Method for preparing battery-grade lithium carbonate by using waste lithium iron phosphate batteries

Abstract

The invention provides a method for preparing battery-grade lithium carbonate by using waste lithium iron phosphate batteries. The method comprises the following steps: step 1, discharging, disassembling and crushing the waste lithium iron phosphate batteries to obtain lithium iron phosphate battery powder; 2, adding a sulfuric acid solution and hydrogen peroxide into the lithium iron phosphate battery powder, and filtering after reaction to obtain a lithium-containing solution and ferrophosphorus slag; 3, calcium hydroxide and sodium hydroxide are sequentially added into the lithium-containing solution to remove impurities, then sodium carbonate is added, and a purified lithium solution is obtained through filtering; 4, adding an organic solvent into the purified lithium solution, fully stirring, and filtering to obtain a sodium sulfate crystal substance and an organic mixed solution; and 5, adding sodium carbonate into the organic mixed solution, fully reacting, filtering, and washing to obtain the battery-grade lithium carbonate.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of waste lithium-ion power batteries, and specifically relates to a method for preparing battery-grade lithium carbonate by utilizing waste lithium iron phosphate batteries. Background Art

[0002] The new energy industry is developing rapidly, and the use of lithium-ion power batteries is increasing year by year. Due to its low raw material cost, high safety, good thermal stability, and excellent electrochemical cycle performance, lithium iron phosphate (LiFePO4) batteries occupy a large market share in power batteries, and the demand in the fields of new energy, base station energy storage, etc. has exploded. The average service life of LiFePO4 batteries is 5 years. LiFePO4 batteries contain valuable metals such as lithium, copper, aluminum and iron. Large-scale recycling of them can effectively alleviate the pressure on domestic lithium resources, while avoiding certain harm to the ecological environment and human health caused by waste batteries.

[0003] At present, acid dissolution is one of the main methods for recovering valuable metal elements in waste lithium iron phosphate batteries. Usually, waste lithium iron phosphate battery powder is leached with sulfuric acid to obtain lithium-containing leaching solution, which is then removed by liquid alkali to obtain purified lithium solution. After the lithium concentration is concentrated, soda ash is added to precipitate to obtain crude lithium carbonate products, and finally further refined to obtain battery-grade or high-purity lithium carbonate products, such as CN117778752A. Since a large amount of sulfuric acid solution and alkaline solution are added throughout the process, the purified lithium solution often contains a large amount of SO4 2- and Na + After further enrichment, the concentration of Na2SO4 approaches saturation, which may lead to the risk of sodium sulfate precipitation. 2- and Na + It will be wrapped in lithium carbonate or adsorbed on the surface of lithium carbonate during lithium precipitation. Conventional water washing process is difficult to remove SO4 2- and Na + It meets the requirements of battery-grade lithium carbonate, but it consumes a lot of water and causes high lithium carbonate loss. Therefore, how to use a more economical and effective method to reduce SO4 2- and Na + content, optimize the lithium carbonate washing method to increase SO4 2- and Na + The removal rate is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] In order to solve one of the technical problems existing in the prior art, the present invention provides a method for preparing battery-grade lithium carbonate using waste lithium iron phosphate batteries. The method comprises the following steps: acid leaching and impurity removal of waste lithium iron phosphate battery powder, and then using a dissolution crystallization method to reduce SO4 in the purified lithium solution. 2- and Na +content, avoid the precipitation of sodium sulfate in the purified lithium solution during the concentration process, increase the concentration multiple of the purified lithium solution, increase the lithium concentration, increase the lithium carbonate conversion rate, and reduce the SO4 2- and Na + The content of SO4 in lithium carbonate is increased by washing at low temperature first and then at high temperature. 2- and Na + The removal rate is achieved, thereby preparing battery-grade lithium carbonate products.

[0005] In order to achieve the above application purpose, the technical solution adopted in this application is as follows: A method for preparing battery-grade lithium carbonate using waste lithium iron phosphate batteries comprises the following steps: Step 1: Discharging, disassembling and crushing the waste lithium iron phosphate batteries to obtain lithium iron phosphate battery powder; Step 2: extracting lithium from the lithium iron phosphate battery powder by acid leaching to obtain a lithium-containing solution and ferrophosphorus slag; Step 3: adding calcium hydroxide and sodium hydroxide to the above lithium-containing solution in sequence to remove impurities, then adding sodium carbonate, and filtering to obtain a purified lithium solution; Step 4: adding an organic solvent to the purified lithium solution, stirring thoroughly and filtering to obtain sodium sulfate crystals and an organic mixed solution; Step 5: Add sodium carbonate to the organic mixed solution, filter and wash after sufficient reaction to obtain the battery-grade lithium carbonate.

[0006] In a specific embodiment of the present invention, in step 4, the organic solvent is selected from one or more of ethanol, acetone, methanol, 2-propanol (isopropanol), acetonitrile, diethylamine, propylamine, butylamine, and ethylenediamine.

[0007] In a specific embodiment of the present invention, in step 5, the washing refers to washing with pure water at low temperature first and then at high temperature; wherein the temperature of the low temperature washing is 10-20°C and the time is 0.5-1.0 h, and the temperature of the high temperature washing is 90-100°C and the time is 0.5-1.0 h; during the two washing processes, the mass ratio of pure water to lithium carbonate is independently (10-20):1.

[0008] In a specific embodiment of the present invention, in step 2, the step of acid leaching lithium is: adding sulfuric acid solution to lithium iron phosphate battery powder to obtain a leachate, and then adding hydrogen peroxide, wherein the concentration of the sulfuric acid solution is 10-50wt%, the concentration of the hydrogen peroxide is 10-30wt%, and the molar amount of H2O2 in the hydrogen peroxide is Fe in the leachate. 2+ The content is 1-2 times the stoichiometric ratio.

[0009] In a specific embodiment of the present invention, in step 2, the pH value of the acid leaching lithium reaction is 2-3, and the reaction time is 3-6 h.

[0010] In a specific embodiment of the present invention, the steps of step 3 are: Add calcium hydroxide to the lithium-containing solution to adjust the pH of the solution to 6-9, and filter after the reaction to obtain a primary filtrate; Sodium hydroxide is added to the primary filtrate to adjust the pH of the solution to 10-11, and then sodium carbonate is added. After the reaction, the solution is filtered to obtain a purified lithium solution.

[0011] Preferably, the molar amount of carbonate ions in the sodium carbonate is 2+ Mg 2+ The total content is 2-5 times of the stoichiometric ratio, the reaction time after adding sodium carbonate is 1.0-2.0 h, the reaction temperature is 50-60°C, and the stirring speed during the reaction is 200-300 r / min.

[0012] In a specific embodiment of the present invention, in step 4, the volume of the organic solvent is 20-50% of the volume of the purified lithium liquid, and during the stirring process, the temperature of the reaction system is 15-25°C, the time is 1.0-2.0 h, and the stirring speed is 100-200 r / min.

[0013] In a specific embodiment of the present invention, the specific operation of step 5 is: Add pure water to the sodium sulfate crystals obtained in step 4, stir and wash, and then filter, combine the filtrate with the organic mixed solution obtained in step 4, and dry the filter residue to obtain high-purity sodium sulfate powder; The combined organic mixed liquid is passed through an evaporation and condensation device to recover the organic solvent, and then evaporated and concentrated to obtain a concentrated liquid; A sodium carbonate solution is added to the concentrated solution, and after sufficient reaction, the solution is filtered and washed to obtain the battery-grade lithium carbonate.

[0014] Preferably, the liquid-to-solid ratio of the pure water to the sodium sulfate crystals is (0.5-1.0) mL:1 g; and the stirring time for adding pure water to the sodium sulfate crystals is 0.5-1.0 h.

[0015] Preferably, after adding the sodium carbonate solution to the concentrated solution, the reaction temperature is 90-95°C, the sodium carbonate solution is a saturated solution at 90-95°C, the molar amount of carbonate ions in the sodium carbonate solution is 1.0-2.0 times the stoichiometric ratio of the lithium ion content in the concentrated solution, and the reaction time is 1-2 h.

[0016] Beneficial effects: (1) The present invention uses an organic solvent to reduce the solubility of sodium sulfate in the purified lithium solution. The sodium sulfate is removed in large quantities, which is beneficial to increase the concentration multiple of the purified lithium solution and the conversion rate of lithium carbonate, while effectively reducing the impurity Na in the lithium carbonate. + 、SO4 2- Content can reach the standard of battery-grade lithium carbonate; (2) The present invention adopts a low-temperature-first-high-temperature washing method when washing lithium carbonate. Low-temperature washing can increase the solubility of lithium carbonate, which is beneficial to increasing the dissolution of sodium sulfate impurities that have formed peritectic during lithium precipitation. Then, high-temperature washing reduces the solubility of lithium carbonate, reduces lithium carbonate loss, increases sodium sulfate elution efficiency, and reduces the amount of washing water used. (3) The process provided by the present invention realizes the efficient removal of sodium sulfate in the lithium-rich solution and the recycling of organic solvents and washing water, and has the advantages of low energy consumption, environmental protection, high efficiency and easy industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for preparing battery-grade lithium carbonate using waste lithium iron phosphate batteries provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] The method for preparing battery-grade lithium carbonate using waste lithium iron phosphate batteries provided in the present application specifically comprises the following steps: Step 1: Discharging, disassembling and crushing the waste lithium iron phosphate batteries to obtain lithium iron phosphate battery powder; Step 2: adding concentrated sulfuric acid and hydrogen peroxide to the lithium iron phosphate battery powder, filtering after the reaction to obtain a lithium-containing solution and ferrophosphorus slag; Step 3: adding calcium hydroxide and sodium hydroxide to the above lithium-containing solution in sequence to remove impurities, then adding sodium carbonate, and filtering to obtain a purified lithium solution; Step 4: adding an organic solvent to the purified lithium solution, stirring thoroughly and filtering to obtain sodium sulfate crystals and an organic mixed solution; Step 5: Add sodium carbonate to the organic mixed solution, filter and wash after sufficient reaction to obtain the battery-grade lithium carbonate.

[0020] Step 1: In the present application, the lithium iron phosphate battery powder can be obtained by using techniques known in the art, and is not limited to the techniques provided in the present application. In a specific embodiment of the present application, the step 1 includes: Discharge: Place the used lithium iron phosphate battery in saturated salt water and allow it to fully discharge for 20 to 40 minutes.

[0021] Disassembly: Place the discharged battery in an oven to dry, disassemble the battery shell to obtain the battery core, and then sort the positive and negative electrodes and diaphragms to obtain the lithium iron phosphate positive electrode sheet.

[0022] Crushing: The obtained lithium iron phosphate positive electrode sheet is crushed by crushing equipment, and the waste lithium iron phosphate battery powder is obtained by vibration screening. Furthermore, the mesh number of the screening treatment is greater than 80 mesh, such as 80 mesh, 100 mesh, 120 mesh, etc., which can screen out some impurities. Those skilled in the art can know that the crushing equipment is at least one of a jaw crusher, a cone crusher, a double-roll crusher, an impact crusher, a fine crusher, and a single-stage hammer crusher.

[0023] Step 2: In the present application, a lithium-containing solution and ferrophosphorus slag are obtained by an acid leaching method for lithium. The acid leaching method for lithium uses a sulfuric acid solution and hydrogen peroxide to selectively extract lithium elements, while avoiding the leaching of a large amount of aluminum and copper in the solid phase.

[0024] In the specific implementation of this application, the specific operation of step 2 is as follows: Add 20% sulfuric acid solution by mass to the lithium iron phosphate battery powder obtained in step 1 to adjust the pH value of the solution to 2-3 to obtain a leachate, and then add hydrogen peroxide. The molar amount of H2O2 in the hydrogen peroxide is 2+ The content is 1-2 times the stoichiometric ratio, and the reaction is carried out for 3-6 hours before filtration, wherein the mass percentage of hydrogen peroxide is 10-30%, the filtrate is heated to 50-60°C and stirred at a rate of 200-300 r / min, and after the reaction is completed, the solid-liquid separation is performed to obtain a lithium-containing solution and ferrophosphorus slag.

[0025] In the present application, waste lithium iron phosphate powder is oxidized, and ferrous ions are oxidized to trivalent ferrous ions to form ferrophosphorus precipitation, while lithium still exists in the solution, thereby separating lithium from ferrophosphorus to obtain a lithium-containing solution and ferrophosphorus slag. At the same time, the content of aluminum and copper elements in the ferrophosphorus slag can be reduced, which is beneficial to improving the purity of ferrophosphorus elements in the ferrophosphorus slag. The reaction in this step is as follows: (1) 2LiFePO4+H2O2+H2SO4→2FePO4↓+Li2SO4+2H2O; (2) 2Al+3H2SO4→Al2(SO4)3+3H2↑; (3) Cu+H2O2+H2SO4→CuSO4+2H2O.

[0026] Step 3: The lithium-containing solution obtained in step 2 contains not only lithium ions but also a large amount of impurity elements, such as aluminum, copper, phosphorus, iron, fluorine, nickel, manganese, etc. The purpose of step 3 is to remove the impurity ions. The present application achieves the purpose of simultaneous recycling of multi-component elements by adding different alkaline substances, adjusting the pH value of the solution, and removing impurities in steps.

[0027] In the specific implementation of this application, the specific operation of step 3 is as follows: (1) Calcium hydroxide is added to the lithium-containing solution to adjust the pH of the solution to 6-9, and the solution is reacted for 1.0-2.0 h and filtered to obtain a primary filtrate. In this way, impurities such as fluorine, phosphorus, aluminum, copper, and iron in the lithium-containing solution can be removed. Calcium hydroxide is selected in this step because, in addition to effectively removing fluorine and phosphorus from the lithium-containing solution, calcium hydroxide can also adjust the pH value required for the precipitation reaction, so that impurities such as aluminum, copper, and iron are formed into hydroxide precipitates and are removed.

[0028] (2) Sodium hydroxide is added to the above-mentioned primary filtrate to adjust the pH value of the solution to 10-11, and then sodium carbonate is added. The reaction is stirred at a constant temperature of 50-60°C for 1.0-2.0 h, and then filtered to obtain a purified lithium solution. The stirring speed during the reaction is 200-300 r / min. In this way, impurities such as calcium, magnesium, nickel, cobalt, and manganese in the lithium-containing solution can be removed. Sodium hydroxide is used in this step because, in addition to precipitating the impurity elements nickel, cobalt, and manganese, sodium hydroxide can also make the subsequent removal of calcium and magnesium better. Sodium carbonate is used in this step to remove calcium / magnesium ions and form calcium carbonate / magnesium precipitates.

[0029] Wherein, the molar amount of carbonate ions in the sodium carbonate is the molar amount of Ca in the primary filtrate. 2+ Mg 2+ The total content is 2-5 times the stoichiometric ratio.

[0030] Step 4: The purified lithium solution obtained in step 3 mainly contains lithium ions, sodium ions, and sulfate ions. If it is concentrated directly, there is a risk of sodium sulfate precipitation, and high concentration of SO4 2- and Na + In the process of lithium precipitation, it will be wrapped in lithium carbonate or adsorbed on the surface of lithium carbonate. In the present application, an organic solvent is first added to the purified lithium solution to reduce the solubility of sodium sulfate in the solution, so that it crystallizes out from the purified lithium solution.

[0031] In the specific implementation of this application, the specific operation of step 4 is as follows: An organic solvent is added to the purified lithium solution, wherein the organic solvent is selected from one or more of ethanol, acetone, methanol, 2-propanol, acetonitrile, diethylamine, propylamine, butylamine, and ethylenediamine, and the added volume of the organic solvent is 20-50% of the volume of the purified lithium solution. The reaction is stirred, the temperature of the reaction system is controlled to be 15-25° C., the stirring speed is 100-200 r / min, the reaction time is 1.0-2.0 h, and after the reaction is completed, sodium sulfate crystals and an organic mixed solution are obtained by filtering.

[0032] Step 5: In addition to the organic solvent, the organic mixed solution obtained in step 4 also contains lithium ions and sulfate ions. The organic solvent is recovered from the organic mixed solution through an evaporation and condensation device, and then evaporated and concentrated to obtain a concentrated solution, and then carbonate is added to carry out lithium precipitation reaction to obtain battery-grade lithium carbonate.

[0033] The sodium sulfate crystals are washed and dried to obtain high-purity sodium sulfate powder, namely, sodium sulphate.

[0034] In order to improve the recovery rate of lithium ions, the sodium sulfate crystals may carry a small amount of lithium ions. The sodium sulfate crystals can be washed and the washing water is combined with the organic mixed solution in step 4 before performing subsequent operations.

[0035] In order to further improve the purity of lithium carbonate, the lithium carbonate can be washed at low temperature first and then at high temperature. The solubility of lithium carbonate is increased at low temperature, which is beneficial to increase the dissolution of sodium sulfate impurities that have formed peritectic during lithium precipitation. The temperature is then increased to reduce the solubility of lithium carbonate, reduce lithium carbonate loss, increase sodium sulfate elution efficiency, and reduce the amount of washing water used.

[0036] In the specific implementation of this application, the specific operation of step 5 is as follows: Pure water is added to the sodium sulfate crystals, stirred and washed, and then filtered to obtain a filtrate and a filter residue, the filtrate is combined with the organic mixed solution in step 4, and the filter residue is dried to obtain glauber salt; The combined organic mixed liquid is passed through an evaporation and condensation device to recover the organic solvent, and then evaporated and concentrated to obtain a concentrated liquid; wherein the recovered organic solvent can be further used in step 4; Adding sodium carbonate solution to the concentrated solution for sufficient reaction to obtain lithium carbonate; The lithium carbonate is first washed with pure water at room temperature, then washed with pure water at a temperature of 90-95° C., and then dried to obtain battery-grade lithium carbonate.

[0037] In order to enable the above-mentioned implementation details and operations of the present application to be clearly understood by those skilled in the art, as well as to demonstrate the significant improvement in the performance of the method for preparing battery-grade lithium carbonate using waste lithium iron phosphate batteries in the embodiment of the present application, the above-mentioned technical scheme is illustrated by means of multiple embodiments below.

[0038] Example 1 The waste lithium iron phosphate battery was discharged, disassembled and crushed to obtain lithium iron phosphate battery powder. 1000 g of lithium iron phosphate battery powder was taken, 20wt% concentrated sulfuric acid was added to adjust the solution pH to 2.5 to obtain a leachate, and then hydrogen peroxide was added to make the molar amount of H2O2 in the hydrogen peroxide equal to Fe in the leachate. 2+ The filtrate was heated to 60°C and stirred at a rate of 300 r / min. Calcium hydroxide was added to adjust the pH value of the solution to 7.0. The reaction was continued for 1.0 h and then filtered. Sodium hydroxide was added to the filtrate to adjust the pH value to 10.5. Sodium carbonate with a stoichiometric ratio of 2 times the calcium and magnesium ion content in the filtrate was added. The reaction was continued at 60°C for 1.0 h and then filtered to obtain the purified lithium solution. Diethylamine was added to the purified lithium solution in a volume of 20% of the volume of the purified lithium solution, and the mixture was stirred at 20°C for 1.0 h at a stirring speed of 100 r / min. After filtration, the residue was washed with pure water at a liquid-solid ratio of 0.5 mL:1 g for 0.5 h. The filtrate was mixed with the washing water and then entered into an evaporation condensation device to recover the diethylamine. The mixture was then heated to 100°C for evaporation to prepare a concentrated solution. When the lithium content in the concentrated solution reached 16 g / L, a saturated sodium carbonate solution of 1.5 times the stoichiometric ratio was added according to the lithium content, and lithium precipitation reaction was carried out at 95°C. After the reaction time was 1 h, crude lithium carbonate was obtained by filtering. The crude lithium carbonate was added with pure water at a liquid-solid ratio of 20 mL:1 g, and was first stirred and washed at room temperature for 1.0 h, and then the temperature was raised to 95°C for stirring and washing for 1.0 h, and then filtered and dried to obtain a lithium carbonate product. The purity of the lithium carbonate was detected to be 99.72%, wherein the sodium ion content was 181 ppm and the sulfate content was 174 ppm, which met the requirements of battery-grade lithium carbonate.

[0039] Example 2 The waste lithium iron phosphate battery was discharged, disassembled and crushed to obtain lithium iron phosphate battery powder. 1000 g of lithium iron phosphate battery powder was taken, 20wt% concentrated sulfuric acid was added to adjust the solution pH to 3.0 to obtain a leachate, and then hydrogen peroxide was added to make the molar amount of H2O2 in the hydrogen peroxide equal to Fe in the leachate. 2+The filtrate was heated to 50 ° C and stirred at a rate of 300 r / min, and calcium hydroxide was added to adjust the solution pH to 9.0. After reacting for 1.0 h, it was filtered. Sodium hydroxide was added to the filtrate to adjust the pH to 10. Sodium carbonate with a stoichiometric ratio of 3 times the calcium and magnesium ion content in the filtrate was added. After constant temperature reaction at 50 ° C for 1.0 h, it was filtered to obtain a purified lithium solution. A mixture of methanol and acetonitrile was added to the purified lithium solution in an amount of 30% of the volume of the purified lithium solution. It was stirred at 22 ° C for 1.0 h, and the stirring speed was 100 r / min. After filtration, the filter residue was washed with pure water at a liquid-solid ratio of 0.5 mL: 1 g for 0.5 h. The filtrate was mixed with the washing water and then entered the evaporation condensation device to recover the methanol and acetonitrile mixture. The temperature was then raised to 100 ° C for evaporation to prepare a concentrated solution. When the lithium content in the concentrated solution reached 16 g / L, a saturated sodium carbonate solution with a stoichiometric ratio of 2 times the lithium content was added according to the lithium content. The lithium precipitation reaction was carried out at 95 ° C for a reaction time of 2 h and filtered to obtain crude lithium carbonate; the crude lithium carbonate was added with pure water at a liquid-to-solid ratio of 10 mL: 1 g, first stirred and washed for 0.5 h at room temperature, then the temperature was raised to 95°C and stirred and washed for 0.5 h, and then filtered, the above washing operation was repeated twice and then dried to obtain a lithium carbonate product. The purity of the lithium carbonate was detected to be 99.65%, of which the sodium ion content was 203 ppm and the sulfate content was 716 ppm, which met the requirements of battery-grade lithium carbonate.

[0040] Example 3 The only difference between this embodiment and embodiment 1 is that: crude lithium carbonate is added with pure water at a liquid-to-solid ratio of 20 mL: 1 g, stirred and washed at 95° C. for 2.0 h, filtered, and dried to obtain a lithium carbonate product. The purity of the lithium carbonate is detected to be 99.55%, wherein the sodium ion content is 289 ppm, and the sulfate content is 786 ppm, which meets the requirements of battery-grade lithium carbonate.

[0041] Example 4 The only difference between this embodiment and embodiment 1 is that diethylamine is replaced by ethylenediamine to obtain a lithium carbonate product, and the purity of the lithium carbonate is detected to be 99.65%, wherein the sodium ion content is 175 ppm and the sulfate content is 148 ppm, which meets the requirements of battery-grade lithium carbonate.

[0042] Comparative Example 1 The waste lithium iron phosphate battery was discharged, disassembled and crushed to obtain lithium iron phosphate battery powder. 1000 g of lithium iron phosphate battery powder was taken, 20wt% concentrated sulfuric acid was added to adjust the solution pH to 2.5 to obtain a leachate, and then hydrogen peroxide was added to make the molar amount of H2O2 in the hydrogen peroxide equal to Fe in the leachate. 2+The filtrate was heated to 60°C and stirred at a rate of 300 r / min, and calcium hydroxide was added to adjust the solution pH to 7.0. After reacting for 1.0 h, the solution was filtered. Sodium hydroxide was added to the filtrate to adjust the pH to 10.5. Sodium carbonate with a stoichiometric ratio of 2 times the calcium and magnesium ion content in the filtrate was added. After constant temperature reaction at 60°C for 1.0 h, the purified lithium solution was filtered. The purified lithium solution was heated to 100°C and evaporated to prepare a concentrated solution. The concentrated solution was heated until trace crystals were precipitated. At this time, the lithium concentration was 8.5 g / L. A saturated sodium carbonate solution with a stoichiometric ratio of 1.5 times the lithium content was added according to the lithium content. The lithium precipitation reaction was carried out at 95°C. After the reaction time was 1 h, the crude lithium carbonate was filtered. The crude lithium carbonate was added with pure water at a liquid-to-solid ratio of 20 mL: 1 g and stirred for 1.0 h at room temperature, and then the temperature was raised to 95°C and stirred for 1.0 h. h later, the product was filtered and dried to obtain a lithium carbonate product. The purity of the lithium carbonate was detected to be 99.08%, with a sodium ion content of 1536 ppm and a sulfate content of 6850 ppm. The sodium ions and sulfate in the lithium carbonate could not be effectively removed by washing.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing battery-grade lithium carbonate using waste lithium iron phosphate batteries, characterized in that: The following steps are involved: Step 1: Discharging, disassembling and crushing the waste lithium iron phosphate batteries to obtain lithium iron phosphate battery powder; Step 2: extracting lithium from the lithium iron phosphate battery powder by acid leaching to obtain a lithium-containing solution and ferrophosphorus slag; Step 3: adding calcium hydroxide and sodium hydroxide to the above lithium-containing solution in sequence to remove impurities, then adding sodium carbonate, and filtering to obtain a purified lithium solution; Step 4: adding an organic solvent to the purified lithium solution, stirring thoroughly and filtering to obtain sodium sulfate crystals and an organic mixed solution; Step 5: Add sodium carbonate to the organic mixed solution, filter and wash after sufficient reaction to obtain the battery-grade lithium carbonate.

2. The preparation method according to claim 1, characterized in that: In step 2, the step of acid leaching lithium is: adding sulfuric acid solution to lithium iron phosphate battery powder to obtain a leachate, and then adding hydrogen peroxide, wherein the concentration of the sulfuric acid solution is 10-50wt%, and the concentration of the hydrogen peroxide is 10-30wt%; Preferably, the molar amount of H2O2 in the hydrogen peroxide is 2+ 1-2 times the stoichiometric ratio of the content; Preferably, the pH value of the acid leaching lithium reaction is 2-3, and the reaction time is 3-6 h.

3. The preparation method according to claim 1, characterized in that: The steps for step 3 are: Add calcium hydroxide to the lithium-containing solution to adjust the pH of the solution to 6-9, and filter after the reaction to obtain a primary filtrate; Sodium hydroxide is added to the primary filtrate to adjust the pH of the solution to 10-11, and then sodium carbonate is added. After the reaction, the solution is filtered to obtain a purified lithium solution.

4. The preparation method according to claim 3, characterized in that The molar amount of carbonate ions in the sodium carbonate is the Ca 2+ Mg 2+ The total content is 2-5 times of the stoichiometric ratio, the reaction time after adding sodium carbonate is 1.0-2.0h, the reaction temperature is 50-60°C, and the stirring speed during the reaction is 200-300 r / min.

5. The preparation method according to claim 1, characterized in that: In step 4, the organic solvent is selected from one or more of ethanol, acetone, methanol, 2-propanol, acetonitrile, diethylamine, propylamine, butylamine, and ethylenediamine.

6. The preparation method according to claim 1, characterized in that In step 4, the volume of the organic solvent is 20-50% of the volume of the purified lithium liquid. During the stirring process, the temperature of the reaction system is 15-25° C., the time is 1.0-2.0 h, and the stirring speed is 100-200 r / min.

7. The preparation method according to claim 1, characterized in that: In step 5, the washing refers to washing with pure water at low temperature first and then at high temperature; The temperature of the low-temperature washing is 10-20°C, and the time is 0.5-1.0 h. The temperature of the high-temperature washing is 90-100°C, and the time is 0.5-1.0 h. During the two washing processes, the mass ratio of pure water to lithium carbonate was independently (10-20):

1.

8. The preparation method according to claim 1, characterized in that: The steps for step 5 are: Add pure water to the sodium sulfate crystals obtained in step 4, stir and wash, and then filter, combine the filtrate with the organic mixed solution obtained in step 4, and dry the filter residue to obtain high-purity sodium sulfate powder; The combined organic mixed liquid is passed through an evaporation and condensation device to recover the organic solvent, and then evaporated and concentrated to obtain a concentrated liquid; A sodium carbonate solution is added to the concentrated solution, and after sufficient reaction, the solution is filtered and washed to obtain the battery-grade lithium carbonate.

9. The preparation method according to claim 8, characterized in that The liquid-to-solid ratio of the pure water to the sodium sulfate crystals is (0.5-1.0) mL: 1 g; The time of adding pure water to the sodium sulfate crystals and stirring is 0.5-1.0 h.

10. The preparation method according to claim 8, characterized in that After adding sodium carbonate solution to the concentrated solution, the reaction temperature is 90-95° C., the molar amount of carbonate ions in the sodium carbonate solution is 1.0-2.0 times the stoichiometric ratio of the lithium ion content in the concentrated solution, and the reaction time is 1-2 h.

Images