Method for recycling multi-source solid waste of red mud by titanium gypsum itself

Abstract

The application belongs to the technical field of solid waste resource processing, and provides a multi-source solid waste recycling method for activating red mud by titanium gypsum itself, which comprises the steps of pretreating red mud, pretreating titanium gypsum, drying and crushing, stirring, pouring, curing and the like. Through selection and proportioning of raw materials and specific setting of each step, a cementing material with low heavy metal leaching risk that can be used in some application scenarios can be obtained, high proportioning amount of Bayer red mud is recycled, and comprehensive recycling of all solid waste including fly ash and titanium gypsum without adding other activators is realized.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a multi-source solid waste reuse method for titanium gypsum-induced red mud. Background Technology

[0002] This invention is the research result of the project "Red mud for saline-alkali land improvement and land reclamation utilization and environmental risk assessment".

[0003] With the annual increase in industrial solid waste emissions, the efficient resource utilization of bulk solid wastes such as red mud, fly ash, and titanium gypsum has become an urgent environmental and resource issue. Red mud includes Bayer process red mud and Kawazu red mud. Bayer process red mud is a highly alkaline waste residue generated during the Bayer process in the aluminum industry, with an annual discharge exceeding ten million tons. Its main components are Fe2O3, Al2O3, and Na2O, with inert minerals such as hematite, boehmite, and anorthite as the main phases. It has extremely low cementing activity, and traditional utilization methods mainly involve stockpiling, which not only occupies a large amount of land but also poses the risk of soil and groundwater pollution from alkaline leachate. Unlike Kawazu red mud, Bayer process red mud is not suitable for building material utilization. Due to its strong alkalinity, it faces many problems in the resource utilization process.

[0004] Fly ash is a byproduct of coal-fired power plants. It is rich in SiO2 and Al2O3, and its phases are mainly quartz and mullite. It also has typical amorphous bulging peaks in the range of 2θ=15°~40°, which has potential pozzolanic activity. However, when used alone, the hydration reaction rate is slow and the early strength is low.

[0005] Titanium gypsum is a byproduct of titanium dioxide production via the sulfuric acid process. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), and its Ca... 2+ With SO4 2- It can participate in the gelation reaction to produce products such as ettringite, but unmodified titanium gypsum has defects such as unstable setting time and large volume shrinkage.

[0006] Existing technologies for the resource utilization of the aforementioned solid wastes primarily focus on activating cementitious activity and improving mechanical properties. For example, the strong alkalinity of red mud can be used to activate the pozzolanic reaction of fly ash, or the sulfate effect of titanium gypsum can be used to promote the formation of hydration products. However, red mud, fly ash, and titanium gypsum, as industrial solid wastes, inevitably contain heavy metals such as lead, cadmium, chromium, and arsenic. Current research and technologies rarely investigate the risk of secondary pollution to soil and groundwater caused by the leaching of heavy metals from cementitious materials prepared from solid waste during long-term service. If solid waste-based cementitious materials are applied to construction projects, roadbeds, and other applications, the release of heavy metals through rainwater leaching and groundwater soaking will violate the environmental protection principles of solid waste resource utilization and may even lead to serious environmental problems.

[0007] Chinese invention patent application CN115974433A discloses a red mud-based cementitious material, its preparation method, and its application. It improves the material strength by using red mud, slag, desulfurized gypsum, and an alkaline activator, but does not address the risk control of heavy metal leaching. Chinese invention patent application CN101624267A discloses a low-temperature ceramic solidifier for Bayer process red mud, which also proposes to achieve its strength requirements by adding a relative amount of activating material, but does not conduct in-depth research on the fixation mechanism of heavy metals in solid waste.

[0008] Therefore, how to achieve stable fixation of heavy metals while stimulating the gelling activity of solid waste and ensuring the mechanical properties of materials has become a key technical bottleneck in the field of Bayer process red mud solid waste recycling. Summary of the Invention

[0009] This invention aims to provide a multi-source solid waste recycling method for red mud self-activated by titanium gypsum to solve the above-mentioned technical problems. This method uses titanium gypsum as a self-activating material without adding additional activating materials, and can achieve the synergistic utilization of various bulk solid wastes such as Bayer process red mud, fly ash, and titanium gypsum. The red mud utilization rate is high, the process parameters are clear, the strength performance is stable and the strength meets the standard (this refers to the strength of cementitious materials without added reinforcing phases), and the risk of heavy metal leaching is very low. It can be widely used in engineering fields such as road base courses and foundation pit backfilling.

[0010] The present invention solves the above-mentioned technical problems by adopting the following specific technical solution: A method for reusing multi-source solid waste from titanium gypsum-induced red mud includes the following steps: S1, Pretreatment of red mud: Bayer process high-iron red mud and water are mixed at a liquid-to-solid ratio of (5~10) ml: 1 g to obtain red mud slurry. Then, CO2 is introduced into the red mud slurry at a rate of 100~125 L / kg. 赤泥 The red mud slurry is introduced for 2 to 6 hours and continuously stirred to stabilize the pH value below 10.5. Then, solid-liquid separation (e.g., pressure filtration) is performed to obtain solid matter, thus obtaining pretreated red mud.

[0011] S2, Pretreated titanium gypsum: Mix titanium gypsum with 4~6mol / L NaOH solution at a liquid-to-solid ratio of (3~5)ml:1g, and stir continuously at 60~80℃ for 1~2h. Then, separate the solid and liquid to obtain a solid, and wash the solid until it is neutral to obtain pretreated titanium gypsum.

[0012] S3, Drying and pulverizing: The pretreated red mud obtained in S1, the pretreated titanium gypsum obtained in S2, and the fly ash are placed into an oven and dried at 100~110℃ for 20~28h. After drying, the dried materials are placed into a ball mill for ball milling to obtain pulverized materials.

[0013] S4, Stirring: Select 62-69 parts by weight of Bayer process high-speed iron red mud, 20-28 parts by weight of titanium gypsum and 8-12 parts by weight of fly ash after crushing in step S3 and put them into a mixer. At the same time, add 30-60 parts by weight of water, stir slowly for 1-3 minutes, and then stir quickly for 1-3 minutes.

[0014] S5, Pouring: After the material from step S4 has been mixed, quickly pour it into the mold while vibrating the mold 18-28 times.

[0015] S6, Curing: After casting, the material and mold are placed together in an environment with a temperature of 18~22℃ and a relative humidity of 93~98% for curing for 0.8~1.2 days. Then, the material is demolded and cured in dry air for 1~2 days. Then, it is placed back into the curing chamber in an environment with a temperature of 18~22℃ and a relative humidity of 93~98% for another 53~62 days to obtain a cementitious material product with low heavy metal leaching.

[0016] Preferably, in step S4, after the Bayer process high-iron red mud, titanium gypsum and fly ash are placed into the mixer, NaOH is first added to the water while stirring until the pH reaches 9.0~10.0 to obtain alkaline water. Then, mineral humic acid is added to the alkaline water to prepare a 0.5~2wt.% humic acid aqueous solution. Then, the humic acid aqueous solution replaces 30~60 parts by weight of water.

[0017] Preferably, in step S6, after demolding and before curing in dry air, a photothermal synergistic curing process is performed, specifically: after demolding, the material is placed in an 800~1000W / m² curing chamber. 2 Irradiate the material in a near-infrared light source for 35-50 minutes, then heat the material to 70-90℃ and maintain this constant temperature for 25-50 minutes; then carry out the curing process in dry air.

[0018] Preferably, in step S1, the Bayer process high-iron red mud contains 46.96~55.36 wt.% Fe2O3 and 21.86~27.35 wt.% Al2O3 by mass percentage of oxides.

[0019] Further preferably, the Bayer process high-iron red mud is a Bayer process red mud solid waste containing, by mass percentage of oxides: Fe2O3: 46.96~55.36 wt.%, Al2O3: 21.86~27.35 wt.%, SiO2: 6.02~9.05 wt.%, Na2O: 4.21~6.65 wt.%, CaO: 2.00~3.96 wt.%, MgO: 0.10~0.51 wt.%, SO3: 0.20~0.60 wt.%, with the balance being impurities.

[0020] Further optimization, in step S4, the process of first slowly stirring for 1-3 minutes and then rapidly stirring for 1-3 minutes specifically involves: first slowly stirring at a speed of 130-150 r / min and 50-70 r / min, and then rapidly stirring at a speed of 270-300 r / min and 110-140 r / min for 1-3 minutes.

[0021] Further preferably, the CO2 source in step S1 is industrial waste gas.

[0022] Further preferably, after solid-liquid separation in step S1 (e.g., after pressure filtration), the solid material (e.g., filter cake) is washed with clean water 2 to 3 times.

[0023] Preferably, in step S2, the titanium gypsum contains, by mass percentage of oxides, SO3: 40.01~51.80 wt.%, CaO: 25.21~32.16 wt.%, Fe2O3: 10.06~16.86 wt.%, SiO2: 2.06~5.01 wt.%, MgO: 1.68~2.95 wt.%, Al2O3: 0.95~1.36 wt.%, Na2O: 0.36~0.81 wt.%, and the balance being impurities.

[0024] Preferably, the dry air in step S4 is an air environment with a temperature of 20~25℃ and a humidity of 30~40%.

[0025] Preferably, in step S3, the ball milling is to pulverize and ball mill the material until the particle size is 80~120 mesh.

[0026] Preferably, the fly ash in step S3 contains, by mass percentage of oxides, SiO2: 43.01~48.93 wt.%, Al2O3: 37.03~42.18 wt.%, CaO: 4.65~6.58 wt.%, Fe2O3: 2.03~5.95 wt.%, MgO: 0.43~0.68 wt.%, SO3: 1.01~1.80 wt.%, and Na2O: 0.61~1.28 wt.%.

[0027] Preferably, the titanium gypsum in step S2 is an industrial by-product gypsum produced during the sulfuric acid process for producing titanium dioxide.

[0028] Preferably, the 60-day compressive strength of the cementitious material product obtained in step S6 is 2.2~3.05 MPa; under acidic conditions, the leaching concentration of V is less than 30 μg / L, the leaching concentration of Cd is less than 4 μg / L, the leaching concentration of As is less than 50 μg / L, the leaching concentration of Pb is less than 40 μg / L, and the leaching concentration of Hg is less than 20 μg / L.

[0029] The compressive strength described in this invention refers to the strength of the cementitious material before the addition of cement or substances such as sodium hydroxide or sodium silicate, and is not the strength of the prior art after the addition of reinforcing phases.

[0030] The technical advantages of this invention are as follows: 1. The primary objective of this invention is not to produce cementitious materials with superior strength or other properties, but rather to effectively utilize existing solid waste to obtain compliant cementitious materials without secondary pollution; that is, the main objective is the reuse of solid waste. This invention uses titanium gypsum as a self-generated solid waste material, along with Bayer red mud (which is difficult to reuse) and fly ash as all solid waste raw materials, to obtain a cementitious material with low heavy metal leaching, achieving the multi-source solid waste reuse effect of titanium gypsum-generated red mud. The calcium sulfate dihydrate contained in titanium gypsum can naturally dissociate into Ca in the hydration system. 2+ and SO4 2- SO4 2- As a natural activating component, it can synergistically interact with the alkaline substances remaining in Bayer process red mud without the need for additional external activators. The alkaline environment provided by the Bayer process red mud disrupts the crystal structure of silicon and aluminum in fly ash, while titanium gypsum provides SO4. 2- It reacts with dissolved active aluminum to form sulfoaluminates such as calcium vanadate; simultaneously, the active silica-alumina component in fly ash (determined by its pozzolanic activity) can react with the aforementioned dissociated Ca 2+A hydration reaction occurs, forming cementitious products such as calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH). By specifically setting the ratio of titanium gypsum, Bayer red mud, and fly ash as raw materials, the requirement of low heavy metal leaching rate can be achieved while meeting the strength requirements. Through the specific ratio setting of raw materials in this invention, a relatively large amount of calcium vanadate and hydration cementitious products are formed, which play a dual role in the physical adsorption and chemical fixation of heavy metals. The formed hydration products can encapsulate heavy metals in a network structure, hindering their migration; and the structure of the formed hydration products contains a large number of pores, which adsorb heavy metals. At the same time, the formed hydration cement itself also has a strong adsorption effect on heavy metals. By specifically setting the preparation process and parameters, during the formation of the hydration product structure, heavy metals can replace calcium ions and directly participate in the formation of the hydration products and be fixed. Therefore, the concentration of heavy metals in the leachate is low, and the risk of heavy metal leaching is relatively low. This ensures that under acidic conditions, the leaching rates of various heavy metals meet the Class V water standards (vanadium reaches the standard limit for drinking water and cadmium reaches the Class III water limit). As a result, the cementitious material formed from solid waste can achieve the reuse of solid waste without secondary pollution during application due to the low heavy metal leaching rate.

[0031] 2. This invention involves specific pretreatment of solid waste raw materials, specifically weak acid elution of Bayer process red mud (CO2 reacts with water to form a weakly acidic body, which then reacts with the red mud) to remove free alkali. Through the specific setup of this invention, approximately 60% of free sodium is removed via weak acid elution. + and some soluble As, Cr 6+ At the same time, avoid excessive dissolution of iron and aluminum oxides (carbonic acid is a weak acid, with an ionization constant Ka1 = 4.3 × 10⁻⁶). -7 Ka2 = 5.6 × 10 -11 This method avoids excessive dissolution of iron and aluminum oxides such as Fe2O3 and Al2O3 in the red mud. Furthermore, because it uses a continuous carbon dioxide inlet method, there is no need to introduce foreign ions, and the product is CaCO3, which is environmentally friendly and provides excellent pretreatment conditions for the subsequent comprehensive utilization of Bayer process red mud.

[0032] By subjecting titanium gypsum to alkaline activation through contact with NaOH solution, the strongly alkaline environment can act on the defect sites and hydroxyl sites on the surface of titanium gypsum particles, disrupting and reconstructing the surface lattice structure, thereby improving surface activity. Although the overall solubility of CaSO4·2H2O does not significantly increase under strongly alkaline conditions, and even the free Ca... 2+ The concentration of Ca2+ may decrease due to the formation of Ca(OH)2 or participation in precipitation reactions, but limited dissolution, ion migration, and interfacial reactions may still occur on its surface, providing local Ca2+ for subsequent reactions with activated silica-alumina components in fly ash and red mud.2+ and SO4 2- This process promotes the formation of hydration products. Higher surface activity increases its reactivity with other raw materials (fly ash, red mud). This activation method enhances the later hydration rate and early strength, particularly benefiting the synergistic reaction with the pozzolanic reaction of fly ash. This reduces pH and soluble heavy metal content from a raw material perspective, preventing excessive alkali reaction or ion interference later. By washing the material to the center after alkali soaking, residual NaOH can be removed, and the alkali solution can be recovered for reuse.

[0033] 3. By setting up a standard wet curing process followed by dry air curing, and then a second standard wet curing, the initial wet curing achieves rapid hydration, skeleton formation, and prevention of cracking. The intermediate dry curing releases internal stress, stabilizes volume, and inhibits excessive expansion. The subsequent wet curing achieves deep hydration, continuous strength enhancement, and structural densification. In a further optimized scheme, infrared light irradiation combined with constant-temperature heating during the dry curing process utilizes the photothermal effect of iron oxide to accelerate CASH gelation, shorten the induction period, and improve early strength to a certain extent. This ensures that the product formed from multi-source solid waste meets strength standards.

[0034] 4. By adding humic acid during the stirring process (in the preferred embodiment), biomacromolecules can rapidly react with Pb in the slurry. 2+ Cd 2+ Plasma further forms stable complexes; and by bridging the particle cross-sections through hydrogen bonding and electrostatic interactions, it enhances density to some extent. Furthermore, the active functional groups in humic acid can, to some extent, react with the Ca released from titanium gypsum. 2+ and SO4 2- Combining, promoting Ca 2+ and SO4 2- The diffusion and reaction of titanium gypsum enhance its self-activation effect. This enables the efficient recycling and reuse of multi-source solid wastes, including Bayer process red mud, fly ash, and titanium gypsum. Combined with the self-activation effect of titanium gypsum, no additional activator is needed in the system of this invention to obtain a qualified cementitious material. Attached Figure Description

[0035] Figure 1 The XRD pattern of the titanium plaster selected in Example 1 of this invention is shown.

[0036] Figure 2 The XRD pattern of the red mud selected in Example 1 of this invention is shown.

[0037] Figure 3 The XRD pattern of fly ash selected in Example 1 of this invention is shown.

[0038] Figure 4 The XRD patterns of the products obtained in Example 1 and Comparative Examples 1 and 2 of this invention are shown.

[0039] Figure 5 Thermogravimetric analysis (TGA) diagrams of the products obtained in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown.

[0040] Figure 6 The Fourier transform infrared spectra of the products obtained in Example 1 and Comparative Examples 1 and 2 of this invention are shown. Detailed Implementation

[0041] The process technology solution of the present invention will be further described below with reference to embodiments and accompanying drawings. Unless otherwise specified, each feature is merely one example of a series of equivalent or similar features. These embodiments are merely for the purpose of aiding understanding the present invention and should not be considered as specific limitations thereof. Example 1

[0042] This embodiment illustrates the multi-source solid waste reuse method of titanium gypsum-induced red mud according to the present invention, including the following steps: S1, Pretreatment of Red Mud: Bayer process high-iron red mud and water are mixed at a liquid-to-solid ratio of 6 ml: 1 g to obtain red mud slurry. Then, CO2 is introduced into the red mud slurry at a rate of 115 L / kg. 赤泥 (115L of carbon dioxide is used per kilogram of red mud), and the carbon dioxide is introduced for 3 hours with continuous stirring to stabilize the pH value of the red mud slurry below 10.5. Then, solid-liquid separation is performed to obtain solid matter, thus obtaining pretreated red mud.

[0043] The Bayer process high-iron red mud is a solid waste containing, by mass percentage of oxides, Fe2O3: 50.96 wt.%, Al2O3: 24.81 wt.%, SiO2: 7.89 wt.%, Na2O: 5.91 wt.%, CaO: 2.99 wt.%, MgO: 0.2 wt.%, SO3: 0.3 wt.%, and 6.94 wt.% impurities.

[0044] XRD analysis of the Bayer process red mud solid waste yielded the following results: Figure 2 The XRD pattern shown; through Figure 2 It can be seen that the red mud used in this embodiment has multiple strong diffraction peaks of hematite at 2θ≈33°, 35°, 40°, 54°, 62°, and 65°, which are the most prominent minerals in the spectrum. That is, the Bayer process red mud used in this embodiment is high-iron red mud, and it is impossible to use existing treatment methods similar to those for Kawazu red mud for solid waste treatment.

[0045] S2, Pretreated titanium gypsum: Titanium gypsum is mixed with 5 mol / L NaOH solution at a liquid-to-solid ratio of 3.5 ml: 1 g, and stirred continuously at 68°C for 1.5 h. Then, solid-liquid separation is performed to obtain a solid, and the solid is washed until neutral to obtain pretreated titanium gypsum.

[0046] The titanium gypsum is a titanium gypsum solid waste containing, by mass percentage of oxides, SO3: 44.73 wt.%, CaO: 28.99 wt.%, Fe2O3: 13.69 wt.%, SiO2: 3.95 wt.%, MgO: 2.12 wt.%, Al2O3: 1.11 wt.%, Na2O: 0.59 wt.%, and 4.82 wt.% impurities.

[0047] XRD analysis was performed on the titanium gypsum solid waste, and the results were as follows: Figure 1 The XRD pattern shown; through Figure 1 It can be seen that the titanium gypsum used in this embodiment has the strongest diffraction peak at 2θ≈10°, which is a characteristic strong peak of gypsum, corresponding to the crystal plane family with the largest interplanar spacing in its crystal structure. It can also be seen that the gypsum crystals of this titanium gypsum have relatively few impurities.

[0048] S3, Drying and pulverizing: The pretreated red mud obtained in S1, the pretreated titanium gypsum obtained in S2, and the fly ash are placed in an oven and dried at 105℃ for 24 hours. The dried materials are then placed in a ball mill for ball milling to obtain powder with a particle size of 80~120 mesh.

[0049] The fly ash is fly ash containing, by mass percentage of oxides, 45.22 wt.% SiO2, 39.75 wt.% Al2O3, 5.64 wt.% CaO, 3.94 wt.% Fe2O3, 0.55 wt.% MgO, 1.40 wt.% SO3, 0.91 wt.% Na2O, and 2.59 wt.% impurities.

[0050] XRD analysis was performed on the fly ash solid waste, and the results were as follows: Figure 3 The XRD pattern shown is obtained through... Figure 3 The distribution of diffraction peaks indicates that while the fly ash contains a limited variety of crystalline phases, the high intensity of characteristic peaks suggests good crystallinity, enabling the active silica-alumina components to react with the dissociated Ca. 2+ A hydration reaction occurs, which meets the requirements of the fly ash needed for activation by mixing with titanium gypsum in this invention.

[0051] S4, Stirring: Select 65 parts by weight of Bayer process high-iron red mud, 25 parts by weight of titanium gypsum and 10 parts by weight of fly ash after crushing in step S3 and put them into a mixer. First, add NaOH to the water while stirring until the pH reaches 10.0 to obtain alkaline water. Then, add mineral humic acid to the alkaline water to prepare an aqueous solution of about 1 wt.%. Then, add 50 parts by weight of the aqueous solution of humic acid to the mixer and stir slowly for 2.2 minutes, and then stir rapidly for 2.5 minutes. (Specifically: First, slowly stir at a speed of 140 r / min rotation and 60 r / min revolution, then quickly stir at a speed of 280 r / min rotation and 120 r / min revolution. This first step of slow stirring gently allows the solid waste powders to come into full contact with water and be initially mixed, avoiding powder splashing and local agglomeration caused by excessive stirring speed, ensuring that each solid waste raw material is evenly immersed in water without premature release and deagglomeration; the second step of rapid stirring can generate sufficient shear force to break the inert layer on the surface of the fly ash and Bayer red mud, which are specific to this invention, promoting the full dissolution of active silica-alumina components and sulfate components, while also promoting SO4.) 2- With Ca 2+ AlO2 - The reaction facilitates the formation of hydration products such as ettringite, thereby enhancing the alkali activation effect of titanium gypsum.

[0052] S5, Pouring: After the material from step S4 has been mixed, quickly pour it into the mold while vibrating the mold 20 times.

[0053] S6, Curing: After casting, place the material and mold together in an environment with a temperature of 20±1℃ and a relative humidity of 95±1% for curing for 1 day, then demold. After demolding, place the material in a 900W / m 2 Irradiate the material in a near-infrared light source for 38 minutes, then heat it to 80°C and maintain this constant temperature for 40 minutes; then cure it in dry air for 1.5 days (dry air is an environment with a temperature of 20~25°C and a humidity of 30~40%), and then place it back into the curing chamber in an environment with a temperature of 20±1°C and a relative humidity of 95±1% for another 58 days to obtain a cementitious material product with low heavy metal leaching.

[0054] XRD analysis of the obtained cementitious material product yielded the following results: Figure 4 The results are shown. Example 2

[0055] This embodiment illustrates the multi-source solid waste recycling method of titanium gypsum self-activated red mud of the present invention without the addition of humic acid. The other settings of this embodiment are the same as those of embodiment 1. The difference is that in step S4, the humic acid aqueous solution is not prepared and added. Instead, 50 parts by weight of water is directly added as a binder.

[0056] Comparative Example 1 This comparative example is used to illustrate a comparative test showing the effects of insufficient red mud addition and excessive titanium gypsum addition. The difference between this comparative example and Example 1 is that in step S4, 50 parts by weight of Bayer process high-iron red mud, 40 parts by weight of titanium gypsum, and 10 parts by weight of fly ash are added to the mixer. All other settings are exactly the same as in Example 1. The compressive strength results are shown in Table 1, and XRD analysis yielded the following results: Figure 4 The results are shown.

[0057] Comparative Examples 1-2 This comparative example demonstrates a further comparative experiment based on the proportions of Comparative Example 1, without the use of pretreated red mud and pretreated titanium gypsum. The difference between this comparative example and Comparative Example 1 is that steps S1 and S2 are omitted, and the process begins directly from step S3. All other settings are exactly the same as in Comparative Example 1.

[0058] Comparative Example 2 This comparative example is used to illustrate a comparative test where the proportions of each raw material are set outside the numerical range of this invention. The difference between this comparative example and Example 1 is that in step S4, 55 parts by weight of Bayer process high-iron red mud, 30 parts by weight of titanium gypsum, and 15 parts by weight of fly ash are added to the mixer (none of these three materials are within the limits of this invention). The other settings are exactly the same as in Example 1. The compressive strength results are shown in Table 1, and XRD analysis yields the following results: Figure 4 The results are shown.

[0059] Comparative Example 2-2 This comparative example demonstrates a further comparative experiment based on the formulation of Comparative Example 2, without the use of pretreated red mud and pretreated titanium gypsum, and without the addition of humic acid. The difference between this comparative example and Comparative Example 2 is that steps S1 and S2 are omitted, and the process starts directly from step S3. In step S4, an equal amount of water is added directly to replace the addition of the humic acid aqueous solution. All other settings are exactly the same as in Comparative Example 2.

[0060] Comparative Example 3 This comparative example is used to illustrate a comparative test where the proportions of each raw material are set outside the numerical range of this invention. The difference between this comparative example and Example 1 is that in step S4, 60 parts by weight of Bayer process high-speed iron red mud, 20 parts by weight of titanium gypsum, and 20 parts by weight of fly ash are added to the mixer (too little red mud and too much fly ash, but the titanium gypsum is within the range defined by this invention). The other settings are exactly the same as in Example 1. The compressive strength results are shown in Table 1.

[0061] Comparative Example 3-2 This comparative example demonstrates a further comparative experiment based on the proportions of Comparative Example 3, without the use of pretreated red mud and pretreated titanium gypsum. The difference between this comparative example and Comparative Example 3 is that steps S1 and S2 are omitted, and the process begins directly from step S3. All other settings are exactly the same as in Comparative Example 3.

[0062] pass Figure 4 It can be seen that under the three proportions in this embodiment, the main phases in the formed materials are similar, mainly consisting of unreacted inert phases from the raw materials, such as the quartz phase in fly ash, the gypsum phase in titanium gypsum, and the hematite phase in red mud. The changes in peak intensity are mainly reflected in the characteristic peaks of gypsum. It can be observed that the peak intensity of gypsum gradually decreases in the order of Comparative Example 1, Example 1, and Comparative Example 2. This is directly related to the gradual decrease in the amount of titanium gypsum in these three proportions and the sulfates involved in the formation of calcium vanadium. In other words, the proportion of gypsum is not necessarily better the more or the less, but rather there is a feasible range. In addition, no obvious diffuse peaks were observed in the 20~40° range. This indicates that the hydration reaction of the three ratios in the system of this invention is weak and the hydration products are few, which is consistent with the result that the highest compressive strength is no more than 2.23 MPa. This also proves that the Bayer process red mud used in this invention cannot be directly applied to high-strength application scenarios. However, the introduction of titanium gypsum can introduce calcium ions and sulfate ions into the system, and the low solubility of calcium sulfate limits the formation of calcium vanadate. The low activity of fly ash and the unstable alkalinity of red mud also hinder the dissolution of active aluminum. Figure 4 The right side shows the XRD patterns of Example 1, Comparative Example 1, and Comparative Example 2, without any local magnification. (See attached image.) Figure 4As shown in this section, the characteristic peaks of calcium vanadate in the XRD pattern exhibit a trend of first increasing and then decreasing with increasing gypsum content. This proves that the formation of calcium vanadate is not necessarily better with more gypsum content. Example 1, with its higher alkalinity and lower sulfate content, is more inclined to form hydration gels rather than calcium vanadate, hence the calcium vanadate peak is slightly lower than that of Comparative Example 2. While Comparative Example 2 has the lowest alkalinity, the highest amount of fly ash allows for the formation of more active aluminum monomers, and the higher sulfate content results in the formation of the most calcium vanadate. It can also be observed that Comparative Example 1 does not show obvious calcium vanadate characteristic peaks, although it does have a certain intensity. This is because the larger amount of gypsum phase exhibits a rod-like structure in the microstructure, which can also act as a skeleton to some extent, providing the material with strong mechanical properties through physical filling. It is also related to the formation of a certain amount of hydration gel products in Comparative Example 1, but the amount is very small, hence no obvious characteristic peaks appear in the XRD. In other words, the total amount of calcium vanadate and hydration gel jointly determines the later performance development of the material.

[0063] The above embodiments and comparative examples underwent specific mechanical property testing and heavy metal leaching risk detection analysis, which were conducted in the following manner: Mechanical property testing of cementitious materials: After the cementitious material specimens were cured to the corresponding age, compressive strength tests were conducted on the cementitious material specimens cured for 14 days, 28 days, and 60 days using a compressive strength testing instrument.

[0064] Hydration mechanism analysis: Cementitious materials were prepared according to the optimized experimental mix and cured under the same conditions for 14, 28, and 60 days. After the curing period, the corresponding cement paste blocks were removed, broken, and the central portion was immersed in a 95% C2H5OH solution for 24 hours to terminate hydration. The hydrated blocks were then vacuum dried at 40℃ for 24 hours until constant weight. The blocks were then removed and prepared into samples for XRD, FT-IR, and TG analysis.

[0065] Heavy metal leaching risk detection: Ten samples of cementitious materials were taken out after standard curing for 28 days. The total amount of six heavy metals (vanadium, cadmium, chromium, arsenic, mercury, and lead) in the cementitious materials was determined according to the standard "Determination of Metal Elements in Solid Waste by Inductively Coupled Plasma Mass Spectrometry" (HJ 766-2015). At the same time, the test blocks were crushed to pass through a sieve with a pore size of 9.5 mm. Leachate was prepared from the cementitious materials after 28 days of curing according to the standards "Leaching Toxicity of Solid Waste by Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007) and "Leaching Toxicity of Solid Waste by Horizontal Oscillation Method" (HJ / T577-2010). The leaching concentration of the above six heavy metals in the leachate under different environments was determined by ICP-OES.

[0066] Mechanical properties were tested on each embodiment and comparative example using the above testing methods, and the results are shown in Table 1. Table 1 is a comparison table of compressive strength data for each embodiment and comparative example.

[0067] Table 1 As shown in Table 1, the compressive strength is influenced by the combined effects of the three raw material dosages. Red mud, as the direct source of alkalinity in this system, directly determines whether an alkali-activated reaction can occur, while the dosage of fly ash determines the content of reactive silica and aluminum in the system. Fly ash has low pozzolanic activity; therefore, a high and sustained alkalinity is required to activate its activity. Combining the compressive strength data, it can be found that when the ratio of red mud to fly ash is 6.5:1 (i.e., Example 1), the system achieves the highest compressive strength on day 60 of curing; that is, Example 1 achieves the highest compressive strength after 60 days. However, the compressive strength on day 60 of Comparative Examples 1, 2, and 3 is significantly lower than that of Example 1. However, Example 1 is not optimal for 28-day compressive strength, indicating that the material ratios set in this invention can guarantee 60-day compressive strength. Therefore, the cementitious material prepared by this invention is suitable for applications requiring high long-term strength. This is because when the ratio of Bayer red mud to fly ash is within the range specified in this invention, more red mud provides a stronger and more sustained alkaline ion source, thus activating more active silica-alumina components, providing a sufficient environment for the continuous hydration reaction. However, red mud itself contains a large amount of inert components, and excessively high red mud content will reduce the fly ash + titanium gypsum raw material components that can directly participate in the reaction, thus adversely affecting the development of strength. Conversely, insufficient red mud content cannot provide a stable alkaline environment for the system, making it difficult for fly ash to be activated, resulting in a weak and slow hydration reaction. That is, for the Bayer red mud, fly ash, and titanium gypsum system specified in this invention, a red mud content of approximately 65% ​​ensures a sufficient source of alkaline ions, while a smaller fly ash content of 10% ensures that it can be effectively activated by a limited number of alkaline ions.

[0068] The product obtained by the specific proportions set in this invention requires a long setting time to achieve the required strength, which is closely related to the incorporation of titanium gypsum. The main component of titanium gypsum is calcium sulfate dihydrate, a natural retarder. Its addition increases the amount of water needed for the standard consistency of the slurry, diluting the reactant concentration and directly leading to an increased setting time and slow development of compressive strength. While the addition of titanium gypsum affects the rapid development of early strength, it promotes the formation of calcium vanadium in the system, thus accelerating the development of later strength. From the compressive strength data, a relatively high dosage of titanium gypsum (25-30%) is needed to effectively promote the development of later strength. This is because calcium sulfate dihydrate has low solubility; to generate more calcium vanadium, more titanium gypsum needs to be added. The properties of the raw materials, red mud and fly ash, also have a significant impact. Therefore, to ensure compatibility between titanium gypsum and other materials, this invention sets the dosage at 20-28 parts by weight. During the research process, this invention discovered that increasing the amount of red mud significantly prolongs both the initial and final setting times. This is because the inert components in red mud act as a physical barrier, hindering the formation of a network structure from hydration products. Fly ash, on the other hand, has a low inherent activity, making its activation process extremely slow. Therefore, the unique characteristic of this system lies in its slow development of mechanical properties and low early strength, which places certain demands on its application scenarios. However, the high red mud content of 65% also provides a new approach for the resource utilization of red mud.

[0069] The heavy metal leaching risk of the products formed by the three solid waste material systems of the present invention was analyzed by using the above detection method, and the results are shown in Tables 2, 3 and 4. Table 2 is a table of total heavy metal data of the raw material mixtures of each embodiment and comparative example before each processing step.

[0070] Table 2 Table 3 shows the heavy metal leaching concentration data in the final products of each example and comparative example determined by the sulfuric acid-nitric acid method.

[0071] Table 3 Table 4 shows the heavy metal leaching concentration data in the final products of each example and comparative example, determined using the horizontal oscillation method.

[0072] Table 4 As shown in Table 2, after mixing the raw materials of Example 1 and the comparative examples according to their respective proportions and measuring their heavy metal content, it was found that, except for the lower total amount of As compared to the other two proportions, the content of the other five heavy metals in the raw materials of Example 1 was the highest among all proportions. Therefore, in terms of the total amount of heavy metals, the leaching risk of Example 1 should be the greatest among all comparative tests.

[0073] However, Tables 3 and 4 show that this is not the case, but rather the opposite to some extent. In order to simulate the leaching risk of heavy metals under different environments, this invention uses the sulfuric acid-nitric acid method to simulate the leaching risk under acid rain conditions, and the horizontal oscillation method (with pure water as the extract) to simulate the leaching risk of heavy metals under surface or groundwater infiltration.

[0074] As shown in Table 3, under acidic conditions, the average leaching concentrations of the six heavy metals in Examples 1 and 2, except for cadmium, were all lower than the leaching concentrations of the comparative proportions. Vanadium reached the limit of 0.05 mg / L required by the surface water quality standards for specific projects of centralized drinking water surface water sources, while cadmium reached the limit of Class 3 water (≤0.005 mg / L) in the groundwater quality standards. Chromium, lead, arsenic, and mercury all met the Class V water standards. Under surface or groundwater infiltration, the vanadium concentration increased, but the average leaching concentration still met the limit.

[0075] By comparing Examples 1 and 2, it can be found that in Example 2, without the addition of mineral-derived humic acid, the leaching concentrations of heavy metals V, As, Cd, and Pb under acidic conditions (Table 3) are all higher than in Example 1. This indicates that without the addition of humic acid in the stirring step of this invention, there is a certain leaching risk for these heavy metals under acidic conditions, but overall, the leaching risk for each heavy metal is lower than that of the comparative examples. Table 4, under groundwater infiltration conditions, shows that the leaching concentrations of heavy metals V, Cr, As, and Pb are all higher than in Example 1. This indicates that without the addition of humic acid in the stirring step of this invention, the leaching concentrations of these heavy metals under surface water or groundwater conditions pose a leaching risk compared to Example 1, but it is generally controllable.

[0076] By comparing Example 1 with Comparative Examples 1, 2, and 3, it can be seen that under acidic conditions, due to the specific formulation settings of the present invention (single condition), the overall leaching risk of each heavy metal under both conditions is lower than that of the comparative examples.

[0077] Meanwhile, Tables 3 and 4 show that changes in pH environment have a certain impact on the leaching risk of cementitious materials. At the same time, the formulation of Example 1 shows excellent heavy metal solidification and stabilization effect. This is because Example 1 forms a relatively large amount of calcium vanadate and hydrated cementitious products, which play a dual role of physical adsorption and chemical fixation of heavy metals. Specifically, (1) the formed hydrated products can wrap heavy metals in the network structure, hindering the migration of heavy metals; (2) the structure of the formed hydrated products contains a large number of pores, which will adsorb heavy metals. At the same time, the formed hydrated cement itself also has a strong adsorption effect on heavy metals; (3) during the formation of the hydrated product structure, heavy metals can replace calcium ions and directly participate in the formation of hydrated products and thus be fixed. Therefore, the concentration of heavy metals in its leachate is low, and the risk of heavy metal leaching is relatively low. This proves that the cementitious material obtained by the present invention can be used in some specific application scenarios, thereby meeting the usage requirements of some application scenarios. The multi-source solid waste of the present invention can be reused and treated using the technical solution of the present invention.

[0078] By comparing Comparative Example 1 and Comparative Example 1-2, and by comparing Comparative Example 3 and Comparative Example 3-2, it can be seen that without the specific pretreatment of red mud and titanium gypsum as described in this invention, the leaching concentrations of V, Cr, As, Cd, and Pb in Comparative Example 1-2 are much higher than those in Comparative Example 1, and the leaching concentrations of V, Cr, and As in Comparative Example 3-2 are much higher than those in Comparative Example 3 (especially under acidic conditions). This is because the Bayer process red mud and titanium gypsum selected in this invention were not subjected to specific separate acid leaching and alkali treatment, and soluble As and Cr were not removed at the raw material stage. 6+ The process of elution and surface lattice activation significantly increases the risk of heavy metal leaching. Although the comparison is based on comparative examples, it clearly demonstrates that within the ternary solid waste system established in this invention, specific acid elution and alkali treatment of Bayer red mud and titanium gypsum can reduce the overall risk of heavy metal leaching in the final product. Furthermore, since the various steps are synergistic, this proves the inventiveness of the specific pretreatment method for these two raw materials in this invention.

[0079] By comparing Comparative Example 2 and Comparative Example 2-2, it can be seen that without pretreatment of red mud and titanium gypsum, and without the addition of humic acid, even with the same other parameters, the leaching risk of certain heavy metals is greatly increased. It can be seen that under acidic conditions, the leaching risk of Cr and Pb increases significantly, and other heavy metal elements also increase to varying degrees. This not only shows that the specific addition of humic acid can further reduce the risk of heavy metal leaching, but also shows that the various steps of the present invention are closely coordinated. For example, in Example 2, the leaching rate did not change so much when humic acid was not added alone, and the leaching rate did not change so much when the ratios were different alone (Comparative Example 2 and Example 1). However, when the ratios, no treatment, and no addition of humic acid were all implemented, a very high leaching risk occurred, thus proving that the various settings of the present invention are coordinated.

[0080] By analyzing the hydration mechanism of Example 1, Comparative Example 1, and Comparative Example 2, the following results were obtained: Figure 5 and Figure 6 The results are shown in Table 5. Table 5 is a table of mass loss data for each temperature range in Example 1, Comparative Example 1, and Comparative Example 2.

[0081] Table 5 Figure 5 Thermogravimetric analysis (TGA) charts of the products obtained in Example 1, Comparative Examples 1 and 2 are shown below. Figure 5 As shown in Table 5, the mass loss changes of the three different proportions of cementitious materials in Example 1, Comparative Example 1, and Comparative Example 2 in the range of 40-1000℃ can be divided into three different stages: I, dehydration stage (40-200℃), II, dehydroxylation stage (200-500℃), and III, decarbonization stage (500-1000℃).

[0082] The mass loss during the dehydration stage is mainly related to the dehydration of bound water from hydration products such as hydration gel and calcium vanadate. The mass loss patterns of these three components within this range indicate that Comparative Example 2 generated the most hydration products, Example 1 also produced a relatively large amount, while Comparative Example 1 had a lower degree of hydration and fewer hydration products. This is because the mass loss during the dehydroxylation stage mainly originates from the decomposition of calcium hydroxide. In this stage, the mass loss is shown as Comparative Example 1 > Example 1 > Comparative Example 2, indicating that Comparative Example 1 had a lower degree of calcium hydration and still contained a large amount of unreacted calcium hydroxide. In contrast, Examples 1 and Comparative Example 2, due to their relatively higher degrees of hydration, consumed a large amount of calcium, resulting in less unreacted calcium hydroxide. The mass loss during the decarbonization stage mainly originates from the decomposition of calcium carbonate, reflecting the degree of carbonization of the samples. In this stage, the mass loss is shown as Comparative Example 2 > Example 1 > Comparative Example 1, indicating that Comparative Example 2 had a higher degree of carbonization. A higher degree of carbonization can cause volume shrinkage or embrittlement, leading to a decrease in compressive strength. Simultaneously, combined with… Figure 4 The XRD patterns shown indicate that although the mass loss of Example 1 and Comparative Example 2 at 40-200℃ is not significantly different, Comparative Example 2 forms far more calvanadate than Example 1, and the mass loss of bound water due to calvanadate is much greater than that of hydrated gel. This suggests that Example 1 forms more C-(A)-SH hydrated gels. Therefore, among Comparative Example 1, Example 1, and Comparative Example 2, Example 1 exhibits higher strength in the later stages due to its more hydrated gel and smaller amount of calvanadate forming a more compact structure. Comparative Example 2 achieves higher strength in the early stages due to the faster reaction of calvanadate, but its strength weakens later due to carbonization. Comparative Example 1 has a lower overall compressive strength because the amount of calvanadate formed is extremely small and cannot effectively fill the hydrated gel structure.

[0083] Figure 6 The Fourier transform infrared (FTIR) spectra of the products obtained in Example 1, Comparative Examples 1 and 2 are shown below. The right side represents the area from 1200 to 900 cm⁻¹ on the left. -1 and 1700~1550cm -1 A magnified view of a specific area. Through... Figure 6 Analysis shows that the three cementitious materials have a thickness range of 400-4000 cm. -1 Multiple peaks appeared at positions within the wavelength range, including 477 cm⁻¹. -1 The peak is due to the bending vibration of O-Si-O, at 874 cm⁻¹. -1 The peak is CO3 2- Out-of-plane bending vibration, 996cm -1 The peaks are all asymmetric stretching vibrations of Si-OT, 1113 cm⁻¹. -1 The peak is the stretching vibration of SO in calcite, at 1452 cm⁻¹.-1 The peak is CO3 2- The asymmetric stretching vibrations of CO, 1621 and 3405 cm -1 The peaks represent the bending vibration of HOH and the stretching vibration of OH, respectively. This indicates that the cementitious materials in all three ratios underwent hydration reactions to varying degrees, with peaks at 996, 1113, and 1621 cm⁻¹. -1 The difference in peak intensity at 996 cm⁻¹ further reflects the difference in the content of hydration products. -1 The peak at 1113 cm⁻¹ is related to the asymmetric stretching vibration of Si-OT in hydrated aluminosilicate gel structures such as CSH, CASH, and NASH. The peaks for the three formulations, from strongest to weakest, are those of Example 1, Comparative Example 2, and Comparative Example 1, indicating that Example 1 formed the most hydrated aluminosilicate gel product. -1 The peak intensity at 1621 cm⁻¹ directly reflects the content of calcite. From strongest to weakest, the results are: Comparative Example 2, Example 1, and Comparative Example 2 again. This indicates that Comparative Example 2 and Example 1 both produced relatively more calcite. -1 The peak intensity difference reflects the difference in bound water content between the two hydration products. The difference among the three formulations is smallest in Comparative Example 1, with little difference between Example 1 and Comparative Example 2. Because calcium vanadate has more bound water, Example 1 produces the most hydration gel in terms of total hydration product volume. Combined with a small amount of calcium vanadate, it has the highest compressive strength. Although Comparative Example 2 has a relatively high calcium vanadate content, its total amount is low, and it also has less hydration gel, resulting in relatively lower compressive strength. This is consistent with the aforementioned... Figure 4 XRD and Figure 5 The results are consistent with those obtained from TGA analysis. This further demonstrates that the specific ingredients and proportions specified in this invention can effectively reuse Bayer process red mud.

[0084] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for multi-source solid waste reuse of red mud generated by titanium gypsum itself, characterized in that, Includes the following steps: S1, Pretreatment of red mud: Bayer process high-iron red mud and water are mixed at a liquid-to-solid ratio of (5~10) ml: 1 g to obtain red mud slurry. Then, CO2 is introduced into the red mud slurry at a rate of 100~125 L / kg. 赤泥 The red mud slurry is introduced for 2 to 6 hours with continuous stirring to stabilize the pH value below 10.

5. Then, solid-liquid separation is performed to obtain solid matter, thus obtaining pretreated red mud. Bayer process high-iron red mud is Bayer process red mud containing 46.96~55.36 wt.% Fe2O3 and 21.86~27.35 wt.% Al2O3 by mass percentage of oxides; S2, Pretreated titanium gypsum: Mix titanium gypsum with 4~6mol / L NaOH solution at a liquid-solid ratio of (3~5)ml:1g, and stir continuously at 60~80℃ for 1~2h. Then, separate the solid and liquid to obtain a solid, and wash the solid until it is neutral to obtain pretreated titanium gypsum. S3, Drying and pulverizing: The pretreated red mud obtained in S1, the pretreated titanium gypsum obtained in S2, and the fly ash are placed into an oven and dried at 100~110℃ for 20~28h. After drying, the dried materials are placed into a ball mill for ball milling to obtain pulverized materials. S4, Stirring: Select 62-69 parts by weight of Bayer process high-speed iron red mud, 20-28 parts by weight of titanium gypsum and 8-12 parts by weight of fly ash after crushing in step S3 and put them into the mixer. At the same time, add 30-60 parts by weight of water, stir slowly for 1-3 minutes, and then stir quickly for 1-3 minutes. S5, Pouring: After the material in step S4 has been mixed, quickly pour it into the mold after the rapid mixing is finished. Vibrate the mold 18 to 28 times while pouring. S6, Curing: After casting, the material and mold are placed together in an environment with a temperature of 18~22℃ and a relative humidity of 93~98% for curing for 0.8~1.2 days. Then, the material is demolded and cured in dry air for 1~2 days. Then, it is placed back into the curing chamber in an environment with a temperature of 18~22℃ and a relative humidity of 93~98% for another 53~62 days to obtain a cementitious material product with low heavy metal leaching.

2. The method for multi-source solid waste reuse of red mud generated by titanium gypsum itself according to claim 1, characterized in that, In step S4, after the Bayer process high-iron red mud, titanium gypsum and fly ash are placed into the mixer, NaOH is first added to the water while stirring until the pH reaches 9.0~10.0 to obtain alkaline water. Then, mineral humic acid is added to the alkaline water to prepare a 0.5~2wt.% humic acid aqueous solution. Then, the humic acid aqueous solution replaces 30~60 parts by weight of water.

3. The method for multi-source solid waste reuse of red mud generated by titanium gypsum itself according to claim 1, characterized in that, In step S6, after demolding and before curing in dry air, a photothermal synergistic curing process is performed. Specifically, after demolding, the material is placed in an environment with 800~1000W / m² heat. 2 Irradiate the material in a near-infrared light source for 35-50 minutes, then heat the material to 70-90℃ and keep it at a constant temperature for 25-50 minutes; then carry out the curing process in dry air.

4. The method for multi-source solid waste reuse of red mud self-activated by titanium gypsum according to any one of claims 1 to 3, characterized in that, In step S2, the titanium gypsum contains, by mass percentage of oxides, SO3: 40.01~51.80 wt.%, CaO: 25.21~32.16 wt.%, Fe2O3: 10.06~16.86 wt.%, SiO2: 2.06~5.01 wt.%, MgO: 1.68~2.95 wt.%, Al2O3: 0.95~1.36 wt.%, Na2O: 0.36~0.81 wt.%, and the balance being impurities.

5. The method for multi-source solid waste reuse of red mud self-activated by titanium gypsum according to any one of claims 1 to 3, characterized in that, The dry air mentioned in step S4 is an air environment with a temperature of 20~25℃ and a humidity of 30~40%.

6. The method for multi-source solid waste reuse of red mud self-activated by titanium gypsum according to any one of claims 1 to 3, characterized in that, In step S3, the ball milling is the process of pulverizing and ball milling the material until the particle size is 80-120 mesh.

7. The method for multi-source solid waste reuse of red mud generated by titanium gypsum self-activation according to any one of claims 1 to 3, characterized in that, The fly ash in step S3 contains, by mass percentage of oxides, SiO2: 43.01~48.93 wt.%, Al2O3: 37.03~42.18 wt.%, CaO: 4.65~6.58 wt.%, Fe2O3: 2.03~5.95 wt.%, MgO: 0.43~0.68 wt.%, SO3: 1.01~1.80 wt.%, and Na2O: 0.61~1.28 wt.%.

8. The method for multi-source solid waste reuse of red mud self-activated by titanium gypsum according to any one of claims 1 to 3, characterized in that, The titanium gypsum mentioned in step S2 is an industrial by-product gypsum produced during the sulfuric acid process for producing titanium dioxide.

9. The method for multi-source solid waste reuse of red mud self-activated by titanium gypsum according to any one of claims 1 to 3, characterized in that, The 60-day compressive strength of the cementitious material product obtained in step S6 is 2.2~3.05 MPa; under acidic conditions, the leaching concentration of V is less than 30 μg / L, the leaching concentration of Cd is less than 4 μg / L, the leaching concentration of As is less than 50 μg / L, the leaching concentration of Pb is less than 40 μg / L, and the leaching concentration of Hg is less than 20 μg / L.

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