Red mud-based artificial soil and preparation method and application thereof

Abstract

The application provides a red mud-based artificial soil and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing red mud, a calcium source and a sodium aluminate solution to obtain a raw slurry; (2) performing a first hydrothermal reaction on the obtained raw slurry to prepare a first clinker slurry, and obtaining a dealkalized red mud after first solid-liquid separation; (3) mixing the dealkalized red mud, detoxified fly ash and water to perform a second hydrothermal reaction, and obtaining a second clinker slurry; (4) sequentially performing second solid-liquid separation and washing on the obtained second clinker slurry to obtain a soil matrix; and (5) mixing the obtained soil matrix with organic matter and culturing to obtain the red mud-based artificial soil. The first hydrothermal reaction is used for dealkalizing the red mud and recovering alkali, the second hydrothermal reaction is used for solidifying active alkali in the red mud, then the introduction of organic matter increases the content of effective nutrients in the artificial soil and forms a granular structure, and finally the red mud-based artificial soil with good performance is prepared.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, and in particular to a red mud-based artificial soil, its preparation method, and its application. Background Technology

[0002] Red mud is a highly alkaline waste residue produced during the alumina extraction process in the aluminum industry. It mainly exists in the form of mud slurry and is called red mud because its main component—iron oxide—is red. Stockpiling red mud wastes a large amount of land resources, and the seepage of red mud and its byproducts also pollutes lakes, rivers, and groundwater.

[0003] Currently, the global utilization rate of red mud is less than 6%. Research on red mud utilization technologies in low-value-added sectors is relatively systematic, such as its use as building and road construction materials, which has been put into practice and achieved some results. However, these methods involve large investments, high production costs, secondary waste generation, and relatively small red mud consumption, necessitating the exploration of new large-scale red mud disposal pathways. Due to its high alkalinity and salinity, red mud is deficient in organic matter and nutrients required by plants, and has high metal toxicity, making it difficult for plants to survive on its surface. If the alkalinity and salinity of red mud can be specifically modified to prepare it into artificial soil and reintegrate it into the Earth's material cycle, the global problem of red mud's unusability and environmental pollution can be solved.

[0004] CN110999753A discloses an artificial ecological matrix and its preparation method. Red mud is crushed, microbial agents are added, and it is mixed evenly with organic compost derived from plants. After a period of maturation, the nutrients in the red mud that are used for plant growth are released. However, relying solely on the release of organic acids from organic matter is insufficient to deeply neutralize the active alkali in the red mud. This method carries the risk of gradual release of active alkali from the red mud and excessive soluble salts.

[0005] CN114773116A discloses a method for preparing and applying a soil remediation material based on coal-based solid waste. The material is mainly prepared from slag, red mud, fly ash, sludge, crop straw, water-retaining agent, stabilizer, and biological fermentation strains through steps such as mixing, drying, calcination, and mixed fermentation.

[0006] The application rate of red mud in the above inventions is relatively low, and it is still insufficient to meet the purpose of absorbing a large amount of red mud stock.

[0007] Artificial soil can replace natural soil and is widely used in soil improvement and ecological restoration processes, making it a functional material with enormous potential demand. Developing artificial soil technology can address the problem of land resource scarcity and can be used in agriculture, artificial vegetation restoration in ecologically fragile areas, artificial arable land, land improvement, grassland improvement, desertification ecological reconstruction, afforestation of barren mountains, and urban greening.

[0008] CN112167005A discloses a method for preparing artificial soil particles based on silt, which involves mixing silt, inorganic cementitious materials, plant growth nutrients, foaming agents and additives to obtain a first mixture, and then granulating the first mixture with water to obtain artificial soil particles based on silt.

[0009] CN114190130A discloses an artificial soil for treating saline-alkali land and its application method. It uses various bulk coal-based solid waste, desert sand and waste sand to create high-quality artificial soil through artificial means, so as to replace or mix with saline-alkali soil that is unsuitable for plant growth, and form a soil structure with planting capacity, water and fertilizer retention capacity and sufficient nutrients.

[0010] The above invention requires the addition of a large amount of cement or soil as a binder and artificial granulation, which is a relatively complex process. It also requires the addition of various auxiliary materials and additives, resulting in high raw material costs.

[0011] To address the shortcomings of existing technologies, there is a need for a method that enables efficient resource utilization, large-scale disposal of red mud, and avoids secondary pollution. Summary of the Invention

[0012] To address the aforementioned technical problems, this invention provides a red mud-based artificial soil, its preparation method, and its application. The method involves mixing red mud with a calcium source and sodium aluminate solution, followed by two hydrothermal reactions to dealkalize and solidify the red mud. Desalination is then achieved through solid-liquid separation and washing. The resulting soil matrix is ​​then mixed with organic matter for cultivation, activating effective nutrients and reconstructing the soil structure, thus yielding the red mud-based artificial soil. The red mud-based artificial soil of this invention possesses high water retention and permeability, contains organic matter, macro-elements, micro-elements, and essential elements for plant growth such as nitrogen, phosphorus, and potassium. It can replace natural soil for soil improvement and ecological restoration, while also effectively disposing of large quantities of industrial solid waste such as red mud and fly ash, achieving resource recycling.

[0013] To achieve this objective, the present invention adopts the following technical solution:

[0014] In a first aspect, the present invention provides a method for preparing red mud-based artificial soil, the method comprising the following steps:

[0015] (1) Mix red mud, calcium source and sodium aluminate solution to obtain raw material slurry;

[0016] (2) The raw slurry obtained in step (1) is subjected to a first hydrothermal reaction to obtain a first chopped slurry, and after a first solid-liquid separation, dealkalized red mud is obtained;

[0017] (3) The dealkalized red mud, detoxified fly ash and water obtained in step (2) are mixed and subjected to a second hydrothermal reaction to obtain a second clinker slurry;

[0018] (4) The second clinker slurry obtained in step (3) is subjected to a second solid-liquid separation and washing to obtain a soil matrix;

[0019] (5) The soil matrix obtained in step (4) is mixed with organic matter and then cultured to obtain the red mud-based artificial soil.

[0020] The strong alkalinity of red mud is due to its high content of alkaline substances, with a pH value typically ranging from 10.3 to 11.3. The pH value of red mud leachate is usually higher than 12.5, and the soluble salt content is usually higher than 8‰. Untreated red mud is difficult to utilize, and plants cannot grow in red mud dumps. In addition, red mud has a small particle size, poor structure and water and air permeability, and also contains harmful substances. Therefore, this invention dealkalizes, recovers, solidifies, desalinates, renders harmless, activates effective nutrients, and restructures red mud to obtain red mud-based artificial soil.

[0021] The method for preparing red mud-based artificial soil according to this invention first involves mixing red mud with a calcium source and sodium aluminate solution to perform a first hydrothermal reaction, thereby removing alkali from the red mud and obtaining dealkalized red mud. Then, the dealkalized red mud is mixed with detoxified fly ash, and a second hydrothermal reaction is performed, utilizing the active components in the detoxified fly ash to fix the residual active alkali in the dealkalized red mud. This invention, through two hydrothermal reactions, yields a soil matrix with a phase composition very similar to soil. Further addition of organic matter for mixed cultivation allows for effective degradation of organic matter by microorganisms, increasing the humic acid content in the soil matrix and simultaneously activating effective nutrients. Furthermore, during the mixed cultivation process, organic acids, red mud, fly ash, and high-valent cations present in the system form a red mud-fly ash-polyvalent metal-organic matter complex. Both of these effects promote the mutual bonding between the originally dispersed red mud particles and fly ash particles, forming a granular structure similar to natural soil, achieving structural reconstruction, and increasing its water retention, fertilizer retention, and aeration properties.

[0022] In this invention, the addition of detoxified fly ash can solidify the residual active alkali after red mud dealkalization. Furthermore, fly ash is fly ash produced after high-temperature combustion of coal, which has high activity and many surface functional groups, making it more conducive to the cementation between particles to form agglomerates. Fly ash can also act as a cementing material to promote the formation of agglomerate structures.

[0023] Preferably, the calcium source includes industrial raw materials with calcium oxide as the main component, industrial waste residue with calcium oxide as the main component, or calcium compounds.

[0024] Preferably, the proportion of calcium oxide in the industrial raw material with calcium oxide as the main component is 25-90 wt%, for example, it can be 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, or 90 wt%, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] Preferably, the proportion of calcium oxide in the industrial waste residue with calcium oxide as the main component is 25-90 wt%, for example, it can be 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, or 90 wt%, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] Preferably, the calcium compound comprises any one or a combination of at least two of calcium hydroxide, calcium oxide, or carbide slag, wherein typical but non-limiting combinations include a combination of calcium hydroxide and calcium oxide, a combination of calcium hydroxide and carbide slag, or a combination of carbide slag and calcium oxide.

[0027] Preferably, the sodium aluminate solution in step (1) has an α... k The range is 1.0-25.0, for example, it can be 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 7.0, 10.0, 12.0, 15.0, 18.0, 20.0 or 25.0, etc., preferably 1.5-20, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] Preferably, the sodium oxide concentration in the sodium aluminate solution is 2-200 g / L, for example, it can be 2 g / L, 5 g / L, 10 g / L, 15 g / L, 25 g / L, 35 g / L, 50 g / L, 60 g / L, 100 g / L or 200 g / L, etc., preferably 5-150 g / L, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] Preferably, the calcium-silicon molar ratio of the calcium source to the red mud is (0.5-10.0):1, for example, it can be 0.5:1, 1.0:1, 2.0:1, 3.0:1, 4.0:1, 5.0:1, 6.0:1, 6.5:1, 7.0:1, 7.5:1, 8.0:1 or 10:1, etc., preferably (1.0-5.0):1, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] Preferably, the liquid-to-solid ratio of the sodium aluminate solution to the solid material composed of red mud and calcium source is (1-20) mL / g, for example, it can be 1 mL / g, 3 mL / g, 5 mL / g, 7 mL / g, 10 mL / g, 13 mL / g, 15 mL / g or 20 mL / g, etc., preferably (1.5-10) mL / g, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] The present invention preferably uses a liquid-to-solid ratio of (1-20) mL / g for the sodium aluminate solution, red mud, and calcium source-based solid material to achieve efficient removal of alkali from the red mud. Adding too little sodium aluminate solution leads to uneven liquid-solid mixing, incomplete reaction, and difficulty in alkali recovery; adding too much sodium aluminate solution significantly increases operational energy consumption, increases the water required for washing, makes industrial implementation difficult, and increases calcium loss, resulting in a substantial increase in cost.

[0032] Preferably, the temperature of the first hydrothermal reaction in step (2) is 40-300℃, for example, it can be 40℃, 70℃, 100℃, 120℃, 200℃, 250℃ or 300℃, etc., preferably 60-240℃, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] The present invention preferably uses a first hydrothermal reaction temperature of 40-300℃ to remove alkali from red mud. When the temperature of the first hydrothermal reaction is too low, the alkali removal efficiency from the red mud will decrease, the reaction will be difficult to carry out, and the resulting red mud-based artificial soil will have a high pH, ​​making it unsuitable for soil improvement, etc. When the temperature of the first hydrothermal reaction is too high, the preparation process will consume more energy and increase the preparation cost.

[0034] Preferably, the time for the first hydrothermal reaction is 0.3-30h, for example, it can be 0.3h, 0.5h, 5h, 10h, 15h, 20h, 25h or 30h, etc., preferably 0.5-5h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, stirring is performed during the first hydrothermal reaction in step (2).

[0036] Preferably, the stirring speed is 50-2000 rpm, for example, it can be 50 rpm, 80 rpm, 100 rpm, 300 rpm, 500 rpm, 700 rpm, 1500 rpm or 2000 rpm, etc., preferably 100-1000 rpm, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] Preferably, the first solid-liquid separation in step (2) is performed using conventional methods in the art, as long as the dealkali-treated red mud can be separated from the liquid, and therefore no special limitation is made. For example, the solid-liquid separation method can be filtration, pressure filtration, and vacuum filtration, but it is not limited to these.

[0038] Preferably, the heavy metal content in the detoxified fly ash in step (3) is lower than the heavy metal limit value of farmland soil in GB15618-2018. If the heavy metal content of the fly ash itself is below the limit value, then detoxification treatment is not required.

[0039] Preferably, the detoxification method for the detoxified fly ash includes physical detoxification or chemical detoxification.

[0040] Preferably, the chemical detoxification method includes wet detoxification using acid and / or alkali.

[0041] Preferably, the mass ratio of the dealkalized red mud to the detoxified fly ash in step (3) is (1-20):1, for example, it can be 1.0:1, 1.5:1, 2.0:1, 3.0:1, 4.0:1, 5.0:1, 7.0:1, 10.0:1, 12.0:1, 15.0:1 or 20.0:1, etc., preferably (2-10):1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] The preferred mass ratio of dealkalized red mud to detoxified fly ash in this invention is (1-20):1. This utilizes the surface functional groups of the fly ash to solidify the residual active alkali in the dealkalized red mud, while simultaneously promoting the formation of aggregate structures. If the mass of the detoxified fly ash is low, the residual active alkali in the dealkalized red mud will not be well solidified, leading to a higher pH in the subsequent artificial soil. Conversely, if the mass of the detoxified fly ash is high, the particle size distribution of the artificial soil will be unbalanced, affecting soil structure formation and reducing the amount of red mud that can be absorbed.

[0043] Preferably, the liquid-to-solid ratio of the solid material composed of water, dealkalized red mud, and detoxified fly ash is (1.0-20) mL / g, for example, it can be 1 mL / g, 3 mL / g, 5 mL / g, 7 mL / g, 10 mL / g, 13 mL / g, 15 mL / g, or 20 mL / g, etc., preferably (1.5-10) mL / g, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] Preferably, the time for the second hydrothermal reaction is 0.5-300h, for example, it can be 0.5h, 5h, 8h, 10h, 15h, 20h, 40h, 45h, 50h, 80h, 85h, 95h, 105h, 155h, 205h, 250h, 275h or 300h, etc., preferably 1-120h, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] Preferably, the temperature of the second hydrothermal reaction is 30-90°C, for example, it can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, preferably 40-90°C, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] The preferred temperature for the second hydrothermal reaction in this invention is 30-90℃, utilizing the active components in the detoxified fly ash to immobilize the residual active alkali in the dealkalized red mud. When the temperature of the second hydrothermal reaction is too low, the hydrothermal reaction effect is poor, and the immobilization effect of the active components on the active alkali is also poor; when the temperature of the second hydrothermal reaction is too high, it may activate the active alkali in the red mud, which is detrimental to lowering the pH of the artificial soil.

[0047] Preferably, stirring is performed during the second hydrothermal reaction.

[0048] Preferably, the stirring speed is 50-2000 rpm, for example, it can be 50 rpm, 80 rpm, 100 rpm, 300 rpm, 500 rpm, 700 rpm, 1500 rpm or 2000 rpm, etc., preferably 100-1000 rpm, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] Preferably, the second solid-liquid separation in step (4) is performed using conventional methods in the art, as long as the solid can be separated from the liquid, and therefore no special limitation is made. For example, the solid-liquid separation method can be filtration, pressure filtration, and vacuum filtration, but it is not limited to these.

[0050] Preferably, the washing in step (4) includes rinsing, two-stage countercurrent washing, or three-stage countercurrent washing.

[0051] Preferably, the mass ratio of the total water used for washing to the mass of solids is (0.1-20):1, for example, it can be 0.1:1, 0.5:1, 1.0:1, 1.5:1, 3.0:1, 3.5:1, 5.0:1, 8.5:1, 9.5:1, 10:1, 11:1, 15:1 or 20:1, etc., preferably (1-10):1, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] Preferably, the organic matter in step (5) includes any one or a combination of at least two of the following: straw, cow dung, sheep dung, oil residue, wine lees, vinegar residue, medicinal residue, or animal leather. Typical but non-limiting combinations include the combination of straw and cow dung, the combination of sheep dung, oil residue and wine lees, the combination of oil residue, wine lees, vinegar residue, medicinal residue, and animal leather, or the combination of straw, cow dung, sheep dung, oil residue, wine lees, vinegar residue, medicinal residue, and animal leather.

[0053] Preferably, the mass ratio of the soil matrix to organic matter is (20-69):(1-30), for example, it can be 20:30, 30:20, 35:15, 40:10, 45:5 or 69:1, etc., preferably (30-49):(1-20), but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the culture temperature is 10-70℃, for example, it can be 10℃, 20℃, 30℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃ or 70℃, etc., preferably 20-60℃, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0055] Preferably, the culture time is 10-100 days, for example, it can be 10 days, 12 days, 14 days, 16 days, 18 days, 20 days, 24 days, 28 days, 30 days, 32 days, 40 days, 50 days, 60 days, 80 days or 100 days, etc., preferably 10-40 days, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0056] Preferably, the water content of the mixture of soil substrate and organic matter in the culture is 10-90 wt%, for example, it can be 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%, etc., preferably 20-80 wt%, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0057] Preferably, the culture is turned over during the cultivation process, and the frequency of turning over is 1-20 times per day. For example, it can be 1 time per day, 2 times per day, 3 times per day, 4 times per day, 5 times per day, 6 times per day, 7 times per day, 10 times per day, 15 times per day, or 20 times per day, preferably 2-10 times per day, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0059] (1) Mix red mud, calcium source and sodium aluminate solution to obtain raw material slurry;

[0060] The calcium source includes industrial raw materials with calcium oxide as the main component, industrial waste residue with calcium oxide as the main component, or calcium compounds; the proportion of calcium oxide in the industrial raw materials with calcium oxide as the main component is 25-90 wt%; the proportion of calcium oxide in the industrial waste residue with calcium oxide as the main component is 25-90 wt%; the calcium compound includes any one or a combination of at least two of calcium hydroxide, calcium oxide, or carbide slag.

[0061] The sodium aluminate solution α k The concentration of sodium oxide in the sodium aluminate solution is 2-200 g / L; the calcium-silicon molar ratio of the calcium source to the red mud is (0.5-10.0):1; the liquid-solid ratio of the solid material composed of the sodium aluminate solution, red mud, and calcium source is (1-20) mL / g.

[0062] (2) The raw slurry obtained in step (1) is subjected to a first hydrothermal reaction at a temperature of 40-300℃ for 0.3-30h to obtain the first clinker slurry, and after the first solid-liquid separation, the dealkalized red mud is obtained.

[0063] The first hydrothermal reaction is carried out by stirring; the stirring speed is 50-2000 rpm;

[0064] (3) The dealkalized red mud, detoxified fly ash and water obtained in step (2) are mixed and subjected to a second hydrothermal reaction at a temperature of 30-90℃ for 0.5-300h to obtain the second clinker slurry;

[0065] The heavy metal content in the detoxified fly ash is lower than the heavy metal limit in farmland soil according to GB15618-2018; the detoxification method of the detoxified fly ash includes physical detoxification or chemical detoxification; the chemical detoxification method includes wet detoxification using acid and / or alkali; the mass ratio of the de-alkali red mud to the detoxified fly ash is (1-20):1; the liquid-solid ratio of the solid material composed of water, de-alkali red mud, and detoxified fly ash is (1.0-20) mL / g; stirring is carried out during the second hydrothermal reaction; the stirring speed is 50-2000 rpm;

[0066] (4) The second clinker slurry obtained in step (3) is subjected to a second solid-liquid separation and washing to obtain a soil matrix;

[0067] The washing process includes rinsing, two-stage countercurrent washing, or three-stage countercurrent washing; the total water consumption to the mass ratio of solids is (0.1-20):1.

[0068] (5) The soil matrix obtained in step (4) and organic matter are mixed and cultured at a temperature of 10-70℃ for 10-100 days in a mass ratio of (20-69):(1-30) to obtain the red mud-based artificial soil.

[0069] The organic matter includes any one or a combination of at least two of the following: straw, cow dung, sheep dung, oil residue, distiller's grains, vinegar residue, medicinal residue, or animal leather;

[0070] The water content of the mixture of soil matrix and organic matter in the culture is 10-90 wt%.

[0071] The culture process involves turning the plants over, with a turning frequency of 1-20 days per turn.

[0072] Secondly, the present invention also provides a red mud-based artificial soil, which is prepared by the red mud-based artificial soil preparation method described in the first aspect.

[0073] The red mud-based artificial soil described in this invention has excellent water and fertilizer retention, balanced nutrient element effects, and also excellent water permeability and air permeability.

[0074] Thirdly, the present invention also provides an application of the red mud-based artificial soil as described in the second aspect, wherein the red mud-based artificial soil is used in the fields of soil improvement or ecological restoration.

[0075] The red mud-based artificial soil described in this invention can be applied to ecological restoration fields such as farmland, forest land, grassland soil improvement or desertification control, and can realize the synergistic treatment and large-scale utilization of two major solid wastes: red mud and fly ash.

[0076] Compared with the prior art, the present invention has at least the following beneficial effects:

[0077] (1) The method for preparing red mud-based artificial soil provided by the present invention recovers the active alkali in red mud through the first hydrothermal reaction and completes the deep dealkalization of red mud. Then, the active components in the bulk solid waste fly ash are activated through the second hydrothermal reaction to synergistically solidify the residual alkali in the red mud after dealkalization. While completing the harmless treatment of red mud, the large-scale disposal of fly ash is also realized simultaneously, and a soil matrix that can be used to prepare artificial soil is obtained. After adding organic matter, the soil matrix is ​​mixed and cultured, gradually forming a granular structure, reducing the soil bulk density, and greatly increasing the water-stable aggregates, realizing structural reconstruction. At the same time, the degradation of organic matter will greatly increase the nutrients in the soil and provide the nutrients required by plants.

[0078] (2) The red mud-based artificial soil provided by the present invention has excellent water and fertilizer retention, balanced nutrient element effects and excellent water permeability and air permeability. It can be widely used in ecological restoration fields such as farmland, forest land, grassland soil improvement or desertification control. It can realize the synergistic treatment and large-scale utilization of red mud and fly ash, two major solid wastes.

[0079] (3) The red mud and fly ash in the red mud-based artificial soil provided by the present invention account for ≥85%, the raw materials are cheap and readily available, the preparation process is simple, the cost is low, and it is easy to achieve large-scale production, which opens up a new way for the large-scale utilization of red mud and fly ash solid waste. Detailed Implementation

[0080] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0081] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0082] The following are typical but non-limiting embodiments of the present invention:

[0083] The fly ash used in the following examples and comparative examples underwent physical detoxification to ensure that the heavy metal content was lower than the heavy metal limit in farmland soil in GB15618-2018.

[0084] Example 1

[0085] This embodiment provides a method for preparing red mud-based artificial soil, the preparation method comprising the following steps:

[0086] (1) First, mix calcium oxide and red mud at a calcium-silicon molar ratio of 2.0:1, and then mix with α k A sodium aluminate solution with a concentration of 2.0 and sodium oxide of 100 g / L was mixed and stirred evenly at a liquid-to-solid ratio of 3 mL / g to obtain a raw material slurry.

[0087] (2) The raw slurry obtained in step (1) is subjected to a first hydrothermal reaction at 100°C for 2 hours. The stirring speed is set to 400 rpm to obtain the first slurry. After the reaction is completed, the alkali-removed red mud is obtained by filtration.

[0088] (3) Mix the dealkalized red mud and detoxified fly ash obtained in step (2) at a mass ratio of 5:1, and then add water at a liquid-solid ratio of 3 mL / g to make a slurry. Then carry out a second hydrothermal reaction at 70°C for 12 hours. The stirring speed of the reaction is set to 400 rpm to obtain the second clinker slurry.

[0089] (4) After filtering the second clinker slurry obtained in step (3), the soil matrix is ​​obtained by rinsing at a total water volume to solid mass ratio of 3:1.

[0090] (5) The soil substrate obtained in step (4) is mixed with straw at a mass ratio of 20:1 and then cultured at 40°C for 20 days with a turning frequency of 5 days / time. During the culture process, the water content of the mixture composed of soil substrate and straw is 40wt%, thus obtaining the red mud-based artificial soil.

[0091] Example 2

[0092] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the rinsing in step (4) is replaced with a three-stage countercurrent washing process.

[0093] Example 3

[0094] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the straw in step (5) is replaced with sheep manure.

[0095] Example 4

[0096] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the calcium-silicon molar ratio of calcium oxide to red mud in step (1) is changed to 1.0:1.

[0097] Example 5

[0098] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that of Embodiment 1 is that the sodium aluminate solution in step (1) is replaced with α-sodium aluminate solution. k It is a 20% sodium aluminate solution.

[0099] Example 6

[0100] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the sodium aluminate solution in step (1) is replaced with a sodium aluminate solution with a sodium oxide concentration of 10 g / L.

[0101] Example 7

[0102] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the liquid-solid ratio of the sodium aluminate solution and the solid material composed of red mud and calcium oxide in step (1) is changed to 10 mL / g.

[0103] Example 8

[0104] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the temperature of the first hydrothermal reaction in step (2) is changed to 60°C.

[0105] Example 9

[0106] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the time for the first hydrothermal reaction in step (2) is changed to 5 hours.

[0107] Example 10

[0108] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the stirring speed in step (2) is changed to 100 rpm.

[0109] Example 11

[0110] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the mass ratio of dealkalized red mud and detoxified fly ash in step (3) is changed to 20:1.

[0111] Example 12

[0112] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and Example 1 is that the liquid-solid ratio of the solid material composed of water, dealkalized red mud, and detoxified fly ash in step (3) is changed to 10 mL / g.

[0113] Example 13

[0114] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the temperature of the second hydrothermal reaction in step (3) is changed to 90°C.

[0115] Example 14

[0116] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the time for the second hydrothermal reaction in step (3) is changed to 1 hour.

[0117] Example 15

[0118] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the stirring speed in step (3) is changed to 1000 rpm.

[0119] Example 16

[0120] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the ratio of the total water volume to the mass of solid matter in step (4) is changed to 1:1.

[0121] Example 17

[0122] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the mass ratio of soil matrix to straw in step (5) is changed to 30:1.

[0123] Example 18

[0124] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the temperature for cultivation in step (5) is changed to 60°C.

[0125] Example 19

[0126] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the frequency of turning over in step (5) is changed to once every 10 days.

[0127] Example 20

[0128] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the cultivation time in step (5) is changed to 40 days.

[0129] Example 21

[0130] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that of Embodiment 1 is that the water content of the mixture of soil matrix and straw in step (5) during cultivation is changed to 60 wt%.

[0131] Example 22

[0132] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Example 1 is that the liquid-solid ratio of the sodium aluminate solution and the solid material composed of red mud and calcium oxide in step (1) is changed to 0.5 mL / g.

[0133] Example 23

[0134] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Example 1 is that the liquid-solid ratio of sodium aluminate solution to the solid material composed of red mud and calcium oxide in step (1) is changed to 23 mL / g.

[0135] Example 24

[0136] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the mass ratio of dealkalized red mud to detoxified fly ash in step (3) is changed to 0.5:1.

[0137] Example 25

[0138] This embodiment provides a method for preparing red mud-based artificial soil. The difference between this method and that in Embodiment 1 is that the mass ratio of dealkalized red mud to detoxified fly ash in step (3) is changed to 25:1.

[0139] Comparative Example 1

[0140] This comparative example provides a method for preparing red mud-based artificial soil. The difference between this method and Example 1 is that steps (1) and (2) are omitted, and the red mud is directly mixed with detoxified fly ash at a mass ratio of 5:1.

[0141] Comparative Example 2

[0142] This comparative example provides a method for preparing red mud-based artificial soil. The difference between this method and Example 1 is that in step (3), the dealkalized red mud and the detoxified fly ash do not undergo a second hydrothermal reaction, but are only physically mixed.

[0143] Comparative Example 3

[0144] This comparative example provides a method for preparing red mud-based artificial soil. The difference between this method and Example 1 is that the rinsing process in step (4) is not performed.

[0145] Comparative Example 4

[0146] This comparative example provides a method for preparing red mud-based artificial soil. The difference between this method and Example 1 is that step (5) does not involve adding straw, and the soil substrate is directly cultured.

[0147] Comparative Example 5

[0148] This comparative example provides a method for preparing red mud-based artificial soil. The difference between this method and Example 1 is that in step (1), sodium aluminate solution is replaced with water.

[0149] The performance of the red mud-based artificial soils provided in Examples 1-25 and Comparative Examples 1-5 was tested, and the results are shown in Table 1.

[0150] Table 1

[0151]

[0152]

[0153] As can be seen from Table 1:

[0154] (1) As can be seen from Examples 1 to 21, the method for preparing red mud-based artificial soil provided by the present invention can effectively ensure the aggregate structure of artificial soil, reduce the pH and soluble salt content of red mud, increase the content of humic acid and effective nutrients, and the soil after cultivation fully meets the needs of plant growth and development.

[0155] (2) As can be seen from the comparison between Example 1 and Examples 22-23, a suitable liquid-solid ratio is very important for the dealkalization of red mud and its subsequent soil utilization. Too large or too small a liquid-solid ratio is not conducive to the recovery of active alkali in red mud, which will affect the fixation of active alkali during secondary hydrothermal treatment, resulting in a higher pH of artificial soil and poorer performance.

[0156] (3) As can be seen from the comparison between Example 1 and Examples 24-25, the appropriate red mud and detoxified fly ash are very important for the formation of the soil structure of artificial soil. If the proportion of red mud is too high, it will lead to insufficient alkali fixation and high pH of artificial soil. If the proportion of detoxified fly ash is too high, it will not be conducive to the large-scale disposal of red mud and will not be conducive to the formation of a healthy soil structure.

[0157] (4) As can be seen from the comparison between Example 1 and Comparative Example 1, the dealkalization of red mud is essential in the soil preparation process. If dealkalization is not carried out, the pH value of the subsequent artificial soil will be too high and it will be difficult to utilize it as soil. As can be seen from the comparison between Example 1 and Comparative Example 2, the detoxified fly ash and red mud cannot achieve synergistic effect through simple physical mixing. It is necessary to activate the solidification reaction of the active components of the detoxified fly ash on the active alkali in the red mud in a specific system. Otherwise, the soil performance will be significantly reduced. As can be seen from the comparison between Example 1 and Comparative Example 3, the washing step after the hydrothermal reaction is essential. During the hydrothermal reaction, some salt is released and needs to be removed from the soil to ensure healthy and high-quality artificial soil. As can be seen from the comparison between Example 1 and Comparative Example 4, the soil organic matter will lack the key components for the formation and development of soil structure if it is cultivated directly without adding organic matter. This will greatly reduce the formation rate of soil aggregates, thereby weakening the soil's resistance to erosion, water retention and fertilizer retention, and affecting soil performance. As can be seen from the comparison between Example 1 and Comparative Example 5, water is added in step (1), which cannot dealkalize the red mud, resulting in a high pH value of the obtained artificial soil.

[0158] In summary, the method for preparing red mud-based artificial soil provided by the present invention recovers the active alkali in the red mud through a first hydrothermal reaction, thereby achieving deep dealkalization of the red mud. Then, the active components in the active waste fly ash are activated through a second hydrothermal reaction to synergistically solidify the residual alkali in the red mud after dealkalization. This completes the harmless treatment of the red mud, simultaneously realizes the large-scale disposal of fly ash, and also yields a soil matrix that can be used to prepare artificial soil.

[0159] The artificial soil prepared by this invention has excellent water and fertilizer retention, balanced nutrient element effects, and excellent water permeability and air permeability. It can be widely used in ecological restoration fields such as farmland, forest land, grassland soil improvement or desertification control, and can realize high-value utilization of red mud and fly ash.

[0160] This invention uses red mud and fly ash as the main raw materials to prepare artificial soil. The proportion of red mud and fly ash in the artificial soil is ≥85%. The raw materials are inexpensive and readily available. The preparation process is simple, low-cost, and easy to achieve large-scale production, opening up a new way for the large-scale utilization of red mud and fly ash solid waste.

[0161] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing red mud-based artificial soil, characterized in that, The preparation method includes the following steps: (1) Mix red mud, calcium source and sodium aluminate solution to obtain raw material slurry; (2) The raw slurry obtained in step (1) is subjected to a first hydrothermal reaction to obtain a first chopped slurry, and after a first solid-liquid separation, dealkalized red mud is obtained; (3) The dealkalized red mud, detoxified fly ash and water obtained in step (2) are mixed and subjected to a second hydrothermal reaction to obtain a second clinker slurry; (4) The second clinker slurry obtained in step (3) is subjected to a second solid-liquid separation and washing to obtain a soil matrix; (5) The soil matrix obtained in step (4) is mixed with organic matter and then cultured to obtain the red mud-based artificial soil.

2. The preparation method according to claim 1, characterized in that, The calcium source mentioned in step (1) includes industrial raw materials with calcium oxide as the main component, industrial waste residue with calcium oxide as the main component, or calcium compounds. Preferably, the proportion of calcium oxide in the industrial raw material with calcium oxide as the main component is 25-90 wt%. Preferably, the proportion of calcium oxide in the industrial waste residue with calcium oxide as the main component is 25-90 wt%. Preferably, the calcium compound includes any one or a combination of at least two of calcium hydroxide, calcium oxide, or carbide slag.

3. The preparation method according to claim 1 or 2, characterized in that, The sodium aluminate solution in step (1) has an α-value. k The value is 1.0-25.0, preferably 1.5-20; Preferably, the sodium oxide concentration in the sodium aluminate solution is 2-200 g / L, more preferably 5-150 g / L; Preferably, the calcium-silicon molar ratio of the calcium source to the red mud is (0.5-10.0):1, more preferably (1.0-5.0):1; Preferably, the liquid-to-solid ratio of the sodium aluminate solution to the solid material composed of red mud and calcium source is (1-20) mL / g, and more preferably (1.5-10) mL / g.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (2), the temperature of the first hydrothermal reaction is 40-300℃, preferably 60-240℃; Preferably, the time for the first hydrothermal reaction is 0.3-30 hours, and more preferably 0.5-5 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The heavy metal content in the detoxified fly ash described in step (3) is lower than the heavy metal limit in farmland soil as specified in GB15618-2018. Preferably, the detoxification method for the detoxified fly ash includes physical detoxification or chemical detoxification; Preferably, the chemical detoxification method includes wet detoxification using acid and / or alkali; Preferably, the mass ratio of the dealkalized red mud to the detoxified fly ash is (1-20):1, and more preferably (2-10):1; Preferably, the liquid-to-solid ratio of the solid material composed of water, dealkalized red mud, and detoxified fly ash is (1.0-20) mL / g, and more preferably (1.5-10) mL / g; Preferably, the second hydrothermal reaction time is 0.5-300 h, more preferably 1-120 h; Preferably, the temperature of the second hydrothermal reaction is 30-90°C, and more preferably 40-90°C.

6. The preparation method according to any one of claims 1-5, characterized in that, The washing process in step (4) includes rinsing, two-stage countercurrent washing, or three-stage countercurrent washing; Preferably, the mass ratio of the total water used for washing to the mass of the solids is (0.1-20):1, and more preferably (1-10):

1.

7. The preparation method according to any one of claims 1-6, characterized in that, The organic matter mentioned in step (5) includes any one or a combination of at least two of the following: straw, cow dung, sheep dung, oil residue, distiller's grains, vinegar residue, medicinal residue, or animal leather; Preferably, the mass ratio of the soil matrix to organic matter is (20-69):(1-30), more preferably (30-49):(1-20); Preferably, the culture temperature is 10-70℃, more preferably 20-60℃; Preferably, the culture time is 10-100 days, more preferably 10-40 days; Preferably, the water content of the mixture of soil matrix and organic matter in the culture is 10-90 wt%, more preferably 20-80 wt%. Preferably, the culture process involves turning the plants over, with the turning frequency being once every 1-20 days, and more preferably once every 2-10 days.

8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Mix red mud, calcium source and sodium aluminate solution to obtain raw material slurry; The calcium source includes industrial raw materials with calcium oxide as the main component, industrial waste residue with calcium oxide as the main component, or calcium compounds; the proportion of calcium oxide in the industrial raw materials with calcium oxide as the main component is 25-90 wt%; the proportion of calcium oxide in the industrial waste residue with calcium oxide as the main component is 25-90 wt%; the calcium compound includes any one or a combination of at least two of calcium hydroxide, calcium oxide, or carbide slag. The sodium aluminate solution α k The concentration of sodium oxide in the sodium aluminate solution is 2-200 g / L; the calcium-silicon molar ratio of the calcium source to the red mud is (0.5-10.0):1; the liquid-solid ratio of the solid material composed of the sodium aluminate solution, red mud, and calcium source is (1-20) mL / g. (2) The raw slurry obtained in step (1) is subjected to a first hydrothermal reaction at a temperature of 40-300℃ for 0.3-30h to obtain the first clinker slurry, and after the first solid-liquid separation, the dealkalized red mud is obtained. (3) The dealkalized red mud, detoxified fly ash and water obtained in step (2) are mixed and subjected to a second hydrothermal reaction at a temperature of 30-90℃ for 0.5-300h to obtain the second clinker slurry; The heavy metal content in the detoxified fly ash is lower than the heavy metal limit in farmland soil according to GB15618-2018; the detoxification method of the detoxified fly ash includes physical detoxification or chemical detoxification; the chemical detoxification method includes wet detoxification using acid and / or alkali; the mass ratio of the de-alkali red mud to the detoxified fly ash is (1-20):1; the liquid-solid ratio of the solid material composed of water, de-alkali red mud, and detoxified fly ash is (1.0-20) mL / g; (4) The second clinker slurry obtained in step (3) is subjected to a second solid-liquid separation and washing to obtain a soil matrix; The washing process includes rinsing, two-stage countercurrent washing, or three-stage countercurrent washing; the total water consumption to the mass ratio of solids is (0.1-20):

1. (5) The soil matrix obtained in step (4) and organic matter are mixed and cultured at a temperature of 10-70℃ for 10-100 days in a mass ratio of (20-69):(1-30) to obtain the red mud-based artificial soil. The organic matter includes any one or a combination of at least two of the following: straw, cow dung, sheep dung, oil residue, distiller's grains, vinegar residue, medicinal residue, or animal leather; The water content of the mixture of soil matrix and organic matter in the culture is 10-90 wt%. The culture process involves turning the plants over, with a turning frequency of 1-20 days per turn.

9. A red mud-based artificial soil, characterized in that, The red mud-based artificial soil is prepared by the method for preparing red mud-based artificial soil according to any one of claims 1-8.

10. The application of the red mud-based artificial soil as described in claim 9, characterized in that, The red mud-based artificial soil is used in the fields of soil improvement or ecological restoration.

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