Red mud-regenerated micro powder synergistically modified cementing material and preparation method thereof

Abstract

The invention discloses a red mud-regenerated micro powder synergistically modified cementing material and a preparation method thereof, and relates to the field of low-carbon cementing materials. The red mud-regenerated micro powder synergistically modified cementing material comprises the following components in parts by weight: 40-60 parts of red mud, 20-40 parts of regenerated micro powder, 3-6 parts of an exciting agent, 1-5 parts of a chelating agent, 10-20 parts of water and 2-4 parts of a water reducing agent, the preparation method of the cementing material comprises the following steps: S1, uniformly mixing a chelating agent and red mud, putting the mixture and water into a ball mill, and carrying out mechanochemical modification to obtain modified red mud slurry; s2, grinding the regenerated micro powder by using a ball mill to obtain finely ground regenerated powder; s3, uniformly mixing the modified red mud, the ground regenerated powder and a water reducing agent, adding an exciting agent, and stirring to obtain the cementing material. The synergistically modified cementing material disclosed by the invention has relatively good mechanical properties and flowability, realizes resource utilization of solid wastes, and is low-carbon and environment-friendly.

Description

Technical Field

[0001] The invention relates to the field of low-carbon cementitious materials, in particular to a red mud-regenerated micropowder synergistically modified cementitious material and a preparation method thereof. Background Art

[0002] Red mud is the solid waste after bauxite is produced into alumina through the Bayer process. It has high alkalinity and complex chemical composition. About 100 million tons of red mud are produced every year in the world, and China's annual production is about 30 million tons. Red mud contains a large amount of iron, aluminum, titanium and other elements, which has potential utilization value. However, the high alkalinity components in red mud will affect the hydration reaction of cement, resulting in uneven distribution of hydration products and unstable setting time. In addition, the fine particles of red mud and the large specific surface area make it poorly dispersed in concrete, thus affecting the overall strength and durability. Therefore, the performance of red mud directly as a building material is poor, which limits its wide application in the construction field.

[0003] Recycled micropowder is a fine powder material recovered from construction waste, and its main components include silica, alumina and a small amount of unhydrated cement particles. With the increase of construction activities, the output of recycled micropowder is also increasing year by year. According to statistics, about 20-30% of the construction waste generated in China each year can be recycled into recycled micropowder. However, as an auxiliary cementitious material, the cementing performance of recycled micropowder is relatively poor, mainly manifested in low strength and poor stability. This is because the recycled micropowder contains more unhydrated particles and other impurities. These components cannot effectively participate in the reaction during the cement hydration process, resulting in the formation of a hydration product with a non-dense structure. In addition, the particle size distribution of recycled micropowder is uneven, which increases the porosity inside the concrete and further reduces its strength and durability. Therefore, the utilization of recycled micropowder is also limited.

[0004] At present, the modification research of red mud and recycled micropowder mainly focuses on physical and chemical methods, including high-temperature calcination, mechanical activation and chemical additive modification. However, high-temperature calcination often consumes a lot of energy and produces secondary pollution, which fails to meet the requirements of low-carbon environmental protection; mechanical activation can reduce the particle size, but has little effect on the solidification of heavy metals in red mud; chemical modification can effectively solidify heavy metals, but it is not enough to improve the activity, so there are limitations in a single modification method.

[0005] Nevertheless, red mud and regenerated micropowder have great potential for synergistic utilization. The present invention optimizes the ratio and treatment process of red mud and regenerated micropowder to complement each other's performance defects and improve the comprehensive performance of the material. At the same time, this synergistic utilization method has the advantage of being green and environmentally friendly, can effectively reduce the storage of industrial waste and environmental pollution, and achieve efficient utilization of resources and environmental protection. Summary of the invention

[0006] The purpose of the present invention is to address the problems of low activity of red mud and regenerated micropowder and difficulty in resource utilization, and to improve the activity of red mud and solidify heavy metals by a synergistic mechanical-chemical modification method. At the same time, by adjusting the ratio and optimizing the chemical composition of the gelling system, a red mud-regenerated micropowder synergistically modified gelling material and a preparation method thereof are provided.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A red mud-regenerated micropowder synergistically modified gelling material, the raw materials of which include the following components in parts by weight: 40-60 parts of red mud, 20-40 parts of regenerated micropowder, 3-6 parts of activator, 1-5 parts of chelating agent, 10-20 parts of water, and 2-4 parts of water reducing agent.

[0009] Preferably, the regenerated micro powder is powder obtained by crushing and screening waste concrete, and its methylene blue value is less than 1.4.

[0010] Preferably, the activator is one or both of water glass and NaOH.

[0011] Preferably, the chelating agent is one of EDTA, sodium hexametaphosphate and sodium polyacrylate.

[0012] Preferably, the water reducer is a liquid polycarboxylic acid high-efficiency water reducer.

[0013] The present invention also provides a method for preparing the red mud-regenerated micropowder synergistically modified gelling material, comprising the following steps:

[0014] S1: the chelating agent and red mud are uniformly mixed and then placed in a ball mill together with water for mechanochemical modification to obtain modified red mud slurry;

[0015] S2: Grinding the regenerated micro powder using a ball mill to obtain finely ground regenerated powder;

[0016] S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the water reducing agent, adding an activator and stirring, the red mud-regenerated micropowder synergistically modified cementitious material is obtained.

[0017] Preferably, the conditions for the mechanochemical modification in step S1 are: the ball mill speed is 400-550 rpm, and the ball milling time is 5-10 min.

[0018] Preferably, the grinding conditions in step S2 are: the ball mill speed is 400-550 rpm, and the ball milling time is 20-40 s.

[0019] The present invention has the following technical effects:

[0020] 1. The present invention makes full use of industrial waste red mud and construction waste recycled micro powder, reducing dependence on natural resources. By converting these wastes into valuable building materials, it not only reduces the demand for traditional cement, but also effectively reduces the storage and treatment costs of waste. Using red mud and recycled micro powder as the main raw materials helps to reduce carbon dioxide emissions generated during cement production, thereby reducing carbon footprint and achieving green and low-carbon environmental protection goals.

[0021] 2. The traditional sintering process requires high temperature treatment and consumes huge energy. The present invention adopts a mechanical-chemical modification method, which effectively improves the activity of the material through the synergistic effect of mechanical ball milling and chemical additives, and significantly reduces energy consumption. The mechanical-chemical modification process is simple to operate and easy to implement. It does not require complex equipment and high temperature environment, which reduces production costs and operating difficulties, and further improves the feasibility and economy of the process.

[0022] 3. Red mud is rich in iron, aluminum, silicon and other elements, while recycled micropowder is mainly calcium. The combination of the two can form a composite material with complementary properties and improve the overall performance. The particle size is refined through ball milling, which significantly increases the specific surface area of ​​the particles and provides more reaction sites. This refinement not only improves the chemical reactivity of the material, but also improves its physical properties, such as strength and durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of the preparation method of a red mud-regenerated micropowder synergistically modified gelling material of the present invention DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] Example 1

[0026] A red mud-regenerated micropowder synergistic modified cementitious material is composed of the following raw materials in parts by weight: 40 parts of red mud, 20 parts of regenerated micropowder, 5 parts of sodium hydroxide, 2 parts of EDTA chelating agent, 10 parts of water, and 3 parts of liquid polycarboxylic acid high-efficiency water reducing agent. The regenerated micropowder is a powder obtained by crushing and screening waste concrete, and its methylene blue value is 1.2.

[0027] The preparation method of the red mud-regenerated micropowder synergistically modified gelling material is prepared according to the following steps:

[0028] S1: The EDTA chelating agent and red mud are evenly mixed and then placed in a ball mill together with water for mechanochemical modification. The ball mill speed is maintained at 500 rpm and the ball milling time is 7 minutes to obtain a modified red mud slurry;

[0029] S2: Grind the regenerated micro powder using a ball mill, keep the ball mill speed at 400 rpm, and the ball milling time is 30 s to obtain finely ground regenerated powder;

[0030] S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the liquid polycarboxylic acid high-efficiency water reducing agent, adding sodium hydroxide and stirring to obtain the red mud-regenerated micropowder synergistically modified gelling material.

[0031] Example 2

[0032] A red mud-regenerated micropowder synergistic modified cementitious material is composed of the following raw materials in parts by weight: 50 parts of red mud, 30 parts of regenerated micropowder, 3 parts of water glass, 1 part of sodium hexametaphosphate chelating agent, 10 parts of water, and 2 parts of liquid polycarboxylic acid high-efficiency water reducing agent. The regenerated micropowder is a powder obtained by crushing and screening waste concrete, and its methylene blue value is 1.2.

[0033] The preparation method of the red mud-regenerated micropowder synergistically modified gelling material is prepared according to the following steps:

[0034] S1: The sodium hexametaphosphate chelating agent and red mud are uniformly mixed and then placed in a ball mill together with water for mechanochemical modification, the ball mill speed is maintained at 400 rpm, and the ball milling time is 5 minutes to obtain a modified red mud slurry;

[0035] S2: Grind the regenerated micro powder using a ball mill, keep the ball mill speed at 500 rpm, and the ball milling time is 20 s to obtain finely ground regenerated powder;

[0036] S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the liquid polycarboxylic acid high-efficiency water reducing agent, adding water glass and stirring, the red mud-regenerated micropowder synergistically modified cementitious material is obtained.

[0037] Example 3

[0038] A red mud-regenerated micropowder synergistic modified cementitious material is composed of the following raw materials in parts by weight: 60 parts of red mud, 40 parts of regenerated micropowder, 6 parts of water glass, 4 parts of sodium hexametaphosphate chelating agent, 10 parts of water, and 4 parts of liquid polycarboxylic acid high-efficiency water reducing agent. The regenerated micropowder is a powder obtained by crushing and screening waste concrete, and its methylene blue value is 1.2.

[0039] The preparation method of the red mud-regenerated micropowder synergistically modified gelling material is prepared according to the following steps:

[0040] S1: The sodium hexametaphosphate chelating agent and red mud are uniformly mixed and then placed in a ball mill together with water for mechanochemical modification. The ball mill speed is maintained at 400 rpm and the ball milling time is 6 minutes to obtain a modified red mud slurry;

[0041] S2: Grind the regenerated micro powder using a ball mill, keep the ball mill speed at 550 rpm, and the ball milling time is 40 s to obtain finely ground regenerated powder;

[0042] S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the liquid polycarboxylic acid high-efficiency water reducing agent, adding water glass and stirring, the red mud-regenerated micropowder synergistically modified cementitious material is obtained.

[0043] Example 4

[0044] A red mud-regenerated micropowder synergistic modified cementitious material is composed of the following raw materials in parts by weight: 50 parts of red mud, 30 parts of regenerated micropowder, 4 parts of activator, 3 parts of sodium polyacrylate chelating agent, 20 parts of water, and 3 parts of liquid polycarboxylic acid high-efficiency water reducing agent. The regenerated micropowder is a powder obtained by crushing and screening waste concrete, and its methylene blue value is 1.2. The activator is a mixture of water glass and sodium hydroxide, with a mass ratio of 8:1.

[0045] The preparation method of the red mud-regenerated micropowder synergistically modified gelling material is prepared according to the following steps:

[0046] S1: The sodium polyacrylate chelating agent and red mud are evenly mixed and then placed in a ball mill together with water for mechanochemical modification. The ball mill speed is maintained at 550 rpm and the ball milling time is 10 min to obtain a modified red mud slurry;

[0047] S2: Grind the regenerated micro powder using a ball mill, keep the ball mill speed at 550 rpm, and the ball milling time is 40 s to obtain finely ground regenerated powder;

[0048] S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the liquid polycarboxylic acid high-efficiency water reducing agent, adding an activator and stirring to obtain the red mud-regenerated micropowder synergistically modified cementitious material.

[0049] Example 5

[0050] A red mud-regenerated micropowder synergistic modified cementitious material is composed of the following raw materials in parts by weight: 60 parts of red mud, 40 parts of regenerated micropowder, 4 parts of activator, 5 parts of sodium polyacrylate chelating agent, 20 parts of water, and 4 parts of liquid polycarboxylic acid high-efficiency water reducing agent. The regenerated micropowder is a powder obtained by crushing and screening waste concrete, and its methylene blue value is 1.3. The activator is a mixture of water glass and sodium hydroxide, with a mass ratio of 9:1.

[0051] The preparation method of the red mud-regenerated micropowder synergistically modified gelling material is prepared according to the following steps:

[0052] S1: The sodium polyacrylate chelating agent and red mud are evenly mixed and then placed in a ball mill together with water for mechanochemical modification. The ball mill speed is maintained at 550 rpm and the ball milling time is 8 min to obtain a modified red mud slurry;

[0053] S2: Grind the regenerated micro powder using a ball mill, keep the ball mill speed at 550 rpm, and the ball milling time is 30 s to obtain finely ground regenerated powder;

[0054] S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the liquid polycarboxylic acid high-efficiency water reducing agent, adding an activator and stirring to obtain the red mud-regenerated micropowder synergistically modified cementitious material.

[0055] Comparative Example

[0056] A gelling material, the raw material composition of which is different from that of Example 1 in terms of weight: 2 parts of EDTA chelating agent are not present, and the rest are the same.

[0057] The preparation method of the cementitious material is different from that of Example 1 in that: Step S1 is to mix red mud and water evenly to obtain red mud slurry; Step S3 is to mix the red mud slurry obtained in Step S1, the ground regenerated powder obtained in Step S2 and the liquid polycarboxylic acid high-efficiency water reducing agent evenly, and then add sodium hydroxide and stir to obtain the cementitious material. The rest is the same.

[0058] The prepared cementitious material was tested for fluidity according to GB / T 8077-2012 "Test method for homogeneity of concrete admixtures", the 28-day compressive strength of the cementitious material was tested according to GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)", and the initial and final setting times were determined according to GB / T 1346-2011 "Test method for water consumption, setting time and stability of cement standard consistency". The test results are shown in Table 1.

[0059] Table 1 Performance test results of comparative examples and embodiments 1 to 5

[0060] Case Flowability(mm) 28d compressive strength (MPa) Initial setting time (min) Final setting time (min) Comparative Example 150 15.23 180 300 Example 1 181 30.66 150 270 Example 2 173 32.51 160 280 Example 3 162 35.42 170 290 Example 4 175 33.91 155 275 Example 5 164 36.84 165 285

[0061] The fluidity of the comparative example is the worst, at 150 mm, because the slurry viscosity is high due to the lack of mechanochemical modification. The fluidity of Example 1 is better, at 181 mm, indicating that the effect of EDTA after short-time ball milling modification is better. The fluidity of Examples 2 and 3 with increased red mud content has decreased, but this effect can be partially compensated by appropriately extending the ball milling time. The fluidity of Examples 4 and 5 using sodium polyacrylate is 175 mm and 164 mm, respectively, showing the different effects of ball milling time and chelating agent type on fluidity.

[0062] The compressive strength of the comparative example is the lowest, which is 15.23 MPa (28 days), because the material performance is poor due to the lack of mechanochemical modification. The compressive strengths of Example 3 and Example 5 are the highest, which are 35.42 MPa and 36.84 MPa, respectively, indicating that increasing the red mud content and appropriately extending the ball milling time significantly improve the compressive strength. The compressive strengths of Example 2 and Example 4 are also relatively high, which are 32.51 MPa and 33.91 MPa, respectively.

[0063] The initial setting time and final setting time of the comparative example are the longest, which are 180 minutes and 300 minutes respectively. The initial setting time and final setting time of Example 1 are shorter, which are 150 minutes and 270 minutes respectively, indicating that the effect of EDTA after ball milling modification is significant. The setting time of Example 3 is longer, indicating that the effect of sodium hexametaphosphate is more significant at high red mud content, and the increase of ball milling time helps to shorten the setting time. The initial setting and final setting times of Examples 4 and 5 are moderate, indicating that sodium polyacrylate has good effects under different red mud contents and ball milling times.

[0064] The carbon emissions of the cementitious material were calculated and the results are shown in Table 2.

[0065] Table 2 Carbon emissions of comparative examples and examples 1 to 5

[0066]

[0067] It can be seen that the carbon emissions of a red mud-recycled micropowder synergistic modified cementitious material compared with cement (about 800kg CO 2 -eq / m 3 ), has significant low-carbon advantages and contributes to the development of a low-carbon circular economy.

[0068] In addition, leaching tests of comparative examples and examples were carried out on the modified red mud to verify the heavy metal solidification effect of the chelating agent, and the test data are shown in Table 3.

[0069] Table 3 Heavy metal leaching results of comparative examples and examples 1 to 5

[0070] Case As(μg / L) Cr(μg / L) Cd(μg / L) Comparative Example 8.16 56.32 2.33 Example 1 3.31 24.24 1.52 Example 2 5.44 35.17 1.84 Example 3 Not detected 13.85 Not detected Example 4 1.22 18.79 0.36 Example 5 Not detected 6.52 Not detected

[0071] Table 2 shows that the modification method can effectively solidify the heavy metals in red mud. The heavy metal solidification effect is related to the dosage of the three chelating agents. Within the scope of the embodiment, as the dosage of the chelating agent increases, the heavy metal leaching decreases. In fact, due to the limitation of the detection equipment, there are undetectable elements in Example 3 and Example 5, indicating that the modification has a good solidification effect. In addition, after the modified red mud is used in the cementitious material, the heavy metals can be further solidified through the hydration reaction. Therefore, the use safety of the red mud-regenerated micropowder synergistic modified cementitious material can be guaranteed.

[0072] The above description is only a preferred specific implementation manner of the present invention, and the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, and they should be covered by the protection scope of the present invention.

Claims

1. A red mud-regenerated micropowder synergistically modified gelling material, characterized in that: The raw materials include the following components in parts by weight: 40-60 parts of red mud, 20-40 parts of regenerated micro powder, 3-6 parts of activator, 1-5 parts of chelating agent, 10-20 parts of water and 2-4 parts of water reducing agent.

2. The red mud-regenerated micropowder synergistically modified gelling material according to claim 1, characterized in that: The regenerated micro powder is a powder obtained by crushing and screening waste concrete, and its methylene blue value is less than 1.

4.

3. The red mud-regenerated micropowder synergistically modified gelling material according to claim 1, characterized in that: The activator is one or both of water glass and NaOH.

4. The red mud-regenerated micropowder synergistically modified gelling material according to claim 1, characterized in that: The chelating agent is one of EDTA, sodium hexametaphosphate and sodium polyacrylate.

5. The red mud-regenerated micropowder synergistically modified gelling material according to claim 1, characterized in that: The water reducing agent is a liquid polycarboxylic acid high efficiency water reducing agent.

6. A method for preparing a red mud-regenerated micropowder synergistically modified gelling material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: the chelating agent and red mud are uniformly mixed and then placed in a ball mill together with water for mechanochemical modification to obtain modified red mud slurry; S2: Grinding the regenerated micro powder using a ball mill to obtain finely ground regenerated powder; S3: after uniformly mixing the modified red mud slurry obtained in step S1, the ground regenerated powder obtained in step S2 and the water reducing agent, adding an activator and stirring, the red mud-regenerated micropowder synergistically modified cementitious material is obtained.

7. The method for preparing the red mud-regenerated micropowder synergistically modified gelling material according to claim 6, characterized in that: The conditions for the mechanochemical modification in step S1 are: the ball mill speed is 400-550 rpm, and the ball milling time is 5-10 min.

8. The method for preparing the red mud-regenerated micropowder synergistically modified gelling material according to claim 6, characterized in that: The grinding conditions in step S2 are: the ball mill speed is 400-550 rpm, and the ball milling time is 20-40 s.

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