Method for synthesizing battery-grade lithium carbonate and iron phosphate by efficiently removing impurities from waste lithium iron phosphate

Abstract

The application discloses a kind of old lithium iron phosphate high-efficiency impurity removal synthesis battery-grade lithium carbonate and iron phosphate method, belong to the field of waste battery recycling.The above-mentioned method includes the following steps: first, the old lithium iron phosphate is treated by combustion in oxidizing atmosphere, the powder obtained is soaked in solvent, is filtered after being mixed uniformly, and the lithium filtrate containing copper and aluminum impurities and lithium extraction residue are obtained;The lithium filtrate containing copper and aluminum impurities is removed by impurity, concentrated, carbonized to obtain lithium carbonate, and the iron phosphate residue is obtained after acid leaching, adjusting the ratio of phosphorus and iron, aging and high-temperature calcination.The method used in the present application can selectively extract high-value lithium from old lithium iron phosphate efficiently, while also avoiding the mixing of impurity metals and iron and phosphorus, which makes it difficult to purify iron phosphate, and the process is simple, the impurity removal rate is high, the valuable metal recovery rate is high, the impurities are completely removed, and it has strong practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of waste battery recycling, in particular to a method for synthesizing battery-grade lithium carbonate and iron phosphate from waste lithium iron phosphate. BACKGROUND

[0002] With the popularity of electric vehicles, the demand for batteries is expanding. As raw materials for lithium iron phosphate, the demand for lithium carbonate and iron phosphate is naturally increasing. The continuous expansion of market demand has caused the price of raw materials to remain high. Therefore, developing new channels to obtain raw materials has become the choice of many manufacturers.

[0003] Currently, after more than ten years of development, electric vehicles have ushered in a wave of waste battery retirement. The sorted waste positive electrode material in these batteries contains a large amount of lithium resources and iron and phosphorus resources. Therefore, extracting high-purity battery-grade iron phosphate and lithium carbonate from waste positive electrode material has become the goal of many manufacturers. However, there are many problems in the development process that are difficult to solve.

[0004] The invention with publication number CN112331949 introduces a method for recovering phosphorus, iron and lithium from waste lithium iron phosphate batteries. The invention uses organic solvent to soak the waste lithium iron phosphate positive electrode sheet to obtain lithium iron phosphate powder. The lithium iron phosphate powder is immersed in an alkali solution to obtain aluminum-removed lithium iron phosphate powder. The aluminum-removed lithium iron phosphate powder is added to a mixed solution of sulfuric acid and hydrogen peroxide, and heated to leach, obtaining an acid leaching solution. The pH value of the acid leaching solution is adjusted to obtain crude iron phosphate. The crude iron phosphate is dissolved, precipitated and calcined to obtain battery-grade iron phosphate. The lithium-containing filtrate is evaporated and concentrated, and then added to an alkali solution to obtain lithium carbonate precipitate, obtaining battery-grade lithium carbonate. This method can remove most of the aluminum through alkali solution, but has the disadvantages of low removal efficiency and incomplete removal. At the same time, lithium is not preferentially extracted, and the concentration of lithium solution contains high content of other salts, resulting in low lithium recovery rate and high impurity content. The invention with publication number CN106450547 discloses a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste. The method includes the following steps: oxidation roasting, positive electrode cleaning, phosphoric acid ball milling activation, acid washing to separate iron phosphate, and lithium precipitation in the filtrate to obtain the target product lithium carbonate. The process flow of this invention is complex, and phosphoric acid ball milling is required, which can easily introduce magnetic substances and other impurities. The aluminum and other impurities in the positive electrode are not effectively removed. The main target product is lithium carbonate, and the obtained iron phosphate product has general indicators. SUMMARY

[0005] The present application aims to provide a method for synthesizing battery-grade lithium carbonate and iron phosphate from waste lithium iron phosphate with high impurity removal rate, high lithium recovery rate and simple process.

[0006] Technical solution: The method for synthesizing battery-grade lithium carbonate and iron phosphate by efficiently removing impurities from waste lithium iron phosphate includes the following steps:

[0007] (1) After the waste lithium iron phosphate is treated by combustion in an oxidizing atmosphere, the obtained powder is soaked in a solvent, mixed uniformly, and filtered to obtain a lithium filtrate containing copper and aluminum impurities and a lithium extraction residue;

[0008] (2) Iron cyanide is added to the lithium filtrate containing copper and aluminum impurities, and after the reaction is completed, filtration is performed to obtain a copper-removed lithium solution;

[0009] (3) An alkali solution is added to the copper-removed lithium solution, and after the pH is adjusted, filtration is performed to obtain an aluminum-removed lithium solution, which is then heated and evaporated to obtain a concentrated lithium solution;

[0010] (4) Under heating conditions, an alkali solution and a carbonizing agent are added to the concentrated lithium solution, and after the reaction is completed, lithium carbonate is obtained;

[0011] (5) The lithium extraction residue obtained in step (1) is dispersed in a solvent, and an inorganic acid is added to dissolve it thoroughly, and an acid leaching solution is obtained by filtration;

[0012] (6) The acid leaching solution is adjusted to a phosphorus-iron ratio, and an alkali solution is used to adjust the pH to obtain a phosphorus iron precipitate, which is then heated and precipitated, filtered, and obtained as dihydrate phosphorus iron, which is then calcined at high temperature to obtain iron phosphate.

[0013] Further, in step (1), the oxidizing atmosphere is one of chlorine or bromine; the combustion treatment conditions are 1-2 h at 150-300℃; the mass ratio of the powder to the solvent is 1:3-5, the solvent is water, and the mixing time is 0.5-1.5 h.

[0014] Further, in step (2), the iron cyanide is one of potassium ferricyanide or sodium ferricyanide; the amount of iron cyanide added is that the molar ratio of ferricyanide ions in the iron cyanide to copper ions in the lithium filtrate is 1-1.2:1.

[0015] Further, in step (3), the alkali solution is sodium hydroxide or ammonia water, and the pH is adjusted to 4.5-5.5; the concentration of the concentrated lithium solution is 20-25 g / L.

[0016] Further, in step (4), the heating condition is 90-100℃, the carbonizing agent is one of carbon dioxide, sodium carbonate or ammonium carbonate, and the carbonizing agent is used until no precipitate is produced in the solution; the alkali solution is ammonia water, and the pH is adjusted to 10.

[0017] Further, in step (5), the inorganic acid is one of hydrochloric acid, sulfuric acid or nitric acid, the molar ratio of inorganic acid to iron in the iron phosphate residue is 1:1-1.2, and the mass ratio of the iron phosphate residue to the solvent is 1:3-4, and the solvent is water.

[0018] Further, in step (6), the iron-phosphorus ratio is 1.05-1.2, and the pH is 1.6-2.0; the precipitation temperature is 90-100 DEG C, and the precipitation time is 1-2 h; and the high-temperature calcination conditions are 600±10 DEG C for 4-5 h.

[0019] Principle: The application ignites the waste lithium iron phosphate in an oxidizing gas, changes the metal impurity ions into soluble salts, separates the lithium phosphate and lithium through solvent immersion, separates the metal impurities and the lithium phosphate, simplifies the impurity removal process of the lithium phosphate, removes impurities from the lithium solution, and precipitates lithium carbonate, and the carbon-containing iron phosphate residue is separated from the metal copper and aluminum, and only needs to be dissolved in acid, adjust the iron-phosphorus ratio, add a precipitating agent, and obtain the battery-grade lithium phosphate after precipitation.

[0020] Advantages: Compared with the prior art, the application has the following advantages:

[0021] (1) Compared with the traditional acid total leaching and selective acid leaching technical solutions, the application burns the waste lithium iron phosphate in halogen oxidizing gases such as chlorine and bromine, which can oxidize the divalent iron in the lithium iron phosphate, and can also oxidize copper and aluminum into water-soluble halides, which can effectively separate the copper and aluminum impurities from the iron phosphate residue, and avoid the mixing of copper and aluminum metal impurities and iron ions to increase the difficulty of impurity removal.

[0022] (2) The application uses the idea of reverse lithium iron phosphate synthesis to efficiently deintercalate lithium ions from the lithium iron phosphate lattice to obtain soluble lithium chloride and insoluble iron phosphate residue, which can improve the recovery rate of lithium phosphate and lithium carbonate.

[0023] (3) The application uses pure water to separate lithium ions from the solid, which eliminates the traditional acid immersion step, greatly reduces the concentration of other salts in the lithium solution, and greatly improves the lithium solubility after concentration and the recovery rate of lithium.

[0024] (4) The process flow of the application is short, and the amount of acid and alkali used is small, which significantly reduces the recovery cost and is more conducive to process engineering. DETAILED DESCRIPTION

[0025] The application will be further described below in combination with specific examples and comparative examples.

[0026] Example 1: The method for synthesizing battery-grade lithium carbonate and iron phosphate with high-efficiency impurity removal from waste lithium iron phosphate, according to the present application, comprises the following steps:

[0027] (1) Heat the waste lithium iron phosphate powder to 150°C under a chlorine atmosphere, and burn for 1 h. Soak the obtained powder in water, with a mass ratio of powder to water of 1:3, stir for 0.5 h, filter, and obtain a lithium chloride filtrate containing copper and aluminum impurities and a lithium extraction residue;

[0028] (2) Add potassium ferricyanide to the lithium filtrate containing copper and aluminum impurities, with a Cu 2+ and (Fe(CN)6) 3- molar ratio of 1:1, to generate a brown-green precipitate, filter, and obtain a copper-removed lithium chloride solution;

[0029] (3) Add ammonia water to the copper-removed lithium chloride solution, adjust the pH to 4.5, filter, obtain an aluminum-removed lithium chloride solution, and then heat and concentrate to 100°C to obtain a concentrated lithium solution with a lithium content of 20 g / L;

[0030] (4) Heat the concentrated lithium chloride solution to 90°C, pass carbon dioxide into the solution, and supplement ammonia water into the solution to maintain the reaction pH at 10. After the reaction is completed, filter to obtain lithium carbonate;

[0031] (5) Disperse the lithium extraction residue with water according to a mass ratio of 1:3, add sulfuric acid to dissolve sufficiently, with a sulfuric acid addition amount and iron molar ratio of 1:1, filter after reacting for 0.5 h to obtain an acid leaching solution;

[0032] (6) Adjust the phosphorus-iron molar ratio of the acid leaching solution to 1.05, adjust the pH to 1.6 with ammonia water to obtain a ferric phosphate precipitate, heat to 90°C, and precipitate for 1 h, filter to obtain dihydrate ferric phosphate, and then calcine at 600°C for 4 h to obtain ferric phosphate.

[0033] Example 2: The method for synthesizing battery-grade lithium carbonate and iron phosphate with high-efficiency impurity removal from waste lithium iron phosphate, according to the present application, comprises the following steps:

[0034] (1) Heat the waste lithium iron phosphate powder to 200°C under a chlorine atmosphere, and burn for 1.5 h. Soak the obtained powder in water, with a mass ratio of powder to water of 1:4, stir for 1 h, filter, and obtain a lithium chloride filtrate containing copper and aluminum impurities and a lithium extraction residue;

[0035] (2) Add potassium ferricyanide to the lithium chloride filtrate containing copper and aluminum impurities, with a Cu 2+ and (Fe(CN)6) 3- molar ratio of 1:1.1, to generate a brown-green precipitate, filter. Obtain a copper-removed lithium chloride solution;

[0036] (3) adding ammonia water to the copper-removed lithium chloride solution, adjusting the pH to 5, filtering to obtain a lithium chloride solution from which aluminum is removed, and then heating and concentrating the solution at 100°C to obtain a concentrated lithium chloride solution with a lithium content of 22 g / L;

[0037] (4) heating the concentrated lithium chloride solution to 95°C, passing carbon dioxide into the solution, adding ammonia water into the solution to maintain the reaction pH at 10, and filtering after the reaction is completed to obtain lithium carbonate;

[0038] (5) dispersing the lithium extraction residue in water at a mass ratio of 1:5, adding sulfuric acid to dissolve the residue, the molar ratio of sulfuric acid to iron being 1:1, filtering after 1 h of reaction to obtain an acid leaching solution;

[0039] (6) adjusting the molar ratio of phosphorus to iron in the acid leaching solution to 1.1, adjusting the pH to 2.0 with ammonia water to obtain iron phosphate precipitate, heating to 95°C, and precipitating for 1 h to obtain iron phosphate dihydrate, which is then calcined at 600°C for 4 h to obtain iron phosphate.

[0040] Example 3: The method for synthesizing battery-grade lithium carbonate and iron phosphate from waste lithium iron phosphate with high efficiency and impurity removal according to the application comprises the following steps:

[0041] (1) heating waste lithium iron phosphate powder to 300°C in a chlorine atmosphere, burning the powder for 2 h, soaking the obtained powder in water at a mass ratio of 1:5, stirring for 1.5 h, and filtering to obtain a lithium chloride solution containing copper and aluminum impurities and lithium extraction residue;

[0042] (2) adding potassium ferricyanide to the lithium chloride solution containing copper and aluminum impurities, the amount of potassium ferricyanide being added in a molar ratio of 1:1.2 to Cu 2+ and (Fe(CN)6) 3- , a brown-green precipitate is generated, and the precipitate is filtered to obtain a copper-removed lithium chloride solution;

[0043] (3) adding ammonia water to the copper-removed lithium chloride solution, adjusting the pH to 5.5, filtering to obtain a lithium chloride solution from which aluminum is removed, heating and concentrating the solution at 100°C to obtain a concentrated lithium chloride solution with a lithium content of 25 g / L;

[0044] (4) heating the concentrated lithium chloride solution to 100°C, passing carbon dioxide into the solution, adding ammonia water into the solution to maintain the reaction pH at 10, and filtering after the reaction is completed to obtain lithium carbonate;

[0045] (5) dispersing the lithium extraction residue in water at a mass ratio of 1:4, adding sulfuric acid to dissolve the residue, the molar ratio of sulfuric acid to iron being 1:1.2, filtering after 1 h of reaction to obtain an acid leaching solution;

[0046] (6) Adjust the molar ratio of phosphorus to iron in the acid leaching solution to 1:1.2, adjust the pH to 1.8 with ammonia water to obtain iron phosphate precipitate, then heat to 95°C and precipitate for 2h, filter to obtain iron phosphate dihydrate, and then calcine at 600°C for 4h to obtain iron phosphate.

[0047] Comparative Example 1: Different from Example 1, in step (1), the combustion treatment is not included, and the waste lithium iron phosphate is directly placed in water for soaking.

[0048] The lithium carbonate and iron phosphate prepared in Examples 1-3 were subjected to content determination, and the results are shown in Tables 1 and 2. As can be seen from Tables 1 and 2, the purity of the lithium carbonate and iron phosphate obtained under the reaction conditions in Example 2 is optimal. Through comparison of the conditions in Examples 1-3, it is found that when the combustion temperature is greater than 200°C, the impurity content in the finished iron phosphate product is significantly reduced, and therefore the temperature has a greater influence on the reaction degree of copper and aluminum metals and chlorine gas. Through comparison of Examples 1-3, it is found that when the molar ratio of phosphorus to iron is 1:1.1 during the aging of iron phosphate in step (6), the main element Fe:P in the finished iron phosphate product is optimal, and when the ratio is too low or too high during the aging process, the main content Fe:P of the iron phosphate will be affected. At the same time, through comparison of Comparative Example 1 and Example 1, it is found that only under the heating condition, part of the copper and aluminum impurities cannot form soluble salts, and will enter the solution during the acid dissolution of the lithium extraction black residue in step (5), resulting in a high content of copper and aluminum impurities in the subsequent precipitation of iron phosphate.

[0049] Table 1 Content table of lithium carbonate prepared in Examples 1-3 and Comparative Example 1

[0050]

[0051] Table 2 Content table of iron phosphate prepared in Examples 1-3 and Comparative Example 1

[0052]

Claims

1. A method for efficiently removing impurities from waste lithium iron phosphate and synthesizing battery-grade lithium carbonate and iron phosphate, characterized in that, Includes the following steps: (1) After the waste lithium iron phosphate is burned in an oxidizing atmosphere, the powder obtained is soaked in a solvent, mixed evenly and then filtered to obtain lithium filtrate containing copper and aluminum impurities and lithium extraction residue; the oxidizing atmosphere is either chlorine or bromine; the conditions for the combustion treatment are: burning at 150-300℃ for 1-2 hours. (2) Add ferricyanide to the lithium filtrate containing copper and aluminum impurities, filter after the reaction is complete, and obtain a lithium solution with copper removed; (3) Add an alkaline solution to the copper-free lithium solution, adjust the pH, filter to obtain an aluminum-free lithium solution, and then heat and evaporate to concentrate to obtain a concentrated lithium solution. (4) Under heating conditions, an alkaline solution and a carbonizing agent are added to the concentrated lithium solution, and lithium carbonate is obtained after the reaction is completed; (5) Disperse the lithium extraction residue obtained in step (1) in a solvent, then add an inorganic acid to dissolve it completely, and filter to obtain an acid leaching solution; (6) Adjust the phosphorus-iron ratio of the acid leaching solution, then adjust the pH with an alkaline solution to obtain ferric phosphate precipitate, then heat it to precipitate, filter it to obtain ferric phosphate dihydrate, and then calcine it at high temperature to obtain ferric phosphate.

2. The method according to claim 1, characterized in that, In step (1), the mass ratio of the powder to the solvent is 1:3-5, and the mixing time is 0.5-1.5h.

3. The method according to claim 1, characterized in that, In step (2), the ferricyanide is either potassium ferricyanide or sodium ferricyanide.

4. The method according to claim 1, characterized in that, In step (2), the amount of ferricyanide added is such that the molar ratio of ferricyanide ions in the ferricyanide to copper ions in the lithium filtrate is 1-1.2:

1.

5. The method according to claim 1, characterized in that, In step (3), the alkaline solution is sodium hydroxide or ammonia water, and the pH is adjusted to 4.5-5.5; the mass concentration of the concentrated lithium solution is 20-25 g / L.

6. The method according to claim 1, characterized in that, In step (4), the heating conditions are 90-100℃, and the carbonizing agent is one of carbon dioxide, sodium carbonate or ammonium carbonate.

7. The method according to claim 1, characterized in that, In step (5), the inorganic acid is one of hydrochloric acid, sulfuric acid or nitric acid, and the molar ratio of the inorganic acid to the iron in the ferric phosphate slag is 1:1-1.

2.

8. The method according to claim 1, characterized in that, In step (6), the phosphorus-iron ratio is 1.05-1.2 and the pH is 1.6-2.

0.

9. The method according to claim 1, characterized in that, In step (6), the precipitation temperature is 90-100℃ and the precipitation time is 1-2h; the high-temperature calcination conditions are: calcination at 600±10℃ for 4-5h.

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