Method for preparing manganese iron phosphate precursor by recycling waste lithium manganese iron phosphate

Abstract

The invention discloses a method for preparing a manganese iron phosphate precursor by recycling waste lithium manganese iron phosphate, and belongs to the technical field of lithium ion batteries. The invention provides a method for preparing a manganese iron phosphate precursor by recycling waste lithium manganese iron phosphate, which comprises the following steps: by taking waste lithium manganese iron phosphate battery powder as a raw material, carrying out acid dissolution and filtration to remove graphite and part of impurities; adjusting the pH value of the filtrate to obtain a lithium-ion-rich solution and a ferromanganese precipitate, and adding sodium carbonate into the lithium-ion-rich solution for concentration and crystallization to obtain battery-grade lithium carbonate; carrying out acid dissolution on the ferromanganese precipitate, removing copper and aluminum impurities in the solution, adjusting the ratio of ferromanganese to phosphorus, and mixing with liquid caustic soda in a nitrogen atmosphere to obtain a ferromanganese phosphate precursor; according to the method, the problems of incomplete recovery and insufficient impurity removal of the manganese iron phosphate lithium battery are solved, the battery-grade lithium carbonate and the manganese iron phosphate precursor are prepared during recovery, the value of the recovered product is improved, and the production requirement of the lithium ion battery is met.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a method for recovering waste lithium manganese iron phosphate to prepare a manganese iron phosphate precursor. Background Art

[0002] As a new type of positive electrode material for lithium-ion batteries, lithium iron manganese phosphate has many advantages, such as high energy density, good cycle stability, excellent safety, cost-effectiveness, environmental friendliness, wide operating temperature range and high rate performance. These characteristics make it widely used in electric vehicles, energy storage systems, consumer electronics and industrial fields. With the widespread application of lithium iron manganese phosphate battery positive electrode materials, how to recycle waste lithium iron manganese phosphate batteries and realize the closed loop of battery materials has become a hot topic for research by enterprises and scientists.

[0003] At present, the recycling of waste ternary lithium batteries and lithium iron phosphate batteries has been industrialized. Due to the different components, the recycling process of ternary lithium batteries and lithium iron phosphate batteries cannot be directly applied to the recycling process of lithium iron manganese phosphate. However, with the release of lithium iron manganese phosphate production capacity and its gradual use in electric vehicle power batteries, there is an urgent need to develop a low-cost, simple to operate, and easy to industrialize process method for recycling waste lithium iron manganese phosphate batteries.

[0004] Patent document CN118145617A provides a method for recycling and reusing waste lithium manganese oxide positive electrode materials to synthesize lithium iron manganese phosphate positive electrode materials, wherein the waste lithium manganese oxide positive electrode materials are mixed with concentrated sulfuric acid solution and then low-temperature roasted, and then the roasted product is subjected to water leaching treatment; after the leaching solution is impurities removed, a solid product containing lithium and manganese is obtained by concentration and drying, and then a phosphorus source and an iron source are added to the solid product according to the corresponding molar ratio, and a lithium iron manganese phosphate precursor is obtained after ball milling; and then the precursor is subjected to high-temperature calcination reaction to obtain the lithium iron manganese phosphate positive electrode material. This scheme requires low-temperature roasting, and no impurity removal method is mentioned in the recycling process. In the process of preferential lithium extraction, the manganese valence state may increase, the manganese element is seriously lost, and the recovery rate of manganese iron is low. Summary of the invention

[0005] The object of the present invention is to provide a method for recycling waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor, which can remove impurities during the recycling process and has a high ferromanganese recovery rate.

[0006] The present invention discloses a method for recovering waste lithium manganese iron phosphate to prepare a manganese iron phosphate precursor, comprising the following steps:

[0007] S1: Evenly mix the collected waste lithium iron manganese phosphate powder with acid solution for acid leaching; add oxidant, filter, remove solid impurities in the filtrate, and obtain ion-rich solution A and filter residue A;

[0008] S2: adding alkali solution to the ion-rich solution A to convert manganese ions and iron ions into precipitates; filtering to obtain a lithium-rich solution B and a filter residue B;

[0009] S3: adding sodium carbonate to the lithium ion-rich solution B to crystallize lithium carbonate;

[0010] S4: adding acid solution to dissolve the filter residue B, remove copper ions and aluminum ions, and obtain solution C;

[0011] S5: adding a phosphorus source, a manganese source and / or an iron source, and adjusting the molar ratio of the sum of the moles of manganese ions and iron ions in solution C to the molar ratio of phosphorus element to 1:(1-1.05); adding an alkali solution in a protective gas atmosphere to precipitate the mixed solution, filtering, washing with water, and drying to obtain a manganese iron phosphate precursor.

[0012] The waste lithium iron manganese phosphate batteries are discharged, disassembled, crushed and sieved to obtain waste lithium iron manganese phosphate powder.

[0013] The acid solution is used together with an oxidant to increase the leaching rate of metal elements. The metal ions in the waste lithium iron manganese phosphate powder are dissolved by the acid solution.

[0014] The components of the filter residue A are graphite and other insoluble impurities.

[0015] Furthermore, in step S1, the acid solution is selected from one or more of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid.

[0016] Furthermore, in step S1, the mass fraction of the acid solution is 10-15wt%; and the ratio of the mass of the waste lithium iron manganese phosphate powder to the volume of the acid solution is 1g:8mL-10mL.

[0017] Furthermore, in step S1, the oxidant is selected from one or two of hydrogen peroxide, oxygen and air.

[0018] Adding an oxidant oxidizes the divalent iron element into trivalent iron element, thereby increasing the leaching rate of the iron element.

[0019] Furthermore, in step S1, after the oxidant oxidizes all the divalent iron elements in the reaction solution into trivalent iron elements, the addition of the oxidant is stopped.

[0020] The amount of oxidant added is controlled to oxidize the divalent iron to trivalent iron, but not to oxidize the divalent manganese ions to tetravalent manganese; ensuring that the manganese element remains at a divalent state while oxidizing the divalent iron, so as to facilitate the subsequent recovery of manganese and iron elements.

[0021] Furthermore, in step S2, the alkali solution is an aqueous solution of sodium hydroxide or potassium hydroxide.

[0022] Furthermore, in step S2, an alkali solution is added to adjust the pH of the solution to 5.0-7.5 to allow precipitation.

[0023] Furthermore, in step S3, after adding sodium carbonate, the mixed solution is heated to 90-100° C. until solid precipitates, and then naturally cooled to obtain lithium carbonate crystals.

[0024] The solubility of lithium carbonate in water decreases with increasing temperature, while the solubility of sodium salt in water increases with increasing temperature. Lithium carbonate and sodium salt are separated by heating evaporation crystallization, and then naturally cooled to obtain lithium carbonate crystals. The purity of lithium carbonate crystals obtained in this way can reach battery grade.

[0025] Furthermore, in step S4, iron powder is first added, stirred evenly, and filtered to remove copper ions.

[0026] The purpose of adding iron powder is to replace metallic copper and reduce trivalent iron ions to divalent iron ions.

[0027] Furthermore, in step S4, sodium fluoride is added, and an alkali solution is added to adjust the pH of the reaction solution to 1-3 to remove aluminum ions.

[0028] First add sodium fluoride, then add alkali solution to make aluminum ions react to form cryolite (Na 3 AlF 6 ), thereby removing it.

[0029] Furthermore, in step S5, an alkali solution is added to adjust the pH of the reaction system to 4.5-6.

[0030] Alkaline solution is added to achieve co-precipitation of manganese, iron and phosphorus to obtain manganese iron phosphate precursor.

[0031] The present invention provides a method for recycling waste lithium iron manganese phosphate to prepare an iron manganese phosphate precursor, using waste lithium iron manganese phosphate battery powder as a raw material, performing acid dissolution to remove graphite and some impurities, adjusting the pH value of the filtrate to obtain a lithium-rich solution and an iron manganese precipitate, adding sodium carbonate to the lithium-rich solution for concentration and crystallization to obtain battery-grade lithium carbonate, performing acid dissolution on the iron manganese precipitate to remove copper and aluminum impurities in the solution, adjusting the ratio of manganese, iron and phosphorus, and mixing with liquid alkali under a nitrogen atmosphere to obtain an iron manganese phosphate precursor. This method solves the problems of incomplete recycling and insufficient impurity removal of lithium iron manganese phosphate batteries, and prepares battery-grade lithium carbonate and iron manganese phosphate precursors while recycling, thereby improving product value and meeting production needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flow chart of a method for recovering waste lithium manganese iron phosphate to prepare a manganese iron phosphate precursor. DETAILED DESCRIPTION

[0033] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the specific embodiments of the accompanying drawings.

[0034] like Figure 1 As shown, waste lithium manganese iron phosphate is recycled to prepare manganese iron phosphate precursor.

[0035] Example 1

[0036] Prepare sodium hydroxide solution: take 500 ml of ultrapure water, add 40 g of sodium hydroxide to prepare a 2 mol / L sodium hydroxide solution;

[0037] S1 acid leaching: weigh 100g of waste lithium manganese iron phosphate battery powder, dissolve it in 10wt% sulfuric acid with a solid-liquid ratio of 1:8 (g:mL), stir evenly and add 30wt% hydrogen peroxide until there is no divalent iron ion (use methyl orange as an indicator to determine the end point of divalent iron oxidation), the mass of hydrogen peroxide added is 20g, stir for two hours, filter to obtain ion-rich solution A and filter residue A, the main component of filter residue A is graphite residue.

[0038] S2 ferromanganese precipitation: Add the prepared 2 mol / L sodium hydroxide to the ion-rich solution A, adjust the solution pH to 5.0, stir to precipitate, and filter to obtain the lithium ion-rich solution B and filter residue B.

[0039] Preparation of S3 lithium carbonate: Add 30 g of sodium carbonate to the lithium ion-rich solution B, and place it in a water bath at 95°C until crystals precipitate. Stop adding and cool naturally to precipitate lithium carbonate crystals. The lithium carbonate content in the precipitated lithium carbonate crystals is 97.21 wt%.

[0040] S4 copper and aluminum removal: Use 10wt% sulfuric acid to dissolve the filter residue B to obtain a crude manganese iron ion solution, and analyze the impurity content of the crude manganese iron ion solution: the copper content is 851.9ppm and the aluminum content is 887.6ppm. (The amount of impurity remover is determined according to the content of copper and aluminum) Add 15g of iron powder to the crude manganese iron ion solution, which can not only remove copper impurities in the solution, but also reduce the trivalent iron element to divalent. Filter to remove the displaced copper solid, and the copper content in the copper removal liquid is 15ppm. Take 500ml of the copper removal liquid, add 7.87g of sodium fluoride to the copper removal liquid, add 60g of 2mol / L sodium hydroxide solution, adjust the pH of the solution to 1.6, precipitate cryolite, filter and remove the cryolite in the solution, and obtain a manganese iron ion solution. The aluminum content in the manganese iron ion solution is 54ppm by measuring.

[0041] S5: Detect and analyze the contents of phosphorus, manganese and iron in the manganese-iron ion solution obtained in step S4, and obtain a manganese content of 33.845 g / L, an iron content of 28.763 g / L, and a phosphorus content of 34.639 g / L. Take 250 ml of the manganese-iron ion solution after impurities removal, add 5.91 g of manganese sulfate, dissolve it and flow it into a flask with 2 mol / L sodium hydroxide solution, heat it in a water bath to 80° C., keep the pH of the mixed liquid at 5.5, pass nitrogen protection throughout the process, stir to precipitate, filter, wash and dry the precipitate to obtain 36.9 g of manganese-iron phosphate precursor (Mn 0.6 ,Fe 0.4)5 (HPO 4 ) 2 (PO 4 ) 2· 4H 2 O.

[0042] Example 2

[0043] Prepare sodium hydroxide solution: Take 500 ml of ultrapure water and add 60 g of sodium hydroxide to prepare a 3 mol / L sodium hydroxide solution.

[0044] S1 acid leaching: weigh 100g of waste lithium manganese iron phosphate battery powder, dissolve it in 15wt% sulfuric acid with a solid-liquid ratio of 1g:10mL, stir evenly and add 30wt% hydrogen peroxide until there is no divalent iron element, stop adding, the mass of hydrogen peroxide added is 20g, stir for two hours, filter to obtain ion-rich solution A and filter residue A, the main component of filter residue A is graphite residue.

[0045] S2 ferromanganese precipitation: add prepared 3 mol / L sodium hydroxide to the ion-rich solution A, adjust the solution pH to 5.5, stir to precipitate, and filter to obtain lithium-rich solution B and filter residue B.

[0046] Preparation of S3 lithium carbonate: 34 g of sodium carbonate was added to the lithium-ion-rich solution B, and the water bath temperature was 90°C. The solution was heated until crystals precipitated and then cooled naturally to precipitate lithium carbonate crystals. The lithium carbonate content in the precipitated lithium carbonate crystals was 97.85 wt%, reaching the standard of battery-grade lithium carbonate.

[0047] S4 copper and aluminum removal: 12wt% sulfuric acid was used to dissolve the filter residue B to obtain a crude manganese iron ion solution, and the crude manganese iron ion solution was analyzed for impurity content: the copper content was 718.8ppm and the aluminum content was 365.6ppm. (The amount of impurity remover was determined according to the content of copper and aluminum) 15g of iron powder was added to the crude manganese iron ion solution, stirred for reaction, and filtered to remove the solids in the mixed solution. The addition of iron powder can not only remove copper impurities in the solution, but also reduce the trivalent iron element to divalent. The copper content in the solution after copper removal is 11ppm. Take 500ml of the copper removal solution, add 7.87g of sodium fluoride to the copper removal solution, add 60g of 3mol / L sodium hydroxide solution, adjust the pH of the solution to 2, precipitate cryolite, filter and remove the cryolite in the solution, and obtain a manganese iron ion solution. The aluminum content in the manganese iron ion solution is 21ppm by measuring.

[0048] S5: Detect and analyze the contents of phosphorus, manganese and iron in the manganese-iron ion solution obtained in step S4, and obtain a manganese content of 38.5 g / L, an iron content of 34.785 g / L, and a phosphorus content of 34.225 g / L. Take 300 mL of the manganese-iron ion solution after impurities removal, add 10.57 g of manganese sulfate, dissolve it and flow it into a flask with 3 mol / L sodium hydroxide solution, heat it in a water bath to 50° C., keep the pH of the mixed liquid at 4.8, pass nitrogen protection throughout the process, stir to precipitate, filter, wash and dry the precipitate to obtain 50.8 g of manganese ferrophosphate precursor (Mn 0.5 ,Fe 0.5 ) 5 (HPO 4 ) 2 (PO 4 ) 2· 4H 2 O.

[0049] Example 3

[0050] Prepare sodium hydroxide solution: Take 500 ml of ultrapure water and add 60 g of potassium hydroxide to prepare a 3 mol / L potassium hydroxide solution.

[0051] S1 acid leaching: Weigh 50g of waste manganese iron phosphate lithium battery powder (lithium content: 4.39%, manganese content: 21.39%, iron content: 13.93%, phosphorus content: 19.48%). Dissolve it in 15wt% sulfuric acid with a solid-liquid ratio of 1g:6mL. Stir evenly and add 30wt% hydrogen peroxide until there is no divalent iron element. Stop adding. The mass of hydrogen peroxide added is 19.4g. After stirring for two hours, filter to obtain ion-rich solution A and filter residue A. The main component of filter residue A is graphite residue.

[0052] S2 ferromanganese precipitation: add 3 mol / L potassium hydroxide to the ion-rich solution A, adjust the pH of the solution to 5.8, stir to precipitate, and filter to obtain lithium-rich solution B and filter residue B.

[0053] Preparation of S3 lithium carbonate: 17 g of sodium carbonate was added to the lithium ion-rich solution B, and the water bath temperature was 100°C. The solution was heated until crystals precipitated, and then cooled naturally to precipitate 11.04 g of lithium carbonate crystals. The lithium carbonate content in the precipitated lithium carbonate crystals was 98.62 wt%, and the lithium recovery rate was 91.88%.

[0054] S4 copper and aluminum removal: Use 12wt% sulfuric acid to dissolve the filter residue B to obtain a crude manganese iron ion solution, and analyze the impurity content of the crude manganese iron ion solution: the copper content is 734.6ppm and the aluminum content is 385.2ppm. (The amount of impurity remover is determined according to the content of copper and aluminum) Add 10g of iron powder to the crude manganese iron ion solution, stir the reaction, filter and remove the solid in the mixed solution, and the copper content in the solution after copper removal is 13ppm. Take 300ml of the copper removal solution, add 7.98g of sodium fluoride to the copper removal solution, add 64g of 3mol / L sodium hydroxide solution, adjust the pH of the solution to 2.1, precipitate cryolite, filter and remove the cryolite in the solution, and obtain a manganese iron ion solution. The aluminum content in the manganese iron ion solution is 18ppm by measuring.

[0055] S5: Detect and analyze the contents of phosphorus, manganese and iron in the manganese-iron ion solution obtained in step S4, and obtain a manganese content of 32.7 g / L, an iron content of 28.64 g / L, and a phosphorus content of 33.25 g / L. Take 300 mL of the manganese-iron ion solution after impurities removal, add 7.86 g of manganese sulfate, dissolve it and flow it into a flask with 3 mol / L sodium hydroxide solution, heat it in a water bath to 50° C., keep the pH of the mixed liquid at 4.8, pass nitrogen protection throughout the process, stir to precipitate, filter, wash and dry the precipitate to obtain 50.68 g of manganese iron phosphate precursor (Mn 0.6 ,Fe 0.4 ) 5 (HPO 4 ) 2 (PO 4 ) 2· 4H 2 O, the manganese recovery rate was 92.35%, and the phosphorus recovery rate was 81.38%.

[0056] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering waste lithium manganese phosphate to prepare a manganese phosphate precursor, characterized in that: The steps include: S1: Evenly mix the collected waste lithium iron manganese phosphate powder with acid solution for acid leaching; add oxidant, filter, remove solid impurities in the filtrate, and obtain ion-rich solution A and filter residue A; S2: adding alkali solution to the ion-rich solution A to convert manganese ions and iron ions into precipitates; Filtering to obtain a lithium ion-rich solution B and a filter residue B; S3: adding sodium carbonate to the lithium ion-rich solution B to crystallize lithium carbonate; S4: adding acid to dissolve the filter residue B, removing copper ions and aluminum ions, and obtaining solution C; S5: adding a phosphorus source, a manganese source and / or an iron source, and adjusting the molar ratio of the sum of the moles of manganese ions and iron ions in solution C to the molar ratio of phosphorus element to 1:(1-1.05); adding an alkali solution in a protective gas atmosphere to precipitate the mixed solution, filtering, washing with water, and drying to obtain a manganese iron phosphate precursor.

2. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 1, characterized in that: In step S1, the acid solution is selected from one or two of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid.

3. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 2, characterized in that: In the step S1, the mass fraction of the acid solution is 10-15wt%; the ratio of the mass of the waste lithium manganese iron phosphate powder to the volume of the acid solution is 1g:8mL-10mL.

4. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 3, characterized in that: In step S1, the oxidant is selected from one or two of hydrogen peroxide, oxygen and air.

5. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 4, characterized in that: In the step S1, after the oxidant oxidizes all the divalent iron elements in the reaction solution into trivalent iron elements, the addition of the oxidant is stopped.

6. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 5, characterized in that: In step S2, the alkali solution is an aqueous solution of sodium hydroxide and potassium hydroxide; the alkali solution is added to adjust the pH of the solution to 5.0-7.5 to cause precipitation.

7. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 1, characterized in that: In the step S3, after adding sodium carbonate, the mixed solution is heated to 90-100° C. until solid precipitates, and then cooled naturally to obtain lithium carbonate crystals.

8. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 1, characterized in that: In step S4, iron powder is first added, stirred evenly, and filtered to remove copper ions.

9. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 8, characterized in that: In the step S4, sodium fluoride is added, an alkali solution is added to adjust the pH of the reaction solution to 1-3, and the aluminum ions are removed by filtration.

10. The method for recovering waste lithium ferromanganese phosphate to prepare ferromanganese phosphate precursor according to claim 1, characterized in that: In step S5, an alkali solution is added to adjust the pH of the reaction system to 4.5-6.

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