A method of soil remediation

Abstract

The application discloses a soil remediation method, belongs to the technical field of soil remediation, and aims at at least one problem of high soil remediation cost, secondary pollution, long-term unstable effect, and poor remediation effect caused by environmental conditions in the prior art. The soil remediation method comprises the following steps: preparing a soil remediation agent, wherein the soil remediation agent is a red mud-based iron-aluminum modified bimetallic magnetic functional material; scattering the soil remediation agent into soil to be remediated; and adding water into the soil to be remediated into which the soil remediation agent is scattered. The application can be used for soil remediation.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, and in particular relates to a soil remediation method. Background Technology

[0002] Soil remediation aims to remove or reduce pollutants in the soil and restore its health and productivity. It mainly includes physical remediation, chemical remediation, and bioremediation.

[0003] Physical remediation methods can directly remove heavy metals and organic pollutants from the soil, thereby rapidly reducing pollutant concentrations. However, these methods are costly and require significant investment. Physical remediation may damage soil structure, affecting soil fertility and ecological functions. Chemical remediation methods reduce the activity of heavy metals and other pollutants by adding chemical reagents, thus reducing their harm to the environment and organisms. However, the use of chemical reagents may lead to secondary pollution problems, and the long-term effects of chemical remediation are unstable, with the risk of pollutant re-release over time. Bioremediation methods utilize the absorption and transformation of microorganisms or plants to remove heavy metals and organic pollutants from the soil. Bioremediation has a long cycle, is greatly affected by environmental conditions, and has poor remediation effects. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a soil remediation method to solve at least one of the problems in the prior art: high cost of soil remediation, secondary pollution, unstable long-term effects, and poor remediation effect due to environmental conditions.

[0005] The objective of this invention is mainly achieved through the following technical solutions.

[0006] This invention provides a soil remediation method, comprising the following steps:

[0007] Step A: Prepare a soil remediation agent, which is a red mud-based iron-aluminum modified bimetallic magnetic functional material;

[0008] Step B: Sprinkle the soil remediation agent into the soil to be remediated;

[0009] Step C: Add water to the soil to be repaired after applying the soil remediation agent.

[0010] Furthermore, the weight ratio of the red mud-based iron-aluminum modified bimetallic magnetic functional material to the area of ​​the soil to be remediated is 1–5:1, g / m². 2 .

[0011] Furthermore, the following steps are included between step B and step C:

[0012] Turn over the soil to be repaired after applying the soil remediation agent to ensure that the soil remediation agent is evenly mixed with the soil to be repaired.

[0013] Furthermore, turning the soil includes the following steps:

[0014] The soil to be repaired, after being treated with soil remediation agent, is then shallowly tilled and then deeply tilled.

[0015] Furthermore, the shallow turning depth is 15–30 cm.

[0016] Furthermore, the deep turning depth is 35-50cm.

[0017] Furthermore, the red mud-based iron-aluminum modified bimetallic magnetic functional material includes magnetic particles and carbon-based materials, with the magnetic particles uniformly embedded on the surface of the carbon-based materials.

[0018] Furthermore, the magnetic particles are composed of the following components by mass percentage: 15-25% zero-valent iron, 9.5-15% zero-valent aluminum, and 30-50% iron and aluminum oxides.

[0019] Furthermore, the carbon-based material is a carbon rod.

[0020] Furthermore, the red mud-based iron-aluminum modified bimetallic magnetic functional material exhibits mesoporous properties.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects.

[0022] A) The soil remediation method provided by this invention uses red mud-based iron-aluminum modified bimetallic magnetic functional material as a soil remediation agent. It does not generate secondary pollution during use, is easy to obtain and prepare, and has the dual functions of "fertilizing and reducing pollution".

[0023] B) The soil remediation method provided by this invention, on the one hand, is that the red mud-based iron-aluminum modified bimetallic magnetic functional material is an organic substance, which can increase the organic matter content of the soil to be remediated after being added to it; on the other hand, the porous structure and large surface area of ​​the red mud-based iron-aluminum modified bimetallic magnetic functional material can provide a good microbial growth environment, promote the decomposition of microorganisms and the transformation of organic matter, and further improve the quality and quantity of soil organic matter; furthermore, the red mud-based iron-aluminum modified bimetallic magnetic functional material can not only adsorb and fix nutrients such as potassium and phosphorus in the soil to be remediated, forming complexes or chelates with the nutrients in the soil to be remediated, increasing their water solubility and mobility, thereby improving the speed and effectiveness, but also promote the nitrification of ammonium nitrogen and increase the content of nitrate nitrogen.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained through the embodiments described and the accompanying drawings, which are particularly pointed out. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 The scanning electron microscope image of the red mud-based iron-aluminum modified bimetallic magnetic functional material of Example 1 of the present invention is shown below.

[0027] Figure 2 The scanning electron microscope image of the red mud-based iron-aluminum modified bimetallic magnetic functional material of Example 2 of the present invention;

[0028] Figure 3 The scanning electron microscope image of the red mud-based iron-aluminum modified bimetallic magnetic functional material of Example 3 of the present invention;

[0029] Figure 4 The X-ray diffraction patterns of the red mud-based iron-aluminum modified bimetallic magnetic functional materials of Examples 1-3 of this invention are shown below.

[0030] Figure 5 The Fourier transform infrared spectra of the red mud-based iron-aluminum modified bimetallic magnetic functional materials of Examples 1-3 of this invention are shown below.

[0031] Figure 6 The magnetization curves of the red mud-based iron-aluminum modified bimetallic magnetic functional materials of Examples 1-3 of this invention are shown.

[0032] Figure 7 The cyclic voltammetry curves of the red mud-based iron-aluminum modified bimetallic magnetic functional materials of Examples 1-3 of this invention are shown.

[0033] Figure 8 The Nyquist impedance diagrams of the red mud-based iron-aluminum modified bimetallic magnetic functional materials of Examples 1-3 of this invention are shown.

[0034] Figure 9 A flowchart illustrating the preparation method of the soil remediation material provided by this invention. Detailed Implementation

[0035] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0036] This invention provides a soil remediation method, see [link to relevant documentation]. Figure 9 It includes the following steps:

[0037] Step A: Prepare a soil remediation agent, which is a red mud-based iron-aluminum modified bimetallic magnetic functional material;

[0038] Step B: Sprinkle the soil remediation agent into the soil to be remediated;

[0039] Step C: Add water to the soil to be repaired after applying the soil remediation agent.

[0040] Compared with existing technologies, the soil remediation method provided by this invention uses red mud-based iron-aluminum modified bimetallic magnetic functional materials as soil remediation agents. It does not generate secondary pollution during use, is easy to obtain and prepare, and has the dual functions of "fertilizing and reducing pollution".

[0041] Specifically, on the one hand, since red mud-based iron-aluminum modified bimetallic magnetic functional materials are organic substances, their addition to the soil to be remediated can increase the organic matter content of the soil. On the other hand, the porous structure and large surface area of ​​red mud-based iron-aluminum modified bimetallic magnetic functional materials can provide a good microbial growth environment, promote microbial decomposition and organic matter transformation, and further improve the quality and quantity of soil organic matter. Furthermore, red mud-based iron-aluminum modified bimetallic magnetic functional materials can not only adsorb and fix nutrients such as potassium and phosphorus in the soil to be remediated, forming complexes or chelates with the nutrients in the soil to be remediated, increasing their water solubility and mobility, thereby improving their speed and effectiveness, but also promote the nitrification of ammonium nitrogen, increasing the content of nitrate nitrogen.

[0042] To fully utilize the red mud-based iron-aluminum modified bimetallic magnetic functional material and ensure thorough remediation of the soil to be remediated, the weight ratio of the red mud-based iron-aluminum modified bimetallic magnetic functional material to the area of ​​the soil to be remediated should be 1–5:1 (g / m²). 2 In other words, 1g of red mud-based iron-aluminum modified bimetallic magnetic functional material is added to 5-10kg of soil to be treated.

[0043] To further improve the remediation effect of the soil to be remediated, the following steps are included between steps B and C:

[0044] Turn over the soil to be repaired after applying the soil remediation agent to ensure that the soil remediation agent is evenly mixed with the soil to be repaired.

[0045] For example, soil turning is divided into shallow turning and deep turning. Therefore, the above-mentioned soil turning includes the following steps:

[0046] The soil to be repaired, after being treated with the soil remediation agent, is then subjected to shallow tillage and deep tillage in sequence. The shallow tillage depth is 15-30cm, and the deep tillage depth is 35-50cm.

[0047] In order to obtain high-performance red mud-based iron-aluminum modified bimetallic magnetic functional materials, specifically, step A above includes the following steps:

[0048] Step 1: Pre-treat the biomass raw materials to obtain biomass pellets;

[0049] Step 2: After pouring red mud, biomass pellets and water (e.g., distilled water) into a beaker, ultrasonically vibrate for 0.5-1 h and stir with a magnetic stirrer for 1-2 h. The mass ratio of red mud, biomass pellets and water is 0.5-2:1:40-60 to obtain a mixture. The mass ratio of red mud to biomass pellets is 0.5-2:1. During ultrasonic vibration, the red mud, biomass pellets and water will be gradually broken up by high-frequency vibration, thereby promoting the thorough and uniform mixing of red mud, treated biomass and water.

[0050] Step 3: Pour the mixture into a hydrothermal reactor for hydrothermal reaction to obtain a hydrothermal reaction slurry. The hydrothermal reaction temperature is 140–180℃, and the hydrothermal reaction time is 0.5–2 hours. Limiting the hydrothermal reaction temperature and time within this range allows the hydrothermal reaction to proceed relatively quickly, thereby ensuring reaction efficiency and yield. At the same time, it also helps to reduce the generation of waste gas, wastewater, and solid waste, thus reducing the impact on the environment.

[0051] Step 4: After the hydrothermal reaction slurry is cooled to room temperature, solid-liquid separation is performed. The obtained solid phase is dried in a vacuum oven at 6-8 Pa and 60-80 °C for 12-14 hours to obtain the hydrothermal reaction product.

[0052] Step 5: The hydrothermal reaction products are subjected to thermal stabilization treatment, cooling, cleaning (at least 3 times to degrade surface oil stains) and vacuum drying in sequence to obtain bimetallic magnetic functional materials.

[0053] For example, the composition of red mud, calculated by mass percentage, includes: 30-40% Fe2O3, 20-30% Al2O3, 10-25% SiO2, 5-20% Na2O, 1-10% TiO2, with the balance being CaO and unavoidable impurities, and the initial pH value of the red mud is 10-12.

[0054] Biomass pellets include one or more of agricultural and forestry waste wood chips (e.g., pine wood chips), corn stalks, walnut shells, coconut shells, and straw, mixed in any proportion, with an average particle size of 75–500 nm.

[0055] Specifically, the specific reaction formulas involved in the preparation of red mud-based iron-aluminum modified bimetallic magnetic functional materials are as follows:

[0056] Tar + H2O → H2 + CO (1)

[0057] Tar + xH2O → zH2 + yCO2 (2)

[0058] Tar → H2 + H2O + C n H m (3)

[0059] C + H₂O → H₂ + CO (4)

[0060]

[0061] 3Fe₂O₃ + C → 2Fe₃O₄ + CO (6)

[0062] 3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂ (7)

[0063] 3Fe₂O₃ + H₂ → 2Fe₃O₄ + H₂O (8)

[0064] Fe3O4 + H2 → 3FeO + H2O (9)

[0065] FeO + H2 → Fe 0 +H2O (10)

[0066] Fe 3+ +Al 0 →Fe 2+ +Al 3+ (11)

[0067] Red mud is a highly alkaline industrial solid byproduct generated during the production of alumina in the aluminum industry. For every ton of alumina produced, 0.8 to 1.8 tons of red mud are emitted as a byproduct. Red mud is rich in Fe and Al. At the same time, due to the preparation process, it is highly alkaline, which is conducive to the loading of bimetals onto the substrate material.

[0068] Based on the concept of industrial solid waste resource utilization, a zero-valent iron-aluminum composite bimetallic magnetic functional material is prepared. Using red mud (a byproduct of aluminum smelting) as the source of iron and aluminum, and carbon-based materials (biomass pellets) as the framework, a coupled bimetallic magnetic functional material is prepared. The abundant iron and aluminum elements in the red mud are loaded onto the carbon-based material framework to prepare the zero-valent iron-aluminum composite bimetallic magnetic functional material. The strong alkalinity of red mud (pH = 10–12) has an activating effect on the material preparation stage, activating the bimetal and promoting electron transfer between the iron-aluminum active substances and the carbon-based material. The process utilizes carbon-based materials as electron shuttles to accelerate electron transfer in bimetallic materials. The carbon-based material framework has a variety of oxygen-containing functional groups and a large specific surface area, which can effectively prevent the agglomeration of active elements (zero-valent iron, zero-valent aluminum, and iron-aluminum oxides) in red mud, protect the two main reducing substances, zero-valent iron and zero-valent aluminum, in the material, and improve the stability, electron transfer process, and adsorption performance of the material. The preparation process is simple and the raw material cost is low, which can solve the problems of high cost, complex process, low efficiency, few reaction sites, and difficulty in recycling of existing magnetic functional materials.

[0069] Simultaneously, by controlling the mass ratio of red mud to biomass pellets, the surface morphology and properties of the material are regulated, ensuring that zero-valent iron particles, zero-valent aluminum particles, and iron-aluminum oxide particles are uniformly embedded on the surface of the material. Controlling the amount of red mud can alter the content of iron and aluminum sources; increasing the mass ratio of red mud promotes the conversion of iron in the material into ferric oxide and ferric oxide to zero-valent iron. Possible conversion processes are shown in formulas 6-10. Controlling the increase in biomass pellets promotes the generation of reducing gases and tar. The generation of CO or H2 is shown in formulas 1-5. The carbothermal reduction process further reduces aluminum oxide in the red mud to generate zero-valent aluminum. Regulating the content of zero-valent iron and zero-valent aluminum improves the overall performance of the material.

[0070] The red mud-based iron-aluminum modified bimetallic magnetic functional material obtained by the above method includes magnetic particles and carbon-based materials (e.g., carbon rods). The magnetic particles are uniformly embedded on the surface of the carbon-based materials. The composition of the magnetic particles by mass percentage includes: 15-25% zero-valent iron, 9.5-15% zero-valent aluminum, and 30-50% iron-aluminum oxides.

[0071] It should be noted that by adjusting the mass ratio of red mud to biomass particles, the specific surface area of ​​red mud-based iron-aluminum modified bimetallic magnetic functional materials can reach 30–100 m². 2 / g, pore size is The pore volume is 0.09–0.15 cm³. 3 / g, maximum current is 0.07~0.09mA, resistance is 65~85Ω. Red mud-based iron-aluminum modified bimetallic magnetic functional material is type IV, belonging to a typical H3 type hysteresis curve, and red mud-based iron-aluminum modified bimetallic magnetic functional material has mesoporous characteristics.

[0072] It should be noted that in step 3 above, the hydrothermal reaction system is under alkaline conditions. During the hydrothermal process, the iron contained in the red mud will be converted into magnetic substances (such as iron(II,III) oxide), making the material magnetic. The alkaline red mud-based iron-aluminum modified bimetallic magnetic functional material is more conducive to the adsorption and fixation of heavy metals and its application in soil remediation and other aspects. At the same time, other substances will also participate in the entire adsorption process, such as calcium oxide and silicon dioxide.

[0073] To maintain the activity of both zero-valent iron and zero-valent aluminum, the mass ratio of red mud to biomass particles is 0.9–1.1:1, for example, 1:1. In this way, zero-valent aluminum can reduce trivalent iron present in the material to divalent iron, further maintaining the divalent iron content and achieving iron cycling. The conversion process is described in Formula 11. This results in more sustained reactivity and a significantly enhanced ability to degrade heavy metals compared to ordinary functional soil remediation agents.

[0074] To further enhance the reactivity and stability of the red mud-based iron-aluminum modified bimetallic magnetic functional material, step 5 above, prior to cooling, includes the following steps:

[0075] The hydrothermal reaction products were thermally stabilized in a tube furnace under a nitrogen atmosphere. The thermal stabilization temperature was 400–800℃, the thermal stabilization time was 1–2 h, and the heating rate was 5–10℃ / min.

[0076] In this way, through thermal stabilization treatment, biomass pellets will generate reducing gases (such as hydrogen and carbon monoxide) during the thermal stabilization process, which will reduce the iron and aluminum oxides in the red mud to generate substances such as zero-valent iron and active aluminum with strong reducing properties; at the same time, it will degrade the bound water in the dried products, increase the specific surface area and oxygen-containing functional groups of the red mud-based iron-aluminum modified bimetallic magnetic functional materials, and enhance the reactivity and stability of the red mud-based iron-aluminum modified bimetallic magnetic functional materials.

[0077] Furthermore, by limiting the thermal stability temperature within the aforementioned range, biomass pellets and red mud can undergo structural transformation or phase transition, thereby increasing the specific surface area of ​​the material and the generation of active components. Specifically, the process is as follows: biomass pellets and red mud complete dehydration below 200°C. When the temperature reaches above 400°C, the biomass pellets begin to undergo pyrolysis. Under anaerobic or low-oxygen conditions, organic matter decomposes into smaller molecules, such as bio-oil, biochar, and gases (CO, H2). During this process, the structure of the biomass pellets undergoes significant changes, with major components such as cellulose, hemicellulose, and lignin beginning to decompose. Simultaneously, red mud forms new mineral phases under a CO or H2 atmosphere (for example, iron begins to transform into the active substance zero-valent iron), and the generated active substances are embedded in the biochar, which has a large specific surface area.

[0078] In order to control the adhesion uniformity and particle size of zero-valent iron and zero-valent aluminum particles, steps 2 to 5 above include the following steps:

[0079] Step 2: Divide the red mud into two parts, with the mass ratio of the first part to the second part being 5:2 to 3;

[0080] After pouring the first batch of red mud, biomass pellets and water into a beaker, the mixture was subjected to ultrasonic vibration and magnetic stirring in sequence to obtain a mixture.

[0081] Step 3: Pour the mixture into a hydrothermal reactor to carry out a hydrothermal reaction, and obtain a hydrothermal reaction slurry;

[0082] The second portion of red mud was poured into another hot water kettle for hydrothermal reaction.

[0083] Step 4: After cooling the hydrothermal reaction slurry and the second batch of red mud after hydrothermal reaction to room temperature, solid-liquid separation is performed. The obtained solid phases are dried to obtain the hydrothermal reaction product and hydrothermal red mud.

[0084] Step 5: The hydrothermal reaction products are subjected to a first thermal stabilization treatment in a tube furnace under a N2 atmosphere to obtain the first-processed product;

[0085] The product from the primary treatment was mixed with hydrothermal red mud and then subjected to a second thermal stabilization treatment to obtain the product from the secondary treatment.

[0086] The secondary processing product was sequentially cooled, cleaned, and vacuum dried to obtain a bimetallic magnetic functional material.

[0087] In this way, the red mud is added in two stages. On the one hand, during the hydrothermal reaction of the mixture, the first batch of red mud and biomass particles undergo a hydrothermal reaction, which can produce carbon rod materials with a large specific surface area and uniform and abundant sites. At the same time, the pore-forming effect is more conducive to the formation of pores in a highly alkaline environment. On the other hand, during the first heat stabilization treatment, uniform and abundant particles can be formed on the surface of the carbon-based material. As a hydrothermal red mud, it can encapsulate the magnetic particles generated during the first heat stabilization treatment, promote the further growth of magnetic particles, and avoid the agglomeration and waste of active materials caused by adding red mud all at once.

[0088] To further promote the growth of magnetic particles, the first thermal stabilization temperature is 400–600℃, the first thermal stabilization time is 0.5–1h, and the first thermal stabilization heating rate is 8–10℃ / min; the second thermal stabilization temperature is 650–800℃, the second thermal stabilization time is 0.5–1h, and the second thermal stabilization heating rate is 5–6℃ / min.

[0089] Considering that the ratio of zero-valent iron to zero-valent aluminum in magnetic particles directly affects the material's performance, the following steps are included between steps 1 and 5 to further control their ratio:

[0090] An aluminum source (e.g., Al2O3 or AlCl3) is added to the hydrothermal reaction product and mixed, with the mass ratio of aluminum source to hydrothermal reaction product being 0.5:1 to 1:1.

[0091] In this way, by adding an additional aluminum source, the ratio of zero-valent aluminum and zero-valent iron in the magnetic particles can be precisely controlled, preventing flocculation and precipitation that occurs when iron and aluminum are added in one step, and promoting the adhesion of more active substances to the carbon rod material to form a more active iron-aluminum bimetallic material.

[0092] In order to effectively pretreat biomass raw materials and ensure that the red mud-based iron-aluminum modified bimetallic magnetic functional materials have good performance and stability in subsequent applications, step 1 above, for example, includes the following steps:

[0093] Step 11: Wash the biomass raw materials multiple times, for example, 3 to 4 times, to degrade the stains on the surface of the biomass raw materials;

[0094] Step 12: Dry the washed biomass raw materials in an oven at 60-80℃ for 12-24 hours;

[0095] Step 13: The dried biomass raw material is crushed and sieved in sequence to obtain biomass particles with a particle size of 50-100 mesh, so as to ensure that the biomass particles are uniform in size.

[0096] Examples 1-5 illustrate the preparation of red mud-based iron-aluminum modified bimetallic magnetic functional materials.

[0097] Example 1

[0098] Pine sawdust was washed three times, dried in an oven at 65℃ for 18 hours, then pulverized and sieved to obtain pine sawdust particles with a particle size of 50-100 mesh. 2g of red mud and 4g of pine sawdust particles (mass ratio 0.5:1) were weighed and reacted in 60ml of distilled water. After sonication for 0.5 hours, the mixture was placed in a magnetic stirrer and stirred at 200rpm for 2 hours at room temperature. The mixture was then poured into a hydrothermal reactor and hydrothermated at 140℃ for 2 hours to allow the minerals in the red mud to better embed into the biomass particles. After the hydrothermal reaction, the mixture was cooled to room temperature for solid-liquid separation. The resulting solid phase was dried in a vacuum oven at 8Pa at 60℃ for 12 hours, and then thermally stabilized in a tube furnace at 400℃ for 2 hours at a heating rate of 8℃ / min and a ventilation rate of 5m / s. After the thermal stabilization test, tar and other impurities on the surface of the material were washed away with deionized water, and the material was vacuum dried and packaged.

[0099] Scanning electron microscopy images show that the red mud-based iron-aluminum modified bimetallic magnetic functional material provided in this embodiment exhibits a rod-like structure, with a small amount of particulate matter adhering to the carbon rods. (See attached image.) Figure 1 This is thanks to the addition of red mud.

[0100] Example 2

[0101] Pine sawdust was washed four times, dried in an oven at 75℃ for 24 hours, then pulverized and sieved to obtain pine sawdust particles with a particle size of 50-100 mesh. 3g of red mud and 3g of pine sawdust (mass ratio 1:1) were weighed and reacted in 60ml of distilled water. The mixture was sonicated for 0.5 hours, then placed in a magnetic stirrer and stirred at 200rpm at room temperature for 2 hours. The mixture was then poured into a hydrothermal reactor and hydrothermated at 180℃ for 0.5 hours to allow the minerals in the red mud to better embed into the biomass particles. After the hydrothermal reaction, the mixture was cooled to room temperature for solid-liquid separation. The resulting solid phase was dried in a vacuum oven at 80℃ for 13 hours under 6Pa of pressure. After drying, it was thermally stabilized at 800℃ for 1 hour in a tube furnace with continuous N2 ventilation at a heating rate of 10℃ / min and a ventilation rate of 6m / s. After the thermal stabilization test, tar and other impurities on the surface of the material were washed away with deionized water, and the material was vacuum dried and packaged.

[0102] Scanning electron microscopy images show that the red mud-based iron-aluminum modified bimetallic magnetic functional material provided in this embodiment exhibits a rod-like structure, in which the layered structure attached to the biochar is clearly visible. (See [link to relevant documentation]). Figure 2 .

[0103] Example 3

[0104] Pine sawdust was washed three times, dried in an oven at 80℃ for 12 hours, then pulverized and sieved to obtain pine sawdust particles with a particle size of 50-100 mesh. 4g of red mud and 2g of pine sawdust (mass ratio 2:1) were weighed and reacted in 60ml of distilled water. The mixture was sonicated for 0.5 hours, then placed in a magnetic stirrer and stirred at 200rpm for 2 hours at room temperature. The mixture was then poured into a hydrothermal reactor and hydrothermated at 160℃ for 1 hour to allow the minerals in the red mud to better embed into the biomass particles. After the hydrothermal reaction, the mixture was cooled to room temperature for solid-liquid separation. The resulting solid phase was dried in a vacuum oven at 70℃ for 14 hours at 7Pa. After drying, it was thermally stabilized at 600℃ for 1.5 hours in a tube furnace with continuous N2 ventilation at a heating rate of 6℃ / min and a ventilation rate of 4m / s. After thermal stabilization, the material surface was washed with deionized water to remove tar and other impurities, then vacuum dried and packaged.

[0105] Scanning electron microscopy (SEM) analysis revealed that the red mud-based iron-aluminum modified bimetallic magnetic functional material provided in this embodiment exhibits a rod-like structure. The synthesized iron and aluminum aggregates into granular particles, and the material surface is rough. (See [link to relevant documentation]). Figure 3 .

[0106] Example 4

[0107] Pine wood chips were washed four times, dried in an oven at 75°C for 24 hours, then crushed and sieved to obtain pine wood chip particles with a particle size of 50-100 mesh. 1.5g of red mud and 3g of pine wood chips (mass ratio 1:1) were weighed, and 60ml of distilled water was used as the reaction medium solution. After sonication for 0.5 hours, the mixture was placed in a magnetic stirrer and stirred at room temperature at 200rpm for 2 hours. The mixture was poured into a hydrothermal reactor and hydrothermally heated at 180℃ for 0.5 h to allow the minerals in the red mud to better embed into the biomass particles. After the hydrothermal reaction, the mixture was cooled to room temperature for solid-liquid separation. The resulting solid phase was dried in a vacuum oven at 80℃ for 13 h at 6 Pa. Then, 0.6 g of red mud was weighed and subjected to a hydrothermal reaction, followed by drying to obtain hydrothermal red mud. The hydrothermal reaction product was first thermally stabilized at 600℃ for 0.5 h in a tube furnace with continuous N2 supply, at a heating rate of 10℃ / min and a gas flow rate of 6 m / s. Finally, the hydrothermal red mud was added to the system and thermally stabilized a second time at 800℃ for 1 h in a tube furnace with continuous N2 supply, at a heating rate of 8℃ / min and a gas flow rate of 6 m / s. After the thermal stabilization experiment, tar and other impurities on the surface of the material were washed away with deionized water, and the material was vacuum dried and packaged.

[0108] Example 5

[0109] Pine sawdust was washed four times, dried in an oven at 75℃ for 24 hours, then pulverized and sieved to obtain pine sawdust particles with a particle size of 50-100 mesh. 3g of red mud and 3g of pine sawdust (mass ratio 1:1) were weighed and reacted in 60ml of distilled water. After sonication for 0.5 hours, the mixture was placed in a magnetic stirrer and stirred at 200rpm for 2 hours at room temperature. The mixture was then poured into a hydrothermal reactor and hydrothermated at 180℃ for 0.5 hours to allow the minerals in the red mud to better embed into the biomass particles. After the hydrothermal reaction, the mixture was cooled to room temperature for solid-liquid separation. The resulting solid phase was dried in a vacuum oven at 80℃ for 13 hours under 6Pa of pressure. After drying, 3g of aluminum source was added and mixed. The mixture was then thermally stabilized at 800℃ for 1 hour in a tube furnace with continuous N2 ventilation at a heating rate of 10℃ / min and a gas flow rate of 6m / s. After the thermal stabilization test, tar and other impurities on the surface of the material were washed away with deionized water, and the material was vacuum dried and packaged.

[0110] The following tests were performed on Examples 1 to 5, respectively, using XRD, XPS, specific surface area, pore volume, average pore size, Fourier infrared spectroscopy, magnetization curve, cyclic voltammetry curve, and Nyquist impedance.

[0111] in, Figure 4The X-ray diffraction (XRD) patterns of Examples 1-3 show the crystal structures of Examples 1-3. The diffraction peaks of zero-valent aluminum are located at 38.5°, 44.7°, 65.1°, and 78.2°, while the diffraction peaks of zero-valent iron are located at 44.7° and 65°. This clearly demonstrates that the preparation method of the present invention can successfully synthesize zero-valent bimetals. Furthermore, Figure 4 The sample also exhibits diffraction peaks of iron(III) oxide, at 43.6° and 58.9°.

[0112] X-ray photoelectron spectroscopy (XPS) further quantitatively elucidated the content of zero-valent iron and zero-valent aluminum in the synthesized samples. See Table 1. Zero-valent aluminum and zero-valent iron were obtained in Examples 1-5. The zero-valent iron contents in Examples 1-5 were 16.57%, 17.25%, 20.25%, 17.57%, and 16.53%, respectively, indicating that increasing the amount of red mud added leads to an increase in zero-valent iron. Meanwhile, the content of zero-valent aluminum was directly proportional to the amount of biomass pellets added. The zero-valent aluminum content in Example 1 was 13.47%. As the amount of biomass pellets decreased, the zero-valent aluminum content in Example 3 was 9.56%, in Example 2 it was 11.57%, in Example 4 it was 11.90%, and in Example 5 it was 11.88%. Analysis suggests that the reduction potential of zero-valent iron (ZV) is -0.44V, while that of zero-valent aluminum (ZV) is -1.66V. Under similar conditions, the formation of ZV is easier to achieve, while the reduction of ZV requires the production of more reducing gases. Furthermore, the production of ZV increases with the amount of biomass, likely because the increased biomass promotes the production of a large amount of reducing gases, thus accelerating the reduction of aluminum in red mud. In other words, during carbothermic reduction, iron oxides are first reduced to Fe. 0 Al is reduced only after the first reduction. In addition, the presence of carbon-based materials can protect and disperse the passivation and agglomeration of zero-valent aluminum.

[0113] Table 1. Zero-valent iron and zero-valent aluminum content (wt.%) in Examples 1-5

[0114] Example 1 31.47％ 51.96％ 16.57％ 32.17％ 54.36％ 13.47％ Example 2 38.12％ 44.63％ 17.25％ 29.37％ 59.12％ 11.51％ Example 3 37.36％ 42.23％ 20.41％ 39.60％ 50.84％ 9.56％ Example 4 38.22％ 44.21％ 17.57％ 28.95％ 59.15％ 11.90％ Example 5 38.50％ 44.97％ 16.53％ 29.05％ 59.07％ 11.88％

[0115] Table 2 shows the specific surface area, pore volume, and average pore size of Examples 1-5. From Table 2, it can be seen that as the amount of red mud added increases, the specific surface area of ​​the material increases from 86.47 m² / s². 2 / g decreased to 31.25m 2 / g, pore size from Increase to The pore volume ranges from 0.125 cm³. 3 / g decreased to 0.096cm 3 / g indicates that the red mud filled part of the pores of the carbon-based material, and the pore size showed a decreasing trend.

[0116] Table 2. Specific surface area, pore volume, and average pore diameter of Examples 1-5

[0117]

[0118] Figure 5 Fourier transform infrared spectroscopy analysis of Examples 1-3 shows the influence of surface functional groups on the materials of Examples 1-3. Figure 5 It can be observed that the addition of red mud introduces abundant iron-containing functional groups at 802, 696, and 553 cm⁻¹. -1 There are relatively obvious absorption peaks at 3482, 1632, 1446 and 1002 cm⁻¹. -1 It is rich in oxygen-containing functional groups. Among them, 3482cm -1 The absorption peak at 1632 cm⁻¹ originates from the stretching vibration of the hydroxyl group (OH). -1 The nearby absorption peak is mainly due to the C=O stretching vibration absorption of lipids and carboxylic acids, at 1446 cm⁻¹. -1 and 1002cm -1 These are the stretching vibration peaks of C=C and CO, respectively. It is noteworthy that these peaks are observed at 802, 696, and 553 cm⁻¹. -1 The absorption peaks at the point are attributed to the stretching vibrations of FeOOH, Fe-OH, and Fe-O, which are related to the iron-aluminum complexes embedded on the surface of the carbon-based material. In Example 2, the stretching vibration of the OH absorption peak is significantly increased; furthermore, the change in the Fe-O absorption peak is also quite prominent, indicating that the carbon-based material provides suitable loading sites for the generated active substances.

[0119] Figure 6 The figures show the magnetization curves for Examples 1-3, with Example 2 exhibiting the strongest magnetism (17.86 emu / g). This reveals that the combination of red mud and biomass particles is optimal, and the appropriate ratio generates more magnetically active substances during the thermal stabilization process. Besides the crucial strong reducing agent zero-valent iron, the formation of substances such as iron(III) oxide also contributes to the magnetism. The presence of pine sawdust during carbothermic reduction produces reducing gases (CO and H2), which reduce the substances in the red mud (RM) into various active substances, thereby enhancing the magnetism.

[0120] Figure 7The cyclic voltammetry curves for Examples 1-3 are shown. The reduction current in the cyclic voltammetry curves reflects the amount of direct electron transfer in the magnetic functional materials, while the loop area of ​​the curve represents the electron transfer rate of the material. The maximum currents of the bimetallic materials synthesized in Examples 1-3 are 0.073, 0.088, and 0.087 mA, respectively, indicating that electrons in the nano-bimetallic materials transfer at a relatively fast rate. In particular, the experimental results show that the direct electron transfer capability of the bimetallic magnetic functional materials increases with the increase of the proportion of red mud, and the direct electron transfer of the material is more affected by the amount of biomass. Furthermore, the synthesized active material assists in the direct electron transfer of the material.

[0121] Figure 8 The Nyquist impedance diagrams for Examples 1-3 illustrate the resistance of the material as electrons pass through; lower resistance means easier electron passage. The resistances for Examples 1-3 are 67.12 Ω, 80.07 Ω, and 82.05 Ω, respectively. This indicates that Examples 1 and 2 have lower resistances, allowing electrons to pass through more easily. This is attributed to the presence of more conductive substances such as Fe3O4 and Al in the synthesized materials, which enhance their ability to transfer electrons during synthesis, highlighting the importance of these substances in the direct electron transfer process.

[0122] The following describes the soil remediation using the red mud-based iron-aluminum modified bimetallic magnetic functional materials described in Examples 1-3. For ease of operation, the soil remediation was conducted under laboratory conditions. The specific remediation methods are as follows:

[0123] The soil samples were sourced from Yunnan Province. Using a five-point sampling method, sufficient soil samples were collected at a depth of 10–15 cm, sealed, and brought back to the laboratory. One kg of soil was used as pre-analytical soil for further processing (e.g., sample grinding, drying at 60–80℃, sieving through a 100–150 mesh sieve) for physicochemical analysis (e.g., pH, organic matter, available potassium, available phosphorus, ammonium nitrogen, nitrate nitrogen, and cadmium, tested according to national standards). Each group of soil samples to be remediated weighed 5–10 kg. Groups 1–3 received 1 g of the soil remediation agent prepared in Examples 1–3, while group 4 served as a blank control. Under identical conditions, Chinese cabbage was planted and grown for 30–35 days, with 30–50 mL of water provided daily. The cadmium content in the roots, stems, and leaves was determined using ICP-OES.

[0124] The physical and chemical properties of the soil and the growth of Chinese cabbage are shown in Tables 3 and 4.

[0125] Table 3. Physicochemical properties of soils from groups 1-3 and the blank control group.

[0126] pH 5.96 7.86 7.74 7.62 Organic matter (%) 5.53 12.65 10.84 12.11 Available potassium (mg / kg) 368.87 490.42 570.51 509.25 Available phosphorus (mg / kg) 19.25 26.50 23.12 26.74 Ammonium nitrogen (mg / kg) 5.03 3.79 4.01 2.89 Nitrate nitrogen (mg / kg) 102.97 221.72 229.42 212.97 Cadmium (mg / kg) 89.65 20.32 18.65 19.08

[0127] Table 3 shows that the soil pH value increased after the addition of the soil remediation agent, which has a positive effect on improving acidic soil and promoting the availability of soil nutrients.

[0128] Table 4 shows the soil conditions for planting Chinese cabbage in groups 1-3 and the blank control group.

[0129]

[0130]

[0131] Table 4 shows that the addition of soil remediation agent helps to alleviate the bioavailability of Chinese cabbage, and the heavy metal content in the stems and leaves of Chinese cabbage meets the limits for contaminants in food according to GB 2762-2022 National Food Safety Standard.

[0132] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A soil remediation method, characterized in that, Includes the following steps: Step A: Prepare a soil remediation agent, wherein the soil remediation agent is a red mud-based iron-aluminum modified bimetallic magnetic functional material; Step B: Sprinkle the soil remediation agent into the soil to be remediated; Step C: Add water to the soil to be repaired after applying the soil remediation agent; Step A includes the following steps: Step 1: Pre-treat the biomass raw material to obtain biomass pellets; Step 2: Pour red mud, biomass pellets, and water into a beaker and then sequentially perform ultrasonic vibration for 0.5-1 h and magnetic stirring for 1-2 h, with a mass ratio of red mud, biomass pellets, and water of 0.5-2:1:40-60 to obtain a mixed liquid, with a mass ratio of red mud to biomass pellets of 0.5-2:1; Step 3: Pour the mixed liquid into a hydrothermal reactor for hydrothermal reaction to obtain a hydrothermal reaction slurry, with a hydrothermal reaction temperature of 140-180 ℃ and a hydrothermal reaction time of 0.5-2 h; Step 4: After cooling the hydrothermal reaction slurry to room temperature, perform solid-liquid separation, and dry the obtained solid phase in a vacuum oven at 6-8 Pa and 60-80 ℃ for 12-14 h to obtain the hydrothermal reaction product; Step 5: Sequentially perform thermal stabilization treatment, cooling, washing, and vacuum drying on the hydrothermal reaction product to obtain a bimetallic magnetic functional material; Red mud-based iron-aluminum modified bimetallic magnetic functional materials consist of magnetic particles and carbon-based materials. The magnetic particles are uniformly embedded on the surface of the carbon-based materials. The composition of the magnetic particles, by mass percentage, includes: 15-25% zero-valent iron, 9.5-15% zero-valent aluminum, and 30-50% iron and aluminum oxides. The specific surface area of ​​the red mud-based iron-aluminum modified bimetallic magnetic functional materials reaches 30-100 m². 2 / g, pore size 55~125 Å, pore volume 0.09~0.15 cm³ 3 / g, maximum current is 0.07~0.09 mA, resistance is 65~85 Ω; Steps 2 to 5 include the following steps: Step 2: Divide the red mud into two portions, with a mass ratio of 5:2~3 between the first and second portions; pour the first portion of red mud, biomass pellets, and water into a beaker and then perform ultrasonic vibration and magnetic stirring sequentially to obtain a mixture; Step 3: Pour the mixture into a hydrothermal reactor for hydrothermal reaction to obtain a hydrothermal reaction slurry; pour the second portion of red mud into another hydrothermal reactor for hydrothermal reaction; Step 4: Cool the hydrothermal reaction slurry and the second portion of red mud after hydrothermal reaction to room temperature and then perform solid-liquid separation. The obtained solid phases are dried to obtain the hydrothermal reaction product and the hydrothermal red mud; Step 5: Perform a first thermal stabilization treatment on the hydrothermal reaction product in a tube furnace under a N2 atmosphere to obtain a primary treated product; mix the primary treated product with the hydrothermal red mud and then perform a second thermal stabilization treatment to obtain a secondary treated product; cool, wash, and vacuum dry the secondary treated product sequentially to obtain a bimetallic magnetic functional material.

2. The soil remediation method according to claim 1, characterized in that, The weight ratio of the red mud-based iron-aluminum modified bimetallic magnetic functional material to the area of ​​the soil to be remediated is 1~5:1, g / m². 2 .

3. The soil remediation method according to claim 1, characterized in that, The following steps are also included between step B and step C: Turn over the soil to be repaired after applying the soil remediation agent to ensure that the soil remediation agent is evenly mixed with the soil to be repaired.

4. The soil remediation method according to claim 3, characterized in that, The soil turning process includes the following steps: The soil to be repaired, after being treated with soil remediation agent, is then shallowly tilled and then deeply tilled.

5. The soil remediation method according to claim 4, characterized in that, The shallow turning depth is 15~30 cm.

6. The soil remediation method according to claim 4, characterized in that, The deep turning depth is 35~50 cm.

7. The soil remediation method according to claim 1, characterized in that, The carbon-based material is a carbon rod.

8. The soil remediation method according to claim 1, characterized in that, The red mud-based iron-aluminum modified bimetallic magnetic functional material has mesoporous properties.

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