Method for removing aluminum from lithium iron phosphate black powder

Abstract

The invention belongs to the field of lithium battery material recovery, and particularly relates to a method for removing aluminum from lithium iron phosphate black powder, which comprises the following steps: S1, discharging a lithium iron phosphate battery to be recovered, and then mechanically crushing and screening out the lithium iron phosphate black powder; s2, the lithium iron phosphate black powder is added into a first-section leaching tank to be leached, and first-section leaching liquid and first-section leaching residues are obtained; s3, acid leaching is adopted for second-stage leaching, and second-stage leaching residues and second-stage leaching liquid are obtained through separation after leaching; s4, heating and precipitating the phosphorus, iron and lithium lixivium to obtain hydrated iron phosphate solid and lithium-containing lixivium; and S5, precipitating the lithium-containing leachate to obtain a lithium carbonate solid.

Description

Technical Field

[0001] The invention belongs to the field of lithium battery material recycling, and in particular relates to a method for removing aluminum from lithium iron phosphate black powder. Background Art

[0002] Lithium iron phosphate battery (LiFePO4 battery) is a lithium-ion battery with lithium iron phosphate as the positive electrode material, which has excellent safety and stability. Compared with other lithium batteries, it is not prone to thermal runaway, reducing the risk of fire and explosion. The high temperature performance and cost-effectiveness of lithium iron phosphate batteries have made them widely used in many fields. The recycling of waste lithium iron phosphate batteries is also rapidly developing.

[0003] As a major power battery waste, lithium iron phosphate faces the problem of impurity removal during recycling. The traditional recycling process completely dissolves the waste lithium iron phosphate black powder, and then removes the impurity metals one by one, which usually leads to excessive loss of major metal elements such as Li, Fe, and P. Due to the limitations of LiFePO4 battery pretreatment, LiFePO4 positive electrode powder often carries residual collector-Al powder, and in the wet recycling process, Al impurities will inevitably enter the acid leaching solution with other components, resulting in the problem of excessive Al content in the recycled FePO4, which reduces the added value of the product and the economic value of recycling. In patent CN118458729A, lithium iron phosphate black powder is slurried and treated with a solution containing sodium chloride, sodium sulfide, sodium phosphate and sodium oxalate to remove aluminum, but the introduction of chloride ions will cause certain corrosion to the equipment. For example, in patent CN115304042B, organic acid is used in combination with chloride salt to leach lithium iron phosphate, lithium and impurities are selectively separated first, and then the leached ferrophosphorus slag is treated to prepare battery-grade iron phosphate. However, this process requires the use of organic acids and chloride salts, which will lead to high recovery costs and equipment corrosion. In application publication number CN116199201A, after lithium iron phosphate is leached with hydrochloric acid, Fe is selectively extracted into the organic phase using the different selectivity of the extractant for Fe and Al, and Fe is stripped into the solution after the Al ions in the solution are removed, which can achieve a higher Fe and P recovery rate, but the use of organic extraction agents will lead to an increase in recovery costs.

[0004] Therefore, how to avoid corrosion of equipment during the aluminum removal process and avoid excessive loss of iron and phosphorus during the aluminum impurity removal process are technical problems that urgently need to be solved in this field.

[0005] It should be noted that the above information disclosed in this background technology section is only used to understand the background technology of the present application concept, and therefore, the above description is not considered to constitute information of the prior art. Summary of the invention

[0006] The embodiment of the present disclosure provides a method for removing aluminum from lithium iron phosphate black powder, comprising the following steps: step S1, discharging the lithium iron phosphate battery to be recycled, then placing the discharged lithium iron phosphate battery in an inert atmosphere for roasting, cooling to room temperature, and mechanically crushing and screening the lithium iron phosphate black powder; step S2, adding the lithium iron phosphate black powder to a first leaching tank and adding a certain amount of leaching agent to remove aluminum, stirring, leaching and filtering to obtain a first leachate and a first leach residue; step S3, recycling the first leachate to treat the lithium iron phosphate black powder, and the first leach residue is subjected to a first leaching and then subjected to a second leaching, the second leaching adopts acid leaching, and after leaching, the second leaching residue and the second leachate are separated, and the second leachate is phosphorus, iron, and lithium leachate; step S4, heating and precipitating the phosphorus, iron, and lithium leachate to obtain hydrated iron phosphate solid and lithium-containing leachate; step S5, precipitating the lithium-containing leachate to obtain lithium carbonate solid.

[0007] In an optional embodiment, the contents of copper, aluminum and fluorine in the lithium iron phosphate black powder screened out in step S1 are all less than 1%.

[0008] In an optional embodiment, the leaching agent in step S2 is one or more of ferrous sulfate and dilute sulfuric acid solution.

[0009] In an optional embodiment, a section of the leaching solution in step S2 is a ferrous sulfate solution, the Fe concentration in the ferrous sulfate solution is 10-30 g / L, the solution pH is controlled at 2.0-3.0, the solid-liquid ratio is 10-20 g / L, the temperature is 50-80°C, and the reaction time is 1-2 h.

[0010] In an optional embodiment, the ferrous sulfate solution can be recycled and the Fe in the solution is greater than 1 g / L, and sulfuric acid is used to adjust the pH of the solution so that the pH of the ferrous sulfate solution is controlled between 2.0 and 3.0.

[0011] In an optional embodiment, the chemical reaction equation occurring during the first leaching process is:

[0012] 2Al+3FeSO4=3Fe+Al2(SO4)3;

[0013] During the recycling process of the ferrous sulfate solution, the Fe element is replaced by Al, resulting in a gradual decrease in the concentration of the Fe element in the solution. When Fe in the ferrous sulfate solution is ≤1g / L, the elements in the ferrous sulfate solution are recovered, including Li, Fe, Al, Cu, and F.

[0014] In an optional embodiment, the acid used in the second-stage leaching in step S3 is sulfuric acid.

[0015] In an optional embodiment, the second-stage leaching temperature is 40-80° C., and the leaching time is 2-4 hours.

[0016] In an optional embodiment, the chemical reaction equation occurring during the second-stage leaching in step S3 is: 2LiFePO4+3H2SO4=Li2SO4+2FeSO4+2H3PO4.

[0017] The beneficial effect of the present invention is that the present invention provides a method for removing aluminum from lithium iron phosphate black powder, and the iron element in the ferrous sulfate solution is used to replace the elemental aluminum in the first leaching process, so as to remove the aluminum element in the lithium iron phosphate black powder. On the one hand, benefiting from the replacement of the iron element with aluminum in the first leaching solution, the iron content in the lithium iron phosphate after the first leaching will increase slightly and the loss of P in the whole process is in a low range, and the overall loss does not exceed 2.08%. On the other hand, the leachate in the whole process does not need to introduce chloride salts, and will not cause corrosion to the equipment.

[0018] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description, claims and drawings.

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A flow chart of a method for removing aluminum from lithium iron phosphate black powder provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The terms used herein are only used to describe specific exemplary configurations and are not intended to be limited. As used herein, the singular articles "one", "an" and "the" may also be intended to include plural forms, unless it is clearly indicated above that this is not the case. The terms "comprise", "include" and "have" are inclusive, and therefore specify the presence of features, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components and / or combinations thereof. The method steps, processes and operations described herein should not be interpreted as necessarily requiring them to be performed in the specific order discussed or shown, unless specifically identified as an execution order. Additional or alternative steps may be adopted.

[0024] As used herein, the phrases "in one embodiment," "according to one embodiment," "in some embodiments," and the like generally refer to the fact that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present disclosure. Therefore, a particular feature, structure, or characteristic may be included in more than one embodiment of the present disclosure, so that these phrases do not necessarily refer to the same embodiment. As used herein, the terms "example," "exemplary," and the like are used to "serve as an example, instance, or illustration." Any implementation, aspect, or design described herein as "example" or "exemplary" is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. On the contrary, the use of the terms "example," "exemplary," and the like is intended to present concepts in a concrete manner.

[0025] Research has found that the disadvantages of the existing technology are: the cost of removing aluminum impurities in the recycling process of lithium iron phosphate batteries is high, and the recovery rate of Fe and P in the process of removing aluminum impurities is low.

[0026] Based on the above research, the embodiments of the present disclosure provide a method for removing aluminum from lithium iron phosphate black powder, which solves the difficulty of removing aluminum impurities in wet recovery of lithium iron phosphate, and at the same time has good economic effects compared with current aluminum removal methods.

[0027] The defects existing in the above solutions are the results obtained by the inventor after practice and careful research. Therefore, the discovery process of the above problems and the solutions proposed by the present disclosure for the above problems below should be the contributions made by the inventor to the present disclosure during the disclosure process.

[0028] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0029] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0030] The disclosed embodiment provides a method for removing aluminum from lithium iron phosphate black powder, comprising the following steps: step S1, discharging the lithium iron phosphate battery to be recycled, calcining it in an inert atmosphere cracking furnace and then cooling it to room temperature, and then mechanically crushing and screening the lithium iron phosphate black powder; step S2, adding the lithium iron phosphate black powder to a first leaching tank and adding a certain amount of leaching agent to remove aluminum, stirring, leaching and filtering to obtain a first leachate and a first leach residue; step S3, the first leachate can be recycled to treat the lithium iron phosphate black powder, and the first leach residue is subjected to a first leaching and then a second leaching, the second leaching adopts acid leaching, and after leaching, the second leaching residue and the second leachate are separated; step S4, heating and precipitating the phosphorus, iron and lithium leachates to obtain hydrated iron phosphate solid and lithium-containing leachate; step S5, the lithium-containing leachate is precipitated to obtain lithium carbonate solid.

[0031] In some embodiments, specifically, the contents of copper, aluminum and fluorine in the lithium iron phosphate black powder sieved out in step S1 are all less than 1%.

[0032] In some embodiments, specifically, the leaching agent in step S2 is one or more of ferrous sulfate and dilute sulfuric acid solution.

[0033] In some embodiments, specifically, a section of the leaching solution in step S2 is a ferrous sulfate solution, the Fe concentration in the ferrous sulfate solution is 10-30 g / L, the solution pH is controlled at 2.0-3.0, the solid-liquid ratio is 10-20 g / L, the temperature is 50-80°C, and the reaction time is 1-2 h.

[0034] In some embodiments, specifically, the ferrous sulfate solution can be recycled and the Fe in the solution is greater than 1 g / L, and sulfuric acid is used to adjust the pH of the solution so that the pH of the ferrous sulfate solution is controlled between 2.0 and 3.0.

[0035] In some embodiments, specifically, the chemical reaction equation occurring during the first leaching process is:

[0036] 2Al+3FeSO4=3Fe+Al2(SO4)3;

[0037] During the recycling process of the ferrous sulfate solution, the Fe element is replaced by Al, resulting in a gradual decrease in the concentration of the Fe element in the solution. When Fe in the ferrous sulfate solution is ≤1g / L, the elements in the ferrous sulfate solution are recovered, including Li, Fe, Al, Cu, and F.

[0038] In some embodiments, specifically, the acid used in the second-stage leaching in step S3 is sulfuric acid.

[0039] In some embodiments, specifically, the second stage leaching temperature is 40 to 80° C., and the leaching time is 2 to 4 hours.

[0040] In some embodiments, specifically, the chemical reaction equation occurring during the second stage leaching is:

[0041] 2LiFePO4+3H2SO4=Li2SO4+2FeSO4+2H3PO4.

[0042] The specific implementation modes of the present invention will be further explained below through examples, but it is not intended to limit the protection scope of the present invention to the scope described in the examples.

[0043] Example 1

[0044] The specific steps are as follows:

[0045] Take 250g of lithium iron phosphate black powder obtained by disassembly and crushing and add it to the reactor. The experimental conditions for the first leaching are a solid-liquid ratio of 15g / L, a reaction temperature of 50°C, a solution pH of 2.3, a reaction time of 1.2 hours, and a concentration of iron in the leaching solution of 10g / L. When recycled, sulfuric acid is used to keep the pH of the leaching solution at about 2.0. After the first leaching, the solution is filtered. The filter residue is subjected to a second-stage leaching. The second-stage leaching conditions are a sulfuric acid concentration of 1mol / L, a reaction time of 4 hours, and the lithium iron phosphate leaching solution and graphite slag are obtained by filtration. The lithium iron phosphate leaching solution uses hydrogen peroxide oxidation and ammonia water to adjust the precipitation of iron phosphate. The pH is controlled at about 2.0, the reaction time is 10 hours, and the aging time is 6 hours. The iron phosphate solid and the lithium-containing solution are filtered to obtain the battery-grade iron phosphate. The lithium-containing solution is refined by conventional lithium precipitation to obtain battery-grade lithium carbonate.

[0046] In the case where the specific steps are the same, the parameters and performances of Examples 1-5 shown in the following table are obtained by modifying some parameters in Example 1:

[0047] Table 1: Changes in the contents of Li, P, Fe and aluminum in Examples 1-5

[0048]

[0049]

[0050] Comparative Example 1:

[0051] Take 250g of lithium iron phosphate black powder obtained by disassembly and crushing and add it to the reactor, use sulfuric acid solution for leaching, the sulfuric acid concentration is 1mol / L, the reaction time is 4 hours, and filter to obtain lithium iron phosphate leachate and graphite slag. The lithium iron phosphate leachate adjusts the solution temperature to 50°C, the pH value to 2.3, the reaction time is 1.2h, and the Al ion concentration in the filtered solution after precipitation is 30mg / L, the iron loss rate is 32.31%, and the phosphorus loss rate is 21.63%. The solution after aluminum removal uses hydrogen peroxide oxidation and ammonia water to adjust the precipitation of iron phosphate, the reaction time is 10 hours, and the aging time is 6 hours. Filter to obtain iron phosphate solid and lithium-containing solution, and the iron phosphate solid can be washed to obtain battery-grade iron phosphate. The lithium-containing solution is refined by conventional lithium precipitation to obtain battery-grade lithium carbonate.

[0052] Referring to Table 1, in Examples 1-5, the iron element in the first leaching has an increment of 1.62%-1.99%. This is because the ferrous sulfate in the first leaching solution reacts with aluminum, and the aluminum element in the lithium iron phosphate black powder is removed by the replacement of iron and aluminum, and the iron element in the first leaching slag is increased at the same time. The impurity aluminum has been removed in the first leaching process, and the second leaching does not need to be removed, so the second leaching iron will not be lost. The second leaching solution of the lithium iron phosphate black powder after aluminum removal in different embodiments can reach a lower aluminum content, but the effect of aluminum removal is also different due to the different time of the first leaching. The longer the leaching time, the better the effect of aluminum removal. In addition, the increment of iron is related to the effect of aluminum removal. The better the aluminum removal effect, the more the increment of iron. In addition, the lithium iron phosphate black powder contains a certain amount of graphite with a certain adsorption capacity. When the leaching time is long, it will also cause more iron-containing salts to be adsorbed on it, resulting in an increase in iron content.

[0053] Continuing to refer to Table 1, it can be seen in Examples 1-5 that the higher the pH of the reaction solution, the less the loss of lithium and phosphorus. This is because at a lower pH value, the solution is more acidic and lithium iron phosphate is more easily leached, resulting in increased loss. However, a higher pH value will cause precipitation of iron ions in the first stage of the leachate, so the preferred pH for the first stage of the leaching process is 2.0-3.0.

[0054] Continuing to refer to Table 1, by comparing Examples 1-5 with Comparative Example 1, the P loss in Examples 1-5 is 1.77%-2.08%, the Fe increase is 1.52%-1.99%, and the aluminum content is 7.79-12.26 mg / L; while in Comparative Example 1, under the same parameters, the Fe loss rate is 32.31%, the P loss rate is 21.63%, and the aluminum content is 30 mg / L; compared with the data of Comparative Example 1, the P loss rate of the present invention is in a lower range, the Fe content is increased, and the aluminum removal effect is better.

[0055] In summary, the present invention provides a method for removing aluminum from lithium iron phosphate black powder, in which the iron element in the ferrous sulfate solution is used to replace the elemental aluminum in a leaching process, thereby removing the aluminum element in the lithium iron phosphate black powder. On the one hand, benefiting from the replacement of the iron element with aluminum in a leaching solution, the iron content in the lithium iron phosphate after a leaching process will increase slightly and the loss of P in the entire process flow is in a relatively low range, and the overall loss does not exceed 2.08%. On the other hand, the leaching solution in the entire process flow does not need to introduce chloride salts, and will not cause corrosion to the equipment.

[0056] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for removing aluminum from lithium iron phosphate black powder, characterized in that: The following steps are involved: Step S1, discharging the lithium iron phosphate battery to be recycled, then calcining the discharged lithium iron phosphate battery in an inert atmosphere, cooling it to room temperature, and then mechanically crushing and screening out the lithium iron phosphate black powder; Step S2, adding lithium iron phosphate black powder into a leaching tank and adding a certain amount of leaching agent to remove aluminum, stirring, leaching and filtering to obtain a leachate and a leaching residue; Step S3, recycling the first-stage leaching solution to treat lithium iron phosphate black powder, and subjecting the first-stage leaching residue to a second-stage leaching after the first-stage leaching, wherein the second-stage leaching adopts acid leaching, and after leaching, the second-stage leaching residue and the second-stage leaching solution are separated, wherein the second-stage leaching solution is a phosphorus, iron, and lithium leaching solution; Step S4, heating and precipitating the phosphorus, iron and lithium leachates to obtain hydrated iron phosphate solid and lithium-containing leachate; Step S5, obtaining lithium carbonate solid by precipitation of the lithium-containing leaching solution.

2. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 1, characterized in that: The contents of copper, aluminum and fluorine in the lithium iron phosphate black powder screened out in step S1 are all less than 1%.

3. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 1, characterized in that: The leaching agent in step S2 is one or more of ferrous sulfate and dilute sulfuric acid solution.

4. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 1, characterized in that: The first leaching solution in step S2 is a ferrous sulfate solution, the Fe concentration in the ferrous sulfate solution is 10-30 g / L, the solution pH is controlled at 2.0-3.0, the solid-liquid ratio is 10-20 g / L, the temperature is 50-80° C., and the reaction time is 1-2 hours.

5. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 4, characterized in that: The ferrous sulfate solution can be recycled and the Fe in the solution is greater than 1 g / L. Sulfuric acid is used to adjust the pH of the solution so that the pH of the ferrous sulfate solution is controlled between 2.0 and 3.

0.

6. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 4, characterized in that: The chemical reaction equation occurring during the leaching process is: 2Al+3FeSO4=3Fe+Al2(SO4)3; During the recycling process of the ferrous sulfate solution, the Fe element is replaced by Al, resulting in a gradual decrease in the concentration of the Fe element in the solution. When Fe in the ferrous sulfate solution is ≤1g / L, the elements in the ferrous sulfate solution are recovered, including Li, Fe, Al, Cu, and F.

7. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 1, characterized in that: The acid used in the second-stage leaching in step S3 is sulfuric acid.

8. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 1, characterized in that: The second stage leaching temperature is 40-80° C., and the leaching time is 2-4 hours.

9. The method for removing aluminum from lithium iron phosphate black powder as claimed in claim 1, characterized in that: The chemical reaction equation occurring during the second stage leaching in step S3 is: 2LiFePO4+3H2SO4=Li2SO4+2FeSO4+2H3PO4.

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