Method for cooperatively extracting lithium from electrolytic aluminum lithium-containing repair slag and lithium iron phosphate positive electrode waste

Abstract

The application discloses a method for cooperatively extracting lithium from electrolytic aluminum lithium-containing overhaul slag and lithium iron phosphate positive electrode waste, and the method is characterized in that: by adding an oxidizing agent, cyanide in the overhaul slag is oxidized and decomposed, and at the same time, iron in the lithium iron phosphate positive electrode waste is also oxidized; and by using sulfuric acid or nitric acid as a leaching agent, lithium-containing substances in the overhaul slag and lithium in the lithium iron phosphate are selectively leached into a solution, so that the leaching rate of lithium is improved, and the purpose of fully recycling lithium is achieved. In addition, fluorine, aluminum and the like in the lithium iron phosphate positive electrode waste and the overhaul slag are also leached into the solution, and by adjusting the pH value of the solution, cryolite products are generated, which can be returned to an electrolytic cell to be used as an electrolyte, lithium in the solution is precipitated after enrichment and concentration, the product has high purity, the production process is simple and controllable, lithium, fluorine, aluminum and the like in the lithium iron phosphate positive electrode waste and the electrolytic aluminum overhaul slag can be cooperatively recycled, and no new pollution is generated.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly production technology, specifically to a method for synergistic lithium extraction from lithium-containing overhaul slag of electrolytic aluminum and lithium iron phosphate cathode waste. Background Technology

[0002] Lithium iron phosphate (LFP) batteries, due to their excellent stability and safety performance, were first applied in my country's transportation sector. In recent years, the earliest LFP batteries in service are facing large-scale scrapping and retirement. Retired LFP power batteries possess both resource and environmental attributes, containing abundant lithium, iron, copper, and aluminum elements. Furthermore, my country lacks lithium resources, and spodumene is of low grade, making mining difficult and costly. Recycling LFP cathode materials is beneficial for resource recycling and can also alleviate the pressure of lithium imports, promoting the healthy development of my country's lithium battery industry. Therefore, developing clean and efficient methods for treating LFP battery waste is of significant practical importance.

[0003] However, the recycling of lithium iron phosphate cathode waste is affected by lithium price fluctuations, and the cathode material recycling process requires sorting or solvent removal of aluminum. Compared with ternary batteries with higher metal content, its recycling economic benefits are not stable enough.

[0004] Lithium-containing overhaul slag from electrolytic aluminum production is highly toxic due to the presence of harmful impurities such as cyanide, classifying it as hazardous waste. Currently, decyanation and harmless treatment processes for this slag are relatively mature. After harmless treatment, the slag is typically used as a cement or brick-making raw material, but valuable elements such as lithium, aluminum, fluorine, and silicon are not effectively utilized. Therefore, simultaneously decyanating and harmlessly treating the slag while extracting lithium, aluminum, and fluorine resources is of great significance. However, the lithium content in lithium-containing overhaul slag from electrolytic aluminum production is typically 0.2%–3%, and directly extracting lithium from this slag presents problems such as a long process flow, high cost, and low economic efficiency.

[0005] If lithium iron phosphate waste and lithium-containing overhaul slag are co-processed using a single process to simultaneously recover and process both raw materials, and to selectively extract lithium, aluminum, fluorine, and other resources from both raw materials, it will help increase the value of the recycled products, reduce process costs, and improve economic efficiency. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for synergistic lithium extraction from lithium-containing overhaul slag of electrolytic aluminum and lithium iron phosphate cathode waste.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for co-extracting lithium from lithium-containing overhaul slag of electrolytic aluminum and lithium iron phosphate cathode waste includes the following steps:

[0009] S1. Battery Discharge: Place the used lithium iron phosphate batteries in a salt solution and discharge the remaining charge of the used lithium iron phosphate batteries through electrolysis.

[0010] S2, Disassembly and Separation: Disassemble the waste lithium iron phosphate batteries processed in step S1 to obtain the positive electrode sheet, negative electrode sheet, shell material and separator of the waste lithium iron phosphate batteries. Then, crush the obtained positive electrode sheet to obtain lithium iron phosphate positive electrode waste.

[0011] S3. Mix the lithium iron phosphate cathode waste obtained in step S2 with the lithium-containing overhaul slag of electrolytic aluminum to obtain mixture M1.

[0012] S4. Add water to the mixture M1 obtained in step S3 and stir evenly to obtain slurry M2;

[0013] S5. Add an oxidant to the slurry M2 obtained in step S4 and stir to react;

[0014] It should be noted that the oxidant acts on two fronts: firstly, it oxidizes and decomposes the cyanide in the overhaul slag; secondly, it oxidizes the iron in the lithium iron phosphate cathode waste. When hydrogen peroxide is used as the oxidant, the cyanide decomposition reaction principle is as follows:

[0015] H₂O₂ + NaCN + H₂O → NaHCO₃ + NH₃↑

[0016] H2O2 + Fe 2+ →Fe 3+ +H2O

[0017] S6. Add an acidic solution as a leaching agent to the material obtained in step S5 and perform acid leaching to leach lithium, fluorine and aluminum ions from lithium iron phosphate cathode waste and lithium-containing overhaul residue of electrolytic aluminum into the solution. After solid-liquid separation, leachate M3 and filter residue are obtained.

[0018] Taking sulfuric acid solution as an example, the main reaction principle of step S6 is as follows:

[0019] H2O2+LiFePO4+H2SO4→FePO4↓+Li2SO4+H2O

[0020] 2LiF + H₂SO₄ → Li₂SO₄ + 2HF↑;

[0021] 2NaF + H₂SO₄ → Na₂SO₄ + 2HF↑

[0022] 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂↑

[0023] Al2(SO4)3+2Na3AlF6=3Na2SO4+4AlF3↓

[0024] S7. Add an alkaline solution to the leachate M3 obtained in step S6 to adjust the pH value. After the precipitation reaction is completed, separate the solid and liquid, and filter to obtain cryolite product and filtrate M4.

[0025] S8. Add alkaline solution to the filtrate M4 obtained in step S7 to adjust the pH value, and obtain filtrate M5.

[0026] S9. Evaporate and concentrate the filtrate M5 obtained in step S8 until lithium is enriched in the concentrate to a set concentration.

[0027] S10. Add carbonate to the concentrated solution obtained in step S9 to precipitate lithium, and filter to obtain crude lithium carbonate product and filtrate M6.

[0028] The chemical reactions that occur during the lithium precipitation process are as follows: 2Li + +Na₂CO₃=Li₂CO₃↓+2Na + .

[0029] S11. The filtrate M6 obtained in step S10 is evaporated and crystallized to recover the salt. After being cooled with distilled water, it is returned to step S4 to prepare slurry M2.

[0030] Furthermore, in step S2, the particle size of the lithium iron phosphate cathode waste is more than 90% smaller than 200 mesh.

[0031] Furthermore, in step S3, the mass ratio of lithium iron phosphate cathode waste to lithium-containing overhaul slag from electrolytic aluminum is 0.5–1:0.5–2.

[0032] Furthermore, in step S4, the mass ratio of water to mixture M1 is 1:1 to 5:1, the stirring method is mechanical stirring, and the stirring speed is 200-1000 r / min.

[0033] Further, in step S5, the oxidant is one or more of hydrogen peroxide, calcium hypochlorite, and sodium hypochlorite; the mass of the added oxidant is 5% to 20% of the mass of the mixture M1, and the stirring reaction time is 0.5 to 2 hours.

[0034] Further, in step S6, the acidic solution is a sulfuric acid or nitric acid solution, the liquid-to-solid ratio of the acidic solution to the mixture M1 is 15-50 mL: 100 g, the acid leaching time is 1-5 h, and the acid leaching temperature is 20-80 °C.

[0035] Further, in step S7, the alkaline solution is a sodium hydroxide or sodium carbonate solution, and the pH value is 8.0 to 9.5.

[0036] Further, in step S8, the alkaline solution is a sodium hydroxide or sodium carbonate solution, and the pH value is 10.5 to 11.5.

[0037] Furthermore, in step S9, the set concentration is greater than or equal to 20 g / L.

[0038] Further, in step S10, the carbonate is sodium carbonate, and the mass ratio of sodium carbonate to mixture M1 is 0.2 to 1:1; the lithium precipitation temperature is 60-85℃, and the lithium precipitation time is 0.5-4h; the crude lithium carbonate product obtained from lithium precipitation is washed with deionized water and then dried to obtain the lithium carbonate product, the mass ratio of crude lithium carbonate product to deionized water is 1:1, the washing temperature is 60-100℃, the drying temperature is 60-110℃, and the drying time is 1-5h.

[0039] The beneficial effects of this invention are as follows:

[0040] (1) This invention mixes lithium iron phosphate cathode waste and lithium-containing overhaul residue from electrolytic aluminum, which solves the problem of low product value when a single material is used, and improves the economic benefits of the recycling process.

[0041] (2) This invention co-processes lithium iron phosphate cathode waste and lithium-containing overhaul slag from electrolytic aluminum, comprehensively recovering resources such as fluorine, aluminum, and lithium. It eliminates the need to separate the active material of lithium iron phosphate cathode from the current collector aluminum foil, simplifying the process and improving the comprehensive utilization rate of resources.

[0042] (3) The present invention uses hydrogen peroxide to decompose and oxidize cyanide in the overhaul slag, while also oxidizing and transforming iron in lithium iron phosphate, which is beneficial for the next step of selective leaching lithium and simplifies the process. Attached Figure Description

[0043] Figure 1 The following are flowcharts of the methods in embodiments 1 and 2 of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0045] Example 1

[0046] The main elemental composition of the lithium iron phosphate cathode waste in this embodiment, by mass percentage (%), is: Li 4.36, Fe 34.38, P 19.76, Al 13.26. The main elemental composition of the lithium-containing overhaul slag from electrolytic aluminum, by mass percentage (%), is: Li 0.28, F 15.14, Al 9.40, Na 8.88, Ca 9.48, C 24.76, Si 5.29, Fe 1.24. The co-extraction of lithium from the lithium iron phosphate cathode waste and the lithium-containing overhaul slag from electrolytic aluminum is achieved according to the following steps: Figure 1 As shown:

[0047] (1) Select waste lithium iron phosphate batteries with an open circuit voltage of 3.3V, immerse them in NaCl solution to release residual charge until the voltage drops to 2V;

[0048] (2) Manually disassemble the discharged waste lithium iron phosphate battery, separate the positive and negative electrodes, crush the obtained positive electrode to obtain lithium iron phosphate positive electrode waste, and the waste particle size is less than 200 mesh, accounting for more than 95%.

[0049] (3) Mix lithium iron phosphate cathode waste with lithium-containing overhaul slag of electrolytic aluminum at a mass ratio of 1:2 to obtain mixture M1;

[0050] (4) Add water to the mixture M1 at a mass ratio of 1:1, and mix it evenly by mechanical stirring to obtain slurry M2 at a stirring speed of 200 r / min;

[0051] (5) Add hydrogen peroxide as an oxidant to slurry M2. The mass of hydrogen peroxide is 5% of the mass of mixture M1. After reacting for 0.5 h, add 98% sulfuric acid solution as a leaching agent for acid leaching. The liquid-solid ratio of sulfuric acid solution added to mixture M1 is 15 mL: 100 g. The leaching reaction time is 5 h and the reaction temperature is 80 °C. After the reaction is completed, filter to obtain leachate M3 and filter residue.

[0052] (6) Add NaOH solution to leachate M3 to adjust the pH value to 8.0. After precipitation reaction for 1 hour, solid-liquid separation is performed and filtered to obtain cryolite product and filtrate M4.

[0053] (7) Add NaOH solution to filtrate M4 to adjust the pH value to 10.5, then evaporate and concentrate until lithium ions are enriched in the concentrate to 20 g / L;

[0054] (8) Add sodium carbonate to the evaporation concentrate, with the mass ratio of sodium carbonate added to mixture M1 being 0.2:1; the lithium precipitation temperature is 85℃ and the lithium precipitation time is 4h; filter to obtain crude lithium carbonate product and filtrate M6;

[0055] (9) The crude lithium carbonate product obtained by lithium precipitation is washed with deionized water and then dried to obtain the lithium carbonate product; the mass ratio of crude lithium carbonate product to deionized water is 1:1, the washing temperature is 60℃, the drying temperature is 60℃, and the drying time is 5h.

[0056] (10) Evaporate and crystallize the filtrate M6 to recover sodium sulfate. After cooling with distilled water, return it to step (4) to be used as slurry M2.

[0057] In this embodiment, the lithium leaching rate was 90.5%, the recovery rate was 84%, and the purity of the obtained lithium carbonate product was 99%.

[0058] Example 2

[0059] In this embodiment, the lithium iron phosphate cathode waste comes from a waste lithium iron phosphate battery recycling company. The mass fractions of Li, Fe, P, and Al are 4.40%, 34.20%, 19.00%, and Al 11.67%, respectively. The main elemental composition of the lithium-containing overhaul slag from electrolytic aluminum, by mass percentage (%), is: Li 0.26, F 15.76, Al 8.76, Na 10.49, Ca 1.54, C 37.85, Si 7.07, Fe 1.07. The following steps are used to achieve co-extraction of lithium from the lithium iron phosphate cathode waste and the lithium-containing overhaul slag from electrolytic aluminum, as follows: Figure 1 As shown:

[0060] (1) Select waste lithium iron phosphate batteries with an open circuit voltage greater than 3.0V, immerse them in Na2SO4 solution to release residual charge until the voltage drops to 2.5V;

[0061] (2) Manually disassemble the discharged waste lithium iron phosphate battery, separate the positive and negative electrodes, crush the obtained positive electrode to obtain lithium iron phosphate positive electrode waste, and the waste particle size is less than 200 mesh, accounting for more than 90%.

[0062] (3) Mix lithium iron phosphate cathode waste with lithium-containing overhaul slag from electrolytic aluminum at a mass ratio of 0.5:0.5 to obtain mixture M1;

[0063] (4) Add water to the mixture M1, with a mass ratio of water to mixture M1 of 5:1. Mix the mixture evenly by mechanical stirring to obtain slurry M2 at a stirring speed of 1000 r / min.

[0064] (5) Add hydrogen peroxide as an oxidant to slurry M2. The mass of hydrogen peroxide is 20% of the mass of mixture M1. After reacting for 2 hours, add 70% nitric acid solution as a leaching agent. The liquid-solid ratio of the amount of nitric acid solution added to mixture M1 is 50 mL: 100 g. The leaching reaction time is 1 hour and the reaction temperature is 20°C. After the reaction is completed, filter to obtain leachate M3 and filter residue.

[0065] (6) Add sodium carbonate solution to leachate M3 to adjust the pH value to 9.5. After precipitation reaction for 1 hour, solid-liquid separation is performed and filtered to obtain cryolite product and filtrate M4.

[0066] (7) Add NaOH solution to filtrate M4 to adjust the pH value to 11.5, then evaporate and concentrate until lithium ions are enriched in the concentrate to more than 20 g / L;

[0067] (8) Add sodium carbonate to the evaporation concentrate, with the mass ratio of sodium carbonate added to mixture M1 being 1:1; the lithium precipitation temperature is 60℃ and the lithium precipitation time is 0.5h; filter to obtain crude lithium carbonate product and filtrate M6.

[0068] (9) The crude lithium carbonate product obtained by lithium precipitation is washed with deionized water and then dried to obtain the lithium carbonate product. The mass ratio of crude lithium carbonate product to deionized water is 1:1, the washing temperature is 100℃, the drying temperature is 110℃, and the drying time is 1h.

[0069] (10) Evaporate and crystallize the filtrate M6 to recover sodium nitrate. After cooling with distilled water, return it to step (4) as a slurry preparation M2.

[0070] In this embodiment, the lithium leaching rate was 93%, the recovery rate was 85%, and the purity of the obtained lithium carbonate product was 99.4%.

[0071] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for synergistically extracting lithium from electrolytic aluminum lithium-containing repair slag and lithium iron phosphate positive electrode waste material, characterized in that, Includes the following steps: S1. Battery Discharge: Place the used lithium iron phosphate batteries in a salt solution and discharge the remaining charge of the used lithium iron phosphate batteries through electrolysis. S2, Disassembly and Separation: Disassemble the waste lithium iron phosphate batteries processed in step S1 to obtain the positive electrode sheet, negative electrode sheet, shell material and separator of the waste lithium iron phosphate batteries. Then, crush the obtained positive electrode sheet to obtain lithium iron phosphate positive electrode waste. S3. Mix the lithium iron phosphate cathode waste obtained in step S2 with the lithium-containing overhaul slag of electrolytic aluminum to obtain mixture M1. S4. Add water to the mixture M1 obtained in step S3 and stir until uniform to obtain slurry M2; S5. Add an oxidant to the slurry M2 obtained in step S4 and stir to react; S6. Add an acidic solution as a leaching agent to the material obtained in step S5 and perform acid leaching to leach lithium, fluorine and aluminum ions from lithium iron phosphate cathode waste and lithium-containing overhaul residue of electrolytic aluminum into the solution. After solid-liquid separation, leachate M3 and filter residue are obtained. S7. Add an alkaline solution to the leachate M3 obtained in step S6 to adjust the pH value. After the precipitation reaction is completed, separate the solid and liquid, and filter to obtain cryolite product and filtrate M4. S8. Add alkaline solution to the filtrate M4 obtained in step S7 to adjust the pH value, and obtain filtrate M5. S9. Evaporate and concentrate the filtrate M5 obtained in step S8 until lithium is enriched in the concentrate to a set concentration. S10. Add carbonate to the concentrated solution obtained in step S9 to precipitate lithium, and filter to obtain crude lithium carbonate product and filtrate M6. S11. The filtrate M6 obtained in step S10 is evaporated and crystallized to recover the salt. After being cooled with distilled water, it is returned to step S4 to prepare slurry M2.

2. The method of claim 1, wherein, In step S2, more than 90% of the lithium iron phosphate cathode waste has a particle size of less than 200 mesh.

3. The method of claim 1, wherein, In step S3, the mass ratio of lithium iron phosphate cathode waste to lithium-containing overhaul slag from electrolytic aluminum is 0.5-1:0.5-2.

4. The method of claim 1, wherein, In step S4, the mass ratio of water to mixture M1 is 1:1 to 5:1, the stirring method is mechanical stirring, and the stirring speed is 200-1000 r / min.

5. The method of claim 1, wherein, In step S5, the oxidant is one or more of hydrogen peroxide, calcium hypochlorite, and sodium hypochlorite; the mass of the added oxidant is 5% to 20% of the mass of the mixture M1, and the stirring reaction time is 0.5 to 2 hours.

6. The method of claim 1, wherein, In step S6, the acidic solution is a sulfuric acid or nitric acid solution, the liquid-solid ratio of the acidic solution to the mixture M1 is 15-50 mL: 100 g, the acid leaching time is 1-5 h, and the acid leaching temperature is 20-80 °C.

7. The method of claim 1, wherein, In step S7, the alkaline solution is a sodium hydroxide or sodium carbonate solution, and the pH value is 8.0 to 9.

5.

8. The method of claim 1, wherein, In step S8, the alkaline solution is a sodium hydroxide or sodium carbonate solution, and the pH value is 10.5 to 11.

5.

9. The method of claim 1, wherein, In step S9, the set concentration is greater than or equal to 20 g / L.

10. The method of claim 1, wherein, In step S10, the carbonate is sodium carbonate, and the mass ratio of sodium carbonate to mixture M1 is 0.2 to 1:1; the lithium precipitation temperature is 60-85℃, and the lithium precipitation time is 0.5-4h; the crude lithium carbonate product obtained from lithium precipitation is washed with deionized water and then dried to obtain the lithium carbonate product, the mass ratio of crude lithium carbonate product to deionized water is 1:1, the washing temperature is 60-100℃, the drying temperature is 60-110℃, and the drying time is 1-5h.

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