Lithium iron phosphate positive electrode powder all-element recovery method

Abstract

The invention provides a lithium iron phosphate positive electrode powder all-element recovery method, and relates to the technical field of new energy material recovery. The method comprises the following steps of lithium salt leaching, purification and impurity removal, freezing crystallization, lithium hydroxide evaporative crystallization, high-temperature alkali leaching, leaching residue acid dissolution and sodium phosphate evaporative crystallization. The lithium element is leached by ferric sulfate, the reaction condition is mild, and generation of acid mist and waste gas is reduced; the phosphorus-iron slag is treated by adopting an alkali pressure boiling method, and phosphorus and iron are respectively extracted in sequence, so that all-element recovery is realized, the product purity is relatively high, and the use amount of acid and alkali is saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy material recycling, more particularly to a method for full-element recovery of lithium iron phosphate positive electrode powder. BACKGROUND

[0002] With the rapid development of the new energy industry, lithium iron phosphate batteries are widely used in power batteries, energy storage and other fields, and the recycling of discarded lithium iron phosphate batteries has attracted increasing attention. Currently, lithium iron phosphate recycling mainly uses oxidative acid dissolution method to preferentially extract lithium, and then separates the iron phosphate in the residue phase from carbon. The main goal of this method is to recover lithium elements, but the purity of the regenerated iron phosphate obtained is not high, and efficient separation and recovery of iron and phosphorus elements have not been achieved. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a method for full-element recovery of lithium iron phosphate positive electrode powder to solve the problem of efficient separation and recovery of iron and phosphorus elements in lithium iron phosphate positive electrode powder.

[0004] To achieve the above purpose, the main technical solution adopted by the present application is a method for full-element recovery of lithium iron phosphate positive electrode powder, comprising the following steps: Step 1, lithium salt leaching: adding iron sulfate solution to lithium iron phosphate positive electrode powder, heating and stirring the obtained slurry under normal pressure, and then performing solid-liquid separation to obtain lithium-containing leaching solution and lithium extraction residue; Step 2, purification and impurity removal: adding an oxidizing agent to the lithium-containing leaching solution to oxidize the divalent iron ions in the lithium-containing leaching solution to trivalent iron ions, then adding sodium hydroxide to adjust the pH value, and filtering the mixture after stirring to obtain a filtrate and a ferric hydroxide filter cake, which can be sent to step 6 together with the leaching residue for acid dissolution; Step 3, freezing crystallization: adding a crystallization mother liquor and a sodium hydroxide solution to the filtrate obtained in step 2, stirring, and cooling to precipitate crystals, and then centrifuging the obtained slurry; Step 4, lithium hydroxide evaporation crystallization: adding the lithium hydroxide solution obtained in step 3 to an evaporator, evaporating by heating, and cooling to obtain crystals, and then performing solid-liquid separation on the mixture of lithium hydroxide solution and crystals, and returning the obtained filtrate to step 3 for batching; Step 5, high-temperature alkali leaching: adding an alkali solution to the lithium extraction residue obtained in step 1 to prepare a slurry, and then performing high-temperature leaching reaction in a container, cooling and solid-liquid separating the obtained slurry after the reaction is completed, and the filtrate is a mixed solution of sodium phosphate and sodium hydroxide; Step 6, leaching residue acid dissolution: adding sulfuric acid to the leaching residue obtained in step 5 and stirring, and then performing solid-liquid separation after the reaction is completed at room temperature to obtain residual carbon residue which is sent to other processes for recycling, and the obtained filtrate is returned to step 1 for batching; Step 7, Sodium phosphate evaporation and crystallization: The filtrate obtained in step 5 is evaporated and concentrated, and crystals are precipitated after cooling. The resulting slurry is then subjected to solid-liquid separation. The resulting filtrate is an alkaline solution, which is returned to step 5 for batching.

[0005] In step 1, the iron-lithium molar ratio of the slurry is 2~3:1, the temperature is controlled at 75℃~95℃ during heating and stirring, and the reaction time is 1h~2h. The resulting lithium extraction slag consists of iron phosphate and carbon slag, while the solutes in the lithium-containing leachate are lithium sulfate, iron sulfate, and ferrous sulfate.

[0006] In step 2, the oxidant is hydrogen peroxide, and the amount of oxidant added is 1.5 to 3 times the theoretical amount; the pH value is adjusted to 10 to 11, and the stirring reaction time is 0.5 to 1 hour.

[0007] In step 3, the molar ratio of sodium hydroxide to lithium sulfate in the solution obtained in step 2 is 1.1~1.2, the stirring time is 1~2h, and the temperature is cooled to 0℃.

[0008] In step 3, the obtained filter cake is sodium sulfate decahydrate, which is remelted by steam heating and then sent to an evaporation crystallization device to obtain sodium sulfate by-product.

[0009] In step 4, the filter cake is composed of lithium hydroxide monohydrate. After drying, lithium hydroxide monohydrate product is obtained. The drying temperature is 80℃-95℃ and the drying time is 4h-8h.

[0010] In step 5, the alkaline solution is a 5%-20% sodium hydroxide solution, the mass ratio of the alkaline solution to the lithium extraction residue is 3-8:1, the reaction temperature of the high-temperature leaching reaction is 140℃-160℃, and the reaction time is 1h-2h.

[0011] In step 6, the leaching residue obtained in step 5 consists of iron oxide and carbon, and the stirring time is 0.5h~1h.

[0012] In step 7, the obtained filter cake is sodium phosphate, which is dried to obtain sodium phosphate product. The drying temperature is 80℃-95℃ and the drying time is 4h-8h.

[0013] The present invention has the following beneficial effects and advantages: This invention uses ferric sulfate to leach lithium, which is a mild reaction condition that reduces the generation of acid mist and waste gas. It uses an alkaline pressure cooking method to treat phosphorus-iron slag, extracting phosphorus and iron elements separately, achieving full element recovery, resulting in high product purity and saving on acid and alkali consumption. Attached Figure Description

[0014] Figure 1 This is a flowchart of a method for the full element recovery of lithium iron phosphate cathode powder according to the present invention. Detailed Implementation

[0015] The present invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 This is a flowchart of a method for the complete element recovery of lithium iron phosphate cathode powder according to the present invention, as shown below. Figure 1 As shown, the method includes the following steps: Step 1, Lithium Salt Leaching: Add the ferric sulfate solution obtained by acid dissolution to the lithium iron phosphate cathode powder to make the iron-lithium molar ratio 2.5:1. After heating and stirring the resulting slurry under normal pressure for 1 hour, solid-liquid separation is performed to obtain lithium-containing leachate and lithium extraction slag. The temperature is controlled at 90℃. The lithium extraction slag consists of ferric phosphate and carbon slag. The solute components of the lithium-containing leachate are lithium sulfate, ferric sulfate and ferrous sulfate.

[0017] Step 2, purification and impurity removal: Add hydrogen peroxide as an oxidant to the lithium-containing leachate to oxidize the ferrous ions in the lithium-containing leachate to ferric ions. The amount of hydrogen peroxide added is 1.5 times the theoretical amount. Then add sodium hydroxide to adjust the pH to 10, stir the reaction for 0.5 hours, and then filter to obtain filtrate and ferric hydroxide filter cake. The ferric hydroxide filter cake can be sent to step 6 for acid dissolution. Step 3, Freeze-crystallization: Add crystallization mother liquor and sodium hydroxide solution to the filtrate obtained in Step 2, so that the molar ratio of sodium hydroxide to lithium sulfate in the above solution is 1.1. After stirring for 1 hour, cool to 0°C to precipitate crystals. Centrifuge the obtained slurry to separate the components. The obtained filter cake is sodium sulfate decahydrate. After being heated and remelted by steam, it is sent to an evaporation crystallization device to obtain sodium sulfate by-product.

[0018] Step 4, Lithium hydroxide evaporation and crystallization: Add the lithium hydroxide solution obtained in step 3 to the evaporator, heat and evaporate, and obtain crystals after cooling. Perform solid-liquid separation on the mixture of lithium hydroxide solution and crystals. Return the obtained filtrate to step 3 for batching. Dry the obtained filter cake at 85°C for 4 hours to obtain lithium hydroxide monohydrate product.

[0019] Step 5, High-temperature alkaline leaching: Add 10% sodium hydroxide solution to the lithium extraction residue obtained in Step 1 and mix to form a slurry. The mass ratio of 10% sodium hydroxide solution to lithium extraction residue is 6:1. Then carry out a high-temperature leaching reaction in a container. The reaction temperature is 160℃ and the reaction time is 1h. After the reaction is completed, the resulting liquid is cooled and solid-liquid separated. The resulting filtrate is a mixed solution of sodium phosphate and sodium hydroxide. Step 6, Acid dissolution of leaching residue: Add sulfuric acid to the leaching residue obtained in step 5 and stir for 1 hour. React at room temperature. After the reaction is complete, perform solid-liquid separation to obtain the residual carbon residue. The resulting filtrate is returned to step 1 for batching. Step 7, Sodium phosphate evaporation and crystallization: The filtrate obtained in step 5 is evaporated and concentrated, and crystals are precipitated after cooling. The resulting slurry is then subjected to solid-liquid separation. The resulting filtrate is an alkaline solution, which is returned to step 5 for batching. The resulting filter cake is dried at 95°C for 4 hours to obtain sodium phosphate product.

[0020] Example 2 Step 1, Lithium Salt Leaching: Add the ferric sulfate solution obtained by acid dissolution to the lithium iron phosphate cathode powder, and then add freshly prepared ferric sulfate solution to make the iron-lithium molar ratio 3:1. After heating and stirring the resulting slurry under normal pressure for 2 hours, solid-liquid separation is performed to obtain lithium-containing leachate and lithium extraction slag. The temperature is controlled at 75℃. The components of the lithium extraction slag are ferric phosphate and carbon slag, and the solute components of the lithium-containing leachate are lithium sulfate, ferric sulfate and ferrous sulfate.

[0021] Step 2, purification and impurity removal: Add hydrogen peroxide as an oxidant to the lithium-containing leachate to oxidize the ferrous ions in the lithium-containing leachate to ferric ions. The amount of hydrogen peroxide added is 1.5 times the theoretical amount. Then add sodium hydroxide to adjust the pH to 10, stir the reaction for 0.5 hours, and then filter to obtain filtrate and ferric hydroxide filter cake. The ferric hydroxide filter cake can be sent to step 6 for acid dissolution. Step 3, Freeze-crystallization: Add crystallization mother liquor and sodium hydroxide solution to the filtrate obtained in Step 2, so that the molar ratio of sodium hydroxide to lithium sulfate in the above solution is 1.1. After stirring for 1 hour, cool to 0°C to precipitate crystals. Centrifuge the obtained slurry to separate the components. The obtained filter cake is sodium sulfate decahydrate. After being heated and remelted by steam, it is sent to an evaporation crystallization device to obtain sodium sulfate by-product.

[0022] Step 4, Lithium hydroxide evaporation and crystallization: Add the lithium hydroxide solution obtained in step 3 to the evaporator, heat and evaporate, and obtain crystals after cooling. Perform solid-liquid separation on the mixture of lithium hydroxide solution and crystals. Return the obtained filtrate to step 3 for batching. Dry the obtained filter cake at 90°C for 4 hours to obtain lithium hydroxide monohydrate product.

[0023] Step 5, High-temperature alkaline leaching: Add 20% sodium hydroxide solution to the lithium extraction residue obtained in Step 1 and mix to form a slurry. The mass ratio of 20% sodium hydroxide solution to lithium extraction residue is 4:1. Then carry out a high-temperature leaching reaction in a container. The reaction temperature is 140℃ and the reaction time is 2h. After the reaction is completed, the resulting liquid is cooled and solid-liquid separated. The resulting filtrate is a mixed solution of sodium phosphate and sodium hydroxide. Step 6, Acid dissolution of leaching residue: Add sulfuric acid to the leaching residue obtained in step 5 and stir for 1 hour. React at room temperature. After the reaction is complete, perform solid-liquid separation to obtain the residual carbon residue. The resulting filtrate is returned to step 1 for batching. Step 7, Sodium phosphate evaporation and crystallization: The filtrate obtained in step 5 is evaporated and concentrated, and crystals are precipitated after cooling. The resulting slurry is then subjected to solid-liquid separation. The resulting filtrate is an alkaline solution, which is returned to step 5 for batching. The resulting filter cake is dried at 85°C for 6 hours to obtain sodium phosphate product.

[0024] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for the complete element recovery of lithium iron phosphate cathode powder, characterized in that, Includes the following steps: Step 1, Lithium salt leaching: Add ferric sulfate solution to lithium iron phosphate cathode powder, heat and stir the resulting slurry under normal pressure, and then perform solid-liquid separation to obtain lithium-containing leachate and lithium extraction residue; Step 2, purification and impurity removal: Add an oxidant to the lithium-containing leachate to oxidize the ferrous ions in the lithium-containing leachate to ferric ions. Then add sodium hydroxide to adjust the pH value. After stirring, filter to obtain filtrate and ferric hydroxide filter cake. The ferric hydroxide filter cake can be sent to step 6 together with the leaching residue for acid dissolution. Step 3, Freeze-crystallization: Add crystallization mother liquor and sodium hydroxide solution to the filtrate obtained in Step 2, stir and cool to precipitate crystals, and then centrifuge the resulting slurry. Step 4, Lithium hydroxide evaporation and crystallization: Add the lithium hydroxide solution obtained in step 3 to the evaporator, heat and evaporate, and cool to obtain crystals. Perform solid-liquid separation on the mixture of lithium hydroxide solution and crystals, and return the filtrate to step 3 for batching. Step 5, High-temperature alkaline leaching: Add alkaline solution to the lithium residue obtained in Step 1 to mix and slurry, and then carry out a high-temperature leaching reaction in a container. After the reaction is completed, cool and separate the solid and liquid in the resulting liquid. The filtrate is a mixed solution of sodium phosphate and sodium hydroxide. Step 6, Acid dissolution of leaching residue: Add sulfuric acid to the leaching residue obtained in step 5 and stir. React at room temperature. After the reaction is complete, perform solid-liquid separation to obtain residual carbon residue, which is sent to other processes for recycling. The obtained filtrate is returned to step 1 for batching. Step 7, Sodium phosphate evaporation and crystallization: The filtrate obtained in step 5 is evaporated and concentrated, and crystals are precipitated after cooling. The resulting slurry is then subjected to solid-liquid separation. The resulting filtrate is an alkaline solution, which is returned to step 5 for batching.

2. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 1, the iron-lithium molar ratio of the slurry is 2~3:1, the temperature is controlled at 75℃~95℃ during heating and stirring, and the reaction time is 1h~2h. The resulting lithium extraction slag consists of iron phosphate and carbon slag, while the solutes in the lithium-containing leachate are lithium sulfate, iron sulfate, and ferrous sulfate.

3. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 2, the oxidant is hydrogen peroxide, and the amount of oxidant added is 1.5 to 3 times the theoretical amount. Adjust the pH value to 10-11 and stir for 0.5-1 hour.

4. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 3, the molar ratio of sodium hydroxide to lithium sulfate in the solution obtained in step 2 is 1.1~1.2, the stirring time is 1~2h, and the temperature is cooled to 0℃.

5. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 3, the obtained filter cake is sodium sulfate decahydrate, which is remelted by steam heating and then sent to an evaporation crystallization device to obtain sodium sulfate by-product.

6. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 4, the filter cake is composed of lithium hydroxide monohydrate. After drying, lithium hydroxide monohydrate product is obtained. The drying temperature is 80℃-95℃ and the drying time is 4h-8h.

7. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 5, the alkaline solution is a 5%-20% sodium hydroxide solution, the mass ratio of the alkaline solution to the lithium extraction residue is 3-8:1, the reaction temperature of the high-temperature leaching reaction is 140℃-160℃, and the reaction time is 1h-2h.

8. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 6, the leaching residue obtained in step 5 consists of iron oxide and carbon, and the stirring time is 0.5h~1h.

9. The method for full element recovery of lithium iron phosphate cathode powder according to claim 1, characterized in that, In step 7, the obtained filter cake is sodium phosphate, which is dried to obtain sodium phosphate product. The drying temperature is 80℃-95℃ and the drying time is 4h-8h.

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