Composite conditioner and method for driving red mud storage yard to rapidly form soil through film-covering type aerobic stacking fermentation

Abstract

The invention discloses a composite conditioner and a method for driving rapid soil formation of a red mud storage yard through film-covering type aerobic stacking fermentation. The composite conditioner takes agriculture and forestry solid waste and calcium-based industrial solid waste as raw materials. According to the method disclosed by the invention, the composite conditioner and the surface red mud are used as stacking fermentation substrates, and are mixed and then subjected to in-situ reinforced aerobic stacking fermentation. The method disclosed by the invention has a soil forming period of 14-45 days, is suitable for ecological management of a large-scale red mud storage yard, can effectively reduce the saline-alkali harm on the surface of the storage yard, utilizes the characteristics of the fermented biomass to quickly improve the red mud nutrition habitat and provide a stable carbon source for vegetation growth, so that the soil formation process of the red mud storage yard is accelerated, and the soil quality of the red mud storage yard is improved. The method can be applied to large-scale red mud absorption and storage yard ecological restoration.

Description

Technical Field

[0001] The present invention belongs to the technical field of ecological restoration of red mud dumps, and in particular relates to a method for rapidly forming soil in a red mud dump by driving a composite conditioner and a film-covered aerobic compost fermentation. Background Art

[0002] Red mud is a highly alkaline solid waste generated during the aluminum smelting process. The production of one ton of aluminum produces approximately three tons of red mud. Red mud is the largest solid waste discharged by the non-ferrous metals industry, with a comprehensive utilization rate of less than 5%, primarily through stockpiling. Global red mud accumulation exceeded 5 billion tons in 2024 and is increasing at a rate of 200 million tons per year. To date, there is no economically viable large-scale disposal method. Red mud stockpiling not only consumes land resources but also causes environmental problems and even poses the risk of dam failure. Therefore, research on ecological red mud disposal technologies and strengthening environmental management of red mud dumps have become urgent tasks for the aluminum industry.

[0003] The soilification of red mud may be a large-scale disposal method with great application prospects and is also the key to achieving ecological restoration of red mud dumps. However, the extreme physical and chemical properties of red mud (strong alkalinity, high salinity, low organic matter, and poor physical structure) seriously restrict its soilification process. Current problems include: 1. The pH value of red mud needs to be reduced from 11.3 to 7.5-8.5 to meet the needs of plant growth. The traditional gypsum improvement method requires the addition of 15%-20% of the red mud mass, but it is easy to cause secondary salt accumulation and heavy metal activation risks; 2. The total nitrogen content of red mud is less than 0.1% and the available phosphorus is less than 5mg / kg. Additional organic or inorganic fertilizers need to be added, but exogenous nutrients are easily lost and the cost is high; 3. The stability of the primary aggregates of red mud is poor (the content of water-stable aggregates is less than 5%). Even after the application of agricultural and forestry waste, there are still problems such as uncontrollable decomposition rate and weak water and fertilizer retention capacity.

[0004] Although the agricultural and forestry waste covering method can improve the surface structure of red mud in the short term, the decomposition cycle is as long as 3-6 months, and the humification products are easily decomposed by microorganisms, resulting in unsustainable improvement effects. Chemical improvers (such as phosphates and humic acid) can reduce alkalinity, but there is a risk of secondary pollution, and it is impossible to improve the fertility of the substrate at the same time. Although bioremediation methods (such as inoculating AM fungi) can promote plant growth, the fungus has poor adaptability and is difficult to colonize in a strong alkaline environment. In response to the above technical bottlenecks, it is urgent to develop a red mud soilification method that can be applied to red mud dumps, simplify the treatment process, and quickly de-alkali and fertilize. Summary of the Invention

[0005] One of the purposes of the present invention is to provide an economical and environmentally friendly composite conditioner for industrial and agricultural solid waste. By combining biomass such as straw, manure, and wheat bran with gypsum-based calcium-based solid waste in a specific ratio, a composite conditioner with synergistic de-alkali and fertilization functions is constructed.

[0006] The second purpose of the present invention is to provide an application method for driving rapid soil formation in red mud dumps by film-covered aerobic composting. Through the in-situ film-covered aerobic composting process, a coupling mechanism of biomass humification and calcium-based mineral reaction is constructed, rapid de-alkali and efficient fertilization are achieved in situ in the red mud dump, and red mud is converted into red mud-based modified soil with good water holding capacity, pore structure and nutrient reserves, meeting the direct planting needs of herbaceous plants and shrubs, and shortening the soil formation period to 14-45 days.

[0007] The invention provides a composite conditioner. The composite conditioner is obtained by pre-treating and mixing biomass obtained by mixing straw, excrement and wheat bran with gypsum-type industrial calcium-based solid waste in a specific ratio.

[0008] The straw is selected from one or more of corn straw, wheat straw, and rice straw; the straw is a straw segment with a length of 1-3 cm; and the amount of straw added is 0.5%-3% of the mass of the red mud.

[0009] The treatment of straw can significantly increase the specific surface area of ​​straw and promote the attachment and decomposition of microorganisms in the subsequent fermentation process.

[0010] The manure is selected from one or more of cow manure, sheep manure, chicken manure or earthworm manure; the moisture content of the manure is 60%-70%; and the amount of manure added is 0.5%-4% of the mass of the red mud.

[0011] The feces are rich in natural microbial communities that can initiate the decomposition of organic matter in the early stages of fermentation.

[0012] The moisture content of the wheat bran is 5%-12%; and the added amount of the wheat bran is 0.4%-2% of the mass of the red mud.

[0013] Wheat bran is used as a nitrogen source supplement, and its fine particle structure can optimize the porosity of the pile and provide fast-acting nitrogen.

[0014] Furthermore, the carbon-nitrogen ratio of the biomass after mixing straw, manure, and wheat bran is (15:1)-(28:1).

[0015] The gypsum-type industrial calcium-based solid waste is selected from one or more of desulfurized gypsum and phosphogypsum; and the added amount of the gypsum-type industrial calcium-based solid waste is 1%-5% of the mass of the red mud.

[0016] The calcium ions contained in gypsum industrial calcium-based solid waste can reduce the alkalinity of red mud and improve the agglomeration structure of red mud through ion exchange reaction.

[0017] Furthermore, the mixing mass ratio of the biomass to the gypsum industrial calcium-based solid waste is (1:1)-(2:1).

[0018] The present invention also provides a method for rapidly forming soil in a red mud dump by using a film-covered aerobic compost fermentation, comprising the following steps:

[0019] S1. The red mud in the red mud dump is crushed and screened to obtain pretreated red mud;

[0020] S2. The composite conditioner is configured according to the amount of pretreated red mud, and the resulting composite conditioner is homogenized and mixed with the red mud in situ to obtain a pile;

[0021] S3. Cover the pile with film to carry out in-situ aerobic fermentation to complete the rapid soil formation of the red mud dump.

[0022] Furthermore, in step S1, the red mud is red mud in a depth range of 0-50 cm in the red mud dump; the crushing and screening treatment specifically includes crushing the red mud to a particle size of less than 5 cm, removing stones and plastic debris larger than 5 cm, and forming a uniform surface treatment layer through leveling operations.

[0023] Furthermore, in step S2, the moisture content of the pile is 55%-70%.

[0024] Furthermore, in step S3, the in-situ aerobic fermentation adopts a film-covered fermentation process.

[0025] The film-covered fermentation process can use an ordinary breathable film or a heat-insulating breathable film to form a closed-heat-insulating-breathable fermentation system.

[0026] While achieving physical coverage, the breathable membrane can maintain gas exchange between the pile and the outside world, ensuring the oxygen supply required by aerobic microorganisms while reducing excessive water evaporation and dust emissions.

[0027] Furthermore, the fermentation period is 10-30 days.

[0028] Preferably, the fermentation process is differentiated by temperature feedback mechanism, specifically:

[0029] When the average temperature of the pile is greater than 60°C, turn the pile and aerate it every two days, and simultaneously add water to the moisture content of 55%-70% to prevent the inactivation of microorganisms due to high temperature;

[0030] When the temperature is between 33-60℃, turn the pile and aerate it every 4 days to promote the continuous decomposition of organic matter;

[0031] When the temperature is less than 33°C, the pile should be turned and aerated every 6 days, and water should be added to the pile to a moisture content of 55%-70%. The pile temperature should be maintained at ≥15°C by covering it with insulation film to ensure the metabolic activity of microorganisms.

[0032] Principle of the present invention:

[0033] Ca2 in gypsum calcium-based industrial solid waste + With Na in red mud pore solution + An equal charge replacement occurs, promoting the dissolution and migration of soluble sodium salts to reduce the alkalinity of the pore fluid. At the same time, it acts as a cementing ion to bridge the negative charge sites on the surface of the red mud particles, promoting the formation of water-stable aggregates larger than 0.25 mm, and improving the porosity and water holding capacity of the red mud. Straw in biomass serves as a lignin and cellulose skeleton material, which gradually degrades and releases carbon substrates such as glucose and hemicellulose during fermentation, providing a long-term energy source for decomposing microorganisms. Natural mesophilic bacteria such as Bacillus subtilis and Streptomyces, as well as fungal spores carried by manure, initiate the decomposition of organic matter in the early stages of fermentation (0-7 days). The ammonium nitrogen and available phosphorus it contains directly supplement the nitrogen and phosphorus nutrients of the red mud. Wheat bran, as a fine-particle nitrogen source, optimizes the porosity of the pile with its high surface area characteristics and provides short-chain carbon and nitrogen compounds to balance the nutrient ratio of the high-carbon matrix of straw. When composting begins, aerobic microbial communities decompose biomass to produce organic acids such as acetic acid and propionic acid, gradually lowering the red mud's pH. Simultaneously, intermediate products of lignin degradation polymerize to form humic and fulvic acids, forming an organic-mineral complex that significantly increases the red mud's nutrient content. The microenvironmental control system constructed by the breathable composting membrane prolongs the medium-temperature fermentation period through a temperature buffering effect. During hot seasons, ventilation and heat dissipation control the temperature difference between the membrane's interior and exterior to prevent microbial inactivation, while also reducing water loss through evaporation. Regular water replenishment maintains the compost's moisture content, providing an optimal hydrolysis environment for extracellular enzymes such as cellulase and ligninase. Ultimately, this achieves a synergistic effect: neutralizing the red mud's alkalinity, increasing nutrients, and improving its physical structure, shortening the red mud's soil-forming cycle.

[0034] Beneficial effects of the present invention:

[0035] (1) The method of the present invention reduces the pH value of red mud from strongly alkaline (12-13) to neutral and low alkaline (7.5-8.5) within 30 days through efficient dealkalization and nutrient reconstruction, and simultaneously increases the carbon and nitrogen content, significantly improving the nutrient-poor conditions of red mud and directly meeting the basic fertility requirements for herbaceous plant colonization;

[0036] (2) The method of the present invention realizes a circular economy model of "waste treatment with waste" through the synergistic restoration of biomass-calcium-based solid waste, and the cost is significantly reduced compared with purchasing external improvers;

[0037] (3) Compared with traditional methods, the method of the present invention does not require the pre-dealkalization of red mud in traditional processes, and directly treats the red mud within the 0-50 cm surface layer of the storage yard, reducing process costs and shortening the treatment cycle to 10-30 days, significantly reducing the difficulty of project implementation;

[0038] (4) The method of the present invention breaks through the pretreatment limitations and cycle bottlenecks of traditional red mud soilification, significantly reduces engineering costs and environmental risks, and provides a scalable technical solution for in-situ ecological restoration of red mud dumps. At the same time, it has significant engineering applicability and broad market promotion prospects in the fields of tailings pond reclamation, mine ecological restoration, and industrial site landscaping. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The salinity and alkali content of red mud in the examples of the present invention and the comparative examples are shown below:

[0040] Figure 2 The temperature changes during the fermentation process in the examples of the present invention and the comparative examples;

[0041] Figure 3 is the change in total organic carbon content between the examples of the present invention and the comparative examples;

[0042] Figure 4 3D fluorescence spectra of the embodiments and comparative examples of the present invention;

[0043] Figure 5 This is a site diagram of the red mud dump applied in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] Example 1

[0045] Red mud from the surface layer of the red mud dump, within a depth of 0-50 cm, was crushed to a particle size of ≤2 cm using a jaw crusher, and any rocks and plastic impurities with a particle size greater than 5 cm were removed. Based on the mass percentage of red mud, 0.5% wheat straw segments (1 cm in length), 2% earthworm manure (60% moisture content), and 1% wheat bran (8% moisture content) were added as exogenous biomass. The carbon-nitrogen ratio (C / N) was controlled at 17:1 after mixing. The mixture was then mixed with 2% desulfurized gypsum as a conditioning agent. The composite conditioner was mechanically mixed with crushed red mud in situ, and the pile was plowed three times with a deep plow and sprayed with clean water to adjust the moisture content of the pile to 60%, forming a strip pile with a thickness of 0.8m, a width of 1.2m and a length of 50m. The surface of the pile was covered with a common polyethylene breathable compost film with an oxygen permeability of 250L / (m2·h) and the edge was compacted and sealed with red mud or surrounding soil. During the fermentation period, temperature feedback control was used to turn the pile and add water. When the central temperature of the pile was greater than 60℃ (high temperature period, 3rd to 7th day), the film was removed every 2 days for turning the pile and adding water to the moisture content of 60%. When the temperature dropped to 33-60℃ (medium temperature period, 8th to 15th day), the pile was turned and added water every 4 days. The entire decomposition cycle was 20 days, during which the maximum temperature of the pile reached 65℃ and the average temperature was maintained at 47℃.

[0046] Example 2

[0047] The process flow was the same as in Example 1, except for the ratio of the biomass in the composite conditioner. Based on the mass percentage of red mud, 2% earthworm manure (60% moisture content) and 1% wheat bran (8% moisture content) were used as the biomass. Wheat straw was not introduced, and the carbon-nitrogen ratio (C / N) was 16:1.

[0048] Example 3

[0049] The process flow was the same as in Example 1, except for the ratio of the biomass in the composite conditioner. Based on the mass percentage of red mud, 0.5% wheat straw segments (1 cm in length) and 2% earthworm manure (60% moisture content) were used as the biomass. Wheat bran was not introduced, and the carbon-nitrogen ratio (C / N) was 25:1.

[0050] Example 4

[0051] The process flow was the same as in Example 1, except for the ratio of the biomass in the composite conditioner. Based on the mass percentage of red mud, 0.5% wheat straw segments (1 cm in length) and 1% wheat bran (8% moisture content) were used as the biomass. No earthworm manure was introduced, resulting in a carbon-nitrogen ratio (C / N) of 15:1.

[0052] Comparative Example 1

[0053] The process flow is the same as that in Example 1, except that the aerobic composting method is different. Natural composting is adopted without covering the permeable composting film.

[0054] Comparative Example 2

[0055] The process flow is the same as that in Example 1, except that desulfurized gypsum is not introduced when preparing the conditioning agent, and biomass is used as the main conditioning component.

[0056] Comparative Example 3

[0057] The process flow is the same as that in Example 1, except that no biomass is introduced when preparing the conditioning agent, and desulfurized gypsum is used as the main conditioning component.

[0058] The pH value of red mud in Examples 1 to 4 and Comparative Examples 1 to 3 changes as follows: Figure 1 As shown. Under different treatment methods, the trend of pH value changes is significantly different. On the 20th day, the pH values ​​are ranked as follows: Example 1 < Example 3 ≈ Example 4 < Example 2 < Comparative Example 1 < Comparative Example 3 < Comparative Example 2. Among them, the pH value of Example 1 dropped significantly, and the decline was particularly rapid in the early stage. On the 20th day, it stabilized at around 7.9, with a drop of 34.2%; the pH value of Comparative Example 2 dropped slowly and always remained at a high level (about 10.0), and its treatment process failed to effectively reduce the alkalinity of red mud; after the 8th day, the pH value of Comparative Example 1 increased significantly, showing a trend of first decreasing and then increasing. During the fermentation process of biomass, acidic metabolites such as lactic acid and acetic acid are produced, which causes the pH to drop; Na in red mud +and Ca in desulfurization gypsum 2+ A displacement reaction occurs, dissolving alkaline minerals. The film coating creates a relatively closed environment, maintaining the fermentation temperature and humidity, promoting microbial activity and chemical reactions, and allowing metabolically produced acidic gases (such as CO2) to accumulate within the system. The combined effects of these three mechanisms significantly reduced the alkalinity of the red mud in Example 1.

[0059] The temperature changes during the fermentation process in Examples 1 to 4 and Comparative Examples 1 to 3 are as follows: Figure 2 As shown. Among them, the temperature of Example 1 changes significantly with time, and the temperature rises rapidly from 0 to 10 days, reaching a peak close to 55°C around the 10th day, and remains at a high level during the period of 5-15 days. Compared with other examples and comparative examples, Example 2 reaches about 40°C around 10 days. Although there is a temperature increase, the magnitude is not as large as that of Example 1; Examples 3 and 4 heat up relatively slowly, and the peak values ​​are also lower. The temperature of Comparative Example 1 is relatively low overall (<22°C); the temperature of Comparative Example 3 changes steadily, always maintaining at around 20°C. The fermentation of Example 1 can be divided into three stages: Days 1-8 are the low-temperature start-up period, Days 9-15 are the high-temperature decomposition period, and the temperature gradually stabilizes after 15 days. In the early stage of fermentation, microorganisms are restricted by the alkaline environment, and their reproduction and heat production are limited, resulting in an extension of the low-temperature start-up period. The suitable activity temperature of decomposing microorganisms is 45-69°C. Example 1 maintains a high temperature for a long time, and the microorganisms in its fermentation system are highly active, metabolically active, and the decomposition reaction is sufficient. In summary, judging from the key factor of temperature change, the fermentation effect of Example 1 is significantly better than that of the other groups.

[0060] The total organic carbon content in Examples 1 to 4 and Comparative Examples 1 to 3 varies as follows: Figure 3 As shown. Among them, the TOC content of Example 1 increases significantly over time. Starting from the 5th day, its TOC value rises rapidly from 2.3g / kg to 9.3g / kg, and is as high as 24.3g / kg on the 15th day, which is significantly higher than that of other groups, and continues to rise in the subsequent time, eventually reaching about 26g / kg. In comparison, although the TOC of Examples 2, 3, and 4 also increases, it is always less than 18g / kg, which is difficult to meet the growth needs of plants. The TOC of Comparative Examples 1, 2, and 3 grows more slowly, especially Comparative Example 3, which lacks biomass to provide mineralizable decomposable substances, and the decomposition process is relatively lagging. The TOC value is always at a low level during the whole process.

[0061] The three-dimensional spectra of the initial red mud, Examples 1 to 4 and Comparative Examples 1 to 3 on the twentieth day are as follows: Figure 4As shown. Among them, the initial red mud humic acid characteristic peaks are concentrated in the three regions of I, II, and IV. After 20 days of composting, the humic acid characteristic peaks in the system of Example 1 red-shifted to the right in the Em direction, moving from the three regions of I, II, and IV to the regions of III and V, and multiple regions showed multiple peaks, showing the complexity of the humic acid components. The macromolecular biomass is gradually decomposed into multiple small molecular substances, and the small molecular compounds are further transformed and polymerized to form humic acid macromolecules. The characteristic peak of fulvic acid gradually disappears and further red-shifts in the Ex direction, indicating that fulvic acid is gradually converted into humic acid. In Example 1, humic acid is gradually formed during the composting process, and the degree of humification is significantly improved, indicating that the red mud composting system has advantages in promoting the humification of organic matter.

[0062] For the red mud dump in Example 1, after the 20th day of the decomposition cycle, the surface covering film was removed and the fermented red mud base soil was flattened and compacted. Subsequently, Bermuda grass seeds were sown. Initially, watering was carried out every two days, and watering was stopped after one week. After 15 days, the grass seeds began to germinate, and after 25 days, the surface of the red mud dump was covered with green. The resulting site map is as follows: Figure 5 shown.

Claims

1. A composite conditioner, characterized in that The composite conditioner is obtained by pre-treating and mixing biomass obtained by mixing straw, feces and wheat bran with gypsum industrial calcium-based solid waste in a specific proportion; the carbon-nitrogen ratio of the biomass after mixing straw, feces and wheat bran is (15:1)-(28:1); and the mixing mass ratio of the biomass and gypsum industrial calcium-based solid waste is (1:1)-(2:1).

2. The composite conditioner according to claim 1, characterized in that The straw is selected from one or more of corn straw, wheat straw, and rice straw; the straw is a straw segment with a length of 1-3 cm; and the amount of the straw added is 0.5%-3% of the mass of the red mud.

3. The composite conditioner according to claim 1, characterized in that The manure is selected from one or more of cow manure, sheep manure, chicken manure or earthworm manure; the moisture content of the manure is 60%-70%; and the amount of the manure added is 0.5%-4% of the mass of the red mud.

4. The composite conditioner according to claim 1, characterized in that The moisture content of the wheat bran is 5%-12%; and the added amount of the wheat bran is 0.4%-2% of the mass of the red mud.

5. The composite conditioner according to claim 1, characterized in that The gypsum-type industrial calcium-based solid waste is selected from one or more of desulfurized gypsum and phosphogypsum; and the added amount of the gypsum-type industrial calcium-based solid waste is 1%-5% of the mass of the red mud.

6. A method for rapidly forming soil in a red mud dump using a film-covered aerobic compost fermentation method using the composite conditioner according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. The red mud in the red mud dump is crushed and screened to obtain pretreated red mud; S2. The composite conditioner is configured according to the amount of pretreated red mud, and the resulting composite conditioner and red mud are homogenized in situ to obtain a pile; S3. Cover the pile with a film to carry out in-situ aerobic fermentation to complete the rapid soil formation of the red mud dump.

7. The method for rapidly forming soil in a red mud dump using a film-covered aerobic compost fermentation method according to claim 6, characterized in that: In step S1, the red mud is red mud in a depth range of 0-50 cm in a red mud dump; the crushing and screening treatment specifically includes crushing the red mud to a particle size of less than 5 cm, removing stones and plastic debris larger than 5 cm, and forming a uniform surface treatment layer through leveling operations.

8. The method for rapid soil formation in red mud dump driven by film-covered aerobic composting according to claim 6, characterized in that: In step S2, the moisture content of the pile is 55%-70%.

9. The method for rapidly forming soil in a red mud dump using a film-covered aerobic compost fermentation method according to claim 6, characterized in that: In step S3, the in-situ aerobic fermentation adopts a film-covered fermentation process; the film-covered fermentation process can use an ordinary breathable film or a heat-insulating breathable film to form a closed-heat-insulating-breathable fermentation system; the fermentation cycle is 10-30 days.

10. The method for rapid soil formation in red mud dump driven by film-covered aerobic composting according to claim 6, characterized in that: In step S3, the fermentation process is differentiated through a temperature feedback mechanism, specifically: When the average temperature of the pile is greater than 60°C, turn the pile and aerate it every two days, and simultaneously add water to the moisture content of 55%-70% to prevent the inactivation of microorganisms due to high temperature; When the temperature is between 33-60℃, turn the pile and aerate it every 4 days to promote the continuous decomposition of organic matter; When the temperature is less than 33℃, turn the pile and aerate it every 6 days, and add water to the pile to a moisture content of 55%-70%; The pile temperature is maintained at ≥15°C by covering with thermal insulation film to ensure the metabolic activity of microorganisms.

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