A method for recycling battery-grade iron phosphate and lithium carbonate from waste lithium iron phosphate battery materials

Abstract

The application discloses a method for recycling battery-grade iron phosphate and lithium carbonate by using waste lithium iron phosphate battery materials. The method comprises the following steps: ①electrified crushing and disassembling the waste lithium iron phosphate battery materials, slurry, concentrated sulfuric acid leaching, pressure filtration, and obtaining an acid leaching solution; ②removing copper, aluminum and fluorine in the acid leaching solution in sequence; ③adjusting the iron-phosphorus ratio and pH value of the solution to precipitate iron phosphate, then aging the iron phosphate, two-stage pressure filtration and washing, drying and roasting to obtain battery-grade iron phosphate; ④removing iron from the solution after precipitating iron phosphate, pressure filtration, evaporation crystallization, adding sodium carbonate to precipitate lithium, and obtaining crude lithium carbonate, which is washed, slurried, carbonized, pressure filtered to prepare lithium bicarbonate filtrate, and then the lithium bicarbonate filtrate is refined, the resin is used to remove calcium and magnesium, thermal decomposition, centrifugal washing separation and drying to obtain battery-grade lithium carbonate. The application has high recovery rate of valuable elements, good impurity removal effect, can obtain battery-grade iron phosphate and lithium carbonate, and has high-efficiency and environmental protection process design, and is suitable for industrial application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery recycling, and particularly relates to a method for recycling battery-grade iron phosphate and lithium carbonate from waste lithium iron phosphate battery materials. BACKGROUND

[0002] New energy vehicles, as one of the emerging industries in China, have developed rapidly in recent years, and the consumption of lithium ion battery industry has also ushered in rapid development. Among them, lithium iron phosphate has become a better choice for lithium ion battery positive materials in the early stage of new energy vehicle development due to its high safety performance, long cycle life, low price and other advantages. Moreover, since the emergence of lithium iron phosphate blade battery on the market, the energy density of lithium iron phosphate battery pack has been improved, reducing the gap with the energy density of ternary material battery pack. Therefore, at present, lithium iron phosphate battery still accounts for a considerable proportion in power batteries. The service life of power batteries is generally 5-8 years, and lithium iron phosphate battery, as an important component of power batteries, will soon enter a large-scale scrap stage. Therefore, carrying out related research on waste lithium iron phosphate battery recycling and realizing the recycling of valuable elements such as iron, phosphorus and lithium in the positive material is an important support for the sustainable development of new energy vehicle industry.

[0003] In the recycling technology of waste lithium iron phosphate battery, the current research direction mainly includes fire recovery, solid phase repair and wet recovery. Among them, the fire recovery has high energy consumption and large equipment investment, and the process from multi-alloy fire smelting products to battery-grade raw materials is relatively long, and the recovery economy is not high; the solid phase repair method is currently in the laboratory research stage, and there is still a certain distance from industrialization. At present, the recycling of waste lithium iron phosphate battery materials mainly adopts wet process. First, the salt water discharge-mechanical crushing / charged crushing, physical separation and other operations are carried out to efficiently separate the components (shell material, separator, copper foil, aluminum foil, electrode material) of waste lithium iron phosphate battery. The obtained electrode material is leached into solution by using inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid or organic acids such as ascorbic acid, citric acid, oxalic acid, formic acid and acetic acid. Then, lithium salt products such as lithium carbonate are obtained by methods such as impurity removal, neutralization and precipitation, and iron and phosphorus are recycled to prepare iron phosphate or lithium iron phosphate.

[0004] The current waste lithium iron phosphate battery wet recovery technology mainly has the following difficulties in the actual production process: 1) the salt water discharge-mechanical crushing disassembly method exists problems such as organic gas and a large amount of fluorine-containing high-salt wastewater disposal; 2) usually 1%-3% of copper and aluminum are contained in the electrode material obtained by disassembly, and in the leaching process, copper and aluminum enter the subsequent solution in the form of impurities, resulting in great pressure for subsequent impurity removal, and the impurity removal effect will affect the quality of the lithium carbonate, iron phosphate or lithium iron phosphate obtained; 3) it is difficult to achieve high valuable metal recovery rate; 4) the whole wet recovery process needs to consider the solution in the production process and wastewater treatment. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a method for recycling battery-grade iron phosphate and lithium carbonate from waste lithium iron phosphate battery materials. The present application uses waste lithium iron phosphate battery materials obtained by electrically crushing and disassembling as raw materials, adopts a wet recovery process, and efficiently recycles iron, phosphorus and lithium elements in the battery to produce battery-grade iron phosphate and lithium carbonate, realizing the recycling of resources.

[0006] To achieve the above purpose, the present application provides the following technical solutions:

[0007] The method for recycling battery-grade iron phosphate and lithium carbonate from waste lithium iron phosphate battery materials provided by the present application comprises the following steps:

[0008] 1) acid leaching: the waste lithium iron phosphate battery is electrically disassembled and crushed to obtain lithium iron phosphate powder; then the powder is slurried, concentrated sulfuric acid is added for leaching, and after leaching is completed, pressure filtration is performed to obtain an acid leaching solution and carbon residue;

[0009] 2) impurity removal of the acid leaching solution: iron filings are added to the acid leaching solution obtained in step 1) for copper removal, and after copper removal is completed, pressure filtration is performed to obtain a copper-removed solution and copper residue; sodium fluoride is added to the copper-removed solution for aluminum removal, and after aluminum removal is completed, pressure filtration is performed to obtain an aluminum-removed solution and aluminum residue; a defluorination agent is added to the aluminum-removed solution for defluorination, and after defluorination is completed, pressure filtration is performed to obtain a de-impurity acid leaching solution and defluorination residue;

[0010] 3) phosphorus iron precipitation: the de-impurity acid leaching solution obtained in step 2) is diluted with water, then sodium phosphate dibasic is added to adjust the iron-phosphorus ratio in the solution, and then liquid alkali and hydrogen peroxide are added for reaction, and after the reaction is completed, pressure filtration is performed to obtain a phosphorus iron precipitation solution and phosphorus iron residue;

[0011] The iron phosphate slag is subjected to preset number of slurry, washing, filter pressing to obtain washed iron phosphate; the washed iron phosphate is slurryed by adding pure water, then acid is added to adjust pH, and aging reaction is carried out by heating, and after the reaction is completed, filter pressing is carried out to obtain iron phosphate aging slag; the iron phosphate aging slag is subjected to preset number of slurry, washing, filter pressing, then flash drying, calcination to remove crystal water, and after cooling, the battery-grade iron phosphate is obtained.

[0012] 4) Lithium precipitation: sodium carbonate is added to the phosphorus precipitated iron solution obtained in step 3) to adjust the pH value of the solution to a set range, iron is removed, then filter pressing is carried out to obtain a filtrate, MVR salt evaporation is used on the filtrate to concentrate to obtain mirabilite and sodium sulfate evaporation crystallization mother liquor; the lithium content in the sodium sulfate evaporation crystallization mother liquor is controlled, then sodium carbonate is added to the evaporation crystallization mother liquor to precipitate lithium, and after the lithium precipitation is completed, filter pressing is carried out to obtain lithium carbonate crude product and lithium precipitation solution;

[0013] The lithium carbonate crude product is slurryed, then carbon dioxide is introduced to carry out carbonization reaction, and after the reaction is completed, filter pressing is carried out to obtain carbonization residue and carbonization filtrate; then the carbonization filtrate is first refined, then calcium and magnesium are removed in a resin tower to obtain lithium bicarbonate solution; the lithium bicarbonate solution is decomposed in a pyrolyzer, the slurry after decomposition is separated by centrifugal washing, and dried to obtain the battery-grade lithium carbonate.

[0014] Preferably, in step 1), the ultrafine powder is slurryed, and the liquid-solid ratio is controlled to be (3-5) mL:1 g; when concentrated sulfuric acid is added for leaching, steam is directly heated, the leaching temperature is controlled to be 90-95 ℃, the leaching time is 3-5 h, and after the leaching is completed, the pH of the slurry is less than 1.

[0015] In some specific embodiments, step 1) further comprises: the carbon residue is subjected to two times of slurry washing, the liquid-solid ratio of washing is (3-5) mL:1 g, and after washing, the carbon residue is outsourced for disposal, and the washing water is returned to step 1) for acid leaching of the lithium iron phosphate ultrafine powder slurry.

[0016] Preferably, in step 2), the amount of iron filings is 1.2-1.5 times the theoretical amount of iron powder used for copper removal (Fe+CuSO4=FeSO4+Cu); the process conditions for copper removal include: using steam to directly heat to control the reaction temperature at 75-80°C, the initial pH of the reaction is less than 1, the reaction time is 1-3h, and the final pH of the reaction is 1-1.5; the process conditions for aluminum removal include: maintaining the temperature of the solution after copper removal at 85-90°C by steam reheat, adjusting the pH of the solution to 1.3-1.6 by adding sodium carbonate, the amount of sodium fluoride is 1-1.2 times the theoretical amount of sodium fluoride used for aluminum removal (Al2(SO4)3+12NaF=2Na3AlF6+3Na2SO4), the reaction time is 2-3h, and the final pH of the reaction is controlled at 1.5-2; the process conditions for fluorine removal include: the fluorine removal agent is a rare earth type adsorbent, preferably a silica gel adsorbent coated with lanthanum oxide film, the reaction temperature is controlled at 75-80°C, the reaction time is 2-3h, and the final pH of the reaction is 2-3. In some specific embodiments, step 2) further includes: slurry washing the copper residue, the liquid-solid ratio of the washing is (3-5)mL:1g, the copper residue after washing is disposed of by a third party, and the washing water is returned to step 1) for lithium ferric phosphate powder acid leaching slurry.

[0017] In some specific embodiments, step 2) further includes: slurrying the aluminum residue at a liquid-solid ratio of (3-5)mL:1g, then adding lime to adjust the pH of the slurry to 5-6, controlling the reaction temperature at 80-90°C, the reaction time is 3-4h, after the reaction is completed, the slurry is pressure filtered to obtain the lithium leaching solution after aluminum residue and the lithium leached aluminum residue, the lithium leaching solution after aluminum residue is returned to step 1) for lithium ferric phosphate powder acid leaching slurry, and the lithium leached aluminum residue is disposed of by a third party.

[0018] In some specific embodiments, step 2) further includes: disposing of the fluorine-removed residue by a third party.

[0019] Preferably, step 3) further includes: diluting the acid leaching solution after impurity removal with water to make the iron content in the solution 0.6-1.1mol / L, then adding sodium dihydrogen phosphate to adjust the molar ratio of iron to phosphorus in the solution to (1.0-1.1):1, adding liquid alkali and hydrogen peroxide, the amount of hydrogen peroxide is 1.1-1.3 times the theoretical amount of hydrogen peroxide used to oxidize divalent iron to trivalent iron, the reaction temperature is controlled at 90-95°C by steam heating, the reaction time is 3-4h, the final pH of the reaction is 1-3, and after the reaction is completed, pressure filtration is performed to obtain the phosphorus precipitation iron solution and the phosphorus acid iron residue;

[0020] The phosphoric iron slag is slurryed, washed and pressure-filtered at least twice according to a liquid-solid ratio (3-5) mL:1 g to obtain washed phosphoric iron; the washed phosphoric iron is slurryed with pure water, and phosphoric acid is added to adjust the slurry pH to <1; the aging reaction temperature is controlled at 90-95 ℃ by steam heating, and the reaction time is 2-3 h; after the aging is completed, the phosphoric iron aging slag is obtained by pressure filtration; the phosphoric iron aging slag is slurryed, washed and pressure-filtered at least three times according to a liquid-solid ratio (3-5) mL:1 g, and then dried by flash evaporation, and then calcined in a rotary kiln to remove crystal water, wherein the high-temperature zone temperature in the furnace is ≥800 ℃, the residence time in the furnace is ≥2.5 h, and the residence time in the high-temperature zone (≥800 ℃) is ≥2 h; after cooling, the battery-grade phosphoric iron is obtained. The washing mode of the phosphoric iron slag and the phosphoric iron aging slag is countercurrent washing.

[0021] Preferably, in step 4), the pH value is 3.5-4.5; the filtrate is mainly a lithium-containing sodium sulfate solution; the lithium content in the sodium sulfate evaporation crystallization mother liquor is controlled to be 25-30 g / L; the process conditions for lithium precipitation include: the reaction temperature is controlled at 80-85 ℃ by steam heating, the reaction time is 3-4 h, and the reaction end point pH is 5-6;

[0022] The process conditions of the carbonation reaction include: the reaction temperature is controlled at 25-40 ℃, the reaction time is 1-3 h, and the lithium content in the solution is 20-25 g / L; the process conditions for the decomposition of the lithium bicarbonate solution in the pyrolyzer include: the decomposition temperature is 90-100 ℃, and the operating pressure is 0.04-0.06 MPaG.

[0023] In some specific embodiments, step 4) further includes: the lithium precipitation solution is sent to an MVR salt concentration process; and the carbonation residue is returned to step 1) for lithium phosphate acid leaching.

[0024] Specifically, in step 1), the main reaction equation involved is: LiFePO4+H2SO4=LiH2PO4+FeSO4; in step 2), the main reaction equation involved is: Fe+CuSO4=FeSO4+Cu, Na2CO3+H2SO4=Na2SO4+H2O+CO2, Al2(SO4)3+12NaF=2Na3AlF6+3Na2SO4; in step 3), the main reaction equation involved is: 2FeSO4+2LiH2PO4+H2O2+2NaOH=2FePO4·2H2O+Na2SO4+Li2SO4; in step 4), the main reaction equation involved is: Li2SO4+Na2CO3=Li2CO3+Na2SO4, Li2CO3+CO2+H2O=2LiHCO3, 2LiHCO3=Li2CO3+CO2+H2O.

[0025] The valuable components in waste old lithium iron phosphate are efficiently leached by sulfuric acid, and the acid leaching solution is subjected to impurity removal treatment, wherein iron powder is used to remove copper without introducing other impurity ions; fluoride complexing is used to remove aluminum, which can deeply remove aluminum ions in the acid leaching solution; then, adsorption type fluoride removal agent is used to remove fluorine, which can remove fluorine ions in the solution without introducing new impurities. The aluminum removal residue in the aluminum removal process is washed with lime water, which can reduce the valuable metal lithium taken away by the aluminum removal residue as much as possible, and the lithium leaching solution of the aluminum residue is returned to the acid leaching process, which can improve the lithium recovery rate of the whole process. The aging operation of the phosphoric iron can reduce the content of impurities wrapped in the phosphoric iron precipitate, and make the particle size distribution of the phosphoric iron uniform; the carbonization and decomposition operation of the precipitated primary lithium carbonate can improve the quality of the lithium carbonate, which is helpful to obtain battery-grade phosphoric iron and lithium carbonate. The solution in the whole process is subjected to MVR concentration treatment, and almost no waste water is discharged.

[0026] The principle of the present application is as follows: the cathode powder obtained by charged crushing and disassembling of waste old lithium iron phosphate battery is used as raw material, the raw material is subjected to leaching by concentrated sulfuric acid and filtration, the solution is subjected to copper removal, aluminum removal and fluorine removal, the iron-phosphorus ratio and pH value are adjusted to precipitate phosphoric iron, the phosphoric iron is subjected to aging, several stages of pressure filtration washing, drying and roasting to obtain battery-grade anhydrous phosphoric iron product; the solution after phosphoric iron precipitation is subjected to iron removal and pressure filtration, evaporation and crystallization to obtain evaporation and crystallization mother liquor, lithium is precipitated by sodium carbonate to obtain crude lithium carbonate. The crude lithium carbonate is subjected to washing, slurry, carbonization, pressure filtration to prepare lithium bicarbonate filter liquor, and then the lithium bicarbonate filter liquor is subjected to precision filtration, resin calcium and magnesium removal, thermal decomposition, centrifugal washing separation and drying to obtain battery-grade lithium carbonate.

[0027] Advantages of the present application

[0028] 1. The present application uses the charged crushing and disassembling waste old lithium iron phosphate battery material as raw material, which avoids the treatment problem of high-salt wastewater containing fluorine and organic matter generated in the salt water discharge process.

[0029] 2. Part of the lithium will enter the aluminum residue in the aluminum removal process with fluorinating agent, which will cause the lithium recovery rate to decrease if not recovered. The present application increases an aluminum residue washing process, so that the lithium recovery rate is high; in addition, a little excess fluorinating agent is generally used in the aluminum removal process, and the fluorine ions in the solution after aluminum removal will affect the performance of the phosphoric iron and lithium carbonate products if not treated. The present application increases the fluorine removal process after aluminum removal. In addition, the present application adds an aging process in the phosphoric iron precipitation step, which is helpful to improve the quality of the phosphoric iron and obtain battery-grade phosphoric iron.

[0030] 3. The impurity removal process of the acid leaching solution in the present application has good effect, and finally battery-grade phosphoric iron and lithium carbonate products can be obtained.

[0031] 4. The valuable element recovery rate of the present application is high, and the comprehensive recovery rate of lithium is greater than 90% and the comprehensive recovery rate of iron is greater than 92% based on the valuable metals in the cathode powder of the waste old lithium iron phosphate battery.

[0032] 5、The process of the present application is reasonable in design, and almost no wastewater needs to be treated in the whole process. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The present application is a process flow diagram. DETAILED DESCRIPTION

[0034] The present application will be further described in detail below in combination with specific examples. The following examples are used to illustrate the present application, but not to limit the scope of the present application.

[0035] The following is an example of an annual treatment of 7500 tons (22.73 tons / d) of lithium iron phosphate battery material engineering.

[0036] Example 1

[0037] The broken lithium iron phosphate battery material is used as raw material, and the main element content is as follows: Li 2.55%, Fe 18.80%, Al 1.2%, PO4 31.56%, C 37.24%, Cu 1.5%, F 0.39%.

[0038] 1) Acid leaching

[0039] The lithium iron phosphate battery material (22.73 tons / d) is slurried with a liquid-solid ratio of 4:1, 98% concentrated sulfuric acid (10.04 tons / d) is added, the acid leaching temperature is controlled at 95°C by steam heating, and the reaction is carried out for 4 hours. After the leaching is completed, the acid leaching liquid (104.75 m 3 / d) and carbon residue are obtained by pressure filtration.

[0040] The main element content in the acid leaching liquid is detected by sampling, which is as follows: Li 5.42 g / L, Fe 40.18 g / L, PO4 67.46 g / L, Cu 2.28 g / L, Al 2.60 g / L, F 0.85 g / L, and the solution pH is about 0.8. The leaching rates of lithium, iron, phosphorus are 98.0%, 98.5%, 98.5% respectively.

[0041] 2) Impurity removal from acid leaching liquid

[0042] Iron filings (0.25 tons / d) are added to the acid leaching liquid, the reaction temperature is controlled at 80°C by steam heating, and the reaction time is 2 hours. After the copper removal reaction is completed, the copper-removed liquid and copper residue (0.24 tons / d) are obtained by pressure filtration. The copper content in the copper-removed liquid is 5 mg / L. The copper residue is washed after slurry, the washing liquid-solid ratio is 3:1, and the copper residue is disposed after washing. The washing water is returned to the step 1) lithium iron phosphate acid leaching slurry.

[0043] The temperature of the copper-removed solution is maintained at 90°C by steam reheat, sodium carbonate (0.57 t / d) is added, the pH of the solution is adjusted to about 1.3, sodium fluoride (2.67 t / d) is further added to remove aluminum, the reaction time is 3 h, and the aluminum-removed solution and aluminum residue (1.82 t / d) are obtained by pressure filtration after the aluminum removal reaction is completed, and the aluminum content in the aluminum-removed solution is 8 mg / L. About 10% of lithium in the solution is transferred into the aluminum residue in the aluminum removal process.

[0044] The aluminum residue is slurried at a liquid-solid ratio of 3:1, lime (0.19 t / d) is added, the reaction temperature is adjusted to 85°C, the reaction time is 4 h, the pH at the reaction endpoint is about 6.0, and the lithium-impregnated aluminum residue solution (5.46 m 3 / d) is obtained by pressure filtration after the reaction is completed. The lithium-impregnated aluminum residue solution contains 9.36 g / L of lithium, and is returned to the lithium phosphate acid leaching process. The lithium-impregnated aluminum residue is outsourced for disposal. The lithium leaching rate in the lithium-impregnated aluminum residue process is 90%.

[0045] The silicon gel adsorbent (1.72 t / d) coated with lanthanum oxide film is added to the aluminum-removed solution to perform a defluorination reaction, the reaction temperature is controlled at 80°C, the reaction time is 3 h, the pH at the reaction endpoint is about 2.0, and the defluorination is completed. The defluorination residue (1.78 t / d) is obtained by pressure filtration after the defluorination is completed, and the defluorination residue is outsourced for disposal.

[0046] The main element contents in the impurity-removed acid leaching solution are as follows: Li 4.88 g / L, Fe 42.55 g / L, PO4 67.46 g / L, Cu 5 mg / L, Al 8 mg / L, and F 6 mg / L.

[0047] 3) Phosphorus acid iron precipitation from the impurity-removed acid leaching solution

[0048] The impurity-removed acid leaching solution (104.75 m 3 / d) contains 42.55 g / L (0.76 mol / L) of iron and 67.46 g / L (0.71 mol / L) of PO4, and the iron to phosphorus ratio is 1.07. 32% liquid caustic (9.30 t / d) and 27.5% hydrogen peroxide (5.52 t / d) are added, the reaction temperature is controlled at 95°C by steam heating, the reaction time is 4 h, the pH at the reaction endpoint is about 3.0, and the phosphorus acid iron-precipitated solution (107.68 m 3 / d) and phosphorus acid iron residue (13.90 t / d) are obtained by pressure filtration after the reaction is completed. The main element contents in the phosphorus acid iron-precipitated solution are as follows: Li 4.75 g / L, Fe 2.32 g / L, PO4 6 mg / L, Cu 5 mg / L, Al 8 mg / L, and F 6 mg / L.

[0049] The phosphorus acid iron residue (13.90 t / d) is slurried, washed, and pressure-filtered twice at a liquid-solid ratio of 3:1, and then pure water (41.7 m 3(d) The washed iron phosphate residue slurry was slurried, 85% phosphoric acid (1.2 t / d) was added to adjust the pH of the reaction to <1, the aging reaction temperature was controlled at 95°C by steam heating, and the reaction time was 3 h. After the aging reaction was completed, the iron phosphate aging residue (13.90 t / d) was obtained by pressure filtration. The iron phosphate aging residue was slurried, washed, and pressure filtered three times according to a liquid-solid ratio of 3:1, and then was placed in a rotary kiln after being dried by flash evaporation to remove the crystal water. The maximum temperature in the furnace was 820°C, the residence time in the furnace was 3.5 h, and the residence time in the high-temperature zone (≥800°C) was 2.5 h. After cooling, the battery-grade iron phosphate (11.22 t / d) was obtained.

[0050] 4) Lithium precipitation

[0051] Sodium carbonate (0.78 t / d) was added to the lithium precipitation solution (107.68 m 3 / d) to adjust the pH to 3.7 for iron removal. After the reaction was completed, pressure filtration was performed, and the filtrate (107.68 m 3 / d) was a main lithium-containing sodium sulfate solution. Sampling detection showed that the lithium content in the solution was 4.75 g / L, and the sodium content was 22.01 g / L. The filtrate was concentrated by MVR salt evaporation to obtain sodium sulfate evaporation crystallization mother liquor (18.27 m 3 / d). The lithium content in the sodium sulfate evaporation crystallization mother liquor was controlled at 28 g / L, and sodium carbonate (3.87 t / d) was added to the evaporation crystallization mother liquor for lithium precipitation. The reaction temperature was controlled at 80°C by steam heating, and the reaction time was 4 h. After the lithium precipitation reaction was completed, the lithium carbonate crude product (2.54 t / d) and the lithium precipitation solution were obtained by pressure filtration. The lithium content in the lithium precipitation solution was about 1.7 g / L, and it was sent to the MVR salt evaporation concentration process.

[0052] The lithium carbonate crude product was slurried according to a liquid-solid ratio of 8:1, and carbon dioxide was introduced to complete the carbonation reaction. The reaction temperature was controlled at 30°C, and the reaction time was 2 h. At this time, the lithium content in the solution was about 21 g / L. After the carbonation reaction was completed, the carbonation residue and the filtrate were obtained by pressure filtration. The carbonation residue was returned to the acid leaching process of step 1), and the filtrate was sent to the precision filtration system for filtration. The filtrate was sent to the sodium-type ion exchange resin tower for calcium and magnesium removal to obtain lithium bicarbonate solution. The lithium bicarbonate solution was sent to a thermal decomposer for decomposition. The decomposition temperature was controlled at 95°C, the decomposition time was 1 h, and the operating pressure was 0.005 MPaG. The slurry after decomposition was separated by centrifugal washing to obtain lithium carbonate, which was dried to obtain battery-grade lithium carbonate.

[0053] The battery-grade iron phosphate product and the lithium carbonate product prepared in this embodiment were subjected to composition and performance detection, and the results are shown in Tables 1 and 2, respectively. The molar ratio of Fe to P in the iron phosphate was 0.990, and the tap density was 0.89.

[0054] Table 1 Fe, P element and impurity content in the iron phosphate product

[0055]

[0056] Table 2 Li2CO3 and impurity content in lithium carbonate product

[0057] Component Li2CO3 Al Ca Mg Na SO4 2- ]]> Content 99.89％ 5 ppm 10 ppm 35 ppm 100 ppm 76 ppm

[0058] In this embodiment, the iron leaching rate in the lithium iron phosphate acid leaching process is 98.5%, and part of the iron in the post-phosphorus iron precipitate solution is not completely precipitated, with a precipitation rate of 94.54%, so the iron recovery rate is 93.12%. The lithium leaching rate in the lithium iron phosphate acid leaching process is 98%, about 1% of lithium is lost in the aluminum removal process, and the precipitation rate in the lithium carbonate lithium precipitation process is about 94%, so the lithium recovery rate is 91.12%.

[0059] Example 2

[0060] The broken lithium iron phosphate battery material is used as raw material, and the main element content is as follows: Li 3.66%, Fe 28.97%, Al 1.50%, P 49.08%, C 20.37%, Cu 1.01%, F 0.39%.

[0061] 1) Acid leaching

[0062] The lithium iron phosphate battery material (22.73 t / d) is slurried at a liquid-solid ratio of 4:1, 98% concentrated sulfuric acid (19.50 t / d) is added, the acid leaching temperature is controlled at 90°C by steam heating, and the reaction is carried out for 5h. After the leaching is completed, the acid leaching solution (112.13 m 3 / d) and carbon residue are obtained by pressure filtration.

[0063] The main element content in the acid leaching solution is obtained by sampling and testing as follows: Li 7.31 g / L, Fe 58.02 g / L, P 98.30 g / L, Cu 1.43 g / L, Al 2.98 g / L, F 0.79 g / L, and the solution pH is about 0.85. The lithium, iron, phosphorus leaching rates in the acid leaching process are 98.5%, 98.8%, and 98.8%, respectively.

[0064] 2) Impurity removal from acid leaching solution

[0065] Iron filings (0.21 t / d) are added to the acid leaching solution, the reaction temperature is controlled at 75°C by steam heating, and the reaction time is 3h. After the copper removal reaction is completed, the copper-removed solution and copper residue (0.23 t / d) are obtained by pressure filtration, the copper content in the copper-removed solution is 7 mg / L, the copper residue is washed after slurry, the washing liquid-solid ratio is 3:1, the copper residue is disposed after washing, and the washing water is returned to the step 1) lithium phosphate acid leaching slurry.

[0066] The decoppered solution was then heated with steam to maintain a temperature of 85°C. Sodium carbonate (0.72 t / d) was added to adjust the solution pH to approximately 1.6. Sodium fluoride (3.27 t / d) was then added to remove aluminum. The reaction lasted for 3 hours. After the decoppering reaction was complete, filter presses were performed to obtain the decoppered solution and aluminum slag (2.03 t / d). The aluminum content in the decoppered solution was 9 mg / L. During the decoppering process, approximately 10% of the lithium in the solution was transferred to the aluminum slag.

[0067] The aluminum slag was slurried at a liquid-solid ratio of 4:1, lime (0.22t / d) was added, the reaction temperature was adjusted to 80°C, the reaction time was 3h, the pH at the reaction end point was about 6.0, and after the reaction was completed, the aluminum slag was filtered to obtain a lithium-soaked liquid (8.12m 3 The aluminum slag leaching solution contained 9.09 g / L of lithium, which was then returned to the lithium iron phosphate acid leaching process. The aluminum slag was then outsourced for disposal. The lithium leaching rate during the aluminum slag leaching process was 90%.

[0068] Silica gel adsorbent wrapped with lanthanum oxide film (2.12t / d) was added to the dealuminized liquid to carry out defluorination reaction. The reaction temperature was controlled at 75°C, the reaction time was 2h, and the pH at the reaction end point was about 2.2. After the defluorination was completed, the impurity-removed acid leaching liquid and defluorination slag (2.19t / d) were obtained by filtration, and the defluorination slag was disposed of externally.

[0069] After testing, the main element contents of the acid leaching solution after impurities removal are as follows: Li 6.58g / L, Fe 59.29g / L, PO498.30g / L, Cu7mg / L, Al 9mg / L, F 7mg / L.

[0070] 3) After impurities are removed, the acid leaching solution is used to precipitate iron phosphate

[0071] Acid leaching liquid after impurity removal (112.13m 3 / d) in which the iron content is 59.29 g / L (1.06 mol / L) and PO4 is 98.30 g / L (1.03 mol / L). At this time, the iron-phosphorus ratio is 1.03. Water is added to dilute the iron content to 180 m 3 / d, at which time the iron content was 0.66mol / L, 32% liquid alkali (14.11t / d) and 27.5% hydrogen peroxide (8.81t / d) were added, the reaction temperature was controlled at 90°C by steam heating, the reaction time was 3h, the pH at the reaction end point was about 2.5, after the reaction was completed, the precipitated iron phosphate solution (199.89m 3 / d) and iron phosphate slag (21.09t / d).

[0072] After testing, the main element contents of the liquid after precipitation of iron phosphate are as follows: Li 3.69g / L, Fe 1.66g / L, PO4 12mg / L, Cu 4mg / L, Al 5mg / L, F 4mg / L.

[0073] The iron phosphate slag (21.09 t / d) was slurried, washed, and pressure filtered twice at a liquid-solid ratio of 3:1, and then pure water (63.17 m 3 The washed iron phosphate slag was slurried, and 85% phosphoric acid (1.9 t / d) was added to adjust the pH to <1. The aging reaction temperature was controlled at 90°C by steam heating, and the reaction time was 2 h. After the aging reaction was completed, the iron phosphate aging slag (21.09 t / d) was obtained by pressure filtration. The iron phosphate aging slag was slurried, washed, and pressure filtered three times at a liquid-solid ratio of 3:1, and then was dried by flash evaporation and was placed in a rotary kiln to remove the crystal water by calcination. The maximum temperature in the furnace was 820°C, the residence time in the furnace was 3.5 h, and the residence time in the high-temperature zone (≥800°C) was 2.5 h. After cooling, the battery-grade iron phosphate (17.03 t / d) was obtained.

[0074] 4) Lithium precipitation

[0075] Sodium carbonate (1.55 t / d) was added to the solution (199.89 m 3 / d) after the precipitation of iron phosphate to adjust the pH to 3.8 for iron removal. After the reaction was completed, pressure filtration was performed. The filtrate (199.89 m 3 / d) was a main lithium-containing sodium sulfate solution. Sampling and testing showed that the lithium content in the solution was 3.69 g / L, and the sodium content was 18.36 g / L. The filtrate was concentrated by MVR salt evaporation to obtain sodium sulfate evaporation crystallization mother liquor (29.50 m 3 / d). The lithium content in the sodium sulfate evaporation crystallization mother liquor was controlled at 25 g / L, and sodium carbonate (5.58 t / d) was added to the evaporation crystallization mother liquor for lithium precipitation. The reaction temperature was controlled at 85°C by steam heating, and the reaction time was 3 h. After the lithium precipitation reaction was completed, pressure filtration was performed to obtain crude lithium carbonate product (3.69 t / d) and lithium precipitation solution. The lithium content in the lithium precipitation solution was about 1.35 g / L, and the lithium precipitation solution was sent to the MVR salt evaporation concentration process.

[0076] The crude lithium carbonate product was slurried at a liquid-solid ratio of 8:1, and carbon dioxide was introduced to complete the carbonation reaction. The reaction temperature was controlled at 30°C, and the reaction time was 2 h. At this time, the lithium content in the solution was about 21 g / L. After the carbonation reaction was completed, pressure filtration was performed to obtain carbonation slag and filtrate. The carbonation slag was returned to the acid leaching process of step 1), and the filtrate was sent to a precision filtration system for filtration. The filtrate was sent to a sodium-type ion exchange resin tower for calcium and magnesium removal to obtain lithium bicarbonate solution. The lithium bicarbonate solution was sent to a thermal decomposer for decomposition. The decomposition temperature was controlled at 95°C, the decomposition time was 1 h, and the operating pressure was 0.005 MPaG. The slurry after decomposition was separated by centrifugal washing to obtain lithium carbonate, which was dried to obtain battery-grade lithium carbonate.

[0077] The composition and performance of the battery grade iron phosphate product and lithium carbonate product prepared in this example were detected, and the results are shown in Table 3 and Table 4, respectively. The molar ratio of Fe and P in the iron phosphate is 0.980, and the tap density is 0.87.

[0078] Table 3 Fe, P element and impurity content in the iron phosphate product

[0079]

[0080] Table 4 Li2CO3 and impurity content in the lithium carbonate product

[0081] Component Li2CO3 Al Ca Mg Na SO4 2- <!-- 7 -->]]> Content 99.85％ 4 ppm 14 ppm 44 ppm 87 ppm 65 ppm

[0082] In this example, the iron leaching rate in the lithium acid leaching process of iron phosphate is 98.8%, and part of the iron in the post-phosphorus acid precipitation solution is not completely precipitated, with a precipitation rate of 95.51%, so the iron recovery rate is 94.36%. The lithium leaching rate in the lithium acid leaching process of iron phosphate is 98.5%, about 1% of lithium is lost in the aluminum removal process, and the precipitation rate in the lithium carbonate precipitation process is about 95%, so the lithium recovery rate is 92.6%.

Claims

1. A method for recovering battery-grade iron phosphate and lithium carbonate from waste lithium iron phosphate battery materials, comprising the following steps: 1) Acid leaching: dismantling and crushing the waste lithium iron phosphate battery to obtain lithium iron phosphate powder; then slurrying the powder, adding concentrated sulfuric acid to leach it, and filtering after leaching to obtain acid leaching solution and carbon residue; 2) removing impurities from the acid leaching liquid: adding iron filings to the acid leaching liquid obtained in step 1) to remove copper, and after the copper removal is completed, filtering to obtain a copper-removed liquid and copper slag; adding sodium fluoride to the copper-removed liquid to remove aluminum, and after the aluminum removal is completed, filtering to obtain an aluminum-removed liquid and aluminum slag; adding a defluorinating agent to the aluminum-removed liquid to remove fluorine, and after the defluorination is completed, filtering to obtain a post-impurity-removed acid leaching liquid and a defluorinated slag; 3) precipitating ferric phosphate: diluting the impurity-removed acid leaching solution obtained in step 2) with water, then adding sodium dihydrogen phosphate to adjust the iron-phosphorus ratio in the solution, then adding liquid caustic soda and hydrogen peroxide to react, and after the reaction is completed, filtering to obtain a precipitated ferric phosphate solution and ferric phosphate slag; The ferric phosphate slag is slurried, washed, and filtered for a preset number of times to obtain washed ferric phosphate; pure water is added to slurry the washed ferric phosphate, acid is added to adjust the pH, heating is performed for aging reaction, and after the reaction is completed, filtering is performed to obtain aged ferric phosphate slag; the aged ferric phosphate slag is slurried, washed, and filtered for a preset number of times, and then flash dried, calcined to remove crystal water, and cooled to obtain the battery-grade ferric phosphate; 4) lithium precipitation: sodium carbonate is added to the ferric phosphate precipitation solution obtained in step 3) to adjust the pH value of the solution to a set range, remove iron, and then filter press to obtain a filtrate, and the filtrate is concentrated by MVR salt evaporation to obtain sodium sulfate and sodium sulfate evaporation crystallization mother liquor; the lithium content in the sodium sulfate evaporation crystallization mother liquor is controlled, and sodium carbonate is added to the evaporation crystallization mother liquor to precipitate lithium. After the lithium precipitation is completed, filter press to obtain a crude lithium carbonate product and a lithium precipitation solution; The crude lithium carbonate product is slurried, and then carbon dioxide is introduced to perform a carbonization reaction. After the reaction is completed, carbonized slag and a carbonized filtrate are obtained by filter pressing. The carbonized filtrate is then finely filtered, and then calcium and magnesium are removed in a resin tower to obtain a lithium bicarbonate solution. The lithium bicarbonate solution is decomposed in a pyrolyzer, and the slurry after decomposition is separated by centrifugal washing and drying to obtain the battery-grade lithium carbonate.

2. The method according to claim 1, characterized in that In the step 1), the pole powder is slurried and the liquid-solid ratio is controlled to be (3-5) mL:1 g; when concentrated sulfuric acid is added for leaching, steam is directly heated to control the leaching temperature to be 90-95° C. and the leaching time to be 3-5 h. After the leaching is completed, the pH of the slurry is <1.

3. The method according to claim 1, characterized in that The step 1) further comprises: performing two slurry washings on the carbon residue, with a liquid-solid ratio of (3-5) mL:1 g, outsourcing the carbon residue after washing, and returning the washing water to the step 1) for acid leaching of lithium iron phosphate powder for slurrying.

4. The method according to claim 1, wherein In step 2), the amount of iron filings is 1.2 to 1.5 times the theoretical amount of iron powder for copper removal; the process conditions for copper removal include: using steam direct heating to control the reaction temperature at 75 to 80° C., the initial pH of the reaction is less than 1, the reaction time is 1 to 3 hours, and the pH at the end of the reaction is 1 to 1.5; the process conditions for aluminum removal include: maintaining the temperature of the solution after copper removal at 85 to 90° C. by steam supplemental heating, adding sodium carbonate to adjust the pH of the solution to 1.3 to 1.6, adding sodium fluoride to remove aluminum, the amount of sodium fluoride used is 1 to 1.2 times the theoretical amount of sodium fluoride for aluminum removal, the reaction time is 2 to 3 hours, and the pH at the end of the reaction is controlled to be 1.5 to 2; the process conditions for fluorine removal include: using a rare earth type adsorbent as the defluorinating agent, including a silica gel adsorbent coated with a lanthanum oxide film, controlling the reaction temperature at 75 to 80° C., the reaction time is 2 to 3 hours, and the pH at the end of the reaction is 2 to 3.

5. The method according to claim 1, wherein The step 2) further comprises: The copper slag is slurried and washed with a liquid-to-solid ratio of (3-5) mL:1 g. The copper slag is outsourced for disposal and the washing water is returned to step 1) for acid leaching of lithium iron phosphate powder; The aluminum slag is slurried at a liquid-solid ratio of (3-5) mL:1 g, and then lime is added to adjust the pH of the slurry to 5-6. The reaction temperature is controlled at 80-90° C. and the reaction time is 3-4 hours. After the reaction is completed, the slurry is filter-pressed to obtain a lithium-soaked aluminum slag liquid and a lithium-soaked aluminum slag. The lithium-soaked aluminum slag liquid is returned to step 1) for acid leaching of lithium iron phosphate powder for slurrying, and the lithium-soaked aluminum slag is outsourced for disposal. The fluorine removal slag is disposed of by outsourcing.

6. The method according to claim 1, characterized in that Step 3) also includes: The acid leaching solution after impurity removal is diluted with water to adjust the iron content of the solution to 0.6-1.1 mol / L, and then sodium dihydrogen phosphate is added to adjust the molar ratio of iron to phosphorus in the solution to (1.0-1.1):1, and liquid caustic soda and hydrogen peroxide are added, with the amount of hydrogen peroxide being 1.1-1.3 times the theoretical amount of hydrogen peroxide required to oxidize divalent iron to trivalent iron; the reaction temperature is controlled at 90-95° C. by steam heating, the reaction time is 3-4 hours, and the pH value at the reaction end point is 1-3. After the reaction is completed, the precipitated ferric phosphate solution and ferric phosphate slag are obtained by pressure filtration. The iron phosphate slag is slurried, washed, and filtered at least twice at a liquid-solid ratio of (3-5) mL:1 g to obtain washed iron phosphate; pure water is added to slurry the washed iron phosphate, phosphoric acid is added to adjust the slurry pH to <1, the aging reaction temperature is controlled to 90-95°C by steam heating, the reaction time is 2-3 hours, after the aging is completed, the iron phosphate aged slag is filtered to obtain, the iron phosphate aged slag is slurried, washed, and filtered at least three times at a liquid-solid ratio of (3-5) mL:1 g, and then after flash drying, it is calcined in a rotary kiln to remove crystallization water, the temperature of the high temperature zone in the furnace is ≥800°C, the residence time in the furnace is ≥2.5 hours, the residence time in the high temperature zone (≥800°C) is ≥2 hours, and battery-grade iron phosphate is obtained after cooling; wherein, the washing method of the iron phosphate slag and the iron phosphate aged slag is countercurrent washing.

7. The method according to claim 1, characterized in that In step 4), the pH value is 3.5-4.5; the filtrate is mainly a sodium sulfate solution containing lithium; the lithium content in the sodium sulfate evaporation crystallization mother liquor is controlled to be 25-30 g / L; the process conditions for lithium precipitation include: controlling the reaction temperature to 80-85°C by steam heating, the reaction time to 3-4 hours, and the reaction endpoint pH to 5-6.

8. The method according to claim 1, characterized in that In step 4), the process conditions of the carbonization reaction include: the reaction temperature is controlled at 25-40°C, the reaction time is 1-3 hours, and the lithium content in the solution is 20-25 g / L; the process conditions for decomposing the lithium bicarbonate solution in the pyrolyzer include: the decomposition temperature is 90-100°C and the operating pressure is 0.04-0.06 MPaG.

9. The method according to claim 1, characterized in that Step 4) also includes: the liquid after lithium precipitation is sent to the MVR salt distillation concentration process; the carbonized slag is returned to the lithium iron phosphate acid leaching process in step 1).

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