Method for efficiently leaching cobalt in battery positive electrode material tailings treated by wet method

Abstract

The invention relates to the technical field of cobalt recovery, in particular to a method for efficiently leaching cobalt in battery positive electrode material tailings treated by a wet process, which comprises the following steps: S1, separately culturing thiobacillus ferrooxidans, leptospirillum ferriphilum, thiobacillus thiooxidans and temperature-resistant thiobacillus oxydans; s2, performing compound culture on the separately cultured thiobacillus ferrooxidans, leptospirillum ferriphilum, thiobacillus thiooxidans and temperature-resistant thiobacillus oxydans to obtain a mixed strain solution; s3, the mixed strain liquid is put into an improved culture medium to serve as a leaching system, the cobalt residues obtained through wet treatment are added into the leaching system to be stirred and leached, and a cobalt-rich solution and leaching residues are obtained; the method provided by the invention realizes green, low-carbon and economic recovery of residual metal elements in the wet-process treated tailings, and is short in process, low in investment, high in efficiency, low in treatment cost and suitable for various waste residues containing heavy metals.

Description

Technical Field

[0001] This invention relates to the field of cobalt recovery technology, specifically to a method for efficiently treating cobalt in the tailings of battery cathode materials using a wet leaching process. Background Technology

[0002] The current recycling of retired power batteries and other cobalt-containing waste materials usually adopts a wet treatment process of strong acid leaching. Cobalt cannot be completely recovered. The wet treatment tailings generated during the recycling process contain less than 1% cobalt, which poses a risk of exceeding the metal limit and is classified as hazardous waste.

[0003] The current method for treating cobalt slag—the tailings from the recycling of retired power batteries and other materials—is landfilling, which wastes the cobalt resources in the tailings and poses environmental risks. Continuing with wet recycling (acid leaching) would be costly, inefficient, and yield little profit, or even result in losses.

[0004] Among various solid waste treatment methods, bioleaching is an effective way to extract metals from waste. Its principle is to utilize the physiological functions of microorganisms to separate and enrich target metals. The types of microbial communities, the amount of energy materials used, and the reaction time are key parameters for controlling the efficiency of bioleaching in practical applications. Current research on the bioleaching of heavy metals from solid waste by acidophilic autotrophic bacteria mainly focuses on single dominant bacteria. However, because the acid-producing types of single bacteria are relatively limited and their maximum acid-producing capacity is limited, it is usually impossible to ensure the timely and effective removal of different types and forms of heavy metals from solid waste after bioleaching treatment.

[0005] Therefore, this invention proposes a method for efficiently treating cobalt in the tailings of battery cathode materials using a wet leaching process to improve the aforementioned problems. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a highly efficient wet leaching method for treating cobalt in the tailings of battery cathode materials.

[0007] A method for efficiently treating cobalt in battery cathode material tailings by wet leaching includes the following steps:

[0008] S1. Culture ferrooxidizing thiobacillus, iron-loving Leptospira, thiooxidizing thiobacillus, and thermostable thiooxidizing thiobacillus separately;

[0009] S2. The separately cultured *Thiobacillus ferrooxidans*, *Leptospira ferrooxidans*, *Thiobacillus thiooxidans*, and thermotolerant *Thiobacillus sulfoxidans* were cultured together at a unit volume cell concentration ratio of 1:1:1:1–3 to obtain a concentration of 1×10⁻⁶ cells / mL. 8 ~1×10 9 Mixed bacterial culture solution with CFU / mL;

[0010] S3. The mixed bacterial culture solution is added to the modified culture medium at a volume ratio of 1:8.5-9.5 to form a leaching system. The cobalt slag obtained by wet treatment is added to the leaching system at a solid-liquid ratio of 100-500 g:1 L and magnetic stirring is continuously performed at 150-250 rpm. The pH is maintained at 1.8-2.0 and the temperature at 38-42℃ during the leaching process. The water evaporated from the leaching system is replenished every day. The leaching time is 6 days to obtain a cobalt-rich solution and leaching residue. The leaching is then complete.

[0011] The modified culture medium comprises: (NH4)2SO4: 2.5–3.5 g / L; MgSO4·7H2O: 0.3–0.6 g / L; K2HPO4: 0.3–0.7 g / L; KCl: 0.1–0.3 g / L; Ca(NO3)2: 0.01–0.05 g / L, with the remainder being distilled water.

[0012] Furthermore, in S1, the culture medium components used for culturing *Thiobacillus ferrooxidans* and *Leptospira ferrophila* separately include: the components of the modified culture medium and FeSO4·7H2O: 20–60 g / L, with the remainder being distilled water, and the culture temperature being 28–32 °C.

[0013] Furthermore, in S1, the culture medium used for culturing Thiobacillus thiooxidans alone includes the components of a modified culture medium and sulfur powder: 3-8 g / L, with the remainder being distilled water, and the culture temperature is 28-32℃.

[0014] Furthermore, in S1, the culture medium components used for culturing thermostable sulfur-oxidizing bacteria alone include: modified culture medium components; FeSO4·7H2O: 20–60 g / L; yeast extract: 0.1–0.3 g / L, with the remainder being distilled water, and the culture temperature being 38–42 °C.

[0015] Further, in S2, the culture medium used for the compound culture includes: components of the modified culture medium; FeSO4·7H2O: 15-40 g / L; sulfur powder: 1-2 g / L; yeast extract: 0.02-0.1 g / L, with the remainder being distilled water, and the culture temperature being 38-42℃.

[0016] The commonly used culture media for the above-mentioned single and combined cultures can provide the normal nutrients for microbial growth; in addition, energy substances for the activity of the strains can be added, and carbon dioxide in the air can be used as a carbon source.

[0017] Furthermore, in S3, the stirring leaching process is divided into a first stage and a second stage:

[0018] First stage: 0 to 4 days before, under a magnetic field strength of 1 to 2 mT, add an activator accounting for 0.3 to 0.5 wt% of the cobalt slag to the leaching system;

[0019] Second stage: 4-6 days, adjust the magnetic field strength of the leaching system to 4-5 mT;

[0020] The activator is prepared as follows: Fe3O4@SiO2 particles are first dispersed in MES buffer solution with pH = 5.5-6 at a solid-liquid ratio of 1g: 22-24ml. Then, a coupling agent with a mass ratio of 1:0.15-0.18 to Fe3O4@SiO2 particles is added and reacted for 30-40 minutes to obtain an activation solution. The activation solution is then reacted with the adsorbed particles at a liquid-solid ratio of 12-15ml: 1g at room temperature for 18-22 hours. After the reaction is completed, the activator is obtained by washing.

[0021] Adding an activator in the early stages of leaching allows the C800 resin and Fe3O4@SiO2 particles to rapidly adsorb cobalt ions in the solution, reducing the inhibitory effect of cobalt ions on the activity of the mixed microorganisms. This enables the mixed microorganisms to maintain high activity and promote the leaching of cobalt ions. Furthermore, the conductivity of Fe3O4 can be utilized by the microorganisms to enhance their extracellular respiration metabolism, accelerating the oxidation and decomposition of cobalt-containing minerals and thus speeding up cobalt leaching. After leaching for a period of time, the microbial activity usually reaches a high level. However, at this point, factors such as mineral encapsulation and the formation of a passivation layer may slow down the leaching rate. Applying a stronger magnetic field can reduce the diffusion resistance around the activator, making it easier for cobalt ions to diffuse to the adsorption sites. At the same time, it allows nutrients and oxygen to come into more sufficient contact with the microorganisms. In addition, a magnetic field of appropriate strength can stimulate the metabolic activity of the microorganisms, thereby further improving the leaching efficiency. It can also quickly separate the activator that has adsorbed cobalt from solid residues such as slag and microorganisms, facilitating the separation of cobalt and other impurities.

[0022] Furthermore, the method for preparing the adsorbent particles is as follows:

[0023] Porous ceramics were dispersed in a 2.5-3.5% sodium alginate solution at a solid-liquid ratio of 12-15 g: 100 ml. C800 resin at a mass ratio of 1:0.6-0.8 to the porous ceramics was then added and stirred continuously for 1.5-2 h to obtain a slurry. The slurry was then injected dropwise into a 2.5-3.5% calcium chloride solution and stirred continuously for 30-35 min to obtain spheres. The spheres were washed with deionized water and then freeze-dried at -50 to -40 °C for 12-24 h to obtain adsorbent particles.

[0024] Porous ceramics possess a large specific surface area, providing attachment space for leaching microorganisms such as *Thiobacillus ferrooxidans*, making it easier for the microorganisms to form stable biofilms on their surface and within the pores. This increases the local concentration and activity of the microorganisms, enabling continuous and efficient leaching of cobalt. C800 resin contains iminodiacetic acid functional groups, exhibiting strong complexing ability and high selectivity for heavy metal ions such as cobalt, effectively reducing the co-adsorption of impurity ions. The large pores of the porous ceramics accelerate the mass transfer of cobalt ions to the resin. Calcium chloride and sodium alginate combine to form a gel state, possessing certain mechanical strength and pH stability, allowing it to withstand the acidic environment of bioleaching and protecting the C800 resin.

[0025] Furthermore, the porous ceramic is a coal gangue-based porous ceramic or a diatomaceous earth-based porous ceramic.

[0026] The aforementioned porous ceramics can react with Co in solution. 2+ Exchange occurs or through the abundant functional groups on the ceramic surface with Co. 2+ Coordination bonds are formed, thereby promoting the leaching of cobalt.

[0027] Furthermore, the coupling agent is an EDC / NHS coupling agent.

[0028] The use of the above-mentioned coupling agent makes the structure of the activator more stable and less prone to decomposition during the leaching process, thereby maintaining efficient leaching.

[0029] Compared with existing methods for microbial leaching of cobalt, the advantages of this invention are:

[0030] (1) This invention synthesizes a highly efficient microbial community and uses a biological wet treatment method with microbial leaching to recover cobalt elements in tailings in a low-carbon and low-cost manner, reducing the cobalt content in tailings to below 0.1%; and achieves green, low-carbon and economical recovery of residual metal elements in tailings by wet treatment. The process is short, with low investment, high efficiency and low cost, and is suitable for various types of waste residues containing heavy metals.

[0031] (2) In the early stage of leaching, the present invention adds an activator, whose C800 resin and Fe3O4@SiO2 particles can quickly adsorb cobalt ions in the solution, reduce the inhibition of cobalt ions on the activity of mixed bacteria, so that the mixed bacteria can maintain high activity to promote the leaching of cobalt ions. The conductivity of Fe3O4 can be used by the bacteria to enhance the extracellular respiration metabolism of the bacteria, thereby accelerating the oxidation and decomposition of cobalt-containing minerals and thus accelerating the leaching of cobalt. After a period of leaching, the activity of microorganisms usually reaches a high level, but at this time, factors such as mineral encapsulation and passivation layer formation may slow down the leaching rate. Applying a magnetic field can reduce the diffusion resistance around the activator, making it easier for cobalt ions to diffuse to the adsorption site. At the same time, it allows nutrients and oxygen to come into full contact with microorganisms. In addition, a magnetic field of appropriate intensity can stimulate the metabolic activity of microorganisms, thereby further improving the leaching efficiency. Attached Figure Description

[0032] Figure 1 This is the kinetic relationship between the bioleaching of cobalt and the functional relationship of MC types in the experimental examples of this invention;

[0033] Figure 2 This is the functional relationship between the bioleaching kinetics of cobalt in the experimental example of this invention and the ratio of Ac to St in MC;

[0034] Figure 3 The experimental examples of this invention use various types of bacteria to determine the cobalt speciation in bioleaching;

[0035] Figure 4 This is the functional relationship of the solid-liquid ratio of cobalt in the bioleaching kinetics of MC40-25St in the experimental example of this invention. Detailed Implementation

[0036] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0037] Example 1: A method for efficiently treating cobalt in battery cathode material tailings using a wet leaching process, comprising the following steps:

[0038] S1. Culture ferrooxidizing thiobacillus, iron-loving Leptospira, thiooxidizing thiobacillus, and thermostable thiooxidizing thiobacillus separately;

[0039] Among them, ferrooxidizobacillus (Af, ATCC 23270) originated from acidic coal mine wastewater containing bituminous coal;

[0040] Iron-loving Leptospira (Lf, AS1.6358) originates from hot springs;

[0041] Thiobacillus thiooxidans (Tt, BJMCC 01101) originated from mine wastewater;

[0042] The thermostable sulfur-oxidizing bacillus (St, DSM 17362) was derived from gold-bearing sulfide concentrate;

[0043] The culture medium components used for culturing *Thiobacillus ferrooxidans* and *Leptospira ferrophila* separately included: modified culture medium components and FeSO4·7H2O: 44.7 g / L, with the remainder being distilled water. The culture temperature was 30℃ and the culture time was 7 days.

[0044] The culture medium used for culturing Thiobacillus thiooxidans alone consisted of the following components: modified culture medium components and sulfur powder: 5 g / L, with the remainder being distilled water. The culture temperature was 30℃, and the culture time was 7 days.

[0045] The culture medium used for the monoculture of thermostable sulfur-oxidizing bacteria consisted of the following components: modified culture medium components; FeSO4·7H2O: 44.7 g / L; yeast extract: 0.1 g / L, with the remainder being distilled water; the culture temperature was 40℃; and the culture time was 7 days.

[0046] S2. The separately cultured *Thiobacillus ferrooxidans*, *Leptospira ferrooxidans*, *Thiobacillus thiooxidans*, and thermotolerant *Thiobacillus sulfoxidans* were cultured together at a unit volume cell concentration ratio of 1:1:1:1 to obtain a concentration of 1×10⁻⁶ cells / mL. 8 Mixed bacterial culture solution (MC40-25St) at CFU / mL;

[0047] The culture medium used for the compound culture included the following components: modified culture medium components; FeSO4·7H2O: 33.5 g / L; sulfur powder: 1.2 g / L; yeast extract: 0.02 g / L, with the remainder being distilled water. The culture temperature was 40℃, and the culture time was 7 days.

[0048] The volume ratio of the mother liquor to the culture medium for each strain was 1:9.

[0049] S3. The mixed bacterial culture solution is added to the modified culture medium at a volume ratio of 1:9 to form a leaching system. Then, cobalt slag obtained from the wet processing of a leading domestic recycling company is added to the leaching system at a solid-liquid ratio of 100g:1L and magnetic stirring is continuously performed at 200rpm. The pH is maintained at 1.9 and the temperature at 40℃ during the leaching process. The water evaporated from the leaching system is replenished daily. The leaching time is 6 days, and a cobalt-rich solution and leaching residue are obtained. The leaching is then complete.

[0050] The modified culture medium comprises the following components: (NH4)2SO4: 3 g / L; MgSO4·7H2O: 0.5 g / L; K2HPO4: 0.5 g / L; KCl: 0.1 g / L; Ca(NO3)2: 0.01 g / L, with the remainder being distilled water.

[0051] Example 2: This example differs from Example 1 in that the separately cultured *Thiobacillus ferrooxidans*, *Leptospira ferrooxidans*, *Thiobacillus thiooxidans*, and thermostable *Thiobacillus sulfoxidans* were cultured together in a unit volume cell concentration ratio of 1:1:1:2 to obtain a concentration of 1×10⁻⁶. 8 Mixed bacterial culture solution with CFU / mL.

[0052] Example 3: This example differs from Example 1 in that the separately cultured *Thiobacillus ferrooxidans*, *Leptospira ferrooxidans*, *Thiobacillus thiooxidans*, and thermostable *Thiobacillus sulfadiazine* were cultured together in a unit volume cell concentration ratio of 1:1:1:3 to obtain a concentration of 1×10⁻⁶. 9 Mixed bacterial culture solution with CFU / mL.

[0053] Example 4: The difference between this example and Example 1 is that the mixed bacterial culture solution is added to the modified culture medium at a volume ratio of 1:8.5 as the leaching system, and the cobalt slag obtained by wet treatment is added to the leaching system at a solid-liquid ratio of 300g:1L.

[0054] Example 5: This example differs from Example 1 in that the mixed bacterial culture solution is added to the modified culture medium at a volume ratio of 1:9.5 as the leaching system, and the cobalt slag obtained by wet treatment is added to the leaching system at a solid-liquid ratio of 500g:1L.

[0055] Example 6: This example differs from Example 1 in that magnetic stirring at 150 rpm is performed continuously, and the pH is maintained at 1.8 and the temperature at 38°C during the leaching process.

[0056] Example 7: This example differs from Example 1 in that magnetic stirring at 250 rpm is performed continuously, and the pH is maintained at 2.0 and the temperature at 42°C during the leaching process.

[0057] Example 8: This example differs from Example 1 in that the modified culture medium consists of the following components: (NH4)2SO4: 2.5 g / L; MgSO4·7H2O: 0.3 g / L; K2HPO4: 0.3 g / L; KCl: 0.1 g / L; Ca(NO3)2: 0.01 g / L, with the remainder being distilled water.

[0058] Example 9: The difference between this example and Example 1 is that the modified culture medium consists of the following components: (NH4)2SO4: 3.5 g / L; MgSO4·7H2O: 0.6 g / L; K2HPO4: 0.7 g / L; KCl: 0.3 g / L; Ca(NO3)2: 0.05 g / L, with the remainder being distilled water.

[0059] Example 10: This example differs from Example 1 in that the culture medium components used for culturing *Thiobacillus ferrooxidans* and *Leptospira ferrooxidans* alone both include: the components of the modified culture medium and FeSO4·7H2O: 20 g / L, with the remainder being distilled water, and the culture temperature is 28°C; the culture medium components used for culturing *Thiobacillus thiooxidans* alone include: the components of the modified culture medium and sulfur powder: 3 g / L, with the remainder being distilled water, and the culture temperature is 28°C; the culture medium components used for culturing thermotolerant thiooxidizing bacteria alone include: the components of the modified culture medium; FeSO4·7H2O: 20 g / L; yeast extract: 0.1 g / L, with the remainder being distilled water, and the culture temperature is 38°C.

[0060] Example 11: This example differs from Example 1 in that the culture medium components used for culturing *Thiobacillus ferrooxidans* and *Leptospira ferrooxidans* alone both include: the components of the modified culture medium and FeSO4·7H2O: 60 g / L, with the remainder being distilled water, and the culture temperature is 32°C; the culture medium components used for culturing *Thiobacillus thiooxidans* alone include: the components of the modified culture medium and sulfur powder: 8 g / L, with the remainder being distilled water, and the culture temperature is 32°C; the culture medium components used for culturing thermotolerant thiooxidizing bacteria alone include: the components of the modified culture medium; FeSO4·7H2O: 60 g / L; yeast extract: 0.3 g / L, with the remainder being distilled water, and the culture temperature is 42°C.

[0061] Example 12: The difference between this example and Example 1 is that the culture medium used for the compound culture includes the following components: modified culture medium components, FeSO4·7H2O: 15g / L; sulfur powder: 1g / L and yeast extract: 0.05g / L, and the culture temperature is 38℃.

[0062] Example 13: The difference between this example and Example 1 is that the culture medium used for the compound culture includes the following components: modified culture medium components, FeSO4·7H2O: 40g / L; sulfur powder: 2g / L and yeast extract: 0.1g / L, and the culture temperature is 42℃.

[0063] Example 14: This example differs from Example 1 in that, in S3, the stirring leaching process is divided into a first stage and a second stage:

[0064] First stage: 0 to 4 days before, an activator accounting for 0.4 wt% of the cobalt slag is added to the leaching system under a magnetic field strength of 1.5 mT;

[0065] Second stage: 4-6 days, adjust the magnetic field of the leaching system to 4.5mT;

[0066] Understandably, after leaching, the residue is eluted with 5% hydrochloric acid and the cobalt in the eluent is also recovered.

[0067] The activator is prepared as follows: Fe3O4@SiO2 particles (purchased from the market, such as Nanjing Dongna Biotechnology) are first dispersed in MES buffer solution at a solid-liquid ratio of 1g:23ml at pH=5.8. Then, EDC / NHS coupling agent (EDS:NHS mass ratio of 1:1) with a mass ratio of 1:0.17 to Fe3O4@SiO2 particles is added and reacted for 35min to obtain an activation solution. The activation solution is then reacted with adsorbed particles at a liquid-solid ratio of 13.5ml:1g at room temperature (25℃) for 20h. After the reaction is completed, the activator is obtained by washing with deionized water.

[0068] The preparation method of the adsorbent particles is as follows:

[0069] Coal gangue-based porous ceramics were dispersed in a 3% sodium alginate solution at a solid-liquid ratio of 13.5 g: 100 ml. C800 resin with a mass ratio of 1:0.7 to the porous ceramics was then added and stirred continuously for 1.8 h to obtain a slurry. The slurry was then injected dropwise into a 3% calcium chloride solution and stirred continuously for 33 min to obtain spheres. The spheres were washed with deionized water and then freeze-dried at -45℃ for 18 h to obtain adsorption particles.

[0070] Example 15: This example differs from Example 14 in that, in the first stage (0-4 days), an activator accounting for 0.3 wt% of the cobalt slag is added to the leaching system under a magnetic field strength of 1 mT; in the second stage (4-6 days), the magnetic field of the leaching system is adjusted to 4 mT.

[0071] Example 16: This example differs from Example 14 in that, in the first stage (0-4 days), an activator accounting for 0.5 wt% of the cobalt slag is added to the leaching system under a magnetic field strength of 2 mT; in the second stage (4-6 days), the magnetic field of the leaching system is adjusted to 5 mT.

[0072] Example 17: The difference between this example and Example 14 is that Fe3O4@SiO2 particles were first dispersed in MES buffer solution with pH=5.5 at a solid-liquid ratio of 1g:22ml, and then a coupling agent with a mass ratio of 1:0.15 to Fe3O4@SiO2 particles was added and reacted for 30min.

[0073] Example 18: The difference between this example and Example 14 is that Fe3O4@SiO2 particles were first dispersed in MES buffer solution with pH=6 at a solid-liquid ratio of 1g:24ml, and then a coupling agent with a mass ratio of 1:0.18 to Fe3O4@SiO2 particles was added and reacted for 40min.

[0074] Example 19: The difference between this example and Example 14 is that the activation solution was stirred and reacted with the adsorbent particles at room temperature for 18 hours at a liquid-to-solid ratio of 12 ml: 1 g.

[0075] Example 20: The difference between this example and Example 14 is that the activation solution was stirred and reacted with the adsorbent particles at room temperature for 22 hours at a liquid-solid ratio of 15 ml: 1 g.

[0076] Example 21: The difference between this example and Example 14 is that the diatomaceous earth-based porous ceramic is dispersed in a 2.5% sodium alginate solution at a solid-liquid ratio of 12g:100ml, and then C800 resin with a mass ratio of 1:0.6 to the porous ceramic is added and stirred continuously for 1.5h.

[0077] Example 22: The difference between this example and Example 14 is that the coal gangue-based porous ceramic is dispersed in a 3.5% sodium alginate solution at a solid-liquid ratio of 15g:100ml, and then C800 resin with a mass ratio of 1:0.8 to the porous ceramic is added and stirred continuously for 2 hours.

[0078] Example 23: The difference between this example and Example 14 is that the slurry is injected dropwise into a 2.5% calcium chloride solution and then stirred continuously for 30 minutes to obtain spheres.

[0079] Example 24: This example differs from Example 14 in that the slurry is injected dropwise into a 3.5% calcium chloride solution and stirred continuously for 35 minutes to obtain spheres.

[0080] Example 25: This example differs from Example 14 in that the sphere is washed with deionized water and then freeze-dried at -40°C for 12 hours.

[0081] Example 26: This example differs from Example 14 in that the sphere is washed with deionized water and then freeze-dried at -50°C for 24 hours.

[0082] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and aims to illustrate the practical application effect of the present invention.

[0083] To demonstrate the advantages of the selected bacterial strains and leaching parameters in this application, the following comparative experiments were conducted:

[0084] The selected tailings were processed by a leading domestic recycling company using existing technology in a wet process production line. Waste power battery cathode materials and other recyclable waste were crushed and sorted before entering a separate wet recycling production line to leach cobalt, producing cobalt slag. Bioleaching experiments were conducted in 3.0L glass beakers. A 2L leaching system (modified culture medium) containing 200mL of bacterial liquid was established in the 3L glass beakers. After pre-culturing, cobalt slag samples were added for bioleaching experiments. The beakers were stirred on a thermostatic magnetic stirrer to fully suspend the waste slag, the suspension position was marked, and evaporated water was added daily. Sampling method for the leaching test: During the experiment, 5mL of suspension was taken, filtered, and stored with added nitric acid. Samples were taken at 2 hours, 6 hours, and 12 hours within one day of the start of the experiment, then every other day thereafter, from day 4 to day 12, after which the leaching experiment was stopped. The nickel and cobalt contents in all samples were determined. The constant temperatures were set to 30℃, 40℃ and 45℃ respectively, and the mass content of cobalt in the liquid of all samples was measured using an inductively coupled plasma mass spectrometer (NexION 2000, PerkinElmer).

[0085] Investigation 1: Investigate the effects of bacterial strain and leaching parameters on cobalt leaching rate.

[0086] like Figure 1 As shown, the strain ratio of this application is compared with the strain ratio and leaching temperature of other control examples;

[0087] Ac is *Thiobacillus kadus* (accession number CGMCC 1.15711), and the remaining leaching conditions are the same as in Example 1:

[0088] MC40-25St refers to the strain, ratio, and leaching temperature of Example 1 in this application;

[0089] MC30-0AS refers to the use of Af, Lf, and Tt as leaching strains in the same volume ratio at 30°C.

[0090] AS refers to the use of Ac and St as leaching strains in the same volume ratio, leaching at 40°C;

[0091] MC40-25Ac refers to the use of Af, Lf, Tt, and Ac as leaching strains in the same volume ratio at 40°C.

[0092] MC40-40AS refers to the use of Af, Lf, Tt, Ac, and St as leaching strains in the same volume ratio, leaching at 40°C.

[0093] MC45-40AS refers to the use of Af, Lf, Tt, Ac, and St as leaching strains in the same volume ratio at 45°C.

[0094] like Figure 1 As shown, the bioleaching rates of the six types of MC (i.e., mixed strains) continuously increased and reached equilibrium at 6 days. The equilibrium ratios were 75.4% for MC30-0AS, 68.9% for AS, 76.6% for MC40-25AS, 79.6% for MC40-25St, 70.8% for MC40-40AS, and 74.4% for MC45-40AS.

[0095] like Figure 2 As shown, MC40 containing three volume concentrations of Ac (25%, 50%, and 75%) and three volume concentrations of St (25%, 50%, and 75%) was used for the bioleaching of cobalt from sludge. The equilibrium ratios of MC40-25Ac were 76.6%, MC40-50Ac was 75.3%, MC40-75Ac was 71.6%, MC40-25St was 79.6%, MC40-50St was 78.7%, and MC40-75St was 72.4%. Therefore, compared with Examples 1 to 3, increasing the proportion of Ac or St in MC from 25% to 75% is detrimental to bioleaching. Furthermore, the equilibrium time for bioleaching nickel and cobalt from the sludge of acid-leached waste lithium batteries is not affected by changes in the concentrations of Ac and St in MC; in addition, when the proportion of St is less than 25%, the equilibrium ratio of bioleaching increases to 79.9%, but the increase is small, and the overall benefit is lower than that of Example 1. Therefore, the strain ratio of Example 1 is more reasonable.

[0096] like Figure 3 As shown, the bioleaching BCR analysis of cobalt by adding six types of MC showed that the leaching fraction of MC30-0AS was 75.6%, that of AS was 71.2%, that of MC40-25As was 78.0%, that of MC40-25St was 82.9%, that of MC40-40AS was 72.6%, and that of MC45-40AS was 77.1%. The residue fractions of MC30-0AS were 18.3%, AS was 21.5%, MC40-25As was 14.9%, MC40-25St was 11.8%, MC40-40AS was 18.9%, and MC45-40AS was 14.8%. Therefore, compared with the other five types of MC, the strain ratio and corresponding leaching temperature of MC40-25St in this application showed the highest cobalt bioleaching rate.

[0097] like Figure 4As shown, to evaluate the effect of the solid-liquid ratio, 200, 400, 600, 800, and 1000 grams of acid-leached sludge were added to a 2-liter leaching system. BCR analysis of cobalt at various solid-liquid ratios was presented. As the solid-liquid ratio of MC40-25St increased from 10% to 50%, the leached portion of cobalt showed a trend of decreasing from 82.9% to 58.9%, while the residue portion continuously increased from 11.8% to 22.1%. Therefore, in the comparison of Examples 1, 4, and 5, MC40-25St with a solid-liquid ratio of 10% is the optimal adaptive microbial consortium for bioleaching cobalt from bioleached sludge. Furthermore, the experimental examples with solid-liquid ratios below 10% showed smaller differences from the 10% state; therefore, considering the overall benefits, a solid-liquid ratio of 10% is superior.

[0098] Comparing Examples 1 and 6-13, the leaching rates of Examples 6-13 were 81.3%, 81.6%, 81.9%, 82.3%, 82.5%, 81.7%, 81.8%, and 82.4%, respectively. Therefore, it can be seen that excessively small or large leaching parameters, excessively small or large component proportions in the modified culture medium, excessively small or large component proportions in the single culture medium, and excessively small or large component proportions in the compound culture medium will all reduce the leaching rate of cobalt. Therefore, from a comprehensive perspective, the parameters of Example 1 are relatively better.

[0099] Investigation 2: Investigate the effect of staged stirring leaching on cobalt leaching rate.

[0100] The difference between Comparative Example 1 and Example 14 is that no adsorbent particles were added;

[0101] The difference between Comparative Example 2 and Example 14 is that Fe3O4@SiO2 particles were not added;

[0102] The difference between Comparative Example 3 and Example 14 is that no magnetic field is applied in the second stage;

[0103] The difference between Comparative Example 4 and Example 14 is that a magnetic field is applied in the first stage and an activator is added in the second stage;

[0104] Comparing Examples 14-20 and Control Examples 1-4, the increases in cobalt leaching rate for each example and control example were 4.46%, 3.26%, 3.50%, 3.50%, 3.62%, 3.25%, 3.37%, 1.83%, 1.52%, 1.93%, and 2.01%, respectively. It can be seen that staged stirring significantly improved the cobalt leaching rate compared to Example 1 because it enhanced cobalt separation and the activity of the mixed bacterial strains. Control Example 1, lacking adsorbent particles, reduced the leaching rate. For the targeted adsorption and separation of cobalt, the lack of Fe3O4@SiO2 particles in Control Example 2 weakened the extracellular respiration metabolism of the bacteria, thereby reducing cobalt leaching. The lack of a magnetic field in Control Example 3 weakened the diffusion rate of cobalt ions, and the presence of impurities during separation made the cobalt leaching test inaccurate. Control Example 4 reversed the order of the activator and magnetic field, which may have inhibited the early microbial activity due to the magnetic field. Therefore, the increase in cobalt leaching rate of Control Examples 1 to 4 was weaker compared to Examples 14 to 20.

[0105] Comparing Examples 14 to 20, it can be seen that applying parameters that are too small or too large in stages, having too small or too large a proportion of Fe3O4@SiO2 particles, and having too small or too large a proportion of adsorbed particles will all reduce the effect of improving the cobalt leaching rate. Therefore, from a comprehensive perspective, the parameter effect of Example 14 is relatively better.

[0106] Investigation 3: Investigate the effect of the preparation of adsorbent particles on the cobalt leaching rate.

[0107] The improvement rates of Examples 21 to 26 were 4.12%, 3.82%, 3.55%, 3.48%, 3.24%, and 3.67%, respectively. Compared with Example 14, the proportion of C800 resin being too small or too large, the sphere preparation parameters being too small or too large, and the freeze-drying parameters being too small or too large would all reduce the effect of improving the cobalt leaching rate. Therefore, from a comprehensive perspective, the parameter effect of Example 14 is relatively better.

Claims

1. A method for efficiently treating cobalt in the tailings of battery cathode materials using a wet leaching process, characterized in that, Includes the following steps: S1. Culture ferrooxidizing thiobacillus, iron-loving Leptospira, thiooxidizing thiobacillus, and thermostable thiooxidizing thiobacillus separately; S2. The separately cultured *Thiobacillus ferrooxidans*, *Leptospira ferrooxidans*, *Thiobacillus thiooxidans*, and thermotolerant *Thiobacillus sulfoxidans* were cultured together at a unit volume cell concentration ratio of 1:1:1:1–3 to obtain a concentration of 1×10⁻⁶ cells / mL. 8 ~1×10 9 Mixed bacterial culture solution with CFU / mL; S3. The mixed bacterial culture solution is added to the modified culture medium at a volume ratio of 1:8.5-9.5 to form a leaching system. The cobalt slag obtained by wet treatment is added to the leaching system at a solid-liquid ratio of 100-500 g:1 L and magnetic stirring is continuously performed at 150-250 rpm. The pH is maintained at 1.8-2.0 and the temperature at 38-42℃ during the leaching process. The water evaporated from the leaching system is replenished every day. The leaching time is 6 days to obtain a cobalt-rich solution and leaching residue. The leaching is then complete. The modified culture medium comprises: (NH4)2SO4: 2.5–3.5 g / L; MgSO4·7H2O: 0.3–0.6 g / L; K2HPO4: 0.3–0.7 g / L; KCl: 0.1–0.3 g / L; Ca(NO3)2: 0.01–0.05 g / L, with the remainder being distilled water.

2. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 1, characterized in that, In S1, the culture medium components used for culturing *Thiobacillus ferrooxidans* and *Leptospira ferrophila* separately included: modified culture medium components and FeSO4·7H2O: 20–60 g / L, culture temperature of 28–32 °C, and culture time of 7 days.

3. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 1, characterized in that, In S1, the culture medium components used for culturing Thiobacillus thiooxidans alone include: modified culture medium components and sulfur powder: 3-8 g / L, culture temperature of 28-32℃, and culture time of 7 days.

4. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 1, characterized in that, In S1, the culture medium components used for the isolated culture of thermotolerant sulfur oxidizing bacteria include: modified culture medium components, FeSO4·7H2O: 20-60 g / L and yeast extract: 0.1-0.3 g / L, culture temperature of 38-42℃, and culture time of 7 days.

5. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 1, characterized in that, In S2, the culture medium used for the compound culture includes the following components: modified culture medium components, FeSO4·7H2O: 15-40 g / L; sulfur powder: 1-2 g / L and yeast extract: 0.02-0.1 g / L, culture temperature: 38-42℃, culture time:

7.

6. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 1, characterized in that, In S3, the stirring leaching process is divided into a first stage and a second stage: First stage: 0 to 4 days before, under a magnetic field strength of 1 to 2 mT, add an activator accounting for 0.3 to 0.5 wt% of the cobalt slag to the leaching system; Second stage: 4-6 days, adjust the magnetic field strength of the leaching system to 4-5 mT; The activator is prepared as follows: Fe3O4@SiO2 particles are first dispersed in MES buffer solution with pH = 5.5-6 at a solid-liquid ratio of 1g: 22-24ml. Then, a coupling agent with a mass ratio of 1:0.15-0.18 to Fe3O4@SiO2 particles is added and reacted for 30-40 minutes to obtain an activation solution. The activation solution is then reacted with the adsorbed particles at a liquid-solid ratio of 12-15ml: 1g at room temperature for 18-22 hours. After the reaction is completed, the activator is obtained by washing.

7. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 6, characterized in that, The method for preparing the adsorbent particles is as follows: Porous ceramics were dispersed in a 2.5-3.5% sodium alginate solution at a solid-liquid ratio of 12-15 g: 100 ml. C800 resin at a mass ratio of 1:0.6-0.8 to the porous ceramics was then added and stirred continuously for 1.5-2 h to obtain a slurry. The slurry was then injected dropwise into a 2.5-3.5% calcium chloride solution and stirred continuously for 30-35 min to obtain spheres. The spheres were washed with deionized water and then freeze-dried at -50 to -40 °C for 12-24 h to obtain adsorbent particles.

8. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 7, characterized in that, The porous ceramic is either coal gangue-based porous ceramic or diatomite-based porous ceramic.

9. The method for efficient leaching wet treatment of cobalt in battery cathode material tailings as described in claim 6, characterized in that, The coupling agent is an EDC / NHS coupling agent.

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