Agricultural and forestry solid waste and microorganism synergistically modified red mud soil-like substrate and preparation method thereof

Abstract

This invention discloses a method for preparing a red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms. This method not only introduces agricultural and forestry solid waste with different carbon-to-nitrogen ratios—high carbon-to-nitrogen ratio solid waste providing a recalcitrant carbon source to maintain long-term metabolism, medium carbon-to-nitrogen ratio solid waste serving as a readily degradable carbon source to accelerate initial fermentation, and low carbon-to-nitrogen ratio solid waste supplementing nitrogen to avoid carbon-to-nitrogen imbalance—but also ensures sufficient carbon source for microorganisms to continuously produce acid and reduce alkali while avoiding excessive nitrogen loss, thus promoting efficient mineralization and humification of organic matter. Furthermore, by introducing biochar-loaded modified microorganisms, the method utilizes the organic acids secreted by microorganisms to deeply reduce alkali, and also utilizes the extracellular polymers secreted by the microorganisms to combine with red mud metal ions to form organic-mineral composite colloids, enhancing the stability of red mud aggregates. This invention features a simple process, low cost, and is suitable for widespread application in fields such as ecological restoration of red mud dumps, mine reclamation, and saline-alkali land improvement.

Description

Technical Field

[0001] This invention relates to the field of red mud resource utilization and ecological restoration technology, specifically to a red mud-like soil matrix and its preparation method that is synergistically modified by agricultural and forestry solid waste and microorganisms. Background Technology

[0002] Red mud is a solid waste generated during the alumina industrial production process, producing approximately 1.0 to 1.5 tons of red mud for every ton of alumina produced. Statistics show that global red mud stockpiles exceed 5 billion tons and continue to grow at a rate of about 120 million tons per year. Red mud is characterized by its strong alkalinity, high salinity, complex mineral composition, and poor agglomeration. Large-scale stockpiling not only occupies land resources but also leads to soil salinization and water pollution due to rainwater leaching, posing a serious threat to the ecological environment.

[0003] Currently, the resource utilization and ecological restoration of red mud are challenging issues in the industry. Traditional methods for red mud soil improvement mainly include physical, chemical, and single-biological methods, but these have several limitations: First, physical improvement can only improve the structure of red mud in the short term and cannot fundamentally reduce its alkalinity and salinity, and the improvement effect decays significantly over time; second, chemical improvement requires a large amount of acidic reagents, which is costly and can easily cause secondary pollution, while also potentially destroying the original mineral utilization value of the red mud; third, in single-biological improvement, ordinary microorganisms have low survival rates and weak metabolic activity due to their difficulty in adapting to the high-alkalinity and high-salinity environment of red mud, making it impossible to achieve a continuous and stable improvement effect. This results in a red mud soil improvement cycle that can last for months or even years, making it difficult to meet the needs of rapid ecological restoration of large-scale red mud dumps.

[0004] Agricultural and forestry solid waste is rich in organic carbon, nitrogen, and various nutrients. If effectively utilized, it can serve as a high-quality organic amendment for red mud soil transformation. Meanwhile, microorganisms play unique roles in organic matter decomposition, mineral transformation, and pH regulation. Screening and domesticating functional microorganisms adapted to the extreme environment of red mud, and synergizing them with agricultural and forestry solid waste, holds promise for overcoming the limitations of traditional methods. However, current technologies lack a mature system for precisely synergizing agricultural and forestry solid waste with different carbon-to-nitrogen ratios with specifically domesticated microorganisms to achieve rapid and efficient red mud soil transformation.

[0005] Therefore, developing a synergistic improvement method that can fully utilize the nutrient supply advantages of agricultural and forestry solid wastes with different carbon-nitrogen ratios, combined with the metabolic activity of modified and domesticated microorganisms, to rapidly reduce the alkalinity of red mud, improve its aggregate structure, and enhance its fertility is of great practical significance and application value for solving the environmental problems of red mud storage and realizing its resource utilization. Summary of the Invention

[0006] The purpose of this invention is to provide a red mud-like soil matrix that is synergistically modified by agricultural and forestry solid waste and microorganisms, and its preparation method, in order to solve the problem that existing technologies lack effective methods for the simultaneous resource utilization of agricultural and forestry solid waste and red mud with different carbon-nitrogen ratios.

[0007] To solve the above-mentioned technical problems, the first solution provided by this invention is a red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms. This matrix is ​​prepared from the following raw materials in parts by weight: 100 parts red mud, 4-20 parts high carbon-to-nitrogen ratio agricultural and forestry solid waste, 3-10 parts medium carbon-to-nitrogen ratio agricultural and forestry solid waste, 3-10 parts low carbon-to-nitrogen ratio agricultural and forestry solid waste, 4.3-9.2 parts adaptive acclimatization-modification functional strains, 1-3 parts porous biochar, and 150-250 parts water. The high carbon-to-nitrogen ratio agricultural and forestry solid waste has a carbon-to-nitrogen ratio ≥ 25, the medium carbon-to-nitrogen ratio agricultural and forestry solid waste has a carbon-to-nitrogen ratio greater than 15 and less than 25, and the low carbon-to-nitrogen ratio agricultural and forestry solid waste has a carbon-to-nitrogen ratio ≤ 15. The adaptive domestication-modified functional strains are obtained by adapting and modifying acid-producing and salt-tolerant strains with red mud extract. The acid-producing and salt-tolerant strains include at least one of Bacillus, Pseudomonas, halophilic bacteria, and alkaliophilic bacteria.

[0008] To solve the above-mentioned technical problems, the second solution provided by the present invention is a method for preparing a red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms, comprising the following steps:

[0009] S1. Pre-treat the red mud to obtain a red mud extract.

[0010] S2. Based on the physicochemical properties of red mud extract, agricultural and forestry solid wastes with different carbon-nitrogen ratios were selected for pretreatment and then mixed evenly according to the formula to obtain compound agricultural and forestry solid wastes.

[0011] S3. Mix the red mud extract with the compound agricultural and forestry solid waste evenly, add water to adjust the field water holding capacity to 60%~70%, and obtain the red mud-agricultural and forestry solid waste mixture.

[0012] S4. The mixture of red mud and agricultural and forestry solid waste is piled up, and the pile is turned over regularly while the moisture and pH are monitored and controlled until the physicochemical properties of the red mud are stable, thus obtaining the preliminary improved red mud.

[0013] S5. Select acid-producing and salt-tolerant strains, and then subject them to adaptive domestication with red mud extract. After modification and screening, adaptive domestication-modified functional strains are obtained.

[0014] S6. Porous biochar was prepared by high-temperature pyrolysis of woody agricultural and forestry solid waste. Adaptive domestication-modified functional strains were loaded into the porous biochar to obtain biochar-loaded modified microorganisms.

[0015] S7. Mix the biochar-loaded modified microorganisms with the initially modified red mud and pile it up. Turn it over regularly and monitor and control the moisture content until the physicochemical properties are stable to obtain the red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in the first solution.

[0016] In some embodiments, step S1 specifically includes: drying the red mud in a 105°C forced-air drying oven until the moisture content is <15%, ball milling and passing it through a 10-mesh sieve to remove large particulate impurities, and obtaining pretreated red mud. The pretreated red mud is then used to prepare a red mud extract at a solid-liquid ratio of 1:5.

[0017] In some embodiments, step S2 specifically includes: based on the physicochemical properties of red mud extract, selecting high carbon-nitrogen ratio agricultural and forestry solid waste, medium carbon-nitrogen ratio agricultural and forestry solid waste, and low carbon-nitrogen ratio agricultural and forestry solid waste, drying them to a moisture content of 18%~20%, and crushing them through a 10~60 mesh sieve using a pulverizer. Subsequently, the high carbon-nitrogen ratio agricultural and forestry solid waste, medium carbon-nitrogen ratio agricultural and forestry solid waste, and low carbon-nitrogen ratio agricultural and forestry solid waste are mixed evenly in a mass ratio of (2~3):(4~6):(2~3) to obtain compound agricultural and forestry solid waste; the high carbon-nitrogen ratio agricultural and forestry solid waste, medium carbon-nitrogen ratio agricultural and forestry solid waste, and low carbon-nitrogen ratio agricultural and forestry solid waste are all acidic or neutral agricultural and forestry processing wastes.

[0018] In some embodiments, step S3 specifically includes: mixing the red mud extract with the compound agricultural and forestry solid waste evenly, wherein the compound agricultural and forestry solid waste is 10% to 30% of the mass of the pretreated red mud, and adding water to adjust the field water holding capacity to 60% to 70%, thereby obtaining a red mud-agricultural and forestry solid waste mixture.

[0019] In some embodiments, step S4 specifically includes: piling the red mud-agricultural and forestry solid waste mixture in flower pots, covering it with plastic wrap with holes for water retention, heat preservation, and ventilation, and allowing it to ferment naturally in an environment of 25±3℃. The pile is turned over once every 3 to 5 days, water is added regularly to maintain the field water holding rate of 60 to 70%, and pH value changes are monitored regularly. After the physicochemical properties of the red mud are stable, preliminary improved red mud is obtained.

[0020] In some embodiments, step S5, the specific steps of adaptive acclimatization include: preparing an acid-producing medium containing 10% red mud extract, inoculating logarithmic growth phase bacterial culture with shaking, increasing the concentration of red mud extract by 5% with each subculture, and screening for strains that can stably grow in 30%~50% red mud extract with a bacterial concentration ≥1×10⁻⁶. 6 CFU / mL of adaptively domesticated functional strains.

[0021] In some embodiments, step S5, the specific steps of modification treatment and screening include: culturing the adaptive acclimatization functional strain to the logarithmic growth phase, centrifuging the bacterial solution, discarding the supernatant, resuspending it in sterile physiological saline, and adjusting the bacterial solution concentration to ≥1×10⁻⁶. 6CFU / mL; Take 5 mL of bacterial culture and place it in a sterile petri dish. Place the dish in a laminar flow hood and induce the bacterial strain to change its characteristics using ultraviolet irradiation, radiation mutagenesis, or chemical mutagen. Then, incubate the bacterial culture for 10 hours. -1 ~10 -6 Serial dilutions were performed to obtain serially diluted bacterial solutions. 0.1 mL of each dilution was evenly spread on LB agar plates containing 5% red mud extract. The plates were incubated at 30-37°C for 24-48 hours. Single colonies with vigorous growth and different morphology from the original strain were selected and transferred to another LB agar plate containing red mud extract for purification and culture to obtain adaptive domestication-modified functional strains.

[0022] In some embodiments, the following steps are included between steps S5 and S6: Based on red mud extract, carbon and nitrogen sources are added to adjust the pH to 8.5-9.5 in liquid culture medium. Adapted and modified functional strains are inoculated into the above culture medium and cultured at 30-37°C with shaking at 200 rpm until the logarithmic growth phase. 50 mL of simulated culture medium is placed in an Erlenmeyer flask, and 1 mL of logarithmic-phase bacterial solution is inoculated. Uninoculated culture medium is used as a blank control. The mixture is cultured with shaking for 36-72 hours. After the culture is complete, the mixture is centrifuged, the supernatant is collected, filtered, and the acid production is tested using HPLC or acid-base titration.

[0023] In some embodiments, step S6 specifically includes: selecting woody agricultural and forestry solid waste, placing it in a covered porcelain crucible and wrapping it with tin foil, pyrolyzing it in a muffle furnace to 500-600℃, naturally cooling it, washing it with deionized water until neutral, drying it, and passing it through a 100-mesh sieve to obtain porous biochar; and culturing the adaptive domestication-modified functional strains to a bacterial concentration ≥1×10⁻⁶. 8 CFU / mL, porous biochar and bacterial culture were mixed at a mass-to-volume ratio of 1:6-12, and incubated at 35±3℃ in the dark on a shaker at 120-180 rpm for 16-24 hours. The mixture was then transferred to sterile petri dishes and air-dried at 35±3℃, stirring every 2 hours, to obtain a loading ≥1×10⁻⁶. 6 CFU / g of biochar-loaded modified microorganisms.

[0024] In some embodiments, step S7 specifically includes: adding biochar-loaded modified microorganisms at 10% to 40% of the mass of pretreated red mud to the initially modified red mud obtained in step S4, placing it in an environment of 25±3℃ for natural fermentation, turning the pile over once every 3 to 5 days, adding water regularly and maintaining the field water holding rate at 60% to 70%, and obtaining a red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms after the physicochemical properties have stabilized.

[0025] Unlike existing technologies, this invention is based on the synergistic preparation of red mud-like soil matrix using multi-element agricultural and forestry solid waste and microbial-biochar composite materials. It constructs a red mud biological improvement system with carbon-nitrogen balance regulation, microbial metabolism-driven processes, and organic-mineral composite stabilization as its core. The specific beneficial effects of this invention are as follows:

[0026] Firstly, regarding the control of the carbon-to-nitrogen ratio, agricultural and forestry solid waste with a high carbon-to-nitrogen ratio provides a recalcitrant carbon source to sustain long-term metabolism, while agricultural and forestry solid waste with a medium carbon-to-nitrogen ratio serves as a readily degradable carbon source to accelerate initial fermentation. Agricultural and forestry solid waste with a low carbon-to-nitrogen ratio supplements nitrogen to prevent carbon-to-nitrogen imbalance. When these three components are mixed in an appropriate ratio, the overall C / N ratio of the system is maintained within the optimal fermentation range of 25-35 for microorganisms. This ensures sufficient carbon source for continuous acid production and alkali reduction by microorganisms, while also preventing excessive nitrogen loss, promoting efficient mineralization and humification of organic matter, and providing a stable material basis for the soilification of red mud.

[0027] Secondly, the addition of agricultural and forestry solid wastes with different carbon-to-nitrogen ratios can initially improve the extreme environment of red mud: on the one hand, it carries nutrients such as organic carbon and nitrogen, and on the other hand, its acidity neutralizes the alkalinity of red mud and reduces salinity. At the same time, it improves the dispersibility of red mud through the humic substances formed by its own decomposition, creating a microenvironment with suitable pH, nutrients and structure for the subsequent addition of microorganisms, which greatly improves the colonization survival rate and metabolic activity of microorganisms.

[0028] Furthermore, by using red mud extract to adapt acid-producing and salt-tolerant strains, selective pressure from high-alkali and high-salt environments can be applied in a targeted manner, eliminating sensitive strains and prompting surviving strains to gradually adjust osmotic pressure, cell membrane permeability, and metabolic pathways, thus stabilizing their adaptation to the extreme environment of red mud and enhancing their acid-producing capacity under stress. Based on this, further modification treatment can be applied to the strains to ultimately obtain adaptively adapted and modified functional strains that are both adapted to the red mud environment and possess highly efficient acid-producing functions.

[0029] Furthermore, the biochar prepared from agricultural and forestry solid waste, after being loaded with microorganisms, possesses a porous structure and functional groups that protect the microorganisms from extreme environmental stresses, enhance adsorption and fixation effects, extend the functional cycle, and strengthen the formation of organic-mineral composite colloids. Through natural composting and fermentation, red mud can be rapidly converted into soil. The process is simple, low-cost, and environmentally friendly, and is suitable for the remediation of red mud dumps, the reclamation of mining areas, and the improvement of saline-alkali land, providing a sustainable and efficient technical path for the resource utilization of red mud.

[0030] This invention fully utilizes the carbon-nitrogen complementarity of different agricultural and forestry solid wastes and the metabolic drive of microorganisms to achieve rapid soilification of red mud through natural composting and fermentation. It does not require the addition of chemical neutralizers or exogenous strong bacterial agents. The process is simple, low-cost, and highly environmentally compatible. It is applicable to fields such as ecological restoration of red mud compost sites, mining area reclamation, and saline-alkali land improvement, providing a sustainable, efficient, and eco-friendly technical path for the resource utilization of red mud. Attached Figure Description

[0031] Figure 1 This is a comparison diagram of the mid-term aggregate structure distribution of the red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms obtained in Examples 1-3 and Comparative Examples 1-3 of this invention;

[0032] Figure 2 This is a comparison diagram of the late-stage aggregate structure distribution of the red mud-like soil matrix obtained by the synergistic modification of agricultural and forestry solid waste and microorganisms in Examples 1-3 and Comparative Examples 1-3 of this invention. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0035] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] The high carbon-to-nitrogen ratio agricultural and forestry solid waste used in the following examples and comparative examples is sugarcane bagasse, the medium carbon-to-nitrogen ratio agricultural and forestry solid waste is distiller's grains, and the low carbon-to-nitrogen ratio agricultural and forestry solid waste is camellia seed meal. The strain used in the biochar-supported modified microorganisms is commercially available halophilic spore-forming bacteria (BJ-J5828). The physicochemical properties of distiller's grains, camellia seed meal, sugarcane bagasse, and red mud are shown in Table 1.

[0037] Table 1 Physicochemical properties of the selected raw materials and red mud

[0038]

[0039] The following examples and batch fermentation tests of materials with the above characteristics and red mud are used to verify their improved properties.

[0040] Example 1

[0041] The specific implementation steps of this embodiment are as follows:

[0042] 1) Pretreatment of red mud and preparation of extract: The red mud was dried in a 105℃ forced-air drying oven until the moisture content was <15%. After ball milling, it was passed through a 10-mesh sieve to remove large particles of impurities, and the pretreated red mud was obtained. The pretreated red mud was used to prepare red mud extract at a solid-liquid ratio of 1:5.

[0043] 2) Pretreatment and uniform mixing of agricultural and forestry solid waste: Sugarcane bagasse, distiller's grains, and camellia seed oil are treated separately. Distiller's grains are dried at 60-70℃ to a moisture content of 18%-20% and then crushed through a 30-mesh sieve. Camellia seed oil is inactivated by high-pressure steam at 121℃ for 25 minutes, cooled, and crushed through a 30-mesh sieve. Sugarcane bagasse is mechanically crushed and then mechanically crushed through a 30-mesh sieve. Subsequently, 2 parts sugarcane bagasse, 6 parts distiller's grains, and 2 parts camellia seed oil are mixed evenly according to the mass fraction to obtain compound agricultural and forestry solid waste.

[0044] 3) Mix the compound agricultural and forestry solid waste with the pretreated red mud: Add water to the red mud extract and the compound agricultural and forestry solid waste and mix evenly. By mass, there are 20 parts of compound agricultural and forestry solid waste and 80 parts of pretreated red mud. Add water to adjust the field water holding capacity to 60%~70% to obtain the red mud-agricultural and forestry solid waste mixture.

[0045] 4) The red mud-agricultural and forestry solid waste mixture is piled in flower pots and covered with plastic wrap with holes for water retention, heat preservation and aeration. It is placed in an environment of 25±3℃ for natural fermentation. The pile is turned over once every 3 to 5 days, and water is added regularly to maintain the field water holding rate of 60 to 70%. The changes in pH, total organic carbon (TOC), electrical conductivity (EC) and aggregate particle size distribution of the red mud-agricultural and forestry solid waste mixture are monitored regularly. The preliminary improved red mud is obtained after the physicochemical properties of the red mud are stable.

[0046] 5) Select halophilic Bacillus (BJ-J5828), and use red mud extract to adapt and acclimate the modified strain to obtain an adapted and acclimatized strain. Then, use ultraviolet light to modify the adapted and acclimatized strain to obtain red mud extract-UV modified halophilic Bacillus. Before the adaptation and acclimatization step, activate the halophilic Bacillus, specifically by preparing LB liquid medium and LB solid plates simultaneously. Inoculate the acid-producing, salt-tolerant strain into the LB liquid medium and culture at 37℃ and 180 r / min for 12 h with shaking to obtain a logarithmic growth phase bacterial culture.

[0047] The specific steps for the adaptation and domestication of halophilic Bacillus to red mud extract include: preparing an acid-producing medium containing 10% red mud extract, inoculating logarithmic growth phase bacterial suspension with shaking culture, increasing the concentration of red mud extract by 5% with each subculture, and screening for strains that can stably grow in 40% red mud extract with a bacterial suspension concentration ≥1×10⁻⁶. 6Adaptation and domestication of salt-tolerant spore-forming bacteria at CFU / mL.

[0048] The specific steps of the modified treatment of halophilic spores include: centrifuging the logarithmic growth phase bacterial culture of the adaptively acclimatized halophilic spores, discarding the supernatant, resuspending it in sterile physiological saline, and adjusting the bacterial concentration to ≥1×10⁻⁶. 6 CFU / mL; 5 mL of bacterial suspension was placed in a sterile petri dish and placed in a clean bench, 30 cm away from the UV lamp. The magnetic stirrer was turned on to ensure uniform irradiation of the bacterial suspension. Irradiation time gradients of 30 s, 60 s, 90 s, and 120 s were set up, with 3 parallel experiments for each time gradient. Immediately after irradiation, the petri dish was wrapped in black cloth and incubated at 30℃ in the dark for 2 h. Subsequently, the bacterial suspension was subjected to 10 -1 ~10 -6 Serial dilutions were performed to obtain serially diluted bacterial solutions.

[0049] The specific steps for the modification and screening of the strains include: taking 0.1 mL of bacterial solution at each gradient dilution and spreading it evenly on LB solid plates containing 5% red mud extract, with 3 replicates for each dilution; incubating the plates in a 37℃ constant temperature incubator for 24 h; picking single colonies with vigorous growth and different colony morphology from the original strains and transferring them to new LB plates containing red mud extract for purification and culture to obtain red mud extract-UV modified acclimatized salt-tolerant Bacillus.

[0050] Before biochar loading, carbon and nitrogen sources were added to the pretreated red mud extract, and the pH was adjusted to 8.5-9.5 in liquid culture medium. Red mud extract-UV modified acclimatized halophilic Bacillus was inoculated into the above culture medium and cultured at 37℃ and 200 rpm until the logarithmic growth phase. 50 mL of simulated culture medium was placed in an Erlenmeyer flask, and 1 mL of logarithmic phase bacterial solution was inoculated. At the same time, "uninoculated culture medium" was set as a blank control. The culture was shaken and cultured for 72 h. After the culture was completed, the supernatant was collected, filtered, and the acid production was tested by HPLC.

[0051] 6) Biochar Preparation and Microbial Loading: Biochar was prepared using sugarcane bagasse as raw material. Domesticated bacterial strains were loaded onto the biochar material to obtain biochar-loaded modified microorganisms. Specifically, pretreated sugarcane bagasse was placed in a covered porcelain crucible, wrapped with tin foil, and placed in a muffle furnace. The temperature was increased to 500℃ at 0℃ / min, held at this temperature for 3 hours, and then naturally cooled. The mixture was washed with deionized water until neutral, dried at 60℃, and passed through a 100-mesh sieve to obtain biochar. Domesticated halophilic Bacillus was cultured until the bacterial concentration was ≥1×10⁻⁶. 8 CFU / mL, biochar and bacterial solution were mixed at a mass-to-volume ratio of 1:10, and incubated at 25°C in the dark at 120 rpm for 16 hours. The mixture was then transferred to a sterile culture dish and air-dried in a constant temperature incubator at 30°C, with stirring every 2 hours to obtain biochar-loaded modified microorganisms.

[0052] 7) Add biochar-loaded modified microorganisms to the pre-treated red mud obtained in step 4) at 20% of the mass of the pretreated red mud, and let it ferment naturally in an environment of 25±3℃. Turn the pile over once every 3 to 5 days, add water regularly and maintain the field water holding rate at 60 to 70%, and monitor the changes in pH, total organic carbon (TOC), electrical conductivity (EC) and aggregate particle size distribution regularly until the physicochemical properties are stable, and obtain the red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms.

[0053] Example 2

[0054] Based on the preparation steps of Example 1, the only difference is that in step 3), 30 parts of compounded agricultural and forestry waste and 70 parts of pretreated red mud are used to obtain a red mud-agricultural and forestry solid waste mixture; in step 7), biochar-loaded modified microorganisms are added to the preliminary improved red mud obtained in step 4) at 30% of the mass of the pretreated red mud; other steps and process parameters are consistent with those of Example 1.

[0055] Example 3

[0056] Based on the preparation steps of Example 1, the only difference is that in step 3), 40 parts of compounded agricultural and forestry waste and 60 parts of pretreated red mud are used to obtain a red mud-agricultural and forestry solid waste mixture; in step 7), biochar-loaded modified microorganisms are added to the preliminary improved red mud obtained in step 4) at 40% of the mass of the pretreated red mud; other steps and process parameters are consistent with Example 1.

[0057] Comparative Example 1

[0058] Based on the preparation steps of Example 1, the only difference is that in step 3), 20 parts of compounded agricultural and forestry waste and 80 parts of pretreated red mud are used to obtain a red mud-agricultural and forestry solid waste mixture, and the pretreated red mud is directly improved without adding modified microorganisms; other steps and process parameters are consistent with Example 1.

[0059] Comparative Example 2

[0060] Based on the preparation steps of Example 1, the only difference is that in step 7), the modified microbial inoculum is directly added to the pre-modified red mud obtained in step 4) at 20% of the mass of the pretreated red mud; the other steps and process parameters are consistent with those of Example 1.

[0061] Comparative Example 3

[0062] Based on the preparation steps of Example 1, the only difference is that in step 3), no compound agricultural and forestry solid waste is added to the pretreated red mud, and only in step 7), biochar-loaded modified microorganisms are added to the preliminary improved red mud obtained in step 4) at 20% of the mass of the pretreated red mud; other steps and process parameters are consistent with Example 1.

[0063] The red mud-like soil matrices synergistically modified with agricultural and forestry solid waste and microorganisms obtained in Examples 1-3 and Comparative Examples 1-3 were tested and analyzed. The specific improvement effects were tested at two time points: mid-term (30 days) and late-term (60 days). Each time point test included performance parameter testing and aggregate structure distribution testing. The performance parameter tests included pH, conductivity, organic carbon content, alkalinity, and bulk density. Mid-term and late-term performance parameters are shown in Tables 1 and 2, respectively. The aggregate structure distribution test used intervals of 0.25 mm, 0.5 mm, 1 mm, and 2 mm. The mid-term and late-term aggregate structure distributions are shown in Tables 1 and 2, respectively. Figure 1 and Figure 2 As shown.

[0064] Table 1. Statistical Table of Mid-Term Performance Parameters

[0065]

[0066] Table 2. Statistics of Post-Performance Parameters

[0067]

[0068] From Tables 1-2 and Appendix Figures 1-2 It can be seen that, compared with Comparative Example 1, Examples 1-6 exhibit the following significant changes:

[0069] Firstly, Comparative Example 1 reduced the pH of the red mud from an initial 10.95 to 8.66, but as time increased, the comparative example showed signs of re-alkalization, and the pH eventually remained at around 8.79. Compared with Comparative Example 1, the pH of the example group decreased significantly and eventually stabilized below 8.5. The decrease increased with the addition of compound agricultural and forestry solid waste and bacterial solution, indicating that synergistic improvement transformed the red mud from a highly alkaline environment to a more mild pH range suitable for organisms and ecosystems.

[0070] Secondly, the organic carbon content was significantly increased. The organic carbon content of Comparative Examples 1-3 was approximately 2.1%-2.35%, while the organic carbon content of Examples 1-3 increased to 2.60%-3.20% in the middle stage and increased slightly further in the later stage. This indicates that the addition of agricultural and forestry solid waste and biochar-loaded modified microorganisms successfully replenished and stably preserved organic matter in the red mud. The electrical conductivity of Comparative Examples 1-3 was 2.34-2.50 mS / cm, while the electrical conductivity of Examples 1-3 mostly decreased to 1.87-2.39 mS / cm in the middle stage and further decreased to 1.82-2.34 mS / cm in the later stage. The decrease in electrical conductivity means that the concentration of dissolved ions, salts, and salt-tolerant alkaline ions in the system decreased, thus proving that Examples 1-3 can significantly reduce the concentration of dissolved ions, salts, and salt-tolerant alkaline ions in the system and improve the improvement effect of red mud-like soil matrix.

[0071] Thirdly, please refer to the appendix. Figures 1-2 Compared to Comparative Examples 1-3, Examples 1-3 showed a significantly higher percentage of large aggregates and a decreased percentage of micro-aggregates. This indicates that the system, originally dominated by micro-aggregates, shifted towards a structure with more large aggregates after the improvement. In other words, the overall structure tended to aggregate after synergistic improvement, exhibiting a transformation from "fine to coarse aggregate dominance." This means that through cementation and aggregation, the particles evolved from a loose, microparticle-dominated structure to a more stable, blocky, and larger aggregate structure.

[0072] In summary, the improved method provided by this invention not only successfully reduces alkalinity, replenishes organic matter, and improves physicochemical properties such as salinity and density, but also significantly enhances matrix stability through structural reorganization. This transforms red mud from an industrial waste into a soil-like material with better physical structure, organic matter reserves, environmental adaptability, and potential ecological resource utilization value. This method has significant implications and promising applications for the resource utilization of red mud, environmental remediation, ecological restoration, and solid waste recycling.

[0073] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0074] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms, characterized in that, It is prepared from the following raw materials in parts by weight: 100 parts red mud, 4-20 parts high carbon-nitrogen ratio agricultural and forestry solid waste, 3-10 parts medium carbon-nitrogen ratio agricultural and forestry solid waste, 3-10 parts low carbon-nitrogen ratio agricultural and forestry solid waste, 4.3-9.2 parts adaptive domestication-modified functional strains, 1-3 parts porous biochar and 150-250 parts water; The carbon-nitrogen ratio of the high carbon-nitrogen ratio agricultural and forestry solid waste is ≥25, the carbon-nitrogen ratio of the medium carbon-nitrogen ratio agricultural and forestry solid waste is greater than 15 and less than 25, and the carbon-nitrogen ratio of the low carbon-nitrogen ratio agricultural and forestry solid waste is ≤15. The adaptive domestication-modified functional strain is obtained by adapting and modifying acid-producing and salt-tolerant strains with red mud extract. The acid-producing and salt-tolerant strains include at least one of Bacillus, Pseudomonas, halophilic bacteria, and alkaliophilic bacteria.

2. A method for preparing a red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms, characterized in that, Includes the following steps: S1. Pre-treat the red mud to obtain a red mud extract; S2. Based on the physicochemical properties of the red mud extract, agricultural and forestry solid wastes with different carbon-nitrogen ratios were selected for pretreatment and then mixed evenly according to the formula to obtain compound agricultural and forestry solid wastes. S3. Mix the red mud extract with the compound agricultural and forestry solid waste evenly, add water to adjust the field water holding capacity to 60%~70%, and obtain a red mud-agricultural and forestry solid waste mixture. S4. The red mud-agricultural and forestry solid waste mixture is piled up, turned over regularly, and the moisture and pH are monitored and controlled until the physicochemical properties of the red mud are stable to obtain the preliminary improved red mud. S5. Select acid-producing and salt-tolerant strains, and after adapting them with the red mud extract, apply modification treatment and screen the strains to obtain adaptively adapted and modified functional strains. S6. Porous biochar is prepared by high-temperature pyrolysis of woody agricultural and forestry solid waste. The adaptive domestication-modified functional strains are loaded into the porous biochar to obtain biochar-loaded modified microorganisms. S7. The biochar-loaded modified microorganisms are mixed and piled with the pre-modified red mud, and the pile is turned over regularly and the moisture content is monitored and controlled until the physicochemical properties are stable to obtain the red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 1. In step S2, the agricultural and forestry solid wastes with different carbon-nitrogen ratios include high carbon-nitrogen ratio agricultural and forestry solid wastes, medium carbon-nitrogen ratio agricultural and forestry solid wastes, and low carbon-nitrogen ratio agricultural and forestry solid wastes.

3. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 1, characterized in that, Step S1 specifically includes: The red mud was dried in a 105℃ forced-air drying oven until the moisture content was <15%. After ball milling, it was passed through a 10-mesh sieve to remove large particles of impurities, thus obtaining pretreated red mud. The pretreated red mud was used to prepare the red mud extract at a solid-liquid ratio of 1:

5.

4. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 1, characterized in that, Step S2 specifically includes: Based on the physicochemical properties of the red mud extract, the high carbon-nitrogen ratio agricultural and forestry solid waste, medium carbon-nitrogen ratio agricultural and forestry solid waste, and low carbon-nitrogen ratio agricultural and forestry solid waste were selected, dried to a moisture content of 18%~20%, and pulverized through a 10~60 mesh sieve. Then, the high carbon-nitrogen ratio agricultural and forestry solid waste, medium carbon-nitrogen ratio agricultural and forestry solid waste, and low carbon-nitrogen ratio agricultural and forestry solid waste were mixed evenly in a mass ratio of (2~3):(4~6):(2~3) to obtain the compound agricultural and forestry solid waste. The high carbon-to-nitrogen ratio agricultural and forestry solid waste, medium carbon-to-nitrogen ratio agricultural and forestry solid waste, and low carbon-to-nitrogen ratio agricultural and forestry solid waste are all acidic or neutral agricultural and forestry processing wastes.

5. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 3, characterized in that, Step S3 specifically includes: The red mud extract is mixed evenly with compound agricultural and forestry solid waste, wherein the compound agricultural and forestry solid waste is 10% to 30% of the mass of the pretreated red mud. Water is added to adjust the field water holding capacity to 60% to 70% to obtain a red mud-agricultural and forestry solid waste mixture.

6. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 1, characterized in that, Step S4 specifically includes: The red mud-agricultural and forestry solid waste mixture was piled in flower pots and covered with plastic wrap to retain water, keep warm and ventilate. It was then placed in an environment of 25±3℃ for natural fermentation. The pile was turned over every 3 to 5 days, and water was added regularly to maintain a field water holding rate of 60 to 70%. The pH value was monitored regularly. Once the physicochemical properties of the red mud were stable, the preliminarily improved red mud was obtained.

7. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 1, characterized in that, In step S5, the specific steps of adaptive domestication include: Prepare an acid-producing medium containing 10% of the red mud extract, inoculate with logarithmic growth phase bacterial culture and shake culture. Increase the concentration of the red mud extract by 5% with each subculture. Screen for strains that can stably grow in 30%–50% red mud extract, with a bacterial concentration ≥1×10⁻⁶. 6 CFU / mL of adaptive domestication functional strains.

8. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 7, characterized in that, In step S5, the specific steps of the modification treatment and screening include: The adaptively acclimatized strain was cultured to the logarithmic growth phase, the bacterial culture was centrifuged, the supernatant was discarded, and the culture was resuspended in sterile physiological saline. The bacterial concentration was adjusted to ≥1×10⁻⁶. 6 CFU / mL; Take 5 mL of bacterial culture and place it in a sterile petri dish. Place the dish in a laminar flow hood and induce the bacterial strain to change its characteristics using ultraviolet irradiation, radiation mutagenesis, or chemical mutagen. Then, incubate the bacterial culture for 10 hours. -1 ~10 -6 Serial dilutions were performed to obtain serially diluted bacterial solutions. 0.1 mL of each dilution was evenly spread on LB agar plates containing 5% red mud extract. The plates were incubated at 30℃~37℃ for 24~48 h. Single colonies with vigorous growth and morphology different from the original strain were selected and transferred to another LB agar plate containing red mud extract for purification culture to obtain the adaptive domestication-modified functional strain. The step between steps S5 and S6 includes the following steps: Based on the red mud extract, add carbon and nitrogen sources, adjust the pH to 8.5-9.5 to prepare a liquid culture medium, inoculate the adaptive domestication-modified functional strain into the above culture medium, and culture it at 30-37℃ with shaking at 200 rpm until the logarithmic growth phase. Take 50 mL of simulated culture medium and place it in an Erlenmeyer flask, inoculate 1 mL of logarithmic phase bacterial solution, and set up an uninoculated culture medium as a blank control. Shake and culture for 36-72 h. After the culture is completed, centrifuge, take the supernatant, filter it, and use HPLC or acid-base titration to test the acid production.

9. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 1, characterized in that, Step S6 specifically includes: Wood-based agricultural and forestry solid waste was selected, placed in a covered porcelain crucible and wrapped with tin foil, and then heated to 500-600℃ in a muffle furnace for pyrolysis. After natural cooling, it was washed with deionized water until neutral, dried, and passed through a 100-mesh sieve to obtain porous biochar. The adaptively acclimatized and modified functional strains were cultured until the bacterial concentration was ≥1×10⁻⁶. 8 CFU / mL, the porous biochar and bacterial culture were mixed at a mass-to-volume ratio of 1:6-12, and incubated at 35±3℃ in the dark on a shaker at 120-180 rpm for 16-24 hours. The mixture was then transferred to sterile petri dishes and air-dried in a constant temperature incubator at 35±3℃, stirring every 2 hours, to obtain a loading ≥1×10⁻⁶ CFU / mL. 6 CFU / g of biochar-loaded modified microorganisms.

10. The method for preparing red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms as described in claim 2, characterized in that, Step S7 specifically includes: The biochar-loaded modified microorganisms are added to the pre-treated red mud obtained in step S4 at 10% to 40% of the mass of the pretreated red mud. The mixture is then placed in an environment of 25±3℃ for natural fermentation. The mixture is turned over every 3 to 5 days, and water is added regularly to maintain a field water holding capacity of 60% to 70%. After the physicochemical properties are stabilized, the red mud-like soil matrix synergistically modified by agricultural and forestry solid waste and microorganisms is obtained.

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