Method for preparing cementing material from thermally activated and modified red mud

Abstract

The invention discloses a method for preparing a cementing material from thermally activated and modified red mud. The method comprises the following steps: 1, selecting red mud, drying the red mud, removing free moisture, and grinding to a target particle size; placing the dried red mud in a high-temperature furnace for calcining; after sintering, cooling the red mud to room temperature by air cooling; and 2, synergistically preparing the cementing material from the pretreated red mud, gypsum and carbide slag. According to the invention, through calcining treatment, a silicon-aluminum mineral structure in the red mud is destroyed and is converted into a high-activity amorphous state, so that the reaction activity of the red mud is remarkably improved; meanwhile, the industrial solid waste red mud is fully utilized, so that the pollution of the industrial solid waste red mud to the environment is reduced, and the cyclic utilization of resources is realized; besides, the red mud subjected to thermal activation modification can efficiently react with an exciting agent, a cementing material with excellent mechanical properties and good durability is prepared, and a reliable technical path is provided for high value-added application of the red mud.

Description

Technical Field

[0001] The present invention belongs to the technical field of red mud activity, and particularly relates to a method for preparing a cementitious material from thermally activated modified red mud. Background Art

[0002] The aluminosilicate structure in Bayer red mud is stable and has low activity. Although domestic and foreign scholars have made certain progress in the thermal activation research of red mud, the composition of red mud varies greatly under different bauxite sources and process conditions, which makes the activation methods and conditions of red mud highly uncertain.

[0003] Due to the general characteristics of high Fe 2 O 3 and Al 2 O 3 contents, low alkali content and low CaO content in Bayer red mud, its activity is insufficient. When directly applied to cement, building materials, soil remediation, etc., it often shows problems such as "difficulty in quickly forming a stable cementitious property with other materials" or "easy to produce efflorescence". In addition, different bauxite sources and different refining processes result in differences in the particle size distribution and mineral phase composition of Bayer red mud, further increasing the difficulty in large-scale industrial utilization.

[0004] Li Shaochun et al. studied the effects of different activation methods on the properties of cement-based materials by mechanically activating and thermally activating Bayer red mud respectively. The results showed that thermal activation had a more significant effect than mechanical activation. High-temperature treatment caused partial dehydroxylation reactions of some minerals in red mud, destroying its stable chemical structure, thus loosening the silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron structures, and forming a metastable aluminosilicate structure. The formation of this structure significantly improved the activity of red mud, providing an important basis for the preparation of high-performance cementitious materials. In contrast, although mechanical activation can, to a certain extent, destroy the surface structure of red mud particles, its effect on the internal stable aluminosilicate structure is limited, so the overall effect is not as significant as thermal activation.

[0005] From the existing research results, the low-activity problem of red mud has become the key bottleneck restricting its efficient utilization. As an industrial waste residue generated during alumina production, red mud has the characteristics of huge output and complex composition. Due to its low natural activity, red mud faces many difficulties in the process of resource utilization, restricting its wide application in the fields of building materials, environmental protection, etc. Therefore, improving the activity of red mud is the primary task for realizing its large-scale resource utilization.

[0006] In summary, when the Bayer red mud with low activity is directly applied to the preparation of cementitious materials, its performance is limited. At present, when preparing cementitious materials by thermally activating and modifying red mud in combination with other solid wastes, the exploration of conditions such as the thermal activation temperature and time of Bayer red mud is not systematic. The influence of different condition combinations on the activation of red mud and other solid wastes has not been fully studied. The selection of solid waste types is limited, and there is a lack of exploration of new or potential solid wastes. The synergistic mechanism is not clear. Summary of the Invention

[0007] In order to overcome the above defects existing in the prior art, the purpose of the present invention is to provide a method for preparing cementitious materials with thermally activated and modified red mud, which has the characteristics of simple process, low cost, environmental protection, high efficiency and excellent performance. Through calcination treatment, the silicon-aluminum mineral structure in the red mud is destroyed and transformed into a highly active amorphous form, significantly improving the reaction activity of the red mud. At the same time, this method makes full use of the industrial solid waste red mud, reduces its environmental pollution, and realizes the recycling of resources. In addition, the thermally activated and modified red mud can react efficiently with activators to prepare cementitious materials with excellent mechanical properties and good durability, providing a reliable technical path for the high-value application of red mud.

[0008] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0009] A method for preparing cementitious materials with thermally activated and modified red mud, comprising the following steps;

[0010] Step 1: Select red mud, perform drying treatment on the red mud to remove free moisture, and grind it to the target particle size; place the dried red mud in a high-temperature furnace for calcination; after calcination, cool the red mud to room temperature by air cooling;

[0011] Step 2: Co-prepare cementitious materials with the pretreated red mud, gypsum and carbide slag.

[0012] In the said Step 1, calcine at a set temperature of 800 - 1000 °C for a certain time of 2 - 4 hours, and control the heating rate at 10 - 15 °C / min during the calcination process.

[0013] Further, in the said Step 1, calcine at a set temperature of 800 °C for a certain time of 2 hours, and control the heating rate at 10 °C / min during the calcination process.

[0014] In the said Step 1, the selected Bayer red mud has a slightly higher calcium content, and the components are specifically in a mass ratio of: Fe 2 O 3 : 10 - 30%; Al 2 O 3 : 20 - 30%; SiO 2 : 20 - 30%; CaO: 15 - 25%; TiO 2: 2 - 10% Na 2 O: 2 - 6% Others: 1 - 5% (including MgO, K 2 O, etc.).

[0015] The specific operation steps of Step 1 are as follows: Step (1): Evenly spread the red mud sample on the tray with a thickness not exceeding 2 cm to ensure uniform drying; preheat the oven:

[0016] Step (2): Preheat the oven to 105 °C and keep the temperature stable during the drying process;

[0017] Step (3): Put the selected red mud into the oven and start timing; during the drying process, the red mud can be turned over every once in a while (such as every 6 hours) to ensure uniform drying.

[0018] Step (4): End the drying: After 24 hours, turn off the oven and take out the red mud; put the dried red mud into a desiccator to cool to room temperature to avoid moisture absorption.

[0019] In Step 1, the target particle size is 50 - 300 μm. This range achieves a balance among activity, cost, and process feasibility and is suitable for most industrial applications.

[0020] The characteristics of the red mud after pretreatment in Step 1 are as follows: Thermal activation destroys the crystal structures of silicon and aluminum minerals in the red mud, transforming them from ordered crystals to amorphous forms, significantly improving the reaction activity of the red mud. Calcination and subsequent grinding treatments refine the red mud particles, significantly increasing the specific surface area and providing more active sites for subsequent chemical reactions. The dissolution rates of elements such as silicon and aluminum in the thermally activated red mud increase, making it easier to react with activators to form geopolymers or other cementitious materials. During the thermal activation process, some mineral phases in the red mud (such as cancrinite, hematite, etc.) will undergo phase changes or decomposition to generate new active phases, further enhancing the chemical activity of the red mud. The thermally activated red mud has higher stability and can adapt to different environmental conditions, providing a basis for preparing high-performance all-solid waste red mud-based cementitious materials.

[0021] In Step 2, the mass ratio relationship among red mud, gypsum, and carbide slag is Gypsum: Carbide slag: Thermally activated red mud = 25:17:58. In Step 2, Gypsum: 10 - 100 μm; Carbide slag: 20 - 150 μm.

[0022] The finer gypsum particles (10 - 100 μm) have a larger specific surface area and can react with the active components (such as Al 2 O 3 、SiO 2)Reactions occur to generate cementitious products such as ettringite (AFt). Fine-grained gypsum is more likely to be evenly dispersed in the mixture, avoiding local concentrations that are too high or too low, thereby improving the overall performance of the cementitious material. Gypsum with an appropriate fineness helps to improve the early strength and later strength of the cementitious material.

[0023] Ca(OH) in carbide slag 2 and CaO are key components in the cementitious reaction. Finer particles (20 - 150 μm) can release active components more quickly, promoting the cementitious reaction. Carbide slag particles play a role of micro-aggregate filling in the cementitious material. Particles with an appropriate fineness can fill the voids between red mud particles, improving the density and strength of the material. Fine-grained carbide slag is more likely to be evenly mixed with red mud and gypsum, ensuring the consistency of the reaction.

[0024] The chemical reactions among the components of the cementitious material obtained in Step 2 are synergistic:

[0025] Red mud: After thermal activation at 800 °C, the silicon-aluminum minerals in red mud transform into highly active amorphous forms, providing abundant silicon and aluminum active components.

[0026] Carbide slag: Carbide slag is rich in CaO and can provide a high concentration of Ca 2+ ions in an alkaline environment, promoting the dissolution of silicon-aluminum components and the geopolymerization reaction.

[0027] Gypsum: The addition of gypsum (CaSO 4 ·2H 2 O) not only regulates the sulfur-aluminum ratio of the system but also reacts with aluminum in red mud to form ettringite (AFt), further enhancing the early strength and stability of the material.

[0028] The synergistic effect of the three is reflected in: Red mud provides a silicon-aluminum source, carbide slag provides a calcium source and an alkaline environment, and gypsum regulates the reaction process and generates a strengthening phase, jointly promoting the hydration reaction of the cementitious material and the improvement of mechanical properties.

[0029] Gypsum can be natural gypsum or industrial by-product gypsum (such as desulfurized gypsum), which has a wide source and low cost, meeting the requirements of resource utilization; Carbide slag: Strong alkalinity (pH > 12) can effectively activate the activity of red mud, while inhibiting the dissolution of heavy metal ions in red mud, improving the environmental safety of the material.

[0030] In the cementitious material prepared from red mud, gypsum, and carbide slag, cementitious products such as ettringite (AFt) crystals and C-S-H gels are obtained; the ettringite (AFt) crystals and C-S-H gels are tightly bound by hydrogen bonds and chemical bonds.

[0031] Ettringite: Provides early strength, fills large pores, but may cause expansion.

[0032] C-S-H gel: provides late strength, fills small pores, and enhances durability.

[0033] Ettringite (AFt) crystals and C-S-H gel jointly affect the properties of the cementitious material through synergistic effects and competitive reactions. By optimizing the raw material ratio and curing conditions, the formation of ettringite and C-S-H gel can be regulated to obtain a cementitious material with excellent properties.

[0034] The cementitious material has a dense and uniform structure. The hydration products of the cementitious material are evenly distributed. Ettringite (AFt) crystals are in regular needle-like or columnar shapes, interweaving to form a strong framework structure. A large amount of C-S-H gel is generated and fills the pores, making the overall material present a highly dense microstructure. The size range of ettringite (AFt) crystals is usually 1 - 10 μm (length) and 0.1 - 1 μm (diameter); the crystal size is affected by the raw material ratio, curing conditions, and the activity of red mud, and has an important impact on the early strength, durability, and microstructure of the material. The pores in the cementitious material are mainly formed between red mud, gypsum, carbide slag particles, between ettringite (AFt) crystals and C-S-H gel, in the tiny channels inside the cementitious material, and in the bubble-like cavities inside the cementitious material. The said cementitious material is applied in the construction field.

[0035] Construction material field

[0036] Cement substitute: As a partial or complete substitute for ordinary Portland cement, it is used to prepare building materials such as concrete and mortar, reducing carbon emissions in cement production.

[0037] Geopolymer material: Used to prepare high-performance geopolymer concrete, suitable for building structures, road engineering, and bridge construction, with the characteristics of high strength, corrosion resistance, and high temperature resistance.

[0038] Advantages of the present invention:

[0039] Excellent mechanical properties:

[0040] High strength: The cementitious material has a relatively high compressive strength, capable of meeting the strength requirements of building structures, road engineering, etc.

[0041] Good toughness: The intertwined structure of C-S-H gel and ettringite crystals endows the material with a certain toughness, improving its crack resistance.

[0042] Good microstructure:

[0043] Dense and uniform: SEM images show that the microstructure of the material is dense and uniform, with reasonable distribution of ettringite crystals and C-S-H gel and low porosity

[0044] The crystal growth is good: The ettringite crystals are in regular needle or column shapes, interweaving with each other to form a strong framework structure, which further enhances the mechanical properties of the material.

[0045] The hydration products of the present invention are abundant: XRD and FTIR analyses show that a large amount of ettringite (3CaO·Al 2 O 3 ·3CaSO 4 ·32H 2 O) and C-S-H gel are generated in the material. These hydration products are tightly bonded through hydrogen bonds and chemical bonds, significantly improving the mechanical properties and durability of the material.

[0046] The chemical bond composition is complex: The FTIR spectrum shows that there are vibration peaks of various chemical bonds such as Si-O-Si, Al-O-Si, O-H, H-O-H, SO 4 2- in the material, indicating that components such as silicate, aluminate, and sulfate fully participate in the hydration reaction, forming a complex and stable chemical bond network.

[0047] The porosity is low: Microstructural analysis shows that the C-S-H gel and ettringite crystals almost completely fill the pores in the material, forming a dense structure with low porosity, thereby improving the impermeability and frost resistance of the material.

[0048] The crystal growth is good: The SEM image shows that the ettringite crystals grow well, are in regular needle or column shapes, and are evenly distributed. This crystal structure provides excellent mechanical strength and stability for the material.

[0049] The reaction is sufficient: Microscopic detection shows that the 800°C thermal activation significantly improves the activity of red mud, making its reaction with carbide slag and gypsum more sufficient, and generating a large number of hydration products that help improve the material properties, such as C-S-H gel and ettringite.

[0050] The high-temperature optimization effect: The 800°C thermal activation temperature not only avoids the problem of insufficient reaction at low temperatures but also prevents the destruction of the mineral structure caused by too high temperatures, achieving the best synergistic reaction effect of red mud, carbide slag, and gypsum.

[0051] In summary, the cementitious material prepared by 800°C thermal activation has characteristics such as a dense structure, abundant hydration products, stable chemical bonds, low porosity, and good crystal growth. These microscopic characteristics together endow the material with excellent mechanical properties, durability, and environmental adaptability. Description of the Drawings

[0052] Figure 1 For the basic properties of Bayer red mud: (a) XRD pattern; (b) particle size distribution diagram.

[0053] Figure 2 are the basic properties of carbide slag: (a) XRD pattern; (b) particle size distribution diagram.

[0054] Figure 3 are the basic properties of desulfurized gypsum: (a) XRD pattern; (b) particle size distribution diagram.

[0055] Figure 4 is the compressive strength diagram of the cementitious material.

[0056] Figure 5 is the XRD pattern (a. 3d; b. 28d) of the hydration products of the heat-activated red mud-based multi-solid waste cementitious material.

[0057] Figure 6 is the FTIR pattern (a. 3d; b. 28d) of the hydration products of the heat-activated red mud-based multi-solid waste cementitious material.

[0058] Figure 7 is the SEM image of the cementitious material (28d). Specific implementation manners

[0059] The present invention will be further described in detail below with reference to the accompanying drawings.

[0060] Example 1: Preparation of cementitious material by calcining red mud at 800°C

[0061] The red mud selected in this example has the following composition: Fe 2 O 3 : 19%; Al 2 O 3 : 25%; SiO 2 : 25%; CaO: 18%; TiO 2 ; 5%; Na 2 O: 3%, others: 5% (including MgO, K 2 O, etc.).

[0062] 1. Calcination conditions

[0063] Temperature: 800°C

[0064] Time: 2 hours

[0065] Heating rate: 10°C / min

[0066] Cooling method: air cooling for 25 minutes

[0067] 2. Raw material ratio

[0068] Calcined red mud: 58%

[0069] Gypsum: 25%

[0070] Carbide slag: 17%

[0071] 3. Preparation Process

[0072] Red mud calcination:

[0073] Dry the red mud and then grind it to 100 - 200 μm.

[0074] Put it into a muffle furnace, heat it up to 800 °C at a rate of 10 °C / min, and keep it warm for 2 hours.

[0075] After calcination, cool it in air for 25 minutes.

[0076] Raw material mixing:

[0077] Mix the calcined red mud, gypsum, and carbide slag evenly according to the mass ratio of 25:17:58.

[0078] Add water and stir:

[0079] Add an appropriate amount of water (water - binder ratio 0.6) and stir until it becomes a uniform slurry.

[0080] Molding and curing:

[0081] Pour the slurry into a mold and vibrate it to make it dense.

[0082] Cure it for 28 days at 20 °C and humidity > 90%. Obtain the gel material.

[0083] Example 2: Preparation of cementitious material by calcining red mud at 900 °C

[0084] The selected red mud components in this example are, Fe 2 O 3 : 20%; Al 2 O 3 : 24%; SiO 2 : 26%; CaO: 17%; TiO 2 ; 6%; Na 2 O: 2%, others: 5% (including MgO, K 2 O, etc.).

[0085] 1. Calcination conditions

[0086] Temperature: 900 °C

[0087] Time: 3 hours

[0088] Heating rate: 12 °C / min

[0089] Cooling method: Air cooling for 30 minutes

[0090] 2. Raw material ratio

[0091] Calcined red mud: 58%

[0092] Gypsum: 25%

[0093] Calcium carbide slag: 17%

[0094] 3. Preparation process

[0095] Red mud calcination:

[0096] Dry the red mud and grind it to 50 - 100 μm.

[0097] Put it into a muffle furnace, heat it up to 900 °C at a rate of 12 °C / min, and hold for 3 hours.

[0098] After calcination, cool it in air for 30 minutes.

[0099] Raw material mixing:

[0100] Mix the calcined red mud, gypsum, and calcium carbide slag evenly according to the mass ratio of 25:17:58.

[0101] Add water and stir:

[0102] Add an appropriate amount of water (water - binder ratio 0.6) and stir until a homogeneous slurry is obtained.

[0103] Molding and curing:

[0104] Pour the slurry into a mold and vibrate it to make it dense.

[0105] Cure it for 28 days at 25 °C and humidity > 90%.

[0106] Example 3. Preparation of cementitious material by calcining red mud at 1000 °C

[0107] The red mud selected in this example has the following components: Fe 2 O 3 : 21%; Al 2 O 3 : 25%; SiO 2 : 26%; CaO: 17%; TiO 2 ; 6%; Na 2 O: 2%, others: 3% (including MgO, K 2 O, etc.).

[0108] 1. Calcination conditions

[0109] Temperature: 1000 °C

[0110] Time: 4 hours

[0111] Heating rate: 15 °C / min

[0112] Cooling method: Air cooling for 20 minutes

[0113] 2. Raw material ratio

[0114] Calcined red mud: 58%

[0115] Gypsum: 25%

[0116] Calcium carbide slag: 17%

[0117] 3. Preparation process

[0118] Red mud calcination:

[0119] Dry the red mud and grind it to 200 - 300 μm.

[0120] Put it into a muffle furnace, heat it to 1000 °C at a rate of 15 °C / min, and hold for 4 hours.

[0121] After calcination, air-cool for 20 minutes.

[0122] Raw material mixing:

[0123] Mix the calcined red mud, gypsum, and calcium carbide slag evenly according to the mass ratio of 25:17:58.

[0124] Add water and stir:

[0125] Add an appropriate amount of water (water-binder ratio 0.3) and stir until a uniform slurry is obtained.

[0126] Molding and curing:

[0127] Pour the slurry into a mold and vibrate it to make it dense.

[0128] Cure for 28 days at 30 °C and humidity > 90%. Obtain the gelling material.

[0129] Specific application examples:

[0130] The Bayer red mud (BRM) raw material used in this application is taken from an alumina enterprise in Guizhou. The composition of the red mud raw material is analyzed by X-ray fluorescence spectroscopy, and the results are shown in Table 1. The main components of the red mud include SiO 2 , Al 2 O 3 , CaO, Fe 2 O 3 and Na 2 O, and these components account for more than 89% of the total mass of the red mud. Among them, the CaO content in the red mud reaches 19.52 wt%, which is relatively high compared with general Bayer red mud, but still lower than the CaO content in sintering red mud. The Fe 2 O 3 content is 18.11 wt%, belonging to the category of low-iron red mud. And Na 2The O content is 4.74 wt%, indicating that the red mud has strong alkalinity. Based on the above compositional characteristics, the Bayer red mud has the potential to be used as an alkaline aluminosilicate raw material and has potential feasibility in the preparation of cementitious materials. Through reasonable process development, its effective utilization in the field of cementitious materials can be achieved.

[0131] Table 1 Main chemical components of Bayer red mud

[0132]

[0133]

[0134] XRD analysis was carried out on the Bayer red mud, and its main mineral components include chlorite ((Fe,Al,Mg) 6 (Si,Al) 4 O 10 (OH) 3 ), katoite (Ca 3 Al 2 (SiO 4 )(OH) 8 ), hematite (Fe 2 O 3 ), diaspore (AlOOH), cancrinite (Na 6 Ca 2 (AlSiO 4 ) 6 (CO 3 SO 4 )(OH) 2 ), quartz (SiO 2 ), calcite (CaCO 3 ), kaolinite (Al 2 Si 2 O 5 (OH) 4 ) and gibbsite Al(OH) 3 ; Cancrinite in the red mud is a feldspathoid mineral, generally a carbonate-aluminosilicate containing sodium and calcium. Gibbsite is the small amount of Al(OH) 2 O 3 remaining after extracting Al from bauxite 3 . Laser particle size testing was carried out on the Bayer red mud raw material to analyze its particle size distribution. As can be seen from Figure 1 (b), the particle size of the red mud is distributed between 0.01 and 305 μm, D50 = 8.967 μm, D10 = 1.217 μm, and D90 = 117.694 μm.

[0135] The carbide slag (CS) raw material used in this example is taken from an enterprise in Guizhou. The composition of the carbide slag raw material is analyzed by X-ray fluorescence spectroscopy. The analysis results are shown in Table 2. The main component is CaO, reaching 91.12%. In addition, there is a small amount of SiO 2 and Al 2 O 3 .

[0136] The phase analysis of the carbide slag is carried out, and the results are as shown in Figure 2 (a). The main minerals in the carbide slag raw material are portlandite (Ca(OH) 2 ) and calcite (CaCO 3 ). Among them, the content of portlandite is relatively large and the characteristic peak is strong. The laser particle size test is carried out on the carbide slag raw material to analyze its particle size distribution. As can be seen from Figure 2 (b), the particle size of the carbide slag is distributed between 0.01 - 3080 μm, D50 = 17.807 μm, D10 = 1.523 μm, D90 = 735.028 μm.

[0137] Table 2 Main chemical composition of carbide slag

[0138]

[0139] The desulfurization gypsum (DG) raw material used in this example is taken from a coal-fired power plant in Guizhou. The chemical components SO 3 and CaO have relatively high contents, reaching 52.02% and 42.80% respectively, accounting for 94.82% of the total mass.

[0140] The phase analysis of the desulfurization gypsum raw material is carried out, and the results are as shown in Figure 3 (a). The main mineral in the desulfurization gypsum raw material is hemihydrate gypsum (CaSO 4 ·0.5H 2 O), and the characteristic peak is strong; the laser particle size test is carried out on the desulfurization gypsum raw material to analyze its particle size distribution. As can be seen from Figure 3 (b), the particle size of the desulfurization gypsum is distributed between 0.01 - 3080 μm, D50 = 10.418 μm, D10 = 1.149 μm, D90 = 660.989 μm.

[0141] Table 3 Main chemical composition of desulfurization gypsum

[0142]

[0143] Mix ratio of cementitious materials prepared by synergistically using thermally activated red mud, gypsum and carbide slag, and the specific mix ratios are shown in the following table: The experimental mix ratios used in the experiment are shown in the following table:

[0144] Table 4 Mix ratio of specimens

[0145]

[0146] 1. Compressive strength of thermally activated red mud-based multi-solid waste cementitious materials

[0147] Using thermally activated Bayer red mud, desulfurized gypsum, carbide slag and other industrial solid wastes, a high-volume thermally activated Bayer all-solid waste cementitious material (red mud content is 58%) was prepared, and systematic compressive strength tests were carried out on the prepared cementitious material specimens. The test results show that the compressive strength of this system at different ages (3d, 7d, 28d) is as Figure 4 shown. It is clearly shown in the figure that the thermal activation temperature has a significant impact on the mechanical properties of the cementitious material. As the thermal activation temperature gradually increases, the compressive strength of the thermally activated red mud-based all-solid waste cementitious material shows a trend of first increasing and then decreasing.

[0148] The thermal activation temperature of Bayer red mud has a decisive impact on the compressive strength of the all-solid waste cementitious material. The cementitious activity of unactivated red mud is extremely low, and it is difficult to form effective hydration products; when activated at 800°C, the content of active alumina and silica in red mud is relatively high, and it can form more hydration products with desulfurized gypsum and carbide slag, significantly improving the compressive strength, especially reaching the optimum at 800°C (11.0 MPa at 28 days); 800°C is the optimum activation temperature under the current test conditions, which can maximize the cementitious activity of red mud, improve the mechanical properties of the material, and provide a scientific basis for the resource utilization of red mud. Therefore, the thermal activation temperature of 800°C provides an important technological basis for the preparation of high-performance red mud-gypsum-carbide slag ternary system cementitious materials.

[0149] 2. XRD analysis of thermally activated red mud-based multi-solid waste cementitious materials

[0150] XRD analysis was carried out on the hydration products of the cementitious material specimens of the thermally activated red mud-gypsum-carbide slag ternary solid waste system cured for 3d and 28d, and the results are as Figure 5 shown. By systematically analyzing the hydration products and mineral compositions of the cementitious materials at different ages, it is found that the main hydration products are ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ﹒26H 2 O), C-S-H gel, calcite (CaCO 3 ), gypsum dihydrate (CaSO 4 ﹒2H2 O), quartz (SiO 2 ), hematite (Fe 2 O 3 ), and calcium aluminosilicate (Ca 2 Al 2 SiO 7 ).

[0151] Generally speaking, to optimize the hydration performance of the red mud-based all-solid waste cementitious material, the thermal activation temperature of red mud needs to be controlled at about 800 °C to maximize the promotion of the formation of hydration products, improve the hydration degree in the early and late stages, and thus enhance the mechanical properties of the cementitious material. This research conclusion provides an important theoretical basis for the resource utilization of red mud and the optimized design of cementitious materials.

[0152] 3 FTIR Analysis of Thermally Activated Red Mud-Based Multi-Solid Waste Cementitious Material

[0153] Through Figure 6 infrared spectral analysis, the chemical bond changes of the cementitious material at different thermal activation temperatures reveal its reaction mechanism and structural characteristics. The O-H vibrations at 3643 cm -1 and 3410 cm -1 indicate that as the temperature increases, the free and hydrogen-bonded O-H bonds gradually participate in the reaction, and the reaction is most complete at 800 °C, generating a large amount of hydration products such as C-S-H gel and ettringite. The H-O-H bending vibration at 1625 cm -1 further confirms the existence of bound water molecules in the hydration products, and the hydration reaction reaches the optimal state at 800 °C. The CO -1 vibrations at 1430 cm -1 and 875 cm 3 2- indicate that the carbonation reaction of the material with carbon dioxide is significantly enhanced at 800 °C, generating more calcium carbonate. The SO -1 vibrations at 1120 cm 4 2- show that gypsum is fully dissolved at 800 °C, and sulfate ions participate in the formation of ettringite in large quantities. The Si-O and Al-O vibrations at 990 cm -1 , 673 cm -1 and 605 cm -1 indicate that the silicon-oxygen bond and aluminum-oxygen bond in red mud fully participate in the reaction at 800 °C, generating a large number of silicate and aluminate structures. In summary, thermal activation at 800 °C can maximize the activation of red mud activity, promote its synergistic reaction with carbide slag and gypsum, and generate cementitious materials with excellent performance.

[0154] 4 SEM Analysis of Thermally Activated Red Mud-Based Multi-Solid Waste Cementitious Material

[0155] Figure 7 The SEM images of the gelling materials of the ternary system of Bayer red mud - gypsum - carbide slag after 28 days of thermal activation at different temperatures are shown. The sample B - 800 thermally activated at 800 °C exhibits the optimal activity, with a dense and uniform microstructure. The ettringite crystals are in regular needle - like or columnar shapes, interweaving with each other to form a strong framework, and a large amount of C - S - H gel is generated and fills the pores, indicating that the thermal activation at 800 °C can maximize the activation of the red mud activity and promote its full reaction with gypsum and carbide slag. In summary, the thermal activation at 800 °C can optimize the red mud activity, promote the hydration reaction, and form a dense and uniform microstructure, thus significantly improving the performance of the gelling material.

[0156] The present invention effectively breaks the stable crystal structure inside the Bayer red mud by adopting a high - temperature thermal activation treatment process, releasing the active silicon - aluminum components to significantly improve the comprehensive performance of the red - mud - based materials. In addition, the present invention realizes the collaborative resource utilization of red mud by compounding auxiliary gelling materials such as carbide slag and desulfurized gypsum in the thermally activated red mud. The work content completed by the present invention will provide a solid scientific basis and technical support for the large - scale resource utilization of red mud in the building materials field, and will also point out the research direction for the efficient utilization of red mud in the future, promoting the industrial development of the Bayer red - mud - based gelling materials.

Claims

1. A method for preparing a cementitious material from heat-activated modified red mud, characterized in that: The steps include: Step 1: Select red mud, dry it, remove free water, and grind it to a target particle size; place the dried red mud in a high-temperature furnace for calcination; after calcination, cool the red mud to room temperature by air cooling; Step 2: Prepare cementitious materials by combining the pretreated red mud with gypsum and carbide slag.

2. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: In the step 1, the calcination is performed at a set temperature of 800-1000° C. for a certain time of 2-4 hours, and the heating rate is controlled at 10-15° C. / min during the calcination process.

3. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: In the step 1, the selected Bayer process red mud components are specifically as follows according to the mass ratio: Fe2O3: 10-30%; Al2O3: 20-30%; SiO2: 20-30%; CaO: 15-25%; TiO2: 2-10% Na2O: 2-6% others: 1-5% (including MgO, K2O, etc.).

4. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: The specific operation steps of step 1 are as follows: Step (1): Spread the red mud sample evenly on a tray with a thickness not exceeding 2 cm to ensure uniform drying; preheat the oven: Step (2): preheat the oven to 105°C and keep the temperature stable during the drying process; Step (3): Place the selected red mud into a drying oven and start timing; during the drying process, the red mud may be turned over at regular intervals (e.g., every 6 hours) to ensure uniform drying. Step (4): Finish drying: After 24 hours, turn off the oven and take out the red mud; place the dried red mud in a dryer and cool it to room temperature to avoid moisture absorption.

5. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: In step 1, the target particle size is 50-300 μm.

6. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: In step 2, the mass ratio of red mud to gypsum and carbide slag is gypsum: carbide slag: thermally activated red mud = 25:17:

58.

7. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: In the step 2, gypsum: 10-100 μm; Carbide slag: 20-150μm.

8. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: The chemical reactions between the components of the cementitious material obtained in step 2 are synergistic: In the cementitious material prepared from red mud, gypsum and carbide slag, cementitious products ettringite (AFt) crystals and CSH gel are obtained; the ettringite (AFt) crystals and CSH gel are tightly combined through hydrogen bonds and chemical bonds.

9. The method for preparing a cementitious material from heat-activated modified red mud according to claim 1, characterized in that: The cementitious material has a dense and uniform structure, the hydration products of the cementitious material are evenly distributed, the ettringite (AFt) crystals are regular needle-shaped or columnar, interweaving to form a solid skeleton structure, and CSH gel is generated in large quantities and fills the pores, making the material as a whole present a highly dense microstructure. The size range of ettringite (AFt) crystals is usually 1-10μm (length) and 0.1-1μm (diameter).

10. The use of the method for preparing a cementitious material from heat-activated modified red mud according to any one of claims 1 to 9, characterized in that: The cementitious material is used in the field of construction.

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