Red mud-based geopolymer composite material, and preparation method and application thereof

Abstract

The application discloses a kind of red mud geopolymer composite material and its preparation method and application, belong to solid waste treatment technical field.The preparation method provided by the application includes the following steps: after mixing uniformly organic amine compound, epoxy organic compound, red mud, auxiliary cementing material, alkaline activator and water, slurry is obtained, then pouring, curing, red mud geopolymer composite material is obtained;Wherein, the organic amine compound contains primary amino group and / or secondary amino group, and at least contains two amino groups;The epoxy organic compound contains at least two epoxy groups in it.The application makes the compound containing amine group and the compound containing epoxy group in-situ crosslinking reaction in the strong alkaline environment of red mud geopolymer, forms organic-inorganic interpenetrating network structure, to significantly improve the mechanical properties of material at the same time, realizes the efficient and stable solidification to fluoride ion.

Description

Technical Field

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

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Red mud is a strongly alkaline solid waste generated during the alkaline process of alumina production from bauxite, primarily composed of metal oxides such as iron, aluminum, and silicon. In the Bayer process, fluoride impurities associated with bauxite are leached with a strong alkali, and a significant portion of this fluoride is released as soluble fluoride ions (F₂). - The presence of soluble fluoride ions in red mud poses a potential environmental risk. These soluble fluoride ions are highly mobile under natural conditions and can pollute groundwater through infiltration or leach into surface water bodies through precipitation, posing a long-term threat to the ecological environment. Although the iron and aluminum oxides contained in red mud have a certain adsorption potential, their inherently alkaline environment makes the surface active sites easily passivated, resulting in a low actual adsorption capacity for fluoride ions and unstable fixation, making it difficult to effectively prevent the long-term leaching of fluoride ions.

[0004] Currently, using red mud as the main raw material and preparing geopolymer materials through alkali activation technology is an important approach to achieving its large-scale resource utilization. This method can effectively solidify some heavy metal ions in red mud and endow the material with certain mechanical properties, providing a feasible solution for the large-scale disposal of red mud. However, existing red mud-based geopolymer technologies mainly focus on the development and optimization of material mechanical properties, and still lack a fundamental solution to the key environmental problem of long-term fixation and migration inhibition of soluble fluoride ions in red mud. When the prepared materials are in contact with the aquatic environment for a long time, fluoride ions may still gradually leach out, which means that the original environmental risks have not been completely eliminated by the resource utilization, thus restricting the environmental safety and widespread application of red mud-based building materials. Therefore, developing a new technology that can simultaneously achieve high-value utilization of red mud solid waste and efficient and stable solidification of fluoride ions is of great practical significance. Summary of the Invention

[0005] In view of this, the present invention provides a red mud-based geopolymer composite material, its preparation method, and its application. The present invention enables an amine-containing compound and an epoxy-containing compound to undergo an in-situ crosslinking reaction in the strongly alkaline environment of the red mud geopolymer, forming an organic-inorganic interpenetrating network structure. This significantly improves the mechanical properties of the material while achieving efficient and stable curing of fluoride ions.

[0006] In a first aspect, the present invention provides a method for preparing a red mud-based polymer composite material, comprising the following steps:

[0007] Organic amine compounds, epoxy organic compounds, red mud, auxiliary cementitious materials, alkaline activators, and water are mixed evenly to obtain a slurry, which is then poured and cured to obtain a red mud-based polymer composite material; the mass fraction of the organic amine compound relative to the red mud is 1~5wt%; the dry basis mass ratio of the red mud, auxiliary cementitious materials, and alkaline activators is (50~70): (20~45): (5~15);

[0008] The organic amine compound contains a primary amino group and / or a secondary amino group, and contains at least two amino groups;

[0009] The epoxy-based organic compound contains at least two epoxy groups;

[0010] The ratio of the total molar amount of amino active hydrogen in the organic amine compound to the total molar amount of epoxy groups in the epoxy organic compound is (0.5~1.5):1.

[0011] Preferably, the organic amine compound is selected from at least one of polyethyleneimine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and hydroxyethylethylenediamine.

[0012] Preferably, the epoxy organic compound is selected from at least one of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and bisphenol A type epoxy resin.

[0013] Preferably, the auxiliary cementing material is selected from at least one of slag, fly ash, silica fume, metakaolin, steel slag, and phosphorus slag.

[0014] Preferably, the alkaline activator is at least one selected from sodium silicate, sodium hydroxide, and potassium hydroxide.

[0015] Preferably, in the mixing step, a silane coupling agent comprising 0.1 to 3 wt% of the red mud mass is also added, wherein the silane coupling agent contains epoxy or amino groups.

[0016] Preferably, the ratio of the mass of water to the total dry mass of red mud, auxiliary cementing material and alkaline activator is (0.3 ~ 0.5): 1.

[0017] Preferably, the curing process specifically involves: first, heating and curing at a temperature of 40~60℃ and a humidity of not less than 90%RH for 12~24 hours, followed by curing at a standard temperature of 20±2℃ and a humidity of ≥95%RH until the specified age.

[0018] Secondly, the present invention provides a red mud-based polymer composite material, which is prepared by the above-mentioned preparation method, and the cumulative leaching concentration of fluoride ions over 28 days is not higher than 2 ppm.

[0019] Thirdly, the present invention provides the application of the above-mentioned red mud-based polymer composite material in the preparation of building materials.

[0020] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0021] (1) This invention involves in-situ mixing of organic amine compounds containing primary and / or secondary amino groups with organic compounds containing polyfunctional epoxy groups in strongly alkaline red mud geopolymer slurry. This allows the active hydrogens of the amino groups to undergo nucleophilic ring-opening addition reactions with the epoxy groups during the formation of the geopolymer gel, generating an organic crosslinked network with stable CN and COC covalent bonds as the core. This network interpenetrates and intertwines with the inorganic silica-alumina network of the geopolymer at the molecular scale, constructing a stable organic-inorganic hybrid structure. This significantly improves the toughness and crack resistance of the material while enhancing its compressive strength.

[0022] (2) The interpenetrating network structure formed in situ in this invention can effectively bind soluble fluoride ions in red mud through both physical encapsulation and chemical adsorption mechanisms. Compared with unmodified red mud base polymers, this material can complicate the migration channels of fluoride ions and increase their binding sites, thereby reducing the cumulative leaching concentration of fluoride ions to below 2 ppm after 28 days, fundamentally solving the problem of long-term environmental leaching risk of fluoride ions during the red mud resource utilization process.

[0023] (3) The preparation process of the present invention is highly compatible with the traditional geopolymer preparation process and does not require complex equipment. At the same time, by introducing a silane coupling agent as an interface bridge, the chemical bonding between the organic and inorganic phases can be further strengthened, thereby improving the interfacial stability and long-term durability of the composite material in humid or corrosive environments. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] In this invention, geopolymer, often simply referred to as "geopolymer," is a class of inorganic polymer materials generated through chemical activation. Its chemical composition is [SiO4]. 4- and [AlO4] 5-A three-dimensional network framework structure is formed by tetrahedral structural units connected by shared oxygen atoms. The negatively charged aluminum-oxygen tetrahedra in this network structure require alkali metal ions (such as Na+) to form the network. + K + ) or alkaline earth metal ions (such as Ca) 2+ This is used to balance the charge and maintain the electrical neutrality of the structure.

[0026] In one embodiment of the present invention, a method for preparing a red mud-based polymer composite material is provided, comprising the following steps:

[0027] Organic amine compounds, epoxy organic compounds, red mud, auxiliary cementitious materials, alkaline activators and water are mixed evenly to obtain a slurry, which is then poured and cured to obtain a red mud-based polymer composite material.

[0028] The organic amine compound contains a primary amino group and / or a secondary amino group, and contains at least two amino groups;

[0029] The epoxy-based organic compound contains at least two epoxy groups;

[0030] The ratio of the total molar amount of amino active hydrogen in the organic amine compound to the total molar amount of epoxy groups in the epoxy organic compound is (0.5~1.5):1.

[0031] This invention involves in-situ mixing and reaction of organic amine compounds containing specific functional groups and epoxy-based organic compounds in a strongly alkaline red mud geopolymer slurry environment. By controlling the ratio of functional groups and process conditions, the cross-linking polymerization reaction of the organic phase and the condensation polymerization reaction of the inorganic geopolymer occur simultaneously and promote each other, ultimately forming an organic-inorganic interpenetrating network structure. This results in a material with high mechanical properties and excellent environmental safety.

[0032] In this invention, the organic amine compound serves to provide reactive amino groups (-NH2 or -NH-) for the formation of an organic cross-linked network. The organic amine compound must contain a primary amino group (-NH2) and / or a secondary amino group (-NH-) because they possess sufficient nucleophilic activity to attack the epoxy group under basic conditions, initiating a ring-opening reaction. Simultaneously, each organic amine compound molecule must contain at least two amino groups, which is a necessary condition for forming a three-dimensional cross-linked network rather than a nonlinear structure.

[0033] In an optional embodiment of the present invention, the preparation method is further preferably as follows: dispersing organic amine compounds and epoxy organic compounds in water to form a uniform organic solution; dry mixing red mud and auxiliary cementitious materials to form a dry mixture; dissolving an alkaline activator in water to form an activator solution; and mixing the dry mixture, organic solution and activator solution uniformly to obtain a slurry.

[0034] In optional embodiments of the present invention, the organic amine compound is selected from at least one of polyethyleneimine (PEI), ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and hydroxyethylethylenediamine. Polyethyleneimine is further preferred in the present invention because it has high functionality and water solubility, enabling it to efficiently form a dense network.

[0035] In an optional embodiment of the present invention, the organic amine compound has a mass fraction of 1-5 wt% relative to the red mud, for example, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, and 5.0 wt%. If the addition amount is too low, the resulting organic network is insufficient to significantly improve material properties; if the addition amount is too high, it may interfere with the hydration and coagulation processes of the geopolymer itself, and increase costs.

[0036] In this invention, the role of the epoxy-based organic compound is to react with the organic amine compound, forming stable CN and COC bonds through ring-opening of the epoxy groups, thus constructing the framework of the organic network. The compound contains at least two epoxy groups to ensure cross-linking with polyamines. In optional embodiments of this invention, the epoxy-based organic compound is selected from at least one of polyethylene glycol diglycidyl ether (PEGDGE), polypropylene glycol diglycidyl ether (PPGDGE), and bisphenol A type epoxy resin. The bisphenol A type epoxy resin may be E-51, which can introduce rigid benzene rings, improving the material modulus and heat resistance.

[0037] In this invention, the ratio of the total molar amount of active hydrogen atoms in all amino groups of the organic amine compound to the total molar amount of active epoxy groups in the epoxy organic compound is controlled at (0.5~1.5):1 to ensure sufficient network formation. For example, ratios can be 0.5:1, 0.8:1, 1.0:1, 1.1:1, 1.2:1, etc., with a preferred range of (0.8~1.2):1. It should be noted that each primary amino group (-NH2) contains 2 active hydrogen atoms; each secondary amino group (-NH-) contains 1 active hydrogen atom; and tertiary amino groups (-N<) do not contain active hydrogen atoms and are not included in the total molar amount of active hydrogen atoms in the amino group.

[0038] In this invention, red mud serves as the primary silica-alumina raw material and the target for fluorine fixation. Its strong alkalinity (pH=11~13) provides the necessary reaction environment for the system. It typically needs to be dried and ground before use to increase its reactivity. Bayer process red mud is more preferred.

[0039] In an optional embodiment of the present invention, the auxiliary cementing material is selected from at least one of slag, fly ash, silica fume, metakaolin, steel slag, and phosphorus slag. These materials typically possess potential hydraulic activity or pozzolanic activity, and can react with alkaline activators to generate additional gel phases, which are used to adjust the silica-alumina-calcium composition of the system, improve workability, and further enhance mechanical properties.

[0040] In this invention, the alkaline activator is used to provide a highly alkaline environment (pH>13), which on the one hand dissolves the silica-alumina phase in red mud and auxiliary cementitious materials, initiating the polymerization reaction; on the other hand, the high pH environment can greatly promote the nucleophilic attack of amino groups on epoxy groups, allowing the organic crosslinking reaction to proceed rapidly at room temperature or medium temperature. In an optional embodiment of this invention, the alkaline activator is at least one of sodium silicate, sodium hydroxide, and potassium hydroxide.

[0041] In an optional embodiment of the present invention, the dry basis mass ratio of the red mud, auxiliary cementitious material, and alkaline activator is (50~70): (20~45): (5~15). This ratio ensures that red mud is the main component, while having sufficient active components (auxiliary cementitious material) and alkaline activator to form a dense geopolymer matrix.

[0042] In an optional embodiment of the present invention, the mass ratio of water to the total dry weight of red mud, auxiliary cementitious material, and alkaline activator is (0.3 ~ 0.5): 1, for example, 0.30:1, 0.35:1, 0.40:1, 0.45:1, or 0.50:1. In this invention, water serves as the reaction medium and mass transfer carrier. The above range ensures that the slurry has good fluidity for casting, while avoiding excessive water usage that could lead to excessively high porosity after hardening, thus compromising strength and impermeability.

[0043] To further enhance the interfacial bonding between the organic network and the inorganic geopolymer matrix, a silane coupling agent, comprising 0.1–3 wt% of the red mud mass, can be added during the mixing step. The silane coupling agent preferably contains an epoxy group (such as γ-(2,3-epoxypropoxy)propyltrimethoxysilane) or an amino group (such as γ-aminopropyltriethoxysilane). Its mechanism of action is as follows: the silanol group (-Si-OH) formed by the hydrolysis of the alkoxy group (-Si(OR)3) at one end of the silane coupling agent can undergo a condensation reaction with the silanol groups on the surface of the red mud and other geopolymer precursors, forming a strong Si-O-Si covalent bond; while the epoxy group or amino group at the other end can participate in the amine-epoxy crosslinking reaction. This constructs a "molecular bridge" between the organic and inorganic phases, significantly improving the long-term durability of the composite material, especially under harsh environments such as humidity and heat.

[0044] This invention involves injecting a uniformly mixed slurry into a mold and vibrating it to compact it, followed by a crucial two-stage curing process. The first stage involves heating and curing at 40-60°C and RH not lower than 90% for 12-24 hours. This stage serves several purposes: first, it provides activation energy for the geopolymerization reaction, accelerating the formation of the gel system; second, it provides the necessary temperature conditions for the amine-epoxy reaction, promoting full cross-linking of the organic network; and third, in the case of a silane coupling agent, the high temperature and humidity environment is beneficial for the hydrolysis and condensation reactions of the silane coupling agent. This stage is crucial for forming a high-strength, high-integrity interpenetrating network. The second stage involves curing at 20±2°C and RH ≥95% for the specified age (typically 7 days, 28 days, or longer). This stage allows the material's properties to develop continuously and stably.

[0045] In another embodiment of the present invention, a red mud-based polymer composite material is provided, which is prepared by the above-described preparation method.

[0046] In the red mud-based polymer composite material of the present invention, the rigid inorganic network provides high compressive strength, while the organic network penetrating it effectively bridges microcracks and blunts crack tip stress, thereby significantly improving the material's toughness (manifested as higher flexural strength and fracture energy) and impact resistance without sacrificing or even increasing compressive strength. The interpenetrating network also enhances the absorption of fluoride ions (F ions) in the red mud. - This material achieves dual fixation. On one hand, the dense network structure physically blocks the migration channels of fluoride ions; on the other hand, the amino groups in the organic network have chemical coordination and hydrogen bond adsorption effects on fluoride ions. According to the "Solid Waste Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007), the cumulative fluoride ion leaching concentration of this material after 28 days is no higher than 2.0 mg / L (i.e., 2.0 ppm), and preferably lower than 1.0 mg / L, ensuring low environmental risk. Furthermore, the stable CN and COC covalent bonds and the Si-O-Si interfacial bonds formed by the addition of silane coupling agents give this material superior water resistance, alkali resistance, and volume stability compared to traditional physically blended polymers or single geopolymers.

[0047] In another embodiment of the present invention, the present invention provides the application of the above-mentioned red mud-based polymer composite material in the preparation of building materials, such as the preparation of non-load-bearing / load-bearing blocks, paving bricks, slope protection components, etc.

[0048] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0049] Example 1

[0050] This embodiment provides a red mud-based polymer composite material.

[0051] The raw materials for this embodiment are as follows: 600g of dried and finely ground Bayer process red mud; 300g of S95 grade slag powder; 100g of solid sodium silicate with a modulus of 1.0; 40.0g of a 30wt% polyethyleneimine (PEI) aqueous solution (PEI solid mass is 12.0g, accounting for 2.0wt% of the dry weight of the red mud); polyethylene glycol diglycidyl ether (PEGDGE), as an epoxy-based organic compound, with a molar ratio of active hydrogen in PEI to the total molar mass of PEGDGE epoxy groups of 1.2:1; 3.0g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), which is 0.5wt% of the dry weight of the red mud; and a total mixing water volume of 380g, which covers the water introduced by the polyethyleneimine aqueous solution itself and the water required to dissolve the solid sodium silicate.

[0052] The preparation process is as follows:

[0053] (1) Dissolve solid sodium silicate in 120g of mixing water to prepare a concentrated alkaline solution, and cool it to room temperature for later use.

[0054] (2) Mix the polyethyleneimine aqueous solution, polyethylene glycol diglycidyl ether and KH-560 with the remaining mixing water and stir evenly to prepare an organic component mixture.

[0055] (3) Dry mix red mud and slag powder in a mixer at 150 rpm for 1 minute to obtain dry mixed material; then pour the concentrated alkali solution prepared in step (1) and the organic component mixture in step (2) into the mixer containing the dry mixed material, and stir at 400 rpm for 4 minutes until a uniform and fluid slurry is formed.

[0056] (4) Pour the uniformly mixed slurry into a mold pre-coated with a release agent, compact it using a vibrating table to remove air bubbles, and then cover it with plastic wrap to prevent moisture evaporation. Place the molded specimen along with the mold in a constant temperature and humidity environment at 55℃ and a relative humidity of not less than 90%RH for the first stage of heat curing, which lasts for 18 hours. After curing, demold the specimen and transfer it to a standard curing room at 20±2℃ and a relative humidity of not less than 95%RH for the second stage of standard curing until the target age, thus obtaining the red mud-based polymer composite material.

[0057] Example 2

[0058] The difference between this embodiment and Example 1 is that γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) is not added in this embodiment; otherwise, it is exactly the same as Example 1.

[0059] Example 3

[0060] The difference between this embodiment and Example 1 is that ethylenediamine is used instead of PEI, polypropylene glycol diglycidyl ether (PPGDGE) is used instead of PEGDGE, and the ratio of the molar amount of active hydrogen in ethylenediamine to the total molar amount of epoxy groups in PPGDGE is controlled to be 1.2:1. The rest is exactly the same as in Example 1.

[0061] Comparative Example 1

[0062] This comparative example provides a red mud-based geopolymer cementitious material that does not contain any organic modifying components.

[0063] The raw materials for this comparative example are as follows: 600g of dried and finely ground Bayer red mud; 300g of S95 grade slag powder; and 100g of solid sodium silicate with a modulus of 1.0. The total water-to-solid ratio is 0.38, and the total amount of mixing water is 380g.

[0064] The preparation method is as follows:

[0065] (1) Dissolve solid sodium silicate in 120g of mixing water to prepare a concentrated alkaline solution, and cool it to room temperature for later use.

[0066] (2) Dry mix red mud and slag powder in a mixer at 150 rpm for 1 minute to obtain dry mixed material; then pour the concentrated alkali solution prepared in step (1) into the mixer containing the dry mixed material and stir at 400 rpm for 4 minutes until a uniform and fluid slurry is formed.

[0067] (3) Pour the uniformly mixed slurry into a mold pre-coated with a release agent, compact it using a vibrating table to remove air bubbles, and then cover it with plastic wrap to prevent moisture evaporation. Place the molded specimen along with the mold in a constant temperature and humidity environment at 55℃ and a relative humidity of not less than 90%RH for the first stage of heat curing, which lasts for 18 hours. After curing, demold the specimen and transfer it to a standard curing room at 20±2℃ and a relative humidity of not less than 95%RH for the second stage of standard curing until the target age, thus obtaining the red mud-based polymer cementitious material.

[0068] Comparative Example 2

[0069] This comparative example is based on Comparative Example 1 with the addition of 24g of vinyl acetate-ethylene copolymer (VAE) redispersible latex powder.

[0070] The preparation method is as follows:

[0071] (1) Dissolve solid sodium silicate in 120g of mixing water to prepare a concentrated alkaline solution, and cool it to room temperature for later use.

[0072] (2) Dry mix red mud, slag powder and VAE redispersible latex powder in a mixer at a speed of 150 rpm for 1 minute to obtain dry mixed material; then pour the concentrated alkali solution prepared in step (1) into the mixer containing the dry mixed material and stir at a speed of 400 rpm for 4 minutes until a uniform and fluid slurry is formed.

[0073] (3) The uniformly mixed slurry is poured into a mold pre-coated with a release agent and compacted using a vibrating table to remove air bubbles. Then, it is covered with plastic wrap to prevent moisture evaporation. The molded specimen, along with the mold, is placed in a constant temperature and humidity environment at 55℃ and a relative humidity of not less than 90%RH for the first stage of heat curing, which lasts for 18 hours. After curing, the specimen is demolded and transferred to a standard curing room at 20±2℃ and a relative humidity of not less than 95%RH for the second stage of standard curing until the target age, thus obtaining the red mud-based polymer composite material.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that this comparative example does not contain PEGDGE and KH-560.

[0076] Comparative Example 4

[0077] This comparative example uses the exact same types and amounts of raw materials as Example 1, but changes the method of introducing the organic components: amine-epoxy crosslinking gel is first prepared under alkaline conditions, and then physically incorporated into the geopolymer matrix in solid powder form. The steps of this comparative example are as follows:

[0078] (1) Preparation of pregel powder: Weigh out equal amounts of 30wt% polyethyleneimine (PEI) aqueous solution and polyethylene glycol diglycidyl ether (PEGDGE) as in Example 1, and then add them to 200g of NaOH solution with pH 10. Stir at 300rpm for 30 minutes at room temperature to allow it to react fully and form a gel. After washing with water until neutral, place the obtained gel in an oven at 80℃ and dry for 48 hours until constant weight to obtain a solid block. Crush the dried solid block using a grinder and pass it through a 100-mesh sieve to obtain pregel powder for later use.

[0079] (2) Dissolve solid sodium silicate in 120g of mixing water to prepare a concentrated alkaline solution, and cool it to room temperature for later use.

[0080] (3) Mix the pregel powder obtained in step (1), 3.0g KH-560 and the remaining mixing water, and stir until the pregel powder is evenly dispersed to prepare a mixed slurry.

[0081] (4) Dry-ground Bayer red mud (600g) and S95 grade slag powder (300g) are pre-mixed in a mixer at 150rpm for 1 minute to obtain dry-mixed material.

[0082] (5) Pour the concentrated alkali solution from step (2) and the mixed slurry from step (3) into the dry mixture from step (4), and stir at 400 rpm for 4 minutes until a uniform slurry is formed.

[0083] (6) The slurry is injected into a mold pre-coated with a release agent and compacted using a vibrating table to remove air bubbles. Then, it is covered with plastic wrap to prevent moisture evaporation. The molded specimen, along with the mold, is placed in a constant temperature and humidity environment at 55°C and a relative humidity of not less than 90%RH for the first stage of heat curing, which lasts for 18 hours. After curing, the specimen is demolded and transferred to a standard curing room at 20±2°C and a relative humidity of not less than 95%RH for the second stage of standard curing until the target age, thus obtaining the red mud-based polymer composite material.

[0084] Test case

[0085] 1. Performance testing methods:

[0086] (1) Compressive and flexural strength: After curing to the specified age (3 days and 28 days), 40mm × 40mm × 160mm prism specimens were tested using a universal testing machine according to the national standard GB / T17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". The flexural strength was obtained from the three-point bending test, and the compressive strength was tested using the broken half of the prism. The flexural / compression ratio (flexural-compression ratio) is used as an important indicator for evaluating the toughness of materials.

[0087] (2) Slurry fluidity: According to GB / T 2419-2005 "Method for Determination of Flowability of Cement Mortar", the diffusion diameter of freshly mixed slurry was tested to evaluate its workability.

[0088] (3) Fluoride ion leaching concentration test: The specimens, after 28 days of curing, were crushed, ground, and sieved through a 0.15 mm sieve. Leaching experiments were conducted according to the Ministry of Ecology and Environment standard HJ / T 299-2007 "Solid Waste Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method". The fluoride ion concentration in the leachate (F...) - The concentration was determined using the fluoride ion-selective electrode method, and the cumulative leaching concentration over 28 days was calculated in ppm (mg / L). This value is the core basis for assessing the environmental risk of materials.

[0089] 2. Test Results

[0090] The test results are shown in Table 1.

[0091] Table 1 Summary of performance test results of Examples 1-3 and Comparative Examples 1-4

[0092]

[0093] Data shows that all embodiments of the present invention comprehensively outperform the unmodified blank geopolymer (Comparative Example 1) in both 28-day compressive strength and flexural strength. Example 1 shows the most outstanding performance, with its compressive strength (38.5 MPa) and flexural strength (10.8 MPa) increasing by approximately 30% and 80%, respectively, compared to Comparative Example 1. More importantly, its flexural / compression ratio (flexural-compression ratio) reaches 0.281, significantly higher than Comparative Example 1's 0.203, indicating that the material's toughness is significantly improved while its strength increases. It is noteworthy that Comparative Example 2 (physically blended with VAE latex powder), although also increasing the flexural-compression ratio to 0.281 by introducing a flexible polymer, exhibits a decrease in compressive strength. This clearly demonstrates a significant difference between the present invention and conventional physical methods in terms of toughening path: the in-situ formed interpenetrating network, while toughening, not only does not weaken the matrix strength but also simultaneously enhances its strength through a reinforcing effect, achieving synergistic optimization of mechanical properties.

[0094] The embodiments of this invention also demonstrate breakthrough effects in solving the core environmental problem of fluoride ion leaching from red mud. As shown in Table 1, the fluoride ion leaching concentration of all embodiments was stably controlled below 1.5 ppm after 28 days, with the optimal concentration in Example 1 being only 0.95 ppm, far lower than that of Comparative Example 1 (13.7 ppm). The leaching concentration of Comparative Example 3 (PEI only) was 8.3 ppm, showing some adsorption effect, but it was orders of magnitude lower than that of Example 1, proving that the single physicochemical adsorption effect is limited. The leaching concentration of Comparative Example 4 (3.5 ppm) was significantly lower than that of Comparative Example 3, but still higher than that of Example 1. This comparison shows that in-situ reaction in alkaline slurry is the key to forming a highly efficient solid fluoride structure. The interfacial bonding between the pregel particles and the geopolymer matrix has defects, making it difficult to achieve molecular-level blocking and stable anchoring of the fluoride ion migration pathway.

[0095] Comparing Example 1 (containing KH-560) and Example 2 (without KH-560), the former has a slight advantage in fluorine fixation performance. This indicates that KH-560 enhances the integrity of the network structure by strengthening the organic-inorganic interface, thereby improving the long-term stable fluorine fixation capability.

[0096] The initial flowability of the slurry in Comparative Example 4 (165 mm) was the lowest among all groups, and its compressive strength (32.1 MPa) was significantly lower than that in Example 1. This is mainly because the pre-gelled powder absorbed a large amount of water during mixing, impairing its workability, and its bonding strength with the matrix as heterogeneous particles was limited. This strongly demonstrates, from the opposite perspective, the irreplaceable nature of the in-situ reaction process of this invention. In-situ reaction avoids organic phase agglomeration, achieving molecular-scale dispersion and bonding, which is the fundamental guarantee for obtaining excellent workability and final performance.

[0097] The above data demonstrate that this invention successfully constructed a uniform and dense organic-inorganic interpenetrating network structure by in-situ initiating an amine-epoxy nucleophilic ring-opening addition reaction in a strongly alkaline red mud geopolymer slurry. This structure achieves a synergistic increase in mechanical strength and toughness, and fundamentally and efficiently solidifies fluoride ions, thus solving a key environmental bottleneck in the resource utilization of red mud.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a red mud-based polymer composite material, characterized in that, Includes the following steps: Organic amine compounds, epoxy organic compounds, red mud, auxiliary cementitious materials, alkaline activators, and water are mixed evenly to obtain a slurry, which is then poured and cured to obtain a red mud-based polymer composite material; the mass fraction of the organic amine compound relative to the red mud is 1~5wt%; the dry basis mass ratio of the red mud, auxiliary cementitious materials, and alkaline activators is (50~70): (20~45): (5~15); The organic amine compound is selected from at least one of polyethyleneimine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and hydroxyethylethylenediamine; The epoxy organic compound is selected from at least one of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and bisphenol A type epoxy resin; The ratio of the total molar amount of amino active hydrogen in the organic amine compound to the total molar amount of epoxy groups in the epoxy organic compound is (0.5~1.5):1; The auxiliary cementing material is selected from at least one of slag, fly ash, silica fume, metakaolin, steel slag, and phosphorus slag.

2. The preparation method according to claim 1, characterized in that, The alkaline activator is at least one of sodium silicate, sodium hydroxide, and potassium hydroxide.

3. The preparation method according to claim 1, characterized in that, In the mixing step, a silane coupling agent comprising 0.1 to 3 wt% of the red mud mass is also added, wherein the silane coupling agent contains epoxy or amino groups.

4. The preparation method according to claim 1, characterized in that, The ratio of the mass of water to the total dry weight of red mud, auxiliary cementitious materials, and alkaline activator is (0.3 ~ 0.5):

1.

5. The preparation method according to claim 1, characterized in that, The curing process specifically involves: first, heating and curing at a temperature of 40~60℃ and a humidity of not less than 90%RH for 12~24 hours, followed by curing at a standard temperature of 20±2℃ and a humidity of ≥95%RH until the specified age.

6. A red mud-based polymer composite material, characterized in that, The red mud-based polymer composite material is prepared by the preparation method according to any one of claims 1 to 5, and its cumulative leaching concentration of fluoride ions over 28 days is not higher than 2 ppm.

7. The application of the red mud-based polymer composite material as described in claim 6 in the preparation of building materials.

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