Method for recycling ternary lithium positive electrode material through photocatalytic microbiological leaching and electrodeposition

Abstract

The invention relates to the technical field of waste lithium battery positive electrode material recovery, and discloses a method for recovering a ternary lithium positive electrode material through photocatalytic microbiological leaching and electrodeposition. The method specifically comprises the following steps: (1) pretreating to obtain a positive electrode material with the purity of more than or equal to 95%; (2) culturing by adopting a 9K liquid culture medium to obtain an activated bacterial solution with the thallus concentration of more than 1 * 10 < 8 > / mL (the ratio of acidithiobacillus acidophilus to thiobacillus ferrooxidans to leptospirillum is 5: 3: 2); (3) mixing a TiO2 / g-C3N4 heterojunction photocatalyst with a positive electrode material, adding an activated bacterial liquid, and carrying out synergistic leaching under the condition that the solid-to-liquid ratio is 1: 15, wherein the leaching rates of Ni, Co and Mn within 72 hours respectively reach 98.3 + / -0.5%, 96.7 + / -0.3% and 94.2 + / -0.4%; and (4) after the leachate is filtered, electro-deposition is carried out by adopting a method of adjusting electrolytic potential and pH step by step, cobalt, nickel and manganese are sequentially and selectively recovered, and lithium is recovered in the form of Li2CO3 (the purity is 99.7%). Compared with the prior art, the method has the advantages that the metal recovery rate is increased while the acid consumption and the waste water and waste gas emission are effectively reduced, and the photocatalyst and the microbial strains can be recycled.

Description

Technical Field

[0001] This invention relates to the field of recycling technology for spent lithium battery cathode materials, specifically to a method for recycling ternary lithium cathode materials by photocatalytic microbial leaching and electrodeposition. Background Technology

[0002] Ternary lithium batteries are widely used in electric vehicles and energy storage systems due to their high energy density and cycle stability. However, with the rapid development of the electric vehicle industry, a large number of ternary lithium batteries are about to be scrapped. How to effectively recover the valuable metals in their cathode materials and realize resource recycling has become an urgent problem to be solved.

[0003] Traditional methods for recycling ternary lithium-ion battery cathode materials mainly include physical separation, chemical leaching, and pyrometallurgy. Physical separation methods are difficult to achieve efficient separation and purification; chemical leaching methods require the use of large amounts of acids, alkalis, and chemical reagents, generating significant amounts of wastewater and waste gas, which has a certain impact on the environment; pyrometallurgical methods require high-temperature conditions, consume a lot of energy, and are prone to generating harmful gases. Electrodeposition, as an emerging metal recycling technology, has advantages such as simple operation and low cost. However, when using electrodeposition alone to recycle ternary lithium-ion battery cathode materials, problems such as low metal ion leaching efficiency and poor selectivity exist.

[0004] Photocatalysis technology utilizes light energy to excite photocatalysts to produce active substances with strong redox capabilities, promoting redox reactions. The method of photocatalytic microbial synergistic leaching and electrodeposition for recovering ternary lithium cathode materials has the following advantages:

[0005] (1) This method uses photocatalysis to efficiently activate active substances, thereby significantly improving the metal leaching rate;

[0006] (2) Microbial leaching provides selective dissolution capability, enabling efficient separation of nickel, cobalt and manganese; the electrodeposition process is simple to operate, has low energy consumption, and avoids the use of large amounts of chemical reagents.

[0007] (3) This technology combination not only achieves a high recovery rate of valuable metals (lithium > 90%, nickel, cobalt and manganese > 95%), but also significantly reduces wastewater and exhaust gas emissions and energy consumption costs, forming an environmentally friendly and economically feasible closed-loop recycling system. Summary of the Invention

[0008] The present invention aims to solve the problems in the above-mentioned background technology and provide a method for photocatalytic microbial leaching and electrodeposition recovery of ternary lithium cathode materials, so as to achieve efficient, green and low-cost cathode material recovery.

[0009] A method for recovering ternary lithium cathode materials by photocatalytic microbial leaching and electrodeposition includes the following steps:

[0010] (1) For waste ternary lithium batteries (LiNi) x Co y Mn z O2, x+y+z=1) are sequentially discharged, disassembled, crushed, calcined and sorted to obtain positive electrode material with a purity ≥95%;

[0011] (2) Add nutrients and deionized water to a mixed bacterial culture containing Thiobacillus acidophilus (ATCC 51756), Thiobacillus ferrooxidans (ATCC 23270) and Leptospira (CSU 206003) and adjust the pH to 2.0±0.5 to obtain an activated bacterial solution;

[0012] (3) The positive electrode material obtained in step (1) is mixed with the photocatalyst at a mass ratio of (7-20):1 to obtain a mixed material. The mixed material and the activated bacterial solution obtained in step (2) are added to an acid-resistant reactor at a mass ratio of 1:(5-10) to continuously leach and obtain leachate.

[0013] (4) Filter the leachate obtained in step (3) and adjust the pH value of the filtrate to 3.5-4.5 to obtain the leachate filtrate. The separated solid residue (unreacted positive electrode material residue, photocatalyst, microbial strains, etc.) is returned to step (3) for cyclic leaching.

[0014] (5) Using the leachate obtained in step (4) as the electrolyte, perform stepwise controlled electrodeposition;

[0015] The first step involves adjusting the electrolyte pH to 3.5-4.5 and the potential to -0.5 to -1.0 V (vs. SCE). After deposition, the cathode is removed, and cobalt metal is stripped away and recovered. The second step involves adjusting the electrolyte pH to 4.5-5.5 and the potential to -1.0 to -1.2 V (vs. SCE) to recover nickel. The third step involves adjusting the pH to 5.5-6.5 and the potential to -1.2 to -1.5 V (vs. SCE) to recover manganese. Finally, a saturated sodium carbonate solution (volume ratio 4:1) is added to the electrodeposition residue, and the mixture is stirred continuously for 4-8 hours. After precipitation and / or filtration, lithium carbonate and the electrodeposition residue are obtained.

[0016] (6) The electrodeposition solution obtained in step (5) is extracted with D2EHPA to remove impurities, and (NH4)2SO4 is added to 5 g / L before being returned to the leaching system. The solution recycling rate is ≥85%.

[0017] Preferably, in step (2), the ratio of Thiobacillus acidophilus (ATCC 51756), Thiobacillus ferrooxidans (ATCC 23270), and Leptospira (CSU 206003) in the mixed microbial community is 5:3:2 based on the number of viable bacteria, and the nutrient is a combination of ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, potassium chloride, calcium nitrate, and ferrous sulfate.

[0018] Further preferably, the mass-to-volume ratios of ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, potassium chloride, calcium nitrate, ferrous sulfate, and deionized water are 2.5-3.5 g / L, 0.3-0.8 g / L, 0.2-0.6 g / L, 0.1-0.5 g / L, 0.01-0.02 g / L, and 40-45 g / L, respectively.

[0019] Preferably, in step (2), the activated bacterial solution is continuously bubbled with sterile air and the dissolved oxygen (DO) is maintained at ≥2 mg / L, and the bacterial concentration is ≥1×10⁻⁶. 8 per mL.

[0020] Preferably, the mass ratio of the positive electrode material to the photocatalyst in step (3) is 15:1, the mass ratio of the mixed material to the activated bacterial solution is 1:10, and the photocatalyst is a core-shell structured type II TiO2 / g-C3N4 heterojunction photocatalyst.

[0021] Further preferably, the heterojunction photocatalyst has a shell thickness of 10-15 nm and a specific surface area ≥150 m². 2 / g, bandgap 2.65 eV, photon yield ≥35%.

[0022] Preferably, 0.1 mol / L Fe is added to the acid-resistant reactor in step (3). 2+ As an electronic intermediary, it is equipped with magnetic stirring to maintain a stirring speed of 50-100 rpm.

[0023] Further preferably, a 200-300W xenon lamp is placed at a distance of 10-15cm from the acid-resistant reactor described in step (3), maintaining a light intensity of 100 mW / cm. 2 The continuous leaching time is 36-72 hours.

[0024] Preferably, the electrodeposition in step (5) is carried out in an electrolytic cell, wherein the anode of the electrolytic cell is a platinum electrode or a titanium electrode, and the cathode is a graphite electrode or a copper electrode.

[0025] Preferably, sulfuric acid with a concentration of 1.0-2.5 mol / L is used to adjust the pH in steps (2), (4) and / or (5).

[0026] Preferably, the ternary lithium battery is one or more of NCM111 / NCM523 / NCM622 / NCM811.

[0027] This invention is based on the core concept of "photocatalytic enhancement of microbial leaching + multi-stage electrodeposition for selective separation", and its process principle is as follows:

[0028] (1) Under illumination in the 300–400 nm wavelength band, the TiO2 / g-C3N4 heterojunction photocatalyst generates electron-hole pairs (e-hole pairs). - / h + Hole (h) + It can react with water or OH-. - The reaction generates ·OH free radicals, and electrons (e) - It can react with dissolved oxygen to form O2. - Or H2O2, these strong oxidizing reactive species can destroy the crystal lattice of ternary materials, causing Ni, Co, and Mn to escape from LiNi. x Co y Mn z It is released into an ionic state in O2.

[0029] (2) Through the metabolic products (Fe) of bacteria such as Thiobacillus acidophilus 3+ H + SO4 2- This process involves oxidizing / acidifying metal ions such as Ni, Co, and Mn in ternary cathode materials, releasing them in solution form. This method is characterized by high selectivity and mild conditions. Microorganisms (such as Thiobacillus acidophilus) oxidize S... 2- or Fe 2+ Generate SO4 2- or Fe 3+ The reaction equation for increasing the redox potential (ORP) is as follows:

[0030] Fe 2+ → Fe 3+ + e - (Microbial catalysis)

[0031] Fe 3+ + M(OH)2→ M 3+ + Fe 2+ +2OH - (M represents Ni, Co, or Mn)

[0032] (3) Adjust the pH of the leachate containing impurities such as Fe and Al to about 4, so that Fe 3+ Al 3+ Removed by precipitation in the form of hydroxide to avoid co-deposition interference in subsequent electrodeposition.

[0033] (4) Based on the differences in the standard reduction potentials of each metal, the sequential selective deposition of Co→Ni→Mn is achieved by stepwise adjustment of pH and potential. This process avoids multi-metal co-deposition and realizes the separation and recovery of high-purity metals. Standard reduction potentials of different metals:

[0034] Co 2+ + 2e - → Co (E 0= –0.85 V)

[0035] Ni 2+ + 2e - → Ni (E 0 = –1.05 V)

[0036] Mn 2+ + 2e - → Mn (E 0 = –1.25 V)

[0037] The beneficial effects of this invention are as follows:

[0038] (1) By combining photocatalysis-enhanced microbial leaching with electrodeposition, this invention significantly improves the recovery rate of nickel, cobalt, manganese and lithium in ternary lithium battery cathode materials. The lithium recovery rate can reach more than 90%, and the total recovery rate of nickel, cobalt and manganese exceeds 95%. This effect has obvious advantages over traditional chemical leaching and physical separation methods, especially in complex battery waste.

[0039] (2) The process of the present invention uses photocatalysis and microbial leaching to dissolve and separate metals under mild conditions, which greatly reduces the use of chemical reagents, thereby reducing the amount of wastewater and waste gas emissions, and achieving a win-win situation for environmental protection and resource recycling.

[0040] (3) The stepwise adjustment of potential and pH value in electrodeposition technology makes the deposition process of different metals such as cobalt, nickel and manganese highly selective, ensuring that the purity of the recovered metal reaches more than 99% and avoiding the cross-contamination problem during multi-metal co-deposition. This technology makes the recovery process of each metal more precise and efficient.

[0041] (4) The photocatalytic microbial leaching and electrodeposition recovery technology system of the present invention forms a closed-loop resource utilization system. The photocatalyst, microbial culture medium and electrolyte can all be recycled and reused, which further improves the utilization efficiency of materials, reduces the environmental burden, and has strong potential for industrial application. Attached Figure Description

[0042] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0043] The present invention will be further illustrated below with reference to comparative embodiments and specific embodiments thereof. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0044] Comparative Example: Chemical Leaching (Wet Process) + Electrodeposition

[0045] (1) The washed positive electrode sheet was dried at 80 °C for 12 hours, then pulverized to 200 mesh and calcined at 600 °C for 2 hours in air. It was then leached at 90 °C for 2 hours with concentrated hydrochloric acid (6 mol / L) at a solid-liquid ratio of 1:10. After the reaction, the sample was filtered to obtain Ni-containing material. 2+ Co 2+ Mn 2+ Li + A mixed solution.

[0046] (2) Adjust the solution pH to 3.0, use a titanium-coated anode and a copper cathode, and maintain a constant current density of 100 A / m. 2 The cathode potential was adjusted to -0.3 V, and Ni-Co alloy (92% purity) was obtained after deposition for 2 hours. The cathode potential was then adjusted to -1.2 V, and manganese oxide was deposited. Excess sodium carbonate was added to the remaining solution to form lithium carbonate precipitate.

[0047] Key performance indicators:

[0048] Nickel recovery rate: 84.3% ±1.2%; Cobalt recovery rate: 78.6% ±1.5%; Manganese recovery rate: 71.8% ±2.1%; Lithium recovery rate: 78.2% ±1.8%. The purity of the Ni-Co alloy product was 89.2% (containing 10.8% oxygen impurities); the purity of lithium carbonate was 98.3%.

[0049] Main defects:

[0050] The cobalt content in the manganese deposits reached 2.8 wt%; the overall energy consumption was 18.7 kWh / kg; and the lithium loss due to high-temperature volatilization was 12%.

[0051] Example: A method for recovering ternary lithium cathode materials by photocatalytic microbial leaching and electrodeposition.

[0052] (1) Raw material pretreatment

[0053] Waste ternary lithium batteries (NCM523 model) were selected and subjected to discharge, disassembly, crushing, calcination and sorting to obtain positive electrode material powder with a purity of ≥95%;

[0054] (2) Microbial culture and activation

[0055] Thiobacillus acidophilus (ATCC 23270), Thiobacillus ferrooxidans (DSM 9463), and Leptospira (JCM7811) were selected, with a bacterial ratio of 5:3:2 based on viable count. A 9K liquid nutrient solution was used for cultivation. The nutrient solution formula was: 3.0 g ammonium sulfate, 0.5 g dipotassium hydrogen phosphate, 0.5 g magnesium sulfate, 0.1 g potassium chloride, 0.01 g calcium nitrate, and 44.2 g ferrous sulfate per liter of deionized water, adjusted to pH 2.0 ± 0.5. After preparation, the culture medium was autoclaved (121℃, 20 minutes), cooled to room temperature, and inoculated under aseptic conditions. Sterile air was circulated during cultivation, with dissolved oxygen ≥ 2 mg / L, until the bacterial concentration reached 1 × 10⁻⁶. 8 Activated bacterial solution is obtained when the number of bacteria per mL is above a certain level.

[0056] (3) Photocatalysis enhances microbial leaching

[0057] The cathode material (mass ratio 1:15) mixed with type II TiO2 / g-C3N4 heterojunction photocatalyst and activated bacterial solution were added to the acid-resistant reactor at a solid-liquid ratio of 1:10. A 300W xenon lamp (light intensity 100 mW / cm², distance 10-15cm) was installed and the illumination time was maintained throughout the entire leaching reaction process. The stirring speed was maintained at 60 rpm, and sterile air was introduced at a ventilation rate of 0.8 (volume / volume / minute). The dissolved oxygen content was ≥2 mg / L to provide oxygen required for microbial metabolism. The leaching was carried out continuously for 72 hours.

[0058] (4) Leachate pretreatment

[0059] After the leaching reaction is complete, to avoid interference from solid particles in the subsequent purification and electrodeposition processes, the leachate is first filtered to obtain the leachate filtrate, as the leaching process consumes H₂. + Add 2 mol / L sulfuric acid dropwise to the leaching filtrate to slowly and precisely adjust the pH to 3.5-4.5. The separated solid residue (unreacted cathode material residue, photocatalyst, microbial remains, etc.) is further returned to photocatalytic leaching treatment according to its composition.

[0060] (5) Selective electrodeposition for metal recovery

[0061] The pretreated leachate is transferred to an electrolytic cell, which should be made of corrosion-resistant materials such as polypropylene, polyvinyl chloride, or stainless steel, and equipped with temperature control, stirring, and pH adjustment devices. High-purity insoluble anodes (platinum electrodes) and inert cathodes (graphite) are selected as electrode materials. The electrolyte temperature is controlled between 25-40℃.

[0062] Based on the differences in deposition potential among different metals, a stepwise adjustment of electrolysis potential and pH is used to selectively recover metals such as cobalt, nickel, and manganese. In the first step, the electrolyte pH is adjusted to 4.0-4.2, and the potential is adjusted to -0.85 V (vs. SCE), preferentially depositing cobalt. After deposition is complete, the cathode is removed, and the cobalt metal is stripped off.

[0063] The second step involves adjusting the electrolyte pH to 5.0-5.1 and the potential to -1.05 V (vs. SCE) to recover nickel. The third step further adjusts the pH to 6.0-6.2 and the potential to -1.25 V (vs. SCE) to recover manganese. A saturated sodium carbonate solution (4:1 volume ratio) is added to the electrodeposition residue, and after reacting for 6 hours, the mixture is filtered to separate the lithium carbonate precipitate and the electrodeposition residue. After each deposition step, the cathode must be replaced or cleaned to prevent cross-contamination of metals.

[0064] (6) After electrodeposition, the solution is extracted with D2EHPA extractant to remove impurities, and (NH4)2SO4 is added to 5 g / L before being returned to the leaching system. The solution recycling rate is ≥85%.

[0065] Key performance indicators:

[0066] Ni leaching rate: 98.3±0.5%; Co leaching rate: 96.7±0.3%; Mn leaching rate: 94.2±0.4%.

[0067] Nickel recovery rate: 96.5% ± 0.8% (↑12.2%); Cobalt recovery rate: 99.2% ± 0.5% (↑20.6%)

[0068] Manganese recovery rate: 94.8% ± 0.7% (↑23.0%); Lithium recovery rate: 93.4% ± 0.6% (↑15.2%); Lithium carbonate purity reached 99.7%.

[0069] The above embodiments and comparative examples have described in detail the preferred embodiments of the present invention; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for photocatalytic microbial leaching and electrodeposition recovery of ternary lithium cathode materials, characterized in that, The method includes the following steps: (1) For waste ternary lithium batteries (LiNi) x Co y Mn z O2, x+y+z=1) is discharged, disassembled, crushed, calcined and sorted to obtain positive electrode material with a purity ≥95%; (2) Add a mixed bacterial culture containing Thiobacillus acidophilus (ATCC 51756), Thiobacillus ferrooxidans (ATCC 23270) and Leptospira (CSU 206003) to nutrients and deionized water and adjust the pH to 2.0±0.5 to obtain an activated bacterial solution; (3) The positive electrode material obtained in step (1) and the photocatalyst are mixed uniformly at a mass ratio of (7-20):1 to obtain a mixed material. The mixed material and the activated bacterial solution obtained in step (2) are added to an acid-resistant reactor at a mass ratio of 1:(5-10) to continuously leach and obtain leachate. (4) Filter the leachate obtained in step (3) and adjust the pH value of the filtrate to 3.5-4.5 to obtain the leachate filtrate. The separated solid residue is returned to step (3) for cyclic leaching. (5) Using the leaching filtrate obtained in step (4) as the electrolyte, perform stepwise controlled electrodeposition: First, adjust the pH of the electrolyte to 3.5-4.5 and the potential to -0.5 to -1.0 V (vs. SCE). After deposition, remove the cathode and strip to recover cobalt metal. Second, adjust the pH of the electrolyte to 4.5-5.5 and the potential to -1.0 to -1.2 V (vs. SCE) to recover nickel. Third, adjust the pH to 5.5-6.5 and the potential to -1.2 to -1.5 V (vs. SCE) to recover manganese. Finally, add a saturated sodium carbonate solution (volume ratio 4:1) to the electrodeposition residue, stir continuously for 4-8 hours, and obtain lithium carbonate and electrodeposition residue by precipitation and / or filtration. (6) The electrodeposition solution obtained in step (5) is extracted with D2EHPA extractant to remove impurities, and (NH4)2SO4 is added to 5 g / L before being returned to the leaching system. The solution recycling rate is ≥85%.

2. The method according to claim 1, characterized in that, In step (2), the ratio of Thiobacillus acidophilus (ATCC 51756), Thiobacillus ferrooxidans (ATCC 23270), and Leptospira (CSU 206003) in the mixed microbial community is 5:3:2 based on the number of viable bacteria. The nutrient is a combination of ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, potassium chloride, calcium nitrate, and ferrous sulfate.

3. The method according to claim 2, characterized in that, The mass-to-volume ratios of ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, potassium chloride, calcium nitrate, ferrous sulfate, and deionized water are 2.5-3.5 g / L, 0.3-0.8 g / L, 0.2-0.6 g / L, 0.1-0.5 g / L, 0.01-0.02 g / L, and 40-45 g / L, respectively.

4. The method according to claim 1, characterized in that: In step (2), the activated bacterial solution is continuously bubbled with sterile air to maintain DO (dissolved oxygen) ≥ 2 mg / L and bacterial concentration ≥ 1×10⁻⁶. 8 per mL.

5. The method according to claim 1, characterized in that: In step (3), the mass ratio of the positive electrode material to the photocatalyst is 15:1, and the mass ratio of the mixed material to the activated bacterial solution is 1:

10. The photocatalyst is a core-shell type II TiO2 / g-C3N4 heterojunction photocatalyst.

6. The method according to claim 5, characterized in that: The heterojunction photocatalyst has a shell thickness of 10-15 nm and a specific surface area ≥150 m². 2 / g, bandgap 2.65 eV, photon yield ≥35%.

7. The method according to claim 1, characterized in that: In step (3), 0.1 mol / L Fe is added to the acid-resistant reactor. 2+ As an electronic intermediary, it is equipped with magnetic stirring to maintain a stirring speed of 50-100 rpm.

8. The method according to claim 7, characterized in that: A 200-300W xenon lamp is placed at a distance of 10-15cm from the acid-resistant reactor described in step (3), maintaining a light intensity of 100 mW / cm. 2 The continuous leaching time is 36-72 hours.

9. The method according to claim 1, characterized in that: The electrodeposition in step (5) is carried out in an electrolytic cell, wherein the anode of the electrolytic cell is a platinum electrode or a titanium electrode, and the cathode is a graphite electrode or a copper electrode.

10. The method according to claim 1, characterized in that, The pH adjustment in steps (2), (4) and / or (5) uses sulfuric acid with a concentration of 1.0-2.5 mol / L.

11. The method according to claim 1, characterized in that: The ternary lithium battery is one or more of NCM111 / NCM523 / NCM622 / NCM811.

Images