Combined pretreatment method and application of red mud

Abstract

The application discloses a combined pretreatment method and application of red mud. The method comprises the following steps: high-temperature calcining the red mud, sieving the red mud after cooling, and obtaining calcined red mud; mixing the calcined red mud with water, and heating and stirring; continuously feeding CO2 gas in an intermittent ventilation mode while maintaining heating and stirring; after the ventilation is completed, performing vacuum filtration separation on the obtained slurry, and obtaining red mud filtrate and red mud residue; and performing freeze-drying on the red mud filtrate, and obtaining red mud-based alkali activator powder. The whole treatment process does not introduce other chemical reagents, and utilizes the alkali of the red mud and the industrial by-product CO2, so that waste is treated by waste, and the environmental benefits are remarkable.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and environmental protection technology, specifically to a combined pretreatment method and application of red mud. Background Technology

[0002] Red mud is a highly alkaline solid waste generated during alumina production, producing 1.0 to 1.8 tons of red mud for every ton of alumina produced. The annual discharge of red mud is substantial, and its large-scale stockpiling not only occupies land but also poses a risk of groundwater and soil pollution due to its high alkalinity and heavy metal content. Therefore, the large-scale, high-value-added resource utilization of red mud is a pressing global challenge that needs to be addressed in both the alumina industry and the environmental protection sector.

[0003] Currently, the main pathways for the resource utilization of red mud include its use in building materials, recovery of valuable metals, and preparation of environmental remediation materials. Among these, using red mud to prepare alkali-activated cementitious materials is considered a highly promising approach. Alkali-activated materials are green building materials made from aluminosilicate raw materials activated by alkaline activators, possessing advantages such as high early strength, good corrosion resistance, and low carbon emissions. The alkali in red mud exists primarily in two forms: water-soluble free alkali (such as NaOH and Na2CO3) and structural alkali bound to the mineral lattice (such as sodium in aluminosilicate minerals like nepheline and calcium nepheline). Existing dealkali removal technologies, such as direct water washing, can only remove some of the free alkali and cannot effectively destroy the sodium-containing mineral structure, leading to incomplete dealkali removal and a tendency for the residual pH to rebound, thus limiting the resource utilization of red mud. To achieve fundamental control over the alkalinity of red mud, it is necessary to develop treatment processes that can effectively destroy its stable mineral structure and release and recover structural alkali. Simultaneously, the treatment process should avoid introducing new pollution and strive to achieve high-value utilization of the treated products.

[0004] Numerous existing technologies have attempted to apply red mud to alkali-activated materials. For example, Chinese invention patent CN121470872A discloses a red mud-based multi-component solid waste cementitious material, its preparation method, and its application. This method directly mixes red mud, slag, fly ash, and silicate cement, using water glass as an alkali activator. While this method utilizes red mud, it essentially relies on commercial chemical alkali agents, failing to fully utilize the inherent alkalinity of the red mud, and its strength is relatively low. Chinese invention patent CN121361979A proposes a red mud-containing steel slag composite cementitious material and its preparation method. This method utilizes the alkaline environment provided by the hydration of steel slag to activate the material through the composite of red mud with slag, steel slag, and fly ash. This method reduces the amount of external alkali used, but the stability and strength development of the material system are often slow, and the utilization rate of the alkali components of the red mud is limited.

[0005] In summary, the existing technology has the following main shortcomings:

[0006] (1) Failure to efficiently utilize the alkalinity of red mud: Most schemes still regard red mud as an inert filler or auxiliary aluminum-silicon source, and a large amount of external strong alkali is still required to activate the reaction. The alkali in red mud (mainly in the form of Na2O) is not effectively recycled as an activating component.

[0007] (2) Complex process or high cost: Whether relying on commercial alkali agents or using high temperature pretreatment, it significantly increases the preparation cost and process complexity of materials.

[0008] Therefore, developing a method for preparing all-solid waste alkali activating materials that can efficiently extract and utilize the alkali content of red mud, with simple process, low cost and stable performance, has important practical significance and industrial value. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a combined pretreatment method and application for red mud. The core of this method lies in the synergistic effect of three steps: calcination activation, water washing for alkali extraction, and carbonation stabilization. This process thoroughly destroys the sodium-containing mineral phase in the red mud, transfers the alkaline components to the liquid phase and fixes them into usable carbonates, while simultaneously obtaining low-alkaline red mud residue with a long-term stable pH.

[0010] To achieve the above objectives, the technical solution designed by the present invention is as follows:

[0011] This invention provides a combined pretreatment method for red mud, comprising the following steps:

[0012] (1) The red mud is calcined at high temperature, cooled and sieved to obtain calcined red mud;

[0013] (2) Mix the calcined red mud with water, and heat and stir.

[0014] (3) Keep heating and stirring, and introduce CO2 gas into the system of step (2) by intermittent aeration.

[0015] (4) After the aeration is completed, the slurry obtained in step (3) is vacuum filtered to separate red mud filtrate and red mud residue; the red mud filtrate is freeze-dried to obtain red mud base activator powder; the red mud base activator powder contains 40~75% Na2O.

[0016] Furthermore, in step (1), the calcination temperature is 700~900℃, the calcination time is 15~60 min, and the sieve mesh size is 200~250 mesh;

[0017] In step (2), the liquid-solid ratio of calcined red mud and water is 6~12 mL / g, the heating temperature is 40~100℃, the stirring speed is 300~320 rpm, and the stirring time is 40~180 min.

[0018] Furthermore, the calcination temperature is 900℃, the calcination time is 15 min, and the sieve mesh size is 200 mesh;

[0019] The liquid-to-solid ratio of the calcined red mud and water was 6 mL / g, the heating temperature was 100℃, the stirring speed was 300 rpm, and the stirring time was 60 min.

[0020] Furthermore, in step (3), the flow rate of the CO2 gas introduced is 0.2 L / min;

[0021] The intermittent ventilation method is as follows: ventilation and stirring for 30 minutes, followed by pausing ventilation and stirring for 30 minutes, with 2 to 4 cycles of ventilation and pausing ventilation, and a total ventilation time of 60 to 120 minutes.

[0022] The present invention also provides a red mud-based base activator powder prepared by the aforementioned combined pretreatment method.

[0023] The present invention also provides an application of the aforementioned red mud-based alkali activator powder in the preparation of all-solid waste alkali activating materials.

[0024] The present invention also provides an all-solid-waste alkali activating material, wherein the raw materials of the all-solid-waste alkali activating material include solid waste and water; the solid waste includes an activator and slag; the activator includes the red mud-based alkali activator powder and carbide slag;

[0025] The content of the activator in the solid waste is 10-20%;

[0026] In the activator, the ratio of red mud-based alkaline activator powder to carbide slag is 1:1~2;

[0027] The liquid-to-solid ratio of the water and solid waste is 0.3~0.5 mL / g.

[0028] Furthermore, the content of the activator in the solid waste is 15%;

[0029] In the activator, the ratio of red mud-based alkaline activator powder to carbide slag is 1:1.6;

[0030] The liquid-to-solid ratio of the water and solid waste is 0.35 mL / g.

[0031] The present invention also provides a method for preparing the all-solid waste alkali activating material, comprising the following steps: weighing red mud-based alkali activator powder, carbide slag and slag according to the above proportions, and mixing them evenly; then adding water according to the above liquid-solid ratio, mixing evenly and then solidifying, and then curing to obtain the all-solid waste alkali activating material.

[0032] Furthermore, the curing time is 24-30 hours; the curing temperature is 18-22℃, the relative humidity is 90-95%, and the curing time is 7-28 days.

[0033] The present invention also provides an application of the aforementioned all-solid waste alkali activating material in the construction of roads, foundations or buildings.

[0034] The principle of this invention:

[0035] (1) Calcination and activation step: The original red mud is calcined at a temperature of 700℃ to 900℃. The purpose of this step is to destroy the crystal structure of stable sodium-containing minerals (such as hydrotalcite, grossular garnet, especially nepheline and calcium nepheline) in the red mud through thermal activation, so that the structural sodium in them is converted into soluble sodium salts or free sodium ions, creating conditions for subsequent water washing and extraction. The calcination temperature is the key parameter to control the effect of this step: if the temperature is too low (<700℃), the mineral decomposition is insufficient; if the temperature is too high (>900℃), recrystallization is likely to occur to form new sodium-containing minerals (such as nepheline), which is not conducive to the dissolution of alkali.

[0036] (2) Water washing and alkali extraction step: Mix calcined red mud with water and stir continuously at 40℃ to 100℃ to fully dissolve the soluble alkali formed after calcination into the aqueous phase. Higher temperature and appropriate liquid-solid ratio can accelerate the mass transfer process and improve the alkali dissolution efficiency and total amount.

[0037] (3) Carbonation stabilization step: This is the key step in achieving alkali recovery and residue stabilization. Carbon dioxide gas is continuously introduced into the mixed slurry after alkali extraction via washing. The dissolved CO2 reacts with OH- in the solution. - The reaction lowers the pH of the system. More importantly, CO2 reacts with Na₂ dissolved from the red mud. + The reaction produces sodium carbonate (Na₂CO₃), which has high solubility, stably retaining the alkaline component in the liquid phase as carbonate. Simultaneously, the decrease in liquid phase pH promotes the continued dissolution and reaction of remaining alkaline substances in the slurry until a new equilibrium is reached. By controlling the CO₂ injection rate (e.g., by controlling the aeration time, such as 30-120 minutes), the final pH of the system can be precisely controlled within the weakly alkaline range of 8 to 9.

[0038] (4) Solid-liquid separation step: The carbonated slurry is filtered or centrifuged to obtain red mud filtrate rich in sodium salt (mainly sodium carbonate) and red mud filter residue with significantly reduced and stable pH.

[0039] The beneficial effects of this invention are:

[0040] (1) Thorough treatment: This invention solves the problem of removing structural alkali from red mud by calcination activation, and the alkali removal efficiency is much higher than that of traditional single water washing method.

[0041] (2) Alkali resource recovery: This invention converts the harmful alkaline components in red mud into valuable sodium carbonate solution, which can be freeze-dried to obtain high-purity (Na2O content can reach more than 70%) mixed alkali salt, which can be used as industrial raw material or alkali activator.

[0042] (3) Permanent stabilization of residue: The CO2 carbonation step of the present invention not only promotes the recovery of alkali, but also neutralizes the alkalinity of the residue, making its pH stable at 8~9 for a long time, eliminating environmental risks. The treated red mud residue can be used as roadbed material, cement admixture or raw material for safe landfill.

[0043] (4) Green and environmentally friendly: The entire treatment process of this invention does not introduce other chemical reagents, but utilizes the alkali of the red mud itself and the industrial by-product CO2, thus treating waste with waste and achieving significant environmental benefits. Attached Figure Description

[0044] Figure 1 The extraction flow chart for red mud-based base activators;

[0045] Figure 2 XRD patterns of raw red mud and red mud calcined at different calcination temperatures (700℃, 800℃, 900℃) and for different times;

[0046] In the figure, a is the XRD pattern of calcined red mud at 700℃; b is the XRD pattern of calcined red mud at 800℃; c is the XRD pattern of calcined red mud at 900℃.

[0047] Figure 3 The graph shows the effect of different parameters on the sodium ion dissolution concentration.

[0048] Figure a shows the pH changes and sodium ion dissolution of calcined red mud 1 under the conditions of a liquid-to-solid ratio of 6 mL / g, a rotation speed of 300 r / min, a room temperature of 20℃, and a stirring time of 60 min; figure b shows the pH changes and sodium ion dissolution of calcined red mud 2 under the conditions of a liquid-to-solid ratio of 6 mL / g, a rotation speed of 300 r / min, a room temperature of 20℃, and a stirring time of 60 min; figure c shows the pH changes and sodium ion dissolution of calcined red mud 3 under the conditions of a liquid-to-solid ratio of 6 mL / g, a rotation speed of 300 r / min, a room temperature of 20℃, and a stirring time of 60 min.

[0049] d represents the Na content of the original red mud at different liquid-to-solid ratios. + Graph showing concentration and pH changes; e represents the original red mud at different stirring times. + Graph showing concentration versus pH changes; f represents the original red mud at different stirring temperatures. + Graph showing the results of concentration versus pH changes;

[0050] g represents the Na content of calcined red mud 1 at different liquid-solid ratios. + The graph shows the results of concentration and pH changes; h represents the Na content of calcined red mud 1 at different stirring times. + The graph shows the results of concentration and pH changes; i represents the Na content of calcined red mud 1 at different stirring temperatures. + Graph showing the results of concentration versus pH changes;

[0051] j is a graph showing the sodium ion dissolution rate of calcined red mud 1 after water washing and alkali extraction, when carbon dioxide gas is introduced for different ventilation times; k is a graph showing the sodium ion dissolution rate of calcined red mud 2 after water washing and alkali extraction, when carbon dioxide gas is introduced for different ventilation times; l is a graph showing the sodium ion dissolution rate of calcined red mud 3 after water washing and alkali extraction, when carbon dioxide gas is introduced for different ventilation times.

[0052] Figure 4 The graph shows the pH monitoring results of three typical red mud filter residues after treatment by the method of this invention at different liquid-solid ratios.

[0053] Figure 5 The figure shows the pH stability monitoring results of three typical red mud filter residues treated by the method of the present invention over 60 days.

[0054] Figure 6 A flowchart outlining the specific steps involved in preparing all-solid waste alkali-activated materials;

[0055] Figure 7 The diagram shows the compressive strength results of the solid waste alkali-activated material.

[0056] In the figure, a shows the compressive strength results at 7 days; b shows the compressive strength results at 28 days.

[0057] Figure 8 The XRD pattern of the alkali-activated material from solid waste is shown.

[0058] Figure 9 SEM images of alkaline-activated materials from solid waste;

[0059] In the figure, a and b are SEM images of the solid waste alkali-activated material D2; c is the SEM image of the solid waste alkali-activated material 5; d is the SEM image of the solid waste alkali-activated material 6; e is the SEM image of the solid waste alkali-activated material 7; and f is the SEM image of the solid waste alkali-activated material 8.

[0060] Figure 10 This is a graph showing the effect of continuous ventilation on pH changes and sodium ion dissolution concentration.

[0061] In the figure, a is the effect curve of pH change and sodium ion dissolution concentration on calcined red mud 1; b is the effect curve of pH change and sodium ion dissolution concentration on calcined red mud 2; and c is the effect curve of pH change and sodium ion dissolution concentration on calcined red mud 3. Detailed Implementation

[0062] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can understand it.

[0063] Experimental materials

[0064] The red mud used in this invention is Bayer process red mud, sourced from an alumina plant in Zhengzhou, Henan Province. Its Na₂O content is 10.73%, and its initial pH (liquid-to-solid ratio 6 mL / g leaching) is 11.1. XRD patterns show that the mineral phases in the red mud include calcite, hydrotalcite, grossular, hematite, and sodium-containing nepheline and calcium nepheline.

[0065] The main components of red mud, carbide slag (CCR), and blast furnace slag (BFS) are shown in Table 1.

[0066] Table 1 Main components of red mud, carbide slag, and mineral slag

[0067]

[0068] Example 1

[0069] Combined pretreatment method for red mud 1

[0070] Combination Figure 1 As shown, the specific steps are as follows:

[0071] (1) Calcination and activation: 100g of red mud was placed in a muffle furnace and calcined at 700℃ for 30 min. After natural cooling, it was ground through a 200-mesh sieve to obtain calcined red mud 1.

[0072] (2) Water washing and alkali extraction: calcined red mud and water are mixed at a liquid-solid ratio of 6 mL / g, and stirred at 300 rpm for 60 min under a temperature of 100℃.

[0073] (3) Carbonation stabilization: While maintaining heating and stirring, CO2 gas was introduced into the slurry at a flow rate of 0.1 L / min. Intermittent aeration was used: aeration and stirring were carried out for 30 minutes, followed by aeration pause and stirring for 30 minutes. The number of cycles of aeration and aeration pause was 3, with a total aeration time of 90 min. The final pH of the slurry was measured to be 8.5.

[0074] (4) Solid-liquid separation: The slurry obtained in step (3) is separated by vacuum filtration to obtain red mud filtrate 1 and red mud residue 1.

[0075] After drying, the red mud filter residue 1 was leached at a liquid-to-solid ratio of 6 mL / g, and the pH of the leachate was measured to be 8.7.

[0076] Red mud filtrate 1 was freeze-dried to obtain red mud-based alkali activator powder 1. XRF analysis showed that its main components were sodium carbonate and sodium sulfate, with a converted Na2O content of 42.5%.

[0077] Example 2

[0078] Combined pretreatment method for red mud 2

[0079] The combined pretreatment method 2 in this embodiment is the same as that in embodiment 1, except that in step (1), 100g of red mud is placed in a muffle furnace and calcined at 800°C for 60 minutes.

[0080] Red mud filtrate 2 and red mud residue 2 were obtained. The final pH of the leachate from red mud residue 2 was 8.6. Red mud filtrate 2 was freeze-dried to obtain red mud-based alkali activator powder 2, which, according to XRF analysis, had a Na2O content of 40.2%.

[0081] Example 3

[0082] Combined pretreatment method for red mud 3

[0083] The combined pretreatment method 3 in this embodiment is the same as that in embodiment 1, except that in step (1), 100g of red mud is placed in a muffle furnace and calcined at 900°C for 15 minutes.

[0084] Red mud filtrate 3 and red mud filter residue 3 were obtained. The final pH of the leachate from the red mud filter residue 3 was 8.8. The red mud filtrate 3 was freeze-dried to obtain red mud-based alkali activator powder 3, which, according to XRF analysis, had a Na2O content of 72.9%.

[0085] Comparative Example 1 (without calcination activation)

[0086] Red mud pretreatment method D1

[0087] The treatment method of this comparative example D1 is the same as that of Example 1, except that the step (1) calcination activation is not performed, and the water washing alkali extraction, carbonation stabilization and solid-liquid separation are performed directly.

[0088] Red mud filtrate D1 and red mud filter residue D1 were obtained. The final pH of the leachate from red mud filter residue D1 was 10.2. Red mud filtrate D1 was freeze-dried to obtain red mud-based alkali activator powder D1, which, according to XRF analysis, had a Na2O content of only 20.1%.

[0089] Comparative Example 2 (stable without carbonation)

[0090] Red mud pretreatment method D2

[0091] The treatment method of this comparative example D2 is the same as that of Example 1, except that step (3) carbonation stabilization is not performed, and only calcination activation, water washing for alkali extraction and solid-liquid separation are performed.

[0092] Red mud filtrate D2 and red mud residue D2 were obtained. The final pH of the leachate from red mud residue D2 was 10.5, and the pH of the leachate from red mud residue D2 increased significantly during subsequent storage.

[0093] Performance testing

[0094] 1. The raw, untreated red mud was calcined at different temperatures and times. XRD analysis was performed on the resulting calcined red mud, and the results are as follows: Figure 2 As shown, at 700℃, the hydrotalcite, grossular, and hematite in the original red mud decompose, forming new phases such as titanium-bearing garnet and sodium titanium oxide. When the temperature rises to 800℃, the phase composition is basically similar to that at 700℃, with no obvious further decomposition or recrystallization. At 900℃, the red mud undergoes significant recrystallization, with the main phases transforming into grossular feldspar, nepheline, and sulfide-bearing sodalite.

[0095] 2. The calcined red mud 1-3 from Examples 1-3 were monitored for pH changes and sodium ion dissolution under the conditions of a liquid-to-solid ratio of 6 mL / g, a rotation speed of 300 r / min, a room temperature of 20℃, and a stirring time of 60 min. The results are as follows: Figure 3 a, Figure 3 b and Figure 3 As shown in c, the overall sodium ion dissolution rate at 700℃ and 800℃ is better than that at 900℃.

[0096] 3. Detection of Na in raw red mud under different water immersion conditions (liquid-to-solid ratio, stirring temperature, stirring time). + Concentration and pH changes, results as follows Figure 3 d、 Figure 3 e and Figure 3As shown in f, with the increase of liquid-to-solid ratio (6~12 mL / g), Na + The overall dissolution rate showed a decreasing trend, but based on the total sodium ion content, the best sodium ion dissolution effect was observed at a liquid-to-solid ratio of 6 mL / g. The water immersion time was within the range of 60–120 min. + The concentration continued to rise, gradually reaching equilibrium after 60 minutes, indicating that the sodium ion content in the solution had approached saturation at 60 minutes. The pH value increased with increasing Na... + The dissolution showed a trend of first increasing and then slowly decreasing, which initially indicates that some alkaline components have been transferred from the solid phase to the liquid phase.

[0097] 4. The Na content of the calcined red mud 1 from Example 1 was determined under different water immersion conditions (liquid-to-solid ratio, stirring temperature, and stirring time). + The trends of concentration and pH change are as follows: Figure 3 g、 Figure 3 h and Figure 3 As shown in figure i, the sodium ion dissolution rate of calcined red mud is significantly better than that of uncalcined red mud. The best sodium ion dissolution effect is achieved when the liquid-to-solid ratio is 6 mL / g, the stirring time is 60 min, and the stirring temperature is 100℃.

[0098] 5. When carbon dioxide gas was introduced into the calcined red mud 1-3 of Examples 1-3 after water washing and alkali extraction, the aeration time was controlled, and the amount of sodium ion dissolution was measured. The results are as follows: Figure 3 j、 Figure 3 k and Figure 3 As shown in Figure 1, CO2 aeration was performed under optimal water immersion conditions (flow rate 0.1 L / min, aeration time 30–120 min). To ensure uniform distribution and sufficient reaction of CO2 in the slurry, and to avoid localized over-acidity or incomplete reaction, intermittent aeration was adopted. With prolonged aeration time, the system pH decreased significantly, gradually decreasing from an initial 11.0 to neutral and even acidic. However, this does not necessarily indicate that the red mud has undergone complete dealkalization; subsequent reactions of the structural alkalis in the red mud will cause a slow pH rebound. Therefore, long-term monitoring of the red mud pH is necessary. The sodium ion dissolution rate of all three types of calcined red mud reached its peak after 90 min of aeration, indicating that CO2 reacts with the dissolved sodium ions. + The reaction has reached saturation, and sodium carbonate is produced, thus achieving alkali fixation and long-term pH stability.

[0099] 6. The original untreated red mud and the red mud filter residues 1-3 obtained in Examples 1-3 were leached in different liquid-solid ratios, and the pH of the leachate was measured. The results are as follows: Figure 4 As shown, the pH of the dried filter residue stabilized between 8.5 and 9.0, which was significantly lower than that of the original red mud (pH=10.99–11.15).

[0100] 7. The red mud filter residues 1-3 from Examples 1-3 were leached at a liquid-to-solid ratio of 6 mL / g. The pH of the three typical red mud filter residues was monitored over 60 days, and the results are as follows: Figure 5 As shown, after long-term storage (60 days), the pH of the leachate from the red mud filter residues 1-3 remained stable at 8.0 to 9.0, proving that the treatment effect of the present invention is permanent and stable.

[0101] 8. When the calcined red mud 1-3 from Examples 1-3 was carbonated and stabilized by passing carbon dioxide gas after washing and alkali extraction, continuous aeration was performed using different aeration times, and the Na+ content was measured. + The trends of concentration and pH change are as follows: Figure 10 As shown, the Na content of red mud at different roasting temperatures is compared under intermittent and continuous aeration modes. + The dissolution behavior indicates that the aeration method significantly affects pH evolution and Na+ by regulating the carbonation rate of the solution. + Dynamic equilibrium of concentration: In red mud roasted at 700℃ for 30 min, continuous aeration can slightly increase Na concentration. + Peak concentration was achieved, avoiding the drastic drop in concentration in the later stages of intermittent mode, thus facilitating stable extraction; in red mud roasted at 800℃ for 60 min, continuous aeration significantly increased Na... + The peak concentration reached 800 mg / L, but the rapid pH drop exacerbated subsequent precipitation losses, necessitating strict control of aeration time to balance extraction efficiency and recovery rate. In red mud roasted at 900℃ for 15 min, continuous aeration not only failed to increase the peak concentration but also led to excessive carbonation and Na+ loss. + The loss was exacerbated, while intermittent aeration, by supplying CO2 in stages, effectively delayed the precipitation reaction and was more conducive to the final retention of Na+. Overall, continuous aeration in low-to-medium temperature roasted red mud can enhance early dissolution and increase peak concentration, while intermittent aeration in high-temperature roasted red mud can better maintain Na+. + The choice between these two factors—concentration stability in the later stages and calcination temperature and extraction target (peak concentration or final recovery rate)—needs to be optimized. The ultimate goal of this invention is to utilize the alkaline substances in red mud; therefore, an intermittent aeration method is chosen to improve the alkali recovery rate.

[0102] Application examples

[0103] Preparation of all-solid waste alkali activation materials

[0104] The raw materials for the all-solid-waste alkaline activating material include solid waste and water; the solid waste includes activator and slag; the activator includes red mud-based alkaline activator powder and carbide slag; the content of activator in the solid waste is 10-20%; the ratio of red mud-based alkaline activator powder to carbide slag in the activator is 1:1-2; the liquid-to-solid ratio of water to solid waste is 0.3-0.5 mL / g. The preparation process is as follows:

[0105] 1. Mix the red mud-based alkali activator powder 3 obtained in Example 3 with carbide slag (CCR) and blast furnace slag (BFS), and the specific proportions are shown in Table 2.

[0106] 2. Add water at a liquid-to-solid ratio of 0.35 mL / g, mix thoroughly, and then pour into a 40mm×40mm×40mm mold.

[0107] 3. Place the sample on a vibration table and compact it for 3 minutes to remove any trapped air. Allow the molded sample to initially cure for 24 hours. After demolding, transfer the sample to a standard curing chamber at a constant temperature of 20±2℃ and a relative humidity of 95%, and test it after 7 and 28 days of curing to obtain the all-solid waste alkali-activated material 1. Before the compressive strength test, sand the top and bottom surfaces of the specimen to ensure that the surface parallelism is controlled within 0.05 mm. Measure its compressive strength. The specific implementation steps for the all-solid waste alkali-activated material are as follows: Figure 6 As shown.

[0108] Table 2. Proportioning of Alkali Activating Materials for All Solid Waste

[0109]

[0110] Comparative Example 3

[0111] Preparation of all-solid waste alkali activating materials D1~D3 (without added red mud-based alkali activator powder)

[0112] The preparation of the solid waste alkali activating materials D1~D3 in this comparative example is the same as that in the application example, and the formulations are shown in Table 2.

[0113] Performance test results

[0114] 1. Compressive strength

[0115] The compressive strength of all-solid waste alkali activating materials 1-12 and D1-D3 was tested at 7 days and 28 days, and the results are as follows: Figure 7 As shown:

[0116] (1) As the activator dosage increased (from 10% to 20%), the compressive strength of each series of materials generally showed a trend of first increasing and then decreasing. When the activator dosage was 15% and the ratio of carbide slag to red mud-based alkali activator powder was 1:1.6, the 28-day compressive strength reached the highest value of 48 MPa, indicating that the red mud-based alkali activator powder extracted in this invention has good alkali activation activity and can completely replace traditional commercial alkali activators.

[0117] (2) Under the same activator dosage, as the proportion of red mud-based alkaline activator powder in the activator increases (i.e., the proportion of carbide slag decreases), the material strength shows a trend of first increasing and then slightly decreasing. When the ratio of carbide slag to red mud-based alkaline activator powder is 1:1.5, the strength at each dosage reaches the optimal level, indicating that the combination of the two has a synergistic activating effect: the Ca provided by carbide slag 2+ Na provided by red mud-based base activator powder + CO3 2- Together, they promote the dissolution of the silica-alumina phase and the formation of hydration products in the slag.

[0118] (3) Compared with the solid waste alkali activating materials D1~D3, the strength of each group of samples with added red mud-based alkali activator powder was significantly improved. The maximum compressive strength of solid waste alkali activating materials D1~D3 at 28 days was only 28.7 MPa, which was much lower than that of solid waste alkali activating materials 1~12, proving that the red mud-based alkali activator powder played a key role in the solid waste system.

[0119] 2. XRD phase analysis

[0120] XRD analysis was performed on the alkali activating materials 5-8 and D2 from the solid waste at a 7-day age. The results are as follows: Figure 8 As shown:

[0121] (1) The main crystalline phases of the sample are calcite and hydrotalcite minerals. There are obvious diffuse peaks in the range of 20°~35° (2θ), indicating that a large amount of amorphous gel phase (CASH gel) has been generated, which is the main source of the strength of the alkali-activated material.

[0122] (2) Compared with the solid waste alkali activating material D2, the crystal peaks of calcite, hydrotalcite and other crystals in the 5-8 of the solid waste alkali activating material are more obvious, and the amorphous gel phase increases, indicating that the hydration reaction is more complete, which is consistent with the compressive strength results.

[0123] 3. SEM microstructure analysis

[0124] SEM analysis was performed on the alkali activating materials 5-8 and D2 from the solid waste at a 7-day incubation period. The results are as follows: Figure 9 As shown:

[0125] (1) The solid waste alkali-activated material 5-8 has a dense structure with few pores and no obvious microcracks. The hydration products are intertwined to form a continuous three-dimensional network structure, which is the microscopic basis for the material's high strength.

[0126] (2) A large amount of amorphous gel phase can be seen filling the gaps between particles in the solid waste alkali activating material 5~8, which is tightly combined with the unreacted slag particles. The interface transition zone is dense and there are no obvious interface cracks.

[0127] (3) The magnified images of the solid waste alkali-activated material (5-8) show that the gel phase exhibits a typical honeycomb or flocculent morphology, consistent with the characteristics of CSH gel. In some areas, a small number of needle-like ettringite crystals are interspersed in the gel phase, playing a reinforcing role.

[0128] (4) Compared with the SEM image of the solid waste alkali-activated material D2, the solid waste alkali-activated materials 5-8 have fewer unreacted particles, more gel phase, and more uniform and dense microstructure, which is consistent with the improvement of macroscopic mechanical properties.

[0129] In summary, this invention provides a combined pretreatment method that can deeply and permanently solve the problem of red mud alkalinity. It not only realizes the resource recovery of harmful components, but also obtains stable treatment residue with low environmental impact, opening up new avenues for the large-scale disposal and high-value utilization of red mud.

[0130] All other parts not described in detail are existing technologies. Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A combined pretreatment method for red mud, characterized in that: Includes the following steps: (1) The red mud is calcined at high temperature, cooled and sieved to obtain calcined red mud; the calcination temperature is 700~900℃, the calcination time is 15~60 min, and the sieve mesh is 200~250 mesh. (2) Mix calcined red mud and water, heat and stir; the liquid-solid ratio of calcined red mud and water is 6~12 mL / g, the heating temperature is 40~100℃, the stirring speed is 300~320 rpm, and the stirring time is 40~180 min; (3) Keep heating and stirring, and introduce CO2 gas into the system of step (2) by intermittent aeration. (4) After the aeration is completed, the slurry obtained in step (3) is vacuum filtered to separate red mud filtrate and red mud residue; the red mud filtrate is freeze-dried to obtain red mud base activator powder; the red mud base activator powder contains 40~75% Na2O; the pH of the leachate of the red mud residue is 8~9. In step (3), the flow rate of CO2 gas introduced is 0.2 L / min; The intermittent ventilation method is as follows: ventilation and stirring for 30 minutes, followed by pausing ventilation and stirring for 30 minutes, with 2 to 4 cycles of ventilation and pausing ventilation, and a total ventilation time of 60 to 120 minutes.

2. The combined pretreatment method according to claim 1, characterized in that: The calcination temperature is 900℃, the calcination time is 15 min, and the sieve mesh size is 200 mesh. The liquid-to-solid ratio of the calcined red mud and water was 6 mL / g, the heating temperature was 100℃, the stirring speed was 300 rpm, and the stirring time was 60 min.

3. A red mud-based alkali activator powder prepared by the combined pretreatment method according to any one of claims 1 to 2.

4. The application of the red mud-based alkali activator powder according to claim 3 in the preparation of all-solid waste alkali activating materials.

5. A solid waste alkali activating material, characterized in that: The raw materials for the all-solid-waste alkaline activating material include solid waste and water; the solid waste includes an activator and slag; the activator includes the red mud-based alkaline activator powder as described in claim 3 and carbide slag. The content of the activator in the solid waste is 10-20%; In the activator, the ratio of red mud-based alkaline activator powder to carbide slag is 1:1~2; The liquid-to-solid ratio of the water and solid waste is 0.3~0.5 mL / g.

6. The all-solid waste alkali activation material according to claim 5, characterized in that: The solid waste contains 15% activator. In the activator, the ratio of red mud-based alkaline activator powder to carbide slag is 1:1.6; The liquid-to-solid ratio of the water and solid waste is 0.35 mL / g.

7. A method for preparing the all-solid waste alkali activating material according to any one of claims 5 to 6, characterized in that: Includes the following steps: Weigh out the red mud-based alkali activator powder, carbide slag, and mineral slag according to the above proportions, mix them evenly, add water according to the above liquid-solid ratio, mix evenly, solidify, and then cure to obtain a solid waste alkali activating material.

8. The application of the all-solid waste alkali activating material according to any one of claims 5 to 6 in the construction of roads, foundations or buildings.

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