A method for co-disposal and utilization of red mud dealkalization, dewatering and drying

Abstract

The present application relates to a kind of red mud dealkalization, dehydration, drying collaborative disposal and gelification utilization method, and the method comprises the following steps: adding dealkalizing agent to fresh bayer process red mud directly, stirring to carry out dealkalization reaction, and obtaining dealkalization red mud slurry;Dealkalization red mud slurry is dehydrated by grading pressurization to obtain dehydrated red mud and alkali-containing waste liquid;Dehydrated red mud is dried by industrial waste heat;After drying, dealkalization red mud is crushed, mixed with activator, stirred with water, injected into standard test mold, and after vibration molding, static curing and demolding, gel-shaped green body is obtained;The green body is transferred into curing box for curing, and the gel material finished product is obtained.The method constructs dealkalization-dehydration-waste heat drying trinity collaborative system, links gelification utilization whole process, realizes the synchronous completion of red mud dealkalization, reduction, activity promotion and gelification utilization, and has good industrial application value.

Description

Technical Field

[0001] This invention relates to the field of red mud solid waste resource utilization technology, and in particular to a method for the synergistic treatment and gelation utilization of red mud through dealkali removal, dehydration, drying and coagulation. Background Technology

[0002] Red mud is a major industrial solid waste generated during alumina production, and its production increases in tandem with alumina output. Simply stockpiling it not only occupies significant land resources but also poses a risk of water, soil, and air pollution due to its high moisture and alkalinity. Therefore, reducing, rendering harmless, and recycling red mud is a crucial research direction for the alumina industry and solid waste treatment. The high moisture, high alkalinity, and low activity of red mud are the core factors restricting its resource utilization. Fresh red mud typically has a high moisture content of 60%-85%, making direct dealkalization and subsequent resource utilization impossible. It must first undergo dehydration and drying processes to reduce the moisture content to a suitable level, followed by dealkalization to lower its alkalinity and adjust its properties before it can be used as a raw material for resource utilization scenarios such as building material preparation.

[0003] Existing technologies generally employ a fragmented process of mechanical dehydration followed by high-temperature drying and then independent dealkalization, which presents numerous insurmountable technical bottlenecks. Dehydration and drying occur before the high-alkali colloidal structure is broken down, resulting in high dehydration resistance. Even after mechanical dehydration, the moisture content remains at 30%-40%. Drying consumes significant amounts of electricity and coal, and free alkali evaporates with water vapor, forming alkaline waste gas and causing secondary air pollution. The dealkalization stage is placed later, using methods such as strong acid neutralization and high-temperature roasting, which easily damages the silica-alumina phase of red mud, generates high-salt wastewater, or leads to particle agglomeration and reduced activity. Furthermore, additional activation is required after dealkalization before it can be used in building material preparation. Red mud treatment and cementitious material preparation are completely disconnected. Dealkalized red mud needs to be re-formulated and its properties adjusted, resulting in products that are mostly low-value-added roadbed materials and non-fired bricks, with defects such as efflorescence and insufficient strength. The entire process is an open process, meaning that alkaline wastewater, alkaline flue gas, and dealkalization waste liquid cannot be fully recycled, leading to serious resource waste and significant environmental hazards. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for the synergistic treatment and gelation utilization of red mud, encompassing dealkalization, dehydration, drying, and gelation. This method is applicable to the large-scale synergistic treatment and gelation utilization of high-moisture, high-alkalinity red mud generated during the Bayer process for alumina production. This method constructs a three-in-one synergistic system integrating dealkalization, dehydration, and waste heat drying, linking the entire gelation utilization process. It achieves simultaneous completion of red mud dealkalization, volume reduction, activity enhancement, and gelation utilization, providing core technological support for the large-scale, low-cost, and green treatment and gelation utilization of Bayer process red mud, and possesses significant industrial application value.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: In a first aspect, embodiments of the present invention provide a method for the synergistic treatment and gelation of red mud dealkalization, dehydration, drying, and utilization, comprising: directly adding a dealkalizing agent to fresh Bayer process red mud and stirring to carry out a dealkalization reaction to obtain a dealkalized red mud slurry; dehydrating the dealkalized red mud slurry by graded pressure to obtain dehydrated red mud and alkaline waste liquid, and recovering soluble sodium salts from the alkaline waste liquid; drying the dehydrated red mud using industrial waste heat and collecting the alkaline flue gas generated during the drying process; pulverizing the dried dealkalized red mud, mixing it with an activator and adding water and stirring, injecting it into a standard mold, and obtaining a gelled green body after vibration molding, static curing and demolding; transferring the green body into a standard curing chamber for curing to obtain the finished gelled material.

[0006] Furthermore, the dealkali agent is a compound system of mineral powder, fly ash and vinegar residue, with a mass ratio of mineral powder, fly ash and vinegar residue of 3:4:3, and the amount of dealkali agent added is 5%-10% of the mass of fresh Bayer process red mud.

[0007] Furthermore, the dealkali removal reaction is carried out at room temperature with stirring at a speed of 100-150 r / min and a reaction time of 30-45 min. After dealkali removal, the total dealkali removal rate of the red mud is not less than 93%, the removal rate of bound alkali is not less than 90%, and the pH value drops to 7.0-8.0.

[0008] Furthermore, the parameters for staged pressure dewatering are: initial pressure 5MPa-7MPa, pressing for 15min-20min; then increase the pressure to 12MPa-14MPa, pressing for 30min-35min, and the moisture content of the red mud after dewatering is reduced to 20%-25%.

[0009] Furthermore, the drying process uses waste heat from alumina production or power plant at a temperature of 120℃-180℃ as a heat source, controls the drying temperature at 80℃-100℃, and the drying time at 50min-70min, so that the moisture content of the dehydrated red mud is reduced to 10%-15%.

[0010] Furthermore, the collection efficiency of alkaline flue gas during the drying process is not less than 98%, the dust removal rate of the collected alkaline flue gas after purification is not less than 99%, and the purified flue gas is reused in the dealkali removal process.

[0011] Furthermore, the dried dealkalized red mud is pulverized to 80-100 mesh, and the content of active silica in the pulverized red mud is not less than 12%, and the content of active alumina is not less than 9%.

[0012] Furthermore, the pulverized dealkalized red mud is mixed with an activator at a mass ratio of 100:10-100:15, wherein the activator is a system of water glass and calcium hydroxide compounded at a mass ratio of 3:1.

[0013] Furthermore, the water-cement ratio in the water-addition and mixing process is 0.45, the standard mold size for injection is 40mm×40mm×160mm, the vibration molding process has an amplitude of 0.5mm, a frequency of 50Hz, and a vibration time of 2min, and the curing and demolding process has a curing temperature of 20℃-22℃ and a curing time of 24h.

[0014] Furthermore, the prepared cementitious material has a 28-day compressive strength of not less than 50 MPa and a 28-day flexural strength of not less than 8 MPa, and there is no efflorescence phenomenon; the purity of the soluble sodium salt recovered from the alkaline waste liquid is not less than 95%.

[0015] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: 1. In the method of this invention, a process design of first dealkali removal followed by dehydration and drying is adopted to address the characteristics of Bayer process red mud. Deep dealkali removal of the red mud is achieved through a compound dealkali removal agent composed of mineral powder, fly ash, and vinegar residue. The vinegar residue neutralizes free alkali, while the mineral powder and fly ash adsorb bound alkali and simultaneously activate the silica-alumina activity of the red mud. This effectively avoids corrosion of the dehydration equipment by the high-alkali medium, improves dehydration efficiency, and lays the foundation for subsequent dehydration and drying processes. The dealkali-removed red mud is then subjected to graded pressurized dehydration to reduce its volume, while simultaneously recovering soluble sodium salts from the alkaline wastewater, thus achieving wastewater resource utilization. Industrial waste heat is used to dry the dehydrated red mud, replacing traditional heating methods and significantly reducing energy consumption in the drying process. The alkaline flue gas generated during drying is collected in a sealed environment, purified, and reused in the dealkali removal process, achieving resource recycling of alkaline waste gas. After being dried and dealkalized, red mud is pulverized and mixed with an activator in a specific ratio. Water is added at a water-cement ratio of 0.45 to form a gelling slurry. A standard mold vibration molding and static curing process is employed to prepare the gelling material, which aligns with the hydration and hardening characteristics of gelling materials. Standard curing fully activates the hydration reaction of the active components in the red mud, producing a high-strength gelling material with a 28-day compressive strength ≥50 MPa and a 28-day flexural strength ≥8 MPa. This solves the problems of efflorescence and insufficient strength in red mud-based gelling materials. This method constructs a three-in-one synergistic closed-loop system of dealkalization, dehydration, and waste heat drying, integrating red mud treatment, resource recycling, and high-strength gelling utilization, filling the technological gap in the co-treatment and efficient utilization of Bayer process red mud through high-strength gelling.

[0016] 2. Excellent synergistic treatment effect, achieving multiple objectives simultaneously. Through the synergistic effect of dealkali removal, dehydration, and waste heat drying, the total dealkali removal rate of red mud is ≥93%, the removal rate of bound alkali is ≥90%, and the moisture content after dehydration and drying is reduced to 10%-15%, completely solving the core problems of incomplete dealkali removal, unreasonable process, and easy corrosion of equipment in the Bayer process; at the same time, it realizes the recycling of waste heat and flue gas resources, and simultaneously completes the reduction, harmlessness, and resource utilization of red mud, improving the treatment efficiency by more than 60% compared with the existing step-by-step process.

[0017] 3. Extremely low energy consumption and controllable operating costs. Utilizing industrial waste heat to replace traditional heating methods reduces energy consumption by more than 70% compared to existing high-temperature drying processes; employing industrial solid waste compound dealkali removal agents eliminates high-pollution and high-energy-consuming processes such as strong acid and high-temperature roasting, significantly reducing dealkali removal costs; the comprehensive energy consumption for treating 1 ton of red mud is ≤18kWh, and the comprehensive cost is ≤30 yuan, which is more than 60% lower than existing step-by-step processes, making it suitable for large-scale industrial applications.

[0018] 4. Red mud exhibits high activity, excellent gelling performance, and high added value. The dealkali removal process simultaneously enhances the gelling activity of red mud. After dealkali removal, the red mud can be directly used for the preparation of high-strength cementitious materials without additional activation. The cementitious system prepared with a water-cement ratio of 0.45 has good formability and sufficient hydration. The finished product has a 28-day compressive strength ≥50MPa, a 28-day flexural strength ≥8MPa, and no efflorescence. It meets the relevant standards for high-performance building cementitious materials and can be widely used in high-performance precast components, high-strength mortar, structural reinforcement, and other fields. The added value of the product is significantly higher than that of traditional red mud-based building materials.

[0019] 5. Simplified process, strong synergy, and high resource utilization efficiency. An integrated process of dealkalization-dehydration-waste heat drying-gelling preparation is constructed, with each process coordinated and seamlessly connected. The process flow is shortened by more than 65% compared with the existing technology, reducing equipment investment and manual intervention, and improving resource utilization efficiency by more than 80%, thus promoting the transformation of Bayer process red mud from stockpiling and disposal to high value-added resource utilization.

[0020] 6. Green and environmentally friendly, with no secondary pollution and fully closed-loop utilization. The entire process has no direct discharge of waste gas, wastewater, or waste residue. The alkaline waste liquid is recycled to obtain soluble sodium salt as an industrial raw material. Waste heat and alkaline flue gas are utilized as resources. All red mud is used for the preparation of high-strength cementitious materials, truly achieving zero pollution and full utilization, which is in line with the concept of green and low-carbon development.

[0021] 7. Highly adaptable and easy to scale up. Specifically designed for Bayer process red mud treatment, the process parameters can be flexibly adjusted according to the initial moisture content and alkalinity of the red mud; it can be directly connected to the waste heat resources of alumina plants and power plants without large-scale modification of existing equipment, is easy to operate and can achieve automated control, and is suitable for both new large-scale production lines and the upgrading and transformation of existing red mud treatment systems, with a wide range of application scenarios. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0023] Figure 1 This is a flowchart of the method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, drying, and gelation provided in the embodiments of the present invention. Detailed Implementation

[0024] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the linguistic context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0025] Generally speaking, the terms "include" and "contain" only indicate that the steps and elements are explicitly identified, and these steps and elements do not constitute an exclusive list, as the method or apparatus may also include other steps or elements.

[0026] To address the problems of existing red mud treatment technologies, such as high dehydration resistance due to the incomplete removal of the high-alkali colloidal structure, high drying energy consumption, secondary pollution from alkaline waste gas, damage to mineral phases after dealkali removal, disconnection between dealkali removal and gelation, and waste of resources in an open process, this paper proposes a method for the coordinated treatment and gelation utilization of red mud through dealkali removal, dehydration, and drying. Figure 1 As shown, it includes: S100 directly adds a dealkali-removing agent to fresh Bayer process red mud and stirs it to carry out a dealkali reaction, obtaining a dealkali-removed red mud slurry. Instead of pre-dehydrating and drying the red mud, the dealkali-removing agent is added directly to initiate the dealkali reaction. The advantages of this approach are: the red mud slurry has a certain degree of fluidity, which facilitates thorough mixing of the dealkali-removing agent and the red mud; and the dealkali reaction can be carried out at room temperature without heating.

[0027] S200 processes dehydrates red mud slurry through classification and pressurization to obtain dehydrated red mud and alkaline waste liquid, from which soluble sodium salts are recovered. The dehydrated slurry is then further dehydrated through classification and pressurization to obtain dehydrated red mud and alkaline waste liquid, which contains the removed sodium salts. Industrial-grade soluble sodium salts can be recovered through subsequent treatment.

[0028] The S300 uses industrial waste heat to dry dehydrated red mud and collects the alkaline flue gas generated during the drying process. It utilizes industrial waste heat (such as waste heat from alumina production or power plant processes) to dry the dehydrated red mud and actively collects the alkaline flue gas generated during drying to prevent direct emission.

[0029] S400 pulverizes dried dealkalized red mud, mixes it with an activator and water, pours it into a standard mold, and obtains a gelled green body after vibration molding, curing, and demolding. Alternatively, dried dealkalized red mud can be pulverized to an appropriate fineness, mixed with an activator and water, poured into a standard mold, and then vibrated, cured, and demolded to obtain a gelled green body.

[0030] S500 transfers the molded preform into a standard curing chamber for curing to obtain the finished cementitious material. The preform is then cured in the standard curing chamber to obtain the final product.

[0031] This method solves the problem of high dehydration resistance caused by performing dehydration and drying without breaking down the high-alkali colloidal structure in the red mud. Dealkali removal is performed while the red mud is still in a slurry state, which breaks down the alkali bonds in the colloidal structure, improving the efficiency of subsequent staged pressure dehydration. After mechanical dehydration, the moisture content can be reduced to 20%-25%, eliminating the need for dehydration followed by dealkali removal as in existing technologies. Simultaneously, industrial waste heat is used for drying, and alkaline flue gas is collected and reused, avoiding secondary pollution from alkaline waste gas. The entire process integrates dealkali removal, dehydration, drying, and gelation preparation into one, changing the resource waste and process disconnect caused by the fragmented processes in existing technologies. Synergy exists between the steps: the dealkali reaction reduces the alkalinity and colloidal stability of the red mud, which is beneficial for dehydration; dehydration reduces the moisture content, which is beneficial for energy saving during drying; the active components (silicon, aluminum) of the dried dealkali-removed red mud are activated and can be used for gelation material preparation without additional activation. Ultimately, the simultaneous reduction, harmlessness, and high-value utilization of red mud are achieved.

[0032] In some further specific examples of this disclosure, the dealkali agent is a compound system of mineral powder, fly ash and vinegar residue, with a mass ratio of mineral powder, fly ash and vinegar residue of 3:4:3, and the amount of dealkali agent added is 5%-10% of the mass of fresh Bayer process red mud.

[0033] Mineral powder typically refers to granulated blast furnace slag powder, fly ash is fly ash produced by coal-fired power plants, and vinegar residue is solid waste generated during vinegar brewing. All three are industrial byproducts and are inexpensive. In this method, the three are combined to achieve a synergistic dealkalization effect: vinegar residue contains organic acids such as acetic acid, which can neutralize free alkali in red mud; mineral powder and fly ash have pozzolanic activity, and their surfaces can adsorb bound alkali. Simultaneously, the active silica and alumina in the mineral powder and fly ash react with alkali during the dealkalization process to generate precursors of cementing substances such as hydrated calcium silicate, thereby simultaneously activating the cementing activity of the red mud. The mass ratio of the three is 3:4:3, and the addition amount is 5%-10% of the red mud mass. If the addition amount is less than 5%, dealkalization will be incomplete; if it is more than 10%, the cost will increase and excessive impurities may be introduced. This compound dealkalizing agent does not require strong acid or high-temperature roasting, avoiding the problems of high-salt wastewater and mineral phase damage caused by strong acid neutralization in existing technologies. Meanwhile, the dealkali removal process is carried out at room temperature, resulting in extremely low energy consumption.

[0034] In some other specific examples of this disclosure, the dealkali reaction is carried out at room temperature with stirring at a speed of 100 r / min to 150 r / min, and the reaction time is 30 min to 45 min. The total dealkali removal rate of the red mud after dealkali removal is not less than 93%, the removal rate of bound alkali is not less than 90%, and the pH value drops to 7.0 to 8.0.

[0035] Room temperature stirring refers to stirring without additional heating; the ambient temperature is typically 20℃-30℃. A stirring speed of 100-150 rpm is considered low to medium speed, ensuring thorough mixing of the dealkali-removing agent and red mud without generating excessive foam. The reaction time is 30-45 minutes. Under these conditions, the total dealkali removal rate of the red mud is no less than 93%, the removal rate of bound alkali is no less than 90%, and the pH value decreases from above 12.5 initially to 7.0-8.0, approaching neutral. Bound alkali refers to alkali chemically bound to the mineral lattice of red mud, which is difficult to remove using conventional methods. This method utilizes the adsorption and ion exchange effects of mineral powder and fly ash to effectively disrupt the structure of bound alkali, thus achieving a bound alkali removal rate of over 90%. The red mud after dealkali removal has a moderate pH value, avoiding efflorescence problems in subsequent cementitious materials. The effectiveness of dealkali removal is fundamental to subsequent dehydration, drying, and gelation. If dealkali removal is incomplete, residual alkali will migrate to the material surface during the curing process, forming a white alkaline substance that reduces the material's strength and service life.

[0036] In some further specific examples of this disclosure, the parameters for staged pressure dewatering are: initial pressure of 5 MPa-7 MPa, pressing for 15 min-20 min; then increasing the pressure to 12 MPa-14 MPa, pressing for 30 min-35 min, and the moisture content of the red mud after dewatering is reduced to 20%-25%.

[0037] Staged pressurization refers to pressing the red mud slurry at a lower pressure for a period of time in a high-pressure plate and frame filter press, followed by increasing the pressure for further pressing. Initial pressing at 5MPa-7MPa for 15-20 minutes allows free water in the red mud slurry to be quickly discharged, forming a preliminary filter cake. Subsequently, the pressure is increased to 12MPa-14MPa for 30-35 minutes. This high pressure breaks down the bound water film between the red mud colloidal particles, further squeezing out capillary water and some weakly bound water. Compared to constant pressure dewatering, staged pressurization avoids excessive initial pressure that could lead to surface densification of the filter cake, hindering the discharge of internal water. The final dewatering result is a moisture content of 20%-25%. This moisture content range meets the feed requirements of subsequent drying processes without excessive energy consumption due to over-dewatering. In existing technologies, simple mechanical dewatering typically results in a moisture content of 30%-40%. This method, by first dealkalizing to break down the colloidal structure and then combining it with staged pressurization, significantly improves dewatering efficiency. The alkaline wastewater contains removed sodium ions and a small amount of organic matter. Soluble sodium salts can be recovered through neutralization, filtration, and concentration, thus realizing the resource utilization of wastewater.

[0038] In other specific examples of this disclosure, the drying process uses waste heat from alumina production or power plant at a temperature of 120℃-180℃ as a heat source, controls the drying temperature at 80℃-100℃, and the drying time at 50min-70min, so that the moisture content of the dehydrated red mud is reduced to 10%-15%.

[0039] The alumina production process generates a large amount of high-temperature waste heat, and power plants also have steam waste heat, with temperatures typically ranging from 120℃ to 180℃. This method directly utilizes this industrial waste heat as a drying heat source, replacing electric heating or coal-fired drying, thus reducing energy consumption. The drying temperature is controlled at 80℃-100℃ for 50-70 minutes, reducing the moisture content of red mud from 20%-25% to 10%-15%. The drying temperature should not be too high, otherwise it will destroy the activated silicon-aluminum active components in the red mud; nor should it be too low, otherwise the drying time will be too long. Within this temperature range, moisture evaporation will not cause a phase transformation in the red mud. The alkaline flue gas generated during the drying process is collected in a closed system to avoid direct emission and air pollution. After purification to remove dust, the collected flue gas can be reused in the dealkali removal process, where the alkaline components can be utilized by the dealkali removal agent, achieving resource recycling of alkaline waste gas.

[0040] In some further specific examples of this disclosure, the collection efficiency of alkaline flue gas during the drying process is not less than 98%, the dust removal rate of the collected alkaline flue gas after purification is not less than 99%, and the purified flue gas is reused in the dealkali removal process.

[0041] A collection efficiency of at least 98% means that the drying equipment should be designed as a closed system or under negative pressure to minimize flue gas leakage. Purification typically employs cyclone dust collectors or bag filters, achieving a dust removal rate of at least 99%. This ensures very low dust content in the reused flue gas, preventing dust from entering the dealkali removal process and affecting the activity of the dealkali removal agent. The purified flue gas is then fed into the dealkali removal reactor, where the alkaline components are absorbed by the reaction, reducing the consumption of the dealkali removal agent. This closed-loop utilization model ensures that no alkaline waste gas is directly emitted from the entire process, meeting green environmental protection requirements.

[0042] In some other specific examples of this disclosure, the dried dealkalized red mud is pulverized to 80-100 mesh, and the content of active silica in the pulverized red mud is not less than 12%, and the content of active alumina is not less than 9%.

[0043] Drying dealkali-treated red mud is prone to clumping or agglomeration, requiring pulverization to 80-100 mesh to ensure uniform mixing with the activator and sufficient surface area for the gelation reaction. More importantly, the pulverized red mud must contain at least 12% active silica and at least 9% active alumina. Here, "active" refers to amorphous silicon and aluminum species capable of participating in the alkali-activated reaction. During dealkali treatment, the silica and alumina components in the mineral powder and fly ash undergo a preliminary reaction with the alkali in the red mud, generating substances with certain gelation activity. Simultaneously, the organic acids in the vinegar residue corrode the surface of the red mud minerals, exposing more active sites. Therefore, the dealkali-treated red mud does not require additional activation treatment; direct pulverization is sufficient to achieve the aforementioned activity indicators. However, in existing technologies, the dealkali-treated red mud often has very low activity, requiring high-temperature activation above 450℃, which is energy-intensive and damages the mineral structure. This method's synergistic dealkali treatment achieves simultaneous dealkali treatment and activation, providing highly active raw materials for subsequent gelation.

[0044] In some further specific examples of this disclosure, the pulverized dealkalized red mud is mixed with an activator at a mass ratio of 100:10-100:15, wherein the activator is a system of water glass and calcium hydroxide compounded at a mass ratio of 3:1.

[0045] The activator initiates the condensation reaction of active silica-alumina components in red mud, generating a three-dimensional network structure of hydrated aluminosilicate gel. This method uses a mixture of water glass and calcium hydroxide at a mass ratio of 3:1. Water glass provides soluble silicates and an alkaline environment, while calcium hydroxide provides calcium ions and additional alkalinity; both synergistically promote the hydration reaction. The mass ratio of red mud to activator is 100:10-100:15, meaning the activator dosage is 10%-15% of the red mud mass. After mixing in this ratio, water is added at a water-cement ratio of 0.45 and stirred. Too little activator will result in incomplete reaction, while too much will increase costs and may lead to efflorescence later. The 3:1 ratio of water glass to calcium hydroxide maintains an initial pH of around 12 in the reaction system, which is beneficial for silica-alumina dissolution but avoids excessively high pH levels that could lead to an overly rapid or uneven reaction. Compared to existing technologies, this method's activator does not involve expensive chemicals and has good compatibility with the de-alkali-activated red mud.

[0046] In some other specific examples of this disclosure, the water-cement ratio during water addition and mixing is 0.45, the standard mold size for injection is 40mm×40mm×160mm, the vibration molding amplitude is 0.5mm, the frequency is 50Hz, and the vibration time is 2min, and the curing and demolding temperature is 20℃-22℃ and the curing time is 24h.

[0047] The water-cement ratio (the ratio of water to the total mass of cementitious materials) is 0.45, which is a suitable ratio. This ensures the slurry has good fluidity for injection into the mold, but avoids excessive water leading to decreased strength or shrinkage cracks later on. The standard mold size of 40mm × 40mm × 160mm is commonly used for testing the mechanical properties of building materials. Vibration molding parameters: amplitude 0.5mm, frequency 50Hz, vibration time 2min. Vibration removes air bubbles from the slurry, making the specimen denser. Too short a vibration time results in insufficient air removal, while too long a time may lead to segregation. The curing temperature is 20℃-22℃, and the mold is removed after 24 hours of curing. The purpose of curing is to allow the cementitious material to initially harden and develop a certain release strength. This temperature range is suitable for the hydration reaction of cement-based materials; temperatures that are too high or too low will affect the hydration rate. Covering with plastic wrap prevents moisture evaporation.

[0048] In some further specific examples of this disclosure, the prepared cementitious material has a 28-day compressive strength of not less than 50 MPa, a 28-day flexural strength of not less than 8 MPa, and no efflorescence; the purity of the soluble sodium salt recovered from the alkaline waste liquid is not less than 95%.

[0049] The 28-day compressive strength is no less than 50 MPa, and the 28-day flexural strength is no less than 8 MPa, meeting the standards for high-strength cementitious materials. These materials can be used in high-performance precast components, high-strength mortar, structural reinforcement, and other fields. The absence of efflorescence means that no white alkaline substances precipitate on the surface of the specimen after 28 days of curing. This is because the dealkali removal process lowers the pH of the red mud to 7.0-8.0, leaving very little residual soluble alkali, which does not migrate to the surface during curing. Furthermore, the purity of the soluble sodium salts recovered from the alkaline wastewater is no less than 95%. These sodium salts can be sold as industrial raw materials, realizing the resource utilization of wastewater.

[0050] The specific steps of this implementation method are as follows: S100 takes fresh Bayer process red mud (moisture content 60%-85%, pH 12.5-13.5) and feeds it into a mixing device. A compound dealkali agent (mineral powder: fly ash: vinegar residue = 3:4:3) is added at a rate of 5%-10% of the red mud mass. The mixture is stirred at room temperature for 30-45 minutes at a stirring speed of 100-150 r / min to complete the deep dealkali removal. The total dealkali removal rate of the red mud is ≥93%, the bound alkali removal rate is ≥90%, and the pH drops to 7.0-8.0.

[0051] The S200 feeds the dealkalized red mud slurry into a high-pressure plate and frame filter press, employing a staged pressure dewatering process: initial pressure 5-7 MPa, pressing for 15-20 min; pressure increased to 12-14 MPa, pressing for 30-35 min, yielding dewatered red mud (moisture content 20%-25%) and alkali-containing waste liquid; the alkali-containing waste liquid is neutralized, filtered, and concentrated to recover soluble sodium salts with a purity ≥95%.

[0052] The S300 feeds dehydrated red mud into a waste heat dryer, using waste heat from alumina production at 120-180℃ or from a power plant as the drying heat source. The drying temperature is controlled at 80-100℃, and the drying time is 50-70 minutes, reducing the moisture content of the red mud to 10%-15%. The alkaline flue gas generated during the drying process is collected in a sealed environment, and after purification treatment, the dust removal rate is ≥99%, which is then reused in the dealkali removal process.

[0053] S400 pulverizes dried dealkalized red mud to 80-100 mesh, with active SiO2 ≥ 12% and Al2O3 ≥ 9% in the pulverized red mud; mix dealkalized red mud and activator at a mass ratio of 100:10-15, add water at a water-cement ratio of 0.45 and stir until a uniform gel slurry is formed; the activator is a system of water glass and calcium hydroxide mixed at a mass ratio of 3:1; pour the gel slurry into a standard mold of 40mm×40mm×160mm, place it on a vibration table, and vibrate for 2 minutes at an amplitude of 0.5mm and a frequency of 50Hz; smooth the surface of the mold with a scraper and cover it with plastic wrap; let it stand for 24 hours at 20-22℃, and then remove the mold to obtain the gelled green body.

[0054] S500 transfers the molded blank into a standard curing chamber, controls the curing temperature at 20±2℃ and the relative humidity at ≥95%, and cures continuously for 28 days. After curing, the finished cementitious material is obtained. The finished product has a 28-day compressive strength ≥50MPa and a 28-day flexural strength ≥8MPa, with no efflorescence.

[0055] The method of the present invention will be described in detail below through specific embodiments and comparative examples: Example 1 A method for the synergistic treatment and gelation utilization of Bayer process red mud, including alkali removal, dehydration, drying, and gelation, comprises the following steps: 1. Dealkali treatment: Fresh Bayer red mud (75% moisture content, pH 13.2) was mixed with 8% red mud mass of dealkali agent (mineral powder: fly ash: vinegar residue = 3:4:3), stirred at room temperature for 40 min at a speed of 120 r / min; the total dealkali removal rate was 94.2%, the bound alkali removal rate was 93.2%, and the pH was 7.5.

[0056] 2. Graded dehydration: Initial pressure 6MPa, pressing for 18min; pressure increased to 13MPa, pressing for 35min; dehydrated red mud moisture content 22%, sodium salt recovered from alkaline waste liquid with a purity of 95.8%.

[0057] 3. Waste heat drying: Waste heat from alumina production at 150℃ is used for drying at 90℃ for 60 minutes; the red mud moisture content is 12%, the flue gas collection efficiency is 98.5%, and the dust removal rate after purification is 99.2%.

[0058] 4. Cementation and molding: Crush the red mud to 100 mesh, mix it with red mud: activator = 100:12, add water at a water-cement ratio of 0.45 and stir to form a uniform slurry; pour it into a 40mm×40mm×160mm mold, vibrate at an amplitude of 0.5mm and a frequency of 50Hz for 2 minutes, scrape it flat and cover it with film, and let it stand at 21℃ for 24 hours before demolding.

[0059] 5. Standard maintenance: 20±2℃, humidity ≥95%, maintenance for 28 days.

[0060] 6. Finished product performance: 28-day compressive strength 53.5 MPa, 28-day flexural strength 8.7 MPa, no efflorescence, meets the standard for high-performance building cementitious materials.

[0061] In this embodiment, it takes 200 minutes to process 1 ton of red mud, consumes 17 kWh of energy, has a comprehensive processing cost of 29 yuan / ton, a waste heat utilization rate of 95%, an alkaline flue gas recovery and utilization rate of 98.5%, and there is no direct discharge of waste gas, wastewater, or waste residue.

[0062] Example 2 A method for the synergistic treatment and gelation of Bayer process red mud, including alkali removal, dehydration, drying, and utilization, is basically the same as that in Example 1, except that the process parameters are as follows: 1. Red mud dealkali removal: Fresh red mud has an initial moisture content of 85%, pH 13.5, total alkali content of 9.3%, and bound alkali content of 7.1%; the amount of dealkali removal agent (mineral powder: fly ash: vinegar residue = 3:4:3) is 10%, the stirring time is 45 min, the speed is 150 r / min, the total dealkali removal rate is 93.8%, the bound alkali removal rate is 92.8%, and the pH is 7.8.

[0063] 2. Grading and dewatering: Initial pressure 7MPa, pressing for 20min, then increase pressure to 14MPa, pressing for 35min, the dewatered red mud moisture content is 20%.

[0064] 3. Waste heat drying: using waste heat from the power plant (temperature 180℃), drying temperature 100℃, time 70min, red mud moisture content 10%; flue gas collection efficiency 99%, dust removal rate 99.5%.

[0065] 4. Gelation molding: Red mud: activator = 100:15, vibration molding parameters are the same as in Example 1, and the mold is removed after curing at 22℃ for 24 hours.

[0066] 5. Standard maintenance: 20±2℃, humidity ≥95% for 28 days.

[0067] 6. Finished product performance: 28-day compressive strength 51.8 MPa, 28-day flexural strength 8.3 MPa, no efflorescence.

[0068] Example 3 A method for the synergistic treatment and gelation of Bayer process red mud, including alkali removal, dehydration, drying, and utilization, is basically the same as that in Example 1, except that the process parameters are as follows: 1. Red mud dealkali removal: Fresh red mud has an initial moisture content of 60%, pH 12.8, total alkali content of 5.8%, and bound alkali content of 4.0%; the dealkali removal agent (mineral powder: fly ash: vinegar residue = 3:4:3) is added at a rate of 5%, the stirring time is 30 min, the speed is 100 r / min, the total dealkali removal rate is 93.2%, the bound alkali removal rate is 91.3%, and the pH is 7.2.

[0069] 2. Grading and dewatering: Initial pressure 5MPa, pressing for 15min, then increase pressure to 12MPa, pressing for 30min, the dewatered red mud moisture content is 25%.

[0070] 3. Waste heat drying: Alumina waste heat (temperature 120℃) is used, drying temperature is 80℃, time is 50min, red mud moisture content is 15%; flue gas collection efficiency is 98%, dust removal rate is 99%.

[0071] 4. Gelation molding: Red mud: activator = 100:10, vibration molding parameters are the same as in Example 1, and the mold is removed after curing at 20℃ for 24 hours.

[0072] 5. Standard maintenance: 20±2℃, humidity ≥95% for 28 days.

[0073] 6. Finished product performance: 28-day compressive strength 50.3 MPa, 28-day flexural strength 8.1 MPa, no efflorescence.

[0074] Example 4 A method for the synergistic treatment and gelation utilization of Bayer process red mud involving alkali removal, dehydration, drying, and gelation is basically the same as that in Example 1, except that: the mass ratio of mineral powder: fly ash: vinegar residue in the alkali removal agent is 2:5:3; and the flue gas introduction rate is 0.7 m³ / h. kg of red mud; activator ratio unchanged; final total alkali removal rate of red mud 93.6%, bound alkali removal rate 90.5%, finished product 28d compressive strength 51.2MPa, 28d flexural strength 8.4MPa, waste heat utilization rate 94%.

[0075] Example 5 A method for the synergistic treatment and gelation of Bayer process red mud, including alkali removal, dehydration, drying, and utilization, is basically the same as that in Example 1, with the following differences: initial pressure of staged dehydration is 7 MPa, pressing for 17 min, then pressure is increased to 14 MPa and pressing for 32 min; residual heat drying temperature is 85℃ and time is 70 min; gel slurry stirring time is 35 min; curing temperature is 20℃ and humidity is 95% for 28 days; the final red mud moisture content is 13%, active Al2O3 content is 9.6%, bound alkali removal rate is 92.5%, and the finished product has a 28-day compressive strength of 53.1 MPa and a 28-day flexural strength of 8.5 MPa.

[0076] Example 6 A method for the synergistic treatment and gelation of red mud using the Bayer process, including dealkali removal, dehydration, drying, and utilization, is basically the same as that in Example 1, with the following differences: the stirring time of the dealkali removal agent is 35 min; the evaporation and concentration temperature of the alkali-containing reaction solution is 110℃; the vibration time for gelation molding is 2 min; the final total dealkali removal rate of the red mud is 94.5%, the removal rate of bound alkali is 93.1%, the purity of soluble salts is 96.3%, the 28-day compressive strength of the finished product is 52.6 MPa, the 28-day flexural strength is 8.4 MPa, there is no efflorescence, and the performance is stable.

[0077] Using the fresh red mud from Example 1 (initial moisture content 75%, pH 13.2, total alkali content 8.1%, bound alkali content 6.2%) as raw material, a comparative experiment was conducted between existing red mud treatment and building material utilization processes and the method of this invention: Comparative Example 1 The existing process of dehydration + electric heating drying + strong acid neutralization and dealkali removal + gelation was adopted, with other conditions consistent with Example 1. The final red mud after dehydration and drying had a moisture content of 14%, a total dealkali removal rate of 68.5%, and a bound alkali removal rate of 52.7%. The dealkali removal residue needed to be activated at 450℃ before it could be used as raw material. The prepared gelled product had a 28-day compressive strength of 22.3 MPa and a flexural strength of 3.5 MPa, and showed obvious efflorescence. It took 380 minutes to process 1 ton of red mud, consumed 85 kWh of energy, cost 86 yuan / ton, and generated 1.2 tons of high-salt wastewater and alkaline waste gas, resulting in serious secondary pollution.

[0078] Comparative Example 2 The existing process of dehydration + coal-fired drying + high-temperature roasting for dealkalization + gelation was adopted, without flue gas recovery and waste heat utilization, and other conditions were the same as in Example 1. The final red mud after dehydration and drying had a moisture content of 16%, a total dealkalization rate of 82.3%, and a bound alkali removal rate of 70.5%. High-temperature roasting caused red mud particles to agglomerate and have low activity. The prepared gelled product had a 28-day compressive strength of 25.8 MPa and a flexural strength of 4.1 MPa. It took 420 minutes to process 1 ton of red mud, consumed 92 kWh of energy, and cost 81 yuan / ton. It generated waste gas and waste residue, caused serious secondary pollution, and wasted fossil energy.

[0079] Comparative Example 3 The existing process of dehydration + waste heat drying + separate chemical dealkalization + gelation preparation was adopted, with no flue gas synergistic dealkalization, and other conditions were the same as in Example 1; the final total dealkalization rate of red mud was 88.6%, and the removal rate of bound alkali was 78.2%; dealkalization requires the addition of a large amount of chemical reagents, which is costly; the prepared gelled product has a 28-day compressive strength of 28.5 MPa and a flexural strength of 4.6 MPa; it takes 280 minutes to process 1 ton of red mud, consumes 35 kWh of energy, costs 65 yuan / ton, and generates alkaline wastewater, resulting in low resource utilization.

[0080] Comparative Example 4 The existing red mud direct dehydration and drying + gelation preparation process is adopted, without the dealkali removal step, and other conditions are the same as in Example 1. The high alkalinity of red mud leads to severe efflorescence of the gelation material, incomplete hydration reaction, 28-day compressive strength of only 14.6 MPa and flexural strength of 2.2 MPa, which cannot meet the requirements for use, and it is easy to produce alkaline exudates, which pollute the environment.

[0081] Comparative experimental results show that, using the synergistic treatment and gelation utilization method of this invention (parameters of Example 1), the final red mud after dehydration and drying has a moisture content of 12%, a total dealkali removal rate of 94.2%, and a bound alkali removal rate of 93.2%. After dealkali removal, it can be directly used as raw material without additional activation. The prepared gelled product has a 28-day compressive strength of 53.5 MPa and a flexural strength of 8.7 MPa, with no efflorescence. It takes 200 minutes to process 1 ton of red mud, consumes 17 kWh of energy, costs 29 yuan / ton, has a waste heat utilization rate of 95%, a flue gas recovery utilization rate of 98.5%, and no direct discharge of waste gas, wastewater, or waste residue. The overall effect far exceeds that of existing processes.

[0082] Compared with existing processes, the method of this invention increases the total alkali removal rate by more than 15%, the combined alkali removal rate by more than 20%, the 28-day compressive strength of the gelled product by more than 40%, the flexural strength by more than 50%, the processing efficiency by more than 45%, reduces energy consumption by more than 75%, and reduces processing costs by more than 60%. Moreover, it eliminates secondary pollution and achieves fully closed-loop utilization, fully verifying the innovation, practicality, and superiority of this invention.

[0083] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying, characterized in that, include: Fresh Bayer process red mud is directly added to a dealkali agent and stirred to carry out a dealkali reaction, resulting in a dealkali-treated red mud slurry; The dealkali-treated red mud slurry is graded and pressurized to obtain dehydrated red mud and alkali-containing waste liquid. Soluble sodium salts are recovered from the alkali-containing waste liquid. The dehydrated red mud is dried using industrial waste heat, and the alkaline flue gas generated during the drying process is collected. The dried dealkalized red mud was crushed, mixed with an activator, and stirred with water. The mixture was poured into a standard mold, and after vibration molding and static curing, the gelled green body was obtained. The molded blank is transferred to a standard curing chamber for curing to obtain the finished cementitious material.

2. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that, The dealkali removal agent is a compound system of mineral powder, fly ash and vinegar residue, with a mass ratio of mineral powder, fly ash and vinegar residue of 2-3:4-5:3, and the amount of dealkali removal agent added is 5%-10% of the mass of fresh Bayer process red mud.

3. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that... The dealkali removal reaction is carried out at room temperature with stirring at a speed of 100-150 r / min and a reaction time of 30-45 min. The total dealkali removal rate of the red mud after dealkali removal is not less than 93%, the removal rate of bound alkali is not less than 90%, and the pH value drops to 7.0-8.

0.

4. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that... The parameters for graded pressure dewatering are: initial pressure 5MPa-7MPa, pressing for 15min-20min; then increase the pressure to 12MPa-14MPa, pressing for 30min-35min, and the moisture content of the red mud after dewatering is reduced to 20%-25%.

5. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that... The drying process uses waste heat from alumina production or power plant at a temperature of 120℃-180℃ as a heat source, controls the drying temperature at 80℃-100℃, and the drying time at 50min-70min, so that the moisture content of the dehydrated red mud is reduced to 10%-15%.

6. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that... The collection efficiency of alkaline flue gas during the drying process is not less than 98%, and the dust removal rate of the collected alkaline flue gas after purification is not less than 99%. The purified flue gas is reused in the dealkali removal process.

7. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that, The dried dealkalized red mud is pulverized to 80-100 mesh, and the content of active silica in the pulverized red mud is not less than 12%, and the content of active alumina is not less than 9%.

8. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that, The pulverized dealkalized red mud is mixed with an activator at a mass ratio of 100:10-100:

15. The activator is a system of water glass and calcium hydroxide compounded at a mass ratio of 3:

1.

9. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that... The water-cement ratio during the water addition and mixing process is 0.45, the standard mold size for injection is 40mm×40mm×160mm, the vibration molding process has an amplitude of 0.5mm, a frequency of 50Hz, and a vibration time of 2min, and the curing and demolding process has a curing temperature of 20℃-22℃ and a curing time of 24h.

10. The method for the synergistic treatment and gelation utilization of red mud through dealkalization, dehydration, and drying as described in claim 1, characterized in that, The prepared cementitious material has a 28-day compressive strength of not less than 50 MPa and a 28-day flexural strength of not less than 8 MPa, and there is no efflorescence phenomenon; the purity of the soluble sodium salt recovered from the alkaline waste liquid is not less than 95%.

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