Method for sectional aluminum removal of waste lithium iron phosphate positive and negative electrode mixed black powder pickle liquor

Abstract

The invention discloses a method for sectional aluminum removal of waste lithium iron phosphate positive and negative electrode mixed black powder pickle liquor, the aluminum removal effect is remarkable, in the manufacturing process of waste lithium iron phosphate positive and negative electrode mixed black powder, part of positive plates are ground into powder and mixed in the waste lithium iron phosphate positive and negative electrode mixed black powder, all aluminum elements enter the pickle liquor in the acid leaching process, the aluminum element content in the pickle liquor reaches 1.5-4 g / l, and the aluminum element content in the pickle liquor reaches 1.5-4 g / l. The invention relates to the technical field of lithium iron phosphate anode and cathode treatment. According to the sectional aluminum removal method for the waste lithium iron phosphate positive and negative electrode mixed black powder pickle liquor, through the sectional aluminum removal process, the aluminum element content can be reduced to 50 ppm or below, the valuation metal element loss is low, and due to the fact that the PH value of the solution is increased in the inert atmosphere, other valuation elements such as Fe < 2 + > do not generate precipitation loss and only exist in aluminum slag in the form of a solution. The problem is solved just by removing aluminum in a segmented manner. In primary aluminum removal, a pH regulator with lower cost is adopted to remove most of aluminum elements, and a small amount of aluminum elements are remained and are finely removed by using an aluminum removal agent.

Description

Technical Field

[0001] The invention relates to the technical field of lithium iron phosphate positive and negative electrode processing, and specifically to a method for removing aluminum in sections by acid leaching of mixed black powder of waste lithium iron phosphate positive and negative electrodes. Background Art

[0002] Lithium iron phosphate (LiFePO 4) is a new type of positive electrode material for lithium-ion batteries. Due to its advantages of abundant iron resources, low price, good cycle performance and high safety performance, it is widely used in the electric vehicle industry under the support and guidance of my country's policies. However, with the rapid growth of the electric vehicle industry. At present, the recycling of waste lithium iron phosphate power batteries is mainly based on wet processes. The pre-treated waste lithium iron phosphate active materials are dissolved by acid leaching, and then purified to remove impurity elements such as aluminum and copper, and finally the metal elements in the leachate are recovered. Aluminum ions are impurity elements in sulfuric acid leachate. When metal elements are subsequently recovered in the form of iron phosphate and lithium carbonate precursors, the introduction of aluminum impurity elements will affect their electrochemical properties, so the aluminum removal process is particularly important. However, under current technical conditions, there are more or less technical defects.

[0003] A Chinese patent document with publication number CN106910889A discloses a method for regenerating positive electrode active material from waste lithium iron phosphate batteries, specifically a method for removing copper from a positive electrode active material leachate and then removing aluminum at a pH of 3 to 5. This method aims to precipitate Al 3+ in the system in the form of Al(OH)3 by adding alkali metal hydroxide to an acidic system. The aluminum removal effect of this method is not ideal. The addition of alkali metal hydroxide to an acidic system will cause the local pH in the system to be high, and white Fe3(PO4)2 precipitates will be generated, resulting in a large loss of PO 4 3- and Fe 2+, and the purpose of removing Al3+ impurities cannot be achieved.

[0004] CN114784405A discloses a method for recycling and removing aluminum from waste lithium iron phosphate batteries, the steps comprising: sequentially performing aluminum removal reaction, solid-liquid separation, i-th washing and leaching treatment on the positive electrode material powder of the waste lithium iron phosphate batteries; wherein the j-th washing adopts the j+1-th washing liquid obtained after the j+1-th washing in the previous batch, and the i-th washing adopts pure water; wherein 2≤i≤6, 1≤j.

[0005] CN116199201A discloses a method for removing aluminum from waste lithium iron phosphate pole piece powder and comprehensive recovery, which belongs to the field of resource recovery and utilization technology; specifically comprises the following steps: 1. using a certain concentration of hydrochloric acid and an oxidant to leach lithium, iron, phosphorus and other impurity elements from waste lithium iron phosphate pole piece black powder; 2. adding an extractant to the solution to extract trivalent iron from the aqueous solution into an organic phase; 3. after shock separation, adjusting the pH value of the aqueous phase to precipitate aluminum elements in the form of aluminum hydroxide and filter them out; 4. after remixing the inorganic phase with the organic phase, adjusting the pH value to obtain iron phosphate precipitate, and filtering; 5. adjusting the pH of the filtrate after filtration, adding phosphate to obtain lithium phosphate.

[0006] The aluminum removal method described in the above scheme is likely to cause loss of other elements during the aluminum removal process, and is likely to introduce impurity elements, thereby increasing the cost of impurity removal. Summary of the invention

[0007] 1. Technical issues to be solved

[0008] In view of the shortcomings of the prior art, the present invention provides a method for segmented aluminum removal from a mixed black powder acid leaching solution of waste lithium iron phosphate positive and negative electrodes, which solves the problem that the existing aluminum removal methods are prone to cause loss of other elements during the aluminum removal process and easily introduce impurity elements, thereby increasing the cost of impurity removal.

[0009] (II) Technical solution

[0010] To achieve the above objectives, the present invention is implemented by the following technical scheme: a method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid in stages, specifically comprising the following steps:

[0011] S1. Adding a pH regulator to the acidic solution to adjust the pH of the solution to between 2.0 and 6.0;

[0012] S2, at the pH value of step S1, start stirring, and stir the reaction in a constant temperature water bath at 30-80°C under an inert atmosphere for 1-3 hours;

[0013] S3, after the reaction is completed, the first solid-liquid separation is performed to obtain a primary aluminum removal liquid. 3+ The content is theoretically calculated, and the aluminum removal agent is added to the primary aluminum removal liquid, stirred for 1-3 hours, and combined with the residual aluminum in the solution to form an insoluble complex;

[0014] S4, after the reaction in step S3 is completed, a second solid-liquid separation is performed to obtain a secondary aluminum removal liquid, which is the final qualified purified liquid. At this time, the aluminum content in the solution can be reduced to below 50 ppm;

[0015] S5. The obtained primary aluminum slag and secondary aluminum slag are washed and purified with water, and the obtained washing water is returned to the acid leaching solution to recover the valuation metals carried away by the aluminum slag.

[0016] Preferably, the acidic solution in step S1 is allowed to contain other metal cation impurities.

[0017] Preferably, the metal cation impurity is Cu 2+ , Fe 2+ and Ti 2+ .

[0018] Preferably, the acidic solution is a sulfuric acid leaching solution of mixed black powder of positive and negative electrodes of waste lithium iron phosphate batteries.

[0019] Preferably, the amount of aluminum removal agent added in step S3 is 3+ The ionic impurities react completely at 1.0-1.5 times the theoretical amount.

[0020] Preferably, the temperature of the aluminum removal process in steps S3 and S4 is 30-80°C.

[0021] Preferably, the aluminum removal process in steps S3 and S4 is carried out under the protection of an inert atmosphere.

[0022] (III) Beneficial effects

[0023] The present invention provides a method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid in stages. Compared with the prior art, it has the following beneficial effects:

[0024] (1) The method of removing aluminum from the waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid in stages has a significant aluminum removal effect. During the production process of the waste lithium iron phosphate positive and negative electrode mixed black powder, part of the positive electrode sheet will be ground into powder and mixed into it. During the acid leaching, all the aluminum elements enter the acid leaching liquid, so that the aluminum content in the acid leaching liquid reaches 1.5-4g / l. After the staged aluminum removal process, the aluminum content can be reduced to below 50ppm.

[0025] (2) The method of removing aluminum by acid leaching liquid of mixed black powder of waste lithium iron phosphate positive and negative electrodes has low loss of pricing metal elements. Due to the increase of solution pH value under inert atmosphere, other pricing elements such as Fe2+ will not generate precipitation loss, but only exist in the aluminum slag as a solution. The aluminum slag can be recycled by washing with water.

[0026] (3) The method of removing aluminum in stages from the mixed black powder acid leaching liquid of the waste lithium iron phosphate positive and negative electrodes has a low aluminum removal cost. The common aluminum removal method currently generally adopts a one-step method to remove aluminum, which either uses a large amount of aluminum removal agent or results in a high loss of metal. The segmented aluminum removal solves this problem. A low-cost PH regulator is used for aluminum removal in one step to remove most of the aluminum element, and the remaining small amount of aluminum element is removed with an aluminum removal agent. The use of aluminum removal agent is greatly reduced, thereby reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0029] See also Figure 1 The embodiment of the present invention provides a technical solution: a method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid in stages, specifically including the following embodiments:

[0030] Example:

[0031] 1. Add a pH regulator to the acid leaching solution of waste lithium iron phosphate black powder. The composition of the acid leaching solution is shown in Table 1 to make the solution pH reach between 2.0 and 6.0.

[0032] Table 1: Composition of waste lithium iron phosphate black powder acid leaching solution

[0033]

[0034] 2. At the pH value described in step 1, start stirring and stir the mixture in a constant temperature water bath at 30-80°C under an inert atmosphere for 1-3 hours.

[0035] 3. After the reaction is completed, the first solid-liquid separation is carried out to obtain a primary aluminum removal liquid, and the composition of the primary aluminum removal liquid is analyzed.

[0036] Table 2: Composition of primary aluminum removal liquid

[0037]

[0038] 4. According to the Al in the primary aluminum removal liquid 3+ The content is calculated theoretically, and 1.0-1.5 times the theoretical amount of aluminum removal agent is added to the primary aluminum removal liquid. Stir and react for 1-3 hours.

[0039] 5. After the reaction in step 4 is completed, a second solid-liquid separation is performed to obtain a secondary aluminum removal liquid, which is the final qualified purified liquid. The secondary aluminum removal liquid is taken for component analysis.

[0040] Table 3: Composition of secondary aluminum removal liquid

[0041]

[0042] Comparative example: After one aluminum removal, the aluminum content of the waste lithium iron phosphate black powder acid leaching liquid can be reduced to between 600-800ppm, and after two aluminum removals, the aluminum content can be reduced to below 50ppm. Among them, a small amount of pricing metal elements (lithium iron, phosphorus, copper, etc.) enter the aluminum removal slag in the form of a solution, which can be recovered by subsequent water washing. The loss of pricing metal elements is small, the aluminum removal cost is reduced, and the aluminum removal effect is significant. However, after adding aluminum removal agent to the acid leaching liquid once, a large amount of pricing elements is lost, the aluminum purification effect is not thorough, and a large amount of aluminum removal agent is consumed, which increases the cost.

[0043] Table 4: Comparative Example Waste LiFePO4 Black Powder Acid Leaching Solution Composition Table

[0044]

[0045] Table 5: Comparative Example Aluminum Removal Liquid Composition

[0046]

[0047] In summary, the aluminum removal effect of the present invention is significant. In the production process of waste lithium iron phosphate positive and negative electrode mixed black powder, part of the positive electrode sheet will be ground into powder and mixed into it. During acid leaching, all the aluminum elements enter the acid leaching solution, so that the aluminum content in the acid leaching solution reaches 1.5-4g / l. After the segmented aluminum removal process, the aluminum content can be reduced to below 50ppm, and the loss of valuation metal elements is low. Due to the increase in the pH value of the solution under an inert atmosphere, other valuation elements such as Fe2+ will not generate precipitation losses, but only exist in the form of solution in the aluminum slag. The aluminum slag can be recycled by subsequent water washing, and the cost of aluminum removal is low. The common aluminum removal method currently generally adopts a one-step aluminum removal method, which either uses a large amount of aluminum removal agent or has a high loss of valuation metal. The segmented aluminum removal solves this problem. A low-cost PH regulator is used for aluminum removal at one time to remove most of the aluminum elements, and a small amount of aluminum elements remain, and an aluminum removal agent is used for fine removal. The amount of aluminum removal agent used is greatly reduced, thereby reducing costs.

[0048] Meanwhile, the contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0049] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0050] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid in stages, characterized in that: The specific steps include: S1. Adding a pH regulator to the acidic solution to adjust the pH of the solution to between 2.0 and 6.0; S2, at the pH value of step S1, start stirring, and stir the reaction in a constant temperature water bath at 30-80°C under an inert atmosphere for 1-3 hours; S3, after the reaction is completed, the first solid-liquid separation is performed to obtain a primary aluminum removal liquid. 3+ The content is theoretically calculated, and the aluminum removal agent is added to the primary aluminum removal liquid, stirred for 1-3 hours, and combined with the residual aluminum in the solution to form an insoluble complex; S4, after the reaction in step S3 is completed, a second solid-liquid separation is performed to obtain a secondary aluminum removal liquid, which is the final qualified purified liquid. At this time, the aluminum content in the solution can be reduced to below 50 ppm; S5. The obtained primary aluminum slag and secondary aluminum slag are washed and purified with water, and the obtained washing water is returned to the acid leaching solution to recover the valuation metals carried away by the aluminum slag.

2. The method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid by segmentation according to claim 1, characterized in that: The acidic solution in step S1 is allowed to contain other metal cation impurities.

3. The method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid by segmentation according to claim 2, characterized in that: The metal cation impurity is Cu 2+ , Fe 2+ and Ti 2+ .

4. The method for removing aluminum from waste lithium iron phosphate positive and negative electrode mixed black powder acid leaching liquid by stages according to claim 2, characterized in that: The acid solution is a sulfuric acid leaching solution of the positive and negative electrodes of waste lithium iron phosphate batteries mixed with black powder.

5. A method for removing aluminum by staged acid leaching of waste lithium iron phosphate positive and negative electrode mixed black powder according to any one of claims 1 to 4, characterized in that: The amount of aluminum removal agent added in step S3 is 3+ The ionic impurities react completely at 1.0-1.5 times the theoretical amount.

6. A method for removing aluminum by staged acid leaching of waste lithium iron phosphate positive and negative electrode mixed black powder according to any one of claims 1 to 4, characterized in that: The temperature of the aluminum removal process in steps S3 and S4 is 30-80°C.

7. A method for removing aluminum by staged acid leaching of waste lithium iron phosphate positive and negative electrode mixed black powder according to any one of claims 1 to 4, characterized in that: The aluminum removal process in steps S3 and S4 is carried out under the protection of an inert atmosphere.

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