Red mud-based composite material as well as preparation method and application thereof

Abstract

According to the red mud-based composite material and the preparation method and application thereof, bentonite, red mud and biomass are mixed in a proper amount of water according to the mass ratio of 1: 1: (1-10), and first suspension liquid is formed; drying the first suspension to obtain a precursor of the red mud-based composite material; the precursor is subjected to a carbon thermal reaction at 300-700 DEG C, ferric oxide in the red mud is converted into zero-valent iron, and the red mud-based composite material is obtained. The red mud is alkaline and promotes manganese ions to form insoluble precipitates, the unique structure and ion exchange capacity of the bentonite can effectively solidify the manganese ions, the biomass has a high specific surface area and a developed pore structure, and the manganese ions are physically adsorbed through Van der Waals' force and pore interception; ferric oxide in the red mud is converted into zero-valent iron in the carbothermal reaction process, and the zero-valent iron can catalytically oxidize ammonia nitrogen, so that the red mud-based composite material synchronously solves the problem of combined pollution of manganese and ammonia nitrogen in the soil.

Description

Technical Field

[0001] This application relates to the technical field of soil remediation, and in particular to a red mud-based composite material, its preparation method, and its application. Background Technology

[0002] Soluble manganese ions and ammonia nitrogen contained in electrolytic manganese slag are the main pollutants. During the stacking process, due to the high moisture content (the colloids of iron, magnesium and other hydroxides make it difficult to filter out the water), they can easily migrate into the soil environment through leachate.

[0003] For soil pollution caused by electrolytic manganese slag, relevant technologies mainly employ physical, chemical, and biological methods for remediation. Physical methods include seepage prevention (such as laying impermeable membranes) and soil washing, which remove soluble pollutants from the soil by blocking the migration path of pollutants or by washing them away. Chemical methods utilize adsorbent materials to adsorb and fix manganese ions and ammonia nitrogen. Biological methods involve cultivating functional microorganisms (such as nitrifying bacteria and denitrifying bacteria) to convert ammonia nitrogen, or using manganese oxidizing bacteria to promote the precipitation of manganese ions.

[0004] Although the relevant technologies can alleviate the pollution of electrolytic manganese slag to some extent, they still have significant limitations: most of the relevant materials focus on the treatment of single pollutants and cannot simultaneously solve the problem of compound pollution of manganese and ammonia nitrogen in the soil. Summary of the Invention

[0005] To address the problems existing in the background technology, this application provides a red mud-based composite material, its preparation method, and its application. Bentonite, red mud, and biomass are mixed in an appropriate amount of water at a mass ratio of 1:1:(1-10) to form a first suspension; the first suspension is dried to obtain a precursor of the red mud-based composite material; the precursor undergoes a carbothermic reaction at 300-700℃, converting iron oxide in the red mud into zero-valent iron, ultimately obtaining the red mud-based composite material. The obtained red mud-based composite material can achieve synergistic remediation of manganese ion enrichment and solidification and ammonia nitrogen oxidation in contaminated soil.

[0006] The details are as follows:

[0007] According to a first aspect of this application, a method for preparing a red mud-based composite material is provided, the method specifically comprising the following steps:

[0008] S1. Mix bentonite, red mud and biomass in an appropriate amount of water at a mass ratio of 1:1:(1~10) to form the first suspension;

[0009] S2. Dry the first suspension to obtain the precursor of the red mud-based composite material;

[0010] The precursor undergoes a carbothermic reaction at 300–700°C, converting the iron oxide in the red mud into zero-valent iron, ultimately yielding a red mud-based composite material.

[0011] Optionally, the particle size of the biomass is 250 μm to 400 μm.

[0012] Optionally, the biomass is crop straw, which is selected from one or more of corn straw, wheat straw, rice straw, and sugarcane bagasse.

[0013] Optionally, the particle size of the red mud is 120 μm to 180 μm.

[0014] Optionally, the drying temperature is 60–90°C.

[0015] Optionally, the carbothermic reaction is carried out in an inert gas atmosphere, wherein the inert gas is nitrogen and / or argon.

[0016] Optionally, the carbothermic reaction time is 2 to 6 hours.

[0017] According to a second aspect of this application, a red mud-based composite material is provided, which is obtained according to the preparation method described above.

[0018] According to a third aspect of this application, an application of a red mud-based composite material is provided, which serves as an adsorbent for adsorbing manganese and ammonia nitrogen in soil.

[0019] Optionally, the application includes:

[0020] The adsorbent is added to contaminated soil for remediation; wherein the amount of adsorbent added is 1 wt% to 10 wt% of the contaminated soil.

[0021] When the remediation time reaches 30 days, the removal rate of manganese ions by the adsorbent is not less than 96%; the removal rate of ammonia nitrogen by the adsorbent is not less than 98%.

[0022] Compared with the prior art, this application has the following advantages:

[0023] This application provides a red mud-based composite material, its preparation method, and its application. The preparation method includes the following steps: mixing bentonite, red mud, and biomass in a mass ratio of 1:1:(1-10) in an appropriate amount of water to form a first suspension; drying the first suspension to obtain a precursor of the red mud-based composite material; subjecting the precursor to a carbothermic reaction at 300-700°C, converting iron oxide in the red mud into zero-valent iron, and finally obtaining the red mud-based composite material. The red mud-based composite material obtained by the above preparation method can be used as an adsorbent to adsorb manganese and ammonia nitrogen in soil.

[0024] The method for preparing the red mud-based composite material provided in this application involves mixing bentonite, red mud, and biomass in a mass ratio of 1:1:(1-10) in an appropriate amount of water to form a first suspension; drying the first suspension to obtain a precursor for the red mud-based composite material; subjecting the precursor to a carbothermic reaction at 300-700℃, which converts iron oxide in the red mud into zero-valent iron, ultimately yielding the red mud-based composite material. Red mud is alkaline, promoting the formation of insoluble precipitates of manganese ions. Bentonite's unique structure and ion exchange capacity effectively solidify manganese ions. Biomass, with its high specific surface area and well-developed pore structure, physically adsorbs manganese ions through van der Waals forces and pore retention. Since the iron oxide in the red mud is converted to zero-valent iron during the carbothermic reaction, and zero-valent iron can catalyze the oxidation of ammonia nitrogen, the red mud-based composite material achieves synergistic remediation of manganese ion enrichment and solidification with ammonia nitrogen oxidation, simultaneously solving the problem of combined manganese and ammonia nitrogen pollution in soil.

[0025] In addition, by using a synergistic combination of three types of solid waste—biomass waste, red mud, and bentonite—resource utilization through carbothermic reaction is achieved, simultaneously solving the problems of manganese slag pollution and solid waste disposal. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart illustrating the preparation method of the red mud-based composite material provided in the embodiments of this application is shown;

[0028] Figure 2 The X-ray diffraction (XRD) pattern of red mud provided in the embodiments of this application is shown;

[0029] Figure 3 A scanning electron microscope (SEM) image of the red mud-based composite material provided in the embodiments of this application is shown;

[0030] Figure 4 The graphs showing the results of zero-valent iron content at different pyrolysis temperatures provided in Examples 1-5 of this application are illustrated.

[0031] Figure 5 The diagram shows the reduction rate of leaching concentration of manganese ions and ammonia nitrogen for the red mud-based composite materials provided in Examples 1-5 of this application;

[0032] Figure 6The diagram shows the reduction rate of leaching concentration of manganese ions and ammonia nitrogen for the red mud-based composite materials provided in Examples 1, 6-8 of this application;

[0033] Figure 7 The graph shows the reduction rate of leaching concentration of manganese ions and ammonia nitrogen with different amounts of red mud-based composite materials provided in this application;

[0034] Figure 8 The diagram shows the reduction rate of leaching concentration of manganese ions and ammonia nitrogen for the materials provided in Example 1 and Comparative Examples 1-2 of this application;

[0035] Figure 9 The diagram illustrates the reduction rate of leaching concentrations of manganese ions and ammonia nitrogen with respect to the repair time provided in the embodiments of this application. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. Based on the embodiments of this application, any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the protection scope of this application. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application.

[0037] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of this application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0038] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of this application specification.

[0039] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0040] Soluble manganese ions and ammonia nitrogen are the main pollutants in electrolytic manganese slag. During storage, due to its high moisture content (the presence of colloids containing iron and magnesium hydroxides makes it difficult to filter out the water), it easily migrates into the soil environment through leachate. Studies have shown that the total manganese concentration in leachate can reach 1818 mg / L, and the ammonia nitrogen concentration can reach 548 mg / L, far exceeding the limits of the Integrated Wastewater Discharge Standard (GB8978-1996). Once these pollutants enter the soil, they lead to the deterioration of soil physicochemical properties. Accumulated manganese ions in the soil can inhibit plant growth and be enriched through the food chain, while ammonia nitrogen can cause soil acidification or alkalization, disrupting the soil microbial community structure. Especially in karst areas, where the soil cover is thin and has poor pollution protection, pollutants can quickly infiltrate and spread through karst channels, further expanding the pollution range and posing a serious threat to the surrounding ecosystem.

[0041] For soil pollution caused by electrolytic manganese slag, relevant technologies mainly employ physical, chemical, and biological methods for remediation. Physical methods include seepage prevention (such as laying impermeable membranes) and soil washing, which remove soluble pollutants from the soil by blocking the migration pathways of pollutants or by leaching. Chemical methods utilize adsorbent materials to adsorb and fix manganese ions and ammonia nitrogen. For example, single biochar adsorbs pollutants through its porous structure, and red mud-bentonite binary composite materials reduce the pollutant content in the soil through ion exchange and complexation. Biological methods involve cultivating functional microorganisms (such as nitrifying and denitrifying bacteria) to convert ammonia nitrogen, or using manganese oxidizing bacteria to promote manganese ion precipitation. In addition, some technologies combine material modification methods, such as acid-base activation of biochar to increase its adsorption capacity and enhance the removal efficiency of pollutants in the soil.

[0042] Although the relevant technologies can alleviate the pollution of electrolytic manganese slag to some extent, they still have significant limitations:

[0043] Firstly, existing materials mostly focus on the treatment of single pollutants. For example, single biochar focuses on the adsorption of manganese ions, and red mud-bentonite composite materials have limited removal effects on ammonia nitrogen, making it difficult to simultaneously solve the problem of combined pollution of manganese and ammonia nitrogen in soil.

[0044] Secondly, the synergistic effect of waste materials is not fully utilized. Most technologies use single or simple binary composite adsorbents and fail to utilize the compositional characteristics of electrolytic manganese slag or other industrial solid wastes to build an efficient synergistic treatment system, resulting in high material costs and low resource utilization.

[0045] Third, the technology has poor applicability in complex environments (such as karst areas), and it is difficult to cope with the rapid migration of pollutants in highly permeable soils. It is also not effective in the deep remediation of long-term contaminated sites. In addition, it has problems such as high treatment costs and difficulty in large-scale application, and cannot meet the needs of efficient, economical and synergistic treatment of soil contaminated by electrolytic manganese slag.

[0046] In order to overcome the difficulty in simultaneously solving the problem of combined pollution of manganese and ammonia nitrogen in soil in related technologies, in view of this, firstly, this application provides a method for preparing red mud-based composite materials; Figure 1 A flowchart illustrating the preparation method of the red mud-based composite material provided in this application is shown; as follows: Figure 1 As shown, the preparation method specifically includes the following steps:

[0047] S1. Mix bentonite, red mud and biomass in an appropriate amount of water at a mass ratio of 1:1:(1~10) to form the first suspension;

[0048] S2. Dry the first suspension to obtain the precursor of the red mud-based composite material;

[0049] The precursor undergoes a carbothermic reaction at 300–700°C, converting the iron oxide in the red mud into zero-valent iron, ultimately yielding a red mud-based composite material.

[0050] Figure 2 The X-ray diffraction (XRD) pattern of red mud provided in the embodiments of this application is shown; from Figure 2 As can be seen from the data, the red mud used in this application contains abundant iron, mainly in the form of Fe2O3.

[0051] It should be noted that the mass ratio of bentonite, red mud, and biomass is 1:1:(1-10). For example, this ratio can be any one of 1:1:1, 1:1:2, 1:1:3, 1:1:5, 1:1:7, or 1:1:10, or any combination thereof. By controlling the mass ratio of bentonite, red mud, and biomass to 1:1:(1-10), the density of active sites in the three raw materials can be maximized, achieving simultaneous adsorption of manganese and ammonia nitrogen. Biomass is agricultural waste; increasing its mass proportion can reduce raw material costs while simultaneously realizing the circular economy value of "treating waste with waste."

[0052] It should also be noted that the precursor undergoes a carbothermic reaction at 300℃ to 700℃. For example, the temperature of the carbothermic reaction can be one or any two of 300℃, 400℃, 500℃, 600℃, and 700℃.

[0053] It should be noted that when a carbothermic reaction occurs at 300–700℃, lignin and cellulose in biomass decompose, forming a well-developed microporous-mesoporous structure, significantly increasing the specific surface area. Furthermore, biomass at these temperatures can be converted into biochar. Biochar not only provides a highly efficient adsorption pore foundation for red mud-based composite materials, but also reacts with the iron oxide in red mud to generate zero-valent iron. This zero-valent iron triggers a Fenton-like effect, catalyzing the oxidation of ammonia nitrogen and the oxidation of NH4+ by hydroxyl radicals (·OH).+ →N2 promotes the metabolism of nitrifying microorganisms and enhances denitrification.

[0054] It should be noted that bentonite possesses a unique layered silicate structure, which provides a framework for composite materials. Bentonite loses its interlayer bound water at temperatures between 300℃ and 700℃, increasing the interlayer spacing and enhancing its ion exchange capacity. Red mud enhances metal adsorption sites; metal oxides in red mud (such as Fe2O3 and Al2O3) may undergo crystal transformations (e.g., the conversion of α-Fe2O3 to γ-Fe2O3) at temperatures between 300℃ and 700℃, increasing their complexation activity for manganese ions. Temperatures below 300℃ cannot activate this structure, while temperatures above 700℃ cause the layered structure of bentonite to collapse and the metal oxides in the red mud to sinter, thus reducing activity.

[0055] The method for preparing the red mud-based composite material provided in this application involves mixing bentonite, red mud, and biomass in a mass ratio of 1:1:(1-10) in an appropriate amount of water to form a first suspension; drying the first suspension to obtain a precursor for the red mud-based composite material; subjecting the precursor to a carbothermic reaction at 300-700℃, which converts iron oxide in the red mud into zero-valent iron, ultimately yielding the red mud-based composite material. Red mud is alkaline, promoting the formation of insoluble precipitates of manganese ions. Bentonite's unique structure and ion exchange capacity effectively solidify manganese ions. Biomass, with its high specific surface area and well-developed pore structure, physically adsorbs manganese ions through van der Waals forces and pore retention. Since the iron oxide in the red mud is converted to zero-valent iron during the carbothermic reaction, and zero-valent iron can catalyze the oxidation of ammonia nitrogen, the red mud-based composite material achieves synergistic remediation of manganese ion enrichment and solidification with ammonia nitrogen oxidation, simultaneously solving the problem of combined manganese and ammonia nitrogen pollution in soil.

[0056] In some embodiments, the biomass has a particle size of 250 μm to 400 μm.

[0057] It should be noted that the particle size of biomass is 250μm to 400μm. For example, the particle size of biomass can be one or any two of the following: 250μm, 270μm, 290μm, 300μm, 320μm, 350μm, 380μm, and 400μm.

[0058] It should also be noted that before the bentonite, red mud and biomass are mixed in an appropriate amount of water to form the first suspension, the following steps are taken: the above biomass is first washed, dried and crushed to obtain pretreated biomass, and the target particle size of the above pretreated biomass is 250μm to 400μm.

[0059] In practice, the biomass material is rinsed with clean water to remove impurities attached to it. The cleaned biomass material is then dried and pulverized to obtain pretreated biomass with a target particle size of 250μm to 400μm. The pretreated biomass is then mixed with bentonite, red mud and water to form a first suspension.

[0060] In this embodiment, the particle size of the biomass is controlled between 250 μm and 400 μm. On the one hand, this improves the pyrolysis efficiency in the carbothermic reaction; the smaller particle size of the pulverized biomass material allows for more uniform heating, enabling faster and more even heat transfer to the interior of the biomass during pyrolysis, avoiding localized overheating or incomplete pyrolysis caused by excessively large material blocks. On the other hand, it enhances reactivity; the increased specific surface area of ​​the pulverized biomass material provides more reactive sites, promoting the pyrolysis reaction. Finally, the biomass also forms abundant pores; the pulverized biomass is more likely to form a rich porous structure during pyrolysis, which further improves the adsorption capacity and water retention performance of the biochar.

[0061] In some embodiments, the biomass is crop straw, which is selected from one or more of corn straw, wheat straw, rice straw, and sugarcane bagasse.

[0062] In this embodiment, crop straw is selected as the biomass raw material. Rich in cellulose, hemicellulose, and lignin, it can be pyrolyzed to form a biochar-based component with abundant porous structures (micropores and mesopores) and numerous polar functional groups (hydroxyl, carboxyl, and carbonyl groups). The porous structure provides physical adsorption sites for manganese ions and ammonia nitrogen (polar molecules), while the polar functional groups enhance the capture capacity of these two pollutants through chemical adsorption mechanisms such as ion exchange and hydrogen bonding. This synergizes with the ion exchange performance of bentonite and the metal complexing properties of red mud, achieving highly efficient removal of complex pollutants.

[0063] Furthermore, corn stalks, wheat stalks, rice stalks, and sugarcane bagasse are all major waste products generated in agricultural production. They are widely available, produced in huge quantities (for example, my country's annual crop straw production exceeds 1 billion tons), and are inexpensive to obtain. Using these types of straw as raw materials can reduce the cost of composite material preparation, while also reducing environmental pollution caused by the burning or indiscriminate dumping of agricultural waste. This aligns with the circular economy concept of "treating waste with waste" and enhances the potential for large-scale application of the technology.

[0064] In some embodiments, the particle size of the red mud is 120 μm to 180 μm.

[0065] It should be noted that the particle size of red mud is 120μm to 180μm. For example, the particle size of red mud can be one or any two of the following: 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, and 180μm.

[0066] It should be noted that before the bentonite, red mud and biomass are mixed in an appropriate amount of water to form the first suspension, the red mud is first dried, crushed and screened to obtain pretreated red mud. The target particle size of the pretreated red mud is 120μm to 180μm.

[0067] In practice, the red mud is dried and then crushed to obtain pretreated red mud with a target particle size of 120μm to 180μm; the above biomass is mixed with bentonite, pretreated red mud and water to form a first suspension.

[0068] In this embodiment, when the red mud particle size is controlled between 120 μm and 180 μm, the red mud can react more fully with bentonite and biomass materials, significantly increasing its specific surface area and exposing more surface active sites (such as metal oxides and hydroxyl groups). These active sites can enhance the adsorption capacity for pollutants such as manganese ions and ammonia nitrogen through complexation and precipitation. If the particle size is greater than 180 μm, the red mud has low surface energy and few active sites, resulting in insufficient reaction contact area and a decrease in the capture efficiency of pollutants. If the particle size is less than 120 μm, although the surface activity is high, particle agglomeration is prone to occur, which reduces the effective reaction interface and may increase the energy consumption and cost in the material preparation process.

[0069] In some embodiments, the drying temperature is 60–90°C.

[0070] It should be noted that the drying temperature is 60–90°C. For example, the drying temperature can be one or any two of 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C. Preferably, it is 75°C–85°C.

[0071] It should be noted that before drying the first suspension, the process includes: ultrasonically treating the first suspension, then stirring it evenly to form a second suspension, and drying the second suspension at 60–90°C to obtain the precursor; the ultrasonic treatment time is 10–60 min; and the stirring time is 1–5 h. For example, the ultrasonic treatment time can be any one or a combination of 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 50 min, and 60 min. For example, the stirring time can be any one or a combination of 1 h, 2 h, 3 h, 4 h, and 5 h.

[0072] In practice, prioritizing ultrasonication of bentonite for 10–60 minutes allows it to easily stack into micron-sized aggregates in water. Ultrasonic cavitation (localized high temperature and pressure) causes it to peel off into single-layer / single-layer silicate sheets (thickness ≈ 1 nm), increasing the specific surface area by 5–10 times. Adding red mud and biomass and continuing ultrasonication for 10–60 minutes reduces the red mud particles from 120–180 μm to approximately 20 μm, fully exposing the pores of the biochar and improving the interfacial bonding strength of the composite material. Then, the three materials are stirred for 1–5 hours. Under shear force, the bentonite suspension (negatively charged) coats the red mud (positively charged) and straw (negatively charged), forming a "bentonite-red mud-straw" core-shell structure. During stirring, the Fe content of the red mud… 3+ It forms a complex with oxygen-containing functional groups (-COOH, -OH) on the surface of biochar, facilitating subsequent co-pyrolysis to generate zero-valent iron (Fe). 0 Lay the foundation.

[0073] In this embodiment, the drying temperature is 60–90°C, which is below the boiling point of water. This allows for slow evaporation of moisture, forming interconnected mesopores (2–50 nm), thus preventing violent boiling from damaging the bentonite-red mud coating. Soluble alkali (Na₂O) in the red mud migrates to the surface at temperatures above 90°C; drying at 60–90°C locks it within the bentonite layers, reducing the risk of alkaline melting and pore blockage during pyrolysis.

[0074] In some embodiments, the carbothermic reaction is carried out in an inert gas atmosphere, wherein the inert gas is nitrogen and / or argon.

[0075] In practice, the inert gas can be nitrogen, argon, or a combination of both. The prepared precursor is placed in a tube furnace and sintered at 300℃ to 700℃ under the aforementioned inert atmosphere to form a red mud-based composite material.

[0076] In this embodiment, biomass (such as crop straw) is rich in organic components such as cellulose and hemicellulose, which are easily oxidized and decomposed at high temperatures (generating CO2, H2O, etc.). An inert gas isolates oxygen, preventing the biomass from being over-oxidized and losing its carbonaceous structure during the carbothermic process, thus ensuring its transformation into biochar with abundant pores and functional groups. Simultaneously, the inert environment retains the carbon elements and some polar functional groups (such as hydroxyl and carboxyl groups) in the biomass, providing the composite material with the active sites required for adsorbing pollutants.

[0077] In the carbothermic reaction, the reducing carbon (such as elemental carbon and volatile organic compounds) produced by biomass decomposition can react with the metal oxide Fe2O3 in red mud to generate zero-valent iron, further enhancing the material's chemical adsorption or precipitation capacity for manganese ions and ammonia nitrogen pollutants. Simultaneously, the inert atmosphere stabilizes the interlayer structure of bentonite, preventing its collapse due to oxidation at high temperatures, ensuring the retention of interlayer pores, and forming a hierarchical porous structure with the pores of red mud and biochar, thereby increasing the specific surface area and adsorption capacity of the composite material.

[0078] In some embodiments, the carbothermic reaction time is 2 to 6 hours.

[0079] It should be noted that the carbothermic reaction time is 2–6 hours. For example, the carbothermic reaction time is one or any two of the following: 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours. The essence of the carbothermic reaction is that the biochar produced by biomass pyrolysis acts as a reducing agent, reacting with the metallic Fe2O3 in the red mud, and simultaneously interacting with the interlayer structure of bentonite (such as intercalation and bonding).

[0080] In this embodiment, by controlling the carbothermic reaction time to 2-6 hours, biomass is fully converted into biochar, and the active metal oxide Fe2O3 in red mud is effectively reduced. The interlayer pores of bentonite and the pores of biochar and red mud form a connected hierarchical pore structure, thereby maximizing the synergistic repair performance of the composite material for manganese ions and ammonia nitrogen.

[0081] Secondly, this application provides a red mud-based composite material, which is obtained according to the preparation method described above.

[0082] Figure 3 This paper shows a scanning electron microscope (SEM) image of the red mud-based composite material provided in an embodiment of this application. Figure 3 a~ Figure 3 e represents the SEM images of red mud-based composite materials obtained at carbothermal reaction temperatures of 300℃, 400℃, 500℃, 600℃, and 700℃. The images show that as the carbothermal reaction temperature (pyrolysis temperature) increases, the porosity of the red mud-based composite material becomes richer, and the composite of red mud, bentonite, and biomass materials becomes more complete. The specific results of the pore size and specific surface area of ​​the red mud-based composite material are shown in Table 1. Table 1 shows that after the precursor undergoes a carbothermal reaction at 300–700℃, the specific surface area increases with increasing reaction temperature, reaching 200 m² at 700℃. 2 The red mud-based composite material formed at a density of 6g or more has a mesoporous-microporous structure (2-50nm), which better retains and physically adsorbs manganese ions.

[0083] Table 1

[0084]

[0085] Thirdly, this application provides an application of a red mud-based composite material, which is used as an adsorbent to adsorb manganese and ammonia nitrogen in soil.

[0086] In some implementations, the application includes:

[0087] The adsorbent is added to contaminated soil for remediation; wherein the amount of adsorbent added is 1 wt% to 10 wt% of the contaminated soil.

[0088] When the remediation time reaches 30 days, the removal rate of manganese ions by the adsorbent is not less than 96%; the removal rate of ammonia nitrogen by the adsorbent is not less than 98%.

[0089] It should be noted that the amount of adsorbent added is 1 wt% to 10 wt% of the contaminated soil; for example, the amount of adsorbent added can be one or any two of the following: 1 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% of the contaminated soil.

[0090] In this embodiment, the adsorbent simultaneously regulates the physicochemical properties of the soil (structural improvement and fertility enhancement). The biomass in the adsorbent serves as a microbial carrier, providing a carbon source for microorganisms, reconstructing the soil microecology, and overcoming the limitations of single passivation / adsorption remediation. This achieves synergistic physicochemical-biological remediation, specifically targeting Mn in manganese-contaminated soil. 2+ Curing and NH4 + Synergistic remediation through -N oxidation simultaneously achieves the triple goals of heavy metal solidification, ammonia nitrogen oxidation, and soil ecological restoration.

[0091] In this embodiment, to enable those skilled in the art to more clearly understand this application, the following embodiments will be used to describe in detail a red mud-based composite material, its preparation method, and its application.

[0092] Example 1

[0093] Step (1): Wheat straw is used as biomass material. It is rinsed with clean water to remove impurities attached to the biomass. The washed wheat straw is dried and then crushed to obtain pretreated biomass of 300-400 μm.

[0094] Step (2): After drying the red mud, crush and sieve it to obtain pretreated red mud with a diameter of 150 μm;

[0095] Step (3): Add 50g of bentonite to 2L of deionized water to make a bentonite suspension, and sonicate the suspension in an ultrasonic instrument for 30min. Then, mix 50g of powdered pretreated red mud and 50g of pretreated biomass and add them to the bentonite suspension to form the first suspension. Continue to sonicate for 30min, and then stir with a magnetic stirrer for 2h to obtain the second suspension. Dry the second suspension in an 80℃ oven to obtain the precursor.

[0096] Step (4): The prepared precursor is placed in a tube furnace and carbothermally reacted at 700℃ under a nitrogen atmosphere for 2 hours to finally obtain the red mud-based composite material.

[0097] Examples 2-5

[0098] The differences between Examples 2-5 and Example 1 are as follows:

[0099] The reaction temperatures in step (4) were adjusted to 300℃, 400℃, 500℃, and 600℃, respectively.

[0100] The remaining implementation steps and dosages are the same as in Example 1, and the red mud-based composite material is obtained.

[0101] Examples 6-8

[0102] The differences between Examples 6-8 and Example 1 are as follows:

[0103] The mass ratios of bentonite, red mud, and biomass in step (3) are adjusted to 1:1:3, 1:1:5, and 1:1:10, respectively.

[0104] The remaining implementation steps and dosages are the same as in Example 1, and the red mud-based composite material is obtained.

[0105] Comparative Example 1

[0106] The difference compared to Example 1 is as follows:

[0107] Only wheat straw is used as biomass, without the addition of bentonite and red mud.

[0108] The remaining implementation steps and dosages are the same as in Example 1, and biomass materials are obtained.

[0109] Comparative Example 2

[0110] The difference compared to Example 1 is as follows:

[0111] Only bentonite and red mud are used, with no biomass added.

[0112] The remaining implementation steps and dosages are the same as in Example 1, to obtain bentonite-red mud material.

[0113] Zero-valent iron content test

[0114] The red mud-based composite materials from Examples 1-5 were subjected to copper ion chemical titration, which consumed Cu... 2+ The amount of zero-valent iron in the red mud-based composite material was inferred by reverse calculation, and the final result was obtained by three repeated tests.

[0115] Figure 4 The following diagrams show the results of zero-valent iron content at different pyrolysis temperatures provided in Examples 1-5 of this application; as shown. Figure 4 As shown, the content of zero-valent iron in the red mud-based composite material increases with the increase of pyrolysis temperature, and reaches 45 mg / g when the pyrolysis temperature is 700℃.

[0116] Tests on adsorption of manganese and ammonia nitrogen in soil

[0117] A soil sample was taken from a manganese slag contaminated area in Guangxi. The soil contained Mn. 2+ The concentration was 4706.36 mg / kg, NH4 + The concentration was 472 mg / kg, Mn 2+ The leaching concentration was 15.84 mg / L, NH4 + The leaching concentration was 1.2 mg / L. The red mud-based composite materials from Examples 1 to 8 were used as adsorbents and added to manganese slag-contaminated soil at a dosage of 5%. The reduction rate of leaching concentration of manganese ions and ammonia nitrogen in manganese slag-contaminated soil by the red mud-based composite materials (adsorbents) was investigated.

[0118] Figure 5 The diagram shows the reduction rate of leaching concentration of manganese ions and ammonia nitrogen for the red mud-based composite materials provided in Examples 1-5 of this application; Figure 6 The diagram shows the reduction rate of leaching concentration of manganese ions and ammonia nitrogen for the red mud-based composite materials provided in Examples 1, 6-8 of this application; as shown. Figure 5 , 6 As shown, the leaching concentration reduction rate of manganese ions and ammonia nitrogen increases with increasing pyrolysis temperature. When the reaction temperature is 300℃, the leaching concentration reduction rate of manganese ions and ammonia nitrogen is only 65% ​​and 48%, respectively, while at 700℃, the leaching concentration reduction rate reaches 96% and 98%, respectively. With increasing biomass mass, the leaching concentration reduction rate of manganese ions and ammonia nitrogen decreases. When the mass ratio of bentonite, red mud, and biomass is 1:1:1, the leaching concentration reduction rate of manganese ions and ammonia nitrogen reaches 96% and 98%, respectively, while at a mass ratio of 1:1:10, the leaching concentration reduction rate is only 75% and 70%, respectively.

[0119] In summary, when the carbothermic reaction temperature is 700℃ and the mass ratio of bentonite, red mud and biomass is 1:1:1, the leaching concentration reduction rate of manganese ions and ammonia nitrogen remains at a high level.

[0120] The red mud-based composite material from Example 1 was added to contaminated soil at concentrations of 1%, 3%, 5%, and 10%, respectively. The reduction rates of leaching concentrations of manganese ions and ammonia nitrogen in manganese slag-contaminated soil by different addition amounts of the red mud-based composite material were investigated. The results are as follows: Figure 7 As shown, when the addition amount is 1-5%, the leaching concentration reduction rate of manganese ions and ammonia nitrogen increases with the addition of composite materials, reaching the highest at 5% addition amount, which are 96% and 98% respectively. When the addition amount continues to increase, the leaching concentration reduction rate of manganese ions and ammonia nitrogen decreases or tends to stabilize. Therefore, the red mud-based composite material with an addition amount of 5% has the best effect on reducing the leaching concentration of manganese ions and ammonia nitrogen in manganese slag contaminated soil.

[0121] The materials obtained in Example 1 and Comparative Examples 1-2 were added at a 5% concentration to test the reduction rate of leaching concentrations of manganese ions and ammonia nitrogen in manganese slag contaminated soil. The results are as follows: Figure 8 As shown in the figure, when the material contains only biomass or bentonite-red mud, under the same conditions, the removal rates of manganese and ammonia nitrogen by single biochar are 38.45% and 45.26%, respectively; the removal rates of manganese and ammonia nitrogen by the red mud and bentonite mixture are 43.45% and 65.34%, respectively; while the red mud-based composite material prepared using the red mud, bentonite, and biomass in this application achieves removal rates of 96.54% and 98.26%, respectively. Therefore, the red mud-based composite material prepared using the red mud, bentonite, and biomass mixture in this application has a synergistic remediation effect on manganese and ammonia nitrogen in contaminated soil, and its effect is superior to that of comparative examples 1-2.

[0122] Figure 9 The diagram shows the reduction rate of leaching concentrations of manganese ions and ammonia nitrogen with respect to the repair time provided in Example 1 of this application, as shown. Figure 9 As shown, with the increase of remediation time, the leaching concentration reduction rate of manganese ions and ammonia nitrogen gradually increased. When the remediation time reached 30 days, the removal rates of manganese and ammonia nitrogen were 96.54% and 98.26%, respectively. Moreover, through continuous monitoring for up to 180 days, the leaching concentration reduction rate remained stable. Therefore, the red mud-based composite material can stabilize and solidify manganese ions and ammonia nitrogen in the soil, and the synergistic remediation effect is significant.

[0123] This application focuses on manganese slag-contaminated soil. Targeting the characteristics of manganese slag-contaminated soil, it selectively uses localized agricultural and forestry fiber waste as raw material for three-dimensional porous biochar. This biochar is then combined with red mud and bentonite through co-pyrolysis to efficiently enrich and solidify manganese ions, adhering to the concept of "treating waste with waste" and achieving resource utilization of solid waste. A red mud-based porous carbothermic composite material is prepared through co-pyrolysis. The carbon in the biochar reacts with the iron oxide in the red mud to generate zero-valent iron, which produces hydroxyl radicals through a Fenton-like reaction, oxidizing NH4+ to NO3- or promoting the metabolism of nitrifying microorganisms, thereby achieving efficient removal of ammonia nitrogen. The prepared red mud-based composite material can regulate the physicochemical properties of manganese slag-contaminated soil, improve soil structure, increase soil fertility, provide a carbon source for soil microorganisms, reconstruct the soil ecology, and provide technical support for the remediation of manganese slag-contaminated soil.

[0124] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0125] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to this application.

[0126] The foregoing has provided a detailed description of a red mud-based composite material, its preparation method, and its applications. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a red mud-based composite material, characterized in that, The preparation method specifically includes the following steps: S1. Mix bentonite, red mud and biomass in an appropriate amount of water at a mass ratio of 1:1:(1~10) to form the first suspension; S2. Dry the first suspension to obtain the precursor of the red mud-based composite material; The precursor undergoes a carbothermic reaction at 300–700°C, converting the iron oxide in the red mud into zero-valent iron, ultimately yielding a red mud-based composite material.

2. The preparation method according to claim 1, characterized in that, The biomass has a particle size of 250 μm to 400 μm.

3. The preparation method according to claim 2, characterized in that, The biomass is crop straw, which is selected from one or more of corn straw, wheat straw, rice straw, and sugarcane bagasse.

4. The preparation method according to claim 1, characterized in that, The red mud has a particle size of 120μm to 180μm.

5. The preparation method according to claim 1, characterized in that, The drying temperature is 60–90°C.

6. The preparation method according to claim 1, characterized in that, The carbothermic reaction is carried out in an inert gas atmosphere, wherein the inert gas is nitrogen and / or argon.

7. The preparation method according to claim 1, characterized in that, The carbothermic reaction time is 2 to 6 hours.

8. A red mud-based composite material, characterized in that, The composite material is obtained by the preparation method according to any one of claims 1-7.

9. An application of the composite material according to claim 8, characterized in that, The composite material is used as an adsorbent to adsorb manganese and ammonia nitrogen in the soil.

10. The application according to claim 9, characterized in that, The applications include: The adsorbent is added to contaminated soil for remediation; wherein the amount of adsorbent added is 1 wt% to 10 wt% of the contaminated soil. When the remediation time reaches 30 days, the removal rate of manganese ions by the adsorbent is not less than 96%; the removal rate of ammonia nitrogen by the adsorbent is not less than 98%.

Images