A red mud solidifying agent and a preparation method thereof

Abstract

This patent application discloses a red mud solidifying agent and its preparation method. The red mud solidifying agent is prepared from the following raw materials: metakaolin, accounting for 18-22% of the total mass of the solidifying agent; the remaining mass of the solidifying agent after removing the metakaolin, by mass percentage, consists of 5-20 parts fly ash, 1-20 parts slag, and 1-15 parts sodium silicate as an alkaline activator. The red mud solidifying agent synergistically solidifies red mud through multiple processes such as geopolymerization, "volcanic ash reaction," and filling-dispersion reaction. The active silica, alumina, and alkali ions abundant in red mud directly participate in the reaction, forming dense, uniform, and high-strength solidified red mud. Using the red mud solidifying agent to solidify red mud can reduce the consumption of building materials such as cement and lime during highway construction, thereby reducing costs and environmental pollution. In addition, it can promote the resource utilization of red mud and the comprehensive utilization of industrial wastes such as fly ash and slag, possessing both economic and environmental value.

Description

Technical Field

[0001] This invention relates to the field of soil stabilizer technology, specifically to a red mud stabilizer and its preparation method. Background Technology

[0002] Red mud is produced in enormous quantities, and its comprehensive utilization has always been a challenge for the aluminum smelting industry. Finding a way to achieve large-scale resource utilization of red mud is a very urgent task. Solidifying red mud with a solidifying agent to increase its strength for use as a road construction material while controlling the diffusion of pollutants is a promising approach for red mud resource utilization.

[0003] The continuous development of highway networks has provided convenient transportation for urban and rural residents and economic development, but it has also brought enormous supply pressure to highway construction materials—especially road base materials, which are used in huge quantities. Using solidified red mud as an engineering filler for highway base and subbase layers can alleviate the supply pressure of highway construction materials and promote the large-scale resource utilization of red mud, possessing both economic and environmental value. However, currently, solidified red mud used in highway base and subbase layers is mainly solidified using traditional solidifying agents such as cement and lime. The production of cement and lime requires the mining of large quantities of rock, and the firing process generates a large amount of CO2, resulting in significant energy consumption for environmental remediation. More importantly, due to the extremely weak engineering properties and alkaline chemical characteristics of red mud, traditional solidifying agents such as cement and lime cannot achieve good solidification results, leading to serious engineering safety and environmental safety risks. These drawbacks limit the large-scale resource utilization of solidified red mud in highway engineering, necessitating the development of economical and environmentally friendly red mud solidifying agents to overcome these difficulties. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the present invention aims to provide a red mud solidifier and its preparation method. The red mud solidifier uses metakaolin, fly ash, slag, etc. as main raw materials, supplemented with alkaline activators such as sodium silicate, to solidify red mud. On the one hand, it can reduce the consumption of building materials such as cement and lime during highway construction, reduce highway construction costs, and reduce environmental pollution. On the other hand, it can promote the large-scale resource utilization of red mud and the comprehensive utilization of industrial wastes such as fly ash and slag, thus having both economic and environmental value.

[0005] The technical solution adopted in this invention is as follows: A red mud solidifying agent, prepared from raw materials comprising the following components:

[0006] Metakaolin accounts for 18-22% of the total mass of the red mud solidifier;

[0007] The remaining mass of the curing agent after removing metakaolin consists of, by mass parts, 5-20 parts fly ash, 1-20 parts slag, and 1-15 parts sodium silicate as alkaline activator.

[0008] In a preferred embodiment of the present invention, the metakaolin has an average particle size of 8-12 μm, the fly ash has an average particle size of 22-26 μm, and the slag has a specific surface area of ​​350-450 m². 2 / kg, the average particle size of sodium silicate is 1-10 μm. In this scheme, the particle size range of metakaolin and fly ash ensures sufficient specific surface area to promote the release of active silica and alumina. The small particle size of sodium silicate improves its solubility and reaction efficiency, thereby enhancing the overall curing effect and material uniformity.

[0009] In a preferred embodiment of the present invention, a nano-filler dispersant is also included. The nano-filler dispersant is one or a mixture of several of nano-silica, nano-alumina, and carbon nanotubes. The amount added, by weight, is 1-10 parts in the remaining mass after removing metakaolin. The reason for adding the nano-filler dispersant in this embodiment is that the extremely small particle size of the nanomaterials allows them to fill the micropores of the solidified red mud, improving the density of the solidified red mud; the extremely large specific surface area of ​​the nanomaterials allows them to uniformly disperse the solidification reactants and solidification reaction products, improving the uniformity of the solidified red mud.

[0010] In a preferred embodiment of the present invention, the nanofiller dispersant is a mixture of three materials: nano-silica, nano-alumina, and carbon nanotubes. By mass fraction, the nanofiller dispersant comprises 0.5–10 parts nano-silica, 0.5–10 parts nano-alumina, and 0.5–10 parts carbon nanotubes. This preferred ratio is chosen because this combination achieves optimal filling and reinforcing effects during curing, exhibiting the highest strength.

[0011] In a preferred embodiment of the present invention, the nano-silica has an average particle size of 60-100 nm and a specific surface area of ​​120-200 nm. 2 / g; the average particle size of the nano-alumina is 20nm, and the specific surface area is 120-150m². 2 / g; the average particle size of the carbon nanotubes is 2-20nm, and the specific surface area is 100-500m². 2 / g. In this scheme, the nanomaterials with the above-mentioned particle size and specific surface area are selected, which have the best filling and dispersing effects.

[0012] In a preferred embodiment of the present invention, calcium chloride is also included, with an addition amount of 1-15 parts by weight of the remaining mass after removing metakaolin. In this scheme, the added calcium chloride reacts with the alkali ions remaining in the curing reaction in a "volcanic ash reaction" to generate cementitious substances such as hydrated calcium silicate, thereby enhancing the curing effect.

[0013] In a preferred embodiment of the present invention, the average particle size of the calcium chloride is 1-10 μm. This particle size range is chosen based on considerations of the activity and dispersibility of calcium chloride in the curing reaction. Smaller particle sizes increase the reaction rate of calcium chloride, enabling it to rapidly form CSH gels, which contribute to improved early strength and final durability of the cured body. Furthermore, this particle size range also avoids excessive particle agglomeration, ensuring uniform distribution of calcium chloride in the curing agent and further improving the curing effect.

[0014] In a preferred embodiment of the present invention, the remaining mass after removing metakaolin contains fly ash: slag: calcium chloride: sodium silicate: nano-filler dispersant in a ratio of 32.26%: 16.13%: 9.68%: 9.68%: 32.26%. This ratio is the optimal ratio observed during the experiment, and the curing agent formed by this ratio exhibits the best curing effect on red mud.

[0015] In a preferred embodiment of the present invention, the nano-filler dispersant comprises nano-silica: nano-alumina: carbon nanotubes in a ratio of 90.9%: 4.5%: 4.5%. This ratio is the optimal ratio observed during the experiment, and the curing agent formed by this ratio exhibits the best curing effect on red mud.

[0016] This invention also provides a method for preparing a red mud solidifying agent, comprising the following steps:

[0017] (1) Dry each raw material except sodium silicate at a temperature of 50-60℃, then mix them evenly according to the proportion of each raw material, dry and seal them for storage.

[0018] (2) Weigh out the appropriate amount of water and add sodium silicate, control the water-cement ratio to be 0.4-0.6, stir until the sodium silicate is completely dissolved, and obtain sodium silicate solution;

[0019] (3) Pour the sodium silicate solution evenly into the mixture in step (1) according to the proportion and stir thoroughly to form a red mud solidifying agent.

[0020] This invention also provides an application of a red mud solidifying agent, characterized by comprising the following steps:

[0021] (1) According to the engineering needs, the prepared red mud curing agent is used to partially replace the conventional cement to form red mud curing agent. The ratio of red mud curing agent to cement is 0-1:1-0.

[0022] (2) The mass ratio of the curing agent to the red mud is 23%-27%;

[0023] (3) Add the red mud solidifying agent into the red mud according to the mass ratio and mix thoroughly;

[0024] (4) Add water to the mixture formed in step (3) according to the optimal moisture content determined by the compaction test and the natural moisture content of the red mud, and stir it evenly again;

[0025] (5) Observe whether there are clumps of powder due to uneven moisture absorption, crush the clumps of powder, and let it sit for 24 hours.

[0026] (6) Compact the material according to the maximum dry density determined by the compaction test;

[0027] (7) Curing is carried out according to the project requirements to form solidified red mud that meets the project requirements.

[0028] Conventional curing agents such as cement and lime solidify red mud through hydration, hydrolysis, and "volcanic ash reaction" to form solidification products. However, the red mud itself does not participate in the solidification reaction, and the alkaline solution formed by the reaction exacerbates the "alkali efflorescence" of the red mud, thus the solidification effect needs improvement. To enhance the solidification effect by involving the red mud itself in the solidification reaction, this invention uses a mixture of metakaolin, fly ash, alkaline slag, and sodium silicate to form a curing agent for synergistic solidification of red mud. During the solidification reaction, the reactive silica, activated alumina, and sodium hydroxide abundant in the red mud participate in the solidification reaction through geopolymerization, improving the solidification effect while simultaneously achieving the goal of "alkali removal" from the red mud. Compared to existing technologies, the advantages of this invention are:

[0029] 1. Metakaolin, fly ash, slag, and sodium silicate participate in the solidification reaction through geopolymerization. The sodium hydroxide abundant in red mud and the added sodium silicate form a composite alkali activator, which together activates the activity of Al2O3, SiO2, and other substances in metakaolin, fly ash, and slag, promotes the formation of Si-O-Al bonds, promotes the full occurrence of the solidification reaction, and effectively consumes the alkali in the red mud, thereby improving the solidification effect.

[0030] 2. The active silica and active alumina in red mud directly participate in the geopolymerization reaction as reactive components, providing more reactive substances for the geopolymerization reaction, further promoting the occurrence of the geopolymerization reaction, and improving the solidification effect;

[0031] 3. The added calcium chloride provides calcium ions to participate in the curing reaction in the form of "volcanic ash reaction" with the hydroxide ions remaining from the geopolymerization reaction, generating curing products such as CSH, which further consumes the alkali in the red mud and improves the curing effect;

[0032] 4. The added nano-sized nano-filler dispersant will fill the micro-pores of the solidified red mud, improving its density;

[0033] 5. The nano-filler dispersant has a very high specific surface area, which will be uniformly distributed in the reactants to form reaction nuclei, playing the role of "site nucleation", promoting the uniform dispersion of reactants and reaction products, and improving the overall strength of solidified red mud.

[0034] 6. The externally added sodium silicate and the sodium hydroxide abundant in the red mud synergistically stimulate the polymerization reaction; at the same time, sodium silicate will also react with metal oxides such as iron and aluminum in the red mud to generate corresponding silicate compounds to improve the overall performance of the solidified red mud.

[0035] 7. This invention effectively utilizes industrial solid waste to prepare red mud solidifier at room temperature, which has the advantages of safety, environmental protection, and cost-effectiveness. It is applicable to road mixing and factory mixing methods, and has the advantages of wide applicability and convenience. Attached Figure Description

[0036] Figure 1 This is the X-ray diffraction (XRD) pattern of the solidified red mud in Example 2 of the present invention.

[0037] Figure 2 This is a field emission scanning electron microscope (SEM) image of the solidified red mud in Example 2 of the present invention. Detailed Implementation

[0038] Typical embodiments embodying the features and advantages of the present invention will be specifically described in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the present invention.

[0039] The red mud used in this embodiment of the invention is Bayer process red mud, provided by a company in Nanchuan District, Chongqing. In the following specific embodiments, the moisture content of the solidified red mud is 15%, and the mass ratio of red mud solidifying agent to red mud is 1:4.

[0040] The main chemical components of the industrial solid waste materials used in the implementation of this invention are shown in Table 1.

[0041] Table 1 Main chemical composition of materials used / %

[0042]

[0043] Example 1

[0044] In this embodiment, metakaolin accounts for a fixed 20% of the curing agent's mass, while fly ash, slag, calcium chloride, sodium silicate, and nano-filler dispersant (nano-silica in this embodiment) together account for 80% of the curing agent's mass. A five-factor, five-level orthogonal experimental design was developed for these five raw materials. The levels of each factor are represented by numbers 1-5, as follows: fly ash (5 parts, 7.5 parts, 10 parts, 15 parts, 20 parts), slag (1 part, 5 parts, 10 parts, 15 parts, 20 parts), calcium chloride (0 parts, 3 parts, 6 parts, 10 parts, 15 parts), sodium silicate (1 part, 3 parts, 6 parts, 10 parts, 15 parts), and nano-filler dispersant (0 parts, 3 parts, 5 parts, 7 parts, 10 parts). Z1-Z25 represent 25 samples.

[0045] Table 2. Five-factor, five-level orthogonal experimental design.

[0046]

[0047] In this embodiment, taking Z2 as an example, the mass of red mud is 246g;

[0048] The red mud solidifying agent accounts for 20% of the mass of the solidified red mud;

[0049] In the preparation of red mud curing agent, metakaolin accounts for 20% of the mass of the curing agent;

[0050] In the curing agent, the remaining mass after removing metakaolin is as follows: fly ash: slag: calcium chloride: sodium silicate: nano-filler dispersant = 19.23%: 19.23%: 11.54%: 11.54%: 38.46%;

[0051] The nano-filler dispersant is nano-silica;

[0052] The preparation and application methods of the red mud solidifying agent are as follows:

[0053] (1) Dry the metakaolin, fly ash, slag, calcium chloride and nano-filler dispersant at 50°C. Then, mix the metakaolin, fly ash, slag, calcium chloride and nano-filler dispersant evenly according to the mass ratio, dry and seal for storage.

[0054] (2) Weigh out the appropriate mass ratio of water and add sodium silicate, control the water-cement ratio to 0.5, stir until the sodium silicate is completely dissolved, and obtain sodium silicate solution;

[0055] (3) Pour the sodium silicate solution evenly into the mixture of step (1) and stir thoroughly to form a red mud solidifying agent;

[0056] (4) Add the curing agent to the red mud and mix thoroughly;

[0057] (5) Add water to the mixture formed in step (4) according to the optimal moisture content determined by the compaction test and the natural moisture content of the red mud, and stir evenly again;

[0058] (6) Observe whether there are lumps of powder, crush the powder that clumps due to uneven moisture absorption, and let it sit for 24 hours.

[0059] (7) Compact the material according to the maximum dry density determined by the compaction test;

[0060] (8) Perform standard condition maintenance according to project requirements.

[0061] According to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009), cylindrical specimens with a diameter of φ50mm×50mm were prepared to test the 28-day unconfined compressive strength of solidified red mud.

[0062] The preparation, application, and testing processes for the remaining 24 groups of red mud solidifying agents were the same as those described above.

[0063] Example 2

[0064] The optimal ratio of the curing agent was determined through orthogonal experiments in Example 1, specifically fly ash: slag: calcium chloride: sodium silicate: nano-filler dispersant = 32.26%: 16.13%: 9.68%: 9.68%: 32.26%. To further improve the mechanical properties of the cured red mud, this example, while maintaining the above optimal ratio, optimized the combination of nano-filler dispersants: a three-factor, five-level orthogonal experiment was conducted using nano-silica, nano-alumina, and carbon nanotubes, as shown in Table 3. The levels 1-5 for the three materials are: nano-silica (0.5 parts, 2.5 parts, 5 parts, 7.5 parts, 10 parts), nano-alumina (0.5 parts, 2.5 parts, 5 parts, 7.5 parts, 10 parts), and carbon nanotubes (0.5 parts, 2.5 parts, 5 parts, 7.5 parts, 10 parts). N1-N25 represent 25 samples.

[0065] Table 3. Three-factor, five-level orthogonal experimental design table

[0066]

[0067]

[0068] Taking N24 as an example, in this embodiment, the mass of red mud is 246g;

[0069] The red mud solidifier accounts for 25% of the red mud mass;

[0070] In the preparation of red mud curing agent, metakaolin accounts for 20% of the mass of the curing agent;

[0071] In the curing agent, the remaining mass after removing metakaolin is as follows: fly ash: slag: calcium chloride: sodium silicate: nano-filler dispersant = 32.26%: 16.13%: 9.68%: 9.68%: 32.26%;

[0072] In the nano-filled dispersant, the ratio of nano-silica: nano-alumina: carbon nanotubes is 55.56%: 41.67%: 2.78%.

[0073] The preparation, application, and testing methods of the solidified red mud and the remaining 24 groups of tests were all in accordance with Example 1, and SEM and XRD tests were performed on the N24 group of samples.

[0074] Example 3

[0075] In this embodiment, a red mud curing agent is used to partially replace the cement curing agent in traditional red mud curing to form a curing agent, thereby preparing the cured red mud. The ratio of cement to red mud curing agent is 75% to 25%.

[0076] The average particle size of cement is 10-30 μm, and its main chemical components include CaO and SiO2.

[0077] The raw materials for the red mud solidifier, including metakaolin, fly ash, slag, calcium chloride, sodium silicate, and nano-filler dispersant, have the same mass fractions as in Example 2. The ratio of the three nanomaterials in the nano-filler dispersant is the optimal ratio of the three nanomaterials obtained in Example 2: nano silica: nano alumina: carbon nanotubes = 90.9%: 4.5%: 4.5%.

[0078] The preparation and application method of the solidified red mud is as described in Example 1, in which cement is used as one of the raw materials for the solidifying agent and is dried and mixed with other raw materials.

[0079] According to the Technical Specification for Construction of Highway Pavement Base Course (JTJ034-2000), the road performance indicators of solidified red mud, such as 7-day immersion compressive strength (7d), splitting strength (3d, 7d, 28d), and compressive rebound (3d, 7d, 28d), were tested.

[0080] Example 4

[0081] In this embodiment, a red mud curing agent is used to partially replace the cement curing agent in traditional red mud curing to form a curing agent, thereby preparing the cured red mud. The ratio of cement to red mud curing agent is 50% to 50%.

[0082] The raw materials and their proportions of the curing agent are the same as those in Example 3.

[0083] The properties of the cement are the same as those in Example 3.

[0084] The preparation, application, and testing methods of the solidified red mud are described in Example 3.

[0085] Example 5

[0086] In this embodiment, a red mud curing agent is used to partially replace the cement curing agent in traditional red mud curing to form a curing agent, thereby preparing the cured red mud. The ratio of cement to red mud curing agent is 25% to 75%.

[0087] The raw materials and their proportions of the curing agent are the same as those in Example 3.

[0088] The properties of the cement are the same as those in Example 3.

[0089] The preparation, application, and testing methods of the solidified red mud are described in Example 3.

[0090] Example 6

[0091] In this embodiment, a red mud curing agent is used to partially replace the cement curing agent in traditional red mud curing to form a curing agent, thereby preparing the cured red mud. The ratio of cement to red mud curing agent is 10% to 90%.

[0092] The raw materials and their proportions for the red mud solidifying agent are the same as those in Example 3.

[0093] The properties of the cement are the same as those in Example 3.

[0094] The preparation, application, and testing methods of the solidified red mud are described in Example 3.

[0095] Example 7

[0096] In this embodiment, a red mud curing agent is used to partially replace the cement curing agent in traditional red mud curing to form a curing agent, thereby preparing the cured red mud. The ratio of cement to red mud curing agent is 0:100%.

[0097] The raw materials and their proportions for the red mud solidifying agent are the same as those in Example 3.

[0098] The preparation, application, and testing methods of the solidified red mud are described in Example 3.

[0099] Example Test Result Analysis

[0100] The test results for each group of examples are shown in Table 4-8.

[0101] Table 4 shows that the 28-day unconfined compressive strength of the solidified red mud in Example 1 reached 2.03 MPa, with an average strength of 2.77 MPa, both higher than the strength of commonly used highway pavement base materials. In Example 2, the lowest compressive strength of the solidified red mud was 2.5 MPa, with an average strength of 4.95 MPa, a significant increase compared to Example 1. This indicates that changing the proportion of the nanofiller dispersant has a significant impact on the compressive strength of the solidified red mud. Table 4: Test results of Examples 1 and 2

[0102]

[0103] Depend on Figure 1 The XRD images shown indicate that the main components of the solidified red mud in group N24 of Example 2 include calcite (CaCO3), Kato stone (Ca3Al2(SiO4)(OH)8), rheinstone (Ca5(SiO4)2(OH)2), dicalcium silicate (Ca2SiO4), Al2O3, and hematite (Fe2CO3) generated by geopolymerization reaction, and hydrated calcium silicate (CSH) and hydrated calcium aluminate (CAH) generated by hydration and hydrolysis reaction; Figure 2 As can be seen from the SEM images, the microstructure of the solidified red mud in group N24 mainly consists of a three-dimensional network of high-density material generated by the geopolymerization reaction and a gel-like material generated by the hydration and hydrolysis reaction. Due to the filling and dispersing effect of the nano-filler dispersant, the microstructure of the solidified red mud is relatively uniform and dense.

[0104] The "Technical Specification for Construction of Highway Pavement Base Course" (JTG D40-2011) specifies the 7-day immersion compressive strength as the evaluation index for the road performance of road base course materials. Table 5 shows the 7-day immersion compressive strength of Examples 3-7, indicating that the solidified red mud prepared in Examples 3-7 has 7-day immersion compressive strengths of 3.2 MPa, 2.1 MPa, 1.4 MPa, 1.1 MPa, and 1 MPa, respectively. According to the requirements for the 7-day immersion compressive strength of base course materials in the "Technical Specification for Construction of Highway Pavement Base Course" (JTG D40-2011) (as shown in Table 6), compared with lime-stabilized or lime-fly ash-stabilized road materials, the solidified red mud prepared in Examples 3-7 meets the application requirements for base and subbase courses in various highway application scenarios. Therefore, the solidified red mud prepared in Examples 3-7 can be applied in engineering projects with reference to lime-stabilized or lime-fly ash-stabilized materials. Compared to cement-stabilized materials, when the red mud curing agent of this invention replaces cement by 25%, the prepared solidified red mud can meet the strength requirements of base and subbase layers for all highway grades. When the replacement ratio is 50%, it cannot meet the strength requirements of base materials for expressways and Class I highways, but it can meet the strength requirements of all other cases. When the replacement ratio is above 75%, it cannot meet the requirements of cement-stabilized materials. Therefore, when the replacement ratio of the red mud curing agent of this invention is below 50%, cement-stabilized materials can be referenced; when the replacement ratio of the red mud curing agent of this invention is above 75%, lime-stabilized or lime-fly ash-stabilized materials can be referenced for engineering applications of the solidified red mud.

[0105] Table 5. 7-day immersion compressive strength of Examples 3-7

[0106]

[0107] Table 6 Standard for 7-day immersion compressive strength of different stability types of base courses

[0108]

[0109] Table 7 shows the splitting tensile strength and compressive resilient modulus of the solidified red mud in Examples 3-7. Table 8 lists the empirical ranges for the splitting tensile strength and compressive resilient modulus of different types of base courses (lime-soil and lime-fly ash soil) in Appendix B of the "Road Design Specification" (JTG D50-2017). This standard is a local standard of Shanghai and is one of the few standards that provides empirical ranges for splitting tensile strength and compressive resilient modulus. The empirical ranges in the standard are not used to restrict the parameter values ​​of the base course materials, but rather to provide a reference value for the above parameters in the absence of experimental data, so as to meet the needs of pavement structure calculations such as the calculation of tensile stress at the bottom of the base course and the calculation of road surface deflection.

[0110] Combining the data in Tables 7 and 8, it can be seen that the test results of the splitting strength and compressive rebound strength of the solidified red mud prepared in Examples 3-7 differ from the design reference values ​​in Appendix B of the "Road Design Specification" (JTG D50-2017). Regarding the splitting strength index, the 3-day splitting strength of all five examples is lower than the standard reference range for lime-fly ash soil and lime-soil; the 7-day splitting strength of Examples 4, 5, 6, and 7 is lower than the standard reference range for lime-fly ash soil and lime-soil, while the 7-day splitting strength of Example 3 is within the standard reference range for lime-fly ash soil and lime-soil; the 28-day splitting strength of Examples 6 and 7 is lower than the standard reference range for lime-fly ash soil and lime-soil, while the 28-day splitting strength of Examples 3, 4, and 5 is within the standard reference range for lime-fly ash soil, and the 28-day splitting strength of Example 5 is also within the standard reference range for lime-soil, while the 28-day splitting strength of Example 3 is higher than the standard reference range for lime-soil.

[0111] Regarding the compressive resilient modulus, the 3-day compressive resilient modulus of Examples 5, 6, and 7 is lower than the standard reference range for lime-fly ash soil and lime-soil. The 3-day compressive resilient modulus of Examples 3 and 4 is within the standard range for lime-soil but lower than the standard range for lime-fly ash soil. The 7-day compressive resilient modulus of Examples 6 and 7 is lower than the standard reference range for lime-fly ash soil and lime-soil. The 7-day compressive resilient modulus of Examples 3 and 4 is within the standard reference range for lime-fly ash soil and lime-soil. The 7-day compressive resilient modulus of Example 5 is lower than the standard reference range for lime-fly ash soil but within the standard reference range for lime-soil. The 28-day compressive resilient modulus of Example 5 is within the standard reference range for lime-fly ash soil and lime-soil. The 28-day compressive resilient modulus of Examples 6 and 7 is lower than the standard reference range for lime-fly ash soil but within the standard reference range for lime-soil. The 28-day compressive resilient modulus of Example 3 is higher than the standard reference range for lime-fly ash soil and lime-soil. The 28-day compressive resilient modulus of Example 4 is within the standard reference range for lime-fly ash soil but higher than the standard reference range for lime-soil.

[0112] In summary, the solidified red mud prepared by this invention has a splitting strength and compressive resilient modulus less than or equal to the standard reference range when the curing time is short (3d, 7d); and a splitting strength and compressive resilient modulus greater than or equal to the standard reference range when the curing time is long (28d).

[0113] Table 7 Splitting strength and compressive resilient modulus of solidified red mud in Examples 3-7

[0114]

[0115] Table 8 shows the relationship between the splitting tensile strength and compressive resilient modulus of Examples 3-7 and the standard value range.

[0116]

[0117]

[0118] In summary, the solidified red mud prepared by this invention meets the road performance indicators (7-day immersion compressive strength) of the road base course structure as required by the "Technical Specification for Construction of Highway Pavement Base Course" (JTG D40-2011). Furthermore, its splitting strength and compressive resilient modulus are not significantly different from the values ​​for lime-soil and lime-fly ash-soil base courses in Appendix B of the "Pavement Design Specification" (JTG D50-2017). Therefore, the red mud solidifier prepared by this invention can be used as a qualified highway pavement base course material with excellent road performance. Moreover, in the absence of relevant experimental data, the splitting strength and compressive resilient modulus of the solidified red mud base course structure can be determined by referring to existing standards for pavement structure calculations, demonstrating its compatibility with existing standards. This invention not only provides strong data support for the large-scale resource utilization of red mud but also offers a new, environmentally friendly, and economical material option for the road engineering field.

[0119] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A red mud solidification agent, characterised in that, Raw material preparation including the following components: Metakaolin accounts for 18-22% of the total mass of the red mud solidifier; The remaining mass of the curing agent after removing metakaolin consists of, by mass parts, 5-20 parts fly ash, 1-20 parts slag, and 1-15 parts sodium silicate as alkaline activator. It also includes a nano-filler dispersant, which is a mixture of nano-silica, nano-alumina and carbon nanotubes. By mass, the nano-silica is 0.5-10 parts, the nano-alumina is 0.5-10 parts, and the carbon nanotubes are 0.5-10 parts. In the remaining mass after removing metakaolin, the amount added is 1-10 parts by mass. It also includes calcium chloride, which is added in the amount of 1-15 parts by mass of the remaining mass after removing metakaolin, and the average particle size of calcium chloride is 1-10 μm; The curing agent accounts for 23-27% of the mass of the red mud; The average particle size of the metakaolin is 8-12 μm, the average particle size of the fly ash is 22-26 μm, the specific surface area of ​​the slag is 350-450 m² / kg, and the average particle size of the sodium silicate is 1-10 μm.

2. A red mud solidifier according to claim 1, characterised in that: The average particle size of the nano-silica is 60-100nm, and the specific surface area is 120-200m² / g; the average particle size of the nano-alumina is 20nm, and the specific surface area is 120-150m² / g; the average particle size of the carbon nanotubes is 2-20nm, and the specific surface area is 100-500m² / g.

3. A red mud solidification agent according to claim 1, characterised in that: The remaining mass of the solidifier after removing metakaolin is as follows: fly ash: slag: calcium chloride: sodium silicate: nanofiller dispersant: 32.26%: 16.13%: 9.68%: 9.68%: 32.26%.

4. The method for preparing the red mud solidifying agent according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Dry each raw material except sodium silicate at a temperature of 50-60℃, then mix them evenly according to the proportion of each raw material, dry and seal them for storage; (2) Weigh out the appropriate amount of water and add sodium silicate, control the water-cement ratio to be 0.4-0.6, stir until the sodium silicate is completely dissolved, and obtain sodium silicate solution; (3) Pour the sodium silicate solution evenly into the mixture in step (1) according to the proportion and stir thoroughly to form a red mud solidifying agent.

5. The application of the red mud solidifying agent as described in claim 1, characterized in that, Includes the following steps: (1) According to the engineering needs, the prepared red mud curing agent is used to replace the conventional cement to form red mud curing agent. The ratio of red mud curing agent to cement is 0-1:1-0, and the addition ratio of red mud curing agent is greater than 0. (2) The curing agent accounts for 23-27% of the mass of the red mud; (3) Add the red mud solidifying agent into the red mud according to the mass ratio, and mix and stir evenly; (4) Add water to the mixture formed in step (3) according to the optimum moisture content determined by the compaction test and the natural moisture content of the red mud, and stir it evenly again; (5) Observe whether there are clumps of powder due to uneven moisture absorption, crush the clumps of powder, and let it sit for 24 hours; (6) Compact the material according to the maximum dry density determined by the compaction test; (7) Curing is carried out according to the project requirements to form solidified red mud that meets the project requirements.

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