A method for leaching lithium from lithium iron phosphate black powder

Abstract

The application discloses a lithium phosphate black powder lithium leaching method and relates to the technical field of lithium battery recycling. The lithium phosphate black powder is slurried with pure water and concentrated sulfuric acid to obtain first slurry; after water is added for reaction, first leaching residue and first leaching liquid are separated, and the first leaching residue is washed to obtain first residue washing water. Oxygen is introduced into the first leaching liquid for reaction, and first iron-phosphorus residue and first oxidized liquid are separated, and the iron-phosphorus residue is washed to obtain second residue washing water. The first oxidized liquid is used to treat new black powder, and the steps of slaking, leaching and oxidation are repeated to obtain second oxidized liquid and second iron-phosphorus residue. In summary, the application uses the waste heat generated by the reaction of concentrated sulfuric acid and lithium phosphate to provide leaching heat, uses normal-pressure oxygen as an oxidizing agent to reduce the cost of the oxidizing agent, the second oxidized liquid can be directly used for lithium precipitation after impurity removal without concentration, the lithium leaching recovery rate is improved, and the first iron-phosphorus residue and the second iron-phosphorus residue can be directly used for preparing battery-grade iron phosphate.

Description

Technical Field

[0001] This application relates to the field of waste lithium-ion battery recycling technology, and in particular to a method for leaching lithium iron phosphate black powder. Background Technology

[0002] With the increasing number of electric vehicles, lithium iron phosphate batteries have seen their market share continue to expand due to their superior safety performance, long cycle life, and low cost. However, the lifespan of lithium iron phosphate batteries is generally only 3-5 years. If a large number of retired batteries are not properly disposed of, it will not only cause serious environmental pollution but also lead to a huge waste of valuable resources such as lithium, iron, and phosphorus. Therefore, the efficient recovery of valuable metals from spent lithium iron phosphate batteries has become a critical issue that the industry urgently needs to address.

[0003] Currently, lithium extraction processes from spent lithium iron phosphate batteries mainly include roasting and wet leaching. Chinese patent CN108767354A discloses a method for recovering valuable metals from spent lithium-ion battery cathode materials. This method involves mixing the cathode material with ammonium sulfate or ammonium bisulfate, roasting at low temperature, and then leaching in water. However, the roasting process generates toxic sulfur-containing gases, polluting the environment, and the low solubility of lithium carbonate in water leads to significant lithium loss. Chinese patent CN108390120A discloses a method for selectively recovering lithium from spent lithium-ion battery cathode materials, using oxidants such as hydrogen peroxide and ammonium persulfate in conjunction with additives for leaching. However, this method requires large amounts of oxidants and additives, resulting in high energy consumption and poor economic efficiency.

[0004] While the traditional sulfuric acid and hydrogen peroxide co-leaching process achieves a high lithium leaching rate, it suffers from drawbacks such as low hydrogen peroxide utilization, the need for steam heating, and the requirement for additional concentration due to low lithium solution concentration, leading to a significant increase in equipment investment and operating costs. Therefore, developing a method for leaching lithium from lithium iron phosphate black powder that features a shorter process, lower energy consumption, higher lithium recovery rate, and higher byproduct utilization value is of significant practical importance. Summary of the Invention

[0005] In order to solve at least one of the above-mentioned technical problems and to develop a process that is low in cost, has a high concentration of leached lithium solution, and whose by-product iron-phosphorus slag can be directly used to prepare battery-grade iron phosphate, this application provides a lithium leaching method for lithium iron phosphate black powder.

[0006] On the one hand, this application provides a lithium leaching method for lithium iron phosphate black powder, which includes the following steps:

[0007] S1. Mix lithium iron phosphate black powder with pure water to form a slurry, add concentrated sulfuric acid, stir and simmer to obtain the first aging slurry;

[0008] S2. Add pure water to the first matured slurry, add sulfuric acid to control the pH value, stir the reaction, and separate the solid and liquid to obtain the first leaching residue and the first leaching liquid. The first leaching residue is washed to obtain the first leaching water.

[0009] S3. Oxygen is introduced into the first leachate, the reaction is stirred, and the solid and liquid are separated to obtain the first iron-phosphorus slag and the first oxidized liquid. The first iron-phosphorus slag is washed to obtain the second washing water.

[0010] S4. Add the same amount of lithium iron phosphate black powder as S1 to the first oxidized liquid, then add concentrated sulfuric acid, stir and simmer to obtain the second aging slurry.

[0011] S5. Add one or more of the first oxidized liquid, the first slag washing water and the second slag washing water to the second matured slurry, add sulfuric acid to control the pH value, stir the reaction, and separate the solid and liquid to obtain the second leaching residue and the second leaching liquid. The second leaching residue is washed to obtain the third slag washing water.

[0012] S6. Introduce oxygen into the second leachate, stir and react, and separate the solid and liquid to obtain the second iron-phosphorus slag and the second oxidized liquid.

[0013] The first and second iron-phosphorus slags can be directly used to prepare battery-grade iron phosphate.

[0014] By adopting the above technical solution, the waste heat from the reaction of concentrated sulfuric acid with lithium iron phosphate is used to provide leaching heat, and atmospheric pressure oxygen is used instead of hydrogen peroxide as the oxidant, which significantly reduces the cost of the oxidant. The lithium solution is concentrated through lithium-rich liquid leaching, and lithium can be directly precipitated after impurity removal without further concentration, thereby improving the lithium leaching recovery rate and significantly enhancing the economic and environmental benefits of recycling waste lithium iron phosphate batteries. Furthermore, the stepwise separation of carbon slag and iron-phosphorus slag is achieved, avoiding the mixing of graphite into the iron-phosphorus slag. The first and second iron-phosphorus slags obtained can be directly used to prepare battery-grade iron phosphate.

[0015] Optionally, in S1, the amount of pure water added is 1 to 4 times the mass of lithium iron phosphate black powder; in S4, the amount of the first oxidized liquid added is 1 to 4 times the mass of lithium iron phosphate black powder.

[0016] By adopting the above technical solution, it is possible to ensure that the lithium iron phosphate black powder is fully slurried to form a slurry with good fluidity, avoiding the problems of difficult stirring and uneven reaction caused by too low solid-liquid ratio; and to prevent the initial lithium concentration from being too low due to excessive liquid addition, thus ensuring the lithium liquid concentration.

[0017] Optionally, in S1 and S4, the amount of pure water added is a multiple of the mass of lithium iron phosphate black powder, and the amount of the first oxidized liquid added is a multiple of the mass of lithium iron phosphate black powder.

[0018] By adopting the above technical solution, the solid-liquid ratio of the first curing and the second curing are completely consistent, so that the exothermic reaction between concentrated sulfuric acid and lithium iron phosphate is the same in both curing processes, and the smoldering temperature is stabilized at 70~90℃, without the need for additional temperature control; at the same time, it ensures that the removal effect of fluorine and organic matter is consistent, avoids the risk of overflow in the subsequent oxidation process, and improves the stability and repeatability of the process.

[0019] Optionally, in S2, the amount of pure water added is 2 to 4 times the amount of the first aging slurry; in S5, the amount of one or more of the first oxidized liquid, the first slag washing water, and the second slag washing water added is 2 to 4 times the mass of the second aging slurry.

[0020] By adopting the above technical solution, the solid-liquid ratio in the leaching process is controlled to ensure that lithium elements are fully dissolved and improve the lithium leaching rate; the lithium concentration is avoided from being overly diluted due to excessive liquid volume, which would prevent it from reaching the concentration required for the preparation of battery-grade iron phosphate; at the same time, closed-loop circulation of the slag washing water is achieved to reduce lithium loss and wastewater discharge.

[0021] Optionally, in S1 or S4, the amount of concentrated sulfuric acid added is 0.5 to 1 times that of lithium iron phosphate black powder.

[0022] By adopting the above technical solution, the crystal structure of lithium iron phosphate is fully destroyed, achieving efficient pre-leaching of lithium and improving the removal of residual fluorine and organic matter such as binders from the black powder.

[0023] Optionally, in S1 or S4, the stirring and simmering time is 1 to 3 hours.

[0024] By adopting the above technical solution, the reaction between concentrated sulfuric acid and lithium iron phosphate is fully guaranteed, the decomposition and removal of fluorine and organic matter are improved, and the risk of subsequent oxidation tank overflow is reduced; the crystal structure of lithium iron phosphate is fully destroyed, creating conditions for the efficient dissolution of lithium in the subsequent leaching stage.

[0025] Optionally, in S2 or S5, the temperature of the stirring reaction is 70~90℃ and the reaction time is 1~2h.

[0026] By adopting the above technical solution, the residual heat generated by the ripening of concentrated sulfuric acid can be used to maintain this temperature range without additional heating, which greatly reduces energy consumption; the lithium dissolution rate is the fastest at this temperature, thus improving leaching efficiency.

[0027] Optionally, in S2 or S5, sulfuric acid is added to control the pH value between 1.0 and 1.5.

[0028] By adopting the above technical solution, while ensuring a high lithium leaching rate, the excessive dissolution of iron and phosphorus is suppressed, reducing oxygen consumption and iron-phosphorus slag volume in the subsequent iron removal stage; avoiding excessive acid due to excessively low pH, which would increase subsequent neutralization costs, and insufficient lithium leaching due to excessively high pH, ​​which would lead to a decrease in lithium recovery rate.

[0029] Optionally, in S3 or S6, the stirring reaction time is 1 to 5 hours.

[0030] By adopting the above technical solution, the oxygenation time is adjusted according to the iron content in the leachate to ensure that ferrous iron is completely oxidized to ferric iron and combines with phosphate to form ferric phosphate precipitate, thus achieving efficient separation of iron and phosphorus from lithium. If the oxygenation time is too short, the iron removal will be incomplete and the subsequent impurity removal will be more difficult. If the oxygenation time is too long, the production efficiency will be reduced and the energy consumption will be increased.

[0031] Secondly, this application provides an iron-phosphorus slag that can be directly used to prepare battery-grade iron phosphate, namely, a first iron-phosphorus slag and / or a second iron-phosphorus slag prepared by a lithium iron phosphate black powder leaching method of this application.

[0032] This application discloses a lithium iron phosphate black powder leaching method that produces iron-phosphorus slag in which graphite is removed, and the content of impurities such as aluminum and copper is low. The iron-phosphorus molar ratio meets the standard requirements for battery-grade iron phosphate. It can be directly used to prepare battery-grade iron phosphate without going through complicated impurity removal, decarbonization and composition adjustment processes, which greatly improves the utilization value of by-products and reduces the overall cost of recycling waste lithium iron phosphate batteries.

[0033] In summary, this invention utilizes the residual heat from the reaction of concentrated sulfuric acid with lithium iron phosphate to provide leaching heat, and uses atmospheric pressure oxygen instead of hydrogen peroxide as the oxidant, significantly reducing the cost of the oxidant. The lithium solution is concentrated through cyclic leaching of lithium-rich solution, eliminating the need for further concentration before direct lithium precipitation after impurity removal, thus improving the lithium leaching recovery rate and significantly enhancing the economic and environmental benefits of recycling waste lithium iron phosphate batteries. Furthermore, it achieves stepwise separation of carbon slag and iron-phosphorus slag, preventing graphite from mixing into the iron-phosphorus slag. The resulting first and second iron-phosphorus slags can be directly used to prepare battery-grade iron phosphate. Attached Figure Description

[0034] Figure 1 This is a flowchart of a lithium iron phosphate black powder leaching method in an embodiment of this application. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] This application designs a lithium leaching method for lithium iron phosphate black powder, including the following steps:

[0037] S1. Mix lithium iron phosphate black powder with pure water to form a slurry, add concentrated sulfuric acid, stir and simmer to obtain the first aging slurry;

[0038] S2. Add pure water to the first matured slurry, add sulfuric acid to control the pH value, stir the reaction, and separate the solid and liquid to obtain the first leaching residue and the first leaching liquid. The first leaching residue is washed to obtain the first leaching water.

[0039] S3. Oxygen is introduced into the first leachate, the reaction is stirred, and the solid and liquid are separated to obtain the first iron-phosphorus slag and the first oxidized liquid. The first iron-phosphorus slag is washed to obtain the second washing water.

[0040] S4. Add the same amount of lithium iron phosphate black powder as S1 to the first oxidized liquid, then add concentrated sulfuric acid, stir and simmer to obtain the second aging slurry.

[0041] S5. Add one or more of the first oxidized liquid, the first slag washing water and the second slag washing water to the second matured slurry, add sulfuric acid to control the pH value, stir the reaction, and separate the solid and liquid to obtain the second leaching residue and the second leaching liquid. The second leaching residue is washed to obtain the third slag washing water.

[0042] S6. Introduce oxygen into the second leachate, stir and react, and separate the solid and liquid to obtain the second iron-phosphorus slag and the second oxidized liquid.

[0043] The first and second iron-phosphorus slags can be directly used to prepare battery-grade iron phosphate.

[0044] Existing technologies generally use steam heating for leaching, and the concentration of lithium solution leached in a single leaching is low. It is necessary to add evaporation and concentration equipment to precipitate lithium, which results in high energy consumption. Hydrogen peroxide is used as an oxidant, which is easy to decompose and has a low utilization rate. The cost of the oxidant is also high. Existing technologies first oxidize to remove iron and then separate carbon slag, which leads to graphite being mixed into iron-phosphorus slag. Iron-phosphorus slag can only be treated as hazardous waste and cannot be utilized for high-value purposes.

[0045] In response to the aforementioned problems of existing technologies through long-term industrial production practice, the inventors developed a process of simmering and ripening with concentrated sulfuric acid. This process utilizes the large amount of heat released from the reaction of concentrated sulfuric acid with lithium iron phosphate to heat the slurry to a suitable reaction temperature, eliminating the need for additional heating. Furthermore, the ripening process with concentrated sulfuric acid disrupts the stable crystal structure of lithium iron phosphate, making it easier to oxidize ferrous iron. Oxidation can also be achieved efficiently using oxygen at atmospheric pressure instead of hydrogen peroxide, reducing the cost of the oxidant. By circulating lithium-rich solution for leaching, the lithium-rich oxidized solution obtained in the first step is used to leach a second batch of new black powder, achieving a cumulative increase in lithium concentration. Moreover, by adjusting the solid-liquid separation sequence, carbon slag is filtered and separated before iron removal through oxidation, resulting in high-purity iron-phosphorus slag with low graphite content, which can be directly used to prepare battery-grade iron phosphate.

[0046] This application also designs an iron-phosphorus slag that can be directly used to prepare battery-grade iron phosphate, using a lithium iron phosphate black powder leaching method of this application to prepare the first iron-phosphorus slag and / or the second iron-phosphorus slag.

[0047] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products.

[0048] Lithium iron phosphate black powder: lithium content 4.04%, iron content 32.1%, phosphorus content 18.5%. Specific Implementation

[0049] Example 1

[0050] Add 400mL of pure water to a 5L reactor, turn on the stirring device, control the stirring speed at 200r / min, slowly add 400g of lithium iron phosphate black powder, and stir evenly to form a uniform slurry.

[0051] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. After the dropwise addition was completed, the mixture was stirred and simmered for 1.5 hours. The heat released from the reaction of concentrated sulfuric acid and lithium iron phosphate was used to maintain the temperature of the system, and the first matured slurry was obtained.

[0052] Add 800 mL of pure water to the first matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add a small amount of concentrated sulfuric acid according to the pH value change of the system, stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5 h.

[0053] After the reaction was completed, a plate and frame filter press was used for solid-liquid separation to obtain the first leached carbon slag and the first leachate. The first leached carbon slag was washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the first washing water were obtained.

[0054] The first leachate was transferred to an oxidation reactor, and stirring was started at a speed of 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 2 hours.

[0055] After the oxidation reaction is completed, plate and frame filter press is performed again to obtain the first iron-phosphorus slag and the first post-oxidation liquid. The first iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the first iron-phosphorus slag product and the second washing slag water are obtained.

[0056] Add 400 mL of the first oxidized liquid to another 5 L reactor, start stirring at 200 r / min, add 400 g of lithium iron phosphate black powder from the same batch as in step 1, and stir until a slurry is formed.

[0057] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry over a period of 30 minutes. After the addition was complete, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0058] Add 800 mL of the first oxidation liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add concentrated sulfuric acid to stabilize the pH value at 1.0~1.5, and continue stirring for 1.5 h.

[0059] After the reaction is completed, plate and frame filter press is performed to obtain the second leached carbon slag and the second leachate. The second leached carbon slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the third washing water are obtained.

[0060] The second leachate was transferred to an oxidation reactor, and stirring was started at 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 2 hours.

[0061] After the oxidation reaction is completed, plate and frame filter press is performed to obtain the second iron-phosphorus slag and the second post-oxidation liquid. The second iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the second iron-phosphorus slag product and the fourth washing water are obtained.

[0062] Example 2

[0063] Add 400 mL of pure water to a 5 L reactor, turn on the stirring device, control the stirring speed at 200 r / min, slowly add 400 g of lithium iron phosphate black powder of the same batch as in Example 1, and stir evenly to form a uniform slurry.

[0064] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. After the dropwise addition was completed, the mixture was stirred and simmered for 1.5 hours. The system temperature was maintained by using the exothermic reaction to obtain the first matured slurry.

[0065] Add 800 mL of pure water to the first matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add a small amount of concentrated sulfuric acid according to the pH value change, stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5 h.

[0066] After the reaction was completed, a plate and frame filter press was used for solid-liquid separation to obtain the first leached carbon slag and the first leachate. The first leached carbon slag was washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the first washing water were obtained.

[0067] The first leachate was transferred to an oxidation reactor, and stirring was started at a speed of 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 3 hours.

[0068] After the oxidation reaction is completed, plate and frame filter press is performed again to obtain the first iron-phosphorus slag and the first post-oxidation liquid. The first iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the first iron-phosphorus slag product and the second washing slag water are obtained.

[0069] Add 400 mL of the first oxidized liquid to another 5 L reactor, start stirring at 200 r / min, add 400 g of lithium iron phosphate black powder of the same batch as in Example 1, and stir evenly to form a slurry.

[0070] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry over a period of 30 minutes. After the addition was complete, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0071] Add 800 mL of the first oxidation liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add concentrated sulfuric acid to stabilize the pH value at 1.0~1.5, and continue stirring for 1.5 h.

[0072] After the reaction is completed, plate and frame filter press is performed to obtain the second leached carbon slag and the second leachate. The second leached carbon slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the third washing water are obtained.

[0073] The second leachate was transferred to an oxidation reactor, and stirring was started at 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 3 hours.

[0074] After the oxidation reaction is completed, plate and frame filter press is performed to obtain the second iron-phosphorus slag and the second post-oxidation liquid. The second iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the second iron-phosphorus slag product and the fourth washing water are obtained.

[0075] Example 3

[0076] The difference between this embodiment and Embodiment 1 is that the stirring reaction time is 4 hours; the details are as follows.

[0077] Add 400mL of pure water to a 5L reactor, turn on the stirring device, control the stirring speed at 200r / min, slowly add 400g of lithium iron phosphate black powder, and stir evenly to form a uniform slurry.

[0078] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. After the dropwise addition was completed, the mixture was stirred and simmered for 1.5 hours. The heat released from the reaction of concentrated sulfuric acid and lithium iron phosphate was used to maintain the temperature of the system, and the first matured slurry was obtained.

[0079] Add 800 mL of pure water to the first matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add a small amount of concentrated sulfuric acid according to the pH value change of the system, stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5 h.

[0080] After the reaction was completed, a plate and frame filter press was used for solid-liquid separation to obtain the first leached carbon slag and the first leachate. The first leached carbon slag was washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the first washing water were obtained.

[0081] The first leachate was transferred to an oxidation reactor, and stirring was started at a speed of 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 4 hours.

[0082] After the oxidation reaction is completed, plate and frame filter press is performed again to obtain the first iron-phosphorus slag and the first post-oxidation liquid. The first iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the first iron-phosphorus slag product and the second washing slag water are obtained.

[0083] Add 400 mL of the first oxidized liquid to another 5 L reactor, start stirring at 200 r / min, add 400 g of lithium iron phosphate black powder from the same batch as in step 1, and stir until a slurry is formed.

[0084] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry over a period of 30 minutes. After the addition was complete, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0085] Add 800 mL of the first oxidation liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add concentrated sulfuric acid to stabilize the pH value at 1.0~1.5, and continue stirring for 1.5 h.

[0086] After the reaction is completed, plate and frame filter press is performed to obtain the second leached carbon slag and the second leachate. The second leached carbon slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the third washing water are obtained.

[0087] The second leachate was transferred to an oxidation reactor, and stirring was started at 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 4 hours.

[0088] After the oxidation reaction is completed, plate and frame filter press is performed to obtain the second iron-phosphorus slag and the second post-oxidation liquid. The second iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the second iron-phosphorus slag product and the fourth washing water are obtained.

[0089] Example 4

[0090] The difference between this embodiment and Embodiment 1 is that the amount of pure water added is 1 times the mass of lithium iron phosphate black powder; the amount of the first oxidation liquid added is 2 times the mass of lithium iron phosphate black powder; the details are as follows.

[0091] Add 800mL of pure water to a 5L reactor, turn on the stirring device, control the stirring speed at 200r / min, slowly add 800g of lithium iron phosphate black powder, and stir evenly to form a uniform slurry.

[0092] 800g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. After the dropwise addition was completed, the mixture was stirred and simmered for 1.5 hours. The heat released from the reaction of concentrated sulfuric acid and lithium iron phosphate was used to maintain the temperature of the system, and the first aging slurry was obtained.

[0093] Add 1600mL of pure water to the first matured slurry, adjust the stirring speed to 300r / min, control the reaction temperature at 80±2℃, add a small amount of concentrated sulfuric acid according to the pH value change of the system, stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5h.

[0094] After the reaction was completed, a plate and frame filter press was used for solid-liquid separation to obtain the first leached carbon slag and the first leachate. The first leached carbon slag was washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the first washing water were obtained.

[0095] The first leachate was transferred to an oxidation reactor, and stirring was started at a speed of 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 3 hours.

[0096] After the oxidation reaction is completed, plate and frame filter press is performed again to obtain the first iron-phosphorus slag and the first post-oxidation liquid. The first iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the first iron-phosphorus slag product and the second washing slag water are obtained.

[0097] Add 800 mL of the first oxidation liquid to another 5L reactor, start stirring at 200 r / min, add 400 g of lithium iron phosphate black powder from the same batch as in step 1, and stir until a slurry is formed.

[0098] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry over a period of 30 minutes. After the addition was complete, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0099] Add 1600 mL of the first oxidation liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add concentrated sulfuric acid to stabilize the pH value at 1.0~1.5, and continue stirring for 1.5 h.

[0100] After the reaction is completed, plate and frame filter press is performed to obtain the second leached carbon slag and the second leachate. The second leached carbon slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the third washing water are obtained.

[0101] The second leachate was transferred to an oxidation reactor, and stirring was started at 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 3 hours.

[0102] After the oxidation reaction is completed, plate and frame filter press is performed to obtain the second iron-phosphorus slag and the second post-oxidation liquid. The second iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the second iron-phosphorus slag product and the fourth washing water are obtained.

[0103] Example 5

[0104] The difference between this embodiment and Embodiment 1 is that the amount of pure water added is 1 times the mass of lithium iron phosphate black powder; the amount of the first oxidation liquid added is 3 times the mass of lithium iron phosphate black powder; as detailed below.

[0105] Add 1200mL of pure water to a 5L reactor, turn on the stirring device, control the stirring speed at 200r / min, slowly add 1200g of lithium iron phosphate black powder, and stir evenly to form a uniform slurry.

[0106] 1200g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. After the dropwise addition was completed, the mixture was stirred and simmered for 1.5 hours. The heat released from the reaction of concentrated sulfuric acid and lithium iron phosphate was used to maintain the temperature of the system, and the first aging slurry was obtained.

[0107] Add 2400 mL of pure water to the first matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add a small amount of concentrated sulfuric acid according to the pH value change of the system, stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5 h.

[0108] After the reaction was completed, a plate and frame filter press was used for solid-liquid separation to obtain the first leached carbon slag and the first leachate. The first leached carbon slag was washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the first washing water were obtained.

[0109] The first leachate was transferred to an oxidation reactor, and stirring was started at a speed of 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 2 hours.

[0110] After the oxidation reaction is completed, plate and frame filter press is performed again to obtain the first iron-phosphorus slag and the first post-oxidation liquid. The first iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the first iron-phosphorus slag product and the second washing slag water are obtained.

[0111] Add 1200mL of the first oxidation liquid to another 5L reactor, start stirring at 200r / min, add 400g of lithium iron phosphate black powder of the same batch as in step 1, and stir evenly to form a slurry.

[0112] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry over a period of 30 minutes. After the addition was complete, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0113] Add 2400 mL of the first oxidation liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add concentrated sulfuric acid to stabilize the pH value at 1.0~1.5, and continue stirring for 1.5 h.

[0114] After the reaction is completed, plate and frame filter press is performed to obtain the second leached carbon slag and the second leachate. The second leached carbon slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the third washing water are obtained.

[0115] The second leachate was transferred to an oxidation reactor, and stirring was started at 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 2 hours.

[0116] After the oxidation reaction is completed, plate and frame filter press is performed to obtain the second iron-phosphorus slag and the second post-oxidation liquid. The second iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the second iron-phosphorus slag product and the fourth washing water are obtained.

[0117] Example 6

[0118] The difference between this embodiment and Embodiment 1 is that the amount of pure water added is 1 times the mass of lithium iron phosphate black powder; the amount of the first oxidation liquid added is 4 times the mass of lithium iron phosphate black powder; as detailed below.

[0119] Add 800mL of pure water to a 5L reactor, turn on the stirring device, control the stirring speed at 200r / min, slowly add 800g of lithium iron phosphate black powder, and stir evenly to form a uniform slurry.

[0120] 800g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. After the dropwise addition was completed, the mixture was stirred and simmered for 1.5 hours. The heat released from the reaction of concentrated sulfuric acid and lithium iron phosphate was used to maintain the temperature of the system, and the first aging slurry was obtained.

[0121] Add 1600mL of pure water to the first matured slurry, adjust the stirring speed to 300r / min, control the reaction temperature at 80±2℃, add a small amount of concentrated sulfuric acid according to the pH value change of the system, stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5h.

[0122] After the reaction was completed, a plate and frame filter press was used for solid-liquid separation to obtain the first leached carbon slag and the first leachate. The first leached carbon slag was washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the first washing water were obtained.

[0123] The first leachate was transferred to an oxidation reactor, and stirring was started at a speed of 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 3 hours.

[0124] After the oxidation reaction is completed, plate and frame filter press is performed again to obtain the first iron-phosphorus slag and the first post-oxidation liquid. The first iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the first iron-phosphorus slag product and the second washing slag water are obtained.

[0125] Add 800 mL of the first oxidation liquid to another 5L reactor, start stirring at 200 r / min, add 200 g of lithium iron phosphate black powder from the same batch as in step 1, and stir until a slurry is formed.

[0126] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry over a period of 30 minutes. After the addition was complete, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0127] Add 1600 mL of the first oxidation liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80±2℃, add concentrated sulfuric acid to stabilize the pH value at 1.0~1.5, and continue stirring for 1.5 h.

[0128] After the reaction is completed, plate and frame filter press is performed to obtain the second leached carbon slag and the second leachate. The second leached carbon slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the carbon slag. After washing, clean carbon slag and the third washing water are obtained.

[0129] The second leachate was transferred to an oxidation reactor, and stirring was started at 250 r / min. Industrial pure oxygen was introduced at a flow rate of 0.5 L / min, and the reaction was carried out for 3 hours.

[0130] After the oxidation reaction is completed, plate and frame filter press is performed to obtain the second iron-phosphorus slag and the second post-oxidation liquid. The second iron-phosphorus slag is washed in two stages of countercurrent, and the washing water volume is twice the mass of the iron-phosphorus slag. After washing, the second iron-phosphorus slag product and the fourth washing water are obtained.

[0131] The lithium leaching recovery rate is calculated as follows: (total lithium content carried in by lithium iron phosphate black powder - total lithium content in slag) / total lithium content carried in by lithium iron phosphate black powder × 100%. The test results are shown in Table 1.

[0132] Table 1

[0133] As shown in Examples 1-6 and Table 1, this invention utilizes the residual heat from the reaction of concentrated sulfuric acid with lithium iron phosphate to provide leaching heat, and uses atmospheric pressure oxygen instead of hydrogen peroxide as the oxidant, significantly reducing the cost of the oxidant. The lithium solution is concentrated to over 19.65 g / L through lithium-rich liquid cyclic leaching, eliminating the need for further concentration and allowing direct lithium precipitation after impurity removal. Simultaneously, the lithium leaching recovery rate is increased to over 99.30%, significantly improving the economic and environmental benefits of recycling waste lithium iron phosphate batteries. Furthermore, the stepwise separation of carbon slag and iron-phosphorus slag is achieved, preventing graphite from mixing into the iron-phosphorus slag. The resulting first and second iron-phosphorus slags have undetectable graphite content and aluminum content below 0.16%, making them suitable for direct use in preparing battery-grade iron phosphate.

[0134] As can be seen from Examples 1-3 and Table 1, increasing the oxygenation time is more conducive to improving the lithium recovery rate.

[0135] As shown in Examples 1, 4-6, and Table 1, in Example 1, when the amount of black powder added in the second oxidation stage was the same as that in the first stage, and the amount of liquid used after slurry oxidation was the same as that used in the first stage, the lithium concentration in the liquid after the second oxidation stage was the highest, reaching 19.65 g / L. As the liquid-to-solid ratio increased in the second aging process, the final lithium concentration continued to decrease, essentially returning to the concentration level of a single leaching, thus negating the purpose of cyclic concentration and requiring subsequent concentration equipment. Therefore, only by maintaining a consistent solid-to-liquid ratio and adding the same amount of black powder in both aging stages can the lithium concentration be cumulatively increased, truly eliminating the need for a concentration step. If the amount of black powder added in the second stage is insufficient or the liquid ratio is too high, the concentration effect is generally poor.

[0136] Comparative Example 1

[0137] Add 2400mL of pure water to a 5L reactor, start stirring, add 800g of lithium iron phosphate black powder, and stir evenly to form a slurry.

[0138] Heat the mixture to 80℃±2℃ by introducing steam, then slowly add 800g of concentrated sulfuric acid with a mass fraction of 98.4%, controlling the pH value at 1.0~1.5, and stir the reaction for 2 hours.

[0139] Slowly add 400g of hydrogen peroxide with a mass fraction of 27.5% over 1 hour, and continue stirring for another hour to oxidize and remove iron.

[0140] After the reaction was completed, plate and frame filter press was performed to obtain iron-phosphorus-carbon mixed slag and leachate; the mixed slag was washed in three stages of countercurrent to obtain washing water and waste residue.

[0141] After impurities are removed from the leachate, a lithium-rich solution is obtained.

[0142] Table 2

[0143] The lithium recovery rate of the technical solution of this invention can reach over 99.30%, which is higher than 99.01% of Comparative Example 1. The stepwise leaching method allows for more complete dissolution of lithium. The lithium concentration of the leachate in Comparative Example 1 is only 12.41 g / L, which cannot meet the requirements for direct lithium precipitation and must undergo a concentration process. The leachate of this invention can directly enter the impurity removal and lithium precipitation process, eliminating the need for a concentration process.

[0144] Comparative Example 1 yielded a mixed iron-phosphorus-carbon slag with high graphite content and 0.28% aluminum impurities, which could not be directly used to prepare battery-grade iron phosphate. The iron-phosphorus slag obtained by this invention is free of graphite and has low impurities, and can be directly used as a raw material for the production of battery-grade iron phosphate, making it a valuable byproduct of the process in this application.

[0145] Comparative Example 2

[0146] The difference between this comparative example and Example 1 is that the leachate pulp is not subjected to solid-liquid separation, but directly undergoes oxidation reaction. The specific steps are as follows.

[0147] Add 400mL of pure water to a 5L reactor, turn on the stirring device, control the stirring speed at 200r / min, slowly add 400g of lithium iron phosphate black powder of the same batch as in Example 1, and stir evenly to form a uniform slurry without lumps.

[0148] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the above slurry. The dropwise addition process was completed within 30 minutes. During the dropwise addition, stirring was maintained to avoid local overheating. After the dropwise addition was completed, stirring was continued and the mixture was simmered for 1.5 hours. The heat released from the reaction of concentrated sulfuric acid and lithium iron phosphate was used to maintain the temperature of the system, and the first aging slurry was obtained.

[0149] Add 800 mL of pure water to the first matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80℃±2℃, add a small amount of concentrated sulfuric acid according to the pH value change of the system, stabilize the pH value in the range of 1.0~1.5, continue stirring and reacting for 1.5 h to obtain the first leachate slurry.

[0150] The first leaching slurry was directly transferred to the oxidation reactor without pre-solid-liquid separation; stirring was started at a speed of 250 r / min, and industrial pure oxygen was introduced at a flow rate of 0.5 L / min. The reaction was carried out for 4 hours to obtain the first oxidation slurry.

[0151] After the oxidation reaction is completed, a plate and frame filter press is used for solid-liquid separation to obtain the first iron-phosphorus-carbon mixed slag and the first post-oxidation liquid. The first iron-phosphorus-carbon mixed slag is washed in three stages of countercurrent, and the washing water volume is three times the mass of the mixed slag. After washing, waste residue and the first washing water are obtained.

[0152] Add 400 mL of the first oxidized liquid to another 5 L reactor, start stirring at 200 r / min, add 400 g of lithium iron phosphate black powder of the same batch as in Example 1, and stir until a uniform slurry without lumps is formed.

[0153] 400g of concentrated sulfuric acid with a mass fraction of 98.4% was slowly added dropwise to the slurry, with the addition time controlled within 30 minutes. After the addition was completed, the mixture was stirred and simmered for 1.5 hours to obtain the second matured slurry.

[0154] Add 800 mL of the first oxidized liquid to the second matured slurry, adjust the stirring speed to 300 r / min, control the reaction temperature at 80℃±2℃, add concentrated sulfuric acid to stabilize the pH value in the range of 1.0~1.5, and continue stirring for 1.5 h to obtain the second leachate slurry.

[0155] The second leaching slurry was directly transferred to the oxidation reactor without pre-solid-liquid separation; stirring was started at a speed of 250 r / min, and industrial pure oxygen was introduced at a flow rate of 0.5 L / min. The reaction was carried out for 4 hours to obtain the second oxidized slurry.

[0156] After the oxidation reaction is completed, a plate and frame filter press is used for solid-liquid separation to obtain a second iron-phosphorus-carbon mixed slag and a second post-oxidation liquid. The second iron-phosphorus-carbon mixed slag is washed in three stages of countercurrent washing, with the washing water volume being three times the mass of the mixed slag. After washing, waste residue and second washing water are obtained.

[0157] Table 3

[0158] The lithium recovery rate and final lithium concentration of the technical solution in Comparative Example 2 are similar to those in Example 1. Example 1 and Comparative Example 2 have little impact on the leaching and concentration of lithium, but the quality of the byproduct iron-phosphorus slag decreases. Comparative Example 2 yields a mixed iron-phosphorus-carbon slag, with graphite and iron phosphate precipitates mixed together, and an aluminum content of 0.25%, making it unsuitable for direct use in the preparation of battery-grade iron phosphate. To achieve high-value utilization, decarbonization and impurity removal processes are required.

[0159] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for leaching lithium iron phosphate black powder, characterized in that, Includes the following steps: S1. Mix lithium iron phosphate black powder with pure water to form a slurry, add concentrated sulfuric acid, stir and simmer to obtain the first aging slurry; S2. Add pure water to the first matured slurry, add sulfuric acid to control the pH value, stir the reaction, and separate the solid and liquid to obtain the first leaching residue and the first leaching liquid. The first leaching residue is washed to obtain the first leaching water. S3. Oxygen is introduced into the first leachate, the reaction is stirred, and the solid and liquid are separated to obtain the first iron-phosphorus slag and the first oxidized liquid. The first iron-phosphorus slag is washed to obtain the second washing water. S4. Add the same amount of lithium iron phosphate black powder as S1 to the first oxidized liquid, then add concentrated sulfuric acid, stir and simmer to obtain the second aging slurry. S5. Add one or more of the first oxidized liquid, the first slag washing water and the second slag washing water to the second matured slurry, add sulfuric acid to control the pH value, stir the reaction, and separate the solid and liquid to obtain the second leaching residue and the second leaching liquid. The second leaching residue is washed to obtain the third slag washing water. S6. Introduce oxygen into the second leachate, stir and react, and separate the solid and liquid to obtain the second iron-phosphorus slag and the second oxidized liquid. The first and second iron-phosphorus slags can be directly used to prepare battery-grade iron phosphate.

2. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S3 or S6, the stirring reaction time is 1 to 5 hours.

3. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S1, the amount of pure water added is 1 to 4 times the mass of lithium iron phosphate black powder; in S4, the amount of the first oxidized liquid added is 1 to 4 times the mass of lithium iron phosphate black powder.

4. The lithium leaching method for lithium iron phosphate black powder according to claim 3, characterized in that, In S1 and S4, the amount of pure water added is a multiple of the mass of lithium iron phosphate black powder, which is the same as the amount of the first oxidized liquid added being a multiple of the mass of lithium iron phosphate black powder.

5. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S2, the amount of pure water added is 2 to 4 times the mass of the first aging slurry; in S5, the amount of one or more of the first oxidized liquid, the first slag washing water, and the second slag washing water added is 2 to 4 times the mass of the second aging slurry.

6. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S1 or S4, the amount of concentrated sulfuric acid added is 0.5 to 1 times that of lithium iron phosphate black powder.

7. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S1 or S4, the stirring and simmering time is 1 to 3 hours.

8. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S2 or S5, the temperature of the stirring reaction is 70~90℃ and the reaction time is 1~2h.

9. The lithium leaching method for lithium iron phosphate black powder according to claim 1, characterized in that, In S2 or S5, sulfuric acid is added to control the pH value between 1.0 and 1.

5.

10. An iron-phosphorus slag directly used for the preparation of battery-grade iron phosphate, characterized in that, The first iron-phosphorus slag and / or the second iron-phosphorus slag are prepared by any one of the lithium iron phosphate black powder leaching methods described in claims 1 to 9.

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