Preparation method of a de-aluminum solution for lithium iron phosphate battery powder and application thereof

Abstract

The application provides a preparation method of an aluminum removal solution for lithium iron phosphate battery powder, and comprises the following steps: S1: dispersing first lithium iron phosphate black powder in water, adding phosphoric acid dropwise until the pH is 3.6-4.6, and performing solid-liquid separation to obtain aluminum removal first residue and aluminum removal first liquid; S2: mixing the aluminum removal first liquid in step S1 with second lithium iron phosphate black powder, adding phosphoric acid dropwise until the pH is 3.6-4.6, and performing solid-liquid separation to obtain aluminum removal second residue and aluminum removal second liquid; S3: repeating the above steps, mixing aluminum removal (n-1) liquid with n lithium iron phosphate black powder, adding phosphoric acid dropwise until the pH is 3.6-4.6, and performing solid-liquid separation to obtain aluminum removal n residue and aluminum removal solution; wherein n is a positive integer and n>2. The aluminum removal solution can be obtained by only using phosphoric acid leaching, and the scheme is simple; the obtained aluminum removal solution can realize deep removal of impurity aluminum in lithium iron phosphate black powder.

Description

Technical Field

[0001] This invention belongs to the field of solid waste recycling and resource utilization technology, specifically relating to a method for preparing an aluminum removal solution for lithium iron phosphate battery powder and its application. Background Technology

[0002] Lithium iron phosphate (LFP) batteries have become a significant trend in power battery technology development due to their numerous advantages, such as readily available raw materials, low cost, environmental friendliness, high theoretical capacity, excellent thermal stability, and outstanding cycle performance. With the widespread application of LFP power batteries, the treatment and recycling of waste LFP batteries has become a major challenge in the new energy field. Since cathode materials account for more than one-third of the total cost of lithium-ion power batteries, their recycling is the core of waste lithium-ion power battery recycling.

[0003] Due to limitations in the pretreatment of LiFePO4 batteries, LiFePO4 cathode powder often contains residual current collector Al powder. During wet recycling, Al impurities inevitably enter the acid leaching solution along with other components, leading to excessive Al content in the recycled FePO4, thus reducing product added value and economic value. Therefore, deep Al removal is a crucial step in the recycling of waste LiFePO4 cathode materials.

[0004] The main aluminum removal processes for LiFePO4 cathode materials include alkaline leaching, selective acid leaching, ion exchange, and chemical precipitation. Among these, alkaline leaching utilizes the amphoteric property of elemental Al, which dissolves in both acids and alkalis. This allows Al impurities to dissolve into the liquid phase while LiFePO4 remains in the solid phase of the leaching residue, achieving selective Al dissolution. However, this process generates a large amount of sodium aluminate wastewater, and the removal of impurities also results in the loss of phosphorus and iron.

[0005] Selective acid leaching is based on the difference in leaching kinetics between metallic Al and LiFePO4 cathode materials in acid. By amplifying the differences in solubility or dissolution rate between components, stepwise leaching and separation of each component are achieved. Because the impurity ion Cl- needs to be strictly controlled in iron phosphate products... - SO4 2- Therefore, phosphoric acid, which does not introduce impurity ions, has been used to remove aluminum impurities from LiFePO4 black powder. However, traditional methods for aluminum removal using phosphoric acid have a high leaching solution-to-solid ratio, high acid consumption, and low economic efficiency. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing an aluminum removal solution for lithium iron phosphate battery powder and its application, which can deeply remove aluminum impurities from lithium iron phosphate battery powder.

[0007] According to a first aspect of the present invention, a method for preparing an aluminum removal solution for lithium iron phosphate battery powder is provided, comprising the following steps:

[0008] S1: Disperse the first lithium iron phosphate black powder in water, add phosphoric acid dropwise until the pH is 3.6-4.6, and after solid-liquid separation, obtain aluminum removal stage slag and aluminum removal stage liquid;

[0009] S2: Mix the aluminum removal first stage liquid from step S1 with the second lithium iron phosphate black powder, add phosphoric acid until the pH is 3.6-4.6, and perform solid-liquid separation to obtain aluminum removal second stage slag and aluminum removal second stage liquid;

[0010] S3: Repeat the above steps, mix the aluminum removal (n-1) stage liquid with the nth lithium iron phosphate black powder, add phosphoric acid dropwise until the pH is 3.6-4.6, and after solid-liquid separation, obtain the aluminum removal nth stage slag and aluminum removal solution;

[0011] Where n is a positive integer and n > 2.

[0012] The prepared aluminum removal solution can be directly recycled for deep aluminum removal from lithium iron phosphate black powder or aluminum removal stage n slag. The number of direct recycling cycles varies with the content of impurity element Al in the lithium iron phosphate black powder. Assuming the impurity Al content in the lithium iron phosphate black powder is 2000 ppm, the aluminum removal solution can be directly used 13 to 16 times. After recovering the aluminum enriched in the aluminum removal solution, the solution can be recycled again.

[0013] According to the E-pH diagram, the corrosion passivation region of Al in aqueous solution is between pH 4.6 and 8.3. When the pH is less than 4.6 or greater than 8.3, aluminum corrosion will occur in aqueous solution.

[0014] Phosphoric acid is a ternary moderately strong acid. Its ionization in aqueous solution occurs in steps, as shown in the following reaction equation:

[0015] H3PO4→H + +H2PO4 - K1 = 7.5 * 10 -3

[0016] H2PO4 - →H + +HPO4 2- K2 = 6.2 * 10 -8

[0017] HPO4 2- →H + +PO4 3- K3 = 2.2 * 10 -13

[0018] From the ionization constant, it can be observed that as the H+ in the solution increases... + H2PO4 - HPO4 2- PO4 3- As plasma concentration increases, the ionization of phosphoric acid in the solution is suppressed, thereby establishing a dynamic equilibrium system.

[0019] According to the E-pH diagram, the reactions of lithium iron phosphate under acidic conditions are as follows:

[0020] 3LiFePO4 + nH2O + 3H + =Fe3(PO4)2·nH2O+3Li + +H3PO4

[0021] The formula for calculating the pH at which the reaction occurs is as follows:

[0022] pH = 1.1112 - lg[Li] + ]-1 / 3lg[H3PO4]

[0023] It can be found that pH and Li + The concentration of H3PO4 is negatively correlated with the concentration of Li in the solution. + H3PO4 inhibits the decomposition of LiFePO4. This aluminum removal solution can be used to remove aluminum impurities from lithium iron phosphate black powder without damaging the structure of lithium iron phosphate. The lithium iron phosphate black powder after impurity removal can be directly used for repair. The black powder generated during the preparation of the aluminum removal solution can also be put back into the aluminum removal solution to continue removing impurity elements.

[0024] In some embodiments, the temperature of the system is 60–80°C during the dripping of phosphoric acid.

[0025] In some embodiments, the concentration of phosphoric acid is 4 to 7 mol / L.

[0026] In some embodiments, the rate at which phosphoric acid is added is 1 to 10 mL / min.

[0027] In some embodiments, the phosphoric acid is added over a period of 0.5 to 6 hours.

[0028] In some embodiments, in step S3, the time for adding phosphoric acid is 0.5 to 1 hour.

[0029] In some embodiments, the aluminum and copper impurity contents in the first, second, and nth lithium iron phosphate black powders are all below 2200 ppm.

[0030] In some preferred embodiments, the first lithium iron phosphate black powder, the second lithium iron phosphate black powder, and the nth lithium iron phosphate black powder are from the same source.

[0031] By repeatedly leaching the same batch of lithium iron phosphate (LFP) black powder, a dynamic equilibrium system suitable for aluminum removal from the LFP black powder gradually forms in the leachate, ultimately yielding an aluminum removal solution suitable for deep aluminum removal from that batch of LFP black powder. Different batches of LFP black powder have different compositions, and the composition of the suitable aluminum removal solution will also differ. If aluminum removal slag is used to prepare the aluminum removal solution, the content of phosphoric acid consumed in the slag is relatively low, requiring the addition of more acid to achieve the desired dynamic equilibrium system. However, excessive acid can damage the structure of lithium iron phosphate.

[0032] This invention is particularly suitable for the deep removal of trace amounts of aluminum from lithium iron phosphate black powder. The aluminum removal solution can be recycled, greatly reducing reagent consumption and wastewater discharge. It is understood that this invention is also applicable to the removal of impurities from lithium iron phosphate black powder with high aluminum content. When the aluminum ion content in the aluminum removal solution reaches a certain level (e.g., 3 mol / L), the aluminum can be removed by conventional methods and then reused in the aluminum removal process of lithium iron phosphate black powder.

[0033] In some embodiments, in step S1, the solid-liquid ratio of the first lithium iron phosphate black powder to water is 1:(8~12)g / mL.

[0034] In some embodiments, in step S2, the solid-liquid ratio of the second lithium iron phosphate black powder to the aluminum removal solution is 1:(8-12)g / mL.

[0035] In some embodiments, the solid-liquid ratio of the nth lithium iron phosphate black powder to the aluminum removal (n-1) stage liquid is 1:(8~12)g / mL.

[0036] In some embodiments, the aluminum removal solution comprises the following components: H3PO4, H2PO4 - HPO4 2- PO4 3- The content of the above components, Fe3(PO4)2·nH2O, is 1-3 mol / L.

[0037] In some embodiments, the pH of the aluminum removal solution is 3.6–4.6. The aluminum removal reaction of the present invention is carried out at 60–80°C, and the aluminum removal solution with a pH in the range of 3.6–4.6 can be used to remove aluminum from lithium iron phosphate black powder while preventing the destruction of the lithium iron phosphate structure.

[0038] In some embodiments, the aluminum removal solution further comprises Al 3+ The Al 3+ The concentration is below 3 mol / L.

[0039] In some embodiments, the aluminum removal solution further contains Fe. 2+The Fe 2+ The concentration is below 3 mol / L.

[0040] According to a second aspect of the present invention, a method for removing aluminum impurities from waste lithium iron phosphate black powder is provided, comprising the steps of the preparation method described in the first aspect of the present invention, and further comprising the following steps:

[0041] Waste lithium iron phosphate black powder is mixed with the aluminum removal solution at a solid-liquid ratio of 1:(8-12)g / mL, and phosphoric acid is added dropwise until the pH is 3.6-4.6. After solid-liquid separation, aluminum removal (n+1) stage slag and aluminum removal liquid are obtained.

[0042] The dealuminated solution can be directly recycled as a dealumination solution.

[0043] According to one embodiment of the present invention, at least the following beneficial effects are achieved:

[0044] 1. This invention can obtain an aluminum removal solution by using only phosphoric acid leaching, which is a simple method; the obtained aluminum removal solution can achieve deep removal of aluminum impurities in lithium iron phosphate black powder.

[0045] 2. The only reagent consumed in the aluminum removal process is phosphoric acid, and the leachate after aluminum removal can be recycled, resulting in low production costs.

[0046] 3. Phosphoric acid with the same acid group as lithium iron phosphate is used in the aluminum removal process, so there is no problem of introducing new impurity elements.

[0047] 4. The aluminum removal solution of the present invention does not damage the structure of lithium iron phosphate during the aluminum removal process, and the black powder after aluminum removal can be directly used for repair. Attached Figure Description

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0049] Figure 1 This is a flowchart of the phosphoric acid system for aluminum removal in Embodiment 1 of the present invention. Detailed Implementation

[0050] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention.

[0051] Unless otherwise specified, the raw materials, reagents or apparatus used in the following examples and comparative examples are available from conventional commercial sources or can be obtained by existing known methods.

[0052] Example 1

[0053] This embodiment provides a method for preparing an aluminum removal solution for lithium iron phosphate black powder. The main element contents of the lithium iron phosphate black powder are shown in the table below:

[0054]

[0055] The preparation method includes the following steps:

[0056] (1) Waste lithium iron phosphate black powder was dissolved in deionized water at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 8 mL / min at 80℃. After 4.5 h, the pH stabilized at 3.8. The filtrate was obtained by vacuum filtration, which was the first stage of aluminum removal solution. The filter residue was dried to obtain the first stage of aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 11.26%, 2.65%, and 3.86%, respectively, and the removal rate of Al was 10.48%.

[0057] (2) Waste lithium iron phosphate black powder was dissolved in the first stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 7 mL / min at 80℃. After 3.3 h, the pH stabilized at 3.8. The filtrate was obtained by suction filtration, which was the second stage aluminum removal solution. The filter residue was dried to obtain the second stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 9.14%, 2.55%, and 3.17%, respectively, and the removal rate of Al was 39.31%.

[0058] (3) Waste lithium iron phosphate black powder was dissolved in the second-stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 6 mL / min at 80℃. After 2.6 h, the pH stabilized at 3.8. The filtrate was obtained by suction filtration, which was the third-stage aluminum removal solution. The filter residue was dried to obtain the third-stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 8.23%, 2.13%, and 2.94%, respectively, and the Al removal rate was 55.65%.

[0059] (4) Waste lithium iron phosphate black powder was dissolved in the aluminum removal stage three solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at 80℃ at a rate of 3 mL / min. After 2.1 h, the pH stabilized to 3.8. The filtrate was obtained by suction filtration, which was the aluminum removal stage four solution. The filter residue was dried to obtain the aluminum removal stage four residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 4.37%, 1.56%, and 1.98%, respectively, and the Al removal rate was 74.52%.

[0060] (5) Waste lithium iron phosphate black powder was dissolved in the fourth stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.5 h, the pH stabilized to 3.8. The filtrate was obtained by vacuum filtration, which yielded the aluminum removal solution. The dried filter residue was the fifth stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.22%, 1.06%, and 1.32%, respectively, and the Al removal rate was 92.55%.

[0061] This embodiment also provides a method for removing aluminum impurities from waste lithium iron phosphate black powder, which further includes the following steps:

[0062] (6) Waste lithium iron phosphate black powder was dissolved in an aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.4 h, the pH stabilized at 3.8. The dealuminated liquid was obtained by filtration and dried to obtain the six-stage dealuminated slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.14%, 1.03%, and 1.22%, respectively, and the Al removal rate was 93.11%. After repairing the six-stage dealuminated slag, lithium iron phosphate cathode material was obtained. The dealuminated liquid can be recycled for the removal of aluminum impurities from waste lithium iron phosphate black powder.

[0063] The above-mentioned aluminum-removed liquid is used to leach waste lithium iron phosphate black powder in a cyclic process, as follows:

[0064] (7) Waste lithium iron phosphate black powder was dissolved in the dealuminized solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized at 3.8. The solution was filtered to obtain the second dealuminized solution, and dried to obtain the dealuminized slag of the seventh stage. The loss rates of Li, Fe, and P during the dealuminization process were measured to be 3.02%, 0.99%, and 1.15%, respectively, and the Al removal rate was 93.14%.

[0065] (8) Waste lithium iron phosphate black powder was dissolved in the second aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized to 3.8. The third aluminum removal solution was obtained by filtration and drying to obtain the aluminum removal stage 8 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 2.95%, 0.96%, and 1.13%, respectively, and the Al removal rate was 93.20%.

[0066] (9) Waste lithium iron phosphate black powder was dissolved in the third aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized to 3.8. The fourth aluminum removal solution was obtained by filtration and drying to obtain the aluminum removal nine-stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 2.96%, 0.94%, and 1.15%, respectively, and the Al removal rate was 93.15%.

[0067] (10) Waste lithium iron phosphate black powder was dissolved in the fourth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized to 3.8. The fifth aluminum removal solution was obtained by filtration and dried to obtain the aluminum removal stage 10 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 2.98%, 0.97%, and 1.10%, respectively, and the Al removal rate was 93.17%.

[0068] (11) Waste lithium iron phosphate black powder was dissolved in the fifth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized to 3.8. The sixth aluminum removal solution was obtained by filtration and dried to obtain the eleventh aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 2.95%, 0.93%, and 1.12%, respectively, and the Al removal rate was 93.13%.

[0069] (12) Waste lithium iron phosphate black powder was dissolved in the sixth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized to 3.8. The solution was then filtered to obtain the seventh aluminum removal solution and dried to obtain the aluminum removal stage 12 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 2.88%, 0.94%, and 1.09%, respectively, and the Al removal rate was 93.02%.

[0070] (13) Waste lithium iron phosphate black powder was dissolved in the seventh aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (7 mol / L concentration) was added dropwise at a rate of 2 mL / min at 80℃. After 0.3 h, the pH stabilized to 3.8. The solution was then filtered to obtain the eighth aluminum removal solution and dried to obtain the thirteenth aluminum removal stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 2.85%, 0.93%, and 1.11%, respectively, and the Al removal rate was 93.22%.

[0071] Example 2

[0072] This embodiment provides a method for preparing an aluminum removal solution for lithium iron phosphate black powder. The main element contents of the lithium iron phosphate black powder are shown in the table below:

[0073]

[0074]

[0075] The preparation method includes the following steps:

[0076] (1) Waste lithium iron phosphate black powder was dissolved in deionized water at a liquid-to-solid ratio of 10:1. Phosphoric acid (concentration of 4 mol / L) was added dropwise at a rate of 10 mL / min at 60℃. After 5.6 h, the pH stabilized to 3.6. The filtrate was obtained by vacuum filtration, which was the first stage of aluminum removal solution. The filter residue was dried to obtain the first stage of aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 15.28%, 3.94%, and 4.27%, respectively, and the removal rate of Al was 11.53%.

[0077] (2) Waste lithium iron phosphate black powder was dissolved in the first stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 8 mL / min at 60℃. After 4.2 h, the pH stabilized to 3.6. The filtrate was obtained by suction filtration, which was the second stage aluminum removal solution. The filter residue was dried to obtain the second stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 12.55%, 3.44%, and 4.06%, respectively, and the removal rate of Al was 36.62%.

[0078] (3) Waste lithium iron phosphate black powder was dissolved in the second-stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 7 mL / min at 60℃. After 3.6 h, the pH stabilized at 3.6. The filtrate was obtained by suction filtration, which was the third-stage aluminum removal solution. The filter residue was dried to obtain the third-stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 11.43%, 3.22%, and 3.86%, respectively, and the removal rate of Al was 56.62%.

[0079] (4) Waste lithium iron phosphate black powder was dissolved in the aluminum removal stage three solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (concentration of 4 mol / L) was added dropwise at a rate of 7 mL / min at 60℃. After 2.9 h, the pH stabilized to 3.6. The filtrate was obtained by suction filtration, which was the aluminum removal stage four solution. The filter residue was dried to obtain the aluminum removal stage four residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 8.22%, 2.41%, and 2.66%, respectively, and the Al removal rate was 70.22%.

[0080] (5) Waste lithium iron phosphate black powder was dissolved in the fourth stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 5 mL / min at 60℃. After 0.9 h, the pH stabilized to 3.6. The filtrate was obtained by vacuum filtration, which yielded the aluminum removal solution. The dried filter residue was the fifth stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 5.24%, 2.01%, and 2.33%, respectively, and the Al removal rate was 88.46%.

[0081] This embodiment also provides a method for removing aluminum impurities from waste lithium iron phosphate black powder, which further includes the following steps:

[0082] (6) Waste lithium iron phosphate black powder was dissolved in an aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 5 mL / min at 60℃. After 0.6 h, the pH stabilized at 3.6. The dealuminated liquid was obtained by filtration and dried to obtain the aluminum removal six-stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 4.37%, 1.66%, and 1.85%, respectively, and the Al removal rate was 92.54%. After repairing the aluminum removal six-stage slag, lithium iron phosphate cathode material was obtained. The dealuminated liquid can be recycled for the removal of aluminum impurities from waste lithium iron phosphate black powder.

[0083] The above-mentioned aluminum-removed liquid is used to leach waste lithium iron phosphate black powder in a cyclic process, as follows:

[0084] (7) Waste lithium iron phosphate black powder was dissolved in the dealuminized solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 5 mL / min at 60℃. After 0.5 h, the pH stabilized to 3.6. The solution was filtered to obtain the second dealuminized solution, and dried to obtain the dealuminized slag from the seventh stage. The loss rates of Li, Fe, and P during the dealuminization process were measured to be 3.88%, 1.24%, and 1.66%, respectively, and the Al removal rate was 93.17%.

[0085] (8) Waste lithium iron phosphate black powder was dissolved in the second aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 3 mL / min at 60℃. After 0.5 h, the pH stabilized to 3.6. The third aluminum removal solution was obtained by filtration and drying to obtain the aluminum removal stage 8 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.66%, 1.15%, and 1.88%, respectively, and the Al removal rate was 94.67%.

[0086] (9) Waste lithium iron phosphate black powder was dissolved in the third aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 3 mL / min at 60℃. After 0.4 h, the pH stabilized to 3.6. The fourth aluminum removal solution was obtained by filtration and drying to obtain the aluminum removal nine-stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.76%, 1.12%, and 1.76%, respectively, and the Al removal rate was 94.32%.

[0087] (10) Waste lithium iron phosphate black powder was dissolved in the fourth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (concentration of 4 mol / L) was added dropwise at a rate of 2 mL / min at 60℃. After 0.3 h, the pH stabilized to 3.6. The fifth aluminum removal solution was obtained by filtration and dried to obtain the aluminum removal stage 10 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.63%, 1.06%, and 1.85%, respectively, and the Al removal rate was 95.02%.

[0088] (11) Waste lithium iron phosphate black powder was dissolved in the fifth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 2 mL / min at 60℃. After 0.3 h, the pH stabilized to 3.6. The sixth aluminum removal solution was obtained by filtration and dried to obtain the eleventh aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.78%, 1.26%, and 1.93%, respectively, and the Al removal rate was 94.83%.

[0089] (12) Waste lithium iron phosphate black powder was dissolved in the sixth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 2 mL / min at 60℃. After 0.3 h, the pH stabilized to 3.6. The solution was filtered to obtain the seventh aluminum removal solution and dried to obtain the aluminum removal stage 12 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.85%, 1.14%, and 1.83%, respectively, and the Al removal rate was 94.76%.

[0090] (13) Waste lithium iron phosphate black powder was dissolved in the seventh aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 2 mL / min at 60℃. After 0.3 h, the pH stabilized to 3.6. The solution was filtered to obtain the eighth aluminum removal solution and dried to obtain the thirteenth aluminum removal stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.66%, 1.16%, and 1.77%, respectively, and the Al removal rate was 95.09%.

[0091] Example 3

[0092] This embodiment provides a method for preparing an aluminum removal solution for lithium iron phosphate black powder. The main element contents of the lithium iron phosphate black powder are shown in the table below:

[0093]

[0094] The preparation method includes the following steps:

[0095] (1) Waste lithium iron phosphate black powder was dissolved in deionized water at a liquid-to-solid ratio of 10:1. Phosphoric acid (concentration of 4 mol / L) was added dropwise at a rate of 9 mL / min at 60℃. After 4.3 h, the pH stabilized to 4.6. The filtrate was obtained by vacuum filtration, which was the first stage of aluminum removal solution. The filter residue was dried to obtain the first stage of aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 9.46%, 2.42%, and 3.01%, respectively, and the removal rate of Al was 8.26%.

[0096] (2) Waste lithium iron phosphate black powder was dissolved in the first stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 8 mL / min at 60℃. After 3.8 h, the pH stabilized to 4.6. The filtrate was obtained by suction filtration, which was the second stage aluminum removal solution. The filter residue was dried to obtain the second stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 9.08%, 2.11%, and 2.84%, respectively, and the removal rate of Al was 25.47%.

[0097] (3) Waste lithium iron phosphate black powder was dissolved in the second-stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 6 mL / min at 60℃. After 3.3 h, the pH stabilized to 4.6. The filtrate was obtained by suction filtration, which was the third-stage aluminum removal solution. The filter residue was dried to obtain the third-stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 8.66%, 2.05%, and 2.36%, respectively, and the removal rate of Al was 46.53%.

[0098] (4) Waste lithium iron phosphate black powder was dissolved in the aluminum removal stage three solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (concentration of 4 mol / L) was added dropwise at a rate of 4 mL / min at 60℃. After 2.7 h, the pH stabilized to 4.6. The filtrate was obtained by suction filtration, which was the aluminum removal stage four solution. The filter residue was dried to obtain the aluminum removal stage four residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 7.31%, 2.01%, and 2.07%, respectively, and the Al removal rate was 63.25%.

[0099] (5) Waste lithium iron phosphate black powder was dissolved in the fourth stage aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 3 mL / min at 60℃. After 0.6 h, the pH stabilized to 4.6. The filtrate was obtained by vacuum filtration, which yielded the aluminum removal solution. The dried filter residue was the fifth stage aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 5.94%, 1.46%, and 1.57%, respectively, and the Al removal rate was 75.49%.

[0100] This embodiment also provides a method for removing aluminum impurities from waste lithium iron phosphate black powder, which further includes the following steps:

[0101] (6) Waste lithium iron phosphate black powder was dissolved in an aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 2 mL / min at 60℃. After 0.6 h, the pH stabilized at 4.6. The solution after aluminum removal was filtered and dried to obtain the aluminum removal six-stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.31%, 1.08%, and 1.47%, respectively, and the Al removal rate was 89.55%. After repairing the aluminum removal six-stage slag, lithium iron phosphate cathode material was obtained. The aluminum removal solution can be recycled for the removal of aluminum impurities from waste lithium iron phosphate black powder.

[0102] The above-mentioned aluminum-removed liquid is used to leach waste lithium iron phosphate black powder in a cyclic process, as follows:

[0103] (7) Waste lithium iron phosphate black powder was dissolved in the dealuminized solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 2 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The solution was filtered to obtain the second dealuminized solution, and dried to obtain the dealuminized slag of the seventh stage. The loss rates of Li, Fe, and P during the dealuminization process were measured to be 3.24%, 0.92%, and 1.33%, respectively, and the Al removal rate was 90.07%.

[0104] (8) Waste lithium iron phosphate black powder was dissolved in the second aluminum-removed liquid at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 2 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The third aluminum-removed liquid was obtained by filtration and drying to obtain the aluminum-removed eight-stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.05%, 0.85%, and 1.24%, respectively, and the Al removal rate was 90.53%.

[0105] (9) Waste lithium iron phosphate black powder was dissolved in the third aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 1 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The fourth aluminum removal solution was obtained by filtration and drying to obtain the aluminum removal nine-stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.04%, 0.88%, and 1.18%, respectively, and the Al removal rate was 90.34%.

[0106] (10) Waste lithium iron phosphate black powder was dissolved in the fourth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 1 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The fifth aluminum removal solution was obtained by filtration and dried to obtain the aluminum removal stage 10 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.11%, 0.92%, and 1.20%, respectively, and the Al removal rate was 90.63%.

[0107] (11) Waste lithium iron phosphate black powder was dissolved in the fifth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 1 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The sixth aluminum removal solution was obtained by filtration and dried to obtain the eleventh aluminum removal residue. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.06%, 0.89%, and 1.25%, respectively, and the Al removal rate was 90.11%.

[0108] (12) Waste lithium iron phosphate black powder was dissolved in the sixth aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 1 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The solution was filtered to obtain the seventh aluminum removal solution and dried to obtain the aluminum removal stage 12 slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.07%, 0.92%, and 1.16%, respectively, and the Al removal rate was 90.33%.

[0109] (13) Waste lithium iron phosphate black powder was dissolved in the seventh aluminum removal solution at a liquid-to-solid ratio of 10:1. Phosphoric acid (4 mol / L concentration) was added dropwise at a rate of 1 mL / min at 60℃. After 0.3 h, the pH stabilized to 4.6. The solution was then filtered to obtain the eighth aluminum removal solution and dried to obtain the thirteenth aluminum removal stage slag. The loss rates of Li, Fe, and P during the aluminum removal process were measured to be 3.13%, 0.94%, and 1.22%, respectively, and the Al removal rate was 90.06%.

[0110] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A process for the preparation of a de-alumination solution for lithium iron phosphate battery powder, characterized by, The method comprises the following steps: S1: dispersing the first lithium iron phosphate black powder in water, adding phosphoric acid dropwise until the pH is 3.6-4.6, and then performing solid-liquid separation to obtain aluminum removal first-stage residue and aluminum removal first-stage liquid; S2: mixing the aluminum removal first-stage liquid obtained in step S1 with the second lithium iron phosphate black powder, adding phosphoric acid dropwise until the pH is 3.6-4.6, and then performing solid-liquid separation to obtain aluminum removal second-stage residue and aluminum removal second-stage liquid; S3: repeating the above steps, mixing the aluminum removal (n-1) stage liquid with the nth lithium iron phosphate black powder, adding phosphoric acid dropwise until the pH is 3.6-4.6, and then performing solid-liquid separation to obtain aluminum removal n-stage residue and aluminum removal solution; wherein n is a positive integer and n>2.

2. The production method according to claim 1, characterized by, During the process of adding phosphoric acid, the temperature of the system is 60-80℃.

3. The preparation method according to claim 1, characterized in that, The concentration of the phosphoric acid is 4-7 mol / L.

4. The method of claim 1, wherein, The rate of adding the phosphoric acid is 1-10 mL / min.

5. The preparation method according to claim 1, characterized in that, The time of adding the phosphoric acid is 0.5-6 h.

6. The method of claim 1, wherein, In step S3, the time of adding the phosphoric acid is 0.5-1 h.

7. The preparation method according to claim 1, characterized in that, The content of aluminum and copper impurities in the first lithium iron phosphate black powder, the second lithium iron phosphate black powder and the nth lithium iron phosphate black powder is less than 2200 ppm.

8. The method of claim 1, wherein, In step S1, the solid-liquid ratio of the first lithium iron phosphate black powder to water is 1:(8-12) g / mL.

9. The method of claim 1, wherein, The solid-liquid ratio of the nth lithium iron phosphate black powder to the aluminum removal (n-1) stage liquid is 1:(8-12) g / mL.

10. A method for removing impurity aluminum from waste old lithium iron phosphate black powder, comprising the steps of the preparation method of any one of claims 1-9, characterized in that, The method further comprises the following steps: mixing waste lithium iron phosphate black powder with the aluminum removal solution at a solid-liquid ratio of 1:(8-12) g / mL, adding phosphoric acid dropwise until the pH is 3.6-4.6, and then performing solid-liquid separation to obtain aluminum removal (n+1) stage residue and aluminum removal solution.

Images