A low-cost iron removal process for sugarcane bagasse hard carbon negative electrode material based on bacterial biological method

Abstract

The application belongs to the technical field of hard carbon negative materials, and particularly relates to a low-cost iron removal process for sugarcane residue hard carbon negative materials based on a bacterial biological method. The low-cost iron removal process for sugarcane residue hard carbon negative materials based on the bacterial biological method comprises the following steps: S1. pretreating the sugarcane residue; S2. obtaining and preparing the bacterial strain; S3. biological iron removal; S4. enhanced iron removal; and S5. separation and recovery. The low-cost green iron removal process for sugarcane residue hard carbon negative materials based on the bacterial biological method has the following advantages: significantly reducing the iron removal cost, significantly reducing environmental pollution, achieving efficient iron removal, realizing resource utilization, being easy to operate and industrialize, having strong adaptability of the bacterial flora, and improving the electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the technical field of hard carbon anode materials, specifically relating to a low-cost iron removal process for sugarcane bagasse hard carbon anode materials based on a bacterial biological method. Background Technology

[0002] With the increasing global energy demand and the growing prominence of environmental issues, the development and application of new energy technologies have received widespread attention. Lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), as important energy storage devices, are playing an increasingly vital role in electric vehicles, portable electronic devices, and energy storage power stations. The negative electrode material is one of the key components of lithium / sodium-ion batteries, and its performance directly affects the battery's energy density, cycle life, and rate performance.

[0003] Hard carbon materials have emerged as one of the most promising anode materials due to their unique structural advantages. This porous material, composed of twisted graphite microcrystalline domains and amorphous carbon, exhibits a significantly larger interlayer spacing (0.36-0.40 nm) than graphite (0.335 nm), which is particularly advantageous for large-sized sodium ions. Rapid insertion / extraction of ions. The synthesis of hard carbon materials using biomass waste as a precursor has become a research hotspot, not only due to its environmental friendliness but also its potential economic value. Sugarcane bagasse, as a vast agricultural byproduct, provides a highly attractive pathway for the preparation of hard carbon materials. Statistics show that China produces tens of millions of tons of sugarcane bagasse annually. However, this bagasse is typically used only for low-value-added applications such as incineration or papermaking. Converting sugarcane bagasse into high-value-added hard carbon materials can effectively realize the high-value utilization of waste, with significant environmental and economic benefits. Compared to traditional resin-based carbon materials, the preparation cost of sugarcane bagasse-based hard carbon materials is significantly reduced. Furthermore, sugarcane bagasse-based hard carbon materials exhibit excellent electrochemical performance and can be used as anode materials for lithium-ion and sodium-ion batteries. Its unique pore and disordered structure promotes rapid ion transport and insertion / extraction, thereby achieving high specific capacity and excellent rate performance. By further optimizing the preparation process, such as controlling the carbonization temperature and introducing heteroatom doping, the electrochemical performance of bagasse-based hard carbon materials can be effectively improved, enabling them to meet the application requirements of high-performance energy storage devices. Against the backdrop of global carbon neutrality, the research and development of bagasse hard carbon materials is accelerating. Recent research shows that surface-modified bagasse hard carbon anodes retain 92% of their capacity after 500 cycles, with performance approaching that of commercial graphite anodes. Although the current market size is only about $200 million, industry forecasts predict that with breakthroughs in sodium-ion battery technology (after 2025), the market size of this material is expected to achieve a compound annual growth rate of 30%. It is foreseeable that this "waste-to-treasure" bagasse hard carbon anode material will play a crucial role in next-generation energy storage systems, driving the new energy industry towards greener and lower-cost development.

[0004] While bagasse hard carbon materials possess numerous advantages, their performance is susceptible to the influence of iron impurities (up to 3000 ppm). Studies have shown that iron impurities have a significant adverse effect on the electrochemical performance of hard carbon materials: firstly, they undergo irreversible reactions with lithium / sodium ions, reducing the initial coulombic efficiency; secondly, iron impurities accelerate electrolyte decomposition, leading to increased electrode polarization and thus shortening cycle life; furthermore, they hinder the diffusion of lithium / sodium ions, affecting the material's rate performance. Therefore, to improve the electrochemical performance of hard carbon materials, iron removal processes are essential, typically requiring iron content below 100 ppm or even lower.

[0005] Acid washing is a commonly used iron removal process. Chen Dong et al. [Research on Surface Modification of Biomass Hard Carbon Anode Material [J]. Power Technology, 2025, 49(03):2083-2089.] selected biomass coconut shell as carbon source. After acid washing and CVD coating treatment, the surface structure of hard carbon was effectively improved, the specific surface area was reduced, the active sites were increased, and the ICE and platform sodium storage capacity of hard carbon material were significantly improved. Patent CN117923464A (A method for preparing biomass hard carbon anode material with reduced pH value) describes in detail the process parameters for acid washing with acids such as hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid or sulfuric acid to remove metal impurities (including iron) in biomass hard carbon anode material. Patent CN118744976A (A Biomass Hard Carbon Anode Material and Preparation Method) proposes a method for preparing hard carbon anode materials using biomass as raw material, including an acid washing pretreatment step to remove impurities (such as iron) from the raw materials; the acid washing conditions are: acid type: 0.1-0.2 mol / L hydrochloric acid or sulfuric acid solution, or a mixed acid containing 0.1 mol / L hydrochloric acid, 0.1 mol / L nitric acid, and 0.1 mol / L hydrofluoric acid. This method emphasizes environmental protection and high efficiency and is suitable for energy storage devices such as sodium-ion batteries.

[0006] The pickling process requires high-concentration acid and waste acid treatment facilities, resulting in high overall costs. Market data shows that when using hydrochloric acid or hydrofluoric acid to remove iron, the pickling cost per ton of hard carbon exceeds 8,000 yuan. This process has three main problems: (1) significant environmental risks, as the acidic wastewater contains high-concentration acid, iron ions, and heavy metals, requiring multi-stage treatment to meet discharge standards; (2) significant safety hazards, as high-concentration acid is highly corrosive to equipment, leading to high on-site operational risks; and (3) low energy efficiency, as the reaction process requires maintaining a high-temperature environment (usually >60℃) and extending the treatment time (4-6 hours), further increasing energy costs. These factors together lead to the traditional pickling method facing dual pressures of economic efficiency and environmental protection.

[0007] In recent years, research on bacterial reduction / adsorption / complexation of iron in the field of biometallurgy has deepened. Some bacteria have shown good conversion, reduction, and adsorption capabilities for iron impurities such as iron oxide, possessing advantages such as being green, efficient, and operating under mild conditions. Therefore, exploring the introduction of bacterial iron removal technology into the green modification treatment of sugarcane bagasse hard carbon anode materials has become a key breakthrough in achieving the combination of high-value utilization of agricultural waste and low-carbon manufacturing. Summary of the Invention

[0008] To address the problems of high cost and heavy pollution associated with existing iron removal technologies, this invention proposes a low-cost, green iron removal process for sugarcane bagasse hard carbon anode materials based on a bacterial biological method. This process utilizes screening for iron-loving bacteria naturally attached to sugarcane bagasse to achieve the oxidative transformation and dissolution removal of iron from the hard carbon material. Compared to traditional acid washing methods, this method has significant advantages: First, by using bacterial communities to replace high-concentration inorganic acids, the amount of chemical reagents used can be significantly reduced. Preliminary estimates suggest the iron removal cost is approximately 1500–2000 RMB / ton of hard carbon, far lower than acid washing. Second, this process generates almost no acidic wastewater, making it environmentally friendly. Furthermore, the process is simple, mild, and suitable for industrial application; the filtrate can be recycled, reducing resource waste; the symbiotic bacterial community exhibits good environmental adaptability, and the synergistic effect of acid-producing bacteria and iron-oxidizing bacteria further enhances iron removal efficiency. This process can effectively reduce the production cost of hard carbon anode materials, improve electrochemical performance, and promote their green preparation and the sustainable development of the new energy materials industry, possessing significant economic and social implications.

[0009] The purpose of this invention is to overcome the shortcomings of existing acid washing methods for iron removal, such as high cost, severe environmental pollution, and potential damage to material structure. It provides a low-cost, environmentally friendly, and efficient iron removal process for sugarcane bagasse hard carbon anode materials. Specifically, this invention aims to replace traditional high-concentration acid washing methods with biological iron removal using bacteria, significantly reducing iron removal costs and the generation of acidic wastewater, thus achieving low-cost and environmentally friendly preparation of sugarcane bagasse hard carbon anode materials. Simultaneously, by screening and enriching highly efficient iron-loving bacteria and optimizing bioreaction conditions, iron removal efficiency is improved, ensuring that the iron content in the hard carbon material meets the requirements of battery anode materials, avoiding damage to the material structure from strong acids, and maintaining the material's excellent electrochemical performance. Furthermore, this invention focuses on resource utilization, reducing costs and pollution through filtrate recovery, providing a simple, easy-to-control, and highly adaptable iron removal process. It particularly emphasizes screening strains from the natural microbial communities attached to sugarcane bagasse itself, reducing external purchase costs and utilizing the synergistic effect of symbiotic microbial communities, thereby promoting the sustainable development of new energy materials and ensuring the performance improvement of lithium / sodium-ion batteries.

[0010] This invention provides a low-cost iron removal process for sugarcane bagasse hard carbon anode materials based on bacterial biological methods, comprising the following steps:

[0011] S1. Pre-treatment of sugarcane bagasse;

[0012] S2. Source and preparation of bacterial strains;

[0013] S3. Biological iron removal;

[0014] S4. Enhanced iron removal;

[0015] S5. Separation and recycling.

[0016] Furthermore, the source and preparation of the bacterial strain in step S2 includes the following steps:

[0017] S21. Enrichment and functional enhancement of sugarcane bagasse compost;

[0018] S22. Isolation and Identification of Functional Strains: Samples were taken in the later stages of enrichment culture, and single colonies were isolated and purified using selective media. The dominant strains were identified morphologically, physiologically and biochemically, and through 16S rRNA gene sequencing to obtain iron-loving functional strains encompassing multiple genera and species. Multiple samples were taken in the later stages of enrichment (days 7, 10, and 14). Single colonies were isolated and purified using the dilution plating method or streak plate method on a basal salt medium containing ferric citrate / ferric oxide (pH 6.0-7.0). Colonies with diverse morphologies were selected for purification and culture, and their ability to dissolve / oxidize sugarcane bagasse hard carbon powder or synthetic iron oxides in liquid media was preliminarily screened. Highly active dominant strains were identified using methods including morphological observation, physiological and biochemical characterization (Gram staining, oxidase, catalase, carbon source utilization, iron metabolism capacity testing), and 16S rRNA gene sequencing. rRNA gene sequence analysis; the identification results cover multiple genera and species, including indigenous genera such as Bacillus, Pseudomonas, Acinetobacter, and Streptomyces, as well as representative strains of introduced genera such as Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, and Burkholderia cepacia;

[0019] S23. Construction and adaptive domestication of complex microbial communities;

[0020] S24. Preparation of bacterial suspension: The domesticated multifunctional bacterial population was cultured on a large scale. The bacterial cells were collected by centrifugation, washed with sterile physiological saline or buffer, and resuspended. The concentration of the bacterial suspension was adjusted to an OD600 value of 1.0-2.0. The domesticated multifunctional bacterial population was then cultured on an optimized medium. Culture conditions: temperature 25-35℃, pH 2.0-7.0 (adjusted according to the dominant bacterial population; slightly acidic pH 5.5-6.5 is preferred), stirring speed 100-200 rpm, cultured to the late logarithmic stage (OD600 0.8-1.5). The bacterial cells were collected by centrifugation (4000-6000g, 10-15 min), washed 1-2 times with sterile physiological saline (0.85% NaCl) or buffer (pH 6.0 phosphate buffer), resuspended, and the concentration adjusted to an OD600 value of 1.0-2.0 to obtain a highly efficient multifunctional bacterial suspension for the biological iron removal step.

[0021] Further, the sugarcane bagasse pretreatment process in step S1 is as follows: the sugarcane bagasse is pre-carbonized in an anaerobic atmosphere at 550℃, and then the pre-carbonized sugarcane bagasse is pulverized to a particle size of 450-550 mesh. The purpose of pretreatment is to provide suitable material morphology and surface properties for subsequent bacterial iron removal. First, the sugarcane bagasse is placed in a reactor or tubular furnace and pre-carbonized in an anaerobic atmosphere at 500-600℃. The preferred temperature range is 550℃, the heating rate is controlled at 5-10℃ / min, the anaerobic atmosphere can be nitrogen or argon, the gas flow rate is 50-100mL / min, the pre-carbonization time is 1-3 hours, preferably 2 hours, and the pressure is maintained at atmospheric pressure. Pre-carbonization can convert the organic matter in the sugarcane bagasse into carbon materials, forming a preliminary hard carbon structure. Then, the pre-carbonized sugarcane bagasse is pulverized to a particle size of 400-500 mesh. The preferred particle size range is greater than 450 mesh. Grinding methods can include ball milling or air jet milling. If ball milling is used, the milling time is 1-2 hours, the milling speed is 200-300 rpm, and the ball-to-material ratio is 10:1. If air jet milling is used, the feed rate is 10-20 kg / h, and the air pressure is 0.6-0.8 MPa. Grinding increases the specific surface area of ​​the material, which is beneficial for the contact between bacteria and iron impurities.

[0022] Furthermore, the sugarcane bagasse composting enrichment and functional enhancement step in step S21 includes:

[0023] S211. Collect fresh sugarcane bagasse, crush it to a particle size ≤2cm, and adjust the initial moisture content to 55-65%;

[0024] S212. Place the pretreated bagasse in a temperature- and gas-controlled environment;

[0025] S213. Inoculation function-enhancing microbial agent, the inoculation amount is 0.1-1.0% of the dry weight of the raw material;

[0026] S214. The enrichment conditions are controlled as follows: temperature 40-50℃, dissolved oxygen 0.5-2.0mg / L, initial C / N ratio (25-30):1, initial pH 5.5-7.5, humidity 55-65%, and the pile is turned over once every 48 hours.

[0027] S215. The enrichment culture period is 7-14 days.

[0028] The enrichment and functional enhancement process of sugarcane bagasse compost aims to enrich indigenous iron-loving microorganisms (such as Bacillus, Pseudomonas, Acinetobacter, Streptomyces, Burkholderia, etc.) and optimize the iron metabolism capacity of the community using exogenous strains, forming a basis for a complex functional microbial community. Selective addition of FeSO4·7H2O (0.5-2.0 g / L) can maintain selective pressure, and pH can be adjusted using phosphate buffers, such as a K2HPO4 / KH2PO4 buffer system.

[0029] Further, the construction and adaptation process of the composite microbial community in step S23 is as follows: 3-5 functionally complementary strains obtained through isolation and identification are selected to construct a composite functional microbial community. This community is then placed in a culture medium containing readily available iron sources and sugarcane bagasse hard carbon powder for gradient pressure adaptation. The concentration of readily available iron sources is gradually reduced by 0.2-0.5 g / L / generation, while the amount of sugarcane bagasse hard carbon powder added is increased by 0.1-0.5 g / L / generation. After 5-10 generations of subculturing, the metabolic efficiency of the microbial community on iron impurities in the sugarcane bagasse hard carbon is improved. A strain library of highly active strains (including indigenous dominant bacteria and introduced functional bacteria) is established. Based on the results of tests on the iron metabolism mechanism (oxidation, dissolution), growth compatibility, and synergistic effects of the strains, 3-5 functionally complementary strains are selected and mixed in a specific ratio to construct the target composite functional microbial community. To enhance its adaptability to sugarcane bagasse hard carbon and its iron removal efficiency, gradient pressure acclimatization was conducted: a) cultured in a medium containing a small amount of FeSO4 (1-2 g / L) and a small amount of hard carbon powder (0.1-0.5 g / L); b) the FeSO4 concentration was gradually reduced (by 0.2-0.5 g / L each time), while the amount of hard carbon powder was increased (by 0.1-0.5 g / L each time); c) after 5-10 generations, the complex microbial community was finally adapted to an environment where sugarcane bagasse hard carbon powder was the main or sole iron source. Adaptability was assessed by monitoring microbial community growth (OD600) and iron conversion rate.

[0030] Further, the biological iron removal step in step S3 is as follows: Pretreated bagasse hard carbon powder is mixed with a bacterial suspension at a solid-liquid ratio of 1:15, and a biological reaction is carried out for 28-72 hours at a temperature of 30℃ and a pH of 6.0-6.5. The purpose of biological iron removal is to remove iron impurities from the bagasse hard carbon material using the biological oxidation or dissolution of bacteria. First, the pretreated bagasse hard carbon powder is mixed with the bacterial suspension, controlling the solid-liquid ratio at 1:10-1:20, preferably 1:15. Then, a biological reaction is carried out at a suitable temperature and pH. The temperature is generally 25-35℃, preferably 30℃; the pH is generally 2-7, adjusted according to the acid and alkali tolerance of the bacterial strain, preferably pH 6.0-6.5; and the biological reaction time is 12-96 hours, preferably 56-72 hours. During the reaction, stirring is carried out at a speed of 100-200 rpm. Depending on the aerobic requirements of the bacteria, aeration can be carried out at a rate of 0.1-0.5 VVM.

[0031] Further, the enhanced iron removal step in step S4 involves adding citric acid or oxalic acid at a concentration of 0.5% during the bioreaction process. Iron removal is enhanced by controlling the redox potential of the system. Adding 0.5% citric acid forms a [Fe(Cit)]- complex with a stability constant logK = 11.5, inhibiting iron redeposition and effectively improving iron removal efficiency. The purpose of enhanced iron removal is to further improve iron removal efficiency. During the bioreaction process, an appropriate amount of auxiliary agent, such as organic acids like citric acid or oxalic acid, is added at a concentration of 0.1-1%, preferably 0.5%. This can be added all at the start of the reaction or in batches to enhance iron dissolution and promote the binding of iron ions with bacteria. Simultaneously, the redox potential of the system is controlled by adjusting the aeration rate or adding a redox mediator. Potassium ferricyanide or potassium ferrocyanide can be selected as redox mediators at a concentration of 0.1-0.5 g / L to promote iron oxidation or reduction and improve iron removal efficiency.

[0032] Furthermore, the separation and recycling step in step S5 includes:

[0033] S51. Filtration is performed through a filter membrane with a pore size of 0.22 μm;

[0034] S52. Wash the hard carbon powder with an acetic acid solution of pH 4.0;

[0035] S53. The washed hard carbon powder is vacuum dried at 70°C;

[0036] S54. Process the filtrate obtained by filtration, recover the iron ions therein, and recycle 20-50% of the filtrate.

[0037] The purpose of separation and recovery is to separate the iron-removed hard carbon material from the bacterial solution and recover valuable substances. After the reaction, solid and liquid are separated by filtration. A suitable filter membrane is selected, such as one with a pore size of 0.22 μm, and the filtration pressure is 0.1-0.3 MPa. Then, the hard carbon powder is washed with deionized water or a weakly acidic solution to remove residual bacteria and culture medium. The washing solution can be deionized water or a pH 4.0 acetic acid solution, etc., and the washing is performed 2-3 times, with each washing lasting 15-30 minutes, and the amount of washing solution used each time is 5-10 times the mass of hard carbon. The washed hard carbon powder is dried at 60-80℃ to constant weight to obtain the iron-removed bagasse hard carbon anode material. The preferred drying temperature is 70℃, and the drying method can be vacuum drying or oven drying, with a drying time of 8-12 hours. The filtrate obtained from filtration is processed to recover iron ions and other valuable substances, and part of the filtrate is recycled to reduce costs. Treatment methods include chemical precipitation, ion exchange, and membrane separation. Chemical precipitation involves adding sodium hydroxide or lime to precipitate iron ions; ion exchange uses ion exchange resins to adsorb iron ions; and membrane separation uses ultrafiltration or reverse osmosis membranes to separate iron ions. The treated filtrate, after being supplemented with nutrients and its pH adjusted, can be recycled as a culture medium at a rate of 20-50%.

[0038] Furthermore, the functional enhancing microbial agent is selected from at least one of Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Burkholderia cepacia, Sulfobacillus thermosulfidooxidans, Acidiphilium spp., Pseudomonasspp., and Shewanella spp.

[0039] Furthermore, when the hard carbon anode material prepared by the above process is applied to the anode of a sodium-ion battery, the initial coulombic efficiency is 89% and the specific capacity is increased to 330 mAh / g.

[0040] This invention provides a low-cost, green iron removal process for sugarcane bagasse hard carbon anode materials based on bacterial biological methods, which has the following significant advantages:

[0041] (1) Significantly reduced iron removal costs. This invention utilizes bacteria for biological iron removal, replacing the traditional high-concentration acid washing method, which greatly reduces the material and processing costs of the iron removal process. According to preliminary estimates, the cost of bacterial iron removal using this invention can be reduced to 1500-2000 yuan / ton of hard carbon, far lower than the traditional acid washing method (over 8000 yuan / ton), representing a cost reduction of 75%.

[0042] (2) Significantly reduced environmental pollution: This invention avoids the use of large amounts of high-concentration acid, reducing the generation of acidic wastewater at the source and lowering environmental pollution. Compared with the traditional acid washing method, this invention generates a significantly reduced amount of waste liquid, and the concentration of harmful substances in the waste liquid is significantly reduced, alleviating the pressure on wastewater treatment and realizing the green and environmentally friendly preparation of sugarcane bagasse hard carbon anode material.

[0043] (3) Achieving efficient iron removal: This invention achieves efficient iron removal by screening and enriching highly efficient iron-loving bacteria and optimizing biological reaction conditions. Experimental results show that the iron content of sugarcane bagasse hard carbon material treated by the process of this invention can be reduced to 60 ppm or even lower, meeting the strict requirements for iron content of battery anode materials.

[0044] (4) Achieving resource utilization: This invention achieves resource utilization of waste through filtrate recovery, further reducing costs, minimizing environmental pollution, and improving resource utilization. The recovered iron ions can be used to prepare other chemical products, and the recycled filtrate can be used as a culture medium, reducing the consumption of culture medium.

[0045] (5) Simple operation and easy to industrialize: The process of this invention is simple to operate and easy to control. It does not require complex equipment and process conditions, making it suitable for industrial production and improving production efficiency.

[0046] (6) Strong adaptability of microbial community and synergistic effect: This invention screens iron-oxidizing / adsorption bacteria from the natural microbial community attached to sugarcane bagasse itself, which saves the cost of purchasing exogenous microbial strains, improves the adaptability of microbial community, and further improves iron removal efficiency by utilizing the synergistic effect of symbiotic microbial community.

[0047] (7) Improved electrochemical performance: The electrochemical performance of the bagasse hard carbon material after being treated by the process of this invention is significantly improved. The first coulombic efficiency of the sodium ion hard carbon anode material is increased by 89%, and the specific capacity is increased to 330 mAh / g.

[0048] In summary, the low-cost, green iron removal process for sugarcane bagasse hard carbon anode material based on bacterial biological methods provided by this invention has significant economic, environmental, and social benefits, and provides strong support for the sustainable development of new energy materials. Detailed Implementation

[0049] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0050] Example 1

[0051] A low-cost iron removal process for sugarcane bagasse hard carbon anode materials based on bacterial biological methods includes the following steps:

[0052] S1. Sugarcane bagasse pretreatment: Take 10 kg of fresh sugarcane bagasse (provided by COFCO Chongzuo Sugar Industry Co., Ltd., moisture content ≤15%), place it in a tube furnace, and pre-carbonize it at 550℃ under nitrogen atmosphere at a rate of 8℃ / min for 2 hours (nitrogen flow rate 80 mL / min). The resulting pre-carbonized product is pulverized by a planetary ball mill (zirconia balls, ball-to-material ratio 10:1, rotation speed 250 rpm, time 1.5 hours) to obtain hard carbon powder with a particle size of 450 mesh (D50 = 28 μm).

[0053] S2. Source and preparation of microbial strains:

[0054] S21. In the compost enrichment stage, crushed sugarcane bagasse (particle size 1.5cm, moisture content up to 60%) was mixed with rice bran (C / N = 28:1), and inoculated with 0.5% exogenous bacterial agent (strains purchased from the China General Microbiological Culture Collection Center: Acidithiobacillus ferrooxidans 0.1%, Leptospirillum ferrooxidans 0.2%, Burkholderia cepacia 0.2%). The compost was enriched for 10 days under the conditions of 45℃, 60% humidity, dissolved oxygen 1.2mg / L, and pH 6.5 (20mM phosphate buffer), and the compost was turned over every 48 hours.

[0055] S22. Isolation and Identification of Functional Strains: Samples were taken in the later stages of enrichment culture, and single colonies were isolated and purified using selective culture media. The dominant strains were identified morphologically, physiologically and biochemically, and through 16S rRNA gene sequence analysis to obtain iron-loving functional strains encompassing multiple genera and species. Multiple samples were taken in the later stages of enrichment (days 7, 10, and 14). Single colonies were isolated and purified using the dilution plating method or streak plate method on a basal salt medium containing ferric citrate / ferric oxide (pH 6.0-7.0). Colonies with diverse morphologies were selected for purification and culture, and their ability to dissolve / oxidize sugarcane bagasse hard carbon powder or synthetic iron oxides in liquid culture media was preliminarily screened. Highly active dominant strains were identified using methods including morphological observation, physiological and biochemical characterization (Gram staining, oxidase, catalase, carbon source utilization, iron metabolism capacity testing), and 16S rRNA gene sequence analysis. The identification results cover multiple genera and species, including indigenous genera such as Bacillus, Pseudomonas, Acinetobacter, and Streptomyces, as well as representative strains of introduced genera such as Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, and Burkholderia cepacia.

[0056] S23. Construction and Adaptation of Composite Microbial Community: The construction and adaptation process of the composite microbial community in step S23 is as follows: 3-5 functionally complementary strains obtained through isolation and identification are selected to construct a composite functional microbial community. This community is placed in a culture medium containing readily available iron and sugarcane bagasse hard carbon powder for gradient pressure acclimation. The concentration of readily available iron is gradually reduced by 0.2-0.5 g / L / generation, while the amount of sugarcane bagasse hard carbon powder added is increased by 0.1-0.5 g / L / generation. After 5-10 generations of subculturing, the metabolic efficiency of the microbial community on iron impurities in the sugarcane bagasse hard carbon is improved. A strain library of highly active strains (including indigenous dominant bacteria and introduced functional bacteria) is established. Based on the results of tests on the iron metabolism mechanism (oxidation, dissolution), growth compatibility, and synergistic effects of the strains, 3-5 functionally complementary strains are selected and mixed in a specific ratio to construct the target composite functional microbial community. To enhance its adaptability to sugarcane bagasse hard carbon and its iron removal efficiency, gradient pressure acclimatization was conducted: a) cultured in a medium containing a small amount of FeSO4 (1-2 g / L) and a small amount of hard carbon powder (0.1-0.5 g / L); b) the FeSO4 concentration was gradually reduced (by 0.2-0.5 g / L each time), while the amount of hard carbon powder was increased (by 0.1-0.5 g / L each time); c) after 5-10 generations, the complex microbial community was finally adapted to an environment where sugarcane bagasse hard carbon powder was the main or sole iron source. Adaptability was assessed by monitoring microbial community growth (OD600) and iron conversion rate.

[0057] S24. Preparation of bacterial suspension: The domesticated multifunctional bacterial population was cultured on a large scale. The bacterial cells were collected by centrifugation, washed with sterile physiological saline or buffer, and resuspended. The concentration of the bacterial suspension was adjusted to an OD600 value of 1.0-2.0. The domesticated multifunctional bacterial population was then cultured on an optimized medium. Culture conditions: temperature 25-35℃, pH 2.0-7.0 (adjusted according to the dominant bacterial population; slightly acidic pH 5.5-6.5 is preferred), stirring speed 100-200 rpm, cultured to the late logarithmic stage (OD600 0.8-1.5). The bacterial cells were collected by centrifugation (4000-6000g, 10-15 min), washed 1-2 times with sterile physiological saline (0.85% NaCl) or buffer (pH 6.0 phosphate buffer), resuspended, and the concentration adjusted to an OD600 value of 1.0-2.0 to obtain a highly efficient multifunctional bacterial suspension for the biological iron removal step.

[0058] S3. Biological iron removal: Mix 100g of hard carbon powder with 1.5L of bacterial suspension (solid-liquid ratio 1:15) in a bioreactor, control the temperature at 29-31℃ and pH at 6.2 (maintained by automatic acid and alkali addition), and react for 72 hours at a speed of 120rpm and an aeration rate of 0.3VVM.

[0059] S4. Enhanced iron removal: Add 0.5 g / L citric acid at the beginning of the reaction, and add 0.3 g / L potassium ferrocyanide twice at 0 hours and 36 hours. Control the redox potential at 430-47020 mV (vs. Ag / AgCl electrode) throughout the process.

[0060] S5. Separation and Recovery: The reaction solution was filtered under pressure (0.2 MPa) through a 0.22 μm PVDF filter membrane. The hard carbon powder was washed three times with pH 4.0 acetic acid solution (10 times the volume each time, shaken for 20 min each time), and then vacuum dried at 70℃ for 10 hours until the moisture content was ≤0.5%. NaOH was added to the filtrate to pH 9.0 to precipitate and recover iron (recovery rate >95%). 40% of the filtrate was replenished with nutrients and recycled.

[0061] Performance testing methods

[0062] Iron content determination: According to the national standard GB / T36590-2018, 0.1g of sample was digested in 5mL HNO3 / HF (3:1) microwave digestion (200℃, 30min), and the volume was adjusted to 50mL. The sample was then filtered through a 0.45μm filter membrane, and the iron ion concentration was detected by ICP-MS.

[0063] Electrochemical testing: Hard carbon, acetylene black, and PVDF were mixed in an 8:1:1 ratio to form a paste, which was then coated onto copper foil (area loading 3 mg / cm²). 2A button cell battery was assembled using a sodium sheet as the counter electrode, 1M NaClO4 / EC:PC (1:1) + 5% FEC as the electrolyte, and glass fiber as the separator. Charge-discharge tests were conducted on the Newway testing system at a current density of 0.1C (1C = 300mA / g) (voltage range 0.01-2.5V). Specific capacity = discharge capacity / mass of active material, and initial coulombic efficiency = (initial discharge capacity / initial charge capacity) × 100%. The iron content was 58ppm. When applied to the negative electrode of a sodium-ion battery, the initial coulombic efficiency was 89%, and the specific capacity increased to 330mAh / g.

[0064] Comparative Example 1

[0065] In Comparative Example 1, *Acidithiobacillus ferrooxidans* was replaced with *Escherichia coli* DH5α (ATCC 53868), with all other parameters identical to those in Example 1. Test results showed that the residual iron content increased to 1250 ppm (58 ppm in Example 1), the initial coulombic efficiency decreased to 72% (89% in Example 1), the specific capacity decreased to 285 mAh / g (330 mAh / g in Example 1), and the capacity retention after 300 cycles was less than 80% (>90% after 500 cycles in Example 1). The root cause was that *E. coli* lacked an iron oxidase system and the ability to secrete ferrophosphate, thus failing to effectively dissolve and convert iron impurities in hard carbon.

[0066] Cost verification: The traditional pickling process (30% hydrochloric acid + waste liquid treatment) costs about 8,000 yuan / ton of hard carbon; the cost of this process (bacterial culture + citric acid + power consumption) has been verified in pilot tests to be 1,750 yuan / ton of hard carbon, with a cost reduction rate of 78.1%, and there is no acidic wastewater discharge.

Claims

1. A low-cost iron removal process for sugarcane bagasse hard carbon anode materials based on bacterial biological methods, characterized in that, Includes the following steps: S1. Pre-treatment of sugarcane bagasse; S2. Source and preparation of bacterial strains; S3. Biological iron removal; S4. Enhanced iron removal; S5. Separation and recycling; Step S2 includes the following steps: S21. Enrichment and functional enhancement of sugarcane bagasse compost; S22. Functional strain isolation and identification: Samples were taken in the later stage of enrichment culture, and single colonies were isolated and purified by selective culture medium. The dominant strains were identified by morphology, physiology and biochemistry and 16S rRNA gene sequence to obtain iron-loving functional strains containing multiple genera and species. S23. Construction and adaptive domestication of complex microbial communities; S24. Preparation of bacterial suspension: The domesticated complex functional bacterial group was cultured in an expanded manner, the bacterial cells were collected by centrifugation, washed and resuspended with sterile physiological saline or buffer, and the concentration of bacterial suspension was adjusted to OD600 value of 1.0-2.

0. The sugarcane bagasse composting enrichment and functional enhancement steps in step S21 include: S211. Collect fresh sugarcane bagasse, crush it to a particle size ≤2cm, and adjust the initial moisture content to 55-65%; S212. Place the pretreated bagasse in a temperature- and gas-controlled environment; S213. Inoculation-enhancing microbial agent, inoculation amount is 0.1-1.0% of the dry weight of raw materials; S214. The enrichment conditions are controlled as follows: temperature 40-50℃, dissolved oxygen 0.5-2.0mg / L, initial C / N ratio (25-30):1, initial pH 5.5-7.5, humidity 55-65%, and the pile is turned over once every 48 hours. S215. The enrichment culture period is 7-14 days; The construction and adaptation process of the composite microbial community in step S23 is as follows: 3-5 functionally complementary strains obtained through isolation and identification are selected to construct a composite functional microbial community. The composite functional microbial community is placed in a culture medium containing readily available iron source and sugarcane bagasse hard carbon powder for gradient pressure adaptation. The concentration of readily available iron source is gradually reduced by 0.2-0.5 g / L / generation, while the amount of sugarcane bagasse hard carbon powder added is increased by 0.1-0.5 g / L / generation. After 5-10 generations of subculturing, the metabolic efficiency of the microbial community on iron impurities in sugarcane bagasse hard carbon is improved.

2. The low-cost iron removal process for sugarcane bagasse hard carbon anode material according to claim 1, characterized in that, The sugarcane bagasse pretreatment process in step S1 is as follows: the sugarcane bagasse is pre-carbonized in an oxygen-free atmosphere at 550°C, and then the pre-carbonized sugarcane bagasse is crushed to achieve a particle size of 450~550 mesh.

3. The low-cost iron removal process for sugarcane bagasse hard carbon anode material according to claim 1, characterized in that, The biological iron removal step in step S3 is as follows: the pretreated bagasse hard carbon powder is mixed with bacterial suspension at a solid-liquid ratio of 1:15, and the biological reaction is carried out for 28-72 hours at a temperature of 30℃ and a pH of 6.0-6.

5.

4. The iron removal process for sugarcane bagasse hard carbon anode material according to claim 1, characterized in that, The enhanced iron removal step in step S4 is as follows: during the biological reaction process, citric acid or oxalic acid is added at a concentration of 0.5%, and iron removal is enhanced by controlling the redox potential of the system.

5. The low-cost iron removal process for sugarcane bagasse hard carbon anode material according to claim 1, characterized in that, The separation and recovery step in step S5 includes: S51. Filtration is performed through a filter membrane with a pore size of 0.22 μm; S52. Wash the hard carbon powder with an acetic acid solution of pH 4.0; S53. The washed hard carbon powder is vacuum dried at 70°C; S54. Process the filtrate obtained by filtration, recover the iron ions therein, and recycle 20-50% of the filtrate.

6. The low-cost iron removal process for sugarcane bagasse hard carbon anode material according to claim 1, characterized in that, The functional enhancement microbial agent is selected from at least one of the following: thiobacillus ferrooxidans, leptospira ferrooxidans, Burkholderia cepacia, thiobacillus thermophilus, acidophilus, pseudomonas, and Shewanella.

7. The low-cost iron removal process for sugarcane bagasse hard carbon anode material according to claim 1, characterized in that, When the prepared hard carbon anode material is applied to the anode of a sodium-ion battery, the initial coulombic efficiency is 89% and the specific capacity is increased to 330 mAh / g.