A method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus mucilaginosus

Abstract

This invention discloses a method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus mucilaginosus, belonging to the field of microbial hydrometallurgical technology. The method involves mixing and sterilizing lithium iron phosphate cathode materials with a modified phosphorus-solubilizing culture medium, followed by inoculation with Bacillus mucilaginosus bacterial solution. After the bacteria enter the logarithmic growth phase, ascorbic acid is added to the system to achieve selective and efficient lithium leaching. After solid-liquid separation to obtain the leachate, the pH value is adjusted to allow Fe... 3+ Fe(OH)3 precipitate is formed and filtered off. Then, a saturated Na2CO3 solution is added to the supernatant to precipitate Li2CO3, thus achieving selective lithium recovery. The method provided by this invention has a simple process flow, low leaching energy consumption, low cost, avoids secondary pollution, achieves efficient lithium recovery from lithium iron phosphate cathode materials, and opens up a new application avenue for Bacillus subtilis.

Description

Technical Field

[0001] This invention relates to the field of microbial hydrometallurgy, and in particular to a method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus mucilaginosus. Background Technology

[0002] Lithium iron phosphate batteries play a vital role in mobile electronic devices and energy storage due to their high energy density, long cycle life, and environmental friendliness. Their theoretical lifespan is approximately 7-8 years, and they are currently facing a concentrated retirement period, accounting for over 60% of all retired batteries, making them the mainstream type of retired battery.

[0003] On the one hand, lithium iron phosphate cathode materials, as a high-grade "urban mine," typically have a higher lithium content than most economically viable primary lithium ores. Inefficient recycling would lead to resource waste. On the other hand, improper handling during the dismantling and recycling of spent lithium iron phosphate batteries can generate harmful waste gases and wastewater, posing a threat to the environment and human health. Therefore, developing a green recycling technology that efficiently leaches lithium and achieves resource regeneration is of great significance. This not only helps reduce environmental pollution but also enables resource recycling, representing a win-win situation for both environmental protection and the economy.

[0004] Currently, chemical leaching is one of the commonly used methods for recovering valuable metals from spent lithium-ion batteries. Highly efficient metal leaching can be achieved using inorganic acids or a combination of organic acids and reducing agents under heating conditions. However, this technology relies on continuous external energy input and the consumption of chemical reagents. Microbial methods, as a green recycling technology, utilize the metabolic processes of specific microorganisms to leach valuable metals. Compared to traditional industrial methods, they are lower in cost, more environmentally friendly, and more suitable for the selective recovery of lithium. Mishra et al. used *Thiobacillus acidophilus* to efficiently leach Co and Li from LiCoO2, with the bacteria operating in an environment containing S... 0 and Fe 2+ When growing in the culture medium, Fe 2+ Oxidized to Fe 3+ This generates H2SO4, which in turn drives rapid metal leaching. Based on this, mixed microbial leaching systems improve leaching efficiency. Liao et al. used a mixed culture of *Thiobacillus acidophilus* and *Thiobacillus thermophilus*, without adding additional Fe... 2+Under the specified conditions, the leaching rates of Co and Li reached 41% and 66%, respectively, significantly higher than the leaching efficiencies when the two bacteria were cultured individually. The results indicate that the synergistic effect of microbial co-culture helps to mitigate acid consumption and maintain a higher density of active cells. In studies utilizing microbial leaching technology to recover valuable metals from lithium-ion batteries, the selection of bacterial strains has certain limitations, mainly focusing on acidophilic microorganisms and some fungi. However, *Bacillus mucilaginosus*, a bacterium with highly efficient phosphorus-solubilizing and potassium-solubilizing functions in agriculture and the environment, has yet to have its application potential in the recovery of valuable metals from spent lithium-ion batteries, and no relevant research reports have been published to date. Summary of the Invention

[0005] The purpose of this invention is to provide a method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus mucilaginosus, in order to solve the problems existing in the prior art. By using heterotrophic bacteria—Bacillus mucilaginosus—as the specific bacteria for leaching lithium from lithium iron phosphate cathode materials, and ascorbic acid as a reducing agent, the method achieves a synergistic effect with the bioleaching of Bacillus mucilaginosus, thereby realizing efficient lithium leaching.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus subtilis, comprising the following steps:

[0008] (1) The lithium iron phosphate cathode material is mixed with the modified phosphorus-solubilizing medium and sterilized to obtain a mixed medium; wherein the solid-liquid mass ratio of the lithium iron phosphate cathode material and the modified phosphorus-solubilizing medium is 5 ~ 20 g: 1 L;

[0009] (2) Inoculate the mixed culture medium with Bacillus mucilaginosus to construct the leaching reaction system. After shaking culture, add ascorbic acid to the leaching reaction system to continue the reaction. After the reaction is completed, perform solid-liquid separation to obtain leaching solution and leaching residue respectively.

[0010] (3) After processing the leachate, lithium can be obtained from the lithium iron phosphate cathode material.

[0011] Preferably, in step (1), the modified phosphorus-solubilizing medium consists of: glucose 10.0 g / L, (NH4)2SO4 2.0 g / L, MgSO4·7H2O 0.5 g / L, MnSO4·H2O 0.03 g / L, FeSO4 0.03 g / L and NaCl 0.3 g / L.

[0012] In the above technical solution, *Bacillus mucilaginosus* is a chemoheterotrophic bacterium capable of disrupting mineral structures and possessing phosphorus and potassium solubilization functions. The organic acids secreted by this bacterium, such as lactic acid, malic acid, and citric acid, promote metal dissolution. Its extracellular polymeric substances (EPS) are mainly composed of tyrosine / tryptophan protein compounds, which form complexes with metal ions in anionic form, preventing local supersaturation of metal ions and thus promoting mass transfer and continuous leaching. This invention, based on *Bacillus mucilaginosus* bioleaching, introduces ascorbic acid as a key electron donor to construct a microbial selective leaching system, achieving selective and efficient lithium leaching. This method has significant advantages overall, including low processing cost, environmental friendliness, and easy process control.

[0013] Preferably, in step (2), the Bacillus mucilaginosus is inoculated in the form of a bacterial solution.

[0014] Preferably, the liquid culture medium for obtaining Bacillus mucilaginosus bacterial suspension consists of: 15.0 g / L casein peptone, 5.0 g / L NaCl and 5.0 g / L soybean peptone, and the culture conditions are: temperature 30-35 ℃, rotation speed 150-200 r / min, and time 12-24 h.

[0015] Preferably, the inoculation amount of the *Bacillus mucilaginosus* bacterial solution is 2% to 10%; the inoculated *Bacillus mucilaginosus* is a bacterium in the logarithmic growth phase with an OD value of [missing value]. 600 =1.2 ~ 1.8.

[0016] Preferably, in step (2), the shaking culture conditions are: shaking culture at 30 ℃ and 160 r / min for 12-24 h. After shaking culture, the bacteria enter the logarithmic growth phase, and OD... 600 = 1.8 ~ 2.0.

[0017] Preferably, in step (2), ascorbic acid with a final concentration of 0.5 to 2.0 g / L is added to the leaching reaction system, and the reaction is continued for 5 to 8 days.

[0018] Preferably, in step (3), the method for treating the leachate includes: adding hydrogen peroxide solution to the leachate, and waiting for Fe... 2+ Completely oxidized to Fe 3+ Adjust the pH to approximately 3.5 using a 1-5 mol / L NaOH solution to allow Fe to... 3+ Fe(OH)3 precipitate is formed and filtered off. Then, Na2CO3 solution is added to the supernatant and precipitated for 60-180 minutes to precipitate Li2CO3, thus obtaining lithium leached from the lithium iron phosphate cathode material.

[0019] The present invention discloses the following technical effects:

[0020] (1) Innovative strain: The innovative application of Bacillus mucilaginosus in the bioleaching of waste lithium iron phosphate cathode materials is different from traditional strong acidophilic bacteria. This strain can efficiently leach lithium iron phosphate cathode materials in a near-neutral and mild environment, fundamentally avoiding the generation of strongly acidic leachate waste liquid, overcoming the acid damage to the environment and equipment caused by traditional bioleaching technology, and opening up a new application path for Bacillus mucilaginosus.

[0021] (2) Short-term, efficient and selective leaching of lithium was achieved: Under the leaching conditions of initial pH 7.0, solid-liquid ratio 5.0 g / L, and inoculum amount 5%, the system spontaneously formed a weakly acidic environment (pH 4.7 ~ 5.6). On the 7th day, the lithium leaching rate reached a maximum of 48.72%, while the iron leaching rate was only 1.96%, demonstrating good selectivity. During the logarithmic growth phase of bacteria, 1.5 g / L ascorbic acid was added as a reducing agent to enhance leaching. On the 5th day, the lithium leaching rate increased to 98.66%, while the iron leaching rate was significantly inhibited to 12.55%, achieving efficient and selective leaching of lithium.

[0022] (3) This invention constructs a selective leaching system for Bacillus mucilaginosus, which leaches metals under weakly acidic conditions (pH 4.3-4.9) by coupling microbial metabolic activity with the electron transfer function of ascorbic acid, and reacts with Fe. 2+ Fe 0 Compared with reducing agents, ascorbic acid neither introduces impurity ions nor consumes acid, and can also promote microbial activity, reducing the difficulty of subsequent separation and purification, thus achieving a balance between economic and environmental benefits. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a process flow diagram of selective leaching of lithium from lithium iron phosphate cathode material by Bacillus mucilaginosus according to the present invention.

[0025] Figure 2 The effect of adding different concentrations of ascorbic acid on the pH of the leaching system was investigated in Examples 1-4; the leaching system without ascorbic acid in Example 1 was used as a control.

[0026] Figure 3The effects of adding different concentrations of ascorbic acid on the leaching efficiency of Li and Fe were investigated in Examples 1-4; among them, the leaching system without the addition of ascorbic acid in Example 1 was used as a control.

[0027] Figure 4 Different solid-liquid ratios were set for Example 1 and Examples 5-7 to detect the effect on the pH of the Bacillus mucilaginosus-ascorbic acid (2.0 g / L) process system;

[0028] Figure 5 Different solid-liquid ratios were set for Example 1 and Examples 5-7 to detect the effect on the leaching efficiency of Li and Fe in the Bacillus mucilaginosus-ascorbic acid (2.0 g / L) process system;

[0029] Figure 6 The variation of viable bacterial counts of Bacillus mucilaginosus in different process systems of Examples 1-4 is shown; among them, the leaching system without the addition of ascorbic acid based on Example 1 is used as a control.

[0030] Figure 7 The surface morphology changes of lithium iron phosphate cathode material before and after bioleaching;

[0031] Figure 8 The results show the phase evolution of the leaching residue from the Bacillus mucilaginosus-ascorbic acid process; (a) uses lithium iron phosphate cathode material as a blank control; (b) uses the leaching system without ascorbic acid in Example 1 as an experimental control; (c)-(f) are the Bacillus mucilaginosus-ascorbic acid leaching systems constructed by adding different concentrations of ascorbic acid in Examples 1-4. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] This invention utilizes Bacillus mucilaginosus to leach lithium from lithium iron phosphate cathode materials. Different leaching conditions were employed, and the optimal leaching conditions were determined. Ascorbic acid was added under these optimal conditions to enhance the leaching effect. The specific process is as follows: Figure 1 As shown. The modified phosphate-solubilizing medium consists of: glucose 10.0 g / L, (NH4)2SO4 2.0 g / L, MgSO4·7H2O 0.5 g / L, MnSO4·H2O 0.03 g / L, FeSO4 0.03 g / L, and NaCl 0.3 g / L; prepared with deionized water. The experimental results in the following examples are the average of three repeated experiments.

[0038] The Bacillus mucilaginosus involved in the following embodiments was donated by the Mining Area Ecological Environment Assessment and Restoration Team of Inner Mongolia University of Science and Technology. However, the present invention is not limited to this strain of Bacillus mucilaginosus. Bacillus mucilaginosus can be obtained through other channels to achieve the technical solution and the technical effects described in the present invention.

[0039] Example 1

[0040] A method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus mucilaginosus includes the following steps:

[0041] (1) Determination of metal content in samples

[0042] Waste lithium iron phosphate batteries underwent pretreatment including discharge, disassembly, separation, and impurity removal to obtain lithium iron phosphate cathode material. Approximately 0.1 g of dried lithium iron phosphate cathode material sample was weighed into a digestion vessel, and 6 mL of concentrated hydrochloric acid, 2 mL of concentrated nitric acid, and 2 mL of deionized water were added. After sealing, the mixture was digested in a microwave digester. The digested solution was transferred and diluted to a 100 mL volumetric flask, and then 10-fold and 100-fold dilutions were prepared. The lithium and iron contents were quantitatively analyzed using an ICP-OES (ICAP700) system from Thermo Fisher Scientific, and were found to be 4.3% and 35.4%, respectively.

[0043] (2) Pre-culture of Bacillus mucilaginosus

[0044] Using an inoculation loop, pick 2-3 loops of vigorously growing mycelium and inoculate it into a liquid culture medium containing: 15.0 g / L casein peptone, 5.0 g / L NaCl, and 5.0 g / L soybean peptone. The medium was prepared with deionized water, and the initial pH was adjusted to approximately 7.3 using a 1 mol / L NaOH solution. The culture was then placed in a shaker at 200 r / min and 30 ℃ for 24 h to obtain samples in the logarithmic growth phase (OD). 600 = 1.2) bacterial solution.

[0045] (3) Selective leaching of lithium from lithium iron phosphate cathode material by Bacillus mucilaginosus

[0046] Add 100 mL of modified phosphorus-solubilizing medium to a 250 mL Erlenmeyer flask, adjusting the initial pH to approximately 7.0 (7.0 ~ 7.5) using a 1 mol / L NaOH solution; mix the lithium iron phosphate cathode material with the medium at a solid-liquid mass ratio of 5.0 g: 1 L, sterilize, and cool to room temperature; [The text abruptly ends here, likely due to an incomplete sentence or missing information.] 600 = 1.2) of Bacillus mucilaginosus bacterial suspension was inoculated into the culture medium at an inoculum volume of 5%; it was then placed in a shaker at 30 ℃ and 160 r / min for 24 h, at which point the bacteria entered the logarithmic growth phase (OD). 600 = 1.8); 1.5 g / L ascorbic acid was added to the bioleaching system; the leaching time was 8 days, and 2 mL samples were taken every 24 h during the leaching process to determine the pH value and the content of leached metal ions in the solution, and sterile water was used to replenish the consumed leachate. After the experiment, the solution was filtered through 0.45 μm filter paper to obtain leachate and leachate residue respectively; hydrogen peroxide solution was added to the obtained leachate, and Fe was added after leaching. 2+ Completely oxidized to Fe 3+ The pH of the leachate was adjusted to approximately 3.5 using a 1 mol / L NaOH solution, so that the Fe...3+ Fe(OH)3 precipitate is formed, then filtered to remove the precipitate. Saturated Na2CO3 solution is then added to the filtrate and precipitated for 180 minutes to precipitate Li2CO3, thus achieving selective recovery of lithium.

[0047] The pH of the leaching system after the addition of ascorbic acid was measured using a pH meter and fluctuated within the range of 4.3 to 4.9, showing a gradually increasing trend. The content of metal ions in the leachate was determined using ICP-OES. Calculations showed that on the 5th day of the leaching reaction, the lithium leaching rate reached a maximum of 98.66%, while the iron leaching rate was only 12.55%. This achieved efficient and selective leaching of lithium from lithium iron phosphate cathode materials.

[0048]

[0049] In the formula, C S V represents the concentration of metal ions in the leachate (unit: mg / L). S It is the volume of the leachate (unit: L), C F M represents the content of metal elements in a sample as determined by ICP-OES (unit: mg / g). F Indicates the mass of the sample (unit: g).

[0050] The lithium iron phosphate cathode material before and after bioleaching was observed using scanning electron microscopy, such as... Figure 7 As shown, the surface becomes rough and the particle distribution is uneven after bioleaching, indicating that the material surface has been eroded by microorganisms.

[0051] The lithium iron phosphate cathode material after leaching was determined using X-ray diffraction, such as... Figure 8 As shown, with the increase of ascorbic acid concentration, the intensity of the characteristic diffraction peak of LiFePO4 decreases, while the intensity of the characteristic diffraction peak of FePO4 increases, indicating efficient lithium leaching.

[0052] Example 2

[0053] The difference from Example 1 is that in step (3), 0.5 g / L ascorbic acid is added to the bioleaching system under aseptic conditions. All other steps are the same.

[0054] Calculations show that on the 7th day of the leaching reaction, the lithium leaching rate can reach up to 39.73%, while the iron leaching rate is only 4.51%; thus, selective leaching of lithium in lithium iron phosphate cathode materials has been achieved.

[0055] Example 3

[0056] The difference from Example 1 is that in step (3), 1.0 g / L ascorbic acid is added to the bioleaching system under aseptic conditions. All other steps are the same.

[0057] Calculations show that on the 8th day of the leaching reaction, the lithium leaching rate can reach a maximum of 57.93%, while the iron leaching rate is only 7.70%; thus, selective leaching of lithium in lithium iron phosphate cathode materials has been achieved.

[0058] Example 4

[0059] The difference from Example 1 is that in step (3), 2.0 g / L ascorbic acid is added to the bioleaching system under aseptic conditions. All other steps are the same.

[0060] Calculations show that on the 5th day of the leaching reaction, the lithium leaching rate can reach up to 95.98%, while the iron leaching rate is only 19.34%; thus, selective leaching of lithium in lithium iron phosphate cathode materials has been achieved.

[0061] Example 5

[0062] The difference from Example 1 is that the solid-liquid mass ratio in step (3) is 10.0 g: 1 L; and 2.0 g / L ascorbic acid is added to the bioleaching system under aseptic conditions. All other steps are the same.

[0063] Calculations showed that the lithium leaching rate could reach up to 68.27%, while the iron leaching rate was only 14.37%. The results indicate that the solid-liquid mass ratio is the key factor in controlling the leaching efficiency, and the method of this invention can achieve selective leaching of lithium under various conditions.

[0064] Example 6

[0065] The difference from Example 1 is that the solid-liquid mass ratio in step (3) is 15.0 g: 1 L; and 2.0 g / L ascorbic acid is added to the bioleaching system under aseptic conditions. All other steps are the same.

[0066] Calculations show that the lithium leaching rate can reach up to 44.30%, while the iron leaching rate is only 8.36%; thus, selective leaching of lithium in lithium iron phosphate cathode materials has been achieved.

[0067] Example 7

[0068] The difference from Example 1 is that the solid-liquid mass ratio in step (3) is 20.0 g: 1 L; and 2.0 g / L ascorbic acid is added to the bioleaching system under aseptic conditions. All other steps are the same.

[0069] Calculations show that the lithium leaching rate can reach up to 37.09%, while the iron leaching rate is only 6.77%; thus, selective leaching of lithium in lithium iron phosphate cathode materials has been achieved.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that the modified phosphorus-solubilizing medium in step (3) is replaced with silicate bacteria medium. The silicate bacteria medium consists of: sucrose 5.0 g / L, Na2HPO4 2.0 g / L, CaCO3 0.1 g / L, MgSO4·7H2O 0.5 g / L and FeCl3 0.005 g / L, with an initial pH of 7.0 and a solid-liquid mass ratio of 10.0 g: 1 L.

[0072] The pH of the leaching system, measured using a pH meter, fluctuated within the range of 6.8 to 7.3 without a significant trend. The content of metal ions in the leachate was determined using ICP-OES. The calculated lithium leaching rate and iron leaching rate were 6.97% and 0.15%, respectively. At this level, efficient lithium leaching could not be achieved. Therefore, the use of a modified phosphorus-solubilizing medium is key to this invention.

[0073] Comparative Example 2

[0074] The difference from Example 1 is that the solid-liquid mass ratio in step (3) is 10.0 g: 1 L, and Bacillus mucilaginosus culture is not inoculated; the other steps are the same.

[0075] The pH of the leaching system, measured using a pH meter, fluctuated within the range of 6.8 to 7.3 without a significant trend. The content of metal ions in the leachate was determined using ICP-OES. The calculated lithium and iron leaching rates were 10.68% and 0.51%, respectively. At these rates, efficient lithium leaching could not be achieved. Therefore, using Bacillus subtilis to achieve efficient and selective lithium leaching is the key to this invention.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that the solid-liquid mass ratio in step (3) is 20 g: 1 L; and ascorbic acid is not added. All other steps are the same.

[0078] Calculations show that on the 5th day of the leaching reaction, the lithium leaching rate can reach a maximum of 23.24%, while the iron leaching rate is only 0.75%; at this point, efficient lithium leaching cannot be achieved.

[0079] Comparative Example 4

[0080] The difference from Example 1 is that the inoculation amount of Bacillus mucilaginosus in step (3) is 2%; and ascorbic acid is not added. All other steps are the same.

[0081] Calculations show that on the 5th day of the leaching reaction, the lithium leaching rate can reach a maximum of 34.20%, while the iron leaching rate is only 0.89%; at this point, efficient lithium leaching cannot be achieved.

[0082] Comparative Example 5

[0083] The difference from Example 1 is that a two-step bioleaching method is used: in step (3), 100 mL of modified phosphate-solubilizing medium is added to a 250 mL Erlenmeyer flask, and its initial pH is adjusted to about 7.0 (7.0 ~ 7.5) using a 1 mol / L NaOH solution; the medium is then placed in the logarithmic growth phase (OD200). 600 = 1.2) Bacillus mucilaginosus culture was inoculated into the culture medium at an inoculation rate of 5%; it was then placed in a shaker at 30 ℃ and 160 r / min for 24 h; lithium iron phosphate cathode material was then added to the medium at a solid-liquid mass ratio of 10.0 g: 1 L, without adding ascorbic acid. All other steps were the same.

[0084] Calculations show that on the 5th day of the leaching reaction, the lithium leaching rate can reach a maximum of 27.27%, while the iron leaching rate is only 0.73%; at this point, efficient lithium leaching cannot be achieved.

[0085] Comparative Example 6

[0086] The difference from Example 1 is that the waste culture medium method is used for bioleaching: in step (3), 100 mL of modified phosphate-solubilizing culture medium is added to a 250 mL Erlenmeyer flask, and its initial pH is adjusted to about 7.0 (7.0 ~ 7.5) using a 1 mol / L NaOH solution; the flask is in the logarithmic growth phase (OD200). 600 = 1.2) Bacillus mucilaginosus bacterial suspension was inoculated into the culture medium at an inoculation rate of 5%; it was then placed in a shaker at 30 ℃ and 160 r / min for 48 h; the bacterial cells were removed by filtration through a 0.22 μm filter membrane, and then lithium iron phosphate cathode material was added to the medium at a solid-liquid mass ratio of 10.0 g: 1 L, without adding ascorbic acid. All other steps were the same.

[0087] Calculations show that on the 5th day of the leaching reaction, the lithium leaching rate can reach a maximum of 35.71%, while the iron leaching rate is only 1.11%; at this point, efficient lithium leaching cannot be achieved.

[0088] Comparative Example 7

[0089] The difference from Example 1 is that the exogenous additive is a 1% hydrogen peroxide solution: In step (3), 100 mL of modified phosphorus-solubilizing medium is added to a 250 mL conical flask, and its initial pH is adjusted to about 7.0 (7.0 ~ 7.5) using a 1 mol / L NaOH solution; the lithium iron phosphate cathode material is mixed with the medium at a solid-liquid mass ratio of 10.0 g: 1 L, sterilized, and cooled to room temperature; the material is in the logarithmic growth phase (OD) 600= 1.2) Bacillus mucilaginosus culture was inoculated into the culture medium at an inoculum volume of 5%; it was then incubated in a shaker at 30 ℃ and 160 r / min for 24 h; 1% hydrogen peroxide solution was added to the bioleaching system. All other steps were the same.

[0090] Calculations show that on the 7th day of the leaching reaction, the lithium leaching rate can reach a maximum of 37.51%, while the iron leaching rate is only 0.92%; at this point, efficient lithium leaching cannot be achieved.

[0091] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for selectively leaching lithium from lithium iron phosphate cathode materials using Bacillus mucilaginosus, characterized in that, Includes the following steps: (1) The lithium iron phosphate cathode material is mixed with the modified phosphorus-solubilizing medium and sterilized to obtain a mixed medium; wherein the solid-liquid ratio of the lithium iron phosphate cathode material and the modified phosphorus-solubilizing medium is 5 ~ 20 g: 1 L; (2) Inoculate the mixed culture medium with Bacillus mucilaginosus to construct the leaching reaction system. After shaking culture, add ascorbic acid to the leaching reaction system to continue the reaction. After the reaction is completed, perform solid-liquid separation to obtain leaching solution and leaching residue respectively. (3) After processing the leachate, lithium leached from the lithium iron phosphate cathode material can be obtained; In step (1), the modified phosphorus-solubilizing medium consists of: glucose 10.0 g / L, (NH4)2SO4 2.0 g / L, MgSO4·7H2O 0.5 g / L, MnSO4·H2O 0.03 g / L, FeSO4 0.03 g / L and NaCl 0.3 g / L, with a pH of 7.0~7.5; In step (2), the Bacillus mucilaginosus is inoculated in the form of a bacterial solution; The liquid culture medium used to obtain Bacillus mucilaginosus bacterial suspension consists of: 15.0 g / L casein peptone, 5.0 g / L NaCl, and 5.0 g / L soybean peptone. The culture conditions are: temperature 30-35 ℃, rotation speed 150-200 r / min, and time 12-24 h.

2. The method as described in claim 1, characterized in that, The inoculation amount of the Bacillus mucilaginosus culture is 2% to 10%.

3. The method as described in claim 1, characterized in that, In step (2), the conditions for the shaking culture are: shaking culture at 30℃ and 160 r / min for 12 to 24 h.

4. The method as described in claim 1, characterized in that, In step (2), ascorbic acid with a final concentration of 0.5 to 2.0 g / L is added to the leaching reaction system, and the reaction continues for 5 to 8 days.

5. The method as described in claim 1, characterized in that, In step (3), the method for treating the leachate includes: adding hydrogen peroxide solution to the leachate, and waiting for Fe... 2+ Completely oxidized to Fe 3+ Adjust the pH value to make Fe 3+ Fe(OH)3 precipitate is formed and filtered off. Then, Na2CO3 solution is added to the supernatant to precipitate Li2CO3, thus obtaining lithium leached from the lithium iron phosphate cathode material.

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