Method for removing aluminum and comprehensively recovering waste lithium iron phosphate pole piece powder

Abstract

The application discloses a kind of waste old lithium iron phosphate pole piece powder aluminum removal and comprehensive recovery method, belong to resource recycling technical field;Specifically including the following steps: 1. using certain concentration hydrochloric acid and oxidizing agent will lithium, iron, phosphorus and other impurity elements from waste old iron lithium pole piece black powder leaching;2. adding extractant to solution, extract trivalent iron from aqueous solution into organic phase;3. after oscillation separation, adjust the pH value of water phase, make aluminum element in the form of aluminum hydroxide precipitate, filter out;4. after inorganic phase and organic phase are mixed again, adjust pH value, obtain iron phosphate precipitate, filter;5. after filtration, adjust the pH of filtrate, add phosphate, obtain lithium phosphate.The application has the advantages of high product recovery rate, good aluminum removal effect, high product purity, can comprehensively recover all elements of phosphoric acid lithium iron, and no excessive iron phosphorus slag and heavy metal wastewater discharge.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resource recycling, and particularly relates to a method for removing aluminum and comprehensively recycling waste lithium iron phosphate pole piece powder. BACKGROUND

[0002] In recent years, lithium ion batteries are widely used in the field of consumer electronics and electric vehicles. Among them, lithium iron phosphate batteries are increasingly favored by the market due to their relatively low price, good safety and other advantages, and the market share gradually increases.

[0003] It is reported that the retired scale of power batteries in China will reach 450,000 tons in 2025. If these retired batteries are not effectively treated and utilized, they will cause great damage to the environment. Therefore, recycling and reusing waste lithium iron phosphate batteries is very necessary and meaningful.

[0004] At present, the mainstream treatment of waste lithium iron phosphate batteries is mainly acid leaching. The aluminum of the positive current collector will enter the leaching solution in the form of aluminum ions as an impurity during the acid leaching process, and finally enter the synthesized iron phosphate, affecting the electrochemical performance of the iron phosphate product. Therefore, in order to recover battery-grade iron phosphate from waste lithium iron phosphate batteries, it is essential to remove aluminum impurities.

[0005] Through the analysis of the published literature, there are mainly two methods for removing aluminum from waste lithium iron phosphate batteries:

[0006] 1. Only by adjusting the pH of the acid leaching solution, the aluminum ions are precipitated in the form of aluminum hydroxide to be removed. For example, the Chinese patent document with publication number CN106910889A discloses a method for removing aluminum ions in the form of aluminum hydroxide precipitate by adding alkali metal hydroxide to adjust the pH of the solution. The disadvantage of this method is that Fe3(PO4)2 precipitate is easily generated and removed at the same time with aluminum hydroxide, resulting in a large loss of PO4 3- 、Fe 2+ .

[0007] 2. The waste lithium iron phosphate pole piece powder is treated by alkali leaching to remove aluminum in the form of aluminate. For example, the Chinese patent document with publication number CN103280610B proposes a method for removing aluminum from black powder by alkali leaching, which removes aluminum in the form of aluminate. In the process of alkali leaching, the charged lithium iron phosphate exists in the form of iron phosphate. In the high alkaline state, the K SP of iron hydroxide is higher than that of iron phosphate, so iron phosphate will be converted into iron hydroxide, and phosphate will enter the solution, causing phosphorus loss. In addition, carbon has strong water absorption, and it is difficult to completely wash out aluminate in the solution through washing, which is still easy to enter the acid leaching solution in the form of aluminum ions in the subsequent acid leaching reaction.

[0008] From the above two examples, since the chemical properties of iron ions and aluminum ions are similar, how to remove aluminum ions without losing iron ions to obtain high-purity iron phosphate has become a big problem in recycling iron phosphate from waste lithium iron phosphate batteries. In order to solve this problem, the present application proposes a method for removing aluminum from waste lithium iron phosphate pole piece powder and comprehensive recovery. SUMMARY

[0009] The present application aims to solve the problem of easy iron and phosphorus loss and incomplete aluminum removal in the current market common aluminum removal method for recycling iron phosphate from waste lithium iron phosphate batteries, and proposes a method for removing aluminum from waste lithium iron phosphate pole piece powder and comprehensive recovery.

[0010] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0011] 1. A method for removing aluminum from waste lithium iron phosphate pole piece powder and comprehensive recovery, characterized in that it comprises the following steps:

[0012] S1, acid leaching oxidation: mix waste lithium iron phosphate black powder with concentrated hydrochloric acid, heat, and stir for a period of time, gradually dissolve lithium, iron, phosphorus and other elements into the hydrochloric acid solution, then add sufficient oxidizing agent, and oxidize Fe 2+ to Fe 3+ ;

[0013] S2, extraction separation: add a certain amount of extractant to the solution prepared in S1, and after extraction is completed, separate the organic phase from the aqueous phase;

[0014] S3, aluminum removal: add lye to the aqueous phase liquid separated in S2 to increase the pH of the solution, so that aluminum precipitates completely in the form of aluminum hydroxide, and then perform filtration operation;

[0015] S4, iron and phosphorus mixing: mix the aqueous phase treated in S3 with the organic phase liquid separated in S2, continue to add lye, increase the pH of the solution and heat, so that iron and phosphorus are precipitated to form iron phosphate, and filtration is performed again; and due to the low boiling point of diethyl ether, it can be collected and reused after heating;

[0016] S5, lithium phosphate preparation: continue to add lye to the filtered solution to adjust the pH, then add phosphate solution, and perform washing and drying to obtain lithium phosphate.

[0017] Preferably, the concentration of hydrochloric acid used in S1 is 6-10 mol / L; the mass ratio of waste lithium iron phosphate powder to hydrochloric acid is 1:4-10, and the mass ratio is preferably 1:6-10;

[0018] The heating temperature in S1 is 60-90℃, and the temperature is preferably 80-90℃;

[0019] The holding and stirring time in S1 is 1-3h, preferably 1-2h.

[0020] Preferably, the extractant used in S2 is an organic extractant, preferably one or more of diethyl ether, polycarbon alcohol or long-chain fatty amine; the mass ratio of aqueous solution to extractant is 1:1-3, preferably 1:1-1.5.

[0021] Preferably, the pH of the adjusted solution in S3 is 1-4, preferably 1-3.

[0022] Preferably, the pH of the adjusted solution in S4 is 2-6, preferably 2-4.

[0023] The heating temperature in S4 is 75-95℃, preferably 85-95℃; the heating time is 2-4h, preferably 3-4h.

[0024] Preferably, the pH of the adjusted solution in S5 is 5-8, preferably 7-8.

[0025] Preferably, the alkali used in S3-S5 is one or more of sodium hydroxide, potassium hydroxide, ammonia, and the concentration of the alkali is 0.5-1mol / L.

[0026] Preferably, the phosphate mentioned in S5 is one or more of potassium phosphate, sodium hydrogen phosphate, sodium phosphate and ammonium phosphate.

[0027] Compared with the prior art, the present application provides a method for removing aluminum and comprehensively recovering waste and old lithium iron phosphate pole piece powder, which has the following beneficial effects:

[0028] The present application takes advantage of the difference in the ability of iron ions and aluminum ions to form complex ions, and innovatively proposes a method of extracting iron ions first and then removing aluminum, which successfully overcomes the problems of iron and phosphorus loss and incomplete removal of aluminum that may occur in the above-mentioned aluminum removal process, and uses low-boiling-point extractants such as diethyl ether, which can be reused after distillation collection: all iron ions enter the organic phase during the extraction process, and after the removal of aluminum ions, the iron ions re-enter the inorganic phase and mix with phosphate ions, and finally all form iron phosphate, and there is no loss of iron and phosphorus in the whole process and the aluminum element is efficiently removed. The remaining lithium chloride solution is treated with phosphate to generate lithium phosphate. All lithium, iron and phosphorus elements are efficiently and highly purified, and there is no heavy metal wastewater discharge in the whole process. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A process flow diagram of a method for removing aluminum and comprehensively recovering waste and old lithium iron phosphate pole piece powder is provided.

[0030] Figure 2 This is the XRD pattern of the iron phosphate recovered in Example 1 of the present invention;

[0031] Figure 3 This is the XRD pattern of the lithium phosphate recovered in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] First, the technical principle implemented by the present invention is described:

[0034] In the presence of Fe 3+ 、Al 3+ In the hydrochloric acid solution, due to Fe 3+ Ions and Cl - Ions generate [FeCL4] - coordinated anions, and Al 3+ There is almost no reaction. Then add an extractant, such as ether (Et2O), to the solution. In a strong acid-ether system, ether reacts with H + Ions combine to form Et2O·H + ions. Due to [FeCL4] - ions and Et2O·H + The ions have large volume and low charge. Therefore, it is easy to form ion association complex Et2O·H + ·[FeCL4] - In this ion association complex, Cl - ions and Et2O replaced Fe 3+ ions and H + The coordinated water molecules of the ion neutralize the charge, are hydrophobic, and can be dissolved in ether. 3+ It transfers from the aqueous phase to the organic phase.

[0035] Al 3+ Ions at 6 mol·L -1 Hydrochloric acid and Cl - The ability of ions to generate complex ions is very weak, so they remain in the water phase. After oscillation separation, the Fe 3+ The organic phase and Al 3+ After separation, Al 3+ Still in the initial state, after adjusting the pH value, aluminum can be removed in the form of aluminum hydroxide. 3+ The ether phase of the ion is remixed with the water phase, and the H+ ion concentration and Cl - ion concentration is obviously reduced. Et2O·H + ·[FeCL4] - is further dissociated into Et2O·H + and [FeCL4] - , Fe 3+ ion is further generated into hydrated iron ion and returns to the aqueous phase. Since the boiling point of ether is low, the ether and water can be separated by distillation. In this way, Fe 3+ returns to the initial state, Fe 3+ and Al 3+ are separated, Fe 3+ ion can be combined with PO43 - to generate iron phosphate by adjusting the pH value.

[0036] Based on the above, the application provides a method for removing aluminum and comprehensively recovering waste lithium iron phosphate pole piece powder, and the specific embodiments are as follows.

[0037] Embodiment 1:

[0038] (1) 5 kg of waste lithium iron phosphate pole piece black powder is slowly added to 30 L of 6 mol / L hydrochloric acid solution, heated to 90℃, and stirred for 2 h, and then filtered.

[0039] (2) After the filtrate is cooled, 1.5 kg of hydrogen peroxide is added to fully oxidize the divalent iron into trivalent iron.

[0040] (3) 10-20 L of ether is added to the solution, and after being fully mixed and dispersed for 30 min-60 min, the solution is layered, the upper layer is the low-density organic phase, and the lower layer is the aqueous phase, and the two phases are separated and collected respectively.

[0041] (4) A certain amount of 25% ammonia water is added to the aqueous phase, and the pH is adjusted to 2-3, and white precipitate is generated, and then filtered.

[0042] (5) After the filtrate and the organic phase separated by extraction are uniformly mixed, a certain amount of ammonia water is introduced, and the pH is adjusted to 3-4, at which time a large amount of yellow precipitate is generated, and then heated to 90-95℃, and stirred for 3-4 h, and the yellow precipitate is changed into powdery white precipitate, and then filtered, washed, and dried to obtain iron phosphate dihydrate.

[0043] (6) The filtrate is introduced into ammonia water, the pH is adjusted to 7-8, a sodium phosphate solution is added until the solution is saturated, white precipitate gradually appears in the solution, and then filtered, washed, and dried to obtain lithium phosphate.

[0044] (7) Iron element is recovered in the form of iron phosphate precipitate, and the precipitation rate is 99.3%, and the aluminum content is 0.005%; lithium element is recovered in the form of lithium phosphate precipitate, and the precipitation rate is 99.1%.

[0045] Based on the above operation, the obtained iron phosphate and lithium phosphate are characterized by XRD.

[0046] Referring to Figure 2 , Figure 2 The XRD pattern of the recovered iron phosphate is shown in the figure, the intensity of each diffraction peak is high, and the peak shape is sharp, which indicates that the recovered iron phosphate has a relatively high crystallinity.

[0047] Referring to Figure 3 , Figure 3 The XRD pattern of the recovered lithium phosphate is shown in the figure, it can be seen that the intensity of each diffraction peak is high, and the peak shape is sharp, which indicates that the recovered lithium phosphate material has a high crystallinity, and there is no obvious impurity peak, which indicates that the recovered is a pure phase of lithium phosphate.

[0048] Example 2:

[0049] Based on example 1 but with the difference that,

[0050] According to the aluminum removal and comprehensive recovery process of the waste old lithium iron phosphate pole piece powder described in example 1, based on the control variable method, the hydrochloric acid concentration, the hydrochloric acid volume, the heating temperature, the holding time, the ether mass, the pH value, the pH adjusting alkali, and the phosphate type are used as experimental variables, the control experiment is designed, and the following experimental data is obtained.

[0051]

[0052]

[0053] In summary, the present application utilizes the difference in the ability of iron ions and aluminum ions to form complex ions, and innovatively proposes a method of extracting iron ions first and then removing aluminum, which successfully overcomes the problems of iron and phosphorus loss and incomplete removal of aluminum that may occur in the above-mentioned aluminum removal process, and uses low-boiling-point extractants such as diethyl ether, which can be reused after distillation collection: all iron ions enter the organic phase during the extraction process, and after the removal of aluminum ions, the iron ions re-enter the inorganic phase and mix with phosphate ions, and finally all form iron phosphate, the whole process has no iron and phosphorus loss and the aluminum element is efficiently removed. The remaining lithium chloride solution is treated with phosphate to generate lithium phosphate. All lithium, iron and phosphorus elements are efficiently and highly purified, and the whole process has no heavy metal wastewater discharge.

[0054] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensive recovery, characterized in that: The following steps are involved: S1, acid leaching oxidation: Mix the waste lithium iron phosphate black powder with concentrated hydrochloric acid, heat, keep warm and stir for a period of time, gradually dissolve lithium, iron and phosphorus elements into the hydrochloric acid solution, then add enough oxidant to 2+ All oxidized to Fe 3+ ; S2, extraction and separation: adding a certain amount of extractant to the solution prepared in S1, and separating the organic phase from the aqueous phase after the extraction is completed; the extractant is an organic extractant selected from one or more of ether, polyols and long-chain fatty amines; S3, aluminum removal: adding alkali solution to the aqueous phase liquid separated in S2 to increase the pH of the solution so that the aluminum is completely precipitated in the form of aluminum hydroxide, and then filtering; S4, iron-phosphorus mixing: remix the aqueous phase treated in S3 with the organic phase liquid separated in S2, continue to add alkali solution to increase the pH of the solution and heat it to precipitate all the iron and phosphorus to form iron phosphate, and filter again; S5. Preparation of lithium phosphate: Alkaline solution is further added to the filtered solution to adjust the pH, and then a phosphate solution is added for washing and drying to obtain lithium phosphate.

2. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The concentration of concentrated hydrochloric acid in S1 is 6-10 mol / L; the mass ratio of the waste lithium iron phosphate powder to concentrated hydrochloric acid is 1:4-10; The heating temperature in S1 is 60-90°C; The heat preservation and stirring time in S1 is 1 to 3 hours.

3. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The mass ratio of the aqueous solution to the extractant in S2 is 1:1-3.

4. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The pH range of the solution after adjustment in S3 is 1-4.

5. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The pH range of the solution after adjustment in S4 is 2 to 6; The heating temperature in S4 is 75-95° C. and the heating time is 2-4 hours.

6. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The pH range of the solution after adjustment in S5 is 5-8.

7. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The alkali solution used in S3-S5 is one or more of sodium hydroxide, potassium hydroxide, and ammonia water, and the concentration of the alkali solution is 0.5-1 mol / L.

8. The method for removing aluminum from waste lithium iron phosphate electrode powder and comprehensively recovering it according to claim 1, characterized in that: The phosphate in S5 is one or more of potassium phosphate, sodium hydrogen phosphate, sodium phosphate, and ammonium phosphate.

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