A method for treating acid mine drainage using composite biochar

Abstract

The application discloses a method for treating acid mine wastewater by using composite biochar and relates to the technical field of wastewater treatment. The application discloses that the composite biochar is used for adsorbing and treating acid mine wastewater. The preparation method of the composite biochar comprises the following steps: Fe-Al bimetallic oxide is used to modify the surface of biochar, and a chitosan layer and a carboxymethyl cellulose layer are alternately deposited on the surface of the modified biochar to obtain modified biochar; acidophilic ferrous-oxidizing bacteria are adsorbed by using the modified biochar to obtain microbial-loaded biochar; the surface of the microbial-loaded biochar is induced to form a hydroxyapatite mineralization film to obtain acid-resistant microbial-loaded biochar; and finally, the acid-resistant microbial-loaded biochar is embedded and fixed to obtain the composite biochar. The composite biochar prepared in the application can stably treat acid mine wastewater for a long time, and is convenient to recycle and utilize.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for treating acidic mine wastewater using composite biochar. Background Technology

[0002] With the rapid development of society and the economy, human demand for mineral resources is increasing. The environmental pollution caused by mining activities, tailings accumulation, and smelting cannot be ignored, the most typical example being acidic mine wastewater. Acidic mine wastewater is discharge with a pH less than 5 produced during and after the mining of non-ferrous metal mines and coal mines, when sulfide minerals in waste rock and tailings are oxidized by thiobacilli (mainly acidophilic ferrooxidizing thiobacilli). Extreme acidity (pH 2.0-3.5) and the presence of abundant sulfate and ferrous ions, along with dissolved large amounts of toxic metal elements (such as Cd, Pd, Cu, Zn, Ni, As, etc.), are key characteristics of acidic mine wastewater. Due to its high acidity, high sulfate concentration, and diverse and high content of heavy metal ions, and the fact that most mines are located upstream of rivers and lakes, if acidic mine wastewater carries large amounts of heavy metals and high concentrations of acid into the environment, it will lead to water acidification, affect the normal survival of aquatic microorganisms, and cause serious negative impacts on mining production and the ecological environment.

[0003] Currently, the main treatment methods used domestically and internationally include chemical methods, adsorption methods, and microbial methods. Among these, chemical methods primarily neutralize acidic mine wastewater by adding reagents, removing heavy metal ions through precipitation. Due to the different types of reagents used, chemical methods are basically divided into neutralization and sulfidation methods. Neutralization involves adding alkaline substances such as limestone and caustic soda, causing metal ions to precipitate with hydroxide ions, thus purifying the water. However, this generates a large amount of calcium sulfate solid waste, which can easily cause secondary pollution. Sulfidation involves adding sulfiding agents to the wastewater, removing heavy metals through precipitation. However, during the wastewater treatment process, the precipitation of metal ions also generates some sulfur dioxide (S). 2- If highly toxic gases (such as H2S) are produced, they will pollute the atmosphere. Adsorption methods primarily remove dual pollutants through adsorption and precipitation; however, the adsorption capacity of adsorbents is limited, making it difficult to treat large quantities of acidic mine wastewater. Microbial methods often employ sulfate-reducing bacteria, which oxidize sulfate ions to sulfur dioxide (S). 2-Microbial methods reduce sulfate ion concentration and the alkaline substances produced during the process can neutralize the acidity of acidic mine wastewater. Wastewater treatment via microbial methods is characterized by low cost, wide applicability, and environmental friendliness. However, microbial methods still have some drawbacks, such as reduced microbial activity and strict requirements for pH and temperature during biodegradation. Therefore, expanding the application scope and pathways of microbial methods, maintaining high microbial activity, and protecting them from external environmental damage have become current research priorities. Summary of the Invention

[0004] The purpose of this invention is to provide a method for treating acidic mine wastewater using composite biochar, thereby solving the following technical problems:

[0005] Microorganisms have strict requirements for pH and temperature in the biodegradation process. If they are added directly to wastewater, their biological activity is easily reduced.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for treating acidic mine wastewater using composite biochar includes the following steps: placing composite biochar in the acidic mine wastewater for adsorption treatment;

[0008] The preparation method of composite biochar includes the following steps:

[0009] S1: The Fe-Al bimetallic oxide modified biochar was immersed in chitosan solution and then washed with water. The washed bimetallic oxide modified biochar was immersed in carboxymethyl cellulose solution and then washed with water. The above steps were repeated 3-5 times to obtain modified biochar.

[0010] S2: Add modified biochar and composite functional bacterial solution to the reaction vessel, adjust the pH to 7-7.5, perform adsorption treatment, static culture, and water washing to obtain microbial-loaded biochar;

[0011] S3: Microbial-supported biochar, calcium chloride dihydrate, dipotassium hydrogen phosphate, and deionized water are mixed together, and the temperature is controlled at 35-40℃. The mixture is stirred and reacted for 24-48 hours. After filtration, washing, and drying, acid-resistant microbial-supported biochar is obtained.

[0012] S4: Add sodium alginate solution, attapulgite clay nanosheet suspension, and polyethyleneimine solution to a reaction vessel for dispersion, add acid-resistant microbial-supported biochar, and continue stirring for 15-30 min to obtain a mixed solution; drop the mixed solution into CaCl2 solution, allow it to stand for crosslinking for 0.5-2 h, wash, and freeze-dry to obtain composite biochar.

[0013] As a further aspect of the present invention: the chitosan solution in S1 is a 1-3 g / L chitosan-acetic acid aqueous solution; the acetic acid aqueous solution contains 1 wt%-3 wt% acetic acid; the carboxymethyl cellulose solution is a 1-3 g / L carboxymethyl cellulose aqueous solution.

[0014] As a further aspect of the present invention: the composite functional bacterial solution in S2 has a live bacteria concentration of 10. 8 -10 9 The CFU / mL aqueous solution of *Thiobacillus ferrooxidans*; the addition ratio of modified biochar and composite functional bacterial solution is 10g:100-200mL; the specific steps of the adsorption treatment are: place in a constant temperature shaker at 30-35℃ with a rotation speed of 150-200rpm for 4-24h.

[0015] As a further aspect of the present invention, the specific steps of static cultivation are as follows: the modified biochar after adsorption of microorganisms is transferred to an Erlenmeyer flask containing a low-salt culture medium and placed in an anaerobic incubator for static cultivation for 24 hours, allowing the microorganisms to colonize and multiply within the pores. After cultivation, the surface free microorganisms are gently rinsed with sterile water to obtain microbially loaded modified biochar.

[0016] As a further aspect of the present invention: the addition ratio of microbially loaded biochar, calcium chloride dihydrate, dipotassium hydrogen phosphate, and deionized water in S3 is 10g: 2-2.5g: 1.5-2g: 50-100mL.

[0017] As a further embodiment of the present invention: the sodium alginate solution is a 2-5 wt% sodium alginate aqueous solution; the attapulgite clay nanosheet suspension is a 0.5-1 wt% attapulgite clay nanosheet aqueous solution; and the polyethyleneimine solution is a 1-2 wt% polyethyleneimine aqueous solution.

[0018] As a further embodiment of the present invention: the addition ratio of sodium alginate solution, attapulgite clay nanosheet suspension, polyethyleneimine solution, and acid-resistant microbial-loaded biochar in S4 is 20-50mL: 5-10mL: 5-10mL: 10g.

[0019] As a further aspect of the present invention: the CaCl2 solution is a 2-3 wt% CaCl2 solution; the volume ratio of the mixed solution to the CaCl2 solution is 30-50:100.

[0020] As a further aspect of the present invention, the preparation method of Fe-Al bimetallic oxide modified biochar includes the following steps:

[0021] A1: Biochar is obtained by crushing, acid leaching, drying, and pyrolyzing biomass raw materials;

[0022] A2: Ferric chloride hexahydrate, aluminum chloride hexahydrate, deionized water, and biochar were mixed and microwaved, then centrifuged, washed, and dried to obtain Fe-Al bimetallic oxide modified biochar.

[0023] As a further aspect of the present invention: the addition ratio of ferric chloride hexahydrate, aluminum chloride hexahydrate, deionized water, and biochar is 1.35-4.05g: 0.757-2.27g: 100mL: 10-20g;

[0024] The specific steps of the microwave reaction are as follows: microwave power 300-500W, temperature control 60-80℃, reaction time 15-30min.

[0025] As a further aspect of the present invention: the biomass raw material consists of 50-60 wt% corn stalks and 40-50 wt% walnut shells; the porosity is improved by the complementarity of lignin and cellulose;

[0026] Crushing specifically refers to breaking biomass raw materials to 2-5mm;

[0027] Citric acid pretreatment specifically involves treating with a 3-8 wt% citric acid aqueous solution for 12-24 hours to remove ash and impurities;

[0028] The drying process involves drying at 70-80℃ to constant weight.

[0029] The pyrolysis process is as follows: In a nitrogen atmosphere, the temperature is increased at a rate of 1-10℃ / min to 300-600℃ and held for 0.5-1h; the temperature is increased at a rate of 5-10℃ / min to 600-700℃ and activated by introducing water vapor for 0.5-1h to generate a hierarchical porous structure.

[0030] The beneficial effects of this invention are:

[0031] This application utilizes the prepared composite biochar to treat acidic mine wastewater, achieving the effects of removing acidic and heavy metals, reducing sulfate, and stabilizing microorganisms.

[0032] (1) Fe-Al bimetallic oxide coating loaded on biochar surface

[0033] This application utilizes microwave-assisted loading of a Fe-Al bimetallic oxide coating onto the surface of biochar. Under acidic conditions, the coating not only consumes hydrogen ions in wastewater through a protonation reaction, increasing the pH value, but also effectively increases the hydroxyl density on the biochar surface, enhancing the acid buffering capacity of the composite biochar. The Fe-Al bimetallic oxide coating loaded on the biochar surface can undergo coordination complexation reactions with heavy metal ions to form stable complexes. Furthermore, under acidic conditions, the coating partially dissolves, releasing iron and aluminum ions that react with phosphate ions in the wastewater to precipitate iron phosphate, aluminum phosphate, etc., resulting in co-precipitation of heavy metal ions. The Fe-Al bimetallic oxide coating loaded on the biochar surface exhibits excellent electron transport capabilities, promoting electron transfer during the metabolism of *Acidithiobacillus ferrooxidans* and improving sulfate reduction efficiency.

[0034] (2) Alternating deposition of chitosan and carboxymethyl cellulose layers on the surface of Fe-Al bimetallic oxide modified biochar

[0035] This application describes the deposition of chitosan and carboxymethyl cellulose layers on the surface of Fe-Al bimetallic oxide modified biochar. Chitosan is a cationic polymer, and carboxymethyl cellulose is an anionic polymer. Their alternating deposition on the biochar surface forms a gradient structure of alternating positive and negative charge layers, creating an electrostatic attraction field that guides *Acidithiobacillus ferrooxidans* (SRB) to migrate to the surface and distribute evenly. The negatively charged surface of SRB creates electrostatic attraction with the positive charge of the chitosan layer and electrostatic repulsion with the negative charge of the carboxymethyl cellulose layer. This balance of attraction and repulsion allows SRB to form a monolayer adsorption on the biochar surface, preventing microbial aggregation. Both chitosan and carboxymethyl cellulose are natural polymers with good biocompatibility, providing a suitable attachment substrate for SRB. Simultaneously, the porous structure formed by the alternating layer deposition provides protection for SRB.

[0036] (3) Microbial loading of biochar surface induces the formation of hydroxyapatite mineralization film

[0037] This application describes the induced formation of a hydroxyapatite mineralization film on the surface of microbially supported biochar. This film exhibits good chemical stability and effectively blocks H₂. + It directly invades microbial cells, providing a suitable metabolic environment for *Thiobacillus ferrooxidans*. Hydroxyapatite can slowly release Ca... 2+ and PO4 3- Ca 2+ It can react with SO4 in wastewater 2- Formation of slightly soluble calcium sulfate precipitate, reducing sulfate concentration; PO4 3-It can form phosphate heavy metal precipitates with heavy metal ions, further enhancing the heavy metal removal effect. Meanwhile, Ca... 2+ As a trace element required for the metabolism of *Acidithiobacillus ferrooxidans*, it can promote microbial activity. The hydroxyapatite mineralization membrane and the Fe-Al bimetallic oxide coating on the biochar surface are bonded by hydroxyl bonds, exhibiting high bonding strength and resisting detachment during dynamic treatment. Simultaneously, the porous structure of the mineralization membrane allows for the absorption of wastewater components (H... + SO4 2- The entry of heavy metal ions does not affect the microbial metabolism and adsorption reaction.

[0038] (4) Acid-resistant microbial-loaded biochar was placed in a composite gel for solidification treatment.

[0039] This application utilizes sodium alginate, attapulgite clay nanosheets, and polyethyleneimine as raw materials to prepare a composite gel; the carboxyl groups in sodium alginate can react with Ca... 2+ An ionic cross-linking reaction occurs, forming a three-dimensional network structure. The amino groups in polyethyleneimine can form hydrogen bonds with the carboxyl groups of sodium alginate, and simultaneously form coordination bonds with the hydroxyl groups on the surface of attapulgite clay nanosheets. The synergistic effect of these three raw materials effectively improves the mechanical strength of the gel. Polyethyleneimine is a cationic polymer, which can neutralize some of the negative charge on the gel surface and reduce H+ under acidic conditions. + The composite gel exhibits excellent acid resistance and dispersibility, enhancing its chemical stability and preventing significant swelling or breakage even after 30 days of continuous operation under acidic conditions. Furthermore, the porous structure of the composite gel effectively traps *Thiobacillus ferrooxidans*, ensuring sufficient contact between wastewater and microorganisms, as well as the adsorption sites.

[0040] The composite biochar prepared in this application involves a multi-mechanism synergistic process of adsorption, neutralization, biological metabolism, and precipitation for treating acidic mine wastewater. The synergistic effect of the Fe-Al bimetallic oxide coating and the hydroxyapatite mineralization membrane determines its extremely strong acid buffering capacity and high heavy metal removal efficiency. The alternating deposition of chitosan and carboxymethyl cellulose layers on the surface ensures uniform microbial loading, and the combination of the mineralization membrane's protection and gel immobilization achieves stable microbial activity and sustained treatment efficiency. The synergistic cross-linking mechanism of the composite gel enhances the material's mechanical strength, making it easy to recycle and reusable. The synergistic effect of these mechanisms ultimately achieves efficient, stable, and sustainable treatment of acidic mine wastewater using composite biochar. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1: A method for preparing Fe-Al bimetallic oxide modified biochar, comprising the following steps:

[0043] A1: 60g of corn stalks and 40g of walnut shells were mixed and crushed to 2mm, treated with 3wt% citric acid aqueous solution for 12h, and dried at 70℃ to constant weight; under nitrogen atmosphere, the temperature was raised to 300℃ at a rate of 5℃ / min and held for 1h; the temperature was raised to 600℃ at a rate of 5℃ / min and activated with steam for 0.5h to obtain biochar;

[0044] A2: 1.35g ferric chloride hexahydrate, 0.757g aluminum chloride hexahydrate, 100mL deionized water, and 10g biochar were mixed and added to a microwave reactor. The microwave power was 300W, the temperature was controlled at 60℃, and the reaction was carried out for 15min. After centrifugation, washing, and drying, Fe-Al bimetallic oxide modified biochar was obtained.

[0045] The preparation method of composite biochar includes the following steps:

[0046] S1: Using chitosan (average molecular weight 3.5 x 10⁻⁶) 6 Prepare a 1 g / L chitosan-acetic acid aqueous solution by mixing chitosan (95% deacetylation degree) with a 1 wt% aqueous solution of acetic acid; carboxymethyl cellulose (molecular weight 4.2 x 10) 8 Prepare a 1 g / L carboxymethyl cellulose aqueous solution with deionized water (degree of substitution 0.7).

[0047] 10g of Fe-Al bimetallic oxide modified biochar was immersed in 100mL of chitosan solution for 30min and then washed with water. The washed bimetallic oxide modified biochar was then immersed in 100mL of carboxymethyl cellulose solution for 30min and then washed with water. The above steps were repeated 4 times to obtain modified biochar.

[0048] S2: Add 10g of modified biochar and 100mL of live bacteria at a concentration of 1×10⁻⁶. 9An aqueous solution of *Thiobacillus ferrooxidans* (CFU / mL) was added to the reaction vessel, the pH was adjusted to 7, and the mixture was placed in a constant temperature shaker at 30℃ and 150 rpm for 24 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static cultivation for 24 h to allow microorganisms to colonize and multiply within the pores. After cultivation, the surface of free microorganisms was rinsed with sterile water to obtain microbially loaded modified biochar.

[0049] S3: Mix 10g of microbial-supported biochar, 2g of calcium chloride dihydrate, 1.5g of dipotassium hydrogen phosphate, and 50mL of deionized water. Control the temperature at 35℃ and stir for 24h. Filter, wash, and dry to obtain acid-resistant microbial-supported biochar.

[0050] S4: Add 25 mL of 2 wt% sodium alginate aqueous solution, 5 mL of 0.5 wt% attapulgite clay nanosheet suspension, and 5 mL of 1 wt% polyethyleneimine aqueous solution to the reaction vessel for dispersion. Add 10 g of acid-resistant microbial-supported biochar and continue stirring for 15-30 min to obtain a mixed solution. Drop the mixed solution into 100 mL of 2 wt% CaCl2 solution, allow it to stand for crosslinking for 0.5 h, wash, and freeze-dry (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0051] Example 2: A method for preparing Fe-Al bimetallic oxide modified biochar, comprising the following steps:

[0052] A1: 60g of corn stalks and 40g of walnut shells were mixed and crushed to 4mm, treated with 5wt% citric acid aqueous solution for 18h, and dried at 75℃ to constant weight; under nitrogen atmosphere, the temperature was raised to 500℃ at a rate of 5℃ / min and held for 0.5h; the temperature was raised to 650℃ at a rate of 10℃ / min and activated with steam for 0.5h to obtain biochar;

[0053] A2: 3g of ferric chloride hexahydrate, 1.5g of aluminum chloride hexahydrate, 100mL of deionized water, and 15g of biochar were mixed and added to a microwave reactor. The microwave power was 400W, the temperature was controlled at 70℃, and the reaction was carried out for 20min. After centrifugation, washing, and drying, Fe-Al bimetallic oxide modified biochar was obtained.

[0054] The preparation method of composite biochar includes the following steps:

[0055] S1: Using chitosan (average molecular weight 3.5 x 10⁻⁶) 6 Prepare a 2 g / L chitosan-acetic acid aqueous solution by mixing chitosan (95% deacetylation degree) with a 2 wt% acetic acid aqueous solution; carboxymethyl cellulose (molecular weight 4.2 x 10⁻⁶) 8 Prepare a 2 g / L carboxymethyl cellulose aqueous solution with deionized water (degree of substitution 0.7).

[0056] 10g of Fe-Al bimetallic oxide modified biochar was immersed in 100mL of chitosan solution for 45min and then washed with water. The washed bimetallic oxide modified biochar was then immersed in 100mL of carboxymethyl cellulose solution for 45min and then washed with water. The above steps were repeated 4 times to obtain modified biochar.

[0057] S2: Add 10g of modified biochar and 150mL of live bacteria at a concentration of 1×10⁻⁶. 9 A CFU / mL aqueous solution of *Thiobacillus ferrooxidans* was added to the reaction vessel, the pH was adjusted to 7, and the mixture was placed in a constant temperature shaker at 35℃ and a rotation speed of 200 rpm for 18 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static incubation for 24 h to allow microorganisms to colonize and multiply within the pores. After incubation, the surface free microorganisms were rinsed with sterile water to obtain microbially loaded modified biochar.

[0058] S3: 10g of microbial-supported biochar, 2.5g of calcium chloride dihydrate, 1.7g of dipotassium hydrogen phosphate, and 70mL of deionized water were mixed and stirred at 35℃ for 48h. The mixture was then filtered, washed, and dried to obtain acid-resistant microbial-supported biochar.

[0059] S4: 25 mL of 2 wt% sodium alginate aqueous solution, 5 mL of 0.5 wt% attapulgite clay nanosheet suspension, and 5 mL of 1 wt% polyethyleneimine aqueous solution were added to the reaction vessel and dispersed. 10 g of acid-resistant microbial-supported biochar was added, and the mixture was stirred for 20 min to obtain a mixed solution. The mixed solution was then added dropwise to 100 mL of 2 wt% CaCl2 solution, allowed to stand for crosslinking for 1 h, washed, and freeze-dried (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0060] Example 3: A method for preparing Fe-Al bimetallic oxide modified biochar, comprising the following steps:

[0061] A1: 60g of corn stalks and 40g of walnut shells were mixed and crushed to 5mm, treated with 8wt% citric acid aqueous solution for 24h, and dried at 80℃ to constant weight; in a nitrogen atmosphere, the temperature was raised to 600℃ at a rate of 10℃ / min and held for 1h; the temperature was then raised to 700℃ at a rate of 10℃ / min and activated with steam for 1h to obtain biochar;

[0062] A2: 4.05g of ferric chloride hexahydrate, 2.27g of aluminum chloride hexahydrate, 100mL of deionized water, and 20g of biochar were mixed and added to a microwave reactor. The microwave power was 500W, the temperature was controlled at 80℃, and the reaction was carried out for 30min. After centrifugation, washing, and drying, Fe-Al bimetallic oxide modified biochar was obtained.

[0063] The preparation method of composite biochar includes the following steps:

[0064] S1: Using chitosan (average molecular weight 3.5 x 10⁻⁶) 6 Prepare a 3 g / L chitosan-acetic acid aqueous solution by mixing chitosan (95% deacetylation degree) with a 3 wt% acetic acid aqueous solution; carboxymethyl cellulose (molecular weight 4.2 x 10⁻⁶) 8 Prepare a 3 g / L carboxymethyl cellulose aqueous solution with deionized water (degree of substitution 0.7).

[0065] 10g of Fe-Al bimetallic oxide modified biochar was immersed in 100mL of chitosan solution for 60min and then washed with water. The washed bimetallic oxide modified biochar was then immersed in 100mL of carboxymethyl cellulose solution for 60min and then washed with water. The above steps were repeated 4 times to obtain modified biochar.

[0066] S2: Add 10g of modified biochar and 200mL of live bacteria at a concentration of 1×10⁻⁶. 9 An aqueous solution of *Thiobacillus ferrooxidans* (CFU / mL) was added to the reactor, the pH was adjusted to 7.5, and the mixture was placed in a constant temperature shaker at 35℃ and 200 rpm for 24 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static cultivation for 24 h to allow microorganisms to colonize and multiply within the pores. After cultivation, the surface of free microorganisms was rinsed with sterile water to obtain microbially loaded modified biochar.

[0067] S3: Mix 10g of microbial-supported biochar, 2.5g of calcium chloride dihydrate, 2g of dipotassium hydrogen phosphate, and 100mL of deionized water. Control the temperature at 40℃ and stir the reaction for 48h. Filter, wash, and dry to obtain acid-resistant microbial-supported biochar.

[0068] S4: 25 mL of 2 wt% sodium alginate aqueous solution, 5 mL of 0.5 wt% attapulgite clay nanosheet suspension, and 5 mL of 1 wt% polyethyleneimine aqueous solution were added to the reaction vessel and dispersed. 10 g of acid-resistant microbial-supported biochar was added, and the mixture was stirred for 30 min to obtain a mixed solution. The mixed solution was then added dropwise to 100 mL of 3 wt% CaCl2 solution, allowed to stand for crosslinking for 2 h, washed, and freeze-dried (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0069] Comparative Example 1: A method for preparing biochar, comprising the following steps: 60g of corn stalks and 40g of walnut shells are mixed and crushed to 4mm, treated with 5wt% citric acid aqueous solution for 18h, and dried at 75℃ to constant weight; under a nitrogen atmosphere, the temperature is raised to 500℃ at a rate of 5℃ / min and held for 0.5h; the temperature is raised to 650℃ at a rate of 10℃ / min and activated by steam for 0.5h to obtain biochar.

[0070] The preparation method of composite biochar includes the following steps:

[0071] S1: Using chitosan (average molecular weight 3.5 x 10⁻⁶) 6 Prepare a 2 g / L chitosan-acetic acid aqueous solution by mixing chitosan (95% deacetylation degree) with a 2 wt% acetic acid aqueous solution; carboxymethyl cellulose (molecular weight 4.2 x 10⁻⁶) 8 Prepare a 2 g / L carboxymethyl cellulose aqueous solution with deionized water (degree of substitution 0.7).

[0072] 10g of biochar was immersed in 100mL of chitosan solution for 45min and then washed with water. The washed bimetallic oxide modified biochar was immersed in 100mL of carboxymethyl cellulose solution for 45min and then washed with water. The above steps were repeated 4 times to obtain modified biochar.

[0073] S2: Add 10g of modified biochar and 150mL of live bacteria at a concentration of 1×10⁻⁶. 9 A CFU / mL aqueous solution of *Thiobacillus ferrooxidans* was added to the reaction vessel, the pH was adjusted to 7, and the mixture was placed in a constant temperature shaker at 35℃ and a rotation speed of 200 rpm for 18 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static incubation for 24 h to allow microorganisms to colonize and multiply within the pores. After incubation, the surface free microorganisms were rinsed with sterile water to obtain microbially loaded modified biochar.

[0074] S3: 10g of microbial-supported biochar, 2.5g of calcium chloride dihydrate, 1.7g of dipotassium hydrogen phosphate, and 70mL of deionized water were mixed and stirred at 35℃ for 48h. The mixture was then filtered, washed, and dried to obtain acid-resistant microbial-supported biochar.

[0075] S4: 25 mL of 2 wt% sodium alginate aqueous solution, 5 mL of 0.5 wt% attapulgite clay nanosheet suspension, and 5 mL of 1 wt% polyethyleneimine aqueous solution were added to the reaction vessel and dispersed. 10 g of acid-resistant microbial-supported biochar was added, and the mixture was stirred for 20 min to obtain a mixed solution. The mixed solution was then added dropwise to 100 mL of 2 wt% CaCl2 solution, allowed to stand for crosslinking for 1 h, washed, and freeze-dried (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0076] Comparative Example 2: The preparation method of composite biochar includes the following steps:

[0077] S1: 10g of Fe-Al bimetallic oxide modified biochar prepared in Example 2, and 150mL of live bacteria with a concentration of 1×10⁻⁶ 9 A CFU / mL aqueous solution of *Thiobacillus ferrooxidans* was added to the reaction vessel, the pH was adjusted to 7, and the mixture was placed in a constant temperature shaker at 35℃ and a rotation speed of 200 rpm for 18 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static incubation for 24 h to allow microorganisms to colonize and multiply within the pores. After incubation, the surface free microorganisms were rinsed with sterile water to obtain microbially loaded modified biochar.

[0078] S2: 10g of microbial-supported biochar, 2.5g of calcium chloride dihydrate, 1.7g of dipotassium hydrogen phosphate, and 70mL of deionized water were mixed and stirred at 35℃ for 48h. The mixture was then filtered, washed, and dried to obtain acid-resistant microbial-supported biochar.

[0079] S3: 25 mL of 2 wt% sodium alginate aqueous solution, 5 mL of 0.5 wt% attapulgite clay nanosheet suspension, and 5 mL of 1 wt% polyethyleneimine aqueous solution were added to the reaction vessel and dispersed. 10 g of acid-resistant microbial-supported biochar was added, and the mixture was stirred for 20 min to obtain a mixed solution. The mixed solution was then added dropwise to 100 mL of 2 wt% CaCl2 solution, allowed to stand for crosslinking for 1 h, washed, and freeze-dried (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0080] Comparative Example 3: The preparation method of composite biochar includes the following steps:

[0081] S1: Using chitosan (average molecular weight 3.5 x 10⁻⁶) 6 Prepare a 2 g / L chitosan-acetic acid aqueous solution by mixing chitosan (95% deacetylation degree) with a 2 wt% acetic acid aqueous solution; carboxymethyl cellulose (molecular weight 4.2 x 10⁻⁶) 8 Prepare a 2 g / L carboxymethyl cellulose aqueous solution with deionized water (degree of substitution 0.7).

[0082] 10g of Fe-Al bimetallic oxide modified biochar prepared in Example 2 was immersed in 100mL of chitosan solution for 45min and then washed with water. The washed bimetallic oxide modified biochar was immersed in 100mL of carboxymethyl cellulose solution for 45min and then washed with water. The above steps were repeated 4 times to obtain modified biochar.

[0083] S2: Add 10g of modified biochar and 150mL of live bacteria at a concentration of 1×10⁻⁶. 9A CFU / mL aqueous solution of *Thiobacillus ferrooxidans* was added to the reaction vessel, the pH was adjusted to 7, and the mixture was placed in a constant temperature shaker at 35℃ and a rotation speed of 200 rpm for 18 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static incubation for 24 h to allow microorganisms to colonize and multiply within the pores. After incubation, the surface free microorganisms were rinsed with sterile water to obtain microbially loaded modified biochar.

[0084] S3: 25 mL of 2 wt% sodium alginate aqueous solution, 5 mL of 0.5 wt% attapulgite clay nanosheet suspension, and 5 mL of 1 wt% polyethyleneimine aqueous solution were added to the reaction vessel and dispersed. 10 g of microbially loaded modified biochar was added, and the mixture was stirred for 20 min to obtain a mixed solution. The mixed solution was then added dropwise to 100 mL of 2 wt% CaCl2 solution, allowed to stand for crosslinking for 1 h, washed, and freeze-dried (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0085] Comparative Example 4: The preparation method of composite biochar includes the following steps:

[0086] S1: Using chitosan (average molecular weight 3.5 x 10⁻⁶) 6 Prepare a 2 g / L chitosan-acetic acid aqueous solution by mixing chitosan (95% deacetylation degree) with a 2 wt% acetic acid aqueous solution; carboxymethyl cellulose (molecular weight 4.2 x 10⁻⁶) 8 Prepare a 2 g / L carboxymethyl cellulose aqueous solution with deionized water (degree of substitution 0.7).

[0087] 10g of Fe-Al bimetallic oxide modified biochar prepared in Example 2 was immersed in 100mL of chitosan solution for 45min and then washed with water. The washed bimetallic oxide modified biochar was immersed in 100mL of carboxymethyl cellulose solution for 45min and then washed with water. The above steps were repeated 4 times to obtain modified biochar.

[0088] S2: Add 10g of modified biochar and 150mL of live bacteria at a concentration of 1×10⁻⁶. 9 A CFU / mL aqueous solution of *Thiobacillus ferrooxidans* was added to the reaction vessel, the pH was adjusted to 7, and the mixture was placed in a constant temperature shaker at 35℃ and a rotation speed of 200 rpm for 18 h. The modified biochar after microbial adsorption was transferred to a conical flask containing low-salt medium and placed in an anaerobic incubator for static incubation for 24 h to allow microorganisms to colonize and multiply within the pores. After incubation, the surface free microorganisms were rinsed with sterile water to obtain microbially loaded modified biochar.

[0089] S3: 10g of microbial-supported biochar, 2.5g of calcium chloride dihydrate, 1.7g of dipotassium hydrogen phosphate, and 70mL of deionized water were mixed and stirred at 35℃ for 48h. The mixture was then filtered, washed, and dried to obtain acid-resistant microbial-supported biochar.

[0090] S4: Add 25 mL of 2 wt% sodium alginate aqueous solution and 5 mL of 1 wt% polyethyleneimine aqueous solution to the reaction vessel for dispersion, add 10 g of acid-resistant microbial-supported biochar, and continue stirring for 20 min to obtain a mixed solution; drop the mixed solution into 100 mL of 2 wt% CaCl2 solution, let it stand for crosslinking for 1 h, wash, and freeze dry (temperature -50℃, vacuum degree 10 Pa, drying for 12 h) to obtain composite biochar.

[0091] Performance testing

[0092] (1) Water treatment performance: with initial pH=2.0 and Pb 2+ Simulated acidic mine wastewater with a concentration of 100 mg / L and a sulfate concentration of 2000 mg / L was used as the treatment target. The composite biochar prepared in Examples 1-3 and Comparative Examples 1-4 was added to the simulated acidic mine wastewater at a rate of 2 g of composite biochar per 100 mL of simulated acidic mine wastewater. The treatment conditions were: temperature 35℃, treatment for 30 days. After treatment, the concentrations of heavy metals and sulfate in the water were measured, and Pb was calculated. 2+ Removal rate and sulfate removal rate, the test results are shown in Table 1;

[0093] After each treatment, the cells were regenerated by acid washing with 0.1 mol / L HCl for 2 hours, followed by washing with deionized water until neutral. This process was repeated 5 times before Pb was measured. 2+ Removal rate and sulfate removal rate, the test results are shown in Table 1;

[0094] Table 1: Statistical Table of Water Treatment Performance Test Data for Examples 1-3 and Comparative Examples 1-4

[0095]

[0096] As shown in Table 1, the composite biochar prepared in this application has a good removal effect on heavy metal ions and sulfate ions in acidic mine wastewater, and maintains a high removal rate even after multiple uses.

[0097] (2) Performance stability test

[0098] The composite biochar prepared in Examples 1-3 and Comparative Examples 1-4 were made into columnar samples with a diameter of 5 mm × 10 mm. The compressive strength of the materials was tested using a universal testing machine with a loading rate of 1 mm / min. After stirring the composite biochar in wastewater (150 rpm) for 30 days, the compressive strength was tested again, and the strength retention rate and the activity retention rate of *Acidithiobacillus ferrooxidans* loaded in the composite biochar were calculated. The test results are shown in Table 2.

[0099] Table 2: Statistical Table of Performance Stability Test Data for Examples 1-3 and Comparative Examples 1-4

[0100]

[0101] As shown in Table 2, the composite biochar prepared in this application still maintains excellent mechanical properties after treatment of acidic mine wastewater; and even after wastewater treatment, the acidophilic ferrooxidizobacillus adsorbed on the composite biochar still maintains high activity.

[0102] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for treating acidic mine wastewater using composite biochar, characterized in that, The process includes the following steps: placing the composite biochar in acidic mine wastewater for adsorption treatment; The preparation method of the composite biochar includes the following steps: S1: The Fe-Al bimetallic oxide modified biochar was immersed in chitosan solution and then washed with water. The washed bimetallic oxide modified biochar was immersed in carboxymethyl cellulose solution and then washed with water. The above steps were repeated 3-5 times to obtain modified biochar. S2: Add modified biochar and composite functional bacterial solution to the reaction vessel, adjust the pH to 7-7.5, perform adsorption treatment, static culture, and water washing to obtain microbial-loaded biochar; S3: Microbial-supported biochar, calcium chloride dihydrate, dipotassium hydrogen phosphate, and deionized water are mixed together, and the temperature is controlled at 35-40℃. The mixture is stirred and reacted for 24-48 hours. After filtration, washing, and drying, acid-resistant microbial-supported biochar is obtained. S4: Add sodium alginate solution, attapulgite clay nanosheet suspension, and polyethyleneimine solution to a reaction vessel for dispersion, add acid-resistant microbial-supported biochar, and continue stirring for 15-30 min to obtain a mixture; drop the mixture into CaCl2 solution, allow it to stand for crosslinking for 0.5-2 h, wash, and freeze-dry to obtain composite biochar; S2 contains a compound functional bacterial solution with a live bacteria concentration of 10. 8 -10 9 Aqueous solution of *Thiobacillus ferrooxidans* at CFU / mL; The preparation method of the Fe-Al bimetallic oxide modified biochar includes the following steps: A1: Biochar is obtained by crushing, acid leaching, drying, and pyrolyzing biomass raw materials; A2: Ferric chloride hexahydrate, aluminum chloride hexahydrate, deionized water, and biochar were mixed and microwaved, then centrifuged, washed, and dried to obtain Fe-Al bimetallic oxide modified biochar. The specific steps of the microwave reaction are as follows: microwave power 300-500W, temperature control 60-80℃, reaction time 15-30min.

2. The method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The chitosan solution in S1 is a 1-3 g / L chitosan-acetic acid aqueous solution; the acetic acid aqueous solution contains 1 wt%-3 wt% acetic acid; the carboxymethyl cellulose solution is a 1-3 g / L carboxymethyl cellulose aqueous solution.

3. The method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The addition ratio of modified biochar and composite functional bacterial solution is 10g: 100-200mL; the specific steps of adsorption treatment in S2 are: place in a constant temperature shaker at 30-35℃ with a rotation speed of 150-200rpm for 4-24h.

4. The method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The addition ratio of microbially loaded biochar, calcium chloride dihydrate, dipotassium hydrogen phosphate, and deionized water in S3 is 10g: 2-2.5g: 1.5-2g: 50-100mL.

5. A method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The sodium alginate solution is a 2-5 wt% aqueous solution of sodium alginate; the attapulgite clay nanosheet suspension is a 0.5-1 wt% aqueous solution of attapulgite clay nanosheets; and the polyethyleneimine solution is a 1-2 wt% aqueous solution of polyethyleneimine.

6. A method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The addition ratio of sodium alginate solution, attapulgite clay nanosheet suspension, polyethyleneimine solution, and acid-resistant microbial-loaded biochar in S4 is 20-50 mL: 5-10 mL: 5-10 mL: 10 g.

7. A method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The CaCl2 solution is a 2-3 wt% CaCl2 solution; the volume ratio of the mixed solution to the CaCl2 solution is 30-50:

100.

8. A method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The addition ratio of ferric chloride hexahydrate, aluminum chloride hexahydrate, deionized water, and biochar is 1.35-4.05g: 0.757-2.27g: 100mL: 10-20g.

9. A method for treating acidic mine wastewater using composite biochar according to claim 1, characterized in that, The biomass raw material consists of 50-60 wt% corn stalks and 40-50 wt% walnut shells; The crushing specifically refers to crushing biomass raw materials to 2-5mm; The drying process specifically involves drying at 70-80℃ to constant weight; The pyrolysis specifically involves: in a nitrogen atmosphere, heating at a rate of 1-10℃ / min to 300-600℃ and holding at that temperature for 0.5-1h; or heating at a rate of 5-10℃ / min to 600-700℃ and activating with steam for 0.5-1h.

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