Improved material based on synergism of microorganisms and minerals as well as preparation method and application of improved material

Abstract

The invention provides an improved material based on microorganism and mineral synergy and a preparation method and application thereof, the application comprises a method for improving saline-alkali soil by using the improved material, and the method comprises the following steps: carrying out water bath shaking culture on a thiobacillus ferrooxidans solution to obtain a thiobacillus ferrooxidans microbial inoculum; the method comprises the following steps: removing impurities from high-sulfur coal gangue, air-drying, crushing and grinding to obtain coal gangue powder; mixing the coal gangue powder with water, inoculating the mixture with a thiobacillus ferrooxidans microbial inoculum for culturing, and introducing fungi to obtain biologically activated coal gangue; determining the application mass ratio and the total application amount of the bioactive coal gangue and the low-sulfur coal gangue; mixing the bioactive coal gangue with low-sulfur coal gangue to obtain an improved material; pretreating the soil to obtain a saline-alkali soil sample; performing mixed culture on the improved material and the saline-alkali soil sample, and verifying effectiveness; and after verification, applying the improvement material to the target saline-alkali soil. According to the method, the high-sulfur coal gangue is activated by using a microbial technology, the saline-alkali soil improvement efficiency is improved, and waste is turned into wealth.

Description

Technical Field

[0001] This invention belongs to the field of environmental remediation and soil improvement technology, and specifically relates to improvement materials based on the synergistic effect of microorganisms and minerals, their preparation methods and applications. Background Technology

[0002] Saline-alkali land is a significant obstacle to global agricultural production and the ecological environment. The core problem of soil salinization and sodium alkalization is excessive soluble salts and exchangeable sodium ions, leading to deterioration of soil physical structure (such as compaction and poor permeability), poor chemical properties (high pH value), and decline in biological functions. Traditional methods for improving saline-alkali land include water conservancy projects (such as irrigation to leach salt), application of chemical amendments (such as gypsum, phosphogypsum, sulfur, ferrous sulfate, etc.), and agricultural biological measures. However, these methods have certain limitations: water conservancy projects consume large amounts of water and require sophisticated drainage systems; chemical amendments are costly, and long-term, large-scale application may pose a risk of secondary pollution; substances such as sulfur have a slow improvement rate and rely on microbial oxidation in the soil to be effective.

[0003] High-sulfur coal gangue is a solid waste generated during coal mining and washing. It has a high total sulfur content and contains certain amounts of calcium, magnesium, and other elements. If improperly stored, the sulfur in it can oxidize and be leached by rainwater, producing acidic mine wastewater that causes serious environmental pollution. Therefore, how to utilize high-sulfur coal gangue in a resource-efficient way and turn waste into treasure is an urgent problem to be solved. Theoretically, the sulfur in high-sulfur coal gangue can be oxidized to produce sulfuric acid, thereby neutralizing soil alkalinity. Simultaneously, the calcium and magnesium ions it contains can replace sodium ions on soil colloids, achieving the goal of improving saline-alkali land. Furthermore, the iron and organic matter in it can promote soil aggregation in saline-alkali land, accelerating the leaching of the replaced sodium ions. However, under natural conditions, this process is very slow, limiting its direct application effectiveness and efficiency.

[0004] Therefore, how to provide a method for improving saline-alkali land based on the modified material of *Thiobacillus ferrooxidans*, and how to activate high-sulfur coal gangue using microbial technology to improve the efficiency of saline-alkali land improvement and turn waste into treasure, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this invention is that traditional methods for improving saline-alkali land have certain limitations, such as high water consumption, high cost, and slow improvement speed.

[0006] To address the aforementioned problems, a first aspect of the present invention provides a method for improving saline-alkali land based on *Thiobacillus ferrooxidans* modified materials. The method includes: expanding and inoculating *Thiobacillus ferrooxidans* bacterial culture into a culture medium for water bath shaking culture; obtaining *Thiobacillus ferrooxidans* inoculum when the bacterial culture reaches a stable mid-to-late stage; removing impurities from high-sulfur coal gangue and sequentially air-drying, crushing, and grinding it to obtain coal gangue powder; mixing the coal gangue powder with water to form an aqueous solid-phase system, and inoculating it with the *Thiobacillus ferrooxidans* inoculum under acidic conditions for culture; and after culture is completed, ... Fungi are introduced into the aqueous solid-phase system for degradation and transformation to obtain bio-activated coal gangue; the application mass ratio and total application amount of the bio-activated coal gangue and low-sulfur coal gangue are determined; the bio-activated coal gangue and low-sulfur coal gangue are mixed according to the application mass ratio to obtain the improved material; soil is taken from the target saline-alkali land and pretreated to obtain saline-alkali soil samples; the improved material and the saline-alkali soil samples are uniformly mixed and cultured according to the total application amount to verify the effectiveness of the improved material; after verification of effectiveness, the improved material is applied to the target saline-alkali land after tillage for improvement.

[0007] In the first aspect, determining the application mass ratio and total application amount of the bio-activated coal gangue and low-sulfur coal gangue includes: calculating the theoretical dry basis application amount G of high-sulfur coal gangue according to formula (1); (1); In equation (1), K is a coefficient, and CEC is the cation exchange capacity of the saline-alkali soil sample. This represents the initial exchangeable sodium percentage of the saline-alkali soil sample. The target exchangeable sodium percentage for the saline-alkali soil sample is determined; the application amount of bio-activated coal gangue is determined based on the theoretical dry basis dosage of the high-sulfur coal gangue; the application mass ratio of bio-activated coal gangue and low-sulfur coal gangue is determined, and the application amount of low-sulfur coal gangue is determined based on the application mass ratio; the total application amount is determined based on the application amounts of bio-activated coal gangue and low-sulfur coal gangue.

[0008] In the first aspect, verifying the effectiveness of the improved material includes: periodically testing the monitoring indicators of the saline-alkali soil sample, determining whether the monitoring indicators reach a preset threshold, and if the preset threshold is reached, verifying the effectiveness of the improved material; wherein, the testing indicators include pH value, electrical conductivity, sodium adsorption ratio, and exchangeable sodium percentage, and reaching the preset threshold includes at least one of the following: pH value drops below 8.5, electrical conductivity drops below 4 dS / m, sodium adsorption ratio drops below 15 with a decrease rate greater than 30%, or soil exchangeable sodium percentage drops below 15%.

[0009] In the first aspect, the process of taking soil from the target saline-alkali land and pre-treating the soil includes: collecting topsoil from the target saline-alkali land at a depth of 0-20cm using a multi-point mixed sampling method, and sequentially air-drying, cleaning debris, grinding and passing the topsoil through a 2mm sieve. In the first aspect, the total application amount accounts for 10%-25% of the mass of saline-alkali soil, and the application mass ratio is 0.5:1-2:1; the improvement material is applied to the target saline-alkali land after tillage for improvement, and the tillage depth is 15-30cm.

[0010] In the first aspect, the culture medium is 9K medium, which contains ferrous sulfate heptahydrate at a concentration of 44.7 g / L. The water bath shaking culture is conducted at a speed of 200 r / min and a temperature of 26°C, and the viable count of the *Thiobacillus ferrooxidans* inoculant is not less than 1.0 g / L. 10 8 The CFU / mL concentration of the *Thiobacillus ferrooxidans* bacterial solution is in a stable late stage, including a color change from light green to reddish-brown with the formation of a yellow precipitate, or an oxidation rate of ferrous ions reaching 80% in the 9K medium. The high-sulfur coal gangue comprises, by mass percentage, total sulfur ≥3%, calcium and magnesium oxides 20%-30%, alumina ≤15%, and iron oxide 10%-20%. In the process of mixing the coal gangue powder with water to form an aqueous solid-phase system, the solid-liquid ratio of the coal gangue powder to the water is 1:1-1:4, or the water content of the aqueous solid-phase system is 35%-65%. The inoculation of the *Thiobacillus ferrooxidans* bacterial agent under acidic conditions further includes introducing acidophilic heterotrophic bacteria into the same system after the *Thiobacillus ferrooxidans* bacterial agent has entered a stable stage.

[0011] Secondly, the present invention provides a method for preparing an improved material based on *Thiobacillus ferrooxidans*. The method includes: expanding and inoculating *Thiobacillus ferrooxidans* bacterial culture into a culture medium for water bath shaking culture; obtaining *Thiobacillus ferrooxidans* inoculum when the bacterial culture is in a stable mid-to-late stage; removing impurities from high-sulfur coal gangue and sequentially air-drying, crushing, and grinding it to obtain coal gangue powder; mixing the coal gangue powder with water to form an aqueous solid-phase system, and inoculating it with the *Thiobacillus ferrooxidans* inoculum under acidic conditions for culture; after culture, introducing fungi into the aqueous solid-phase system for degradation and transformation to obtain bio-activated coal gangue; determining the application mass ratio of the bio-activated coal gangue to low-sulfur coal gangue; and mixing the bio-activated coal gangue and low-sulfur coal gangue according to the application mass ratio to obtain the improved material.

[0012] In the second aspect, the culture medium is 9K medium, which contains ferrous sulfate heptahydrate at a concentration of 44.7 g / L. The water bath shaking culture is conducted at a speed of 200 r / min and a temperature of 26°C, and the viable count of the *Thiobacillus ferrooxidans* inoculant is not less than 1.0 g / L. 10 8 CFU / mL, the *Thiobacillus ferrooxidans* bacterial suspension is in the stable mid-to-late stage, including the color of the bacterial suspension changing from light green to reddish-brown and producing a yellow precipitate, or the oxidation rate of ferrous ions in the 9K medium reaching 80%; the composition of the high-sulfur coal gangue, by mass percentage, includes total sulfur ≥3%, calcium and magnesium oxides 20%-30%, alumina ≤15%, and iron oxide 10%-20%; In the second aspect, in the process of mixing the coal gangue powder with water to form an aqueous solid-phase system, the solid-liquid ratio of the coal gangue powder to the water is 1:1-1:4 or the water content of the aqueous solid-phase system is 35%-65%; the process of inoculating the *Thiobacillus ferrooxidans* agent under acidic conditions for cultivation further includes: after the *Thiobacillus ferrooxidans* agent has entered a stable stage of cultivation, introducing acidophilic heterotrophic bacteria into the same system.

[0013] Thirdly, the present invention provides an improved material based on *Thiobacillus ferrooxidans*, which is prepared by the aforementioned preparation method. The improved material has the following uses: for improving saline-alkali land.

[0014] Beneficial Effects: This invention proposes a method for improving saline-alkali land based on *Thiobacillus ferrooxidans* modified materials. First, *Thiobacillus ferrooxidans* bacterial culture is expanded and inoculated into a culture medium for water bath shaking culture. When the *Thiobacillus ferrooxidans* bacterial culture reaches the mid-to-late stable stage, *Thiobacillus ferrooxidans* inoculum is obtained. High-sulfur coal gangue, after removing impurities, is sequentially air-dried, crushed, and ground to obtain coal gangue powder. Then, the coal gangue powder is mixed with water to form an aqueous solid-phase system, and *Thiobacillus ferrooxidans* inoculum is inoculated under acidic conditions for culture. After culture, fungi are introduced into the aqueous solid-phase system for degradation and transformation, resulting in bioactivated coal gangue. *Thiobacillus ferrooxidans*, as an acidophilic chemoautotrophic bacterium, can degrade and transform sulfur (S, S) through oxidation-reduction of sulfur (S, S). 2- (etc.) and ferrous ions (Fe 2+The process involves obtaining energy from sulfur dioxide and ferric iron, which can then be converted into acidic substances and effective calcium and magnesium ions that are readily available to saline-alkali soils by ferrous thiobacillus. This process activates and corrodes the sulfur dioxide in high-sulfur coal gangue, increasing its surface area and promoting the dissolution of organic matter. Furthermore, the acidic substances and ferric iron produced can further enhance free radical activity, promoting the decomposition of large organic molecules in high-sulfur coal gangue into small organic molecules that can be utilized by soil bacteria. Furthermore, ferric iron and organic matter can promote the aggregation of saline-alkali soils and accelerate sodium leaching, thus enabling the pre-activation of high-sulfur coal gangue from industrial solid waste using microbial technology. This accelerates the release of its effective components, significantly shortens the improvement cycle, and improves its efficiency in improving saline-alkali land. By organically combining *Thiobacillus ferrooxidans* with high-sulfur coal gangue, the environmentally polluting high-sulfur coal gangue can be transformed into a valuable soil conditioner, achieving "waste treatment with waste," turning waste into treasure. This not only disposes of solid waste but also provides low-cost materials for saline-alkali land improvement, making it cost-effective and environmentally friendly. During the activation process, the introduction of fungi can promote the further depolymerization and transformation of the complex organic carbon structure in the coal gangue through the secretion of extracellular enzymes. A soil amendment was prepared by mixing bio-activated coal gangue and low-sulfur coal gangue. The low-sulfur coal gangue improved the aeration and water leaching conditions of saline-alkali soil through the particle skeleton effect, thereby achieving physical structure regulation and overall improvement of the physicochemical properties of saline-alkali soil. The application mass ratio and total application amount of bio-activated coal gangue and low-sulfur coal gangue were determined. The amendment was prepared according to the application mass ratio, and the amendment was uniformly mixed and cultured with saline-alkali soil samples according to the total application amount to precisely control the application amount of the amendment. The effectiveness of the amendment was verified. After the effectiveness was verified, the amendment was applied to the target saline-alkali land after tillage to ensure the application effect of the amendment and avoid blind application. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating a method for improving saline-alkali land using modified materials based on *Thiobacillus ferrooxidans* in an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0018] Furthermore, throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0019] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0020] Example 1 like Figure 1 As shown, this embodiment provides a method for improving saline-alkali land based on *Thiobacillus ferrooxidans* modified materials. The method includes: S101 inoculating *Thiobacillus ferrooxidans* bacterial culture into a culture medium for water bath shaking culture, obtaining *Thiobacillus ferrooxidans* inoculum when the bacterial culture is in the stable mid-to-late stage; S102 removing impurities from high-sulfur coal gangue and then sequentially air-drying, crushing, and grinding it to obtain coal gangue powder; S103 mixing the coal gangue powder with water to form an aqueous solid-phase system, and inoculating it with the *Thiobacillus ferrooxidans* inoculum under acidic conditions for culture, and after culture is completed, in the aqueous solid-phase system... Fungi are introduced to degrade and transform the coal gangue, resulting in bio-activated coal gangue. S104 determines the application mass ratio and total application amount of the bio-activated coal gangue and low-sulfur coal gangue. S105 mixes the bio-activated coal gangue and low-sulfur coal gangue according to the application mass ratio to obtain an improved material. S106 collects soil samples from the target saline-alkali land and pre-treats the soil to obtain a saline-alkali soil sample. S107 uniformly mixes and cultivates the improved material and the saline-alkali soil sample according to the total application amount to verify the effectiveness of the improved material. S108, after verification of effectiveness, the improved material is applied to the plowed target saline-alkali land for improvement. Specifically, impurities in the high-sulfur coal gangue are manually removed, and the material is crushed using a jaw crusher and ground to below 150 mesh before use.

[0021] Specifically, this invention proposes a method for improving saline-alkali land based on *Athiopyrobacter ferrooxidans*, which achieves saline-alkali land improvement through the synergistic effect of chemical and physical structural regulation. First, *Athiopyrobacter ferrooxidans* bacterial culture is expanded and inoculated into a culture medium for water bath shaking culture. When the *Athiopyrobacter ferrooxidans* bacterial culture reaches the mid-to-late stable stage, *Athiopyrobacter ferrooxidans* inoculum is obtained. High-sulfur coal gangue, after removing impurities, is sequentially air-dried, crushed, and ground to obtain coal gangue powder. Then, the coal gangue powder is mixed with water to form an aqueous solid-phase system, and *Athiopyrobacter ferrooxidans* inoculum is inoculated under acidic conditions for culture. After culture, fungi are introduced into the aqueous solid-phase system for degradation and transformation, resulting in bioactivated coal gangue. *Athiopyrobacter ferrooxidans*, as an acidophilic chemoautotrophic bacterium, can degrade and transform sulfur (S₂, S₂) through oxidation-reduction of sulfur (S₂, S₃). 2- (etc.) and ferrous ions (Fe 2+ The process involves obtaining energy from sulfur dioxide and ferric iron, which can then be converted into acidic substances and effective calcium and magnesium ions that are readily available to saline-alkali soils by ferrous thiobacillus. This process activates and corrodes the sulfur dioxide in high-sulfur coal gangue, increasing its surface area and promoting the dissolution of organic matter. Furthermore, the acidic substances and ferric iron produced can further enhance free radical activity, promoting the decomposition of large organic molecules in high-sulfur coal gangue into small organic molecules that can be utilized by soil bacteria. Furthermore, ferric iron and organic matter can promote the aggregation of saline-alkali soils and accelerate sodium leaching, thus enabling the pre-activation of high-sulfur coal gangue from industrial solid waste using microbial technology. This accelerates the release of its effective components, significantly shortens the improvement cycle, and improves its efficiency in improving saline-alkali land. By organically combining *Thiobacillus ferrooxidans* with high-sulfur coal gangue, the environmentally polluting high-sulfur coal gangue can be transformed into a valuable soil conditioner, achieving "waste treatment with waste," turning waste into treasure. This not only disposes of solid waste but also provides low-cost materials for saline-alkali land improvement, making it cost-effective and environmentally friendly. During the activation process, the introduction of fungi can promote the further depolymerization and transformation of the complex organic carbon structure in the coal gangue through the secretion of extracellular enzymes. A soil amendment was prepared by mixing bio-activated coal gangue and low-sulfur coal gangue. The low-sulfur coal gangue improved the aeration and water leaching conditions of saline-alkali soil through the particle skeleton effect, thereby achieving physical structure regulation and overall improvement of the physicochemical properties of saline-alkali soil. The application mass ratio and total application amount of bio-activated coal gangue and low-sulfur coal gangue were determined. The amendment was prepared according to the application mass ratio, and the amendment was uniformly mixed and cultured with saline-alkali soil samples according to the total application amount to precisely control the application amount of the amendment. The effectiveness of the amendment was verified. After the effectiveness was verified, the amendment was applied to the target saline-alkali land after tillage to ensure the application effect of the amendment and avoid blind application.

[0022] In some possible implementations, determining the application mass ratio and total application amount of the bio-activated coal gangue and low-sulfur coal gangue includes: calculating the theoretical dry basis application amount G of high-sulfur coal gangue according to formula (1); (1); In equation (1), K is a coefficient, and CEC is the cation exchange capacity of the saline-alkali soil sample. This represents the initial exchangeable sodium percentage of the saline-alkali soil sample. The target exchangeable sodium percentage for the saline-alkali soil sample is determined; the application amount of bio-activated coal gangue is determined based on the theoretical dry basis dosage of high-sulfur coal gangue; the application mass ratio of bio-activated coal gangue and low-sulfur coal gangue is determined, and the application amount of low-sulfur coal gangue is determined based on the application mass ratio; the total application amount is determined based on the application amounts of bio-activated coal gangue and low-sulfur coal gangue; wherein the total application amount accounts for 10%-25% of the mass of saline-alkali soil, and the application mass ratio is 0.5:1-2:1. Specifically, before calculating the theoretical dry basis dosage G of high-sulfur coal gangue according to formula (1), the following is also included: measuring the cation exchange capacity CEC and the initial exchangeable sodium percentage of the saline-alkali soil sample. Set the target exchangeable sodium percentage for the saline-alkali soil sample. Choose a K value, where K is an empirical coefficient of 150-300. A larger K value can be chosen if the soil conditions are more complex or the expected activity of the coal gangue is lower.

[0023] This is because adding sufficient calcium ions (Ca) to the soil... 2+ It can displace sodium ions (Na) +This reduces the percentage of exchangeable sodium in saline-alkali soil. Therefore, the high-sulfur coal gangue calculation formula (1) of this invention is based on the cation exchange principle of soil chemistry and combined with high-sulfur coal gangue of specific components. By introducing a correction factor, coefficient K, the actual application amount under microbial activation conditions is corrected. Then, the application amount of bio-activated coal gangue is determined based on the theoretical dry basis application amount of high-sulfur coal gangue. Then, the application mass ratio of bio-activated coal gangue and low-sulfur coal gangue is determined. Based on the application mass ratio, the application amount of low-sulfur coal gangue is determined. Finally, the total application amount is determined based on the application amount of bio-activated coal gangue and the application amount of low-sulfur coal gangue. This ensures that the application amount and effect of the amendment can be precisely controlled according to the specific conditions of saline-alkali soil, avoiding blind application, and is highly targeted and controllable. The application ratio of bio-activated coal gangue to low-sulfur coal gangue is typically selected within the range of 0.5:1 to 2:1. This ratio is used to determine the amount of low-sulfur coal gangue used. This range is an empirically optimized range derived from extensive field trials, aiming to balance the contributions of chemical and physical amendments. In practical applications, the total application rate (10%-25%) can be adjusted appropriately within this range based on the specific physical structure of the soil (such as the degree of compaction and permeability). For example, for soils with poor physical structure, a higher proportion of low-sulfur coal gangue (such as 3:2) can be selected. This ratio is a guideline, and its fundamental purpose is to ensure that the total application rate is within an effective and economical range.

[0024] In some possible implementations, verifying the effectiveness of the improved material includes: periodically testing the monitoring indicators of the saline-alkali soil sample, determining whether the monitoring indicators reach a preset threshold, and if the preset threshold is reached, verifying the effectiveness of the improved material; wherein, the testing indicators include pH value, electrical conductivity (EC), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP), and reaching the preset threshold includes at least one of the following: pH value drops below 8.5, electrical conductivity drops below 4 dS / m, sodium adsorption ratio drops below 15 with a decrease rate greater than 30%, or soil exchangeable sodium percentage drops below 15%.

[0025] This is because by regularly testing the pH, EC, SAR, and ESP of saline-alkali soil samples, it is determined whether the pH, EC, SAR, and ESP have reached preset thresholds. If one of the following conditions is met: pH drops below 8.5, EC drops below 4 dS / m, SAR drops below 15 with a decrease rate greater than 30%, or ESP drops below 15%, the effectiveness of the amendment material is verified. Once the effectiveness verification of the amendment material is confirmed, it can be applied to the field. Through the laboratory effectiveness verification step, it can be ensured that the application amount and effect of the amendment material can be precisely controlled according to the specific conditions of the saline-alkali soil, avoiding blind application.

[0026] In some possible implementations, verifying the effectiveness of the improved material includes: periodically testing the monitoring indicators of the saline-alkali soil sample to determine whether the monitoring indicators reach preset thresholds. If the preset thresholds are reached, the effectiveness of the active amendment is verified. The testing indicators include pH value, electrical conductivity (EC), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP). The preset thresholds are preferably: pH value dropping below 8.0, electrical conductivity dropping below 3 dS / m, sodium adsorption ratio dropping below 15 with a decrease rate greater than 30%, or soil exchangeable sodium percentage dropping below 10%.

[0027] In some possible implementations, verifying the effectiveness of the improved material further includes: if the preset threshold is not reached, checking and optimizing the culture activity of the *Thiobacillus ferrooxidans* agent and repeating steps S101, S103, S104, and S107 sequentially; or reselecting the addition ratio and repeating step S107; or checking and optimizing the high-sulfur coal gangue and repeating steps S102, S103, S104, and S107 sequentially; until the monitoring index reaches the preset threshold. Specifically, checking and optimizing the culture activity of the *Thiobacillus ferrooxidans* agent includes: (1) checking the activity of the strain: checking and confirming whether the *Thiobacillus ferrooxidans* agent after culture has reached a viable count of not less than 1.0 × 10⁻⁶. 8 If the standard of CFU / mL is not met, the culture conditions (temperature, shaking speed), culture medium composition or preservation status of the *Thiobacillus ferrooxidans* strain need to be checked. For strains preserved for a long time, it may be necessary to perform 1-2 more generations of transfer to restore viability; (2) Optimize the culture time: Ensure that the *Thiobacillus ferrooxidans* strain is inoculated and expanded in the middle and late stages of the logarithmic growth phase (when the bacterial solution is dark red), at which time the strain activity is the highest. The reselection of the addition ratio includes selecting a larger application ratio as the reselected addition ratio based on the range of the addition ratio (e.g., 1:5-1:20) (e.g., adjusting from 1:10 to 1:6). The inspection and optimization of high-sulfur coal gangue includes: (1) verifying the composition: check whether the total sulfur content of high-sulfur coal gangue is not less than 3%, and whether the CaO+MgO content is between 20% and 30%. If the composition does not meet the standards, qualified coal gangue raw materials need to be replaced; (2) optimizing the particle size: ensure that the coal gangue powder is ground to below 150 mesh to increase the specific surface area, which is conducive to the attachment and activation of microorganisms.

[0028] This is because if pH, EC, SAR, and ESP do not reach the preset thresholds (e.g., the decrease in pH and ESP is not significant), it indicates that the activity or dosage of the current activated composite amendment is insufficient. In this case, it is necessary to check and optimize the culture activity of the *Thiobacillus ferrooxidans* agent and repeat steps S101, S103, and S106 sequentially, or reselect the addition ratio and repeat step S106, or check and optimize the high-sulfur coal gangue and repeat steps S102, S103, and S106 sequentially until the monitoring indicators reach the preset thresholds. Through the cycle of "preparation-verification-feedback optimization," the optimal amendment scheme for a specific saline-alkali land can be quickly determined, ensuring the reliability and universality of the method.

[0029] In some possible implementations, the process of collecting soil from the target saline-alkali land and pre-treating the soil includes: collecting topsoil from the target saline-alkali land at a depth of 0-20 cm using a multi-point mixed sampling method; sequentially air-drying the topsoil, removing debris, grinding it, and passing it through a 2 mm sieve. The multi-point mixed sampling method is an "S"-shaped multi-point mixed sampling method.

[0030] Those skilled in the art will understand that the “S”-shaped multi-point mixed sampling method is used to select 5-10 points to collect topsoil from the target saline-alkali land at a depth of 0-20cm. The topsoil is then air-dried, cleaned of debris, ground, and passed through a 2mm sieve to obtain a homogenized saline-alkali soil sample.

[0031] In some possible implementations, before uniformly mixing and culturing the improved material and the saline-alkali soil sample according to the added ratio, the method further includes: adjusting the moisture content of the saline-alkali soil sample to 60%-70% of the field water holding capacity of the target saline-alkali land with deionized water.

[0032] In some possible implementations, the improved material is applied to the target saline-alkali land after tillage, with the tillage depth being 15-30 cm.

[0033] In some possible embodiments, the culture medium is 9K medium, wherein ferrous sulfate heptahydrate is added at a concentration of 44.7 g / L, the analytical purity of ferrous sulfate heptahydrate is greater than 99.5%, the water bath shaking culture is performed at a speed of 200 r / min and a temperature of 26°C, and the viable count of the *Thiobacillus ferrooxidans* inoculum is not less than 1.0 g / L. 10 8CFU / mL, the *Thiobacillus ferrooxidans* bacterial culture is in the stable mid-to-late stage, including the color of the bacterial culture changing from light green to reddish-brown and producing a yellow precipitate, or the oxidation rate of ferrous ions in the 9K medium reaching 80%. Short-term preserved strains are stored at room temperature, while long-term preserved strains are cryopreserved in glycerol. The *Thiobacillus ferrooxidans* bacterial culture medium is sterilized by total liquid filtration or ferrous sulfate culture medium filtration. The 9K medium is sterilized at 120°C for 20 minutes. Filtration sterilization requires a <0.22 micron filter membrane, and all equipment is sterilized.

[0034] Those skilled in the art will understand that the culture medium is 9K medium, which contains ferrous sulfate heptahydrate at a concentration of 44.7 g / L, and the ferrous sulfate in the 9K medium can serve as a supplementary energy source; the water bath shaking culture is conducted at a speed of 200 r / min and a temperature of 26°C, ensuring sufficient oxygen. The culture conditions can be flexibly adjusted according to the activity of the preserved strain, and the required number of viable *Thiobacillus ferrooxidans* is no less than 1.0. 10 8 CFU / mL; The color of the bacterial culture of *Thiobacillus ferrooxidans* changes from light green, orange-yellow, orange-red, dark red to reddish-brown, eventually forming a yellow precipitate. This is also a sign that the strain is in the middle to late stage of its stationary phase. Therefore, the completion time of cultivation can be determined by the color change of the bacterial culture or by the oxidation rate of ferrous ions in the culture medium reaching 80%, to ensure the viability of the strain. Generally, the water bath shaking culture time is 3-4 days. The best time for expansion culture is in the middle of the logarithmic growth phase of the strain, that is, just before the dark red bacterial culture is about to produce a precipitate. Long-term stored strains need 2-3 generations of transfer to enhance their viability.

[0035] In some possible embodiments, the high-sulfur coal gangue comprises, by mass percentage, total sulfur ≥3%, calcium and magnesium oxides (CaO + MgO) 20%-30%, alumina ≤15%, and iron oxide 10%-20%. SiO2, Fe2O3, and K2O are not specifically required. The total content of water-soluble and acid-soluble calcium and magnesium oxides is preferably 8%-15%, but the specific content needs to be determined based on the cation exchange capacity and exchangeable sodium percentage of the target saline-alkali soil. In the process of mixing the coal gangue powder with water to form an aqueous solid-phase system, the solid-liquid ratio of the coal gangue powder to the water is 1:1-1:4 (g:mL), or the water content of the aqueous solid-phase system is 35%-65%. The inoculation of the *Thiobacillus ferrooxidans* agent under acidic conditions further includes: after the *Thiobacillus ferrooxidans* agent has entered a stable stage, introducing acidophilic heterotrophic bacteria into the same system.

[0036] This is because, in the aqueous solid-phase system formed by mixing coal gangue powder with water, the solid-liquid ratio of coal gangue powder to water is 1:1-1:4 (preferably 1:2-1:3) or the water content of the aqueous solid-phase system is 35%-65% (preferably 45%-55%). Within this range, the system can ensure the dissolved oxygen and ion mass transfer conditions required for microbial growth and reaction, and can also keep the material in a stirable aqueous solid-phase state, which is suitable for engineering operation. After the *Thiobacillus ferrooxidans* inoculant enters the stable stage, acidophilic heterotrophic bacteria are introduced into the same system. The acidophilic heterotrophic bacteria can reduce the accumulation level of low-molecular-weight organic metabolites produced during the growth of *Thiobacillus ferrooxidans* in the reaction system by metabolizing them, thereby weakening the metabolic inhibition effect on the sulfur oxidation reaction and maintaining the stable progress of the pyrite mineral oxidation reaction.

[0037] In some possible implementations, the volume ratio of the acidophilic heterotrophic bacteria to the *Thiobacillus ferrooxidans* inoculum is 5:1-10:1, or equivalently, the inoculum amount of the acidophilic heterotrophic bacteria accounts for 0.5%-3% (v / v) of the reaction system volume, preferably 1%-2% (v / v). With the above ratio setting, the acidophilic heterotrophic bacteria can effectively metabolize low-molecular-weight organic metabolites such as pyruvate and acetic acid produced by sulfur-oxidizing bacteria without significantly competitively inhibiting the sulfur oxidation reaction.

[0038] In some possible embodiments, the acidophilic heterotrophic bacterium is *Acidiphilium cryptoum* DSM 2389ᵀ or a functionally equivalent strain; the cryptic acidophilus is cultured in a modified 9K organic carbon medium, which is composed of 9K inorganic salts with the addition of a low-molecular-weight organic carbon source, selected from sodium pyruvate or sodium acetate, at an amount of 1.0–2.0 g / L. The culture conditions are: initial pH 3.0–3.5, culture temperature 28–32 ℃, and aerobic shaking culture at a shaking speed of 150–180 r·min⁻. 1 The hidden acidophilic bacteria are not used as the initial inoculum, but are introduced into the same reaction system after *Thiobacillus ferrooxidans* enters the logarithmic growth phase. Their role is to metabolize low-molecular-weight organic metabolites such as pyruvate and acetic acid produced during the growth of *Thiobacillus ferrooxidans*, thereby maintaining the stable progress of the sulfur oxidation reaction.

[0039] In some possible embodiments, the fungus is *Cryptococcus albidus* CBS142ᵀ or a functionally equivalent strain thereof, and the inoculum amount of the fungus is 2%-5% (v / w) based on the wet weight of coal gangue, preferably 3% (v / w). The *Cryptococcus albidus* CBS142ᵀ is cultured in YPD fungal medium, which, per 1 L, comprises the following: 10 g yeast extract, 20 g peptone, and 20 g glucose. The culture conditions are: initial pH 5.0–6.0, culture temperature 26–30 ℃, and can be cultured by shaking or static incubation, wherein the shaking rotation speed is 120–150 r·min⁻. 1 The fungus is not co-cultured with *Thiobacillus ferrooxidans* and *Lystrophic acidophilus*, but is introduced into the treatment system after the oxidation reaction of pyrite minerals is basically completed. Before introduction, the pH of the system is adjusted to 4.5–5.5 to promote fungal growth and the activity of its extracellular enzymes.

[0040] In some possible implementations, during the microbial activation stage, *Thiobacillus ferrooxidans* is used as the main desulfurizing bacterium. The inoculation amount of the *Thiobacillus ferrooxidans* agent is controlled at 5%-15% (v / v) based on the total volume of the reaction system, preferably 8%-12% (v / v), which can ensure that the oxidation reaction of pyrite minerals starts within a reasonable time and maintains a high reaction rate, while taking into account the cost of agent preparation.

[0041] In some possible embodiments, the total amount of the *Thiobacillus ferrooxidans* inoculant, the acidophilic heterotrophic bacteria, and the fungi accounts for 6%-20% (v / v) of the reaction system volume, preferably 10%-15% (v / v). Specifically, the total amount is determined based on the reaction initiation rate and system stability, using the redox potential (ORP) rise rate, Fe... 2 The oxidation rate and the rate of change of pH in the system are used as process control indicators. Under the premise of ensuring that the reaction can start and maintain stable oxidation within a predetermined time, a lower amount of bacterial agent is selected to balance treatment efficiency and engineering cost.

[0042] In some possible implementations, the low-sulfur coal gangue is selected from coal gangue produced during coal mining or washing, and its total sulfur content is lower than that of the high-sulfur coal gangue. The low-sulfur coal gangue has a low content of pyrite minerals, and its total sulfur content is not higher than 0.5%. Its mineral composition is mainly composed of one or more of quartz, feldspar, and clay minerals. The low-sulfur coal gangue does not participate in the microbial culture stage of the high-sulfur coal gangue, but is applied together with the bio-activated coal gangue to saline-alkali soil after the microbial treatment is completed and bio-activated coal gangue is obtained, so as to provide physical structure regulation during the saline-alkali soil improvement process.

[0043] In some possible implementations, the low-sulfur coal gangue is crushed and screened before being applied to the target saline-alkali land. The screened low-sulfur coal gangue has a particle size of 0.5–2 mm. The low-sulfur coal gangue and the bio-activated coal gangue are co-incorporated into the topsoil of the target saline-alkali land.

[0044] Example 2 This second embodiment provides a method for preparing an improved material based on *Thiobacillus ferrooxidans*. The method includes: expanding and inoculating *Thiobacillus ferrooxidans* bacterial culture into a culture medium for water bath shaking culture; obtaining *Thiobacillus ferrooxidans* inoculum when the bacterial culture is in the stable mid-to-late stage; removing impurities from high-sulfur coal gangue and then sequentially air-drying, crushing, and grinding it to obtain coal gangue powder; mixing the coal gangue powder with water to form an aqueous solid-phase system, and inoculating it with the *Thiobacillus ferrooxidans* inoculum under acidic conditions for culture; after culture, introducing fungi into the aqueous solid-phase system for degradation and transformation to obtain bio-activated coal gangue; determining the application mass ratio of the bio-activated coal gangue and low-sulfur coal gangue; and mixing the bio-activated coal gangue and low-sulfur coal gangue according to the application mass ratio to obtain the improved material.

[0045] Specifically, this embodiment provides a method for preparing a modified material based on *Thiobacillus ferrooxidans*. First, *Thiobacillus ferrooxidans* bacterial culture is expanded and inoculated into a culture medium for water bath shaking culture. When the *Thiobacillus ferrooxidans* bacterial culture reaches the mid-to-late stable stage, *Thiobacillus ferrooxidans* inoculum is obtained. Simultaneously, high-sulfur coal gangue is removed of impurities and then sequentially air-dried, crushed, and ground to obtain coal gangue powder. Then, the coal gangue powder is mixed with water to form an aqueous solid-phase system, and inoculated with the *Thiobacillus ferrooxidans* inoculum under acidic conditions for culture, causing the pyrite minerals in the coal gangue to undergo biological oxidation. When the sulfur oxidation reaction enters a stable stage... Subsequently, acidophilic heterotrophic bacteria were introduced into the same system. Through their metabolism of low-molecular-weight organic metabolites such as pyruvate and acetic acid produced by sulfur-oxidizing bacteria, the oxidation reaction of pyrite minerals was maintained. After the oxidation reaction of pyrite minerals was basically completed, fungi were introduced. Through the action of their secreted extracellular enzymes, the stable organic carbon skeleton structure in coal gangue was degraded and transformed to obtain bio-activated coal gangue. Finally, the bio-activated coal gangue and low-sulfur coal gangue were mixed to obtain improved materials, which can be directly applied to the topsoil of saline-alkali land. Through the synergistic effect of chemical regulation and physical structure regulation, the overall improvement of the saline-alkali land's geochemical properties was achieved.

[0046] In some possible embodiments, the culture medium is 9K medium, wherein ferrous sulfate heptahydrate is added to the 9K medium at a concentration of 44.7 g / L, the water bath shaking culture is performed at a speed of 200 r / min and a temperature of 26°C, and the viable count of the *Thiobacillus ferrooxidans* inoculum is not less than 1.0. 10 8 CFU / mL, wherein the *Thiobacillus ferrooxidans* bacterial solution is in the stable mid-to-late stage, including the formation of a yellow precipitate or an oxidation rate of ferrous ions reaching 80% in the 9K medium; the composition of the high-sulfur coal gangue, by mass percentage, includes total sulfur ≥3%, calcium and magnesium oxides 20%-30%, aluminum oxide ≤15%, and iron oxide 10%-20%; In some possible implementations, in the process of mixing the coal gangue powder with water to form an aqueous solid-phase system, the solid-liquid ratio of the coal gangue powder to the water is 1:1 to 1:4, or the water content of the aqueous solid-phase system is 35% to 65%.

[0047] In some possible implementations, the improved material is used for improving saline-alkali land.

[0048] It should be noted that the improved material prepared by the method of Acidithiobacillus ferrooxidans based on this embodiment 2 is the same as the improved material described in this embodiment 1. Its implementation principle and technical concept are exactly the same as those in embodiment 1. Therefore, for the parts not described in detail in this embodiment 2, please refer to embodiment 1. They will not be repeated here.

[0049] To further illustrate the technical solution of this application and support the technical problem to be solved by this application, specific examples of the method for improving saline-alkali land based on the modified material of *Thiobacillus ferrooxidans* are provided below, as in Examples 3-4. It should be noted that the high-sulfur coal gangue used in Examples 3-4 all came from a mine in Shanxi Province, and its chemical composition (mass percentage) is as follows: total sulfur 4.2%, CaO 18.5%, MgO 7.3% (total calcium and magnesium oxides CaO+MgO=25.8%), Fe2O3 16.1%, Al2O3 10.5%.

[0050] Example 3 This embodiment 3 provides a method for improving saline-alkali land based on *Thiobacillus ferrooxidans* as a modifier. A slightly saline-alkali farm was selected as the experimental site. The soil type in the experimental area was silty loam, and the tillage depth was 0–20 cm. The physicochemical properties of the soil before treatment were as follows: soil pH was 8.4, and electrical conductivity (EC) was 2.8 dS·m⁻. 1 The exchangeable sodium percentage (ESP) is 12.6%. Improvement goals: to rapidly reduce soil alkalinity and sodium ion damage, and improve soil structure.

[0051] The method includes: Preparation of *Thiobacillus ferrooxidans* bacterial agent (S201): Take the preserved *Thiobacillus ferrooxidans* glycerol cryovial and thaw it at room temperature to obtain *Thiobacillus ferrooxidans* bacterial suspension. Inoculate the *Thiobacillus ferrooxidans* bacterial suspension at a 10% inoculum into sterilized 9K medium (sterilized at 120℃ for 20 minutes). The 9K medium has been supplemented with 44.7 g / L of analytically pure ferrous sulfate heptahydrate (ferrous sulfate solution sterilized by filtration through a 0.22-micron filter membrane). Place the medium in a water bath shaker at 200 r / min and 26℃ for incubation. After approximately 3 days of incubation, the bacterial suspension color changes from light green to orange-yellow, then orange-red, and finally deep red. The oxidation rate of ferrous ions exceeds 80%, and the viable cell count reaches 2.5 × 10⁻⁶. 8 CFU / mL indicates that the *Thiobacillus ferrooxidans* bacterial culture is in the mid-to-late stable stage, and the seed fermentation broth preparation is complete, yielding *Thiobacillus ferrooxidans* inoculum, which can be used for subsequent steps. For long-term preserved strains with insufficient viability, 2-3 generations of transfer can be performed to restore viability; S202 High-sulfur coal gangue pretreatment: After removing impurities, the high-sulfur coal gangue is air-dried, crushed and ground, and then passed through a 200-mesh sieve to obtain coal gangue powder. Preparation of S203 bio-activated coal gangue: Coal gangue powder and water were mixed at a solid-liquid ratio of 1:1.25, and the initial pH was adjusted to 2.0 to form an aqueous solid-phase system. Under acidic conditions, 10% (by volume) of *Thiobacillus ferrooxidans* inoculum was inoculated and cultured with shaking at 26°C. After 5 days of culture, when the system's ORP continued to rise and Fe... 2 When the concentration of *Acidiphilium cryptum* DSM 2389ᵀ bacterial suspension (with a viable count of not less than 1.0 × 10⁺) decreases significantly, introduce the *Acidiphilium cryptum* DSM 2389ᵀ bacterial suspension at a volume ratio of 8:1 (to *Acidiphilium ferrooxidans* inoculum and *Acidiphilium cryptum*). 8 After culturing for 7 days (CFU / mL), once the oxidation reaction of pyrite minerals was basically completed, the pH of the system was adjusted to 5.0. Cryptococcus albidus CBS 142ᵀ (biomass, i.e., dry weight not less than 5.0 g / L) bacterial culture was introduced at 3% of the wet weight of coal gangue and cultured for 5 days to obtain bio-activated coal gangue. S204 Determines the application mass ratio and total application rate: This embodiment is for slightly saline-alkali land and adopts an empirically validated scheme to simplify operation and ensure effectiveness. Total application rate: The total application rate of the amendment materials (bio-activated coal gangue + low-sulfur coal gangue) accounts for 15% of the soil mass; Internal ratio: The mass ratio of bio-activated coal gangue to low-sulfur coal gangue is 2:1. Therefore, the amount of bio-activated coal gangue used is 10%, and the amount of low-sulfur coal gangue used is 5%.

[0052] The ratio is based on the preferred empirical value for treating this type of mild salinization. It can effectively improve the physical structure of the soil while ensuring the effect of chemical improvement, and the total dosage falls within the effective range of 10%-25%. Preparation of S205 modified material: Bio-activated coal gangue and low-sulfur coal gangue with a particle size of 0.5-2mm are mixed at a mass ratio of 2:1 to obtain the modified material; S206 saline-alkali soil pretreatment: The topsoil layer of the target saline-alkali land with a depth of 0-20cm was collected using the "S"-shaped multi-point mixed sampling method. The topsoil layer was then air-dried, cleaned of debris, ground, and passed through a 2mm sieve to obtain saline-alkali soil samples. S207 validity verification experiment: Weigh 500g of saline-alkali soil sample that has passed through a 2mm sieve, mix it thoroughly with 50g of amendment material (amendment material: saline-alkali soil sample = 1:10), and adjust the moisture content to 70% of field capacity with deionized water. Place the mixture in a plastic cup and incubate it in a 25℃ constant temperature incubator for 30 days. Weigh the mixture regularly and add water to maintain humidity. At the same time, set up control group 1 and control group 2. Control group 1 is a control with only an equal amount of unactivated coal gangue powder (1:10) added, and control group 2 is a blank saline-alkali soil control without any amendment material added.

[0053] After cultivation, the saline-alkali soil samples were analyzed and tested to verify the effectiveness of the improvement material. The results are shown in Table 1. Table 1 detection indicators initial value Experimental group (after 30 days) Control group 1 (not activated, after 30 days) Control group 2 (blank, 30 days later) pH value 8.4 7.8 8.3 8.4 EC (dS / m) 2.8 1.7 2.5 2.8 ESP (%) 12.6 8.9 11.5 12.7 in conclusion: The modified material prepared in this embodiment can significantly improve the physicochemical properties of slightly saline-alkali soil, reducing ESP from 12.6% to 8.9%, fully achieving the expected improvement target. The comparison with control group 1 demonstrates that microbial activation is the key to the improvement effect.

[0054] Field demonstration application of S208 improved material: The improved material was mixed into the topsoil layer (0–20 cm) of the experimental area at 15% of the soil mass, of which bio-activated coal gangue accounted for about 10% and low-sulfur coal gangue accounted for about 5%. After tilling and mixing, the mixture was irrigated and washed.

[0055] Monitoring the effects of the improvement: After 30 days of natural incubation and leaching, the changes in soil indicators in the experimental area were measured and are shown in Table 2.

[0056] in conclusion: The empirical value scheme (total dosage 15%, internal ratio 2:1) adopted in this embodiment showed significant effects in the improvement of mild saline-alkali land, and all key indicators were effectively improved, proving the reliability and efficiency of the scheme in practical applications.

[0057] Table 2 detection indicators initial value Improved Group (45 days later) Improvement range pH value 8.4 7.8 Decrease of 7.1% EC (dS / m) 2.8 1.7 Reduced by 39.3% ESP (%) 12.6 8.9 Decrease of 29.4% Saturated hydraulic conductivity (cm / h) 0.19 0.27 Increased by 42.1% Example 4 Example 4 provides a method for improving saline-alkali land based on *Thiobacillus ferrooxidans* as a modifier. A moderately saline-alkali land was selected as the experimental site. The soil type in the experimental area was loamy clay, and the tillage depth was 0–20 cm. The soil physicochemical properties before treatment were as follows: pH 8.9, electrical conductivity 4.1 dS·m⁻. 1 The exchangeable sodium percentage is 21.3%, and the ion exchange capacity is 16.0 cmol(+) / kg. This soil has a heavy clay texture and a high bulk density (1.45 g / cm³). 3 The low saturated water conductivity (0.2 cm / h) indicates a problem of caking. Therefore, improvement schemes should focus on improving the physical structure.

[0058] Improvement goals: The improvement goals are to reduce ESP to below 15% and significantly improve soil permeability.

[0059] The method includes: Preparation of *Thiobacillus ferrooxidans* bacterial agent (S201): Take the preserved *Thiobacillus ferrooxidans* glycerol cryovial and thaw it at room temperature to obtain *Thiobacillus ferrooxidans* bacterial suspension. Inoculate the *Thiobacillus ferrooxidans* bacterial suspension at a 10% inoculum into sterilized 9K medium (sterilized at 120℃ for 20 minutes). The 9K medium has been supplemented with 44.7 g / L of analytically pure ferrous sulfate heptahydrate (ferrous sulfate solution sterilized by filtration through a 0.22-micron filter membrane). Place the medium in a water bath shaker at 200 r / min and 26℃ for incubation. After approximately 3 days of incubation, the bacterial suspension color changes from light green to orange-yellow, then orange-red, and finally deep red. The oxidation rate of ferrous ions exceeds 80%, and the viable cell count reaches 2.5 × 10⁻⁶. 8 CFU / mL indicates that the *Thiobacillus ferrooxidans* bacterial culture is in the mid-to-late stable stage, and the seed fermentation broth preparation is complete, yielding *Thiobacillus ferrooxidans* inoculum, which can be used for subsequent steps. For long-term preserved strains with insufficient viability, 2-3 generations of transfer can be performed to restore viability; S202 High-sulfur coal gangue pretreatment: After removing impurities, the high-sulfur coal gangue is air-dried, crushed and ground in sequence, and then passed through a 150-mesh sieve to obtain coal gangue powder. Preparation of S203 bio-activated coal gangue: Coal gangue powder and water were mixed at a solid-liquid ratio of 1:3 and the initial pH was adjusted to 2.0 to form an aqueous solid-phase system. Under acidic conditions, 12% (by volume) of *Thiobacillus ferrooxidans* inoculum was inoculated and cultured with shaking at 26°C. After 5 days of culture, when the system's ORP continued to rise and Fe... 2 When the concentration of ⁺ decreased significantly, Acidiphilium cryptum DSM 2389ᵀ bacterial solution was introduced at a volume ratio of 6:1 (Acidobacterium ferrooxidans inoculum to Acidiphilium cryptum) and cultured for another 7 days. After the oxidation reaction of pyrite minerals was basically completed, the pH of the system was adjusted to 5.0, and Cryptococcus albidus CBS 142ᵀ bacterial solution was introduced at 4% of the wet mass of coal gangue and cultured for 5 days to obtain bio-activated coal gangue. S204 determines the application mass ratio and total application amount: Step 1: Calculate the theoretical dry basis consumption of high-sulfur coal gangue.

[0060] Parameter selection criteria: Initial ESP = 21.3%, Target ESP = 15.0%. Soil CEC = 16.0 cmol(+) / kg. Given that the soil is moderately saline and alkaline with a sticky texture, stronger improvement measures are needed; the empirical coefficient K is set to 200.

[0061] According to the formula provided by the present invention The calculated effective component content (G) of coal gangue required per unit of soil is ≥200. 16 (21.3-15)=20160mg / kg soil=20.16 dry basis high-sulfur coal gangue / kg soil, that is, about 20.2 grams of high-sulfur coal gangue powder (dry basis) need to be applied per kilogram of soil to ensure the improvement effect; Step 2: Determine the application rate of bio-activated coal gangue based on the theoretical dry basis dosage of high-sulfur coal gangue. Calculation of the amount of bio-activated coal gangue used: In the preparation process of this embodiment, the solid-liquid ratio of high-sulfur coal gangue powder to water is 1:3 (g:mL), and inoculation with bacterial agent is required (the total inoculation amount accounts for about 15% of the system volume). It is calculated that approximately 4.74 grams of bio-activated coal gangue wet material can be prepared from each gram of high-sulfur coal gangue dry basis. Brief description of the calculation of the yield coefficient (4.74) for bio-activated coal gangue: Based on 1 kg dry weight: 1 kg dry weight + 3 kg water = 4 kg basic system. Then, add *Thiobacillus ferrooxidans* bacterial solution (4 L × 12% = 0.48 L), acidophilic heterotrophic bacteria solution (0.48 L / 6 = 0.08 L), and fungal solution (approximately 0.182 L, representing 4% of the total mass of 4.56 kg). The density of the bacterial solution is approximately equal to that of water, therefore the final total mass of wet material ≈ 1 + 3 + 0.48 + 0.08 + 0.182 = 4.742 kg. Yield coefficient = 4.742.

[0062] Therefore, 20.16 g of dry basis raw material can be used to prepare wet material = 20.16 g × 4.74 ≈ 95.6 g wet material / kg soil.

[0063] Therefore, the application rate of bio-activated coal gangue was determined to be 9.56% of the soil mass. For ease of operation, it was rounded up to 10% in practical applications.

[0064] Step 3: Determine the amount of low-sulfur coal gangue to be used based on the amount of bio-activated coal gangue applied. Calculation of low-sulfur coal gangue dosage: Given the soil compaction, based on experience, a higher proportion of low-sulfur coal gangue should be selected within the mass ratio range of 0.5:1 to 2:1 to rapidly build soil porosity. In this embodiment, a ratio of bio-activated coal gangue to low-sulfur coal gangue of 1:1 is selected.

[0065] Based on the selected 1:1 ratio, the amount of low-sulfur coal gangue used is 10% × 1 = 10%.

[0066] Step 4: Verify the total usage and determine the final plan: Total application rate = 10% (bioactivation) + 10% (low sulfur) = 20%.

[0067] Verification results: The total dosage of 20% falls within the safe and effective range of 10%-25% specified in this invention, indicating that the scheme is reasonable. Final dosage determination: Therefore, the application scheme is determined as follows: bio-activated coal gangue accounts for 10% of the soil mass, and low-sulfur coal gangue accounts for 10%, mixed in a 1:1 mass ratio.

[0068] Preparation of S205 modified material: Bio-activated coal gangue and low-sulfur coal gangue with a particle size of 0.5-2mm are mixed at a mass ratio of 1:1 to obtain the modified material; S206 Saline-alkali Soil Pretreatment: The topsoil layer with a depth of 0-20cm in the target saline-alkali land was collected using the "S"-shaped multi-point mixed sampling method. The topsoil layer was then air-dried, cleaned of debris, ground, and passed through a 2mm sieve to obtain saline-alkali soil samples. S207 effectiveness verification experiment: Weigh 500g of saline-alkali soil sample and mix it thoroughly with 100g of amendment material (amort material: saline-alkali soil sample = 1:5). Adjust the moisture content to 70% of field capacity with deionized water, place it in a plastic cup, and incubate it in a constant temperature incubator at 25℃ for 30 days. At the same time, control group 3 and control group 4 were set up. Control group 3 was a mixture of only an equal amount of unactivated coal gangue, and control group 4 was blank saline-alkali soil without any amendment.

[0069] Results and Analysis: The test results are shown in Table 3. Table 3 detection indicators initial value Experimental group (after 30 days) Control group 3 (not activated, after 30 days) Control group 4 (blank, 30 days later) pH value 8.9 8.2 8.7 8.9 EC (dS / m) 4.1 2.5 3.8 4.1 ESP (%) 21.3 14.5 19.5 21.5 Conclusion: Laboratory verification shows that the modified material prepared based on the dosage calculated using the G formula can significantly improve moderately saline-alkali soil, reducing ESP from 21.3% to 14.5%, successfully achieving the preset target (<15%). However, the effect of unactivated coal gangue is limited, proving that microbial synergistic activation is a key step. These results demonstrate the accuracy of the dosage formula in this invention and the effectiveness of the entire technical solution.

[0070] Field demonstration application of S208 soil amendment: The amendment was mixed into the topsoil layer (0–20 cm) of the experimental area at 20% of the soil mass and applied to 1 mu of experimental field. After being mixed into the topsoil layer of 0–20 cm by rotary tiller, the soil was irrigated and washed. The amendment contained approximately 12% bio-activated coal gangue and approximately 8% low-sulfur coal gangue.

[0071] Monitoring of improvement effect: The changes in soil indicators measured in the field after 45 days are shown in Table 4.

[0072] Field validation conclusions: The results of the field trials were in high agreement with the laboratory validation, indicating that the method of this invention also has a significant and stable improvement effect under moderately saline-alkali soil conditions. Soil chemical properties (pH, EC, ESP) and physical structure (bulk density, hydraulic conductivity) were improved simultaneously, making it suitable for field promotion and application.

[0073] Based on the effects of the embodiments, the preferred embodiment of the present invention is as follows: the bio-activated coal gangue and low-sulfur coal gangue are mixed at a mass ratio of 2:1. For slightly saline-alkali land, the total application amount of the amendment material accounts for 15% of the soil mass; for moderately saline-alkali land, it accounts for 20%; and for severely saline-alkali land, it accounts for 25%.

[0074] Table 4 detection indicators initial value Improved Group (45 days later) Improvement range pH value 8.9 8.2 Reduced by 7.9% EC (dS / m) 4.1 2.5 Reduced by 39.0% ESP (%) 21.3 14.5 Decreased by 31.9% <![CDATA[Soil bulk density (g / cm 3 )]]> 1.45 1.28 Reduced by 11.7% Saturated hydraulic conductivity (cm / h) 0.2 0.31 Increased by 55.0% In summary, the method for improving saline-alkali land based on *Thiobacillus ferrooxidans* of this invention involves sequentially introducing *Thiobacillus ferrooxidans*, acidophilic heterotrophic bacteria, and fungi into the same technical route to bioactivate high-sulfur coal gangue. The resulting bioactivated coal gangue is then mixed with low-sulfur coal gangue and directly applied to saline-alkali land, achieving synergistic improvement through chemical and physical structural regulation. Specifically, *Thiobacillus ferrooxidans* drives the bio-oxidation reaction of pyrite minerals in the coal gangue; acidophilic heterotrophic bacteria metabolize low-molecular-weight organic metabolites generated during sulfur oxidation to maintain reaction stability; fungi degrade the stable organic carbon skeleton structure in the coal gangue; and low-sulfur coal gangue improves the physical structure and leaching conditions of the saline-alkali soil. The above components work synergistically within the same methodological system, enabling the improved materials to be directly applied to saline-alkali land in the field with comprehensive improvement effects. They can not only effectively reduce soil pH and salinity (EC), but also significantly reduce ESP and SAR, fundamentally improving the sodium alkalization problem of the soil, promoting the formation of soil aggregates, restoring soil health, and are highly operable and easy to promote. The method steps are clear, the parameters are well-defined, and the microbial culture and activation process is easy to control and scale up, which is conducive to its promotion and application in actual agricultural production.

[0075] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0076] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0077] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for improving saline-alkali land based on the synergistic effect of microorganisms and minerals, characterized in that, The method includes: The bacterial culture of *Thiobacillus ferrooxidans* was expanded and inoculated into a culture medium and then cultured in a water bath with shaking. When the bacterial culture of *Thiobacillus ferrooxidans* was in the middle and late stages of stability, the bacterial agent of *Thiobacillus ferrooxidans* was obtained. After removing impurities, high-sulfur coal gangue is air-dried, crushed, and ground to obtain coal gangue powder. The coal gangue powder is mixed with water to form an aqueous solid-phase system, and then inoculated with the ferrooxidizum bacteria under acidic conditions for cultivation. After cultivation, fungi are introduced into the aqueous solid-phase system for degradation and transformation to obtain bio-activated coal gangue. The application mass ratio and total application amount of the bio-activated coal gangue and low-sulfur coal gangue were determined. The bio-activated coal gangue and low-sulfur coal gangue are mixed according to the application mass ratio to obtain the improved material; Soil samples were taken from the target saline-alkali land and pretreated to obtain saline-alkali soil samples; The improved material and the saline-alkali soil sample were uniformly mixed and cultured according to the total application amount to verify the effectiveness of the improved material; After verifying its effectiveness, the improved material was applied to the target saline-alkali land after tilling for improvement.

2. The method according to claim 1, characterized in that, The determination of the application mass ratio and total application amount of the bio-activated coal gangue and low-sulfur coal gangue includes: Calculate the theoretical dry basis dosage G of high-sulfur coal gangue according to formula (1); （1）； In equation (1), K is a coefficient, and CEC is the cation exchange capacity of the saline-alkali soil sample. This represents the initial exchangeable sodium percentage of the saline-alkali soil sample. The target exchangeable sodium percentage for the saline-alkali soil sample; The application rate of bio-activated coal gangue was determined based on the theoretical dry basis dosage of the high-sulfur coal gangue. Determine the application mass ratio of bio-activated coal gangue and low-sulfur coal gangue, and determine the application amount of low-sulfur coal gangue based on the application mass ratio. The total application amount is determined based on the application amount of bio-activated coal gangue and low-sulfur coal gangue.

3. The method according to claim 2, characterized in that, The verification of the effectiveness of the improved material includes: The monitoring indicators of the saline-alkali soil samples are tested regularly to determine whether the monitoring indicators have reached the preset threshold. If the preset threshold is reached, the effectiveness of the improvement material is verified. The detection indicators include pH value, electrical conductivity, sodium adsorption ratio, and exchangeable sodium percentage. Reaching the preset threshold includes at least one of the following: pH value drops below 8.5, electrical conductivity drops below 4 dS / m, sodium adsorption ratio drops below 15 with a decrease rate greater than 30%, or soil exchangeable sodium percentage drops below 15%.

4. The method according to claim 3, characterized in that, The process of taking soil from the target saline-alkali land and pretreating the soil includes: A multi-point mixed sampling method was used to collect topsoil from the target saline-alkali land at a depth of 0-20cm. The topsoil was then air-dried, cleaned of debris, ground, and passed through a 2mm sieve.

5. The method according to claim 1, characterized in that: The total application rate is 10%-25% of the soil mass of saline-alkali land, and the application mass ratio is 0.5:1-2:1; the improvement material is applied to the target saline-alkali land after tillage for improvement, and the tillage depth is 15-30 cm.

6. The method according to claim 1, characterized in that: The culture medium is 9K medium, which contains ferrous sulfate heptahydrate at a concentration of 44.7 g / L. The water bath shaking culture is conducted at a speed of 200 r / min and a temperature of 26 °C. The viable count of the *Thiobacillus ferrooxidans* inoculum is not less than 1.0 g / L. 10 8 CFU / mL, the *Thiobacillus ferrooxidans* bacterial suspension is in the stable mid-to-late stage, including the color of the *Thiobacillus ferrooxidans* bacterial suspension changing from light green to reddish brown and producing a yellow precipitate, or the oxidation rate of ferrous ions in 9K medium reaching 80%; The composition of the high-sulfur coal gangue, by mass percentage, includes total sulfur ≥3%, calcium and magnesium oxides 20%-30%, aluminum oxide ≤15%, and iron oxide 10%-20%. In the process of mixing the coal gangue powder with water to form an aqueous solid-phase system, the solid-liquid ratio of the coal gangue powder to the water is 1:1-1:4 or the water content of the aqueous solid-phase system is 35%-65%. The inoculation of the *Thiobacillus ferrooxidans* agent under acidic conditions further includes: after the *Thiobacillus ferrooxidans* agent culture enters a stable stage, introducing acidophilic heterotrophic bacteria into the same system.

7. A method for preparing modified materials based on the synergistic effect of microorganisms and minerals, characterized in that, The preparation method includes: The bacterial culture of *Thiobacillus ferrooxidans* was expanded and inoculated into a culture medium and then cultured in a water bath with shaking. When the bacterial culture of *Thiobacillus ferrooxidans* was in the middle and late stages of stability, the bacterial agent of *Thiobacillus ferrooxidans* was obtained. After removing impurities, high-sulfur coal gangue is air-dried, crushed, and ground to obtain coal gangue powder. The coal gangue powder is mixed with water to form an aqueous solid-phase system, and then inoculated with the ferrooxidizum bacteria under acidic conditions for cultivation. After cultivation, fungi are introduced into the aqueous solid-phase system for degradation and transformation to obtain bio-activated coal gangue. Determine the application mass ratio of the bio-activated coal gangue and low-sulfur coal gangue; The bio-activated coal gangue and low-sulfur coal gangue are mixed according to the application mass ratio to obtain the improved material.

8. The preparation method according to claim 7, characterized in that: The culture medium is 9K medium, which contains ferrous sulfate heptahydrate at a concentration of 44.7 g / L. The water bath shaking culture is conducted at a speed of 200 r / min and a temperature of 26 °C. The viable count of the *Thiobacillus ferrooxidans* inoculum is not less than 1.0 g / L. 10 8 CFU / mL, the *Thiobacillus ferrooxidans* bacterial suspension is in the stable mid-to-late stage, including the color of the *Thiobacillus ferrooxidans* bacterial suspension changing from light green to reddish brown and producing a yellow precipitate, or the oxidation rate of ferrous ions in 9K medium reaching 80%; The composition of the high-sulfur coal gangue, by mass percentage, includes total sulfur ≥3%, calcium and magnesium oxides 20%-30%, aluminum oxide ≤15%, and iron oxide 10%-20%.

9. The preparation method according to claim 8, characterized in that: In the process of mixing the coal gangue powder with water to form an aqueous solid-phase system, the solid-liquid ratio of the coal gangue powder to the water is 1:1-1:4 or the water content of the aqueous solid-phase system is 35%-65%. The inoculation of the *Thiobacillus ferrooxidans* agent under acidic conditions further includes: after the *Thiobacillus ferrooxidans* agent culture enters a stable stage, introducing acidophilic heterotrophic bacteria into the same system.

10. A modified material based on the synergy of microorganisms and minerals, characterized in that, The modified material, prepared by the method according to any one of claims 7-9, has the following uses: Used to improve saline-alkali land.

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