Method for realizing vegetation coverage of red mud stockyard by interlayer controlling saline-alkali and application thereof

Abstract

The application provides a method and application for realizing vegetation coverage of red mud stockyard by interlayer salt and alkali control, and relates to the technical field of red mud ecological vegetation recovery methods. The method first uses inorganic regulating agent and weathered coal gangue to improve the matrix of red mud, the adding amount of the inorganic regulating agent and the weathered coal gangue is 1-5% of the dry weight of the red mud, the water content is adjusted to 40-70%, and after natural aging, the agglomerated structure is formed, the alkalinity of the red mud is reduced, and the fertility of the red mud is increased; then new coal gangue and straw interlayers are added between the improved red mud matrix and the untreated red mud underlayer to reduce the influence of the return salt and alkali of the stockyard on the growth of plants; finally, salt and alkali tolerant plants are sowed by ploughing. The red mud improvement, interlayer salt and alkali control and salt and alkali tolerant plant mixed sowing technology provided by the patent make the community diversity and stability of the red mud stronger, effectively solve the plant death phenomenon caused by the return salt and alkali of the red mud, and realize long-term vegetation coverage.

Description

Technical Field

[0001] This invention belongs to the technical field of red mud ecological vegetation restoration methods, specifically relating to a method and application of layered salt and alkali control to achieve vegetation coverage of red mud dumps. Background Technology

[0002] Aluminum is an economical and practical non-ferrous metal, second only to iron in global consumption. It is widely used in various sectors of the national economy and defense construction. Producing one ton of aluminum requires approximately two tons of alumina. Red mud is a waste product generated during the leaching of alumina from molten bauxite at high temperatures. The most common method of disposing of red mud is land-based stockpiling. However, stockpiling not only occupies a large amount of land resources but also incurs high costs for dam construction and daily maintenance, significantly increasing overall costs. Furthermore, red mud is highly alkaline (pH 9-13), has high salinity (EC 1.4-28.4 mS / cm), contains a variety of metals (Cr, As, Cd, V, Ni, etc.), is highly toxic, and has a fine structure (average particle size 2-100 μm). It easily generates dust and causes water and soil salinization, seriously threatening the stockpile site and its surrounding ecological environment.

[0003] Red mud, a major industrial solid waste, is difficult to remove due to its chemical alkalinity and the unclear behavior of its harmful substances, making its comprehensive utilization a global challenge. Red mud dumps are typical mining waste sites with slow natural weathering. Improving the surface substrate can reduce the alkalinity of the red mud, improve its physical structure and chemical properties, accelerate surface reclamation and vegetation restoration, and achieve natural ecological reconstruction, making it the most promising large-scale red mud disposal method. However, due to the high salinity and alkalinity of red mud, salt and alkali are transported with water, making the improved substrate highly susceptible to salt and alkali return, leading to re-salinization. As a result, while the improved surface substrate can support vegetation growth well, plants often die after a period of time due to salt and alkali stress. Therefore, controlling salt and alkali return is crucial in research on red mud dump vegetation restoration. Numerous studies have also proposed some salt and alkali control schemes.

[0004] The most common methods for reducing alkalinity in red mud are adding gypsum, seawater, and carbon dioxide. However, using seawater to reduce the alkalinity of red mud is often used in alumina plants near the sea, and adding excessive seawater can cause the accumulation of salt, colloidal particles, and sediments in the red mud matrix, making subsequent fertilization of the red mud after seawater-based alkalinity reduction more difficult and hindering vegetation establishment. While neutralizing red mud with carbon dioxide can consume liquid alkali (CO3),... 2- OH - and Al(OH)4 -While methods can lower pH and reduce industrial carbon dioxide emissions, the reaction of carbonic acid with hydroxide ions can cause pH rebound. Furthermore, carbon dioxide can only neutralize liquid-phase alkali, and its reaction with mineral alkalis in red mud is extremely slow, almost nonexistent. Carbon dioxide primarily affects the form of alkalinity in red mud, not the solubility of alkalis, thus failing to fundamentally solve the problem of high alkalinity in red mud restricting plant growth. Gypsum neutralization of red mud is effective in reducing the alkalinity of red mud with high iron and low calcium content, such as Bayer process red mud, but it has no effect on the large quantities of combined process and sintered process red mud currently stockpiled (where calcium content is much higher than iron content). Therefore, there is an urgent need to research environmental materials with long-lasting alkalinity-reducing functions to achieve alkalinity regulation of different types of red mud. The main component of ferrous sulfate heptahydrate is ferrous sulfate, which has better solubility than gypsum. Ferrous sulfate can neutralize both the liquid and solid phase alkali of the combined process red mud and can also lower the pH of Bayer process red mud by about 2 units. However, gypsum has a better effect on reducing alkali in Bayer process red mud than ferrous sulfate. Therefore, gypsum is still chosen as the regulator for Bayer process red mud.

[0005] Chinese invention patent CN106034458A discloses a method for preventing dust and environmental pollution from red mud dumps. First, it modifies the combined process red mud using ferrous sulfate and nitrohumic acid. The ferrous sulfate is added at 3-10% of the dry weight of the combined process red mud, and the nitrohumic acid is added at 5-20% of the dry weight. After natural aging for more than 10 days, it meets the basic conditions for plant growth. Second, a drainage layer and a buffer layer are added between the modified combined process red mud and the lower layer of red mud in the dump to reduce the impact of salt and alkali reactions on plant growth. The drainage layer includes inclined filter pipes and a layer of coarse and fine gravel. The buffer layer uses an acidic material with good water retention. After the substrate has stabilized, salt-tolerant plants such as Caragana korshinskii are selected for cultivation. This invention can prevent environmental problems such as dust, soil, and groundwater pollution from red mud dumps.

[0006] Chinese invention patent CN112655515A discloses a method for soilification of red mud. The method involves modifying red mud with acidic organic residue and gypsum, applying the resulting modified red mud mixture to a barrier layer, then covering the surface of the mixture with straw and allowing it to mature, thus soilifying the red mud. The barrier layer consists of, from top to bottom, a straw layer, a gypsum layer, and a gravel layer. The red mud soil obtained using this method has a significantly reduced salinity and alkali content, making it suitable for subsequent vegetation planting.

[0007] In the technical methods for controlling salinity and alkali in red mud, the use and selection of the blocking layer material are crucial. Coal gangue is a black, carbonaceous solid waste generated during coal mining and washing. The stockpiling, spontaneous combustion, and leaching of heavy metals from coal gangue pollute the atmosphere, water bodies, and soil. Coal gangue is a high-quality silica-alumina mineral material with a stable structure, chemical inertness, and contains abundant carbon, nitrogen, and other nutrients, providing essential nutrients for plant growth. Its large-particle structure also has good water and salt regulation properties. Therefore, using coal gangue to improve the physicochemical properties of red mud while inhibiting its salinization and alkali return has high application potential.

[0008] This invention compares the growth of *Leymus chinensis* (a grass), *Caragana korshinskii* (a legume), and a mixture of *Leymus chinensis*, *Caragana korshinskii*, and three Chenopodiaceae plants on red mud substrates. It evaluates the impact of plant growth on the physical, chemical, and biological properties of the red mud substrate and proposes a method for controlling salinity and alkali in red mud dumps through layering. This method improves red mud dumps, enabling self-sustaining long-term vegetation cover, thus addressing waste disposal issues. It offers advantages such as resource availability, ecological sustainability, and economic sustainability, making ecological reconstruction of red mud dumps possible. Summary of the Invention

[0009] This invention addresses the problems existing in the prior art by providing a method and application for controlling salinity and alkali in red mud dumps to achieve vegetation coverage. Its purpose is to solve the problem of ineffective vegetation reconstruction caused by salinization and alkali return in current red mud storage, and to improve the physical and chemical properties of red mud and maintain its fertility in the long term by using salt-tolerant plants. At the same time, it provides a new way for the large-scale resource reuse of coal gangue, and also provides a simple, efficient, and waste-to-waste method for red mud dump vegetation to maintain the stability of the ecosystem in the long term.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] On the one hand, the present invention provides a method for achieving vegetation cover in red mud dumps by layering and controlling salinity, comprising the following steps:

[0012] Step 1: Improve the matrix of red mud

[0013] The Bayer process red mud matrix was modified using gypsum and weathered coal gangue. The amount of gypsum added was 1%-5% of the dry weight of the red mud, and the amount of weathered coal gangue added was 1%-5% of the dry weight of the red mud. After adjusting the moisture content to 40%-70%, the matrix was mixed evenly and allowed to age naturally to obtain the modified Bayer process red mud growth matrix for later use.

[0014] Alternatively, ferrous sulfate and weathered coal gangue can be used to improve the matrix of red mud obtained by the combined method. The amount of ferrous sulfate added is 1%-5% of the dry weight of red mud, and the amount of weathered coal gangue added is 1%-5% of the dry weight of red mud. After adjusting the moisture content to 40%-70%, they are mixed evenly and allowed to age naturally to become the red mud growth matrix improved by the combined method, which can be used for later use.

[0015] Step 2: Laying a layer of salt-alkali control material

[0016] The salt-alkali control material includes a straw layer and a fresh coal gangue layer; the fresh coal gangue layer is placed below the straw layer and is laid flat after installation.

[0017] Step 3: Backfill with improved red mud.

[0018] Cover the improved red mud growth substrate from step one onto the salt-controlling material from step two. The thickness of the red mud growth substrate should be 10-50cm to obtain the improved red mud after backfilling. After tilling, sow the seeds.

[0019] Step 4: Mixed sowing of salt-tolerant plants

[0020] After sterilizing the seeds of salt-tolerant plants with hydrogen peroxide solution and cleaning them with distilled water, they are sown in the improved red mud backfill substrate during the growing season. The sowing density for grass and chenopodiaceae plants is 150-300 seeds per square meter, and the sowing density for legumes is 20-50 seeds per square meter.

[0021] Preferably, in step one, the particle size of the weathered coal gangue is less than 2 mm, and the amount of weathered coal gangue added is 2-5% of the dry weight of the red mud.

[0022] More preferably, the amount of weathered coal gangue added is 3% of the dry weight of red mud.

[0023] Preferably, in step one, the natural aging time is 50-100 days.

[0024] More preferably, the natural aging time is 70 days.

[0025] Preferably, in step one, the amount of gypsum added is 3% of the dry weight of red mud, and the amount of ferrous sulfate added is 3% of the dry weight of red mud.

[0026] Preferably, in step one, the moisture content is adjusted to 50-70%.

[0027] Preferably, the adjusted moisture content is 50%.

[0028] Preferably, in step two, the straw interlayer is selected from at least one of corn straw, wheat straw, rice straw, and cotton straw.

[0029] Preferably, in step two, the straw length of the straw interlayer is 3-10cm and the thickness of the interlayer is 2.5-8cm.

[0030] More preferably, the straw in the straw separator has a length of 5cm and a thickness of 5cm.

[0031] Preferably, in step two, the new coal gangue interlayer consists of coal gangue with a particle size of 1-6 mm and an interlayer thickness of 2.5-5 cm.

[0032] More preferably, the new coal gangue interlayer has coal gangue with a particle size of 5-6 mm and an interlayer thickness of 5 cm.

[0033] Preferably, in step three, the depth of tilling is equal to the thickness of the red mud after backfilling with improved substrate.

[0034] Preferably, in step three, the thickness of the red mud growth substrate is 15-25 cm.

[0035] Preferably, in step three, the thickness of the red mud growth substrate is 20 cm.

[0036] Preferably, in step four, the salt-tolerant plant seeds are selected from at least one of the following: grasses, gooseberries, and legumes.

[0037] More preferably, the salt-tolerant plant seeds are selected from at least one of the following: Leymus chinensis, Suaeda salsa, Haloxylon ammodendron, Salicornia glutinosa, Alfalfa, and Caragana korshinskii (Caragana korshinskii).

[0038] Preferably, in step four, the concentration of the hydrogen peroxide solution is 20-35%, and the sterilization time is 5-15 minutes.

[0039] More preferably, the concentration of the hydrogen peroxide solution is 30%, and the sterilization time is 10 minutes.

[0040] Preferably, in step four, the growing season is May to June.

[0041] Preferably, in step four, the sowing specifically involves: a sowing density of 200 seeds per square meter for both grasses and chenopodiaceae, and a sowing density of 30 seeds per square meter for legumes.

[0042] More preferably, when the sowing is mixed sowing, the mixed sowing ratio of crested wheatgrass, white-stemmed saltgrass, alfalfa, and caragana is 4-5:2-3:2-3:1-2, and the mixed sowing ratio of crested wheatgrass, white-stemmed saltgrass, and alfalfa is 1-3:1-3:1.

[0043] More preferably, when the sowing is mixed sowing, the sowing ratio of crested wheatgrass, white-stemmed halophyte, alfalfa, and caragana is 4:3:2:1, and the sowing ratio of crested wheatgrass, white-stemmed halophyte, and alfalfa is 2:2:1.

[0044] Preferably, in step four, the sowing depth is 1-3 cm.

[0045] More preferably, the sowing depth is 1-2 cm.

[0046] On the other hand, the present invention provides the application of the above method in regulating the salinity of red mud, increasing the fertility of red mud, and sowing salt-tolerant plants.

[0047] Preferably, the specific application method of sowing salt-tolerant plants includes the following steps: sterilizing the seeds of salt-tolerant plants with hydrogen peroxide solution, washing them with distilled water, and then sowing them in the red mud after backfilling the substrate during the growing season; the sowing density for grass and chenopodiaceae plants is 150-250 seeds per square meter, and the sowing density for legumes is 20-50 seeds per square meter.

[0048] More preferably, the salt-tolerant plant seeds are selected from at least one of the following: grasses, gooseberries, and legumes.

[0049] More preferably, the salt-tolerant plant seeds are selected from at least one of the following: Leymus chinensis, Suaeda salsa, Haloxylon ammodendron, Salicornia glutinosa, Alfalfa, and Caragana korshinskii.

[0050] More preferably, the concentration of the hydrogen peroxide solution is 20-35%, and the sterilization time is 5-15 minutes.

[0051] More preferably, the concentration of the hydrogen peroxide solution is 30%, and the sterilization time is 10 minutes.

[0052] More preferably, the growing season is May to June.

[0053] More preferably, the sowing is specifically as follows: the sowing density for grasses and chenopodiaceae plants is 200 seeds per square meter, and the sowing density for legumes is 30 seeds per square meter.

[0054] More preferably, when the sowing is mixed sowing, the mixed sowing ratio of crested wheatgrass, white-stemmed saltgrass, alfalfa, and caragana is 4-5:2-3:2-3:1-2, and the mixed sowing ratio of crested wheatgrass, white-stemmed saltgrass, and alfalfa is 1-3:1-3:1.

[0055] More preferably, when the sowing is mixed sowing, the sowing ratio of crested wheatgrass, white-stemmed halophyte, alfalfa, and caragana is 4:3:2:1, and the sowing ratio of crested wheatgrass, white-stemmed halophyte, and alfalfa is 2:2:1.

[0056] More preferably, the sowing depth is 1-3 cm.

[0057] More preferably, the sowing depth is 1-2 cm.

[0058] Because Bayer process red mud is characterized by high iron and low calcium content, gypsum is added to reduce alkalinity by continuously releasing calcium ions that react with hydroxide, carbonate, and bicarbonate ions in the red mud. Similarly, combined process red mud is characterized by high calcium and low iron content, and ferrous sulfate is added to reduce alkalinity by continuously releasing iron ions that react with hydroxide, carbonate, and bicarbonate ions in the red mud. While higher addition amounts of either process are generally more beneficial for reducing red mud alkalinity—for example, a 10% addition can lower the pH from 10 to around 8—high additions can lead to increased volume and significantly increase the salinity of the red mud, which is detrimental to plant growth.

[0059] In this invention, salt-tolerant plants are selected based on local dominant species. The main functions of these plants are to increase surface coverage of the stockpile, suppress dust, slow runoff, reduce water evaporation, and inhibit salt rise and salt and alkali return. At the same time, the rhizosphere action of the plants can improve the aggregation structure of the red mud, and the organic acids produced by root exudates and rhizosphere microbial exudates can further regulate the alkalinity of the red mud. Plant residues also help to improve fertility, enabling the red mud growth substrate to sustainably provide the nutrients necessary for plant growth.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. In the method of the present invention, the addition of gypsum and ferrous sulfate is reasonable. While reducing the alkalinity of red mud, the addition of reasonable amounts controls the volume increase and salt content of red mud, which is more conducive to plant growth.

[0062] 2. In the method of the present invention, weathered coal gangue is used to improve the red mud matrix, which has higher surface activity and nutrient controlled release performance, which is conducive to quickly transforming the red mud into a matrix that can support plant growth. The alkaline environment of the red mud is also more conducive to the release of humic components in the weathered coal gangue, thereby providing more effective nutrients for plant growth.

[0063] 3. In the method and application of the present invention, selecting suitable salt-tolerant plants and sowing methods can not only improve the aggregate structure of red mud and regulate its alkalinity, but also help improve the fertility of red mud and promote plant growth.

[0064] 4. This invention uses improved and layered salt-alkali control technology to transform red mud into a substrate that can support the long-term growth of salt-alkali tolerant plants, enabling red mud dumps to be covered with vegetation to reduce the risk of environmental pollution. It provides a new method for red mud disposal by performing one-time harmless treatment at low cost and has broad application prospects. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the structure of the present invention for controlling salinity and alkali and achieving vegetation cover in red mud dumps;

[0066] Figure 2 This refers to the alkalinity and nutrient status of the red mud growth substrate in this invention;

[0067] Figure 3 This is a distribution diagram of aggregates in the red mud growth matrix of this invention;

[0068] Figure 4 This is a diagram showing the effect of the interlayer material of this invention on the EC of the surface red mud;

[0069] Figure 5 This is a graph showing the germination rate of the salt-tolerant plants of this invention in the red mud growth substrate;

[0070] Figure 6 This is a diagram showing the growth characteristics of the salt-tolerant plants of this invention in the red mud growth substrate;

[0071] Figure 7 This is a graph showing the dry weight results of the mixed-soil-tolerant plants of the present invention growing in red mud substrate;

[0072] Figure 8 This is an example diagram of the simulated test process for the salt-alkali control layer of the present invention;

[0073] Figure 9 This invention relates to the effect of the salt-alkali control material of the interlayer on the salt-alkali properties of the red mud growth matrix. Detailed Implementation

[0074] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed in this application. Those skilled in the art can make various changes and modifications to the invention based on the disclosed content, and such changes should also fall within the scope of protection claimed in this application.

[0075] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of the present invention are obtained through conventional commercial means.

[0076] I. Basic Physicochemical Properties of Raw Materials Used

[0077] 1. Basic physical and chemical properties of red mud

[0078] 1.1 Basic Physicochemical Properties of Red Mud from Combined Processing

[0079] The combined process red mud was sourced from an aluminum company in Shanxi Province. The combined process red mud had a pH of 10.6, a total alkalinity of 0.2 cmol / kg, a basicity of 44.1%, a total salt content of 7.1 g / kg, and TOC, available nitrogen, and available phosphorus contents of 3.5 g / kg, 2.3 mg / kg, and 13.4 mg / kg, respectively. Its main chemical components were: Ca 197 g / kg, Al 19.0 g / kg, Fe 9.1 g / kg, Na 31.7 g / kg, and K 1.4 g / kg. Its specific surface area was 10.2 m². 2 / g, particle size ranges from 0.9 to 68 μm, with an average particle size of 9.72 μm. The main mineral components are Katoite (Ca3Al2(SiO4)(OH)8) and Sodalite (Na6Al6Si6O4). 24 )·2Na2SO4), calcite (CaCO3) and hematite (Fe2O3).

[0080] 1.2 Basic Physicochemical Properties of Bayer Process Red Mud

[0081] The Bayer process red mud was sourced from an aluminum company in Guangxi. The Bayer process red mud has a pH of 10.3, a total alkalinity of 2.8 cmol / kg, a basicity of 20.8%, a total salt content of 1.6 g / kg, and TOC, available nitrogen, and available phosphorus contents of 0.7 g / kg, 6.7 mg / kg, and 0.8 mg / kg, respectively. Its main chemical components are: Ca - 101.3 g / kg, Al - 19.7 g / kg, Fe - 315.7 g / kg, Na - 35.2 g / kg, and K - 1.1 g / kg. Its specific surface area is 7.9 m². 2 The particle size ranges from 0.39 to 51.5 μm, with an average particle size of 6.78 μm. The main mineral components are nepheline (Na8(AlSiO4)6(CO3)(H2O)2), calcite (CaCO3), and ferruginous zeolite (Ca3(Fe2O3)2). 0.87 Al 0.13 )2(SiO4) 1.65 (OH) 5.4 ), gibbsite (Al(OH)3) and hematite (Fe2O3).

[0082] 2. Physical and chemical properties of coal gangue.

[0083] Weathered coal gangue and freshly discharged coal gangue were used as improvement and interlayer materials, respectively.

[0084] Both the newly discharged coal gangue and the 30-year weathered coal gangue came from a coal company in Inner Mongolia. The weathered coal gangue had a pH of 6.1, a total salt content of 0.3 g / kg, and TOC, available nitrogen, and available phosphorus contents of 172.5 g / kg, 71.8 mg / kg, and 1.7 mg / kg, respectively. Its main chemical components were 14.8% Al, 6.0% Si, 7.6% Ca, 2.4% Fe, 0.09% Na, and 0.3% K. The newly discharged coal gangue had a pH of 5.6, a total salt content of 0.3 g / kg, and TOC, available nitrogen, and available phosphorus contents of 119.9 g / kg, 10.3 mg / kg, and 2.2 mg / kg, respectively. The main chemical components are 11.0% Al, 8.5% Si, 0.5% Ca, 0.4% Fe, 0.5% S, 0.1% Na, and 0.2% K. It is predominantly composed of particles larger than 1 cm, with particle sizes mainly distributed in the range of 0.005-2 cm. For subsequent use, it is crushed to a particle size of less than 2 mm. The main mineral component of both freshly discharged coal gangue and weathered coal gangue is kaolinite (Al₄₂(Si₄O₂)₃). 10 (OH)8), diaspore (AlOOH) and hematite (Fe2O3).

[0085] 3. Physicochemical properties of straw

[0086] Corn and wheat straw were used as interlayer materials. Both corn and wheat straw were sourced from Henan Province and are rich in essential nutrients for plant growth, such as carbon, nitrogen, and phosphorus, making them important sources of organic fertilizer. Simultaneously, straw mulching effectively regulates water and salt movement, inhibits soil moisture evaporation, improves soil permeability, facilitates salt leaching, and plays a role in water retention. The above indicates that red mud is a highly alkaline, high-salt, silty industrial waste containing harmful and toxic substances. Furthermore, the mineralogical characteristics of red mud are similar to those of parent materials (olivine, pyroxene, and feldspar), weathering products (amorphous gibbsite and iron ore), and secondary minerals (kaolinite, gibbsite, and goethite). Red mud also contains some non-metallic elements (phosphorus and sulfur, etc.), thus possessing the potential for soil conversion, but it must undergo dealkalization and fertilization to enable it to support plant growth. Moreover, one of the important factors hindering long-term vegetation cover in red mud dumps is salt and alkali return; therefore, necessary salt and alkali control measures are crucial for maintaining long-term vegetation cover. Coal gangue is acidic, has large particles, and is rich in nutrients such as organic matter, which can make up for the deficiencies in the physical structure and chemical properties of red mud soil. Straw, as a potential source of humus, can improve the fertility of the bottom layer of the red mud growth substrate and effectively inhibit groundwater evaporation and salt upwelling.

[0087] II. Red Mud Matrix Improvement Methods

[0088] The main reason for the high alkalinity of red mud is that it contains a large amount of liquid-phase alkali (sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium aluminate) and mineral alkali (tricalcium aluminate and desilication products). Neutralization measures targeting the liquid-phase and solid-phase alkali in red mud can effectively reduce its pH. Usually, using regulators to lower the pH of red mud to 7-9 can meet the basic conditions for the growth of salt-tolerant plants. Further addition of acidic organic materials can simultaneously inhibit the continuous release of mineral alkali from red mud and increase the nutrient content of the red mud growth substrate.

[0089] The specific measures are as follows: Green vitriol and weathered coal gangue are used to improve the red mud from the combined process, while gypsum and weathered coal gangue are used to improve the red mud from the Bayer process. The green vitriol used is industrial grade, with a ferrous sulfate heptahydrate content greater than 90% and a particle size of 0.18 mm; the gypsum used is industrial grade, with a calcium sulfate dihydrate content greater than 98%, and is in powder form. The detailed improvement steps are as follows: First, the dried and hardened red mud is pulverized; second, green vitriol is added to the combined process red mud, and gypsum is added to the Bayer process red mud, with the addition amount being 1%-5% of the dry weight of the red mud. After mixing evenly, weathered coal gangue is added, with the addition amount being 1%-5% of the dry weight of the red mud. Water is then added to adjust the moisture content to 40%-70%, stirred evenly, and allowed to age naturally for 50-100 days.

[0090] III. Laying a layer of salt-alkali control material

[0091] Due to climatic factors such as temperature differences and alternating wet and dry periods, as the temperature of the surface red mud rises, soluble salts and alkalis in the lower red mud layer migrate upwards with the evaporation of water, leading to salt and alkali return phenomena in red mud stockpiles. Therefore, layered salt and alkali control technology is used to reduce the long-term impact of salt and alkali return from the lower red mud layer on plant growth.

[0092] The specific measures are as follows: A 2.5-5cm thick layer of straw is added beneath the red mud growth substrate, and a 2.5-5cm thick layer of freshly dumped coal gangue is added beneath the straw layer. After laying, the surface is leveled uniformly. All the materials used for the layers are solid waste, achieving the goal of treating waste with waste.

[0093] IV. Backfilling and mixed sowing of salt-tolerant plants

[0094] The improved red mud growing substrate is laid on top of a layer of salt- and alkali-controlling material, and then sown after tilling. Salt-tolerant plants from the Poaceae, Leguminosae, and Chenopodiaceae families can be selected, including *Leymus chinensis*, *Suaeda salsa*, *Haloxylon ammodendron*, *Salvia splendens*, alfalfa, and *Caragana korshinskii*. Seeds are sterilized with a 30% hydrogen peroxide solution for 10 minutes, then rinsed thoroughly with water. The sowing density for *Leymus chinensis*, *Suaeda salsa*, *Haloxylon ammodendron*, and *Salvia splendens* is 150-200 seeds per square meter, while the sowing density for *Caragana korshinskii* and alfalfa is 30-50 seeds per square meter. The sowing depth should not exceed 2 cm.

[0095] Before using the seeds, 100 seeds were randomly selected and tested for germination potential under dark conditions at room temperature (25℃). Seeds with a germination rate of over 90% were considered viable and could be sown.

[0096] After sterilization, rinse thoroughly with water.

[0097] The sowing density for grasses and chenopodiaceae is 200 seeds per square meter, and the sowing density for legumes is 30 seeds per square meter. Alfalfa is mixed with other salt-tolerant plants, and the sowing density is lower than that for salt-tolerant plants.

[0098] When sowing mixed grasses, the ratio of crested wheatgrass, white-stemmed saltgrass, alfalfa, and caragana is 4:3:2:1, and the ratio of crested wheatgrass, white-stemmed saltgrass, and alfalfa is 2:2:1.

[0099] Sow seeds after rain in late May at a depth of 2 cm.

[0100] Example 1: Experiment on Red Mud Matrix Improvement Method

[0101] The Bayer process red mud was modified using gypsum and weathered coal gangue. The red mud was crushed and mixed with gypsum. The amount of gypsum (GP) added was 3% of the dry weight of the red mud, and the amount of weathered coal gangue added was 2% of the dry weight of the red mud. The weathered coal gangue was crushed to a particle size of less than 2 mm, and the moisture content was adjusted to 50%. After being mixed evenly, the mixture was allowed to age naturally for 70 days to obtain the modified red mud growth matrix 1, which was then used for later use. The thickness of the red mud growth matrix was 20 cm.

[0102] The matrix of red mud obtained by combined process was improved by using ferrous sulfate and weathered coal gangue. The red mud was crushed and mixed with ferrous sulfate. The amount of ferrous sulfate (FS) added was 3% of the dry weight of red mud, and the amount of weathered coal gangue added was 2% of the dry weight of red mud. The weathered coal gangue was crushed to a particle size of less than 2 mm, and the moisture content was adjusted to 50%. After being mixed evenly, it was naturally aged for 70 days to obtain the improved red mud growth matrix 2, which was then used for later use. The thickness of the red mud growth matrix was 20 cm.

[0103] After the above improvements, the physicochemical properties (alkalinity and nutrient status) of the improved red mud growth substrate are as follows: Figure 2 As shown:

[0104] A combined method was used to improve the matrix of red mud. The alkalinity, including pH, ESP (basicity), and TA (total alkalinity), decreased from 10.6, 44.1%, and 0.2 cmol / kg to 8.3, 35.2%, and 0.1 cmol / kg, respectively; EC (electrical conductivity) increased from 2.4 mS / cm to 3.7 mS / cm; and the TOC (total organic carbon), available nitrogen, and available potassium content of red mud increased from 3.5 g / kg, 2.3 mg / kg, and 1.4 g / kg to 8.6 g / kg, 20.1 mg / kg, and 4.01 mg / kg, respectively.

[0105] The Bayer process was used to improve the matrix of red mud, reducing alkalinity (pH, ESP, and TA) from 10.3, 20.7%, and 2.8 cmol / kg to 8.0, 12.7%, and 0.8 cmol / kg, respectively; increasing EC from 0.5 mS / cm to 3.1 mS / cm; and increasing the TOC, available nitrogen, and available potassium content of the red mud from 0.7 g / kg, 6.7 mg / kg, and 1.1 g / kg to 5.7 g / kg, 28.5 mg / kg, and 3.87 mg / kg, respectively.

[0106] Because red mud contains a large amount of calcium and iron, forming insoluble Ca-P and Fe-P compounds, the available phosphorus content is slightly reduced. However, the application of organic matter can promote the release of this phosphorus. The content of silt-clay particles (<0.054 mm) in the red mud improved by the combined process and the Bayer process was significantly reduced, while the content of large aggregates was significantly increased, from 10.58% and 2.52% to 27.37% and 6.52%, respectively. This greatly improved the physical structure of the red mud. The distribution diagram of aggregates in the red mud growth matrix is ​​shown below. Figure 3 Example 2: Screening Test of Red Mud Growth Matrix Modifier

[0107] The key to preparing red mud growth substrate lies in two aspects: alkalinity control and fertility enhancement.

[0108] 2.1 Alkalinity Regulation

[0109] Red mud was improved according to the red mud matrix improvement method in Example 1, wherein the amount of gypsum and ferrous sulfate added is as shown in Tables 1 and 2.

[0110] Table 1 shows the effects of gypsum and ferrous sulfate addition on the alkalinity of Bayer process red mud and combined process red mud.

[0111] Table 2 shows the effects of gypsum and ferrous sulfate addition on the conductivity of Bayer process red mud and combined process red mud.

[0112] After adding different proportions of gypsum and ferrous sulfate to two types of red mud, the alkalinity of the red mud, such as pH and ESP, decreased significantly with the increase of gypsum and ferrous sulfate addition, while EC showed an increasing trend (Tables 1 and 2).

[0113] Table 1

[0114]

[0115] Table 2

[0116] The effect of gypsum on reducing alkalinity is limited by the solubility of calcium sulfate. With a 1% gypsum addition, the pH of red mud tends to decrease with increasing curing days, reaching equilibrium after 35 days and then ceasing to change. Adding 3%, 5%, and 7% gypsum can all lower the pH of red mud below 9. Furthermore, due to the long-term release of solid alkali in red mud, the salinity varies with different curing days. Generally, gypsum additions above 1% neutralize the pH of Bayer process red mud with a slight increase in curing days, reaching equilibrium after 35 days as solid alkali release and gypsum dissolution occur, and the red mud pH tends to stabilize. The ESP (exposure potential) of red mud decreases with increasing addition amount and curing days. Generally, maintaining a red mud pH of 5.5-9.0, EC below 5 mS / cm, and ESP below 40% is considered an acceptable range for plant growth. Therefore, considering the minimum environmental requirements for plant growth and minimizing the need for bulking and cost savings, an addition of less than 3% gypsum and ferrous sulfate would result in high alkalinity. While an addition of more than 3% would help lower the pH, it would lead to a significant increase in salinity, which is not conducive to long-term plant establishment. A 3% addition of gypsum and ferrous sulfate is sufficient. Furthermore, at a 3% addition, both gypsum and ferrous sulfate can react fully with the alkaline substances in the red mud in a short period. Although there is a slight rebound in alkalinity, it is not significant. Therefore, separate maintenance is not necessary (if the addition of gypsum and ferrous sulfate is large, maintenance for at least 7 days is required before adding organic materials), but rather they can be directly used together with organic materials for maintenance.

[0117] 2.2 In terms of increasing fertility

[0118] Red mud was improved according to the red mud matrix improvement method in Example 1. At the same time, based on the neutralization of Bayer process red mud and combined process red mud with 3% added gypsum and ferrous sulfate, in order to increase the nutrient content of the red mud growth matrix, different proportions of vinegar residue, furfural residue, fresh coal gangue, weathered coal gangue, peat, nitrohumic acid and citric acid were added to the improved red mud. The specific addition amounts are shown in Table 3.

[0119] Among them, vinegar residue is the residue produced during the vinegar brewing process, with a pH of 4.4, a TOC of 163.5 g / kg, a total nitrogen content of 1.3 g / kg, and a total phosphorus content of 1.1 g / kg. It is commonly used to make dry feed and cultivation substrate. Furfural residue is the waste from the hydrolysis of agricultural by-products to produce the chemical raw material furfural. It has a pH of 3.5, a TOC of 183.3 g / kg, a total nitrogen content of 5.2 g / kg, and a total phosphorus content of 0.9 g / kg. It is commonly used as a cultivation substrate, adsorbent, and for improving saline-alkali land. Coal gangue is the residue from the coal mining and washing processes. The solid waste discharged during the process typically contains 20%-30% carbon. The properties of freshly discharged coal gangue and weathered coal gangue differ significantly. Freshly discharged coal gangue has a pH of 5.6, a TOC of 119.9 g / kg, a total nitrogen content of 2.6 g / kg, an available nitrogen content of 10.3 mg / kg, a total phosphorus content of 0.8 g / kg, and an available phosphorus content of 2.2 mg / kg. Weathered coal gangue has a pH of 6.1, a TOC of 172.5 g / kg, a total nitrogen content of 8.1 g / kg, and an available nitrogen content of 71.8 mg / kg. The total phosphorus content is 0.9 g / kg, and the available phosphorus content is 1.7 mg / kg. Peat moss is widely distributed in many parts of my country. It is a natural organic matter formed by the accumulation of plant residues after incomplete decomposition by microorganisms. Peat moss has a pH of 4.3, a TOC of 188.6 g / kg, a total nitrogen content of 6.4 g / kg, and a total phosphorus content of 0.6 g / kg. The price of peat moss is approximately 180-1000 yuan / ton. It is commonly used to improve desertified and saline-alkali soils. Nitrohumic acid is the regenerated humic acid produced by the oxygenation of lignite through nitric acid oxidation. The transformation results in the degradation of large-molecule lignite organic matter into small-molecule soluble humic acid, with a content as high as 70%-80%. Nitrohumic acid is priced at 1000-1500 yuan / ton, with a pH of 2.0, a TOC of 192.7g / kg, a total nitrogen content of 16.3g / kg, and a total phosphorus content of 0.6g / kg. It is often used to improve saline-alkali soil. Citric acid (C6H8O7), as an important organic acid, is priced at 130-280 yuan / ton, with a pH of 2.0. It is often used as an acidity regulator and food additive.

[0120] All the organic materials used in the embodiments of this invention are industrial grade. The vinegar residue, furfural residue and coal gangue (including newly discharged coal gangue and weathered coal gangue) were purchased from a vinegar company in Shanxi, a fertilizer company in Shijiazhuang and a coal company in Inner Mongolia. The peat, nitrohumic acid and citric acid were purchased from a trading company in Baishan City, a biotechnology company in Shanxi and a chemical technology company in Suzhou, respectively.

[0121] Considering that the main factor limiting vegetation growth in red mud is salinity, finding an organic material that is both rich in organic matter and acidic to sustainably reduce the alkalinity of red mud is of great significance for achieving long-term and sustainable ecological reconstruction of red mud. Therefore, based on the determination of carbon, nitrogen, and phosphorus contents of different organic materials, the total organic carbon content, from highest to lowest, was found to be: nitrohumic acid (abbreviated as nitro in Table 3, 192.7 g / kg), peat (188.6 g / kg), furfural residue (abbreviated as furfural in Table 3, 183.3 g / kg), weathered coal gangue (abbreviated as weathered in Table 3, 172.5 g / kg), vinegar residue (163.5 g / kg), and freshly discharged coal gangue (abbreviated as freshly discharged in Table 3, 119.9 g / kg); the total nitrogen content, from highest to lowest, was: nitrohumic acid (16... The seven organic materials included: 0.3 g / kg weathered coal gangue (8.1 g / kg), peat moss (6.4 g / kg), furfural residue (5.2 g / kg), freshly discharged coal gangue (2.6 g / kg), and vinegar residue (1.3 g / kg). The total phosphorus content of these organic materials was similar, ranging from a minimum of 0.6 g / kg to a maximum of 1.1 g / kg. All seven organic materials were capable of providing nutrients to plants. Therefore, based on the effect of adding organic materials on the salinity and alkalinity of the red mud growth substrate, combined with factors such as long-term effectiveness and cost, a suitable organic amendment was finally selected.

[0122] Table 3

[0123]

[0124]

[0125] Note: In the table, 3% neutralization refers to Bayer process red mud and combined process red mud after neutralization with 3% gypsum and ferrous sulfate; furfural refers to furfural residue; new discharge refers to new discharge coal gangue; weathering refers to weathered coal gangue; nitro refers to nitro humic acid; and citric acid refers to citric acid.

[0126] Table 3 shows the changes in pH and EC of red mud after adding different organic materials. All seven organic materials have a certain neutralizing capacity, and their order of decreasing pH of the red mud is as follows: citric acid, nitrohumic acid, weathered coal gangue, peat moss, freshly discharged coal gangue, furfural residue, and vinegar residue. The addition of each organic material led to a further increase in the EC of the red mud. At a 2% organic material addition, the EC of Bayer process red mud, from highest to lowest, was: peat moss, weathered coal gangue, vinegar residue, nitrohumic acid, furfural residue, freshly discharged coal gangue, and citric acid. For the combined process red mud, except for citric acid, the EC remained relatively stable with the addition of the other organic materials. Therefore, higher amounts of organic materials also lead to an increase in the salt content of the red mud growth substrate. Considering the carbon, nitrogen, and phosphorus content of the organic materials, the salinity and alkalinity of the red mud substrate after addition, and the cost of use, weathered coal gangue was ultimately selected as the organic amendment for the red mud growth substrate, and the curing time was determined to be 70 days.

[0127] Example 3: Screening Test of Layered Salt-Alkali Control Materials

[0128] Column tests were used to screen for interlayer alkali control materials. The acrylic column was 50cm high and 15cm in inner diameter, sealed at the bottom. The soil column was filled sequentially from the bottom with 25cm of unmodified red mud (the EC of the combined process red mud is higher than that of the Bayer process red mud, therefore only red mud with high salt content was selected for the column test), 10cm of interlayer material, and 10cm of combined process red mud (simulating salt and alkali return; no cultivation trials were conducted, therefore 10cm of combined process red mud was used). After the soil column was filled, water infiltration began, with an irrigation volume of 4.5L (marked at the water level). A constant-temperature heating blanket was placed at the bottom of the soil column, heated daily from 8:00 to 18:00. When the water level dropped below the red mud sample, water was added to the marked water level. After 5 weeks, when the water level dropped below the red mud sample, the evaporation test ended, and surface red mud samples were taken to measure EC.

[0129] The combined red mud matrix improvement method is the same as in Example 1: the red mud is crushed and mixed with ferrous sulfate. The amount of ferrous sulfate (FS) added is 3% of the dry weight of the red mud, and the amount of weathered coal gangue added is 2% of the dry weight of the red mud. The weathered coal gangue is crushed to a particle size of less than 2 mm, and the moisture content is adjusted to 50%. After mixing evenly, the mixture is naturally aged for 70 days to obtain the red mud growth matrix improved by the combined method.

[0130] The experimental interlayer material was set into 8 treatments: no interlayer as the control (CK), 10cm high 1-2mm fresh coal gangue (FC1), 10cm high 3-4mm fresh coal gangue (FC2), 10cm high 5-6mm fresh coal gangue (FC3), 5cm high 1-2mm fresh coal gangue + 5cm high corn stalks (FW1), 5cm high 3-4mm fresh coal gangue + 5cm high corn stalks (FW2), 5cm high 5-6mm fresh coal gangue + 5cm high corn stalks (FW3), and 10cm high corn stalks (W).

[0131] The results of the influence of the interlayer material on the EC of the surface red mud are shown in Figure 4 .

[0132] The results showed that the EC of the upper red mud under FW3 treatment was the lowest, followed by W. The mixed interlayer material of larger-sized fresh coal gangue and straw could effectively block the upward migration of salt.

[0133] Example 4: Screening Test for Salt-Tolerant Plants

[0134] A method for achieving vegetation cover in red mud dumps by layering and controlling salinity includes the following steps:

[0135] Step 1: Improve the matrix of the red mud, as in Example 1, specifically as follows:

[0136] The Bayer process red mud was modified using gypsum and weathered coal gangue. The red mud was crushed and mixed with gypsum. The amount of gypsum (GP) added was 3% of the dry weight of the red mud, and the amount of weathered coal gangue added was 2% of the dry weight of the red mud. The weathered coal gangue was crushed to a particle size of less than 2 mm, and the moisture content was adjusted to 50%. After being mixed evenly, it was naturally aged for 70 days to obtain the Bayer process modified red mud growth substrate 1, which was ready for use.

[0137] The matrix of red mud prepared by the combined method was improved by using ferrous sulfate and weathered coal gangue. The red mud was crushed and mixed with ferrous sulfate. The amount of ferrous sulfate (FS) added was 3% of the dry weight of the red mud, and the amount of weathered coal gangue added was 2% of the dry weight of the red mud. The weathered coal gangue was crushed to a particle size of less than 2 mm, and the moisture content was adjusted to 50%. After being mixed evenly, the mixture was allowed to age naturally for 70 days to obtain the red mud growth matrix 2 improved by the combined method, which was then ready for use.

[0138] Step 2: Lay a layer of salt-alkali control material; Step 3: Backfill with the improved red mud matrix, as in Example 3, specifically:

[0139] From bottom to top, the layers are: 25cm high red mud, 10cm high interlayer material (5cm high 5-6mm fresh coal gangue + 5cm high straw), and 20cm high improved red mud growth substrate (step one).

[0140] Step 4: Sowing salt-tolerant plants

[0141] Salt-tolerant plant seeds were sterilized with 30% hydrogen peroxide solution for 10 minutes, rinsed three times with 100 ml of distilled water, and then 50 seeds were placed in red mud growth substrate for germination rate experiments at room temperature. The number of germinated seeds was counted, and germination was terminated when a root of at least 20 mm in length was grown.

[0142] A total of 12 salt-tolerant plant seeds were collected, including 6 grasses: Reed, Bermuda grass, Leymus chinensis, Alternaria alternifolia, Leymus chinensis, and Stipa grandis; 3 legumes: Alternaria scabra, Alfalfa, and Caragana korshinskii; and 3 goosegrasses: Suaeda salsa, Haloxylon ammodendron, and Salicornia glutinosa.

[0143] The germination rate (%) of seeds is calculated as follows: Germination rate (%) = 100 × number of germinated seeds / total number of seeds.

[0144] The experiment was conducted in triplicate. The germination rates of various seeds in the two red mud growth substrates are shown in Table 4.

[0145] Table 4

[0146]

[0147]

[0148] Table 4 shows that among the grasses, *Elymus sibiricum* could germinate in both types of red mud substrates, with germination rates of 36% and 30%, respectively, while the remaining plants showed almost no germination. The germination rates of legumes were generally unsatisfactory, with only *Caragana korshinskii* showing germination in Bayer process red mud. The germination rates of Chenopodiaceae were relatively high, and all three species could germinate in both types of red mud substrates. Based on these results, *Elymus sibiricum*, *Caragana korshinskii*, *Haloxylon ammodendron*, *Suaeda salsa*, and *Salvia splendens* are relatively ideal, tolerant plants suitable for growth in red mud substrates.

[0149] Furthermore, it is worth noting that the use of external additives usually leads to a significant increase in the salt content of red mud, which is detrimental to the later growth of plants. Therefore, many studies leach the treated red mud before planting to reduce the salt content of the substrate. However, in the actual reclamation of red mud dumps, this measure is not easy to implement, and the filtrate is difficult to treat. This invention, through screening various additives and salt-tolerant plants, proposes reasonable addition amounts and maintenance days, as well as tolerant plants that can adapt to the permeability and high salinity of red mud bottoms, ultimately determining a feasible and long-lasting red mud vegetation cover method.

[0150] Example 5: Germination rate test of red mud growth substrate

[0151] The method for improving the matrix of red mud is the same as in Example 1, specifically as follows:

[0152] Gypsum and weathered coal gangue were used to improve the matrix of Bayer process red mud. The red mud (500g) was crushed and mixed with gypsum (GP). The amount of gypsum (GP) added was 3% (15g) of the dry weight of the red mud, and the amount of weathered coal gangue added was 2% (10g) of the dry weight of the red mud. The particle size of the weathered coal gangue was crushed to less than 2mm. 251mL of water was added to each type of red mud, and after thorough mixing, the mixture was weighed and the weight recorded. Subsequently, the weight was measured daily to calculate the water loss. The lost water was replenished to maintain a moisture content of 50% before thorough mixing. After natural aging for 50 days, the resulting matrix was the Bayer process red mud growth substrate. The combined red mud was modified using ferrous sulfate and weathered coal gangue. The red mud (500g) was crushed and mixed with ferrous sulfate at a concentration of 3% (15g) of the dry weight of the red mud, and the weathered coal gangue was added at a concentration of 2% (10g) of the dry weight of the red mud. The weathered coal gangue was crushed to a particle size of less than 2mm. 251mL of water was added to each type of red mud, and after mixing thoroughly, the mixture was weighed and the weight recorded. Subsequently, the weight was measured daily to calculate the lost moisture. The lost moisture was replenished to maintain a moisture content of 50%, and the mixture was then thoroughly mixed. After natural aging for 50 days, the resulting substrate for the combined red mud growth process was ready for use.

[0153] The sowing of salt-tolerant plants is the same as in Example 4, specifically:

[0154] Salt-tolerant plant seeds were sterilized with a 30% hydrogen peroxide solution for 10 minutes, rinsed three times with 100 ml of distilled water, and then 50 seeds were placed in a red mud growth substrate. Germination rate experiments were conducted at room temperature in late May. The number of germinated seeds was counted, and germination was terminated when a root of at least 20 mm in length was grown.

[0155] Five salt-tolerant plant seeds were identified: Leymus chinensis, Caragana korshinskii, Suaeda salsa, Haloxylon ammodendron, and Salicornia glutinosa.

[0156] The germination rate (%) of seeds was calculated as follows: Germination rate (%) = 100 × number of germinated seeds / total number of seeds. The experiment was conducted in triplicate. The germination rates of various seeds in the two red mud growth substrates are shown below. Figure 5 As shown.

[0157] from Figure 5 It can be seen that among the two red mud growth substrates, the germination rate of white-stemmed Haloxylon ammodendron was the highest, at 79.7% and 81.3% respectively; Elymus spp. was second, but the germination rate of Elymus spp. in Bayer process red mud was second only to white-stemmed Haloxylon ammodendron, at 77.3%.

[0158] Example 6: Pot Experiment with Red Mud Growth Matrix

[0159] The red mud matrix was improved in the same manner as in Example 1, specifically as follows:

[0160] Gypsum and weathered coal gangue were used to improve the matrix of Bayer process red mud. The red mud was crushed (2000g red mud) and mixed with gypsum. The amount of gypsum added was 3% of the dry weight of the red mud (60g gypsum), and the amount of weathered coal gangue added was 2% of the dry weight of the red mud (40g weathered coal gangue). The particle size of the weathered coal gangue was crushed to less than 2mm. 1050mL of water was added to each type of red mud, and after stirring evenly, the weight was recorded. Subsequently, the weight was measured daily and the water loss was calculated. The corresponding water loss was replenished to maintain the moisture content at 50% and then mixed evenly. After natural aging for 70 days, the Bayer process red mud growth matrix was obtained and ready for use.

[0161] The matrix of red mud from the combined process was improved using ferrous sulfate and weathered coal gangue. The red mud was crushed (2000g) and mixed with ferrous sulfate. The amount of ferrous sulfate added was 3% of the dry weight of the red mud (60g), and the amount of weathered coal gangue added was 2% of the dry weight of the red mud (40g). The particle size of the weathered coal gangue was crushed to less than 2mm. 1050mL of water was added to each of the two types of red mud, and after stirring evenly, the weight was recorded. Subsequently, the weight was measured daily and the water loss was calculated. The corresponding water loss was replenished to maintain the moisture content at 50% and then mixed evenly. After natural aging for 70 days, the resulting matrix of red mud from the combined process was ready for use.

[0162] Salt-tolerant plant seeds were sterilized with 30% hydrogen peroxide solution for 10 minutes and washed three times with 100 ml of distilled water. 200 seeds of *Leymus chinensis*, 100 seeds of *Caragana korshinskii*, 200 seeds of *Haloxylon ammodendron*, and 200 seeds of *Suaeda salsa* were placed separately in red mud growing medium. Pot experiments were conducted at room temperature in late May. After 15 days, *Leymus chinensis* seedlings were thinned to 60 cm and *Caragana korshinskii* seedlings to 30 cm. The moisture content was maintained at 50% on the first day of planting, followed by weekly addition of 5.37 mm water (totaling 95 mL, calculated based on local average rainfall) for 12 consecutive weeks. After the 13th week, the plants were collected, and plant height and root length were measured. The plant samples were then dried at 65℃ for 2 days, and the dry weight of the roots and aboveground parts was measured separately. Each treatment was performed in triplicate.

[0163] Fresh and dry weights, plant heights, and root lengths of various plants in two different red mud growing substrates Figure 6 As shown, (a) is the growth substrate for red mud from the combined process, and (b) is the growth substrate for red mud from the Bayer process.

[0164] Example 7: Growth Experiment of Salt-Tolerant Plants in Mixed Sowing

[0165] The matrix of red mud is improved, specifically as follows:

[0166] The Bayer process red mud was modified using gypsum and weathered coal gangue. The red mud was pulverized (10 kg) and mixed with gypsum at a ratio of 3% (300 g) of the dry weight of the red mud. The mixture was placed in a rectangular plastic basin (52 × 38 × 20 cm, with drainage holes at the bottom). The weathered coal gangue was added at a ratio of 2% (200 g) of the dry weight of the red mud, with the particle size of the weathered coal gangue crushed to less than 2 mm. 5250 mL of water was added to each type of red mud, and the mixture was stirred thoroughly.

[0167] The matrix of the combined process red mud was improved by using ferrous sulfate and weathered coal gangue. The red mud was crushed (10 kg of red mud) and mixed with ferrous sulfate at a ratio of 3% (300 g) of the dry weight of the red mud. The mixture was placed in a rectangular plastic basin (52 × 38 × 20 cm with drainage holes at the bottom). The weathered coal gangue was added at a ratio of 2% (200 g) of the dry weight of the red mud. The particle size of the weathered coal gangue was crushed to less than 2 mm. 5250 mL of water was added to each type of red mud and the mixture was stirred evenly.

[0168] Red mud without any added materials was used as a control group.

[0169] Subsequently, 160 mL of water was sprayed evenly onto the red mud and the two red mud growth substrates every day for 14 consecutive days to reduce salinity as much as possible.

[0170] Salt-tolerant plant mixed planting: Selected wheatgrass, white-stemmed halophyte, alfalfa and caragana as mixed planting varieties, and carried out mixed planting growth test at room temperature at the end of May.

[0171] Specifically, the seeds of these four salt-tolerant plants were sterilized with a 30% hydrogen peroxide solution for 10 minutes, washed three times with 100ml of distilled water, and mixed evenly in a ratio of 4:3:2:1 (i.e., 20 seeds of *Leymus chinensis*, 15 seeds of *Haloxylon ammodendron*, 10 seeds of alfalfa, and 5 seeds of *Caragana korshinskii*). They were planted in wide and narrow rows, with a row spacing of 13cm for wide rows and 12cm for narrow rows. The rectangular plastic pot was divided into 12 sections, and 4-5 seeds were sown in each section. After sowing, 80mL of water was added daily until early August, at which point the plants were collected. After cleaning the plants, they were dried at 65℃ for 2 days according to different varieties. The dry weight of the different varieties was measured, and the results are as follows: Figure 7 As shown.

[0172] Example 8: Layered Salt-Alkali Control Simulation Test

[0173] The red mud growth substrate was improved, and the specific steps and parameters were the same as in Example 6.

[0174] A 1m high, 15cm diameter plexiglass column was used as the apparatus for the layered salt-alkali control simulation experiment. First, a 60cm thick layer of red mud was filled in. Then, a 5cm thick layer of fresh coal gangue with a particle size of 5-6mm was laid on top of the red mud. Next, a 5cm thick layer of corn stalks with a length of 5cm was laid on top of the fresh coal gangue layer. Finally, a 20cm thick layer of red mud growth substrate was filled in. The specific process of the layered salt-alkali control simulation experiment is as follows: Figure 8 As shown in the figure. Each treatment was set up in triplicate, with each plating layer. The treatment without a plating layer served as a control. Based on local rainfall, 80 ml of deionized water was added daily for 12 weeks. The lower 60 cm section of the plexiglass column was wrapped with a small electric heating blanket (60×30 cm, 75W) to simulate the salt and alkali return process. The heating blanket temperature was set to 40℃, and heating began 10 hours after water rinsing each day, continuing for 4 hours. After 12 weeks, samples from the top 10-20 cm were taken for the determination of salt and alkali related indicators. The results are shown in the figure. Figure 9 As shown. Among them, Figure 9 In the above, control (C) refers to the combined process red mud control without a barrier layer; barrier layer treatment (C) refers to the combined process red mud with a barrier layer of salt-alkali control material added; control (B) refers to the Bayer process red mud control without a barrier layer; barrier layer treatment (B) refers to the Bayer process red mud with a barrier layer of salt-alkali control material added.

[0175] The results show that the interlayer treatment is beneficial to reducing the impact of salt and alkali return on the red mud growth substrate.

[0176] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for controlling salinity and alkali in red mud dumps to achieve vegetation cover, characterized in that, Includes the following steps: Step 1: Improve the matrix of red mud The Bayer process red mud matrix was modified using gypsum and weathered coal gangue. The amount of gypsum added was 1%-5% of the dry weight of the red mud, and the amount of weathered coal gangue added was 1%-5% of the dry weight of the red mud. After adjusting the moisture content to 40%-70%, the matrix was mixed evenly and allowed to age naturally to become the modified Bayer process red mud growth matrix for later use. Alternatively, ferrous sulfate and weathered coal gangue can be used to improve the matrix of red mud obtained by the combined method. The amount of ferrous sulfate added is 1%-5% of the dry weight of red mud, and the amount of weathered coal gangue added is 1%-5% of the dry weight of red mud. After adjusting the moisture content to 40%-70%, they are mixed evenly and allowed to age naturally to become the red mud growth matrix improved by the combined method, which can be used for later use. Step 2: Laying a layer of salt-alkali control material The salt-alkali control material consists of a straw layer and a fresh coal gangue layer; the fresh coal gangue layer is placed below the straw layer and is laid flat after installation. The straw in the straw separator is 5cm long and the separator is 5cm thick. The new coal gangue interlayer consists of coal gangue with a particle size of 5-6mm and an interlayer thickness of 5cm; Step 3: Backfill with improved red mud. The improved red mud growth substrate from step one is covered on top of the salt-alkali control material from step two. The thickness of the red mud growth substrate is 10-50cm, resulting in red mud with improved backfill substrate. After tilling, the red mud is sown. Step 4: Mixed sowing of salt-tolerant plants After sterilizing the salt-tolerant plant seeds with hydrogen peroxide solution and cleaning them with distilled water, they are sown in the red mud that has been backfilled with improved substrate during the growing season. The sowing density for grass and chenopodiaceae plants is 150-300 seeds per square meter, and the sowing density for legumes is 20-50 seeds per square meter. In step four, when the sowing is mixed sowing, the mixed sowing ratio of crested wheatgrass, white-stemmed saltwort, alfalfa, and caragana is 4:3:2:

1.

2. The method according to claim 1, characterized in that, In step one, the particle size of the weathered coal gangue is less than 2mm, and the amount of weathered coal gangue added is 2-5% of the dry weight of red mud; the moisture content is adjusted to 50-70%; and the natural aging time is 50-100 days.

3. The method according to claim 1, characterized in that, In step one, the amount of gypsum added is 3% of the dry weight of red mud, and the amount of ferrous sulfate added is 3% of the dry weight of red mud.

4. The method according to claim 1, characterized in that, In step two, the straw interlayer is selected from at least one of corn straw, wheat straw, rice straw, and cotton straw.

5. The method according to claim 1, characterized in that, In step three, the thickness of the red mud growth substrate is 15-25 cm.

6. The method according to claim 1, characterized in that, In step four, the concentration of the hydrogen peroxide solution is 20-35%, and the sterilization time is 5-15 minutes.

7. The method according to claim 1, characterized in that, In step four, the sowing is specifically as follows: the sowing density for grasses and chenopodiaceae plants is 200 seeds per square meter, and the sowing density for legumes is 30 seeds per square meter; the sowing depth is 1-3 cm.

8. The application of the method according to any one of claims 1-7 in regulating the salinity of red mud, increasing the fertility of red mud, and sowing salt-tolerant plants; wherein when sowing is mixed sowing, the mixed sowing ratio of crested wheatgrass, white-stemmed halophyte, alfalfa, and caragana is 4:3:2:

1.

9. The application according to claim 8, characterized in that, The specific application method of sowing salt-tolerant plants includes the following steps: sterilizing the salt-tolerant plant seeds with hydrogen peroxide solution, cleaning them with distilled water, and then sowing them in the red mud after backfilling the substrate during the growing season; the sowing density for grass and chenopodiaceae plants is 150-250 seeds per square meter, and the sowing density for legumes is 20-50 seeds per square meter.

10. The application according to claim 9, characterized in that, The salt-tolerant plant seeds are selected from at least one of the following: grasses, gooseberries, and legumes.

11. The application according to claim 8, characterized in that, The concentration of the hydrogen peroxide solution is 20-35%, and the sterilization time is 5-15 minutes.

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