Directional cyclic leaching method for lithium iron phosphate black powder

Abstract

A directional cyclic leaching method for lithium iron phosphate black powder, the lithium iron phosphate black powder being leached by means of introducing ozone into an ammonia water system.

Description

Method for directional circulation leaching of lithium iron phosphate black powder Technical Field

[0001] The present disclosure relates to the technical field of resource utilization of lithium iron phosphate black powder, and in particular to a method for directional circulation leaching of lithium iron phosphate black powder. Background Art

[0002] With the development of the new energy industry and the widespread adoption of lithium iron phosphate batteries, a large amount of discarded batteries continues to be generated. Discarded batteries contain a large amount of valuable metals and their compounds. Simply discarding them not only wastes resources but also causes serious environmental pollution. Recycling discarded batteries to generate profits while mitigating environmental pollution and achieving green development has become a pressing issue.

[0003] During the initial crushing and sorting of lithium iron phosphate batteries, some copper, aluminum, and nickel are difficult to completely separate. This results in the resulting black powder containing some copper and aluminum metals in addition to carbon powder and lithium iron phosphate. The copper remaining in the slag is detrimental to the repair, regeneration, or decomposition and synthesis of the lithium iron phosphate. The atmospheric pressure acid leaching method commonly used in wet processes also struggles to completely extract the copper, hindering the subsequent comprehensive utilization of the ferrophosphorus slag.

[0004] In view of this, the present disclosure is proposed.

[0005] Summary of the Invention

[0006] The purpose of the present disclosure is to provide a method for directional circulation leaching of lithium iron phosphate black powder to improve the leaching rate of lithium and copper.

[0007] The present disclosure is achieved as follows:

[0008] In a first aspect, the present disclosure provides a method for leaching lithium iron phosphate black powder, comprising:

[0009] Ozone is introduced into a mixture of lithium iron phosphate black powder and ammonia water to perform oxidation leaching and solid-liquid separation to obtain a leachate and ferrophosphorus slag.

[0010] In some embodiments, in the oxidative leaching step, the ratio of the molar amount of ammonia in the ammonia water to the molar amount of copper in the lithium iron phosphate black powder is (10-20):1.

[0011] In some embodiments, the ratio of the mass of lithium iron phosphate black powder to the volume of ammonia water in the mixed solution is 1:(5-7) g / ml.

[0012] In some embodiments, the ratio of the ozone gas introduction rate to the mass of the lithium iron phosphate black powder in the mixed solution is 0.02 L / (min.g) to 0.2 L / (min.g).

[0013] In some embodiments, the ratio of the ozone gas introduction rate to the mass of the lithium iron phosphate black powder in the mixed solution is 0.06 L / (min.g) to 0.16 L / (min.g).

[0014] In some embodiments, the oxidative leaching step is performed under stirring conditions with a stirring rate of 150 rpm to 550 rpm.

[0015] In some embodiments, the oxidative leaching step lasts for 2 hours to 6 hours.

[0016] In some embodiments, the temperature is between 18°C ​​and 25°C.

[0017] In some embodiments, the lithium content in the ferrophosphorus slag is 0.11 wt% to 0.42 wt%, and the copper content in the ferrophosphorus slag is 0.08 wt% to 0.50 wt%.

[0018] In some embodiments, the leaching rate of copper in the lithium iron phosphate black powder in the oxidative leaching step is 89.5 wt % to 91.2 wt %, and the leaching rate of lithium in the lithium iron phosphate black powder is 89.4 wt % to 95.4 wt %.

[0019] In some embodiments, the leachate is heated to evaporate ammonia and part of water therein, and then solid-liquid separation is performed to obtain copper oxide residue and copper removal solution.

[0020] In some embodiments, ammonia and part of water in the leachate are distilled off at 75°C to 100°C.

[0021] In some embodiments, the heating of the leachate is stopped after 40 vol% to 85 vol% of the water is evaporated.

[0022] In some embodiments, water in the copper removal solution is distilled off to obtain lithium hydroxide crystals.

[0023] In some embodiments, water in the copper removal solution is evaporated at a temperature above 80° C. to obtain lithium hydroxide crystals.

[0024] In some embodiments, the lithium iron phosphate black powder includes the following components: 2.5 wt% to 2.6 wt% of lithium, 15 wt% to 16 wt% of iron, 9 wt% to 9.5 wt% of phosphorus, 1.7 wt% to 1.8 wt% of aluminum, and 5 wt% to 5.5 wt% of copper.

[0025] The present disclosure has the following beneficial effects:

[0026] This disclosure introduces ozone into an ammonia solution to leach lithium iron phosphate black powder. The ozone's oxidizing properties oxidize the iron in the lithium iron phosphate to trivalent, allowing lithium ions to escape from the lithium iron phosphate structure, achieving leaching and separation. Simultaneously, ammonia forms a complex with the copper ions in the lithium iron phosphate black powder, further promoting the oxidative leaching of copper. This simple leaching and separation method allows for efficient leaching and separation of the lithium iron phosphate black powder, facilitating subsequent recycling of the components. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0028] FIG1 is an XRD diagram of the lithium iron phosphate black powder used in the Examples and Comparative Examples;

[0029] FIG2 is an XRD diagram of the lithium hydroxide product obtained in Example 1. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0031] The present disclosure provides a method for leaching lithium iron phosphate black powder, comprising:

[0032] Ozone is introduced into a mixture of lithium iron phosphate black powder and ammonia water to perform oxidation leaching and solid-liquid separation to obtain a leachate and ferrophosphorus slag.

[0033] The method of leaching lithium iron phosphate black powder by introducing ozone into an ammonia water system utilizes the oxidizing property of ozone to oxidize the iron in the lithium iron phosphate to trivalent, so that the lithium ions are released from the lithium iron phosphate structure. As shown in Formula 1, the use of strongly oxidizing ozone is more conducive to destroying the lithium iron phosphate structure than using air or oxygen, thereby achieving the purpose of leaching and separation. At the same time, ammonia can form a complex with copper ions, as shown in Formula 2, further promoting the oxidation and leaching of copper, thereby better processing battery powder with a high copper content. O3+2LiFePO4+NH3·H2O=2FePO4+2LiOH+O2+NH3 (1) O3+4NH3·H2O+Cu=Cu(NH3)4(OH)2+3H2O (2)

[0034] In some embodiments, in the oxidative leaching step, the ratio of the molar amount of ammonia in the ammonia water to the molar amount of copper in the lithium iron phosphate black powder is (10-20):1, specifically 10:1, 15:1, 20:1 or any value between (10-20):1.

[0035] Theoretically, copper and ammonia react in a stoichiometric ratio. However, to fully leach the copper from the black powder, excess ammonia can be added to increase the copper leaching rate. Furthermore, because the portion of the liquid phase that fails to form a complex with copper is less stable, it easily escapes from the solution as ammonia gas, resulting in ammonia loss. For this reason, the molar ratio of ammonia to copper can be further increased. However, excessive ammonia consumption leads to high energy consumption in subsequent separations and low utilization of the ammonia raw material. Therefore, the molar ratio of ammonia to copper is preferably controlled within the range of (10-20):1.

[0036] In some embodiments, the ratio of the mass of lithium iron phosphate black powder to the volume of ammonia water in the mixed solution is 1:(5-7) g / ml, specifically 1:5 g / ml, 1:5.5 g / ml, 1:6 g / ml, 1:6.5 g / ml, 1:7 g / ml or any value in between 1:(5-7) g / ml.

[0037] Since ozone is a gas and lithium iron phosphate black powder is a solid, in order to ensure sufficient contact between the solid and the gas, the content of lithium iron phosphate black powder in the mixed liquid needs to be appropriate. If the content is too low, the probability and difficulty of being captured by ozone and interacting with ozone will increase. If the content is too high, it may affect the dispersion effect of ozone in the mixed liquid, and also increase the difficulty of the reaction between ozone and lithium iron phosphate black powder.

[0038] In some embodiments, the ratio of the ozone gas introduction rate to the mass of the lithium iron phosphate black powder in the mixed solution is 0.02 L / (min.g) to 0.2 L / (min.g), specifically 0.02 L / (min.g), 0.05 L / (min.g), 0.1 L / (min.g), 0.15 L / (min.g), 0.2 L / (min.g), or any value between 0.02 L / (min.g) and 0.2 L / (min.g). The ozone introduction rate is adjusted to provide sufficient oxidant for the oxidation of copper and iron on the one hand, and to avoid waste caused by excessive ozone introduction on the other hand.

[0039] Theoretically, there is a certain proportional relationship between the amount of ozone used and the amount of lithium iron phosphate black powder used. However, in reality, as the amount of lithium iron phosphate used increases, the ratio of the ozone gas introduction rate to the mass of lithium iron phosphate black powder in the mixed liquid can be slightly reduced. One possible reason is that as the amount of lithium iron phosphate black powder increases, the volume of the mixed liquid also increases, and the amount of ozone dissolved in the mixed liquid increases, thereby improving the utilization efficiency of ozone.

[0040] In some embodiments, the ratio of the ozone gas introduction rate to the mass of the lithium iron phosphate black powder in the mixed solution is 0.06 L / (min.g) to 0.16 L / (min.g).

[0041] For example, when the mass of lithium iron phosphate black powder in the mixed liquid is 48g to 52g, the ozone gas introduction rate is 3L / min to 8L / min. Specifically, the ozone gas introduction rate can be 3L / min, 4L / min, 5L / min, 6L / min, 7L / min, 8L / min, or any value between 3L / min and 8L / min. Although an ozone gas introduction rate that is too fast will facilitate a more complete reaction of the lithium iron phosphate black powder, excessive ozone will escape from the liquid before it can participate in the reaction, resulting in lower utilization rate. An ozone gas introduction rate that is too slow will result in lower reaction efficiency, which is not conducive to improving production efficiency.

[0042] In some embodiments, the oxidative leaching step is carried out under stirring conditions, and the stirring rate is 150rpm to 550rpm, specifically 150rpm, 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm or any value between 150rpm and 550rpm.

[0043] Stirring helps to evenly distribute the reactants in the system and improve the uniformity of the reaction system. However, since the present oxidative leaching system contains three phases: solid, liquid, and gas, the density difference between the solid and gas phases is relatively large. If the stirring rate is too high, the solid phase may concentrate toward the reactor wall under the action of centrifugal force, while the gas phase concentrates near the rotating shaft. This may make it difficult for the solid and liquid phases to effectively contact, thereby affecting the efficiency of oxidative leaching. In addition, if the stirring rate is too low, the uniformity of the reaction system is relatively poor. Therefore, the stirring rate in this embodiment needs to be reasonably selected.

[0044] In some embodiments, the oxidative leaching step is performed for 2 to 6 hours, specifically 2 hours, 4 hours, 6 hours, or any value between 2 hours and 6 hours, and the temperature is 18°C ​​to 25°C, specifically 18°C, 20°C, 22°C, 24°C, 25°C, or any value between 18°C ​​and 25°C.

[0045] As the oxidative leaching step time increases, the leaching rates of lithium and copper increase, but the improvement in leaching rate is not significant after 6 hours. Regarding the duration of the oxidative leaching step, since the oxidative leaching step can be performed at room temperature, the oxidative leaching is performed at room temperature in this embodiment. Increasing the temperature is beneficial for improving the leaching efficiency. However, as the temperature increases, the loss of the reaction solution due to ozone carryover increases, and some ammonia gas that reacts with copper is also lost, which may also reduce the leaching efficiency. Therefore, based on comprehensive considerations, the oxidative leaching is performed at room temperature in this embodiment.

[0046] In some embodiments, the lithium content in the ferrophosphorus slag is 0.11 wt% to 0.42 wt%, and the copper content in the ferrophosphorus slag is 0.08 wt% to 0.50 wt%.

[0047] The ferrophosphorus slag obtained after the oxidative leaching step is mainly composed of ferrophosphate and carbon powder, which is mixed with a small amount of incompletely leached lithium and copper, but the inclusion amount is relatively low. The ferrophosphorus slag can subsequently be removed of aluminum and carbon impurities through alkaline washing, roasting, etc. to obtain relatively pure ferrophosphate.

[0048] In some embodiments, the leaching rate of copper in the lithium iron phosphate black powder in the oxidative leaching step is 89.5 wt % to 91.2 wt %, and the leaching rate of lithium in the lithium iron phosphate black powder is 89.4 wt % to 95.4 wt %.

[0049] The leached copper and lithium exist in the leachate, the main components of which are Cu(NH3)4(OH)2 and LiOH. In this embodiment, the leaching rates of copper and lithium in the lithium iron phosphate black powder are relatively high.

[0050] In some embodiments, the leachate is heated to evaporate ammonia and part of water therein, and then solid-liquid separation is performed to obtain copper oxide residue and copper removal solution.

[0051] When the Cu(NH3)4(OH)2 in the leachate is heated, it decomposes and releases ammonia, generating copper hydroxide, which further decomposes to generate copper oxide. Finally, copper is separated from the leachate in the form of copper oxide, as shown in Formula 3. Cu(NH3)4(OH)2=CuO+H2O+4NH3↑ (3)

[0052] The solid phase obtained by solid-liquid separation is copper oxide filter residue. The copper oxide filter residue is washed with water to remove soluble impurities therein to obtain relatively pure copper oxide.

[0053] In some embodiments, ammonia and part of water in the leachate are evaporated at 75°C to 100°C. Specifically, the temperature can be 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or any value between 75°C and 100°C.

[0054] Since the decomposition of Cu(NH3)4(OH)2 to release ammonia and the formation of copper oxide require relatively high temperatures, the temperature in this step is controlled above 75°C. In theory, the higher the temperature, the more efficient the evaporation of ammonia and water. However, if the copper oxide precipitates too quickly, the content of lithium hydroxide and other substances contained in it will increase, resulting in lithium loss and hindering the purity of the copper oxide.

[0055] In some embodiments, the leachate is heated in a water bath to evaporate ammonia and some water. Heating in a water bath helps to uniformly heat the leachate and prevents local copper oxide precipitation from being too rapid.

[0056] In some embodiments, the heating of the leachate is stopped after 40 vol% to 85 vol% of the water is evaporated. Specifically, the amount of evaporated water can be 40 vol%, 50 vol%, 60 vol%, 70 vol%, 80% or any value between 40 vol% and 85 vol% of the leachate.

[0057] As the water in the leachate evaporates, the concentration of lithium hydroxide contained therein also increases. In order to prevent lithium hydroxide from precipitating together with copper oxide, heating is stopped when 40% to 85% of the volume fraction of water is evaporated.

[0058] In some embodiments, water in the copper removal solution is evaporated to obtain lithium hydroxide crystals, which facilitates further recycling of lithium resources.

[0059] In some embodiments, water in the copper removal solution is evaporated at a temperature above 80° C. to obtain lithium hydroxide crystals.

[0060] The purpose of heating the copper removal liquid is to remove the moisture therein, so the purpose can be achieved even at a lower temperature. However, if the temperature is too low, the evaporation rate is too slow, resulting in low efficiency. Therefore, in some embodiments, the temperature for heating the copper removal liquid is controlled to be above 80°C, specifically 80°C, 85°C, 90°C, 95°C, 100°C or any value above 80°C.

[0061] In some embodiments, the copper removal solution is heated in a water bath to evaporate water in the copper removal solution to obtain lithium hydroxide crystals.

[0062] In some embodiments, the main components of the lithium iron phosphate black powder are carbon powder and lithium iron phosphate.

[0063] In some embodiments, the lithium iron phosphate black powder includes the following components: 2.5 wt% to 2.6 wt% of lithium, 15 wt% to 16 wt% of iron, 9 wt% to 9.5 wt% of phosphorus, 1.7 wt% to 1.8 wt% of aluminum, and 5 wt% to 5.5 wt% of copper.

[0064] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0065] The XRD pattern of the lithium iron phosphate black powder used in the following examples and comparative examples is shown in FIG1 , wherein the contents of lithium, iron, phosphorus, aluminum, and copper are shown in the following table.

[0066] Table 1 Lithium iron phosphate black powder composition

[0067] Example 1:

[0068] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, comprising the following specific steps:

[0069] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0070] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0071] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0072] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0073] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0074] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0075] (7) The filtrate was collected in a beaker and evaporated to dryness in a water bath at 95°C to obtain lithium hydroxide crystals. The product was washed three times with 20 mL of deionized water each time and air-dried. The XRD pattern is shown in Figure 2. The washing solution was mixed with the next batch of copper removal solution and evaporated for concentration.

[0076] Example 2:

[0077] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the ozone flow rate is different, comprises the following specific steps:

[0078] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0079] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0080] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 5.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0081] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0082] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0083] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0084] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0085] Example 3:

[0086] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the ozone flow rate is different, comprises the following specific steps:

[0087] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0088] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0089] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 3.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0090] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0091] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0092] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0093] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0094] Example 4:

[0095] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the amount of ammonia used is different, comprises the following specific steps:

[0096] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 10 times the molar amount of copper.

[0097] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0098] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0099] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0100] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0101] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0102] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0103] Example 5:

[0104] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the amount of ammonia used is different, comprises the following specific steps:

[0105] (1) Prepare ammonia solution: Measure a certain volume of concentrated aqueous ammonia and add deionized water to bring the volume to approximately 300 mL. The molar amount of ammonia added should be 5 times the molar amount of copper.

[0106] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0107] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0108] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0109] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0110] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0111] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0112] Example 6:

[0113] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the oxidation leaching time is different, comprises the following specific steps:

[0114] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0115] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0116] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 4 h.

[0117] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0118] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0119] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0120] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0121] Example 7:

[0122] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the oxidation leaching time is different, comprises the following specific steps:

[0123] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0124] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0125] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 2 h.

[0126] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0127] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0128] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0129] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0130] Example 8:

[0131] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the stirring rate is different, comprises the following specific steps:

[0132] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0133] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0134] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 200 rpm at room temperature and allow the reaction to proceed for 8 h.

[0135] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0136] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0137] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0138] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0139] Example 9:

[0140] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the stirring rate is different, comprises the following specific steps:

[0141] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0142] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0143] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 700 rpm at room temperature and allow the reaction to proceed for 8 h.

[0144] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0145] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0146] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0147] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0148] Example 10:

[0149] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the amount of water evaporated by heating the leachate is excessive, comprises the following specific steps:

[0150] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0151] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0152] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0153] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0154] (5) Collect the leachate in a beaker and place it in a 90°C water bath. Heat and stir to evaporate the ammonia. Stop heating when 95% of the volume of water has been evaporated.

[0155] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0156] (7) Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product three times with 20 mL of deionized water each time and air dry. The washing solution is mixed with the next batch of copper removal solution and evaporated to concentrate.

[0157] Example 11:

[0158] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that the heating temperature of the leaching solution is different, comprises the following specific steps:

[0159] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 40 times the molar amount of copper.

[0160] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0161] (3) Insert a vent tube below the liquid surface and introduce ozone at a flow rate of 8.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and allow the reaction to proceed for 8 h.

[0162] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water three times, 100 mL each time, to obtain a leachate and leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferric phosphate and carbon powder, and the aluminum and carbon impurities can be removed by alkali washing, roasting, etc.

[0163] (5) Collect the leachate in a beaker, place it in a 100°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0164] (6) Filter and wash the precipitate with deionized water three times, 30 mL each time, to obtain copper oxide residue and copper removal solution.

[0165] (7) The filtrate was collected in a beaker and evaporated to dryness in a water bath at 95°C to obtain lithium hydroxide crystals. The product was washed three times with 20 mL of deionized water each time and air-dried. The XRD pattern is shown in Figure 2. The washing solution was mixed with the next batch of copper removal solution and evaporated for concentration.

[0166] Comparative Example 1:

[0167] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, comprising the following specific steps:

[0168] Weigh 50g of lithium iron phosphate black powder into a three-necked flask, add 300mL of deionized water, and introduce ozone through a vent tube extending below the liquid surface at a rate of 8.0L / min. Stir at 300rpm at room temperature for 8 hours. After the reaction, filter and wash the precipitate with deionized water to obtain a leachate and leach residue (ferrophosphorus residue).

[0169] The leachate was collected in a beaker and placed in a 90°C water bath. After 70% of the water volume was evaporated, heating was stopped. The precipitate was filtered and washed with deionized water to obtain copper oxide residue and copper removal solution.

[0170] Collect the filtrate in a beaker and evaporate to dryness in a 95°C water bath to obtain lithium hydroxide crystals. Wash the product with 50 mL of deionized water and air-dry. Combine the washings with the next batch of copper removal solution and evaporate and concentrate.

[0171] Comparative Example 2:

[0172] A method for leaching lithium iron phosphate black powder with ammonia and oxygen, which differs from Example 1 in that oxygen is used instead of ozone and the oxygen flow rate is increased, comprises the following specific steps:

[0173] (1) Prepare ammonia solution: Take a certain volume of concentrated aqueous ammonia and add deionized water to make the volume about 300 mL. The molar amount of ammonia added should be 20 times the molar amount of copper.

[0174] (2) Weigh 50g of lithium iron phosphate black powder into a three-necked flask, pour in the prepared ammonia water, and mix well.

[0175] (3) Extend the vent tube below the liquid surface and introduce oxygen at a flow rate of 12.0 L / min. Maintain the stirring rate at 500 rpm at room temperature and react for 8 h.

[0176] (4) After the reaction is completed, the precipitate is filtered and washed with deionized water to obtain a leachate and a leach residue (ferrophosphorus slag). The leach residue is mainly composed of ferrophosphate and carbon powder, and the aluminum and carbon impurities therein can be removed by alkali washing, roasting, etc.

[0177] (5) Collect the leachate in a beaker, place it in a 90°C water bath, and heat and stir to evaporate the ammonia. Stop heating after 70% of the volume of water has been evaporated.

[0178] (6) filtering and washing the precipitate with deionized water to obtain copper oxide residue and copper removal solution.

[0179] (7) Collect the filtrate in a beaker and evaporate it to dryness in a water bath at 95°C to obtain lithium hydroxide crystals. Wash the product with 50 mL of deionized water and air dry. Mix the washing solution with the next batch of copper removal solution and evaporate and concentrate.

[0180] Finished product quality:

[0181] Table 2 compares the composition of the ferrophosphorus slag obtained by oxidation leaching in the embodiment and the comparative example. It can be seen that when the black powder is directly oxidized and leached without adding ammonia water, copper will remain in the ferrophosphorus slag and will not enter the leachate, which increases the difficulty of recycling the ferrophosphorus slag.

[0182] Table 2 Copper and lithium residues in leached residue (wt%)

[0183] Table 3 shows the leaching rate of lithium element when leaching lithium iron phosphate black powder in the embodiment and the comparative example. It can be seen that the ozone oxidation leaching method has a good leaching effect on lithium.

[0184] Table 3 Cu and Li leaching rates (%)

[0185] Table 4 shows the purity of copper oxide and lithium hydroxide obtained in Examples and Comparative Examples.

[0186] Table 4 Purity of copper oxide and lithium hydroxide (wt%) Industrial Applicability

[0187] This method, which introduces ozone into an ammonia solution to leach lithium iron phosphate black powder, leverages the oxidizing properties of ozone to oxidize the iron in the lithium iron phosphate to trivalent form, releasing lithium ions from the lithium iron phosphate structure and leaving them in the solution as lithium hydroxide, achieving leaching and separation. Ammonia also forms a complex with copper ions, further promoting the oxidative leaching of copper. This simple leaching and separation method allows for efficient leaching and separation of the lithium iron phosphate black powder, facilitating subsequent component recovery and industrial application.

Claims

1. A method for leaching lithium iron phosphate black powder, characterized in that: include: Ozone is introduced into a mixture of lithium iron phosphate black powder and ammonia water to perform oxidation leaching and solid-liquid separation to obtain a leaching solution and ferrophosphorus slag.

2. The method for leaching lithium iron phosphate black powder according to claim 1, characterized in that: In the oxidation leaching step, the ratio of the molar amount of ammonia in the ammonia water to the molar amount of copper in the lithium iron phosphate black powder is (10-20):

1.

3. The method for leaching lithium iron phosphate black powder according to claim 1 or 2, characterized in that: The ratio of the mass of lithium iron phosphate black powder to the volume of ammonia water in the mixed solution is 1:(5-7) g / ml.

4. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 3, characterized in that: The ratio of the ozone gas introduction rate to the mass of the lithium iron phosphate black powder in the mixed solution is 0.02L / (min.g) to 0.2L / (min.g).

5. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 4, characterized in that: The ratio of the ozone gas introduction rate to the mass of the lithium iron phosphate black powder in the mixed solution is 0.06L / (min.g) to 0.16L / (min.g).

6. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 5, characterized in that: The oxidation leaching step is carried out under stirring conditions with a stirring rate of 150 rpm to 550 rpm.

7. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 6, characterized in that: The oxidation leaching step is performed for 2 to 6 hours at a temperature of 18 to 25°C.

8. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 7, characterized in that: The lithium content in the ferrophosphorus slag is 0.11wt% to 0.42wt%, and the copper content in the ferrophosphorus slag is 0.08wt% to 0.50wt%.

9. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 8, characterized in that: In the oxidation leaching step, the leaching rate of copper in the lithium iron phosphate black powder is 89.5wt%-91.2wt%, and the leaching rate of lithium in the lithium iron phosphate black powder is 89.4wt%-95.4wt%.

10. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 9, characterized in that: The leaching solution is heated to evaporate ammonia and part of water therein, and then solid-liquid separation is performed to obtain copper oxide filter residue and copper removal solution.

11. The method for leaching lithium iron phosphate black powder according to claim 10, characterized in that: The ammonia and part of the water in the leaching solution are evaporated at 75°C to 100°C.

12. The method for leaching lithium iron phosphate black powder according to claim 10 or 11, characterized in that: The heating is stopped after the leaching solution is heated to evaporate 40 vol% to 85 vol% of the water.

13. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 12, characterized in that: The water in the copper removal solution is evaporated to obtain lithium hydroxide crystals.

14. The method for leaching lithium iron phosphate black powder according to claim 13, characterized in that: The water in the copper removal solution is evaporated at above 80°C to obtain lithium hydroxide crystals.

15. The method for leaching lithium iron phosphate black powder according to any one of claims 1 to 14, characterized in that: The lithium iron phosphate black powder includes the following components: 2.5wt% to 2.6wt% lithium, 15wt% to 16wt% iron, 9wt% to 9.5wt% phosphorus, 1.7wt% to 1.8wt% aluminum and 5wt% to 5.5wt% copper.

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