Microbial agent for extracting heavy metals in incineration fly ash and application method thereof

Abstract

The invention relates to the technical field of bioleaching, in particular to a microbial agent for extracting heavy metals in incineration fly ash, which comprises a compound bacteria solution, an activating agent and a carrier in a liquid-solid ratio of 1ml: 0.4 g: (4-5g), the compound bacteria liquid comprises thiobacillus ferrooxidans, bacillus and leptospirillum ferriphilum in a volume ratio of 1: 1: (0.8-1.2); the carrier comprises an algae-based compound, rhamnolipid and sodium alginate in a mass ratio of (3-5): 1: 1; the application method of the microbial agent comprises the following steps: S1, fly ash pretreatment; s2, heavy metal leaching; s3, merging and extracting; sulfuric acid and ferric sulfate are generated through sulfur oxide and ferrous ions, an acid environment is created, heavy metal is directly dissolved, the contact area is increased by dispersing fly ash particles through bacillus and rhamnolipid, and the leaching rate of Cr, Cu and Zn is increased; the carrier and the activating agent provide attachment points for microorganisms and can buffer the impact of high-concentration heavy metal ions in the fly ash on the microorganisms.

Description

Technical Field

[0001] This invention relates to the field of bioleaching technology, specifically to a microbial agent for extracting heavy metals from incineration fly ash and its application method. Background Technology

[0002] Incineration fly ash is the precipitate collected by the flue gas purification system during the incineration of municipal solid waste and the bottom ash settling at the bottom of the flue and chimney. Incineration fly ash possesses both heavy metal hazard characteristics and persistent organic pollutant (POP) hazard characteristics. It contains high concentrations of easily leached heavy metals such as Pb, Cd, Cu, Cr, and Zn, as well as highly hazardous dioxins and furans. These pollutants can contaminate water bodies and soil, thereby harming the health of plants, animals, and humans.

[0003] The main technologies for removing heavy metals from fly ash of municipal solid waste incineration include the following categories, which need to be selected comprehensively based on the target heavy metal, cost, treatment scale, and final disposal requirements: 1. Pretreatment technology, but it treats high-salinity wastewater and has a high residual rate of sparingly soluble heavy metals (such as Cr and Cd); 2. Chemical stabilization / solidification technology, but its long-term stability is affected by the environment (pH, redox conditions); 3. High-temperature treatment technology, but it has high energy consumption and requires control of the volatilization of heavy metals in flue gas (such as Hg and Cd); 4. Wet extraction technology, but the reaction cycle is long; 5. Combined processes.

[0004] Therefore, this invention aims to design a microbial agent for extracting heavy metals from incineration fly ash. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a microbial agent for extracting heavy metals from incineration fly ash and its application method.

[0006] A microbial agent for extracting heavy metals from incineration fly ash comprises a compound bacterial solution with a liquid-to-solid ratio of 1 ml: 0.4 g: 4-5 g, an activator, and a carrier; The composite bacterial solution comprises *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira ferrophila* in a volume ratio of 1:1:0.8~1.2, with a bacterial concentration of 1~10×10⁻⁶. 8 CFU / mL; The carrier comprises an algae-based complex, rhamnolipid, and sodium alginate in a mass ratio of 3 to 5:1:1.

[0007] Furthermore, the activator is prepared by the following method: Graphene oxide was dispersed in an ethanol solution at a solid-liquid ratio of 1g:60~150ml, and then 7-hydroxy-4-methylcoumarin (8~12wt%) and 2-hydroxyethylamine (4~6wt%) were added. The mixture was stirred at room temperature for 12~24h. After the reaction was completed, the mixture was freeze-dried to obtain hydroxylated graphene oxide. Apatite and deionized water were mixed at a ratio of 0.2~0.4g:100mL to obtain a mixed solution. Then, hydroxylated graphene oxide was added to the mixed solution at a solid-liquid ratio of 1g:25~30ml. After stirring, mixing, precipitation, washing and drying, the matrix material was obtained. The matrix material was mixed with a tannic acid solution with pH 5.5-6 at a solid-liquid ratio of 1g:80-100ml for 2-3 days by shaking, centrifugation, filtration, precipitation washing and drying to obtain the activator.

[0008] The surface of hydroxylated graphene oxide is rich in functional groups such as hydroxyl and carboxyl groups, which can adsorb heavy metal ions in fly ash through complexation. Apatite can solidify heavy metals by exchanging them with calcium sites, thereby transferring heavy metals from fly ash. The composite of hydroxylated graphene oxide and apatite forms a porous network structure, increasing the adsorption sites for heavy metals and providing attachment points for microbial activity. Tannic acid enhances the complexation effect of the activator and reduces the surface tension of the liquid, thereby enhancing the wettability and permeability of the leaching system on the fly ash surface, thus promoting the dissolution of heavy metals from fly ash. High concentrations of heavy metals are highly toxic to microorganisms, while the activator reduces the concentration toxicity by adsorbing heavy metal ions. Furthermore, the phosphate ions released by apatite when dissolved in the culture medium can provide energy for microbial activity, thereby improving microbial activity.

[0009] Furthermore, the freeze-drying temperature is -60 to -50°C, and the time is 24 to 28 hours.

[0010] The freeze-drying process avoids the functional group decomposition or unnecessary chemical reactions caused by conventional heat drying at high temperatures, retains the chemical activity of hydroxylated graphene oxide, and has a large specific surface area, which is conducive to the attachment of microorganisms and the adsorption of heavy metals.

[0011] Furthermore, the preparation method of the algae-based complex is as follows: The straw cellulose is alkalized to obtain alkalized cellulose. The alkalized cellulose is then immersed in a citric acid solution with a mass fraction of 80-85% at a temperature of 60-70°C for 2.5-3.5 hours, followed by washing and drying to obtain modified cellulose. Diatomaceous earth was impregnated in a 15-20% sulfuric acid solution and stirred at 65-70°C for 1.5-2 hours. After washing until neutral, it was dried and passed through a 250-mesh sieve. The sieved diatomaceous earth, sodium dodecylbenzenesulfonate, and deionized water were then mixed in a ratio of 1-1.2g:0.2g:3ml and dried to obtain a mixture. The mixture was then calcined in a high-temperature furnace at 450-500°C for 1.5-2.5 hours. The calcined product, coupling agent, and modified cellulose were mixed at a mass ratio of 1:0.05:0.8~1, reacted at 50~55℃ for 2~3 hours, washed, and vacuum dried to constant weight to obtain the algae-based complex.

[0012] Citric acid-modified cellulose provides a weak acid buffer to counteract the alkalinity of fly ash and introduces carboxyl groups on the cellulose surface. Diatomaceous earth has a porous structure, enabling both to effectively capture heavy metal ions in fly ash through ion exchange, surface complexation, and physical adsorption. This enriches heavy metals and accelerates the oxidative dissolution of heavy metals by microorganisms. Sodium dodecylbenzenesulfonate reduces the surface tension of water, preventing the aggregation of diatomaceous earth and keeping it highly dispersed. After calcination, it creates pores in the diatomaceous earth, which better adsorbs heavy metals and improves the extraction efficiency of heavy metals from fly ash.

[0013] Furthermore, the alkalization treatment method is as follows: the straw cellulose powder is dispersed in a sodium hydroxide solution with a mass fraction of 58-62% at a solid-liquid ratio of 1g:10-15ml for alkalization, the alkalization temperature is 20-30℃, and the alkalization time is 45-105min.

[0014] The cellulose molecular chain is broken down, exposing more hydroxyl groups and transforming into a more reactive alkali cellulose form, thereby increasing the reactivity of cellulose.

[0015] Furthermore, the coupling agent is KH-550.

[0016] KH550 can react with the groups on the surface of modified cellulose and with diatomaceous earth to form an interface layer, thereby improving the bonding strength between the modified cellulose and diatomaceous earth.

[0017] Furthermore, the preparation method of the microbial inoculant is as follows: First, *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira* were cultured separately. Then, the separately cultured *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira* were combined and cultured in a specific ratio to obtain a compound bacterial solution. After sterilization, the algae-based complex, rhamnolipin, and sodium alginate are mixed according to the specified ratio. Then, an activator is added according to the specified ratio. After stirring and mixing evenly, the mixture is ball-milled to obtain a powder with a particle size of 70~100μm. The powder is added to the composite bacterial solution according to the specified ratio, and stirred at 25~35℃ for 12~24h. Then it is dried naturally to obtain the microbial agent.

[0018] Ferrous sulfobacillus and iron-loving Leptospira produce sulfuric acid and ferric sulfate by oxidizing sulfur and ferrous ions, creating an acidic environment and directly dissolving heavy metals. Bacillus and rhamnolipin increase the leaching rate of Cr, Cu, and Zn by dispersing fly ash particles and increasing the contact area. The algae-based complex forms a three-dimensional network structure with sodium alginate, providing attachment points for microorganisms and buffering the impact of high concentrations of heavy metal ions and pH fluctuations in fly ash on microorganisms. Rhamnolipin can reduce the surface tension of the liquid, improve the wettability and permeability of the fly ash surface in the leaching system, and promote the dissolution of heavy metals. The activator reduces the concentration toxicity by adsorbing heavy metal ions, and the phosphate ions released by the dissolution of apatite in the culture medium can provide energy for the activity of the microorganisms, thereby improving the activity of microorganisms.

[0019] A method for applying a microbial inoculant for extracting heavy metals from incineration fly ash, as described in any of the above, includes the following steps: S1. Fly ash pretreatment Under a nitrogen atmosphere, the incineration fly ash is kept at 380~420℃ for 70~80 minutes, and then washed with three-stage countercurrent water washing to obtain pretreated fly ash. S2, heavy metal leaching Microbial inoculants were inoculated into the culture medium at a solid-liquid ratio of 1g:8~10ml to form a leaching system. Pretreated fly ash with a mass ratio of 1:10~12 to the microbial inoculants was then added to the leaching system for leaching. The pH of the leaching system was maintained at 1.8~2.2, the temperature at 30~40℃, and the time was 10~15 days to obtain leaching residue and leaching solution. S3, Merge and Extract The leaching residue is eluted to obtain an eluent and an eluent residue. The leaching solution and the eluent are mixed to obtain an extract of heavy metals.

[0020] Further, the components of the culture medium include: ferrous sulfate 40.0~50.0 g / L, ammonium sulfate 3.0~4.5 g / L, potassium dihydrogen phosphate 0.5~1.0 g / L, magnesium sulfate heptahydrate 0.4~0.6 g / L, potassium chloride 0.1~0.3 g / L, glucose 2.0~5.0 g / L, sulfur powder 1.0~2.0 g / L, and the balance being water.

[0021] The above-mentioned culture medium can provide nutrients for microorganisms, maintain their activity, and facilitate leaching.

[0022] Compared with existing microbial agents for extracting heavy metals, the advantages of this invention are: (1) The present invention obtains a bacterial agent by combining a compound bacterial solution, an activator and a carrier. In the compound bacterial solution, ferrous thiobacillus and iron-loving Leptospira produce sulfuric acid and ferric sulfate by oxidizing sulfur and ferrous ions, creating an acidic environment and directly dissolving heavy metals. Bacillus and rhamnolipids increase the leaching rate of Cr, Cu and Zn by dispersing fly ash particles and increasing the contact area. In the carrier, the algae-based complex forms a three-dimensional network structure with sodium alginate, providing attachment points for microorganisms and buffering the impact of high concentration of heavy metal ions and pH fluctuations in fly ash on microorganisms. Rhamnolipids can reduce the surface tension of the liquid, improve the wettability and permeability of the fly ash surface in the leaching system, and promote the dissolution of heavy metals. The activator reduces the concentration toxicity by adsorbing heavy metal ions, and the phosphate ions released by the dissolution of apatite in the culture medium can provide energy for the activity of the strain, thereby improving the activity of microorganisms.

[0023] (2) In the activator prepared in this invention, the surface of hydroxylated graphene oxide is rich in functional groups such as hydroxyl and carboxyl groups, which can adsorb heavy metal ions in fly ash through complexation. Apatite can replace heavy metal ions with calcium sites to solidify heavy metals, thereby transferring heavy metals from fly ash. The composite of hydroxylated graphene oxide and apatite forms a porous network structure, which increases the adsorption sites of heavy metals and provides attachment points for microbial activities. Tannic acid can improve the complexation effect of the activator on the one hand, and reduce the surface tension of the liquid on the other hand, thereby enhancing the wettability and permeability of the leaching system on the fly ash surface, thus promoting the dissolution of heavy metals from fly ash. High concentrations of heavy metals are highly toxic to microorganisms, while the activator reduces the concentration toxicity by adsorbing heavy metal ions. Furthermore, the phosphate ions released by the dissolution of apatite in the culture medium can provide energy for the activity of the microorganisms, thereby improving the activity of microorganisms. Attached Figure Description

[0024] Figure 1 This is a graph showing the heavy metal extraction rate results of Experiment 1, which is an example of the application of microbial agents of the present invention. Figure 2 This is a graph showing the heavy metal extraction rate results of Experiment 2 in the application experiment of the microbial agent of this invention; Figure 3 This is a graph showing the heavy metal extraction rate results of Experiment 3 in the application experiment of the microbial agent of this invention; Figure 4 This is a graph showing the heavy metal extraction rate results of Experiment 4 of the application experiment of the microbial agent of this invention. Detailed Implementation

[0025] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0026] Example 1: A microbial agent for extracting heavy metals from incineration fly ash, comprising a compound bacterial solution with a liquid-to-solid ratio of 1 ml: 0.4 g: 4.5 g, an activator, and a carrier; The composite bacterial solution comprises *Thiobacillus ferrooxidans* (accession number ATCC 23270), *Bacillus* (accession number CGMCC 1.231), and *Leptospira ferrophila* (accession number AS 1.6358) in a volume ratio of 1:1:1, with a bacterial concentration of 5 × 10⁻⁶. 8 CFU / mL; The carrier comprises an algal-based complex, rhamnolipid, and sodium alginate in a mass ratio of 4:1:1; The activator is prepared by: Graphene oxide was dispersed in an ethanol solution at a solid-liquid ratio of 1g:100ml, and then 10wt% of 7-hydroxy-4-methylcoumarin and 5wt% of 2-hydroxyethylamine were added. The mixture was stirred at room temperature (25°C) for 18h. After the reaction was completed, the mixture was freeze-dried at -55°C for 26h to obtain hydroxylated graphene oxide. Apatite and deionized water were mixed at a ratio of 0.3 g: 100 mL to obtain a mixed solution. Then, hydroxylated graphene oxide was added to the mixed solution at a solid-liquid ratio of 1 g: 28 mL. After stirring and mixing, the precipitate was washed with deionized water and then dried at 80 °C for 8 h to obtain the matrix material. The matrix material was mixed with a tannic acid solution at pH 5.8 at a solid-liquid ratio of 1g:90ml for 2 days, centrifuged at 4000rpm for 3min, filtered, the precipitate was washed with deionized water and dried at 60℃ for 6h to obtain the activator. The preparation method of the algae-based complex is as follows: The straw cellulose was subjected to alkalization treatment. The alkalization treatment method was as follows: the straw cellulose powder was dispersed in a 60% sodium hydroxide solution at a solid-liquid ratio of 1g:12ml for alkalization at a temperature of 25℃ for 75min to obtain alkalized cellulose. The alkalized cellulose was then immersed in an 83% citric acid solution at a temperature of 65℃ for 3h, washed with deionized water, and dried at 60℃ for 1h to obtain modified cellulose. Diatomaceous earth was impregnated in an 18% sulfuric acid solution and stirred at 68°C for 1.8 hours. It was then washed with deionized water until neutral, dried, and passed through a 250-mesh sieve. The sieved diatomaceous earth, sodium dodecylbenzenesulfonate, and deionized water were mixed in a ratio of 1.1 g: 0.2 g: 3 ml and dried at 60°C for 30 minutes to obtain a mixture. The mixture was then calcined in a high-temperature furnace at 480°C for 2 hours. The calcined product, KH-550 coupling agent and modified cellulose were mixed at a mass ratio of 1:0.05:0.9, reacted at 52℃ for 2.5h, washed with deionized water, and vacuum dried at 60℃ to constant weight to obtain the algae-based complex. The preparation method of the above-mentioned microbial inoculant is as follows: First, *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira* were cultured separately. Then, the separately cultured *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira* were combined and cultured in a specific ratio to obtain a compound bacterial solution. It should be noted that the above culture process and the culture medium used are existing technologies and are not specifically limited here. After sterilization, the algae-based complex, rhamnolipin, and sodium alginate are mixed according to the specified ratio. Then, an activator is added according to the specified ratio. After stirring and mixing evenly, the mixture is ball-milled to obtain a powder with a particle size of 80~90μm. The powder was added to the composite bacterial solution according to the specified ratio, stirred and reacted at 30°C for 18 hours, and then naturally dried at 25°C for 24 hours to obtain the microbial agent.

[0027] Example 2: A method for extracting heavy metals from incineration fly ash using the microbial agent prepared in Example 1, comprising the following steps: S1, fly ash heat treatment Under a nitrogen atmosphere, the incineration fly ash is kept at 400℃ for 75 minutes, and then washed with three-stage countercurrent water washing to obtain pretreated fly ash. S2, heavy metal leaching The microbial agent was inoculated into the culture medium at a solid-liquid ratio of 1g:9ml. The components of the culture medium included: ferrous sulfate 45 g / L, ammonium sulfate 4.2 g / L, potassium dihydrogen phosphate 0.8 g / L, magnesium sulfate heptahydrate 0.5 g / L, potassium chloride 0.2 g / L, glucose 3.5 g / L, sulfur powder 1.5 g / L, and the balance being water. This was used as the leaching system. Pretreated fly ash with a mass ratio of 1:11 to the microbial agent was then added to the leaching system for leaching. The pH of the leaching system was maintained at 2, the temperature at 35℃, and the time was 12 days, resulting in leaching residue and leachate. S3, Merge and Extract The leaching residue is eluted to obtain an eluent and an eluent residue. The leaching solution and the eluent are mixed to obtain an extract of heavy metals.

[0028] Example 3: This example differs from Example 1 in that the microbial agent includes a compound bacterial solution with a liquid-to-solid ratio of 1 ml:0.4 g:4 g, an activator, and a carrier; the compound bacterial solution includes *Acidithiobacillus ferrooxidans*, *Bacillus*, and *Leptospira ferrophila* in a volume ratio of 1:1:0.8, and the bacterial concentration of the compound bacterial solution is 1 × 10⁻⁶. 8CFU / mL; the carrier comprises an algal-based complex, rhamnolipid, and sodium alginate in a mass ratio of 3:1:1.

[0029] Example 4: This example differs from Example 1 in that the microbial agent includes a compound bacterial solution with a liquid-to-solid ratio of 1 ml:0.4 g:5 g, an activator, and a carrier; the compound bacterial solution includes *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira ferrophila* in a volume ratio of 1:1:1.2, and the bacterial concentration of the compound bacterial solution is 1 × 10⁻⁶. 9 CFU / mL; the carrier comprises an algal-based complex, rhamnolipid, and sodium alginate in a mass ratio of 5:1:1.

[0030] Example 5: This example differs from Example 1 in that graphene oxide is dispersed in an ethanol solution at a solid-liquid ratio of 1g:60ml, and then 7-hydroxy-4-methylcoumarin (8wt% of graphene oxide) and 2-hydroxyethylamine (6wt% of graphene oxide) are added.

[0031] Example 6: The difference between this example and Example 1 is that graphene oxide is dispersed in an ethanol solution at a solid-liquid ratio of 1g:150ml, and then 12wt% of 7-hydroxy-4-methylcoumarin and 4wt% of 2-hydroxyethylamine are added.

[0032] Example 7: This example differs from Example 1 in that the reaction is stirred at room temperature for 12 hours, and after the reaction is completed, it is freeze-dried at -50°C for 24 hours to obtain hydroxylated graphene oxide.

[0033] Example 8: This example differs from Example 1 in that the reaction is stirred at room temperature for 24 hours, and after the reaction is completed, it is freeze-dried at -60°C for 28 hours to obtain hydroxylated graphene oxide.

[0034] Example 9: The difference between this example and Example 1 is that apatite and deionized water are mixed at a ratio of 0.2g:100mL to obtain a mixed solution, and then the hydroxylated graphene oxide is added to the mixed solution at a solid-liquid ratio of 1g:25ml.

[0035] Example 10: The difference between this example and Example 1 is that apatite and deionized water are mixed at a ratio of 0.4g:100mL to obtain a mixed solution, and then the hydroxylated graphene oxide is added to the mixed solution at a solid-liquid ratio of 1g:30ml.

[0036] Example 11: This example differs from Example 1 in that the matrix material and a tannic acid solution with pH=5.5 are mixed by shaking for 2 days at a solid-liquid ratio of 1g:80ml.

[0037] Example 12: This example differs from Example 1 in that the matrix material and a tannic acid solution with pH=6 are mixed by shaking for 3 days at a solid-liquid ratio of 1g:100ml.

[0038] Example 13: The difference between this example and Example 1 is that the alkalization treatment method is as follows: the straw cellulose powder is dispersed in a 58% sodium hydroxide solution at a solid-liquid ratio of 1g:10ml for alkalization at a temperature of 20℃ for 45min.

[0039] Example 14: The difference between this example and Example 1 is that the alkalization treatment method is as follows: the straw cellulose powder is dispersed in a 62% sodium hydroxide solution at a solid-liquid ratio of 1g:15ml for alkalization at a temperature of 30℃ for 105min.

[0040] Example 15: This example differs from Example 1 in that the alkalized cellulose is impregnated in an 80% citric acid solution at a temperature of 60°C for 2.5 hours.

[0041] Example 16: This example differs from Example 1 in that the alkalized cellulose is impregnated in a citric acid solution with a mass fraction of 85% at a temperature of 70°C for 3.5 hours.

[0042] Example 17: The difference between this example and Example 1 is that the diatomaceous earth was impregnated in a 15% sulfuric acid solution, stirred at 65°C for 1.5 hours, and then washed until neutral.

[0043] Example 18: The difference between this example and Example 1 is that the diatomaceous earth was impregnated in a 15% sulfuric acid solution, stirred at 70°C for 2 hours, and then washed until neutral.

[0044] Example 19: This example differs from Example 1 in that the sieved diatomaceous earth, sodium dodecylbenzenesulfonate, and deionized water are mixed in a ratio of 1g:0.2g:3ml and dried to obtain a mixture. The mixture is then placed in a high-temperature furnace and calcined at 450°C for 1.5h.

[0045] Example 20: This example differs from Example 1 in that the sieved diatomaceous earth, sodium dodecylbenzenesulfonate, and deionized water are mixed in a ratio of 1.2g:0.2g:3ml and dried to obtain a mixture. The mixture is then placed in a high-temperature furnace and calcined at 500°C for 2.5 hours.

[0046] Example 21: The difference between this example and Example 1 is that the calcined product, KH-550 coupling agent and modified cellulose are mixed at a mass ratio of 1:0.05:0.8 and reacted at 50°C for 2 hours.

[0047] Example 22: This example differs from Example 1 in that the calcined product, KH-550 coupling agent, and modified cellulose are mixed at a mass ratio of 1:0.05:1 and reacted at 55°C for 3 hours.

[0048] Example 23: The difference between this example and Example 1 is that the powder is added to the compound bacterial solution according to the ratio and stirred at 25°C for 12 hours.

[0049] Example 24: This example differs from Example 1 in that the powder is added to the composite bacterial solution according to the specified ratio and stirred at 35°C for 24 hours.

[0050] Example 25: The difference between this example and Example 2 is that the incinerated fly ash is kept at 380°C for 70 minutes.

[0051] Example 26: The difference between this example and Example 2 is that the incinerated fly ash is kept at 420°C for 80 minutes.

[0052] Example 27: This example differs from Example 2 in that the microbial agent is inoculated into the culture medium at a solid-liquid ratio of 1g:8ml. The components of the culture medium include: ferrous sulfate 40.0 g / L, ammonium sulfate 3.0 g / L, potassium dihydrogen phosphate 0.5 g / L, magnesium sulfate heptahydrate 0.4 g / L, potassium chloride 0.1 g / L, glucose 2.0 g / L, sulfur powder 1.0 g / L, and the remainder is water, which serves as the leaching system. Pretreated fly ash with a mass ratio of 1:10 to the microbial agent is then added to the leaching system for leaching. The pH of the leaching system is maintained at 1.8, the temperature at 30℃, and the leaching time is 10 days.

[0053] Example 28: This example differs from Example 2 in that the microbial agent is inoculated into the culture medium at a solid-liquid ratio of 1g:10ml. The components of the culture medium include: ferrous sulfate 50.0 g / L, ammonium sulfate 4.5 g / L, potassium dihydrogen phosphate 1.0 g / L, magnesium sulfate heptahydrate 0.6 g / L, potassium chloride 0.3 g / L, glucose 5.0 g / L, sulfur powder 2.0 g / L, and the remainder is water, which serves as the leaching system. Pretreated fly ash with a mass ratio of 1:12 to the microbial agent is then added to the leaching system for leaching. The pH of the leaching system is maintained at 2.2, the temperature at 40℃, and the leaching time is 15 days.

[0054] Experimental Example: The description of this experimental example is based on the scheme described in Example 2, and aims to illustrate the practical application effect of the present invention.

[0055] 1. To investigate the effects of the component ratio and preparation of microbial inoculants on the extraction rate of heavy metals in incineration fly ash.

[0056] The difference between Comparative Example 1 and Example 1 is that the microbial inoculant does not include an activator; from Figure 1 The results show that, compared with the embodiments of this application, the control example lacks an activator, which reduces the attachment points provided for microbial activity and decreases the adsorption capacity for heavy metal leaching. Therefore, the extraction rate is significantly lower than that of the embodiments of this application. Comparing Examples 1, 3-4, and 23-24, it can be seen that too small or too large a proportion of activator, as well as too small or too large a preparation parameter, will reduce the extraction rate of heavy metals by the microbial agent. Therefore, from a comprehensive perspective, the parameter effect of Example 1 is relatively better.

[0057] 2. To investigate the effect of activator preparation on the extraction rate of heavy metals in incineration fly ash.

[0058] The difference between Comparative Example 2 and Example 1 is that the raw material used is graphene oxide instead of hydroxylated graphene oxide; from Figure 2 The results show that the graphene oxide in Comparative Example 2 was not modified by hydroxylation, which weakened its complexation effect on heavy metal ions and the strength of its composite with apatite, etc. Therefore, the extraction rate was significantly lower than that of the embodiments of this application. Comparing Examples 1 and 5-12, it can be seen that too small or too large a proportion of graphene oxide, too small or too large a hydroxylation parameter, too small or too large apatite proportion, and too small or too large a shaking mixing parameter will reduce the extraction rate of heavy metals by the microbial agent. Therefore, from a comprehensive perspective, the parameters of Example 1 are relatively better.

[0059] 3. To investigate the effect of the preparation of algae-based complexes on the extraction rate of heavy metals in incineration fly ash.

[0060] from Figure 3 The results show that, compared with Examples 1 and 13 to 22, the extraction rate of heavy metals by microbial agents is reduced when the simplified processing parameters are too small or too large, the alkalization cellulose impregnation parameters are too small or too large, the diatomaceous earth impregnation parameters are too small or too large, the preparation parameters of the mixture are too small or too large, and the coupling agent mixing parameters are too small or too large. Therefore, from a comprehensive perspective, the parameters of Example 1 are relatively better.

[0061] 4. To investigate the effect of applying microbial agents to incineration fly ash on the extraction rate of heavy metals from incineration fly ash.

[0062] from Figure 4 The results show that, compared with Examples 2 and 25-28, both excessively small or large pretreatment parameters for incineration fly ash and excessively small or large microbial leaching parameters will reduce the extraction rate of heavy metals by microbial agents. Therefore, from a comprehensive perspective, the parameters in Example 2 are relatively better.

Claims

1. A microbial agent for extracting heavy metals from incineration fly ash, characterized in that, It includes a compound bacterial solution with a liquid-to-solid ratio of 1ml:0.4g:4~5g, an activator, and a carrier; The composite bacterial solution comprises *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira ferrophila* in a volume ratio of 1:1:0.8~1.2, with a bacterial concentration of 1~10×10⁻⁶. 8 CFU / mL; The carrier comprises an algal-based complex, rhamnolipid, and sodium alginate in a mass ratio of 3 to 5:1:

1.

2. The microbial agent for extracting heavy metals from incineration fly ash as described in claim 1, characterized in that, The activator is prepared by: Graphene oxide was dispersed in an ethanol solution at a solid-liquid ratio of 1g:60~150ml, and then 7-hydroxy-4-methylcoumarin (8~12wt%) and 2-hydroxyethylamine (4~6wt%) were added. The mixture was stirred at room temperature for 12~24h. After the reaction was completed, the mixture was freeze-dried to obtain hydroxylated graphene oxide. Apatite and deionized water were mixed at a ratio of 0.2~0.4g:100mL to obtain a mixed solution. Then, hydroxylated graphene oxide was added to the mixed solution at a solid-liquid ratio of 1g:25~30ml. After stirring, mixing, precipitation, washing and drying, the matrix material was obtained. The matrix material was mixed with a tannic acid solution with pH 5.5-6 at a solid-liquid ratio of 1g:80-100ml for 2-3 days by shaking, centrifugation, filtration, precipitation washing and drying to obtain the activator.

3. The microbial agent for extracting heavy metals from incineration fly ash as described in claim 2, characterized in that, The freeze-drying temperature is -60~-50℃, and the time is 24~28h.

4. The microbial agent for extracting heavy metals from incineration fly ash as described in claim 1, characterized in that, The preparation method of the algae-based complex is as follows: The straw cellulose is alkalized to obtain alkalized cellulose. The alkalized cellulose is then immersed in a citric acid solution with a mass fraction of 80-85% at a temperature of 60-70°C for 2.5-3.5 hours, followed by washing and drying to obtain modified cellulose. Diatomaceous earth was impregnated in a 15-20% sulfuric acid solution and stirred at 65-70°C for 1.5-2 hours. After washing until neutral, it was dried and passed through a 250-mesh sieve. The sieved diatomaceous earth, sodium dodecylbenzenesulfonate, and deionized water were then mixed in a ratio of 1-1.2g:0.2g:3ml and dried to obtain a mixture. The mixture was then calcined in a high-temperature furnace at 450-500°C for 1.5-2.5 hours. The calcined product, coupling agent, and modified cellulose were mixed at a mass ratio of 1:0.05:0.8~1, reacted at 50~55℃ for 2~3 hours, washed, and vacuum dried to constant weight to obtain the algae-based complex.

5. The microbial agent for extracting heavy metals from incineration fly ash as described in claim 4, characterized in that, The alkalization treatment method is as follows: straw cellulose powder is dispersed in a sodium hydroxide solution with a mass fraction of 58-62% at a solid-liquid ratio of 1g:10-15ml for alkalization at an alkalization temperature of 20-30℃ and an alkalization time of 45-105min.

6. The microbial agent for extracting heavy metals from incineration fly ash as described in claim 4, characterized in that, The coupling agent is KH-550.

7. The microbial agent for extracting heavy metals from incineration fly ash as described in claim 1, characterized in that, The preparation method of the microbial inoculant is as follows: First, *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira* were cultured separately. Then, the separately cultured *Thiobacillus ferrooxidans*, *Bacillus*, and *Leptospira* were combined and cultured in a specific ratio to obtain a compound bacterial solution. After sterilization, the algae-based complex, rhamnolipin, and sodium alginate are mixed according to the specified ratio. Then, an activator is added according to the specified ratio. After stirring and mixing evenly, the mixture is ball-milled to obtain a powder with a particle size of 70~100μm. The powder is added to the composite bacterial solution according to the specified ratio, and stirred at 25~35℃ for 12~24h. Then it is dried naturally to obtain the microbial agent.

8. The method for applying a microbial inoculant for extracting heavy metals from incineration fly ash as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1, fly ash heat treatment Under a nitrogen atmosphere, the incineration fly ash is kept at 380~420℃ for 70~80 minutes, and then washed with three-stage countercurrent water washing to obtain pretreated fly ash. S2, heavy metal leaching Microbial inoculants were inoculated into the culture medium at a solid-liquid ratio of 1g:8~10ml to form a leaching system. Pretreated fly ash with a mass ratio of 1:10~12 to the microbial inoculants was then added to the leaching system for leaching. The pH of the leaching system was maintained at 1.8~2.2, the temperature at 30~40℃, and the time was 10~15 days to obtain leaching residue and leaching solution. S3, Merge and Extract The leaching residue is eluted to obtain an eluent and an eluent residue. The leaching solution and the eluent are mixed to obtain an extract of heavy metals.

9. The application method of the microbial agent for extracting heavy metals from incineration fly ash as described in claim 8, characterized in that, The culture medium comprises: ferrous sulfate 40.0~50.0 g / L, ammonium sulfate 3.0~4.5 g / L, potassium dihydrogen phosphate 0.5~1.0 g / L, magnesium sulfate heptahydrate 0.4~0.6 g / L, potassium chloride 0.1~0.3 g / L, glucose 2.0~5.0 g / L, sulfur powder 1.0~2.0 g / L, and the balance being water.

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