A method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder

Abstract

A method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder, by adding Cr 3+ to induce the formation of crystal nuclei to remove aluminum. The present invention has the following advantages: 1) High-efficiency aluminum removal: Using Cr 3+ induced precipitation technology to achieve deep removal of aluminum at high temperature and low pH; 2) High lithium recovery rate: The lithium recovery rate in the purified liquid exceeds 99%, which can be directly used to prepare battery-grade Li2CO3 and FePO4; 3) Simplified process: Compared with the existing technology, the process is more concise and efficient, carried out under normal pressure throughout the process, with good operability and potential for industrial application; 4) Environmental and economic benefits: There is no excessive introduction of harmful substances throughout the process, reducing the impact on the environment, and achieving good economic benefits through comprehensive resource recovery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium iron phosphate battery recycling, and particularly 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 increasing demand for green energy, lithium-ion batteries have been widely used in fields such as electric vehicles, electronic devices, and aerospace. Lithium iron phosphate (LiFePO4, abbreviated as LFP) as a cathode material has become one of the most widely used cathode materials in lithium-ion batteries due to its high theoretical capacity, excellent lattice stability, and low cost. However, after long-term cyclic use, irreversible changes will occur in the internal structure of the battery (such as the blockage of lithium diffusion channels), which usually limits the service life of the battery to 8-10 years. With the rapid growth of electric vehicles, it is expected that the annual retirement volume of batteries will reach 30 GWh in the next five years, and the generation of a large number of waste batteries is inevitable. It is worth noting that the batteries contain toxic organic substances and heavy metals, which will cause great harm to human health and the ecological environment if not properly treated. In addition, the batteries also contain a large amount of resources such as Li, Fe, and P, 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] Currently, the process for industrial large-scale recycling of waste lithium iron phosphate batteries is as follows: First, the battery is charged and crushed into powder in a nitrogen atmosphere, then organic impurities such as binders, separator papers, and electrolytes are removed by high-temperature calcination, then the copper foil-aluminum foil mixture and battery black powder are obtained by screening, and finally the corresponding materials are obtained by separating copper and aluminum. Although the black powder is treated by the above process, it is still inevitable to mix in aluminum and copper impurities in actual industrialization. Research shows that when the aluminum content in the black powder exceeds 50 ppm, the battery capacity will decrease. Therefore, how to deeply separate aluminum during the black powder recycling process is one of the key technical problems.

[0004] The reported aluminum removal processes mainly fall into two categories. One is to directly separate aluminum from the black powder solid, and the other is to remove aluminum from the leaching solution. The first category mainly dissolves the Al2O3 solid into AlO2 by an alkali solution. - , such as CN117142449A, CN116553502A, CN113912033A, etc. all introduce related processes. However, it is found that about 5% - 10% of lithium ions are lost during the alkali washing process, resulting in a decrease in lithium recovery rate and affecting economic benefits. The second category is to first dissolve the black powder with an acid solution to obtain a solution containing Li + , Fe 2+ , Al 3+ , Cu 2+ , PO43- The leaching solution, and then aluminum is converted into a precipitate by a neutralization method or a chemical precipitation method. The neutralization method is to add NaOH, ammonia water, LiOH, Na2CO3 or other substances that can hydrolyze or ionize to produce OH - to adjust the pH value of the solution to 3-6, so that aluminum precipitates in the form of Al(OH)3, such as the solutions disclosed in CN116750740A, CN110112481A, etc. However, in fact, when pH≥3, it is very easy to generate LiFePO4 precipitate, resulting in a large loss of lithium and affecting the recovery efficiency. The chemical precipitation method is to use a precipitant such as sodium fluoride, ammonium fluoride, potassium fluoride, etc. to precipitate aluminum in the form of aluminum fluoride (AlF3), 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 the product performance, but also corrode the pipes and equipment of the recovery system. In addition, further subdividing, there is also research on obtaining iron phosphate and lithium solution through selective acid leaching oxidation (such as CN118495566A, CN118637576A, etc.). Since these two products still contain copper and aluminum impurities, further impurity removal is required respectively, resulting in a complex process, cumbersome steps, and reduced economic benefits.

[0005] CN113816353A discloses a method for removing aluminum from the acid leaching solution of waste lithium iron phosphate batteries by iron-aluminum coprecipitation. The steps include: acid-dissolving the black powder to obtain a mixed solution containing iron, lithium and phosphorus; adding hydrogen peroxide for an oxidation reaction or adding Fe 3+ to adjust the Fe 3+ concentration in the leaching solution to 1.2-4 times that of Al 3+ concentration, and then adjusting the pH of the leaching solution to 0.2-7.5 and the temperature to 20-90°C for coprecipitation reaction, solid-liquid separation to obtain an iron-aluminum coprecipitate and an aluminum-removed solution; supplementing an excessive phosphorus source in the aluminum-removed solution and adding an excessive amount of hydrogen peroxide to oxidize Fe 2+ to Fe 3+ , then carrying out a precipitation reaction, solid-liquid separation to obtain iron phosphate dihydrate precipitate and a lithium-rich solution. This solution realizes the precipitation of Al 3+ by adding Fe 3+ and has the advantages of environmental protection and non-toxicity. However, the required precipitation reaction time is 10-48h, resulting in a long production cycle and high operating costs, and it does not have good industrial application prospects.

[0006] CN116002646A discloses a method for the comprehensive resource recovery of valuable components in waste lithium iron phosphate batteries. The steps include: leaching the mixed black powder of the positive and negative electrodes of waste lithium iron phosphate batteries with an acid solution, and sequentially removing titanium by high-temperature coprecipitation, recovering copper by replacement precipitation, precipitating aluminum by complexation precipitation, oxidizing and precipitating iron phosphate at high temperature and high acid, and washing with hot phosphoric acid to obtain hydrated iron phosphate with good battery performance, while lithium is recovered in the form of lithium carbonate. In this solution, the removal of titanium and aluminum is achieved by adding Fe 3+ However, the removal rate of aluminum is only 80-90%. To achieve deep removal of aluminum, sodium fluoride needs to be further added for complexation precipitation. As a result, the entire process is complex, fluoride ion impurities are introduced, leading to poor economic and environmental benefits. Summary of the Invention

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

[0008] The technical solution adopted by the present invention to solve its technical problems is a method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder, which removes aluminum by adding Cr 3+ to induce the formation of crystal nuclei.

[0009] Furthermore, in the method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder of the present invention, by adding an appropriate amount of Cr 3+ to induce the formation of crystal nuclei, and by synergistically controlling the pH and temperature of the solution, Al is precipitated in the form of Cr （1-x） Al x PO4 to achieve deep removal of aluminum.

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

[0011] The method for removing aluminum and comprehensive recovery of waste lithium iron phosphate black powder of the present invention specifically includes the following steps:

[0012] S1. Acid leaching: Mix the waste lithium iron phosphate black powder with an acid solution and react under stirring to obtain a solution and carbon slag;

[0013] The solution contains elements such as Li, Fe, P, Al, and Cu;

[0014] S2. Aluminum removal: Add a certain amount of induced precipitant Cr 3+ and an acid solution to the solution obtained in S1, control the pH of the solution, and react at a certain temperature, followed by solid-liquid separation to obtain an aluminum-removed solution and aluminum slag.

[0015] S3, Copper removal: Add iron powder to the aluminum-removed liquid obtained in S2 for reduction copper removal, and perform solid-liquid separation to obtain a purified liquid and copper slag;

[0016] S4, Oxidation separation: After adjusting the pH value and the molar ratio of phosphorus to iron of the purified liquid obtained in S3, add an oxidant for oxidation and aging, and perform solid-liquid separation to obtain iron phosphate dihydrate precipitate and lithium-rich liquid;

[0017] S5, Preparation of anhydrous iron phosphate: Calcinate the iron phosphate dihydrate obtained in S4 to obtain anhydrous iron phosphate;

[0018] S6, Preparation of lithium carbonate: Adjust the pH of the lithium-rich liquid obtained in S4 to remove Fe 3+ , and then add carbonate to precipitate lithium to obtain lithium carbonate.

[0019] As a preferred solution, during the acid leaching process of S1, the acid solution can be any single acidic solution or combined acidic solution that can provide free H + . The H + concentration of the acid solution 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. Leach for more than 2 h at room temperature.

[0020] As a preferred solution, during the aluminum removal process of S2, the Cr 3+ added can be provided by at least one of chromium sulfate, chromium chloride, or chromium nitrate. Further preferably, the corresponding anion of Cr 3+ is preferably the same as the anion in the acid solution during the acid leaching process of S1.

[0021] As a preferred solution, after adding Cr 3+ during the aluminum removal process of S2, the concentration of Cr 3+ in the solution is 0.5 - 12 g / L, preferably 1 - 5 g / L. Research shows that if the concentration of chromium ions is too low, there are not enough induced crystal nuclei and the aluminum removal effect is poor; if the concentration of chromium ions is too high, when the Cr 3+ concentration reaches a certain level, the aluminum removal effect does not increase with the increase of the Cr 3+ concentration, and adding too much chromium ions will cause waste of raw materials and is uneconomical.

[0022] As a preferred solution, during the aluminum removal process of S2, add an acid solution to control the pH of the solution to 0.5 - 1.5, preferably 0.8 - 1.2.

[0023] As a preferred solution, during the aluminum removal process of S2, the acid solution can be any single acidic solution or combined acidic solution that can provide free H + .

[0024] As a preferred embodiment, during the aluminum removal process of S2, the reaction temperature is 70 - 110°C, and the preferred temperature is 80 - 100°C. The preferred reaction time is 1 - 5 h. If the aluminum removal temperature is too low, the aluminum removal effect is not good; if the aluminum removal temperature is too high, the aluminum removal effect will not increase anymore, and increasing the temperature is meaningless but consumes extra energy and is not very economical.

[0025] As a preferred embodiment, 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. At room temperature, the reaction is carried out for 20 - 60 min. The excessive iron powder can be separated by means such as filtration, and the obtained iron-copper mixed slag can be dissolved in dilute acid to dissolve the iron in it, thus obtaining relatively pure copper powder.

[0026] As a preferred embodiment, during the oxidation and separation process of S4, the pH value of the obtained purified liquid is adjusted to 0.4 - 1.6, and the molar ratio of phosphorus to iron is adjusted to 1:1 - 1.05:1. The phosphorus source used during the adjustment of the molar ratio of phosphorus to iron is at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, sodium dihydrogen phosphate, etc. Research shows that too high or too low pH value and molar ratio of phosphorus to iron will affect the synthesis quality of iron phosphate and cannot meet the standards of iron phosphate for batteries.

[0027] As a preferred embodiment, during the oxidation and separation process of S4, the oxidant is at least one of persulfate, hydrogen peroxide, pure oxygen, ozone, and air. The addition amount of the oxidant is not less than the theoretical molar amount of the oxidant required to convert all Fe 2+ completely into Fe 3+ required.

[0028] As a preferred embodiment, during the oxidation and separation process of S4, the oxidation and aging reaction temperature is 50 - 90°C, the oxidation reaction time is 2 - 3 h, and the aging time is 1 - 3 h.

[0029] As a preferred embodiment, during the preparation process of anhydrous iron phosphate in S5, the calcination temperature is 500 - 700°C, and the calcination time is 2 - 6 h.

[0030] As a preferred embodiment, during the preparation process of lithium carbonate in S6, the pH of the lithium-rich liquid is adjusted to 3 - 6, and the un-precipitated Fe 3+ in the solution is removed; then the pH of the solution is adjusted to 10 - 13, and the temperature is adjusted to 90 - 98°C. Then carbonate is added to precipitate lithium. According to the theoretical molar amount required for lithium ions, carbonate is added more than 2 times in excess, that is, more than 3 times the theoretical molar amount required for lithium ions, to ensure complete precipitation of lithium ions.

[0031] As a preferred embodiment, the substances for adjusting pH during the preparation process of lithium carbonate in S6 are at least one of sodium hydroxide, ammonia water, lithium hydroxide, and sodium carbonate.

[0032] As a preferred solution, in the process of preparing lithium carbonate in S6, the carbonate is at least one of ammonium carbonate, sodium carbonate, and ammonium bicarbonate.

[0033] The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder of the present invention lies in that by adding an appropriate amount of Cr 3+ to induce crystal nucleus formation, and by synergistically controlling the pH and temperature of the solution to promote Al to precipitate in the form of Cr （1-x） Al x PO4, realizing the deep removal of aluminum. The method of the present invention can, while efficiently removing impurity aluminum and copper (the highest removal rates can reach 99.8% and 99.9% respectively), achieve a lithium recovery rate of over 99% at most in the purified solution, and can further obtain battery-grade Li2CO3 and FePO4 products, thus realizing the full resource utilization of valuable elements in the 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 is suitable for large-scale industrial production.

[0034] The main process flow of the method for removing aluminum and comprehensive utilization of waste lithium iron phosphate battery black powder of the present invention: acid leaching, precipitation for aluminum removal, iron powder for copper removal, oxidative aging of iron phosphate, and carbonate precipitation of lithium, thereby realizing the full resource recovery of valuable components in the black powder. The main ions in the acid leaching solution are Li + , Fe 2+ , Cu 2+ , Al 3+ , PO4 3- and so on. When the pH of the acid leaching solution ≥ 3, it is very easy to form LiFePO4 precipitation, resulting in a large loss of Li + . Therefore, it is necessary to strictly control the pH of the solution during the aluminum removal process. Research shows that when the pH value of the solution is 0 - 4, the order of the ease of forming precipitation between PO4 3- and ions is Cr 3+ >Fe 3+ >Fe 2+ >Cu 2+ . Therefore, the key to the technical solution of the present invention lies in providing nucleating seeds by adding a small amount of induced precipitant Cr 3+ , and at the same time promoting the Cr (1-x) Al x PO4 precipitate obtained by promoting aluminum precipitation at high temperature, so as to realize the deep removal of aluminum in the acid leaching solution under low pH and high temperature conditions. Although Cr 3+ is introduced, it only serves as an induced precipitant and the required amount is very small; moreover, through experimental verification, the final obtained leaching solution contains only 1 - 8 mg / L of Cr 3+ , meeting the requirements of iron phosphate and lithium carbonate for batteries.

[0035] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0036] 1) High-efficiency aluminum removal: The Cr 3+ induced precipitation technology is adopted to achieve deep removal of aluminum at high temperature and low pH.

[0037] 2) High lithium recovery rate: The lithium recovery rate in the purified liquid exceeds 99%, and it can be directly used to prepare battery-grade Li2CO3 and FePO4.

[0038] 3) Process simplification: Compared with the prior art, the process is more concise and efficient, and it is carried out under normal pressure throughout the process, with good operability and potential for industrial application.

[0039] 4) Environmental protection and economic benefits: No excessive harmful substances are introduced during the whole process, reducing the impact on the environment, and achieving good economic benefits through comprehensive recovery of resources. Brief Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0041] Figure 1 XRD pattern of the iron phosphate recovered in Example 1;

[0042] Figure 2 XRD pattern of the lithium carbonate recovered in Example 1;

[0043] Figure 3 Precipitation efficiency diagram of aluminum at different reaction temperatures. Detailed Description of the Embodiments

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further details the present invention in combination with specific embodiments and drawings.

[0045] Example 1

[0046] The main element contents in the waste lithium iron phosphate battery black powder used in this example are shown in Table 1.

[0047]

[0048] The method for removing aluminum and comprehensively recovering waste lithium iron phosphate black powder in this example specifically includes the following steps:

[0049] S1. Acid leaching: 100 g of waste lithium iron phosphate black powder is uniformly mixed with 1.7 mol / L sulfuric acid solution (hydrogen ion concentration is 3.4 mol / L) at a liquid-solid ratio of 3 mL / g, stirred and reacted at room temperature for 2 h, and then centrifuged and filtered to obtain a solution and carbon residue; the solution contains elements such as Li, Fe, P, Al, and Cu.

[0050] S2. Aluminum removal: Appropriate amounts of Cr2(SO4)3 and H2SO4 are added to the solution obtained in S1 to initiate a precipitation reaction, controlling the Cr concentration in the solution system to be 3.6 g / L, adjusting the pH of the solution system to 0.96, the reaction temperature to 90 °C, and the reaction time to 3 h. After the reaction, it is centrifuged and filtered to obtain an aluminum-removed solution and aluminum residue. 3+ The concentration of Cr in the solution system 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 h. After the reaction, it is centrifuged and filtered to obtain an aluminum-removed solution and aluminum residue.

[0051] S3. Copper removal: Iron powder (the added amount of iron powder is 1 times the theoretical molar amount of iron powder required to convert all copper ions into copper) is added to the aluminum-removed solution obtained in S2, and the reaction is carried out at room temperature for 30 min for reduction and copper removal. After solid-liquid separation, a purified solution and copper residue are obtained.

[0052] S4. Oxidation and separation: Phosphoric acid is added to the purified solution obtained in S3 to make the molar ratio of phosphorus to iron in the solution 1.02:1 and the pH value 1.6. H2O2 (the added amount of H2O2 is 1.2 times the theoretical molar amount of the oxidant required to convert all Fe into Fe) is added, and then it is placed in a water bath at 70 °C for an oxidation reaction for 2 h and aged for 3 h. After filtration, washing, and drying, iron phosphate dihydrate and a lithium-rich solution are obtained. 2+ All Fe is converted into Fe 3+ required oxidant's theoretical molar amount of 1.2 times), and then placed in a 70 °C water bath for an oxidation reaction for 2 h and aged for 3 h. After filtration, washing, and drying, iron phosphate dihydrate and a lithium-rich solution are obtained.

[0053] S5. Preparation of anhydrous iron phosphate: The iron phosphate dihydrate obtained in S4 is calcined at 500 °C for 6 h to obtain anhydrous iron phosphate.

[0054] S6. Preparation of lithium carbonate: NaOH is added to the lithium-rich solution obtained in S4 to adjust the pH to 3.5 to remove the unprecipitated Fe in the solution; then the pH of the solution is adjusted to 11, the temperature is adjusted to 90 °C, sodium carbonate is added in an amount 2 times in excess of the theoretical molar amount required for lithium ions, stirred and reacted for 1 h. After precipitation, centrifugation, and filtration, it is washed twice with hot water to obtain battery-grade lithium carbonate. 3+ ; Then the pH of the solution is adjusted to 11, the temperature is adjusted to 90 °C, sodium carbonate is added in an amount 2 times in excess of the theoretical molar amount required for lithium ions, stirred and reacted for 1 h. After precipitation, centrifugation, and filtration, it is washed twice with hot water to obtain battery-grade lithium carbonate.

[0055] Examples 2 to 11

[0056] The methods of Examples 2 to 5 are the same as those of Example 1, except for the sulfuric acid concentration and liquid-solid ratio in step S1. The specific parameters are shown in Table 2.

[0057]

[0058] As can be seen from Table 2, by comparing Examples 1 to 5, both the sulfuric acid concentration and the liquid-solid ratio during the acid leaching process have an impact on the leaching rate of lithium. However, in order to maximize the recovery rate of lithium, experiments should be carried out under the optimal leaching conditions for lithium.

[0059] Examples 6 to 11 are the same as the method of Example 1, the difference being the Cr in step S2 3+ concentration, reaction time, reaction temperature, and pH value in the solution. The specific parameters are shown in Table 3.

[0060]

[0061] As can be obtained from Table 3, the Cr in step S2 3+ concentration, reaction temperature, reaction time, and solution pH all have an impact on the removal rate of aluminum. By comparing and analyzing Example 1 with Example 6 and Example 8 respectively, it can be concluded that without adding Cr additionally 3+ or without increasing the temperature, partial removal of aluminum can be achieved, but the precipitation efficiency is less than 55% in both cases. This shows that introducing the induced precipitant Cr 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 demand for Cr 3+ but also shorten the reaction time and improve the reaction efficiency. In short, adopting the "acid leaching - high-temperature precipitation for aluminum removal - iron powder for 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 having broad application prospects.

[0062] Result analysis:

[0063] The ion concentrations in the acid leaching solution (i.e., the solution obtained from acid leaching in step S1) and the purification solution (i.e., the purification solution obtained in step S3) in the examples were measured by inductively coupled plasma atomic emission spectrometry (ICP), and then the ion precipitation efficiency α and recovery efficiency β were calculated. The experimental results are shown in Table 4.

[0064] The calculation formulas for the precipitation efficiency α and recovery efficiency β are as follows:

[0065]

[0066] β = 1 - α, where C1 and C2 are the ion concentrations in the acid leaching solution and the purification solution respectively, and V1 and V2 are the volumes of the acid leaching solution and the purification solution respectively.

[0067]

[0068] It can be obtained from Example 1 in Table 4 that through the process of the present invention, the efficient removal of impurities aluminum and copper in the black powder was successfully achieved, and the precipitation rates were 99.8% and 99.9% respectively. Moreover, the recovery rate of lithium in the purified liquid was 99.1%, and the introduced chromium concentration was only 5.3 mg / L, laying a foundation for the comprehensive utilization of the black powder leaching solution.

[0069] The iron phosphates recovered in Examples 1 and 6 - 11 were subjected to component analysis, and the test results are shown in Table 5. The iron phosphate obtained in Example 1 was subjected to XRD detection and analysis, and the structure is as Figure 1 shown.

[0070]

[0071] From Figure 1 it can be seen that the characteristic peaks of the XRD pattern are sharp, the peak width is narrow, presenting a complete crystal structure, which is highly consistent with the standard card PDF#29 - 0715, indicating that the recovered iron phosphate has a relatively high crystallinity. Table 5 shows the product quality of the battery - grade iron phosphate prepared in Example 1 and Examples 6 - 11. Among them, the iron phosphates obtained in Examples 1, 9, 10, and 11 all meet the standard requirements of "HG / T 4701 - 2021 Iron Phosphate for Batteries".

[0072] The lithium carbonates recovered in Examples 1 and 6 - 11 were 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 is as Figure 2 shown.

[0073]

[0074] From Figure 2 it can be seen that the intensities of each diffraction peak are relatively high and the peak shapes are sharp, indicating that the recovered lithium phosphate material has a high crystallinity, and there are no obvious impurity peaks, and it is highly matched with the standard card PDF#80 - 1307, indicating that the recovered is a pure - phase lithium phosphate. Table 6 shows the product quality of the battery - grade lithium carbonate prepared in Examples 1 and 6 - 11. Among them, the lithium carbonates obtained in Examples 1, 7, 9, 10, and 11 meet the standard requirements of "YS / T 582 - 2013 Lithium Carbonate for Batteries".

[0075] Control experimental group:

[0076] The operation steps and conditions, etc. are the same as those in Example 1. The only difference is that in the aluminum - removal process in step S2, the reaction temperatures were taken as 60°C, 70°C, 80°C, 85°C, and 95°C respectively, and the influence of different temperatures on the aluminum precipitation behavior was investigated. The specific experimental results are as Figure 3 shown.

[0077] 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%. With the increase of the reaction temperature, the precipitation rate of aluminum increases rapidly. When the reaction temperature is 90 °C, the precipitation effect of aluminum is better, reaching 99.8%. Further increasing the temperature has no significant effect on the removal behavior of aluminum. Thus, 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 and comprehensive utilization of waste lithium iron phosphate black powder, characterized in that, By adding an appropriate amount of Cr 3+ induced the formation of crystal nuclei, and promoted the precipitation of Al in the form of Cr （1-x） Al x PO4 by synergistically controlling the pH and temperature of the solution, achieving deep removal of aluminum; during the aluminum removal process, the pH of the solution was controlled to be 0.5 - 1.5, and the reaction temperature was 70 - 110 °C; Specifically, it includes the following steps: S1. Acid leaching: Mix the waste lithium iron phosphate black powder with the acid solution and react under stirring to obtain a solution and carbon slag; S2. Aluminum removal: Add a certain amount of induced precipitant Cr to the solution obtained in S1 3+ and acid solution, control the pH of the solution, carry out the reaction at a certain temperature, and perform solid-liquid separation to obtain aluminum-removed solution and aluminum slag; S3. Copper removal: Add iron powder to the aluminum-removed solution obtained in S2 for reduction copper removal, and perform solid-liquid separation to obtain a purified solution and copper slag; S4. Oxidation separation: After adjusting the pH value and the molar ratio of phosphorus to iron of the purified solution obtained in S3, add an oxidant for oxidation and aging, and perform solid-liquid separation to obtain iron phosphate dihydrate precipitate and lithium-rich solution; S5. Preparation of anhydrous iron phosphate: Calcinate the iron phosphate dihydrate obtained in S4 to obtain anhydrous iron phosphate; S6. Preparation of lithium carbonate: Adjust the pH of the lithium-rich solution obtained in S4 to remove Fe 3+ , and then add carbonate to precipitate lithium to obtain lithium carbonate.

2. The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder according to claim 1, characterized in that, During the S1 acid leaching process, the acid solution is any single acidic solution or combined acidic solution that can provide free H + ; and / or, the H + concentration of the acid solution is 0.5 - 6 mol / L; and / or, the liquid-solid ratio of the acid solution to the waste lithium iron phosphate black powder is 1 - 5 mL / g; and / or, leaching is carried out for more than 2 h at room temperature.

3. The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder according to claim 1, characterized in that, Cr added during the aluminum removal process of S2 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, the concentration of Cr in the solution 3+ Is 0.5 - 12 g / L; and / or, an acid solution is added during the aluminum removal process of S2 to control the pH of the solution to be 0.5 - 1.5; and / or, during the aluminum removal process of S2, the acid solution is any single acidic solution or combined acidic solution that can provide free H + ; and / or, the reaction temperature during the aluminum removal process of S2 is 70 - 110 °C; and / or, the reaction time is 1 - 5 h.

4. The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder according to claim 1, characterized in that, During the copper removal process of S3, the addition amount of iron powder is not less than the theoretical molar amount of iron powder required to convert all copper ions into copper; and / or, at room temperature, the reaction time is 20 - 60 min.

5. The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder according to claim 1, characterized in that, S4 oxidation separation process, adjusting the pH value of the obtained purified liquid to 0.4 - 1.6 and adjusting the molar ratio of phosphorus to iron to 1:1 - 1.05:1; and / or, during the process of adjusting the molar ratio of phosphorus to iron, the phosphorus source used 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 addition amount of the oxidant is not less than the theoretical molar amount of the oxidant required to convert all Fe 2+ into Fe 3+ ; and / or, in the S4 oxidation separation process, the oxidation and aging reaction temperature is 50 - 90°C, the oxidation reaction time is 2 - 3 h, and the aging time is 1 - 3 h.

6. The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder according to claim 1, characterized in that, During the preparation process of anhydrous iron phosphate in S5, the calcination temperature is 500 - 700 °C, and the calcination time is 2 - 6 h.

7. The method for removing aluminum and comprehensive utilization of waste lithium iron phosphate black powder according to claim 1, wherein During the preparation of lithium carbonate, adjust the pH of the lithium-rich solution to 3-6 to remove the un-precipitated Fe in the solution 3+ ; 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 amount more than 2 times the theoretical molar amount required for lithium ions; and / or, the substance for adjusting pH during the preparation of lithium carbonate in S6 is at least one of sodium hydroxide, ammonia water, lithium hydroxide, and sodium carbonate; and / or, the carbonate during the preparation of lithium carbonate in S6 is at least one of ammonium carbonate, sodium carbonate, and ammonium bicarbonate.

Images