Method for removing aluminum from waste lithium iron phosphate black powder and comprehensively utilizing waste lithium iron phosphate black powder

Abstract

The invention discloses a method for removing aluminum from waste lithium iron phosphate black powder and comprehensively utilizing the waste lithium iron phosphate black powder. According to the method, Cr < 3 + > is added to induce crystal nucleus to form removed aluminum. The method has the following advantages that (1) aluminum is efficiently removed, specifically, the Cr < 3 + > induced precipitation technology is adopted, and deep removal of aluminum is achieved at high temperature and low pH; 2) the lithium recovery rate is high: the recovery rate of lithium in the purified liquid exceeds 99%, and the purified liquid can be directly used for preparing battery grade Li2CO3 and FePO4; 3) flow simplification: compared with the prior art, the flow is simpler and more efficient, the whole process is carried out under normal pressure, and the method has good operability and industrial application potential, and 4) environmental protection and economic benefits: no excessive harmful substances are introduced in the whole process, the influence on the environment is reduced, and good economic benefits are realized through comprehensive recovery of resources.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium iron phosphate battery recycling, and specifically relates to a method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization. Background Art

[0002] With the development of sustainable economy and the growing demand for green energy, lithium-ion batteries have been widely used in electric vehicles, electronic devices, aerospace and other fields. As a cathode material, lithium iron phosphate (LiFePO4, referred to as LFP) has become one of the most widely used cathode materials in lithium-ion batteries due to its advantages such as high theoretical capacity, excellent lattice stability and low cost. However, after long-term cycling, the internal structure of the battery will undergo irreversible changes (such as blockage of lithium diffusion channels), which usually limits the battery life to 8-10 years. With the rapid growth of electric vehicles, it is expected that the annual retirement of batteries will reach 30GWh in the next five years, and the generation of a large number of waste batteries is inevitable. It is worth noting that batteries contain toxic organic substances and heavy metals, which will cause great harm to human health and the ecological environment if not handled properly. In addition, batteries also contain a large amount of Li, Fe, P and other resources, which have high recycling value. Therefore, recycling waste lithium iron phosphate batteries is not only of great significance to environmental protection, but also has significant economic benefits.

[0003] At present, the process of industrial-scale recycling of waste lithium iron phosphate batteries is as follows: first, the battery is charged and crushed into powder in a nitrogen atmosphere, and then organic impurities such as binders, diaphragm paper and electrolyte are removed by high-temperature calcination, followed by screening to obtain a copper foil and aluminum foil mixture and battery black powder, and finally the corresponding materials are obtained by separating copper and aluminum. Although the black powder is processed through the above process, it is inevitable that aluminum and copper impurities are mixed in in actual industrialization. Studies have shown that when the aluminum content in the black powder exceeds 50ppm, the battery capacity will be reduced. Therefore, in the process of black powder recycling, how to deeply separate aluminum is one of the key technical problems.

[0004] The aluminum removal processes reported so far are mainly divided into two categories: one is to directly separate aluminum from black powder solids, and the other is to remove aluminum from the leaching solution. The first category mainly dissolves Al2O3 solids into AlO2 by alkali solution. - , such as CN117142449A, CN116553502A, CN113912033A, etc. all introduced related processes. However, research has found that about 5% to 10% of lithium ions are lost during the alkaline washing process, resulting in a decrease in lithium recovery rate and affecting economic benefits. The second type is to first dissolve the black powder with acid to obtain a lithium-containing + , Fe 2+ 、Al 3+ , Cu 2+ PO43- The leaching solution is then converted into precipitate by neutralization or chemical precipitation. The neutralization method is to add NaOH, ammonia, LiOH, Na2CO3 or other substances that can hydrolyze or ionize to produce OH - The solution pH is adjusted to 3-6, and aluminum is precipitated in the form of Al(OH)3, such as the solutions disclosed in CN116750740A, CN110112481A, etc. However, in fact, when the pH is ≥ 3, it is easy to generate LiFePO4 precipitation, resulting in a large loss of lithium and affecting the recovery efficiency. The chemical precipitation method is to precipitate aluminum in the form of aluminum fluoride (AlF3) through precipitants such as sodium fluoride, ammonium fluoride, potassium fluoride, etc., as shown in the solutions disclosed in Chinese patent applications with publication numbers CN11391203A and CN118405674A. Although this method can effectively remove aluminum, the large amount of fluoride ions introduced will not only reduce product performance, but also corrode the pipelines and equipment of the recovery system. In addition, there are further studies on obtaining iron phosphate and lithium solution by selective acid leaching oxidation (such as CN118495566A, CN118637576A, etc.). Since these two products still contain copper and aluminum impurities, they need to be further removed separately, which leads to complicated processes and cumbersome steps, and reduces economic benefits.

[0005] CN113816353A discloses a method for removing aluminum from the acid leaching solution of waste lithium iron phosphate batteries by co-precipitation of iron and aluminum, the steps comprising: acid dissolving black powder to obtain a mixed solution containing iron, lithium and phosphorus; adding hydrogen peroxide for oxidation reaction or adding Fe 3+ To adjust the Fe content in the leaching solution 3+ Concentration of Al 3+ The concentration of the leaching solution is 1.2 to 4 times, and the pH of the leaching solution is adjusted to 0.2 to 7.5 and the temperature is 20 to 90°C to perform a coprecipitation reaction and solid-liquid separation to obtain an aluminum-iron coprecipitate and an aluminum-removed liquid; an excess phosphorus source is added to the aluminum-removed liquid, and an excess of hydrogen peroxide is added to remove Fe 2+ Oxidized to Fe 3+ After that, precipitation reaction is carried out and solid-liquid separation is performed to obtain dihydrated iron phosphate precipitate and lithium-rich solution. 3+ To achieve Al 3+ The precipitation of chlorinated carbon has the advantages of being environmentally friendly and non-toxic. However, the required precipitation reaction time is 10 to 48 hours, resulting in a long production cycle and high operating costs, and does not have a good prospect for industrial application.

[0006] CN116002646A discloses a method for recycling the valuable components in waste lithium iron phosphate batteries. The steps include: leaching the mixed black powder of the positive and negative electrodes of the waste lithium iron phosphate batteries with acid solution, removing titanium from the obtained acid leaching solution by high-temperature coprecipitation, recovering copper by substitution precipitation, coordinating aluminum precipitation, high-temperature high-acid oxidation precipitation of iron phosphate, and washing with hot phosphoric acid to obtain hydrated iron phosphate with good battery performance, and recovering lithium in the form of lithium carbonate. This scheme adds Fe 3+ To achieve the removal of titanium and aluminum, the aluminum removal rate is only 80-90%. In order to achieve deep aluminum removal, sodium fluoride needs to be further added for coordination precipitation. As a result, the entire process is complicated, fluoride ion impurities are introduced, resulting in poor economic and environmental benefits. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization with relatively simple operation, high aluminum and copper removal rates and high lithium recovery rates.

[0008] The technical solution adopted by the present invention to solve the technical problem is to provide a method for removing aluminum from waste lithium iron phosphate black powder and comprehensively utilizing the waste lithium iron phosphate black powder by adding Cr 3+ Induce nucleation to remove aluminum.

[0009] Furthermore, the method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization of the present invention is to add an appropriate amount of Cr 3+ Induce the nucleus formation and promote the formation of Al with Cr by synergistically controlling the pH and temperature of the solution （1-x） Al x It precipitates in the form of PO4 to achieve deep removal of aluminum.

[0010] Furthermore, in the method for removing aluminum from waste lithium iron phosphate black powder and its comprehensive utilization of the present invention, the pH of the solution is controlled to be 0.5-1.5 during the aluminum removal process, and the reaction temperature is 70-110°C.

[0011] The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive recovery of the present invention specifically comprises the following steps: S1, acid leaching: mixing the waste lithium iron phosphate black powder with acid solution and reacting them under stirring to obtain a solution and carbon slag; The solution contains elements such as Li, Fe, P, Al, and Cu; S2, aluminum removal: add a certain amount of inducing precipitation agent Cr to the solution obtained in S1 3+ and acid solution, control the pH value of the solution, react at a certain temperature, and separate the solid and liquid to obtain aluminum removal liquid and aluminum slag.

[0012] S3, copper removal: adding iron powder to the aluminum removal liquid obtained in S2 to perform reduction and copper removal, and solid-liquid separation to obtain purified liquid and copper slag; S4, oxidation separation: after adjusting the pH value and the ratio of the amount of phosphorus and iron substances in the purified liquid obtained in S3, an oxidant is added for oxidation and aging, and solid-liquid separation is performed to obtain a dihydrated iron phosphate precipitate and a lithium-rich liquid; S5. Preparation of anhydrous ferric phosphate: calcining the dihydrated ferric phosphate obtained in S4 to obtain anhydrous ferric phosphate; S6, preparation of lithium carbonate: adjusting the pH of the lithium-rich solution obtained in S4 to remove Fe 3+ , then add carbonate to precipitate lithium to obtain lithium carbonate.

[0013] As a preferred solution, during the acid leaching process in step S1, the acid solution may be any acid solution that can provide free H, such as sulfuric acid, hydrochloric acid, nitric acid, etc. + A single acid solution or a combination of acid solutions. + The concentration is 0.5-6 mol / L, preferably 3-5 mol / L. The liquid-solid ratio of the acid solution to the waste lithium iron phosphate black powder is 1-5 mL / g, preferably 2-4 mL / g. Leaching is carried out at room temperature for more than 2 hours.

[0014] As a preferred solution, the Cr added during the S2 aluminum removal process 3+ It can be provided by at least one of chromium sulfate, chromium chloride or chromium nitrate. More preferably, Cr 3+ The corresponding anions are preferably the same as the anions in the acid solution during the S1 acid leaching process.

[0015] As a preferred solution, Cr is added during the S2 aluminum removal process. 3+ After that, Cr in the solution 3+ The concentration of chromium ions is 0.5-12 g / L, and the preferred concentration is 1-5 g / L. Studies have shown that if the concentration of chromium ions is too low, there are not enough induced nuclei, and the aluminum removal effect is poor; if the concentration of chromium ions is too high, when Cr 3+ When the concentration reaches a certain level, the aluminum removal effect does not change with Cr 3+ The increase in concentration increases, and adding too much chromium ions will cause a waste of raw materials and is uneconomical.

[0016] As a preferred solution, acid solution is added during the aluminum removal process of S2 to control the pH of the solution to 0.5-1.5, preferably 0.8-1.2.

[0017] As a preferred solution, during the S2 aluminum removal process, the acid solution can be any acid solution that can provide free H, such as sulfuric acid, hydrochloric acid, nitric acid, etc. + A single acid solution or a combination of acid solutions.

[0018] As a preferred solution, the reaction temperature in the aluminum removal process of S2 is 70-110°C, preferably 80-100°C. The preferred reaction time is 1-5h. If the aluminum removal temperature is too low, the aluminum removal effect is poor; if the aluminum removal temperature is too high, the aluminum removal effect is no longer improved, and increasing the temperature is meaningless, but consumes extra energy, which is not very economical.

[0019] As a preferred solution, during the copper removal process of S3, the amount of iron powder added is not less than the theoretical molar amount of iron powder required to convert all copper ions into copper. The reaction is carried out at room temperature for 20 to 60 minutes. Excess iron powder can be separated by filtering or other means, and the iron in the obtained iron-copper mixed slag can be dissolved by dilute acid to obtain relatively pure copper powder.

[0020] As a preferred solution, in the S4 oxidation separation process, the pH value of the purified liquid is adjusted to 0.4-1.6, and the ratio of the phosphorus-iron substance is adjusted to 1:1-1.05:1. The phosphorus source used in the process of adjusting the ratio of the phosphorus-iron substance is at least one of phosphoric acid, ammonium phosphate, diammonium phosphate, diammonium hydrogen phosphate, sodium phosphate, and sodium dihydrogen phosphate. Studies have shown that too high or too low pH value and the ratio of the phosphorus-iron substance will affect the synthesis quality of iron phosphate and cannot meet the standards of iron phosphate for batteries.

[0021] As a preferred solution, in the S4 oxidation separation process, the oxidant is at least one of persulfate, hydrogen peroxide, pure oxygen, ozone, and air. The amount of the oxidant added is not less than the amount of Fe 2+ All converted into Fe 3+ Theoretical molar amount of oxidant required.

[0022] As a preferred solution, in the S4 oxidation separation process, the oxidation and aging reaction temperatures are 50-90°C, the oxidation reaction time is 2-3 hours, and the aging time is 1-3 hours.

[0023] As a preferred solution, in the preparation process of S5 anhydrous ferric phosphate, the calcination temperature is 500-700° C. and the calcination time is 2-6 hours.

[0024] As a preferred solution, during the preparation of S6 lithium carbonate, the pH of the lithium-rich solution is adjusted to 3-6, and the unprecipitated Fe 3+ Remove; then adjust the solution pH to 10-13, and the temperature to 90-98°C. Then add carbonate to precipitate lithium. Add carbonate more than 2 times the theoretical molar amount required for lithium ions, that is, add more than 3 times the theoretical molar amount required for lithium ions to ensure complete precipitation of lithium ions.

[0025] As a preferred solution, the substance used to adjust the pH in the preparation process of S6 lithium carbonate is at least one of sodium hydroxide, ammonia water, lithium hydroxide and sodium carbonate.

[0026] As a preferred solution, the carbonate in the S6 lithium carbonate preparation process is at least one of ammonium carbonate, sodium carbonate and ammonium bicarbonate.

[0027] The core of the method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization of the present invention is to add an appropriate amount of Cr 3+ Induce the nucleus formation and promote the formation of Al with Cr by synergistically controlling the pH and temperature of the solution （1-x） Al x PO4 is precipitated to achieve deep removal of aluminum. The method of the present invention can efficiently remove impurities of aluminum and copper (the highest removal rates can reach 99.8% and 99.9%, respectively), and the recovery rate of lithium in the purified solution can reach up to 99%, and battery-grade Li2CO3 and FePO4 products can be further obtained, thereby realizing the full resource utilization of valuable elements in black powder. The whole process is simple and efficient, and the whole process is carried out under normal pressure, with good operability, significant economic and social benefits, and suitable for large-scale industrial production.

[0028] The main process flow of the invention for removing aluminum from waste lithium iron phosphate battery black powder and its comprehensive utilization is: acid leaching, precipitation to remove aluminum, iron powder to remove copper, oxidation aging of iron phosphate and carbonate precipitation of lithium, so as to achieve full resource recovery of valuable components in black powder. The acid leaching solution mainly contains Li + , Fe 2+ , Cu 2+ 、Al 3+ PO4 3- When the pH of the acid leaching solution is ≥3, it is easy to form LiFePO4 precipitation, resulting in Li + A large amount of loss occurs, so the pH of the solution must be strictly controlled during the aluminum removal process. Studies have shown that when the pH value of the solution is 0-4, PO4 3- The order of precipitates formed with ions from easy to difficult is Cr 3+ >Fe 3+ >Fe 2+ >Cu 2+ Therefore, the key to the technical solution of the present invention is to add a small amount of inducing precipitation agent Cr 3+ Provides nucleation seeds and promotes the Cr precipitate induced by aluminum at high temperature (1-x) Al x PO4 precipitate, thus achieving deep removal of aluminum from the acid leaching solution under low pH and high temperature conditions. 3+ , but it is only used as an inducing precipitant and the required amount is very small; and it has been verified by experiments that the Cr in the final immersion solution 3+ Only 1-8 mg / L, which meets the requirements of iron phosphate and lithium carbonate for batteries.

[0029] Compared with the prior art, the technical solution of the present invention has the following advantages: 1) Efficient aluminum removal: using Cr 3+ Induced precipitation technology achieves deep removal of aluminum at high temperature and low pH.

[0030] 2) High lithium recovery rate: The lithium recovery rate in the purified liquid exceeds 99%, and can be directly used to prepare battery-grade Li2CO3 and FePO4.

[0031] 3) Process simplification: Compared with existing technologies, the process is simpler and more efficient. The entire process is carried out under normal pressure and has good operability and potential for industrial application.

[0032] 4) Environmental protection and economic benefits: The entire process does not introduce excessive harmful substances, reducing the impact on the environment, and achieving good economic benefits through comprehensive recycling of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0034] Figure 1 This is the XRD pattern of the iron phosphate recovered in Example 1; Figure 2 This is the XRD pattern of the lithium carbonate recovered in Example 1; Figure 3 This is the precipitation efficiency diagram of aluminum at different reaction temperatures. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0036] Example 1

[0037] The contents of main elements in the black powder of waste lithium iron phosphate batteries used in this embodiment are shown in Table 1.

[0038]

[0039] The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive recovery of the present embodiment specifically comprises the following steps: S1, acid leaching: 100g of waste lithium iron phosphate black powder and 1.7mol / L sulfuric acid solution (hydrogen ion concentration is 3.4mol / L) are uniformly mixed at a liquid-solid ratio of 3mL / g, stirred for reaction at room temperature for 2h, and centrifuged to obtain a solution and carbon slag; the solution contains elements such as Li, Fe, P, Al, and Cu; S2, aluminum removal: add appropriate amount of Cr2(SO4)3 and H2SO4 to the solution obtained in S1 to initiate precipitation reaction and control the Cr content in the solution system. 3+ The concentration is 3.6 g / L, the pH of the solution system is adjusted to 0.96, the reaction temperature is 90°C, the reaction time is 3 hours, and after the reaction is completed, centrifugal filtration is performed to obtain aluminum removal liquid and aluminum slag; S3, copper removal: add iron powder to the aluminum removal liquid obtained in S2 (the amount of iron powder added is 1 times the theoretical molar amount of iron powder required to convert all copper ions into copper), react at room temperature for 30 minutes to reduce and remove copper, and separate the solid and liquid to obtain a purified liquid and copper slag; S4, oxidation separation: phosphoric acid is added to the purified solution obtained in S3, so that the ratio of phosphorus and iron in the solution is 1.02:1 and the pH value is 1.6, and H2O2 is added (the amount of H2O2 added is 2+ All converted into Fe 3+ The mixture was added with 1.2 times the theoretical molar amount of the required oxidant), and then placed in a water bath at 70°C for oxidation reaction for 2 hours and aged for 3 hours, filtered, washed, and dried to obtain ferric phosphate dihydrate and lithium-rich solution; S5. Preparation of anhydrous iron phosphate: calcining the dihydrated iron phosphate obtained in S4 at 500° C. for 6 h to obtain anhydrous iron phosphate; S6. Preparation of lithium carbonate: Add NaOH to the lithium-rich solution obtained in S4 to adjust the pH to 3.5, and remove the unprecipitated Fe 3+ ; Then adjust the pH of the solution to 11, the temperature to 90°C, add sodium carbonate in an excess of 2 times the theoretical molar amount required for lithium ions, stir the reaction for 1 hour, centrifuge and filter the precipitate, then wash it twice with hot water to obtain battery-grade lithium carbonate.

[0040] Embodiments 2 to 11 The methods of Examples 2 to 5 are the same as those of Example 1, except for the sulfuric acid concentration and liquid-to-solid ratio in step S1. The specific parameters are shown in Table 2.

[0041]

[0042] It can be seen from Table 2 that, by comparing Examples 1 to 5, the sulfuric acid concentration and liquid-to-solid ratio during the acid leaching process will affect the lithium leaching rate. However, in order to maximize the lithium recovery rate, the experiment should be carried out under the optimal lithium leaching conditions.

[0043] The methods of Examples 6 to 11 are the same as those of Example 1, except that the Cr in step S2 is 3+ Concentration, reaction time, reaction temperature and pH value in the solution, the specific parameters are shown in Table 3.

[0044]

[0045] From Table 3, we can see that Cr 3+ The concentration, reaction temperature, reaction time and solution pH all have an impact on the aluminum removal rate. By comparing Example 1 with Example 6 and Example 8, it can be concluded that without adding Cr 3+ When the temperature is not raised, some aluminum can be removed, but the precipitation efficiency is less than 55%. 3+ And high temperature conditions are necessary for deep aluminum removal. By comparing Examples 1, 8, and 9, it can be seen that increasing the reaction temperature can not only reduce the 3+ In short, the "acid leaching-high temperature precipitation aluminum removal-iron powder copper removal" process technology not only simplifies the impurity removal process, but also solves the problem of lithium loss, providing a feasible industrial solution for the recycling and reuse of waste lithium iron phosphate batteries, and has broad application prospects.

[0046] Result analysis: The concentrations of various ions in the acid leaching solution (i.e., the solution obtained by acid leaching in step S1) and the purified solution (i.e., the purified solution obtained in step S3) in the embodiment were measured by inductively coupled plasma atomic emission spectrometry (ICP), and then the ion precipitation efficiency α and the recovery efficiency β were calculated. The experimental results are shown in Table 4.

[0047] The calculation formulas for precipitation efficiency α and recovery efficiency β are as follows:

[0048] β=1-α, where C1 and C2 are the concentrations of ions in the acid leaching solution and the purified solution, respectively, and V1 and V2 are the volumes of the acid leaching solution and the purified solution, respectively.

[0049]

[0050] It can be concluded from Example 1 in Table 4 that the process of the present invention successfully achieved efficient removal of impurities aluminum and copper in black powder, with precipitation rates of 99.8% and 99.9%, respectively. Moreover, the recovery rate of lithium in the purified liquid was 99.1%, and the concentration of introduced chromium was only 5.3 mg / L, laying a foundation for the comprehensive utilization of black powder leachate.

[0051] The iron phosphate recovered in Examples 1, 6 to 11 was analyzed for components, and the test results are shown in Table 5. The iron phosphate obtained in Example 1 was analyzed by XRD, and the structure was as follows: Figure 1 shown.

[0052]

[0053] Depend on Figure 1 It can be seen that the characteristic peaks of the XRD spectrum are sharp, the peak width is narrow, and the complete crystal structure is presented, which is highly consistent with the standard card PDF#29-0715, indicating that the recovered iron phosphate has a relatively high degree of crystallinity. Table 5 shows the product quality of the battery-grade iron phosphate prepared in Examples 1 and 6 to 11, among which the iron phosphate obtained in Examples 1, 9, 10, and 11 all meet the requirements of the standard "HG / T4701-2021 Iron Phosphate for Batteries".

[0054] The lithium carbonate recovered in Examples 1, 6 to 11 was subjected to component analysis, and the test results are shown in Table 6. The lithium carbonate obtained in Example 1 was subjected to XRD detection and analysis, and the test structure was as shown in Table 6. Figure 2 shown.

[0055]

[0056] from Figure 2 It can be seen that the intensity of each diffraction peak is high and the peak shape is sharp, indicating that the recovered lithium phosphate material has high crystallinity and no obvious impurity peaks, and highly matches the standard card PDF#80-1307, indicating that the recovered lithium phosphate is pure phase. Table 6 shows the product quality of battery-grade lithium carbonate prepared in Examples 1, 6 to 11, among which the lithium carbonate obtained in Examples 1, 7, 9, 10, and 11 meets the standard requirements of "YS / T 582-2013 Battery-Grade Lithium Carbonate".

[0057] Control experimental group: The operation steps and conditions are the same as those in Example 1. The only difference is that in the aluminum removal process in step S2, the reaction temperatures are set to 60°C, 70°C, 80°C, 85°C, and 95°C, respectively. The effects of different temperatures on the aluminum precipitation behavior are investigated. The specific experimental results are as follows: Figure 3 shown.

[0058] The experimental results show that temperature has a significant effect on the precipitation behavior of aluminum. When the reaction temperature is 60°C, the precipitation rate of aluminum is still only 22.3%. As the reaction temperature increases, the precipitation rate of aluminum increases rapidly. When the reaction temperature is 90°C, the aluminum precipitation effect is better, reaching 99.8%. Further temperature increase no longer has a significant effect on the removal behavior of aluminum. It can be seen that controlling the reaction system at a higher temperature is extremely important for the deep removal of aluminum in the acid leaching solution.

Claims

1. A method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization, characterized in that: By adding Cr 3+ Induce nucleation to remove aluminum.

2. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 1, characterized in that: By adding an appropriate amount of Cr 3+ Induce the nucleus formation and promote the formation of Al with Cr by synergistically controlling the pH and temperature of the solution （1-x） Al x It precipitates in the form of PO4 to achieve deep removal of aluminum.

3. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 1 or 2, characterized in that: During the aluminum removal process, the pH of the solution is controlled at 0.5-1.5 and the reaction temperature is controlled at 70-110°C.

4. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 3, characterized in that: The specific steps include: S1, acid leaching: mixing the waste lithium iron phosphate black powder with acid solution and reacting them under stirring to obtain a solution and carbon slag; S2, aluminum removal: add a certain amount of inducing precipitation agent Cr to the solution obtained in S1 3+ and acid solution, control the pH value of the solution, react at a certain temperature, separate the solid and liquid to obtain aluminum removal liquid and aluminum slag; S3, copper removal: adding iron powder to the aluminum removal liquid obtained in S2 to perform reduction and copper removal, and solid-liquid separation to obtain purified liquid and copper slag; S4, oxidation separation: after adjusting the pH value and the ratio of the amount of phosphorus and iron substances in the purified liquid obtained in S3, an oxidant is added for oxidation and aging, and solid-liquid separation is performed to obtain a dihydrated iron phosphate precipitate and a lithium-rich liquid; S5. Preparation of anhydrous ferric phosphate: calcining the dihydrated ferric phosphate obtained in S4 to obtain anhydrous ferric phosphate; S6, preparation of lithium carbonate: adjusting the pH of the lithium-rich solution obtained in S4 to remove Fe 3+ , then add carbonate to precipitate lithium to obtain lithium carbonate.

5. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 4, characterized in that: During the acid leaching process, the acid solution is any acid solution that can provide free H + A single acidic solution or a combination of acidic solutions; and / or, H + The concentration is 0.5 to 6 mol / L; and / or, the liquid-to-solid ratio of the acid solution to the waste lithium iron phosphate black powder is 1 to 5 mL / g; and / or, leaching is performed at room temperature for more than 2 hours.

6. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 4, characterized in that: Cr added during S2 aluminum removal 3+ Provided by at least one of chromium sulfate, chromium chloride or chromium nitrate; and / or, Cr is added during the aluminum removal process of S2 3+ After that, Cr in the solution 3+ The concentration is 0.5-12 g / L; and / or, during the aluminum removal process of S2, acid is added to control the pH of the solution to 0.5-1.5; and / or, during the aluminum removal process of S2, the acid is any acid that can provide free H + a single acidic solution or a combined acidic solution; and / or, the reaction temperature during S2 aluminum removal is 70 to 110° C.; and / or, the reaction time is 1 to 5 hours.

7. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 4, characterized in that: During S3 copper removal, the amount of iron powder added is not less than the theoretical molar amount of iron powder required to convert all copper ions into copper; and / or, the reaction is carried out at room temperature for 20 to 60 minutes.

8. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 4, characterized in that: In the S4 oxidation separation process, the pH value of the obtained purified liquid is adjusted to 0.4-1.6, and the ratio of the amount of phosphorus and iron substances is adjusted to 1:1-1.05:1; and / or, the phosphorus source used in the process of adjusting the ratio of the amount of phosphorus and iron substances is at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and sodium dihydrogen phosphate; and / or, in the S4 oxidation separation process, the oxidant is at least one of persulfate, hydrogen peroxide, pure oxygen, ozone, and air; and / or, the amount of the oxidant added is not less than the amount of Fe 2+ All converted into Fe 3+ The theoretical molar amount of the required oxidant; and / or, in the S4 oxidation separation process, the oxidation and aging reaction temperature is 50 to 90°C, the oxidation reaction time is 2 to 3 hours, and the aging time is 1 to 3 hours.

9. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 4, characterized in that: During the preparation of S5 anhydrous ferric phosphate, the calcination temperature is 500-700°C and the calcination time is 2-6 hours.

10. The method for removing aluminum from waste lithium iron phosphate black powder and comprehensive utilization according to claim 4, characterized in that: During the preparation of S6 lithium carbonate, the pH of the lithium-rich solution is adjusted to 3-6, and the unprecipitated Fe 3+ remove; then adjust the solution pH to 10-13, and the temperature to 90-98°C; then add carbonate to precipitate lithium; and / or, add carbonate in an excess of more than 2 times the theoretical molar amount required for lithium ions; and / or, the substance for adjusting the pH in the preparation process of S6 lithium carbonate is at least one of sodium hydroxide, ammonia water, lithium hydroxide, and sodium carbonate; and / or, the carbonate in the preparation process of S6 lithium carbonate is at least one of ammonium carbonate, sodium carbonate, and ammonium bicarbonate.

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