A red mud based geopolymer material and a method of making the same

Abstract

The application discloses a red mud-based geopolymer material and a preparation method thereof. After red mud and alkali liquor are wetly ball-milled and activated, glass sludge and alkaline water glass are added to stimulate a geopolymerization reaction, and the red mud-based geopolymer material is obtained. The geopolymer has high mechanical strength, and the compressive strength can be comparable to that of P.C32.5 cement. Meanwhile, a large amount of two solid wastes, i.e., red mud and glass sludge, is accommodated, and high-value-added utilization of the solid waste resources is realized.

Description

Technical Field

[0001] This invention relates to a geopolymer, specifically to a red mud-based geopolymer material, and also to a method for obtaining a geopolymer from industrial solid waste red mud through wet ball milling and alkali activation, belonging to the field of solid waste resource utilization technology. Background Technology

[0002] Bayer process red mud is a major byproduct of my country's aluminum smelting industry. With the increasing demand for aluminum products year by year, the generation and disposal of red mud has created significant environmental problems. Red mud itself is alkaline, and its fine particles easily cause dust pollution after air drying, occupying large amounts of land during storage. While there are ways to utilize red mud for adsorption, catalysis, passivation, and rare metal recovery, these methods have low resource utilization rates. Therefore, there is an urgent need for a method that can consume red mud in large quantities.

[0003] Glass sludge is produced during the polishing and rinsing processes in the glass processing industry. It has a certain degree of alkalinity and its main component is amorphous silica. It can be used as an additive in the production of cement-based materials.

[0004] Geopolymers possess a three-dimensional network aluminosilicate structure. Compared to traditional cement, they are synthesized through alkali activation, eliminating the carbon dioxide release process during calcination, thus earning them the title of green building materials. Research on the generation of geopolymers from red mud is increasing year by year. Highly active metakaolin and fly ash are already being added to their synthesis process. Expanding new avenues for the co-processing of industrial solid waste with red mud also represents a new approach to the resource utilization of solid waste.

[0005] Currently, the main activation methods for red mud are calcination and mechanical activation. Calcination increases the processing cost of red mud. In mechanical activation, due to the fine and sticky particles of red mud, agglomeration and adhesion occur during dry milling, affecting the milling efficiency. To date, there is very little research on improving the activity of red mud for the synthesis of geopolymers through wet ball milling combined with alkali activation. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the first objective of this invention is to provide a red mud-based geopolymer that possesses high mechanical strength, with compressive strength comparable to P.C32.5 cement. Simultaneously, it absorbs large quantities of both red mud and glass sludge, achieving high-value utilization of solid waste.

[0007] The second objective of this invention is to provide a method for preparing red mud-based geopolymers. This method uses a combination of chemical reagents and wet ball milling to achieve efficient activation of red mud, and then utilizes alkaline water glass and glass sludge to stimulate the geopolymer reaction. This solves the problem of low polymerization activity of red mud raw materials in geopolymer production, while avoiding the problem of high energy consumption in the process of calcination to improve reaction activity, as well as the problem of low activation efficiency of dry ball milling. This method is low in cost, can reduce energy consumption in the solid waste treatment process, and is more energy-saving and environmentally friendly.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a red mud-based geopolymer material. The method involves activating red mud with alkaline solution through wet ball milling, followed by adding glass sludge and water glass to stimulate a polymerization reaction, thereby obtaining the material.

[0009] This invention employs mechanical ball milling assisted by chemical activation to achieve a highly efficient activation process for red mud. Wet ball milling, compared to dry ball milling, is more conducive to the dispersion of red mud particles, reducing agglomeration and significantly improving the activation efficiency. Under mechanical force, the red mud particles become smaller, their specific surface area increases, and their reactivity increases. Simultaneously, mechanical ball milling under alkaline conditions fully utilizes mechanical energy to promote the dissolution of effective components such as silicon and aluminum in the red mud, greatly increasing its reactivity. Furthermore, the addition of alkaline water glass stimulates the geopolymer reaction between the activated red mud and glass sludge. The introduction of silica is crucial for geopolymerization. Glass sludge provides active silica, CaO, and Na₂O. Firstly, the active silica in glass sludge is amorphous silica with high reactivity. It dissolves in alkaline solutions to generate silicate ions, which react with the silica-alumina leached from activated red mud slurry to form new geopolymers. Thus, glass sludge can be used to adjust the active silica-alumina ratio. The silica-alumina ratio in red mud is around 1.07, and introducing glass sludge can increase this ratio, leading to higher-quality geopolymers. Secondly, the active alkalis such as CaO and Na₂O in glass sludge can be fully utilized to promote chemical activation, thereby enhancing the geopolymerization activity. Thirdly, the active calcium oxide in glass sludge can generate CSH gel during the geopolymerization reaction, filling the silica-alumina polymer network and effectively improving the strength and mechanical properties of the geopolymer material.

[0010] As a preferred embodiment, the alkaline solution is a sodium hydroxide solution with a concentration in the range of 4.0–6.0 M. The concentration of the alkaline solution affects the degree of activation of the red mud. If the concentration of the alkaline solution is too low, the effective components in the red mud cannot be fully dissolved, and the activation effect cannot be achieved. If the concentration of the alkaline solution is too high, a hydration reaction will occur, causing a sharp decrease in the fluidity of the red mud slurry, which is detrimental to the subsequent geopolymer reaction with glass sludge. Therefore, the alkaline solution is further preferably a sodium hydroxide solution with a concentration in the range of 4.8–5.2 M.

[0011] As a preferred embodiment, the alkaline solution and red mud are measured at a liquid-to-solid ratio of 0.35–0.5 mL / g. More preferably, the alkaline solution and red mud are measured at a liquid-to-solid ratio of 0.40–0.42 mL / g. If the liquid-to-solid ratio is lower than this, the fluidity of the slurry is insufficient, which is detrimental to molding. If the liquid-to-solid ratio is higher than this, efflorescence is likely, resulting in some waste of the alkaline solution. Furthermore, the increased liquid content is also very detrimental to the early strength of the geopolymer.

[0012] As a preferred embodiment, the ball mill activation conditions are: ball mill speed of 300–500 r / min, ball-to-material ratio of 8–12, and ball milling time of 3–8 min. During mechanical ball milling, the ball milling conditions are crucial for the activation of red mud. If the ball milling activation is insufficient, the collision and contact between the red mud and the alkaline solution are inadequate, resulting in insufficient activity enhancement of the red mud under alkaline activation. Conversely, if the ball milling activation is excessive, the alkaline solution can easily trigger a hydration reaction, which can reduce the strength of the geopolymer and increase energy consumption during the grinding process.

[0013] As a preferred embodiment, the glass sludge and red mud are weighed in a ratio of 55-70% : 30-45% by mass. More preferably, the glass sludge and red mud are weighed in a ratio of 58-62% : 38-42% by mass. The mass ratio of red mud to glass sludge needs to be controlled within an appropriate range. Given that glass sludge mainly contains active SiO2 and has a very low Al2O3 content, the glass sludge content should ideally not be too high. If the glass sludge content increases, the strength of the resulting geopolymer will decrease, possibly because the low aluminum content in the glass sludge affects the reaction process. Similarly, given the low activity of SiO2 and Al2O3 in red mud itself, if the red mud content is too high, the strength of the resulting geopolymer will also decrease, mainly because the low-activity components in the red mud are not fully activated, resulting in insufficient reactivity and inadequate mechanical strength. Therefore, the ratio of red mud to glass sludge should be strictly controlled within an appropriate range.

[0014] As a preferred embodiment, the glass sludge comprises the following main components by mass percentage: SiO2 60–70%, Al2O3 1–5%, MgO 1–5%, CaO 5–10%, and Na2O 8–12%. The glass sludge contains a large amount of amorphous silica, which can adjust the silica-alumina ratio of the system and improve the activity of the geopolymerization reaction. The glass sludge also contains a certain amount of calcium oxide and sodium oxide components, which, as alkaline components, are very beneficial in the alkaline activation process of the geopolymerization reaction. In particular, calcium oxide can generate CSH gel in the geopolymerization reaction, which can fill the silica-alumina polymer network and effectively improve the strength of the geopolymerized material.

[0015] As a preferred embodiment, the alkaline water glass is composed of water glass and sodium hydroxide solution at a mass ratio of 8–10:24–26. The modulus of the water glass is 3.2–3.4 M. The concentration of the sodium hydroxide solution is 4.8–5.2 mol / L. The sodium hydroxide solution primarily provides an alkaline environment, which accelerates the dissolution of effective silicon and aluminum, effectively promoting the rapid attainment of equilibrium in the reaction system. Meanwhile, the water glass provides free silicate ions, which can rapidly participate in the geopolymerization process, enhancing the strength of the geopolymer.

[0016] As a preferred embodiment, the amount of alkaline water glass added is 30-40% of the total mass of red mud and glass sludge. A certain proportion of alkaline water glass is required to achieve a good activation effect. If the amount of alkaline activator is too high, the cost will increase, and the introduction of a large amount of alkali solution will also reduce the strength of the geopolymer.

[0017] This invention also provides a red mud-based geopolymer material, obtained by the aforementioned preparation method. The geopolymer of this invention achieves a maximum 28-day compressive strength of 33 MPa, comparable to P.C32.5 cement.

[0018] The present invention provides a method for preparing a red mud-based polymer material, which specifically includes the following steps:

[0019] 1) Raw material pretreatment: Dry the red mud and grind the glass sludge into powder and pass it through a 200-mesh sieve for later use.

[0020] 2) Mechanochemical activation: Dry red mud and sodium hydroxide solution are ground in a high-speed planetary mill for a certain period of time in a certain proportion to obtain red mud geopolymer slurry.

[0021] 3) Alkali activation: Weigh the corresponding red mud geopolymer slurry according to the mass fraction, add alkali activator and a certain proportion of glass sludge powder, and stir the solid and liquid thoroughly to form a uniform geopolymer slurry.

[0022] 4) Curing: Add the slurry into the mold and place it in an 80℃ oven for curing. After 24 hours, remove the mold and cure the test block at room temperature to obtain the red mud-based polymer.

[0023] Compared with existing technologies, the technical solution of this invention brings beneficial technical effects:

[0024] 1) This invention employs wet ball milling in conjunction with alkali activation, which can rapidly and efficiently activate red mud. Compared with dry ball milling, wet ball milling can reduce ball milling noise, fully utilize the heat generated during the ball milling process, and improve the ball milling activation efficiency of red mud.

[0025] 2) This invention can simultaneously treat two types of solid waste: red mud and glass sludge. At the same time, geopolymers, as a way to consume large amounts of industrial solid waste, can greatly reduce the pressure of industrial solid waste storage.

[0026] 3) The geopolymer synthesized from red mud and glass sludge in this invention can achieve a compressive strength of 33 MPa after 28 days, which is comparable to P.C32.5 cement and has practical application prospects. Attached Figure Description

[0027] Figure 1 The images shown are XRD patterns of the red mud and glass sludge raw materials in the examples.

[0028] Figure 2 The image shows the XRD pattern of the geopolymer S1-2 prepared in Example 1.

[0029] Figure 3 SEM image of geopolymer S1-2 prepared in Example 1.

[0030] Figure 4 SEM image of geopolymer S5-2 prepared in Example 5. Detailed Implementation

[0031] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0032] The materials used in the following examples include Bayer red mud from the Shandong branch of Chinalco Group and glass sludge from Nanbo Group in Zhaoqing City, Guangdong Province. Their chemical compositions are shown in Table 1. The equipment used was a high-speed planetary mill XQM-4L, with the mill speed set at 400 r / min, the ball-to-material ratio set at 10, and the total liquid-to-solid ratio in the geopolymer slurry at 0.5 mL / g. All samples were dried in an oven before use.

[0033] Table 1 Chemical composition of raw materials

[0034]

[0035] Example 1

[0036] 100g of red mud was sequentially poured into a ball mill jar with 40g of 2M, 5M, and 10M sodium hydroxide solutions. After grinding for 5 minutes, 56g of the above slurry, 9g of 5M sodium hydroxide solution, 25g of 3.4M water glass solution, and 60g of glass sludge powder were mixed sequentially and quickly stirred until homogeneous. The mixture was then poured into a 20mm×20mm×20mm mold and cured at 80℃ for 1 day. After demolding, the mixture was placed in a standard curing chamber at a temperature of 20℃±2℃ and a relative humidity of 95%RH or higher for 28 days. Geopolymer samples were obtained and numbered S1-1, S1-2, and S1-3. The fluidity of the obtained red mud slurry and the 7-day and 28-day compressive strength of the geopolymer are shown in Table 2.

[0037] Table 2. Compressive strength of geopolymers synthesized in the examples at different ages.

[0038]

[0039] After wet milling and alkali activation, the red mud, when combined with glass sludge to synthesize a geopolymer, achieved a compressive strength of 33.02 MPa after 28 days, comparable to P.C32.5 cement. During ball milling activation with sodium hydroxide solutions of varying concentrations, generally increasing the sodium hydroxide concentration improved the strength of the geopolymer. However, when the sodium hydroxide solution reached 10M, the fluidity of the resulting red mud slurry decreased sharply. This is likely due to the increased activity of the red mud under the influence of high-concentration sodium hydroxide, leading to a certain degree of hydration, which is detrimental to the subsequent reaction with glass sludge. Considering both compressive strength and the need for chemical conservation, a 5M sodium hydroxide solution was selected.

[0040] XRD analysis showed that sample S1-2 exhibited a diffuse peak around 26° at 7 days, a characteristic peak of amorphous silica, primarily originating from the glass sludge in the sample. Compared to the raw materials, the characteristic peak of gibbsite in the red mud disappeared at 7 days, indicating that gibbsite dissolved in the alkaline solution and re-participated in the geological polymerization reaction. At 28 days, a large "bump-shaped" peak appeared between 20° and 40°, indicating the formation of new amorphous silica-alumina substances during the reaction, which explains the increased compressive strength at 28 days.

[0041] From the SEM image, Figure 3 The agglomerated particles in the mixture likely originate more from red mud, and in terms of particle size, the agglomerated particles are generally less than 1 μm in size. This is in contrast to dry-milled powders. Figure 4The particles are concentrated below 10μm, indicating that wet ball milling is more efficient. Figure 3 The material also exhibits a ceramic-like morphology with a certain network structure, which may explain the high strength of this geopolymer. During the geopolymerization process, gibbsite and sodalite in the red mud, as well as amorphous silica in the glass sludge, dissolve under strongly alkaline conditions and then rearrange themselves into an amorphous silica-alumina geopolymer with a certain regular structure.

[0042] Example 2

[0043] 100g of red mud and 40g of 5M sodium hydroxide solution were sequentially poured into a ball mill jar and milled for 3min, 5min, and 10min respectively. Then, 56g of the above slurry, 9g of 5M sodium hydroxide solution, 25g of 3.4M water glass solution, and 60g of glass sludge powder were taken and mixed together. After being quickly stirred evenly, the mixture was poured into a 20mm×20mm×20mm mold and cured at 80℃ for 1 day. After demolding, the mixture was placed in a standard curing chamber at a temperature of 20℃±2℃ and a relative humidity of 95%RH or higher and cured for 28 days. Geopolymer samples were obtained and numbered S2-1, S2-2, and S2-3 respectively. The fluidity of the obtained red mud slurry and the 7-day and 28-day compressive strength of the geopolymer are shown in Table 3.

[0044] Table 3. Red mud slurry fluidity and 7-day and 28-day compressive strength of geopolymer.

[0045]

[0046]

[0047] As shown in Table 3, the fluidity of the red mud slurry decreases with increasing ball milling activation time. The medium for wet milling of red mud is a 5M sodium hydroxide solution. During ball milling, silica and aluminum in the red mud are leached under strong alkaline conditions. With increasing ball milling time, these leached silica and aluminum may react again, generating certain hydration products. Therefore, it is necessary to control the wet milling time. Compared with wet milling for 5 minutes, wet milling for 3 minutes increases the compressive strength, indicating that, within a certain time, increasing the wet milling time can promote the rapid reaction between the alkaline solution and the red mud particles, and the rapid leaching of silica and aluminum in the red mud. However, as the wet milling time increases to 10 minutes, the strength decreases instead. This may be because hydration has already occurred in the red mud slurry, and the reaction with the glass sludge may be hindered. Therefore, the optimal wet milling time of 5 minutes was finally selected.

[0048] Example 3

[0049] Several portions of 100g red mud and 40g of 5M sodium hydroxide solution were sequentially poured into a ball mill jar and ground for 5 minutes. The resulting slurry was then mixed sequentially with a certain mass of 5M sodium hydroxide solution, 3.4M water glass solution, and glass sludge powder. The mixture was quickly stirred until homogeneous and then poured into a 20mm×20mm×20mm mold. The mold was then cured at 80℃ for 1 day, demolded, and placed in a standard curing chamber at 20℃±2℃ and a relative humidity of 95%RH or higher for 28 days. Geopolymer samples were obtained, numbered S3-1, S3-2, and S3-3. The raw material ratios and the 7-day and 28-day compressive strengths of the synthesized geopolymers are shown in Table 4.

[0050] Table 4. Ingredient ratios and 7-day and 28-day compressive strengths of the synthesized geopolymers.

[0051]

[0052] In the examples S3-1, S3-2, and S3-3, the mass ratios of red mud to glass sludge were 2:8, 4:6, and 6:4, respectively, and the total mass ratio of sodium hydroxide solution to water glass solution in the system was 1:1. In the synthesis of geopolymers, the silica-alumina ratio is a crucial parameter. Depending on the chemical composition of the red mud and glass sludge raw materials, different blending ratios correspond to different silica-alumina ratios. It can be seen that in S3-2, when the glass sludge content is 60%, the compressive strength of the material reaches a relatively ideal state.

[0053] Example 4

[0054] Several portions of 100g red mud and 40g of 5M sodium hydroxide solution were sequentially poured into a ball mill jar and ground for 5 minutes. The resulting slurry was then mixed sequentially with a certain mass of 5M sodium hydroxide solution, 3.4M water glass solution, and glass sludge powder. The mixture was quickly stirred until homogeneous and then poured into a 20mm×20mm×20mm mold. The mold was then cured at 80℃ for 1 day, demolded, and placed in a standard curing chamber at 20℃±2℃ and a relative humidity of 95%RH or higher for 28 days. Geopolymer samples were obtained, numbered S4-1, S4-2, and S4-3. The raw material ratios and the 7-day and 28-day compressive strengths of the synthesized geopolymers are shown in Table 5.

[0055] Table 5. Raw material proportions and 7-day and 28-day compressive strengths of the synthesized geopolymers.

[0056]

[0057] In the example samples, the proportion of water glass in the total alkaline activation solution was 40%, 50%, and 60% for S4-1, S4-2, and S4-3, respectively, thus adjusting the silicon-to-aluminum ratio of the system. Water glass can provide a liquid silicon source, which is beneficial for the reaction system to reach equilibrium quickly. Therefore, the 7-day intensity increases with the increase of the proportion of water glass. However, for the 28-day intensity, increasing the proportion of sodium hydroxide solution can activate more silicon and aluminum in the system to participate in the reaction process, thus resulting in a higher subsequent intensity.

[0058] Example 5

[0059] Several portions of 100g red mud and 40g of 5M sodium hydroxide solution were poured into a ball mill jar and ground for 5 minutes. Then, 56g of the above slurry, 9g of 5M sodium hydroxide solution, 25g of 3.4M water glass solution and 60g of glass sludge powder were mixed and quickly stirred evenly to prepare a geopolymer slurry, sample number S5-1.

[0060] 56g of red mud powder that has passed through a 200-mesh sieve and 84g of glass sludge powder were poured into a ball mill jar and ground for 5 minutes. 100g of the powder was then mixed with 25g of 5M sodium hydroxide solution and 25g of 3.4M water glass solution and stirred quickly and evenly to prepare a geopolymer slurry, sample number S5-2.

[0061] The above-mentioned geopolymer slurry was poured into 20mm×20mm×20mm molds in sequence, and then cured at 80℃ for 1 day. After demolding, it was placed in a standard curing chamber with a temperature of 20℃±2℃ and a relative humidity of 95%RH or higher for 28 days. The 7-day and 28-day compressive strengths of the synthesized geopolymer are shown in Table 6.

[0062] Table 6. Compressive strength of geopolymers synthesized in the examples at different ages.

[0063]

[0064] Example 5 compares the results of wet and dry milling with the same material ratio. In terms of compressive strength, the 7-day and 28-day compressive strengths of the material after wet milling are superior to those after dry milling. This may be because the alkaline solution more completely activates the red mud during wet milling, fully utilizing the silicon and aluminum in the red mud. SEM images show that the material structure of the wet-milled sample is more regular, which may also be the reason for its superior strength.

Claims

1. A method for preparing a red mud-based polymer material, characterized in that: After red mud is activated by wet ball milling with sodium hydroxide solution, glass sludge and alkaline water glass are added to stimulate the polymerization reaction, thus obtaining the product. The concentration of the sodium hydroxide solution is in the range of 4.0~6.0M; The glass sludge and red mud are weighed in a mass percentage ratio of 55-70%:30-45%; The glass sludge contains the following main components by mass percentage: SiO2 60-70%, Al2O3 1-5%, MgO 1-5%, CaO 5-10%, Na2O 8-12%.

2. The method for preparing a red mud-based polymer material according to claim 1, characterized in that: The sodium hydroxide solution and red mud are measured at a liquid-to-solid ratio of 0.35~0.5 mL / g.

3. The method for preparing a red mud-based polymer material according to claim 1, characterized in that: The conditions for ball mill activation are: ball mill speed of 300~500 r / min, ball-to-material ratio of 8~12, and ball milling time of 3~8 min.

4. The method for preparing a red mud-based polymer material according to claim 1, characterized in that: The alkaline water glass is composed of water glass and sodium hydroxide solution with a concentration of 4.8-5.2 mol / L in a mass ratio of 8-10:24-26; The modulus of the water glass is 3.2 to 3.

4.

5. A method for preparing a red mud-based polymer material according to claim 1 or 4, characterized in that: The amount of alkaline water glass added is 30-40% of the total mass of red mud and glass sludge.

6. A red mud-based polymer material, characterized in that: It is obtained by the preparation method described in any one of claims 1 to 5.

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