is completed, pressure filtration is carried out to obtain an acid dipping liquid and graphite residue; (2) copper extraction: the acid dipping liquid obtained in step (1) is subjected to copper extraction by ZJ980 copper extractant to obtain a copper-removed liquid and a high-purity copper sulfate solution, and the high-purity copper sulfate solution is used for producing cathode copper; (3) ammonium sulfate aluminum removal: ammonium sulfate is added to the copper-removed liquid obtained in step (2) to remove aluminum to obtain an aluminum-removed liquid and aluminum-removed residue; (4) adjusting iron-phosphorus ratio, oxidation, and synthesizing iron phosphate: ammonium dihydrogen phosphate is added to the aluminum-removed liquid to adjust the iron-phosphorus molar ratio of the solution to 1:1-1.05, then hydrogen peroxide is added for oxidation, and an ammonia water solution is added to synthesize iron phosphate precipitate by controlling the pH of the solution, and after the reaction is completed, an iron phosphate slurry is obtained; (5) aging, phosphoric acid washing, and pure water washing: the iron phosphate slurry obtained in step (4) is subjected to high-temperature aging, the aged slurry is subjected to pressure filtration to obtain an aged liquid and aged iron phosphate residue, and the aged iron phosphate residue is subjected to phosphoric acid washing and multiple pure water washing to obtain washed iron phosphate after pressure filtration; (6) iron phosphate drying and calcination to prepare battery-grade iron phosphate: the iron phosphate obtained in step (5) is dried and calcined to obtain battery-grade iron phosphate products; (7) lime impurity removal and ammonia removal: lime milk is added to the aged liquid obtained in step (5) to remove iron, phosphorus, and silicon impurities in the solution, and to remove ammonium ions in the solution to avoid a large amount of sodium carbonate being consumed due to the reaction between ammonium ions and sodium carbonate during the lithium precipitation process; (8) evaporation concentration to extract lithium, sodium carbonate lithium precipitation, and washing: the impurity-removed liquid obtained in step (7) is subjected to evaporation concentration to deeply remove ammonia and calcium, and a lithium-rich liquid with a lithium concentration of 15-20 g / L is obtained; sodium carbonate solution is added to the lithium-rich liquid to synthesize crude lithium carbonate, and the crude lithium carbonate is washed with pure water; (9) carbonization, resin calcium and magnesium removal, pyrolysis, and drying: the crude lithium carbonate obtained in step (8) is slurried by adding water at a certain liquid-solid ratio, then carbon dioxide is introduced for carbonization, pressure filtration is performed to obtain a carbonized liquid and calcium carbonate residue; the carbonized liquid is subjected to deep removal of calcium and magnesium in the solution by calcium and magnesium removal resin; the calcium and magnesium-removed liquid is subjected to high-temperature pyrolysis and drying to obtain battery-grade lithium carbonate.

2. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material according to claim 1, characterized in that: In step (1), the concentration of the sulfuric acid solution is 2-5 mol / L, the liquid-solid ratio is 3-6 mL / g, the acid dipping temperature is 25°C, and the acid dipping time is 2-6 h.

3. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material according to claim 1, wherein: In step (3), the concentration of ammonium sulfate is 10-15%, the reaction temperature is 30-60°C, the reaction pH is controlled to be 0.5-1.0, and the reaction time is 0.5-1 h.

4. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material according to claim 1, wherein: In step (4), the amount of hydrogen peroxide is 1.5-3 times the theoretical amount based on the iron molar amount, the oxidation time is 1-3 h; the concentration of the ammonia water solution is 5-15%, the pH for synthesizing iron phosphate is controlled to be 1-3, the reaction time is 1-4 h, and the reaction temperature is 25°C.

5. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material as claimed in claim 1 wherein: The aging temperature of the iron phosphate slurry in step (5) is 60-100°C, and the aging time is 8-16 h; after aging, the iron phosphate residue is slurried with pure water at a liquid-solid ratio of 5-10 mL / g, the temperature of the phosphoric acid washing is 50-80°C, and the washing time is 1-3 h; the iron phosphate residue after phosphoric acid washing is slurried with pure water at a liquid-solid ratio of 5-10 mL / g, the number of pure water washing is 2-5 times, the temperature of each pure water washing is 50-80°C, and the time of each pure water washing is 1-4 h.

6. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material according to claim 1, wherein: The drying temperature of the iron phosphate in step (6) is 70-100°C, and the drying time is 8-16 h; the calcination temperature of the iron phosphate is 500-700°C, and the calcination time is 1-4 h.

7. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material as claimed in claim 1 wherein: The lime milk concentration in step (7) is 20-30%, the impurity removal and deamination pH is 10-14, the impurity removal and deamination temperature is 70-100°C, the impurity removal and deamination time is 1-4 h, the ammonia gas after deamination is absorbed by an absorption tower, and the absorbed ammonia water is recycled to the iron phosphate synthesis process.

8. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material as claimed in claim 1 wherein: The evaporation concentration temperature of the impurity-removed liquid in step (8) is 70-100°C; the amount of sodium carbonate added is 1-2 times the theoretical amount based on the molar amount of lithium, the concentration of the sodium carbonate solution is 200-400 g / L, the lithium precipitation temperature is 70-100°C, and the lithium precipitation time is 1-4 h; the washing number of the crude lithium carbonate is 2-5 times, and the washing temperature is 70-100°C.

9. The method of preparing battery grade iron phosphate and lithium carbonate from spent cathode material as claimed in claim 1 wherein: The crude lithium carbonate in step (9) is slurried with pure water at a liquid-solid ratio of 15-30 mL / g and then carbonized; the pyrolysis temperature of the calcium and magnesium-removed liquid is 70-100°C, and the pyrolysis time is 1-4 h; the lithium carbonate drying temperature is 70-100°C, and the drying time is 1-4 h.

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